1. Investment Casting Also called “Lost Wax”
Term investment comes from fact that the pattern is invested with refractory material

2. History dates back to 1100 BC ancient Egyptians, Romans
Modern times, before WWII - Jewelers and Dentists use the process
WWII principal commercial uses began - aircraft engine parts
most expensive foundry method

3. 1. Molten wax or plastic is injected into a metal die to make the patterns

4. 2. Patterns are attached to gates and risers (tree)

5. 3. Dipped in slurry of refractory material repeatedly
slurry is a - silica flower suspended in a water-ethyl silicate solution

6. 4. Flask is placed around coated wax assembly

7. 5. Investment molding mixture (sand) is poured around patterns filling flask

8. 6. Work table is vibrated to settle mold material around patterns

9. 7. Molds dry for 6-8 hours - Then wax melted out at 200-300 deg
burnout and preheating at 1200 to 1900 deg

10. 8. mold is poured statically, with centrifugal action, or vacuum

11. 9. metal solidifies and mold is broken up and gates removed

12. Adv: over sand casting:
1. Surface smoothness 2. Close tolerances 3. Minimum machining 4. Capability of producing intricate shapes and sizes

13. Dis:
1. Not easily mechanized 2. Requires an individual pattern for each casting made 3. Requires many operations to complete the process

14. Three additional techniques:

15. 1. Ceramic shell investment casting
formed around pattern by dipping shell into a refractory slurry

16. 2. Frozen mercury instead of wax mercury freezes at about 40 deg f.
so use dry ice to keep mercury patterns frozen
mercury is allowed to warm up after being invested in refractory cement
mercury melts out of the mold

17. 3. Precoating is not used
wax patterns are directly invested in the mold material
mixture is placed under vacuum to remove air bubbles next to patterns

18. Parts made:
office equipment
gears
cams
valves
ratchets
jewelry