René Ring's team at the plant in Georgsmarienhütte, Harderberg was responsible for the mold development. "We apply a master mold and use several mold packages for the different rim diameters. This gives the customer a lot of flexibility." The subsequent process is then as follows: A carbon preform, prepared by the customer, is placed over the inner core of the mold, and four sliders, which form the round outer contour of the rim, then move simultaneously. The press closes and the epoxy matrix material is metered through a distribution star. After a curing time of approximately 15 minutes, the mold opens, the sliders open and an ejector ring presses the rim body, which has shrunk to the core (diameter 20 inches), upwards. The mold is flexible from diameter 18 inches to 22 inches with the rim width from 8 inches to 12 inches. The finishing takes place through a series of downstream processes.
The know-how is in the mold
The many moving parts in the mold were cause for the greatest challenge, which was to seal the complete system at a high cavity pressure. Normally, the pressing force alone is sufficient to seal a mold, where the horizontal sealing surface is located solely between the upper and lower parts of the mold. In the case of the rim project, however, the undercuts and C-shaped contours of the part required the four sliders to make demolding possible at all, not to mention the moving ejector ring. To retain the vacuum in the mold and thus prevent low-viscosity material from escaping, the team strove to achieve the best possible manufacturing precision and with it a good design. The locking force is generated by four barrels on the top of the master mold, and locking elements mounted underneath, which move into recesses on the sliders and block them. With a mold temperature of 120 to 130 degrees Celsius, it was necessary to protect the pneumatic and electronic components with insulation boards.
The mold weighs a total of 4.9 tons. It was manufactured in 2023 in Harderberg, then prototyped in the KraussMaffei TechCenter in Munich, where it was optimized once again, and finally delivered with the complete system to the customer. Since the fundamental requirement of a rim is that it is round, René Ring's team is particularly proud of the fact that, "we achieved a concentricity precision of less than 2/100 millimeters." But not only that. Another remarkable achievement was successfully producing a good part with the very first shot.
The carbon rim has already been exhibited at the JEC Composites Show in Paris and R&D Manager Tyson Hsiao praised the excellent collaboration. "It was important for us to have an experienced, full-service provider for HP-RTM at our side, who offered great proficiency in systems, processes and mold technology. This gave us the ability to concentrate on our role: the production of the carbon blanks. As a result, the cogs meshed, producing a perfect wheel."
