New development direction of laser welding technology

Laser welding technology is a comprehensive technology integrating laser technology, welding technology, automation technology, material technology, mechanical manufacturing technology and product design. It is ultimately embodied as a complete set of special equipment and a matching process. As an important part of advanced manufacturing technology, laser welding technology has broad application prospects in the future aviation manufacturing industry. The development direction of laser welding technology mainly includes the following aspects:

　　1. Filler wire laser welding

Laser welding generally does not fill the welding wire, but the assembly gap of the weldment is very high, and it is sometimes difficult to guarantee in actual production, which limits its application range. The use of filler wire laser welding can greatly reduce the requirements for assembly clearance. For example, for aluminum alloy plates with a thickness of 2mm, if filler wires are not used, the gap between the plates must be zero to obtain good forming. For example, if φ1.6mm welding wires are used as filler metals, the weld can be guaranteed even if the gap is increased to 1.0mm. Good shape. In addition, the filler wire can also adjust the chemical composition or perform multi-layer welding of thick plates.

　　2. Beam rotating laser welding

　　The method of rotating the laser beam for welding can also greatly reduce the requirements for the assembly of the weldment and the beam alignment. For example, when the 2mm thick high-strength alloy steel plate is butted, the allowable seam assembly gap is increased from 0.14mm to 0.25mm; for the 4mm thick plate, it is increased from 0.23mm to 0.30mm. The allowable error of the alignment between the center of the beam and the center of the weld is increased from 0.25mm to 0.5mm.

　　3. On-line inspection and control of laser welding quality

　　Using the plasma light, sound, and charge signals to detect the laser welding process has become a research hotspot at home and abroad in recent years, and a few research results have reached the level of closed-loop control. The sensors used in the laser welding quality inspection and control system and their functions are briefly introduced as follows:

　　 (1) Plasma monitoring sensor

　　1) Plasma optical sensor (PS): Its function is to collect the characteristic light of plasma-ultraviolet light signal.

　　2) Plasma Charge Sensor (PCS): The nozzle is used as a probe to detect the potential difference formed between the nozzle and the workpiece due to the uneven diffusion of the plasma charged particles (positive ions, electrons).

　　 (2) System function

　　 1) Identify what kind of method the laser welding process belongs to. Stable deep penetration welding process, with plasma, strong PS and PCS signals;

　　 Stable thermal conduction welding process, no plasma is generated, PS and PCS signals are almost equal to zero;

In the 　　 mode unstable welding process, plasma is generated and disappeared intermittently, and the PS and PCS signals intermittently rise and fall accordingly.

2) Diagnose whether the laser power transmitted to the welding area is normal. When other parameters are constant, the strength of the PS and PCS signals has a corresponding relationship with the power incident on the welding area. Therefore, by monitoring the PS and PCS signals, you can know whether the light guide system is normal and whether the power of the welding zone fluctuates.

　　3) Automatic tracking of nozzle height. The PCS signal decreases as the nozzle-workpiece distance increases. Using this rule for closed-loop control can ensure that the nozzle-workpiece distance remains unchanged, and realize automatic tracking in the height direction.

　　4) Automatic optimization of focus position and closed-loop control. In the deep penetration welding range, when the beam focus position fluctuates, the plasma light signal received by the PS also changes, and the PS signal at the best focus position (the hole is the deepest at this time) is the smallest. According to the discovered law, the automatic optimization and closed-loop control of the focus position can be realized, so that the fluctuation of the focus position is less than 0.2mm, and the fluctuation of the penetration depth is less than 0.05mm.

  Summarize:

While widely using laser welding technology, people also continue to conduct in-depth research on it. In view of its shortcomings, the heating performance of other heat sources is used to improve the heating of the laser to the workpiece. On the basis of maintaining the advantages of laser heating, Laser and other heat sources are used for composite heat source welding, mainly including laser and arc, laser and plasma arc, laser and induction heat source composite welding, and dual laser beam welding. Hybrid welding can increase welding penetration, improve joint performance, reduce equipment costs, and increase welding speed and productivity. In short, laser welding has high production efficiency, stable and reliable processing quality, and good economic and social benefits. In an era where new equipment, new materials, new technologies and new processes are constantly emerging and constantly updated, producers must not only understand the characteristics, advantages and requirements of laser welding, but also recognize the many innovations and future trends in this field. Only in this way can they grasp The trend of technology can always be at the forefront of the times.