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Düsseldorf — One key to increased penetration of carbon fiber-reinforced composites in the auto sector is reducing processing costs. The latest resin transfer molding (RTM) technology from KraussMaffei is touted as a high efficiency option that could accelerate adoption of such composites.

October 16, 2013

2 Min Read
K 2013: Carbon fiber-polyurethane composites produces class A finish

Düsseldorf — One key to increased penetration of carbon fiber-reinforced composites in the auto sector is reducing processing costs. The latest resin transfer molding (RTM) technology from KraussMaffei is touted as a high efficiency option that could accelerate adoption of such composites.

A production cell giving live demonstrations at the KraussMaffei booth (15/B27/C24/C27/D24) was manufacturing a production-line-ready carbon-fiber-reinforced roof shell with a polyurethane matrix (PUR) for the Roding Roadster R1 sports car. The component can be used as is, or painted straight away because the fiber structure is not visible on the surface.

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The quick closing movements of the RTM mold carrier in the CFRP production cell ensure that process times are short.

Class A surfaces are assured through adoption of a two-stage process. Explains Nicolas Beyl, President, Reaction Process Machinery at KraussMaffei, "Firstly, a carbon fiber preform is robotically placed in an RTM compression molding tool and impregnated with a PUR matrix material (from Henkel). This 2-mm-thick semi-finished part is then robotically transferred to a second RTM compression molding station where the 0.2-mm-thick surface layer, an aliphatic polyurethane system from Rühl, is applied to form a UV-stable surface coating." The part is then trimmed to its final shape. Overall fiber content of the final part is about 50%.

The polyurethane for both the part core and its surface is poured in when the mold is slightly open (compression RTM). This produces only a very low flow resistance, which allows injection of the polyurethane system with high pour rates. Then the mold is closed and the part is shaped. The process not only improves fiber wetting but also prevents fibers from moving around to any great extent.

Two RimStar Nano 4/4 metering machines equipped for high-temperature processes - in which material temperatures can reach up to 80 °C - are used to prepare the polyurethane resin matrix. The wear-optimized design of the pumps in the RimStar series ensures long-lasting process reliability with all current matrix systems such as polyamide (PA), polyurethane (PUR) and epoxy resin (EP). The machines have a special vacuum-assisted storage tank system and an extremely precise, energy-efficient temperature control system with a stable operating point right up to the mixing head.

The 950-kg Roding Roadster R1 vehicle - with an output power of 320 hp and a carbon fiber content of 120 kg - successfully demonstrates the potential of modern lightweight construction. The vehicle is manufactured by Roding Automobile GmbH, a German technology company that specializes in developing and producing lightweight structures from carbon-fiber reinforced plastic.

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