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 are generated in the weldment. After welding, important products need to eliminate welding stress and correct welding deformation.

Modern welding technology has been able to weld welds with no internal and external defects and mechanical properties equal to or even higher than those of the connected body. The mutual position of the welded bodies in space is called a welded joint. The strength of the joint is not only affected by the quality of the weld, but also related to its geometry, size, stress and working conditions. The basic forms of joints include butt joint, lap joint, T-joint (orthogonal joint) and corner joint. The cross-sectional shape of the butt joint weld is determined by the thickness of the welded body before welding and the groove form of the two edges. When welding thicker steel plates, grooves of various shapes are made at the edge for penetration, so that the electrode or wire can be fed more easily. The groove forms include grooves welded on one side and grooves welded on both sides. When choosing the groove form, in addition to ensuring penetration, factors such as ease of welding, less filler metal, small welding deformation and low groove processing costs should be considered.

When two steel plates with different thicknesses are butted together, in order to avoid serious stress concentration caused by the rapid change of the cross-section, the edge of the thicker plate is often gradually thinned to achieve the same thickness at the two edges. The static and fatigue strength of butt joints are higher than other joints. For connections under alternating, shock loads or working in low temperature and high pressure vessels, welding of butt joints is often preferred. The pre-welding preparation of the lap joint is simple, the assembly is convenient, and the welding deformation and residual stress are small, so it is often used in the installation of joints and unimportant structures on site. In general, lap joints are not suitable for working under conditions such as alternating loads, corrosive media, high or low temperatures. The use of T-joints and corner joints is usually due to structural needs. The working characteristics of incomplete fillet welds on T-joints are similar to fillet welds on 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 the penetration fillet weld is similar to that of the butt joint.

Fillet joints have low bearing capacity and are generally not used alone. They are only improved when they are welded through, or when there are fillet welds inside and outside. They are mostly used at the corners of closed structures. Welded products are lighter than riveted parts, castings and forgings, which can reduce dead weight and save energy for transportation vehicles. The welding has good sealing performance and is suitable for manufacturing various types of containers. The development of joint processing technology to combine welding with forging and casting can produce large-scale, economical and reasonable cast-welded structures and forged-welded structures, with high economic benefits. The welding process can effectively utilize materials, and the welding structure can use materials with different properties in different parts, giving full play to the advantages of various materials to achieve economical and high quality. Welding has become an indispensable and increasingly important processing method in modern industry.

In modern metal processing, welding developed later than casting and forging, but it developed rapidly. The weight of welded structures accounts for about 45% of steel production, and the proportion of aluminum and aluminum alloy welded structures is also increasing. In 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 and reliability, such as improving the existing welding energy such as arc, plasma arc, electron beam, laser, etc.; using electronic technology and control technology, improve the process performance of the arc, and develop a reliable and lightweight arc tracking method.

On the other hand, it is necessary to improve the level of welding mechanization and automation. For example, the welding machine realizes program control and digital control; develops a special welding machine that automates the whole process from preparation process, welding to quality monitoring; promotes and expands CNC welding on automatic welding production lines. Manipulators and welding robots can improve the level of welding production and improve welding hygiene and safety conditions.