The quest for higher quality at the same price point or retained quality at a lower cost has driven the automotive industry forward for a century. Yet in recent times, the game has dramatically changed. Through a combination of legislation, changing market demands and, to a lesser extent, integrity, environmental responsibility has become critical to vehicle manufacturers and suppliers. Many other industrial sectors have followed suit, but the guidelines outlining the
A consequence of replacing mild steel with virtually any other material is the likelihood that the manufacturer will also need to replace spotwelding with other joining technologies. “The new materials on the BIW horizon fall into four main categories,” says 3M Technical Sales Specialist Jeff Kapp. “There are highstrength steels, aluminium, composites - from SMC to high-performance carbon fibre composites - and cast magnesium. One thing they have in common is not being as readily spot-weldable as mild steel. High-strength steel is typically the first choice replacement material, but because of rather complex metallurgy, its performance is massively affected by the heat processes involved in welding. The effects in terms of stress concentration tend to be exaggerated. Adhesives are generally a much kinder joining process.” With regard to aluminium, one of the challenges facing manufacturers is the much greater co-efficient of expansion it has when compared to steel. Dimensional stability is also an issue, particularly as aluminium is more prevalent on larger, higher-quality vehicles where the quality of joins and accuracy of shut lines is perceived to be of greater significance. 3M has developed a 2K (two pack) adhesive that, without the need for processes such as induction heating, replaces spot welds applied to the hem for dimensional stability and stiffness. The product also offers improved sealing and anti-corrosion performance. “The 2K adhesive allows the parts to be semi-cured before they go into paint – so you achieve a much better level of dimensional stability,” says Kapp.
requirements for product improvement in the automotive industry are unique. Aerodynamics and tribology might nibble at the periphery, but the main agent of change has been materials science.
Lightweighting and a greater use of recycled material have become massive drivers in production, though each has to co-exist within the ‘cheaper or better’ mantra and fit the established development framework. All things considered, it makes for one of the most interesting upheavals in automotive history.
Lightweighting by JSP
A good example that ticks all the above boxes is PSA’s collaboration with materials supplier JSP. The expanded polypropylene (EPP) ARPRO foam seat core developed by the partnership has resulted in a rear bench seat for Citroën’s new C3 that offers a 2.2kg weight saving over the same seat in the outgoing model (see opening photo). The material, which is a common component in bumpers, door panels, headrests, etc., has recently been specified for seat cores by several other manufacturers, including Volkswagen, Porsche and Volvo, and while the choice of ARPRO is predominantly driven by its weight-saving advantages, it also has the potential to reduce tooling costs, improve body-in-white (BIW) flexibility and enhance ergonomics in trim and final assembly.
“ARPRO is a closed-cell material, an excellent energy absorber for front or side impact and occupant protection, providing a material structure that is very resilient,” explains JSP Application Development Manager Bert Suffis. “It’s used throughout the vehicle, but increasingly in seat cores where it can provide anti-submarining capabilities. Traditionally, a stamped BIW metal part or a complex wire-frame insert has done that job, but these solutions are heavy and require a higher manufacturing investment.
“With regard to investment, obviously integrating an anti-submarining ramp into BIW requires capital-intensive stamping tools and welding operations; usually a separate tool for each body shape derivative. Wire frames are less costly but are very heavy. The ARPRO seat core requires significantly less capital investment and allows greater flexibility with the platform because the BIW can be flatfloored.” Forming ARPRO for research purposes can be done without tooling, as the material has the same physical characteristics in prototype form as the mass-produced component. This helped in the rapid development of the new seat core. Initial results showed a like-for-like saving of 1.79kg, but through lower polyurethane seat content and a revised fastener system (made possible by the lower weight seat), the eventual saving was 2.2kg per unit. These advantages mean that rather than employing a complicated mounting mechanism, PSA’s line staff are able to clip the seat into the vehicle at a much faster rate.
“The core itself is a moulded part,” says Suffis, “manufactured using steam chest moulding, a relatively lowinvestment method of production. It uses aluminium cavity tooling rather than the hardened steel of an injection mould or stamping tools.”
A further advantage of the new core is the removal of hog rings. Instead of the usual fifty or sixty staples on the underside of the seat, the new seat is assembled by putting the polyurethane pad on top of the core, with the cover slotted and locked into the ARPRO. In addition to removing metal from the vehicle and making assembly easier, the new design also makes disassembling the seat at end-of-life a faster and simpler process.
A good example of the BIW flexibility offered by ARPRO is in Volvo’s XC60 SUV, where the integrated child seat requires a slightly different structure to the standard model. “With traditional measures a separate metal part would have been required; basically one version for a model fitted with the child seat and another for a model without the seat. Normally, this would have meant an extra tool. In co-operation with Volvo and the seat supplier, the ARPRO version was developed to use the same tool for both variants, so in addition to the weight reduction, the plant investment savings was considerable.”
Environmental swings and roundabouts
The greening of the automotive industry is usually viewed as one unified effort to make vehicles more environmentally sympathetic. In reality, the legislative requirements of different ‘green’ objectives are often at cross purposes, sometimes requiring a manufacturer to compromise one environmental programme to satisfy the needs of another. Volvo’s use of ARPRO is one of the company’s many initiatives in a wide-ranging environmental programme, but the process can create unforeseen problems.
“Certainly there are conflicts,” says Andreas Andersson, who is responsible for recycling in Volvo’s Environment department. “I have targets to meet that are based around getting recycled materials into new car programmes, and there are weight attribute leaders who have a similar remit to reduce weight. These two aims are not always compatible, so it is much harder to get recycled material into a new programme than it has been because reducing weight has become very much the focus of the industry. A few years ago, introducing recycled material was relatively straightforward, because you could create recycled parts weighing the same as virgin material. Now, with the onus on using lighter materials, manufacturing something from recycled materials isn’t always the most suitable course of action. It isn’t impossible to use recycled material in lightweight applications, but it is tougher and demands greater creativity.”
Andersson points to Volvo’s wheel arch liners as an illustration of his point. These were previously formed using only recycled plastics, but in 2009, Volvo targeted a 30% weight saving for the part. Unable to develop a moulding process which delivered the required reduction using recycled material, Volvo eventual adopted a hybrid mixture containing 50% reground plastic and 50% virgin polymers. It hits the weight target and is typical of the everyday compromises many manufacturers are now making.
Volvo’s environmental credentials are well known, but even so, the carmaker needed to alter its material selection and manufacturing preferences to meet the demands of legislation, in particular the EU’s End of Life Vehicles (ELV) directive. “It had an effect on the way we think about manufacturing and the product,” explains Andersson. “It was obvious that we needed full material disclosure, so the first thing we did when ELV came in was set up a reporting system for our suppliers, effectively controlling the materials they delivered to us. For instance, the heavy metals that were part of the ELV: we needed to know exactly where they were and how much was being used in the supply chain. We needed to follow the trail back to the source and phase them out. That’s when we began to create a materials database that we still use today. Mercury and cadmium did not present too large a problem as we did not use much of those. Phasing out lead was more difficult and getting rid of hexchromium was a tough job.”
The work done to remove heavy metals in Volvo products has a direct influence on the ways in which recycling is approached. Without the inherent hazards, careful dismantling has given way to shredding. “We used to do a lot of design for disassembly and dismantling, but over the last few years that has changed. Now, in common with most of the European automotive industry, our strategy is geared towards using a shredder and applying after-shredder technologies to separate the materials: magnetic separation; floatation; density separation, etc., all manner of techniques that sort the vehicle back into its constituent components. Today the role of product designers and production planners is not so much to create a vehicle that can be dismantled, but instead to ensure the vehicle doesn’t contain any hazardous materials that would cause problems in the shredding operation.”
Material reuse at Ford
The notion of automotive components being recycled into new automotive components certainly has an admirable neatness, and the industry is quick to highlight such success, but often it isn’t the preferred route. “Our absolute driver is to minimise what goes to landfill,” says Mike Rivers, ELV Manager at Ford. “We are focussed on reducing the cost, the waste and the environmental impact of landfilling. We would like to reuse, but where that isn’t possible, the next step is to recycle. Metal is very simple and largely takes care of itself, but plastics are more complicated. We don’t necessarily have a preference to recycle for automotive use but in many cases, we require our suppliers to incorporate a percentage of recycled matter, meaning automotive materials get sucked back into the system. ” End-of-life isn’t the only recycling point. Ford has been particularly adept with its recycling of damaged components, in particular the vast tonnage of bumpers that it retrieves from its dealer networks. “Instead of putting a damaged bumper into a landfill, we ask our dealers to use the equipment racks they send back to our depots to return bumpers to us.”
The waste bumpers were exclusively recycled into new bumpers, but as Ford dealers repair cars from other OEMs – with different plastic types – Rivers says the carmaker had to look to other areas for reuse of the material. “We now sort the plastic and granulate it for use in a range of applications. We still do bumpers, but also washer fluid bottles and bottle tops, batteries, wheel-arch liners and other products for which visual quality is not essential. The important part is that over 98% of what comes back to us is recovered and recycled into something useful.”
Recycling carbon fibre
Exotic materials have long been the staple of equally exotic cars, but as the law of diminishing returns sets in for conventional materials, the quest for weight saving sees exotic become less so, and more commonplace in mass production.
Carbon composite brake discs are lightweight, longlasting - and very expensive. Disc manufacturers put forward €80,000 as the vehicle price point where such parts become economically viable, a number that represents only a small fraction of the total market. Yet the so-called Rebrake programme is investigating the possibilities of using recycled and scrap carbon fibre in order to reduce costs to where carbon composite discs might appear on cars costing €40,000, opening up the possibility of using the material at the upper end of the mass market sector.
Rebrake involves various automotive and non-automotive specialists. Ceramic disc specialist Surface Transforms is joined by high-performance disc system specialist AP Racing and other experts from the fields of rail, aerospace and industrial braking. Federal-Mogul is working on a compatible brake pad, while the UK’s Loughborough University is an academic partner.
Carbon fibre-reinforced silicon carbide matrix composites (C/SiC) have the potential to be used in high-performance brake applications because of low density and superior friction performances at elevated temperatures. Unlike racing brakes, which use a carbon-carbon friction coupling, they work when cold, making them suitable for road use. Further, with a specific gravity of around 2.2, they are 70% lighter than a typical iron disc.
“It’s a big saving, especially on a road car where the disc is an unsprung rotating mass,” says Anthoni Sznerch, Business Development Director at Surface Transforms. “Designing from the get-go with a ceramic disc means the suspension upright and all of the suspension geometry could also be lighter. Aside from the environmental issues associated with weight saving, less weight means less inertia to stop. By losing unsprung mass for the same suspension system, the car becomes more stable and thus more manoeuvrable, with less of the gyroscopic effect trying to drag the wheel off its hub.”
The bigger picture
In a similar way to the arguments surrounding electric cars, the environmental credentials of carbon products are challenged when viewed holistically. Reduced emissions at point-of-use are largely meaningless if they are achieved through increased emissions in the manufacturing (or power-generating) process. The heat-intensive process required to produce carbon fibre automotive products isn’t a natural fit with a green agenda, but Sznerch argues that in the case of discs, the criticism isn’t entirely valid. “A carbon-silicon carbide rotor does take time to make and is quite energy intensive, but the benefit comes over its lifetime and usage. Alongside the weight saving, a carbon ceramic rotor doesn’t wear out and doesn’t fatigue. It should be good for the lifetime of the vehicle, whereas you might change metal rotors two or three times. Looking at energy usage in those terms, these rotors do have advantages.” The project started by looking to utilise off-cuts of carbon fibre pre-preg material and recycled carbon composites, ground down and converted back into a milled carbon, though the use of recycled material has been sidelined. “We looked at including it in the (brake) pad formulation, but didn’t see any particular benefit to including it in our standard ceramic formulation,” says David Pindar, Friction Products Research Manager at Federal-Mogul’s Friction Technology Centre. “It wasn’t detrimental, but if you consider a pad is designed to wear out, and most of the ingredients you could use instead are readily available and at relatively low cost, there isn’t any particular benefit – but that doesn’t mean something won’t be discovered in the future.” “We’re making more mileage from the off-cut route,” agrees Sznerch. “Around 30% of carbon fibre fabric is scrap. The material is supplied on a roll and sheets are cut from it; even with the most sophisticated nesting programmes a lot is left on the cutting table. It also has a limited shelf-life; in the aerospace sector, it is instantly rendered unusable the day after it’s expiry date. Realistically, it’s still good for a couple of years in terms of its chemical capability.”
Is there enough material available to guarantee viability for a mass-market automotive product? “We think so,” says Sznerch, “though it is difficult to quantify. But one of the instigators of this project is the fact that carbon fibre use is increasing, and is forecast to increase quite dramatically over the next 20-30 years. As usage increases, so the availability of off-cuts will increase – so supply will be on a growth curve, and we think we can take advantage of that.”
While metal replacement was the hot topic for plastics suppliers ten years ago, in many cases the replacing materials had their own usage issues. Now those plastics are increasingly being superceded by newer engineering polymers designed with modern applications in mind. Eastman Chemical has a long association with the automotive industry. Its Tenite cellulosic materials created the first soft-touch instrument panels and the material continues to be used. The company’s adhesives and coating additives have also come to the fore; a newly-developed co-polyester with the brand name Tritan is the latest product to be introduced for the automotive sector.
“If you talk to vehicle OEMs or Tier One suppliers, the topic tends to be future needs, and understanding where trends are pointing,” says Marty Boykin, Eastman’s Market Development Manager for Tritan. “As a raw material supplier, we must be aware of future trends in the industry and develop products that better meet those needs. Recycling is important, lightweighting is important, reducing VOCs is important. When enough people are asking for the same things, the plastics industry is very good at solving problems.”
“Historically plastic has been used for metal and glass replacement. Twenty years ago, headlamp covers were made from glass; today it’s rare to see something that isn’t polycarbonate. Body panels have gone from steel to aluminium to composites and thermoplastics, and we are looking at a continuation of that trend. Today we’re not offering materials that will change the landscape in the way that metal replacement did, but we are beginning to offer plastics that will present improvements vis-à-vis other plastics, particularly in areas such as impact resistance, chemical resistance and, in some cases, process cost. “Tritan has properties that are similar to polycarbonate and styrenic-based polymers, with very high impact resistance, tensile strength and high elongation. It offers good chemical resistance and it’s clear with very high light transmission. It fits into applications for lenses and optics, but can also be coloured and blended with polycarbonates or ABS.”