Anti-corrosion design and development direction of automobile body

Anti-corrosion design and development direction of automobile body

Body corrosion is directly related to the appearance and service life of the car. This is one of the key research topics in automotive construction and corrosion protection. Domestic Vehicle Anti-Corrosion Design and Testing Still in its infancy, this article focuses on measures to improve the anti-corrosion performance of automotive bodies in three aspects: structure, materials and manufacturing process, and outlines the future direction of research in anti-corrosion material for automobile bodies. -corrosion technology.

With the rapid development of the automotive industry, corrosion of automotive bodies has become an increasing concern. Automotive body corrosion can be divided into appearance corrosion, structural corrosion and corrosion byperforation. Appearance corrosion refers to the damage and rust on the appearance of the car body, which directly affects the appearance of the car and customer satisfaction; structural corrosion refers to the corrosion of the structural parts of the car body, which directly affects the safety and service life of the car; Puncture corrosion refers to the poor anti-corrosion ability of the car\'s interior cavity or seals. , corrosive media can easily accumulate, causing rust and penetration of the body, seriously affecting the appearance and service life of the car. The car corrosion problem exhibited by CCTV 3.15 belongs to car body perforation corrosion. At present, the domestic vehicle anti-corrosion design and testing is still in its infancy. How to guarantee anti-corrosion qualityn vehicles by optimizing the design of the structure, materials and manufacturing processes is at the center of research by automobile manufacturers.

Anti-corrosion measures for automotive design

Structural design

Automotive design engineers have good design capabilities in terms of structural strength and other aspects, but often ignore the impact of structure on the anti-corrosion performance of the vehicle body. However, many corrosion and rust problems are caused by unreasonable structural design, so the vehicle body design stage should be considered. Key considerations:

(1) Seam design

The car body is made of metal steel plates and the seam is the weak part of the coating itself, and corrosive environments suchthat water and mud easily accumulate in the gaps, causing rapid corrosion of metal plates. Therefore, when designing, it is necessary to pay attention to the direction in which the car moves and the direction in which corrosive fluids such as water cannot penetrate, as shown in the figure “Diagram of design of joint openings”; in structural design, attention should be paid to using the entire steel plate for stamping to reduce gaps. The design of the body joints must also take full account of the suitability of subsequent painting, sealing and wax injection, so the joint design is the result of careful consideration.

(2) Cavity design

The body cavity is very important to increase the strength of the car and reduce weightof the car. Reasonable cavity design will lead to poor exhaust and drainage, electrophoresis dead spots, acid and alkali residue, corrosion and severe puncture corrosion. Therefore, the cavity design should reasonably arrange the position of the cavity to improve electrophoresis, wax injection, etc. The practicability of the anti-corrosion process is convenient for the subsequent coating and sealing of glue, which can not only isolate the external corrosive medium and avoid corrosion, but also achieve the effect of reducing car noise. Hollow corrosion is one of the most common bodywork corrosions. In addition to optimizing the structural design, many automakers use cavity anti-corrosion technologies such as cavity wax injection and highly corrosion-resistant materials.

(3) CProcess hole design

In order to meet the needs of electrophoresis, wax injection and installation process, the body was designed with many craft holes . The number, position, size, spacing and distribution of these holes directly affect the distribution of coatings and waxes and the accumulation of corrosive substances, which in turn affects the anti-corrosion performance of the bodywork. In principle, increase the holes of the electrophoresis process in the internal cavity as much as possible to increase the thickness of the paint film. Combined with the electrophoresis production line and body cavity structure, the air holes are reasonably designed and arranged to avoid air chambers and generate electrophoresis blind spots. The design of processing holes should not only fully consider the impact on the anti-corrosion performance of the bodyworke, but also involve stamping dies and costs, welding devices and positioning, body strength and rigidity, noise reduction, etc. , consideration of multiple ions is necessary for best results. .

Material Selection

Body material is not only related to the safety and comfort of resistance and body rigidity, but also directly affects anti-corrosion performance and service life. Therefore, how to reasonably select body materials has always been an important part of automotive design. Currently, the most commonly used body materials include medium and low strength steel plates, high strength steel plates and aluminum alloys.

(1) Medium and low tensile steel sheets

High tensile steel sheetsMedium and low ance used for automotive bodies in general include ungalvanized steel plates and galvanized steel. Most of the global automotive industry uses galvanized steel sheets to improve the corrosion resistance of the car body. According to the survey of the Swedish Corrosion Institute, non-galvanized steel sheets generally only meet the corrosion protection requirements of 6 years, and double-sided galvanized steel sheets must be used to meet a corrosion protection of 12 years (galvanized layer 7~10μm). At present, galvanized steel sheets commonly used in automobiles include hot-dip galvanized steel sheets and electro-galvanized steel sheets. In order to prevent corrosion of steel sheets during transportation and storage, hot-dip galvanized steel sheets are generally used. For protection against oil, electrozin steel panelsFords generally use pre-phosphating protection. The thickness of the zinc layer, the type and appearance quality of the galvanized steel sheet directly affect the anti-corrosion performance of the automobile body, so choosing a suitable galvanized steel sheet is the key point. of the material design of the steel sheet of the car body.

(2) High-strength steel plates

With the progress of automotive lightening, the application high strength steel Automobile license plates have also increased more and more widely, in order to solve the problem of difficulty in forming high strength steel plates, advanced hot forming technology can be used . Ordinary galvanized layers will be destroyed under high temperature stamping, so the development of suitable coatings is an important aspect for the promotion and application ulexterior of high-strength steel sheets.

Europe and the United States have developed Al-Si, Fe-Al, Zn-Fe and other coatings, which can not only prevent the formation of scale on the steel plate during hot forming, but also affect the electrophoretic painting. The cohesion and the coating itself have a certain anti-corrosion effect, which can reduce structural corrosion and improve the anti-corrosion quality and service life of the vehicle. Since the coating builds up and is easily scratched during the thermoforming process, it will cause the substrate to crack in severe cases. Therefore, the currently coated high-strength steel plates and forming technology are monopolized by foreign countries and mainly rely on imports.

(3) Aluminum aluminum alloy

It has the advantages of light weight, casting easy and goodcorrosion resistance, so it is an ideal material to reduce the weight of the car body and improve the anti-corrosion performance and service life of the car body. Since pure aluminum is relatively soft, in order to meet the strength requirements of the vehicle body, many models use a body composed of a mixture of aluminum alloy, steel and aluminum plates. high strength steel. However, there is a potential difference between aluminum and steel, which are prone to contact corrosion. Those with more negative potential, the aluminum will corrode, affecting the appearance and lifespan of the car. Therefore, how to effectively avoid contact corrosion between aluminum and steel is the key to using aluminum-steel hybrid structure. At present, the main solution to solve contact corrosion is to use glue and sealing materialscheite to isolate the corrosive environment, or to add joints between the two.n aluminum and steel to avoid any contact. With the optimization of body structure design and the continuous development of new sealing processes, aluminum alloys are increasingly being used in automobile bodies.

Manufacturing Process

Automotive manufacturing mainly consists of four processes: stamping, welding, painting and coating. final assembly. Each process has an impact on the anti-corrosion of the bodywork. Stamping is the first step in the manufacturing of automobile bodies. The main effects on body anti-corrosion are stamping burrs, stamping oil and apparent stamping quality.

The apparent quality of the stamping is smooth, avoiding the remaining surface impurities and minimizing the damage to the galvanized layer.

Many car manufacturers such as Volkswagen, General Motors, Ford, etc. considered the stamping process as an important quality control point for the anticorrosion of automotive bodies. Welding involves assembling the stamped body panels into a wStrike body by welding. Defects such as weld pores, oxide scale, welding slag, damage to the galvanized layer, etc. should be avoided, which will result in poor paint adhesion and a reduction in the anti-corrosion performance of galvanized steel plates.

Coating process is a key process for automobile body anti-corrosion, which mainly includes pretreatment, electrophoresis, bottom PVC, thick and thin seals , the threshold PVC, the intermediate coating. , color paint, varnish and air cavity injection wax.

It should be noted thate: a) Pretreatment requires the formation of a uniform and dense phosphating film on the body surface; b) Electrophoresis requires no scratches, pinholes, leveling, cracks, etc., and can meet process and performance evaluation standards such as thickness testing, corrosion experiments , adhesion testing and evaluation of liquid wax wetting performance; d) Reasonable arrangement of thickness and density to improve the anti-corrperformance osion of the car body; e) Select the appropriate intercoat to strengthen the bonding strength between the electrophoretic paint and the topcoat; f) The varnish not only beautifies the appearance of the car, but also can resist the erosion of the car body by natural environments such as solar radiation, rainwater, salty substances, acidic substances,etc., and has a certain anti-corrosion effect; g) Using cavity wax injection technology to effectively avoid body structure corrosion and puncture corrosion. Final assembly is the assembly of the body and parts to form a complete vehicle, which is the final step in the automobile manufacturing process. Particular attention should be paid to the assembly process: a) Avoid any mismatch between parts and body or loose assembly. The contact surface between the body and the parts can be moved. Friction, sliding or vibration can cause paint damage or thinning, red rust or even rust penetration, resulting in qualified car bodies and parts manufactured at high cost cannot be used to assemble a qualified car; b) Reasonably design bindings and parametersassembly to prevent paint damage and wear.

Future research directions

Developing body materials with excellent anti-corrosion properties

With the demand for luxury, beautiful and lightweight cars, more and more new materials and processes will be applied to car bodies. At present, aluminum alloys, modified plastics and some composite materials are being studied more. At present, many high-end cars produced by foreign automakers use aluminum alloys as exterior body panels and structural parts, and some cars even reach over 80%. The way of adding different alloying elements to aluminum to develop special processing methods to further improve the strength and anti-corrosion properties and reducee production costs will be the focus of future research on aluminum alloys. Plastic has the advantages of light weight, high corrosion resistance, high decorativeness and easy molding. The strength and rigidity of plastic can be improved through modifications. After years of research, ultra-lightweight carbon fiber reinforced plastic (CFRP) has been successfully used in some high-end sports cars. Composite materials such as lightweight rolled steel plates, foam alloy plates and honeycomb aluminum composite plates are also under development, and anti-corrosion materials for automobile bodies show a diversified trend . The development of highly anti-corrosion body materials can not only improve the appearance and performance of the car, but also improve the quality of the car. More importantly, thisIt can improve the intrinsic quality of the car and extend its service life.

Develop advanced anti-corrosion bodywork manufacturing processes. With the development of manufacturing and materials industries, various automobile manufacturers continue to develop advanced body manufacturing processes to improve the anti-corrosion performance of vehicle bodies. For example, the degree of automation is improved, the manufacturing process is shortened, and the corrosion between processes is effectively reduced; custom laser welding technology is used to improve the quality of spaces; Swing bar conveyors, fully suspended inverted conveyors (Ro-Dip) and multi-functional shuttles are used to achieve 360° rotation of the body in the electrophoresis tank and optimize the entry and exit angle of the tank to increase foexhaust function, so that the liquid from the tank in the internal cavity can flow completely, eliminate the bubbles in the internal cavity, solve the problem of thin paint film in the internal cavity, and increase the uniformity of the paint. paint thickness.

Application of computer simulation technology to the anti-corrosion design of automobile bodies. Electrophoresis is essentially an electrochemical process of depositing a coating onto a substrate. Through computer simulation technology and electrochemistry combined, it simulates the distribution of power lines in the car body and the flow of corrosive media such as water in the car body to improve the penetration of electrophoresis, improve the film thickness distribution of the electrophoretic coating on the car body, and avoid the dead zones of the cavity electrophoresis, amthus improving the anti-corrosion performance of the bodywork. Simulation technology can not only detect various corrosion defects as early as possible, identify the problem and reduce production costs, but also evaluate the effects of design changes, thereby significantly reducing design time and reducing manufacturing costs. vehicle prototypes. For example, whether adding reinforcement plates will have a negative effect on the thickness of electrophoretic coating, whether process holes can be eliminated or reduced, these questions are currently mainly exploited by experiment and subsequent experiences. The development time is long, and the electrophoresis simulation technology can be used more quickly. Property Assessment. At present, automobile manufacturers in developed countries in Europe and the United States have gradually developed ssimulation systems to simulate the electrophoresis thickness of bodywork and put them into real production, thus becoming an indispensable tool in the development of new cars.

Conclusion

Automotive body anticorrosion research is a comprehensive subject of structural design, material selection , manufacturing processes and anti-corrosion tests. With the vigorous development of China\'s automobile industry and the continuous improvement of customer requirements, various automobile manufacturers have gradually strengthened research on automobile body anti-corrosion technology. On the one hand, they continue to learn and introduce advanced technologies and testing methods from other companies, and on the other hand, they combine China\'s national conditions and usage environment, develop their own anti-corrosion bodywork technologytomobile. However, in general, compared with automobile factories in developed countries such as Europe and the United States, the anti-corrosion technology of domestic automobiles is relatively immature. Therefore, how to improve the performance of domestic automobiles? Improving the quality of car body anti-corrosion, reducing vehicle anti-corrosion costs and improving product competitiveness are of great importance to the development of the Chinese automobile industry.

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