Producers explore the prospects for EPC castings.

While a handful of foundries have dived into the innovative technology of expendable pattern casting, most remain on the sidelines trying to assess the nuances of using foam patterns to produce high quality, dimensionally accurate metal castings. But as foundries and casting users continue to understand the process, its use is expected to grow.

in looking ahead toward the prospects for EPC through 1995 (90-115) J.A. Troxier, Jr., Robinson Foundry, expects that the process will make significant inroads into some important casting markets, including automotive, during the next five years.

His high expectations for EPC are based on at least three inherent advantages of the process: enhanced dimensional accuracy of the castings; uniform surface finish and striking appearance; and cost. "Costs associated with the EPC process should decrease, or at least increase at a lower rate, while costs for conventional casting methods can only increase," according to Troxler.

Among the markets he sees as holding the best potential for EPC are gray iron automotive, agricultural parts, nontransportation engines, valves, pumps and compressors. Aluminum castings produced in EPC also should present some growth opportunities according to Troxler.

Despite the generally favorable outlook for EPC, much work remains to be done to better understand the process. Within the area of production, Troxler cites reducing the cost of tooling; foam piece joining technology; improved net shape techniques; and coating removal, control or elimination as important areas for research. Several of these areas were addressed during the EPC sessions of this year's Casting Congress.

The foam patterns, themselves, along with their coatings have presented casting producers with some significant difficulties in controlling the EPC process. E.H. Niemann and G.B. Kelly, Arco Chemical, in presenting their studies on pattern shrinkage (90-116) pointed to one of the basics of using foam patterns.

"Molded EPS patterns shrink with time due to molecular relaxation of the stresses in the cell walls and equilibration of the gas composition in each cell with the surrounding air," according to the authors. Shrinkage must be accounted for in foundry foam patterns to meet casting tolerances."

in addition, the authors noted, because the shrinkage of foam patterns is reproducible, it is also controllable. As a guideline they suggest that the total shrinkage value of 0.70.8% (depending on the molding method used) is still a good general guideline to use in designing tools for EPS molding.

Other EPC topics covered this year included the use of vacuum in producing EPC aluminum castings; pattern coatings; new materials for foam patterns; vibration techniques for compacting EPC molds; and producing EPC parts starting with design.