Study On Surface Adhesion Powder By Laser Direct Metal Deposition With 316L Stainless Steel

Direct Metal Deposition(DMD)is a digital additive manufacturing technology rapidly developed by the theory of layered manufacturing and based on the rapid prototyping and simultaneous laser surface cladding.It can also achieve highperformance rapid repair of damaged parts and multi-material composite layout and gradient structure manufacturing of the same part.As one of the important parts of Future Industry 4.0,DMD technology has been widely used in many fields such as national defense,aerospace,mold manufacturing,biomedical,and nuclear energy industries.However,DMD is a very complicated physical process,with many influencing factors and high process sensitivity.The use of DMD to achieve "shapeperformance controlling" still has great challenges.At present,the surface quality formed by DMD with 316 L stainless steel is poor and with bad powder adhesion phenomenon,which has become a stumbling block that restricts the development of this technology and wide industrial application.Firstly,the interaction between laser beam,powder particles and molten pool in DMD process is studied.316 L austenitic stainless steel powder is used as part material.High-speed camera monitoring system is established to observe the interaction between laser beam,powder and molten pool.Furthermore,the formation mechanism of surface powder adhesion is analyzed,and three types of powder adhesion on laser direct metal deposition forming surface were proposed.What’s more,the law of powder adherence under different process conditions in DMD is studied.According to the observation results of ultra-depth microscope,three methods to comprehensively characterize the degree of powder adhesion by means of roughness,surface coefficient and average height are proposed.In the CW mode,the greater degree of surface powder adhesion is as the powder feeding rate rises,the smaller degree of powder adhesion becomes as the carrier gas flow decreases,and the effect of the line energy density on the degree of surface powder adhesion is not obvious.What’s more,in the quasi-CW mode,the duty ratio is the key factor affecting the surface powder.When the quasi-CW duty rate is 20%,the degree of powder adhesion on forming surface is smallest.The pulse frequency and the linear energy density don’t have an obvious effect on the degree of powder adhesion.Finally,the obtained stable forming process is applied to the manufacturing of aero-engine bearing housing parts,and a scheme of step forming with the upper,middle and lower parts is formulated.According to the actual forming effect,forming method of rotating shaft and linear shaft linkage and forming method of the synergy between quasi-CW and CW are further proposed.Considering the deposition efficiency and surface quality,the forming method of the synergy between quasi-CW and CW improves the degree of powder adhesion on the formed surface to some extent.