(August 8, 2011) WARREN, Mich. — The three-dimensional rapid prototyping technology that lets designers and engineers fabricate almost anything they can imagine has led the skilled trades technicians who work in the shop around the clock six days a week to innovations of their own at General Motors.

The lab technicians can directly transfer digital designs for just about any part on a car or truck to the selective laser sintering (SLS) or stereo lithography (SLA) machines that generate parts in hours without any dedicated tooling.

The only limitation beyond a designer’s imagination is the physical size of the machines. Parts being generated must be no larger than the 500 x 500 x 750 millimeter dimensions of the fabrication chambers that contain the powered plastic or liquid resin.

No problem for smaller pieces like interior trim or parts for a one-third scale model to be tested in GM’s wind tunnel. As part orders come in from GM design and engineering facilities around the world, technicians use a graphical design program to arrange computer models of the parts within the envelope of the chamber to maximize the output of every batch.

 “As long as the parts aren’t touching, we can keep filling the envelope,” said technician Timothy Breault. “When we get hot orders for parts that are small enough, we can even add them on the fly to the top of a build that is already in progress.”

Larger parts suitable for full-scale wind tunnel testing, such as the lower front splitter for the 2013 Camaro ZL1, require a different approach. In this case, the lab techs developed a mechanism that would allow the joining of multiple smaller pieces to make one larger part. As they prepare build sets, larger parts can now be sliced into multiple smaller sections that fit within the RP machines.  Thanks to the precise forming that is possible with RP manufacturing, integrated lap joints with a series of matching holes can be generated so that no drilling is required for assembly.

After the parts cool, the segments are temporarily connected with standard Cleco expanding fasteners while being assembled. The technicians also devised standard joining pins that are produced in the RP machine from the same material as the rest of the part. Pins are snipped off, glued into the holes and then trimmed with a rotary tool. The rapid prototyping machines produce parts to such precise tolerances that virtually no trimming or filling is required and the seams are almost invisible.

“Things that we do now within a day or two days, would take months to build by hand,” said Michael Marchwinski, a lab technician who began his career at GM Design 28 years ago as an apprentice wood model maker.

GM RP techs Timothy Breault (left) and Michael Marchwinski use a graphical design program to arrange computer models of those parts in the SLS chamber to maximize the output of every batch.

Using rapid prototyping to produce parts invariably saves tens of thousands of dollars and weeks of time compared to traditional methods. The technicians came up with a way to save even more by reusing some of the raw material. Traditionally, only virgin resins were used for rapid prototyping, but the technicians developed a recycling process for the powered SLS material.

The shop staff worked with 3D Systems, the equipment supplier, to extract a portion of the used material and return it to the delivery vessels where it is blended with virgin material for future use. 

The 15-person staff that operates the Warren 3D Rapid Prototype Lab was recruited from a variety of GM operations.

“When I came into skilled trades in 1995, they had just started opening up a program where new apprentices would be trained on the whole Tech Center site, learning many different skills,” said lab technician Thomas Kelley. “Thanks to my training in several areas, Superintendant John Green thought I would be a good fit here.”

The RP team is constantly on the lookout for ways to improve efficiency and produce better quality parts.  “We’re really dedicated to what we are doing, we all enjoy the work and we want to see a good product come out,” said Marchwinski.