Cost efficiency through the use of UV-resistant plastics in dynamically and statically highly-stressed components: What really happened!

摘要

Requirements for plastics in the commercial vehicle sector are hard: plastics are brought to their limits not only by service lives considerably longer than of cars but also by their very high loading profile. Very high acceleration forces well into the double-digit G range are experienced in particular by components attached to the truck frame which means that generally speaking high-grade and insensitive plastics must be used here. Until now PET/PC blends have been used at MAN for large panel components in the bumper area. Their higher strength as compared with standard plastics was the decisive factor here. The disadvantage of insufficient UV resistance was solved by painting the components. In order to save the cost of painting for the black central area during a redesign of the plastic bumpers of the heavy TGS/X series, the blends were now to include ASA. Lower strength and toughness had to compensated by a clever design. This applies in particular to the large center section. With an unsupported span of 1.5 m, length variations of approx. ±10 mm occur in hot and cold conditions. To permit this change in length to occur without causing damage, various concepts were examined: 'floating' attachment points with selective freedoms of movement, crowning of the components, and the appropriate coordination between the unreinforced blends and the glass-fiber-reinforced load-bearing components. A structural component with a higher glass content has the positive effect of greater stiffness and the negative effect of lower longitudinal expansion compared with the unreinforced panels connected to it by welding. An optimum solution was achieved here by simulation and validation. The goal of a reduction in system cost was achieved, firstly, by the material cost savings due to the lower relative material costs of ASA as compared with PET/PC, and secondly by the omission of painting. With the switch to ASA a robust design was created which meets all the requirements.