According to gas and water assist technology company Maximator GmbH, the company has adapted its water assist technology for its high pressure resin transfer molding (HP-RTM) of carbon fiber parts for the new BMW 7 series. This is the first time Maximator has adapted a water assist system for use in structural fibre reinforced composite processing. The system is normally used for injection molding.

Maximator gave the technology to BMW’s plant in Landshut, Germany, where it was used for a curved round-section CFRP roof carrier structural part of the new BMW 7-series.

The equipment consists of a water treatment unit and a pressure unit. These were customized for the application at BMW: It has a 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, according to René Himmelstein, vice president sales and marketing for units and components at Maximator. The close proximity of the valves to the pressure unit was crucial to successfully implement the HP-RTM process.

Himmelstein said the type of component involved has previously had a foam core, around which the carbon fiber braiding is first applied, prior to impregnation by injection with epoxide 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 the carbon fibre 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 sufficiently to remove the part without deformation.

As the water is exposed to the typically high temperature arising in the HP-RTM process, 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.