The seam formed by laser welding machine to connect two connected bodies is called weld seam. Both sides of the weld will be affected by welding heat during welding, and the structure and properties will change. This area is called heat affected zone. Due to the different welding materials and welding current of workpiece materials during welding, overheating, embrittlement, hardening or softening may occur in the weld and heat affected zone after welding, which also degrades the weldment performance and worsens the weldability. This requires adjustment of welding conditions. Preheating the interface of weldment before welding, heat preservation during welding and post welding heat treatment can improve the welding quality of weldment.
In addition, welding is a local rapid heating and cooling process. The welding area cannot expand and contract freely due to the constraints of the surrounding workpiece body. After cooling, welding stress and deformation will occur in the weldment. This is also a common problem of traditional contact welding. All important products need to eliminate welding stress and correct welding deformation after welding. The use of non-contact laser welding process can avoid these steps.
Modern welding technology has been able to weld welds without internal and external defects, with mechanical properties equal to or even higher than that of the connected body. The mutual positions of the welded bodies in space are called welded joints. The strength of the joints is not only affected by the weld quality, but also related to their geometric shape, size, stress conditions and working conditions. The basic forms of joints include butt joint, lap joint, T-joint (positive joint) and corner joint.
1. The cross section shape of the butt joint weld depends on the thickness of the welded body before welding and the groove form of the two joint edges. When welding thick steel plates, grooves of various shapes shall be made at the edges for penetration, so that welding rods or welding wires can be easily fed. The groove forms include single-sided welding groove and double-sided welding groove. When selecting the groove form, factors such as convenient welding, less filler metal, small welding deformation and low groove processing cost shall be considered in addition to ensuring penetration.
When two steel plates with different thicknesses are butt jointed, in order to avoid serious stress concentration caused by sharp changes in section, the thicker plate edges are often gradually thinned to the same thickness at the two joint edges. The static strength and fatigue strength of butt joints are higher than those of other joints. Butt joint welding is often preferred for the connection working under alternating and impact loads or in low temperature and high pressure vessels.
2. The preparation before welding of lap joint is simple, the assembly is convenient, and the welding deformation and residual stress are small, so it is often used in the field installation of joints and unimportant structures. Generally speaking, lap joint is not suitable for working under alternating load, corrosive medium, high temperature or low temperature.
3. T-joints and corner joints are usually used due to structural needs. The working characteristics of fillet welds with incomplete penetration on T-joints are similar to those of lap joints. When the weld is perpendicular to the direction of the external force, it becomes a front fillet weld. At this time, the shape of the weld surface will cause different degrees of stress concentration; The stress of fillet weld with penetration is similar to that of butt joint.
The bearing capacity of corner joint is low, and it is not used alone generally. It can be improved only when there is penetration welding or when there are fillet welds inside and outside. It is mostly used at the corners of closed structures.
In modern metal processing, welding technology developed later than casting and forging technology, but it developed rapidly. The weight of welded structures accounts for about 45% of the steel output, and the proportion of aluminum and aluminum alloy welded structures is also increasing.
For the future welding process, on the one hand, new welding methods, welding equipment and welding materials should be developed to further improve the welding quality and safety reliability; On the other hand, it is necessary to improve the level of welding mechanization and automation, such as program control and digital control of welding machine; Develop a special welding machine that automates the whole process from preparation, welding to quality monitoring; In the automatic welding production line, the promotion and expansion of CNC welding manipulators and welding robots can improve the level of welding production and improve the health and safety conditions of welding.
