Caterpillar's Track-type Tractor Div. (Peoria, IL) just boosted the strength and fatigue resistance of a radiator-guard mounting system on its D8 Track-type tractor. To save steps, the design team used technologies that reduce drawing time and eliminate costly metal tooling. Using 3D CAD, rapid prototyping, and investment casting, engineers brought the prototype to market in one-fourth the typical time.
Waltham, MA-based Parametric Technology Corp.'s Pro/ENGINEER(R) software helped Caterpillar engineers generate electronic solid models in a fraction of the time it would take to render comparable drawings in the traditional manner. Engineers then download the solid model into an Actua 2100 Office Modeler Rapid prototyping system, manufactured by 3D Systems (Valencia, CA). By outputting layers of wax methodically over a period of hours, the Actua system produces solid-wax models that can be used in investment casting.
Caterpillar produced two wax patterns. Each represents one-half of the prototype. "The Office Modeler saves time, steps, and costs," asserts Caterpillar Manufacturability Engineer David Fee. "Using it, we didn't have to pay an outside source for wax patterns. And, it allows us to go directly from electronic models to investment casting, without the interim step and added expense of metal tooling."
The prototype requires two 40-lb castings. "While most casting vendors need 12 weeks to produce these kind of parts, Northern Precision Casting Co. (Lake Geneva, WI) delivered in 15 working days," says Fee. "We trust their expertise. NPC produced prototypes for us before, and we felt they would provide both the quality and turnaround we sought."
But turnaround wasn't the only hurdle. NPC's investment-casting facility typically produces castings that weigh less than 20 lb. To accommodate two 40-lb castings, NPC used two wax clusters to create one ceramic mold.
To invest the patterns in ceramic as one part, NPC built two investment casting clusters, then glued the two patterns together. Engineers melted the wax from the ceramic investment in a steam autoclave process, leaving one seamless mold. "The wax patterns created by Office Modeler work well and autoclave nicely," says NPC Sales Manager Jim Giovannetti.
"The real challenge for us was to orient the gating on cluster so that when the molten steel was poured into the ceramic mold from two separate cups, it would ensure proper filling of the entire mold cavity," Giovannetti explains. "We only had one shot to get it right--there was no chance for testing or experimentation." To address this, NPC researched metal pouring, cooling, grain flow, and shrinkage patterns to determine the ideal location for the gates.
The two-piece production process and the gating design proved successful. Nondestructive testing and x-rays on the final casting, performed by NPC, showed excellent integrity throughout the part. The prototype is now in the field, with results and full production plans pending.