At present, the main development direction of automotive materials technology in the world is lightweight and environmental protection. The relative density of automobile plastics is low. Making exterior parts with plastics instead of steel can reduce the self weight of automobile and achieve the purpose of energy saving. Reducing the vehicle mass is one of the most effective measures to reduce the vehicle displacement and improve the combustion efficiency. It is estimated that the fuel consumption can be reduced by 6% ~ 8% for every 10% reduction in the vehicle's own mass.
Application of plastics in automobiles
1. Introduction to plastics
1.1 types of plastics
（1） According to the use characteristics, plastics are divided into general plastics, engineering plastics and special plastics. General plastics refer to plastics with large output, wide use, good molding and low price, such as polyethylene, polypropylene, phenolic, etc. engineering plastics refer to those that can withstand certain external forces, have good mechanical properties, high and low temperature resistance and good dimensional stability, and can be used as engineering structures Special plastics have special functions, such as fluoroplastics and silicone.
（2） According to the physical and chemical properties, it can be divided into thermosetting plastics and thermoplastics. Thermosetting plastics refer to those that can be cured or insoluble (molten) under heating or other conditions Thermosetting plastics have the advantages of good strength and heat resistance and are not easy to deform under pressure; the disadvantages are complex molding process and low production efficiency. Thermoplastics refer to plastics that can be heated, softened and cooled and hardened repeatedly within a specific temperature range. Its advantages are simple molding process, high productivity, certain mechanical properties and can be recycled; its disadvantages are heat resistance Poor, low stiffness.
1.2 composition of plastics
Synthetic resin is the main component of plastics, and an appropriate amount of additives are added to increase its process performance and service performance. Additives include fillers and reinforcing materials, fillers, plasticizers, curing agents, stabilizers, lubricants, antistatic agents, flame retardants, etc.
1.3 modified plastics
The characteristics of plastics are light weight, no corrosion, good impact resistance, high transparency, good wear resistance and insulation, low thermal conductivity, good general formability and coloring, low processing cost. The use of a large number of plastics in automobile design can comprehensively reflect the requirements for automobile design performance, namely lightweight, safety, anti-corrosion, beautiful appearance and comfort It is beneficial to reduce costs and save material resources. However, due to the poor dimensional stability, high thermal expansion rate, easy combustion and easy aging of ordinary plastics, many characteristics can not be compared with metal materials. Therefore, the plastics used in automobiles are not a single variety, but modified, also known as "modified plastics".
2. Lightweight embodiment of automotive plastics
Using elastomers and foamed plastics that can absorb impact energy and vibration energy to make dashboard, seats, headrests and other products can reduce the damage to human body during collision and improve the safety factor of automobile. Structural parts mostly use high-strength engineering plastics to reduce mass, reduce cost and simplify process, such as using plastics as some parts on fuel tank, engine and chassis.
3. Personalized development of automotive plastics
The use of automotive plastics also helps the development of automobiles in the direction of personalization. Plastic products have a large degree of freedom in design, and can be made into transparent, translucent or opaque products, with a variety of appearances. In addition, plastic processing performance is good, and complex products can be formed at one time and produced in batch, with high efficiency, low cost and remarkable economic benefits. If calculated by unit volume, plastic products can be produced The cost of is only 1 / 10 of that of non-ferrous metals.
4. Types of automotive plastics
With the continuous development of new plastic materials, plastics are expanding in the field of automotive applications:
4.1 application of nanocomposites
Thermoplastic polyolefin (TPO based) nanocomposites are used in automotive interior and exterior trim parts, which have the advantages of light weight, high dimensional stability, high strength and good impact resistance at low temperature. TPO nanocomposite automotive treads have been used in general motors cars, with high hardness, light weight, no brittleness at low temperature and easy recovery.
Toyota used nano polypropylene composite materials in front and rear bumpers, reducing the thickness of the original bumper from 4mm to 3mm and reducing the weight by about 1 / 3. Toyota has successively launched polypropylene nanocomposites for automotive interior parts.
The intervention of nanoparticles not only improves the strength, rigidity and toughness of the polymer, but also helps to improve the light transmittance, barrier, heat resistance and UV resistance of the polymer. Due to the simple processing and obvious effect, the industry is optimistic about the market prospect of polymer nanocomposites.
4.2 sprayable and non sprayable plastics
The conductive polyphenylene ether / polyamide material developed by American GE company enables the body plastic parts to carry out cathodic electrophoresis together with metal stamping parts (i.e. full on-line spraying), so as to eliminate the color difference between non-metallic parts and metal parts of automobile body.
In addition, the PC / PBT material and SLX film used to manufacture automobile body panels can produce plastic body outer panels, front and rear fenders and rear compartment doors through in mold decoration injection molding process, which can achieve the effect of paint and reduce the production cost. This technology has been used in the production of automobile body panels abroad.
4.3 lens and plastic glass for plastic parts
The headlamp lens made of special polycarbonate produced by GE company of the United States is coated with anti scratch coating, which is brighter than glass lens, more resistant to breakage and more accurate in optical processing.
The United States has attached another 20 to the three-layer safety glass of the windshield μ M thick polyurethane film. Most buses in the United States use acrylic resin plate, and the plasticization of windshield glass can achieve the purpose of energy saving and passenger safety.
4.4 fiber reinforced thermoplastic
Long fiber reinforced thermoplastic (LFRT) is a new lightweight and high-strength engineering structural material. Because of its light weight, low price and easy recycling, its application in automobile has developed rapidly.
The use of natural fibers such as flax and sisal reinforced plastics to make body parts has been recognized in the automotive industry. The tensile strength of flax reinforced polypropylene is higher than that of steel, the stiffness is not lower than that of glass fiber reinforced materials, and the parts are easier to recycle. For operators, skin rash and respiratory diseases caused by glass fiber can be avoided. Some enterprises in Jiangyin have opened Start producing such materials.
5. Application in power transmission system
The engine valve cover and oil pan are molded or pressed by glass fiber reinforced plastics such as polyamide, reactive injection molding polyurethane and epoxy resin; the cylinder gasket and sealing gasket of the engine are made of high-performance or traditional synthetic rubber produced by special processes, including Cr and frm; wear-resistant polypropylene molding materials are used in wear-resistant molded products such as gears and shafts. Van and cargo vehicles In vehicle, composite materials (glass and carbon fiber) The metal shaft replaced by the transmission shaft reduces the weight, reduces the noise and vibration, and makes the work more smooth. The transmission shaft made of fiber reinforced plastic by GKN technology company in the UK reduces the weight by 50% ~ 60%, the torsional resistance is 1.0 times greater than that of steel, and the bending stiffness is 1.5 times greater. DuPont has developed a composite glass fiber reinforced nylon 66 for the active collective plastic ventilation system of V6 engine 。
6. Body
There are three main modes for the application of plastics in automobile body: (1) all outer covering parts and structural parts are made of Plastics: it is mainly used in high-grade sports cars. The skeleton structural parts are made of carbon fiber reinforced plastics, and the outer covering parts are made of glass fiber reinforced plastics, which is very expensive. (2) Combination of metal skeleton and all plastic outer covering parts with vehicle body: the vehicle body adopts glass fiber reinforced thermoplastic polyester injection molding, and its equipment is 8800t injection molding machine, which is expensive. (3) some plastic outer covering parts are used: some high-end cars adopt metal parts for skeleton structure, while some outer covering parts adopt plastic parts.
7. Develop plastic functional parts
The bracket, bracket and multi-functional parts are made of glass fiber reinforced thermoplastic (GMT). The intake manifold made of plastic can reduce the weight by 40% ~ 60%, with smooth surface and low flow resistance. It can improve the engine performance, and play a certain role in improving combustion efficiency, reducing fuel consumption, reducing vibration and noise reduction. A method of adding conductive filler into matrix polymer is developed "Composite conductive plastics" and "conductive polymer compounds" with conductivity of plastics themselves are selected for automobile production with their high functional properties.
8. Instrument panel and interior trim system
Many foreign automobile factories use foam polyurethane to make door plank, which not only can reduce weight, strength, sound absorption and safety performance, but also widely used in the American car market because of its low price. Not only polypropylene is used instead of ABS, but also some models are made of polypropylene. The dashboards used in China can be divided into rigid dashboard and soft dashboard two. The hard instrument panel is generally modified polypropylene, which is injection molded and used in economical vehicles. The soft instrument panel is polyurethane reactive foam molding, which is usually used in medium and high-grade cars.
Conclusion the innovative application of plastic materials will be the key point that will receive the most attention and attention in automobile manufacturing. In the future of energy shortage and deepening attention to environmental protection, automobile will depend on the development of plastic technology to a large extent, in addition to the innovation of engine and new raw materials. Whoever can take the lead in material selection and application can obtain greater benefits.
