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.
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 pres- sure was just upping the ante.” To ensure casting soundness, Eck had a long list of objec-
tives to accomplish. Aside from a complex core assembly, the simulation helped determine several localized hot spots that would require chills and risers. “Our team of skilled mold- ers was able to successfully incorporate these chills and gage core positions in this complicated assembly,” Weiss said. T e 116-lb. production casting holds the two-mode par-
allel stator assembly used in Allison Transmission’s H40/50 EP hybrid system. T e 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. “T at 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. “T ey have a tight fl at- ness 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.” T e reconfi guration of the part to fi t with Eck’s modifi ed
low pressure process began with a design based on functional- ity—in short, it is a casting design that comes with all the com- plexity an engineer could dream up built directly into the part. “T e EP 40/50 [housing] is a perfect part to be sand cast,”
said Art McGrew, a former Allison engineer who worked on the project. “T e more complexity you can put in, the better. We put in all the features knowing that it would be give- and-take and we would learn which ones would work on the casting and which ones would make it more costly.” T e design began with multiple tubes intended to be cast into the part and several cast-in inserts. T rough collabora- tion with Eck, manufacturer partner Remy International Inc. , Pendleton, Ind., and machine shop Metal Technologies Inc., Auburn, Ind., the number of tubes came down, with the balance being replaced by post-process drilling. But the cast-in inserts—a cast iron center hub, a steel tube and eight cast iron support lugs—stayed. T e low pressure fi lling and slight reduction in complex-
ity has fi xed that problem and enhanced the bonding of the inserts to the base metal. However, the process does not come without an uptick in price. “T ere is more cost involved in low pressure,” Weiss said.
“Mounting it and fi lling it is more expensive than fi lling it with a ladle. But that diff erence in cost was easily compen- sated for by lower scrap.” In the end, Allison tasked Eck to assist it in making an
assembly with all the durability of a standard transmission but with hybrid capabilities added. Only a perfectly sound casting with multiple features cast-in would satisfy those requirements. Plus, the piece is highly visible in the hybrid drivetrain, so the look of the component was important. “We wanted a bus transmission fi rst,” McGrew said. “You
The cope assembly included a complex core assembly that required proper venting.
24 | MODERN CASTING May 2011
don’t baby this thing. It does everything a traditional trans- mission does, and they don’t hold back on it.”
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