Understanding

VISI Flow

VISI Flow 20
 INTRODUCTION

This document is intended to provide basic information on how to get started using the
VISI Flow analysis packages.

To run movies just CTRL + click on the icons.

If you experience some problem in running these videos, download an appropriate
Codec (e.g. http://download.techsmith.com/tscc/tscc.exe).

All the documentation is available as a guided on-line help that can also be printed
(document Flow.chm located under "..\Documents\your language\Help" in your
installation directory). This context sensitive on-line help, that covers all major working
sections, can be invoked through the F1 key.

Pre-requisite
During this exercise, it is assumed a basic knowledge of the VISI software.

Object
The following example will detail the Flow interface and highlight some of the required
techniques to run a filling to shape analysis, including thermal calculation. During this
training example the procedure to build and edit a mould model will be explained in detail.

SUMMARY
(CTRL + click on each line to go to the relevant guide section)

1. Analyzing a Component
Mesh model creation & preparation
Define moulding conditions for a Filling analysis, run analysis calculations, and
view the results
Define moulding conditions for a Holding analysis, run the calculation, and view
the results
Define the moulding conditions for a Shape analysis, run the calculation, and view
the results
2. Run the Complete Mould
Inserting the feeding system (hot runners, hot tip, and sprue)
Inserting the cooling lines and mould cavity extension
Define the moulding conditions for a mould conditioning system Thermal analysis,
run the calculation, and view the results
Viewing the results of a Filling to Shape analysis with Thermal integration
3. Appendixes
Modelling considerations and tips
Calculation Strategy and tips
Filling Calculation input and result description and tips
Sequential Moulding calculations
Holding Calculation input and result description and tips
Shape Analysis input and result description and tips
Thermal Analysis input and result description and tips
General Tips (Reports, etc.)

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 1. Analyzing a Component

Mesh Model Creation & Preparation

Run VISI

File > Open Select the file named “Body.wkf”

located in \Visi20\Workf\Sample\Flow\Part

The geometry should look as below:

Before setting up any analysis it is important to check that the part is a valid solid
component with no corruptions or errors. It is important to have a good quality solid,
because any corruptions may affect the analysis calculations.

Please ask the instructor for assistance or an explanation of what checks to make
before creating the mesh for analysis. For example, before running the command
available under the Mesh menu it is always worthwhile to Simplify Bodies (Operation
menu).

A Solid/Surface model is not used for creating analysis within VISI Flow, so a
triangularization mesh needs to be created from the cad data.

VISI Flow uses a special surface triangularization mesh created inside VISI from a
solid or surface model. While it looks similar to a STL file used for creating rapid
prototype parts its main difference is the regularity of the shape of the triangles
created. The triangles that are created need to be as uniform as possible, and as
close to equilateral as possible to achieve the best analysis results.

Before creating a triangularization mesh you should ensure that you have a solid
model or a united sheet body.

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Flow > Wizard
video

Starting from any solid model or mesh, the Wizard allows a fast modelling of the cavity
providing basic checks and mesh repair tools.

After clicking on the part, specify the desired element size. For a complete explanation
of the available options, read the subsequent Create Mesh section.

Verify and automatically repair the model.

Always Check element connectivity and, if the case, fix the problems though the Mesh
tools.

Refer to the next Mesh menu paragraphs to better understand each option.

Make sure of the appropriate element orientation.

The thickness calculation is automatically run. To refine the calculated values, if the
case, consult the Thickness section to learn about the many available options.

Note that during this guided procedure it is possible to stop the process at any instant
or call for other useful functions such as the Dynamic section dialog.

The part can be straight away formatted and analysed or additional details, such as
gate and runners, can be added through the common Model Preparation commands.

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 Mesh > Create Mesh
video

After clicking on the part, the following window appears to choose the desired
element size.

Suggested element
dimension

Visualize the results of

the mesh discretization

Elements dimension
for the final
triangularization

To create a very uniform

spider web mesh

The element size is automatically suggested depending on the dimensions of the

model.

It may be necessary to make compromises when choosing a triangle dimension to best

define critical feature of a component and minimise part distortion.

For example, the hinge detail shown, instead of the

suggested size of 3 mm (1/8”) it has been worthwhile
using an element size of 2 mm (1/16”) to have 3
elements along the shortest dimension of the hinge
feature.

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When selecting a triangle size make use of the Preview button to visualize the results
and judge if the triangle dimension selected will deform the components shape or
create an excessive number of triangles. Consider that a level of deformation of the
components shape will not influence the results.

Starting from the initial triangularization that best represents our component (for this
example, we will specify an element dimension of 2.5 mm) we will ReMesh the part
with a triangle size of 4.5 mm and the default parameters.

Mesh suitability checks

video

At this stage it’s mandatory to verify the mesh data before progressing onto assigning
material thickness to the mesh elements.

Select the Cleanup icon to perform various operations on meshes to remove

various types of abnormalities associated with triangles' connectivity, holes, gaps, etc.

The generic toolbar encompassing two tabs of this dialogue contains icons to perform
generic operations such as load factory default values, set current default values, load
current default values, undo all, undo immediate and redo.

Cleanup toolbar in the Operations tab of this dialogue provides various icons to
perform respective operations on meshes. Operations are performed on meshes only
when respective icons on this toolbar are clicked. Clicking OK on the bottom of the
dialogue box will only confirm the actions performed through the toolbar. Clicking
Cancel on the contrary undoes the operations performed so far.

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 Fix all
Generic toolbar
Orient normals

Optimize mesh

Operations on mesh

Check it only if you experience calculation problems

Default value of 0.01 is commonly us

To check for any unconnected triangles after performing all cleanup operations

Click the Fix all icon to perform all the selected operations from Options. This section
provides facilities to fix geometry of mesh triangles. Various operations in this are:

 Fix vertex edge disjoints: Check this to automatically search whole mesh for any
vertex-edge disjoint pairs and fix them automatically. This operation works on a gap
tolerance, which means the distance between the vertex and the edge. Default
value is 0.1 (mm) which should automatically fix usually occurring anomalies.
 Fill simple holes: Check this to automatically fill any planar holes present in the
mesh.
 Fix degenerate triangles: Check this to delete any degenerate triangles found in
the mesh. When this check box is ticked the relevant edit box will be enabled to
provide minimum area below which triangles are considered degenerate. Default
value for this is 0.01 (mm2).
 Fix overlapping triangles: Check this to delete any overlapping triangles present in
the mesh.
 Fix non-manifold triangles: Check this to delete any non-manifold triangles present
in the mesh. Non-manifold triangles are triangles whose edges (at least one) are
shared by more than one triangles.

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 Fix overhang triangles: Check this to delete any triangles that are overhanging
from the rest of the mesh. Overhanging means triangles with two of its edges
unconnected/unshared with the rest of the mesh.
 Fix aspect ratio of triangles: Check this to relax mesh from triangles with huge
aspect ratio. Triangles with aspect ratio above given value (by default 20) will be
removed and mesh is adjusted accordingly so as not to create any holes or
connectivity issues. Triangles positioned at 90 degrees respect to other (border
elements) will not be removed. When this check box is ticked the field at right will
be enabled to provide with a threshold value for aspect ratio. This operation also
takes into consideration the value specified to check for any degenerate triangles
while removing triangles with aspect ratio above given value.

Aspect ratio is defined as the ratio of longest edge length and shortest altitude inside
triangle. By checking it we can detect and remove geometrically or mathematically
convoluted elements that simply will not work or, in the worst case, will not allow the
completion of the analysis calculation. It is suggested to run this command only if all
the elements are connected so to keep their connectivity. By adjusting the aspect
ratio, overlapping and zero area elements may be generated. These unsuitable
elements will need to be corrected before we progress any further.

Typically, it is not necessary to remove elements with a wrong shape factor.

Options in the Parameters section allow to:

 Mesh tolerance: The default value of 0.01 is the

most commonly used for meshes but this
parameter could be modified based on source
and nature of data and application. The modified
value will be applicable only for the operations
performed through this dialogue. Mesh tolerance
is an important value for triangle meshes which
jigs up vertices and there by edges and triangles
of a mesh so as to remove any duplicate vertices.

 Use default tolerance: If this check box is ticked

the default tolerance value is used for all the
operations performed otherwise the tolerance
value specified in Mesh tolerance will be used.
 Check: Check this box if, after performing all
cleanup operations on meshes, mesh has to be
checked for any unconnected triangles. The
resultant number of unconnected triangles are
displayed in the message area below all parameters.

The Results tab displays number of degenerate, overlapping and non-manifold

triangles, elements above given aspect ratio, simple holes and vertex-edge disjoint
pairs fixed as a result of operations performed on meshes.

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Click the Orient Normals icon to orient all triangles in a consistent direction.

In fact, all the mesh triangles have a positive and negative vector. After executing this
command all normals should be consistently oriented outwards (positive vector),
except in very limited cases where some partially overlapping triangles are present or
in cases where there are multiple patches of triangles which are unconnected to each
other. In cases like this mesh has to be cleaned up to achieve proper orientation for
those triangles.

As an alternative, elements with a negative vector can be inverted by the Reverse

Normals command.

Before progressing, your mesh data needs to be consistently coloured. The activation
of Double sheet shading colour in the Graphic parameters permits to identify correct
and wrong oriented elements. In fact, this setting allows to set the shading on sheet
bodies with different colour on the sides of them. The colour will be in agreement with
the face normal direction.

Optimize Mesh is an important operation whenever meshes have any vertices or

edges which share same coordinates within a specific tolerance value. For example,
vertices or edges which share same coordinates to a tolerance value such as 0.01
and the Mesh tolerance used is 0.001 then these vertices/edges will appear duplicate
in the mesh. In this situation if the Mesh tolerance is varied to 0.01 and this icon is
clicked then these vertices and thereby corresponding edges will be made unique,
removing unconnected triangles.

Use this command after any mirror of symmetrical areas of the model.

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In case the mesh will need to be further refined, additional mesh tools are available:

Collapse Triangle Merge Vertices

Orient Normals Delete/detach Triangles

Cleanup Change Attributes

Fill Holes

Check Triangle Attributes

Reverse Normals Add Triangles

The Check command controls the mesh for any unconnected triangles (to run a
shape analysis, connectivity must be complete).

A dialogue will pop up on demand if the icon

to the left is clicked. This optional dialog will

provide the facility to change colours of
unconnected triangles and their surrounding
triangles along with displaying number of
unconnected triangles. It also provides facility to
reset triangle attributes of the mesh. If this
optional dialog is not opened a simple message
is displayed with number of unconnected
triangles and all unconnected triangles in the
mesh are highlighted in red colour.

When colours of unconnected triangles and their

surrounding triangles are modified using the optional
dialog to the right, display of those triangles can be
filtered using the second tab (Element/Colour/Style)
by switching on/off different colours as used for triangles in the mesh.

It is possible to connect the nodes of the triangles displayed in the previous image in
several ways.

With Merge vertices the program

condenses two nodes into a single vertex. The
first selected node is moved toward the second
one and mesh is adjusted accordingly. To
select the vertices it is advisable to activate the
Enhanced Pick.

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As an alternative you may also Add triangles to a mesh manually: just pick the
vertices to add elements. A triangle is added for each trio of points picked.

With these simple commands you can connect all the elements. Note that it could be
necessary to reset the triangle colour through the (Element/Colour/Style) tab. The
correct joining together is achieved when the appropriate message is displayed after
reissuing the verify connectivity command.

Now that the mesh has been prepared, the following steps will guide you through the
procedure for setting up a model for analysis. Many of the relevant parameters will be
explained during the preparation process.

Flow > Model Preparation

When clicking on Model Preparation, the program calls for the Wizard. Since the mesh
has already been prepared, just answer No to close the Wizard.

Understanding the interface:

1 2 3 4 5 6 7 8

9 10 11 12 13

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 1. Add Cavity Mesh
2. Project Information
3. Show Thickness 9. Thickness
4. Triangle Information 10.Feeding Channels
5. Select Element by Pick 11.Cooling Channels
6. Refresh Channels Graphic 12.Format for the Analyses
7. Refresh Tree 13.Analysis Browser
8. VISI Flow Configuration

We suggest you give each model a different name if you are working in the same
folder. Using the suggested file names will prevent the standard files (shown in
parenthesis) from being overwritten. This will allow you to pick up an exercise at any
point.

First of all select the mesh to be added to the VISI Flow Project. You may have
different cavities composing the shot.

The mesh will be placed on a layer (by default called MESH) and coloured (in cyan) as
specified in the VISI Flow Configuration.

Note that this triangular surface mesh, saved in the “.WKF” file, is not used by the
analysis calculations. VISI Flow creates an internal adaptive super-structure for the
analysis process, a technique that is unique to VISI Flow. The triangular mesh is only
used for displaying the calculation results. The super-structure (saved in the “.MDF” file)
is generated during the formatting process that is performed after some mesh suitability
checks and the computation of local thicknesses.

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At this stage we are ready to assign the part thickness to the models mesh elements.

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Select the Thickness icon to open the relevant menu.

Assign temperature to triangles

Assign thickness
Assign temperature by body selection

Thickness calculation

Show temperature
Refine thickness

Run the Thickness Calculation.

video

When this computation is complete, the thickness distribution is displayed. You can
modify the range of calculated values by right clicking on the icon.

Two methods, with different parameters, are available to

compute thickness: Maximum Sphere and through
Hexahedral Mesh. The Configuration allows to set the
preferred thickness calculation algorithm.

The Maximum Sphere method is used by default. The

thickness at any point is defined by the largest sphere that
can be placed at that point, in the direction of facet normal,
without intersecting other facets. Because we are fitting a
sphere, this method gives a much better measure of thickness in 3 dimensions when
compared to other methods.

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You should now have a mesh model with all the elements assigned a thickness, this is
normally adequate to give a good representation of the model.

You may have noticed the scattered thickness distribution in the internal thickest area’s
and some elements with a reduced value on some of the cylindrical bosses. This is due
to the slight distortion of the model data accepted when the mesh has been generated.
Reducing the mesh size can improve the results, but this will lead to longer calculation
times. The variation of element thickness in these area’s won’t substantially diminish the
quality of the results.

In our example we will improve the thickness distribution by using the assign thickness
commands.

Select the Assign Thickness Icon.

video
A new dialog box will be presented:

To pick the elements to be modified

Activate this option to display the thickness

To open a window with sophisticated options for the se
values within the specified Range

To select an element with the required thickness or introduce

To specify
its value
a thickness Range (first of all, check the box) by introd

To pick two triangles that will def

To apply Confirm the thickness set modifications

thickness
variations
caused by
draft angles

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Let’s start with the bosses. Just enter the Thickness of 3 mm (or pick any element that
already has a 3mm thickness assigned to it), select the elements to be edited and
confirm your choice with the Apply button. Do the same for the close ribs.

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You will get this result:

Thickness values that could be modified

When selecting individual elements that need the thickness value changing, to save
picking a large number of elements one at a time VISI Flow offers the possibility to
select triangles by angular deviation (very useful in many occasions), by connectivity
or by visibility.

Select only Visible Elements

Select Triangles by Angular Deviation

Select Connected Triangles

See also the Selection Icons help for further details. Ask your instructor for other
methods of selecting triangles for changing their thickness values.

Fix now the scattered thickness distribution in the internal thickest area’s:

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Format the Model for the Analyses
video

Once the thickness assignment has been completed, it is possible to format the model
for the analysis.

In all the cases where the model has been modified and not yet saved before
formatting, select the Save option available in the File pull-down menu.

The window that is displayed will allow you to automatically conduct all the verification
checks on the model. This important aspect of the part preparation is forced to alert
the user of wrong model description and avoid calculation errors due to incorrect
models.

In case of error messages, return to the appropriate phase of the modelling process.

If no messages are displayed after the verification of the part, the program starts
formatting your model. This operation will create the super-structure and the
hexahedral mesh used by the calculation modules.

At the end of this operation the Analyses Browser is automatically open.

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Flow > Analyses

Understanding the interface:

1 2 3 4 5 6 7

8 9 10 11 12 13

1. Show Thickness
8. Create New Study
2. Triangle Information
9. Thermal Analysis
3. Project Information
10. Filter Analysis
4. Refresh Channels Graphic
11. Calculation Manager
5. Refresh Tree
12. Analysis Browser
6. Flow Configuration
13. Analysis Results
7. Material Characterization

The following steps will guide you through the preparation procedure for setting up an
injection moulding analysis. Many of the relevant parameters will be explained during
the preparation process.

Define the Moulding Conditions of the Filling Phase

For a deeper explanation of the various options please refer to the “Filling calculation
input and result description and tips” section of the Appendix.

Click the Create New Study icon or right click on the Filling analysis label, in the
Studies tree, to introduce the calculation inputs for the selected technology, in this
case the Standard thermoplastic injection moulding.

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 Fill in the Filling analysis dialog box as shown below:

Enter Filling Analysis name

Select the appropriate material

Define the melt entry points

Enter a Name for the filling results (BODY1-A)

Click the Material Manager icon to choose a grade from the databases.

By default, the Plast data bank will be displayed: it contains generic material grades,
not linked to any manufacturer. These databases carry a *.maf extension.

Vero database

Specific producers (within

Right click on the desired
the polymer family name)
grade to display information
and user defined material
about its properties
databases

Select the M430_01 PA 6/6 30% glass reinforced grade.

Right click on a grade to add it to an existing group of favourite materials or to

review information about its properties.

Confirm your material selection with the OK button.

Now click the icon to add an Injection point from which the molten material will
enter the cavity. An injection element can be the sprue, nozzle or any node of the
component.

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Multiple melt entry points can be selected without the need to add complete runner
systems to the model. An injection element will be identified by an arrow in the model
space. Use the Pick button to quickly create a list of injection elements.

Select the injection point on the node at the positions shown in the figure.

At this time all the information required to run an analysis are available.

Select the Moulding tab to display the processing conditions.

Accept the suggested values for melt and moul

Confirm the suggested value for the Volume/Pressure chang

Change the suggested Injection time to 4 seconds and accept all of the other default
values.

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Go back to the General tab to enter the analysis settings into the description field: this
will help us easily see the analysis settings when viewing the calculation results. In our
example the data (M430_01 (PA 6/6 30% gr) - 4s 300°C 90°C 95%) refer respectively
to the material grade, injection time, melt and mould temperatures and V/P change
point.

Click OK to save the moulding conditions.

Then simply right click on the analysis name

BODY1-A (BODY1.FES) you just created and
select Run to start the calculation.

The Calculation Manager opens by showing the running analysis.

When the calculation is complete a message is displayed. You may now close the
Calculation Manager.

Simply right click on the analysis name or select the icon to Load Results.

The next section is intended to help you to better understand the analysis results. For
a deeper explanation of the different variables please refer to the “Filling calculation
input and result description and tips” section of the Appendix. Other documentation is
available as a guided on-line help that can also be printed. This context sensitive on-
line help, that covers all major working sections, can be invoked through the F1 key.

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VERO SOFTWARE 22
 We will now start to analyse our filling calculation.

General tools
Variable’s animation

Evolution of the filling and packing phas

Field variables

Click the Quality icon to get an indication of the overall quality of your part coming
from the results obtained for the filling Pressure, flow front Temperature, Shear Stress,
and Frozen Skin under a given set of moulding conditions.

The indicated variables, linked to

the requested quality, can be
evaluated separately since their
improvement produce an overall
better quality.

The aim is to optimise the

processing window available to
the moulding technicians.

When reviewing the results of the

filling analysis, try to take a global
look at the result variables. For
example, you can accept higher
cooling of the flow front if the
frozen skin level is low. You may also accept some how high stress levels if the
temperatures are high.

The visualization for most of the field variables during the filling and holding phases
can be animated. This provides a striking illustration of the dynamic changes of these
variables during cavity filling and packing.

Just click the Play button to start the animation.

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The following gives a description of the variable results in the pull down list.

Isochrones – To display the development of the filling phase to understand the

advancing flow front pattern. Used to accurately track the formation of weld lines and
the potential of air traps (see also relevant icons in the General tools).

The Time Step slide bar lets you select a short shot, which is basically a save created
during the analysis calculation at a number of set intervals. The number of short shots
can be set through the Configuration. (Ask your instructor for more information)

You can control the progress of the melt front also specifying a time step to animate
the filling with the desired pace.

By moving the sliding cursor to focus in the area of your interest or by setting the
Minimum and the Maximum values of this variable, you can examine the details of the
weld line formation. An enlargement of the area, will provide a good understanding of
where the melt fronts come in contact so producing areas of potential weld lines and/or
air trapping (see also the Orientation of the main flow stream in each element and the
Temperatures in relation to the material characteristics).

Reduced scale respect to the total filing time

Temperature

Welding line

Orientation

Providing that you can evacuate the air, the quality of the weld lines is determined by
the temperature of the flow front. Higher temperatures will mean better welding.
Click the relevant icons to get a global overview about weld lines and air traps.
The first function highlights the potential formation of weld lines. Their real
influence on part quality is to be evaluated reading the previous described variables.
The prediction of potential of air traps can be simply weighed up through its
option.

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Note that the graphics indicating both weld and traps is saved on the active layer.

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Temperature – Average temperature of the material across the thickness in each
element. It can be obtained at different time intervals and at the end of filling. To
obtain high quality mouldings, the temperature difference in all elements describing
the part should be within a narrow range. It requires that the heat lost by conduction
due to the cold mould surface be compensated for by the heat generated by friction.

The maximum allowable difference depends on the plastic. A rule of thumb is the
following: at the end of flow, the material should not cool down more than 15 to 20°C
when compared with its typical average value. Whenever possible, it is desirable to
heat the material about 10 to 15°C by friction in the runners. In very difficult filling
situations, one can even accept heating the material by 10 to 15°C due to friction in
the part near the gate.

This quality evaluation can be done, for typical situations, selecting the Single
Variable through the Quality .

The quality of the moulding can be easily evaluated by the highlighting of the elements
with variable values outside the category limits. Practical considerations, coming from
long term Vero experience, will be used during the display of the variable for which those

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elements with a value higher or lower than the set category limits will be shown in
different colours.

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An expert technologist may then determine the best moulding conditions by examining
these results. For example, if the material Temperature goes below the minimum
value the technologist might try to reduce the injection time. In situations where the
maximum value of the shear stress is too high as well, he may decide that the best
solution will be to increase the melt or the mould temperature.

Temperature - Peak and Local End Flow – In addition to the above typical instantaneous
values calculated in the last moment of flow movement inside the considered element, it is
also possible to evaluate the peak (maximum value of the element temperature profile) and
the average value of local temperature at the end of the filling time.

Pressure – Pressure distribution in any element at each specific time during filling.
The values clearly indicate areas of over packing that can cause differential shrinkage
and consequent warpage. The program performs the calculation of the initial holding
phase for all flow paths already filled.

Click the Chart icon to display a graph showing the filling Pressure vs. the Time.
The injection pressure increases during the filling phase until it reaches 95% – the
default value set for the V/P Change – and then drops down to a pressure equal to the
75% of the one reached at that moment.

The maximum injection pressure should non exceed the moulding machine capability
with a “safety margin” usually about 20%, also because a typical injection moulding
machine is rated on hydraulic pressure, multiplied by the so called intensification
factor which represents the surface ratio between the oil cylinder and the plastic barrel
(usually in the order of 10–15 times).

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If at the beginning of a series of analyses when runners and gates are not yet included
in the model, as in this example, consider the extra pressure which will be required for
them (see Single Variable through the Quality ).

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The Chart tab permits to setup
and display variable graphs
from the evolution of
main computed variables.

Many fields are available

through the window to
customize your graph:

Click the Display chart button to show a graphic diagram. Any time you confirm the
variable selections a new diagram is created.

By using the two fields at right of each variable it is possible to modify the graph
accordingly to the selected range of values for each variable and the colour as well.

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The Orange line indicates the Flow Rate of the material entering the cavity. In this
example the material flow stays constant until it again reaches the V/P Change where
it then starts to drop to achieve the set pressure requirements.

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Opening Force – Force acting on the mould that needs to be opposed by moulding
machine clamping force. It is generated by the filling pressure acting on the projected
area of the model. It can be determined at various instants during the injection time. In
cases where the Pressure for the subsequent holding phase, specified in the filling
calculation inputs, is higher than the pressure required for filling, the final stage must
be evaluated carefully. In fact, during the pre-holding phase after the V/P Change the
final pressure distribution might not be equalized in the whole part and give an under
estimation of the clamping force required in the packing phase. It is recommended
that an holding analysis be done in all cases where the clamping force during the
holding phase is a critical requirement. In these situations it is safe to assume an
opening force during holding phase equal to the projected area multiplied by the
considered pressure.
Note that for semi-crystalline materials, easy to flow but requiring high holding
pressure to maintain low shrinkage, the clamping force requirements may come from
the holding instead of the filling phase.

The considered Projected Area is the projection of the model on the XY plane of the
screen, so take care to orient the model correctly. This option calculates projected
area and opening force of the part oriented as in the displayed view. To orient the
model correctly, it is convenient to bring it to its Front view and then, with rotational
commands, put the model in the desired orientation and finally call the Opening Force
option.

Shear Stress – Ratio between the shear force which drives the flow and the area
resistant to flow. It is a function of the material viscosity and the flow rate. The stress
displayed is the maximum across the thickness of the element at various instants
during filling and serves to gauge the quality of the part. During cooling, part of the
stress at the end of the filling relaxes, but a residual stress remains frozen in and will
be one of the causes tending to distort the part. The shear stress should not go above
a specific limit that is a function of the type of plastic. Typically, in the part, it should
not exceed 0.3 to 0.7 MPa (see Single Variable through the Quality ).

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Shear Rate – This gradient is the difference in velocity between adjacent laminar
layers within the flow channel, divided by the distance between them. The maximum
shear rate across the thickness of the segment is shown. See the shear stress
considerations.

Frozen Skin – Percentage of material frozen during part filling. For example, 10% of
frozen skin on a 3 mm thick part means that the frozen layer in each side is 0.15 mm.
This variable is essential to optimize the
moulding conditions and is a very interesting
index used to judge the quality of the part
because it measures the frozen orientation (the
polymer solidifies during the flow in oriented non
crystalline form). The allowable amount
depends on the type of material (see Single
Variable through the Quality ).

Frozen Skin - Local End Flow – In addition to the typical instantaneous values
calculated in the last moment of flow movement inside the considered element, it is
also possible to know the average value of local frozen skin at the end of the filling
time.

T. Holding Time – The evaluation of the no-flow time with “Technical” values
(minimum packing pressure times normally considered adequate to control the
shrinkage with pressure conditions not inferior to the suggested values for the specific
category of polymers) integrates the Theoretical values. These values give a practical
indication of the packing of the part.

No-Flow Time – Time until all layers of the

element reach the no-flow temperature of
the resin (as specified in the material
database) starting at the end of part filling.
These values give a first indication of the
packing of the part (theoretical maximum
holding time for each element).

T. Cooling Time – The visualization of the

cooling time with “Technical” values
(experimental ejecting conditions that are
acceptable in practice even if the complete
solidification of the thickness section has
not been yet reached) integrates the
Theoretical values. This time is used as a practical reference to set the cooling time.

Freezing Time – Time required for the centre of the element to reach the freezing
temperature of the resin (as specified in the database) starting at the end of the filling
of the part. It normally represents the maximum cooling time since some parts can be
ejected with a partially hot core (see Single Variable through the Quality ).

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When you feel that you have achieved the best obtainable results for the filling
analysis we will prepare the next phase of the analysis, the packing or holding phase.

Define the Moulding Conditions for the Packing Phase

For a deeper explanation of the various options please refer to the “Holding
calculation input and result description and tips” section of the Appendix.

Right click on the filling analysis name and select Create holding to introduce the
inputs for this phase of the moulding process.

The packing calculation settings window will be

displayed, Holding Time and Cooling Time will
automatically be suggested by the program
following the indications taken from the filling
analysis.

Confirm the suggested packing

pressure taken from the database

Enter the following analysis description (10.8h, 45c, 50MPa) that refers respectively to
the holding and cooling times and holding pressure. This will help us easily see the
analysis settings when viewing the calculation results.

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Usually, for the first packing analysis, a somehow higher value (+ 10%) of the
technical holding time of the section near the gate is taken as the moulding machine
holding time. We may verify later on that the gate would remain open for the desired
time.

As input for the cooling time, a value ranging from the minimum and the maximum will
be taken with the selection depending on the size and shape of the part as well as on
the type of ejection and quality requirements. Small parts with simple shapes can be
ejected while still hot where large and complex parts are requiring longer cooling to
reach enough rigidity to be ejected.

Click OK to save the packing conditions.

Then simply right click on the holding analysis

BODY1-A-H (BODY1-H.HLD) file you just created
and select Run to start the calculation.

The Calculation Manager opens by showing the

running analysis.

When the calculation is complete a message is displayed and you may close the
Calculation Manager.

Simply right click on the holding phase analysis name or select the icon to
Load Results.

To judge the quality of the moulding, many of the field variables available during the
filling phase are also available from the beginning of the holding phase to the end of
the cooling time.

Temperature – Average value for each element at the indicated time. No precise
rules can be applied to know the best value at each time. Uniformity is what counts
the most.

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 Pressure – Distribution of the holding pressure in any element at the specified time.
Excessive pressure drop during packing should be avoided since it generates different
density with a consequently high tendency to deform. The pressure must drop to
atmospheric at the end of cooling. If it does not take place, you must reduce the
holding pressure or the packing time providing this will not influence too negatively the
volumetric shrinkage and the potential of sinks and voids. If you cannot act on the
holding conditions you should increase the cooling time.

Time from the start of filling to end

Rescale the variable range to the current time step

A suggested approach is to start analyzing the graphs with the many variables that
can be seen as function of time. In fact, it is possible to trace any element in the more
significant regions of the model (different thickness, far and near from the gate, the
gate itself) to display the evolution, at any instant, of the field variables

Check the Draw Chart

box to diagram the
evolution of the current
variable, for each
selected entity , by
reading the conditions in
each short shot or
holding view.

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To remove a graph just uncheck the box.

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Shear Stress – This variable should be kept at a much lower level than in filling,
generally it is in an order of times lower. Its uniformity is very important to part quality.
Look at the entirely of values: little spots are normally not so important.

Frozen Skin – To display the frozen skin formation. See the considerations about
temperature. Move through the holding phase to see the growing of this variable up to
the complete solidification, at least of the significant areas, at the end of cooling.

Density – This variable is related to the entering mass during the holding phase and
to the temperature. It should be noted that the density displayed is the value at the
considered temperature. Uniformity of density is essential to avoid potential warpage.
See also the considerations about its graph evolution.

The Entered Mass is

one of the first
variables to look at to
verify that the mass
continues to enter until
the desired holding
time is reached
because the gate
should not have a
premature freezing.
When we get the
displayed curve, with
the mass continuing to
enter until the
assigned holding time
is reached, we are
sure that our gate
stays open for the required time. Ideally, we should have a stop of the mass entering
the cavity at an instant before the set time since, in the opposite condition, we do not
know if the gate stays open much longer.

Volumetric Shrinkage – The local volumetric shrinkage is the difference between the
melt and solid volume divided by melt volume of each small element representing the
part. This variable is related to the entering mass during the holding phase. The
computed volumetric shrinkage considers cooling of the element to room temperature
with relaxation of the pressure. As for the density, uniformity of this variable for
sections with the same thickness, is essential to avoid potential warpage because it is
one of the internal strains responsible of final linear shrinkage and deformation out of
the plane (warpage).
The volumetric shrinkage must not be confused with the linear shrinkage of the
dimension (as percentage variation of the original distance) displayed by the warpage
analysis. Just as an indication, consider that the linear shrinkage can be estimated in
the order of 1/3 of the volumetric shrinkage. The volumetric shrinkage can be modified
by changing the holding pressure or the time of its application: higher values lead to
lower shrinkage while the contrary will give opposite results. The actual linear
shrinkage between specific locations on the part can be easy determined at the end of
the subsequent shape analysis.

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Sink/Void – Thickness reduction or creation of internal voids as percentage of the
thickness. It considers that the volume contraction, generated by a premature drop of
pressure in the melt, acts completely on the thickness. When pressure does not
compensate the melt shrinkage, the surface will sink (a valley is formed on the
surface) if the layers already solidified can be deformed. Otherwise, if the external
solid layers are very rigid, a void (a bubble) will be formed inside the element. A
“perfect” moulding has zero areas with such a kind of defects so the result will just be
a blue colour picture.
As explained, sinks/voids are generally connected with poor packing which may also
depend on the part geometry. In parts with varying thickness you may accept local
spots with the potential of sinks/voids if they are not in critical areas.

Opening Force – To compute machine clamping force requirements during the filling
and packing phases. For semi-crystalline materials, easy to flow but requiring high
holding pressure to maintain low shrinkage, the clamping force requirements may
come from the holding instead of the filling phase.

Orientation – For unreinforced materials represents the orientation of the main

flow stream in each element.

For the fibre reinforced grades are

displayed the results of the calculation of
the fibre’s orientation, as a function of the
deformation and vorticity tensor,
determined by the flow conditions. The
comparison with the filling phase
orientation, still based on the velocity
vectors, permits to comprehend the
vorticity effects generated by the filling
conditions. Obviously this aspect, that
mainly influences the areas with a radial expansion of the flow, may result in a
different deformation behaviour. Actually the only way to see its influence is to

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continue with the dedicated analysis for the calculation of the final moulded part shape
prediction.

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 Define the Moulding Conditions for the Shape Analysis

For a deeper explanation of the various options please refer to the “Shape analysis
input and result description and tips” section of the Appendix.

The next step in the analysis process is to set up and calculate the distortion
of the moulded component from the moulding conditions that we have used in
the Filling and Holding analysis.

Right click on the holding analysis name and select Create shape to introduce the
inputs for this phase of the moulding process.

The Shape analysis dialog box will be displayed.

Just click OK to save the calculation conditions.

Just confirm the name of the calculation results

To select the constraints in case of physical fixing

Constrained Nodes – The program automatically constrains the model and filters
all rigid movements. In fact, the calculation lets the structure reaching the equilibrium
of the internal tensions.

Do not select any constraints whenever the part is not physically fixed because this
would delete some loads from the structure hence changing the final shape of the
part. In fact, between constrained nodes the model cannot move and shrink and so
the internal forces are not free to relax (each constrained node can neither move nor
rotate).

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This option is to be used only in cases the part is physically fixed, for example in
presence of inserts. In fact, in that area, the part is “locked” by the insert so cannot
move and shrink, such as parts like “car fans” with an insert in the central hole.

Click the Constrained Nodes button to quickly create a list of nodes. The entity of
the model identified as constrain is indicated by an arrow. Use Delete to erase a
potential constrain from the list or Edit to modify its location.

Click the Auto Constrains button and just select a body to fix all the nodes at
contact with the body.

This feature is fundamental to simulate Insert Moulding where the metal insert blocks
the shrinkage of plastics.

Simply right click on the shape analysis name

BODY1-A-H-SH (BODY1-H-SH.SHA) you just
created and select Run to start the calculation.

The Calculation Manager opens by showing the

running analysis.

The computation starts with a pre-processor of the

data from the holding analysis. It reads the results
of the filling and post filling analyses and
integrates them with the material data to determine the internal loads on the structure
and the local material strength. During this pre-processing phase, some key informa-
tion about its progression is displayed on screen.

An optimization module is then used to reduce the bandwidth of the strength matrix.
Then the last module performs the calculation. The evolution of the calculation can be
followed on the screen with the sole purpose to know its progress and the expected
time to completion.

Once the message indicating that the calculations are completed appears, you
can close the Calculation Manager and view the results.

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 Simply right click on the shape analysis name or select the icon to Load
Results.

For a complete overview of the different options please refer to the “Shape analysis input
and result description and tips” section of the Appendix.

When the warpage results have loaded a new View Shape tab will be displayed.

Deformation

Export deformed STL model

Warpage animation

Sections

Original geometry

Evaluate warpage components

Display displacement of the model

With the three On Axes options you can evaluate the distribution of part
Thedisplacement
Minimum and(deformed
Maximumnodes). The Global
fields allow option h
for interactive

The first check we will make of the components moulding distortion will be a visual
check.

The View deformed body slide bar lets you look at the final shape of the part after
moulding. To better evaluate the distortion a scale factor can be used. The
deformation is displayed by default at a scale 1:1. The value specified in the field at
right, that can be animated through the slider, magnifies the distortion of the model
along the three Cartesian axes. To highlight area’s of the most distortion, try using a
larger scale factor.

A transparent image of the undeformed model will also be displayed as a visual

reference.

Note that it is possible to export an STL file of the Deformed model,

so dimensional comparisons can be made inside any CAD.

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VERO SOFTWARE 44
The part can be easily sectioned at any desired location to allow precise
measuring of warpage.

The effect on Warpage of the different internal loads can be split into their contributors.

The shrinkage outcome is caused by variation in

crystalline content and volumetric shrinkage
from area to area of the part. Orientation causes a different shrinkage in parallel and
perpendicular flow directions. Shrinkage due to differential temperature is typically
dictated by a poor cooling system layout. In fact, temperature differences from one
side of the mould to the other cause variations in shrinkage through the thickness of
the component. Note that the final shape of the injected part is depending on all the
three effects.

Select the options available through Displacement to assign dimensional values to

the calculated distortion. Obviously, in case of
magnification of the model distortion the

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values of the displacement displayed in the colour scale remain unchanged
independently from the scale factor of the deformation.

The results are displayed on the part after moulding to give you a better evaluation of
the direction and amount of the final shape. If the View deformed body tick box is not
selected the model will be shown without deforming the component.

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The most intuitive method of displaying the distortion of the component is with the On
Axes option.

For example, the above red area’s show node movement in a positive “Z” direction
and the blue area’s show node movement in a negative “Z” direction.

You can also measure the Variation of distance of two locations on the actual part,
with respect to the original model, starting from any desired Reference Node or Point.

In the absence of any deformation, the Variation of Distance and Deviation (on a
percent base instead of absolute values) are referred to the moulded part increased
by the typical linear shrinkage percentage (or the average value you can measure
from the calculation).

The Centre of the body is often the best choice when analyzing the Global
displacement. For parts showing uniform shrinkage without warpage, the deviations
will increase in any direction proportionally to the distance from the centre.

Whenever the displacements on a specific axis is of interest, it is often better to

choose a node at its origin. Remember that the program determines the new position
of nodes only relative to the considered axis, but any translation of a node in the other
axes also modify its coordinate in the considered axis. The opportunity to define a
Linear Shrinkage (%) helps determine the best shrinkage allowance to use in tool
construction, highlighting the tolerances that will be obtained for the moulded part after
applying this correction. The calculation applies this shrinkage factor to any
displacement and, whenever the displacement of a specific node versus the reference
node is identical to this percentage of their distance, the deviation will be zero.

If the applied shrinkage factor is too high, the scale will show positive numbers. This
means we are making an excessively large cavity due to great a shrinkage allowance
and the dimensions of our moulded part are too large. Since the deviations generally
are not identical in the various sections of the part, we should play with different
factors to confine the deviations where they can be best tolerated.

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 The Plane option permits to evaluate
the distance of the displaced nodes
from it (planarity). After selecting this
feature, click on the Define button to
display the Workplane manager. Then,
reduce the scale range to evaluate the
planarity.

Using reference planes to make your

distortion evaluations is like placing the
part on a desk to evaluate some points
with a measuring “comparison”
instrument.

Select the Linear Shrinkage icon from the Measure tab.

After selecting two points of the part, this option estimates the linear shrinkage of the
dimension as percentage variation of the original distance. The two length distances
between the selected nodes (the first value is the models size, and the second is the
size after model displacement) are also displayed.

It is also possible to Measure Displacement of the part.

Create or select exiting reference planes to calculate the distance of desired nodes
from them. This distance has a positive value in the case the node is located above
the plane (hence in the direction of the plane normal) and a negative value if the node
shifted under the plane (in the opposite direction respect to the normal).

Since this part does not fit to explain the Ovalization option, please refer to the “Shape
analysis input and result description and tips” section of the Appendix.

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 2. Run the Complete Mould

In this section we will learn how to add cooling channel layouts and the cavity
extension also adding the gating and runner system. Actually, a typical step by step
procedure to analyse an injection mould is to start just by simulating the most
convenient melt entry points (as in the previous section), and then add the runner
system to observe what happen assuming an uniform mould temperature.

With VISI Flow it is possible

to accurately describe,
along with the part,
the gate, the runner system
(cold, hot or insulated runners),
the hot tips, the mould inserts,
and the cooling lines.

Run VISI

File > Open Select the file named “Body_Mould.wkf”

located in \Visi18\Workf\Sample\Flow\Mould

The geometry should look as above.

VERO SOFTWARE 49
We’ll start work on the feeding system.

Activate layer 20 (Core Insert)

There are several alternatives to accomplish the task to describe the cold runners:

 Assign Property from the Feeding Channels menu: to insert the properties that will
define the characteristics of the runners;

 Runner by Injection Points from the Gates - Runners menu (it requires the Mould
license): to create the injection circuit starting from the injection point, creating
gates and then the runners;

 Analyze Runners from the Mould Assistant menu: to automatically transfer the
CAD geometric information of the feeding system to the analysis environment;

 Define Runner by Triangles or Set up Triangles as Runners from the Feeding

Channels menu: to add runner and gate size attributes to the feed mesh.

The simplest and fastest way to describe the runner system is to use Curves. The
next section explains this procedure.

Create (or, for example, Merge from an IGES file) the centre axes of the
runners (cyan lines).

Layer 7 (Runners Curves) has the required curves generated.

Gate curves

Runners curves

Now we must insert the properties that will define the characteristics of this section of
the feeding system.

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 Move node

Select the Feeding Channels icon. Check element connectivity

Split curve Define runners by triangles

Set up triangles as runners

Assign property

Assign occurrences Add a spill over

Add an hot tip

Move segment extreme

Select the Assign Property icon (available through the Feeding Channels
menu) and pick the first curve of the cold runners: the gate.

You will now need to fill in the Properties dialog box.

All the required values for each curve are given below. For example property Name,
type, and values to be put on each curve.

4
3
2

Assign the following values to the curves:-

([1] - Property Name GATE, Type GATE, diameter 1 mm), gate connection with part.
([2] - Name COLD1, Type COLD TAPERED, starting diameter 1 mm and ending 2.8
mm, and 6 as N. of Elements), last gate section connected to the runner.
([3] - Name COLD2, Type COLD TAPERED, starting diameter 2.8 mm and ending 5.1
mm, and 6 as N. of Elements), connection to the horizontal runner.
([4] - Name COLD3, Type COLD, and 5.1 mm as diameter Value), horizontal runner.

VERO SOFTWARE 51
VERO SOFTWARE 52
Take care when assigning a tapered property to the curves. In fact, the
allocation of the diameters inserted in the database depends on the direction
of the curve.

When you have assigned runner values to all the

curves, you will need to verify the connection
between the curves and between the mesh model
and the curves.

To verify the appropriate joining together Check

Element Connectivity.
Any elements that are not connected and thus stopping
the flow of polymer through the runner system to the
cavity will be highlighted.

Activate layer 3 (Mesh)

Delete the small “gate” elements since it they are not

necessary with this representation of the runners.

With the Move Node command connect the closest

node of the mesh (this node will be moved towards the
second location) to the gate curve (its selected vertex will remain in the same
position). After the selection and confirmation of the 2 nodes to be condensed, the
program merges them into a single node.

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Do the same for the opposite gate.

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The most integrated solution is to build the runners through the Mould features so to
link this information to VISI Flow and make it able to recognize them.

Activate layer 4 (Part) and layer 20 (Core Insert)

Select Create Runners through Gates - Runners from the Mould menu. This function
allows to create straight, radial or custom circuits starting from the runner channel to
the gates.

Choose Custom as Circuit Type. The system gives the possibility to create and select
a 2D layout through the Pick Custom Circuit icon.
Then, choose the semi-circular circuit section.

On the mask click “Pick the Injection Points” , then select a location on the part,
the vertical face and the gate direction. Do the same for the opposite gate.

Selecting “Draw Gates” the system creates the gates starting from the selected points
following the set directions. Introduce the desired gate dimensions.

From the Gate tab click the Gate Selection icon and pick the runner curve to
automatically generate the two injection points.

Please ask the instructor for assistance or an explanation about Mould commands.

VERO SOFTWARE 55
Once again, you need to verify the connection between the curves (automatically
created by the Mould commands) and the mesh model.

Activate layer 3 (Mesh) and layer 14 (Runners)

Select Check Element Connectivity to verify that the gate curve is longer than
necessary. You may Move the Segment Extreme (be first selection) of the curve
towards the closest node of the mesh. The program merges them into a single node.
Do the same for the opposite gate.

For the Analyze Runners option, that transfers the CAD geometric information of the
feeding system to the analysis environment, follow the indications of the next
paragraph about hot runner description.

For the Define Runner by Triangles and Set up Triangles as Runners options to
add runner and gate size attributes to the feed mesh please refer to the “Modelling
consideration and tips” section of the Appendix.

Just note that, after the mesh the solid runners, the elements in common between
part and sprue must be removed and their nodes connect. Once the portions of
the model have been properly connected, we must run a thickness calculation for the
runner triangles.

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VERO SOFTWARE 57
Mould Assistant > Analyze Runners

Now we are ready to define the rest of the feed system.

This can be done automatically with Analyze Runners: the easiest way to proceed.

This unique utility allows to automatically transfer the

CAD geometric information of the feeding system to the
“analysis environment” dramatically cutting the times
required for modelling.

Activate layer 0 (Hot Runner) deactivating all the other

layers.

Run the Analyze Runners function.

Select all the solid elements. A menu appears giving

you the opportunity to specify the type of runner and
relevant attributes.

For the thermal analyses, to take into account that hot

runners are isolated respect to the metallic mould block,
you must also define the thickness of this isolation by
specifying a Gap and also the value of the External
Diameter (by default, a multiplication factor is applied).

Select the OK button to pick the melt entry point

and the exit element (see circles on the image).
For the Runner’s geometric information to be
transferred to the mesh elements.

On the chosen layer (in this example: HOT Runner

2 flow) you will find the curves with automatically
attached the properties that will define the
characteristics of this section of the runners.

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Let’s continue with the cold runner connected with the sprue.

Run again the Analyze Runners function selecting all the solid elements.

In the window, check the Cold property type.

Select the OK button to pick again the entry
point and the exit element (see circles on the
image). On the chosen layer (in this example:
COLD Runner 2 flow) you will find the curves
with automatically attached the properties
that will define the characteristics of this cold
runner.

Complete the feeding system description with the hot tip.

To improve the quality of the results, the description of the Hot Tips, fundamental
components of the hot runner system, is done using a triangularized solid. This allows
you to give a detailed description of this important area and is the easiest and most
precise way to proceed.

Activate layer 22 (Hot Tip) deactivating all the other layers.

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The hot tips must be generated by meshing the solid model representing the “plastic”
flowing through the tip.
The simplest way to generate the solid model of the “plastic” tip is to create a Cylinder
(from the Solid  forms menu) surrounding the hot tip and then extract its Cavity
(Operation menu).

Follow the next few recommendations when creating these elements.

If possible, remove very thin faces, such as the one highlighted

in orange at left, and delete the extra plastic in the geometry that
is not important to flow or have been created in the clearances:
they just produce very low thicknesses without adding significant
precision to the calculation.
To save up calculation times describe all the cylindrical sections
of the hot tip with 2D elements and just mesh the remaining
areas.
In this example you must also remove the part of the cold runner
(highlighted in yellow), connected with the sprue that we have
already described in the previous section.

Just Cut Bodies (Modelling menu) and Unite the remaining solids.

Please ask the instructor for assistance or an explanation about the above CAD
commands.

Run Create Mesh from the Mesh menu.

After clicking the solid element representing the hot tip, a window appears to choose
the desired element size. To obtain a detailed description of this area, typically a
small element dimension is selected.

For this example, we specify an element dimension of 1 mm for the initial

triangularization and then we will ReMesh the hot tip with a triangle size of 1.5 mm
and the default parameters.

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Then, select the mesh representing the hot tip and add it to the Flow Project.

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Since the hot tip must be connected to the rest of the runners system, to work in an
easier way move its mesh on a different layer with Change Attributes (available in
the Mesh menu).

With the Move Node command (available through

the Feeding Channels menu) connect the closest
node of the mesh (this node will be moved towards the
second location) to the final part of the hot runner
system (its selected vertex will remain in the same
position). After the selection and confirmation of the 2
nodes to be condensed, the program merges them into
a single node.

Do the same for the cold runner and the

bottom hot tip area.

To verify the appropriate joining together

Check 2D Element Connectivity.
Finally, ensure the connection between the
sprue and the cold runner.

Wrong situations can be easily fixed though the Split curve command available
through the Feeding Channels menu.

The last operation is the Thickness calculation for the hot tip.

Note that the calculation of part thicknesses acts only on the active layers. This can be
very useful to work on specific areas as for this situations.

Activate layer 23 (Hot Tip Mesh) deactivating all the other layers.

In case of “massive” parts such as hot tips, it is suggested to compute thickness using
the through Hexahedral Mesh method. With this algorithm the thickness at any point
is defined by measuring the distance of opposite triangles and through the
hexahedrons created between them. Open the Flow Configuration to change the
thickness calculation algorithm.

When completed, you can view the thickness distribution: you should now have a
mesh with some elements without any thickness assigned (grey colour).

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To improve the thickness distribution select the Assign Thickness icon to get the
result displayed in the next figure.

At last, pick the Add an Hot Tip icon

(available through the Feeding Channels
menu) and select all the elements of this ending
part of the hot runner system.

The final part of the modelling process is to add the cooling system. There are
different alternatives to accomplish this task:

 Assign Property from the Cooling Channels menu: to insert the properties that will
define the characteristics of these elements;

 Draw Coolant Path from the Mould Assistant menu: to automatically transfer the
CAD geometric information of the cooling system to the analysis environment.

The simplest and fastest way to describe the cooling system is to use
Curves. The next section explains this procedure.

Let’s start with the cooling system detailed in the tooling plates shown on layers 5, 15
& 19 and composing the Inject layer group.

The system has been converted

to a solid on Layer 24 (Cavity
Cooling) just to give you a
better understanding of the
coolant path.

Create (or Merge from an IGES

file) the centre axes of the
cooling channels (blue lines).

Layer 27 (Cavity Cooling

Curves) has the required
curves generated.

Now we must insert the

properties that will define the characteristics of this section of the cooling system.

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 Select the Cooling Channels icon.

Split curve
Check element connectivity

Assign property
Define cavity extension

Move segment extreme Add an insert

Select the Assign Property icon (available through the Cooling Channels
menu) and select all of the curves.

You will now need to fill in the Properties dialog box.

Cooling channels considered in the thermal analysis

When you have assigned channel values to all the curves, you will
need to verify the connection between them.

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To verify the appropriate joining together Check Element Connectivity. Any
elements that are not connected and thus stopping the flow of coolant through the
cooling system will be highlighted.

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Mould Assistant > Draw Coolant Path

The remnant of the cooling system can be modelled automatically with the Draw
Coolant Path utility.

This unique tool allows to automatically transfer the CAD geometric information of the
cooling system to the “analysis environment” dramatically cutting the times required
for modelling.

The cooling system detailed in the tooling plates on layers 8, 16 & 20, and composing
the Eject layer group, has been converted to a solid on Layer 25 (Core Cooling) just
to give you a better understanding of the coolant path.

Activate layer 20 (Core Insert) deactivating all the other layers.

Run the Draw Coolant Path function.

Select all the solid elements. A menu appears giving you the opportunity to specify
colour and layer for the cooling lines that will be generated.

Select the OK button to pick the

coolant entry point and the exit
element. For the channel’s geometric
information to be transferred to the
mesh elements.

This utility will interrogate tube

elements and display all the potential
Path available.

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A dialog box is displayed asking if you wish to add Baffles and Fountains. In this
exercise we will not add these features so just click Ok.

On the chosen layer (in this

example: Core Cooling
Curves) you will find the
curves with automatically
attached the properties that
will define the
characteristics of this
section of the cooling lines.

Check that the connectivity

between all the elements is
correct and there are no
gaps that can affect the
analysis. Select the
Check 2D Element
Connectivity icon.

To complete the model setup we will insert the mould extension.

(Overall cavity size)

Activate the Flow group of layers.

Pick the Define Cavity Extension icon.

This feature allows the complete description of the mould block containing the cavity
and the cooling circuits.

Note that the program accepts hot runners outside the cavity block. This avoids
enlarging the mould extension in any case in which the runner layout is extended with
respect to the part cavity. This will
increase the precision of the
calculation.

While part of the hot runners could

be outside the cavity block, the
cooling circuits must be completely
contained with the extension.

In any case, an excessive mould

extension could be reduced by
deleting some of the cooling
elements.

The program displays a green box indicating the minimum cavity block dimension that
can be accepted. It can be resized using the tools available in the window.

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Activate layers 19 & 20 to resize the block surrounding the model accordingly to the
maximum extension of these inserts.

Save the complete model with the cooling channel layout and the cavity extension
under the new name BODY_MOULD1 (BODY_MOULD.WKF).

Format the Model for the Analyses

The window that is displayed will allow you to automatically conduct all the verification
checks on the model. This important aspect of the model preparation is forced to alert
the user of wrong model description and avoid calculation errors due to incorrect
models. If no messages are displayed after the verification of the part, the program
starts formatting your model.

A good practice in assigning meaningful

names to the files of the various steps of
the analyses can be of great help for any
further access to them (see Appendix).

Confirm the choices to let the program

format your model. This operation will
create the super-structure and the
hexahedral mesh used by the calculation
modules.

At the end of this operation the Analyses Browser is automatically open.

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 Define the Moulding Conditions for the Thermal Analysis

For a deeper explanation of the various options please refer to the “Thermal analysis
input and result description and tips” section of the Appendix.

Click the Thermal Analysis icon or right click on the Thermal analysis
label, in the Studies tree, to introduce the calculation inputs.

Fill in the Thermal analysis dialog box as shown below:

Enter thermal analysis name

Define the coolant circuits

Select the metal Select the appropriate material

Enter a Name for the thermal results (BODY1-A-T)

Click the Material Manager icon and select the M430_01 PA 6/6 30% glass
reinforced grade from the Plast data bank.

Click the Manage Metal Material icon to choose a grade from the databases.
By default, the Mold data bank will be displayed: it contains generic material grades,
not linked to any manufacturer. These databases carry a *.mld extension.

Select the Mold M220 - Tool Steel Carbon Steel [0.5% C] material.

VERO SOFTWARE 69
 Click the Circuits button to display a window to specify their properties.

Click Add to pick where the coolant enters into the circuit. After confirm with the right
mouse click, the circuit will be added to the list and displayed on the screen.

The labels beside the circuit name

indicates respectively a standard,
parallel or linked circuit.

By placing individual cooling circuits

onto separate layers the process of
To select the node where the coolant enters into the circuit defining the channels is greatly
simplified for very complicated mould
conditioning systems.

The total required flow rate is often in

the range of 70-100 dm3/min per kg
of material moulded at the same
time. For example, a shot of 100 g
with a cycle time of 20 seconds
requires flow rate of respectively 2.1
or 3 dm3/min. In any case, the
program allows to make an
estimation of the flow rate required
by the thermal conditioning fluid by
suggesting, depending on the number of circuits and the estimated cycle time, an
indicative value for a single cooling circuit.

Click the Fluid icon to choose a coolant from the

databases.

By default, the Fluid data bank will be displayed: it

contains generic coolants. These databases carry a
*.flu extension.

Select the Fluid F100 - To change the values

Watercoming
coolant.
from the flow rate estimation

Select the Moulding Data tab to specify the moulding cycle times.

Confirm the proposed Mould Open Time that is the time during which the mould is
open. It should also include cycle dead time and the time for mould opening and
closing.

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Change the Total Mould Closing Time to 35 seconds to compute the cooling time for
the part for this given time. Of course, the mould open time is to be added to this total
mould closing time to obtain the Total Cycle Time.

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Go back to the General tab to enter the analysis settings into the description field: this
will help us easily see the analysis settings when viewing the calculation results.

Click OK to save the moulding conditions.

Then simply right click on the analysis name

BODY1-A-T (BODY1-T.THE) you just created and
select Run to start the calculation.

The Calculation Manager opens by showing the running analysis.

The computation starts with a pre-processor module that prepares geometry and
thermal internal loads for the next steps while the subsequent module writes matrix
binary files.

The calculation program solves by a Preconditioned Conjugate Gradient Method the

matrix giving the temperature distribution in the solid cavity block. The evolution of the
calculation can be followed on the screen.

Note that it is possible to stop the

calculation with the desired
residual error. This permits, for
extreme cooling situations that
would require numerous
iterations with consequent long
calculation times, to evaluate the
conditioning system in a fast way
allowing for possible
modifications.

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The final module calculates the cavity surface temperature distribution and the cooling
fluid temperature.

Once the message indicating that the calculations are complete, close it and
simply right click on the analysis name or select the icon to Load
Results.

All the variables are displayed at the end of the Total Cycle Time. This time, indicated
at the bottom of the screen, includes the total mould closing time (specified during the
introduction of the input data, or the one calculated for a designated reference
element to reach its ejection temperature in the centre of the section or for a fraction
of it) and the defined mould open time in order to take into account the latter's thermal
dissipation effect.

Material Temperature – Average temperature of the material in each element. In

case of presence of hot runners with their typical melt temperatures it is suggested to
reduce the maximum value of the scale to display only the temperatures of the part.

Solid Fraction – This variable allows you to judge the fraction of plastics that has
reached the ejection temperature - this material is considered as solidified. The ideal
moulding quality is the one in which all elements have an average temperature below
the ejection temperature. In practical moulding the part can be ejected also at lower
values of the “solid” fraction.

Surface Temperature – To display the part cavity temperature distribution.

Section – To cut the cavity block through any desired section plane to look at its
temperature distribution in any point. A window appears to allow the selection of any
cutting plane. Note that the working layer must be active.

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The mould extension and possible special inserts are also displayed for easy
evaluation of the temperature distribution. In addition, to provide a better interpretation
of the calculation results, the cooling lines are graphically represented with their
effective dimensions.

It is also possible to display and save animations of the mould cavity sections
along the specified axis.

Fluid Temperature – Temperature of the coolant in the cooling channels.

Reynold Number – Represents the ratio of inertia and viscous forces. The evaluation
of this number is not so important if its value is higher than the minimum that ensures
a turbulent flow. This aspect is already examined during the pre-calculation at the end
of the description of each circuit.

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In this last part of the exercise we complete the simulations repeating the
filling analysis on the base of the preceding thermal situation. Then we
continue with the holding and cooling phases to the final shape prediction
analysis.

Define the Moulding Conditions with Thermal Integration

Click the Create New Study icon or right click on the Filling analysis label, in the
Study tree, to introduce the calculation inputs for the Standard thermoplastic injection
moulding.

To incorporate a filling calculation with the results of the thermal analysis completed in
the previous step go the Moulding tab and click on the Thermal Analysis
Integration icon to load the desired analysis (in this case pick the BODY1-T file).

The mould temperature distribution is obtained

Pick the thermal analysis to be integrated with the

Change the suggested Injection time to 5 seconds (to take into account the two
cavities) and accept all of the other default values.

Go back to the General tab to enter the Name for the filling results (BODY1A-T) and a
Description.

The material comes from the thermal analysis.

Note that the last element of the hot runner system has been automatically selected
as melt entry point.

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 Material loaded from the Thermal Analysis

The last element of the hot runner system is autom

Melt entry point

Now right click on the filling analysis name and select Create holding to introduce the
data for the subsequent packing phase.

Set the same holding time of the first not integrate

The cooling time is obtained from the thermal analysis

Regarding the Cooling Time, to simplify the introduction of data and reduce possible
interpretation mistakes in cases where the packing phase simulations are integrated
with the mould thermal analysis, it is automatically set, with no option to modify. In this
case, the Cooling Time is set as a function of the Total Mould Closing Time entered
during the preparation of the thermal analysis data.

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For the final stage, right click on the holding analysis name and select Create shape
to prepare the warpage analysis.

Now we will use the option to run several analyses in

sequence.

Open the Calculation Manager and add the

calculations to be done. To load calculation settings
from other folders just move through the folder tree.
To remove a calculation from the list just select it and then click the button.

At the end of the setting of calculations click on the Run button to start multiple
analyses.

VERO SOFTWARE 77
 3. Appendixes

Modelling considerations and tips

What is the maximum allowable number of triangles for a mesh model?

The maximum allowable number of triangles is 300.000. Note that the program has
the capability to reduce the total number of elements by eliminating those elements
with poor shape factors. For very large and complex parts it is possible to import up to
600.000 triangles (then reduce the exceeding elements with cleaning options such as
merging of nodes, removing of zero area elements, etc).

Is it possible to use STL files?

The VISI Flow package uses a special surface triangularization prepared by the
Create Mesh feature available through the Mesh menu. While it looks similar to a
STL file used for the creation of stereo lithographic prototype component’s it sensibly
differs from it. The main differences can be found in the regularity of the triangles and
in the optimisation of their number. The triangular elements that will be generated are
also used to display results and calculate material thickness values to create the
calculations super-structures.

The surface triangularization for a typical STL file creates a minimum number of
triangles to reproduce all the details of the model (very few elements in a flat surface
and many elements to reproduce fillets). Because of this irregular triangle size it is not
suitable for displaying the calculation results from an analysis. For this reason you
must remesh it with the Create Mesh feature. If not satisfied by the result you might
run Create Mesh once again to get the proper “spider web” like mesh.

Some specialized applications (e.g. HyperMesh from Altair) can handle this kind of
generation of controlled surface triangularization and can export a STL file suitable for
the VISI Flow package.

Do elements have to be equilateral triangles?

The triangles should be as uniform as possible, and as close to equilateral as
possible. The best results are obtained with these kind of elements. A small
percentage of elements with poor aspect ratio can be tolerated. One should avoid
having such elements in a critical area. These can be identified near the gate and
near changes of section thickness.

What about the level of accuracy of the model?

The Preview of the triangularization available with Create Mesh will help in defining
the best triangle size to use, so not to exaggerate the number of elements or deform
the shape of the part. When deciding to reduce the number of elements because they
seem excessive, consider that a reasonable level of deformation of the parts shape
will not influencing the results.

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As an additional guideline for the convenient number of triangles note that:
 complex models, with side dimensions of 150–300 mm (6” to 12”) and
several fillets, are normally described with 30.000–90.000 triangles;
 with larger parts, for example with side dimensions of 300–500 mm (12” - 20”),
the number of triangles, which depends on the total number of surfaces (e.g.
many ribs) included in the model, can be of a few hundred thousands. Minor
details are often not considered in the analysis if they do not represent a critical
region regarding weld line location, etc. (e.g. small ribs).

For the following simple part (size 50x30x80 mm) the appropriate number of triangles
(about 4.800) of the central figure was obtained with a maximum edge length of 3
millimetres. At left look at an unacceptable result with too few and distorted – not
equilateral – triangles while at right the model has too many triangles obtained with mesh
size of 1 mm.

The triangle size, as already explained at the beginning of the “Mesh model creation &
preparation” section, can also depend on the size of
critical details of the model being analysed. So it maybe
necessary to make compromises when choosing a
triangle size to best define critical feature of a
component and minimise part distortion. For the hinge at
right it might be also necessary to make manual
refinements to the thickness values to perfectly describe
the details of the part.

Does the calculation use the triangularized model?

Actually, the calculation does not work on this triangular surface mesh but it uses an
internal mesh composed by adaptive super-structures which distinguish the VISI Flow
package. The outside triangles covering all the surfaces are just used to display the
results. The super-structure is generated during the calculation process.

VERO SOFTWARE 79
In the case of multiple symmetrical cavities is it possible calculate just one of them?
The analysis of only one cavity is absolutely the best strategy. Typically just model
one cavity with its portion of runners (that’s to say the portion of runners not in
common with other cavities). The flow rate to be set (displayed below the injection
time field during the input of filling data) should be the one to fill only this portion of the
mould. The difference in the results normally is just in the pressure drop due to the
whole runner system, but the optimization of the moulding for the part (the evaluation
of temperature, stress, sink, shrinkage, and so on) can be easily done in this way
saving a lot of calculation time.

For naturally balanced multi-cavity moulds it is possible to use the runner’s repetitions
(Occurrence) feature available when introducing the properties that will define the
characteristics of the runners.

How to take advantage from model symmetry?

In this example the model is symmetrical through the X-Axis, to speed up the mesh
creation that is required for analysis, we can take advantage of the parts symmetry.

Cut the
part

through the X-Axis as shown below. Then detect and delete the faces highlighted red.

VERO SOFTWARE 80
To help reduce calculation times and improve the quality of the triangularization mesh
it is recommended that minor features such as text or small ribs be removed from the
model. These features should only be removed if they do not effect critical regions of
the part being analysed.

In this example we will remove the material identification from the model.

Mesh the united surface model of half

the component. This process will
reduce the number of triangles being
handled and reduce the setup time
inside VISI Flow.
When you have validated the mesh
of the half component through the commands available in the Mesh menu, you must
add the cavity and calculate part thickness as you would with a complete component.

Now we are ready to mirror half of the mesh data to create a whole component.

How to manage model modifications after the analysis?

Just mesh the desired portions of the model (for example the modified areas) that can
be updated (adding them as a new cavity) in the original Flow Project without the need
to repeat the complete modelling process. It is suggested to mesh the portion of the
model to be added by selecting the same triangle density (element dimension) of the
original part.

For example, after the initial analysis

without a feeding system - to decide on
an acceptable gate location - we want to
add the runner and gate details.
Just mesh the newly modelled
runner, add it as cavity, and
remove the original sections of the model
that will be replaced by the one added
with the sprue. Then, connect the nodes
of the original triangles with the one
just included. After the merging process it
is suggested to remove the inconsistent elements that it may have been
generated.

When the imported portion of the model has been properly connected to the original
one, we must run a thickness calculation for the new triangles. Note that the

VERO SOFTWARE 81
calculation of part thicknesses acts only on the active layers. This can be very useful
to work on specific areas of very complex parts.

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How to assign the appropriate properties to the feeding system mesh?
Two possibilities are available in the Feeding Channels menu:

 Define Runner by Triangles: to add runner and gate size attributes to the feed
mesh;

 Set up Triangles as Runners: to quickly

assign the feed attribute to the mesh.

Move to a different layer and change the

colour to the triangles of the runner system.
This will simplify the addition of the feed
attributes to the mesh and make simpler
future thickness modifications.

Pick the Define Runners by Triangles icon.

Let’s start with the central part of the sprue.

Select the triangles of this area of the runner. A menu appears giving you the
opportunity to specify the style of runner and add relevant sizes. In this case we
select the Cold Trapezoidal kind introducing the appropriate size (9, 12 and 6.7 mm).
This option automatically calculates the runner’s Equivalent Diameter.

Select the most appropriate

geometry type and provide
its values

Select the OK button. For the Runner values to be assigned to the mesh elements.

VERO SOFTWARE 83
 Do the same operations with
the remaining parts of the
feed (Cold Plate with 15 and
4.5 mm) and the gates (Cold
Plate with 18 and 1.5 mm).

This option permits to easily modify the runner and gate dimensions of any section
with the relevant update of the calculated Equivalent Diameter.

Pick the Set up Triangles as Runners icon.

Just select all the cold runner and gate elements.

Check thickness assignment and correct where necessary.

Note that in some cases, depending on the shape of the runners, the alternative
through Hexahedral Mesh calculation could provide more accurate thickness
distributions.

VERO SOFTWARE 84
What is the significance of the connectivity check?
Connectivity refers to how the triangles within the model are joined together.
To ensure the correct element connection, it is recommended that you use the
Check tool available in the Mesh menu.

While a small number of unconnected elements is acceptable when creating a filling

analysis, when preparing a model for the warpage/shape analysis you must ensure
the model has 100% connectivity.

Any elements that are not connected, along with their surrounding triangles, will be
highlighted whenever the icon to the left is clicked

For the best analysis results it is also crucial to verify the connectivity of any runner
system curves that have been created using the Check Element Connectivity tool.

To ensure that the analysis calculates the melt front entering the cavity correctly it is
important to have the runner elements in contact with the model mesh.

Note! That it is essential to connect the runner system elements (the gate) to the
nodes of the triangles representing the part. The above example was obtained by
deleting the triangles of the model that are not in contact with the gate element and
then inserting 4 new triangle elements that are in contact with the gate element.

Remember to check the elements connectivity of the new elements and assign them
the thickness of those deleted.

How to judge and complete the thickness values assigned by VISI Flow?
Two methods are available to compute thickness: the preferred calculation algorithm
can be set through the Flow Configuration.

Maximum Sphere: This method is used by default. The thickness at any point is
defined by the largest sphere that can be placed at that point, in the direction of facet
normal, without intersecting other facets.

Through Hexahedral Mesh: The thickness at any point is defined by measuring the
distance of opposite triangles and through the hexahedrons created between them.

VERO SOFTWARE 85
It is important to verify the thickness distribution that is assigned to the mesh by the
automatic calculation. A number of elements might have no thickness assigned
(black/grey) or wrong values.

Use the Assign Thickness tool to modify the areas of the part where you judge that
the calculated thickness is incorrect.

When the result is satisfactory, run the Refine Thickness command to assign to all
the empty triangles (gray) the value of there nearest calculated triangle. In area’s of
changing wall thickness the system will take an average thickness value for the gray
triangles. No changes are made to any triangle that already has a thickness value
assigned to it.

After running this command all triangles will have an assigned thickness that will be
adequate for a good representation of the model. If not, repeat the above procedure.

When describing hot runners and externally heated runners with a pin inside (valve
gate), must all the property fields be filled?
For filling to shape analyses entering only the flow diameters is acceptable. On the
other hand, for the thermal analyses we have to take into account that these runners
are included in hot nozzles so you must specify the value of the External Diameter. In
addition, since these nozzles are isolated from the metallic mould block, you must also
define the thickness of this isolation by specifying a Gap.

How to describe rectangular and fan gates?

These elements, very important in controlling the final shrinkage and warpage, must
be modelled in VISI.

How to describe tunnel gates?

A gate element, with a diameter equal to D and a length of 0.5D up to 0.5 mm (0.020”)
max, must be used for tunnel gates which have no definable land length. (As illustrated
in Figure 1 below.) The remaining part of the tunnel feed should be represented with a
single curve with the Cold Tapered property.

(Fig. 1) (Fig. 2)

For conical tunnel gates, the definition of the first gate element should be made
according to above Figure 2.

VERO SOFTWARE 86
How to describe hot bushings?
Since the gate is at the boundary between the part and the hot nozzle, we recommend
using a short cold gate element to represent the gate, this will most accurately
represent the gates cooling time which could limit the packing of a component.
Typically we suggest making the gate length of a few tenths of a millimetre (0.04”
to .012”). Normally it should not be less than half of its diameter and, in many cases,
a minimum value of 0.5 mm (0.020”) is used, even for small gates.

How to describe the entire mould for the thermal analyses?

The Define Cavity Extension option allows the complete description of the mould
block containing the cavity and the cooling circuits. The building material for both
mould block and inserts will be assigned during the preparation of the thermal
calculation.

While all the cooling lines must be inside the cavity block, the model of the mould can
accept cold and hot runners outside the cavity block. This avoid useless enlarging of
the mould extension in all the cases in which the runner's layout is very extended with
respect to the part cavity.

How to describe parting lines for the thermal analyses?

Parting lines may be introduced with the same procedure used to create the mould
inserts. The parting line of the cavity block is used to consider the different heat
exchange in this area. In fact, this region cannot be considered solid since it is
composed of two blocks splitting at every cycle time. It is not mandatory to model the
real parting line with absolute precision, but it is sufficient to define the major plane of
division. We have to understand that we are looking at an area where there is a
discontinuity between the two halves of the cavity not covered by plastics.
For most of the injection moulds with an adequate cooling channels layout, the
definition of the parting line does not add much precision to the calculation since the
two mould halves should be efficiently cooled. On the other hand, for moulds with very
large contact surfaces outside the part cavity projected area, parting line introduction
might improve the accuracy of the results. This could especially play a role in the limit
situations with high differences in the cooling of the two mould halves.
Parting line is not an insert, but our experience has demonstrated that representing it
with a thickness of 0.05 mm, combined to its particular thermal properties assigned
with the relevant VISI Flow module, allows to model with reasonable precision special
heat boundaries for common injection moulds.

How to verify the cooling circuits before formatting the model?

Select the Check Element Connectivity option available in the Cooling Channels menu.

How to check the properties of the model?

The following options will offer you a number of tools that
can be used to check the entities and properties of the model.

VERO SOFTWARE 87
 Calculation strategy and tips

What is the standard approach to analyzing the moulding process?

The first step is to determine the best flow conditions with VISI Flow Filling, assuming the
part has a uniform mould surface
temperature. Use melt entry points to
create preliminary analysis to evaluate
the best gate position. With the gate
located model in the feed system and
fine tune the analysis to obtain the best
overall part Quality possible.

 This means achieving uniformity of

the melt temperature (typically not
more than 10°C heating and 10-15°C
cooling);
 Acceptable shear stress (generally in
the range of 0.5-0.7 MPa);
 Frozen skin (less than 10-15%);
 Considerations should be made about
moulding machine capabilities, such as
maximum pressure and clamping force.

The moulding conditions may require updating, requiring a number of analysis to be

conducted. In extreme cases, changes maybe required to gate and runner layouts, and
possible part modifications (e.g. flow leaders added).

Once the filling phase is considered acceptable, we move to analyze the packing and
cooling phases included with the VISI Flow Filling module.
The time value for holding pressure & cooling time are key inputs for this analysis.
Values are automatically entered by the software depending on the results from the
filling analysis.
In cases where the gate is correctly located in the thickest region of a moulding, the
first input (Holding time) is made equal to the minimum value of the T. holding time in
the section near the gate and the second input (Cooling time) as the Freezing times
of this section.
Regarding the holding pressure it is typical to start with the suggested value (always
available when creating an analysis with the Plast database) unless this condition is
much lower than the pressure obtained at the end of the filling phase.
To fine tune the holding conditions look at the:
 Sink/void variable at the end of cooling, which should show an almost zero value.
 Also examine the volumetric shrinkage, for unreinforced materials this should be in
the range of three times their typical linear shrinkage.
By altering the holding time and pressure time we can normally solve any problems.
In some cases – for example, with small gate or runners that solidify too soon – the
solution will require a return to VISI Flow Filling (modelling and filling phases).

VERO SOFTWARE 88
When the filling and holding conditions are acceptable, we start the VISI Flow Shape,
warpage analysis. Unacceptable deformation of a part will need a review of all the
previous activities. The solution may come from different moulding conditions (even if
we have found the ones that seemed good) or by modifying the geometry of the part if
we think that the deformation is strictly associated with its shape. In some cases of
minor warpage, we may guess that a marginal local variation on mould temperature
can solve the problem.

With the completion of shape analysis we should have maximised our processing
window for the moulding conditions, the next phase is to look at the design of the
thermal conditioning system. This is done using VISI Flow Thermal and may require
a number of calculations to be conducted, changing circuit diameters, flow rates etc.

In the case of the mould surface temperature not being similar to the assumptions
made for the filling analysis, instead of further modifying the cooling system we can
choose to look at the influence of the temperature distribution calculated by the
thermal module on warpage. To do this, simply select a previous VISI Flow
Thermal mould analysis result when specifying the VISI Flow Filling calculation
conditions.

How to run several analyses in sequence?

Use the Calculation Manager available with the Analysis Browser.

Note that the calculations all require results from previous analysis, so obviously it is
necessary to carefully set up all the calculation conditions to be executed. For
example, before preparing the holding phase inputs you must have set up the filling
calculation. Also consider that the final shape analysis cannot be calculated without
results from the filling and holding calculations

How to introduce new materials?

The Material Characterization program for polymer description, available in the

Analysis Browser, guides you through adding new or modifying existing polymer
grades to the material database for filling, holding, and final shape analyses.

It is also possible to contact the VISI Flow Support Team (vflowinthl@vero.it) for
getting materials added.

In both cases you must fill in the Material Data Requirements forms available in the
manual’s folder (\Documents\Common\Flow\Manuals). In fact, typical technical
material data sheets often do not contain the data required for the material
characterization. If the material data sheet does not give the required values you
should ask the supplier; if the supplier does not provide the data it is not possible to
add the material to the database, so we could only try to look for a material with
similar characteristics.

VERO SOFTWARE 89
In addition to the above fundamental polymer characterization, the Virtual Resin
Laboratory application, available through the Flow menu, permits to create and test
each kind of resin when data from producer/compounder are meagre or not properly
provided. It will improve user interaction with the material databases management and
benefit the R&D departments of the plastics processors which are always researching
the best material performances related to the costs.

The Virtual Resin Laboratory is based on an intelligence included in the VISI Flow
material database and it works by following an interactive iterated approximation. The
application is able to put together data coming from different databases and different
grades by following the wizarded user’s instructions which might be very few (polymer
family, density, MFR) or much more detailed.

How to archive the analysis results?

The creation of analysis calculations produces a large number of files, which over time
can fill a high percentage of your hard disk. Because of this VISI Flow includes an
utility that compresses and extracts all the calculation files for convenient storage.

The Compress Analysis utility, to archive personal projects, is available in the

window that appears whenever Load Results.
To uncompress results files from the desired analysis archives click the Open file
button available through the Analysis Browser.

What to do if the calculation stops before the cavity is completed?

In the case of you encountering an error during a calculation, please provide to the
VISI Flow Support Team (vflowinthl@vero.it) with a screen shot of the error
message.
Then generate a compressed archive with the WKF file to help identify the source of
potential problems that may be encountered with imperfect models. Please also
include the result_name.FES file containing the moulding conditions of the filling
analysis, the result_name.HLD for holding, the result_name.SHA file for shape, and
the result_name.THE file for thermal calculation. These files contain all the necessary
information to duplicate the incomplete analysis and allow the VISI Flow Support
Team investigate the problem.

VERO SOFTWARE 90
 Filling calculation input and result description and tips

What is the meaning of the inputs fields when creating a calculation?

To facilitate a new analysis of a part using some of the preceding moulding conditions
click the inputs of an already saved calculation button.

Name – The file name in which the results of the calculation will be recorded. If a
name that has been previously used is entered, the program will give a warning, since
the existing results will be over written. Experience has proved that, while not
essential, a good practice in assigning meaningful names to the files of the various
steps of the analyses can be of great help for any further access to them.

Grade – Material used for the analysis. Click the Material Manager icon to display
the list of available grades. Material properties, such as the rheological and thermal
characterizations, are recorded for each Grade. The Supplier, Code and Description
fields assist in identifying the specific grade to be selected. Grades are grouped in
Databases that can be easily selected from the combo box. If your unfamiliar with this
kind of analysis or the technical data for plastic resins, it is recommended that you use
a material from the Plast file, since the other databases may not contain values for
typical initial moulding conditions.
Databases with the polymer family name

Search options

The Search options allow you to easily seek through the selected material data bank,
or through all databases, by typing key words to focus on a required material grade.
Many filters are available to fine tune your search. Right click on a grade to add it

VERO SOFTWARE 91
to an existing group of favourite materials or to display information about its
properties.

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To encourage the selection of materials from Vero’s Plast database, complete
information is provided including MFR
data (historical Melt Flow Rate index),
typical linear shrinkages, and tensile
modulus.
Additional data can be shown through
the Material Characterization
program available in the Analysis
Browser.

Viscosity Factor – This option allows

you to modify the fluidity of the selected
material. By changing this value
calculations can be run with a defined
MFR being a fraction or a multiple of the
one selected from the material
databases.

Machine Index (under construction) – This entry defines the moulding machine
variables. From a database that includes a complete characterization of a wide range
of moulding machines, the program setups the limitations dictated by the selected
machine. Note that the selection of a specific machine should be used only when the
calculation is confined to analyzing the related factors of this machine. It is likely to be
used primarily for examining current operations, or in case circumstances dictate the
use of a particular machine.

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Injection Time – The time interval in seconds to complete the filling of the cavity
using a uniform flow rate. If a flow rate profile is being used, the total injection time will
be displayed beside the Machine Flow Rate Program toggle. The program suggests
a reasonable injection time depending on material, part volume and gates. In case of
modification of the number of injection points click the button to recalculate the
most appropriate filling time.

Flow Rate – Following the injection time box, the maximum flow rate value is
displayed. The value is obtained from the volume of the cold cavity and the entered
filling time. A skilled moulder can judge flow rates suitability compared with the
capability of the moulding machine to be used (to fill the part with this “velocity”). In
case of selection of a specific moulding machine, the maximum flow rate value is
limited according to its specifications.

Concerning the moulding machine capability, never forget that it is not just the max
pressure that can limit the moulding conditions with a given moulding machine. In
addition to the mould dimensions, you must ensure that the required injection volume
can be achieved by the moulding machine being used, normally in a range of 20–70%
to avoid high melt residence times (which can degrade the polymer) at the lower limit
or provide a poor melt (non homogenous) in the upper limit. You must also verify that
the max flow rate used in the analysis fits with the injection rate of the machine with an
adequate margin, especially if the moulded part requires high pressures.

The next two input values are suggested by the software to provide a good initial
starting point for users who are not familiar with specific material grades. This typical
data can be changed if required by the analysis. These suggestions are always
available for the material updated and maintained directly by Vero. If this data is not
available please refer to a similar material in the Plast file when in doubt regarding
reasonable values.

Melt Temperature – The temperature of resin entering the injection elements. In

reality it is the temperature of the material leaving the moulding machine nozzle. The
nozzle can also be included in the model. The melt temperature value entered must
be within the typical range of values. Higher values can be entered, but only after
selecting the No Check box.

Mould Temperature – The temperature of the cavity surface that is applied to all
elements which do not have a temperature assigned as an attribute (e.g. hot runners).
To enter a mould temperature value below the typical one select the No Check
box.

Thermal Analysis Integration – The results of a previous thermal analysis can be

loaded from memory and integrated with the new filling analysis. The default blank
field means that no integration is required.

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Machine Flow Rate Program – By default the filling flow rate is set at a constant
value, only changing when the V/P is reached. By selecting this option, the Flow rate
profile sheet will be activated, allowing you to change the flow rate profile to follow
special moulding needs, for example, a reduction in flow rate when the flow first meets
a small pin that could be deflected.
After having activated the Machine flow rate
profile look at this function’s options. A machines
flow rate profile up to the V/P Change point can
be fully controlled. Ten steps are provided giving
the ability to control the volume and the flow rate
for each step, by changing their percentage with
the bottom fields. The default volume increments,
at which it is possible to change the injection
speed, are set to 10% increments. The flow rate
cannot be greater than 100%, which refers to the
flow rate obtained by dividing the total part volume (only the cold elements) by the
injection time. For example, it is possible to
maintain a constant flow rate up to 80% of the
part volume and then change it from 82% to
100% in uniform increments. A small difference
in the increments can be due to the values being
rounded up/down.
Note that if the V/P Change is set to 95% and
Pressure at End Filling to 0, the flow rate profile
after 95% of the cavity volume is filled will be
computed to stay at the pressure limited at the
moment of the V/P Change instead of following
the indicated profile.

By adjusting the flow rate profile, the updated injection time will be displayed beside
the Machine Flow Rate Program toggle.

V/P Change – This variable controls the percentage value of material entering the cavity
under volumetric control (flow rate), when the percentage value is met the final filling
phase changes to pressure control. The switch point is
expressed as a percentage of the volume of the mould
cavity. The default value is 95% which is typically used
in practical moulding conditions due to the fact that the
volumetric controlled filling phase must be terminated
to avoid extremely high pressures.

If it is necessary to optimize a runner system, it is

practical to enter a low V/P percentage. This
method allows you to balance the flow within a
runner system and interrogate the flow conditions
near the gate without wasting time calculating a complete mould. If this method is
used the calculation can be stopped at the required V/P Change value. It is
necessary to check the Stop at selected volume box in the Advanced sheet, otherwise
the calculation will not stop at the desired V/P Change value.

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Pressure at End Filling – This input allows you to specify the pressure in the
injection element at the end of the filling phase.
In the following two examples, the calculation will
adjust the flow rate to stay within the maximum set
filling pressure. To achieve this, the software will
adjust the injection time.

 if a value of 0 is entered, filling switches at V/P

Change to a pressure equal to the 75% of the one
reached at that moment;
 if a value greater than 0 is entered, filling
continues with a linear pressure interpolation to
the set value.

The typical holding pressure (see grade properties

through the Material Manager) for the subsequent
packing phase can be used. Considerations about
mould design and machine clamping force can
dictate different value.

If the part geometry and gate location is such that

the pressure required to fill the cavity after reaching
the V/P Change is higher than the value set, the
warning message “Unable To Stay In Specified
Conditions” will be displayed. This does not mean that something is wrong during the
calculation and you will still get a result. To eliminate the problem you might accept
the pressures indicted by the program or make a new calculation setting a defined
pressure value.

Pressure Limit – During the injection phase controlled by volume (flow rate), the flow
rate will be altered by the system so the pressure does not exceed the specified
pressure limit value. The default value 0 means that no limit is set.

Volume Starting Pressure Check – This value allows you to specify the percentage
of the cavity filling at which you want to limit the pressure. This value is expressed as
a percentage of the volume of the mould.

Opening Force – In addition to the maximum

filling pressure it is possible to specify a maximum
value for the opening force. Check this box and
then select the appropriate model orientation
so the program can calculate and display the
projected area to be considered.
Click the button to let the program calculate
the projected area value.

During the analysis the program will indicate a warning if, to stay in the required limits,
the filling time becomes too long, which could effect the quality of the final part.

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Opening Force Limit – Allows the ability to set a maximum value for the opening
force.

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Cycle Non-Filling Time – This is the time during which the material in the hot runner
system is immobile and its temperature/viscosity can change causing different
pressure drops. This time is normally the total moulding cycle minus the injection time.
It can be longer, if the purpose is to simulate a machine stoppage. In this case, the
machine dead time is to be added to the previously defined cycle non-filling time. This
variable is used to consider the behaviour of runnerless moulding systems with
insulated runners heated from the inside (calculation of cooling before filling).

Stop at Selected Volume – Check this box to terminate the calculation at the value
specified in the V/P Change field. It can be useful to speed up the initial analysis,
especially when runner optimization is required, to verify the balancing and see a
snapshot of the flow conditions near the gate without wasting the time for the
calculation of the complete mould.

How to set up a calculation with sequential moulding?

The simulation of sequential filling through multiple valve gates, with option to open
each gate at a selected time, is included in the VISI Flow Filling package.

The more and more popular cascade moulding technology takes advantage of the
options that permit to control the filling and the holding phases in advance of the
design of the entire hot runner system (open example Plateseq1.wkf located in \
Visi18\Workf\ Sample\Flow\Sequential).

To use this feature, the model must have one

mono-dimensional gate or cold element (the
valve gate) connected on one side to a cold
runner or to the cavity and on the other to a
hot runner segment. Note that only one
element must depart from the valve gate.
These gates must not be confused with the
injection element which is the melt entry point
into the model.

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Run VISI

File > Open Select the file named “Plateseq.wkf”

located in \Visi18\ Workf\ Sample\Flow\Sequential

The geometry should look as below.

From the General tab, select the Injection point from which the molten material will
enter the cavity as indicated in the image.

Go to the Advanced tab and click the Sequential Moulding button to create a
list of valve gates.

Sequential gate Element # 40

Trigger on element # 2487 to get the flow front position for valve gate opening

Use the pick button to select a mono-dimensional gate or cold runner. Click
Add Gate to store the selected Element in the list. If this element, corresponding to the
last segment of the valve gate, is not of the correct type or is not connected on both of
its sides, the program gives a warning message and does not accept the input.

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The fields at the bottom of the window allows you to control the defined valve gates by
their actuation time or by specifying a flow front position for their opening.

For each Element, you are prompted to enter its Opening time. In theory, you can
open the gate at any time, regardless of the flow front position. In fact, from the
moulding point of view, some gates may actually be operated before the flow reaches
them, but this situation only applies in very special cases, for example for fibre re-
orientation.

The default value of 0 means that the gate will open when the flow reaches it on the
cavity side - not the hot runner side. This 0 input helps you find a time which must be
considered just as a starting point since, to avoid a new weld line, the gate should be
activated only when a significant amount of melt has moved below it.

Instead of providing a time for the opening of the valve gates, it is also possible to
specify a flow front position. To do this activate the Trigger on element option and
select the desired element located in the gate area through the button that will appear
at the right of the Opening time field. In this case you may not define the initial gate in
the list of sequential gates and open the others at a given flow front position.

Flow front position specification

Valve gate in the list

If only one sequential gate is defined and the Opening time is 0, practically we are
simulating a normal moulding.

For each element, you are also prompted to enter its Closing time. The default value
of 1000 means that the gate practically will never close.

After the specification of any valve gate actuation Save the data.

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To analyse the filling calculation use the same tools available for the traditional
moulding.

To prepare the data for the holding phase of a sequential moulding analysis, go once
again to the Advanced tab. A sheet to specify the closing time of the valve gates and
the holding pressure applied to them is available.

The fields at the bottom of the window allows you

to control the defined valve gates during this
phase of the moulding process.

For each valve gates is possible to specify a

different Holding pressure to work with.

The Closing Time is made infinite by default

(1000 seconds) which means that the entry of the
melt will continue up to the solidification of the
cold sections near the valve gates. When filling
different parts (family moulds) or the same part in
area with different thicknesses, where we would
like to control the packing phase, a closing time
can be assigned to each valve gate. Of course this time must not be higher than the
holding time.

Is it possible to take into account specific moulding situations?

Many of the settings available in the VISI Flow Configuration allow to support the
evolution of the technology which is requiring more complex
parts to be made with ever stringent moulding conditions.

Due to the importance acquired by these options, any

modification of the default calculation parameters will be
indicated in the bottom area of the Analysis Browser.

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Advanced calculation settings include:
 Flow Rate Interpolation for the determination of the advancing flow front;
 opportunity to take into account the Elongational effects on the cavity pressure drop
of flow entering in sections at different thickness;
 Convergence of pressure drop computation from the injection element to each of
the flow fronts;
 melt Compressibility value of polymers;
 prediction of the Fibre's orientation distribution due to vortex phenomenon in
proximity of important flow expansions.

What is the data displayed during the calculation?

When a calculation is started key information about the progress of the calculation is
displayed on the screen, such as the percent of Volume filled at that time.

The calculation module can be Paused or Stopped by pressing the relevant

buttons at the bottom of the page.

The result_filename.fb file contains the name and date of the used calculation modules,
the names of the result and mould files and, in some cases, program messages that
alert you to unusual conditions. The message may include errors encountered during
the calculation and/or a list of elements that have frozen before the mould finished
filling. The file is rewritten every time a calculation is started. If error messages appear
during a calculation, please report the problem and where within the software (name of
the specific module) the error occurs. These errors are not dependent on the
calculation, moulding conditions, etc. The program handles all the possible errors in this
area, by writing a message to the result_filename.fb file and closing the result file
appropriately. These are infrequent errors related to hardware problems.

How to interpret the results of the calculation?

Welding Lines – The best approach regarding weld lines is to choose a gate location
so weld lines are created in non critical area’s of a component to reduce there effect
on mechanical properties or surface appearance. If this is not feasible, then an
alternative approach is to have the weld lines formed as early as possible during the
filling phase, this will assure the best melt temperature to form the strongest possible
weld line. The angle between the meeting of material flows also plays a role in weld
line quality with particular reference to the surface appearance. A distinction between
a head to head weld line and a merging situation where the two material flows come in
contact at an almost parallel direction. Angles of 50 degrees or more are considered
acceptable situations to avoid an appearance of surface defects. The quality of the
surface near a weld line is related to the specific grade and colour of the material and
only practical experience with the same material can give the real answer. It is
worthwhile to remember that the quality of the surface also depends on the mould
temperature and on the amount of frozen skin in the flow front.

Temperature - Peak and Local End Flow – In an ideal moulding (a central gated
disk) no difference can be found between the temperature of the flow front and the
local temperature at the end of flow since there is no local flow reduction due to part
geometry which will cause cooling down only during the remaining part of the fill.

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While the temperature profile of the advancing flow front is normally almost flat, in the
area where the flow stops before the end of filling the profile of the temperature
becomes parabolic and the difference between the Peak End of Flow and Local End
of Flow temperatures can be significant if the filling time is important and the flow
stops very early.

Thin parts with relative long filling times and unbalanced material flow (e.g. a long strip
gated near one end, having relatively large differences in situations of material flow
stop), the difference between temperature and frozen skin can be very significant and
it can happen that a portion of the part is already over packed during the filling phase.
This result is more likely to happen with amorphous materials.

Pressure – The development of the cavity pressure can be seen by moving from one
view to the next. You should understand that the pressure on the flow front is at
atmospheric conditions. Once the flow stops the pressure tends to build up locally but,
due to the compressibility of the
material, it takes time to reach a
maximum value.
Note that a phenomena of
unbalancing near the 100% of filling
– imperfect equilibrium of pressure
distribution, due to almost not
appreciable differences in the part
geometry and the mathematical
convergence on the calculation of
flow distribution – occurs also in
practice and it is the reason why a
safety factor in clamping force is
usually required to avoid flashing.
With injection moulding, it is always possible that minor differences in local
temperature or cavity thickness can cause apparently identical areas to reach
pressurization at slightly different times.

For some additional general considerations about the pressure requirements for
runners and gates plot the graph
for filling Pressure vs. the Time.

It is impossible to classify the

percentage of pressure required by
the feeding system compared with
that of the cavity, because it mainly
depends on the size and thickness of
the part as well as the length and
type (hot, cold, etc.) of runner
system. If filling of the part requires
low pressures, try to design runners
that require high pressures and take
advantage of the heat generated by friction to allow you to lower the melt temperature.
A temperature increase of 10–15°C throughout the whole feed system is seen as

VERO SOFTWARE 103

appropriate. Do not allow sudden increase in short elements like the gate: it will create
unstable conditions.

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Do not accept a pressure graph like the one shown in the previous figure, even if you
do not find excessive shear stress which is often associated with this situation. The
cold runner, and maybe the gate, are to small.
Just check in the first “view” (short shot) the local temperature increase. A solution can
be found by using a longer injection time at a constant flow rate or by the creating a
profiled flow rate. Care must be taken not to generate excessive cooling of the material.

Do not be surprised to see a pressure value that does not start at

the 0 value. If in your analysis is using hot runners, they will already
be charged with material. For material to pass through them and
start entering the cavity, the flow requires a given pressure. In some
cases this pressure drop in hot runner systems can be as high as
80 MPa.

How to reduce excessive pressure drops?

There are various ways to do this. One, that should be used as the
very last option, is to increase the mould temperature. With
excellent moulding conditions (short filling times) the influence on
the pressure is not great, but it will contribute to increased cooling
times. Another alternative, that’s not so detrimental to the cooling
time is when the mould cooling system is very efficient, this can be
found in an increase in the melt temperature.

An increase of filling time (lower flow rate), providing to not generate an excessive
cooling of the melt flowing into the cold
cavity, will reduce the pressure. Using
the option to limit the cavity pressure,
the program will take care of lowering
the flow rate when the set value is
reached. When using this option care
must be taken to verify the actual filling
time which may result in longer than
expected times, causing undesired
excessive cooling. We have noticed
that, due to machine limitations, some
commercial parts are filled during
packing without the moulder
appreciating it!

Looking at the above graph, at about 2.3 seconds of the filling time, the pressure
reaches a maximum value, the software then slows the velocity to stay inside the limit
(identical behaviour of the moulding machine). The abscissa values tell you the total
filling time as well.

In this example the filling time was set to 5 seconds, the software needed to increase
this time to 6.5 seconds to stay within the set maximum pressure. You will need to
look carefully at the flow front temperature to ensure that it does not cool down too
much.

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Opening Force – The value of the opening force during the filling phase is typically
evaluated at the V/P changeover (by default 95% but it can also be anticipated
depending on the pressure evolution – see its graph). This anticipation of the
changeover before 100% is due to the moulding machine inertia and 95% is quite
reasonable for most moulding machines. The opening force value in this situation is
the maximum required for the filling phase. In fact the part is quite completed with the
correct “filling” pressure distribution in the whole part.

In the case you set a pressure after the V/P changeover, the value of the last short
shot (100% of the final view) gives an idea of the opening force requirements due to
the holding phase. Therefore, an accurate determination of the maximum opening
force requires to verify the value at the V/P change (if pressure was higher at that
time) and at the beginning of the packing phase where polymer is still hot and
pressure evenly distributed. Of course, in the case you profile the holding pressure
values with the time you have to apply the opportune considerations. If you do not
make the holding calculation and plan to increase the pressure during it, you can
estimate the maximum value by multiplying the holding pressure value by the
projected area.

To recapitulate, the opening force requirements for filling are estimated at the 95%
(V/P changeover) where:
 the part is quite completely filled, the pressure distribution ranges from a min
value on the flow front (zero) to the maximum in the runners, the real process
switches to pressure control.
The program also makes an estimation of the opening force requirements at the 100%
(final view) where:
 the pressure distribution is quite homogeneous in the whole part (at the set
value, if specified, to have a good packing,) as in the real process to avoid
pressure peaks at the end of filling.

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Shear Stress – The shear stress variable is linked to the Temperature and Frozen
Skin values. High stresses can be found in situations of high velocity and hot material
or low velocity and cool material. The latter occurs due to high material viscosity.
The moulded part quality is effected by the level of shear stress that is frozen into the
part during material cooling. In the case of high velocity & hot material much higher
stress values can be accepted due to the material having more time to relax thanks to
the higher material temperature compared to low velocity & cool material.

As for the Temperature and Frozen Skin (but also for filling Pressure that contributes
to the indication of the overall properties of your part) the quality evaluation of this
variable is done with the General Tools option.

The highest shear stress values are normally seen near the gate during the filling
phase. Increasing the melt temperature can reduce this. High shear stress at the end
of filling is very common, this is due to the reduction in the flow front. Programming the
flow rate or reducing the pressure after the V/P changeover can solve the problem.
Shear stress in combination with the level of frozen skin also provides an indication of
stress frozen into a moulded part. Parts with high frozen in stresses are subject to
crazing and/or stress cracking. Acceptable stress levels can be established
experimentally by correlating computed values for stress with observed levels of
crazing. An indication of the maximum critical shear stress value is given in the Plast
database for each resin.

Shear Rate – This gradient is the difference in velocity between adjacent laminar
layers within the flow channel, divided by the distance between them. The maximum
shear rate across the thickness of the segment is shown. See the stress
considerations.

Frozen Skin – The frozen skin is very important when moulding very thin wall section
parts with crystalline materials. It may also be important for large parts (bumper, etc.)
which need very long filling times and the heat transfer to the mould can be higher
than the heat dissipation.

Low frozen skin values indicate easily filled parts and long term dimensional stability.

For the best part quality and for most resins, it is recommended that the frozen skin be
maintained below 10%. However, it has been seen that very good parts have been
moulded from glass reinforced and mineral reinforced materials with much higher
frozen skin levels, provided that the percentage does not vary excessively throughout
the part.

Orientation – Material fibre orientation (available in the General Tools) is used to

better understand the filling pattern in order to judge potential causes of warpage. The
examination of velocity vectors is very important for materials with anisotropic
shrinkage, like glass reinforced resins.
It is also used to localize weld lines.

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T. Holding Time – Particular attention should be paid to the material freezing time of
the gate and runner areas. In the case of gate or runner
elements freezing off before the elements within the part,
the pressure within the runner cannot reach the cavity to
compensate the volumetric shrinkage of the material.

Is it possible to use hot runners to reduce the Cycle Time

and Opening Force requirements?
Provided hot runners are setup with the correct isolation,
they may reduce moulding cycle times. The influence of
hot runners on the opening force is not so great, due to the projected area of the cold
runner being removed. The pressure requirements for the two runner systems can be
quite different. Remember that in the part the pressure drop will be the same for both
feeding systems.

Holding Calculation input and result description and tips

What is the meaning of the inputs for the calculation?

Material – The material property data (mainly the PVT characterization) are recorded
in databases that carry a *.mah extension.

The program automatically loads the same material code used in the linked filling
analysis.

If the material database for the holding phase does not contain exactly the same
grade used for the filling calculation, indicated in the bottom area of the Analysis
Browser, the program displays a message.

By default, the Vero’s Plast database, that contains generic material grades not linked
to any manufacturer, will be displayed.

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The most similar resin can be coupled with the one previously used for the flow
analysis (e.g. filling phase done with PP MFR=14, holding phase done with PP
MFR=6).

The Search options allow you to easily seek through the material databases by typing
key words to focus on a required material grade. After confirming the choice, the
selected material is loaded into memory.

Filling – The name of the filling analysis currently loaded in memory.

Name – The file name in which the results of the holding calculation will be recorded.
If a name that has been previously used is entered, the program will give a warning,
since the existing results will be over written. The field below the result name offers
the opportunity to enter a description for the analysis.

Holding Pressure – A pressure value will be automatically inserted matching the

value used for the V/P Change of the filling analysis. If no value was entered for the
filling analysis V/P Change then the typical value for each material is suggested. For
the resin in the Plast database, updated and maintained directly by Vero, this value is
always available. With material databases other than Plast, the data could be not
available and the user must enter an appropriate value. When in doubt regarding
reasonable values refer to a similar material in the Plast file. Different values can be
dictated by experience or results from previous calculations (excessive clamping
force, residual pressure into cavity, etc.).

Holding Pressure Profile – By selecting this option, the Holding pressure profile
sheet will be activated. The profile sheet option provides the ability to change the
holding pressure profile to perform special
moulding needs. The default setting
calculates the holding phase with a constant
holding pressure during the holding time. The
profile sheet allows you to alter the holding
pressure by splitting the holding phase into 10
adjustable stages.

The default time increments, at which it is

possible to change the value of the holding
pressure, are set to 10% increments. The
holding pressure value cannot be greater than
100% of the previously entered holding pressure, which is considered to be the
maximum.

Holding Time – The holding time should never be much longer than the gate’s no-
flow time obtained during the filling analysis. It should be noted that the calculation
determines the actual gate freeze-off time and the discontinuation of the holding
pressure in the cavity. It is well known by experienced moulders that a large (thick)
gate, positioned on thin sections will not allow proper packing of the thicker sections if
the difference between the two is significant. The holding calculation allows you to
find out if a specific difference can be tolerated: the evaluation relies on the
visualization of the results relative to the presence of sink-void in the thickest section.

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For parts analyzed without gate elements, the packing time is selected by looking at
the T. Holding Time of the thickest relevant section: this gives the initial indication of
the packing of the part while the No-flow Time gives the theoretical maximum holding
time for each element.

Longer holding time reduces shrinkage. On the other hand, long holding time can
cause delays in the cycle time because it reduces the time available for plasticating. It
is common to limit the holding time for shorter values that to balance shrinkage to a
reasonable amount.

Holding pressure also influences shrinkage. The same shrinkage values may be
obtained with shorter holding times by using higher holding pressures.

Cooling Time – Indicates the best cooling time for part ejection, values taken from the
previous filling analysis. A practical reference can be taken from viewing the results of
the Freezing Time in a relevant component section. For high cycling moulds, where
excellent ejection systems are provided allowing parts to be ejected with a partially hot
core, the Technical Cooling Time is used as a reference.

To simplify the introduction of data and reduce possible interpretation mistakes, in

cases where the packing phase simulation is integrated with a thermal analysis, the
cooling time is automatically set, with no option to modify the value. It is set as a
function of the Total Mould Closing Time entered during the creation of the thermal
analysis or of the Cooling Time calculated with reference to a significant element with
its ejection temperature.

What is the data displayed during the calculation?

When a calculation is started key information about the progress of the calculation is
displayed on the screen, such as the time elapsed since the end of the filling time.

The calculation module can be Paused or Stopped by pressing the relevant

buttons at the bottom of the page.

The result_filename.fh file contains the name and date of the used calculation module,
the names of the result and mould files and, in case, program messages which alert of
unusual conditions. The message may include errors encountered during the
calculation. This file is rewritten every time a calculation is started. If error messages
appear during the calculations, please report the exact problem and the program
where the error occurs. These errors are not dependent on the calculation, moulding
conditions, etc., because the programs handle all the possible errors in this area by
writing a message to the result_filename.fh file and closing the result file appropriately.
Fortunately, these are infrequent errors related to hardware problems.

How to interpret the results from a calculation?

Temperature – The best moulding quality is achieved in parts where all elements
have an average temperature below the no-flow temperature at the end of the holding
phase. The frozen skin variables allow you to judge when the no-flow temperature is
effectively reached (elements with frozen skin equal to 100%).

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Pressure – With good moulding conditions you should find an almost uniform
distribution of pressure at the beginning of the holding phase. To get the appropriate
scale check the Current Step radio button.

Moving to the subsequent situation you should see the reduction of the pressure along
the flow path but it should not be too significant until the end of the holding time.

By interrogating the Chart we can make the following considerations.

The Entered Mass graph, can highlight the condition of the gate freezing off, care has
to be taken so not to create mass packing in the cold runner system. Generally this
condition is recognizable with a reduction in the slope of the curve. The best way to
be sure if the gate is freezing off, is to monitor the gate elements and watch the time
they reach their no-flow temperature with the development of the frozen skin.

Note that the amount of the entering mass can range from a few percent with
amorphous polymer filled with high pressures up to 10% for thick parts in semi-
crystalline materials.

The Pressure evolution may present a peak during filling (area at left of the vertical
red line in the picture) and a reduction in the
holding phase (area at right). It is interesting
to note that the curves representing elements
at different distances from the gate (select
them through the Draw Chart option) show
that all are loosing almost the same level of
pressure until the end of the holding phase,
then the pressure reaches zero before the
ending of the cooling time. This is an essential
requirement of successful injection moulding:
part ejection should not be done before almost
all pressure is relaxed within the cavity.

Interpreting the Temperature values of the polymers freezing temperature (available

by right clicking on a grade through the
Material Manager), gives the ability to
judge if the set cooling time is sufficient to
successfully eject the part.

Note that typically, 100% of the Frozen

Skin is obtained well before reaching the
materials freezing temperature. In fact,
the parameter that determines the frozen
skin is the no-flow temperature, this is by
definition higher than the freezing
temperature.

The difference is generally not so great with semi-crystalline polymers for which, after
solidification, the material is rigid enough to be ejected.

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A typical curve for the Density (at the current local temperature) has 3 steps.

Step 1: Density increases until the end of

the entering mass.
Step 2: Density remains constant if the
pressure in the cavity keeps the material
pushed against the wall of the cavity.
Step 3: Density increases due to thermal
contraction (the part starts to shrink into
the cavity so its volume decreases with
time).

To achieve good quality moulding we

need to see 3 phases in the selected
trace elements: the relative curve length depends on the specific part and moulding
conditions. The use of relatively high pressures with short holding times will cut down
the first phase and increase the second.

Volumetric Shrinkage considers the freezing of a part up to room temperature and

atmospheric pressure. In extreme (worst) cases, the value can even become
negative, this means due to high residual pressure at ejection the part will become
larger than the cavity. In this condition it is likely that the part will be damaged during
ejection from the cavity. The target of the volumetric shrinkage is mainly dependent on
the type of polymer. As a guideline, we can define 4 categories:

Amorphous reinforced: 0.5 - 1.5 Amorphous not reinforced: 1.5 - 3.0

Semi-crystalline reinforced: 3.0 - 4.5 Semi-crystalline not reinforced: 4.5 - 7.0

The values apply to thicknesses of 2-4 mm with the typical mould temperature of the
specific polymer. Variations of wall thickness will give different values with lower
shrinkage in thin parts. Since differences in shrinkage may influence warpage, care
must be taken to gate in the thickest material section to control volumetric shrinkage
of that area. Then, if the thinnest section is showing a too low shrinkage, you should
consider programming the holding phase in a way to maximize the shrinkage of thin
areas and minimize the shrinkage of the thickest sections. To achieve this may need
to use a low holding pressure during the beginning of the phase and increase it after
the thin sections have solidified.

For a flat part with a constant thickness, the shape of a strip for example, a uniform
volumetric shrinkage should give a uniform linear shrinkage value in the direction of
the material flow. If the material has an anisotropic behaviour (e.g. glass reinforced),
we should expect two linear shrinkage values (a low value in the direction of flow and
a much higher value transverse to flow.

Also, minor temperature differences on the opposite faces of the mould can cause
different volumetric shrinkages on the geometric opposite layers across the flow
direction, causing warpage. Consequently, correct filling conditions (uniform melt
temperature at the end of filling) are basic to obtain a correct packing phase (uniform
volumetric shrinkage), but flow orientation and temperature distribution across
sections also play a role on the final shape of the moulded part.

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Thickness variations, in addition to making it very difficult to get a uniform volumetric
shrinkage, influence flow path and consequent fibre orientation. The result of all these
factors may be difficult to estimate even in a qualitative way. Only the dedicated
module for the calculation of the final moulded part shape prediction makes this
estimation quantitative and hence is a big step towards producing quality parts.

Shape Analysis input and result description and tips

Description of the meanings for the calculation inputs

Holding Analysis – Name of the packing phase analysis currently loaded in memory

Shape – The name of the file in which the results for the final shape prediction
calculation are recorded. If a name that has been previously used is entered, the
program will give a warning, since the existing results will be over written. The field
below the result name offers the opportunity to enter a description for the analysis.

How to determinate the ovalisation of a model?

Since the need of parts without ovalisation is key to many mouldings and the moulding
conditions influence such special case of warpage, the feature available from the
Measure tab automates the determination of the (O) ovalisation of the model.

When clicking on this option the

program asks for the selection of the
desired entity type.

This functionality draws a circle

representing the Interpolated
Diameter (its value is displayed
beside the ovalisation percentage
with respect to the (A) original diameter of the part) and two blue and red lines,
indicated in the report respectively as (C) Minimum and (B) Maximum Diameter axis,
which correspond to the displacement respect to the original diameter.

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 Thermal Analysis input and result description and tips

Description of the meanings for the calculation inputs

Name – The name of the file in which the results for the thermal calculation are
recorded. If a name that has been previously used is entered, the program will give a
warning, since the existing results will be over written. The field below the result name
offers the opportunity to enter a description for the analysis.

Filling Analysis Integration – The results of a previous Filling Analysis can be

loaded from disk and integrated respectively with the new thermal analysis. With this
integration the thermal calculation uses the material and mould temperature
distributions coming from an optimised Filling analysis.
The default blank field means that no integration is required.

In the Circuit window, the calculation inputs not already described are:

Links – A link is defined as a connection between two existing cooling channels

outside the cavity block. No heat transfer is considered in the link. To create a circuits
with links just select the coolant entry points.

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The presence of links is indicated by yellow curves that help in verifying how they are
connecting channels.

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Fluid Temperature – This is the temperature of the coolant entering the cavity block.
The value must be in a range between the minimum possible temperature of the
specified fluid (for example above the freezing point of water) and a maximum (for
instance below the boiling point of water). Typically, the fluid temperature is set at
about 10-15°C below the target temperature of the mould cavity walls at the end of the
cycle.

Flow Rate – This is the flow rate of the coolant. Higher fluid flow rates improve
cooling, but can lead to poor quality of cooling in terms of temperature uniformity at
the cavity surface. This is especially true if the fluid temperature is significantly lower
than the mould temperature.

After confirming the data for all of the circuits, a message window appears warning in
case of Laminar flow in an element. Increase the flow rate of the indicated circuit to
obtain turbulent flow conditions which are essential for efficient cooling.

Diameter Variation – The value of the cooling channel diameter is assigned as a

property during the modelling process. The option given by this field improves the
speed of making different calculations by allowing faster modifications of the cooling
line diameter. Enter a positive number to increase the diameter or a negative value to
reduce it.

Larger channel diameters help cooling, but require a much higher flow rate to reach
turbulent flow. Turbulent flow is considered a requirement to achieve adequate heat
transfer.

Rugosity – Factor used to compute the pressure drop in a circuit without perfectly
smooth surfaces or with deposits. If, after the pressure drop calculation for the circuit,
the pressure value is well in the permissible range, this factor does not matter much.
Normally, the default value is confirmed.

Colour – To change the default circuit colour so to allow its easier identification.

Fixed Cycle – Check this box to make a calculation of the cooling time for the part
with reference to a significant entity with its ejection temperature. Obviously, this
information overrides the Total mould closing time input.

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Reference Entity/Ejection Temperature – The cooling time for the part can be
computed with reference to a significant entity with its ejection temperature. This last
value comes from the material database and is always suggested by the program.
The typical data can be changed if required by part properties quality.

The computed cooling time will be the time for the centre of the section of the
reference entity to reach the specified ejection temperature. For this reason, the
average temperature of this entity at that moment can be somehow lower than this
value due to the typical temperature profile. In the cases when the mould surface
temperatures of the reference entity are different, the solid fraction does not reach
100% because the actual highest temperature value is shifted toward the hottest
surface.

Reference Fraction – It refers to the fraction of entity thickness we need to be

solidified (below the freezing temperature) before ejection. This input is normally equal
to 100 (freezing of 100% of thickness) for parts with ordinary sections below 3 mm. It
can be reduced for thicker parts without particular dimensional requirements if we
think that a fraction allows the sufficient rigidity. This opportunity can even be used for
very thin parts providing we can assure proper cooling after ejection and avoid their
deformation due to free fall during ejection.

Solid mesh of the cavity

Solid mesh generation

Different matrix pre-conditioners

The next two inputs set the typical data for each specific category of materials. This
can be helpful to set good initial starting points but, of course, the data can be
changed within the appropriate range according to specific moulding needs.

Melt Temperature – Temperature of the resin entering the defined injection element.
This may be the temperature entering the machine nozzle or leaving it whenever the
nozzle is not included in the model.

Mould Temperature – Assigned starting temperature of the cavity surface.

Mesh Number – These values generate the dimension of the solid mesh for the cavity
block along each axis. More than 8 million of cubes (200x200x200 along each axis)
can be generated for the thermal calculations. The maximum precision of the results is
obtained with the default value that can be reduced to allow faster calculations.

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Mesh Dimension – The value, for the three Cartesian axes, depends on the selected
number of mould mesh in each direction.

Solver – To assure the solution in the most disparate cooling conditions, the
calculation modules have implemented a technique that calls in sequence, whenever
necessary, one of the available matrix pre-conditioners. In some particular conditions,
whenever the calculation modules are not able to find the solution to the matrix, it is
possible to force the program to start the calculation with a different solver.

What to do if the thermal calculation takes very long times?

It is possible to stop the calculation with the desired residual error. This permits, for
extreme cooling situations that would require numerous iterations with consequent
long calculation times, to evaluate the conditioning system in a fast way allowing for
possible modifications.

Tips about the Report Preparation

Is it possible to set up reports?

The option available through the Report tab greatly simplifies the preparation of the
analysis documentation by organizing, in an automatic but controlled way, a document
in .xml format. This can easily be viewed with Internet Explorer browser.

Is it possible to print the analysis results displayed on the screen?

The graphic images of the analyses can be Copied to the clipboard with the option
available in the Window menu. and later saved to disk. The image can then be saved
in any desired format, edited and/or printed with all major image processing programs
(e.g. Windows Paintbrush).

It is also possible to printout the numeric reports of the analysis. It includes, the Filling
Summary (*.fbr), the Holding Summary (*.fhr), Shape Summary (*.fsr), and Thermal
Summary (*.ftr) files. These files can be printed with any text editor. To maintain the
alignment of numbers, the word processor should use a non-proportional font (e.g.
Courier).

How to create analysis animations of filling or warpage etc?

The visualization for most of the field variables can be animated. This provides a
striking illustration of the dynamic changes of these variables during cavity filling and
packing, whenever evaluating the final shape of the part or while sectioning the mould
cavity block within the thermal analysis. When satisfied click to store the movies
under the specified name. The animations can then be used on a Web site or in a
presentation.

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 Tips about setting moulding machines

How to set a moulding machine using the data provided from an analyses?
All the key moulding data is provided by the VISI Flow packages. Care should be
taken to use a machine with a capability exceeding the values presented by the
analysis!

Injection time: remember that the value you set as input corresponds to the time to
complete the filling of the cold cavity using a uniform flow rate. Total injection time is
longer in case of programmed injection or in other situations such as an important
reduction of pressure at the V/P changeover or with limits for the maximum filling
pressure or clamping force.

The actual filling time in these situations is found by looking at the Time step or at the
Chart. Since standard moulding machines set what is called injection time as the total
time to fill plus the time for packing/holding, the splitting of the 2 times is determined
by the reaching of the volume/pressure changeover set as volume to be filled
(displacement of the screw) or reaching of a given pressure. The reference to set the
filling phase can be taken by the flow rate that appears in the graph of the evolution of
filling. Some machine allows to enter the flow rate and its evolution in the case of
programming, for the others which do not have such possibility the velocity of the
screw displacement can be easily computed by knowing the diameter of the cylinder.
With the information of the section area we can see how much volume will be filled per
unit of length of displacement so we can determine how many unit of length should be
done per unit of time. The filling represented by the VISI Flow volume corresponds at
the total displacement from the starting to the V/P changeover. The continuation of the
displacement from this changeover up to what is called “cushion” (typically at a much
lower velocity) will be determined by the holding pressure set in packing phase and
should not exceed the cushion limit with the set time. The entered mass, found as
result of the packing analysis, is used to know the value of this displacement. This for
the obvious reason to guarantee the possibility of the melt to enter in a cavity for the
desired time.

Melt temperature: common moulding machines do not set the melt temperature but it
is a result of the barrel temperature, screw rotation and back pressure. Typically the
zone near the nozzle is set equal to the desired melt temperature while the other have
an ascending profile from the hopper. As well known by moulding setters, this
temperature profile as well as the screw rotation is changed according to the ratio
between machine capability and shot weight. Not obtaining the right melt temperature
entering in the mould cavity will prejudge the correspondence of results.

Mould temperature: this is the temperature of the cavity surface at the end of cycle
and should not be confused with the coolant fluid temperature which in the typical
moulding has differences in the order of 20°C or more. The actual setting of the
coolant temperature with its flow rate and the local temperatures of the mould cavity
can be determined by the VISI Flow Thermal module. VISI Flow Filling analyses not
integrated with the previous module assume uniform mould temperature.

V/P change/cushion: see the consideration about the injection time.

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