1. Laser power. There is a threshold of laser energy density in laser welding. If it is lower than this value, the penetration is very shallow. Once it reaches or exceeds this value, the penetration will be greatly improved. Only when the laser power density on the workpiece exceeds the threshold value (related to the material), the plasma will be generated, which marks the progress of stable deep penetration welding.
2. Beam focal spot. Beam spot size is one of the most important variables in laser welding, because it determines the power density. But for high power laser, its measurement is a difficult problem, although there are many indirect measurement technologies.
3. Material absorption value. The absorption of laser by materials depends on some important properties of materials, such as absorptivity, reflectivity, thermal conductivity, melting temperature, evaporation temperature, etc., of which the most important is absorptivity.
4. Welding speed. The welding speed has a great influence on the penetration. Increasing the speed will make the penetration shallow, but too low speed will lead to excessive melting of materials and workpiece penetration. Therefore, there is a suitable welding speed range for a certain laser power and a certain thickness of a certain material, and the maximum penetration can be obtained at the corresponding speed value.
5. Shielding gas. Inert gas is often used to protect the molten pool during laser welding. When some materials are welded without considering surface oxidation, the protection can also be ignored. However, helium, argon, nitrogen and other gases are often used for protection in most applications to prevent the workpiece from oxidation during welding.
6. Lens focal length. Focusing mode is usually used to focus laser during welding, and 63~254mm (2.5 "~10") focal length lens is generally used. The focus spot size is proportional to the focal length. The shorter the focal length, the smaller the spot size. However, the focal length also affects the focal depth, that is, the focal depth increases synchronously with the focal length, so a short focal length can improve the power density. However, because of the small focal depth, the distance between the lens and the workpiece must be accurately maintained, and the penetration depth is also small. Due to the influence of spatter and laser mode during welding, the shortest focal depth used in actual welding is mostly 126 mm (5 "). When the seam is large or the weld needs to be increased by increasing the spot size, a lens with a focal length of 254mm (10 ") can be selected. In this case, higher laser output power (power density) is required to achieve the deep penetration keyhole effect.
7. Focus position. During welding, in order to maintain sufficient power density, the focus position is very important. The change of the relative position of the focus and the workpiece surface directly affects the weld width and depth.
8. Laser beam position. When laser welding different materials, the position of the laser beam controls the final quality of the weld, especially the butt joint is more sensitive than the lap joint. For example, when the hardened steel gear is welded to the low carbon steel drum, the correct control of the laser beam position will be conducive to the production of welds mainly composed of low carbon components, which have good crack resistance. In some applications, the geometry of the workpiece to be welded requires the laser beam to deflect an angle. When the deflection angle between the beam axis and the joint plane is within 100 degrees, the workpiece's absorption of laser energy will not be affected.
9. The laser power at the starting and ending points of welding is gradually increased and decreased. In laser deep penetration welding, no matter the depth of the weld, pinholes always exist. When the welding process is terminated and the power switch is turned off, a dent will appear at the end of the weld. In addition, when the laser welding layer covers the original weld, excessive absorption of the laser beam will occur, resulting in overheating or porosity of the weldment.
Source: Automatic motion control technology
