Research On Quality Of Powder Forming And Mechanical Property Of 18Ni-300 By Selective Laser Melting

18Ni-300 die steel is widely used in precise die moulds,aerospace and other industries.Selective laser melting(SLM)technology was used to manufacture mold cores with conformal cooling water channels in this thesis.The rapid prototyping parts have strict requirements regarding the surface quality and mechanical properties.This thesis studies the effect of four forming process parameters including laser power,scanning speed,scanning spacing,and layer thickness on the performances of 18Ni-300 die steel samples,with the method of orthogonal experiment.The performances indicate the relative density,hardness,tensile strength,dimensional accuracy,roughness and mechanical properties.The weightiness of these five performances were determined by the analytic hierarchy process,and the multi-objective optimization of the comprehensive performance was performed to obtain the optimal process parameters.Finally,mold cores with conformal cooling water channels were made with the optimal process parameters.With the increase of laser power,the relative density,hardness,and tensile strength show a trend of first increase and then decrease,and the dimensional deviation and surface roughness show a trend of first decrease and then increase.As the scanning speed increases,the relative density increases first and then decreases,both the hardness and tensile strength show a decreasing trend,both the dimensional deviation and surface roughness decrease first and then increase.As the scanning spacing increases,the relative density,hardness,and tensile strength show a trend of first increase and then decrease,and the dimensional deviation and surface roughness show a trend of first decrease and then increase.With the increase of the layer thickness,the relative density,hardness,and tensile strength show a decreasing trend,and the dimensional deviation and surface roughness show a trend of first decrease and then increase.Multi-objective optimization of the weightiness of these five performances was conducted by the analytic hierarchy process.The best process parameters obtained are 260 W for laser power,500mm/s for scanning speed,0.02 mm for layer thickness,and 0.11 mm for scanning interval.Based on these process parameters,samples with relative density of 99.99%,hardness of 430 HV,tensile strength of 1240 MPa,dimensional deviation of 0.0551 mm,and surface roughness of 5.81μm were manufactured.With the best process parameters,mold cores with conformal cooling water channels were made.We found that the performance of mold cores had reached the optimal effect,and theforming quality and performance met the requirements of the mold core.