What is casting?
Casting is a process of pouring molten metal into a mould cavity and allowing it to solidify. The shape of the solidified object is determined by the shape of the mould cavity.
Where cast products are used?
- Ship-building industry
- Automobile industry
- Aerospace industry
- Manufacturing industry
- Household appliances
- Etc.
Where cast products are not used?
- Products with high dimensional accuracy
- Products subjected to considerable cyclic loads
- Products require good surface finish
Why Casting ?
- Construction may be simplified, no assembly.
- Mass production at high production rates.
- Very large, heavy metal objects may be cast
- Good engineering properties
- Intricate of shapes
- May be cast in a single operation.
- Some metals can only be cast to shape
- Resistance to working stress
What are the limitations in Casting?
- Casting defects.
- Limitations in making thin & complex structures
- Limitations in toughness & strength
- Surface finish & dimensional accuracy
- Shrinkage & porosity.
Types of materials used for Casting
- Ferrous metals
Cast iron, Wrought iron, Alloy cast iron, Steel, etc.
- Non-ferrous metals
Copper alloys, Aluminum alloys, Magnesium alloys, Tin alloys, etc.
- Cast Iron is an iron alloy with the carbon content of 2%-4%
- Wrought iron is an iron alloy with a very low carbon content (less than 0.08%)
- Alloy cast irons are the casting alloys which are based on the iron (Fe) – carbon (C) – silicon (Si) system.
- Steel is an alloy of iron and carbon containing less than 2% carbon and 1% manganese and small amounts of silicon, phosphorus, Sulphur and oxygen.
Selection of materials in Casting
- Fluidity (Effect of Phosphorous)
- Shrinkage
- Different Mechanical Properties
- Melting Temperature
- Cooling Speed
- Weight
- Wear Resistance
Casting Materials
Gray Cast Iron
- It is the most common cast iron and the most widely used cast material based on weight.
- can be machined easily
- cost-effective at high volumes
- suited to a variety of applications
- Damping or vibration control
- High strength to weight ratios
- Dimensional stability
Ductile Iron
- Greater strength
- Improved wear resistance
- Stronger toughness
- Superior ductility
- Reduced weight
- Reduced shrinkage
Aluminum
- Aluminum casting is also a widely used method, due in large part to the superior versatility of the metal
- corrosion resistance
- high thermal/electrical conductivity
- good mechanical properties and strength at high temperatures make it an effective choice for many casting processes.
Steel
- Steel is a tough casting material well-suited for parts that will be subjected to exceptional wear, shock or heavy loads
- corrosion resistance
- applications involving elevated temperatures
- Steel is often mixed with chromium, iron, and nickel to further improve its corrosion or heat resistance
Copper
- electrical conductivity
- Good malleability
- Superior ductility
- Good conduction of heat
- However, copper and castings can be subject to surface cracking, porosity and formation of internal cavities. Consequently, it is often mixed with other metals (silicon, nickel, zinc, chromium, tin and silver) to alleviate these issues.
Zinc
- Zinc’s low melting point (425 ˚C) makes it a suitable material for die-cast applications
- zinc may be an economical option for casting small, high-volume parts.
What is a ‘Foundry’?
Foundry Is a workshop dedicated for metal casting.
How foundries are classified?
Based on the metal to be cast
- Steel foundry
- Cast iron foundry
- Light alloy foundry
- Brass foundry
Based on the type of work
- Jobbing foundry –which specialize in small orders for wide variety of engineering shapes
- Repetition foundry –for mass production of large numbers of identical castings of a particular shape & composition.
Basic Requirements of Casting Process
- Mould Cavity
- Melting Process
- Pouring Techniques
- Solidification Process