Page - 148 - in 3D Printing of Metals

Metals 2016,6, 313 Figure2.Processparametersetofvarious formingmorphology inasingle-layersinglepass (SLSP). Theprocessparametersweredividedintofourcategories.Witharelativelylowdepositionvelocity andhighflowrate, CategoryAcaneasily cause anaccumulationof themelt because the feeding speedof themelt is toohigh for thegivendepositionvelocity, leading toasignificant incrementof themicro-coatingwidth andanaccumulationofmoltenmetal at the starting and stoppingof the SLSP.Theseproblemsremainunfavorable to thesuccessfuloperationof themultilayer single-pass (MLSP)process. Asa result, the formingefficiencywas low, as shown inFigure 3a. ForCategory C,with a highdeposition velocity and a lowflowrate, themoltenmetal draggeddue to surface tension,whichcausednecking. Thepositionofnecking leads toadecrease inmechanicalproperties in SLSP. The subsequent experiments in RegionCwere consequently discarded, as presented in Figure3c. ForCategoryD,withahighflowrateanddepositionvelocity,microvibrationoccurred in the3D-platform.Hence, the formingdefectswereaggravated, resulting inburranddistortions, as shown in Figure 3d. ForCategory B, the flow ratematchedwellwith the deposition velocity, andthesurfacequalitywassatisfactory,asshowninFigure3b. Figure3.Various formingmorphologywithdifferentcombinationsofprocessparameters. (a)Melt flowing. (b)Excellent formation. (c) Incomplete fusion. (d)Uncontrolledarea. 148