The power density (Power Density) of high energy beam welding reaches above 105 W/cm2.
The beam is composed of a single electron, photon, electron and ion or a combination of two or more particles. The heat sources belonging to high power density are: plasma arc, electron beam, laser beam and composite heat source laser beam + Arc (TIG, MIG, Plasma).
The main areas of focus for current high-energy beam soldering are: 1 The large-scale of high-energy beam devices - large-scale power and large-scale processing of parts (and even parts integration). 2 The development of new equipment, such as pulse working mode and short-wavelength laser. 3 The intelligence of the equipment and the flexibility of processing. 4 beam quality improvement and diagnosis. 5 Study on the interaction mechanism of beam, workpiece and process medium. 6 beam composite. 7 welding of new materials. 8 extensions of the application area.
1. The latest development of laser welding
1.1 New laser
(1) DC Slab CO2 laser, (2) diode-pumped YAG laser, (3) CO laser, (4) semiconductor laser, and (5) excimer laser.
1.2 Large-scale laser power, pulse mode and high-quality beam mode
Take the US PRC company as an example. A few years ago, the CO2 laser used for cutting was 1500~2000W, and the recent leading product was 4000~6000W. The thickness of 6000W cuttable stainless steel and carbon steel were 35mm and 40mm respectively.
1.3 Equipment intelligence and flexible processing
Especially for the YAG laser, it is extremely convenient to process due to the transmission of available optical fibers.
Its main features are: 1 multi-purpose machine. 2 Multi-station (up to 6) processing is possible with one laser machine. 3 fiber lengths up to 60m. 4 open control interface. 5 has a long-distance diagnostic function.
1.4 Beam composite
The most important is laser-arc composite. During deep-fusion welding, plasma is generated above the molten pool. When combined processing, the plasma generated by the laser is beneficial to the stability of the arc; the combined processing can improve the processing efficiency; and the welding of materials with poor weldability such as aluminum alloy, duplex steel, etc. can be improved. Properties; can increase the stability and reliability of welding; usually, laser wire bonding is very sensitive, and it is easy and reliable to be combined with the arc.
Laser-arc composites are mainly lasers with TIG, Plasma and GMA. Through the mutual influence of laser and arc, each method's own deficiencies can be overcome, and a good composite effect is produced.
GMA has low cost and uses wire filling. It has strong applicability. The disadvantages are shallow penetration depth, low welding speed and high thermal load on the workpiece. Laser welding can form deep and narrow welds with high welding speed and low heat input, but the investment is high, the preparation precision of the workpiece is high, and the adaptability to aluminum and other materials is poor. The composite effect of Laser-GMA is manifested in the fact that the arc increases the bridging property of the gap for two reasons: one is to fill the welding wire, and the other is to increase the arc heating range; the arc power determines the width of the top of the weld; the plasma generated by the laser is reduced. The arc is ignited and maintained to make the arc more stable; the laser power determines the depth of the weld; and further, the recombination leads to increased efficiency and increased weldability.
From the energy point of view, the laser arc recombination has a significant improvement in welding efficiency. This is mainly based on two effects, one is that higher energy density leads to higher welding speed; the other is the superposition effect of two heat source interactions.
Comparison of GMA, laser wire and laser arc composite methods for welding line energy, weld section and energy utilization.
The Laser-TIG Hybrid can significantly increase the welding speed, which is about 2 times that of TIG welding; the tungsten burning loss is also greatly reduced, and the life is increased; the groove angle also reduces the weld area to be similar to that of laser welding. Avon University's Fran and Fei Laser Technology Institute has developed a laser double-arc hybrid welding, which can increase the welding speed by about 1/3 and the line energy by 25% compared with laser single-arc hybrid welding.
There is also a report on Laser-plasma hybrid welding at the University of Conventry's Modern Connection Center. The advantages are: increasing the welding speed and penetration; due to arc heating, the metal temperature is increased, the reflectivity of the metal to the laser is lowered, and the absorption of light energy is increased. Based on the low-power CO2 laser test, it is also carried out on a 12 000 W CO2 laser and a 2 kW YAG laser for fiber transmission, and the PALW is used as a basis for the robot.
1.5 Study on the interaction between laser, workpiece and shielding gas
1.6 Laser welding of aluminum alloy
Aluminum alloys are widely used due to their high specific strength and good corrosion resistance. The difficulty in CO2 laser welding of aluminum alloys is mainly due to high reflectivity and good thermal conductivity, difficulty in reaching evaporation temperature, difficulty in inducing the formation of small pores (especially when the Mg content is relatively small), and easy generation of pores. In addition to surface chemical modification (such as anodizing), surface coating, surface coating, etc., laser-TIG, laser-MIG reports are also available, and the MIG-DC electrode position method is strong due to surface cleaning. The alloying effect with the wire is good.
Recently, L Cretteur of Belgium and S Marya of France performed CO2 laser welding of mixed gas and flux on 6061 aluminum alloy. Under the given test conditions, it shows that 70% He+30% Ar, the direction of the air flow is opposite to the welding direction, and the effect is good for the back side of the weld when penetration welding, 75% LiF+25%LiCl The flux acts to remove oxidation, improve the bonding of the molten metal to the backing base metal, and has a "upward" effect on the back weld, forming a regular weld bead in a wide parameter range. Welding of 6061 aluminum alloy shows that the weld strength can reach 90% of the base metal.
1.7 Laser cladding
Compared with other surface modification methods, laser cladding has faster heating speed, less heat input and minimal deformation; high bonding strength; low dilution rate; the thickness of the modified layer can be precisely controlled, locality is good, and accessibility is good. high productivity.
In addition to civilian products, laser cladding is also used in the heat-resistant and wear-resistant layers of aircraft engine Ni-based turbine blades.
2. Recent advances in electron beam welding and plasma arc welding
The development of foreign electron beam welding can be summarized as: the development of ultra-high energy density devices, the intelligentization of equipment, the diagnosis of electron beam characteristics, the study of beam and material action mechanism, and the research of non-vacuum electron beam welding equipment and processes.
In Japan, an ultra-high pressure electron beam welder with an accelerating voltage of 600 kV and a power of 300 kW has been introduced. It can weld 200 mm stainless steel at a time, with an aspect ratio of 70:1.
Japan, Russia and Germany have carried out research on double gun and wire-filled electron beam welding technology. On the basis of the first welding of the large-thickness plate, the top undercut or undercut defect is compensated by the second filling; the double-grab is used in Japan to realize the ultra-high-speed welding of the thin plate, and the reverse surface has no splash and is well formed.
The successful development of bimetal and trimetal strip electronic beam welding machines in France has also attracted attention.
Regarding non-vacuum electron beam welding, the wire joining of the rotating parts of the base material Al Mg0.4 Si1.2 was realized in Germany. The wire material was AlMg4.5Mn, the wire feeding speed was 35m/min, and the welding speed was as high as 60m/min. The study was done on a 25kW electron beam welder at the University of Stuttgart.
Non-vacuum electron beam welding has been highly valued in the automotive industry. For example, in the manual transmission, the non-vacuum electron beam welding of the synchronizing ring and the gear has a productivity of more than 500 pieces per hour.
Recently, German and Polish scholars jointly developed a non-contact temperature measuring device installed in a vacuum chamber during vacuum electron beam welding. The measuring point has a minimum diameter of 1.8 mm and is mainly used for brazing of ceramics and hard alloys. Random heat flow interference, high measurement accuracy.
In plasma arc welding, variable polarity plasma arc welding and aluminum alloy perforated plasma vertical welding are one of the concerns.
3. Status of domestic high energy beam welding
In China, high-energy beam welding has increasingly attracted the attention of more concerned people such as welding, physics, lasers, materials, machine tools, computers and so on. At the domestic level of equipment, there is a certain gap with foreign countries, but in terms of process research, the level is relatively close, and even in some aspects, it has its own characteristics.
3.1 Laser welding
In the production and research of equipment, it mainly produces kilowatt-class CO2 laser equipment and solid-state YAG laser equipment below 1 kW.
Domestic research on laser welding mainly focuses on laser welding plasma formation mechanism, characteristic analysis, detection, control, deep-fusion laser welding simulation, laser-arc composite heat source application, laser surfacing and so on. From the perspective of sound and electricity, Tsinghua University analyzed the acoustic signal of the penetration state, and proposed the mathematical model of the equivalent circuit and electrical characteristics of the laser welding plasma. In the suppression of the negative effects of the plasma, Zhang Xudong and Chen Wuzhu of Tsinghua University proposed The side suction method; Xiao Rongshi and Zuo Tiezhen of the National Center for Production, Research and Research Laser Technology proposed a double-layer internal and external circular tube blowing heterogeneous gas method; Liu Jinhe of Northwestern Polytechnical University proposed an external magnetic field method.
3.2 Electron beam welding
China's self-developed electron beam welding machine began in the 1960s. Up to now, it has developed and produced hundreds of different types and functions of electron beam welding machines, and formed a technical team for research and production, which can provide low-power electronic products for the domestic market. Beam welder.
In recent years, the introduction of key components (electron guns, high-voltage power supplies, etc.) and the introduction of other components have been introduced. The advantage of this method is that the equipment not only maintains a high level of technology, but also greatly reduces the cost. Provide users with better after-sales service.
At present, the special beam welding machine for automobile gears represented by the EBW series of the Institute of Electrical Engineering of the Academy of Sciences occupies the main market share of domestic automotive gear beam welding; China's small and medium power electron beam welding machines have approached or caught up with the advanced products of similar foreign products. Level, and the price is only about 1/4 of the similar products abroad, with obvious performance and price advantage.
In the mechanism and process research, Beijing Aviation Technology Research Institute, Beijing University of Aeronautics and Astronautics, Tianjin University, Shanghai Jiaotong University, Northwestern Polytechnical University, China Science and Technology Institute, Guilin Institute of Electrical Science, Xi'an Aero Engine Company, Aerospace Materials and Process Research The work carried out involves the hole kinetics of the molten pool, electron beam brazing, joint fatigue crack propagation behavior, joint residual stress, wire-filling welding, and weld trajectory teaching during partial vacuum welding.
3.3 Plasma arc welding
In the field of plasma arc welding equipment, Northwestern Polytechnical University carried out research on pulsed plasma spray welding technology. By connecting high-frequency IGBT contactless switches between the workpiece and the nozzle anode (nozzle), the transfer arc and non-transfer arc were successfully realized. The high frequency alternates to achieve plasma spray welding under a single power source. Xi'an Jiaotong University has carried out research on variable polarity plasma arc welding equipment suitable for Al, Mg and its alloys. The positive and negative half waves of the main arc are respectively powered by two DC power sources, and the workpiece (aluminum) is polarized. Welding, which not only stabilizes the arc, but also has a reliable cathode cleaning effect. Beijing Aeronautical Technology Research Institute carried out the "one-pulse-hole" process research of pulsed plasma arc welding; in the perforation plasma arc welding small hole characteristics and behavior detection, Harbin Institute of Technology, Beijing Institute of Aeronautical Technology and Tsinghua University respectively passed the spectrum Spectrum analysis of information, arc voltage and current, detecting the establishment, closure and pore size of small holes; Wang Xibao and Zhang Wenzhao of Tianjin University analyzed the transport operation of powder in transfer arc during plasma arc powder surfacing and its main influencing factors The iron-based alloy powder and boron carbide powder, the transport velocity distribution in the arc column under different parameters and the powder flux distribution along the cross section of the arc column are calculated. In terms of important applications, Xi'an Aero Engine Company realized the improvement of an aero engine process by using self-made power equipment and imported plasma torch.