Webasto AG

Low Pressure Injection-Compression Process for Panoramic Polycarbonate Roof Module

OEMs are increasingly eager to substitute polycarbonate for glass, for two reasons. First is the weight differential. A polycarbonate piece can be almost half the weight of the same piece in laminated glass. A second reason is the design flexibility and formability of polycarbonate, allowing shaping that follows design, as well as functional integration of such features as ribs, spacers, or guide rails that can be molded right into the panel.

Until now, polycarbonate was used to produce rather small pieces, such as headlight lenses and covers, backlights, small roof panels, small side windows and other small optical parts. Producing a large panel as big as a square meter of acceptable quality at a reasonable price was unattanable. For such a panel size, the injection process required injection at very high pressure, typically up to 1000 bar, which resulted in drawbacks in both the process itself and the ultimate quality and durability of the molded piece.

Webasto took up the challenge of producing a 1.2 square meter optical quality polycarbonate roof for the 2008 smart fortwo coupe. They innovated an advanced low pressure injection/compression process involving both angled and parallel plates, in an injection molding press requiring only one-fourth the clamping force of a conventional process. This resulted in a much smaller press with greatly reduced footprint and operating costs, but greater precision and low internal stresses as well.

They also innovated an in-line, all clean-room process with no interruptions for handling, trimming, or storing parts, with molding and coating in-line. They also innovated a coating process combining both spray and flow coating, to insure that the resulting coating layer is absolutely uniform across the part and of exactly the right thickness everywhere.

The new Webasto process is able to produce polycarbonate parts of this size reliably and cost effectively, with low internal stress, remarkable optical quality, high reliability, and durability.

Webasto with its innovative process has opened the door to a number of new polycarbonate-based automotive applications which could not be considered until now, due to the size of the parts, the expected quality and durability level, and the economics involved. They are being rewarded with new automotive applications.