Welding process of square tube

According to the welding deformation theory, the main factors affecting the welding deformation are: the larger the weld size, the more deposited metal, and the larger the deformation; When the weld size is equal, the larger the heat input of the weld, the larger the deformation formed; When welding large and long welds, the deformation of section welding is smaller than that of straight welding; The welds are arranged asymmetrically or symmetrically but asymmetrically. The more serious the deviation of the welds, the greater the deformation; The smaller the rigidity of the component, the greater the deformation.

Through process experiment and process analysis, it is confirmed that the square tube butt weld adopts double-layer CO2 gas maintenance welding. H08Mn2SiA, 1.2mm welding wire is used as welding material; The maintenance gas is pure CO2. The welding current of the first layer of weld is 200~250A, and that of the second layer is 240~320A; The arc voltage is 24~26V. The process requirements are: the first layer of weld must be fully welded to ensure good back formation; Welding current, arc voltage, wire feeding speed and welding speed can be adjusted according to the equipment model.

Welding sequence In order to reduce deformation, the welding sequence of rectangular butt welding shall be based on the following criteria: adopt symmetrical skip welding in layers and sections from the middle to both sides. The welding deformation generated is smaller than that of straight through welding, which is conducive to the dispersion and release of stress and avoids complex stress in weldments. During straight through swing welding, the narrow plastic deformation zone formed at the beginning of the welding only appears once, and because of continuous swing welding, the heat input is large, the heating area is large, and the plastic deformation zone formed by shrinkage is large, so the shrinkage deformation after welding is large.

In the case of layered and segmented skip welding, the cross section of each layer is very small, so the heat required is small. In addition, each layer is divided into several sections to stop the skip welding. Each section of welding is basically to re-establish the temperature field on the cold steel plate. Each time a narrow plastic deformation zone appears, so the average width of the plastic deformation zone (i.e. the size of horizontal shrinkage) is smaller than that of the corresponding layered straight through welding, and the longitudinal shrinkage is also small, The welding deformation is smaller than that of the straight through swing welding with one continuous filling.

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