Page - 67 - in 3D Printing of Metals

Metals 2017,7, 91 The failure types described occur independently of geometric variation and orientation in manufacturing. Therequiredmaximumloading toexceedstabilityandthuscompressivestrength remainssimilar. Theestablishedresultsprovideevidence that regardlessofgeometrical considerations (differentheights,diameters)andthemethod(EBM,SLM)thedetermineddeformationbehavior is characteristicof thespecimensunder investigation. It remainsunclearhowgreat the influencesare that are causedbyprobabledeviationsof rodpositions fromtheacting load (planeparallelism)or byproduction-related faults (e.g., the crossoverbetween thebaseand topareaof the rod). Just as interestingwouldbeanyfunctionalassociationsbetweentheorientationof thespecimens testedand the levelof influencing imperfections. Figure16showstherelationbetweenequivalentdiameterandcompressionstrength. Figure16.RelationbetweenequivalentdiameterandcompressivestrengthforSLMparts (HIP)and EBMparts (NoHIP) in theorientations0◦ and45◦. Bothmanufacturingsystemsinprinciplebehave identically.Compressionstrength increasesas expectedwith increasingequivalentdiameters. SLMpartsshowedhighercompressionstrengthvalues thantheEBMparts.While thedifferencebetweentheorientationsof theEBM-manufacturedparts is not relevant, thedifference in theSLM-manufacturedparts is clearlyvisible. A linear relationship was found between equivalent diameter and compression strength. EBMparts inbothorientationsshowedahighcorrelation(0◦—R2=0.977;45◦—R2=0.969). Incontrast, theSLMparts in the45◦orientationshowedalowercorrelation(R2 =0.846). Thecorrelation in the0◦ orientation isprovidedin therangeof theEBMparts (R2 =0.969). AsshowninFigure10, itappears that thespecificmanufacturingaccuracyof thestruts (diameter) hasaninfluenceonthecourseoftheresults. EBMpartsshowedthesamecourseinresults,especially in themeasured innerdiameter. Thisarea is themost importantarea for theacceptanceof loadingforce. Thevalues for0◦ and45◦orientedpartsarecomparable. TheSLMpartshowevershowdifferences in the0◦ and45◦orientation. Thedifferences in the45◦orientationaregreater than in0◦orientation. Thisprovidesclear information that thecompressionstrengthvalue isdefinitivelyaffectedbythearea of thestrut thatcanholdtheactingforce inacleardefinedstructureofacircle. Thiswascomparedto Suardetal. [34]whohavedescribedtheinfluenceofthediameteronmechanicalproperties. Itconfirms thatstrutorientation in themanufacturingprocess influences the formationof thesurfacesandthus also theroughness. This increase in theroughnessRa of theSLMspecimens leads toareduction in the cross-sectionandthus toa lowcompressivestrength. Figure17showedtherelationbetweenheightandcompressionstrength. SLM-andEBM-manufacturedpartsinprincipleshowedanidenticalbehavior.Compressionstrength decreased as expected with increasing height. SLM parts showed higher values for compression strengththantheEBMparts. Thedifferencesbetweentheorientationsof theEBM-manufacturedand SLM-manufacturedpartsaresmall. 67