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1 | 13 Design for Investment Casting INTRODUCTION The investment casting process is capable of producing complex castings with tight tolerances and superior surface finish and can meet the highest performance standards such as in aircraft jet engine applications other advantages of the process include the ability to cast materials that are impossible to forge and difficult to machine and to produce prototypes through direct machining of wax patterns. Investment casting is a uniquely flexible process for making parts of high complexity and it is therefore ideally suited to reduced part count designs one of the main objectives of design for manufacture and assembly DFMA . There are two types of investment casting processes solid mold investment casting and ceramic shell mold investment casting. The two processes differ primarily in the way the mold is formed. In the solid mold process the wax or plastic pattern is placed into a container and mold material is poured around the pattern solidifying into a solid block. In the shell process the pattern is dipped or invested in the mold material leaving a coating of uniform thickness. The coating is allowed to dry and the dipping process is repeated. The multiple coats form a hard ceramic shell mold. The ceramic shell mold process described in this chapter is the major form of investment casting for engineering applications. PROCESS OVERVIEW A simplified representation of the ceramic shell mold investment casting process is shown in Fig. . The process starts with the fabrication of a wax or plastic 549 Marcel Dekker Inc. 270 Madison Avenue New York New York 10016 550 Chapter 13 FIG. Simplified ceramic shell mold investment casting process. Marcel Dekker Inc. 270 Madison Avenue New York New York 10016 Design for Investment Casting 551 pattern. The pattern has the same shape as the final cast part but with dimensional allowances for the shrinkage that occurs during the casting process. Usually a number of .

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