Automotive companies constantly seek to improve vehicle operating efficiency and thus improve fuel efficiency, especially in light of the ongoing upward climb in gas prices. Improving efficiency, however, is no longer easy; the low hanging fruit has already been picked. So, in their pursuit of this goal, automakers and major auto suppliers are turning to tech savvy partners to help them turn innovative ideas into reality. This was the situation recently when an axle manufacturer partnered with 3-Dimensional Services of Rochester Hills, MI, on an innovative new testing device.

In this instance 3-Dimensional was asked to focus its expertise on a transfer case oil flow testing system for a new axle design for cars and light trucks. “Our customer needed to make sure that the actual oil flow within the transfer case is what they envisioned it to be,” said Scott Duffie, senior sales engineer, 3-Dimensional. “This is a key aspect of efficient operation for the axle and, ultimately, for the vehicle itself.”

To test that, they created a prototype of the new transfer case, cycled oil through it during test bed operation, to “see” what would happen. “See” being the operative word. “Typically this part would be a casting,” noted Duffie, and despite the marvels of today’s sensor technology, it is still tough to see what’s happening on the other side of a cast iron wall. To get a better understanding of how the new design actually performed, the axle manufacturer opted to go with a clear plastic transfer case prototype. They needed a partner who could bring the required rapid prototyping, molding, and precision machining skills together and do it quickly.

First, the engineers at 3-Dimensional quickly created a master pattern using stereolithography (SLA). Based on the part’s CAD design, the SLA’s laser beam cures light sensitive polymers into the shape of the part.

For many applications an SLA prototype is sufficient. 3-Dimensional engineers’ intimate knowledge of the technology, however, led them to conclude that for this application a tougher, more resilient prototype than could be created with SLA was required. Thus the SLA master pattern was used to create a silicone tool.

Before that could happen, though, the master pattern had to be hand polished to a mirror finish. This was to ensure that the resulting tool, and thus the eventual prototype, would be left with no surface finish defects that could impede smooth oil flow or viewing.

The polishing entailed wet sanding alternating with a painting technique that 3-Dimensional employs in these cases. “The painting technique helps us identify surface areas that might be suspect and thus require more attention,” explained Duffie. “Once that tooling is complete then we’ll close it all off and pour urethane into it. After 24 hours of cure we pull the tool apart and we’re left with the prototype.”

Well, almost. First, 24 helicoils needed to be inserted. These provided the means to attach the transfer case to the rest of the prototype axle so that realistic cycling tests could be run. The part’s mating surfaces were machined flat on a mill, then pilot holes were drilled into the urethane, then a tap was run. Into these drilled and tapped holes the helicoils, or threads, were inserted on a CNC vertical milling center. These strong steel threads would enable the customer’s engineers to assemble and disassemble the part as many times as they saw fit.

“The entire operation took just three weeks,” said Duffie. In that length of time we provided a tough, clear transfer case prototype in which they could see and study every aspect of oil flow under a variety of conditions. Unexpectedly, they were also provided with an improvement on their original design.

“There were some strengthening ribs in their original design that our analysis concluded were not necessary and would, in fact, inhibit the viewing of smooth oil flow,” recalled Duffie. “They let us eliminate them and, after their subsequent testing, were pleased with the result.”

The 3-Dimensional Services Group, consisting of 3-Dimensional Services, Urgent Plastic Services, and Urgent Design & Manufacturing, provides rapid prototyping services that allow them to design, engineer and build functional prototype parts and low-to-medium volume production parts. Their capabilities encompass virtually all relevant processes, including injection molding and casting, stamping, CNC machining, robotic and manual welding, laser cutting and welding, waterjet, hydroforming, tube bending, vibration welding, casting and pattern fabrication, RIM tooling, SLA, LOM and SLS rapid prototyping, and assembly.

3-Dimensional Services
www.3dimensional.com