Page - 135 - in 3D Printing of Metals

Metals 2017,7, 113 substantial increase instiffness. Therimaroundthecentralholewas loadedwithavertical forceof 600N,which is lowenoughtocauseonlyelasticdeflection. In thesizingoptimization, the topfaceof thepartwasselectedasdesignregion. Theareaaroundthecentralholewasexcludedtoaccount for the fact thataflat region isneededtoapply theexternal load. Thiswouldalsobe thecase inareal suspensiondome. Thesolverminimizes thedisplacementof the loadedrimunder theconstraint that theadded materialvolumemustnotexceedthevolumeof thepatchwithacrosssectionof1×4mminFigure4b. Also,amaximumthickness increaseof1mmisspecified. Theresultofsizingoptimizationiscompared to thestiffnessofbothothercases. Thecomparisonofall caseswasperformedusingfiniteelement analysis. Inaddition, lasercladdingexperimentswerecarriedout toproduce the tailoredcladding shown inFigure4c. Thestiffnessof thebasicvariant andof thepartwith local reinforcementwas tested inexperimentsunderstatic loads. 2.3.2. LaserCladdingExperiments Inorder toapproach thesolutionwithreinforcement, experimental trialsusing lasercladding wereperformed.Aring-shapedthickeningofAlSi10Mgwithawidthof4mm,athicknessof1mm andanouterdiameterof40mmwasappliedtoapre-shapedsample (alloyENAW6082)withawall thicknessof1mm,accordingtoFigure4a. The lasersourcewasafibercoupleddiode laser (λ=1025 and1040nm)withanoutputpowerof2kW.Thebeamdiameterwas0.6mm,theintensitydistribution top hat. The beam followed a spiral pathwith a pitch of 0.3mmper revolution. Claddingwas performedwitha feedof4000mm/min,a laserpowerof860Wandapowder feedrateof1.2g/min. Three layershadtobecladdedtoachieve thedesiredthickness.Alasercladspecimenwascutanda crosssectionwaspreparedusingstandardmetallographic techniques. 2.3.3. TestingofComponentStiffness Inorder toestimate thepotentialof the local reinforcement, thickenedbytailored lasercladding (Figure4c)andnon-thickened(Figure4a)componentswere testedunderstatic loads inaZwickZ250 testingmachine(ZwickGmbH&Co.KG,Ulm,Germany). Surfacemachiningoperationswereapplied before testing to improve thesurfacequalityandtocorrect thegeometry forprecisecomparisonof the results. Furthermore thisallowsaparallelalignmentof the topfacewhere the loadisappliedto the bottompedestal.Duringtheexperiments the force-displacementcharacteristicswererecorded. 2.4.Demonstrator II:FlangingofLocallyCladSheet 2.4.1.DemonstratorGeometry Thisdemonstrator is concernedwith themanufacturingofa local claddingonsheetmetalblanks, whicharesubsequentlyprocessedbyholeflanging.Holeflangesare important functionalelements in manysheetmetalparts. Theyprovidestiffness,allowforpositioningandfixation,etc. Increasingthe wall thicknessof theflangemaybenecessary forsubsequentoperationssuchascuttinga thread into theflange,asdetailed in the introductionof thepaper. Thecasestudycomprises themanufacturingof claddedblanks in twodifferentvariants, claddingontheoutsideof theflange,Figure5a,andonthe insideof theflange,Figure5b. Figure5. Investigatedtypesof thecladdingfor local reinforcement: claddingontheoutsideofflange (a) andcladdingonthe insideof theflange(b). 135