Investigation On The Hybrid Technology Of Selective Laser Sintering/Isostatic Pressing About Stainless Steel Powder

At present, Selective Laser Sintering (SLS) is a more developed and widely applied technology of Rapid Prototyping (RP), so it has been paid attention to by researchers all along in the world. But relative density of SLS parts is often lower and their mechanical performance is worse so as to hinder its development and application strongly. Although relative density of SLS parts was improved by infiltrating lower melting point metal in the past, their mechanical didn't still meet requirements. In order to manufacture high relative density, better mechanical performance and complicated parts, Isostatic pressure (IP) technology is introduced into SLS which is named as SLS/IP technology. Complicated AISI304 and AISI316L metal parts are manufactured by SLS/IP, then densification mechanism, metallurgical structure and mechanical performances of AISI304 and AISI316L SLS/IP metal parts are analyzed by TG, XRD, SEM and tension test etc. Their mathematic physics models of dimensional precision are derived under SLS parts evenly shrinking in degreasing process, CIP, high sintering and HIP, so the theory is established for analyzing the dimensional precisions of SLS samples further. Main research contents and conclusions are below.(1) Mechanisms of SLS forming and thermal degreasing about AISI304 and AISI316L powders are investigated with their technology parameters. Mixed and coated composites of SLS are manufactured by resin E12 and nylon PA12, and optimized SLS technology parameters are determined, which include preheat temperature, laser power, scan speed, can interval and layer thickness. They are respectively 50-55℃,19-20W, 1900-2000mm/s, 0.1-0.12mm,0.1-0.12mm and 150-165℃, 15-17W, 1800-2000mm/s, 0.1-0.15mm, 0.1-0.15mm/s.According to thermal degreasing mechanism and TG curves of E12 and PA12, their thermal degreasing technologies of SLS prototype are set up.(2) Canning materials used in SLS/Cold Isostatic Pressing (CIP) are investigated, which include natural rubber latex and silicon rubber, and natural rubber latex is firstly introduced into SLS/CIP. Compared with silicon rubber, complicated SLS parts could be sealed by natural rubber latex, which films more easily and is suitable for SLS/CIP canning material.(3) Mechanisms and technologies of AISI304 and AISI316L parts after thermal degreasing are investigated with effects of their technology parameters on them, and their densification mechanics of SLS/CIP and minimal SLS/CIP threshold are brought forward. Thereinto, according to CIP theory and property of SLS degreasing part, densification mechanics of above stainless steel SLS/CIP parts is sintering neck crushing, metal rearranging and its plastic deformation. The threshold of SLS/CIP pressure is 400MPa when AISI304 degreasing part is CIPped. After CIP of 650MPa, high sintering of 1350℃and HIP of 1200℃/120MPa, relative density of AISI304 part is 86%, 95% and 98% respectively, and its mechanical performance is Young's modulus of 93.15GPa, yield strength of 306MPa, tension strength of 577.5MPa and elongation percentage of 32.05%, which are close to solution treatment AISI304 dense material. The threshold of SLS/CIP pressure is 300MPa when AISI316L degreasing part is CIPped. After subsequent high sintering of 1320℃and HIP of 1250℃/120MPa, its relative density Its relative density is over 95%, and its mechanical performance is Young's modulus of 142.5GPa, yield strength of 277MPa, tension strength of 649.49MPa and elongation percentage of 45.7%.(4) Effects of Cu and FeB on relative density, Young's modulus, yield strength, tension strength and elongation percentage of AISI304 parts are investigated in high sintering and HIP with effects of Si and FeMn on relative density, Young's modulus, yield strength, tension strength and elongation percentage of AISI316L parts. According to liquid sintering and XRD, relative density of SLS/IP AISI304 parts could be improved. NixCuy solid solution is precipitated in austenite with mechanical performances improving when content of of Cu increases from 1% to 3%, and eutectics of Fe-B and Ni-B are precipitated along grain boundary so that their mechanical performances worsen gradually when content of of FeB increases from 0.5% to 5%. In addition, relative density of AISI316L SLS/IP parts could be improved gradually with addition of Si and FeMn, but Cr23C6 is precipitated along grain boundary with addition of Si so as to worsen their mechanical performances, but their mechanical performances could be improved with addition of FeMn in high sintering and HIP.(5) Dimensional precision of SLS part in each process in SLS/IP are investigated, corresponding solved methods being introduced, and mathematic physics models of dimensional precision are brought forward after degreasing. Mathematic physics models of dimensional precision in SLS/CIP, high sintering and HIP are maily brought forward, which are respectively andhi eonelusion,lower relative density and worse meehanieal Performanee of SLS Partshave been avoided by SLS/I P,whleh imProves SLS,俪dens aPPlieation domain of SLSand establishes foundation for manufaeturing dense,high Performanee,high definition andeomPlieated metal Parts.