General Motors (GM) was an early adopter of rapid prototyping (RP) technology for parts and subassemblies as well as for electrical/electronic applications. In the latter realm, for example, it developed a two-mode hybrid powertrain control system in less than the expected development time – four years from initial design to vehicle production.
Larry Nitz, executive director of hybrid and electric powertrains, says model-based design and rapid prototyping allow GM engineers to work at a higher level of abstraction and verify designs early. “This ability to simulate and correct systems before committing to hardware allows us to try new control strategies virtually, while the use of production code generation accelerates design iterations and eliminates translation errors common in hand coding,” he says.
Dave Bolognino, director of design fabrication operations, adds that rapid prototyping technology reduces product development time, saves costs, and gives GM designers more options. It also eliminates tooling and permits the production and testing of multiple iterations of a part or assembly “with superb precision at little to no incremental expense.” Bolognino calls RP “a game-changer of epic proportion,” and adds that the lab manufactures more than 20,000 components a year.
Once mathematical models of parts and subassemblies are completed, digital CAD (computer aided design) files are transferred to GM’s RP lab. The lab uses two fabrication processes, selective laser sintering (SLS), and stereo lithography apparatus (SLA). Both processes build up finished products from raw material in layers. Primary development partners are 3D Systems Corp. for hardware, and Materialise, Inc. for software.
SLS machines are used to fuse plastic, metal, ceramic or glass powders in cross-sections. A laser scans a pattern on the surface of the powder, fusing the particles together and adding a layer .004-inch thick. The part takes shape as additional layers of powder are added, scanned, and fused to the previous one.
SLA combines photochemistry and laser technology to build parts from liquid photopolymer resins. An ultraviolet laser traces the section onto the surface of the resin, curing the liquid into a solid as it scans. Materialise software calculates the required structure based on the original 3D model of the part to use as little material as possible.
Bolognino says both technologies were used during development of the Chevrolet Volt – including design, development and validation of the battery cooling system – and the Electric Networked Vehicle (EN-V) concept.