Page - 105 - in 3D Printing of Metals

Metals 2016,6, 280 Theyieldstress increaseswith the increaseof thestructuresize.Whenthesizeswerebetween1.0 and1.5mm, thestructuregradually returnedtonormalyieldstrength levelsof thematerial. Thus, whentheminimumstructuresize ismore than1.5mm,themechanical characteristicswill almostnot beaffectedbythedefectsbroughtbytheSLMprocess. TheredesignedstopperandconnectingplateweremanufacturedbytheSLMprocessandthe resultsareshowninFigure28. Themassof theoriginal stopper is795.2gandthatof theredesigned oneis580.0gwithaweightreductionofabout27%.At thesametime, themassof thesolidconnecting plate is3733.6g. Theweightdecreasedto2150.9gwithaweightreductionofabout42.4%after the redesignof the innerstructures. Figure28.Final redesignedstopper (up) andconnectingplate (down)withoriginalparts. Besides,after theapplication test showninFigure25, theconnectingplatewas takenout tocheck fordamage. Thereareonlyslightwearmarksonthetoothsurface,andotherpartsofthestructurewere still ingoodcondition.Accordingtothesetestswecanconcludethattheproposedlightweightstructure redesignmethodcandecrease theweightandcostofparts. Besides, theredesignedcomponentshave goodmechanical characteristicsandcanmeet therequirementsofuse. 5.Conclusions In thispaper, the tensile testsofpartsmanufacturedbytheSLMprocesswereperformedtostudy thecharacteristicsofSLMcomponents. Thesampleswerefracturedatabout1069.6MPaintensile tests, weaker than1340MPa,which is thenormalvalueof the tensile strengthof IN718partsmanufactured bycasting. Thismaybebecauseof themicro-segregationof IN718duringSLMprocessing.Agroup of standard parts which have lattice structureswith different sizesweremanufactured by SLM. Themechanical testsof thesecandidateswerealsoperformedtostudythe trendsof theyieldprocess ofdifferentstructuresizes. Thecompressiontestingresults showthatwhentheminimumstructure size is larger than1.5mm,themechanical characteristicswillhardlybeaffectedbyprocessdefects. Thispaper investigatedanewdesignmethodof lightweightpartsmanufacturedbyselective lasermelting (SLM)basedon the “Skin-Frame”. Thismethoddisassembledparts by their shapes andforceconditionsandreconstructedthe innerstructuresofeachdividedonebythecorresponding framework structureswhichwereoptimizedby thefinite elementmethod. Then,wemixed them togetherbytheir topological relationship.Optimizedfoundationframeworkscanbereservedtobuild a framework library,which cangreatly shorten thedesign timeusing thismethod. Thedesignof newparts canbeas easyas selecting fundamental frameworks tofill theparts, though, of course, it requires substantial time tobuild this library. Thestopperandconnectingplatewereredesigned bythismethod,withweightdecreasesofabout27%and42.4%,respectively. Besides, theconnecting 105