Using CFRP in automotive: the 580g door


In addition to the glass reinforced door module which is now in volume production, Brose has also been presenting a door study based on carbon fibre. The polyolefin door may be up to 800g lighter than a conventional door, however the carbon door will achieve a weight saving in excess of 11kg by comparison to a metal door.


By contrast to classic plastic door systems, the carrier plate with its glass fabric reinforced PP will save around 350g of weight; by comparison to conventional steel doors the saving may even be as much as just under 1.2kg, whilst still retaining the same level of crash safety and high functional integration. (photos: Brose)

The carrier plate of the polyolefin door module features an intelligent material mix, saving 350g of weight compared to conventional plastic door systems and as much as 1.2kg compared to standard steel doors – while maintaining crash safety and high functional integration. Fitted with a lightweight window regulator drive and closure system, this design saves OEMs another 460g of weight per door. Brose already delivers weight savings today by using plastic for its door systems: in addition to the lighter base material, functional elements are integrated into the plastic carrier. Consequently, the number of components can be reduced, thus cutting weight and costs.

Bearing this in mind, Brose invested in a fully automated injection moulding system with an in-line compounding process as well as in relevant material research. The result is a highly economical injection moulding process with in-house material formulations for large-volume production. At the IAA 2013 the company was presenting the next generation of highly-integrated door systems featuring an intelligent material mix: the functional carrier consists of glass fabric reinforced polypropylene (PP) combined with functional elements made of long glass fibre reinforced plastic such as speaker holders, cable fasteners or holders.

However, the material process comprises only a single step: the heated mat of glass fabric reinforced PP is press moulded into shape while the functional elements of glass fibre reinforced PP are injection moulded. Weighing only 580g and featuring a carrier wall thickness of just 0.5mm, this solution is as safe as standard door systems in crash tests.

Holistic lightweight approach: every gram counts

For Brose as a system supplier, the weight of the complete solution counts. This is why all main door components are continuously being refined in line with the carrier plate development to make them lighter and more efficient. Two examples: a new high-end lock variant combines almost all drive performance tasks for a door lock in a multifunctional flex-pole actuator.

This new, electromechanical principle dispenses with up to three standard motors and consequently saves almost 360g of weight. An additional 100g of weight are saved with the smallest and most lightweight window regulator drive of the supplier’s product range.

Carbon door

The carbon fibre reinforced polymer (CFRP) prototype features a layered structure designed to withstand specific stresses, saving an additional 4kg of weight per door compared to aluminium and as much as 11kg compared to steel. Pinpoint strength thanks to material mix CFRP provides design potential for high-precision shaping of the wall thickness, fibre orientation and layer structure: where more strength is required, the material can be reinforced or the fibre orientation adjusted without affecting the ultra-thin wall strength in other areas. Thus, it is possible to dispense with reinforcement sheets used in standard systems against stress caused by door lowering, wind forces and torsion in the door inner panel.

Aramid fibres with increased ultimate strain for crash-relevant areas ensure crash safety whereas carbon fibres are used in areas requiring great strength and/or stiffness. The concept door also features an integrated side impact beam – a component that OEMs assemble in the outer door panel of standard door systems. At Brose, this crash-relevant component comes with a woven and thus flexible carbon fibre chamber profile, filled with integral foam. Additional costs that pay off due to long cycle times and low quantities, fibre composites are still regarded as unviable for volume production of high-quality vehicle parts.


Using the CFRP door structure, maximum functional integration can achieve a considerable reduction both in the number of components and costs. It is only the external skin that still needs to be mounted and bolted together and this means a considerable reduction in assembly costs on the part of the automotive manufacturer.    

According to experts, the material and production costs for carbon parts are likely to drop significantly by 2020. In addition, the composites industry is intensively exploring more efficient processing technologies to enable quick, reliable and low-cost production of high-quality CFRP parts: the cycle time of the resin transfer moulding (RTM)  process – particularly suitable for the production of shell parts – has decreased from approximately 15min to less than 5min over the last two years and this figure continues to decline. The pultrusion process or pull-braiding is used for profile parts such as the side impact beam. Here it is possible to manufacture straight and bent profiles in a continuous process at comparably low tool costs. Since both methods produce virtually no waste, material costs can also be reduced.




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