Research On Molten Pool Behavior And Forming Control Of Combined Wire-Powder Direct Laser Deposition For Additive Manufacturing

Combined wire-powder direct laser deposition is based on laser as the heat source,powder and wire material are simultaneously filled in the molten pool,and deposition is performed layer by layer to achieve additive manufacturing.Its essence is threedimensional laser cladding,and it is a new additive manufacturing technology.This product has the advantages of high efficiency,high density,and flexible adjustment which is suitable for the additive preparation of metal matrix composites.As a new type of metal matrix composites,WCp/Al has a wide application prospect due to its excellent mechanical and physical properties.In order to solve the problems of poor formability and uneven distribution of reinforcing particles in WCp/Al composites prepared by simultaneous laser deposition additive of silk powder,the finite element analysis software ANSYS and FLUENT were used to simulate the temperature field and stress of the simultaneous laser deposition process.The field and the molten pool flow behavior,based on which the relevant laser deposition forming experimental study.A three-dimensional finite element model similar to the real sedimentary layer was established using ANSYS software.The temperature and stress fields of the laser deposition three-dimensional forming process were numerically simulated and the postprocessing module was used.The results were extracted and integrated.Based on the simulation results,the distribution of temperature field and stress field and the dynamic change law of the laser forming process of the narrow wall and block structures were studied.The laser power,scanning speed,interval time between layers,and scanning were analyzed.The impact of the path,proposed several forms of regulation and control methods.Using the decreasing laser power that increases with the number of deposition layers,it is possible to suppress the pool temperature and pool size from excessively increasing with the deposition process and to favor the forming stability.With the reciprocating scanning method,the residual stress area is reduced compared to the sequential scanning method.Small,the stress distribution is more uniform,and the residual stress is symmetrically distributed along the scan path,which is beneficial to the uniformity of the microstructure and mechanical properties of the formed component.A model for flow of molten pool in combined wire-powder direct laser deposition was established.The flow mechanism of the fluid in the molten pool is explained by calculations.The Marangoni vortex is generated at the fusion line of the weld pool.Two symmetric eddies are formed on the cross-section of the molten pool.Two different sizes of the molten pool are generated radially outward.In the vortex,the vortex at the front of the center is strong;the fluid on the upper surface flows from the center of the bath to the surroundings.The effects of particle size and incident velocity on the distribution of reinforcement particles were analyzed.The relationship between particle utilization and particle size was small.When the diameter of WC particles was 60 ?m and 80 ?m,the distribution of particles in the sedimentary layer was relatively uniform.During the deposition process,the micro-melting or non-fusion is maintained,and the grain size cannot be too small.When the grain incidence velocity is reduced to less than 1.5 m/s,the particles in the sediment layer are distributed uniformly and the “sinking bottom” phenomenon is not easy to occur during the deposition process.In the process,the flow rate of the powder can be adjusted to adjust the injection rate of the particles,and the distribution in the sediment layer can be adjusted to some extent.Based on the semiconductor laser rapid prototyping system,the WCp/Al composite laser deposition forming experiment was carried out.By comparing the wall structure formation under different laser power schemes,it is found that the deposition layer with reduced laser power is relatively stable,there is no situation of stay,and the deposition quality is good,which verifies the rationality of the calculation model.The lateral lap joint tests with different lap ratios were carried out.The ideal lap joint rate was 27.39% with theoretical calculation and actual forming,which laid the foundation for the multilayer multi-layer deposition forming block structure.The size of the powder sent affects the incident velocity of the WC,and the WC distribution is affected by the WC incident velocity.The experiment found that with the increase of powder gas supply,the phenomenon of WC subsidence became evident.When the powder gas feed was low(5 L/min and 10 L/min),the WC incident velocity was low,and an ideal WC distribution was obtained,which was in agreement with the simulation results.