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The quality of the welding of the body directly determines the quality of the subsequent processes. The assembly quality of the body is not good, which not only affects the appearance of the vehicle, but also causes leakage, wind noise, road noise and door closing obstacles. Therefore, the welding should attract enough attention. .
In the automotive industry, welding is a key link in the manufacture of automotive parts and bodywork. It plays a special role in connecting the upper and lower. At the same time, there are many models of automobile products, complex forming structures, specialized parts production, standardization, and quality of automobile manufacturing. The comprehensive requirements of efficiency and cost have determined that automotive welding processing is a multidisciplinary, cross-disciplinary and technologically integrated production process. In the current manufacturing of automotive parts and body-in-white, the main welding methods are resistance spot welding, CO2 gas shielded welding and laser welding, as well as argon arc welding and electron beam welding.
Characteristics of welding technology
Welding is an important part of the automotive manufacturing process. The body-in-white of the car, the engine and the gearbox are all inseparable from the application of welding technology. In the welding process of automobile bodies mainly based on "steel structure", automotive welding has different requirements from welding of other products:
1. High dimensional accuracy requirements for welded parts
In order to ensure the assembly accuracy and dimensional stability of the product, it is required to minimize the precision deviation of the thin plate parts before welding and the thermal stress and deformation after welding.
2. High performance requirements for weld joints
Weld joints not only meet static and dynamic mechanical properties, but also have severe low cycle fatigue performance requirements.
3. High quality and consistent requirements for batch welding production
4. High cycle and high efficiency requirements for welding production process
5. For the quality control and guarantee of “zero defectâ€, the requirements for monitoring and information management of automated welding process are put forward.
In recent years, the automotive industry has played an active role in promoting the application and promotion of new welding technologies. In view of the development goals of “lighter, safer, better performance and lower cost†for automotive products, current automotive welding technology is rapidly expanding and expanding based on traditional material connection concepts and methods, and is advanced to advanced The direction of quantitative welding manufacturing is developing.
Main welding method
The automotive industry is one of the most widely used industries for welding. The main welding methods are as follows:
Resistance welding
Resistance welding is a method in which pressure is applied through an electrode after the workpiece is combined, and the electric current is welded by the contact surface of the joint and the resistance heat generated by the adjacent portion, and is currently widely used in automobile manufacturing.
In the spot welding process, the factors affecting the quality of the solder joint are: welding current, welding pressure, shape of the end face of the electrode, ferromagnetic material passing through the electrode, and shunting. Especially in the welding workshop where there are many soldering equipments, the welding machines working at the same time sense each other and have an impact on the power grid, resulting in poor stability and consistency of welding quality. Therefore, resistance spot welding control technology is particularly important. At present, the control mode has evolved from single mode control to multi-mode control. The adjustment parameters have been developed from initial univariate adjustment to multivariable adjustment. The welding current, welding time and welding pressure can be adjusted simultaneously during the welding process.
2. Gas shielded welding
The use of an applied gas as an arc medium and protection of the arc and arc welding of the weld zone, referred to as gas shielded welding. As an efficient welding method, CO2 gas shielded welding has been widely used in China's automobile industry due to its small welding deformation and low welding cost. However, there are still some problems in the practical application of CO2 gas shielded welding: taking the most widely used short-circuit transition form in CO2 gas shielded welding as an example, the arc voltage, welding current or welding loop inductance is not properly matched, or the dry elongation of the welding wire is not suitable. Both may cause unstable arc welding, splashing and incomplete penetration, which have a great influence on the weld bead forming and the mechanical properties of the weld. In addition, the short-circuit transition welding requires high dynamic characteristics of the welding power source. If the selection is wrong, the range of parameters for stabilizing the welding arc is narrow, which will affect the quality of the welding.
3. Laser welding
Laser welding is the use of a laser beam generated by laser excitation, through the focusing system and focusing to the weldment joint, converting light energy into heat energy, melting the metal to form a joint. Compared with traditional spot welding, laser welding has unparalleled advantages in terms of welding accuracy, efficiency, reliability, automation, weight reduction and cost reduction. Laser welding is considered to be one of the most promising manufacturing technologies of the 21st century.
The key to laser welding equipment is high-power lasers. There are two main types of lasers. One is solid-state lasers. The main advantage is that the generated beams can be transmitted through optical fibers for flexible manufacturing systems or remote processing. The other type is a gas laser, also known as a CO2 laser, which uses molecular gas as a working medium to operate continuously and output high power.
In the automotive industry, laser technology is mainly used for body welding and part welding, such as welding of the canopy and side panels (see Figure 1). However, laser welding requires high precision assembly of the weldment and requires that the position of the beam on the workpiece cannot be significantly offset. Otherwise it is easy to cause soldering defects.
Figure 1 Using a laser-welded canopy eliminates surface irregularities and eliminates edging
The refined welding production method represented by laser welding promotes the advancement of automotive welding technology with a new technical concept. In addition, some new connection methods are also the first to be applied in automotive manufacturing. For example, variable polarity MIG/MAG welding methods, laser-arc hybrid welding methods, magnetic pulse welding methods, bonding and mechanical connection methods have been successfully applied in the manufacture of various new models.
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