Page - 61 - in 3D Printing of Metals

Metals 2017,7, 91 Figure10.Measuredexternaldiametersandmeasuredinnerdiameters forsinglestruts. Resultsare shownasmeanvalueswith thecorrespondingstandarddeviations (n=10foreachdesign). AsshowninFigure4, theadditivelymanufacturedstrutsdeviate fromthe idealcircularshape. Themeasurementsof the innercircle in themaximumpermissibleorientationaswellasof thepossible externalcirclediameterofferaninterestinginsightonmanufacturingquality. Thestrutsproducedusing SLMshowsmallerdeviations thantheEBM-manufacturedstruts. The45-degreeorientedsamplesare always larger thanthe0-degreeorientedsamples.While the largeoutercross-sectionsof the0-degree orientedsamplesveryslightlydiffer fromtheCADdataspecifications, thedifferences fromthedesired valuesshownfor the45-degreeorientedsamplesaresignificantly larger. Thedeviationsof theouter diameters tend to be smallerwith increasing nominal values. The supporting cross-sections also increasinglyapproachdesiredspecificationvalueswith largerdiameters. Largemeasurablediameters increasingly tendtowardszerodeviation. Thedeviationsareprocessdependentandlead, inparticular at45degrees, toanenhancementof theeffect. Thedeviation of the 45-degree oriented specimens froma circular shape as seen in Figure 4 leads toanincrease in theouterdiameter. Themorepronouncedsplittingof thesurface in theEBM processclearlyreduces thecoherently formedmaterialarea in the interiorof thestrut. Thus,while the valuesmeasuredoutsidearecloser toCADdataspecifications thaninthecaseof theSLMsamples, the internal structuresneverthelessdeviatemoremeasurably fromthedesireddimension. ComparisonofSLMManufacturedPartswithandwithoutHeatTreatment ThefabricationaccuraciesdeterminedinSection3.1were identifiedfor thesamplesoriginating fromtheseriesnamedinSection2.1.Thesewere theheat-treatedSLMsamplesandtheEBMsamples withoutheat treatment. The influenceofheat treatment in combinationwithaneffectivepressure (HIP) on component accuracywas thendetermined (Figure 11). Comparedwere SLMspecimens with diameters according to the design specification of 1.1 mm in the orientations 0◦ and 45◦. Specialemphasiswasagainplacedoncomparingpost-treatmentsusingheatandpressure (difference betweenHIPandNoHIP). Atwo-sample t-testwasperformedtostatisticallyexaminesignificantdifferencesbetweenthe means.Nostatisticallysignificantdifferencewasdeterminedwhentheresultswerecompared. It can beconcludedthat the treatmentof theSLM-producedsampleswithHIPtreatmenthasnoeffecton 61