Numerical Simulation Of Temperature Field And Optimization Of Scanning Path In Laser Cladding

Laser cladding technology has received extensive attention in recent years due to its low dilution rate and high deposition efficiency.However,in the laser cladding process,the energy loading of the laser heat source and the time-varying uneven temperature field distribution caused by its characteristics of rapid heating and cooling can cause defects such as stress deformation,crack tendency,reduced accuracy,and poor mechanical properties easily.The scanning sequence of the laser determines directly the distribution of the instantaneous temperature field of the workpiece and affects the structure and performance of the coating.In this paper,based on the welding sequence of the " withdraw welding " in welding technology,compared with the traditional one-way sequential long path,a new segmented oriented scanning path is proposed,and the second segmented path is used as the basis for further feedback based on the temperature field.A feedback path for segmented scanning is proposed.Through the combination of numerical stimulation and experiment,the influence of the laser scanning path on the instantaneous temperature field and the structure and performance of the subsequent coating is studied.The specific research content is as follows:In this paper,a three-dimensional numerical model is established to simulate the instantaneous temperature field distribution of laser cladding.The laser cladding experiments are carried out,and the comparison of the shapes of the molten pool shows that the calculated results are in good agreement with the experimental results,which proves that the parameters used in the model can predict accurately the laser melting thermal behavior of the cladding process.Besides,a numerical model of the laser cladding temperature field under different scanning paths was established.The study found that the segmented guided scanning path can reduce significantly the maximum temperature gradient of the coating during the entire cladding process compared with the unidirectional long path scanning.As the frequency increases,the temperature gradient decreases.In addition,segmented guided scanning can increase the maximum temperature of the molten pool.It is beneficial to improve the uniformity of the composition of the coating and reduce the porosity.Based on the secondary segmented guiding path,the temperature of each location point is extracted after each segment of cladding,and the lowest temperature location is taken as the starting point of the next segment of cladding,and so on to obtain a feedback path based on temperature field feedback.After the comparison of the feedback path based on the temperature field,the sequential segmented path can improve the temperature,size uniformity and area of the molten pool,which is beneficial to strengthen the composition uniformity and bonding performance of the coating.In addition,the feedback path has the effect of reducing the local heat accumulation of the substrate.Compared with segmented scanning,the feedback path has the effect of reducing the maximum temperature gradient of the coating in the orientation perpendicular to the scanning direction and along the scanning direction.At the same time,the instantaneous cooling rate of the coating under the feedback path is reduced compared with the segmented path,and the overall data change has also a more stable distribution.The segmented guiding scanning path will not change the shape of the coating grains.However,the grain size of the coating in the segment-oriented scanning mode is small,and the number of segments has no significant effect on the grain size of the coating.The grain size of the coating under the feedback path is larger than the segmented path and the one-way sequential long path scanning.Different scanning methods have a greater impact on the microhardness of the coating,specifically: the one-way sequential scanning method is higher than the segmented guided scanning,and the latter is higher than the feedback path scanning.And the more segments,the lower the microhardness of the coating.In addition,the cooling rate and hardness of the coating under segmented scanning reduce at the overlap region.Therefore,the greater the number of segments,the more unfavorable the uniformity of the coating microhardness distribution.The residual stress on the coating surface under the segmented guided scanning mode is higher than that under the unidirectional long-path scanning mode,and as the number of segments increases,the greater the residual stress on the coating surface.The residual stress of the coating surface under the feedback path is lower than the above two scanning methods.The paper has 60 pictures,6 tables,and 119 references.