The welding process principle and characteristics of laser welding head

The welding process principle and characteristics of laser welding head

1, the welding principle of laser welding head

Laser welding uses a laser as a welding heat source and a robot as a motion system. The special advantage of the laser head heat source is its extraordinary heating capacity, which can concentrate a large amount of energy at a very small point of action. Therefore, it has the characteristics of high energy density, concentrated heating, fast welding speed and small welding deformation, which can realize the rapid connection of thin plates.

When the power density on the laser head spot is large enough (>106W/cm2), the metal is rapidly heated under the laser irradiation, the surface temperature rises to the boiling point in a short time, and the metal evaporates. The metal vapor leaves the surface of the molten metal pool at a certain speed, creating additional stress to react with the molten metal, causing it to slope downward, forming small pits below the laser spot. As the heating process progresses, the laser can be injected directly into the bottom of the pit, forming elongated "holes". When the recoil pressure of the metal vapor is in equilibrium with the surface tension and gravity of the liquid metal, the pores will go no further. When the point density is very high, the resulting small holes will penetrate the entire thickness of the plate to form deep penetration welds. The hole is advanced in the welding direction and the beam is relative to the workpiece. The weld formed when the metal melts in front of the hole flows back around the hole and solidifies again.

Figure (1)

2, the characteristics of laser welding head welding method

The laser welding head welding 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 processing with high melting point and high hardness.

(3) No wear and consumption of electrodes, tools, etc.

(4) No pollution to the environment.

(5) Long-distance, hard-to-reach components and multi-channel simultaneous or time-sharing welding can be achieved through optical fibers.

(6) It is easy to change the laser output focal length and welding spot position.

(7) It can be easily installed on robotic equipment.

Laser head hybrid welding technology has obvious advantages. For laser head hybrid welding, its advantages are mainly reflected in: no sagging on the back of the weld, and a wide range of applications; for laser-MIG welding, its advantages are mainly reflected in: fast welding speed, large welding depth, less welding heat, and high welding strength , The welding seam width is small, the welding seam bulge is small, so that the whole system production process is stable, the equipment is excellent and usable, the welding preparation workload is small, the welding processing workload 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 combined laser and TIG welding are:

(1) Use low-intensity laser instead of high-power laser, and use arc-enhanced laser to weld metal materials.

(2) When welding thin parts, it can be welded at high speed.

(3) It can increase permeability, improve weld formation, and obtain high-quality welded joints.

(4) The accuracy requirements of the end face interface of the base metal can be relaxed.

For example, when the CO2 laser head power is 0.8kW, the TIG arc current is 90A, and the welding head welding speed is 2m/min, the welding capacity of the 5kW CO2 laser welding head can be equal. When a 5kW CO2 laser beam is combined with a 300A TIG arc at a welding speed of 0.5-5m/min, the penetration depth is 1.3-1. Only 6 times that of a 5kW CO2 laser beam.

2. Laser plasma arc hybrid welding

Laser plasma hybrid welding adopts coaxial mode, as shown in Figure 2. The plasma arc is generated by a 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 additional energy for laser welding, increasing the welding speed and further improving the efficiency of the entire welding process; Reduces susceptibility to hardening and residual stress, and improves weld microstructure and performance.

Figure II)

3. Laser-MIG hybrid welding

The basic principle of laser-MIG hybrid welding is shown in Figure 2. 2. 2. 4. In addition to delivering electrical energy into the welding area, the laser also delivers heat into the weld metal. Laser hybrid welding technology does not use two welding methods sequentially, but uses both welding methods simultaneously in the welding area. Laser and arc will affect the performance of hybrid welding to varying degrees. In the laser-MIG hybrid welding, volatilization occurs not only on the workpiece surface but also on the filler wire, causing more metal to volatilize, thereby making the energy transfer of the laser easier.

Welding has the characteristics of low power consumption, good welding bridging, good arc stability, and the welding structure is easy to fill with metal. However, laser beam welding is characterized by a large depth of fusion, fast welding speed, low heat input, and narrow weld seams, but welding thicker materials requires a higher power welding laser. 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 correction work of welding deformation after welding. Laser-MIG hybrid welding will create two separate weld pools, and the heat input of the back arc will also act as a post-weld tempering treatment to reduce the weld hardness (especially the welded steel). Due to the high welding speed of laser hybrid welding, production time and costs can be reduced.

4. Double laser welding head welding technology

During the welding process of the laser welding head, due to the high power density of the laser head, the welding base metal is rapidly heated, melted and vaporized to generate high temperature metal vapor. Under the continuous action of the high power density laser, the plasma cloud is easily generated, which not only reduces the laser absorption of the workpiece, but also makes the welding process unstable. If the power density of the continuously irradiated laser decreases after the larger deep penetration pinhole is formed, and the formed larger deep penetration pinhole absorbs more laser light, as a result, the effect of the laser light on the metal vapor is reduced, and the plasma cloud can be reduced or disappeared.

Therefore, pulsed laser and continuous laser with high peak power, or two pulsed lasers with large differences in pulse width, repetition frequency and peak power are used for hybrid welding of workpieces. During the welding process, two lasers irradiate the workpiece together to form a large deep penetrating hole, and then stop the irradiation of one laser at the right time to make the plasma cloud small or disappear, absorb and utilize the laser energy to improve the workpiece and improve welding Deep penetration, improve welding ability.

4. Conclusion

Laser hybrid head welding combines two welding methods. It has its own advantages, with the best welding effect, faster welding speed and stronger welding bridging ability. It is one of the most advanced welding methods available, achieving the perfect combination of high welding speed and good welding quality. Laser hybrid welding technology is a brand new welding technology in the automotive industry, especially the assembly gap requirements that cannot be achieved by laser beam welding, or are not economically feasible. It has a wide range of applications and high efficiency, while reducing investment costs, shortening production time, saving production costs and improving productivity, with stronger competitiveness.