Rapid Prototyping: How It's Done at GM
On the campus of the General Motors Technical Center in Warren, Michigan, is a 9,000 ft² laboratory where they’re building a wide variety of prototypes—from bumpers to spoilers and almost everything in between—with selective laser sintering (SLS) and stereolithography (SLA), technology that’s commonly referred to as “rapid prototyping” (RP) and which is becoming known as “additive manufacturing” (AM). The GM RP lab features 18 machines from 3D Systems Corp. (3dsystems.com), which makes it one of the places with the greatest concentration of AM equipment outside of companies that specialize in the process (typically known as “service bureaus”).
Why Use RP?
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 in order to build bigger parts, sections are produced, then assembled.
Not only are parts made for aesthetic assessment, there are also functiona 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 air flow 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 (see: autofieldguide.com/articles/the-future-of-automotivetransportation).
Beyond prototyping, components were actually 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 really our first heavy usage on a small fleet,” he says. Which is an example of AM at GM—limited, but nonetheless 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.”
By James Gaffney, Product Engineer, Precision Grinding and Patrick D. Redington, Manager, Precision Grinding Business Unit, Norton Company (Worcester, MA)
Ram Truck chief exterior designer Joe Dehner talks about how they’ve developed the all-new pickup. “We’ve been building trucks for over 100 years,” he says. “Best I could come up with is that this is our 15th-generation truck.”
Automotive manufacturers are meeting CAFE fuel-efficiency standards through lightweighting, which requires simulation software for design engineers.