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EPC Conference stresses process advantages.

EPC Conference Stresses Process Advantages

During the last decade, expendable pattern casting (EPC), sometimes called the lost foam process, has consistently gained credibility within the foundry industry as a viable casting process. But the ultimate success of EPC will be determined through its acceptance by casting users and design engineers. To further acquaint these decision makers with the process, the Society of Manufacturing Engineers in cooperation with the American Foundrymen's Society sponsored a seminar on EPC on Nov 6-7 which drew more than 60 to Schaumburg, Illinois. Seventeen presentations from foundries, researchers and casting users and designers were discussed.

The EPC process can be used for casting nearly all major foundry alloys. Generally, the process involves embedding a coated foam pattern of the part to be cast in unbonded sand and pouring molten metal into a foam pouring cup attached to the pattern. During pouring the molten metal replaces the foam pattern creating the final cast part.

"The primary advantages of EPC," according to Raymond Monroe, Steel Founders' Society of America, "are the elimination of cores, elimination of the parting line and elimination of bonded sand. Each of these advantages are a natural result of the use of plastic foam patterns." But Monroe adds that "The selection of an appropriate part is key to success [with EPC]. Large volume parts that require extensive coring and machining show the best pay off with the process. Unfortunately, these parts are also the most difficult to cast successfully. One major limitation of the process is the design and manufacture of tools for producing the foam patterns."

Larry McFarland, Caterpillar, Inc., lists the major process advantages of EPC from the designer and user point of view as lower piece part cost, reduced casting weight, improved cosmetics and design flexibility. EPC's major disadvantages, says McFarland, include new job start-up time, the shortcomings of traditional foam materials in casting ductile iron and tooling costs. But McFarland is confident that the process is viable for many casting applications. The key to future EPC growth, he says, is gaining the confidence of design engineers.

Success Stories

While a variety of castings are currently being produced successfully by EPC, Raymond Donahue, Brunswick Marine Power, described a particularly innovative application of the process. In this case, a water jacketed, cylinder block previously requiring ten diecast parts was consolidated into one casting to capitalize on the EPC process. According to Donahue, "The consolidation also eliminated several machining operations as well as the need for several gaskets and more than 50 fasteners. With less than half the capital costs for facilities and tooling, the production rate for the EPC process is three times that for diecasting. [The part] was so complicated that new quality standards had to be established for the inner hidden walls that were inaccessible for direct inspection of soundness and coating removal."

John Troxler, Robinson Foundry, Inc., presented four successful applications of producing gray iron castings by EPC: electric motor housings, water main valves, engine manifolds and components and cases and housings. In the case of the motor housings which were originally produced in green sand, converted to the shell process, today are being produced in EPC and is a good example of the evolutionary process and design advantages offered by the process.

"The first stator frame pattern mimicked the shell core production method as four quadrants were glue-assembled into a pattern," explains Troxler. "The good results achieved led to the development of similar stator frames in two halves, requiring only two glue joints. Machine stock was further reduced for one-pass machining. Process stability and casting performance then led to the construction of a larger stator frame tool in only one piece of foam. The improved dimensional control led to the capability to cast-in holes that had been previously drilled (22 in all). "The original tool which produced four foam quadrants," adds Troxler, "began production in 1985. It is presently being modified to run in halves to improve dimensions and allow more cast-in features."

Future of EPC

In assessing the future potential of EPC, Norm Lillybeck, John Deere & Co., notes that "industrial expendable pattern casting has for the last 10 years been the subject of intense industry-wide research and development targeting a wide range of commercial and military metalcasting applications ... The pattern and tool building industry, the plastics industry and the foundry equipment industry have invested significantly in new technology to support and operate the process and are continuing with ambitious development programs."

Despite these efforts, Lillybeck acknowledges that "growth in use of EPC is expected to be slow, particularly in the first (present) stage of growth since by its nature it can only occur part by part, with new tooling required for each part. Until the process is better known and proven, development will tend to proceed one part at a time."
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Title Annotation:Society of Manufacturing Engineers/American Foundrymen's Society Joint Conference; expendable pattern casting
Author:Thomas, Susan P.
Publication:Modern Casting
Date:Jan 1, 1991
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