The reconfiguration of the part to fit with Eck’s modified low
pressure process began with a design based on functionality—in short, it is a casting design that comes with all the complexity an engineer could dream up built directly into the part. “The EP 40/50 [housing] is a perfect part to be sand
cast,” said Art McGrew, a former Allison engineer who worked on the project. “The 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.” The design began with multiple tubes intended to be
cast into the part and several cast-in inserts. Through collaboration with Eck, manufacturer partner Remy Inter- national 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. The low pressure filling and slight reduction in complex-
ity has fixed that problem and enhanced the bonding of the inserts to the base metal. However, the process does not come without an uptick in price. “There is more cost involved in low pressure,” Weiss said.
“Mounting it and filling it is more expensive than filling it with a ladle. But that difference in cost was easily compensated 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 first,” McGrew said. “You don’t baby this thing. It does everything a traditional trans- mission does, and they don’t hold back on it.”
Supporting Packaging Changes I
t was a change in mindset, more than engineering or economic challenges, that brought Daimler Trucks, Portland, Ore., back to a casting for its Western Star
model front cab support bracket. In the early 2000s, the bracket was being produced in
the metalcasting process. But the component, two of which are used to connect a tube that helps hold up the cab of a heavy truck, began to diverge among different Western Star
platforms. Among mid-size trucks, large trucks and others, Daimler found it needed multiple configurations in order to make the bracket fit the packaging requirements. As volumes fell for the individual components, the need for a casting less- ened, and Daimler began making the brackets via fabrication. “[Going back to a casting] was something that was on
the books the entire time, but it was manpower and timing that really dictated the change,” said Marcus Mahler, a man- ager in Daimler’s chassis cab mounting department. When the timing was right (in late
2009) and the Daimler engineers put their heads together to design a bracket that would satisfy all the platforms, the volumes once again justified the one-time tooling costs associated with a sand casting. “For five to 600 trucks, developing
the casting had a several year payback. But to do a casting that meets a family of applications is business-justified,” Mahler said “[The Daimler analysis group] took the packaging requirements and used a program called OptiStruct to produce a
Fig. 1. The support brackets (in red at top left) are required to offer greater stiffness than the tube supported by the two castings. 24 Metal Casting Design anD PurChasing May/June 2011
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