BC-5183冰箱门壳滚压成型及专机设计【说明书+CAD】
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Journal of Materials Processing Technology 186 (2007) 7781Cold roll forming of a U-channel made of high strength steelM. LindgrenDalarna University, SwedenReceived 16 June 2005; received in revised form 3 November 2006; accepted 6 December 2006AbstractCold roll forming is a bending process where the bending occurs gradually in several forming steps from an undeformed strip to a finishedprofile. The process is very interesting for the sheet metal industry due to the high speed in which the profile can be produced. High strength steelhas, in recent years, become more common in cold roll forming. These materials have advantages but also disadvantages that affect the design ofthe process.Simple models in literature K.F. Chiang, Cold roll forming, ME Thesis, University of Auckland, August 1984 predict that the longitudinalpeak membrane strain in the flange of a profile is independent of the material properties. However, Ingvarsson L. Ingvarsson, F orenklad teorif or rullforming av element ar v-profil, j amf orelse mellan normalt och h ogh allfast st al, VAMP 15- rullforming 23 april 2001 compared mild andultra high strength in a roll forming experiment and the conclusion was that the material properties will affect the finished profile. This paper is afundamental study performed in order to understand the observation by Ingvarsson L. Ingvarsson, F orenklad teori f or rullforming av element arv-profil, j amf orelse mellan normalt och h ogh allfast st al, VAMP 15- rullforming 23 april 2001.The objectives of this study are to investigate the change in the longitudinal peak membrane strain at the flange edge and the deformation lengthwhen the yield strength increases. These are important since they can be used to determine the number of forming steps and the distance betweenthem when designing the cold roll forming machine. The result from the simulations show that the longitudinal peak membrane strain decreasesand the deformation length increases when the yield strength is increased. 2007 Published by Elsevier B.V.Keywords: Cold roll forming; High strength steel; Finite element analysis1. IntroductionIn cold roll forming a profile is formed in several formingstepsfromanundeformedstriptoafinishedprofile(Fig.1).Theformingprocessisgeometricallycomplicatedduetothefactthatthe forming does not only occur in the tools but also betweeneach forming stand. When creating the tools the tool designermust decide how many forming steps the profile demands. Thenumber of steps is dependent on the shape of the cross-section,tolerance, thickness and the material properties.Itisimportanttominimisethenumberofstepsasthisreducesthe cost of the cold roll forming machine. Then the process canbeacompetitivealternativealsoforsmallerproductionvolumes.Therefore the knowledge of how high strength steel affects thenumber of forming steps is important.Existing relations between the longitudinal peak membranestrain, deformation length and the yield strength of the mate-E-mail address: mlgdu.se.rial have been investigated and compared with finite elementanalysis in this study.2. NotationsThe notations are given below and in Fig. 2: L, deformation length; a, flange length; t, thickness of the strip; Y, bend angle; r, distance from the bending zone; z, distance from where the bending starts; e, the longitudinal membrane engineering strain at the flange.3. BackgroundThe profile is formed in several steps and that will cause lon-gitudinal strain in the flange. The strain develops as the materialin a flange of a profile will travel a longer distance than the0924-0136/$ see front matter 2007 Published by Elsevier B.V.doi:10.1016/j.jmatprotec.2006.12.01778M. Lindgren / Journal of Materials Processing Technology 186 (2007) 7781Fig.1. Theprofileisformedinseveralformingstandsfromanundeformedstripto a finished profile.material in the bending zone. Panton et al. 1 concluded thatthe longitudinal peak strain occurs when the strip is in contactwith the rolls for the first time. The peak strain should not beplastic as plastic strain will give a residual stress that causesdefects on the profile as wave edges, longitudinal curvature, etc.Bhattacharyya et al. 2 created a model of the deformationlengthbyminimisingthetotalplasticworkforaU-channel.Theobtained model predicts that the deformation length is indepen-dent of yield strength. It is written as:L =?8a33t(1)Chiang 3 derived a model for the longitudinal engineeringstrain in the flange based on minimising of the plastic workdue to stretching and bending of the profile. It is written as:e =932?t2a6?r2z2?0ra0zL(2)The model overestimated the strain when the strip approachedthe tool. Therefore Chiang derived an improved expression bya geometrical consideration for the peak strain, leading to:e =?1 + 2?aL?2(1 cos) 1(3)This model showed that the longitudinal strain is uniform inthe deformation zone. All models predict that the behaviour isindependent of the material properties.Ingvarsson 4 compared mild steel with ultra high strengthsteel in an experiment where a V-section was cold roll formedwiththesamenumberofformingstands.Theultrahighstrengthsteelgaveastraightprofile,butnotthemildsteel.Theconclusionwas that fewer forming stands could be used when ultra highstrength steel is being roll formed.4. ApproachFinite element simulations are used in the current study toevaluate the yield strength influence on peak strain and defor-mation length. Since the analytical formulas for longitudinalpeak membrane strain do not account for the yield strength.Several papers have been written about the finite elementsimulation on cold roll forming for example 57.Fig. 2. One half of the U-channel. The strip is formed by a bend angle (Y8) in the contact zone between the rolls. It will cause a longitudinal membrane strain (e) inthe flange.M. Lindgren / Journal of Materials Processing Technology 186 (2007) 778179Table 1Series of experiments where the forming steps are 08 (feeder roll)108108 and08 (feeder roll)208208, when seven different yield strengths are used0810810808208208200MPa400MPa600MPa800MPa1000MPa1200MPa1400MPa5. The finite element modelFourteen different simulations have been carried out withvarying yield strengths and bend angles (Table 1). The finiteelement package MARC/MENTAT was used to perform thesimulations.The simulation starts from an undeformed strip and stopswhen the material reaches the second forming step. The total-,plastic- and elastic longitudinal peak membrane strain at theedge of the flange, are evaluated.5.1. The geometryThe model consists of four forming stands where the firsttwo stands are used as a belt feeder to the others (Fig. 3). Thelengthofthestripis800mmsothattheformingsteps08(feederrolls)108108 and 08 (feeder rolls)208208 are engaged atthe same time when the simulation has come to an end. Anevaluation of the longitudinal peak membrane strain and thedeformation length is then performed for the first forming stepwhere bending occurs.The cross-section geometry of the strip is, width 40mm,flange length (a) 10mm, bending radius 3mm and the thick-ness (t) of the strip is 1.5mm. Due to the symmetry only half ofthe strip is modelled.Fig. 3. Four forming stands are used. The two first stands are used as a beltfeeder. The other two forming stands have the same bend angle (Y).The strip is modelled with 1600 thick shell elements. Themesh size is 4mm1mm in the bending zone and in otherregions the mesh size is 4mm4mm.The strip is modelled with a bilinear thick shell element typenumber 75 8. This is a four-node element that calculates themembrane strain in the middle surface. Three layers of integra-tion points are used in the thickness direction.Therollsaremodelledasrigidsurfacesandtheyrotate,givingthe strip an initial speed of 0.6m/s. The speed is then increasedby 0.5% in each forming stand to counteract buckling.5.2. ContactTheclearancebetweenthetoolsis1.5mmandthestripthick-ness is 1.504mm, which gives a contact pressure of 560MPa.The friction is modelled as Coulomb friction and the frictioncoefficient is 0.1.Fig. 4. The fictive tensile test data for seven different materials. They have been implemented in the finite element program as a table.80M. Lindgren / Journal of Materials Processing Technology 186 (2007) 7781Fig.5. Whenthevirginyieldstrengthincreasesthelongitudinalpeakmembranestrain will decrease. When the plastic strain goes to zero the total strain willflatten out and the strain is purely elastic.5.3. Material modelThe material is modelled as an elasto-plastic material. Thematerial hardening is isotropic and the von Mises yield surfaceandtheassociatedflowruleareused.Afictivetensiletestdataisimplemented in the finite element program as a table. The yieldstrengthisthenscaledsothematerialstartstoyieldinsevendif-ferentpointsfrom200to1400MPa(Fig.4).Themodelaccountfor large deformations and strains. An additive decompositionof total strain rate into elastic and plastic strain rates is assumed.6. Result and discussionFig. 5 shows the peak longitudinal membrane strain of theedge due to bending from an originally flat strip to a 108 anglefor the different simulations. The result for each simulation isdenoted by the virgin yield strength of the flow stress in Fig. 4used in respective simulation. This value is given on the hori-zontal axis in Fig. 5. The simulations show for a bend angle of108 that the total (plastic and elastic) strain decreases when thevirgin yield strength increases. The total strain decreases morein the beginning when plastic strain is present.Fig. 6 is the bend angle 208 and the behaviour is similar asin Fig. 5. The difference between the cases is that the strainbecomes purely elastic at higher material virgin yield strength.The strain is also greater for a bending angle of 208, whichagrees with Chiang 3.The deformation length, Eq. (1), is the distance betweenwhere the transverse bending starts and the forming stands. Inthis study a strain based deformation length is used. It is definedas the distance from the forming stand to the point in the flangeedge where the strain is greater than 2e5. The strain baseddeformationlengthforthecases108and208willincreasewhenthe yield strength increases (Fig. 7). The length is greater for theFig. 6. The behaviour for the longitudinal peak membrane strain is similar tothe case with a forming step of 108. But now is the curve for the elastic andplastic longitudinal peak membrane strain displaced to a higher level of virginyield strength.bend angle 208 than 108, which agrees with Bhattacharyya etal. 2.Figs. 7 and 8 are the simulation results for the peak strainand the deformation length compared with the models, Eqs. (1)and (3), that Bhattacharyya et al. and Chiang derived. One cansee that they do not agree due to the large simplifications in theassumed pattern and material behaviour in their models 2,3.The assumptions for the deformation length were: The material is rigid perfectly plastic. Bending takes place only along the fold-line. The longitudinal bending of the web and the out-of-planebending of the flange can be neglected. The flange adopts the shape that minimises the plastic work.Fig. 7. The deformation length for bend angle 108 and 208 will increase whenthe yield strength increases. The length is greater for bend angle 208.M. Lindgren / Journal of Materials Processing Technology 186 (2007) 778181Fig. 8. The simulations are compared with the model Chiang derived, Eq. (3),and one can see that they do not agree well.Themodelforthepeakstrain,Eq.(3),hastheadditionalassump-tionthattheflangeedgeremainsstraightduringthedeformation.7. ConclusionsThe simulations show that the longitudinal peak membranestrain decreases, the deformation length increases for materi-als with higher yield strength. This information has not beenpossible to obtain from simple models as in Eqs. (1)(3).Decreasing longitudinal peak membrane strain gives lessresidual stresses in the flange of the profile and quality prob-lems as wave edges, longitudinal curvature, end flare, etc. willdecrease. It will make it possible to use fewer forming stepsfor profiles made of high strength steel. However, high strengthsteel has larger spring back that has to be accounted for. This isthe explanation why Ingvarsson 4 obtained a straight V-profilewhen ultra high strength steel was used. Ingvarsson 4 used thesame number of forming steps for both the mild and the ultrahigh strength steel. For mild steels were the forming steps toofew and larger residual stresses were present after the forming.The latter gave a V-profile with a longitudinal curvature.Increasingdeformationlengthleadstothehorizontaldistancebetween the forming steps must increase when high strengthsteel is used.AcknowledgementsThe author thanks ORTIC AB, Swedish Knowledge Foun-dation, Jernkontoret and Dalarna University for their technicaland financial support.References1 S.M. Panton, S.D. Zhu, J.L. Duncan, Geometric constraints on the formingpath in roll forming channel sections, Proc. Inst. Mech. Eng. 206.2 D. Bhattacharyya, P.D. Smith, C.H. Yee, L.F. Collins, The prediction ofdeformation length in cold roll forming, J. Mech. Work. Tech. 9 (1984)181191.3 K.F.Chiang,Coldrollforming,METhesis,UniversityofAuckland,August1984.4 L. Ingvarsson, F orenklad teori f or rullforming av element ar v-profil,j amf orelse mellan normalt och h ogh allfast st al, VAMP 15- rullforming 23april 2001.5 M. Brunet, S. Mguil, P. Pol, Modelling of a roll-forming process with acombined 2D and 3D FEM code, J. Mater. Process. Technol. 8081 (1998)213219.6 M. Farzin, M.S. Tehrani, E. Shameli, Determination of buckling limit ofstrain in cold roll forming by finite element analysis, J. Mater. Process.Technol. 125126 (2002) 626632.7 M. Lindgren, Finite element model of roll forming of a U-channel profile,To be presented at International Conference on Techn. of Plasticity, Verona,2005.8 MARC, Element Library, vol. B, Marc Analysis Research Corporation,USA.黄河科技学院毕业设计(文献翻译) 第 8 页 毕业设计文献翻译 院（系）名称工学院机械系 专业名称机械设计制造及其自动化 学生姓名盛忠杰 指导教师郭长江2012年 03 月 10 日一种高强度钢U形管道的滚压成型 M. Lindgren摘要：滚压成型是一种把待加工金属薄板通过逐步加工成固定形状的结构的弯曲过程。由于可以在较高的速度下把剖面可被制作出来从而使这个过程在钣金行业显得非常有价值。高强度钢近年来,在冷滚轧中变得越来越普遍。这些材料的优势,但也有影响设计过程缺点。一些简单的模型在文献中K.F.江 对冷滚轧成型、我的主题,1984年8月,奥克兰大学预测,纵向膜应变峰值的法兰轮廓是独立于材料性能的。然而 Ingvarson做了比较普通和超高强度的滚压成型实验并且结论是该材料的性能将直接影响到要完成的轮廓。本文是通过一些基本研究来观察来了Ingvarson的研究结果的。本研究旨在探讨改变法兰边的纵向膜应变峰值和当屈服强度的增加是的变形长度。这是很重要的，因为当设计滚压机时它们可以用来确定成型步骤数量和步骤间距。仿真结果表明，当屈服强度增加的时候膜应变峰值减小而纵向长度增加。关键词：滚压成型 高强度钢 有限元分析1.前言在滚压成型过程中，从待加工板材到加工好的轮廓需要数个步骤。这几何复杂成形工艺是由于这样的事实,即成形不仅发生于各个工具而且在每个形成步骤之间。当设计工具时，设计者必须知道成型过程中需要几个步骤，而步骤个数是由横断面形状，抗弯性，厚度及材料性能决定的。尽可能地减少步骤数是很重要的，因为这可以降低滚压机的成本。其次这样的工艺用于较小批量生产也较有竞争力。因而关于高强度薄板是如何影响成型步骤的数量方面的知识是很重要的。在这篇论文对纵向峰值膜应变 、变形长度和材料的屈服强度之间存在的关系进行了研究并做了有限元分析。2.符号说明各符号如下几图表2中： L变形长度 a法兰长度 t带钢厚度 Y 弯曲角 r 到弯曲区的距离z 到弯曲起点的距离 e 法兰出工程膜应变3 背景轮廓是在几个步骤之后完成的，因此会在法兰处产生纵向应变。法兰处的应变应该比弯曲处的更严重。Panton 用公式（1）得出了这样的结论：当条钢第一次与滚子接触时纵向峰值应变就产生了。峰值应变不应该是塑料性的因为塑性应变会给我一个残馀应力导致像波纹边缘及纵向弯曲等之类的缺陷。Bhattacharyya 用公式 (2)通过最小化总塑性得出了U型长板条的应变长度模型。通过所得到的模型他测算到变形长度与屈服强度无关。公式是这样： （1）Chiang 3用拉伸和弯曲来最小化塑性从而导出了一个纵向工程应变的模型。公式是这样: (2)这个模型过高估计了钢条与工具接触时产生的应变。因此，蒋通过对应力峰值的几何方面考虑得出一个改进式，即导出： （3）该模型表明,纵向应变变形带均匀一致。所有的模型公式都显示这种现象与材料性能无关。在一个实验中，Ingvarsson 4在有同样步骤数的滚压成型中比较了低碳钢和超高强度钢。超高强度钢比低碳钢得到的型材更符合要求。结于是便得到结论：当超高强度钢用于滚压时所需步骤更少。图一 板料通过几个滚压步骤形成所要求的型材4方法 有限元模拟是现在研究评估屈服强度对峰值应变和变形的长度影响的方法。因为膜应变公式不能解释关于屈服强度的内容。现在已经有好几篇文章论述了将有限元分析用于滚压分析的方法如57图二 U形管的一半 带钢在接触区中的滚轮间通过形成弯曲角。它将在法兰上造成纵向膜应
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