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河南机电高等专科学校毕业设计（论文）任务书系 部： 材料工程系 专 业： 模具设计与制造 学生姓名: 学 号: 设计(论文)题目： 转换支架模具设计 起 迄 日 期: 06年3月20日5月10日指 导 教 师: 发任务书日期: 06年3月15日任务书填写要求1毕业设计（论文）任务书由指导教师根据各课题的具体情况填写，经学生所在专业的负责人审查、系主管领导签字后生效。此任务书应在毕业设计（论文）开始前一周内填好并发给学生；2任务书内容必须用黑墨水笔工整书写或按教务处统一设计的电子文档标准格式（可从教务处网页上下载）打印，不得随便涂改或潦草书写，禁止打印在其它纸上后剪贴；3任务书内填写的内容，必须和学生毕业设计（论文）完成的情况相一致，若有变更，应当经过所在专业及系主管领导审批后方可重新填写；4任务书内有关“系”、“专业”等名称的填写，应写中文全称，不能写数字代码，学生的“学号”要写全号，请规范化填写；5任务书内“主要参考文献”的填写，应按照国标GB 771487文后参考文献著录规则的要求书写，不能有随意性；6有关年月日等日期的填写，应当按照国标GB/T 740894数据元和交换格式、信息交换、日期和时间表示法规定的要求，一律用阿拉伯数字书写。如“2002年4月2日”或“2002-04-02”。毕 业 设 计（论 文）任 务 书1本毕业设计（论文）课题来源及应达到的目的：本设计的课题为转换支架，是老师从用于实际生产的众多课题中筛选出来的，具有一定的代表性和可学习性。通过对本设计的完成可使我们对模具的设计有一个初步的了解，以便使我们把所学习的理论知识能够和实际生产向结合，使我们在即将走上的工作岗位上更快的进入角色。2本毕业设计（论文）课题任务的内容和要求（包括原始数据、技术要求、工作要求等）：设计题目：转换支架材料：Q235料厚：3 内容：（1）设计说明书（2）转换支架模具装配图（3）模具各主要零件图（4）典型零件的加工工艺卡所在专业审查意见：负责人： 年 月 日系部意见：系领导： 年 月 日 河南机电高等专科学校毕业设计(论文)开题报告学生姓名： 学 号： 专 业： 模具设计与制造 设计(论文)题目： 转换支架模具设计 指导教师： 2006年 5 月9 日开题报告填写要求1开题报告（含“文献综述”）作为毕业设计（论文）答辩委员会对学生答辩资格审查的依据材料之一。此报告应在指导教师指导下，由学生在毕业设计（论文）工作前期内完成，经指导教师签署意见及所在专业审查后生效；2开题报告内容必须用黑墨水笔工整书写或按教务处统一设计的电子文档标准格式（可从教务处网页上下载）打印，禁止打印在其它纸上后剪贴，完成后应及时交给指导教师签署意见；3 “文献综述”应按论文的格式成文，并直接书写（或打印）在本开题报告第一栏目内，本科学生写文献综述的参考文献应不少于15篇（专科生不少于10篇，不包括辞典、手册）；4有关年月日等日期的填写，应当按照国标GB/T 740894数据元和交换格式、信息交换、日期和时间表示法规定的要求，一律用阿拉伯数字书写。如“2002年4月26日”或“2002-04-26”。 毕 业 设 计（论 文）开 题 报 告1结合毕业设计（论文）课题情况，根据所查阅的文献资料，撰写1500字左右（本科生200字左右）的文献综述(包括目前该课题在国内外的研究状况、发展趋势以及对本人研究课题的启发)：文 献 综 述在进行毕业设计之前，必须做好一切准备工作，而收集有关设计课题研究方面的资料、文献是最为重要的。在设计工作开始时，只有对课题研究的内容有了，充分地了解，才会有设计目的和方向；所以收集、查阅有关文献资料是必要的。在设计之前首先应该对国内外的模具发展现状和发展趋势有所了解，以便在设计过程中能够正确、合理地设计出一套模具。下面就先分析一下国内外的模具发展现状与发展趋势以及我国的模具发展现状。1. 目前，电子、汽车、电机、电器、仪器、仪表、家电、通讯和军工等产品中，6080的零部件，都要依靠模具成型。用模具成型的制件所表现出来的高精度、高复杂性、高一致性、高生产率和低消耗，是其他加工制造方法所无法比拟。模具在很大程度上决定着产品的质量、效益和开发能力。随着工业产品质量的不断提高，冲压产品的生产正呈现出多品种、少批量，复杂、大型、精密，更新换代速度快等变化特点，冲压模具也正向高效、精密、长寿命、大型化方向发展。为适应市场的变化，随着计算机技术和制造技术的迅速发展，冲压模具设计与制造技术正在由手工设计、依靠工人的经验和常规的机械加工技术向计算机辅助设计（CAD）、数控加工中心进行切削加工、数控线切割、数控电火花等为核心的计算机辅助设计与制造（CAD/CAM）技术方面转变。模具的发展现状及发展趋势如下详述：1）.CAD/CAM技术的应用：CAD/CAM是一项高科技、高效益的系统工种，是模具设计与制造行业的有效辅助工具；通过它能够对产品、模具结构、成型工艺、数控加工及成本等进行设计和优化。现在已经广泛地应用与模具的设计与制造加工的过程中，并还在不断地发展和创新。2）.模具标准件：有关专家认为，模具标准件的应用将日渐广泛，模具标准化及模具标准件的应用能极大地影响模具制造周期。使用模具标准件不但能缩短模具制造周期，而且能提高模具质量和降低模具制造成本.我国的模具标准化程度达到30%以下，而国外先进国家达到70%80%左右。这样，不仅有利于国内的模具制造的发展，也有利于模具的国际化发展。3）.模具的制造精度：国外的制造水平能够是制造公差达到0.0030.005 mm，表面的粗糙度达到Ra 0.0002 mm以下（花10以上）；我国的制造水平可以是制造公差达到0.010.02 mm,模具表面的粗糙度达到Ra0.00160.0008 mm（花78）。由此可见，如今模具技术的发展水平还是很高的，但也可以看出我国在这方面的技术与国外先进国家还有很大的差距。4）.模具的使用寿命：国外的冲压模具的使用寿命，（合金钢制模）5001000万次，（硬质合金制模）2亿次；我国的冲压模具的使用寿命分别为：100400万次，60001亿次。模具的使用寿命的加长就意味着模具的制造成本降低，从而提高了生产效益。5）.模具的加工制造设备：国外已经广泛地使用了数控加工中心，线切割，电火花，化学腐蚀等先进的设备，大大地提高了模具的制造周期。2.我国的模具业的发展现状：进入21世纪，随着科学技术的发展，我国的工业化程度也有了很大地提高，特别是在模具行业有了很大地发展。如：在模具设计与制造上，不但自己可以制造一些大型，精密，复杂，高效，长寿命的模具，并且能够出口到国外，打开国外的市场。但是，目前我国的冲压技术与工业发达国家相比还相当落后，主要原因是我国在冲压基础理论及成型工艺，模具标准化，模具设计，模具制造工艺及设备等方面与工业发达国家尚有相当大的差距，导致我国的模具在寿命，效率，加工精度，生产周期等方面与工业发达国家的模具相比差距相当大。因此这就需要我们努力去研究，推动我国模具业的发展。3.在查阅、收集有关资料的时候，不仅使我对模具业的发展现状及发展趋势、模具的设计与制造技术等有了更多，更全面地了解；而且收集到了许多有关本课题的研究，与本课题相关、相似的东西，查找各种有关模具设计与制造方面的经验公式，和经验数据；通过查阅资料和文献能够将课堂上所学习到的理论知识，与实际生产当中的实例相结合去更好地成设计任务；并且使我在课程设计上有了更多的设计思路，也有了更多的考虑空间，同时也使我在设计的过程中能够从多方面地去考虑问题模具设计的合理性及对设计好的模具在工作过程中可能会出现的问题及解决办法。 毕 业 设 计（论 文）开 题 报 告本课题的研究思路（包括要研究或解决的问题和拟采用的研究方法、手段（途径）及进度安排等）：1. 先通过收集和查阅各种文献资料和与同学老师的交流、指导，对目前国内外的模具（冲压模具）的发展状况和发展趋势进行深入的了解，预计用时间四天；2. 拿到工件的结构简图，对工件进行结构形状、尺寸精度、加工工艺性等方面作出详细地分析，并查阅相关资料看是否符合常规零件结构设计，预计用时两天；3. 经过对工件的结构工艺性分析，拟订可行的冲压工艺方案，并经过分析，研究、比较，选择一种最为合理的冲压工艺作为生产应用，估计用时间两天；4. 进行主要的设计计算，利用各种经验公式或者经验数据对冲压力（冲裁力、卸料力、总冲压工艺力），压力中心的位置，工作零部件的刃口尺寸的设计计算以及弹性卸料元件橡胶的设计，预计需用时间四天；5. 根据工件的结构，材料，生产批量来进行模具的总体设计，包括模具的类型，定位方式，卸料方式，导向方式等方面的设计；在设计中，应该综合考虑模具的安装，维修，生产效率等，预计用时间两天；6. 对模具的主要零部件进行设计，主要有凸模、凹模、定位板、卸料板、模架和导柱导套等零件，根据工作需要的强度来设计尺寸，包括各零件的图纸，预计需用时间五天；7. 模具的总装图和工作原理（有装配简图）需要用时间两天；8. 模具主要零部件的加工工艺过程（凸模、凹模、定位板、卸料板）分析与设计，预计用时间两天；9. 模具的装配与调试，预计用时两天； 毕 业 设 计（论 文）开 题 报 告指导教师意见：1对“文献综述”的评语：2对本课题的研究思路、深度、广度及工作量的意见和对设计（论文）结果的预测： 指导教师： 年 月 日所在专业审查意见： 负责人： 年 月 日毕业设计/论文任务书 题目： 转换支架模具设计 内容：（1）设计说明书（2）转换支架模具装配图（3）模具各主要零件图（4）典型零件的加工工艺卡 原始资料:设计题目：转换支架材料：Q235料厚：3插图清单图1.2.01 零件图.3图3.1.01 零件排样图5图3.3.01 凹模型口图.7图1 冲孔凸模.12图1 落料凸模.13图5.2.01 固定挡料销.14图6.1.01 模柄.16图7.01 转换支架模具装配图18表格清单表3.1.01 条料计算.5表-3.2.01 冲压力计算.6表3.4.01 模具刃口尺寸计算.8表3.5.01 卸料橡胶设计计算.10表9.1.01 转换支架模具的装配.20（转换支架模具设计）摘 要本设计的题目是加工转换支架的复合模具，通过对方案的选择排样的计算，冲压力的计算和压力中心确定的计算以及凸凹模刃口的计算等使本副模具基本符合冲压要求。复合模具的精度要求很高导向要求十分精确，在设计本副模具时遇到很大的阻力经过对各方案的选择和排除最终才选择此方案。通过近三周的拼搏，本副级进模具设计终于完成。由于设计者的能力所限，设计中的不足之处还有好多。还有复合模具益采用四角导柱模架实用模具技术手册，本模具的冲裁力不大精度基本能保证的前提下选择了中间导柱模架。相信不久本模具投入市场一定能带来很好的效益服务大众，服务社会。关键词:复合模、 Mold design of the processing quartz form iron core Abstract： Topic that design originally to process quartz form compound die ,iron of core enter mould , rank the calculation of kind through the choice to the scheme, it makes this pair of moulds accord with the request of pressing basically to press calculation , calculation which the pressure centre confirm and calculation of the protruding concave mould blade of strength ,etc., compound die enter precision of mould expect very much and lead demanding to be very accurate, the obstruction that it is very great to meet while designing this pair of moulds is through and gets rid of and chooses this scheme to the choice of every scheme finally. Through the striving of nearly three weeks, this each enters mold design to finish at last.The because designer one it restrict with ability, have much weak point in design. There is compound die that enters benefit of the mould and adopts four mao and leads the post mould shelf - practical mould technical manual , the blanking strength of this mould leads the post mould shelf the middle not quite choosing under the prerequisite that the precision can be guaranteed basically. Can unquestionably bring very good benefit and serve the general public to invest the market while believing a mould soon, serve the society. 毕业设计/论文说明书目录绪论1第一章 零件工艺性分析.3第二章 拟订冲裁件的工艺方案4第三章 主要设计计算.53.1 排样方式的确定极其计算53.2 冲压力计算63.3 压力中心的确定及相关计算.63.4 模具工作零件刃口尺寸计算的73.5卸料装置设计.9第四章 模具总体设计114.1 模具类型的选择.114.2 定位方式的选择.114.3 卸料，出件方式的选择.114.4 导向方式的选择.11第五章 主要零部件设计.125.1 工作零件的结构设计 冲孔凸模设计125.1.2 落料凸模设计.125.1.3 凹模设计13 5.1.3定位零件的设计145.3 导料板的设计145.4 卸料部件的设计145.4.1卸料板的设计.155.4.2卸料螺钉的选用.15第六章 模架及其它零部件设计.166.1 模柄的设计166.2 模架的设计.16第七章 模具总装图18第八章 冲压设备的选定.19第九章 模具的装配.20设计总结.21致谢22参考文献23河南机电高等专科学校毕业设计（论文）评语（学生自行填写后，交指导教师处审核后打印，由指导教师进行签名）学生姓名： 班级: 学号： 题 目： 综合成绩： 指导者评语：【填写说明】：1本格式仅适合于打印情况下使用，要求在学生答辩前完成，请指导者将评语内容直接打印在本栏目内（用4号仿宋体，A4纸型），禁止打印在其它纸上后剪贴在此处。2评语填写内容：1）完成“毕业设计（论文）任务书”规定工作的情况；2）创新性评价；3）写作的规范化程度；4）存在的问题；5）建议成绩评定；6）是否可以提交答辩。 指导者(签字)： 年 月 日毕业设计（论文）评语评阅者评语：【填写说明】：1本格式仅适合于打印情况下使用，要求在学生答辩前完成，请评阅者将评语内容直接打印在本栏目内（用4号仿宋体，A4纸型，不必打印在“指导者评语”的背面），禁止打印在其它纸上后剪贴在此处。2评语填写内容：1）论文选题的价值与意义； 2）创新性评价；3）工作量大小； 4）写作的规范化程度；5）存在的问题； 6）建议成绩评定；7）是否可以提交答辩。 评阅者(签字)： 年 月 日答辩委员会（小组）评语：【填写说明】：1本栏目由答辩委员会（小组）根据学生答辩时回答问题的情况（知识面掌握、逻辑思维能力、口头表达能力、回答问题的正确性等）以及各成员投票的综合结果填写，并给出成绩（可手写，也可打印，但必须与“评阅者评语”打印在同一张纸上）。2禁止打印在其它纸上后剪贴在此处。 答辩委员会（小组）负责人(签字)： 年 月 日河南机电高等专科学校毕业设计论文论文题目：转换支架模具设计系 部 材料工程系 专 业 模具设计与制造 班 级 学生姓名 学 号 指导教师 2006年 5 月 10 日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