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RRIM Technology and Mold Filling Simulations in the Automotive industry
Updated: 2005-01-31 00:00 Source: share:

The BMW X3 aerodynamic package, which comprises more than 15 components including polyurethane front and rear valance panels, wheel arch trims, rear spoiler and side sills, is really taking off on the market. Many X3 owners are having the extensive range of accessories fitted to their vehicles by their BMW dealers to emphasize the car's sporty character and powerful contours, a tendency that mirrors the trend toward personalization in the automotive industry. Swiss-based Spider Industries manufactures the aerodynamic package using Bayflex? 180, a polyurethane from Bayer MaterialScience.
Just seven months or so after winning the contract from BMW, Spider Industries delivered the first accessory kit. "We were only able to achieve this fast turnaround thanks to the PUR-RRIM process, the cooperation between all partners involved and the many years' experience that Bayer MaterialScience, BMW and ourselves have with this technology," says Lorenzo Carlet, CEO of Spider Industries, a subsidiary of Lackiertechnik Weiss. The polyurethane RRIM (reinforced reaction injection molding) process involves mixing two liquid raw materials, a glass-fiber-containing polyol and an isocyanate, in a mixing head at around 180 bar and then metering the mixture into a temperature-controlled mold configured for an internal pressure of 60 bar. The two components react with each other in the mechanically closed mold to form the desired molded part. The major advantage of the process is that the internal mold pressure is lower than when processing thermoplastics, meaning the molds used are more cost-effective and can be produced faster than the steel molds needed for the injection molding of thermoplastics.

"Thanks to the support from Bayer MaterialScience, the molds were well-suited to producing the accessory components from the very beginning, so they could be fitted to the vehicle perfectly – despite, for example, the size and complexity of the front valance panel," says Bernd Laue, project manager at BMW Accessories. This was achieved through mold filling simulations, also known as mold flow analyses, which were carried out by the experts from Bayer MaterialScience before constructing the molds. For example, the BMS scientists were able to determine on computer the orientation of the fibers which strengthen Bayflex? 180. "Fiber orientation influences the material shrinkage, which in turn has to be precisely factored in by oversizing the mold in order to ensure an accurately-fitting component," says Dirk Brüning, a specialist in computer-aided engineering from the Bayer MaterialScience Polyurethanes Business Unit. The Bayer experts also simulated where air might be trapped in the molds during filling and provided vents at these points.

The project was realized quickly thanks to the advantages offered by the RRIM process and mold filling simulations, the latter making a key contribution to optimizing the manufacturing process early on.
The benefit of using Bayflex? 180 polyurethane to manufacture the aerodynamic package is its excellent flow behavior. "The material meets the high demands placed on external body components like the front and rear valance panels," says Dr. Andreas Stumpf of Bayer MaterialScience, team manager for Bayflex? RIM applications in automotive construction. Bayflex? 180 is noted for its high impact strength and molded parts made from it are not damaged by flying stones or other minor impacts. What's more, this special polyurethane grade displays extremely high dimensional stability – both in arctic cold and tropical heat.


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