Research On Melting Structure Regulation Mechanism Of Molten Pool In Plasma Arc Powder Additive Manufacturing On Laser Energy

Additive manufacturing technology has become a new star in the world's industrial manufacturing industry.This field integrates emerging materials research and development technology,computer measurement and control and other cutting-edge technologies,and integrates and develops into a popular advanced manufacturing technology discipline.The technical difficulties of additive manufacturing of metal components are mainly focused on the adjustment of the macro and micro structure of the formed structure.In this paper,an experimental platform for laser energy-assisted plasma arc loaded powder-based additive manufacturing is established.The two process methods of pulsed laser-assisted arc additive manufacturing and continuous laser-assisted arc additive manufacturing are studied from the aspects of macroscopic morphology and microstructure.Combined with numerical simulation technology,and structural load acoustic emission detection technology,systematically explore the mechanism of laser energy control plasma arc powder additive manufacturing molten pool melting structure.Through studying the structure characteristics of the sample structure of different laser arc heat source composite modes,the application of laser energy can refine the structure of the remelting zone,and the effect of controlling the melting structure is the most obvious when laser excitation is in the front of the molten pool.Applying a proper laser energy can improve the local fluidity of the additive molten pool,improve the forming quality of the fused structure,increase the efficiency of powder cladding,and reduce the forming coefficient,which is conducive to the formation of fine structures.However,when the laser power is too large and the heat input is too large,the stability of the molten pool decreases and collapses,which is not conducive to stack formation.Comparing single-arc additive manufacturing and laser-assisted arc additive manufacturing samples,it is found that the single-arc sample structure is mainly coarse columnar crystals,and the interlayer transition area of the multilayer additive sample is continuously growing crystal grains;after applying pulsed laser,a refined grain layer appears in the interlayer transition area to eliminate the phenomenon of columnar grain growth through the interlayer.With the peak power of the pulsed laser increases,the grain refinement effect in the non-interlayer region is enhanced,and the grain orientation is more uniform;the continuous laser-controlled interlayer region melting structure has a laser power threshold effect.When the laser power exceeds 300 W,the remelting zone appears in the interlayer transition zone,the grain refinement effect is remarkable.Observed from the longitudinal section direction,the laser energy refines the width of the crystal layer up to millimeter level,and effectively reduces the grain orientation strength and internal dislocation density.Through the mechanical performance test,it is found that the application of auxiliary laser energy produces a fine-grain strengthening effect,which can basically eliminate the hole phenomenon in the formed structure,improve the compactness of the structure,and improve the transverse and longitudinal plastic toughness and tensile strength of the formed structure.Comparing the tensile strength of the two dimensions,it is found that pulsed laser energy can effectively reduce the anisotropy of the transverse and longitudinal tensile strength of the formed parts.In particular,in the longitudinal tensile test,it is found that the interlayer transition zone is a weak area of performance.Through the molten pool image information and the flow field calculation method,the pulse laser excited molten pool oscillation effect is studied,and it is found that the molten pool fluid flow state is the most significant when the laser excites the head of the molten pool.With the aid of the structurally loaded acoustic emission system,the physical model of the propagation of the oscillating mechanical wave on the surface of the molten pool excited by the pulsed laser is analyzed.It is concluded that the strong flow of the molten pool is the main reason for the pulse laser to control the microstructure.The stirring effect of continuous laser energy and the interface remelting effect work together to produce a significant control effect on the melting structure of the additive molten pool.In summary,the mechanism of pulsed laser and continuous laser control of plasma arc powder-carrying powder additive manufacturing molten pool fusion structure control mechanism is proposed.