Numerical Research On Powder Paving Process Of Nylon Powder Selective Laser Sintering

Additive manufacturing technology is one of the technologies that have attracted much attention from various countries in recent years.Selective laser sintering has a wide range of forming materials,simple manufacturing process,high flexibility,high material utilization rate,low cost,etc.It has shown broad application prospects in the development of new products,mold manufacturing,production of small batch products,etc.It has been successfully applied to automotive,shipbuilding,aerospace and other fields,and the technology is developing rapidly and has become the most mature technology and most widely used additive manufacturing It has become one of the most mature and widely used additive manufacturing technologies.As an intermediate process of selective laser sintering,the powder laying process has an important impact on the quality of the sintered parts.In this paper,discrete element numerical simulation is used as the main research tool to carry out the research of selective laser sintering powder laying process of nylon powder,the main contents are as follows.(1)The basic physical parameters required for nylon powder simulation were measured experimentally,and the experimental rest angle was used as the calibration target of the simulation model,and the central composite test was used to analyze its significant influencing factors,and the response surface method was used to calibrate the parameters to be determined for the nylon powder simulation model.The accuracy of the calibration parameters is verified by comparing the experimental and numerical simulation results of lifting the rest angle of the circular tube,and the discrete element model of nylon powder is established.(2)Based on the Hertz-Mindlin with Johnson-Kendall-Roberts contact model,a discrete element model of nylon powder under different powder spreading methods is established,and the velocity partitioning of powder flow behavior under different powder spreading methods is studied,focusing on the phenomenon of particle convection circulation in the roller powder spreading process and the particle segregation in the powder spreading layer caused by it;the numerical The simulation results show that the powder can be divided into three regions according to the velocity,avalanche region,slow flow region and quasi-stationary region during the powder spreading process in different powder spreading methods.The convective circulation phenomenon generated by the roller in the powder spreading process can achieve more particle rearrangement,thus producing better powder bed flatness,but at the same time also intensifies the particle segregation phenomenon,changing the powder spreading process parameters can better improve this phenomenon.(3)The parameters of the roller powder spreading process(powder spreading thickness,roller diameter,roller rotation speed and roller translation speed)are used as the optimization variables,and the three indexes of apparent density of powder spreading layer,standard deviation of apparent density of powder spreading layer and surface roughness of powder spreading layer are used as the optimization objectives;the samples are taken based on the Latin hypercube sampling method,and the Kriging agent model is established through the discrete element method of calculation and simulation,and the Kriging agent model is established based on the agent model.A multi-factor multi-objective optimization model based on genetic algorithm was established to optimize the nylon powder roller spreading process,and finally the optimization results were compared with the experimental results to verify their accuracy and reliability.The research content of this paper has a certain reference value to guide the optimization of the powder spreading process,which can reasonably configure the optimal roller spreading process parameters according to the requirements of different working conditions,and can also predict the spreading quality of a certain set of process parameters for nylon powder.The research results of this paper have important engineering application value to improve the quality of roller powder spreading and part sintering.