Numeriacl Simulation On Temperature Field And Morphology Evolution Of Molten Pool During Selective Laser Melting Processing

As an advanced technology of manufacturing industry,the laser additive manufacturing technology could reach the high performance alloy structure without mold and make the alloy with high flexible and fast near net forming,possessing huge application prospect The SLM mainly includes two technologies:laser solid forming and selective laser melting(SLM).However,for SLM,due to the complex coupling behavior of multiple physical fields involved in the melting process of laser selection,it is difficult to obtain accurate evolution information such as the shape size and temperature field of the melting pool through only experimental observation,which limits the optimization and upgrading of forming quality.Numerical simulation technology,because of its advantages of easy operation and low cost,has opened up an effective way for the present research.The simulation software FLOW-3D was used to study the distribution of temperature field and the evolution of size in the process of single-layer and single-channel scanning.The causes of defects in the forming process were discussed,which provided guidance for process parameter selection and process optimization.The main conclusions are as follows:1.The evolution of the temperature field and morphology of the molten pool was obtained during the different process parameters.With the increase of scanning speed,the maximum temperature of molten pool decreased and the depth of molten pool increased,but the length of molten pool increased.At the same time,when the particle size was small,excellent surface could be obtained.The optimal process parameters of laser power and scanning speed were determined with the surfac e roughness as the quantitative standard,and a set of data was finally obtained:laser power P=500W,scanning speed v=0.8m/s,particle size 15?m-30?m.2.With the increase of line energy density,convection in the molten pool accelerated heat and mass transfer,and the fluid in the molten pool transfer from inside to outside.The molten pool became wide and shallow,and could reach the dense powder layer.The recoil pressured not only depresses the spot but also make the pool flow backward.3.The fundamental reason for the spheroidization reaction was that the substrate was melted because the powder layer did not absorb enough heat.The laser power and the reduction of the thickness of the powder layer were effective methods to eliminate the spheroidization reaction;However,irregular adhesion of randomly distributed powder on the edge of molten pool and molten pool would inevitably lead to unevenness,which could be effectively reduced by refining particles,but couldn't be completely eliminated.4.The influence of scanning path and scanning distance on the defects of the melting pool in the process of multi-channel scanning were obtained.Compared with the s-type path,the z-type scanning method could obtain stable melting pool and effectively eliminated the heat accumulation after reentry;Scanning spacing should not be greater than the effective width of a single channel,that was,the width of the melting area of the substrate,which could effectively improve the melting deposition efficiency and energy utilization rate.