Laser Repair Welding Technology

At present, many metal products are replaced by titanium alloys, but during welding repair, they still depend on laser equipment. Titanium alloys have higher strength and corrosion resistance than other materials, instead of the application of technology in other industries, especially in high-tech applications, such as the external structure of engine, machine parts and other products, which not only reduces the weight of the products themselves. The quality and safety of the machine are also improved. In order to make full use of it, it is often necessary to use a variety of facilities in the production process. For example, in the welding repair, it is necessary to use an excitation welding machine to repair and weld, and in the marking, laser lasers can also be used as the main equipment. Therefore, the titanium alloy material and laser equipment are also interrelated.

Laser welding machine can be used to treat titanium alloy welding from large parts to process products. Fixtures can be installed to achieve high-efficiency production. In the degree of precision, the product is not limited by the operation of laser welding machine, and can be used efficiently and quickly for all kinds of specifications and shapes. In the quality, there are also high-performance and fast fusion that other equipment can not compare with. It surpasses the application level of traditional equipment. The period from repairing to welding can be shortened by such a fast and efficient application. Therefore, the cost can be greatly saved and the cost-effective matching can be achieved.

From the combination of the characteristics of the laser welding machine and the performance of the titanium alloy, the laser technology used for the repair of large-scale devices can often avoid the demanding requirements of the traditional manufacturing technology for equipment and large-size raw materials, and can solve the complex cavity structure. Laser technology is the best choice for both cost and material in the welding of titanium alloys. Titanium alloy materials are often used in parts and machinery, so there are many repair and welding positions. From the defects of process technology and equipment production, to the defects caused by the defects, cracks and dimensions of the parts, the development progress of the model is seriously affected. . However, the repair technology based on laser welding technology came into being. Compared with the conventional repair technology, it has the characteristics of high repair performance, good equipment accessibility, small size limitation, short repair cycle and low comprehensive cost. It is suitable for titanium alloy. The repair of expensive parts can save the parts that are not repairable by conventional technology (including the parts of the operating aircraft), and provide a new and quick solution to solve the defects, damage and corrosion of high-tech development and parts use. The way, the application of laser repair technology in China has a small scale, ensuring the application of advanced engineering and the use of parts, laser welding and repair of full-size structural static and fatigue assessment, compliance verification based on standards, ensuring Safe and reliable use of various industries; laser welding machine uses deep research on repairing internal mechanism, including forming and heat treatment process and organization, performance control, internal stress distribution law and elimination, suppression of deformation and cracking, etc.; laser welding and repair quality evaluation technology research, Establish a complete technical documentation system, including Manufacturing standards and test standards; laser welding and repair manufacturing technology research, development of engineering applications complete sets of equipment, improve form stability, improve real-time detection means, to achieve the best match between accuracy (size and shape) and speed.

Laser welding can be divided into pulsed laser spot welding and continuous laser welding (including high frequency pulse continuous welding) according to the different output energy of the laser. According to the power density on the spot after focusing, it can be divided into fusion welding and small hole welding. In the case of fusion welding, where the power density on the laser spot is not high, the surface of the metal material does not exceed its boiling point when heated. After the absorbed laser energy is converted into thermal energy, the workpiece is melted by heat conduction, and its penetration profile is approximately hemispherical. This heat transfer fusion welding process is similar to non-melting arc welding.

Small hole welding is when the power density on the laser spot is sufficiently large, the metal is rapidly heated under the irradiation of the laser, and the surface temperature rises to the boiling point in a very short time, and the metal is vaporized. The metal vapor leaves the surface of the bath at a certain speed. An additional pressure is generated to counteract the molten metal, causing it to sag downwardly, creating a small pit under the action of the laser spot. As the heating process progresses, the laser can be directed into the bottom of the pit to form an elongated aperture. When the recoil pressure of the metal vapor is balanced with the surface tension and gravity of the liquid metal, the small holes are no longer deep. When the spot power density is large, the resulting holes will penetrate the entire plate thickness to form a penetration weld (or weld). In continuous laser welding, the apertures advance in the welding direction as the beam is directed relative to the workpiece. The metal melts in front of the small hole, bypasses the small hole and flows backward, and then re-condenses to form a weld.

When the plasma cloud in the laser welding process is laser welded under the condition of high power density, it can be found that in the laser and metal action area, the metal evaporation is extremely intense, and the red metal vapor escapes from the small hole, and the metal surface is melted. There is a blue plasma cloud above the pool, which is accompanied by small holes. The generation of the plasma cloud is related to the power density of the laser, the nature of the metal to be soldered, the shielding gas, and the like. And adversely affecting the welding process, the laser energy obtained on the metal surface is reduced, the weld penetration is reduced, the surface of the weld is widened, and the welding process is unstable.

The common method to overcome the influence of plasma cloud in welding process is to blow inert gas on the surface of molten pool by nozzle, which can be removed by mechanical blowing force of gas to make it deviate from the top of molten pool. The lower temperature gas can also be used to reduce the temperature of the high temperature gas above the molten pool and suppress the high temperature conditions for producing plasma clouds. High frequency pulsed laser welding can also be used, so that the heating time of each laser pulse is less than the time of more ion cloud formation (about 0.5 ms), then the heating of plasma cloud has not yet been generated. In addition, high-speed welding or laser welding with section wavelength can also be used to reduce the interference of plasma cloud on the welding process. There are also devices for removing plasma clouds, including a control host and an induction coil connected via the control host, which is positioned directly above the plasma cloud and the host controls the induction coil to generate alternating magnetic fields for rapid removal of plasma clouds.

Laser welding and cutting should not use long focus lens. That is to say, the beam diameter D on the focal plane is related to the lens focal length f and the beam divergence angle theta (d=ftheta). In order to obtain a high enough power density during laser welding and cutting, it is generally not allowed to have a large beam divergence angle, nor to use a long focal length focusing lens. Laser fusion welding should not be used in University welding. Because laser fusion welding transmits laser energy to the workpiece through heat conduction, the laser energy utilization rate is low, the welding speed is slow, the penetration is shallow, and it is not easy to weld thick plate workpiece. The keyhole produced by laser deep penetration welding is characterized by the fact that the laser entering the keyhole is almost completely absorbed by the multiple reflection of plasma and the hole wall. It has high energy utilization rate, deep penetration of weld and fast welding speed. It is an efficient welding method suitable for thick plate welding and high-speed thin plate welding with keyhole effect.

For the sake of safety, corresponding warning signs should be put on the entrance of laser welding site. Laser beam transmission routes require higher than human height and are transmitted in closed pipes. When the laser is turned on or the capacitor of the pulser is charged, an acoustooptic warning is given. During laser operation, eye closure and skin should be avoided from direct or diffuse laser irradiation. When conditions permit, the working site should be closed with only observation holes with attenuation devices. Operators can operate outside the enclosure or remotely. Workplaces should be equipped with ventilation devices and fire safety devices.

Essence of Laser Welding
Prospect of Laser Welding