Carmaker BMW AG has started using water assist for its high pressure resin transfer molding of carbon fiber parts in its new 7 series car.
Maximator GmbH of Germany developed the technology, which is normally used in injection molding, for use for the first time in structural fiber reinforced composite processing.
At Fakuma 2015 in October, René Himmelstein, vice president sales and marketing for units and components at Maximator, spoke about the equipment supplied to BMW's plant in Landshut, Germany, where it is used for a curved section of a CFRP roof carrier structural part of the new BMW 7 series.
The new 7 series launched at the Frankfurt auto show in September, and BMW advertising focuses on its extensive use of carbon fiber.
Maximator equipment installed at BMW in Landshut consists of a water treatment unit and a pressure unit. These have been tailor-made for the application at BMW, as has the special water injector with multiple integrated monolithic valves, resulting in it being much larger and heavier than injectors conventionally used with water assist injection molding, Himmelstein said. Key to successful implementation in HP-RTM is the close proximity of the valves to the pressure unit.
Himmelstein said the type of component involved has previously had a foam core, with carbon fiber braiding applied prior to impregnation by injection with epoxy resin. In the new water assist version, a plastic tube has replaced the foam core and is held under water pressure in the compression mold during carbon fiber braiding application from a braiding machine installed at BMW Landshut. The water is removed only after the resin has cured in a HP-RTM compression mold .
Because of the high temperature in HP-RTM, a combination of pure, demineralized water and particular metal alloys ensures that no corrosion occurs. The curing process, and therefore cycle time, was minimized to an acceptable level for serial production by heating the water. Himmelstein says there was close cooperation with the press producer, toolmaker and epoxy resin supplier.