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. Latest developments in 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 power of CO2 lasers used for cutting was mainly 1500~2000W, and the recent leading products were 4000~6000W. The thickness of 6000W cuttable stainless steel and carbon steel were 35mm and 40mm respectively. Mm.
1.3 Equipment intelligence and flexible processing
Especially for the YAG laser, it is extremely convenient for processing 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 primarily 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, 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, 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 significantly increases the welding speed, which is about 2 times that of TIG welding; the tungsten burnout 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. Compared with laser single-arc hybrid welding, the welding speed can be increased by about 1/3 and the line energy can be reduced by 25%.
There is also a report on Laser-plasma composite welding at the Modern Connection Center at Conventry University in the UK. 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 is the basis for PALW for robots.
1.5 Laser welding of aluminum alloy
Aluminum alloys are widely used due to their high specific strength and good corrosion resistance. The difficulty of CO2 laser welding of aluminum alloy 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 anodization), surface coating, surface coating, etc., laser-TIG and laser-MIG are also reported. 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 is shown that: 70% He+30% Ar, the direction of the airflow 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 an "upward" effect on the back weld, forming a regular weld bead in a wide parameter range. Welding of the 6061 aluminum alloy shows that the weld strength can reach 90% of the base metal.
1.6 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.
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