ENGINEERING INSIGHT
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The boxes and trays inside the centrifuge must withstand rotational speeds of 2000 rpm and acceleration forces of 1200 g.
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A manufacturer of laboratory centrifuges has developed a device that sediments and separates blood. The Rotomat incorporates a drum motor and six boxes and drip trays. The boxes have a complicated geometry and must withstand rotational speeds of 2000 rpm and acceleration forces of 1200 g. Andreas Hettich GmbH (Tuttlingen, Germany) determined that the use of conventional manufacturing technologies to produce the device would require complex tooling and time-consuming assembly. The firm decided to investigate other options. One that showed promise was laser sintering, part of the e-Manufacturing technology developed by EOS GmbH (Krailling, Germany).
Laser Sintering Versus Injection Moulding
Laser sintering systems melt and solidify powders that are deposited in successive layers to build a product. Plastic, metal, or sand powders can be used. The process has evolved over the years from a rapid prototyping and rapid tooling technology to a flexible batch-quantity manufacturing technique. Laser sintering is the core technology behind EOS GmbH’s e-Manufacturing platform, which allows companies to go directly from electronic data to fast, flexible, and cost-effective production.
When it first evaluated e-Manufacturing as an alternative production method, Hettich set as a baseline that it be at least as economical as injection moulding. The evaluation included intensive testing of the laser-sintered boxes under production conditions. The results showed that the boxes, made of a polyamide 12 material, behaved similarly to samples that were injection moulded.
In other aspects, laser-sintered parts did more than simply match the performance of their injection-moulded counterparts. In particular, the technology affords considerable design freedom. For example, internal structures can be easily realized, a capability that was used to its full advantage by design engineers at Hettich.
Conventional production methods required the box fixtures to be moulded separately. Consequently, additional tooling would have to be designed and built, and the boxes would need to be assembled. Laser sintering allowed the company to integrate the fixtures into the box design. While the modified parts were minimally more expensive to produce, the elimination of a set of tooling and a reduction in assembly work more than made up for it. In addition, the new design improved functionality and added value to the product.
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Laser sintering enabled the integration of fixtures into boxes that are part of the Rotomat device, thus avoiding additional tooling and assembly costs.
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Laser sintering also enables parts production to be performed on demand. Design changes and product variations can be implemented quickly and at minimal cost. For example, the technology allows Hettich to offer different versions of the Rotomat to accommodate various blood bags.
By adapting its production methods to laser sintering technology, Hettich was able to design and manufacture a product with increased functionality without increasing costs, notes EOS GmbH.
EOS Partners with Micromachining Firm
A supplier of laser sintering systems since 1989, EOS GmbH recently announced a cooperative agreement with a manufacturer of laser-based micromachining equipment. 3D-Micromac AG (Chemnitz, Germany) specializes in the processing of powder materials in submicrometre grain sizes. The partnership will allow EOS to expand into microtechnology applications, says EOS founder and CEO Hans J. Langer.
Based on laser sintering, the systems from 3D-Micromac enable the processing of layers as thin as 1 µm. A special coating device applies the layers while a pulsed solid-state laser locally melts the powder. Detail resolutions down to 30 µm can be achieved. The technology enables the production of microcomponents in various metallic materials; ceramic parts are currently under development.
The two firms intend to establish a technology centre for the development, production, and commercialization of laser-sintered miniature components.
