Page - 70 - in 3D Printing of Metals

Metals 2017,7, 91 4.Conclusions The properties of single Ti6AL4V struts fabricated via SLM and EBM were examined experimentallyforselecteddifferentgeometricaldimensions. Twobuildingorientationswithvariations in theheightanddiameterof the individual strutswere integrated in the tests. Thefollowingspecificconclusionshavebeenreached: • Cross-sectionaccuracyof fabricatedstruts Allmanufacturedstrutsdeviate fromthegivendiameter fromCADdata. TheSLMpartsshowahigheraccuracythantheEBMparts. NogeometricdifferencescouldbedeterminedbetweentheHIPedandNOHIPedSLMparts. • Thevaluesof roughnessobtainedforSLM-andEBM-manufacturedTi6Al4Vpartscorrespond to those from the literature. The SLM parts have significantly lower Ra and RZ values in bothorientations. • Different hardness values between EBMand SLMwere determined and supported by their different respective microstructures. The No HIPed EBM parts showed the highest values for hardness. TheHIPed SLMparts showed the lowest values according tomicrostructure. Thehardnessof the45◦orientedpartswithoutheat treatmentwassignificantly lower thanof the 0◦orientedparts.Heat-treatedparts showednodifferences independenceontheorientation. • Basedontestsunderuniaxial loadingconditions, theinfluenceofstrutorientationoncompression strengthwasdemonstrated. Afunctional correlationbetweencompressivestrengthandslenderness ratio (λ) aswellas betweenequivalentdiameter(d)andheight(L)ofEBMandSLMpartscouldbeestablished. Modifications in diameter lead to a larger influence on compressive strength than modifications inheight. Astrutorientationof45degrees leads toamoderatedecrease in thecompressionstrength ofEBMandSLMparts. Both themicrostructure and the cross-section accuracy of fabricated struts aswell as roughnessareresponsible fordifferences incompressivestrength. The specimens produced show2 types of stability failure—symmetric and antimetric buckling—at thesamecompressivestrength levels. Inourwork,wecoulddemonstrate the importanceof theexact fabricationandwhat influence thequality of a single strut has onmechanical properties. The results are strongly affectedby the microstructureandtheroughnessofstruts.Hardnessandcompressivestrengthexactlyconfirmthe dependenceofmaterial behavior as a functionoforientation. Orientation is a crucialdetermining fundamentalanalysis factorofmechanicalcharacteristicsandthusforms, taking intoconsideration geometrical influences, an essential basis for the constructive design of medical-engineering applications inwhichrodstructuresareused. Theresultsobtainedthe influenceof theslenderness ratioandespecially the influenceof thediameteronthemechanicalpropertiesprovidesanexcellent basis foratransfer intomedicalapplications. Theknowledgegainedfromthecomparisonsof theEBM- andSLM-manufacturedsingle struts canbepracticallyapplied toproblems in thefieldofadditive manufacturedparts. Of special interest are the influences that resulted in the different failure types of the specimens.Both the influences fromspecimenorientationduringmechanical testingaswellas from production-causedinhomogeneitiesneedtoberegardedseparately in future. Besidescompressivestresses, results frombendloadingalsoneedtobe taken intoconsideration both instaticaswellasvibrationtests. Theresultsbrought forwardhererepresentonlyapartof the necessary informationrequiredfor the translation intomedicalapplications. 70