Principles and Characteristics of Handheld Laser Welding
1. The principle of Handheld Laser Welding.
Laser welding uses laser as welding heat source and robot as motion system. The special advantage of the laser heat source is that it has an extraordinary heating capacity and can concentrate a large amount of energy on a small point of action, so it has the characteristics of high energy density, concentrated heating, fast welding speed and small welding deformation. Realize the fast connection of thin plates. When the power density on the laser spot is large enough (>106 W/cm2), the metal is heated rapidly under the irradiation of the laser, and its surface temperature rises to the boiling point in a very short time, and the metal vaporizes. The metal vapor leaves the surface of the molten metal pool at a certain speed, generating an additional stress that reacts to the molten metal, causing it to dent downward, creating a small pit under the laser spot. As the heating process progresses, the laser can be directly injected into the bottom of the pit, forming a long and thin "small hole". When the recoil pressure of the metal vapor balances with the surface tension and gravity of the liquid metal, the small hole no longer goes deep. When the spot density is high, the small holes produced will penetrate the entire plate thickness to form a deep penetration weld. The small hole advances in the welding direction with the beam relative to the workpiece. The metal melts in front of the small hole, flows back through the small hole, and re-solidifies the weld formed.
2. Characteristics of Handheld Laser Welding method
The handheld laser welder method has the following characteristics:
1. High energy density, suitable for high-speed welding.
2. The welding time is short, the thermal deformation and heat affected zone of the material itself are small, and it is especially suitable for high melting point and high hardness processing.
3. No wear and tear of electrodes, tools, etc.
4. No pollution to the environment.
5. It can realize long-distance, difficult-to-reach parts with ordinary methods, multiple simultaneous or time-sharing welding through optical fiber.
6. It is easy to change the laser output focal length and solder joint position.
7. It is easy to mount on the robot device.
Laser hybrid welding technology has significant advantages. For laser hybrid welding, Handheld Laser Welding the advantages are mainly reflected in: there is no phenomenon of sagging on the back of the weld during burn-through, and the application range is wider; for laser-MIG welding, the advantages are mainly reflected in: higher welding speed, large welding depth, and Less welding heat, high welding seam strength, small welding seam width and welding seam protrusion are small, so that the production process stability of the whole system is good, the equipment availability is good, and the workload of welding seam preparation and welding seam processing after welding is small , The welding production time is short, the cost is low, and the production efficiency is high.
3. The main form of laser-arc hybrid heat source welding
1. Laser-TIG hybrid welding
The characteristics of Handheld Laser Welding and TIG hybrid welding are:
(1) Using arc to enhance the effect of laser, low-power laser can be used instead of high-power laser to weld metal materials.
(2) High-speed welding is possible when welding thin parts.
(3) It can increase penetration depth, improve weld formation, and obtain high-quality welded joints.
(4) It can alleviate the precision requirements of the base metal end face interface. For example, when the CO2 laser power is 0.8kW, the TIG arc current is 90A, and the welding speed is 2m/min, it can be equivalent to the welding capacity of a 5kW CO2 laser welder. The 5kW CO2 laser beam is combined with a 300A TIG arc to weld At a speed of 0.5 to 5m/min, the penetration depth obtained is 1.3 to 1.6 times that of the 5kW CO2 laser beam welding alone.
2. Laser-plasma arc hybrid welding
Laser plasma hybrid welding uses the coaxial method .The plasma arc is generated by the ring electrode, and the laser beam passes through the middle of the plasma arc. The plasma arc has two main functions: on the one hand, it provides extra energy for laser welding, increases the welding speed, and improves the efficiency of the entire welding process; On the one hand, the plasma arc surrounds the laser, which can produce the effect of heat treatment, extend the cooling time, reduce the sensitivity of hardening and residual stress, and improve the microstructure performance of the weld.
3. Laser-MIG hybrid welding
The basic principle of laser-MIG hybrid welding .In addition to the arc inputting energy to the welding zone, the Handheld Laser Welding also inputting heat to the weld metal. The laser hybrid welding technology does not act on the two welding methods in sequence, but the two welding methods act on the welding zone at the same time. Laser and arc affect the performance of hybrid welding in different degrees and forms. During laser-MIG hybrid welding, volatilization not only occurs on the surface of the workpiece, but also on the filler wire, which makes more metal volatilize, which makes the laser energy transmission easier. MIG welding is characterized by low power source cost, good weld bridging, good arc stability, and easy to improve weld structure through filler metal. The characteristics of laser beam welding are large penetration depth, high welding speed, low heat input, and narrow weld seams. However, welding thicker materials requires more powerful welding lasers. At the same time, the molten pool of laser hybrid welding is smaller than that of MIG welding, and the deformation of the workpiece is small, which greatly reduces the work of correcting welding deformation after welding. Laser-MIG hybrid welding will produce two independent molten pools, and the heat input from the arc behind also plays the role of post-weld tempering
4. Double laser beam welding technology
In the laser welding process, due to the high laser power density, the welding base material is rapidly heated and melted and vaporized to generate high-temperature metal vapor. Under the continuous action of high power density laser, it is easy to generate plasma cloud, which not only reduces the absorption of laser by the workpiece, but also makes the welding process unstable. If after the formation of larger deep penetration holes, reduce the laser power density to be irradiated, and the larger deep penetration holes that have been formed will absorb more laser light, as a result, the effect of the laser on the metal vapor is reduced, and the plasma The cloud can be reduced or disappeared. Therefore, use a pulsed laser with a higher peak power and a continuous laser, or two pulsed lasers with large differences in pulse width, repetition frequency and peak power to perform hybrid welding on the workpiece. During the welding process, the two lasers Jointly irradiate the workpiece to periodically form larger deep penetration holes, and then stop a beam of laser irradiation at an appropriate time, which can make the plasma cloud small or disappear, improve the absorption and utilization of laser energy by the workpiece, increase the welding penetration, and increase Welding ability.
Four, conclusion Laser hybrid welding combines the two welding methods.
It uses the advantages of both to obtain the best Handheld Laser Welding effect, higher welding speed and good welding seam bridging ability. It is one of the most advanced welding methods at present, achieving the perfect combination of high welding speed and good welding quality. Laser hybrid welding technology is a new welding technology in the automotive industry, especially for assembly gap requirements that cannot be achieved or economically unfeasible in laser beam welding. It has a wide range of applications and high-efficiency characteristics, while reducing investment costs, shortening production time, saving production costs and increasing productivity, and has stronger competitiveness.
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