Page - 132 - in 3D Printing of Metals

Metals 2017,7, 113 Figure1. (a)Arivetnut inserting loads intoa sheetmetal component; (b)Hole-flangingoperation withextremethinningof theflange. Tailoredblanksandpatchworkblanks [1]aresemi-finishedproductswithavariable thickness. Theyallowformaterial cost savingsofupto10%[2]andcanhavethicknessdifferencesofupto50% withinasteel strip/blank[3]. Threemaintypesof tailoredblankscanbedistinguished[1],Figure2: • TailorWeldedBlanks (TWB),wheresheetmetalblankswithadifferent thicknessare joinedbya weldingprocess; • TailorRolledBlanks (TRB),where thicknessvariations in thesheetmetalareaccomplishedby changingtherollgapheightduringrolling;and • PatchworkBlanks (PB),wherea local increase in thesheet thickness ismadepossiblebywelding, gluingorsolderingsheetmetalpatchesontosheetmetalblanks. Figure2.Threemainvariantsof tailoredblanks. As shown inFigure 2, both the geometry of the thickened zones and the course of the sheet thickness are geometrically limitedwith commercially available tailored blanks. Evenpatchwork blanks, themostflexiblevariantof tailoredblanks,haveseveral limitations fromatechnologicaland economicpointofview, including: • aconstant,not load-optimizedthicknessof thepatch; • theproductionofscrapduringblankingof thepatches; • ahighsusceptibility tocorrosion in thegapbetweensheetmetalandpatch; • aproblematic furtherprocessing(including lowformabilityandspringback); • withpatchesattachedbygluingahighsusceptibility toageing. Apossiblesolutionfor theapplicationshowninFigure1 is tomanufacture local reinforcements using emerging additivemanufacturingprocesses such asLaserMetalDeposition (LMD). In this paper, the term‘lasercladding’willbeused,whichstands for thesametechnologybut ismoreprecise withrespect to the fact that layersaredeposited. Theprincipleof lasercladding isshowninFigure3. The laserbeammeltsa thin layerof thesubstrateaswellas the introducedpowderparticles, leading toa layerwithnearly100%densityandmetallurgicalbonding to thesubstrate. Thepowder is fed byadisc feeder inacarriergasstreamofargon. Thecarriergasalsoshields themeltpool fromthe surroundingatmosphere [4]. Themethodisprimarilyusedfor localwearprotection[5]andfor the repairofhigh-qualitycomponents, e.g., jet-engineparts [6]. Comparedtoothercladdingmethods like PTA(PlasmaTransferredArc) lasercladdinghas theadvantageofhighprecisionandminimumheat 132