Numerical Simulation Of The Forming Process Of The Powder Feeding Type Laser Cladding

Laser cladding,as an additive manufacturing technology is widely applied to engineering fields.In the process of powder feeding type laser cladding,the molten pool is created by the high energy laser beam heating the substrate,the cladding layer is formed after cooling the heated particles entering the molten pool.The geometry size,the processing efficiency,and the comprehensive performance of the cladding layer are affected by the interaction of molten pool-laser-powder and the complex temperature history in the deposition process of line-surface-layer.The quality of the cladding layer will be directly affected by the fluctuation of powder utilization rate in the powder feeding process,the change of thermal property parameters and the phenomenon of heat accumulation in the multi-pass cladding process.The analysis of the numerous process parameters of the laser cladding technology involves complex multi-physical field coupling mechanism,and the experimental observation of the evolution of metal powder particles and the molten pool is limited by the number of particles and the hightemperature characteristics.The change of the powder flow field,the fluid flow and the process of heat transfer in the cladding layer can be calculated and analyzed by the numerical simulation model.Based on the Euler-Lagrange method,the powder flow model is described and established.The carrier gas flow rate,the velocity of metal powder particles,the incident direction of particles,the size of metal particles and other parameters are studied.The results show that the carrier gas flow rate has little influence on the gas phase convergence distance.The utilization ratio of the powder particles with the different incident directions and velocities varies greatly with carrier gas flow.The deflected particles reduce the utilization ratio of the powder particles.The utilization ratio of the powder particles can be improved by reducing the particle size without considering the phenomenon of powder agglomeration.The particles with a smaller size,near the center of the laser beam and the sufficient laser action time can obtain a higher average temperature.The numerical model of cladding layer evolution is established.The free surface of the molten pool is described and calculated based on the ALE method.The influence of the fluid flow in the molten pool on the cladding morphology and the process of heat transfer is calculated and analyzed.The results show that the surface tension drives the convection in the molten pool,which changes the morphology and temperature distribution of the cladding layer.When the surface tension temperature coefficient is negative,the fluid flows from the high-temperature center of the molten pool to the edge of the cladding layer,increasing the width and length of the molten pool.When the surface tension temperature coefficient is positive,the fluid flows from the edge of the cladding layer to the high-temperature center of the molten pool.The convection in the cladding layer enhances the heat transfer in the direction of penetration and increases the depth of the molten pool.The convergence properties of powder flow are simulated.The results show that the diameter of the powder feeding pipes,the convergence angle,and the increment of the interlamination affect the convergence characteristics of the powder flow and the particle temperature.When the convergence characteristics are constant,the width and height of the cladding layer increase with the laser power and decrease with the scanning speed.The time-variant powder utilization affects the morphology of the cladding layer and the redistribution of energy during deposition.