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弯钩形零件弯曲模结构与设计【说明书+CAD】,弯钩形,零件,弯曲,结构,设计,说明书,CAD

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河南机电高等专科学校毕业设计论文设计题目：弯钩形零件弯钩模设计 设 计 者：张 磊 指 导 教 师：杨 占 尧材 料 工 程 系 模 具 专 业 0 3 5 班2006.05.10毕业设计任务书设计题目：弯钩形零件弯曲模的设计设计时间：10周设计任务：1.完成工件弯曲工艺分析及模具设计工艺过程 2绘制模具装配图及各零件图 3编写设计说明书目录1 工件的工艺性分析12 工艺方案的确定13 模具结构形式的确定14 工艺设计1 毛坯尺寸的计算1 弯曲力的计算2 弯曲凸、凹模的间隙2 弯曲模工作部分尺寸计算215 模具的总体设计36 模具主要零件的设计4 凸模部分4 凹模部分47 模具其他主要零件设计及选用5 顶件装置的设计5 弹簧的选用5 顶杆的设计6 顶件板的设计6 斜楔、滑块设计7 滑块之间的行程关系7 斜楔、滑块的尺寸设计7 应有可靠的当块7 斜楔与滑块的结构、尺寸78选定设备89校核压力安装尺寸910画装配图和零件图911编写技术文件912模具的制造和装配913 弯曲模试冲时出现的缺陷10总结 12致谢 13参考文献 14工件工艺卡 15凸模加工工艺过程卡 16活动凹模加工工艺卡 17 弯钩形零件弯曲模结构与设计1 工件的工艺性分析： 该工件零件图如上所示，由零件图可知。该制件形状简单，尺寸不大，厚度适中，一般批量，属普通弯曲件，但零件上端口处有两个45的内弯，且长度确定，在设计模具时应注意并控制回弹。由于制件时内弯，要考虑合适的取件方案。因有一定的批量，应注意模具材料和结构的选择。2 工艺方案的确定：根据制件的工艺性分析，其有两道工序，有弯曲和内弯，因为此工件是上端内弯，因此合理的工艺方案是弯曲折弯。先将平板毛坯弯曲成“U”形，再对上端进行弯钩内弯。零件成形后，由于工件内弯，可纵向取出，此方案是较为合理。3 模具结构形式的确定：因工件材料较薄，弯曲中为保证工件平整，采用弹性顶尖装置。由于零件是内弯，需采用活动凹模，斜楔，靠斜楔与滑块作用使工件内弯，活动凹模上设有弹性回复装置。4 工艺设计：（1）：毛坯尺寸的计算计算毛坯尺寸，相对弯曲半径为 K/t=4/2=25 式中：K弯曲半径(mm) t料后（mm）可见，制件属于圆角半径较大的弯曲件，应先求弯曲变形区中性层曲率半径（mm） =+Kt由文献冷冲压工艺及模具设计中表32查得K0.39L， r弯曲半径 K中性层系数 （40.39x2）mm =4.78 mm由表35查得，最小弯曲半径rmin0.5t1mm L考虑到工件的质量问题及弯曲工艺要求，取弯钩处弯曲半径为rt2 mm 。毛坯长度L48166.570.5mm考虑工件的误差，取L72mm，b221.1mm 。（2）弯曲力的计算 为有效控制回弹，采用校正弯曲，F核PA P材料单位弯曲校正力 A校正部分投影面积查得材料15的单位校正力为50mpa.F=50(48+6.5)*22 =50*54.5*22 =59950N 60KN（3）弯曲凸、凹模的间隙 C=t+k*tC弯曲凸、凹模单边间隙t料厚材料厚度正偏差k 系数由表查得k 0.05c =t+kt =2+0.05x2 =2.1mm2c=4.2mm（4）弯曲模工作部分尺寸计算 （由于制件精度不高，凸、凹模制造公差均采用IT9级）由于工件外形尺寸要求相对精度高，计算尺寸时，要先计算凹模的尺寸，然后根据凹模尺寸莱计算凸模尺寸。由手册查得冲压件未注尺寸的极限偏差L1=482.2L2=161.1L3=6.50.8 凹模尺寸 bd=(L-1/2) =46.9圆角半径Vd=3t=6mm(查表)t2mm时，Vd（3-6）t深度由表3-17得，L=16mm则凸模尺寸，（bd-2c） =(46.9-4.2) =42.7Vp=V=4mm考虑到本工件精度要求不同，取凹模尺寸为48 ，凸模43.8 ，Vp=4mm, Vd=6mm。5 模具的总体设计根据所需压弯力的大小，初步考虑使用160KN的压力机，模具结构草图如下，只要有上模板、凸模、凹模、活动凹模、下模板、垫板等组成。初步设计模具闭合高度196mm支撑板外轮廓尺寸为210X210mm下模板外轮廓尺寸为270X100mm（上面为便于视图清晰，留有一定尺寸，实际为闭合状态）6 模具主要零件的设计凸模部分由于该工件的端面是额“ ”形 的，该工件是先弯成 “ ”，后再“ ”形顶端内弯，因此，可把凸模设计成整体式，结构如下： 由于该工件 毛坯式矩形，工件是内弯，所以，当工件成形后，可纵向取出工件，（取工件时需注意安全）。凹模部分 凹模是活动凹模，设计成滑块式，左右两件相对称，斜面与工件斜面相配合，结构简单，便于机械加工。模具开启时模具闭合时凹模设计成活动滑块，靠斜楔作用力使工件内弯，斜楔见装配图。 7 模具其他主要零件的设计及选用(1）顶件装置的设计考虑到工件的工艺结构及制件精度，采用弹性顶件装置是设计时，根据所需的顶件力选择合适的弹簧。 弹簧的选用：由顶件力选择弹簧由于顶件力校大，选用强力弹簧。外径D30.5mm，内径d17.5mm，自由高度h63mm。 顶杆的设计由于弹簧内径D=17.5mm,取顶杆直径D=16mm，长度L121mm。结构如图所示： 上端部长度为 2mm，起定位作用。 顶件板设计：顶件板与凸模一起压紧工件，尺寸应比工件大，其结构如图所示： 弹性装置结构如图所示： 斜楔、滑块的设计在工件内弯过程中，需有较大的侧向力，则应采用斜楔结构，通过斜楔机构将滑块的垂直运动转化为凸凹模的运动方式倾斜运动，提供侧向力进行内弯曲。 斜楔、滑块之间的行程关系确定斜楔的角度主要考虑到机械效率，行程和受力状态。这里取斜楔角为40度。为使滑块平稳可靠工作 S/S1=0.8391 S滑块行程S1斜楔行程S=4.6mmS1=5.478mm与滑块接触长度，b斜面斜度/5 b1.3mm则滑块斜面L 1.3+5.478/cos40=8.45mm,为使滑块有可靠长度，取L=10mm。 斜楔、滑块尺寸设计： 滑块长度取（21）H2,因此是凹模增大，保证其斜面长度， 由工件工艺可知，滑块高度H2=16mm，L2=6050mm，取55mm。为保证滑块运动的平稳，滑块宽度满足B22.5L2.B2=40mm L2B2/2.540/2.516mm。L255满足上式。 应有可靠的当块挡块与支撑板设计成一体，如装配图所示：斜楔与滑块采用橡皮复位。 斜楔与滑块结构、尺寸如图所示。滑动模块结构图： 斜楔滑块工作图如装配图所示。8 选定设备：由所得的弯曲力出算设备该零件所需的弯曲力为F=60KN。模具闭合高度H=196mm模具外廓尺寸为270X100mm现有160KN压力机，其型号为J23-16F，其主要参数如下：公称压力：160KN滑块行程：80mm最大装模高度：205mm最大封闭高度调节量：45mm台面尺寸：300mmX450mm模柄尺寸（孔）：40mm根据模具闭合高度，弯曲力，外轮廓尺寸等数据选择此设备是合适的。9 校核压力机安装尺寸：模座外形尺寸为270X100mm，闭合高度为196mm，而J23-16F型压力机工作台尺寸为450X300mm，最大闭合高度为205mm，调节量为45mm，故在工作台上可以安装；模柄孔尺寸也与本副模具所选模柄尺寸相符。10 装配图和零件图：见附图。11 编写技术文件：见工艺卡。12 模具的制造和装配：模具的制造：弯曲凸、凹模、斜楔均采用T8A，淬硬58-62HRC，在淬火前应先试模，在加工凸、凹模时，先加工凹模，凸模按加工出的凹模来配制加工，要保证双面间隙。凸、凹模圆角半径加工应一致，工作部分表面进行抛光。斜楔，滑块滑动面采用铣刨，淬硬后磨平。模具的装配：在装配前，检查模具零件的加工质量。主要组件装配：装配：模柄3是从上模板的下面向上压入的，在安装凸模固定板的垫板之前，先把模柄装好。模柄与上横板之间的配合要求是H7/m6，先在压力机上将模柄压入，再加工定位销孔和螺纹孔，然后把模柄端面突出部分锉平或磨平。安装好模柄后，用角尺检查模柄与上模座上平面的垂直度。凸模、斜楔装配：凸模、斜楔与固定板的配合要求为H7/m6，装配时，先在压力机上将凸模、斜楔压入固定板内，检查凸模、斜楔的垂直度，然后将固定板的上平面与凸模、斜楔一齐磨平。总装配：模具的主要组件装配完毕后开始进行总装配。因为此模具为无导柱模具，凸、凹模间隙在模具安装到机床上时进行调整，上、下模装配次序没有特别要求，则对上、下模分别安装。上模安装：上述已安装好了模柄、凸模、斜楔，安装垫板后，找正位置，装入销钉，拧紧螺钉即可安装上模完成。下模：（1）把活动凹模装入固定板中，磨平底面，侧面，安装滑块回复装置，如图中所示。（2）在凹模上安装定位板，然后在支撑板上安装好盖板。（3）把固定板安装在下模座上，找正位置后，先在下模座上投窝，加工螺纹孔，然后加工销钉孔，装入销钉（注：要限位销的安装），拧紧螺钉，然后安装好顶件装置。（4）把分别安装好的上、下模进行检查，然后把已装入固定板的凸模，插入凹模中，检查是否完全闭合，如有，检查安装并进行调整。（5）凸凹模的间隙调整：当装配完成后，采用塞尺法来测凸、凹模之间的间隙是否均匀，如不均匀进行调整，也可在装配完成后进行试弯，检查零件是否合格及表面质量。（6）在生产条件下进行试弯，弯曲成形的工件按零件产品图或试样进行检查验收。在验收过程中，如发现产品有各种缺陷，则要仔细分析。找出原因，并对模具进行适当的调整和修理，然后再进行试弯，直到模具正常工作并得到合格的弯曲件为止。然后打标记交付生产使用。13 弯曲模试冲时出现的缺陷，原因及调整 冲件的弯曲角度不够原因： 凸凹模的弯曲回弹角制造小。 凸模进入凹模深度太浅。 凸模之间间隙过大。 校正弯曲的实际单位校正力过小。调整方法： 修正凸凹模，使弯曲角度达到要求。 加深凹模深度，增大冲件的有效弯曲变形区域。 按实际情况采取措施，减小凸凹模的配合间隙。 增大校正力或修整凸凹模形状，使校正力几种在变形部位。 工件的弯曲位置不合要求 原因： 定位板位置不正。曲件两侧受力不平衡产生便移。 压料力不足 方法：重装定位板，保证其位置正确 分析方法：据实际情况修正凸、凹模，增大间隙值。取措施减小压料力。在试模后确定。 表面擦伤：原因：凹模圆角半径过小，表面粗糙度不合要求。润滑不良使坯料粘附于凹模。凸、凹模之间间隙不均匀。方法：增大凹模圆角半径，降低表面粗糙度值。 合理润滑。 修正凸、凹模，使间隙均匀。 弯曲部位产生裂纹：原因：材料的塑性差。 弯曲线与板料的纤维方向平行。方法：将坯料退火后弯曲。 使弯曲线与板料的纤维方向成一定的弯曲角度。 总 结随着产品向精密化和复杂化的发展，产品零件也日益复杂，级进模的工位数随之增加，精度要求提高，寿命要求更高，这对级进模的设计就提出了新的要求。由于级进模冲压生产效率高，操作简单安全，模具寿命长，产品质量高，生产成本较低等特点，现国民经济发展的同时，各种家用电器、仪表电器、汽车等也越来越多的走进了千家万户，而家用电器的生产也随着生产技术的发展越来越多地采用多工位级进模生产。弯钩形零件弯钩模设计，是理论知识与实践有机的结合，更加系统地对理论知识做了更深切贴实的阐述。也使我认识到，要向做为一名合格的模具设计人员，必须要有扎实的专业基础，并不断学习新知识新技术，树立终身学习的观念，把理论知识应用到实践中去，并坚持科学、严谨、求实的精神，大胆创新，突破新技术，为国民经济的腾飞做出应有的贡献。致 谢凉风习习，绿树成荫，在这大地万物都吸足了养分拼命抽枝成长的季节，我们也将带着多年学习所吸取的养分投入到社会实践中去，去体现自身的人生价值，实现人生的理想。当然，这一切都离不开老师对我们的精心培养和浇灌，而这次的毕业设计，更系统地把所学专业知识运用到实践中去，使我们所学专业知识更加牢固，更加系统化，能顺利地完成毕业设计，这和指导老师的精心指导和谆谆教诲是分不开的，在这里我衷心地感谢原老师、杨老师、翟老师、程老师、余老师对我的指导和帮助，是你们不辞劳苦地为我们讲解了学习中遇到的各种问题，使我掌握了模具设计在这个现代化工业生产中充当生力军的技能知识，使你们为我实现了自身的人生理想插上了坚实的翅膀。我会带着你们殷切的期望和百倍的热情投入到以后的工作和生活中去，去实现自身的人生价值，为社会的发展做出最大的贡献。此致敬礼参考文献： 冷冲模设计与制造 高鸿庭主编 机械工业出版社 冷冲压模具设计指导 王芳主编 机械工业出版社 冷冲模设计指导 史铁梁主编 机械工业出版社 冲压工艺与模具设计 王芳主编 机械工业出版社 冷冲模设计与制造 姜奎华主编 机械工业出版社 冲压工艺学 姜奎华、肖景容主编 机械工业出版社 模具设计与制造简明手册 冯丙尧主编 上海科学技术出版社 冲模设计应用实例 模具实用技术手册 机械工业出版社 冲压模具图册 杨占尧主编 机械工业出版社 模具制造技术 罗大金主编 机械工业出版社工件工艺卡产品名称：弯钩形零件材料牌号：15规格71*22*2mm毛坯尺寸：板料71*22mm工序：“U”形弯曲内弯设备：J2316F工艺装配：弯曲模检验：按产品图纸检验14 目录1 工件的工艺性分析12 工艺方案的确定13 模具结构形式的确定14 工艺设计1 毛坯尺寸的计算1 弯曲力的计算2 弯曲凸、凹模的间隙2 弯曲模工作部分尺寸计算25 模具的总体设计36 模具主要零件的设计3 凸模部分3 凹模部分37 模具其他主要零件设计及选用4 顶件装置的设计5 弹簧的选用5 顶杆的设计5 顶件板的设计5 斜楔、滑块的设计7 滑块之间的行程关系7 斜楔、滑块的尺寸设计7 应有可靠的当块7 斜楔与滑块的结构、尺寸78 选定设备89 校核压力安装尺寸910. 画装配图和零件图911. 编写技术文件912. 模具的制造和装配913 弯曲模试冲时出现的缺陷10总结11致谢12参考文献13工件工艺卡14凸模加工工艺过程卡15活动凹模加工工艺卡16 Int J Adv Manuf Technol (2002) 19:253259 2002 Springer-Verlag London LimitedAn Analysis of Draw-Wall Wrinkling in a Stamping Die DesignF.-K. Chen and Y.-C. LiaoDepartment of Mechanical Engineering, National Taiwan University, Taipei, TaiwanWrinkling that occurs in the stamping of tapered square cupsand stepped rectangular cups is investigated. A commoncharacteristic of these two types of wrinkling is that thewrinkles are found at the draw wall that is relatively unsup-ported. In the stamping of a tapered square cup, the effect ofprocess parameters, such as the die gap and blank-holderforce, on the occurrence of wrinkling is examined using finite-element simulations. The simulation results show that the largerthe die gap, the more severe is the wrinkling, and suchwrinkling cannot be suppressed by increasing the blank-holderforce. In the analysis of wrinkling that occurred in the stampingof a stepped rectangular cup, an actual production part thathas a similar type of geometry was examined. The wrinklesfound at the draw wall are attributed to the unbalancedstretching of the sheet metal between the punch head and thestep edge. An optimum die design for the purpose of eliminatingthe wrinkles is determined using finite-element analysis. Thegood agreement between the simulation results and thoseobserved in the wrinkle-free production part validates theaccuracy of the finite-element analysis, and demonstrates theadvantage of using finite-element analysis for stamping diedesign.Keywords: Draw-wall wrinkle; Stamping die; Stepped rec-tangular cup; Tapered square cups1.IntroductionWrinkling is one of the major defects that occur in the sheetmetal forming process. For both functional and visual reasons,wrinkles are usually not acceptable in a finished part. Thereare three types of wrinkle which frequently occur in the sheetmetal forming process: flange wrinkling, wall wrinkling, andelastic buckling of the undeformed area owing to residualelastic compressive stresses. In the forming operation of stamp-ing a complex shape, draw-wall wrinkling means the occurrenceCorrespondence and offprint requests to: Professor F.-K. Chen, Depart-ment of Mechanical Engineering, National Taiwan University, No. 1Roosevelt Road, Sec. 4, Taipei, Taiwan 10617. E-mail: fkchen?.twof wrinkles in the die cavity. Since the sheet metal in the wallarea is relatively unsupported by the tool, the elimination ofwall wrinkles is more difficult than the suppression of flangewrinkles. It is well known that additional stretching of thematerial in the unsupported wall area may prevent wrinkling,and this can be achieved in practice by increasing the blank-holder force; but the application of excessive tensile stressesleads to failure by tearing. Hence, the blank-holder force mustlie within a narrow range, above that necessary to suppresswrinkles on the one hand, and below that which producesfracture on the other. This narrow range of blank-holder forceis difficult to determine. For wrinkles occurring in the centralarea of a stamped part with a complex shape, a workablerange of blank-holder force does not even exist.In order to examine the mechanics of the formation ofwrinkles, Yoshida et al. 1 developed a test in which a thinplate was non-uniformly stretched along one of its diagonals.They also proposed an approximate theoretical model in whichthe onset of wrinkling is due to elastic buckling resulting fromthe compressive lateral stresses developed in the non-uniformstress field. Yu et al. 2,3 investigated the wrinkling problemboth experimentally and analytically. They found that wrinklingcould occur having two circumferential waves according totheir theoretical analysis, whereas the experimental results indi-cated four to six wrinkles. Narayanasamy and Sowerby 4examined the wrinkling of sheet metal when drawing it througha conical die using flat-bottomed and hemispherical-endedpunches. They also attempted to rank the properties thatappeared to suppress wrinkling.These efforts are focused on the wrinkling problems associa-ted with the forming operations of simple shapes only, suchas a circular cup. In the early 1990s, the successful applicationof the 3D dynamic/explicit finite-element method to the sheet-metal forming process made it possible to analyse the wrinklingproblem involved in stamping complex shapes. In the presentstudy, the 3D finite-element method was employed to analysethe effects of the process parameters on the metal flow causingwrinkles at the draw wall in the stamping of a tapered squarecup, and of a stepped rectangular part.A tapered square cup, as shown in Fig. 1(a), has an inclineddraw wall on each side of the cup, similar to that existing ina conical cup. During the stamping process, the sheet metalon the draw wall is relatively unsupported, and is therefore254F.-K. Chen and Y.-C. LiaoFig. 1. Sketches of (a) a tapered square cup and (b) a steppedrectangular ne to wrinkling. In the present study, the effect of variousprocess parameters on the wrinkling was investigated. In thecase of a stepped rectangular part, as shown in Fig. 1(b),another type of wrinkling is observed. In order to estimate theeffectiveness of the analysis, an actual production part withstepped geometry was examined in the present study. Thecause of the wrinkling was determined using finite-elementanalysis, and an optimum die design was proposed to eliminatethe wrinkles. The die design obtained from finite-element analy-sis was validated by observations on an actual production part.2.Finite-Element ModelThe tooling geometry, including the punch, die and blank-holder,weredesignedusingtheCADprogramPRO/ENGINEER. Both the 3-node and 4-node shell elements wereadopted to generate the mesh systems for the above toolingusing the same CAD program. For the finite-element simul-ation, the tooling is considered to be rigid, and the correspond-ing meshes are used only to define the tooling geometry andFig. 2. Finite-element mesh.are not for stress analysis. The same CAD program using 4-node shell elements was employed to construct the meshsystem for the sheet blank. Figure 2 shows the mesh systemfor the complete set of tooling and the sheet-blank used in thestamping of a tapered square cup. Owing to the symmetricconditions, only a quarter of the square cup is analysed. Inthe simulation, the sheet blank is put on the blank-holder andthe die is moved down to clamp the sheet blank against theblank-holder. The punch is then moved up to draw the sheetmetal into the die cavity.In order to perform an accurate finite-element analysis, theactual stressstrain relationship of the sheet metal is requiredas part of the input data. In the present study, sheet metalwith deep-drawing quality is used in the simulations. A tensiletest has been conducted for the specimens cut along planescoinciding with the rolling direction (0) and at angles of 45and 90 to the rolling direction. The average flow stress ?,calculated from the equation ? ? (?0? 2?45? ?90)/4, for eachmeasured true strain, as shown in Fig. 3, is used for thesimulations for the stampings of the tapered square cup andalso for the stepped rectangular cup.All the simulations performed in the present study were runon an SGI Indigo 2 workstation using the finite-element pro-gram PAMFSTAMP. To complete the set of input data requiredFig. 3. The stressstrain relationship for the sheet metal.Draw-Wall Wrinkling in a Stamping Die Design255for the simulations, the punch speed is set to 10 m s?1and acoefficient of Coulomb friction equal to 0.1 is assumed.3.Wrinkling in a Tapered Square CupA sketch indicating some relevant dimensions of the taperedsquare cup is shown in Fig. 1(a). As seen in Fig. 1(a), thelength of each side of the square punch head (2Wp), the diecavity opening (2Wd), and the drawing height (H) are con-sidered as the crucial dimensions that affect the wrinkling.Half of the difference between the dimensions of the die cavityopening and the punch head is termed the die gap (G) in thepresent study, i.e. G ? Wd? Wp. The extent of the relativelyunsupported sheet metal at the draw wall is presumably dueto the die gap, and the wrinkles are supposed to be suppressedby increasing the blank-holder force. The effects of both thedie gap and the blank-holder force in relation to the occurrenceof wrinkling in the stamping of a tapered square cup areinvestigated in the following sections.3.1Effect of Die GapIn order to examine the effect of die gap on the wrinkling,the stamping of a tapered square cup with three different diegaps of 20 mm, 30 mm, and 50 mm was simulated. In eachsimulation, the die cavity opening is fixed at 200 mm, and thecup is drawn to the same height of 100 mm. The sheet metalused in all three simulations is a 380 mm ? 380 mm squaresheet with thickness of 0.7 mm, the stressstrain curve for thematerial is shown in Fig. 3.The simulation results show that wrinkling occurred in allthree tapered square cups, and the simulated shape of thedrawn cup for a die gap of 50 mm is shown in Fig. 4. It isseen in Fig. 4 that the wrinkling is distributed on the drawwall and is particularly obvious at the corner between adjacentwalls. It is suggested that the wrinkling is due to the largeunsupported area at the draw wall during the stamping process,also, the side length of the punch head and the die cavityFig. 4. Wrinkling in a tapered square cup (G ? 50 mm).opening are different owing to the die gap. The sheet metalstretched between the punch head and the die cavity shoulderbecomes unstable owing to the presence of compressive trans-verse stresses. The unconstrained stretching of the sheet metalunder compression seems to be the main cause for the wrink-ling at the draw wall. In order to compare the results for thethree different die gaps, the ratio ? of the two principal strainsis introduced, ? being ?min/?max, where ?maxand ?minare themajor and the minor principal strains, respectively. Hosfordand Caddell 5 have shown that if the absolute value of ? isgreater than a critical value, wrinkling is supposed to occur,and the larger the absolute value of ?, the greater is thepossibility of wrinkling.The ? values along the cross-section MN at the samedrawing height for the three simulated shapes with differentdie gaps, as marked in Fig. 4, are plotted in Fig. 5. It is notedfrom Fig. 5 that severe wrinkles are located close to the cornerand fewer wrinkles occur in the middle of the draw wall forall three different die gaps. It is also noted that the bigger thedie gap, the larger is the absolute value of ?. Consequently,increasing the die gap will increase the possibility of wrinklingoccurring at the draw wall of the tapered square cup.3.2Effect of the Blank-Holder ForceIt is well known that increasing the blank-holder force canhelp to eliminate wrinkling in the stamping process. In orderto study the effectiveness of increased blank-holder force, thestamping of a tapered square cup with die gap of 50 mm,which is associated with severe wrinkling as stated above, wassimulated with different values of blank-holder force. Theblank-holder force was increased from 100 kN to 600 kN,which yielded a blank-holder pressure of 0.33 MPa and 1.98MPa, respectively. The remaining simulation conditions aremaintained the same as those specified in the previous section.An intermediate blank-holder force of 300 kN was also usedin the simulation.The simulation results show that an increase in the blank-holder force does not help to eliminate the wrinkling thatoccurs at the draw wall. The ? values along the cross-sectionFig. 5. ?-value along the cross-section MN for different die gaps.256F.-K. Chen and Y.-C. LiaoMN, as marked in Fig. 4, are compared with one another forthe stamping processes with blank-holder force of 100 kN and600 kN. The simulation results indicate that the ? values alongthe cross-section MN are almost identical in both cases. Inorder to examine the difference of the wrinkle shape for thetwo different blank-holder forces, five cross-sections of thedraw wall at different heights from the bottom to the line MN, as marked in Fig. 4, are plotted in Fig. 6 for both cases.It is noted from Fig. 6 that the waviness of the cross-sectionsfor both cases is similar. This indicates that the blank-holderforce does not affect the occurrence of wrinkling in the stamp-ing of a tapered square cup, because the formation of wrinklesis mainly due to the large unsupported area at the draw wallwhere large compressive transverse stresses exist. The blank-holder force has no influence on the instability mode of thematerial between the punch head and the die cavity shoulder.4.Stepped Rectangular CupIn the stamping of a stepped rectangular cup, wrinkling occursat the draw wall even though the die gaps are not so significant.Figure 1(b) shows a sketch of a punch shape used for stampinga stepped rectangular cup in which the draw wall C is followedby a step DE. An actual production part that has this typeof geometry was examined in the present study. The materialused for this production part was 0.7 mm thick, and the stressstrain relation obtained from tensile tests is shown in Fig. 3.The procedure in the press shop for the production of thisstamping part consists of deep drawing followed by trimming.In the deep drawing process, no draw bead is employed onthe die surface to facilitate the metal flow. However, owingto the small punch corner radius and complex geometry, asplit occurred at the top edge of the punch and wrinkles werefound to occur at the draw wall of the actual production part,as shown in Fig. 7. It is seen from Fig. 7 that wrinkles aredistributed on the draw wall, but are more severe at the corneredges of the step, as marked by AD and BE in Fig. 1(b).The metal is torn apart along the whole top edge of the punch,as shown in Fig. 7, to form a split.In order to provide a further understanding of the defor-mation of the sheet-blank during the stamping process, a finite-element analysis was conducted. The finite-element simulationwas first performed for the original design. The simulatedshape of the part is shown from Fig. 8. It is noted from Fig.8 that the mesh at the top edge of the part is stretchedFig. 6. Cross-section lines at different heights of the draw wall fordifferent blank-holder forces. (a) 100 kN. (b) 600 kN.Fig. 7. Split and wrinkles in the production part.Fig. 8. Simulated shape for the production part with split and wrinkles.significantly, and that wrinkles are distributed at the draw wall,similar to those observed in the actual part.The small punch radius, such as the radius along the edgeAB, and the radius of the punch corner A, as marked in Fig.1(b), are considered to be the major reasons for the wallbreakage. However, according to the results of the finite-element analysis, splitting can be avoided by increasing theabove-mentioned radii. This concept was validated by theactual production part manufactured with larger corner radii.Several attempts were also made to eliminate the wrinkling.First, the blank-holder force was increased to twice the originalvalue. However, just as for the results obtained in the previoussection for the drawing of tapered square cup, the effect ofblank-holder force on the elimination of wrinkling was notfound to be significant. The same results are also obtained byincreasing the friction or increasing the blank size. We concludethat this kind of wrinkling cannot be suppressed by increasingthe stretching force.Since wrinkles are formed because of excessive metal flowin certain regions, where the sheet is subjected to large com-pressive stresses, a straightforward method of eliminating thewrinkles is to add drawbars in the wrinkled area to absorb theredundant material. The drawbars should be added parallel tothe direction of the wrinkles so that the redundant metal canbe absorbed effectively. Based on this concept, two drawbarsare added to the adjacent walls, as shown in Fig. 9, to absorbthe excessive material. The simulation results show that theDraw-Wall Wrinkling in a Stamping Die Design257Fig. 9. Drawbars added to the draw walls.wrinkles at the corner of the step are absorbed by the drawbarsas expected, however some wrinkles still appear at the remain-ing wall. This indicates the need to put more drawbars at thedraw wall to absorb all the excess material. This is, however,not permissible from considerations of the part design.One of the advantages of using finite-element analysis forthe stamping process is that the deformed shape of the sheetblank can be monitored throughout the stamping process, whichis not possible in the actual production process. A close lookat the metal flow during the stamping process reveals that thesheet blank is first drawn into the die cavity by the punchhead and the wrinkles are not formed until the sheet blanktouches the step edge DE marked in Fig. 1(b). The wrinkledshape is shown in Fig. 10. This provides valuable informationfor a possible modification of die design.An initial surmise for the cause of the occurrence of wrink-ling is the uneven stretch of the sheet metal between the punchcorner radius A and the step corner radius D, as indicated inFig. 1(b). Therefore a modification of die design was carriedout in which the step corner was cut off, as shown in Fig.11, so that the stretch condition is changed favourably, whichallows more stretch to be applied by increasing the step edges.However, wrinkles were still found at the draw wall of thecup. This result implies that wrinkles are introduced becauseof the uneven stretch between the whole punch head edge andthe whole step edge, not merely between the punch corner andFig. 10. Wrinkle formed when the sheet blank touches the steppededge.Fig. 11. Cut-off of the stepped corner.the step corner. In order to verify this idea, two modificationsof the die design were suggested: one is to cut the whole stepoff, and the other is to add one more drawing operation, thatis, to draw the desired shape using two drawing operations.The simulated shape for the former method is shown in Fig.12. Since the lower step is cut off, the drawing process isquite similar to that of a rectangular cup drawing, as shown inFig. 12. It is seen in Fig. 12 that the wrinkles were eliminated.In the two-operation drawing process, the sheet blank wasfirst drawn to the deeper step, as shown in Fig. 13(a). Sub-sequently, the lower step was formed in the second drawingoperation, and the desired shape was then obtained, as shownin Fig. 13(b). It is seen clearly in Fig. 13(b) that the steppedrectangular cup can be manufactured without wrinkling, by atwo-operation drawing process. It should also be noted that inthe two-operation drawing process, if an opposite sequence isapplied, that is, the lower step is formed first and is followedby the drawing of the deeper step, the edge of the deeper step,as shown by AB in Fig. 1(b), is prone to tearing because themetal cannot easily flow over the lower step into the die cavity.The finite-element simulations have indicated that the diedesign for stamping the desired stepped rectangular cup usingone single draw operation is barely achieved. However, themanufacturing cost is expected to be much higher for the two-operation drawing process owing to the additional die cost andoperation cost. In order to maintain a lower manufacturingcost, the part design engineer made suitable shape changes,and modified the die design according to the finite-elementFig. 12. Simulated shape for the modified die design.258F.-K. Chen and Y.-C. LiaoFig. 13. (a) First operation and (b) second operation in the two-operation drawing process.simulation result to cut off the lower step, as shown in Fig.12. With the modified die design, the actual stamping die forproduction was manufactured and the production part wasfound to be free from wrinkles, as shown in Fig. 14. The partshape also agreed well with that obtained from the finite-element simulation.In order to further validate the finite-element simulationresults, the thickness distribution along the cross-section GHobtained from the simulation result as indicated in Fig. 14,Fig. 14. The defect-free production part.was compared with those measured from the production part.The comparison is shown in Fig. 15. It can be seen in Fig.15 that the predicted thickness distribution by finite-elementsimulation agrees well with that measured directly in theproduction part. This agreement confirms the effectiveness ofthe finite-element analysis.Fig. 15. The simulated and measured thickness distribution along GH.Draw-Wall Wrinkling in a Stamping Die Design2595.Summary and Conc