Laser Selective Melting Density Prediction Model And Experimental Verification

Laser selective melting(SLM)is widely used in aerospace and mold manufacturing because of its high precision and simple manufacturing process.However,due to poor fusion,laser selective melting is easy to produce pore problems,which affect the forming quality of the forming parts.Moreover,the complex changes of its multiple physical fields lead to the poor fusion pores and density in the forming parts are difficult to predict.The observation and measurement of porosity and density by repeated experiments is too long and expensive,which is not conducive to the application of laser selective melting in the field of new material additive.Therefore,it is of great significance to predict the porosity and density by establishing a model.In this paper,a density prediction model was established and improved for the pores generated by poor fusion,and pore morphology,location and density prediction values were studied under different process parameters.The research contents are as follows:(1)The morphology of molten pool was simulated by different density of powder layer,and the influence of different density of powder layer on the morphology of molten pool was studied.The results show that the collapse of molten pool will occur after solidification due to the loose and empty powder layer.The collapse depth of molten pool decreased from 39.8μm to 21.26μm with the increase of powder density from 0.2 to 0.6.When the resulting density exceeds 0.6,the collapse depth of molten pool has little change.According to the simulation,when the density of powder layer is 0.8,there is a large gap between the actual total mass of powder layer and the theoretical calculation.Therefore,the density of powder layer is 0.6 in the simulation,and the surface of powder layer is approximately reduced by 20μm to measure the morphology and size of molten pool.In addition,the stability time of molten pool morphology is studied under different process parameters.It is found that the stability time of molten pool morphology is also different under different process parameters.The general rule is as follows: with the increase of scanning speed,the stability time of molten pool morphology decreases.Therefore,in the measurement,in order to obtain more accurate topography and size,we should select the appropriate measurement position according to the law.(2)The multi-physical field of multi-channel printing is simulated by different process parameters.A variety of defects in multi-channel printing are found,and the causes of defects are analyzed.By analyzing the flow field of the molten pool,it is found that as the scanning velocity decreases from 1850mm/s to 1250mm/s,the laser energy density increases,resulting in the molten flow velocity in the molten pool increases from1.81m/s to 2.29m/s,which makes it easier to produce molten spatter phenomenon in the molten pool.In addition,with the increase of molten flow rate,under the action of Marangoni force,the high temperature molten liquid melts the edge of the molten pool,which enlarges the molten pool size and inhibits the pores caused by poor fusion to a certain extent.(3)Based on the changes of molten pool morphology caused by the size fluctuation,vertical displacement and deflection Angle fluctuation of molten pool morphology in actual printing,the density prediction model was optimized,and the random fluctuation coefficient of molten pool morphology size was added.The model was optimized based on the change of molten pool morphology and size and molten pool spacing on the twodimensional observation plane.Based on the above optimization,the influence of preset process parameters of molten pool size fluctuation coefficient,vertical displacement coefficient,deflection Angle fluctuation coefficient,deflection Angle fluctuation coefficient,deflection Angle,scanning spacing and thickness on the predicted value of molten pool morphology and density were studied,and the appropriate wave coefficient of molten pool morphology and preset process parameters were obtained.(4)Under the conditions of four groups of process parameters,the laser selective melting HR-2 stainless steel experiment found that the molten pool morphology of the molten pool size fluctuations,molten pool deflection phenomenon,proving that the model has a good agreement with the actual molten pool morphology.Finally,through the comparison between the experiment and the predicted density prediction,it is found that the error of the predicted density value is less than 2%,which proves the validity and reliability of the predicted density model.