Mechanism And Simulation Of Particle Acceleration,Erosion And Convective Heat Transfer During Abrasive Water Jet Machining

Abrasive water jet machining(AWJM)is a new non-traditional machining technology which has developed rapidly since 1980 s.The particle velocity is an important factor affecting the erosion depth of the target material in AWJM,which directly affects the erosion process and the surface morphology of the target material after erosion.At the same time,water also plays a role of convection heat transfer in the process of erosion,which can properly avoid the burning of target material due to local high temperature in the process of AWJM.The three processes are interlinked.However,most of the existing studies have studied the particle acceleration,erosion and convective heat transfer separately in AWJM.In addition,most of the researches on the acceleration only stay in theory,and there are relatively few studies on simulation of particle acceleration.In the research on the erosion of AWJM,most of them only discuss the results of the erosion,and there are few studies on the transient state of the erosion process.Meanwhile,in the research on the convective heat transfer of AWJM,the effect of process parameters on the convective heat transfer performance is not comprehensive enough.Therefore,this paper takes the high-strength alloy steel18 Cr Ni Mo7-6 plane target as the object of AWJM.Through the method of combining theory and simulation,it not only studies the acceleration process of the particle in sand pipe,but also studies the process of particle eroding the target material after the acceleration of particle is completed.In addition,the convective heat transfer process of AWJM is also studied.The main research methods and contents are as follows:(1)Firstly,the acceleration mechanism of particle in AWJM was studied,the force analysis of particle was carried out and the corresponding motion equation was established,and the variation state of the pellet velocity in the sand tube was explored.The results show that the particle accelerates in the sand tube under the combined action of inertial force FD,Stokes force FS,additional mass force FA and pressure gradient force FP.The particle velocity increases with the increase of particle movement time.The rate of increase is relatively rapid in the early period,which has dropped significantly in the later period,and finally approaches to the fluid velocity infinitely.(2)Three different methods were used to establish the simulation model of particle acceleration in AWJM.The influence of jet velocity,particle diameter and particle density on the variation of particle velocity was investigated,and the theoretical velocity was compared with the simulation velocity.The results show that the smaller the particle diameter and particle density,the faster the particle acceleration.When the length of sand tube is the same,the particle outlet velocity decreases with the increase of particle diameter and pellet density.Comprehensive comparison of the changes of the particle velocity between the theoretical model and the three simulation models,it is found that the SPH-FEM coupling method simulation is more consistent with the theoretical calculation results.(3)Analyzed the mechanism of the particle eroding the target,and then established an erosion simulation model of AWJM by using ABAQUS software,and analyzed the changes of the pit morphology on the target surface during the process of erosion.At the same time,the influence of the initial particle velocity,the particle diameter,the particle density and the particle incident angle on the pit morphology of the target surface was explored.The results show that with the increase of the initial particle velocity,particle diameter and particle density,the pits on the target surface increase and the material removal volume increases too.With the increase of the particle incident angle,the depth of the spherical pits on the target surface increases,the width decreases,and the material removal volume increases.(4)The flow field distribution of AWJM was analyzed,and then the simulation model of convective heat transfer under different parameters of AWJM was established by using FLUENT software.The influence rules of jet velocity,jet angle and jet diameter on the convective heat transfer characteristics of AWJM were analyzed.The results show that the convective heat transfer coefficient increases with the increase of jet velocity and jet diameter.As the jet angle decreases,the convective heat transfer coefficient decreases in the upstream direction of the impinging center,but increases in the downstream direction of the impinging center.