Chengdu steel structure welding deformation and control correction

Steel structure connections are generally welded, and full penetration welding is generally used for some important welds. During metal welding, during the local heating and melting process, the temperature of the metal in the heating zone and the surrounding base metal is very different, resulting in instantaneous stress during the welding process. After cooling to the original temperature, the tensile stress zone of the entire joint area weld and the near seam area and the base metal in the compressive stress zone value reach equilibrium, which produces the welding residual stress of the structure itself. At this time, under the action of welding stress, various forms of deformation occur in the structure of the weldment. The existence of residual stress and the generation of deformation are mutually converted, and it is not difficult to find ways to prevent the reduction and correction of deformation by recognizing the law of deformation.

First, the form and cause of welding deformation: The deformation that

occurs after welding of the steel structure can be roughly divided into two situations: that is, the deformation of the overall structure and the local deformation of the structure. The deformation of the overall structure includes the longitudinal and transverse shortening and bending (i.e. warping) of the structure. Local deformation is manifested as convex bending, wavy, angular deformation and so on.

1.1 Common basic forms of deformation

, the basic forms of common welding deformation are as follows: the deformation of shortening the length (longitudinal shrinkage) and narrowing of width (lateral shrinkage) generated after the plate groove butt welding; Angular deformation generated after butt welding of plate groove; The angular deformation of the welded member is different along the longitudinal axis of the component and the distortion deformation caused by the inconsistency between the longitudinal contraction of the flange and the web. After the sheet is welded, the compressive stress zone of the base metal is deformed by warping of the board surface due to instability; Due to the longitudinal and transverse shrinkage of the weld relative to the asymmetry of the neutral axis of the member, the overall bending of the member is caused by this deformation.

These deformations are all basic deformation forms, and various complex structural deformations are the development, transformation and synthesis of these basic deformations.

1.2 Causes of welding deformation: Local and uneven heating of the weldment during the welding process is the cause of welding stress and deformation. During welding, the metal in the weld and the heating zone near the weld expands, and because the cooler metal around prevents this expansion, compressive stress and plastic shrinkage deformation occur in the welding area, resulting in different degrees of lateral and longitudinal shrinkage. Due to the shrinkage in these two directions, various deformations of the welded structure are caused.

Second, the factors affecting the deformation of the welding structure:

There are many factors affecting the amount of welding deformation, and sometimes the same factor has opposite effects on longitudinal deformation, transverse deformation and angular deformation. Comprehensively analyzing the influence of various factors on various deformations and grasping their influence laws is the basis for taking reasonable measures to control deformation. Otherwise, it is difficult to achieve the desired effect.

1) The influence of weld cross-sectional area

: weld cross-sectional area refers to the metal area within the fusion line, the larger the weld area, the greater the amount of plastic deformation caused by shrinkage during cooling.

2) The influence of welding heat input: Under normal circumstances, when the heat input is large, the heating high temperature zone range is large, and the cooling rate is slow, so that the plastic deformation zone of the joint increases, and the deformation increases regardless of the longitudinal, transverse or angular deformation. However, when the surface overlay welding, when the heat input increases to a certain extent, because the temperature of the entire plate thickness is close, even if the heat input continues to increase, the angular deformation no longer increases, but decreases. ,

3) The influence of preheating and interlayer temperature of the workpiece: the higher the preheating temperature and interlayer temperature, it is equivalent to an increase in heat input, which slows down the cooling rate and increases the shrinkage deformation. ,

4) The influence of welding methods: Among the several methods commonly used in building steel structure welding, in addition to electroslag welding, submerged arc welding has the largest heat input, and shrinkage deformation is the largest under other conditions such as weld area. The heat input of manual arc welding is centered, and the shrinkage deformation is smaller than that of submerged arc welding. CO2 gas shielded welding heat input is the smallest, and the shrinkage deformation response is also the smallest. ,

5) The influence of weld position

on deformation: Due to the asymmetry of weld position in the structure, asymmetry of weld position, etc. will cause various deformations. ,

6) The influence of the rigidity of the structure on the welding deformation: the rigidity of the structure

mainly depends on the shape of the structure and its cross-sectional size, the structure with less rigidity, the welding deformation is large; Large rigid structure, small deformation after welding. ,

7) The influence of assembly and welding specifications on welding deformation: Due to the different assembly methods adopted, there is also an impact on the deformation of the structure. After the overall assembly is completed, the welding is carried out, and its deformation is generally less than that of welding while assembling. ,

In the engineering welding time, due to the comprehensive effect of various conditions and factors, the law of welding residual deformation is more complicated, and understanding the influence of each factor alone is convenient for specific comprehensive analysis of the specific situation of the project.