Experimental Study And Numerical Simulation On Flow Properties Of Nylon And Its Composite Powder

Select Laser Sintering(SLS)is an important branch of the material rapid prototyping technology.It is by the layer by layer powder paving,and layer by layer scanning sintering to directly manufacture parts.As the intermediate process of SLS,the powder paving process has a crucial influence on the quality of the sintered parts.In general,how to spread an uniform,defect-free and high-density powder layer is one of the prerequisites for good sintering,that is,the better the fluidity of the powder,the better the spreading performance of the powder and its subsequent sintering quality.Therefore,the research on the influencing factors of powder flow has a crucial effect on providing powder spreading performance and sintering quality.In this paper,the SLS raw material-nylon powder as the research object,the fluidity of nylon powder and carbon fiber/nylon powder was explored by experiment and numerical simulation and the influence of ambient temperature,physical properties of powder and additives on the powder flow was also investigated.The research will be carried out through the following several aspects:(1)The micro-morphology and particle size distribution of nylon powder were measured by super-depth microscopy and laser particle size.The physical properties of nylon powder were measured by powder comprehensive tester and direct shear apparatus.The effects of powder sample capacity,powder temperature and additives on the fluidity of nylon powder were studied and analyzed.At the same time,the influence of carbon fiber content and temperature on the fluidity of carbon fiber /nylon powder was also investigated.(2)The model of the powder particles was established in discrete element software PFC5.0.The rolling resistance model is selected as the contact model between the nylon powder particles and the carbon fiber / nylon powder,and based on the contact model,van der Waals forces was joined by adding FISH function.The repose angle model and direct shear test model of nylon powder and composite powder were established,and the microscopic parameters of the contact model are calibrated by numerical simulation.(3)Based on the DEM simulation,the regularity of particle size,particle size distribution and temperature on the fluidity of nylon powder was analyzed.The simulation results show that the particle size distribution and uniform distribution of particles have a certain effect on the fluidity of nylon powder,and the influence ofnylon particles on Gaussian distribution is not obvious.At the same time,the simulation results are compared with the experimental results of the angle of repose of nylon powder at different temperatures.The results show that the contact model is feasible and the contact parameters are rationality.(4)The stress state of the powder is analyzed when the powder is subjected to SLS process,and the drum test bed with the similar stress state was designed and fabricated.The influence of the ambient temperature,the drum speed and the powder filling rate on the fluidity of the nylon powder is analyzed.The experimental results show that as the increasing of the powder filling rate,the ambient temperature and the drum speed,the powder fluidity will become weakened on different degrees.