有色金属板料弯曲成形机理分析及其质量影响研究

摘要I有色金属板料弯曲成形机理分析及其质量影响研究摘要弯曲成形作为材料塑性成形中的一种重要加工方法，且铜、铝等有色金属弯曲件亦越来越多的得到应用，而目前研究却大多集中在薄钢板上，所以有必要对有色金属中厚板料的弯曲成形机理及其质量影响进行深入研究。已有研究表明材料在弯曲成形过程中一面受拉、一面受压，且弯曲件上同时存在着弹性变形和塑性变形，虽然表面上弯曲成形过程中受力及产生的变形相对简单，但内部成形机理和其质量影响尚不是很清楚。而本文主要研究的是有色金属T2纯铜板料的弯曲成形机理分析及其质量影响，所做的实验不但证实了很多前人总结的理论，还发现了一些以前因为各种因素而没有注意到的规律。本文研究依据金属板料的三点式自由弯曲实验，实验对象为凸模半径与板料厚度比为R/t=1和2的T2纯铜板料，采用极细油墨笔对其表面进行了网格化处理。首先通过三点式自由弯曲实验装置进行了板料的弯曲成形实验，并使用数码相机拍摄了成形过程中试件每一时刻的照片，通过图像处理得到了试件的网格变化图。在此基础上进行了弯曲成形的机理分析及其质量影响研究。弯曲成形的机理分析主要基于本文实验所得到的网格变化图，首先分析了弯曲件在成形过程中的轮廓变化，通过网格图的叠加发现板料在成形过程中其直臂部分也同时存在弹性变形和塑性变形，且其变形在有校正力作用下时大于无校正力时。然后研究了弯曲件的弯曲圆角的曲率半径变化，得出其半径在弯曲过程中有逐渐减少的趋势，并将小于凸模的半径。最后研究了弯曲件最重要的几何精度——成形角度，通过实验结果和数值模拟分析后，发现弯曲件成形过程其直臂内外侧的角度并不是相同的，而是有着由内到外逐渐增大的趋势，虽然这一差异并不是很大，在本文的实验统计平均结果为0.4°到0.8°之间，而且这一差异在弯曲力消除、试件回弹后将变得更小，但仍大于0.2°的实验测量误差。在此基础上研究了弯曲件的各划分层的回弹率，得出弯曲件在有校正力时的回弹将小于无校正力时，且回弹率的大小有内到外逐渐减小的趋势。通过实验完成后试件的表面照片分析了弯曲件的外形变化规律，得出其表面缺陷形成原因为晶格变形造成的，并分析了弯曲件弯曲圆角内外侧晶格变形原理。昆明理工大学硕士学位论文II然后对试件的表面做了金相显微照片，得到其沿内外侧曲率顶点直线等间距点上的金相照片，并以此为基础研究了弯曲件的组织变化规律，佐证了外形分析的各种假设。最后分析了弯曲成形中材料的组织变化原因及机理。关键词：弯曲成形；三点式自由弯曲；T2纯铜；回弹；金相组织AbstractIIITheMechanismAnalysisandImpactsofQualityStudyofNon-ferrousMetalSheetBendingFormingAbstractBendingisanimportantprocessingmethodinplasticforming.Copper,aluminumandothernon-ferrousmetalbendingpartsarebeingmoreandmorewidelyadopted.Butthepresentstudyismostlyconcentratedinthesheetsteel,soitisnecessarytoresearchthenon-ferrousmetalthicksheet'sbendingforming.Studieshaveshownthattheoutsideofbendingpartisintension,andtheinsideisincompressionintheformingprocess.Thereareelasticdeformationandplasticdeformationintheprocessingofformingatthesametime.Theinternalformingmechanismanditsqualityinfluenceisnotclear,althoughthestressanddeformationoftheproduceseemssoeasy.Andthispapermainlystudiedthenon-ferrousmetalT2purecopperplatematerialformingmechanismanalysisanditsqualityinfluence.Theexperimentaccomplishedinthispapernotonlyconfirmedmanyprevioussummarizetheory,alsofoundsomelawsthatneglectedbecauseofvariousfactors.Thispaperstudyontheexperimentofthreepointfreeofsheetmetalbending,T2purecopperplatewasadoptedasexperimentalobject,theratioofpunchradiusandsheetthicknesswasR/t=1and2.Thesurfaceofthespecimenwasmeshedbyuseofveryfineinkpen.Firstofall,theformingprocesswasaccomplishedontheexperimentalfacilityofthreepointfreeofsheetmetalbending.Andphotosofthespecimenintheformingprocesswereshottedoneverymomentbyuseofdigitalcamera.Thegridprofilesofspecimenweregottenbyimageprocessing.Theanalysisofthemechanismofformingandstudyoftheimpactsofqualityweredevelopedonthebasisoftheexperiment.Theanalysisofmechanismofformingcompletedbasedonthegridprofilesgettenbytheexperiment.Firstly,theprofilechangesofthespecimenwereanalysed.Thestraightarmofthesheetalsohadelasticdeformationandplasticdeformationbyanlysisofthegridmapssuperposition.Andthedeformationinacorrectionforcewas昆明理工大学硕士学位论文IVgreaterthanwhenundernocorrectionforce.Thenstudiedthefilletradiusofcurvaturechangeofbendingparts,obtainedtheconclusionthattheradiushadthetendencyofbeengraduallyreduceinthebendingprocess,evenbeenlessthanpunchradiusintheend.Finallythebendingforminganglewasanalysedatlength.Aftertheanalysisoftheexperimentalresultsandnumericalsimulation,theinsideandoutsideofthebendingpartweren’tstrictequalledintheformingprocess.Therewasatrendthattheanglewouldincreasegraduallyfrominsidetooutside.Althoughthedifferencewasnotverybig,theexperimentalstatisticalaveragebetween0.4°and0.8°inthispaper.Andthedifferencewouldbemoresmallafterspringback.Butit’ssizestillbeenmorethanexperimentalmeasurementerrorwhosesizewasabout0.2°.Everylayers’springbackrateswereresearchedonthebasisofangledataTab..Itisconcludedthatthespringbackratesofthebendingpartsinacorrectionforcewouldbelessthannocorrectionforce,andtherewasatrendthatthesizeoftheresilientratewoulddecreasegraduallyfrominsidetooutside.Thebendingpartsshapechanginglawwasanalysedthroughthephotosofthespecimens’surfaceaftertheexperiment.Andthereasonsofthesurfacedefectformationwerefoundbycauseoflatticedeformation.Furthermore,thelatticedeformationprincipleofthebendingparts’insideandoutsidewasanalyzed.Andthenthemetallographicmicroscopephotosshottedonthesurfaceofthespecimenweregetteninthelineofthevertexfrominsidetooutsideevenlyspaced.Thebendingpartsorganizationchangelawwasobtainedbytheanalysisofmetallograph.Andvariouskindsofhypothesiswereconfirmed.Atlast,analyzedthecausalfactorsandmechanismofthematerialstructuralchangesintheformingprocessweresummarized.KeyWords:bendingforming;threepointfreebending;T2purecopper;springback;metallurgicalstructure目录V目录摘要..........................................................................................................IAbstract.......................................................................................................III第一章绪论...............................................................................................11.1引言...............................................................................................11.2研究历史与研究现状...................................................................21