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To optimize the bracket for the horizontal green sand casting pro- cess, the team had to design a bracket shape that would eliminate the need for multiple cores. As designed for the weldment, the part included several areas of back-draft. Dotson’s product manager Chris Witt guessed it would have taken four or five cores to pro- duce the casting. “With some minor design changes,


The award winning casting replaced a welded bracket that fit on John Deere’s skid loader engines.


price by 48% and the on-line scrap rate by 10%. The casting also fetched the 2010


AFS/Metal Casting Design & Purchas- ing Casting of the Year award.


From Liability to Benefit In the interaction between Dotson


and Deere that yielded the great sav- ings and reduced number of scrapped brackets, G&V Machine Co., Ixonia, Wis., played catalyst. Deere had a vague notion that its weldment needed to be produced in the metalcasting process. The machine shop not only knew what specific casting process would produce the part the company needed, it knew the right casting supplier for the job. Chris Griswold, G&V’s vice presi-


dent of manufacturing, said his team briefly considered a gray iron casting to achieve maximum cost reduction on Deere’s bracket, but the material would have been a liability in the high impact and vibration application of a skid loader engine. The design team settled on ductile iron for its strength. The team also knew the tight dimensional tolerances of a nobake cast part would be overkill for the bracket and that a green sand part would serve its purposes. Taking into account these factors,


production requirements of 7,000 pieces per year, and the weight and size of the component (10.7 lbs., 15 x 6 x 5 in.), G&V knew the metalcaster for the job.


20


The 10.7-lb. bracket (in gold) attaches the alternator and air conditioner compressor to the skid loader engine.


MODERN CASTING / June 2010


“Dotson is very easy to deal with,” Griswold said. “The engineering and turnaround is very fast.” Armed with a CAD drawing of


Deere’s weldment, G&V brought Dotson into the design fold early in the conversion process, seeking to optimize the benefits of metalcasting while maintaining high castability to keep costs and scrapped castings down.


we knew we could make it more eco- nomically,” Witt said. “We reduced ma- terial so the part was naturally drafted, we worked toward a uniform wall thickness so there weren’t any areas that were hanging over, and we added draft to the base of the cylindrical bosses.” The resulting design, positioned with the long axis vertical in the mold, re- quired one core to produce a small slot for the engine’s throttle control. What’s more, the cast version of


the bracket was designed with angles and surface alignment that allow for accurate mounting surfaces and hole positioning and horizontal CNC ma- chining with one setup. Dotson also added a feed path to ensure the part’s bosses would be porosity free and a number of stiffening ribs to eliminate flexibility in the part and help it come through shakeout without damage. In addition to the redesign, one final factor helped sell Deere on the cast


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