Further weight reductions in passenger vehicles are needed to meet new fuel economy standards in China. Beginning in 2015, passenger vehicles in the country must reach an average fuel consumption of 6.9 litres per 100 km, compared with previous standards of 8 litres/100km.

Further efforts will be required to develop new materials and processing technologies to achieve the necessary reduction in vehicle weights, says Wan Xinming, vice president of China Automotive Engineering Research Institute. He was quoted by the China Plastics and Rubber Journal.

Wan says long fiber reinforced thermoplastics are one of the most important trends in automotive lightweight construction and he expects them to be a major material of choice because carbon fiber reinforced plastics are still too expensive for mass production.

Replacing metals with plastics can provide multiple benefits. For example, in 2008 a front-end module made of metal comprised 15 parts, while in 2014 an all-plastic frame with metal parts reinforcement can result in a 30% reduction in weight, as well as reducing the number of parts, says Xiong Fei, chief engineer at Geely Automobile. Similarly, a vehicle cross-beam made of plastic composite can weigh 2 kg, 50% less than its metal counterparts. And a wheel fender made of plastic can reduce the weight by 40%.

Shang Hongbo, chief engineer in the non-metal material department of the Beiqi Foton Automotive Engineering Research Institute, was quoted by the publication as saying that an oil tank made of plastics can reduce weight by one-third, as well as offering higher efficiency, design freedom and corrosive resistance. It is also anti-static and offers a long life.

Refining part structures is another way to reduce vehicle weight. Traditional bumpers made of general polypropylene with talc powder usually have a wall thickness of about 3 mm and weigh 4-5 kg. Currently some parts with a 2.5 mm or even 2 mm thickness are achievable. For high-strength polypropylene, Geely uses a 2.5 mm design that reduces weight by 0.8 kg, or 10-15% per part, says Fei.

On the machinery side, new solutions are being developed for fiber-reinforced plastics, including both glass and carbon fibers. Fibers help to improve stiffness and heat resistance, but adding them into plastics affects melt flow and demands higher injection temperature and pressure. Cedar Yang, from the design department at Zhejiang Hengdao Keji, says that a hot runner system is effective at optimizing the melt flow.

Other developments discussed at a recent conference include the use of thin-walled or foamed plastics. Honeycomb structures, in which a structure reinforced by glass fiber is sandwiched between two honeycomb panels, are becoming increasingly popular. The honeycomb structure provides high structural strength, strong mechanical properties and low VOC emissions, and reportedly can be produced efficiently and bonds well with woven materials.

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