Page - 62 - in 3D Printing of Metals

Metals 2017,7, 91 themanufacturingprecisionof themanufactured items. Theresults listed inSection3.1 (SLMwith HIP)are transferable to theSLM-manufacturedsampleswithoutHIP treatment. It alsoallows the conclusionthataHIPprocesshasno influenceonthestabilityof thediameterof theEBMsamples. Figure 11. Boxplots of themeasured equivalent diameters of SLMandEBMmanufacturedparts. Boxplots give themedianvalue, the interquartile range (IQR: interval between the 25th and75th percentile,bluerectangle)andtheextremumvalues (n=10measurements). 3.2. SurfaceQuality For thequalificationof theouteras-built surfacequalityof thestruts,a roughnessmeasurement wascarriedout. TheroughnessvaluesRa andRzwereobtained,asshowninFigure12. Figure12. Boxplotsof themeasuredRa andRz values for theSLM-andEBM-manufacturedparts. Boxplots give themedianvalue, the interquartile range (IQR: interval between the 25th and75th percentile, blue rectangle) and the extremum values (n = 4 struts); statistical significance levels (*p<0.05; ***p<0.001). The roughnessRa of SLM-manufactured (HIPandNoHIP)partswas significantly (p<0.001) lower in the0◦orientationthanin the45◦orientation. TheEBMpartsshowedtheoppositebehavior. Here, theRa values in the45◦orientationare lower than in0◦orientation.AsSuardetal. [34]have described, surface roughness and the resulting strut shapedependon the orientationduring the buildingprocess.Whereasverticallyorientedstrutsdisplayuniformroughnessvalues,ahorizontalor oblique orientation leads to increased roughness. The reason is the energy flow into the powder bed. Due to this energy flow, powder particles repeatedly tend to adhere to the struts on the underside. This phenomenon causes deviations from the present geometry as well as porosity deviations. Theeffectofpowderadhesionisalsodescribedin[43]. Thisphenomenoncausesdifferences in theroughnessasa functionof theorientation. TheSLMpartshaveahigher roughnessRa of the 62