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machining might be the best option. “In the past, if it was just a bolt


going through a hole, you could get away with an as-cast surface,” Ruff said. “Now it seems like you see less and less of that. Customers want those dimensions held more closely because, especially with complex assemblies such as those seen in many automo- tive applications, everything depends on everything else. If one dimension


is not held suffi ciently tight and with a stack up of tolerances, the casting may be within specifi cation, but the assembly may not be.” On the aluminum permanent mold


and diecasting side, complex part geom- etries require complicated tooling, which increases the price and reduces tool life. One permanent mold aluminum caster has found that adding more machining to a part can make it less expensive. Aluminum castings can be ma-


The holes in this ductile iron support bracket were as-cast using cores, which eliminated drilling. As-cast holes in iron castings reduce mass and provide better properties around the cored hole compared to holes drilled afterward.


chined on similar equipment to gray iron but at higher speeds and feeds. L A Aluminum, Hayden Lake, Idaho, machines 80-85% of its parts in-house and in recent years has invested in dual spindle lathes, vertical and hori- zontal machining capabilities, and 4 and 5 axis CNC machines. According to Michelle Richter, sales and market- ing manager for the company, the emphasis on machining has made it an effi cient part of the overall produc- tion process, taking out cost rather than adding it. “We can machine accurately every


time,” Richter said. “Castings vary over the life of the tool/mold.” With each new part, L A Alumi- num aims to build a simple tool for casting and machine-in the features. According to Richter, a complex cast- ing will result in higher scrap rates. A feature like cast-in holes requires the use of pins in permanent mold casting, which often wear more quickly than the tool and eventually lead to cast- ings that are out of tolerance. Richter said the machine shop will always machine-in an accurate hole. “It is so much easier to improve the


machining process with new equipment,” Richter said. “A lot of my customers that used to do cast-in features brought ma- chining in-house [for similar reasons].” When a feature must be machined, the designer can use a few methods— when possible—to simplify the type


@ 26 | METAL CASTING DESIGN & PURCHASING | Sept/Oct 2012


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