The Simulation Research On The Deposition Morphology Of Laser Additive Manufacturing Based On Coaxial Powder Injection

Laser additive manufacturing is one of the most popular advanced manufacturing technology, which has a high usage rate of material, short production cycle and outstanding mechanical properties of formed pieces. It has been widely applied in aerospace, bio-medical and other fields. The dynamic characteristics and solidification behavior of molten pool directly affects forming precision, metallurgical defect, microstructure and mechanical properties. However, experimental techniques can no longer obtain the dynamic characteristics and evolution laws of the molten pool. This paper has analyzed these issues by involving most physical processes in laser additive manufacturing, and numerical model is achieved to investigate the molten pool’s dynamic evolution and the deposition’s morphology.Firstly, high-speed camera was used to obtain the picture of distribution of powder flow in the air. By using the characteristics that different gray values represent different concentrations in the picture, the convergence characteristics of the powder beam were analyzed. The power density distribution of laser beam was measured by the laser beam profiler, and the mathematical model coupling laser beam and powder was established. The calculation of laser energy attenuation and powder temperature distribution was realized by this model. The results show that:Attenuation of laser energy is inversely proportional to particle size, and proportional to powder feed rate.Secondly, the deposition’s morphology and the transient evolution of the molten pool were studied. A three-dimensional transient-mathematical model coupling laser, powder and molten pool was established. This model is used to deal with the boundary gas/liquid conditions by using the Level Set method. The main driving forces of the liquid flow in the molten pool were considered, which contain surface tension, thermal capillary force, surface curvature, buoyancy and other factors. At the same time, the melting and solidification processes at the solid/liquid interface are described by using a porous continuum model. The corresponding mathematical model solving program was developed by using Fortran programming language based on the finite volume method. The Simulation results show that:During the beginning of laser additive manufacturing process, the "growth" of molten pool is a dynamic changing process with the increment of temperature rising rate, its morphology varies more significance; After a while, molten pool’s temperature and absorption of powder remain stable; During laser additive manufacturing process, the temperature of molten pool is higher than that of deposition, and the gradient of temperature of molten pool’s frontier border is larger than its behind border.Finally, the influences of laser power, scanning speed and powder feeding rate on the deposition profile and the temperature of the molten pool were studied in this paper. The related process experiment was carried out with the same process parameters, the simulation and experimental results show that:With the increment of laser power, the increment of cladding height is relatively small, while that of cladding width is relatively large; With the increment of scanning speed, the angle between solid-liquid or gas-liquid and surface of substrate decrease; And when the powder delivery rate is large, the movement of powder into the molten pool would cause the decrement of molten pool’s temperature; The relative errors between the experimental results and the simulation results are less than 11% in the height and width of the deposition layer.