Discrete Element Simulation Of Radiative Heat Transfer Characteristics Of Nylon Powder In SLS Process

Selective Laser Sintering(SLS)technology has been rapidly developed in the 21st century,and its products involve multiple fields.Exploring the nature of the sintering process and improving the mechanical properties of the sintered part are both challenges to the advancement of the SLS process and a problem for the development of the SLS.In order to solve the above problems,a deep analysis and understanding of the heat transfer characteristics of the powder sintering process are required.In many numerical models of heat transfer between powder particles,heat radiation between particles is often neglected,mainly because the calculation of heat radiation is very complicated or the ratio of the radiation heat transfer amount to the total heat transfer amount is small.However,from the point of the SLS process,thermal radiation can not be ignored.Therefore,it is necessary to construct a heat transfer numerical model considering the laser radiation and heat radiation between particles,which facilitates further analysis and study of the heat transfer characteristics between powders in SLS from a microscopic perspective.The main contents are as follows:A laser-particle heat radiation model based on Discrete Element Method(DEM)is established.In this model,the laser intensity obeys the Gaussian distribution.By modifying the position and other parameters,the radiation of any illuminated section under laser irradiation can be simulated.Based on the propagation characteristics of light,laser refraction,laser penetration and laser reflection are considered in the model,which makes the model more in line with the actual radiation conditions.Under the same conditions,the simulation results of the model are compared with the prediction results.The comparison results verified the correctness of the laser-particle heat radiation model constructed in this paper.Based on Stephen Boltzmann's law,a particle-particle heat radiation model considering obstacles among circular particles is established.This model calculates the total radiation between two particles by integrating and accumulating the radiation between two equal parts of two particles respectively.The influence of different particle sizes and different equal fractions on the accuracy of the calculation results was explored.To balance the computational efficiency with the accuracy of the results,the model divides the particle surface according to its diameter and defines an equalization rule.Under the same radiation conditions,the calculation results of the particle-particle heat radiation model of this paper are compared with the calculated results of the COMSOL heat radiation model.The comparison results verified the correctness of the heat radiation model in this paper.Above model is coupled with DEM contact model and heat conduction model,this coupling model can be directly used for SLS sintering numerical simulation.By changing parameters such as laser power and laser scanning rate,the heat transfer law of powder particles under different sintering process parameters can be observed.These results prove that it is feasible to apply these model established in this paper to SLS sintering simulation.These work can provide a reference for further investigation of the heat transfer characteristics in SLS process.