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With such tight tolerances on flatness and surface finish, cooling lines were placed in specific areas of the cavity so a uniform temperature could be achieved.

profile that houses the stator motor assembly.

• A positional specification is required for the five cover mount cores. These as-cast positional dimensions are called back to a couple of machined cores that are in turn called back to the machined bore cores on the cover side, as well as the mounting bosses on the outer section of the part. All other surfaces of the casting not specifically called out could not exhibit any flash, heat check or washout that exceeded the tolerance. Any imperfection must be fixed before more castings are made. Te customer expects the castings coming out of the die after 100,000 rounds to look like those that were made when the die was new. Furthermore, the ejec- tor pin flash can not exceed a certain tolerance or be loose in any way. Tis ensures no loose particles will find their way into the stepper motor or electronics after the assembly phase. Te outside mounting bosses are to be nearly perfect, and the bosses are expected to be clean of any imperfections so their integrity does not come into question. Due to the restrictions of the print and virtually no way to vent these mounting bosses, making this feature without any defects proved challenging. Porosity specifications on the machined surfaces also

played a significant role in the quality of the casting. Specifi- cally, the thicker section of the bore core is machined and cannot show any porosity that exceeds a certain amount. Tese bores, as well as the part, must be leak tight and are leak tested. Tese parts house electrical components, so no moisture can be allowed to breach the housing. Te center bore cores also have a maximum machin-

ing stock on each side to reduce run out and chatter. Tis tight window for machining stock can cause prob- lems with non-cleanup if the diecast dimen- sions have excessive variation.

The customer gave

several different call outs for the die cast- ing’s surface finish. These surface finishes are critical for the seal surfaces and breather port to ensure the adhesives used on the

surfaces adhere to the part sufficiently. No moisture must enter the assembled housing. Surface tension testing is also important when determining whether proper adhe- sion will occur. Die spray is a critical component when adhesion may be an issue.

Part and Tool Design The electrical housing was already in production

when it came to Imperial, so almost no changes could be made to improve the casting or its processing. The diecaster made a few requests to improve the castabil- ity of the part, with the only major request of changing some of the part’s geometry. Imperial requested to make the ribs on the mounting bosses thicker so the bosses would be easier to fill, reducing any chance of non-fill. Because the part was already in production, with finish- ing and assembly processes in place based on the original design, this request was denied. Thus the challenge was left to tool design and the casting process at Imperial to ensure a more than adequate casting would be produced. Imperial determined a two-cavity die would be used so the high-volume part could be produced at low levels of scrap and high levels of productivity. From there, different runner designs were suggested and modeled to find an appropriate way to fill the casting. Due to the as-cast sealing surface specifications, it was challeng- ing to gate the part in a manner that would provide suf- ficient fill while maintaining the specifications. Te as-cast seal groove surrounds the entire part, and gating directly into the standing steel that forms this feature would cause accelerated erosion. Te customer design included a portion of the flange with a thicker wall, which would allow for gating above the seal groove steel instead of directly into it. Tis design was locked, so the area for gating was limited.

This is a magnified view of the breather port. 30 | MODERN CASTING September 2016

Once a few poten- tial tooling designs were chosen that might address the challenge, casting process modeling simulations were run to find an optimal runner

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