Study On Residual Stress Of Laser Cladding Remanufacturing Coating

The process of laser cladding can strengthen surface properties of substrate like hardness,wear resistance,corrosion resistance and so on.Laser cladding has become the key part of remanufacturing engineering.However,the heating rate and cooling rate are very fast in the process of laser cladding,which leads to the distortion of workpiece and the cracking of cladding layer and hinders the development of laser cladding technology in remanufacturing engineering.Aiming at this problem,the residual stress of cladding layer is comprehensively evaluated by the method of experimental research and numerical simulation.In this paper,the shape of the workpiece and the process parameters of cladding are taken as the research object to research the residual stress of cladding layer,which has great significance to controlling stress and improving even eliminating the cracks in the cladding layer,and to promote the development of laser cladding in the field of remanufacturing engineering.In this paper,the finite element simulation software SYSWELD is used to simulate the process of laser cladding.And the method of “birth and death element” is introduced to realize the overlapping of cladding layer.In order to ensure the accuracy of the simulation,the heat source model is checked by comparing with the actual shape of molten pool.At the same time,the thermal physical parameters of cladding powder were simulated by using software of Jmatpro.And the thermal physical parameters of Ni based alloy in the material library of software were modified.Software of Visual-Environment was used to build the substrate model of concave,convex and planar surfaces model.SYSWELD software was used to simulate the temperature field and the stress field on the process of laser cladding.The results show that the Von-Mises stress of the cladding layers of the three models is small on the center of the cladding layer,and becomes larger at the edge of cladding layer,and the stress is largest on the HAZ.Due to differences in the shape of the substrate,heat dissipation model is different,the peak temperature of the concave model's cladding layer is lowest,the cooling rate is slowest.And the regularity of the convex model's cladding layer is opposite.The Von-Mises stress of the cladding layer is the largest on the convex model,but the concave models' is the smallest.Numerical simulation and experimental measurement results show that the process parameters of laser cladding have a great influence on the residual stress of the cladding layer.With the increase of laser scanning speed,residual stress of cladding layer is increased.The experimental results of laser cladding are in good agreement with the simulation results that increase of the laser scanning speed can increase the quantity and length of the cracks.When overlapping rate is less than 35%,with the increase of overlapping rate,the residual stress of cladding layer is decreased.But,when the overlapping rate is higher than 35%,with the increase of it,the residual stress is increase.The influence of scanning path on the residual stress is complex.The residual stress resulted by scanning path of contractive type is the best compared with the results of sequential type,S-type type and diffused type.Its residual stress distribution was homogeneous.Laser cladding of the gate was simulated by means of software of SYSWELD.The results show that the distribution of the Von-Mises stress in cladding layer is fluctuant along horizontal direction.The residual stress of the last two cladding layer on gate and area around hole is high,which is about 480 MPa and 305 MPa.Along thickness direction,the distribution of the residual stress whose maximum stress is 508 MPa is uniform.The existence of the hole on the gate has an influence on the temperature field and residual stress distribution of the cladding layer.The closer the round hole is,the greater the residual stress is,the more easily the cladding layer cracks.With the increase of the number of cladding layer,the deformation of the gate plate becomes more and more serious.The processes of laser cladding on easy wear out area was simulated.The results show that the high stress region is mainly distributed at the areas of end of each cladding layer and the second cladding layer.And the average stress in local laser cladding layer is better than the strss in entire gate cladding layer.However,the Von-Mises stress in entire gate cladding layer is better.When the gate is repaired,the entire cladding process is recommended.