Structural Design Of Negative Poisson's Ratio And Optimization Of Selective Laser Melting(3D Printing) Process

In the present article,structural optimization has been done and SLM process which is competitive in the fabrication of complex components with overhanging structures,has been used in the manufacturing of tailored NPR parts.Moreover,fine AlSi10 Mg raw powder has been used and the influence of laser scanning speed on forming precision and mechanical properties has been investigated.The main conclusions obtained are as follows:A quantitatively optimized simulation on the inclination angle of a tailored re-entrant symmetric NPR structure based on the SLM process is presented,aiming at proving the forming quality.Parametric modeling of re-entrant honeycomb NPR parts as well as the verify of the influence of mesh refine times on results convergence are done in the article and Poisson's ratio of NPR parts are obtained by collecting the data of the tracing face using FEA software.The optimal inclination angle is 9° and the corresponding re-entrant angle is 79°.Taking the fillet and stress concentration into consideration,a novel method of designing the tailored NPR structure has been put forward and NPR component is finished base on the design of NPR unit.Both NPR units and NPR components have been fabricated using different laser scanning speeds with SLM apparatus.It can be verified for NPR unit that the addition of inclined struts is doing good to the forming without support structures.Simultaneously,how the scanning speed affect the forming quality of overhanging structure is also studied.The optimal scanning speed is 2000 mm/s when the laser power is 300 W,while unit NPR parts fabricated using this parameter are dense and of regular and uniform molten pools.As for the NPR components,the orientation and support structures have been optimized and the forming dimensions under different scanning speeds also have been studied.It can be found that the overall size is smaller than the designed one but it increases with the increase of scanning speed.What's more,the dimensions on the height direction became larger and floated less in the horizon direction when the component was separated from the substrate.Uniaxial compression tests of SLMed NPR units and NPR components were carried out,and the Poisson's ratio of the unit was calculated,though it was lower than simulated for particle agglomeration.FEA method was also used to simulate the compression test of the NPR component,the maximum stress was about 22 MPa and it's quite consistent with the compressive stress obtained in the test.In addition,local fracture morphologies under different scanning speeds were studied and the deformation failure mold was also put forward.