1. Chapter 14
Part 3

2. Casting and Molding
Foundry industry is mostly considered primary manufacturers
Make stock for secondary manufacturers
Secondary manufacturers finish the parts

3. Cast Iron Specific to the casting process Types: Sold in ingot form
Ductile
Gray
High-alloy
Malleable
White
(others)
Sold in ingot form

5. Casting Processes Some processes use liquid metal, some use powders
Processes classified by type of mold used
Permanent (reusable)
Consumable (destroyed)

6. Powder Metallurgy Compacting metal powders in a permanent mold
Ferrous and non-ferrous metals
97% of the initially used raw material is in finished part
Near-net-shape process
Close to desired shape, no additional machining for part shape
May still need machining of threads, holes, or other unusual design features
Little shrinkage compared to other casting
High volume process (thousands of parts per hour)
Cost of tooling is too high to use in low volume applications

7. Steps involved in powder metallurgy
Powder mixing
Compacting
Sintering - holding the part at a temp just below it’s melting temp for a short time. Creates a bond between the powder particles.
Part is fragile before sintering (green compact)
Can be broken if handled roughly
Secondary heat treating may be applied to strengthen

8. Immersing porous P/M parts into oil or resin after sintering
Impregnation
Immersing porous P/M parts into oil or resin after sintering
Provides lubrication, less friction
Used on moving parts (bearings)
Care must be taken to make sure oil isn’t removed
Cardboard, paper wick oil away

9. Drawing another metal into the P/M part Improves mechanical properties
Infiltration
Drawing another metal into the P/M part
Improves mechanical properties
Also seals pores of the part
Helpful if part is to be plated

10. Used to make a wide variety of parts
P/M Injection Molding
Finely ground powders coated with resin, used in a conventional injection molding press.
Used to make a wide variety of parts
Gears
Cams
Appliance parts

11. Die Casting Molten metal forced under pressure into a permanent mold
Low melting point metals
Zinc
Lead
Tin
One of the fastest casting methods
2 piece dies

13. Permanent Mold Casting
Molten metal poured into a mold through a gating system
Normally an automated process
Usually a turntable with stations
Each mold is cleaned out with air then filled with molten metal
Machine cools each part, opens the molds and ejects the parts

15. Sand Casting Most used process
Expendable sand mold destroyed to remove the part
Sand can be reused
A pattern is used to make the mold
Pattern must be slightly larger than the finished part (shrinkage)
Sand is packed around the pattern inside a box called a flask
Used to make engine blocks and cylinder heads

17. Investment Casting Similar to sand casting, uses a consumable mold
Precision process for materials that are hard to work with or difficult to machine
Pattern made from wax or expanded polystyrene
Pattern is dipped in ceramic refractory slurry, dried then repeated until desired thickness of mold is achieved
Mold is placed in an oven to melt the pattern
Molten metal is poured in the mold
Mold is broken off of finished part

18. Centrifugal Casting Mold cylindrical parts from plastics and metals
Same process for either material
Relies on rotating forces to form material against a mold
Popular for making:
Pipes
Tanks
Bearing rings