1. Manufacturing Processes
Metal Casting II
Manufacturing
Processes

2. Outline Sand Casting Shell Mold Casting Composite Molds
Expendable Pattern Casting
Plaster Mold Casting
Ceramic Mold Casting
Investment Casting
Pressure Casting
Vacuum Casting
Die Casting
Centrifugal Casting
Squeeze Casting and Semisolid Metal Forming
Casting Single Crystals
Rapid Solidification
Melting
Design Considerations

3. Examples of Cast Parts

4. Examples of Cast Parts

5. Typical Casting Metals
Aluminum
Aluminum-silicon alloy
Aluminum-copper
Brass
Gray cast iron
Copper
Lead
Steel

6. Casting Processes

7. Sand Casting
Uses a mold made of compressed sand; after the metal solidifies, the sand is broken away

8. Sand Casting Pattern Full sized model of the part Core
Full sized model of the interior surfaces of the part
Sand Silica (SiO2)
90% sand
3% water
7% clay

9. Sand Casting

10. Sand Casting

11. Example of a Sand Casting Mold

12. Sand Casting Advantages:
Almost no limit on size, shape, weight or complexity; low cost; almost any metal
Limitations:
Relatively poor tolerances and surface finish; machining often required; low production rate
Common metals:
Cast irons, steel, stainless steel, casting alloys of aluminum and copper, magnesium and nickel

13. Sand Casting Size limits: 1 oz – 6000 lb Thickness limits:
As thin as 3/32 in, no maximum
Tolerances:
1/32 in for the first 6 in, .003 in for each additional inch; additional increment across the parting line
Draft allowance:
1 - 3°
Surface finish:
µin

14. Shell Casting
Casting process in which the mold is a thin shell (typically 3/8 inch) made of sand held together by a thermosetting binder

15. Shell Casting

16. Shell Casting Advantages:
Higher production rate than sand casting; high dimensional accuracy and smooth finish
Limitations:
Requires expensive metal patterns; resin adds to cost; part size is limited
Common metals:
Cast irons, casting alloys of aluminum and copper

17. Shell Casting Size limits:
1 oz minimum; usually less than 25 lb; mold area usually less than 500 in2
Thickness limits:
1/16 – ¼ in depending on material
Tolerances:
.005 in/in
Draft allowance:
¼ - ½°
Surface finish:
50 – 150 µin

18. Composite Molds Made from 2 or more different materials
Good for complex shapes such as turbine blades

19. Expendable Pattern Casting
Polystyrene pattern vaporizes on contact with molten metal

20. Foam Pattern of an Engine Block

21. Plaster Mold Casting
Uses a mold made of plaster (gypsum) with talc and silica, which is broken away after the metal solidifies
The mold has a relatively low thermal conductivity; a somewhat uniform grain structure can be produced

22. Plaster Mold Casting Advantages:
High dimensional accuracy and smooth finish; can make net- or near-net-shaped parts
Limitations:
Lower temperature nonferrous metals only; long molding time; mold material is not reusable; maximum size limited
Common metals:
Primarily aluminum and copper

23. Plaster Mold Casting Size limits: 1 oz – 15 lb Thickness limits:
As thin as .025 in
Tolerances:
.005 in on the first 2 in; .002 in per additional inch
Draft allowance:
½ - 1°
Surface finish:
µin

24. Ceramic Mold Casting
Uses a mold made of refractory ceramic materials which can be used for high-temperature applications

25. Ceramic Mold Casting

26. Ceramic Mold Casting Advantages:
Intricate detail, close tolerances, smooth finish
Limitations:
Mold material is expensive and not reusable
Common metals:
Ferrous and high-temperature nonferrous metals are most common; can be used with alloys of aluminum, copper, magnesium, titanium and zinc

27. Ceramic Mold Casting Size limits: Several ounces to several tons
Thickness limits:
As thin as .05 in, no maximum
Tolerances:
.005 in on the first inch; .003 in per additional inch
Draft allowance: 1°
Surface finish:
µin

28. Investment Casting
Uses a wax pattern which is coated with refractory materials to form a mold; the wax is then melted out and the mold cavity is filled with metal
Can be used for high precision complex shapes from high melting point metals that are not readily machinable

29. Investment Casting

30. Example of a Wax Injection Mold

31. Example of a Wax Pattern

32. Example of a Coated Pattern

33. Example of Finished Castings

34. Investment Casting Advantages:
Excellent surface finish; high dimensional accuracy; nearly unlimited intricacy; almost any metal; no flash or parting line
Limitations:
Expensive patterns and molds; high labor costs; limited size
Common metals:
Mainly aluminum, copper and steel; also used with stainless steel, nickel, magnesium and precious metals

35. Investment Casting Size limits:
As small as 1/10 oz; usually less than 10 lb
Thickness limits:
As thin as .025 in, less than 3 in
Tolerances:
.005 in on the first inch; .002 in per additional inch
Draft allowance:
none required
Surface finish:
µin

36. Pressure Casting
Pressure casting forces the metal up into the mold chamber by applying a small amount of pressure

37. Vacuum Casting

38. Permanent Mold Casting (Pressure/Vacuum)
Advantages:
Good surface finish and dimensional accuracy; metal mold causes rapid cooling and fine grain structure; molds can be used up to times
Limitations:
High initial mold cost; shape, size and complexity are limited; mold life is very limited with metals with high melting points
Common metals:
Alloys of aluminum, magnesium and copper most common; iron and steel can be used in graphite molds; alloys of lead, tin and zinc also used

39. Permanent Mold Casting (Pressure/Vacuum)
Size limits:
Several ounces to about 150 lb
Thickness limits:
Minimum depends on material but generally thicker than 1/8 in; maximum about 2 in
Tolerances:
.015 in for the first inch and .002 in for each additional inch; .01 in added across the parting line
Draft allowance:
2 - 3°
Surface finish:
µin

40. Die Casting
Another form of permanent mold casting; molten metal is forced into the mold cavity at pressures ranging from .7 MPa MPa

41. Die Casting

42. Die Casting

43. Example of a Die Casting Mold

44. Centrifugal Casting
Uses a rotating mold to form hollow cylindrical parts such as pipes, gun barrels and lamp posts

45. Vertical Centrifugal Casting

46. Centrifugal Casting Advantages:
Can produce a wide range of cylindrical parts; good dimensional accuracy and cleanliness
Limitations:
Limited shape; spinning equipment may be expensive
Common metals:
Iron, steel, stainless steel, alloys of aluminum, copper and nickel

47. Centrifugal Casting Size limits:
Up to 10 ft in diameter and 50 ft in length
Thickness limits:
Wall thickness .1 – 5 in
Tolerances:
Outer diameter within .1 in; inner diameter within about .15 in
Draft allowance:
1/8 in / ft
Surface finish:
µin

48. Semicentrifugal Casting
Uses a rotating mold to form parts with radial symmetry, such as wheels with spokes

49. Squeeze Casting
A combination of casting and forging; a die applies pressure as the metal solidifies

50. Casting Single Crystals
Uses a slow crystal-growth solidification procedure to produce parts made of a single crystal with no grain boundaries
A helical constriction only allows one crystal of favorable orientation to grow into and fill the mold chamber

51. Casting Single Crystals

52. Rapid Solidification
Cools metal rapidly at rates as high as 106 K/s so that it cannot crystallize and instead forms an amorphous glasslike structure

53. Melting Furnaces
Cupola
Crucible Furnace
Induction Furnace

54. Melting Furnaces Cupola
A vertical cylindrical furnace used for melting cast iron

55. Melting Furnaces Crucible furnace
Melts metal without direct contact with a burning fuel mixture

56. Melting Furnaces Induction furnace
Uses an alternating magnetic field to heat the metal

57. Design Considerations

58. Design Considerations

59. Design Considerations

60. Design Considerations

61. Casting Alloys

62. Summary
A variety of casting processes are available for different applications
Design considerations must be taken to prevent casting defects