Demanding specifications made casting this part a challenge.
A
t first glance, the auto- motive electrical hous- ing appeared to be a standard aluminum die
casting with few features that would cause concern during production. Te 1.74-lb. part houses the circuit board and stepper motors that control the shifting of the transmission and has an annual volume of 1.2 million. Design- wise, it doesn’t seem to be overly
complex, but the leak tightness and surface finish requirements proved to be stumbling blocks in achieving series production for the new part. Imperial Die Casting (Liberty,
South Carolina), a division of RCM Industries Inc., agreed to take on the challenge of produc- ing the part, but several difficul- ties originated with the print. As-cast surfaces are referenced
back to multiple machining sur- faces. Furthermore, these multiple machining surfaces are referenced independently to cast features, creating issues with the dimensional tolerances. Due to multiple tiers and worldwide part usage, design changes were severely limited. Because so much is already invested once the part is machined, the customer wanted the variations in the casting to be minimized across multiple casting tools, as well as 32 different machining fixtures, all in production at the same time. The customer’s superior func-
tional performance demanded stringent dimensional requirements and several positional and dimensional features must be held within a tight window: • The flatness profile around the seal groove for the entire part is held within a close tolerance with an additional tighter flatness specifica- tion for each each 1 x 1-in. (25 x 25-mm) section.
This inside view of the stepper motor housing shows the locations of the seal groove, motor mount cores and cover mount cores.
• A positional specification is placed on the four motor mount cores. These as-cast positional dimen- sions are called back to a machined
September 2016 MODERN CASTING | 29
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