| Laser cladding technology is a green and efficient advanced manufacturing technology.It is also the basis for solid metal forming and additive manufacturing.It is suitable for rapid prototyping of complex parts.It is widely used in aerospace,large equipment and biomedical fields.Because the laser cladding process is a multi-physics coupling and multi-process parameter interaction process,the complex heat and mass transfer phenomena in the cladding process affect the performance of the final formed part,which restricts the promotion and development of the technology.In order to manufacture parts with high performance and high reliability,it is necessary not only to overcome the defects caused by the process in the forming process,but also to understand the mechanism of heat and mass transfer during the forming process and further control the solidification structure.In this paper,316 L stainless steel alloy coating was prepared on 45# steel by laser cladding technology.The dynamic model of three-dimensional transient laser cladding was established by using the commercial software FLUENT.The heat and mass transfer in the process,using the VOF method to track the dynamic growth process of the deposited layer during the cladding process,compared with orthogonal experiments to investigate the effects of different process parameters on the geometrical appearance of the cladding layer and the solidification characteristics of the molten pool.Establish a quantitative relationship of process-structure-performance and provide a theoretical basis for laser cladding additive manufacturing.The results of current research are summarized as follows:(1)The effects of different laser power scanning speeds and powder feeding rates on the geometrical features of the cladding layer were analyzed.The main factors affecting the geometry of the cladding layer were analyzed.The comparison between the orthogonal experiment and the numerical simulation results showed that the deviation of the melting width,height and deep is approximately 6.85%,8.35%,and 10.14%,respectively,which indicates the reliability of the numerical simulation model.(2)Based on the numerical simulation results,the quadratic regression fitting is performed,and the quantitative relationship between the process parameters and the characteristic parameters of the cladding layer is summarized.The fitting results are used for prediction,and the experimental verification under the same parameters is performed.Compared with the experimental results,the maximum error of the regression fitting is 27.24% and the average error is 7.68%.The maximum error with the numerical simulation results is 15.43%,and the average error is 6.83%.Compared with the experimental results,the maximum error is 55.97% and the average error is 24.47%.The maximum error with numerical simulation results is 50.54%,and the average error is 20.39%.(3)The evolution process of the molten pool and the flow characteristics of the melt during the laser cladding process are studied.The results show that the peak temperature of the temperature field during the laser cladding increases with the increase of the laser power and decreases with the increase of the scanning speed,which shows laser power plays a leading role on the temperature field evolution.The flow field distribution of the melt shows the smaller flow velocity exists at the center of the molten pool,while the larger flow velocity exists at margin of the molten pool.It is found that the melt flow at the front margin of the molten pool is larger than the rear margin,which indicate that the melting process is more intense than the solidification process.(4)The solidification characteristic parameters of different positions on the solidification interface of the laser cladding pool were analyzed,and the solidification structure characteristics were predicted according to the undercooling theory.The simulation results show that the temperature gradient G increases from the top to the bottom end of the solidification interface of the laser cladding pool,and the solidification rate R decreases.According to the values of G×R and G/R,the top area microstructure is finer than the bottom region.(5)The influence of process parameters on the solidification characteristic parameters during the laser cladding process was studied,and the influence of process parameters on the microstructure was revealed.The increase of the process parameters would cause the decrease of temperature gradient G and G×R.The grain at the solidification interface increases,and the increase of the scanning speed causes the increase of temperature gradient G,and the increase of solidification rate R,and the G×R,which makes obtaining the finer grains during the solidification. |
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