| 3D printing is a technology that bases on digital model file and it can construct the objects by sintering layer by layer.Selective Laser Sintering(SLS)realizes the superposition forming through layered sintering of the powder materials with laser,It is hitherto the most matured 3D printing technology.PA2200 has good mechanical property and it is easy to be processed in SLS,hence PA2200 is at present the most commonly used sintering material.However,during the sintering process,lots of powders are not sintered,and the recycling of these powders plays an important part in cost reduction.However,the impact of the recycling on the forming part is not clear since the powders are subjected to high temperature in the sintering process.This essay investigated the effect of recycling time on the properties of part using EOS P110 3D printing system and EOS PA2200 powders.SEM,DSC,XRD,IR,and MI were used to study the effect of recycling on properties of the powders.The results suggested that the morphology,size,and distribution of the powders were not changed,yet the melting point of the powders increased 3℃.Moreover,the crystallinity of the new powders was 51%,and after the first recycling it increased to 53%,and then it decreased slightly.The melt index decreased from 18.39g/10min(new powders)to 12.4g/10min(the eighth recycling powders),and the structure of some molecular chains changed.Analysis of mechanical properties shows that the mechanical properties of new powder sintered sample are worse than that of first recycling sintered sample and from the first recycling to the eighth recycling,the tensile strength,impact toughness and hardness of sintered sample decreases,while ductility and elastic modulus increased at first and then decreased.Effect of powder recycling on sample of different building method is investigate through XY/Y,YZ/Y and YZ/Z three building methods.It showed that the tensile strength,ductility and impact toughness of sample with XY/Y and YZ/Y building are better than YZ/Z building and this trend is more obvious with the recycling time increase.The tensile strength of sample with XY/Y and YZ/Y building is almost the same,while the ductility of sample with YZ/Y building is better than XY/Y building.For hardness,sample with XY/Y building is higher than sample with YZ/Y and YZ/Z building.The difference between three building is small.The shrinkage during the SLS PA12 process may lead to the warping of the parts,which will affect the dimensional accuracy and shape accuracy of the parts.At the same time,secondarysintering and the surplus of Z axis also have impacts on dimensional accuracy of the parts.Causes and effects of secondary sintering and the surplus of Z axis were analyzed and the effect of powders recycling on the warping of the parts was analyzed by arc length method and chord length method.It turns out that the warping degree increased with the recycling time and finally tended to be stable.The X、Y、Z sizes of the parts were measured to investigate the effect of powders recycling on the dimensional accuracy of the parts.The results suggested that recycling made the size deviation of three dimensions decrease at first and then increase.Surface roughness of the SLS part varies from surface to surface,which are subjected to the property of the powders.The cause of the roughness difference of side surface,bottom surface,and upper surface of the sample and the effect of powders recycling on surface roughness were also analyzed.The results shows that the surface roughness of the side surface,bottom surface,and upper surface of the new powder forming part was 10.31μm,9.8μm,and 8.03μm while that of the first time recycling powder forming part was 7.36μm,6.4μm,and 6.2μm.From the first recycling to the eighth recycling,the roughness of three surfaces all increased. |
PDF Full Text Request