With the trend towards high-quality, high-efficiency, automated, flexible, and intelligent manufacturing, laser welding technology is increasingly being used in the automotive body manufacturing field. This article mainly introduces the commonly used laser welding technologies in the automotive industry and provides examples of their practical application in JAC Motors.
Laser welding technology, as a laser processing technology, was first applied to welding thin and small parts as early as 1964. With the rapid development of the automotive industry and the continuous improvement of people's demands, in order to meet the requirements of safety, environmental protection and energy conservation, and to realize the automation, flexibility and intelligent development of welding product manufacturing, laser welding technology began to be applied to the field of automotive body manufacturing in the 1980s.
Classification of laser welding technology
1. Laser brazing
Laser brazing is a welding method that uses a laser as a heat source and a filler metal (called brazing filler metal) with a melting point lower than that of the base metal. After being heated and melted, the liquid brazing filler metal wets the base metal, fills the joint gap, and diffuses with the base metal to achieve a connection. Its principle is shown in Figure 1. The application of laser brazing in welding not only makes products more aesthetically pleasing and improves sealing, but also significantly increases the strength of the welded area, thereby enhancing the overall safety performance of the vehicle.
Laser brazing is currently the most widely used welding process in automotive body welding. Its main advantage lies in producing a smooth surface while avoiding the melting of zinc plating. It is often used on the following parts of the vehicle body: the joint between the left and right side panels and the roof (eliminating the need for a rubber sealing strip on the roof, which is both aesthetically pleasing and cost-effective); the joint between the upper and lower parts of the trunk's outer panel; and the joint between the upper and lower sections of the C-pillar.
2. Laser melting welding
Laser fusion welding is a welding method that uses a laser as a heat source to melt a portion of the base material of two plates at the corner joint (while simultaneously melting the nearby welding wire to fill the corner joint of the two plates), forming a liquid metal. After cooling, a reliable connection is formed. Its process principle is shown in Figure 2.
Laser fusion welding can be specifically divided into laser penetration welding, laser fusion welding (without filler wire), and laser fusion filler wire welding, etc., and is mostly used for welding automotive roofs and floors.
3. Laser remote welding
Laser remote welding utilizes a galvanometer scanning head mounted on the sixth axis of a robot. Laser trajectory movement is achieved solely through the reflection of the galvanometer's movement, eliminating the need for a robotic arm to follow the laser. Laser remote welding systems offer high flexibility and efficiency; one system can replace 6-9 conventional robotic spot welding units. Maintaining a laser head distance of over 500mm from the workpiece extends the lifespan of the lens protective glass.
Compared to traditional welding, the biggest advantage of laser remote welding lies in its increased productivity. The rapid movement of the scanning head's lenses significantly reduces the time spent on positioning the robotic arm, thereby drastically shortening manufacturing time. Compared to the average speed of 0.5 weld points/s for resistance spot welding, laser remote welding achieves a speed of 3-4 weld points/s, making full use of the laser beam. Through mass production testing, laser remote welding has reduced the time by 80% compared to traditional resistance welding.
Another important manifestation of the high flexibility of scanning lenses is the diversity of welding shapes. If the weld is C-shaped, its welding speed is significantly increased compared to a linear weld. Laser remote welding is mostly used in automotive body-in-white sub-assemblies. Figure 3 shows some actual examples of laser remote welding.
4. Laser hybrid welding
Laser hybrid welding mainly refers to laser and MIG arc hybrid welding. In this process, the laser and the arc interact and complement each other, and its process principle is shown in Figure 4.
Laser-MIG hybrid welding is more economical than laser welding. Laser-MIG welding utilizes both a laser beam and an electric arc, resulting in high welding speed, stable welding process, and high thermal efficiency, while also allowing for larger weld assembly gaps. The molten pool in laser-MIG hybrid welding is smaller than that in MIG welding, with lower heat input, a smaller heat-affected zone, and less workpiece deformation, significantly reducing post-weld correction work. The combined effect of laser-MIG hybrid welding is shown in Figure 5.
Advantages and disadvantages of laser welding
1. Advantages of laser welding
(1) The laser beam has a small laser focal spot and high power density, which can weld some high melting point and high strength alloy materials.
(2) The weld has high strength, fast welding speed, narrow weld and good surface condition, eliminating the need for post-weld cleaning and other work.
(3) The heat input is small, the heat-affected zone is small, the workpiece shrinkage and deformation are small, and no post-weld straightening is required.
(4) The overlap edge is shorter than that of traditional spot welding, which is beneficial to the lightweighting of the vehicle body and the reduction of costs.
(5) Multiple simultaneous or time-sharing welding of parts that are difficult to reach by ordinary methods can be achieved through optical fiber.
(6) High production efficiency, stable and reliable processing quality, and good economic and social benefits.
2. Disadvantages of laser welding
(1) Laser welding requires high precision in workpiece assembly due to the small size of the focused laser spot and the narrow weld seam. The position of the workpiece must be extremely precise, and the position of the laser beam on the workpiece must not deviate significantly and must be within the focusing range of the laser beam. If the workpiece assembly precision or the beam positioning precision does not meet the requirements, welding defects can easily occur. The requirements for weld seam shape in laser welding are shown in Figure 6.
(2) Laser filler wire welding process control is relatively difficult. Laser filler wire welding is a type of fusion welding, where the focused laser spot irradiates both the workpiece and the welding wire. The molten pool is relatively small, and accurate control of the relative position of the laser wire is crucial to ensure that the continuously fed welding wire melts uniformly.
(3) The weld solidifies relatively quickly, which may result in defects such as porosity and embrittlement.
(4) Due to the large amount of spatter, the weld of the penetration weld is rougher than that of the brazing weld, but the strength is much stronger than that of the ordinary spot weld.
(5) Compared with other welding methods, lasers and their related systems are more expensive and require a large initial investment.
The aforementioned conditions place high demands on the technical and economic capabilities of vehicle manufacturers, thus limiting the widespread application of laser welding technology in China. Currently, its application in body-in-white manufacturing in my country is relatively limited, although several manufacturers have already achieved good results.
Conclusion
Based on the practical application results of laser welding technology in automobile factories, it can be seen that laser welding not only reduces vehicle weight and improves assembly precision, but also significantly enhances vehicle body strength, providing better safety and comfort for users. It is believed that with continuous breakthroughs in laser welding technology and advancements in manufacturing processes, laser welding will undoubtedly become an important component of future automotive body-in-white manufacturing processes.
