Welding is a local rapid heating and cooling process. The welding zone 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. Important products need to eliminate welding stress and correct welding distortion after welding.
Modern welding technology has been able to weld welds that have no internal and external defects and whose mechanical properties are 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, force and working conditions. The basic forms of joints include butt joints, overlap joints, T-joints (orthogonal joints) and corner joints.
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 joints. When welding thick steel plates, grooves of various shapes are made at the joint for penetration, so that the welding rod or wire can be fed in more easily. The groove forms include one-sided welding groove and two-side welding groove. When selecting the groove form, in addition to ensuring the penetration of the weld, consideration should be given to factors such as convenient welding, small amount of filler metal, small welding deformation and low processing cost of the groove.
When two steel plates with different thicknesses are butted, in order to avoid severe stress concentration caused by sharp changes in cross-sections, the thicker plate edges are often gradually thinned to achieve the same thickness at the two joint edges. The static strength and fatigue strength of butt joints are higher than other joints. For connections that work under alternating or impact loads or in low-temperature and high-pressure vessels, butt joint welding is often preferred.
The pre-welding preparation of lap joints is simple, easy to assemble, and the welding deformation and residual stress are small, so it is often used in the installation of joints and unimportant structures on the site. Generally speaking, lap joints are not suitable for working under conditions such as alternating loads, corrosive media, and high or low temperatures.
The use of T-joints and angle joints is usually due to structural needs. The working characteristics of the incomplete fillet weld on the T-joint are similar to the fillet weld of the lap joint. When the weld is perpendicular to the direction of the external force, it becomes a front fillet weld. At this time, the surface shape of the weld will cause different degrees of stress concentration; the force of the welded fillet is similar to that of butt joints.
The corner joint has a low load-bearing capacity and is generally not used alone. It can only be improved when the weld is penetrated or when there are fillet welds inside and outside. It is mostly used at the corners of closed structures.
Welded products are lighter than riveted parts, castings and forgings, which can reduce their own weight and save energy for transportation vehicles. The welding has good sealing performance and is suitable for manufacturing various types of containers. Develop joint processing technology to combine welding with forging and casting, which can produce large, economical and reasonable cast-welded structures and forging-welded structures with high economic benefits. The use of welding technology can effectively use materials, and the welding structure can use materials with different properties in different parts, and give full play to the advantages of various materials to achieve economy and high quality. Welding has become an indispensable and increasingly important processing method in modern industry.
