Assembly - January 2009 - (Page 14) Assembly Innovations New Process for Molding Auto Parts Uses Less Resin M Mazda has developed a new plastic molding technology that substantially reduces the weight of plastic parts for vehicles. Photo courtesy Mazda Motor Corp. azda Motor Corp. (Hiroshima, Japan) has developed a new plastic molding technology that substantially reduces the weight of plastic parts for vehicles. The technology lowers the amount of plastic resin needed to mold bumpers, consoles and other parts by 20 percent to 30 percent. foam to expand. This means that large plastic parts, with low density and good rigidity, can be made from the same volume of resin. Parts molded with the new process have a multilayer structure. The bubbles in the outer layer of plastic are kept microscopic, to ensure the part is strong and rigid, while the size of the bubbles in the core layer can be adjusted to reduce the part’s overall density as needed. The technique can be used to mold nearly all the plastic parts in a vehicle. Besides producing stronger, lighter structures with less material, the new process also enhances the thermal insulative and acoustic characteristics of the parts. Mixing gas with the liquid resin during molding is not new. Older plastic foaming methods use a gas formed through the thermal decomposition of organic and inorganic compounds. However, residual chemicals from the foaming agents can adversely affect some plastics and impair their ability to be recycled. Using SCFs to foam the plastic avoids these complications. Mazda’s new process is a variation on traditional injection molding. The process involves mixing the raw plastic resin with a “supercritical fluid” (SCF) made from a common inert gas, such as nitrogen or carbon dioxide. A substance becomes an SCF when it’s exposed to such a high temperature and pressure that its liquid and gaseous phases become indistinguishable. An SCF can diffuse through solids like a gas, and dissolve materials like a liquid. As SCFs, nitrogen and carbon dioxide raise the fluidity of liquid plastic resin and cause the material to expand rapidly when injected into a mold. The resin forms a foam with a standardized microcell structure, so smaller amounts of resin are needed to fill the mold. Mazda’s new technique also relies on the “core-back expansion molding process.” Once the foamed resin has filled up the mold, the volume of the mold is increased, causing the Mobile Robot Drills Holes in Airplane Components A Spanish engineering team has developed a light, portable robot that precisely drills holes in wing spars and other large aeronautical components during the assembly stage. Traditionally, such components are drilled using large, stationary machinery. In contrast, the robot moves over aircraft components while they are fixed to a tool holder. Dubbed Roptalmu, the robot was designed for Airbus España (Madrid, Spain) by engineers at Fatronik-Tecnalia (San Sebastian, Spain), a private, nonprofit manufacturing research center. Roptalmu consists of an automatic moving platform and a three-axis drilling robot. Once the platform is positioned near the part to be drilled, the robot fixes itself to the tool holder of the part and automatically moves over it. The robot can drill a range of materials, including aluminum, titanium and carbon fiber. A set 14 ASSEMBLY / January 2009 www.assemblymag.com http://www.assemblymag.com
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