business-justified,” Mahler said “[Te Daimler analysis group] took the packaging requirements and used a program called OptiStruct to produce a computer-optimized proposal.” Te one-size meets all design—
required to be 10 times stiffer than the tube between the cab and casting and capable of withstanding ultimate load requirements associated with impact considerations (Fig. 1)—was introduced in the third quarter of 2009, and Daim- ler then moved to find a supplier that could produce the design economically. Te truck maker took the bracket to several suppliers, including a Mexican caster that no-quoted the part due to its prohibitive size and an east coast sup- plier that returned an exorbitant price tag. Lethbridge Iron Works Co. Ltd. (LETH IRON), Lethbridge, Canada, was the only caster capable of produc- ing the part in the appropriate size while keeping the costs down through near-net-shape manufacturing. According to Bart Davies, company
co-owner, LETH IRON was able to quote the part without machining through the use of intricate coring (a total of 10 are used) and precise robotic grinding. “Te near-net-shape was one of the
main drivers,” he said. “Daimler had quoted this job with basically all the holes drilled. We tackled it with a new way of doing things. I wouldn’t call it machining, but we’re doing things that a lot of people would call machin- ing—fixturing it in a robotic grinder and grinding the four bosses while the casting is being cleaned.” According to Mahler, LETH IRON
project engineer Dan Hoefert had a unique vision. Many at Eck thought the component could be produced
Unique Process, Application W
hen engineers from Allison Transmission, India- napolis, delivered drawings for a hybrid bus sta- tor housing to Eck Industries, Manitowoc, Wis.,
via gravity pour in nobake sand—albeit not without some difficulty. Hoefert was in favor of using the company’s modi- fied 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 vice president of sales and engineering. “But we simu- lated both processes [using computer modeling software],
introduced cores for features other metalcasters had recommended for post- machining. Some of the cores proposed included one degree of draft on the mounting surfaces, which was then ground off in the cleaning process. Te metalcaster’s automatic robotic grinding capability also allowed Daimler engi- neers to manipulate the part’s standard wall thicknesses and other features. “Originally, the casting didn’t have
the ‘windows’ in the casting,” Mahler said. “From our design experience, we thought that would create problems for the metalcaster.” Te final part design delivered by
LETH IRON represented a consoli- dation of three castings, seven welded assemblies and 16 low-level parts into two castings, zero welded assemblies and four low-level parts (Fig. 2). A change in material from 65-45-12 ductile iron to 80-55-06 increased ultimate tensile and yield strength by about 23% each, while sacrificing 50% ductility, a tradeoff crash load testing showed was justified. Te new component also is 7 lbs. lighter than its 42-lb. predecessor. “So many designers don’t under- stand what can be done with a casting,” Davies said. “Sometimes they have unnecessary material in places, don’t understand cores and are unaware of the new technology that is available. We have a couple of people that spend their days on the phone talking to engineers about how to make the most economical casting.”
Fig. 2. The assembly (bottom) replaced three cast- ings, seven weldments and 16 low-level parts.
and the clear winner was the low pressure simulation.” Hoefert said he believed filling and feeding the housing
through its thin wall sections would be difficult, and Eck’s pressure-programmable low pressure filling would offer con- trol of the filling process and continue to apply feed pressure through the gating system during solidification. “Te idea of filling a nobake sand mold in low pressure
ONLINE RESOURCE Visit
www.moderncasting.com for a Casting of the Year audiocast.
May 2011 MODERN CASTING | 23
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73 |
Page 74 |
Page 75 |
Page 76