Page - 89 - in 3D Printing of Metals

Metals 2016,6, 280 proposed to seek amicro-structure ofmaximum stiffnesswith the constraint of volume fraction optimization. The inverse homogenization theory was also applied to estimating the effective mechanicalpropertiesof scaffoldmaterialswhicharearrayedbyperiodicalbasecells. However, thestructure topologicaloptimizationwill alwayschange theshapeof thecomponents. Theshapeofparts shouldnotchange,especiallywhenthepartsareassembledwithother traditional componentsorshouldmeet therequirementsofaerodynamics. Thispaperinvestigatesanewdesignmethodforlightweightpartsmanufacturedbyselectivelaser melting(SLM)basedonthe“Skin-Frame”andexplores the influenceofmachiningdefectsonSLM partswhichhavedifferent sizesbytheexperimentalmethod. Theproceduresof thenovel, lightweight redesignmethodwereresearched.Astopperandconnectingplatewereredesignedwith thismethod. TheseredesignedpartswerefabricatedbySLMandshowedgoodmechanicalcharacteristics. Theresults showthat the lightweightpartsdesignedbythismethodcansatisfy theuserequirements. 2. ExperimentalSection 2.1.Materials Thelatticestructuresandtensiletestsamplesweremadefromaniron-nickelalloy(IN718)powder with anaverageparticle size of 30± 10μm. The chemical compositionof thepowder consists of Ni (53.5%), Cr (19%), Fe (18.3%),Nb (5%),Mo (3%max), Ti (1%max),Al (0.43%max). The SEM micro-graphof the IN718powder isshowninFigure1. Ithasgoodmechanical characteristicsandis widelyusedinaerospace industry.All samples for thisstudyweremanufacturedbyEOSINTM280 systemwhichutilizeda200Wytterbiumfiber laser. Thismachinehasaneffectivebuildingvolume of250mm×250mm×325mm. Tensile candidateswere fabricated inaverticalbuildorientation, with thecylinderaxisparallel to thebeamdirection. Figure1.SEMmicro-graphof the IN718powder. The 100 μm diameter laser beam was scanned at 1200 mm/s in argon gas environments surrounding the buildingparts. The oxygen level in theprocess chamberwasmaintainedbelow 0.1%.Thebuildingplatformwaspreheatedto80 ◦Candmaintainedat that temperature. Thehatch spacingwas0.05mmandthe layer thicknesswas50μmwithaspotdiameterof0.1mm. 2.2. ProcessofTensileTest Tensilesamplesweredesignedaccordingto theChineseGB/T228-2010standard. Figure2shows thesizesofsamples for the tensileexperiment. Thediameterofparts is10mmwhile therestof the parametersdependonthe testmachine. ThesamplesweredesignedbyCADsoftware thenexported asasingleSTLfile format to theSLMmachine formanufacturing. 89