As the use of plastics in automotive manufacturing continues to expand, with many options available today.
Linde Gases started to get into the automotive industry around 15 years ago as a natural consequence of its involvement with the foaming of plastics. The progress was evolutionary rather than revolutionary, taking the company from foams for mattresses and insulation boards into car seats.
“We added more applications, such as gas injection moulding for hollow plastic parts, such as door handles,” says Ralfe Heniger, head of the plastic and cryo team at Linde Gases. Heniger anticipates increasing sales in the automotive industry over the next ten years. “About 150kg per car is currently made of plastic; we expect to see that grow,” he says.
The proportion of plastic has also grown over the past decade or so, although the increase has not been constant. There was a pause, even perhaps a reverse, three years ago but the upward trend has now resumed. This is due to the fact that suppliers and converters of plastics are finding ever more applications for polymers and their compounds, including powertrains and high temperature areas. As the drive for lighter weight continues, the impetus to innovate is maintained. How far can this trend go? The limit seems to be set only by imagination.
Toyota’s ME.WE concept, which was designed by Jean-Marie Massaud in collaboration with ED2, Toyota’s European design and development centre, has a tubular framework of aluminium and body panels made from foamed polypropylene (PP). Bamboo is the material of choice for the roof, floor and bonnet. The body as a whole tips the scales at just 14kg, while the entire road-legal vehicle, complete with powertrain, weighs just 750kg. This makes it 20% lighter than compact B-segment cars.
The world may not yet be ready for ME.WE and it could be some years before its unusual looks are widely seen on the road, but other cars with high plastic content are already in series production. The BMW i3 electric car has a passenger compartment made from carbon fibrereinforced plastics (CFRP). With all its batteries in place it weighs 1,195kg, which is comparable to a conventional vehicle with internal combustion engines and a full tank of fuel.
Realistically, however, both the i3 and the Toyota concept car are at the outer limits, representing the new frontier of automotive design and production. The more prosaic advance of plastics has occurred piece by piece – be it an underfloor panel which improves airflow, an engine cover, or thermoplastic parts on the tailgate of the latest Range Rover Sport.
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Each piece does make a difference. DSM, one of the world’s leading producers of polyamide (PA) compounds, supplies a Stanyl PA 4.6 which is used to make a chain tensioner that is fitted to Audi engines. It is lighter than the part it replaces and also has lower friction characteristics. This is calculated to reduce emissions by 2g/km, which may not sound like much but represents about 2kg per month, ie 24kg each year. Similarly, a brake pedal which has been jointly developed by Lanxess and BondLaminates is made of PA 6 with 47% glass fibre reinforcements; at 355g, it is 50% lighter than steel components. Interior applications for non-traditional materials range from air vents for heating and cooling to door handles, steering wheels and entire dashboard carriers. BASF’s Elastoskin I polyurethane spray system can be used for high-grade, softtouch surfaces such as instrument panels, door modules, armrests and centre consoles. Elastoflex E, meanwhile, is designed for back-foaming.
The Opel Astra OPC/Vauxhall Astra VXR sports coupe has a seat shell made from a BASF Ultramid thermoplastic laminate with endless fibre reinforcement and was the first production vehicle in the world with a seat shell based on this technology. An unreinforced grade serves as impregnating material for the glass fibre fabric, while an impact-modified, short glass fibre-reinforced Ultramid is used as the overmoulding material for the essential ribs and edges of the part. It is produced by conventional injection moulding and the high strength of the laminate enables the wall thicknesses to be reduced considerably, which helps to cut the weight of the seat shell by 45%.
A similarly large contribution in terms of area and weight saving, and a major step forward in technique and application, can be found in the Mercedes SLK convertible.
The base version of the car is equipped with an electrohydraulic vario roof system with a 0.8 sq. m element made of Bayer MaterialScience’s Bayblend T85 XF. The PC+ABS roof element, manufactured by Peguform of Germany, is claimed to exhibit high energy absorption in crash situations and retains resilience even at temperatures well below freezing.
Its temperature of deflection under load of 127°C (0.45 MPa, ISO 75-1, -2) enables the unreinforced material to satisfy the high thermal requirements placed on horizontal bodywork parts. High chemical and stress-cracking resistance is coupled with 10-15% better flowability, compared with standard material.
The advance embodied by this component is that it is fitted in a horizontal location and covers a large area, with low levels of stress and warpage, and yet without heavy ribbing and reinforcement.
While LED illumination is now quite common, improvements in lens materials have made them practical and reliable; the gassing and clouding which troubled headlight fittings in the past are now a thing of the past. The SLK features an ambient illumination system which uses a special colour setting of EMS-Grivory’s Grilamid TR 90 UV. The visible area of the lighting trim appears black in reflected light, while providing high and smooth transmission without colour changes in transmitted light areas. The material satisfies crash behaviour requirements.
Almost every week brings an announcement of a new material or technology for interior equipment, whether it’s BASF Basotect foam being selected for sound insulation on the Porsche Panamera or greater use of recycled PET in headliner fabrics. Technology advances are just as important. Linde’s gas injection technology helps to reduce weight by hollowing out the core of components like doorhandles, and to cut cycle time by improving cooling – again, by using injected gases.
Under-hood & powertrain applications
Siemens Corporate Technology in Munich, Germany, is collaborating with Roding Automotive in the development of wheel hub-mounted electric motors. A Japanese company, SIM-Drive Corporation, recently unveiled its SIM-CEL advanced all-electric car concept, incorporating in-wheel motors. The car, which aims at high performance including rapid acceleration, a high top speed and a 325km range, was developed in collaboration with 26 outside organisations including DSM Engineering Plastics.
DSM contributed to the development of three parts for the prototype: a body panel in EcoPaXX bio-based PA 410; a wheel cover centre cap in the same material; and a heat sink for the LED headlights in Stanyl TC polyamide 46. EcoPaXX is designed to replace metal and is at least 50% lighter. It is also claimed to have very good flow properties for an excellent surface finish, as well as sufficiently high temperature resistance to enable in-line painting along with the rest of the vehicle. It absorbs little water, has very good dimensional stability and enough elasticity to enable snapfit assembly.
Along with the development of concept vehicles, DSM has designed and produced an EcoPaxx crankshaft cover. This incorporates integral seals in PTFE and liquid silicone rubber (LSR), as well as various metal inserts. It will be used on Volkswagen’s new MDB modular diesel engine platform across its Audi, Seat, Skoda and VW brands. System costs for the EcoPaXX cover are claimed to be considerably lower than aluminium and the weight has been reduced too; the EcoPaXX grade is 45% less dense than aluminium.
Also under the hood, Röchling Automotive claims that its PP intake manifolds can achieve the same mechanical strength as PA, but with lower density and 15% cost and weight savings. VW is using the material on two reference engines: a one-litre, three-cylinder petrol engine in Brazil and Europe and a 1.6-litre, four-cylinder petrol engine in China.
Sumps have to handle heat and the potentially corrosive effects of engine oil – two characteristics which have ruled plastics out for a long time. However, the potential for weight saving was clearly too much to resist and polymer sumps are becoming quite widespread.
The complexity of its shape makes this component an ideal candidate for construction in plastic, according to Lanxess, as injection moulding is more efficient than metal production techniques. The developments in long fibrereinforcement technologies and adaptation to heat and differentials in coefficients of expansion between PA 6 and 66 grades have been so successful that the material is being used in truck engines.
Lanxess and BBP Kunststoffwerk Marbach Maier jointly developed a pan initially made of heat-stabilised PA 66 reinforced with 35% glass fibres, sold under the trade name Durethan AKV 35 H2.0. The model which entered series production is used in the 12.8-litre Euro-6 engines of the Mercedes Actros. After further analysis, 35% glass fibrereinforced Durethan BKV 35 EF H2.0 (PA 6) became the material of choice; its good flowability reduces wear on the tool, which helps in the complex manufacturing process of large truck sumps. The shot weight amounts to 8kg/part.
Evonik has established a very solid reputation on solutions for under-hood applications. Its 8000-series coolant line systems resist corrosion and vibration-induced cracking. The outer polyamide layer provides high low-temperature impact strength, better resistance to stone impact and more chemical resistance than elastomer hoses. They can withstand external temperatures exceeding 150°C for brief periods.
Going still deeper, Evonik’s Vestakeep high-temperature polymer has a melting point of 340°C and a continuous working temperature of 250°C, which makes it suitable for overmoulding with die-cast aluminium. The low-friction properties of Vestakeep 2000CF30, a medium viscosity, 30% carbon fibre-reinforced compound, are claimed to make it suitable for use in the bearings and gears of transmission systems.
Sunroofs, engine supports & beyond
Dutch company Polyscope is a leader in the development and production of styrene, maleic anhydride and N-phenylmaleimide (SMA and SMANPMI) terpolymers, which it markets as Xiran. The company’s recently launched Xiran IZ grades are designed to be highly efficient in increasing the high heat performance of engineering plastic, especially styrenics. They offer a glass transition temperature (Tg) of 175°C or higher and can be exposed to greater processing temperatures. Citroën’s DS3 uses Xiran grades in its large thermoplastic sunroof frames.
In slightly cooler surroundings, VW’s up! has an eccentric tensioner with a tension pulley developed by Schaeffler. ContiTech supplied the timing belt that drives the camshaft, shock absorber mounts and membranes for regulating fuel flow.
Meanwhile, BASF’s world-first plastic engine support will be used to locate the six-cylinder diesel engine in the new Mercedes GL Class. The part is moulded from Ultramid A3WG10 CR, a highly reinforced specialty polyamide which has been optimised for high mechanical loads and is 30% lighter than aluminium equivalents. The company is now working on the development of injection-moulded thermoplastic components which are reinforced with steel cord fabrics, in partnership with steel cord manufacturer Bekaert (Belgium) and Voestalpine Plastics Solutions.
Chemical companies are also involved in load-bearing areas. DuPont Performance Polymers recently debuted Jounce Bumper, a spring used in car shock absorbers which is made from Hytrel TPC-ET, and has launched a range of long-chain polyamides, including modified 612 and renewably sourced 610, which are aimed at replacing PA 12 on brake and fuel systems applications.
The reach of plastics in automotive manufacturing seems set to continue. Toyota’s ME.WE and the SIM-SEL concepts may look outlandish today, but the ideas their predecessors demonstrated are now commonplace. The likelihood is that a new evolutionary stage is not far away.