Seite - 136 - in 3D Printing of Metals

Metals 2017,7, 113 2.4.2. ProductionofTailoredLaser-CladdedBlanks As sheet metal, the aluminum alloy EN AW 6082 was chosen, as in the first demonstrator. Circular blanks of 2mmthickness and 76mmdiameterwere cut. As powder for laser cladding, thecastalloyAlSi12wasused.ATrumpfTruLaserCell7040 (TRUMPFGmbH&Co.KG,Ditzingen, Germany) operatedwith aCO2 laserwith amaximumpower of 5000Wwas used for cladding. Thesheetmetalblankwascooledduringtheweldingprocessusingawater-cooledaluminumplate, whichwaspositionedbelowthesample.At thesametime, thespecimenwasheld inplacebyafixture systemtoreduce theheat-inducedwarping.Claddingswithadiameterof20mmandathicknessof 0.75mmwereprogrammed. Thefinalheightof thecladdingrelative to thebasesheetwas0.7mmon average.Alaserpowerof3400W,a feedrateof400mm/min,apowdermassflowrateof1.6g/min andamixtureofheliumandargonasshieldinggaswereusedasprocessparameters. Threecladding strategieswere investigated(Figure6). Figure6. Investigatedcladdingstrategies forcreatingadisc-shapedreinforcement. (a) straightpathof the laserbeamwithparallel offset; (b) straightpathof the laserbeamwithparallel offset+circular outline; (c) spiralpathof laserbeam. 2.4.3. LightOpticalMicroscopy(LOM) Laser-claddedspecimenswerecutandcrosssectionswereprepared. Thesampleswereground flatwithsuccessivelyfinergradesofSiCpaperandthendiamondpolisheduntil alldeepscratches fromgrindingwereremoved(9μm/for10min,3μm/forabout30min,1μm/for5min). In thefinal stage, the sampleswereetchedwithKeller reagent (3mLHCl+5mLHNO3+1mLHF+190mL water) forrevealingthe ‘weldmicrostructure’. Themicroscopicexaminationof theetchedsampleswas conductedusinganopticalmicroscopefromLeicaMikrosystemeVertriebGmbH,Wetzlar,Germany. 2.4.4.Hole-FlangingExperiments Hole-flangingoperations insheetmetalpartsare typicallyperformedusingapunchthatdeforms apiercedsheetmetal intoamatrix, seeFigure7a. Thesheetmetal is clampedusingablankholder. In the case consideredhere, the areadeformedby theflangingoperation is thickenedusing laser cladding. Thespecimengeometry is showninFigure7b. Table2givesanoverviewof theexperimental tests thatwereperformed. Inadditiontosamples withacladdingof0.7mmonspecimenswith2.0mmthickness,monolithic sheetmetalof 2.0mm and2.5mmthicknesswas tested. The thicknessof the incladspecimenscorresponds to theclearence betweenpunchandmatrice for t=2.5mmand is smaller in thecaseof t=2mm. For thecladded specimens,aslightly larger thicknesswaschosentoexertpressureduringforming,hencedecreasing thechance todamagetherelativelybrittlecladmaterial. 136