A light beam consists of a single electron, photon, electron and ion or a combination of two or more particles. High power density heat sources include plasma arc, electron beam, laser beam and composite heat source laser beam+arc (TIG, MIG, plasma).
At present, the main fields of high-energy beam welding are: ① Large-scale high-energy beam equipment-large-scale power and large-scale machinable parts (even parts integration). ② Develop new equipment, such as pulse working mode and short wavelength laser. ③ Intelligent equipment and flexible processing. ④ Improvement and diagnosis of beam quality. ⑤ Study the interaction mechanism among light beam, workpiece and machining medium. ⑥ Beam recombination. ⑦ Welding of new materials. (8) Expansion of application fields.
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 laser power amplification, pulse mode and high quality beam mode
Take American PRC Company as an example. In previous years, the power of CO2 laser used for cutting was mainly1500 ~ 2,000 W, while the leading products in recent years were 4,000 ~ 6,000 W. The thickness of stainless steel and carbon steel that can be cut at 6,000 W is 35 mm and 40 mm respectively.
1.3 intelligent equipment and flexible processing
Especially for YAG laser, it can be transmitted through optical fiber, which brings great convenience to processing.
Its main features are as follows: ① One machine has multiple functions. ② One laser machine can be used for multi-station (up to 6) processing. ③ The maximum length of optical fiber can reach 60m. ④ Open the control interface. ⑤ It has remote diagnosis function.
Beam recombination of 1.4
The most important thing is laser-arc recombination. In deep penetration welding, plasma is generated above the molten pool, and in compound machining, the plasma generated by laser is beneficial to the stability of arc. Compound machining can improve machining efficiency; It can improve the weldability of materials with poor weldability such as aluminum alloy and dual-phase steel; Can increase the stability and reliability of welding; Usually, laser wire welding is very sensitive, so it becomes easy and reliable to combine arc.
Laser-arc recombination is mainly composed of laser and TIG, plasma and GMA. Through the interaction between laser and arc, the shortcomings of various methods can be overcome, and then a good composite effect can be produced.
GMA has the advantages of low cost and strong applicability due to the use of filler wire, but has the disadvantages of deep melting depth, low welding speed and large thermal load on the workpiece. Laser welding can form a deep and narrow weld seam, with high welding speed and low heat input, but it requires high investment, high precision of workpiece preparation and poor adaptability to aluminum and other materials. The composite effect of laser -GMA is that the arc increases the gap bridge for two reasons: one is to fill the welding wire, the other is to have a wider arc heating range; The arc power determines the width of the weld top; The plasma generated by laser reduces the resistance of arc initiation and maintenance, making the arc more stable; The laser power determines the depth of the weld; In addition, recombination leads to the increase of efficiency and the enhancement of welding adaptability.
From the point of view of energy, laser arc recombination can significantly improve welding efficiency. This is mainly based on two effects. One is that the higher the energy density, the higher the welding speed. The second is the superposition effect of the interaction between two heat sources.
Comparison of linear energy, weld cross-section and energy utilization among GMA, laser wire-adding and laser arc hybrid welding.
Laser -TIG composite can significantly improve the welding speed, which is about twice that of TIG welding. The bur loss of that tungsten electrode is also greatly reduce, and the service life is prolonged; The included angle of the groove also reduces the welding area, similar to laser welding. Flawn Hof Institute of Laser Technology, University of Ahern has developed a laser double-arc hybrid welding technology. Compared with laser single arc composite welding, the welding speed can be increased by about 1/3 and the linear energy can be reduced by 25%.
Laser-plasma hybrid welding is also reported in the Modern Connection Center of Conventry University in the UK. Its advantages are: improving welding speed and penetration; Due to arc heating, the temperature of metal rises, which reduces the reflectivity of metal to laser and increases the absorption of light energy. Based on the experiment of low-power CO2 laser, it will be carried out on 12 000W CO2 laser and 2kW YAG laser transmitted by optical fiber, which lays the foundation for the robot's PALW.
1.5 study on the interaction between laser, workpiece and shielding gas
Laser welding of 1.6 aluminum alloy
Aluminum alloy is widely used because of its high specific strength and good corrosion resistance. The main difficulties of CO2 laser welding aluminum alloy are high reflectivity, good thermal conductivity, difficult to reach evaporation temperature, difficult to induce the formation of pores (especially when the content of Mg is relatively small), and easy to produce pores. In addition to surface chemical modification (such as anodic oxidation), surface coating and surface coating, laser-TIG and laser -MIG are reported to improve the absorption rate, among which MIG- DC electrode positioning method is better because of its strong surface cleaning effect and alloying effect of welding wire.
Recently, L Cretteur of Belgium and S Marya of France welded 606 1 aluminum alloy with CO2 laser of mixed gas and flux. Under the given experimental conditions, when 70%He+30%Ar, the gas flow direction is opposite to the welding direction, the effect is better; Aiming at the sagging defect on the back of weld seam during penetration welding, the flux of 75% LiF+25%LiCl was used to remove oxidation, which improved the combination of molten metal on the back and base metal, made the back weld seam have the effect of "upturning" and formed regular weld seam in a wide range of parameters. The welding of 606 1 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 the advantages of fast heating speed, less heat input and less deformation. High adhesive strength; Low dilution rate; The thickness of the modified layer can be accurately controlled, with good positioning, easy access and high production efficiency.
Laser cladding is not only used for civil products, but also for cladding and repairing the heat-resistant and wear-resistant layer of nickel-based turbine blades of aircraft engines in Britain and the United States.
2. The latest development of electron beam welding and plasma arc welding.
The development of electron beam welding abroad can be summarized as follows: the development of ultra-high energy density devices, the intelligence and flexibility of equipment, the diagnosis of electron beam current characteristics, the study of interaction mechanism between beam and substance, and the research of non-vacuum electron beam welding equipment and technology.
Japan has developed an ultra-high voltage electron beam welder with an accelerating voltage of 600kV and a power of 300kW, which can weld 200 mm stainless steel at a time, and the depth-width ratio is 70: 1.
Japan, Russia and Germany have carried out research on double-gun wire-filled electron beam welding technology. On the basis of the first welding of thick plate, the concave or undercut defect at the top is compensated by the second wire filling; Japan has realized ultra-high speed welding of thin plates with double grippers, and the reverse side has no splash and good forming.
The electron beam welding machine for bimetallic and trimetallic thin strips successfully developed in France has also attracted considerable attention.
As for non-vacuum electron beam welding, Germany has realized wire-filling welding of rotating parts with Al Mg0.4 Si 1.2 as the base material, and the wire-filling material is AlMg4.5Mn, the wire feeding speed is 35m/min and the welding speed is as high as 60m/min. This research was completed on a 25kW electron beam welder in Stuttgart University.
Non-vacuum electron beam welding has attracted much attention in the field of automobile manufacturing. For example, the non-vacuum electron beam welding of synchronous ring and gear of manual transmission has exceeded 500 pieces/hour.
Recently, German and Polish scholars have developed a non-contact temperature measuring device installed in a vacuum chamber during vacuum electron beam welding. The minimum diameter of the measuring point is 1.8 mm, which is mainly used for brazing ceramics and cemented carbide. The device can eliminate the interference of random heat flow and has high measurement accuracy.
In plasma arc welding, variable polarity plasma arc welding and aluminum alloy perforation plasma vertical welding are one of the problems that people pay attention to.
3. Present situation of high energy beam welding in China.
In China, high-energy beam welding is paid more and more attention by welding, physics, laser, materials, machine tools, computers and other related personnel. There is a certain gap between China and foreign countries in terms of equipment level, but in terms of technology research, the level is relatively close, and even it has its own characteristics in some aspects.
3. 1 laser welding
In terms of equipment production and research, we mainly produce kilowatt CO2 laser equipment and solid YAG laser equipment below 1 kilowatt.
The domestic research on laser welding mainly focuses on the formation mechanism, characteristic analysis, detection and control of laser welding plasma, simulation of laser deep penetration welding, application of laser-arc composite heat source, laser surfacing and so on. Tsinghua University analyzed the acoustic signal of penetration state from the angle of sound and electricity, and put forward the equivalent circuit and mathematical model of the electric characteristics of laser welding plasma. In suppressing the negative effects of plasma, Zhang Xudong and Chen Wuzhu of Tsinghua University put forward the side suction method; Xiao Rongshi and Zuo Tiechuan of the National Industry-University-Research Laser Technology Center put forward the method of blowing different gases through double-layer inner and outer circular tubes; Liu Jinhe of Northwestern Polytechnical University put forward the method of external magnetic field.
3.2 Electron beam welding
China's self-developed electron beam welder began in the1960s. Up to now, hundreds of electron beam welders with different types and functions have been developed and produced, and a technical team has been formed, which can provide low-power electron beam welders for the domestic market.
In recent years, key components (such as electron gun, high voltage power supply, etc. ) has been imported, and other parts are matched in China. The advantage of this method is that the equipment not only maintains a high technical level, but also greatly reduces the cost, and can also provide better after-sales service for users.
At present, the special electron beam welding machine for automobile gears, represented by EBW series of Institute of Electrical Engineering, Chinese Academy of Sciences, occupies the main market share of electron beam welding for automobile gears in China. China's small and medium-power electron beam welding machine has approached or caught up with the advanced level of similar foreign products, and its price is only about 1/4 of that of similar foreign products, with obvious cost performance advantages.
In terms of mechanism and technology research, the work carried out by Beihang University, Beihang University, Tianjin University, Shanghai Jiaotong University, Northwestern Polytechnical University, China Institute of Science and Electrician, Guilin Institute of Electrical Appliances, Xi 'an Aero-Engine Company and Institute of Aerospace Materials and Technology involves keyhole dynamics of molten pool, electron beam brazing, fatigue crack propagation behavior of joints, residual stress of joints, wire filling welding, weld trajectory teaching in local vacuum welding and so on.
3.3 plasma arc welding
In plasma arc welding equipment, Northwestern Polytechnical University has carried out research on pulsed plasma spray welding technology. By connecting the high-frequency IGBT contactless switch between the workpiece and the anode (nozzle) of the spray gun, the high-frequency alternating operation of the transfer arc and the non-transfer arc is successfully realized, and the plasma spray welding under a single power supply is realized. Xi Jiaotong University has carried out research on variable polarity plasma arc welding equipment suitable for aluminum, magnesium and their alloys. The positive and negative half waves of the main arc are powered by two DC power supplies respectively, which realizes the variable polarity welding of the workpiece (aluminum), which not only stabilizes the arc, but also has a reliable cathode cleaning function. Beijing Institute of Aeronautics and Astronautics has carried out the research on "one pulse and one hole" technology of pulsed plasma arc welding. In the aspect of detecting the characteristics and behavior of keyhole in plasma arc welding, Harbin Institute of Technology, Beihang University and Tsinghua University respectively detect the establishment, closure and size of keyhole through spectral information, arc voltage and current spectrum analysis; Wang Xibao and Zhang Wenzhong of Tianjin University analyzed the powder transmission behavior and its main influencing factors in the process of plasma arc powder surfacing, and calculated the transmission velocity distribution of iron-based alloy powder and boron carbide powder in the arc column under different parameters and the distribution of powder flow along the cross section of the arc column. In important applications, Xi 'an Aero-Engine Company improved the process of an aero-engine by using self-made power supply equipment and imported plasma welding torch.