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Bayer, Krauss-Maffei Process Cuts Molding Costs
RIM teams with injection molding for automotive interior parts
Doug Smock, Contributing Editor -- Design News, May 13, 2007
A new process developed in Germany significantly reduces the cost to apply a decorative skin of polyurethane to injection molded thermoplastic.
“We see good potential for the new technology particularly with coated parts for car interiors – for example armrests, decorative trim, door handles, post finishers, glove compartment flaps, center consoles and slip-resistant trays for the center console,” says Rainer Protte, who is in charge of the development project at Bayer MaterialScience AG. It may able be possible to use the process to produce components such as door liners and instrument panels. Possible applications for automotive bodywork include colored decorative strips or post-finished coated with a clear coat (deep gloss).
In the new process, a thermoplastic material is fed into a mold through one barrel of an injection molding machine while a reactive polyurethane stream is injected using mixhead technology developed by Krauss-Maffei Kunststofftechnik GmbH.
After thermoplastic is injected into the first mold cavity, the mold opens, and the molded part is moved into a second cavity, using a sliding table or a swivel-platen molding machine. After the mold closes again, the reactive two-component stream is pumped into the cavity. While the polyurethane is curing on the thermoplastic part, the cycle is simultaneously beginning again in the first cavity.
Variable Thicknesses
The process allows a wide variety of layer thicknesses, tactile properties and cosmetic finish. Coatings can be applied that are less than 1 mm or as thick as several millimeters in solid or expanded form.
The technology was tested on cup holder trim for a luxury class car already produced through conventional systems by fisher automotive systems of Horb, Germany, and Auburn Hills, MI. The cup holder is made of a blend of polycarbonate/ABS, and the decorative coating is an aliphatic two-component system that is still under development. Bayer says the urethane adheres well to the ABS/PC and does not display streaks, bubbles or color separation.
Design of the mold was a challenge, however, because the viscosity of the polyurethane system prior to curing is very low compared to thermoplastics. The mold developed by Fisher needed to be very accurate and well ventilated.
In the production system currently used by fisher, parts are molded and then sent to a coating line, which uses a second tool. The new process avoids logistics costs as well as the cost of the second tool. Yield rates rise because there is no chance of the plastic part becoming soiled or damaged before the coating is applied.
The process will not be commercially available until development work on the new reactive system is completed.
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 Automotive prototype shows finish of polyurethane and strength of thermoplastic. |
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