Multicomponent injection molding, in a single mold, with one of the materials a PUR coating that protects its thermoplastic substrate: that's the beauty of a technology that was first discussed five years ago and now is claiming its initial commercial success, and in no less of a project than the new BMW 5 Gran Turismo.
Sometimes a novel technology appears briefly but then quietly disappears. This time, one first highlighted at the K show in 2004 has made its way into commercial production at fischer automotive systems GmbH, a German processor of plastic automotive systems. The new technology being employed, called DirectSkinning, grew out of the work first presented by plastics processing machinery manufacturer KraussMaffei at that event. The initial technology was known as SkinForm.
The first commercial DirectSkinning part, a decorative panel, seals off a kinematic drawer located on the dashboard, directly above the central console, of the BMW 5 Gran Turismo series. The approximately 1.4-mm-thick PUR covering for the panel is based on plastics supplier Bayer MaterialScience's Bayflex LS (Light Stable) material. The panel is produced in five colors.
"Our joint project demonstrates that DirectSkinning is ready for series production and can be used to manufacture injection moldings with high-quality, colored decorative polyurethane surfaces for vehicle interiors," stated Michael Baumeister, head of production and logistics at fischer's facility in Horb, Germany.
In DirectSkinning, the "skin"—PUR coating—is applied using reaction injection molding (RIM) equipment directly to an injection molding part in the same mold in which the thermoplastic parts are formed (the process also has been developed for use in multiple molds). In this case, the moldings fischer processes are from a polycarbonate/acrylonitrile-butadiene-styrene (PC/ABS) blend, Bayblend T85, also supplied by Bayer.
After molding of the thermoplastic substrate, the PUR system is injected into the closed mold via a mixing head, coating the substrate. "When a rotary-table or swivel-platen mold is used, the two production steps can be performed in parallel, for example, thus ensuring short cycle times and high productivity," explains Andreas Bürkle, who is in charge of the DirectSkinning project at fischer automotive.
The thickness and color of the PUR coating layer can be controlled. The investment and floorspace required is less than if two machines—one each for injection and RIM—are required, and more significantly the logistics are simplified as parts are ready to ship as they leave the processing cell. Also significant is that no paint lines are required.
According to Bayer, the light stability of the decorative panel's polyurethane surfaces has been tested via heat aging, hot-light aging, climatic change, and solar simulation testing, with that testing showing virtually no surface defects, discoloring, yellowing, or hardness fluctuations over the service life of the component. —[email protected]