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Options In Rapid Prototyping Technology

Stratasys, Inc. (Minneapolis, MN; www.stratasys.com) is the exclusive North American distributor of the “CAD to Metal” process from Arcam AB (Mölndal, Sweden; www.arcam.com). This process uses electron-beam melting (EBM) to transform titanium alloy (Ti6Al4V and Ti6Al4V ELI) or cobalt chromium (ASTM F75) powder into real metal parts.

Stratasys, Inc. (Minneapolis, MN; www.stratasys.com) is the exclusive North American distributor of the “CAD to Metal” process from Arcam AB (Mölndal, Sweden; www.arcam.com). This process uses electron-beam melting (EBM) to transform titanium alloy (Ti6Al4V and Ti6Al4V ELI) or cobalt chromium (ASTM F75) powder into real metal parts. Although medical implants (using cobalt chromium powder) is a big application area, the auto industry uses EBM, as well. Parts up to about 8 x 8 x 8 in. are built by layering metal powder. A 4-kW electron beam operating in a vacuum chamber melts the layer of powder along a contour defined by a solids modeler. Upon completion, the net-shape part is cleaned. (Its “semi-rough” finish can be polished as needed using conventional machining methods.) Larger metal parts can be created by e-beam welding parts together. EBM operates like a picture tube, explains Kirby Quirk, senior sales executive, direct metals manufacturing, for Stratasys. Basically magnets steer and accelerate electrons through a little aperture. “There are no moving parts. No mirrors, servos, nothing to get out of whack or out of adjustment. You don’t have to worry about dust on the mirrors. It makes no noise. It just runs.”

Another advantage of this system is that the e-beam source does not waver from the time it’s installed till the time it burns out. This is unlike the lasers used in conventional RP and direct manufacturing systems. “Lasers are like people,” explains Quirk. “Once they are born, they get weaker and slower as they get older.” Moreover, replacing the e-beam element costs a fraction of what it costs to replace the laser in conventional systems. Plus, like a light bulb, replacing the e-beam source is a cinch. (The life expectancy of the e-beam source is not yet known.) Because metal parts are produced directly, the lead and prep times for casting and traditional machining are greatly reduced, in some cases eliminated. The functional prototypes, being that they’re made out of metal, can withstand actual operating conditions, including mechanical loads and temperatures.

Stratasys now offers the FDM Vantage X, which starts at $99,000. There are two configurations. The “A” configuration uses ABS, ABSi, and PC-ABS materials; the “P” configuration, PC, PC-ISO (a medical modeling material), and PC-ABS. Model resolution is 0.005 in. for ABS, ABSi, and PC-ABS materials.

Stratasys has beefed up its Eden line of PolyJet RP systems, which are manufactured by Israel-based Objet Geometries. These office systems use a printhead that passes from left to right to deposit a layer of photopolymer. The modeling material is fully cured with UV light during the build process. There are now six Eden systems, ranging from the Eden250, which has a 10.1 x 9.8 x 8-in. build envelope, to the Eden500, which has a 19.7 x 15.7 x 7.9-in. build envelope. The trend, explains Fred Fischer, Stratasys product manager for the Eden Distribution Line, is that “the jetting of resins is replacing the old way of making high-resolution parts, which is the vat-and-laser technology.” He cites cleanliness (better) cost (lower) and speed (generally faster) as reasons. What’s more, he says, “It’s simpler.”

 

Ducati Speeds Development

During the development of a new engine for a road bike based on its Desmosedici race bike, Ducati Motor Holding S.p.A. (Bologna, Italy; www. ducati.com) first built the engine out of polycarbonate. Not quite the same as the real thing, but close enough to validate the new engine design. In working to develop the engine, Ducati used Stratasys FDM (fused deposition modeling) systems. According to Piero Giusti, R&D CAD Manager for Ducati Motor Holding, Ducati has assembled and analyzed an entire engine without machining a single metal piece.

In designing the new engine based on its Desmosedici MotoGP race bike, Ducati used Unigraphics NX2 CAD/CAE software (www.ugs.com/products/nx/). The engine layout—a twin-cylinder, oval-piston configuration—was designed to have the power and torque of a conventional twin-cylinder engine, plus the necessary performance to compete against multi-cylinder engines. Ducati then produced an engine model assembled with polycarbonate components built within the 16 x 14 x 16 in. build envelope of its in-house Stratasys FDM Titan system. Then the design strategy changed. A new engine was designed with an L-shaped layout and four round pistons using a two-by-two firing order, which reproduced the working cycle of a twin-cylinder engine. Again, the engineers built a new prototype out of polycarbonate.

In the past, Ducati employed RP service bureaus to make such prototypes. In designing and building a previous engine, that approach took 28 months. With FDM in-house, designing and assembling the Desmosedici engine took only 8 months. “Prior to purchasing the FDM RP systems, our service-bureau expenses totaled approximately 1 million euro per year. That was much higher than the cost of purchase, maintenance, and materials for our two FDM machines,” says Giusti.

Non-engine components are developed with RP, as well. For example, a mudguard modeled in polycarbonate and mounted on a prototype motorbike has completed tests at speeds in excess of 136 miles/hour. In fact, Ducati Corse, a division focused on motorbikes for SBK and MotoGP championships, regularly tests RP models in wind tunnel.

“For designing the vehicle structure—frame assembly, vehicle body, wheels, forks, etc.—we needed accuracy of about 0.3 mm/meter; for the engine, 0.05 to 0.1 mm/meters is satisfactory,” continues Giusti. “Keep in mind that precision is not a fundamental requirement [at this stage]; we needed an impressive, 3D object fast to use as an instrument aid for our designers. It is fundamental we get an object to investigate in hours, not in weeks. We ‘invent’ our designs virtually with our CAD systems, but we always verify them ‘physically’ with our rapid prototypes.”