6KEYS A


pattern tooling, the components generally have higher prices than forged, sand cast or permanent mold cast parts. However, the higher cost can be made up with reduced machining achieved through as-cast near-net-shape tolerances. Investment castings do not require taper to be removed from the mold because the


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ceramic shells are cracked off the part. Tis allows castings with 90-degree angles to be designed without shrink allowance and with no additional machining. To produce the wax mold patterns used in the investment casting process, a


split-cavity aluminum die must be built. Depending on the complexity of the casting, various combinations of aluminum, ceramic or soluble cores may be used to produce the desired configuration. Most tooling for investment casting falls be- tween $1,000 and $10,000. For short runs, rapid prototype models can be created in hours and used as patterns. Te number of parts needed to make investment casting practical varies based on


how many casting runs will occur. If a run size of 50 will be produced 10 times per year, the tooling for the wax patterns likely will be paid off after the 10th


36 | METAL CASTING DESIGN & PURCHASING | Nov/Dec 2011 run. Further, AN MCDP STAFF REPORT


finished investment casting is only as good as the design and specifications provided by the customer. Te process’ design flexibility and metal applications make it a viable option for design engineers searching for a manufactur- ing method that requires minimal machining


(Table 1). To achieve the optimal part at the best price, review these guidelines for investment casting design.


Know How Shape and Volume Affect Cost Due to the costs and labor associated with investment casting molds and


TO INVESTMENT CASTING DESIGN


Unlock investment casting’s full design capabilities for close tolerances and intricate configurations by following these guidelines.


additional repairs to the tool will not be needed because wax does little to cause wear defects to the tool material. Generally, toolmakers say 25 castings are required to pay off the tooling. Once a tool is purchased, it likely will need only one or two replacement pieces at a time. Some investment casting facilities,


mainly in the automotive industry, produce more than 100,000 parts per month. Te high part numbers depend on how willing a metalcasting facility is to expand its capacity. For standard orders, the bulk of investment castings produced fall in the range of 100 to 10,000 pieces per year.


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Use the Expansive Alloy Menu


Generally, any ferrous or nonferrous


material can be investment cast. Car- bon, tool and alloy steel and 300, 400, 15-5PH and 17-4PH stainless steel are the most common ferrous alloys poured. Te rise in ductile iron casting demand has increased the use of the


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