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Beyond Rapid Prototyping: Direct Manufacturing

When Linear Mold started using laser-sintering for tooling inserts, it accelerated mold production and reduced costs.

Direct metal laser-sintering (DMLS) is different than common machining/milling techniques, which produce parts by removing material.

Direct metal laser-sintering (DMLS) is different than common machining/milling techniques, which produce parts by removing material. DMLS is an additive process: a part is made by "growing" it in layers, each layer being a very, very thin slice of a computer-aided design (CAD) solid model. In some production applications, DMLS can replace the more-conventional machining processes. This was the case for Linear Mold & Engineering (Livonia, MI; www.linearmold.com), which installed a couple of DMLS machines to complement its conventional machine tools for manufacturing molds and mold inserts. Three years later, Linear Mold has the numbers showing that DMLS replaced certain production steps, reduced production time, and ultimately reduced costs-to the tune of 15% to 30%, depending on the complexity of the part.

 

Neighborly help

John Tenbusch, president, founded Linear Mold in 2003. The company manufactures plastic injection molds, foam tooling, and prototype parts for a variety of plastic components. The 50-person company is basically a one-stop shop for design, tool construction, and injection molding. Tenbusch himself has over 15 years experience prototyping plastic injection molded parts. This is on top of the years he was a model maker dating back to the days of Mylar. "I'm a wood model maker by trade and ended up being a CAD guy," he says. When he founded Linear Mold, Tenbusch had a neighbor who was also a mold maker and, over time, had "gotten into some technology, into software, things like that." The neighbor landed a job with Electro Optical Systems-EOS of North America (Novi, MI; www.eos.info). There were times when the neighbor helped Tenbusch by creating some mold designs on his laptop at home. One day, the neighbor told Tenbusch to see "this stuff," namely the EOS laser-sintering technology. He told Tenbusch, "All these little hand loads that you guys want a specific way, you can, instead of CNC cutting, grow them right to net data."

"Yeah. Right," Tenbusch thought.

Tenbusch had heard about stereolithography technologies, such as stereolithography apparatus (SLA) and selective laser sintering (SLS). The technology just didn't seem adequate. Stereolithography materials were brittle, so molding pressures sometimes caused molds and inserts to split. Fine details sometimes got lost. The pressure of the plastic going through a mold could blow a structural rib apart. And so on.

The neighbor prevailed and made a couple of inserts for Linear Mold. "We used them and had no problems," says Tenbusch. Linear Mold also had EOS grow inserts for some epoxy composite injection molds. "Great success," continues Tenbusch.

In November 2005, Linear Mold bought an EOSINT M 270 machine from EOS. This DMLS machine uses a ytterbium-fiber 200-W laser to "draw" 3D CAD data on a layer of metal powder evenly spread across a build platform. This layer of powder measures 20- to 40-microns thick. The laser melts the powder, creating a thin slice of the CAD solid model. After the melt is complete, excess powder is removed, the build platform is lowered by the thickness of the slice, and more powder is spread over the build platform. And so on until the CAD model is translated into an extremely dense metalized part (98% to 100%) within a work volume measuring 9.85 in. x 9.85 in. x 8.5 in.

The combination of fine metal powder, the laser's extremely fine resolution, and the fine resolution of the motor driving the build platform yield a part with an excellent surface finish, as well as repeatable accuracy of ±50 microns. "This technology has the tolerancing that's required for what we're doing," says Tenbusch. Whereas machining the molds typically required two weeks, jobs are being accomplished in a few days. Machining is now limited to the core side of the mold.

The finished molded part has a Class A appearance on the A side because it's coming off an aluminum mold. Because the B side is from cast epoxy, it might not look pretty, but it's totally 100% functional. It has all the details, the rib towers, everything.

 

Calculating time savings

After two-and-a-half years of costing out more than 50 tool and mold projects for a variety of industrial customers, Tenbusch has concluded that DMLS was saving Linear Mold money. Equally important, the company could attract more business by competing on faster delivery times. "In the prototyping world, it's all about speed and cost," says Tenbusch. This is important when customers compare Linear Mold, for instance, to offshore shops. "We might not be as inexpensive, but we can produce it faster."

For instance, using conventional methods (CNC and EDM machining) to make single-cavity tool inserts for one project would have taken 210 hours. It took 80.5 hours to build the inserts on the EOS system, plus 16 hours of mold-assembly time. Another project involved creating a single-cavity aluminum MUD injection mold tool. Conventional machining would have taken four weeks; with DMLS, six days. Manufacturing a prototype tool for a visor clip using DMLS took eight days, down from four weeks using conventional machining. In another job, manufacturing a four-cavity family of mold inserts using conventional machining would have taken five weeks; with DMLS, three weeks.

Tenbusch is quick to point out that he still needs the traditional CAD designer to do the design work for the mold. However, once that design is done, it's loaded into the EOS machine and the operator hits the "Go" button. "You might let it run all weekend long, growing all of your inserts, with all of the details," explains Tenbusch. "Then when you come in Monday morning, you take the inserts off the plate and start assembling them into a mold base." Much, much faster than before.