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Abstract: The effective technical means of modern automobile body repair is welding technology, welding technology and welding process affect the quality and efficiency of body repair. The article first analyzes the structure of the car body and the damage of the car body, briefly describes the current welding technology, and then introduces the application of several types of advanced welding technology in body repair, including inert gas shielded welding, resistance spot welding, and laser welding. Body repair personnel need to select welding technology and welding technology for different body materials and welding technology, and promote the effective repair work.

Welding is a production operation that needs to be carried out in the automotive industry and in the maintenance of automobiles. With the improvement of people's living standards, the number of cars is increasing, and residents are more and more concerned about the quality of cars. In addition, the improvement of the driving performance of the automobile also brings about the problem of damage to the automobile body. The increase of the driving speed increases the damage degree of the vehicle body, and the body damage also becomes a common phenomenon. At present, the key issue of the repair of the body of the private car is the replacement and repair of the body sheet metal. The repair of the body is guaranteed by the sheet metal and welding process.

1 Introduction to welding technology and body damage

(1) Welding technology.

Welding techniques can be divided into three main aspects according to the physical characteristics of the welding process. The first is fusion welding. The fusion welding mainly welds the material through the thermal effect. The metal melts when heated to a certain temperature. A filler metal is added between the two connecting members to form a whole after the metal is cooled and solidified. Depending on how the metal is melted, the fusion weld can be subdivided into gas welding, arc welding, plasma heating welding, and the like. At present, gas welding and arc welding are the most widely used in automobile body repair. The second is pressure welding, which uses motor heating to heat the welded parts and apply a certain pressure to ensure that the joints can be tightly coupled. Among them, the resistance spot welding technology is a necessary procedure for the body to be connected. Due to the material and thickness limitation of the body, the electric welding does not cause large deformation, so it is widely used in the repair of the body. When performing resistance welding, it should be ensured that the welding is continuous along the same direction of the vehicle body to ensure that the body does not undergo stress concentration and cracking. The third is brazing. The filling material used for brazing is a brazing material. The melting point of the brazing material is usually lower than the melting point of the material of the connecting member. The brazing material is melted and dropped on the joint, and the joint can be joined after condensation. This welding technology is limited by modern automotive body materials and has a limited range of uses.

(2) Body damage.

The structure of modern automobile bodies can be summarized into two main types, load-bearing and non-loading bodies. In addition, some scholars have also designed welding techniques and processes for the collision damage of automobiles. The material of the body is steel plate, and the wall thickness of the body is relatively thin. The forming method of the body is mostly stamping die forming, and then the entire body appearance is formed by welding. The structure of the body includes the hood, the top cover, the front and rear doors, the door support, the rear wing panel, the trunk lid, etc. When the vehicle collides, the damaged parts include the front, the back, and the side, and after the collision damage, Repaired by welding techniques. The body of the car is affected by the force and the direction of the force during the collision. It is necessary to combine the whole body to analyze the force and judge the damage of the body. The first condition for the collision repair of the vehicle body is to accurately judge the damage degree of the vehicle body. The finite element analysis method is widely used and the effect is better. Some scholars also conduct collision detection through collision simulation to analyze the damage.

2 Application of advanced welding technology in body repair

Modern body materials use new materials and manufacturing processes. The traditional body materials are low carbon steel. Low carbon steel has good welding performance. After heating and cooling, the strength does not change much, but the low carbon steel material is soft. Need to increase the thickness of the material. Most of the modern body materials are high-strength steel and ultra-high-strength steel. Since the welding of these materials has certain requirements and the strength will decrease after the welding is completed, higher requirements are imposed on the modern welding process. Modern welding technology mainly includes: inert gas shielded welding, resistance spot welding, laser welding.

(1) Inert gas shielded welding.

The thickness of the automobile body plate is about 1 mm, the welding current is very stable and a small current is used. Since most of the body welding motors are industrial welding machines, the welding current is variable and unstable, and the voltage network changes are very disadvantageous for the welding of the body sheet. of. Therefore, the inert gas shielded welding motor should choose a special welding machine. In the welding of inert gas shielded welding wire, the welding wire should be increased directly to reduce deformation. For the repair of the roof cover, resistance spot welding has been gradually replaced by laser welding. Laser welding not only has high repair efficiency, but also can effectively guarantee the quality of the welding point. The welding depth of laser welding is large, and the repair of thick low carbon steel body is thick. Has a good repair effect, and the welding effect of the opposite material

Other welding effects are better. When repairing the side of the weld, laser welding can reduce the number of spot welds and increase the smoothing effect of the weld.

3 car body

The problem of damage to the car body is increased, and the types and degrees of damage are numerous. The body repair personnel need to fully understand the properties of the car body, welding control problems, thermal stress deformation, etc., and have some understanding of the key factors affecting the car body damage. In addition, with the improvement of the scientific level, body repair personnel need to learn new welding knowledge and translate it into practical application, pay attention to record and repair in the process of automobile repair diagnosis. Continue to summarize and accumulate experience. Improve the quality and efficiency of body repair. .

4 smelting and pouring

The part is smelted with molten steel in a medium frequency induction furnace. The ingredients are: 0.12 kg for aluminum wire, 0.98 kg for slag removal agent, 0.26 kg for CaSiMn, 115 kg for ordinary carbon steel scrap, 13 kg for medium manganese, and high manganese. 13 kg. The pouring temperature of molten steel is 1575~1595 ft, and the melting temperature is 1615~1635 ft. In order to ensure that the shell has good high temperature strength and burnt out residual wax, organic matter and other substances in the shell mold, the molten steel can be quickly and completely poured into the entire cavity. When pouring, the principle of red shell casting must be followed, that is, it must be ensured at the same time. The baking time of the shell should not be less than 30 min and the baking temperature of the shell should not be less than 1050 ft. After the pouring is completed, the mold is placed in a sand car for air cooling, and the air cooling time is 25 minutes.

5 heat treatment

After the investment casting process is cleaned, the high-manganese steel is heated to 950 ft or more to keep warm and solid solution, and then directly quenched to maintain the austenite structure at a high temperature to room temperature, which is what we usually call "water toughness treatment". Process" However, the part will form a scale on the surface after conventional heat treatment. In actual production, the shot blasting process is generally used to carry out the treatment of removing scale.

In order to solve the problem of magnetic non-compliance, the traditional "water toughness treatment process" has been improved. First, the mesh belt type heat treatment furnace is divided into two sections, the front section is the heating section, and the rear section is the cooling section. During the heat treatment, the ammonia decomposing atmosphere is passed to the mesh belt furnace, so that the casting is protected by the reducing atmosphere during heating and cooling. Secondly, the cooling water channel is arranged in the cooling section to cool the furnace body, and the casting is not in direct contact with the cooling water. The improved heat treatment process curve is shown in Figure 1. In order to increase production efficiency, heating and cooling rates are as fast as possible in production. Although the high-manganese steel has poor heat transfer properties, cracks do not occur due to the relatively small size of the castings and rapid heating and cooling.

6 Conclusion

After high manganese steel, using investment casting process and improved heat treatment furnace, qualified automotive deep hole thin wall casting products are produced. The product not only meets the required surface quality requirements and dimensional accuracy, but also meets the requirements of non-magnetic, and the product qualification rate has reached more than 96%. Compared with the deep-hole thin-walled parts produced by the hot-forging method of copper-zinc alloy, the cost of parts produced by the investment casting process of high-manganese steel is reduced by 45%~55%, and the economic benefit is very considerable.