I. Overview
Laser welding technology is widely used in aerospace, shipbuilding, vehicle manufacturing and other industrial fields. For the equipment used in high-power laser welding, gas lasers and solid-state lasers are mainly used. Compared with gas lasers, solid-state lasers have a short wavelength, and the light beam can be transmitted through optical fibers. It can be combined with robots and welding machines, and has the characteristics of flexible automation. It is the development direction of welding lasers. Harbin Welding Research Institute is the earliest research institute in China to develop high-power solid-state laser welding technology. In recent years, Harbin Welding Research Institute has followed the international cutting-edge welding technology, focusing on the research and application development of high-power solid-state laser (Nd:YAG) + arc hybrid heat source welding technology. In order to promote the application of laser and laser + arc hybrid heat source welding technology in China's production field, this paper focuses on the research results and application of laser and laser + arc hybrid heat source welding conducted by Harbin Welding Research Institute.
Second, the research and application of laser welding technology
1. Research on laser welding technology
In the mid-1990s, Harbin Welding Institute introduced the 2kW Nd:YAG solid-state laser from HAAS, Germany, focusing on the prediction of weld shape (mainly weld penetration) based on neural network laser welding parameters. The research can not only predict the weld penetration according to different laser welding parameters, but also give effective laser welding parameters according to different penetration depths, which has important guiding significance for experimental research and production.
In order to monitor the stability of small holes during laser deep-fusion welding, Harbin Welding Research Institute took the lead in researching the coaxial visual sensing technology of Nd : YAG laser welding process in China. The Nd:YAG laser welding process coaxial vision sensing system can not only realize the monitoring and research of the small hole state, but also can detect the weld penetration and the penetration of the workpiece based on the monitoring of the small hole shape. The comparison between the measured value and the experimental value of the weld penetration indicates that the detection error of weld penetration is not more than 12% when the workpiece is not penetrated; and the weld penetration depth is significantly larger than the workpiece thickness after the workpiece is penetrated. Therefore, the penetration of the workpiece can be detected based on the comparison between the detected value of the weld penetration and the thickness of the workpiece after the workpiece is penetrated. Figure 1 shows a small-hole coaxial visual image captured by a carbon steel material with a laser power of 1200 W and a welding speed of 1.8 m/min. The laser focal length is located on the surface of the workpiece. Figure 2 shows the coaxial visual image of the acquired small hole. Based on the extracted 3D grayscale image.
2. Application of laser welding technology
The laser welding technology developed by Harbin Welding Research Institute is mainly used in the civil manufacturing industry. The main applications include automotive gearbox combination gear welding, gearbox gear and shaft welding, and car steering gear booster cylinder welding. See Figure 3) and the welding of the premium car light bracket (see Figure 4). The weld seam of the steering wheel of the car steering gear for the car is a saddle-shaped weld; the weld form of the high-vehicle lamp bracket is a space three-dimensional curved weld. Laser-robot three-dimensional space welding technology makes it easy to weld space three-dimensional welds. Figure 5 shows the premium car light bracket in welding.
In addition, Harbin Welding Research Institute applies laser welding technology to the welding of stainless steel conveyor belts, the welding of stainless steel electronically controlled switchgear, the welding of new thin-walled stainless steel radiators (see Figure 6) and other fields of civil product manufacturing. The welding of precision instrument parts for military weapons and equipment is also an important application field of laser welding technology of Harbin Welding Research Institute.
Research and application of laser + arc hybrid welding technology
1. Research on laser + arc hybrid heat source welding technology
"Laser + arc hybrid heat source welding" is a new welding method. This new welding method not only has the high adaptability of general arc welding, but also has the characteristics of large melting depth, high speed and low deformation of laser as welding heat source. High-quality and efficient welding technology developed rapidly in recent years. The research and development of laser + arc hybrid heat source welding technology of Harbin Welding Research Institute is mainly aimed at the compounding of high-power solid-state laser (Nd:YAG) + GMAW arc. The research direction is mainly low-carbon steel laser + short-circuit transition MAG arc composite heat source welding characteristics, Aluminum/steel large spot Nd:YAG laser + pulse MIG composite heat source high-melting-brazing technology and high-strength aluminum alloy high-power solid-state laser (Nd:YAG) + pulse MIG arc hybrid heat source welding technology.
(1) Low carbon steel laser + MAG short-circuit arc hybrid heat source welding characteristics study shows that the single short-circuit MAG arc welding is at a small welding current (30 ~ 60A) and a higher welding speed (> 1.5m / min), It is difficult to obtain a stable welding process. Figure 7 shows the voltage and current waveforms of the short-circuit transition MAG arc welding when the arc voltage is 16V, the welding current is 50A, and the welding speed is 1.5m/min. A laser is added on the basis of the short-circuit transition arc, and the laser power exceeds 900 W, which is located in the deep-fusion welding mode region, and a stable short-circuit process can be obtained under the condition of high-speed welding. Figure 8 shows the voltage and current waveforms of the composite voltage when the arc voltage is 16V, the welding current is 50A, the welding speed is 1.5m/min, and the laser power is 1200W. Small current short circuit MAG arc and high power laser composite have high speed and low deformation welding characteristics, suitable for welding with gap thin plates. Fig. 9 is the butt joint of carbon steel material with different thickness plates (plate thickness 1.2mm+1.8mm), and the weld seam is formed when the butt gap is 0.7mm. The test conditions are welding voltage 14V, welding current 50A, laser power 2000W, welding speed 2m/ Min.
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