that would fill the part adequately. Each runner design was simulated with different vari- ables such as: tip diameter, die tem- perature, slow shot velocity, fast shot velocity, and start of fast shot. After the simulation, the optimal design was chosen to produce the tool so produc- tion could start. 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. Standard practices at Impe- rial dictate thermal oil lines are used to pre-heat and stabilize the cavity temperatures, and water lines are used to cool the shot blocks and runner blocks. Initial simulations revealed areas of the cavities that would absorb more heat than others, indicating a need for additional cooling in these areas, such as in the standing steel near the gates. The use of cooling lines helps ensure as little shock as possible to the steel during the initial startup of the die and also maintains the temperature during pro- duction. Due to tight dimensional tolerances, all the cores in the tool were covered with a chromium-based coating to help prevent tool wear and reduce soldering. This coating also allowed the dimensions throughout the cores to be held within the required tolerance. A vacuum also was applied to reduce any gas porosity that may occur. After the initial startup of the tool, minor porosity
was discovered on the outside of the two snouts after machining. Te amount of machining stock was 0.02 in. (0.5 mm) on each side of the bore cores. Te snouts have a considerable amount of thickness, so shrink porosity would be a common finding. To reduce that amount of porosity exposed by machining, stock was added on both the inner and outer diameters of the cores. Tis reduced the amount of machining stock and reduced the chances of exposing porosity. Tough the part looks simple, significant challenges stemmed from the tolerances, low porosity, leak tightness and surface finish requirements, with limited changes allowed by the customer. Tis brought on challenges in design and process that required extensive analysis of the part. With a focus on tool design and quality production pro-
cesses, Imperial met these obstacles, and has been producing the part at high volume, serial production rates since 2011.
September 2016 MODERN CASTING | 31
Shown is the outside view of the stepper motor housing. The center bore cores have a maximum machining stock on each side to reduce runout.
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