Welding precautions

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. After welding, important products need to eliminate welding stress and correct welding deformation.

Modern welding technology can already produce welds with no internal or external defects and mechanical properties equal to or even higher than those of the connected objects. The mutual positions of the welded bodies in space are called welded joints. In addition to being affected by the quality of the weld, the strength of the joint is also related to its geometry, size, stress and working conditions. The basic forms of joints include butt joints, lap 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 joining edges. When welding thicker steel plates, various shapes of grooves are made at the joint edge for welding penetration, so that the welding rod or wire can be fed more easily. The groove forms include single-sided welding grooves and double-sided welding grooves. When selecting the groove form, in addition to ensuring weld penetration, factors such as ease of welding, small amount of filler metal, small welding deformation and low groove processing costs should also be considered.

When two steel plates with different thicknesses are butted together, in order to avoid severe stress concentration caused by sharp changes in cross-section, the thicker edge of the plate is often gradually thinned until the two joint edges are of equal thickness. The static strength and fatigue strength of butt joints are higher than other joints. For connections that work under alternating, impact loads or in low-temperature and high-pressure vessels, welding of butt joints is often preferred.

The pre-welding preparation of lap joints is simple, the assembly is convenient, and the welding deformation and residual stress are small. Therefore, it is often used to install joints and unimportant structures on construction sites. Generally speaking, 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 operating characteristics of incomplete fillet welds on T-joints are similar to those of 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 surface shape of the weld will cause varying degrees of stress concentration; the stress situation of the penetration fillet weld is similar to that of a butt joint.

The load-bearing capacity of corner joints is low and is generally not used alone. It can only be improved when welding is penetrated or when there are fillet welds both inside and outside. It is mostly used at the corners of closed structures.

Welded products are lighter than riveted parts, castings and forgings. For transportation vehicles, they can reduce their own weight and save energy. 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 to produce large-scale, economical and reasonable cast-welded structures and forged-welded structures with high economic benefits. The welding process can effectively utilize materials. The welded structure can use materials with different properties in different parts, giving full play to the strengths of various materials to achieve economy 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 processes, but it developed very quickly. The weight of welded structures accounts for approximately 45% of steel production, aluminum and aluminum alloy welding