According to Mahler, LETH IRON
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www.moderncasting.com for an audiocast with Daimler Designer Marcus Mahler.
computer-optimized proposal.” The one-size meets all design—re-
quired 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 intro- duced in the third quarter of 2009, and Daimler then moved to fi nd a supplier that could produce the design economi- cally. The truck maker took the bracket to several suppliers, including a Mexi- can caster that no-quoted the part due to its prohibitive size and an east coast supplier 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. “The 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 machining—fi xturing it in a robotic grinder and grinding the four bosses while the casting is being cleaned.”
Front Cab Support Bracket Lethbridge Iron Works Co. Ltd., Lethbridge, Canada
Material: Ductile iron. Process: Green sand. Weight: 35.3 lbs. Dimensions: 18 x 16 x 9 in. Application: Heavy truck cab support. Converted From: Weldment. • The durable ductile iron bracket supports the front of the cab on Daimler’s Western Star model trucks.
• The redesign of the component delivered a 22% weight savings and 35% cost savings per vehicle.
MAY/JUNE 2011 METAL CASTING DESIGN AND PURCHASING 25
introduced cores for features other metalcasters had recommended for post-machining. Some of the cores pro- posed included one degree of draft on the mounting surfaces, which was then ground off in the cleaning process. The 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.” The fi nal part design delivered by
LETH IRON represented a consolida- tion 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 sacrifi cing 50% ductility, a tradeoff crash load testing showed was justifi ed. The new com- ponent also is 7 lbs. lighter than its 42-lb. predecessor. “So many designers don’t under-
stand what can be done with a cast- ing,” Davies said. “Sometimes they have unnecessary material in places, don’t understand cores and are un- aware 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 castings, seven weldments and 16 low-level parts.
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