MANFUCTURING TECHNOLYG SEMESTER Q/A .

1.State any four types of patterns.

Solid or Single Piece Pattern. Single piece pattern is the cheapest pattern among all other types
of pattern. ...

Two- Piece Pattern. Two- piece pattern is also called as split piece pattern. ...

Multi Piece Pattern. ...

Match Plate Pattern. ...

Gated Pattern. ...

Skeleton Pattern. ...

Sweep Pattern. ...

Loose Piece Pattern.

2. Define casting.

Casting is a manufacturing process in which a liquid material is usually poured into a mold,

which contains a hollow cavity of the desired shape, and then allowed to solidify. The solidified
part is also known as a casting, which is ejected or broken out of the mold to complete the
process. Casting materials are usually metals or various time setting materials that cure after
mixing two or more components together; examples are epoxy, concrete, plaster and.clay.
Casting is most often used for making complex shapes that would be otherwise difficult or
uneconomical to make by other methods. Heavy equipment like machine tool beds, ships'
propellers, etc. can be cast easily in the required size, rather than fabricating by joining several
small pieces .

3. What function of core.

The core is the center of our body and it functions to stabilize the trunk while the arms and
legs move during functional movements. When we view it this way, we see that the core
actually includes: Muscles that stabilize the hips.

4. Which process is called lost waxing method? Why?

lost-wax process, also called cire-perdue, method of metal casting in which a molten metal is
poured into a mold that has been created by means of a wax model. Once the mold is
made, the wax model is melted and drained away.

5. Point out the types of furnace used for melting ferrous material and Why?

Induction furnaces are the most common type used by both ferrous and non-ferrous foundries.
Copper coils heat the metal using alternating currents. The flux reacts with impurities.
Reverberatory furnaces melt metals in batches using a pot-shaped crucible that holds the
metal over an electric heater or fuel-free burner.

6. List out the various types of welding.

MIG – Gas Metal Arc Welding (GMAW) ...

TIG – Gas Tungsten Arc Welding (GTAW) ...

Stick – Shielded Metal Arc Welding (SMAW) ...

Flux-cored – Flux-cored Arc Welding (FCAW) ...

MANFUCTURING TECHNOLYG SEMESTER Q/A .
Spark your Interest.

7. Define Welding.

join together (metal parts) by heating the surfaces to the point of melting with a blowpipe, electric
arc, or other means, and uniting them by pressing, hammering, etc.

"steel plates were being welded"

8. Define resistance welding process.

Resistance welding is the joining of metals by applying pressure and passing current for a
length of time through the metal area which is to be joined. The key advantage of resistance
welding is that no other materials are needed to create the bond, which makes this process
extremely cost effective.

9. Name the types of flames.

There are three types of flames natural flame, carburizing flame and oxidizing flame.

10. What is submerged arc welding?

A shielding gas is not required. The arc is submerged beneath the flux blanket and is not
normally visible during welding.

This is a well established and extremely versatile method of welding.

The electrode may be a solid or cored wire or a strip made from sheet or sintered material.
The flux may be made by either fusing constituents to form a glassy slag (which is then crushed
to form a powder) or by agglomerating the constituents using a binder and a corning process.
MANFUCTURING TECHNOLYG SEMESTER Q/A .
11. What are the four major drawbacks of hot working?

The disadvantages are: Undesirable reactions between the metal and the surrounding
atmosphere (scaling or rapid oxidation of the workpiece) Less precise tolerances due to
thermal contraction and warping from uneven cooling. Grain structure may vary throughout
the metal for various reasons.

12. Classify the types of extrusion.

Types of the metal extrusion process

 Direct Extrusion.
 Indirect Extrusion.
 Hydrostatic Extrusion.
 Lateral or Vertical Extrusion.
 Hot extrusion.
 Cold Extrusion.
 Impact Extrusion.
13. Explain the term Extrusion process.

Extrusion is a process where a material undergoes plastic deformation by the application
of a force causing that material to flow through an orifice or die. The material adopts the
cross-sectional profile of the die and if the material has suitable properties, that shape is retained
in the final extrudate.

14. What are the different types of rolling mills.

Four Types of Rolling Mills

 Four-high rolling mill. A four high rolling mill is used for reducing material to
minute thicknesses. ...
 Cluster rolling mill. ...
 Continuous Mill. ...
 Planetary Rolling Mill.
15. What is forging.

Forging, a metal shaping technique using compressive, localized forces, has

been a staple metal fabrication technique since the time of the ancient
Mesopotamians. Since its origins in the fertile crescent, forging has
experienced significant changes, resulting in a more efficient, faster, and more
durable process. This is because today, forging is most commonly performed
with the use of forging presses or hammering tools that are powered by
electricity, hydraulics or compressed air. Some of the common materials used
for forging are carbon steel, alloy steel, microalloy steel, stainless steel,
aluminum, and titanium.
16. Explain Shearing.
Shearing, also known as die cutting, is a process that cuts stock without the formation of
chips or the use of burning or melting. Strictly speaking, if the cutting blades are straight the
MANFUCTURING TECHNOLYG SEMESTER Q/A .
process is called shearing; if the cutting blades are curved then they are shearing-type
operations.

17. Name the operations of sheet metal working.

Different Types of Sheet Metal Operations are:

Shearing Operation. Blanking & Fine Blanking Operation. Punching Operation.
Piercing Operation
18. What is super plastic forming operation.
Superplastic forming is a specialist process used for deforming metal sheet to extremely
large plastic strains to produce thin-walled components to the near-net shape. Stretching
of the sheet during superplastic forming is much higher than with rolling and sheet forming.

19. Define hydro forming process.

Hydroforming is a specialized type of die forming that uses a high pressure hydraulic fluid to

press room temperature working material into a die. 

20. Explain drawing.

Drawing, or sketching, is one of the fundamental types of art. Whether they are
painters, sculptors, or digital artists, many artists will learn to draw as a
fundamental artistic skill. But drawing is not just a precursor to other types of
visual art; it is a recognized art form itself.
21. What are the characteristic of thermoplastics.
Properties: Hard, brittle, opaque, good electrical and heat resistance, resistant to
deformation under load, low cost, resistant to most acids.

22. What are the types of plastics

The Basics On 7 Common Types of Plastic

 1) Polyethylene Terephthalate (PET or PETE)
 2) High-Density Polyethylene (HDPE)
 3) Polyvinyl Chloride (PVC or Vinyl)
 4) Low-Density Polyethylene (LDPE)
 5) Polypropylene (PP)
 6) Polystyrene (PS or Styrofoam)
 7) Other.
23. Name the parts made by rotational moulding.

Environmental products which include litter bins, road cones, bollards, traffic dividers and road
signs. Floats, buoys and pontoons. Automotive products such as truck mudguards, ducting,
diesel fuel tanks, toolboxes and tractor dashboards. Kayaks, canoes and boats.

24. Differentiate thermosetting and thermoplastic polymers.

Difference Between Thermoplastic and Thermosetting Plastic

MANFUCTURING TECHNOLYG SEMESTER Q/A .
Thermoplastic Thermosetting Plastic

Thermoplastics have low melting points and low Thermosetting plastics have high melting points
tensile strength. and tensile strength.
25. Explain thermoforming.

Thermoforming is a process of heating a thermoplastic sheet to its softening point. The sheet is
stretched across a single-sided mold and then manipulated.

Part-b 13 mark

1. Describe the various steps involved in sand moulding process.

The 6-Step Process of Sand Casting

Publish Date: October 30, 2019 | Category: Molding

    

Photo: Glenn McKechine
Also known as sand molding casting, sand casting is a casting-based manufacturing process that involves
the use of a sand mold. It’s used to create metal products and components in a variety of sizes and shapes.
To put its popularity into perspective, statistics show over half of all metal castings — about 60% — are
produced using sand casting. Below, you’ll learn more about the six primary steps of sand casting.

Step #1) Place Mold Pattern in Sand

The first step of sand casting involves the placement of the mold pattern in sand. The size and shape of the
casting is directly influenced by the mold. Therefore, manufacturing companies must create new molds to
create metal products and components in specific sizes and shape.

Step #2) Set Up the Gating System

Most casting processes involve the use of a gating system, and sand casting is no exception. Consisting of
a pouring cup and tunnels or “gates” to the mold, it’s used to funnel the molten mold into the mold cavity.
After placing the mold pattern in sand, manufacturing companies will set up a gating system such as this.
MANFUCTURING TECHNOLYG SEMESTER Q/A .
Step #3) Remove the Mold Pattern
With the gating system set up, manufacturing companies can then remove the mold pattern from the sand.
The mold pattern is no longer relevant at this point. When the mold pattern is placed inside sand, the sand
takes its shape. As a result, the mold pattern can be removed.

Step #4) Pour Molten Metal Into Mold Cavity

Now it’s time to pour the molten metal into the mold cavity. Sand casting supports a variety of different
metals and alloys, some of which include iron, steel, aluminum, bronze, magnesium, zinc and tin.
Depending on the specific metal or alloy used, manufacturing companies may need to heat it up to 3,000
degrees Fahrenheit. Once the metal or alloy has turned from a solid state to a liquid state, it’s poured into
the mold cavity.

Step #5) Wait for Metal to Cool

After the molten metal has been poured into the mold cavity, manufacturing companies must wait for it to
cool. Again, different types of metal take different lengths of time to cool. As the molten metal cools, it
will revert from a liquid state back to a solid state.

Step #6) Break Open Mold to Remove the Metal Casting

The sixth and final step of sand casting involves breaking open the mold to remove the newly created
metal casting. While molds patterns are typically reusable, the actual molds are not. Therefore,
manufacturing companies must recreate a new mold each time they want to create a new metal product or
component using sand casting.

2. Explain the Different types of Patters with a neat sketch.

Different Types of Pattern

n casting process, Pattern is the replica of the device which is the output of casting
process. This when molded in sand forms mold. After filling mold with the molten metal
there is a formation of casting. Patterns play a very important role in casting as they
decide the quality as well as perfection in a particular casting process. Gates and
runners are the most important components in several types of pattern. Pattern is the
basic requirement for creation of mold and it is always bigger than the size of casting.
There should be a proper selection of pattern so it must be able to sustain rough
handling. It forms mold cavity for casting processes. The patterns may be made of
metals like aluminium, brass, plaster and wax.

There are some of the features of best pattern material used for designing:

• Water resistant.
• Cheap in cost and have very less weight.
• Long lasting and hard.
• Industry oriented patterns are mostly designed simple and they are repairable.
MANFUCTURING TECHNOLYG SEMESTER Q/A .
During patterning processes, to handle any structural problems different allowances are
made. These allowances include shrinkage allowances, Machining Allowance, shake
allowances, Draft allowances and finally distortion allowances.
Following are some of the key factors that decide the types of patterns of casting you
must choose:

• Features of the particular casting process,

• Number of castings that are to be created and
• Physical specifications, means size of casting.

Types of Patterns
The various kinds of patterns that we use in casting process are

1) Single piece pattern

2) Two piece pattern
3) Gated pattern
4) Multi piece pattern
5) Match plate pattern
6) Skeleton pattern
7) Sweep pattern
8) Lose piece pattern
9) Follow board pattern
10) Cope and drag pattern
11) Segmental pattern and
12) Shell pattern

1) Solid or Single Piece Pattern

Single piece pattern is the cheapest pattern among all other types of pattern. This
pattern generally used in simple processes. It is applied in small scale production. It is
often used for the generation of large castings such as stuffing box of steam engine and
for creating simple shapes, flat surfaces like simple rectangular blocks. The important
characteristic of this pattern is that there is no need of joint in the mold area. In this
pattern one surface is considered as flat portion. This flat surface is used for parting
MANFUCTURING TECHNOLYG SEMESTER Q/A .
plane. Sand tools are used to cut the sand which ultimately make gating system. The
molding becomes a difficult task if there is absence of this flat surface. It is expected to
lie in cope or drag.

2) Two- Piece Pattern

Two- piece pattern is also called as split piece pattern. It is the popularly used for
intricate castings. The shape of casting decides the exact place of parting plane. This
parting plane may be flat or irregular surface. In two- piece pattern half part is always
molded in drag and other half part is molded in cope. The cope part of the pattern has
dowel pins. These dowel pins are used to align the two halves of split piece pattern.
Holes in the drag half of the two- piece pattern match exactly with dowel pins. It is used
in applications where it is very difficult to withdraw casting from the mold. Two- piece
patterns are used where the depth of casting is very high.

3) Multi Piece Pattern

Sometimes castings have very difficult and complicated designs. In such difficult
situations multi piece types of patterns are used. 3 or more patterns are included in
multi piece pattern.
For instance, if we consider three- piece pattern which comes under multi piece pattern.
This three- piece pattern consists of top, bottom and middle parts. The bottom part is
drag, top part is cope where the middle part is termed as check box.

4) Match Plate Pattern

Basically Match plate pattern is a split pattern. Cope and drag areas are on the opposite
faces of metallic plate. This metallic plate is termed as Match Plate. This type of pattern
requires very less hard work and gives very high output. Because the gates and runners
are also on the match plate. This is used in various manufacturing industries. This is
very expensive and gives accuracy as well as high yield. This pattern is widely used for
casting metals like aluminium.

5) Gated Pattern
Gated types of patterns are used to make multiple components inside the single mold.
Gated pattern is nothing but the pattern consisting one or more patterns. For joining
different patterns gates are used. These are loose patterns where gates and runners
have already attached. These patterns are very expensive. Due to their high cost they are
used for creating small castings. These small castings further are used in molding
machines as well as in mass producing processes.

6) Skeleton Pattern
Skeleton pattern is used for castings which have simple size and shape. These castings
are usually large in size. The only disadvantages of skeleton types of patterns are – it is
applicable for small number of components and it is not cheap. Economically, it is not
the best pattern. Stickler is used to remove extra sand. These are nothing but frames of
wood that highlight the area which is to be cast. These patterns also help molder. They
are widely used in process of pit or floor welding.
MANFUCTURING TECHNOLYG SEMESTER Q/A .
7) Sweep Pattern
In sweep pattern we make use of wooden board. This wooden board of proper size is to
be rotated about one edge to shape the cavity as circular or rotational symmetry. Sweep
pattern is often used when we have to create casting in very short interval of time. Molds
of extensive symmetrical casting can be made easily with the help of sweep pattern.
Sweep pattern consists of three parts spindle, base and sweep which is wooden board.
Spindle is directed in vertical direction and base is attached with sand.

8) Loose Piece Pattern

It is very difficult to remove one piece of solid pattern which is above or below the
parting plane having projections from the mold. With the help of loose piece types of
patterns projections can be made by loose pieces. It requires skilled labor work as well
as it is very expensive. There is one disadvantage of this loose piece pattern is that their
shifting can be done due to ramming process.

9) Cope and Drag Pattern

Cope and drag pattern is a split pattern. This pattern has cope and drag on separate
plate. Cope and drag pattern has two parts which are separately molded on molding box.
After molding parts, these two separate parts are combined to form the entire cavity.
Cope and drag pattern is almost like two-piece pattern. This pattern types are used in
the production of large castings where the molds are very heavy and unhandy for a user.

10) Follow Board Pattern

Follow board pattern consists of tool that is a simple wooden board which is used for
several reasons. The wooden board is used as a base in follow board pattern for
molding process. This pattern is used in processes where casting structures are weak
and they may break after the application of force.

11) Segmental Pattern

It is just a similar to that of sweep pattern. The working structure of segmental pattern
and sweep pattern is almost similar. For designing require shape or structure of mold
they both employ a part of pattern. As the name suggest segmental pattern is in the
form of segments and used for molding circular or round structures. In sweep pattern
there is complete rotation but in segmental pattern there is no complete rotation. For
creating mold, we can rotate partly to get required output.

12) Shell Pattern

Shell pattern is specially used for obtaining hollow shaped structure. Along the center
the parting process is done. The resultant halves produced after parting are both
doweled.

3. Explain the construction and operation of Cupola furnace with diagram

MANFUCTURING TECHNOLYG SEMESTER Q/A .

The cupola furnace is a melting device used to melt cast iron, bronze, and
other alloying elements. It is mainly used to convert iron to cast iron.

The Kapila furnace was first built in China during the period of the Warring
States (403 –221 BCE). The cupola furnace is cylindrical in shape, and the
equipment of this furnace is fitted vertically inside this cylindrical shell with
a door. For many years the cupola furnace was used to melt iron in iron
castings as it produces a better cast iron than pig iron.The top of the cupola
furnaces is sometimes fitted with a cap to avoid gases harmful to the
environment, and this cap also protects from rainwater.

The cupolas shell is made of steel and consists of refractory brick and
plastic refractory patching materials. The bottom of this shell is lined with a
mixture of clay and sand and is a temporary lining. Sometimes coal is
mixed with the soil lining so that when the coal is heated, it rots, and the
bond becomes brittle.

For many years the cupola furnace was used to melt iron in iron castings
as it produces a better cast iron than pig iron.The top of the cupola
furnaces is sometimes fitted with a cap to avoid gases harmful to the
environment, and this cap also protects from rainwater.
MANFUCTURING TECHNOLYG SEMESTER Q/A .
 The wood is first ignited over a bed of sand.
 When the wood starts burning properly, the coke is thrown from
the top to the well at a predetermined height of about 40 inches.
This makes a 40-inch coke bed.
 Then the combustion begins in the coke bed using fire from the
burning wood and air from the trees.
 At this time, aerial explosions have flown at lower than normal
rates to provoke coke.
 When the coke starts to burn properly after about 3 hours of
burning, alternating layers of limestone, pig iron, and coke are
charged until it reaches the level of the charging door.
 At this time, an air blast is carried out at a normal blowing rate, and
combustion occurs more rapidly in the coke bed.
 All the oxygen from the air blast is consumed by combustion in the
combustion zone.
 The chemical reaction that occurs is C + O2 -> CO2 + Heat.
 It is an exothermic reaction, and the temperature in the combustion
zone varies from 1150 to 1850 ° Celsius.
 The portion of the coke bed above the combustion zone is a
reducing zone.
 This region prevents oxidation of the metal charge while leaving it
over and through.
 Ho carbon dioxide goes up through this region; some of it is
reduced by the following reaction, CO2 + C -> 2CO
 The zone of dilution of iron above the zone is a melting zone
where solid iron is converted into molten iron.
 This molten iron falls down through the coke bed and collects in
the well.
 In this region, sufficient carbon compacts are extracted by the
molten metal and are characterized by the following chemical
reaction: – 3 Fe + 2 CO -> Fe3 C + CO2
 Above the melting zone, there is a preheating zone, where the
inward gases are preceded by and the temperature of this zone is
about 1900 degrees Celsius.
 In addition to limestone, fluorspar and soda ash are also used as
flux materials.
 The main function of the flux is to remove impurities from the iron
and protect the iron from oxidation.
MANFUCTURING TECHNOLYG SEMESTER Q/A .
 For normal blast rates, the first molten iron appears in the tap hole
within 5 to 10 minutes after the start of the air blast.
 The charging door remains closed until the metal melts.
 The content of the charge goes down as the melting proceeds.
 The rate of charging, i.e., the rate of adding layers of charge, is
equal to the rate of melting. The furnace is kept throughout the
process.
 When the melting process is over and no more molten irons are
required, the charge feeders stop, and the air blast also stops.
 The bottom plate opens when the prop is removed, and the slag is
removed.
 The copula furnace is generally not used for more than 4 hours but
may be used for 10 hours of continuous operation.
 The cupola furnace operates on a simple principle that produces
carbon dioxide and heat from the combustion of coke and causes
iron to melt.
 Iron melts when it flows downwards.
4. Define die-casting. Explain Pressure die casting process with a neat sketch

Die casting
From Wikipedia, the free encyclopedia

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An engine block with aluminum and magnesium die castings

Die casting is a metal casting process that is characterized by

forcing molten metal under high pressure into a mould cavity. The mold cavity is
created using two hardened tool steel dies which have been machined into shape
and work similarly to an injection mold during the process. Most die castings are
made from non-ferrous metals,
MANFUCTURING TECHNOLYG SEMESTER Q/A .
specifically zinc, copper, aluminium, magnesium, lead, pewter, and tin-based alloys.
Depending on the type of metal being cast, a hot- or cold-chamber machine is used.
The casting equipment and the metal dies represent large capital costs and this
tends to limit the process to high-volume production. Manufacture of parts using die
casting is relatively simple, involving only four main steps, which keeps the
incremental cost per item low. It is especially suited for a large quantity of small- to
medium-sized castings, which is why die casting produces more castings than any
other casting process.[1] Die castings are characterized by a very good surface
finish (by casting standards) and dimensional consistency. Die casting equipment was
invented in 1838 for the purpose of producing movable type for the printing industry. The first die
casting-related patent was granted in 1849 for a small hand-operated machine for the purpose of
mechanized printing type production. In 1885 Otto Mergenthaler invented the Linotype machine,
which cast an entire line of type as a single unit, using a die casting process. It nearly completely
replaced setting type by hand in the publishing industry. The Soss die-casting machine,
manufactured in Brooklyn, NY, was the first machine to be sold in the open market in North
America.[2] Other applications grew rapidly, with die casting facilitating the growth of consumer
goods, and appliances, by greatly reducing the production cost of intricate parts in high volumes.
[3]
 In 1966,[4] General Motors released the Acurad process.[5]
The main die casting alloys are: zinc, aluminium, magnesium, copper, lead, and tin; although
uncommon, ferrous die casting is also possible.[6] Specific die casting alloys include: zinc
aluminium; aluminium to, e.g. The Aluminum Association (AA) standards: AA 380, AA 384, AA
386, AA 390; and AZ91D magnesium.[7] The following is a summary of the advantages of each
alloy:[8]

 Zinc: the easiest metal to cast; high ductility; high impact strength; easily plated;
economical for small parts; promotes long die life.
 Aluminium: lightweight; high dimensional stability for very complex shapes and thin
walls; good corrosion resistance; good mechanical properties; high thermal and
electrical conductivity; retains strength at high temperatures.
 Magnesium: the easiest metal to machine; excellent strength-to-weight ratio; lightest
alloy commonly die cast.
 Copper: high hardness; high corrosion resistance; highest mechanical properties of
alloys die cast; excellent wear resistance; excellent dimensional stability; strength
approaching that of steel parts.
 Silicon tombac: high-strength alloy made of copper, zinc and silicon. Often used as
an alternative for investment cast steel parts.
 Lead and tin: high density; extremely close dimensional accuracy; used for special
forms of corrosion resistance. Such alloys are not used in foodservice applications
for public health reasons. Type metal, an alloy of lead, tin and antimony (with
sometimes traces of copper) is used for casting hand-set type in letterpress
printing and hot foil blocking. Traditionally cast in hand jerk moulds now
predominantly die cast after the industrialisation of the type foundries. Around 1900
the slug casting machines came onto the market and added further automation, with
sometimes dozens of casting machines at one newspaper office.
As of 2008, maximum weight limits for aluminium, brass, magnesium, and zinc castings are
estimated at approximately 70 pounds (32 kg), 10 lb (4.5 kg), 44 lb (20 kg), and 75 lb (34 kg),
respectively.[9] By late-2019, press machines capable of die casting single pieces over-100
kilograms (220 lb) were being used to produce aluminium chassis components for cars.[10]
The material used defines the minimum section thickness and minimum draft required for a
casting as outlined in the table below. The thickest section should be less than 13 mm (0.5 in),
but can be greater.[11]
MANFUCTURING TECHNOLYG SEMESTER Q/A .

Metal Minimum section Minimum draft

Aluminium alloys 0.89 mm (0.035 in) 1:100 (0.6°)

Brass and bronze 1.27 mm (0.050 in) 1:80 (0.7°)

Magnesium
1.27 mm (0.050 in) 1:100 (0.6°)
alloys

Zinc alloys 0.63 mm (0.025 in) 1:200 (0.3°)

There are a number of geometric features to be considered when creating a parametric model of
a die casting:

 Draft is the amount of slope or taper given to cores or other parts of the die cavity to
allow for easy ejection of the casting from the die. All die cast surfaces that are
parallel to the opening direction of the die require draft for the proper ejection of the
casting from the die.[12] Die castings that feature proper draft are easier to remove
from the die and result in high-quality surfaces and more precise finished product.
 Fillet is the curved juncture of two surfaces that would have otherwise met at a sharp
corner or edge. Simply, fillets can be added to a die casting to remove undesirable
edges and corners.
 Parting line represents the point at which two different sides of a mould come
together. The location of the parting line defines which side of the die is the cover
and which is the ejector.[13]
 Bosses are added to die castings to serve as stand-offs and mounting points for
parts that will need to be mounted. For maximum integrity and strength of the die
casting, bosses must have universal wall thickness.
 Ribs are added to a die casting to provide added support for designs that require
maximum strength without increased wall thickness.
 Holes and windows require special consideration when die casting because the
perimeters of these features will grip to the die steel during solidification. To
counteract this effect, generous draft should be added to hole and window features.

There are two basic types of die casting machines: hot-chamber machines and cold-chamber

machines.[14] These are rated by how much clamping force they can apply. Typical ratings are
between 400 and 4,000 st (2,500 and 25,400 kg).[8]
MANFUCTURING TECHNOLYG SEMESTER Q/A .
Hot-chamber die casting[edit]

Schematic of a hot-chamber machine

Hot-chamber die casting, also known as gooseneck machines, rely upon a pool of molten metal
to feed the die. At the beginning of the cycle the piston of the machine is retracted, which allows
the molten metal to fill the "gooseneck". The pneumatic- or hydraulic-powered piston then forces
this metal out of the gooseneck into the die. The advantages of this system include fast cycle
times (approximately 15 cycles a minute) and the convenience of melting the metal in the casting
machine. The disadvantages of this system are that it is limited to use with low-melting
point metals and that aluminium cannot be used because it picks up some of the iron while in the
molten pool. Therefore, hot-chamber machines are primarily used with zinc-, tin-, and lead-based
alloys.[14]

Cold-chamber die casting[edit]

A schematic of a cold-chamber die casting machine.

These are used when the casting alloy cannot be used in hot-chamber machines; these include
aluminium, zinc alloys with a large composition of aluminium, magnesium and copper. The
process for these machines start with melting the metal in a separate furnace. [15] Then a precise
amount of molten metal is transported to the cold-chamber machine where it is fed into an
unheated shot chamber (or injection cylinder). This shot is then driven into the die by a hydraulic
or mechanical piston. The biggest disadvantage of this system is the slower cycle time due to the
need to transfer the molten metal from the furnace to the cold-chamber machine. [16]
MANFUCTURING TECHNOLYG SEMESTER Q/A .

Mold or tooling[edit]

The ejector die half

The cover die half

Two dies are used in die casting; one is called the "cover die half" and the other the "ejector die
half". Where they meet is called the parting line. The cover die contains the sprue (for hot-
chamber machines) or shot hole (for cold-chamber machines), which allows the molten metal to
flow into the dies; this feature matches up with the injector nozzle on the hot-chamber machines
or the shot chamber in the cold-chamber machines. The ejector die contains the ejector pins and
usually the runner, which is the path from the sprue or shot hole to the mould cavity. The cover
die is secured to the stationary, or front, platen of the casting machine, while the ejector die is
attached to the movable platen. The mould cavity is cut into two cavity inserts, which are
separate pieces that can be replaced relatively easily and bolt into the die halves. [17]
The dies are designed so that the finished casting will slide off the cover half of the die and stay
in the ejector half as the dies are opened. This assures that the casting will be ejected every
MANFUCTURING TECHNOLYG SEMESTER Q/A .
cycle because the ejector half contains the ejector pins to push the casting out of that die half.
The ejector pins are driven by an ejector pin plate, which accurately drives all of the pins at the
same time and with the same force, so that the casting is not damaged. The ejector pin plate
also retracts the pins after ejecting the casting to prepare for the next shot. There must be
enough ejector pins to keep the overall force on each pin low, because the casting is still hot and
can be damaged by excessive force. The pins still leave a mark, so they must be located in
places where these marks will not hamper the casting's purpose. [17]
Other die components include cores and slides. Cores are components that usually produce
holes or opening, but they can be used to create other details as well. There are three types of
cores: fixed, movable, and loose. Fixed cores are ones that are oriented parallel to the pull
direction of the dies (i.e. the direction the dies open), therefore they are fixed, or permanently
attached to the die. Movable cores are ones that are oriented in any other way than parallel to
the pull direction. These cores must be removed from the die cavity after the shot solidifies, but
before the dies open, using a separate mechanism. Slides are similar to movable cores, except
they are used to form undercut surfaces. The use of movable cores and slides greatly increases
the cost of the dies.[17] Loose cores, also called pick-outs, are used to cast intricate features, such
as threaded holes. These loose cores are inserted into the die by hand before each cycle and
then ejected with the part at the end of the cycle. The core then must be removed by hand.
Loose cores are the most expensive type of core, because of the extra labor and increased cycle
time.[11] Other features in the dies include water-cooling passages and vents along the parting
lines. These vents are usually wide and thin (approximately 0.13 mm or 0.005 in) so that when
the molten metal starts filling them the metal quickly solidifies and minimizes scrap. No risers are
used because the high pressure ensures a continuous feed of metal from the gate. [18]
The most important material properties for the dies are thermal shock resistance and softening at
elevated temperature; other important properties include hardenability, machinability, heat
checking resistance, weldability, availability (especially for larger dies), and cost. The longevity of
a die is directly dependent on the temperature of the molten metal and the cycle time. [17] The dies
used in die casting are usually made out of hardened tool steels, because cast iron cannot
withstand the high pressures involved, therefore the dies are very expensive, resulting in high
start-up costs.[18] Metals that are cast at higher temperatures require dies made from higher alloy
steels.[19]

Die and component material and hardness for various cast metals

Cast metal

Die
Tin, lead & zinc Aluminium & magnesium Copper & brass
component

Material Hardness Material Hardness Material Hardness

290–330  42–48 HR 38–44

P20[note 1] H13 DIN 1.2367
HB C HRC
Cavity
inserts
46–50 42–48 H20, H21, 44–48
H11 H11
HRC HRC H22 HRC
MANFUCTURING TECHNOLYG SEMESTER Q/A .

46–50
H13
HRC

46–52 44–48 40–46

H13 H13 DIN 1.2367
HRC HRC HRC

Cores

42–48
DIN 1.2367
HRC

48–52 DIN 37–40 DIN 1.2367 37–40

Core pins H13
HRC 1.2367 prehard HRC prehard HRC

46–48
48–52 H13 HRC 42–46
Sprue parts H13 DIN 1.2367
HRC DIN 1.2367 44–46 HRC
HRC

40–44
40–44 42–48 DIN 1.2367 HRC
Nozzle 420 H13
HRC HRC H13 42–48
HRC

46–50 46–50 46–50

Ejector pins H13[note 2] H13[note 2] H13[note 2]
HRC HRC HRC

42–48 42–46
DIN
Plunger shot 46–50 H13 [note 2]
HRC HRC
H13[note 2] 1.2367[note 2]
sleeve HRC DIN 1.2367[note 2] 42–48 42–46
H13[note 2]
HRC HRC

4140 4140
Holder block ~300 HB 4140 prehard ~300 HB ~300 HB
prehard prehard

The main failure mode for die casting dies is wear or erosion. Other failure modes are heat
checking and thermal fatigue. Heat checking is when surface cracks occur on the die due to a
large temperature change on every cycle. Thermal fatigue is when surface cracks occur on the
die due to a large number of cycles.[20]

Typical die temperatures and life for various cast materials[21]

MANFUCTURING TECHNOLYG SEMESTER Q/A .

Brass (leaded
Zinc Aluminium Magnesium
yellow)

Maximum die life [number of 1,000,00

100,000 100,000 10,000
cycles] 0

Die temperature [C° (F°)] 218 (425) 288 (550) 260 (500) 500 (950)

Casting temperature [C° (F°)] 400 (760) 660 (1220) 760 (1400) 1090 (2000)

Process[edit]
The following are the four steps in traditional die casting, also known as high-pressure die
casting,[5] these are also the basis for any of the die casting variations: die preparation, filling,
ejection, and shakeout. The dies are prepared by spraying the mould cavity with lubricant. The
lubricant both helps control the temperature of the die and it also assists in the removal of the
casting. The dies are then closed and molten metal is injected into the dies under high pressure;
between 10 and 175 megapascals (1,500 and 25,400 psi). Once the mould cavity is filled, the
pressure is maintained until the casting solidifies. The dies are then opened and the shot (shots
are different from castings because there can be multiple cavities in a die, yielding multiple
castings per shot) is ejected by the ejector pins. Finally, the shakeout involves separating the
scrap, which includes the gate, runners, sprues and flash, from the shot. This is often done using
a special trim die in a power press or hydraulic press. Other methods of shaking out include
sawing and grinding. A less labor-intensive method is to tumble shots if gates are thin and easily
broken; separation of gates from finished parts must follow. This scrap is recycled by remelting it.
[14]
 The yield is approximately 67%.[22]
The high-pressure injection leads to a quick fill of the die, which is required so the entire cavity
fills before any part of the casting solidifies. In this way, discontinuities are avoided, even if the
shape requires difficult-to-fill thin sections. This creates the problem of air entrapment, because
when the mould is filled quickly there is little time for the air to escape. This problem is minimized
by including vents along the parting lines, however, even in a highly refined process there will still
be some porosity in the center of the casting.[23]
Most die casters perform other secondary operations to produce features not readily castable,
such as tapping a hole, polishing, plating, buffing, or painting.

Inspection[edit]
See also: Casting defect

After the shakeout of the casting it is inspected for defects. The most common defects
are misruns and cold shuts. These defects can be caused by cold dies, low metal temperature,
dirty metal, lack of venting, or too much lubricant. Other possible defects are gas
porosity, shrinkage porosity, hot tears, and flow marks. Flow marks are marks left on the surface
of the casting due to poor gating, sharp corners, or excessive lubricant. [24]
MANFUCTURING TECHNOLYG SEMESTER Q/A .
Lubricants[edit]
Water-based lubricants are the most used type of lubricant, because of health, environmental,
and safety reasons. Unlike solvent-based lubricants, if water is properly treated to remove all
minerals from it, it will not leave any by-product in the dies. If the water is not properly treated,
then the minerals can cause surface defects and discontinuities.
Today "water-in-oil" and "oil-in-water" emulsions are used, because, when the lubricant is
applied, the water cools the die surface by evaporating depositing the oil that helps release the
shot. A common mixture for this type of emulsion is thirty parts water to one part oil, however in
extreme cases a ratio of one-hundred to one is used. [25] Oils that are used include heavy residual
oil (HRO), animal fat, vegetable fat, synthetic oil, and all sorts of mixtures of these. HROs are
gelatinous at room temperature, but at the high temperatures found in die casting, they form a
thin film. Other substances are added to control the viscosity and thermal properties of these
emulsions, e.g. graphite, aluminium, mica. Other chemical additives are used to
inhibit rusting and oxidation. In addition emulsifiers are added to improve the emulsion
manufacturing process, e.g. soap, alcohol esters, ethylene oxides.[26]
Historically, solvent-based lubricants, such as diesel fuel and kerosene, were commonly used.
These were good at releasing the part from the die, but a small explosion occurred during each
shot, which led to a build-up of carbon on the mould cavity walls. However, they were easier to
apply evenly than water-based lubricants.[27]

Advantages[edit]
Advantages of die casting:[11]

 Excellent dimensional accuracy (dependent on casting material, but typically 0.1 mm

for the first 2.5 cm (0.004 inch for the first inch) and 0.02 mm for each additional
centimeter (0.002 inch for each additional inch).
 Smooth cast surfaces (Ra 1–2.5 micrometres or 0.04–0.10 thou rms).
 Thinner walls can be cast as compared to sand and permanent mould casting
(approximately 0.75 mm or 0.030 in).
 Inserts can be cast-in (such as threaded inserts, heating elements, and high strength
bearing surfaces).
 Reduces or eliminates secondary machining operations.
 Rapid production rates.
 Casting tensile strength as high as 415 megapascals (60 ksi).
 Die casting fluid length is unaffected by solidification range, unlike permanent molds,
sand castings, and other types.[28]
 Corrosion rates for die castings are slower than those for sand castings due to the
smoother surface of the die castings.[29]
Disadvantages[edit]
The main disadvantage to die casting is the very high capital cost. Both the casting equipment
required and the dies and related components are very costly, as compared to most other
casting processes. Therefore, to make die casting an economic process, a large production
volume is needed. Other disadvantages are:

 The process is limited to high-fluidity metals. Increased scrap rates can be caused by
fluidity failure, and scrap costs in die casting are high. [30]
 Die casting involves a large number of parts, so questions of repeatability are
particularly important.[31]
 Casting weights have previously been limited to between 30 grams (1 oz) and 10 kg
(20 lb),[note 3][11] but from 2018 shots of 80 kilograms (180 lb) have become possible.[32]
 In the standard die casting process the final casting will have a small amount of
porosity. This prevents any heat treating or welding, because the heat causes the
MANFUCTURING TECHNOLYG SEMESTER Q/A .
gas in the pores to expand, which causes micro-cracks inside the part and exfoliation
of the surface. However, some companies have found ways of reducing the porosity
of the part, allowing limited welding and heat treating. [4] Thus a related disadvantage
of die casting is that it is only for parts in which softness is acceptable. Parts
needing hardening (through hardening or case hardening) and tempering are not
cast in dies.
5. Explain the different types of casting defects.

Different types of casting defects are unwanted occurrences on a casting

during the casting process. It may lead to bad shape, weak casting, and poor
functionality. Casting defects are broken down into five main categories: gas
porosity, shrinkage, mold material, pouring metal, and metallurgical Casting
defects. Some casting defects can be repaired while some are tolerated.

To avoid any of these types of casting defects, one needs to have a clear
understanding of its types and their remedies. These defects are less when the
technical level of each operation is perfectly done. That could be achieved by
skills of the operator, management quality, and good and maintained
equipment.

Types of Casting Defects

The following are types of casting defects and their remedies: Gas porosity
takes place on casted metal when it traps gasses like nitrogen, oxygen, or
hydrogen during casting. The casting defect appears on metals as small holes,
rounded, or circular cavities. The holes are formed when the casting cools
and solidifies because the solid form of metal cannot store a lot of gas as of
the liquid form.

Gas porosity casting defects are caused by an escape route on mold and cores
at which gases can pass and when mold and cores do not allow dry before
use. Gas porosity casting defects are classified into three:
MANFUCTURING TECHNOLYG SEMESTER Q/A .
Pinholes:
pinholes are very tiny holes found in the cope outer part of the mold, in a
poorly vented pocket. These casting defects are sometimes referred to as
porosities. Pinholes usually appear in large numbers at the surface of the
casting.

Subsurface blowhole:
blowholes are larger cavities located inside the casted metal. These types of
gas porosity casting defects are difficult to locate before machining and it
requires harmonic, ultrasonic, magnetic or x-ray analysis.

Read more: How sand casting is done

Open holes:
These blowholes appear on the surface of the casted metal which makes it
easier to detect than the subsurface blowholes.

Shrinkage casting defects

These types of casting defects occur during the solidification of the casting.
Its porosity appears with angular edges when compared with round surfaces
of gas porosity. Shrinkage casting defects happen because metals are less
dense as a liquid than a solid. these branches of casting defect might also be
paired with cracks. Shrinkage with large cavities can cause the casting to
eventually break under stress.

Read more: 4 Different Types of Metal Casting Process

These defects should always be expected during solidification. So, one
should factor shrinkage allowance into the pattern design during casting.
Specifically, alloys, shrink when changing from molten to solid because their
density in a molten state is lower than that of a solid state. One can prevent
shrinkage casting defects by improving the overall casting structure which
includes, designing a running (gate) system with risers to enables a
MANFUCTURING TECHNOLYG SEMESTER Q/A .
continuous flow of molten metal, reduce casting temperature to reduce the
total volume deficit, and by increasing local heat dissipation by inserting
cooling ribs or coils, and internal chills. Shrinkage types of casting defects
are classified into two:

Open Shrinkage defects:

These casting defects are located at the surface as pipes and burrow into the
casting. It is open to the atmosphere and allows air to enter as the shrinkage
cavity is formed.

Closed shrinkage defects:

these casting defects are also known as shrinkage porosity. It usually appears
at the top of the hot spots or isolated pools of the hot liquid. Closed shrinkage
defects are formed within the casting. Some can be seen with the bare eye
while but some cannot.

Mold material casting defects

Mold material casting defects occurs on sands and can always be prevented
by modifying the mold. These casting defects can affect the cast in several
ways:

Cuts and washes:

these casting defects occur when a molten metal erodes the molding sand. It
is shown on the casting as areas of excess metal. Cuts and washes can be
caused by a molten metal flowing at an extremely high velocity, allowing the
flow of too much metal through the gate. Cuts and washes are prevented
when the gating system is properly designed, improving the mold and core
strength and adding more binders to the facing and core sand Fusion:
fusion is a thin crust with a brittle, glassy appearance firmly joined to the
casting. This is caused when sand grains are fused with molten metal. It takes
place when molten metal with extreme hot velocity is poured and low
refractoriness of clay or sand. Silica sand is mostly used during casting due to
its high refractoriness. Remember, refractoriness is the ability of molding
material to resist the temperature of liquid metal to avoid fusion. To prevent
fusion casting defects is by reducing the temperature of the pouring metal
and improving the refractoriness of molding materials.
MANFUCTURING TECHNOLYG SEMESTER Q/A .
Run Out:
these casting defects occur when the molten metal escaped through the mold,
which could lead to incomplete or missing casting. Run-out casting defects
are caused by the mold or flask and they can be prevented by designing the
casting mold with precision. One should also inspect and repair any defective
molds before casting. Reducing the temperature of molten metal can stop the
wear and tear of the mold. Using quality raw materials for mold work will
help in resisting high temperatures.

Swell:
these casting defects occur on the vertical face of the castings caused by low
strength mold and improper or bad ramming of the mold. To prevent swell
casting defects, mold should be built to withstand the pressure of liquid
metal. Otherwise, the mold shape changes by moving a bit back and causes
swells. These casting defects can also be prevented when the mold is
properly rammed.

 Drops:
these casting defects occur when the casting is still liquid. It is caused when
pieces of metal drop into the liquid metal. It appears as an irregular-shaped
projection on the surface of the casting. Using sand with lower strength, soft
ramming, insufficient fluxing of molten metal, and absence of reinforcement
of sand projection in the cope can lead to drops casting defects.

 Rattail, Veins, and Buckles:

these casting defects occur in the casting as irregular lines or cracks. The rat
tail appears on casting when the hotness of the metal causes the sand to
expand which may be caused by poor expansion properties of the sand, the
hot pouring temperature of the metal, and poor design.

Metal penetration:
These casting defects occur when molten metal penetrate gaps in the molding
sand. These types of casting defects appear as the rough and uneven surface
finish of the casting which is visible to the naked eye. Metal penetration is
caused by various issues which include: using sand with low strength and
high permeability, using large or coarse sand grain, soft ramming of sand,
and lack of mold wash. All these can be prevented when high strength, small
grain size, low permeability, and hard ramming of sand. Metal penetration
can be removed from the surface of the casting by grinding down the affected
parts.
MANFUCTURING TECHNOLYG SEMESTER Q/A .
Metallurgical defects

Metallurgical casting defects come in two types, they are, Hot tears and hand
spots. These types of casting defects may fall in any of the two.

Read: Foundry work and Processes

Hot tear/crack:
these casting defects take place in the branching pattern as narrow cracks.
These cracks are obvious while some are required. These cracks are seen
after the casting cools when it’s about to solidify. The hot tear occurs if the
casted metal does not have sufficient strength to resist tensile forces during
solidification and it is mostly caused by poor mold design.

Hot/ hard spots:

these casting defects are spots that are harder than the surrounding area. This
spot cools quickly than the surrounding material. Hard spots casting defects
are results of improper cooling practice and can be avoided by correcting
cooling practice and considering changing the metal’s chemical composition.
The casting defects can interfere during machining and increase tool wear.

Pouring defects
MANFUCTURING TECHNOLYG SEMESTER Q/A .
Pouring casting defects occurs during the pouring process. These defects are
categories into four:

Cold shut/ lap:

these casting defects appear on the surface of the casting. It occurs as a line
or cracks with a round edge on the casting surface. The defect leads to a full
rejection of casting because it creates a weak spot. It is caused when molten
metal enters the mold from two gates, the steams will meet at a junction. Low
temperatures can prevent fusion at the junction, causing the steams to solidify
before fusion, creating a cold shut. These types of casting defects are usually
caused as a result of lacking fluidity of the molten metal, or a poor design of
the gating system, which is prevented by increasing fluidity of the molten
metal.

 Misruns:
these casting defects are closely related to cold shut defects. It occurs when
the liquid metal is too cold to flow through the mold cavity before freezing
and solidifying. The liquid metal does not fill the mold cavity. The misrun
casting defect is an unfilled portion of the mold. To prevent misrun casting
defects, the molding design, gating system design, and molten metal fluidity
have to be check.

Read more: Different Types of Die Casting and its applications

 Cold shots:
these casting defects are solid globules of the surface of the casting. It is
caused by the splattering during the pouring of the liquid metal. These cold
shuts are typically ball, drop, or pearl-shaped. To prevent splattering and cold
shots, the pouring procedures should be modified, and adjusting the gating
system designs by reducing the gate speed.

Slag inclusion (scab):

these casting defects are irregular metallic crusts located on the casting
surface. They are typically thick but can be tough and seen with the naked
eye. Scabs are usually sharp edges, irregular shapes and are firmly bonded to
the casting. Removing scabs from the cast will expose a rat tail underneath.
These types of casting defects are caused when molten metal is containing
slag particles is poured into the mold cavities and solidifies together. Slag can
be removed in several ways which include: melting the metal with flux in a
vacuum, inert atmosphere, or adding a ceramic filter into the gating system.
MANFUCTURING TECHNOLYG SEMESTER Q/A .
Also check: Different types of Foundry tools and equipment
Casting shape defects

These types of casting defects occur in the overall shape of the casting. These
include:

Shift/ mismatch:
these casting defects occur when the mold shift due to misalignment of the
cope (upper) and drag (lower) parts of the mold. Mold shift is usually
reflected as a horizontal displacement. These casting defects occur when the
box pins loose, inaccurate pattern dowel pins, or carelessness in placing the
cope on the drag, leading to misalignment. To avoid misalignment, these
three causes must be examined.
Flash, Fin, and Burrs:
these casting defects are one of the most occurring casting defects. This
defect is also called fin and burrs which are unwanted or excess materials
attached to the cast. Flash is a waste material that turns into dross after being
melted. Flashes are caused due to crack and gap on the core surface which is
caused due to insufficient weight on the mold or improper clamping of the
flask can lead to the gap. To avoid flash, there should be enough weight on
the top part of the mold so the two parts fit together tightly.

Read more: What is die casting? and its advantages and disadvantages

Warping:
these casting defects are unwanted casting deformity that occurs over time
that may lead to change in dimensions of the product. These types of defects
take place during solidification. They are caused by the different rates of
solidification of different sections, which causes stress in the adjoining walls.
Heat treatment can help in removing the residual stress in iron casting.
That is all for this article, types casting defects and their remedies. I hope you
got a lot from this article, if so, kindly share it with other students. Thanks for
reading, see you next time!
MANFUCTURING TECHNOLYG SEMESTER Q/A .
Pouring defects

Pouring casting defects occurs during the pouring process. These defects are
categories into four:

Cold shut/ lap:

these casting defects appear on the surface of the casting. It occurs as a line
or cracks with a round edge on the casting surface. The defect leads to a full
rejection of casting because it creates a weak spot. It is caused when molten
metal enters the mold from two gates, the steams will meet at a junction. Low
temperatures can prevent fusion at the junction, causing the steams to solidify
before fusion, creating a cold shut. These types of casting defects are usually
caused as a result of lacking fluidity of the molten metal, or a poor design of
the gating system, which is prevented by increasing fluidity of the molten
metal.

 Misruns:
these casting defects are closely related to cold shut defects. It occurs when
the liquid metal is too cold to flow through the mold cavity before freezing
and solidifying. The liquid metal does not fill the mold cavity. The misrun
casting defect is an unfilled portion of the mold. To prevent misrun casting
defects, the molding design, gating system design, and molten metal fluidity
have to be check.

Read more: Different Types of Die Casting and its applications

 Cold shots:
these casting defects are solid globules of the surface of the casting. It is
caused by the splattering during the pouring of the liquid metal. These cold
shuts are typically ball, drop, or pearl-shaped. To prevent splattering and cold
MANFUCTURING TECHNOLYG SEMESTER Q/A .
shots, the pouring procedures should be modified, and adjusting the gating
system designs by reducing the gate speed.

Slag inclusion (scab):

these casting defects are irregular metallic crusts located on the casting
surface. They are typically thick but can be tough and seen with the naked
eye. Scabs are usually sharp edges, irregular shapes and are firmly bonded to
the casting. Removing scabs from the cast will expose a rat tail underneath.
These types of casting defects are caused when molten metal is containing
slag particles is poured into the mold cavities and solidifies together. Slag can
be removed in several ways which include: melting the metal with flux in a
vacuum, inert atmosphere, or adding a ceramic filter into the gating system.

Casting shape defects

These types of casting defects occur in the overall shape of the casting. These
include:

Shift/ mismatch:
these casting defects occur when the mold shift due to misalignment of the
cope (upper) and drag (lower) parts of the mold. Mold shift is usually
reflected as a horizontal displacement. These casting defects occur when the
box pins loose, inaccurate pattern dowel pins, or carelessness in placing the
cope on the drag, leading to misalignment. To avoid misalignment, these
three causes must be examined.
MANFUCTURING TECHNOLYG SEMESTER Q/A .
Casting shape defects

These types of casting defects occur in the overall shape of the casting. These
include:

Shift/ mismatch:
these casting defects occur when the mold shift due to misalignment of the
cope (upper) and drag (lower) parts of the mold. Mold shift is usually
reflected as a horizontal displacement. These casting defects occur when the
box pins loose, inaccurate pattern dowel pins, or carelessness in placing the
cope on the drag, leading to misalignment. To avoid misalignment, these
three causes must be examined.

Warping:
these casting defects are unwanted casting deformity that occurs over time
that may lead to change in dimensions of the product. These types of defects
take place during solidification. They are caused by the different rates of
solidification of different sections, which causes stress in the adjoining walls.
Heat treatment can help in removing the residual stress in iron casting. That
is all for this article, types casting defects and their remedies. I hope you got
a lot from this article, if so, kindly share it with other students. Thanks for
reading, see you next time!

5. Explain lost wax - Investment casting processes with neat sketch.

lost-wax process, also called cire-perdue, method of metal casting in which a

molten metal is poured into a mold that has been created by means of a wax model.
Once the mold is made, the wax model is melted and drained away. A hollow core
can be effected by the introduction of a heat-proof core that prevents the molten
metal from totally filling the mold. Common on every continent except Australia, the
lost-wax method dates from the 3rd millennium BC and has sustained few changes
since then.

To cast a clay model in bronze, a mold is made from the model, and the inside of this
negative mold is brushed with melted wax to the desired thickness of the final
MANFUCTURING TECHNOLYG SEMESTER Q/A .
bronze. After removal of the mold, the resultant wax shell is filled with a heat-
resistant mixture. Wax tubes, which provide ducts for pouring bronze during casting
and vents for the noxious gases produced in the process, are fitted to the outside of
the wax shell, which may be modeled or adjusted by the artist. Metal pins are
hammered through the shell into the core to secure it. Next, the prepared wax shell is
completely covered in layers of heat-resistant plaster, and the whole is inverted and
placed in an oven. During heating, the plaster dries and the wax runs out through the
ducts created by the wax tubes. The plaster mold is then packed in sand, and molten
bronze is poured through the ducts, filling the space left by the wax. When cool, the
outer plaster and core are removed, and the bronze may receive finishing
touches. See also investment casting; sculpture: Reproduction and surface-finishing
techniques.
founding, the process of pouring molten metal into a cavity that has
been molded according to a pattern of the desired shape. When the metal solidifies,
the result is a casting—a metal object conforming to that shape. A great variety of
metal objects are so molded at some point during their manufacture.

The most common type of mold is made of sand and clay; ceramics, sand with

cement, metals, and other materials are also used for molds. These materials are
packed over the face of the pattern (usually made of wood, metal, or resin) that forms
the cavity into which the molten metal is to be poured. The pattern is removed from
the mold when its shape is able to be retained by the mold material. Molds are
usually constructed in two halves, and the two halves are joined together once the
pattern has been removed from them. Pins and bushings permit precise joining of
the two halves, which together are enclosed in a mold box. The metal is then poured
into the mold through special gates and is distributed by runners to different areas of
the casting. The mold must be strong enough to resist the pressure of the molten
metal and sufficiently permeable to permit the escape of air and other gases from the
mold cavity; otherwise, they would remain as holes in the casting. The mold material
must also resist fusion with the molten metal, and the sand at the mold surface must
be closely packed to give a smooth casting surface.

The making of patterns for foundries requires care and skill. Patterns are uniformly
larger than the desired casting in order to compensate for shrinkage during drops of
temperature and the liquid-to-solid phase change. Polystyrene foam patterns remain
in the mold and evaporate upon contact with the poured metal; wax patterns are
melted out of the mold prior to the pouring of the molten metal. Metal molds are
used in that type of founding known as die-casting. Often a hollow space is desired
within the casting; in this case a core of fine sand is placed in one of the mold halves.
Core boxes made of wood, metal, or resin are also used in this regard.

Modern foundries capable of large-scale production are characterized by a

high degree of mechanization, automation, and robotics, and
microprocessors allow for the accurate control of automated systems.
Advances in chemical binders have resulted in stronger molds and cores
and more accurate castings. Accuracy and purity are increased in vacuum
conditions, and further advances are expected from zero-gravity casting in
space. die-casting, forming metal objects by injecting molten metal under pressure
into dies, or molds. An early and important use of the technique was in the
Mergenthaler Linotype machine (1884) to give line-long combinations of letters, but
MANFUCTURING TECHNOLYG SEMESTER Q/A .
the appearance of the mass-production automobile assembly line gave die-casting its
real impetus. Great precision is possible, and products range from tiny parts for
sewing machines and automobile carburetors to aluminum engine-block castings.

The two major die-casting techniques differ only in how the molten metal is
introduced: in the cold-chamber process, the metal is ladled into a chamber; a
plunger impels the metal into the cold die cavity, in which it quickly hardens.

In the piston, or gooseneck, process the plunger and its cylinder are submerged in
the molten metal, the metal being admitted through a hole in the top of the cylinder
when the plunger is retracted; the advance of the plunger forces the metal into the
die cavity as before. The die core is in position in the die cavity when the metal enters
and fills the space around it; as soon as the metal hardens, the die core is retracted.
The die is then opened, and the finished casting is ejected.

In modern die-casting the sequence is governed electronically.

6. Explain the principle and working of ultrasonic welding process with a neat sketch. Also
write the advantages and disadvantages.