Rapid Prototyping: How It’s Done at GM

Why is GM using it? Because of two big drivers in auto today: Reducing product development cost and time-to-market.

The lab is manned by 15 specialists who work three shifts, six days a week, taking part orders from GM design centers all over the world to crank out some 20,000 unique parts a year. Parts are built from one of two additive technologies: SLS, where a laser fuses layers of powdered material together, or SLA, where a laser cures liquid polymer, layer by layer. Parts are built within hours and then express shipped to their destination, allowing designers and engineers to spend more time evaluating changes and less time waiting for parts compared to conventional prototyping methods.

“The return on investment has been significant, especially when you figure in the elimination of tooling,” says Dave Bolognino, GM Director of Design Fabrication Operations. He uses a register vent as an example. “If you look at the complexity in that part alone, back in the old days, somebody would have to carve that or make it in clay just to get a look at it. Now we can go right to the machine and get a functional part much, much quicker than you could ever get an aesthetic part.”

Bolognino says the automaker has been using additive technology for the past 20 years. But back in the early days, he says, the speed, materials, and accuracy limited the technology to just vehicle mockups. Now, it has advanced to a point where bumpers, grilles, spoilers, and mirrors—parts that would be difficult to quickly make any other way—can be accurately built.

The only limitation is the work envelope of the machines. The lab’s largest machine features a work envelope of 500 x 500 x 750 mm, so to build bigger parts, sections are produced, and then assembled.

Aerodynamics Testing

Not only are parts made for aesthetic assessment, but there are also functional applications, like aerodynamic testing, both of scale and full-sized vehicle models. “The big thing is the materials now,” Bolognino says, citing advancements such as 3D Systems’ DuraForm EX, which is said to offer the toughness of injection-molded ABS parts. “Now we can make real, tangible stuff that we can put into wind tunnels.”
Here’s how the testing typically works:
• Parts are designed and then digitally analyzed with computational fluid dynamics (CFD) software
• The design files for the parts are sent to the AM equipment, where 1/3-scale models are produced
• Parts are assembled into a vehicle and physically tested in the wind tunnel
• Performance is evaluated and design changes are made
• The process repeats
Bolognino says aerodynamics testing has doubled over the past two years due to the company’s ability to quickly build and test multiple iterations of parts. And these parts aren’t just limited to things like side mirrors and grilles. The RP lab is also capable of building detailed models of engines, transmissions, brake lines, and drive shafts, which help engineers analyze airflow through the engine bay.

Not Just For Prototyping

One of GM’s most public applications of RP technology was in developing the Electric Networked Vehicle (EN-V) personal urban mobility concept vehicle. Three models of the EN-V—the Jiao, Xiao and Miao—were designed and five units of each model were built.
Beyond prototyping, components were manufactured with the RP technology for the vehicles. “The brackets, a lot of the interior parts, the ductwork—ordinarily you’d have to tool that up rather expensively, Bolognino says. Instead, they were additively built-in DuraForm EX and integrated into the vehicles. “That was our first heavy usage on a small fleet,” he says. This is an example of AM at GM—limited, but production.
Bolognino also cites the Chevrolet Volt: The pre-production test fleet built in 2009 included 80 vehicles “We made several interior part runs when suppliers who were under contract were unable to deliver or when there was a late part change,” he says. The parts were built and installed directly into the test vehicles.
So what does the future hold for this technology? Bolognino says, “I couldn’t see us making a whole production run with this technology, but you never know.” He adds, “A few years ago I wouldn’t have said we’d be where we are today.”