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Sometimes a change in casting process may be in order. Ge- ometries requiring complicat- ed cores, expensive tool and extensive machining when


produced in green sand could be produced cleanly in lost foam or investment casting. “I would look at the as-


The cost of tooling maintenance, dimensional stability, and reproduc- ibility dictated drilling rather than casting the holes in this aluminum control knuckle.


how much stock to use based on a best guess or professional society guidelines. As they make the part in production, they might reduce the stock used by monitoring the quality and actual dimensions of the part.” Cost of machining operations de- pends largely on the equipment being used, as well. New machine tools are on the market today that can perform multiple operations in diff erent orien- tations with just a single loading and unloading operation. “What we are seeing from a ma-


chining standpoint is that more com- plex machines are being used,” Ruff said. “Five-axis machines with two spindles can handle all these complex angles without a problem and per- form them concurrently. With a dual spindle machine and some automa- tion, you can machine two parts at one time with minimal direct labor cost.” According to Ruff , availability of the high-end, sophisticated machines is tight, but if you are able to fi nd open capacity or make the investment in your own business, your main costs would be in the fi xtures to hold the part in place and perishable tools, such as inserts. “T ey’ve made it easier to machine


parts—and less costly,” he said. Machining time and cost also de-


pends on the size of machining equip- ment used. Smaller machines generally work faster than bigger machines. By maneuvering the part design to fi t into a smaller envelope, you could signifi - cantly cut machining cost and time.


Sept/Oct 2012 | METAL CASTING DESIGN & PURCHASING | 29


cast tolerance [of the casting processes],” Shah said. “If the designer chooses the pro- cess accordingly, they can get near-net-shape features and minimize the machining.”


With so many variables aff ecting


cost for machined or as-cast features, Ruff said it is important to sit down with the casting supplier and ma- chine house to discuss design options, particularly if a feature cannot be designed into the mold and would require a core.


“Casting designers should ask their suppliers what the price of the casting would be with or without the cored features and ask the ma- chinist the price to machine all the holes, and compare those for the optimum solution.” 


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