Study On Process Of Selective Laser Melting And Plasma Electrical Signal Analysis

In this paper,a set of powder bed device for laser selective melting is designed to investigate the laser selective melting process of 316 L powder.The plasma electrical signals in the forming process were collected.Besides the plasma electrical signal characteristics and single melt track characteristics were analyzed.In the selective laser melting additive manufacturing,single melt track forming is the basis of the final part forming.Through the control variate method,the forming conditions under different laser power,different scanning speed and different metal powder thickness are investigated.Through the analysis of single melting macro forming,it is found that the melt track can be divided into five types: " spherical melt track","intermittent melt track ","necking melt track","available melt track" and "over-melt track";By analyzing the cross section forming shapes of single melt track,it is found that cross section forming shapes of melt track can be divided into four types: "spherical forming shape","shoal forming shape","heat conduction forming shape" and "deep penetration forming shape".Only the melt track is " available melt track " and the section shape is "heat conduction shape",the forming is better than others.In the case of single melt track forming,the proper distance between the melt tracks should be selected,and the appropriate process parameters can better control the forming process.Different cross section forming shapes correspond to characteristics of different plasma electrical signals in time domain and the autocorrelation coefficients,and different SLM shapes can be classified by plasma electrical signals.When the cross section shape is "spherical forming shape",the corresponding electrical signal is an empty signal;When the cross section shape is "shoal forming shape",the negative voltage plasma electrical signals appear at very little time;When the cross section shape is "thermal conductivity forming shape",the negative voltage signals appear in a majority of time,and the 0V voltage signals appear in a few time.Besides,it is found that the periodicity characteristic could not appear in electrical signal by autocorrelation analysis;When the cross section shape is " deep penetration forming shape ",the plasma signals are all negative voltage signals,and the voltage amplitude increases with the increase of heat input.Besides,it is found the periodicity characteristic could appear in the electrical signal by autocorrelation analysis,and the cycle time increases with the increase of heat input.