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A lightweight transmission crossmember using a zero-waste process

News International-French

26 Mar 2019

A high-performance molding compound from Hexcel has been used to produce a carbon fiber-reinforced plastic (CFRP) transmission crossmember using a zero-waste process ideal for high-volume manufacture. The automotive part is comparable with aluminum versions in terms of its performance and price, but could be 30–35% lighter.

A lightweight transmission crossmember using a zero-waste process

A lightweight transmission crossmember using a zero-waste process

The transmission crossmember has been developed by Hexcel and the Institute of Polymer Product Engineering (IPPE) at the University of Linz, Engel and Alpex.

Hexcel's Director of Sales and Marketing for Automotive, Achim Fischereder, says:

"These parts connect either side of a vehicle's chassis together and support its transmission, and must be stiff, strong, and resistant to fatigue. As they are exposed to the road, they must also be resistant to stone chipping and corrosion caused by water and salts."

To meet these requirements, the partners selected HexMC-i 2000, which is the best-performing molding compound currently on the market, to produce the part. HexMC-i 2000 has been designed specifically to bridge the price–performance gap between sheet-molding compounds (SMCs) and prepregs, and is stiffer than steel at approximately a fifth of the density. Further, its mechanical performance is highly consistent. 

HexMC-i 2000 comprises randomly orientated rectangular chips of unidirectional carbon fiber-reinforced prepreg impregnated with Hexcel's M77 snap-curing epoxy resin to form a 2000gsm sheet material. The molding compound can cure in as little as two minutes to produce lightweight, strong and stiff parts.

The compression moulding of carbon fibre Sheet Moulding Compounds (SMCs) is a promising option for the high volume manufacture of structural carbon fibrereinforced plastic parts.

To produce the transmission crossmember, preforms of HexMC-i 2000 are laid up in molds fabricated by Alpex and compression-molded using a v-duo press that has been tailored for the application from Engel. Ribs, aluminum inserts and other functions can be molded into the part using the single-stage process, reducing component-count in comparison with metal versions of the part and keeping costs low.  

Crucially, any offcuts from the preforms can be interleaved between the plies of material to provide additional reinforcement in key areas—meaning that the process generates no waste whatsoever. 
Another option being explored by the partners is to transform these offcuts into carbon fiber mat prepreg using techniques developed by Carbon Conversions Inc. (CCI), a company in which Hexcel acquired a stake in late 2016.

Thanks to advanced finite element method (FEM) simulation techniques developed by IPPE, the design of the part is highly optimized, and it demonstrates the strength and fatigue-resistance demanded by the application. 

Achim Fischereder concludes:

"Hexcel is looking forward to working with our partners to further harness the benefits of high-performance HexMC-i 2000. Using the predictable, zero-waste process we have developed, we have shown that we can match the performance and price of metallic structural components while reducing weight significantly."