Polystyrene pattern vaporizes as metal enters the mold 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 beads expand - fill cavity heat also bonds beads die cooled and pattern removed

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

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

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 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 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