The automotive industry is a production-oriented industry that requires a lot of processing and testing, and is also one of the most widely used industries for laser technology. Safety, comfort, energy saving and environmental protection have been the themes of the development of the world automotive industry, and the development of laser technology, as one of the main processing methods in modern automotive production, is also mainly focused on this theme and combined with the own characteristics of this profession. Due to the advantages of laser welding process superiority, high efficiency, good flexibility, etc., with the concept of automotive lightweight, safety performance concept is increasingly enhanced, laser welding and cutting process in the automotive industry will receive more attention and widely used.
Laser self-melting welding, that is, the welding of two or more parts of their own melting and eventually cooling cohesion into one, the welding method does not need to add auxiliary flux or filler, completely using the workpiece's own material fusion together.
When the laser spot irradiates the surface of the workpiece with a power density of 106W/cm2 or more, the workpiece is rapidly heated under laser irradiation and its surface temperature rises to the boiling point in a very short time, causing the metal to melt and vaporize, forming an elongated hole filled with metal vapor in the liquid metal, and when the recoil pressure of the metal vapor balances with the surface tension of the liquid metal and gravity, the hole no longer continues to When the recoil pressure of the metal vapor is balanced with the surface tension of the liquid metal and gravity, the hole does not continue to deepen and forms a small hole with a stable depth, around which is the welding pool.
In body manufacturing, the use of laser welding technology can improve the flexibility of product design, reduce manufacturing costs, improve the stiffness of the body, and improve the competitiveness of the product. Laser welding welding speed is faster, so the heat-affected zone of the welded joint is smaller than other welding methods, and there is almost no welding distortion. This can greatly improve the structure and matching dimensions of the body, the flatness and sealing effect of the door cover and side surround, the matching and sealing of the windshield and wind window, as well as achieve a high quality connection of multi-layer panels and achieve higher body strength.
In addition, since modern car bodies mostly use galvanized steel or high-quality high-strength steel, if the traditional spot welding technology is adopted, a larger welding current and welding pressure must be used due to the three-layer plate and galvanization, which will inevitably result in a decrease in the quality of welded joints and serious deformation of welded joints, thus leading to a decrease in assembly quality. The only feasible is to use medium frequency spot welding connection technology and laser fusion welding connection technology. As far as spot welding itself is concerned, the strength of the welded joint can be high, but the part without the welded joint is still intermittently separated, and the overall strength of the body is lower than the strength of the laser welded joint welded into one piece.
The discontinuity of spot welding and its own characteristics: such as welded joints are easily deformed, especially in the welding of three-layer plate connections, galvanized plate connections and high-strength steel connections, the welding deformation is larger, resulting in the reduction of flatness and gaps at the welded joints, and spot welding will cause the heat-affected zone around the welded joints of the parent material to decrease in strength, and the fracture area of the vehicle is often in this area when it is severely impacted.
