http://www.twi-global.
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Design Part 5
Job Knowledge 94
Part 1
Part 2
Part 3
Part 4
The previous Job Knowledge articles looked at fillet and partial/full penetration butt welds. The
final three weld types to be dealt with in this series on weld design are the edge weld, the spot
weld and the plug weld.
The edge weld is a specialised weld that has limited fields of application and is mostly used for the
joining of sheet metal components although it may be used for the fabrication of tube to tubesheet
welds. The edge weld is frequently used as an alternative to a corner weld where achieving an
accurate fit may be difficult, particularly on thin section components. Instead, by raising a flange
on one of the components and clamping the two components together a weld can be made along
the edge. Sealing the lid on a can is one ideal application as the lid can be pushed in to the can,
resulting in a minimal gap and a self jigged joint (Fig.1). The weld size and penetration is limited
so this weld type is generally only possible on thin components using methods such as TIG,
plasma TIG or the power beam welding processes.
Fig.1. Edge weld used to seal container lid
This type of edge weld may also be used for tube to tubesheet welding where, by machining a
pintle onto the tubesheet, the tube can be inserted through the tube hole and an edge weld made,
(Fig.2) This has the advantage that the heat sink is more evenly balanced when attempting to
weld a thin tube to a thick tubesheet. In tubesheets of limited weldability or where postweld heat
treatment is essential it is possible to deposit a ring of weld metal round the tube hole. This ring
may then be machined to provide the pintle so that the residual stresses are reduced and the
tube/tubesheet weld is made in good weldability weld metal. This results in a reduction in residual
stress in the tubesheet and a reduction in the risk of cracking.
Fig.2. Edge weld used to weld tube to tubesheet joints
Alternatively, if PWHT is required the tubesheet and its weld rings can be PWHT'd, the pintles
machined on and non-destructively examined (NDE) and the tube/tubesheet welds made in the
thin section, removing the need for a second PWHT cycle. Because of the accuracy of these
machined joints the welding process, generally TIG, is frequently mechanised or fully automated.
The spot weld, Fig.3, is normally associated with resistance welding where two thin sheets are
overlapped and held in close contact by pressure from the welding electrodes during the welding
cycle. The resistance spot weld could therefore be regarded as self jigging. Spot welding with the
arc welding processes also uses a lap type joint but presents a more difficult problem in that the
joint must be firmly clamped together such that there is no gap between the two surfaces. Failure
to do this means that the weld metal may spill into the gap and full fusion to the underlying plate
may not be achieved. Good jigging and fixturing is therefore essential.
Fig.3. Spot welds
Applications of this joining method include sheet metal work and the lining ('wallpapering') of
ducts, tanks etc with thin, corrosion-resistant sheets. The greatest strength of the welds is
developed when the welds are in shear parallel to the plate surfaces.
As mentioned earlier, penetration into the parent metal from the various arc welding processes is
limited, around 4mm with TIG (perhaps as much as 10mm with activated flux TIG), 10mm with
plasma-TIG and 6mm with MAG welding. The thickness of the upper plate that must be fully
penetrated to provide a sound weld is therefore similarly limited. An additional problem with MAG
welding is that the filler wire is fed continuously into the weld pool so that a large lump of excess
weld metal may be deposited on the plate surface. Autogenous TIG or plasma-TIG will give a weld
flush with or slightly below the plate surface. The process can be partially mechanized. Special
torches are available that, when held against the plate surface, give the correct electrode/work
piece distance and timers on the welding power source that may be set to give the desired arc
time.
To enable thicker plate to be joined by 'spot welding' a circular or elongated hole may be machined
through the top plate, enabling either a plug or a slot weld to be made by filling the hole with weld
metal. Whilst this may seem tobe a simple and easy process the strength of this type of joint
depends upon full fusion of the weld metal with the vertical wall of the hole cut into the upper
plate, see Fig.4. As with a fillet weld, lack of fusion in this area will result in a reduction in the
throat thickness of the joint. It is therefore essential that the welder directs the welding arc into
the bottom corner of the joint and does not simply puddle the weld metal into the hole. With small
diameter plug welds this can be a difficult and skilled operation and welders need to be adequately
trained to ensure that they can achieve full fusion.
Fig.4. Plug and slot welds
Since the strength of the plug or slot weld is determined by the throat it may not be necessary to
fill the hole completely unless the weld must be flush with the surface of the plate for cosmetic
reasons. Besides being unnecessary from the point of view of joint strength, a completely filled
hole will have high residual stresses. These may cause unacceptable distortion and will increase
the risk of cold cracking in carbon and low alloy steels.
This brief series of Job Knowledge articles has concentrated on the design of joints for welding.
The designer also needs to remember that, not only must the joints be suitable for welding, they
must in addition enable any non-destructive testing required by the contract or specification to be
carried out. Provision therefore needs to be made to allow adequate access for the positioning of
radiographic film and the radiation source, or to enable the correct scanning patterns to be used if
the joint is to be ultrasonically tested.
Whilst NDE of butt welds is reasonably straightforward, radiography or ultrasonic examination of
fillet welds is not generally regarded as being possible. The designer must therefore take into
account the possibility of undetected defects in this type of joint.
This article was written by Gene Mathers.
http://www.mtm-inc.com/av-20100416-vacuum-chamber-design-weld-joint-design.html
Edge Welds
The correct style edge weld uses full penetration welds where the two sides meet. The incorrect
style edge weld has an elongated section where the two sides meet without a full penetration
weld. This leaves a pocket for contamination, or leaves a trapped volume between the two
surfaces.
These are just a few examples of weld styles that you may encounter during the design of a
vacuum system. This by no means covers all the possibilities, but by using the basic concepts
described here you will increase your success for a properly operating vacuum system.
If this article was of interest to you, drop us a line and let us know. Your feedback will help us
determine what type of content you would like to see in our newsletter and posted to the website.
http://www.weldguru.com/SMAWNomenclatureandJoints.html
Edge Joints
Edge Joints for Light Sheets and Plates
Edge Joints Figure 6-20
This type of joint is used to join two or more parallel or nearly parallel members.
It is not very strong and is used to join edges of sheet metal, reinforcing plates in flanges of I
beams, edges of angles, mufflers, tanks for liquids, housing, etc.
Two parallel plates are joined together as shown in view A, figure 6-20.
On heavy plates, sufficient filler metal is added to fuse or melt each plate edge completely and to
reinforce the joint.
b. Light sheets are welded as shown in view B, figure 6-20. No preparation is necessary other than
to clean the edges and tack weld them in position.
The edges are fused together so no filler metal is required. The heavy plate joint as shown in view
C, figure 6-20, requires that the edges be beveled in order to secure good penetration and fusion
of the side walls.
http://www.industrial-lasers.com/articles/print/volume-31/issue-1/features/keys-to-laser-welding-
lap-and-edge-joints.html
Keys to laser welding lap and edge
joints
02/03/2016
Optical tools allow for adaptability in welding
TOM GRAHAM
As material selections in automotive manufacturing move further into the high-strength
realm, along with the more prevalent usage of difficult-to-weld materials such as aluminum,
developing robust processes for joining these materials becomes ever more critical.
Adaptation of technologies such as real-time seam tracking, gap bridging, beam oscillation,
and integrated clamping to laser-related processes allows for them to be used in a more
mainstream approach.
To ensure integrity of the product, various joint designs are needed to establish that the
finished weldment can achieve all of the necessary requirements for fitness in service.
Flanges, for instance, are added to joints to increase structural strength and stability and can
occur in a various array of automotive parts, including doors, windows, beams, and pillars.
Most flanges, however, are designed to enable efficient welding with current resistance
welding and laser optic offerings. These flanges, often with longer length than is necessary so
as to accommodate part/process variation, add extra weight to vehicles that are already
requiring weight reduction in order to meet upcoming federal standards (e.g., CAFÉ
standards—fleet-wide average of 54.5 mpg by 2025). What if it was possible to reliably
process flanges, as well as drastically reduce flange length and still maintain a robust
manufacturing process? The solutions noted hereafter can offer strong potentials for weight
reduction and open up enhanced design opportunities.
FIGURE 1. Current laser welding is done with direct
fusion between two materials.
Laser edge welding of seams
Typically, edge welding is done with direct fusion between the two materials (FIGURE 1).
Using this approach, it is necessary to maintain close to zero gap to ensure proper welding of
the joint. The idea presented in FIGURE 2 depicts a method of gaining improved depth of
fusion while reducing flange length by more than half of current standards. The ability to
process in this manner is provided via a combination of features, including optical seam
tracking, integrated clamping, and beam oscillation capabilities, in one tool—the Scansonic
FSO (Flange Welding Optic).
FIGURE 2. Scansonic FSO allows for improved depth of
fusion while reducing flange length.
As with many welding processes, one of the largest obstacles is guaranteeing that the energy
used for joining is accurately positioned in the joint. Workpiece tolerances, process
robustness, and robot accuracy all play into achieving good welds. The ability to find the
joint using optical seam tracking via usage of laser triangulation provides a means of
accurately positioning the laser spot to the process. The seam tracking data is then fed back to
the optic controller, which translates the information to reposition the galvo motors in the
head to direct the laser beam to the required location. This system has the ability to provide
various inclination angles to accommodate alterations in joint position for two- and three-
layer welds as flange heights change relative to one another. The addition of an integrated
clamping unit on the head not only secures the part at a position directly related to the process
tool center point, it also provides an opportunity for reduced tooling costs to clamp and hold
the seam. The design of the clamping unit allows for reaching into openings or structures
where flanges might be present, and its fast open-and-close clamping mechanism (200ms)
provides a good foundation for high-volume applications.
These new technologies offer added benefit from a weld reliability standpoint to be able to
meet the welding requirements needed for materials such as aluminum, boron, and ultra-high
strength steels. Usage of the oscillation motors, in addition to those tied directly to beam
location/tracking, enables two-axis oscillation at speeds of up to 1000Hz, providing a
cleaning action for oxide layers, additional time for gas out of zinc particles, or post-weld
annealing for fragile microstructures.
An example of the cleaning action for the weld can be seen in the case of zero-gap welding of
galvanized material. In the case of welding zinc material, a gap (~0.1mm) is typically
mandatory to ensure that the zinc has a place to escape as it vaporizes at a temperature more
than half that of the base material. If not properly set up, this gas expulsion can get trapped in
the solidifying molten pool and show up in the form of porosity in the finished weld. The
addition of the oscillation feature enables a "remelting" of the pool, thus allowing the zinc to
be brought to the surface and not remain entrapped in the weld. With the samples noted
in FIGURE 3, only x modulation is used to help ensure proper handling of zinc from the
weld.
FIGURE 3. Flange welding of galvanized material with and without
oscillation using Scansonic FSO.
For structural components, it is often necessary to join relatively dissimilar materials such as
boron steels to either electrolytically galvanized or hot-dipped material. Based on the ability
to control the beam location relative to the joint and utilize oscillation, it provides a melt pool
that "floats" on the workpiece (FIGURE 4). Distortion that may show up in the workpiece
does not necessarily impact the finished quality due in part to the adaptive nature of the
process. The product's ability to accommodate variation in real time enables a stability that
has typically hampered similar process approaches in the past.
FIGURE 4. Edge welding of dissimilar metals.
Adaptive remote welding
In the case that a lap fillet is the functional joint that needs to be processed, similar issues are
seen here as well regarding joint location and required overlap. A complementary solution
exists that includes some of the features noted above regarding optical seam tracking and
beam oscillation. However, in lieu of clamping, this offering comes equipped with "gap
bridging" technology. In the majority of laser welding applications, zero gap is the ideal
condition to ensure proper fusion between the upper and lower sheets. Should gaps be seen in
lap edge configurations, there are now options to help support sound welding of this
configuration.
If wire is needed for chemistry- or gap-related conditions, there are options for use of the
tactile seam tracking system to accommodate for gaps, as filler metal can be used to bridge
them. However, with remote welding, it is not feasible to bring wire to the joint with any
sense of consistency, especially when using optical seam tracking for beam placement in the
joint. Without filler metal, how is it possible to automatically bridge the gap? The Scansonic
RLWA (Remote Laser Welding - Adaptive), which utilizes a 500mm standoff and offers real-
time seam finding and tracking via its process controls located internal to the head, now has
an option called "gap bridging." The end result is one where the laser spot position relative to
the seam is controlled in a dynamic nature, not simply shooting to a programmed point in
space.
FIGURE 5. Modulation characteristics for the gap-bridging algorithm in the
Scansonic RLWA.
Now that the beam is able to be accurately placed into the seam, the ability to process a lap
joint with high reliability is possible. The issue still comes back to gaps in the material, which
typical laser processes struggle to accommodate. With gap bridging algorithms predefined
within the system controls of the RLWA, the optic has the ability via the seam tracking
package to identify gaps in the joint and automatically adjust various conditions to process
the joint. Through modulation of laser power, spot size, y offset of beam relative to joint
edge, and application of beam oscillation in the x and ydirections, this enables a wicking of
the molten material to bridge the joint (FIGURE 5). Gaps measuring half the upper material
thickness or less can easily be addressed with both steel and aluminum, while further studies
show abilities beyond that in certain situations (FIGURE 6).
FIGURE 6. Examples of gap bridging for lap fillet weld using the Scansonic RLWA
with no additional filler metal.
Outlook
The ability to add varying levels of adaptivity as an integral part of the laser welding process
allows for greater robustness, less rework, and higher first-pass quality to the finished
product. Utilization of tools such as optical seam tracking, integrated clamping, beam
oscillation, and gap-bridging algorithms enable the user to further gain the advantages seen
from laser welding (e.g., processing speeds, low thermal input, etc.) and now be more broadly
applied, opening up opportunities not feasible in the past.
TOM GRAHAM (tgraham@abicorusa.com) is manager of the Key Accounts Group for
Abicor Binzel Robotic Systems, Frederick, MD, www.abicorusa.com.
http://www.telaverus.com/index.php/engineering-resources/welding-symbols.html
Welding Symbols
Welding symbols are used on engineering drawings to communicate the types of welds the welder must create
as determined by engineering, the designer or draftsperson. Understanding welding symbols on drawings is
essential for any person involved in metal fabrication and design where sheet metal or structural steel welding is
required.
The key to understanding weld symbols is to look at the graphical part of the symbol as a representation of the
shape of the desired weld. All of the standard welding symbols use a shape to help explain the desired outcome.
17 Standard Welding Symbols Used In
Engineering Drawings
Welding Symbol Chart - Weld Types
Bevel Fillet Weld Flange Flange Flare Bevel Flare V J Groove Plug Weld Scarf Seam Slot Weld Spot Square
Groove Corner Weld Edge Weld Groove Weld Groove Weld Groove Weld Projection Groove
Weld Weld Weld Weld Weld
Do more with the Weld Symbols app for iPhone, iPad and iPod Touch! Also available
on Android.
Bevel Groove Weld
^ Top ^
Fillet Weld
Flange Corner Weld
Flange Edge Weld
Flare Bevel Groove Weld
Flare V Groove Weld
J Groove Weld
Plug Weld
Scarf Groove Weld
Seam Weld
Slot Weld
Spot Projection Weld
Square Groove Weld
Stud Weld
Surfacing Weld
U Groove Weld
V Groove Weld
