Lightweight and strong, plastic composites are increasingly used in automotive manufacturing but is Henry Ford’s all-plastic car concept coming any nearer to reality, asks Malcolm Wheatley
Located in a leafy suburb of the Canadian capital of Ottawa, the country’s National Research Council (NRC) is one of the world’s premier scientific and technology institutions, with expertise ranging from aerospace engineering to high throughput DNA sequencing, and from neutron beam physics to photonics and nanotechnology.
But as part of a programme of working closely with industry, the NRC has developed an innovative partnership with Magna Exteriors and Interiors, an operating unit of Magna International. The result is a joint Magna NRC Composite Centre of Excellence, located at Magna’s facility in Concord, Ontario.
Equipped with leading edge moulding equipment for thermoplastic composites, as well as high-pressure resin transfer moulding (HP RTM) machinery, teams from Magna and NRC work together on developing lightweight and durable automotive parts using plastics and plastic-based composite technology, intent on achieving the high volume, near-net shape, short cycle time environment required by the automotive industry.
It’s here, for instance, that Magna’s manufacturing expertise in direct in-line compounding and Direct Long Fibre Thermoplastics – now in its fourth generation – has been successively refined.
To appreciate the technology, relates Will Harney, executive director of R&D at Magna Exteriors and Interiors, it’s necessary to first consider how plastic and plastic-based composites are conventionally reinforced to develop highstrength, high-stiffness parts for automotive applications. Simply put, glass fibres comprise the core of the extrudedand- cut material pellets that are fed into plastic injection moulding machines as raw material.
“But the limit of the fibre is the limit of the pellet and so strength and stiffness are proportional to fibre length,” he explains. “In-line compounding adds fibre at the moulding stage itself, rather than incorporating it within the pellet. And by adding fibre at the melt stage at the time of the injection, you can cut the fibre to a longer length: 15-20mm, versus 6-12mm pellet length.”
Lightweight efficiency and strength
The prime impetus, of course, is to reduce vehicle weight, thereby shifting the power-to-weight ratio firmly in the direction of better fuel efficiency and reduced carbon dioxide emissions.
“A 10% reduction in vehicle weight offers 57% fuel savings, provided that the vehicle’s powertrain is also downsized, and 34% fuel savings if there is no change in the powertrain,” says Dagmar van Heur, vice-president at specialist performance plastics manufacturer Styron Automotive. “Overall, we calculate savings in carbon dioxide emissions of 25.3lbs for each pound of reduced weight over the life of the vehicle.”
Better still, plastics’ impact on performance is more broad than just fuel efficiency, speed and acceleration. Structurally, and on vehicle exteriors, for instance, plastics and plasticbased composites don’t rust and can have better impact-resisting properties. In vehicle interiors, they offer good scratch resistance, UV light stabilisation and ductility – even at low temperatures.
“More than 50% of a typical vehicle’s volume is composed of plastics and polymer composites, but these materials only account for approximately 10% of total vehicle weight,” says Keith Christman, the NRC’s managing director of plastics markets. “The use of plastic resins and composites in light vehicles has grown significantly during the last 50 years. The average light vehicle now contains 377 pounds of plastics and composites, 9.2% of the total weight. This is up from 286 pounds in 2000 and 194 pounds in 1990. In 1960, less than 20 pounds were used.”
Venkatakrishnan Umamaheswaran, director of automotive marketing at SABIC Innovative Plastics, a business unit of Saudi Arabian-owned plastics and chemicals manufacturer SABIC, agrees. “We see a global average of 160kg (353lbs) per vehicle on average – and we see that growing as the push to lightweighting drives automotive manufacturers’ agendas,” he says.
What’s more, he points out, plastics and plastic-based composites have a vital role to play in improving safety: “When used in crumple zones, lightweight plastic components can help absorb energy and save vehicle weight at the same time, as well as reducing space and volume requirements compared to steel-based equivalents, and shortening cycle times.”
Take, for example, the announcement in November 2012 that Mitsubishi Motors Corporation had selected SABIC’s next generation NORYL GTX 989 resin for the front fenders of its 2013 Outlander Sport crossover.
This application, the first automotive body panel to be constructed using the resin, leverages the improved mechanical performance of the material – a blend of polyamide and modified polyphenylene ether – and also delivers a 10°C improvement in heat tolerance, making it a candidate for use in higher temperature online painting. And from an environmental point of view, the use of plastic instead of steel reduced vehicle weight by 3 kg (approximately 7 pounds), potentially resulting in 45% less energy consumption and 47% less carbon dioxide emissions per fender over the vehicle’s whole lifecycle.
But the real story is the impact on manufacturing. The vehicle’s fenders are the first automotive body panels to be produced using two-cavity injection moulding with NORYL GTX resin, allowing Mitsubishi to cut cycle times in half as well as reduce tooling costs.
By adopting two-cavity injection moulding for the Outlander Sport’s front fender, which allows both the left and right fender components to be produced in one shot, the company was able to significantly cut cycle time. In addition, this approach significantly reduced capital costs because only one tool was created, rather than two separate tools. In Europe, Jaguar Land Rover’s new Range Rover Evoque, meanwhile, makes extensive use of Styron’s polypropylene based INSPIRE performance polymers, as well as the company’s heat resistant MAGNUM ABS resin. Each, it turns out, was selected due to characteristics such as improved processability, material durability in high-temperature environments, and a low level of carbon emissions associated with their production.
Better still, from a manufacturing point of view, both plastics come as self-colouring materials, offering eight colours within three assorted design themes, neatly combining just-in-time production efficiency and economy of supply with a high degree of end-purchaser flexibility of specification and choice.
VELVEX, another Styron plastic, is a reinforced elastomer recommended for unpainted interior trim applications, and is reckoned by Styron to offer better scratch and mar resistance together with a uniform low gloss than established materials such as most talc-filled polypropylene, polyamide/ ABS or ABS products.
Again self-colouring, it avoids vehicle manufacturers having to choose between unpainted materials without appropriate levels of scratch resistance or uniform gloss, and painted parts which met this requirements, but only at the increased cost of an additional painting step.
Obstacles to plastics’ progress
Recyclability, for one, is far more of an issue than it was even a decade ago – but also more complicated, as the varieties of plastic in a vehicle multiply beyond simple polypropylene and polyamide blends. So, whereas recycling once meant stripping a vehicle of major components with a value in the second-user market and crushing what remained, dismantling is now talked of as the likely best route forward.
“As with domestic recycling, the issue is developing the infrastructure,” says SABIC’s Umamaheswaran. “Legislation will probably be required and we see Europe acting as the driver for this at the moment. Among European manufacturers, Renault and BMW have made significant advances, but there isn’t a magic bullet and steel-plastic composite components, and other such hybrids, certainly complicate the proposition.”
“Today’s lightweighting agenda has typically involved using polypropylene and similar materials in applications such as bumpers and fascias,” says SABIC’s Umamaheswaran. “But look at newer applications and it’s often about replacing steel in structural areas: using NORYL GTX 989 resin for the front fenders of the Mitsubishi Outlander, for instance, saves around 3kg (7lbs).”
Similarly, he adds, it’s possible to replace heavy glass with lightweight, coated polycarbonate, at a weight-saving of around 50%. The curved rear quarter windows of Citroën’s DS5, points out Umamaheswaran, have won an award from SABIC for precisely this, using LEXAN GLX resin coated with an Exatec 900, a proprietary two-layer system that combines a weatherable underlayer with a plasma top layer for abrasion and scratch resistance, and protection from UV degradation.
“It’s a 3D design that cannot physically be executed with glass, and which also cuts overall glazing weight by one fifth,” says Umamaheswaran. “These are the largest rear quarter windows in production and also the first to use injection compression moulding to reduce residual stresses.”
“The engineers who are designing cars are metal engineers, and the problem that they have when working with plastics and plastic-based composites is that you need to design ‘in’ these materials, and not in metal: the characteristics are very different,” says Styron’s van Heur. “You don’t have fibres in metals and so the impact-resistance and strength characteristics are very different from fibre-reinforced plastics.” An example of this is the first full thermoplastic, mono material lift gate ever produced for a production vehicle, in the shape of the new Renault Clio.
Targeting a weight reduction of 10% as well as easy recyclability, engineering teams from Styron and Renault worked closely over a two-year period to develop a lift gate manufactured in thermoplastic from three separate parts.
CFRP simplifying cost and procedure
The more exotic the material, the greater the degree of unfamiliarity. While traditional carbon fibre approaches have proved prohibitive in terms of cost, for instance, today’s carbon fibre reinforced plastic (CFRP) technology is attracting attention because its offers both a reduced cost and simpler manufacturing processes .
BMW, for instance, has a joint venture with German plastics specialist SGL Group, with the intention of incorporating extensive amounts of CFRP in the BMW i3 urban electric car, slated for launch in 2013.
“BMW appear very serious about CFRP in a mass production manufacturing environment,” says industry expert Richard Gane, a 30-year blue chip consulting firm veteran, ex-automotive manufacturing engineer, and a director of procurement consultants Vendigital. “The technology is more like injection moulding than traditional carbon fibre: there’s no laying-up, or pre-preg, or resin transfer moulding. It’s really changing the economics of carbon fibre.”
Among vehicles currently in production, Audi’s A8 is generally reckoned to have made extensive use of plastic and plastic-based composites, including a 100cm x 85cm x 32cm spare wheel recess manufactured from Durethan, a 60% glass fibre-reinforced polyamide produced by German speciality chemicals company LANXESS, and then injection moulded to produce the wheel recess by Dutch company Vestalpine Plastics Solutions.
The 60% reinforcement delivers a significant improvement in stiffness compared to standard 30% glass fibre reinforced polyamide, reports LANXESS. Furthermore, as required by Audi for components that are to be located close to the exhaust system, it also retains its stiffness at high temperatures.
Coincidentally, back at Magna, engineers there too are proud of their contribution to the Audi A8. Indeed, points out the company’s Harney, Magna won an award from the Society of Plastics Engineers for the front end carriers it supplies on the Audi A8. These are manufactured through an injection moulding process that combines stamped aluminium reinforcements and a mat of reinforced thermoplastic material, which replaces traditional steel stampings.
“The mat is a unique, lightweight organic sheet which can reduce the weight of components and systems significantly, while maintaining the structure,” notes Harney. “Parts manufactured with this process can provide all of the features that injection moulded designs can offer, while also providing the structural requirements precisely where they are specifically needed.” That said, Magna’s eyes are firmly fixed on a greater prize – one again involving the joint Magna NRC Composite Centre of Excellence, but also pulling in expertise from Zoltek Companies Inc., the world’s largest producer of commercial carbon fibre, via a second collaborative partnership.
Its purpose: to develop low-cost carbon fibre sheet moulding compounds, combining Zoltek’s Panex 35 commercial carbon fibre combined with Magna’s EpicBlendSMC sheet moulding compound formulations and production expertise. The new material, named EpicBlendSMC EB CFS Z, will be part of the Magna Exteriors and Interiors’ EpicBlendSMC product line, allowing Magna to offer an expanded range of lightweight parts and sub systems for automotive, commercial truck and other markets. Additionally, Magna Exteriors and Interiors will be able to offer the EB CFS Z sheet moulding compound for sale directly to moulders.
“With this collaboration, we now have a strong partner in the development of carbon fibre sheet moulding compounds,” says Harney. “It’s a partnership that further positions Magna to produce lightweight products that help our customers meet the demand for more cost-effective energy efficient solutions.”
In short, plastics have made significant inroads into automotive manufacture in the past few decades and look set to continue that trend in future too.
