Manufacture Of The Device For Welding With Trailing Rolling And Pressing And Research Of Control Of Welding Distortion

In this dissertation, a new technology named Welding with Trailing Rolling and pressing (WTRP) is put forward to control welding distortion and prevent welding hot cracking. Via the frictional rollers, constant force is exerted to the metal of the welding line and the weld bead respectively, and then the strain field and the plastic yielding field of the weld metal are compelled to change on purpose. In this way, WTRP can not only prevent welding hot cracking effectively, but also reduce the residual distortion caused by longitudinal and transverse shrinkage of weld metal obviously, and strengthen the weak welding line during the process of welding. In a word, this technology can weld thin plate-shell structures of aluminum alloy with little distortion and free-hot-cracking.Air compressor is chosen as the pressure power and electromotor is chosen as the rotation power of WTRP device. According to corresponding requirement, the structure of the device is designed and the dimensions are determined. The integrated WTRP equipment used for straight welding is designed and developed.In order to find out the theory of WTRP, finite element method (FEM) is employed to study the plastic flow and change of the strain field in the work piece caused by WTRP. The front rolling staff exerts transverse compressive stress on the welding line which is in the brittle temperature range, which will counteract the tensile strain which leads to hot cracking. The rear rolling staff stretches longitudinal and transverse compressive plastic deformation of the welding line adequately, thus reduces the residual deformation in the work piece.WTRP can change the appearance of the welded work piece. The surface of common welded work piece is very crude and the transition region between weld toe and weld bead is acute, which leads to stress concentration. However, the weld surface is very smooth after WTRP and the transition region is much better.Metallograph shows that the crystal grain of the WTRP weld work piece is finer , the metallurgical structure is more compact than common weld work piece and there are less gas cavities and shrinkage cavities in the WTRP weld work piece. LY12 aluminum alloy work piece is employed to investigate the influence of WTRP on hot cracking. The results show that the air pressure (P) and the distance between the front rolling staff and the weld torch (Lc) have great influence on the hot cracking rate. In certain range, the hot cracking rate decrease with the increasing of P and the decreasing of Lc. The hot cracking rate of common work piece is as high as 37.1%, while under proper parameters, there is no hot cracking in the WTRP work piece.In respect of straight plate welding, LY12 aluminum alloy thin plates are used, and the dimension of the work piece is 135mm×75mm×2mm. After adjusting the air pressure of the cylinder, the experimental results show that the deflection deformation of common work piece is 4.1mm while decreasing to 0.12 mm after WTRP, which decreased by 97.07%. After adjusting the distance between the weld torch and the rolling staff, the experimental results show that the deflection deformation of common work piece is 1.28mm while decreasing to 0.16 mm after WTRP, which decreased by 87.5%.