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5th September 2019, Stamford, CT

Hexcel composites make rapid inroads in automotive

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The company is pursuing growth in the automotive industry. © Hexcel

The company is pursuing growth in the automotive industry. © Hexcel

Hexcel Group is currently building a solid platform to support its future growth in the automotive industry.

Around 70% of Hexcel’s business is with the commercial aerospace industry, but the company’s Industrial Products division is pursuing growth in a number of end-user sub-markets. One of these is the automotive industry, to which the company already supplies a number of products, including thousands of square metres of HiMax triaxial carbon reinforcements for wheels.

One key factor for building on this success, however, lies in taking a realistic attitude to what composites can and can’t do.

“If we think about replacing existing metal parts with composites without changing the design environment they are in, there are immediate problems,” says Hexcel’s Director of Sales and Marketing for Automotive, Achim Fischereder. “Composites are very different from metals, with different limitations and design boundaries. This extends to how they are integrated into the structure, too.”

Key differences

In addition, he adds, there are key differences between composites based on carbon and glass fibres.

“Carbon fibre-based products have a clear advantage when stiffness is the driving parameter for part design. Achieving a viable business case, however, is more challenging, due to the higher fibre price compared to glass fibre. When designers are looking for high energy absorption, which is critical for crash driven applications, or excellent fatigue performance, glass fibre-based products can actually be the better choice.”

One success story with glass fibre composites has been the development of HexPly M901 prepreg, developed specifically for leaf springs. In this application HexPly M901 offers a cure time of less than 15 minutes, even for very thick part sections, with 15% higher mechanical performance than standard prepregs and enhanced fatigue properties. HexPly M901 provides a Tg of up to 200°C, following post-cure and is available in areal weights of up to 1,600 gsm.

Hexcel supplies a number of products for automotive, including HiMax triaxial carbon reinforcements for wheels. © Hexcel

Hexcel supplies a number of products for automotive, including HiMax triaxial carbon reinforcements for wheels. © Hexcel

“This automotive industry application is highly cost-competitive and draws on the accumulated know-how from our wind energy business, where we have mastered the cost-efficient production of heavy weight glass prepregs,” Fischereder says. “Carbon fibre parts, meanwhile, can provide other advantages.”

Zero waste

He cites as an example, the use of HexMC-i 2000 for new vehicle transmission crossmembers.

Hexcel has developed a zero-waste process ideal for the high-volume manufacturing of these parts, which connect either side of a vehicle’s chassis together and support its transmission.

“Transmission crossmembers have to be stiff, strong and resistant to fatigue,” says Fischereder, “and because they are exposed to the road, they must also be resistant to stone chippings, as well as the corrosion caused by water and salts.”

HexMC-i 2000 comprises randomly oriented rectangular chips of unidirectional carbon fibre-reinforced prepreg impregnated with Hexcel’s M77 snap-curing epoxy resin. The moulding compound can cure in as little as two minutes to produce lightweight, strong and stiff parts.

Achim Fischereder, Hexcel’s Director of Sales and Marketing for Automotive. © Hexcel

Achim Fischereder, Hexcel’s Director of Sales and Marketing for Automotive. © Hexcel

Designed specifically to bridge the price-performance gap between sheet-moulding compounds (SMCs) and prepregs, HexMC-i 2000 is stiffer than steel at approximately a fifth of the density and its mechanical performance is highly consistent.

Transmission crossmembers based on it are comparable with aluminium versions, in terms of performance, but can be 30-35% lighter. They are produced by preforms laid up in moulds and compression-moulded. Ribs, aluminium inserts and other functions can be incorporated into the part in a single-step moulding 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 and as a result, the process generates no waste whatsoever.

Hybrids

Hexcel also sees great potential in hybrid structures of composites and metals.

“In crash-related structures, metal can be very effectively locally reinforced with composite patches and we have also proven that prepreg patches can be used for NVH management. This concept was used, for example, to modify the vibration behaviour of an aluminium subframe with carbon patches,” Fischereder explains. “The result was the same vibration behaviour as a 50% heavier steel subframe. In addition, the market has not yet fully explored the opportunities that arise from the combination of carbon and glass to yield the best part properties at the lowest possible costs.

Sleek surfaces

Hexcel materials including HiMax and PrimeTex fabrics, as well as HexPly XF3 surfacing films are also now widely employed in cosmetic applications, to provide vehicles with the sleek surfaces first popularised in Formula 1.

Carbon non-crimp fabrics. © Hexcel

Carbon non-crimp fabrics. © Hexcel

HiMax non-crimp fabrics are characterised by smooth flat surfaces which allow for high performance laminates with surface layers of PrimeTex fabric to achieve the woven carbon look. HiMax fabrics are further designed for resin infusion processing and can be further personalised with the HexStitch specialist stitching technique.

PrimeTex fabrics are flat woven and spread in both warp and weft, increasing their closure factor to 99.9%. The highly uniform fabrics are ideal for very lightweight structures, combining aesthetic appeal with high mechanical performance (including shear and compression strength) and very low porosity. Very light weight carbon fibres such as AS4 3K, at 98gsm and IM 12K, at 160gsm, are now standard products in the PrimeTex range.

B pillar. © Hexcel

B pillar. © Hexcel

HexPly XF3 epoxy surfacing films can further enhance surfaces and require minimum preparation for painting. They are co-curable with a range of HexPly prepregs at 120⁰C and above and are available in weights of 300gsm. They are extremely easy to handle, with good tack and drape and can also be sanded. In comprehensive tests, they have demonstrated excellent resistance to ageing tests.

A key example of superior surface finishing with these Hexcel materials is to be found in Lamborghini’s Aventador LP700-4 which features a carbon fibre composite monocoque. Hexcel’s HexPly M47 prepreg, reinforced with PrimeTex carbon fabrics, and XF3 surfacing film were selected to meet the technical challenges and high mechanical performance requirements for the carbon roof – along with a Class A finish.

Electric vehicles

Looking to the future, Hexcel sees a tremendous opportunity in the growth of electric vehicles (EVs).

Carbon roof. © Hexcel

Carbon roof. © Hexcel

“Most of our ongoing projects in the higher volume segment are for electric vehicles where requirements differ compared to internal combustion engine (ICE) cars,” Fischereder says. “The opportunities for composites in EV relate specifically to the integration of the battery into the car structure, as well as the changing crash test requirements which are linked to the higher car weight and the fact that in addition to the passengers, there is now also a battery that  needs to be protected. This is an area where we believe composites can provide very efficient solutions and the work we are doing with Volkswagen on hybrid metal-composite structures is an example of where the market is heading.

 “We are now ready to support designers of autonomous vehicles and flying cars and our unique heritage in aerospace and automotive surely makes us an ideal partner for those designing the vehicles of tomorrow,” he concludes.

www.hexcel.com

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