1. Polystyrene pattern vaporizes as metal enters the mold
Lost Foam
Full mold
Evaporative pattern
Polystyrene pattern vaporizes as metal enters the mold

2. History 1958 - process disclosed 1962 - used commercially
patent expired - use grows

3. Patterns one piece or several pieces glued together
one piece pattern requires no 2 part split mold
eliminates need for cores since pattern is not removed from mold

4. Making Foam Patterns raw polystyrene beads placed in preheated die
beads expand - fill cavity
heat also bonds beads
die cooled and pattern removed

5. Pattern coating foam pattern coated with water based refractory slurry
dipping - best uniformity but buoyancy is a problem
brushing - slow, non uniform
flow coating (pouring) non uniform
spray - uniform coat but not suitable for complex shapes
Slurry dries

6. Casting Process coated pattern suspended in flask
flask filled with loose sand
vibrated to compact
molten metal poured in
pattern vaporizes and is vented into surrounding sand

7. Advantages simple - no parting lines, cores, etc. inexpensive flasks
foam is inexpensive
minimum finishing and cleaning required
can be automated
thin wall sections

8. Advantages (Cont.) almost unlimited design of patterns cast in inserts
zero draft
back draft
pilot holes
key-ways
less machining

9. Disadvantages Cost of die to make foam patterns
polystyrene shrinks with age
about .100”/ft and ceases after about 30 days
75% of shrinkage occurs in first 7 days
casting size dependent on pattern age

10. Application
Ford - fully automated line of aluminum intake manifolds