Welding is a necessary process in modern machinery manufacturing and is widely used in automobile manufacturing. The engine, gearbox, axle, frame, body and carriage of the car are inseparable from the application of welding technology. In the manufacture of automotive parts, spot welding, projection welding, seam welding, spheroidal welding, electrode arc welding, CO2 gas shielded welding, argon arc welding, gas welding, brazing, friction welding, electron beam welding and laser welding, etc. Among the welding methods, since spot welding, gas shielded welding, and brazing have large production capacity, high degree of automation, high speed, low consumption, small welding deformation, and easy operation, they are particularly suitable for automotive body sheet covering parts, so It is the most widely used in automobile production. In the investment cost, spot welding accounts for about 75%, and other welding methods only account for 25%.
With the development of the automobile industry, the automobile body welding production line is gradually developing towards full automation. In order to catch up with the international level, efforts are being made to improve the quality of automobile manufacturing while increasing production. As we all know, the premise of realizing automation is that the manufacturing precision of parts is very high, it is hoped that the welding deformation is minimal, and the appearance of the welding parts is refreshed, so the welding technology is required to be higher and higher. China faces the opportunities and challenges of joining the WTO. The promotion and application of new technologies in welding plays an extremely important role in the brand promotion of the automobile industry.
I. Application of welding methods and parts used in the automotive industry
The automotive industry is one of the most widely used in welding applications, and the welding methods used are also numerous. The applications are as follows:
(1) Spot welding is mainly used for body assembly, floor, door, side wall, rear wall, front axle and small parts.
(2) Multi-spot welding is used for underbody, truck compartments, doors, hoods and trunk lids.
(3) Projection welding and spheroidal welding are used for body parts, shock absorber stems, brake shoes, screws, nuts and small brackets.
(4) Seam welding is used for the roof cover rain cover, shock absorber head, fuel tank, muffler and oil pan.
(5) Butt welding is used for steel rings, exhaust valve stems, tools, etc.
2. Electric arc welding
(1) CO2 protection welding is used for welding of car boxes, rear axles, frame, shock absorber valve stems, cross beams, rear axle shell pipes, drive shafts, hydraulic cylinders and jacks.
(2) Argon arc welding is used for welding and repair welding of oil pan and aluminum alloy parts.
(3) Welding rod arc welding is used for thick plate parts such as brackets, spare tire frames, and frame.
(4) Submerged arc welding is used for half-bridge casings, flanges, pressure vessels for natural gas vehicles, etc.
3. Special welding
(1) Friction welding is used for automotive valve stems, rear axles, axles, steering rods and on-board tools.
(2) Electron beam welding is used for gears, rear axles, and the like.
(3) Laser welding is used for underbody, gears, parts blanking and trimming.
4. Oxyacetylene welding
Used for repair welding of body components.
Used for welding of heat sinks, copper and steel, and hard alloys.
Second, the application of new welding technology in the automotive industry
Today, there are many advanced welding techniques in the automotive industry. Here are just a few new welding techniques related to body welding.
1. Energy saving and control technology of resistance welding
(1) Joint-mounted spot welding machine The most widely used in the automotive industry is the hanging spot welding machine. One workshop is often dozens or hundreds of units, and its capacity is mostly above 100kVA. It has been widely used in the welding of automobile sheets. Applications.
(2) Resistance welding machine At present, the resistance welding machine uses a large amount of AC 50Hz single-phase AC power supply with large capacity and low power factor. Development of three-phase low-frequency resistance welding machine, three-phase secondary rectification contact welding machine (already used in ordinary spot welding machine, seam welding machine, projection welding machine) and IGBT inverter resistance welding machine can solve grid imbalance and improve The problem of power factor (up to 0î€9 or above). At the same time, it can further save energy, which is beneficial to the realization of the microcomputer control of the parameters, and can be better applied to the welding of welding aluminum alloy, stainless steel and other difficult-to-weld metals. In addition, the weight of the device can be further reduced.
(3) Control of resistance welding Southwest Jiaotong University developed a rim welding PLC (programmable controller) intelligent controller for the welding of aluminum alloy rims in a factory. The original machine was modified to solve the welding of aluminum alloy rims. Quality issues have improved welding productivity. Later, the same factory developed the PLC seam welding controller, which solved the seam welding problem for the general cleaning requirements. Through the development of these two controllers, it is proved that the PLC has stronger anti-interference ability and higher reliability than the single-chip microcomputer controller; it is smaller than the industrial control machine controller and low in cost, and is completed by using the universal single-phase power frequency AC resistance welding machine. Difficult butt welding and seam welding work.
2. Gas protection welding technology
(1) The key to the waveform control method of surface tension transition is to complete one droplet transfer with two current pulses, the first current pulse forms a droplet and grows up until the droplet is short-circuited with the workpiece; the second The current pulse is a short-time narrow pulse and continuously detects its di/dt, and at the same time controls the current pulse value to generate an appropriate electromagnetic contraction force, so that the droplet neck shrinks and becomes thin, and finally the surface tension of the molten pool is broken and completed. 1 droplet transfer without splashing.
(2) Inverter power supply waveform control Utilizes the good dynamic characteristics and flexible controllability of the inverter power supply, adopts waveform control, and suppresses the current rise at the initial stage of the short circuit to reduce the electromagnetic force hindering the droplet transition when the bridge is formed. And bursting, reducing the splash of large particles, and facilitating the spread of the droplets in the molten pool; when the droplets are spread out in the molten pool, the current is rapidly increased to accelerate the formation of the neck, and then slowly rise to a lower peak. To reduce the splash when the bridge breaks.
(3) New technology of argon arc welding TIG welding has two types of non-melting poles (TIG) and melting poles (MIG), which are used in the welding of non-ferrous metals and high-alloy steels in the automotive industry. In order to improve the formation of CO2 gas shielded welding and reduce splashing, a mixed gas protective weld with 80% or 20% Ar is added.
3. High energy beam heat source welding and processing technology
The high energy beam heat source refers to a heat source (electron beam, ion beam and laser) whose energy density is greater than 5Ã—108 W/m 2 , and has applications in the automobile industry. At present, new technologies developed abroad include:
(1) Laser and arc composite heating welding Laser welding can weld narrow and deep welds, and arc welding can weld wide and shallow welds; the former has large investment and the latter has low cost, and the combination of the two characteristics will greatly improve Welding efficiency. The design of the torch for laser and arc hybrid heating welding is particularly important. The angle between the two heat sources should be as small as possible, and the torch is also designed as a laser + double arc power supply.
This method has been used in steel structures of 4 to 8 mm thick and is intended for use in thinner automotive parts production and aluminum alloy welding. In addition to its application in welding and precision cutting, lasers also form oil-repellent fine patterns or remelted composite layers on the friction surface to improve wear resistance.
(2) Plasma application Plasma welding of argon gas protection has been used in various industries, mainly for alloy steel and non-ferrous metal processing. At present, air plasma cutting has been widely used in the cutting of general steel and non-ferrous metals. The domestic railway passenger car factory has introduced underwater plasma cutting to reduce deformation and improve precision. The engine valve body has long been plasma-welded with a fill ring. In the past ten years, powder plasma surfacing has been greatly developed, and it is possible to carry out fine surfacing of thin layers of small fusion ratio and to weld various special alloy surfaces.
Third, the development trend of welding new materials in the automotive industry
With the development of cars becoming increasingly compact, lightweight, and the application of new materials, the material composition of cars has changed significantly. In the future, car body materials are still mainly steel plates. In order to reduce the thickness of steel plates, high-strength steel plates will be widely used. At the same time, in order to improve the anti-corrosion performance of the car body, many auto manufacturers in the world have applied galvanized steel plates in the production of cars. In addition, materials such as aluminum alloys, plastics, and ceramics are also used. According to experts' predictions, by the end of the century, there will be no all-aluminum body or all-plastic body in the production of large-scale cars.
Galvanized steel sheet
When discussing the problem of metal plate welding used in the automotive industry at the meeting of the American Welding Society branch, experts pointed out that the most promising method of welding galvanized steel is laser welding. However, since the process is not sufficiently automated now, it is necessary to improve the contact spot welding method widely used in the automotive industry. The main disadvantage of this method is the large amount of zinc transition in the contact between the weldment and the electrode, which causes the electrode to burn faster. It is therefore recommended to use Al2O3 dispersion particle reinforced Cu-Zn and Cu-Cr alloy electrodes, which can be soldered with minimum reactance to ensure minimum solder joint size.
2. High strength steel plate
In order to achieve the lightweight of automobiles and improve the safety performance of automobiles, the application of high-strength steel sheets in automobiles is increasing year by year. Nowadays, a new generation of high-strength steel sheet materials, ultra-fine grain steel, has appeared. The steel grade mainly refers to the fact that the strength and toughness of steel materials are doubled compared with the existing steel products based on the further improvement of economic indicators. The new generation of ultra-fine grain steel has ultra-fine grain, high cleanliness and high uniformity in its structure.
The new generation of ultra-fine grain steels currently used for research mainly have two types of 400MPa grade and 800MPa grade.
In the study of a new generation of steel, there is no gap between China and the international level. It is almost at the same time. On the same day, the two countries have a leading position in the world. However, due to the short time of emergence, there are not many units involved in the research, mainly based on the Iron and Steel Research Institute and the Department of Mechanical Engineering of Tsinghua University. After some research on the welding technology of ultra-fine grain steel, some advanced results have been achieved.
3. Aluminum alloy
Aluminum alloy has the advantages of light weight, high strength and corrosion resistance. It is an excellent building material, and parts of aluminum alloy materials are gradually being used in the automotive industry. Aluminum alloy welding has five main features:
(1) The surface of the aluminum alloy has a dense oxide film (melting point of about 2050 Â° C). If it is not removed during welding, it will affect the melting quality of the base metal and form a quality problem such as inclusion.
(2) The thermal conductivity is large (about 4 times that of steel), the conductivity is good, and if the welding speed is the same as that of steel, the welding heat input is 2 to 4 times larger than that of the steel.
(3) The coefficient of linear expansion is large, and the weldment tends to generate large thermal stress, deformation and crack.
(4) It is prone to stomata.
(5) The strength of the aluminum alloy welded joint is reduced.
These characteristics of aluminum alloy welding are precisely the problems we should take seriously when developing welding equipment and welding processes. Only in this way can we develop equipment, materials and welding processes suitable for aluminum alloy welding.
Fourth, the overall development trend of automotive industry welding
1î€ Development of automated flexible production systems
Looking at the welding status of the entire automotive industry, it is not difficult to analyze the development trend of the automotive industry's welding: development of automated flexible production systems. Industrial robots, because of the combination of automated production and flexible production characteristics, have been used in large and rapid use of robots in recent years. In terms of welding, spot welding robots and arc welding robots are mainly used.
The welding production line is highly automated, and a 6-degree-of-freedom robot is widely used. The robot has a welding tongs storage library, which can automatically grab the required welding tongs from the storage according to the different requirements of the welding parts or the changes of the welding products. Transmission devices have evolved into more flexible, induction-guided cars that are unmanned.
2î€ Development of lightweight combined intelligent automatic welder
The level of domestic automotive welding is quite different from that of foreign countries. In recent years, domestic automobile manufacturers have attached great importance to the automation of welding. For example, the automation rate of 13 production lines of the Jetta body welding shop introduced by FAW is over 80%. Each line is controlled by a computer (programmable controller PLC-3) to automatically transfer and weld the workpiece. The welding is carried out by the R30 polar coordinate robot and the G60 toggle robot 61. The robot drive is controlled by a microcomputer, digital and text display, and tape recorder input and output programs. The robot's action uses a point-to-point sequence trajectory with a high level of welding automation, which improves working conditions, improves product quality and productivity, and reduces material consumption.
Similar high-level production lines have joint ventures and introductions in Shanghai, Wuhan and other places, including advanced automobile manufacturing technologies in Germany, the United States, France and Japan. However, these are still far from adapting to the rapid development of China's national automobile industry. We must adhere to technological innovation, accelerate the development of energy-efficient new welding materials, new processes and new equipment, develop and apply robotic technology, and develop lightweight and smart smart devices. To establish an efficient and economical welding automation system, it is necessary to transform traditional industries with computer and information technology to improve the grade.
It is believed that in the near future, through our joint efforts, the welding technology of the domestic automotive industry will gradually shorten the gap with the advanced foreign welding technology, and meet the opportunities and challenges brought by the WTO to the automotive industry.
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