Things to Ponder:
1. What are the main considerations when making a pattern in sand casting?
Key Considerations of Pattern in Casting
2 factors you should consider when you create different kinds of patterns.
Materials of Casting Pattern
Your casting pattern materials should these properties:
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Lower cost and less weight: with the lower cost and less weight you are easier to
find the balanced point of costs and returns.
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Resistance of water: choosing the material with resistance of water protects your
casting pattern from rusting. Casting patterns with this kind of material will have a
long lifetime and produce high quality patterns.
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Durable: durable material provides a long lifetime of your casting pattern, so you
should consider the durable property of the material before you choose casting
pattern materials.
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Versatile: various industries need casting patterns to create the casting process, so
the versatile property of casting pattern material is very important. It ensures the
pattern can be used in many kinds of industries, and repaired easier.
Types of pattern allowances
Other factors like the type of casting pattern and the properties of casting metal should also
consider. Therefore, there have some casting pattern allowances you should pay attention to
during pattern making manufacturing process.
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Draft allowances: draft allowances creates a taper for removing casting patter
without any distortion. And the accurate angle of taper depends on the type of mold
and surface, and the complexity of the casting pattern.
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Shrinkage allowance: usually the casting pattern has a bigger size of the mold,
because most metal material contracts when it cools. The shrinkage allowance
compensates for the cooling shrink of metal, and the precise parameter of the
allowance depends on the metal material.
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Distortion allowance: casting patterns have a special design for avoiding the
expected cooling distortion. We call it a distortion allowance.
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Machining allowance: excess material in the finishing stage for compensating some
loss materials.
2. What are the advantages and disadvantages of metal sand-casting?
Advantages of Sand casting
Disadvantages of Sand casting
Simple production process
Handmade process
Low cost Casting molds
Low strength
Lower production costs
Low dimensional accuracy
Wider material choice
Rough surface quality
High complexity shapes
More casting defects
Short lead time
Unstable casting quality
3. What are the applications of metal casting?
On the basis of application, the major body assembly components that use metal casting
procedure for manufacturing cross-car beam, seat frames, front doors, alloy wheels.
Furthermore, the huge contribution of body assembly in overall vehicle weight and increase use
of lightweight resources in body assembly components are the major factors that may raise the
demand for products.
By Application
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Body assembly
Engine parts
Transmission parts
Medical Devices
Other
OCCUPATIONAL HAZARDS IN METAL CASTING
Identify at least five Occupational Hazards that may be present in metal casting
process and how to mitigate the hazard.
Chemicals and solvents: Alkalis, detergents, and other substances used in
metal casting can cause serious burns or dermatitis if they are exposed to the
skin.
Fumes: Molten metal can produce toxic fumes with very tiny particles that can
penetrate deep into the lungs. Workers can develop molten metal fever if these
fumes contain aluminum, cadmium, copper, iron, silver, zinc, or other metals.
Fumes from Styrofoam or polyurethane can also produce carbon monoxide,
hydrogen cyanide, and other toxic gases.
Dust particles: Sand handling and shakeout produce dangerous dusty
conditions in the workplace. Small, jagged particles of asbestos, cotton, and
silica are caught in the lungs and cannot be removed, causing scarring. This
condition makes it difficult to breathe, eventually damaging the heart.
Electrical hazards: Foundries often use a number of electrical devices that
require proper fuses and wiring, which may deteriorate over time. Electrocution is
also a risk when using an electric kiln.
Fire: Metal casting may involve using torches, gases, hot metals, and kilns,
creating the risk of explosion or fire.
Heat: The intense heat required to melt metal may unexpectedly start or
accelerate other chemical reactions and cause an accident. Some workers
become used to working in intense heat, however, there are long-term health
risks associated with working in high-temperature environments, including
increased anxiety and loss of concentration.
Hot surfaces: Molten metal and hot surfaces create hazards for workers who
may be burned accidently. In addition to direct burn hazards, the overall heat in
the working environment is known to increase the frequency of accidents in
general.
Noise: Hazardous levels of noise exceeding 105 decibels may be produced in
foundries with tumbling furnaces or modeling machines or in operations involving
sand shakeout or grinding.
Radiation: Ultraviolet and infrared light that is often present in foundries can
damage the eyes.
Repetitive movements: Any job that requires repetitive movements can cause
nerve damage and result in carpal tunnel syndrome or other painful conditions.
Vibration: Workers in certain types of foundries may be exposed to whole-body
vibrations from shakeout operations as well as pneumatic tools, conveyor belts,
and forklifts. Hand-held grinders and chippers expose workers to hand or arm
vibration hazards.
MITIGATING THE HAZARD:
1. Wear eye protection, gloves, spats (covering top of feet), and thick clothing protecting
all exposed skin on arms and legs. NO polyester or synthetic clothing.
2. Sand Floor in pouring area shall be clear of all objects not involved in pouring.
3. Clamp or weight up molds that require it.
4. Metal added to heat must be free of moisture and impurities.
5. Metal added to heat during melt must be preheated.
6. Skimmers and other melting tools must be preheated before use.
7. Move slowly while removing crucible from furnace and moving to mold.
8. Do not look into exhaust during operation.
9. Inspect crucibles before use.
10. Inspect propane lines.
11. Use outdoors only.
12. No alcohol or drug use.
13. Wear respiratory protection while melting copper-base alloys (brass, bronze).
Lab 3.c Common Defects
Identify at least five common defects that can be observed in sand-casting process and
the physical and chemical tests that can be made in the product and how can it be
avoided.
1.) Hot tear/crack
Cracks appear in the form of irregular crevices in a branched pattern. Some cracks are obvious
and easily seen, while others can require magnification. Cracks occur as the casting cools,
towards the end of solidification.
Causes and prevention of hot tears and cracks:
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If the solidifying metal does not have sufficient strength to resist tensile forces during
solidification, hot tears will appear.
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Hot tears are mostly caused by poor mold design. Modifying the mold to improve
collapsibility can easily resolve these issues.
2.) Misruns
Misruns occur when the liquid metal is too cold to flow to the extremities of the mold cavity
before freezing and solidifying. The liquid metal does not completely fill the mold cavity. The
misrun is the unfilled portion or space in the mold.
Causes and prevention of misruns:
The reasons for premature solidification are similar to those for cold shut. If you have a misrun,
check:
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Mold design
Gating system design and
Molten metal fluidity
3.) Slag Inclusion
It is usually detected in the sandblasting and machining processes.
Prevention:
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Control the raw material and melting input
Qualify the metal melting process to ensure the pure alloy liquid obtained
Optimize the pouring system
Properly pouring technique
4.) Blowholes
To detect the interior casting quality, x-ray, harmonic, ultrasonic, or magnetic analysis are
applied to scan blowholes. Blowholes also can be found in the machining steps.
Prevention:
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Make sure the molding sand is dry and permeable. It should be noted that the
coarser sand is, the more permeable it is. Even using sand that is too fine can
prevent optimal permeability.
5.) Metal penetration
These sand casting defects are visible to naked eyes and lower casting aesthetic.
Prevention:
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Use the small sand size
Increase sand mold and core strength
Provide enough hard ramming to the sand mold
Apply a mold wash to add a protective layer against metal penetration