For many years, laser has been widely used in the field of welding. along with Laser technology With further development and diversification, its application range in welding is also expanding.
Overview of traditional welding
Most of the traditional (non laser) welding technologies currently used are derived from arc welding. When using this kind of welding, first make the two metals contact or close together. Usually, the edge of the metal may have been formed to facilitate welding. A high pressure is formed between the electrode and the contact area, resulting in an arc that can melt the welding material (or, in some cases, other repair materials or the electrode itself). The molten welding material fills or covers all gaps between workpieces and binds the parts together after solidification. The main advantage of most arc welding methods is that they have relatively low cost, especially in terms of fixed equipment cost. Moreover, arc welding technology has high acceptance and wide application, and has established perfect production and test standards. Therefore, it does not need long-time learning to apply relevant processes.
The main disadvantage of arc welding is that it will subject the parts to high temperature. This will form metallographic structure in the molten welding material, resulting in the reduction of weld strength, and the heat affected area near the weld is relatively large. In addition, the diameter of the arc is affected by the local electric field, so it cannot be set independently.
Most laser welding technologies can be classified into two basic categories, namely "deep penetration" welding and "heat conduction" welding. These two welding modes can be carried out by self melting (i.e. without welding repair material) or using welding repair material when necessary.
Deep penetration, or deep penetration welding. It is common to weld thick materials with high laser power. In deep penetration welding, the laser is focused together to form a very high power density on the workpiece. In fact, the part focused by the laser beam will vaporize the metal, resulting in a blind hole (i.e. deep penetration hole) in the metal molten pool. The metal vapor pressure will block the surrounding molten metal and keep the blind hole open during welding. The laser power is mainly absorbed by the melt at the boundary between steam and melt and the wall of deep melt hole. The focused laser beam and deep penetration hole move continuously along the welding track. The welding material melts in front of the deep penetration hole and re solidifies behind to form the weld.
The small deep penetration hole area forms an accurate narrow melting zone, which has a higher aspect ratio (the ratio of depth to width) than the arc welding method. Moreover, the highly concentrated heat means that the substrate of the workpiece can play an effective role in heat dissipation. Therefore, the welding area can be heated and cooled rapidly. This minimizes the area affected by high temperature and reduces grain growth. Therefore, the weld produced by laser is usually stronger than arc welding, which is one of its main advantages.
Laser welding can also provide better flexibility than arc welding because it can be used for a large number of materials, including carbon steel, high-strength steel, stainless steel, titanium, aluminum, and precious metals. Because the difference of melting temperature and heat conduction of materials will not have a significant impact on the welding process, laser welding can also be used to weld different materials.
In addition, if all processing steps are considered, laser welding has obvious cost advantages over traditional methods, especially the accurate heat application can minimize the deformation of welding points and the whole component. Therefore, in many cases, post-processing is not necessary. Moreover, laser welding can project laser beam over a long distance, and there is basically no power loss, which makes it easy to integrate into other production processes, and can be well integrated with industrial robots. Finally, it can realize new product configuration with smaller flange size, which is very important for light vehicles. At present, carbon dioxide and fiber lasers can easily meet the requirements of laser beam parameters and power for deep penetration welding. Since the absorptivity of most metals increases with the shortening of wavelength, a fiber laser with a wavelength of about 1 micron can provide higher processing efficiency than a carbon dioxide laser with a wavelength of 10.6 microns.
Fiber laser can perfectly meet the requirements of deep penetration welding. The output power they provide is generally between 500 watts and 10 kW, and the solder joint diameter can be easily focused in the necessary range of 40 microns to 800 microns, even at a relatively large processing distance. From a practical point of view, the use of laser beam transmission fiber can expand the integration selection and promote the application of laser in production environment. Finally, fiber laser has the characteristics of high reliability, excellent uptime and low purchase cost, which makes it an economically feasible and attractive choice for production welding applications.