For additive techniques, “rapid” is a bit of a misnomer because the manufacturing processes involved are relatively slow. In fact, it can take hours or even days to build a part. The term arose because laser sintering, stereolithography, fused-deposition modeling, and other technologies build parts directly (thus rapidly), layer by layer from CAD data. Other common terms are “free-form fabrication” and “direct-digital manufacturing” (DDM). Rapid techniques free engineers from traditional “design for manufacture” schemes. Instead, DDM lets users practice “manufacture for design,” meaning conventional DFM constraints such as draft angles are not an issue.
In fact, DDM can produce geometric shapes that are difficult if not impossible to make using any other method. So says Denis Cormier, Associate Professor of Industrial and Systems Engineering at North Carolina State Univ., Raleigh, N.C. “For example, we use electron beams to build lattices out of metals such as titanium, copper, and aluminum,” he says. “Applications include lightweight aerospace structures, hip stems with engineered stiffness, and high-surface-area heat exchangers. Basically, we take an STL file of a shape and fill the volume with a repeating structure using a voxelization algorithm. Finished parts can be chemically etched to improve ductility,” he says.
DDM also implies so-called “indirect” manufacturing where rapid manufacturing builds the tooling that then makes finished parts. Express Pattern Inc., of Vernon Hills, Ill., for instance, says it uses stereolithography to make patterns for investment casting. The thermoplastic pattern is embedded in a sand or plaster cast. Heating in an industrial oven burnouts the pattern, leaving the investmentcasting shell. And Met-L-Flo, Sugar Grove, Ill., says using indirect methods to build jigs and fixtures cuts costs and ensures tool repeatability.
The Walt Disney Co., Burbank, Calif., uses a gamut of manufacturing technologies from old-world craftsmen to fused-deposition modeling in making objects such as large cartoon statues and benches for theme parks. “Sometimes our craftsmen just mold a shape in clay and cast it into a tool,” says J. Douglas Smith, Disney Manager Applied Technology. “On the other hand, we might design a seat for a water ride by first creating a 3D model in CAD and then performing FE analysis. CAD models go to one of our fused-deposition machines or to CAM and our five-axis mill,” he says.
Finally, there was a lot of buzz about rapid devices and software on display. For instance, a machine called the Connex500 from Objet Geometries Inc., Billerica, Mass., jets two different materials (which can have differing mechanical and physical properties) in many preset combinations. The company says this allows the early simulation of double-injection- molded products, which cuts costs and risks associated with creating complex molds. One of the more interesting software examples was e- Stage from Materialise, Ann Arbor, Mich. Users send a CAD model for stereolithography to e-Stage. It uses the 3D shape to generate the exact built support structure needed and attaches this data to the model. The file goes to a RP machine to make the part. The software eliminates manual editing and the associated errors.
Make contact: North Carolina State Univ., ncsu.edu
Express Pattern Inc., expresspattern.com Met-L-Flo, met-l-flo.com
Walt Disney Co., disney.go.com/index
Objet Geometries Inc., 2objet.com
Materialise, materialise.com
