Study On The Change Of Molten Pool Size And Forming Height During Laser Cladding

Laser cladding is a technology that uses high-energy laser beam to irradiate and instantly melt the powder material and local matrix material,so that the cladding layer and the substrate form a good metallurgical bond.It is one of the main ways to realize 3D printing of metal parts.It can be used not only for repairing and remanufacturing of failed parts,but also for direct forming of metal parts.In order to study the change of the size of the molten pool with the increase of the number of cladding layers in the multi-layer laser cladding process,as well as the information of the temperature field change and temperature history of the entire cladding process,a three-dimensional heat conduction model based on energy conservation is established.The numerical simulation results show that the peak temperature of the molten pool increases firstly with the increase of the number of cladding layers,but it does not continue to increase after reaching a certain number of layers.However,the size of the molten pool increases with the number of layers,which provides some guidance for the laser cladding control system based on the size of the molten pool.When studying the internal information of the molten pool,the heat transfer model ignores the fluid flow of the molten metal in the molten pool,and the heat transfer in the molten pool is mainly dominated by the convection of the fluid.Fluid flow has a great influence on the temperature field distribution and shape of the molten pool.Therefore,a heat transfer and fluid flow model based on the conservation of energy,momentum and mass is established.The model considers the effects of Marangoni convection,buoyancy,etc.on temperature and velocity fields,and introduces a relative energy-mass ratio(REMR)to measure the laser energy absorbed by per unit mass of metal powder.The experimental and simulation results show that with the increase of REMR the bottom boundary of the molten pool gradually changes from shallow arc shape to wave shape,and finally becomes deep arc shape.At the same time,the dilution ratio and REMR have a linear relationship within a certain process parameter range.Finally,in order to improve the dimensional accuracy of the cladding,we have established a defocusing control system based on laser displacement sensing.By monitoring the change of forming height and defocusing during the cladding forming process,the defocusing amount is optimized.Range to improve the dimensional accuracy of the cladding and the efficiency of powder utilization.The defocusing amount is controlled in the optimum range by monitoring the change of forming height and defocusing amount during cladding forming process,so as to improve the dimensional accuracy of cladding parts and the efficiency of powder utilization.