Source: plastic.nstl.gov.cn
Multi-material refers to the technology of combination of a variety of materials in the body of the automobile, especially body skeleton and shell. In addition to the original iron and steel material, aluminum, magnesium, CFRP (carbon fiber reinforced composite material) and other lightweight materials are used. If a variety of materials are properly used on different positions, the body weight can be significantly reduced compared to that when only steel is used.
The technology of applying multi-materials will have to address the problem of cost. The cost of lightweight materials is often higher than that of steel. While a common welding method is used in joining steel parts, dissimilar materials cannot be welded the same way. In order to assemble the car body with dissimilar materials, a special welding technology needs to be developed, and factory production line also needs to invest in new equipments. Therefore, multi-material technology has only been applied in some high-end cars production.
Statistics show that when 10% of weight is reduced in a car, the fuel efficiency can be increased by 6-8%. The effect of weight reduction of magnesium alloy and carbon fiber composite material is relatively obvious.
Multi-material is the trend of the future
The global automobile industry is currently speeding up the development of multi-material technology. This practice can improve the engine fuel efficiency and reduce greenhouse gas emission. By using the technology, Mercedes Benz C Class reduces the weight of the white body (car body before painting) by about 70% compared with that of the previous generation. Its fuel efficiency increases by more than 30%.
In recent years, more and more automobile enterprises use the multi-material technology, especially manufacturers in Europe and the United States. In addition to Daimler, BMW AG launched EV i3 in November 2013 in Europe. CFRP is used in most parts of the EV i3 body. Ford’s best-selling pickup model F-150 2015 is equipped with the aluminum car body. The British Jaguar Land Rover launched XE in spring of 2015 in Europe. Aluminum accounts for about 75% in the surface area of the white car body.
It is understood that the developed countries in Europe, the United States and some emerging countries will tighten the exhaust regulations in future. For example, according to the European Union Law, at present the upper limit of CO2 in the exhaust emission of the newly registered vehicles is 130 grams per kilometer on average; by 2021, the average carbon emission of new cars sold within the EU shall not exceed 95g/ km, and by 2025 the automobile carbon emission is expected to be 68 to 78 grams. In 2015 China’s allowed emission of CO2 per kilometer of automakers (average value of vehicles sold) is 160g. By 2020, CO2 emission will be about 120g. By 2025, it will be only 116g.
Survey shows that by 2020 the body weight of gasoline car needs to be 12% lower than that in 2014, and by 2030 it needs to reduce by 37%, so as to reach the emission reduction goal set by Europe and the United States.
A variety of factors show that only by using multiple materials, different countries are more likely to reach the goal of lightweight automobile and long-term emission reduction. Despite the facts that the car manufacturers are facing such a pressure and the use of lightweight materials still has all sorts of problems, multi-materials is inevitablly still the future of automobile industry.
