Simulation And Process Optimization Of Selective Laser Sintering On Polyamide 6

Owing to good thermal stability and excellent mechanical properties,PA6(polyamide6)has been widely used in industry.Selective laser sintering(SLS)is a kind of additive manufacturing technology,which uses infrared laser as energy source to stack powder layer by layer under the control of computer.PA6 is a high-performance polymer material,and the process temperature should be kept in the "sintering window".So the required temperature is high(170 ℃ ～ 196 ℃),and the demand of temperature uniformity is rather higher.Aiming at the lack of research on process parameters,this paper mainly carried out the following work:First,the effects of laser power and scanning speed on the precision,density and tensile strength of workpiece are studied by experimental method.The results show that the larger the heat input per unit time is,due to the size surplus effect of laser beam,the larger the positive deviation of the three dimensions on the workpiece is.And the densification degree and tensile strength of the part increase initiatly due to the increase of bonding degree,and then decrease due to the over sintering.Then,the temperature field finite element model of PA6 in SLS process is established.The simulation results show that PA6 can keep a good melting state during the forming process because of the high preheating temperature and the low thermal conductivity of material.With the increase of laser power and the decrease of scanning speed,the three dimensions of molten pool increase due to the increase of heat input rate.At the same time,the simulation results of different process parameters are verified by single-layer sintering experiment,and the minimum relative error is ～2.7%.Through the simulation of double layer,the differences of node temperature distribution under three different scanning paths:long side,long side and short side crossing and short side are analyzed.Furthermore,the calculation model of linear elastic stress in the sintering process of small-size parts is established.It is found that the thermal stress,residual stress and warpage of the parts are small.With the increase of laser power and the decrease of scanning speed,the degree of warpage raises because of the increase of temperature gradient.The warpage value of large-scale parts is simulated by the inherent strain model,and the relative error is19.4% by comparing with the experiment.Finally,through polynomial fitting or response surface method,the recommended process map or function are established for molten pool,accuracy,densification,and mechanical properties.The surface morphology,thermal properties,crystal morphology and mechanical properties of the parts with optimal process parameters are compared with injection molded parts to provide guidance for production.