| Additive manufacturing is hailed as one of the disruptive technologies leading the fourth industrial revolution.Among them,laser cladding can prepare coating with minimal dilution rate,high deformation,high bonding force and good mechanical properties on the surface of the matrix,so as to significantly improve the wear resistance,corrosion resistance,heat resistance,oxidation resistance and other properties of the matrix,has been applied in aerospace,automotive,petroleum,chemical,metallurgy,electric power,machinery and other fields.Laser cladding has the characteristics of high temperature,high strain rate,nonlinear and time varying,which leads to the problems of low geometric accuracy and unstable structure.In order to restrain the deformation of the parts after laser cladding,the 316 L stainless steel laser cladding powder with a controlled heat input method is used to meet the demand of advanced manufacturing with high quality and high efficiency.The mapping relationship between the heat-flow characteristics of the molten pool and the evolution of forming morphology and microstructure under multiple thermal cycles was explored.The influence of scanning path on the temperature,deformation,microstructure and mechanical properties of the matrix was clarified,and a performance optimization control method based on different scanning sequence and process parameters was proposed.This research has a certain reference significance for the prevention and control of plastic deformation and other quality anomalies in laser cladding process and the subsequent engineering practice promotion of high quality and efficient laser cladding.The main research work of this paper is as follows:(1)Based on the multi-source information fusion monitoring platform for laser cladding process,the laser cladding process signals from thermocouple,high-speed camera,infrared pyrometer,and thermal imager were got in real time.The extraction of temperature field distribution was developed using thermal imager with a temperature measurement range of200-2000°C.A coaxial camera was employed to monitor the molten pool morphology in real-time.It provides technical support for the analysis of transient change process characteristics of molten pool under different laser scanning paths during laser cladding.(2)The mechanism of restraining residual stress and thermal deformation of the cladding layer by different laser scanning paths was investigated.The formation mechanism of residual stress in laser cladding layer and the influence of different laser scanning path on residual stress in laser cladding layer are discussed.Based on the experiments,the relationship between the deformation of cladding deposition matrix with different laser scanning path and process parameters was studied.(3)The influence of different laser scanning paths on the inner quality of laser cladding sediments was studied.Thermal deformation and heat-affected zone phenomena of laser cladding sedimentary layer were investigated,the microstructure of laser cladding layer was analyzed by different laser scanning path and process parameters.The influence of microhardness and microcrack of different laser scanning paths on the properties of laser cladding sedimentary layer is illustrated.Finally,the experimental results show that the optimum laser scanning path can effectively suppress the temperature change of the cladding layer and the deformation of the substrate,and improve the microstructure and microhardness of the cladding parts.The temperature variance of the substrate and molten pool has been reduced to 335.1 °C and 1774.4 °C,respectively,using the proposed scanning sequence and optimized process parameters.The substrate’s deformation was reduced to 3.4 mm,and the average microhardness was improved to 240.5 h V. |
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