Laser welding principle and equipment
Laser welding uses a laser as a welding heat source and a robot as a motion system. The advantage of the laser heat source is that it has a very high heating capacity and can concentrate a large amount of energy on a small welding point, so it has the characteristics of high energy density, concentrated heating, fast welding speed, small welding deformation, etc. Quick connection.
When the power density on the laser spot is sufficiently large (greater than 106 W/cm 2 ), the metal is rapidly heated by the laser irradiation, the surface temperature thereof rises to the boiling point in a very short time, and the metal is vaporized. The metal vapor leaves the surface of the molten metal bath at a certain speed, creating an additional stress that reacts to the molten metal, causing it to sag downward, creating a small bump under the laser spot. As the heating process progresses, the laser can be directed into the bottom of the pit to form an elongated "small hole." 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 density is large, the resulting small holes will penetrate the entire plate thickness to form a deep penetration weld. The metal melts in front of the small hole, flows around the small hole to the rear, and re-solidifies to form a weld (Fig. 2), so the laser weld has a deep and narrow feature.
Figure 2 Principle of laser welding
Laser hybrid welding combines two arcs, and the two arcs interact and support each other, forming a larger weld pool than laser welding (Figure 3), thus better bridging capability and allowing for larger weld assembly clearances. At the same time, the molten pool of laser hybrid welding is smaller than that of MIG welding.
Figure 3 Comparison of laser welding, MIG laser hybrid welding and MIG welding head forming
FAW-Volkswagen laser welding joint type
Magotan's 42m laser welds ensure the overall dimensional accuracy, body strength and rigidity. Magotan's laser welding is mainly in the connection of the top and side panels of the body, the splicing of the slabs of the bottom plate, the splicing of the slabs of the inner panel of the door, the bottom and side panels, the rear panel, the front and rear wind windows and the door frame. Junction.
Commonly used laser welding is connected with cold-rolled steel sheets, hot-rolled steel sheets of less than 0.02% carbon equivalent, hot-dip galvanized and electrogalvanized steel sheets. Generally, the material of the steel sheets must meet the corresponding technical standards to achieve high-quality connections. Achieving quality connectivity depends on three main elements: design, processing, and materials. Figure 4 shows the possibilities of welding and the relationship between the quality of the welded joints between joint design and manufacturing. In addition to the general principles of design, such as the design of the end face, the necessary pre-weld preparation, the description of the properties of the welded joint, the welding process, the clamping technology, the accessibility of the laser beam, the machining accuracy and the post-weld rework The role.
Figure 4 Relationship between weldability and influencing factors
In order to obtain a better laser weld, the following principles must be followed: joints are formed by the interconnection of weld zones, and the design requirements of the workpiece must be considered for each joint type. The form of the weld depends ultimately on the design of the welding end face and the scope and type of machining preparation. For the use of metal-coated steel sheets, it is necessary to pay attention to the design of the exhaust passages in the joint area. The design of the gaps is generally selected according to the thickness of the coatings between 0.05 and 0.2 mm, and can also be solved by designing a certain sheet angle. In addition, the clamping design and pre-treatment of the workpiece must ensure that the exhaust is unobstructed.
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