Welding is a necessary modern machinery manufacturing process method, widely in automotive applications. Car engines, transmissions, axles, frame, body, six total Chengdu car without welding technology. In the manufacture of automotive parts, spot welding, projection welding, seam welding, projection welding rolling, welding arc welding, CO2 gas shielded arc welding, arc welding, gas welding, brazing, friction welding, electron beam welding and laser welding, and other types of welding methods, as Welding Supplies , gas welding, brazing has produced large, high degree of automation, high-speed, low power, welding deformation is small, easy to operate features, so the cover sheet for automotive body parts particularly suitable, so , the most widely used in automobile production. Investment costs in the spot in about 75%, only 25% of other welding methods.

With the auto industry, auto body welding production lines are fully automated direction gradually, in order to catch up with international standards, to improve production, we request that efforts to improve the quality of automotive manufacturing. As we all know, the premise is to automate the manufacture of precision parts and components to very high hopes minimum welding distortion, welding parts look to be fresh, and called for increasing welding technology. China's accession to the WTO is facing opportunities and challenges, welding in the promotion and application of new technologies to enhance the brand of the automotive industry has an extremely important role.

A welding method used in the automotive industry and parts of the application

Automotive industry is the most widespread application of welding one of the industries, the use of a wide range of welding methods, its application as follows:

1 Resistance Welding

(1) spot welding is mainly used for body assembly, flooring, doors, side panels, the latter around, front axle and small parts. (2) Multi-spot for the underbody, trucks cars, doors, hood and trunk cover. (3) convex projection welding and roll welding for body parts, shock absorber stem, brake shoes, screws, nuts and small such as a stent. (4) seam welding for body rain canopy cover, shock absorber seals, fuel tank, muffler and oil pan, etc. (5) welding for steel ring, discharged into the air valve stem, cutting tools and so on.

2 arc welding

(1) CO2 welding for the trunk, rear axle, frame, shock absorber stem, beam, shell and tube rear axle, drive shafts, hydraulic cylinders and jacks welding. (2) TIG for the oil pan, aluminum welding and repair welding of parts. (3) electrode arc welding for thick parts such as brackets, spare tire racks, frames, etc. (4) submerged arc welding for the half-pipe, flanges, pressure vessels and other natural gas vehicles.

3 special welding

(1) friction welding for automotive valve stem, rear axle, axle, steering rod and the attendant tools. (2) for electron beam welding gear, rear axle. (3) Laser Welding for underbody, gear, parts, materials and trimming the next and so on.

4. Oxyacetylene welding

Welding for body assembly.

5 brazing

For the radiator, copper and steel, carbide welding.

Second, the automobile industry in the new welding technology
Today, the automotive industry a lot of advanced welding technology, just to name a body welding and welding related to new technology.
1 resistance welding control technology and energy-saving
(1) conjoined hanging spot welding is the most widely used in the automotive industry hanging spot welding machine, a workshop is often tens or hundreds, mostly in its capacity above 100kVA, in the automotive sheet metal welding has been widely the application.
(2) a lot of resistance welding machine current resistance welding machine AC 50Hz single-phase AC power, large capacity, low power factor. Development of three-phase low-frequency resistance welding machine, three-phase secondary rectifier contact welding (in ordinary type spot welder, seam welding machine, welding machine in the application) and IGBT inverter welding machine, can solve the power imbalance and improve the Power factor (up to 0? 9 or above) the problem. At the same time can be further save energy and help achieve the parameters of the computer control, can be better suited for welding aluminum, stainless steel and other difficult to weld metal welding. It may also further reduce the weight of equipment.
(3) the control of resistance welding Southwest Jiaotong University, aluminum rims for a factory rim butt welding developed into a PLC (programmable controller) intelligent controller, the original machine was modified to address the welding of aluminum alloy rim quality problems and improve welding productivity. Developed PLC after the same factory seam welding controllers, general clean-up required to solve parts of the seam welding problems. Through the development of these two controllers, single-chip microcomputer that the PLC controller than anti-interference ability, high reliability; IPC controller than the small, low cost, using a common frequency of single-phase AC resistance welding machines completed the difficult work of welding and seam Welding Alloys.
2 gas shielded welding
(1) Surface Tension Transfer waveform control method is the key method of current pulse with two complete a droplet transition, the first current pulse to form a droplet and make it grow, until the short circuit droplet and workpiece; No. 2 short current pulse is a narrow pulse and continuous detection of the di / dt, while the value of the control current pulse to produce the appropriate magnetic contraction, contraction of the droplet neck thinner, and finally pulled off by the surface tension of molten pool, complete a metal transfer without causing splash.

(2) power inverter power inverter waveform control using dynamic characteristics of a good and flexible controllability, the use of waveform control, in the early phase of inhibition of short circuit current increased to reduce the electromagnetic force when the newly formed droplet transfer bridge barriers and burst-off, reducing the large particles splash and droplet in the pool help spread out; when the droplet spread out in the pool after the current rapidly increases to accelerate the formation of necking, later slow rise to a lower peak , so that when the splash off the bridge to reduce the explosion.

(3) TIG welding of new technologies have a very non-melting (TIG) and MIG (MIG) two, non-ferrous metals are used in automotive and high-alloy steel welding. In order to improve the forming CO2 gas shielded arc welding and reduce splash, with added 80% or 20% Ar mixed gas shielded arc welding.

3 high-energy beam welding and heat processing technology

Heat source is a high energy beam energy density is greater than 5 × 108W/m2 the heat source (electron beam, ion beam and laser), are applied in the automotive industry, is currently abroad, development of new technologies:

(1) heating laser and arc hybrid welding Laser welding can weld a narrow and deep welds, welding arc welding can weld a wide and shallow; the former investment, which is low cost, a combination of both features will greatly enhance the welding efficiency. Heating laser and arc welding torch composite design is particularly important to the angle between two heat sources as small as possible, the torch is designed to power the laser + dual arc.

This method has been 4 ~ 8mm thick steel used, is intended to be used thinner aluminum automotive parts manufacturing and welding. In addition to precision laser welding and cutting applications, also the friction surface to form fine patterns or remelted composite storage layer to improve the wear resistance applications.

(2) the application of argon plasma, plasma welding and cutting protection already in various industrial applications, mainly for steel and non-ferrous metal processing. Current air plasma cutting has been widely used in general cutting of steel and nonferrous metals, the introduction of the domestic railway passenger car plant underwater plasma cutting, in order to reduce distortion and improve accuracy. Engine valve body already filled circles using plasma welding. Over the last decade, plasma powder surfacing have great development, can be smaller than the thin layer of material fine fusion welding, welding of special alloys to the surface.

Third, the automotive industry development trend of new welding materials

With the development of increasingly compact car compact, lightweight, application of new materials to make cars a significant change in the composition of materials, steel is still the future of car body materials mainly for the plate thickness decreases, the extensive use of high strength steel. Meanwhile, in order to improve the body's anti-corrosion, many car manufacturers in the world car production in large-scale application of galvanized steel. In addition, the use of aluminum, plastic and ceramic materials. Experts predict that by the end of the century and will not appear in high-volume production of aluminum car body or plastic body.

1 galvanized steel

In the American Welding Society chapter meeting to discuss the application of automotive sheet metal welding problems, the experts pointed out that welding galvanized steel is the most promising method of laser welding. However, due to automation of the process is now not enough to be widely used in the automotive industry improve the contact spot welding method. The main drawback of this approach is in contact with the electrode welding pieces of zinc electrode leaving a large number of transition and rapid burning. Therefore recommend the use of Al2O3 particle dispersion strengthened Cu-Zn and Cu-Cr alloy electrode can be welded under the minimum reactance in order to guarantee the minimum size of welded joints.

(2) high strength steel

In order to achieve the car's lightweight, improve vehicle safety performance, high-strength steel in automotive applications is increasing every year, now there a new generation of high-strength steel material - ultra-fine grain steel. The steel mainly refers to the further improvement in economic indicators, based on the steel material strength, toughness than existing steel double. A new generation of ultra-fine grain steel in the organizational structure with ultra-fine grain, high purity, high uniformity of properties.

Currently used to study a new generation of ultra-fine grain steel are 400MPa and 800MPa grade level two.

In the study of a new generation of steel, China and the international level and there is no gap, almost the same time start, with Japan and South Korea lead the world live together. However, due to appear shorter, so the unit does not participate in many studies, mainly steel-based Research Institute and Department of Mechanical Engineering, Tsinghua University. In the ultra-fine grain steel welding technology for some of the research, made some advances.

3 aluminum alloy

Aluminum is light weight, high strength and corrosion resistance, etc., is an excellent building material, automobile industry is also increasingly using aluminum alloy components. There are five main aluminum alloy welding characteristics:

(1) the surface layer of dense aluminum oxide film (melting point of about 2050 ℃), can clear it without welding, melting will affect the quality of basic metals, such as the formation of mixed quality. (2) large thermal conductivity (about 4 times steel), good conductivity, welding and steel to achieve the same welding speed, the welding heat input welding steel than 2 ~ 4 times. (3) linear expansion coefficient, weldment have a greater thermal stress, deformation and cracking tendencies. (4) prone to holes. (5) reduce the strength of aluminum alloy welded joints.

Aluminum welding of these characteristics, it is our welding equipment and welding in the development process should be taken seriously, the only way to develop a suitable aluminum alloy welding equipment, materials and welding processes.
Fourth, the overall trends in automotive welding
1? Development of automated flexible manufacturing systems
Throughout the welding status of the automotive industry, welding is not difficult to analyze the trend of the automotive industry: the development of flexible automated production systems. And industrial robots, automation and flexibility due to the production set of features in one, so the large-scale car production in recent years, the rapid use of the robot. In welding, the main use of the spot welding robots and welding robots.
Welding production line is to be highly automated, widely used in 6 degrees of freedom robot, and robot welding clamp with a repository, according to the different requirements of welding or welding parts of the product change, caught from the repository for automatic welding required clamps. Transmission devices already developed into a more flexible use of unmanned sensor-driven car.
2? Development of lightweight modular intelligent automatic welding machine
The level of domestic and foreign automotive welding lags far behind. In recent years, the domestic car manufacturers attach great importance to welding automation. Such as FAW Jetta body welding workshop introduced 13 automated production lines more than 80%. Each line by the computer (programmable logic controller PLC-3) control, automatic transmission parts and welding. Polar coordinates by the R30-type welding robot and G60 61 sets of toggle-type robot for the robot driven by computer control, digital and text display, the tape recorder input and output procedures. Robot action sequences using point-of-step path, with a high level of automation of welding, both to improve the working conditions, improved product quality and productivity, and reduce material consumption.
A similar high level of production line in Shanghai, Wuhan and other places and the introduction of joint ventures, including Germany, the United States, France and Japan advanced automotive manufacturing technology. But these, after all, still far short of the rapid development of China's national automobile industry needs, we must insist on technology innovation, to accelerate the development of energy efficient welding new materials, new technology and new equipment, development and application of robot technology, the development of portable smart intelligent devices the establishment of efficient and economical welding automation systems, computer and information must transform traditional industries, improve grades.
I believe, in the near future, through our joint efforts, the domestic auto industry, welding technology will be gradually reduced with the advanced level of gap welding technology, the automotive industry to meet the WTO brings opportunities and challenges.

Qinghai-Tibet Railway runs through China's western Qinghai, Tibet, the two provinces, across the Qinghai-Tibet Plateau, the average across the board for more than 4 000 m altitude, frost heave in permafrost thaw, cold, snow and more, large diurnal temperature, light intensity and other natural roadbed and track conditions on the line to bring a lot of adverse effects. Laying of the Qinghai-Tibet line CWR for improving speed, reducing track maintenance, lower operating costs and achieve leapfrog development strategy railway, is of great significance.
Ministry of Railways major research projects "section of the Qinghai-Tibet grid lines look CWR test section --- Key Technology Research", at the Oasis to Jade Everest count 2318546 km between the three operative shop CWR test, which laid 50kgPm rail 1611442 km, laying 60 kgPm rail 71710 47 km, are used the temperature range of stress-type seamless line.
On-site welding and lock welding unit is currently used mainly domestic pressure Welding Wire and aluminum welding two kinds of heat welding process. Thermite weld strength is only about 70% of the base metal, weld cast the organization as the organization, often produced with casting defects and breakage rate, is not favored by experts. Pressure weld strength, breakage rate, but in special circumstances the Tibetan Plateau (average sea level air pressure is 60% to 70% oxygen in air than in sea level by 38 to 46%, the welding quality can be not meet the TBPT1632 -91 "welded rail
Joints technical conditions, "the technical requirements, to be in practice, further research and discussion.
2 traditional pressure welding pressure welding and CNC Performance Comparison
Mobile pressure welding equipment including: crimping machine (with push-convex device), heater, control box, water cooling, high pressure electric pump station and some auxiliary facilities, such as end mills, profiling grinding machine, piping systems, oxygen bottles, acetylene bottles and generators and so on.
2.1 The traditional pressure welding
Traditional welding are manual and pneumatic control, each operation (clamp, put the fire, gas flow and ratio, pressure conversion, etc.) control the process parameters of the low accuracy, poor stability parameters. Thus the joint quality is often affected by human factors, show a great volatility, breakage rate increased, the CWR potential safety hazard, endanger traffic safety.
2.2 new pressure welder CNC
Test section of the Qinghai-Tibet Railway CWR developed using the newest digital pressure welding equipment, welding the whole process to achieve the order of the closed-loop control and intelligent control. No manual welding process, welding process to ensure the stability and consistency, completely eliminating the human factor of the joint quality. Main features:
1) the order of the welding process control and flexible control: PLC as the core sequence of welding operations process control, high time, low time, upset the input parameters such as pressure time control program, the program automatically by the control and welding time Automatic conversion. Rail welding conditions according to the actual needs, but also can be adjusted in real-time manual intervention.
2) heat input control: the use of closed-loop control of welding parameters, put the fire from the heater control module, the ratio of the heating gas flow control module with the joint, put fire to achieve amplitude, frequency, size, flow, temperature of the flame characteristics associated with welding precise control of parameters.
3) extrusion welding control: welding the rail pressure "three-stage pressure" process solidified in the PLC control program, the use of pressure sensors, displacement sensors, closed-loop control method to achieve real-time control of welding pressure, flexible adjustment and automatic conversion and the top forging displacement of closed-loop control.
4) with welding parameters on-line detection, recording, storage.
3 high altitude of the main welding process
3.1 Oxygen, acetylene flow
Pressure welding of the welding flame is generally used oxygen - acetylene flame or oxygen - propane flame, in fact, most of the use of oxygen - acetylene welding. The flame structure and flame shape and temperature distribution is mainly determined by the combustion ratio.
Combustion than: β0 = VkPVa (Vk is the volume of oxygen; Va is the volume of acetylene).
Low-lying areas in the Mainland (altitude ≤ 1 000 m), pressure welding using a weak carbon flame, β0 is generally 0185 - 0195. However, in the Qinghai-Tibet line altitude> 3 000 m of the region, there is no mature experience to draw on the scene to determine the ratio of the combustion air pressure welding to the mainland in the past can not guarantee the quality of welding experience. To this end, we altitude 4 300 m stations were jade Everest trial, made a first-hand information, should be controlled burn in 0196 than the β0 ~ 111.
Pressure welding 60 kgPm U71Mn rail 15 through the drop test of the joint, the welding of oxygen, acetylene flow rate recorded in Table 1.
3.2 Heater
Pressure welding various parts of the flame of intensity heaters, directly affects the quality of Nickel Alloy Welding Electrodes. Fracture occurs on the spot, incomplete penetration and over-burning, if no other reason, is certainly the appropriate parts of the flame low or high power, need to debug on the heater fire hole. Low-lying areas in the Mainland (altitude ≤ 1000 m), pressure welding 60 kgPm U71Mn fire heater used rail hole pattern (38 × 2 = 76 holes) shown in Figure 1.
Figure 1 60 kgPm rail heater flame intensity can not meet the fire-hole under the conditions of the plateau pressure welding technology requirements. Similarly, we altitude 4 300 m stations were jade Everest trial, debugging, summed up a set for high altitude areas of the fire-hole configuration in Figure 2. The number of fire hole 39 × 2 = 78 holes.
4 results
Test section of the Qinghai-Tibet Railway CWR site used by the new welding pressure welding process, welding quality to fully meet its
TBPT1632 -91 "rail welding joint technical conditions," the technical requirements, pressure welding 60 kgPmU71Mn rail 15 drop test specimens are given in Table 2.
5 Conclusion
CWR test section of the Qinghai-Tibet Railway construction experience has fully proved that pressure welding pressure welding using advanced numerical control equipment, excluding man-made factors on the welding quality. At the same time, the welding process according to different environments, different altitude adjustment, optimization, summed up a world of experience welding pressure plateau railway scene, plateau for the future, seamless cold special circumstances to provide a reference line construction experience