Residual Stress Numerical Analysis Of Laser+GMAW Hybrid Welding

As a new type of high efficiency welding technology, laser+GMAW hybrid welding combines the merits of both laser welding and GMAW and compensates the shortcomings of each component, having the features including high welding speed, large weld penetration, stable welding process, good weld formation and small residual stress and distortion, which is of significant application potential in the field of industrial manufacture. During welding, due to local non-uniform heating of workpiece, it is inevitable to generate the welding residual stress, which has an important influence on mechanical properties of welded joint and consequently directly causes a potential threat to the safety of welded structure. Thus, it is necessary to analyze the distribution feature of residual stress in order to promote the application of hybrid welding. However, the study on residual stress in laser+GMAW hybrid welding is currently focused on butt-welding of thin plate or bead-on-plate welding and there are few researches involving medium thick plate and its butt-welding. In addition, owing to limitations in experimental condition, numerical simulation technology has become an important way of investigating welding residual stress. In this paper, through combining the numerical simulation and experimental detection, the residual stress in laser+GMAW hybrid welding is studied, providing technical support and basic data for deeply understanding the hybrid welding process feature and optimizing welding parameters, which has theoretical significance and practical value.The plate butt-welding experiments of laser+GMAW hybrid welding were carried out under different welding conditions using Q235 low carbon steel, Q460 ultra-fine grained steel and 6061 aluminum alloy. The residual stress at the surface of workpiece was measured by means of blind hole method. Based on macro heat transfer, an adaptive heat source for laser+GMAW hybrid welding is selected according to the geometric feature of weld cross section, in which arc heat input is regarded as an double ellipsoid heat source model and laser energy is described using a cone heat source. On the basis of thermal-elastic-plastic theory, a three dimensional finite element model for residual stress in laser+GMAW hybrid butt welding is developed using ANSYS software. The residual stress in laser+GMAW hybrid welding is numerically calculated and the distribution characteristics for different welding processes are investigated.The study results show that, the calculated residual stress in laser+GMAW hybrid welding agrees well with the experimental one, indicating the accuracy and adaptivity. For the butt welding of 6-mm thick plate of Q235 steel, with enhancing welding speed, both the longitudinal and transverse stresses tend to increase. Regarding butt-welding of Q460 ultra-fine grained steel plate of 12-mm thickness, high longitudinal tensile stress is generated in the weld and its vicinity for both single pass and multi-pass welding. The width of the area with high longitudinal stress in laser+GMAW single pass hybrid welding is close to that in multi-pass hybrid welding, but both of them are obviously larger than that in GMAW multi-pass welding. For 6-mm thick 6061 aluminum alloy plate, when raising the weld speed, the peak value of longitudinal residual stress at the weld and the width of the region with high stress increase. As to 12-mm thick 6061 aluminum alloy plate, under the condition of full weld penetration and good weld quality, the width of the area with high longitudinal tensile stress in laser+GMAW single pass hybrid is obviously narrower than that in GMAW multi-pass welding and the peak stress in hybrid welding is also relatively low, which is 224MPa.