The automobile industry is a "machine to change the world" and an important pillar industry for promoting national economic development. The automobile industry is heavily invested in high-tech and high-end equipment, which reflects the national manufacturing technological level. Every automobile is a crystallization of modern high technologies. The automobile industry is the largest user of robots, computer numerical control machine tools, and automatic production lines. Modern automobiles also make extensive use of novel materials, processes, equipment, and electronic technologies. The popularity of automobiles has met the people’s enormous demand for travel, so the quality of automobiles has a direct impact on the safety of use. In the automobile manufacturing process, the value of car body accounts for approximately 1/5 of that of the whole car, and the weight of car body accounts for 1/3 of that of the whole care. As a result, the manufacturing quality of car body is directly related to the overall safety and comfort of the vehicle. At the same time, the choice of car body materials is critical in the lightweight development of a car. Stamping, welding, painting, and final assembly are all parts of the automobile body manufacturing process. The welding process, for example, is used to create a body-in-white by welding stamping sheet metal parts together. Poor welding quality can cause deformation and cracking of body sheet metal and abnormal noise, and even endanger the personal safety of passengers.

Steel has been traditionally used as the body material of automobiles. Because the steel plates that make up the body are generally thin, the welding of the body is primarily resistance spot welding, which is widely used in the welding of underbody, side wall, frame, roof, door, and body assembly with as many as 4000-6000 welding spots. In addition, CO₂ gas shielded welding, stud welding, arc welding, brazing, and other technological methods are used in the automobile body manufacturing process. Traditional welding technologies for automobile body can essentially meet the quality requirements of an automobile body after welding. As the quantity of produced automobiles grows, the demands for high automobile body manufacturing efficiency increase. Different automobile body parts and welding joint forms have higher requirements for the flexible automobile body manufacturing. Special welding requirements, such as lightweight material welding and dissimilar material welding, have higher requirements for the welding process. It can be seen that high-quality and efficient welding of automobile body is the development trend, and the traditional welding process struggles to meet this demand.

Laser welding technology, as an advanced forming technologyin opto-mechatronics, has many advantages including high energy density, fast welding speed, low welding deformation, and good flexibility. It has become increasingly popular in the welding of automobile body in recent years. Laser welding is a fast and precise welding method that uses a high energy density laser beam as a heat source. The use of laser welding for automobile body has obvious advantages. For example, there is no mechanical contact between the welding device and the weldment, which reduces pollution to the workpiece. Because the heat energy of the laser beam is concentrated, the heat affected zone is small and the thermal deformation and damage are weak. Laser welding produces a beautiful welding seam with excellent mechanical properties. Welding robots and numerical control systems allow for a precise control of energy output, fast welding speed, and high production efficiency. As a result, the laser welding technology can not only improve the precision and efficiency in the car body process, but also improve the rigidity and strength of the car body, and thus the vehicle driving comfort and safety are improved.

The laser welding technology for automobile body is divided into two categories: the laser welding technology and the laser welding intelligent technology. Aiming at the laser welding process of automobile body, the structures of the commonly used materials are summarized (Table 1). The characteristics of the most commonly used laser welding processes for automobile body as well as information on welding parts, welding forms, and welding materials applicable to automobile body are also summarized (Table 2). Then, the commonly used laser deep penetration welding, laser filler welding, laser brazing, and laser-arc hybrid welding processes for automobile body are introduced, with a focus on the principles of these four laser welding processes. In conjunction with the welding characteristics of automobile body, the research progress of various welding processes for automobile body is expounded and summarized. In addition, the new laser welding process is described. These processes primarily include laser spot welding, laser wobble welding, multi-laser beam welding, and remote laser welding. This paper discusses the intelligent laser welding technology for automobile body from two perspectives: welding seam tracking and defect online detection. The welding seam tracking technology employs an advanced vision sensor to identify and track the welding seam of an automobile body before and during welding, and it corrects the movement path of the welding robot in real time to ensure welding stability. For example, the welding seam tracking system developed by Scansonic Company in Germany can achieve a dynamic and accurate identification of welding seams (Fig. 13). The key to detecting weld defects is to create a correlation model between defects and monitoring signals. Ma et al. have developed a correlation model between multivariable signals and porosity defects using visual sensing and a keyhole depth measuring device, and accurately identified the blowhole defects (Fig. 14). Finally, this paper summarizes the current problems in the laser welding process and the intelligent technology, and the future development trend is prospected.

The laser welding technology has become an indispensable and important technology in the development of lightweight automobile body. The laser welding process for lightweight body materials and dissimilar materials still requires extensive research and exploration. At the same time, an intelligent welding system with weld tracking, weld defect detection, and closed-loop control of welding parameters is required.