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The small hole is a heat source of a particularly high heat absorption source, and the heat is absorbed from the small hole to the periphery, thereby forming a melting zone called a molten pool around the small hole. As the beam moves relative to the workpiece, the molten metal fills the pores and solidifies to form a weld. Laser deep-melt penetration welding is closely related to laser power density. The lower the effective power density of the laser, the more unstable the pore effect is, and even the formation cannot be formed, and the penetration depth is small.
If the output beam mode is not good, even if the effective power is sufficient, the pinhole effect is not formed because the focusing performance is not good. In general, penetration is directly related to laser power density and is a function of human laser power and spot diameter.
The welding speed is too fast, it is difficult to form a small hole effect, so that the metal is not penetrated and the self-quenching speed is too fast, the weld strength is lowered, and the harmful gas in the weld is too late to escape, which increases the weld porosity and affects the bending resistance. Strength and weld appearance. The welding speed is too slow, the weld bead expands to both sides, the heat affected zone is overheated, the metallographic structure of the weld is coarse, and sometimes cracks are generated, which seriously affects the welding quality, and the heat affected zone expands, and the metal in the melting zone evaporates. The entire weld bead is sunken.
Effect of defocusing amount on the weld The defocus amount of the laser beam focus position has a great influence on the penetration depth, melting efficiency and weld shape. When the focus is on the negative defocus amount below the weld, the penetration can be increased, but the weld will be formed and the focus will be on the weld. The amount of defocus will be formed, and a “nail head†weld will be formed, and the penetration will be reduced. When the focus is located at a suitable distance below the weld for negative defocus welding, the resulting weld is nearly parallel and the maximum penetration is obtained.
The laser welding process parameters and results of the double gear are listed as hydrogen as protective gas. The parameters of the medium test piece are the best process parameters for welding. When the plasma suppresses the laser power density to less than the time resistance, the metal in the small holes is largely evaporated, and the laser energy is further absorbed to ionize, forming a plasma cloud above the small holes. When there is a thin plasma above the small hole, the plasma can prevent the reflection of the surface light of the workpiece, which is beneficial to the welding of the workpiece. When the plasma concentration increases, the absorption of the laser increases, and even the laser is completely cut off until the plasma is irradiated. The body disappears and is extremely unfavorable for welding.
The laser welding machine uses a one-way side blowing method to align the copper tube nozzle to the middle of the plasma to blow off the control plasma, and obtains a good effect.
The color of the weld surface is also an indicator of the quality of the gear. Since the gear is easily contaminated by dust and oil during handling and storage before welding, the surface of the weld after welding is dark brown, which seriously affects the appearance quality. The usual solution is to first clean the gears with oil, then dry them and then weld them.
Although the method solves the problem, the cleaning and drying process is increased, resulting in an increase in the manufacturing cost of the parts. In the actual welding process, the weld to be welded is quickly burned at a speed and power, and the pollutants on the surface are burned into powder, blown off by the protective gas, and then welded according to the above method. The surface of the weld is grayish white, which has no effect on the welding efficiency and has achieved satisfactory results.
Weld metallographic laser welding has a fast heating speed, and the weld pool cools rapidly, which is quite different from conventional welding in metallographic structure. The liquid-solid interface of the weld pool has a large temperature gradient. The heat affected zone of the weld is small, and the weld zone is a finer dendritic structure. Moreover, the laser welding has a purifying effect on the molten pool, and the impurities in the weld are less than the base material.
This is because the metal strongly reflects the wavelength of the laser, while the non-metal is easily absorbed, causing the impurities in the molten pool to vaporize and escape. Tests have shown that the strength of the laser welded weld is close to that of the base metal, and the impact toughness of the weld is even higher than that of the base metal.
Conclusion The improper selection of laser welding process parameters may lead to small concave holes in the joints of the gear welds and the surface of the welds are dark brown, and even defects such as pores and cracks seriously affecting the quality of the products. By optimizing the process parameters, these problems are successfully solved without the use of a "type power" method, which greatly reduces the cost of the equipment.
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