Study On The Circulation And Utilization Of Nylon Powder For Selective Laser Sintering

Selective laser sintering(SLS)is a kind of 3D printing technology which uses laser as energy source and various powders as raw materials.The technology has attracted much attention because of its simple forming process,high precision,wide application materials and the structure of the sintered parts without the restriction of the process.Nylon(PA)powder is currently the most commonly used SLS molding material.The PA powder is aged during the SLS molding process,and the products sintered again by the recovered powder have poor performance.There is a lot of "orange peel" texture on the surface,resulting in low recycling rate and high cost of PA powder.Therefore,it is of great practical significance for the circulation and utilization of PA powder.This article takes PA12 powder as the research object.The main research contents and results are as follows:Because the SLS formation of PA12 powder is carried out under the condition of low oxygen content.In order to simulate the aging of PA12 in SLS molding process,the vacuum aging of PA12 powder was studied.The result shows thatthe melt flowability of PA12 powder after aging obviously decreased,and the molecular weight increased obviously,but the mechanical properties and thermal properties did not change a little and were slightly improved.The main reason for the low recycling rate of recycled powder is the decrease of fluidity of powder melt after aging..The mechanical blending method was used to blend and modify PA12 recovered powder and the unsintered powder.The melt flowability of the powder after blending can be significantly improved,but it has little effect on the mechanical and thermal properties of the recycled powders.In order to save costs,blending is usually done in a 1:1 ratio.Three kinds of hyperbranched resin Hyper C100,Hyper HPN202 and Hyper C181 were used as the rheological modifiers for the PA12 recovery powder,and the plastic modification was carried out by mechanical blending.Three kinds of hyperbranched resins can effectively improve the melt fluidity of PA12 recovery powder,and the melt indexincreases with the increase of the addition amount.Hyper HPN202 has the best improvement effect.When the addition amount is 1 wt%,the melt flow index increases by200%.The tensile strength increased slightly,and the impact strength and flexural modulus were almost the same as those without addition.The softening point of VEKA increased by5.6 °C.Phthalic anhydride,aniline and benzoic acid were used as capping agents,and solvent-precipitation method was used to prepare capped PA12 powder.The vacuum aging of the modified capped powder was studied.The result shows that the three capping agents can effectively improve the phenomenon of increasing molecular weight and decreasing melt fluidity in the aging process of PA12 powder.Before and after aging,the thermal properties and mechanical properties of the capped PA12 powder changed little.Among them,the improvement effect of phthalic anhydride is best.When aged for 24 hours,the melt flow index of the uncapped PA12 powder decreased by 62.6%,the viscosity average molecular weight increased by 175.6%.However,the melt flow index of PA12 powder terminated by o-phthalic anhydride,aniline and benzoic acid decreased by 17.5%,26.1%and 31.8%,and the viscosity average molecular weight increased by 29.1%,49.5% and62.1%,respectively.