Seite - 142 - in 3D Printing of Metals

Metals 2017,7, 113 themicrostructure (andthustheproperties)of thebasematerial. Since lasercladdingwouldbethe lastprocess step in themanufacturing routeof the component, straighteningandoftenalsoaheat treatment isnooption. Futureworkhas to focusonsizingoptimization(minimizedcladareasand cladthickness),onstrategies toquicklyextract theheatbycoolingandtoexploreadequatecladding strategieswhichminimizedistortion. Claddinga sheetprior to formingalso causesdistortion,whichmustbehandled in the same wayas for claddingonanalready formedcomponent (see above). However, straighteningmight alsobeanoption.Amajor issue is the formabilityof the laser-claddedmaterial. In this respect, the bestchoicewillbe touse thesamematerialas thesubstrate,andtoperformaheat treatmentprior to forming. In thisstudy,AlSi12wasusedforreasonsofavailabilityofpowderandprocessparameters. It is knownthat thesealloyshave limited formability. However, theflangingexperiments and the metallographicanalysis showthat, tosomeextent,holeflangingof laser-claddedaluminumblanks seemspossible. Although theultimate strainofAlSi12 is in the rangeoffive to sixpercent, ahole expansionratioof1.4wasachieved in thecasewhere thecladding is inside theflange. The total sheet thickness of theuncladmaterial (2.0mmand2.5mm)was chosen in suchaway that the sheet is drawninto thediewith(2.0mm)andwithout (2.5mm)clearance. Formingis feasible inbothcases for all hole expansion ratios. In caseof the cladmaterial, the likelinessof failure in thebrittle clad layer is reducedby formingunderdirect contactpressureof thepunch,whichexerts a stress state of favorable triaxiality. Thisway, the largestof the threeholeexpansionratioswasviablewhile the smallerexpansionratiosshowedfailure. Presumably, thepresenceof largerporescausedfailure in the lattercases. Formabilityof lasercladmaterialwillbesubject to largevariance in theas-built condition since thesizeandspatialdistributionofporescannotbecontrolled. Formingofspecimenswith laser claddingsontheoutsideof theflange led to failure inall cases,presumablydue to the fact that the superimposedpressurewasmissing in thesecases.However, it seemsviable toplasticallydeformclad material tosomeextentunder largesuperimposedpressure. Nevertheless, futureworkshouldfocusoncladdingthesameorat leastsimilaralloys. To improve formability, laserheat treatmentdirectlyaftercladdingmaybeanoption. If suitablealloysare tested and their suitability for forming is proven, a new type of tailored lightweightmaterial, tailored laser-claddedblanks,wouldbeavailable,with thepotential tooutperformexisting tailoredblanks in applicationswhere freelydesignedreinforcementsareneeded. Production considerations. Additive manufacturing is still a time-consuming process and therefore it isunlikely that tailored laser-claddedblanksorcomponentswillbeanoption formass productionHowever, introducingthedielessadditivemanufacturingprocessessuchas lasercladding into conventionalproduction chainsof sheetmetal components offers thepotential forproducing locallyreinforcedparts,whichcanbeproducedwithout themanufacturingofanewtoolsor theuseof fastenersorconnectors. Theprocess times in the twocasestudieswas in theorderof10–20s,which is compatibleevenwithcycle times in theautomotive industry. Material efficiency. Additivemanufacturing processes based onmetal powder are typically consideredmoreenergy intensive thanconventionalmanufacturingprocessesdueto theproduction ofpowder,ofwhichonlya limitedfractionof thesizedistribution isused,anddueto the fact that the powder ismelted in theadditivemanufacturingprocess. In lightweightcomponents,highmaterial efficiencymaybeachievedbyapplicationofadditivemanufacturingprocesses (mainly lasercladding), since theproductionofpatchesusedinpatchworkblanksbyblanking/piercingoperationscreatesa largeamountofwaste.Also,additivemanufacturingopensupthechanceofdistributing thematerial preciselyaccordingto theapplied loads.With locallyvariablematerial thicknesses,minimalweight designsmaybe achieved so that in total, lessmaterial is used in a given sheetmetal component thanwithconventional solutions. Reinforcementscanalsobeappliedtoplateorbulkcomponents, whichcouldbeexplored in futurestudies. 142