| Though typically a casting, this clear plastic transfer case prototype produced by 3-Dimensional Services allowed an axle manufacturer to view oil flow within the prototype. |
There is no time for trials and no room for error, and that fact is establishing a more standard role for prototypes in the development of cast products and casting production programs. Automakers today are constantly seeking to improve vehicle operating efficiency and thus improve fuel efficiency. Improving product efficiency, however, gets harder all the time: the most achievable improvements have been made. So, automakers and their major suppliers increasingly turn to advanced technology suppliers to help them convert innovative ideas into reality. That was how 3-Dimensional Services came to partner with an axle manufacturer on a new testing device.
3-Dimensional Services specializes in design, engineering and analysis, in-house tool construction, and complete prototype capability for first-off parts and low- to medium-volume production runs. Its advanced processes, manufacturing technologies, and staff make it possible to deliver prototype parts up to 70% faster than conventionally equipped prototype shops.
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. “When our customer creates a new axle design they’ve got to make sure that the actual oil flow within the transfer case is what they envision it to be,” explained senior sales engineer Scott Duffie. “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, cycle oil through it during test bed operation, and “see” what would happen.
“Typically this part would be a casting,” Duffie noted, but even with advanced sensors it is tough to see through cast iron. So, to get a better understanding of how the new design actually performed, the producer opted for a clear plastic transfer case prototype. They needed a partner to provide rapid prototyping, molding, and precision machining, and do it quickly.
First, 3-Dimensional used stereolithography (SLA) to create a master pattern. Based on the part’s CAD design, the SLA’s laser beam cured the light-sensitive polymers into the shape of the part. SLA, selective laser sintering (SLS), and metal laminating are three prototyping technologies 3-Dimensional offers. For many applications an SLA prototype is sufficient but for this application a tougher, more resilient prototype was required. So, the SLA master pattern was used to create a silicone tool.
First, the master pattern had to be hand polished to a mirror finish to ensure that the resulting tool, and thus the eventual prototype, would have no surface defects that might impede smooth oil flow or viewing. Polishing involved wet sanding alternating with a painting technique. “The painting technique helps us to identify surface areas that might be suspect, and thus require more attention,” according to Duffie. “Once that tooling was complete, then we closed it all off and poured urethane into it. After 24 hours of cure we pulled the tool apart and we were left with the prototype.”
But first, 24 helicoils had to be inserted in order 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, and 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 allow the customer’s engineers to assemble and disassemble the part as many times as necessary. There was no question of the part having to wait for a machine to become available: 3-Dimensional has over 40 CNC machining centers and 75 knee mills and lathes.
“The entire operation took just three weeks,” Duffie said. In that 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, the axle maker also got an insight to an improvement for 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,” Duffie recalled. “They let us eliminate them and, after their subsequent testing, were pleased with the result.”