Composite Parts Made Fast

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Although composite materials are desirable for automotive use due to their weight-to-strength ratio, among other attributes, unless you’re talking about making comparatively limited production runs, the cycle time to produce parts is prohibitive. (And we’ll say nothing about the cost.)

Over in the U.K., the National Composites Centre (NCC) at the University of Bristol is working to create processes through which the cycle time for composite parts will be less than five minutes.

Work is being done on a 36,000-kN, upstroke short-stroke press from Schuler AG (schulergroup.com) that has a clamping surface of 3.6 x 2.4 m. 

According to NCC business development director Tom Hitchings, “We have installed the world’s largest, openly accessible, high-rate manufacturing press for composites.”

Hitchings notes, “This is aimed at supporting sectors such as automotive, where developing high-rate, low-cost manufacture of composite components is critical. This press is producing parts within less than five minutes.” Parts are being produced with the high-pressure resin transfer molding (HP-RTM) process. Carbon fiber fabrics are placed in a vacuum mold, the mold is filled with resin, then the parts are hardened by the heat and pressure generated by the press. Depending on the size of the part, resin pressures can vary between 60 and 150 bar.

To help speed the process, the vacuum mold is opened by just a few tenths of a millimeter, and the resin is quickly injected. This also helps make sure that the resin spreads on the carbon fiber mat thoroughly and evenly.

Through the use of HP-RTM, parts with complex geometries can be achieved. The process parameters help ensure that there is high surface quality and minimized pores or gaps. Because of variations that can exist in the part geometry, it may be that the mold center of loading is not in the middle of the press; parallelism control on the Schuller press maintains the appropriate orientation through the cycle.

In the upstroke, short-stroke press, the working stroke is performed by the bed plate that’s driven by several short-stroke cylinders. The advantage of this press configuration compared with a more typically downstroke press is that there are higher closing speeds—on the order of 1,000 mm/sec—and shorter pressure build up times: <0.3 sec.