Study On The Formation Mechanism Of Residual Stress Of Arc Additive And The Elimination Control Of Hammering

The forging die has been in the bad working environment of repeated high temperature,high load and alternating stress for a long time.The working surface strength and wear-resistant performance need to undergo severe tests.In the service process,there are often wear failure,fatigue failure and fracture failure,even the formation of cracks,which seriously affects the service life of the forging die.In order to reduce the cost of die,Wire and Arc Additive Manufacturing(WAAM)is applied to crack repair of forging die,and the problem of residual stress relief after arc fuse repair is the key to improve its service life.Through the high frequency hammering of the hammerhead in the weld bead and its heat affected zone,the hammering treatment technology can reduce the residual tensile stress and form the residual compressive stress zone on the hammered surface at the same time.Therefore,it is widely used in the elimination of residual stress after arc melting.Therefore,based on the arc fuse hammering experiment,a single-layer multi-channel fuse hammering finite element model is established to study the effect of each process parameter of fuse hammering on the residual stress relief and surface flatness improvement of the workpiece area,and to seek the best fuse hammering parameter,so as to realize the optimization of fuse hammering process path and improve the service life of the fuse product repair mold.Using the fuse hammering finite element model which is highly matched with the actual situation can quickly and accurately realize the optimal control of the fuse hammering mold repair process,reduce the repair cost and effectively improve the repair quality,provide a reference for the residual stress relief treatment in the actual fuse hammering production,and have an important meaning for the development of the mold wire and arc additive repair technology to automation,high efficiency and high quality.The main work and conclusions are as follows:(1)Based on the pneumatic follow-up welding hammering equipment independently developed by Dajiang Jiexin Co.,Ltd.,the experiments of welding and hammering were carried out on a flat plate using 2.4 mm RMD wire.The welding voltage and current were 32 V and 360 A respectively,and the moving speed of wire was 420-480 mm / min.Using X-ray stress tester to test the residual stress of the wire and arc additive products and the hammering products,the accuracy of the finite element simulation results of them are verified and compared.(2)Based on the experimental data of single pass of wire and arc additive,a high matching finite element model of experiments was built by using ABAQUS software,and the temperature field cloud chart of 45 steel and the shape of weld bead under different speed of wire and arc additive were dynamically simulated and reproduced.The distribution trend of residual stress is the same under different speed of wire and arc additive.The weld and hot melt zone are mainly residual tensile stress.Due to the interaction of heat input and weld bead structure size,the transverse residual stress decreases first and then increases,while the longitudinal residual stress increases with the increase of the speed of fuse deposition.(3)Based on ABAQUS software,the finite element model of single pass welding and hammering is constructed.The simulation results show that the weld bead has obvious plastic deformation after hammering treatment,the height of the weld bead decreases obviously,while the width of the weld bead widens,the residual tensile stress inside the weld bead and in the heat affected area is effectively released,and the compressive stress is produced in the surface compression area.The reduction of longitudinal residual tensile stress is more than 25% after peening,and the effect of reduction is better than that of transverse residual tensile stress.(4)In the process of multi-channel wire and arc additive,due to the preheating and reheating effect between adjacent weld beads,the temperature of subsequent weld beads is 200 ? higher than that of the previous weld beads,and the thermal cycle curve of the joint presents multi peak change.The residual stress on the parts of multi-channel wire and arc additive products is asymmetric along the direction of the vertical weld bead,and the residual tensile stress in the weld bead connection area increases with the increase of the weld bead spacing.With the increase of weld bead spacing,the value of residual tensile stress is basically similar but the range is expanding,while the value of residual compressive stress is increasing but the range is decreasing.(5)By constructing the response surface model between the hammering process parameters and the residual stress,we can know that the hammerhead diameter,the hammerhead moving speed,the weld bead spacing and their interaction have a great influence on the residual stress of the fuse product workpiece.In order to obtain the smaller residual stress,the small weld bead spacing fuse products need to match the small hammer diameter and the slow hammer moving speed,while the large weld bead spacing wire and arc additive products need to match the big hammer diameter and the fast hammer moving speed.When the weld bead spacing is 7.2mm,the optimal residual stress reduction results can be obtained by using a hammer with a diameter of 8mm and a moving speed of 1200 mm / min.