| Laser cladding technology can be seen everywhere in daily life and is closely related to our lives,but it also has its drawbacks.Due to the processing characteristics of laser cladding,the material temperature ramp up and down speed is fast,and it is difficult to measure the specific temperature change process,and the rapid temperature ramp-up brings a complex temperature gradient,which directly affects the quality of the cladding layer.At present,it is still a difficult problem to obtain the change law of the temperature field and stress field of the molten pool.In this paper,the temperature change law and residual stress distribution in laser cladding was studied by numerical simulation technology,and the growth mechanism of forming structure is analyzed,and finally the correctness of the model is verified by experiments.Firstly,the user subprogram is written in Fortran language to realize the movement of the double elliptical heat source model along the preset path direction,and effectively reduce the error between the simulation and the experimental results by adjusting the heat source parameters,so as to ensure the accuracy of the finite element modeling.Then,the influence of different laser material technical parameters(laser power and scanning speed)on the temperature field in the cladding process is studied,its regularity was explored,and the distribution of residual stress is analyzed.These include the following:The change law of molten pool morphology and melting width and penetration depth affected by processing parameters,the temperature field of laser cladding is studied.The results show that in the case of a certain scanning speed,the size of the energy output by the laser per unit area is proportional to the size of the molten pool generated by high temperature,because the more energy input per unit area,the larger the melting volume of the substrate and coating material,and the more cladding layers melt with the matrix material,so that the area of the molten pool increases.When the laser power is constant,the size of the molten pool of the scanning speed is inversely proportional,because the faster the scanning speed,the shorter the time for the laser to irradiate the base material,and the less energy absorbed by the matrix material,resulting in a smaller size of the molten pool.After obtaining the temperature field calculation results,the stress calculation is realized by applying the temperature field ODB file as a load in the predefined field of the stress field.It is found that the residual stress and the size of the laser power are directly proportional,inversely proportional to the scanning speed,and the comprehensive influence of laser processing parameters is analyzed,and the lowest dilution rate and residual stress can be guaranteed when the scanning speed is 10mm/s and the laser power is 3600 W,so the cladding effect is the best.Temperature gradient(G)and cooling rate(R)are important factors affecting the size and morphology of grains in the cladding layer,and it is found that with the decrease of G/R value,the grains gradually refine from columnar crystals to equiaxed crystals,and the temperature gradient gradually decreases as the distance from the dividing line formed by the coating and the matrix,and the cooling rate gradually increases,resulting in the change of grains in the cladding layer.The hardness of the cladding layer is mainly affected by the dilution rate,and the dilution rate is low when the laser power is low or the scanning speed is fast,and the hardness is high.At the lap surface,the hardness curve decreases significantly,and the hardness near the lap surface is significantly lower than in other areas.However,on the left and right sides of the lap surface,the hardness value of the cladding layer is basically uniform.In addition,when the particle size difference of columnar crystals is slight,the growth trend of columnar crystals has little effect on hardness. |
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