If you haven't finished high school, how about learning an automobile welding technology?

First, the development of automobile body welding technology

1. Overview of automobile body welding technology development

Before 1990s, China's automobiles were mainly commercial vehicles, with low production speed and unchanged products for decades. Car body welding technology is mostly simple fixture, transmission machinery and manual operation, using manual spot welding. The car body equipment is designed and manufactured by the process department of the automobile factory, just to meet the production needs of our factory. Until the 1990s, after the introduction of foreign automobile production technology, foreign advanced automobile body welding technology and equipment were introduced into China, and the domestic automobile industry put forward new demands for the domestic automobile body welding equipment industry, which promoted the development of domestic automobile body welding equipment.

In recent years, with the rapid development of China's automobile industry, automobile body welding technology and equipment have made great progress. Whether it is welding technology, welding equipment or welding production line equipment, it has formed the ability to develop, design and manufacture all the equipment of automobile body welding workshop suitable for various production schemes, as well as the ability to develop and manufacture some high-end automobile body parts welding production lines. However, compared with foreign advanced companies, there are still some gaps in the new requirements of automobile production, such as new body material welding technology, new intermediate frequency spot welding equipment, laser welding equipment, flexible production technology and equipment for multi-variety vehicles, which need independent research and development.

2. Present situation and development of automobile industry

The China Automobile Association pointed out that last year, China's automobile production and sales exceeded190,000, a record high, once again setting a new global record and ranking first in the world for four consecutive years. China's automobile output has exceeded180,000 vehicles for three consecutive years, and the automobile industry has entered a stable development stage with relatively high total output. The production and sales of automobiles in China in recent ten years are shown in figure 1.

Figure 1 Automobile Production and Marketing in China in Recent Ten Years

With the rapid development of China's automobile industry, a multi-variety and full-range production and supporting system for complete vehicles and parts has been formed. In order to maintain the steady and rapid development of China's automobile industry, China put forward "Automobile Industry Revitalization Plan" in 2009. Put forward to strengthen the research and development of key technologies, speed up technological transformation and enhance quality of enterprise; Take new energy vehicles as a breakthrough, strengthen independent innovation, cultivate independent brands, form new competitive advantages, and promote the sustained, healthy and stable development of the automobile industry. The State Council proposed "to improve the four technologies of stamping, welding, painting and final assembly in automobile body manufacturing".

In view of the development trend of the world automobile industry and the actual situation of China's industry, the automobile industry is developing in the direction of environmental protection, low carbon, energy saving, safety, comfort and diversification, which requires the automobile to adopt new energy, new structure, new materials and new technologies. The technical level and quality of car body welding directly affect the strength, safety and productivity of car body structure. This brings new characteristics to the production of car body welding and puts forward new requirements for car body welding.

3. Production characteristics of modern body welding

According to the characteristics of modern automobile body welding production, a series of new requirements are put forward for body structure, welding technology and equipment.

(1) Lightweight car body promotes the application of new materials and the development of new welding technology.

(2) Pursuing car body safety and improving car body welding quality.

(3) Improve the quality of the car body and the welding geometric accuracy.

(4) Adapting to various vehicles and realizing flexible hybrid welding production.

(5) The vehicle type is accelerated and the welding equipment is updated.

(6) High reliability and high beat production require high automation of welding production line equipment.

(7) Using information engineering technology to develop car body welding production line equipment.

Second, new body materials and new welding technology

1. New body materials

With the development of automobile industry, in order to save energy and safety, a large number of new materials are used in automobile body. The structural materials of car body gradually developed from single steel structure to high strength and high quality steel structure, and then to light alloy and composite structure.

(1) The use of high-strength steel poses a new challenge to the welding process. Due to the properties of high strength steel, the plastic temperature range is narrowed, and a large electrode pressure is needed to obtain the same plastic deformation, which leads to the narrowing of the applicable welding process range. Usually, the traditional spot welding process is improved and optimized, and proprietary technologies such as pulse spot welding and intermediate frequency spot welding are adopted to increase welding pressure and control welding process to obtain good solder joint quality.

In recent years, the rapid development of laser welding technology has greatly improved the welding performance and joint welding strength of high-strength steel plates.

Because of its high strength, small rebound, good formability and good corrosion resistance, high-strength steel has been successfully applied to high-strength functional parts of white body, such as A-B-C column reinforcement plate, doorsill, seat, skeleton, bumper reinforcement plate, longitudinal beam and cross beam. Hot stamping, intermediate frequency spot welding and laser welding are important means to realize stamping and high quality welding of ultra-high strength steel body parts.

(2) Light alloy materials In recent years, in order to further reduce the body weight, foreign automobile manufacturers began to use light alloys (aluminum alloy, magnesium alloy and even titanium alloy) in the body structure design, which brought new problems to the body welding.

Aluminum alloy is difficult to weld. At present, TIG/MIG welding, riveting /TOX connection or adhesive bonding are often used. The friction stir spot welding technology recently invented by the welding research institute is said to solve the automobile body welding of aluminum alloy and obtain good welding strength. However, because there is a small hole in the center of the welding spot of friction stir spot welding, it is often used in the inner plate structure.

(3) In order to reduce the weight of the car body, some car companies use carbon fiber reinforced polymer composite to manufacture the car body and chassis parts, which can reduce the weight of the car body by 50%~65%. There are also automobile R&D personnel who have successfully used resin transfer molding technology to trial-produce automobile carbon fiber flooring. Of course, the connection of carbon fiber composites is completely different from the welding of metals.

2. New welding technology of car body

(1) New resistance welding technology Intermediate frequency resistance welding: The control power supply of intermediate frequency inverter DC resistance welding (referred to as intermediate frequency resistance welding for short) is to convert three-phase alternating current into pulsating direct current through a rectifier circuit, and then convert it into intermediate frequency square wave through an inverter circuit composed of power switching devices, and then connect it to a transformer, and then rectify it into less pulsating direct current for welding workpieces.

Intermediate frequency resistance welding has many advantages:

First, the welding quality is good. The response time of intermediate frequency welding current is 1ms, and the adjustment accuracy and monitoring accuracy are greatly improved. Therefore, the welding quality is greatly improved and the control accuracy is also high.

Second, the welding speed is fast. Inverter DC output of resistance spot welding machine, centralized heating, shortening welding time.

Third, the energy-saving effect is obvious. The transformer of inverter welding machine works at high frequency with little loss. DC output improves the power factor and has obvious energy saving effect.

Fourth, the volume and quality of the equipment. The transformer of inverter DC resistance spot welding machine is greatly reduced and the equipment is lighter.

Fifth, it can be widely used in spot welding of dissimilar metals.

Sixth, energy conservation and environmental protection. Intermediate frequency welding is a three-phase balanced load, which has much less impact on the power grid than single-phase AC welding, reduces the requirements for power supply system and conforms to the national energy policy.

At present, medium frequency resistance welding has been widely used in automobile welding production. In the production of body parts, fixed high-power medium-frequency resistance spot welding equipment is mainly used for projection welding or multi-head spot welding of body parts; In the car body welding production line, medium frequency resistance welding suspension spot welding machine or robot spot welding machine is adopted; At present, medium frequency spot welding is widely used to weld galvanized steel plates and high strength steels. Jiefang Company has applied intermediate frequency welding technology in batch in the production preparation of new products.

In order to improve the quality of robot spot welding and reduce the robot grasping load, robot intermediate frequency spot welding electrode holders have been widely used in the car body welding production line. At present, the IF spot welding electrode holders, supporting power supply and welding controller used by domestic automobile manufacturers are mostly provided by foreign companies, such as Bosch, NIMAK, Ogara, Japan, etc.

Servo spot welding machine: servo technology is developed with the extensive application of welding robots. In order to ensure efficient production mode, reduce the impact of pneumatic electrode holder on workpiece surface during spot welding, improve workpiece surface quality, and realize accurate control of electrode holder pressure process, a new type of electrode holder-servo electrode holder came into being. The electrode holder driven by motor servo, referred to as servo electrode holder, is a kind of high-performance robot electrode holder which can improve the quality of spot welding in recent years. Faw liberation J6 welding production line adopts servo electrode holder, and the application effect is ideal, as shown in Figure 2.