Lost Foam Full mold Evaporative pattern Polystyrene pattern

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

History § 1958 - process disclosed § 1962 - used commercially § 1975 - patent expired - use grows

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

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

Pattern coating § foam pattern coated with water based refractory slurry l l 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

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

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

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

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

Application § Ford - fully automated line of aluminum intake manifolds