Deep inside the GM Design building where future products from Chevrolet, Buick, GMC and Cadillac take shape and substance, an elite team fashions components, intricate sub assembles and entire scale model cars from highly specialized three-dimensional rapid prototyping manufacturing equipment.
In an already secure building, access to the RP Lab requires additional clearance because of the work performed there, Operating around the clock, the highly trained team of technicians is vital to the global base of GM designers, aerodynamicists and engineers who achieve huge gains in creativity, flexibility and accuracy along with dramatic savings in time and money.
The Rapid Prototype Laboratory features two fabrication processes - selective laser sintering (SLS) and stereo lithography apparatus (SLA). Both processes build up finished products from raw material in layers.
“Think of it as the reverse of slicing off cold-cuts at the deli counter, where each slice is created and joined back to the whole,” said Dave Bolognino, director of GM Design Fabrication Operations. “RP technology eliminates tooling plus it permits the production and testing of multiple iterations of a part or assembly with superb precision at little to no incremental expense. It’s a game-changer of epic proportion.”
Selective laser sintering (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 adding a layer four-thousandths of an inch thick. As each new layer of powder is added, scanned and fused to the previous one the part gradually takes shape within the 28-inch-cubed reservoir. To the naked eye, the plastic used in the SLS process looks much like powdered sugar with individual grains measuring just 550 microns or about two-hundredths of an inch across.
Technicians carefully position as many jobs as they can together within that space to maximize the throughput of each build request. The SLS manufacturing process is self-supporting, meaning un-fused powder cradles the part as it is being fabricated, often without need for additional finishing or trimming.
After it cools, the excess powder is shaken off and a portion is recycled with the finished part put to use immediately or joined with other components to make larger assemblies.
Stereo lithography (SLA) combines photochemistry and laser technology to build parts from liquid photopolymer resins. The parts are also built up in layers as a UV laser traces the section onto the surface of the resin, curing the liquid into a solid as it scans. Because the resin won’t support the parts being formed, a fine lattice-like structure is generated below each part during the manufacturing process. Highly specialized software from Materialise Inc. automatically calculates the required structure based on the original 3D model of the part so that it uses the least possible amount of material. When the parts are complete, the bottom plate rises out of the vat of resin and the lattice support is snapped off by hand leaving a ready-to-use part.
Both technologies were used on breakthrough vehicles like the pre-production Chevrolet Volt and advanced concepts like the Electric Networked Vehicle, known as the EN-V. In the case of the Volt, RP technology was used in areas ranging from design, development and validation of the battery cooling system to helping to lower its coefficient of drag.
“Thanks to the rapid pace of production from the RP Laboratory, GM’s aerodynamics lab has been to double its capacity of testing scale models over the past two years, contributing to improved fuel efficiency on future GM vehicles,” said Bolognino.
Labor-intensive projects that used to take weeks or months to sculpt in clay and then cut and cast in molds are now produced in a fraction of that time and expense. From Brazil and China to Australia and Germany, as soon as the designer finishes creating a mathematical model in the Computer Aided Design (CAD) system, the digital file can be directly transferred to the RP Lab, which never sleeps. The lab manages a continuous flow of receiving, scheduling, manufacturing and express shipping of more than 20,000 components a year.
GM Design has been on the leading edge of rapid prototyping technology for nearly two decades and is highly regarded as a beta tester and innovator of new materials, formulas and processes by its supplier partners, 3D Systems Corp. and Materialise.