Castings of the Year: Unique Process, Application W
hen engi- neers from Allison
Transmission, Indianap- olis, delivered draw- ings for a hybrid bus stator housing to Eck Industries, Manitowoc, Wis., project engineer Dan Hoefert had a unique vision. Many at Eck thought
the component could be produced via grav- ity pour in nobake sand—albeit not with- out some difficulty. Hoefert was in favor of using the company’s modifi ed low pressure mold filling, a sand casting process adapted from a low pressure permanent mold machine. “We had several opposing camps,” said David Weiss, Eck’s
The cope included a complex core assembly that required proper venting.
just upping the ante.” To ensure casting soundness, Eck had a long list of objectives to accomplish. Aside from a complex core assembly, the simula- tion helped determine several localized hot spots that would re- quire chills and risers. “Our team of skilled molders was able to successfully incorpo- rate these chills and gage core positions in this complicated as- sembly,” Weiss said. The 116-lb. produc-
tion casting holds the two-mode parallel sta-
vice president of sales and engineering. “But we simulated both processes [using computer modeling software], and the clear winner was the low pressure simulation.” Hoefert said he believed fi lling and feeding the housing
through its thin wall sections would be diffi cult, and Eck’s pressure-programmable low pressure fi lling would offer control of the fi lling process and continue to apply feed pressure through the gating system during solidifi cation. “The idea of fi lling a nobake sand mold in low pressur
was not really anything new here at Eck Industries, but the idea of having to assemble a mold upside-down and then fl ip, transfer and fi ll it in low pressure was a concern,” Hoefert said. “Some here thought the job was a gamble no matter how you looked at it, and opting to go with low pressure was
tor assembly used in Allison Transmission’s H40/50 EP hybrid system. The key to the success of the design lies in the fl at bottom deck of the housing, which must meet zero-porosity and no-leak customer requirements. “That deck varies in thickness from about 1 in. in the
middle, with relation to the bores, and it sweeps out to about 3 in. thick at the ends,” Hoefert said. “They have a tight fl atness requirement on machining this surface, since the valve bodies mounted to this deck are assembled without a gasket and maintain a pressure-tight seal.” It is the combination of iron chills and blind risers that
ensure a solid, porosity-free deck in the top (or bottom, as it sits in the hybrid bus drivetrain) section of the casting. “By the time the metal arrives at the top half of the mold,
it is moving at a slow, consistent velocity,” Hoefert said. “Any gas formed by the fragile cores hanging from this top half of the mold can vent away from the casting.”
Hybrid H40/50 EP System Stator Housing Eck Industries, Manitowoc, Wis.
Material: Aluminum. Process: Nobake. Weight: 116 lbs. Dimensions: 18 x 18 x 21 in. Application: Hybrid bus stator housing. Converted From: Fabrication. • The housing holds the two-mode parallel stator assembly used in Allison Transmission’s H40/50 EP hybrid system.
• The casting is a complex aluminum design that offers tight concentricity tolerances across multiple large core assemblies, utilizes multiple cast-in features, and meets zero-porosity and no-leak customer requirements.
MAY/JUNE 2011 METAL CASTING DESIGN AND PURCHASING 23
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