Laser Polishing Process,Numerical Simulation And Polished Surface Properties Of Die Steel S136D

S136D die steel is a kind of plastic die steel,which is mainly used in the molding of plastic products.The smoothness of the mold surface will seriously affect the quality of the product.Usually,the mechanical,chemical or electrochemical effect is used to reduce the material on the surface of the workpiece to produce a smoother and more flat surface.However,this not only wastes raw materials,but also has the problems of high cost and difficult treatment of waste.Laser polishing is a non-contact surface polishing technology that can be used to polish the surface of a material without losing its own material.In this paper,laser is used to polish S136D die steel.The research contents are as follows:(1)Under the existing conditions,a large number of laser polishing experiments were carried out on S136D die steel,and the effects of laser power,scanning speed,scanning distance and other parameters on the surface roughness were analyzed.In order to further reduce the surface roughness,double laser polishing method was adopted.The experimental results show that the surface roughness can be greatly reduced from 7.973?m to 0.872?m with a reduction rate of 89.06%under the action of only continuous laser,and the roughness can be further reduced to 0.67?m under the action of double laser.Compared with the initial surface roughness,the roughness can be reduced by 91.6%.(2)The continuous laser,double laser and convex structure are simulated numerically.The changes of velocity,temperature,capillary force and thermocapillary force in molten pool are analyzed.It is described that capillary force and thermocapillary force are dominant at different time and position.In order to simulate surface convex more accurately,active elements P and S are added to the numerical simulation of convex structure The causes of the bulge structure are analyzed and verified by experiments.The results show that in the continuous laser simulation,the width of the simulated molten pool is 353.3?m,and the actual molten pool width is 408.6?m.Compared with the real size,the simulation error is 13.5%.In the simulation of convex structure,the errors of convex parameters l₁,l₂and l₃are 2.58%,42.2%and 9.3%,respectively(3)The microstructure of the sub surface layer of the material with different energy density and after double laser polishing was analyzed.The element changes in each region of the sub surface layer were described,and the decrease of the hardness of the remelted layer under high energy density was explained.The changes of the surface phase and the mass fraction of?-Fe and?-Fe were analyzed.The residual stress and corrosion resistance of the material surface were tested.The experimental results show that the hardness and Young's modulus of the matrix are increased at 1500J/cm²and 3000J/cm²,and decreased at 4500J/cm².The corrosion resistance of the three energy densities and the dual laser polishing is higher than that of the original sample.Moreover,there is residual stress in the material after laser polishing,and the residual stress will increase with the increase of energy density.The residual stress after double laser polishing is greater than that of single laser polishing.