Numerical Simulation And Experimental Study Of Laser Inner Wall Cladding Process

Laser inner wall cladding technology provides a green,efficient and excellent solution for the preparation of inner wall reinforced coatings.However,in the actual cladding process,due to the high locality and transient nature of the material's melting-solidification process,stress and deformation will inevitably occur,which seriously affects the dimensional accuracy and performance of the part,and even jeopardizes the safe service of the part.This paper presents numerical simulation method combined with experimental verification to study the evolution of temperature and stress during laser inner wall cladding process.Also,the interactions between the key parameters such as temperature and residual stress and different inner wall size,shape and process conditions are investigated.Which may provide a theoretical basis on the future research.In this paper,ABAQUS software is used as the computing platform.According to the characteristics of the laser inner wall cladding process,the heat source subroutine is programmed by FORTRAN to establish a mobile heat source model.The "element progressive activation" method is used to simulated single-layer,single-layer multi-channel and multi-layer multi-channel laser inner wall.The single control variable method is used to investigate the temperature field characteristics and stress evolution process of laser inner wall cladding under different process parameters and structural dimensions.The accuracy of the numerical simulation temperature field was verified by the thermocouple temperature measurement method,the cladding depth and the dilution ratio.The residual stress of the laser inner wall cladding was measured by the X-ray diffraction tilting fixed ? method,and the numerical simulation stress field was also verified by experiment.Finally,the effects of different process parameters and structure sizes on the macroscopic morphology,microstructure and properties of the cladding layer were analyzed by optical microscopy(OM)and Vickers hardness tester.The main conclusions of this paper are summarized as follows:(1)The temperature field simulation results show that the temperature gradient in the radial direction(the direction of the vertical substrate surface)is significantly larger than the temperature gradients in the other two directions.The main reason is that the heat dissipation is mainly in the radial direction during the cooling process of the molten pool;And the temperature gradient is the largest at the solid-liquid interface of the molten pool.As the scanning speed and wall thickness increase,both the temperature gradient and the cooling rate increase.As the laser power and curvature increase,the temperature gradient increases,but the cooling rate decreases.(2)Stress field simulation results show that excessive temperature gradient is the main reason for thermal stress.The hoop stress is greater than the radial stress and the axial stress.A large tensile stress is generated at the junction of the cladding layer and the substrate,where the crack is in a high position,and a transverse crack perpendicular to the scanning direction is easily generated.Under different process parameters: the tensile stress on the path AD increases with the increase of power.Large stresses are easily generated under high-speed cladding.Under different structural dimensions,the stress increases with the increase of the wall thickness.The smaller the curvature,the smaller the stress.When the curvature is 0,the stress on the path AD is 488 MPa.(3)The characteristic point acquisition temperature is consistent with the simulated historical temperature curve trend,and the temperature field change process is better restored.The deviation of the cladding depth and the simulation results between the experimental and simulation results is 4.52%,and the variation trend of the dilution rate has a high degree of coincidence,indicating the correctness of the temperature field simulation.The experimental measurement of the residual stress on the inner wall cladding layer is 700~800 MPa,which shows a good agreement between numerical and experimental results.(4)The cooling rate affects the size of the crystal grains.The larger the cooling rate existing,the smaller crystal grains will occur.The hardness increases with the decrease of power,scanning speed and wall thickness The hardness on the flat plate is slightly larger than the inner wall.The results of the thermal-stress evolution process obtained by numerical simulation will help understand the distribution of temperature and stress during cladding of the inner wall and provide a theoretical basis for the laser inner wall cladding technology.