Study On Calculation Methods Of Transient Temperature Field During Selective Laser Melting

In recent years,Selective Laser Melting(SLM)has become an international research hotspot as a promising advanced metal additive manufacturing technology.During the process of SLM,the high-speed moving laser heat source will cause the non-uniform temperature field in the powder bed,which will generate thermal stress and thermal deformation inside the parts.And inappropriate energy input will cause defects inside the material and affect the forming quality.Therefore,in order to optimize the process parameters and improve the quality of forming parts ultimately,it is necessary to understand the temperature distribution in the powder bed during the process of SLM and to study and analyze the prediction methods of the complex transient temperature field with multi-scale and multi-physics during the forming process.The transient temperature field in process of SLM is calculated by analytical method and numerical simulation method in this paper.The effect of process parameters on temperature field and the effect of heat source model and material state on the results of temperature field are discussed.Finally,the two methods are compared and analyzed by scanning experiments.Firstly,the thermal physical process of SLM is analyzed in detail in this paper.And the heat source models used widely are compared.To overcome limitations of existing heat source models,the body heat source with linear attenuation in depth direction is built according to the attenuation law of laser in Ti-6Al-4V powder which was proposed by F.Verhaeghe.And the body heat source is used in the following analysis of temperature field.Secondly,analytical calculations to the SLM process temperature field are obtained by the Green's function method in this paper.In the process,the powder bed and substrate in SLM are regarded as the compound dielectric material with different materials and the thermal physical parameters are simplified reasonably.The analytical expression of the temperature field is deduced by using the Gauss surface heat source or the body heat source with linear attenuation in depth direction,and the results are visualized by MATLAB.In the specific calculation,two cases are discussed: one case is that the powder bed and substrate are regarded as an infinite flat plate with specified thickness,the bottom surface of the substrate is applied adiabatic boundary conditions and the top surface is applied radiative and convective boundary conditions.The other case is that the powder bed and substrate are regarded as a finite rectangular plate,the bottom surface of the substrate is applied adiabatic boundary conditions and the other surfaces are applied radiative and convective boundary conditions.Finally,the numerical simulation of temperature field under the same conditions is analyzed by using ANSYS Parametric Design Language.The correctness of the analytical method is verified by comparison with the result of numerical simulation.Thirdly,the simulation of the temperature field during the SLM is carried out by using the ANSYS finite element software in this paper.In the simulation process,more thermal physical processes are considered,including the change of thermal physical parameters with the change of material state and temperature,latent heat of phase change(including latent heat of vaporization),and the influence of process parameters on the temperature field are discussed in detail.The effects of material state change and heat source model on the results of temperature field simulation are also discussed.Finally,the analytical and numerical results are analyzed and compared with the scanning experimental results under the same process parameters.The comparison result verifies the correctness and validity of analytical model and the finite element numerical model.By comparing the sintering width and the predicted width in the scanning experiment with moderate energy input,the predicted values of the two methods can be compared with the experimental values.But the prediction error of numerical simulation method is smaller than that of analytical method.In addition,the prediction of the influence of process parameters on temperature field shows a good agreement with the experimental results.The two methods can predict the temperature distribution under different combinations of parameters accurately.Therefore,the results of this paper have certain guiding significance for the determination of process parameters before experiment.