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metals Article MorphologyAnalysisofaMultilayerSinglePassvia NovelMetalThin-WallCoatingForming XinWang*, JunDu,ZhengyingWei,XueweiFang,GuangxiZhao,HaoBai,WeiLiu, ChuanqiRenandYunfeiYao StatekeyLaboratoryofManufacturingSystemEngineering,Xi’anJiaotongUniversity,Xi’an710049,China; jundu2010@mail.xjtu.edu.cn(J.D.); zywei@mail.xjtu.edu.cn(Z.W.); fangxuewei0920@gmail.com(X.F.); zgx6464946@gmail.com(G.Z.); zzujixiebaihao@163.com(H.B.); tyutliuwei@163.com(W.L.); legend7718@163.com(C.R.);yyf931012@stu.xjtu.edu.cn(Y.Y.) * Correspondence: linkwangxin@aol.com;Tel.:+86-15667083308 AcademicEditor:ManojGupta Received: 30 June2016;Accepted: 24November2016;Published: 9December2016 Abstract:Throughusinganovelmicro-coatingmetaladditivemanufacturing(MCMAM)process in thisstudy, the formingcharacteristicsof themultilayersingle-passspecimenswere investigated. The forming defects including the porosity and the bonding quality between layers were analyzed. Moreover, we also attempted to study the effect of process parameters such as flow rate, deposition velocity, and layer thickness on the formingmorphology. Based on the results, theoptimizationofprocessparameterswas conducted for the fabricationof thin-wallMCMAM. Finally, estimationcriteria for the integrityof the interfacialbondwereestablished. Keywords: additivemanufacturing; formingdefects;bondingquality; formingmorphology 1. Introduction Additive manufacturing (AM) has attracted much attention from the public due to its unique advantages, such as unrivalled design freedom and short lead times [1]. It can produce high-performancemetalcomponentsrapidlyusingalloypowderorwiresasrawmaterialandapplying ahigh-power laserorelectronbeamasaheatsource [2–5].However, thehighcapital costsandslow throughputprintinghaveseverelyrestricted itsapplication. To overcome the shortages of traditional AM,micro-coatingmetal additivemanufacturing (MCMAM)hasbeenproposedasacommercialmanufacturing technology.Comparedwith traditional metalAMtechnologies,MCMAMhasshownseveraladvantages.Atfirst, itprovidesahighermaterial utilizationthanselective lasermelting(SLM)withahighdepositionrate. Second, itproduces lessdust pollutionthanpowder-basedequipmentwhenthepowdermaterialwasrecycled. Third, ithasa lower equipmentcost thanSLMandelectronbeammachining(EBM)[6]. Xiongetal. investigatedtheformingcharacteristicsofamultilayersinglepasswiththeapplication ofGMAW-basedadditivemanufacturing [7]. Jorge et al. developeda fuseddepositionmodeling (FDM)systemformetals thatcandepositelectronicstructuresdirectly [8]. Yaoetal. adoptedametal dropletdepositionmanufacturingprocess toreduceproductdevelopment timeaswellas thecostof manufacturing[9].However,depositionaccuracywasdifficult tocontrol. Inaddition, thenovelmetal additivemanufacturingprocessproposedinthispaperwasanalyzedusinganumerical simulation method.Nevertheless, the influencesofprocessparametersontheformingmorphologyhavenever beenmentioned[10]. Therefore, thispaper is aimedat investigating the effects of themajorprocessparameters on the formingmorphologyandthebondingqualitybetweenlayersduringthemicro-coatingadditive Metals 2016,6, 313 145 www.mdpi.com/journal/metals