Research On The Density Of Stainless Steel Parts Formed By Powder-Bed Laser Fusion

Metallic powder-bed laser fusion process can directly produce metallic parts with complex feature,and is one of the main additive manufacturing process.However,due to its complicated procedure and rather many impact factors,the density of formed parts often fails to meet the requirements in application.In this thesis,the density of the parts formed with metallic powder-bed laser fusion was experimentally studied.The specific research contents are as follows:Experimental study on forming foundation.In order to study the effect of process parameters on the density of a formed part and to establish the correlation between process parameters and density,firstly,the formability of 316L stainless steel powder was studied in single pass scanning test,then,orthogonal test of bead overlap in a single layer was performed,and the influences of laser power,scanning speed,and overlap rate on the surface status of the layer were disclosed and the value range of the process parameters for a fully-fused first layer were obtained.Density test of forming part.Stainless steel parts were formed and their densities were measured by drainage method.The effects of laser power,scanning speed,and overlap ratio on the densities of formed parts were obtained.Among them,laser power has the greatest influence on the density,overlap ratio less,and scanning speed the least.The density of the part formed in the process with the powder thickness of 0.06mm,laser power 150W,scan speed 60mm/s,and overlap ratio 55%is the highest.In addition,the porosity of the formed part is calculated imaging method,and its density is quantitatively analyzed.The relationship between laser energy input density and density is studied.The microstructure analysis showed that the micro structure of metallographic structure was mainly composed of granular and columnar crystals.The analysis of mechanical properties showed that the yield strength was obviously higher than that of a casting part,and the tensile strength is similar to,and the elongation is less than,and the higher the density was,the better the mechanical properties were.Experimental study on the effects of the structure of a formed part on density.The results of experiments of forming thin-walled and mesh features showed that under certain process parameters,the densities of the formed thin-walled and mesh features were higher than that of a solid feature because of less scanning vector length,better cooling effect and less heat accumulation.However,thin wall and network structure were apt to bond powder grains,resulting in poor dimensional accuracy.