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Modern welding technology has been able to weld the weld without internal and external defects, whose mechanical properties are equal to or even higher than the connected body. The mutual position of the welded body in space is called 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 are butt joint, lap joint, T-joint (forward joint) and corner joint.
The cross section shape of butt joint depends on the thickness of the welded body before welding and the groove form of the two edges. When welding thick steel plate, in order to weld through, the groove of various shapes is made at the edge, so that the welding rod or welding wire can be easily put in.
There are two types of groove: one side welding groove and two sides welding groove. When selecting the groove form, in addition to ensuring the penetration, the factors such as convenient welding, less filler metal, small welding deformation and low groove processing cost should also be considered. When two steel plates with different thickness butt joint, in order to avoid the serious stress concentration caused by the sharp change of cross section, the thicker plate edge is often gradually thinned to achieve the same thickness at the two joint edges. The static strength and fatigue strength of butt joint are higher than other joints. Butt joint welding is often preferred for joints working under alternating and impact loads or in low temperature and high pressure vessels.
The lap joint has the advantages of simple preparation before welding, convenient assembly, small welding deformation and residual stress, so it is often used in the field installation of joints and unimportant structures. Generally speaking, lap joints are not suitable for working under alternating load, corrosive medium, high temperature or low temperature.
The use of T-joints and corner joints is usually due to structural needs. The working characteristics of fillet weld with incomplete penetration on T-joint are similar to those of lap joint. When the weld is perpendicular to the direction of the external force, it becomes a positive fillet weld, and the shape of the weld surface will cause different degrees of stress concentration; the stress condition of the penetrated fillet weld is similar to that of the butt joint. The bearing capacity of fillet joint is low, so it is not used alone. It can be improved only when it is fully welded or when there are fillet welds inside and outside. It is mostly used in the corner of closed structure. Welding products are lighter than riveting parts, castings and forgings, which can reduce self weight and save energy for transportation vehicles. The sealing performance of welding is good, which is suitable for manufacturing all kinds of containers.