铜垫片冲压成形工艺与模具设计【落料-冲孔复合模】

铜垫片冲压成形工艺与模具设计【落料-冲孔复合模】,落料-冲孔复合模,铜垫片冲压成形工艺与模具设计【落料-冲孔复合模】,垫片,冲压,成形,工艺,模具设计,落料,冲孔,复合 中期检查表学生姓名学 号指导教师选题情况课题名称铜垫片冲压成形工艺与模具设计难易程度偏难适中偏易工作量较大合理较小符合规范化的要求任务书有无开题报告有无外文翻译质量优良中差学习态度、出勤情况好一般差工作进度快按计划进行慢中期工作汇报及解答问题情况优良中差中期成绩评定：所在专业意见： 负责人： 2014 年 2 月 22日设计任务书系 部： 专 业： 学 生： 学 号： 设计题目： 铜垫片冲压成形工艺与模具设计 起迄日期: 指导教师： 2013 年 11 月2日毕 业 设 计 任 务 书1本毕业设计课题来源及应达到的目的： 在完成该课题之后，应对冲压工艺生产较为熟悉，能熟练掌握相关设计手册的使用，能独立完成一套模具的设计及模具工作零件加工工艺的编制，能够运用软件完成模具装配图及零件图的绘制。2本毕业设计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）：（1）了解目前国内外冲压模具的发展现状；（2）工件的结构工艺分析；（3）折弯垫片冲压成形与模具设计，并编写设计说明书一份；（4）绘制模具总装图一张，并画出非标准零件的零件图； （5）编制主要零件加工工艺过程卡。原始资料：工件图材料：Q215生产量：大批量所在专业审查意见：负责人： 年 月 日系部意见：系领导： 年 月 日II 机 械 加 工 工 艺 过 程 卡 零件号零 件 名 称凸模工序号工 序 名 称设 备夹 具刀 具量 具工 时名 称型 号名 称规 格名 称规 格名 称规 格01020304050607080910下料锻造热处理粗车外形精车外形热处理磨外圆抛光钳修锯床锻床退火炉车床车床淬火炉磨床油石卡盘卡盘带锯锻锤车刀车刀砂轮油石直尺直尺游标卡尺千分尺千分尺 编制 校对 审核 批准 机 械 加 工 工 序 卡 工序名称粗铣六面工序号03零件名称凹模零件号02-11零件重量同时加工零件数1材 料毛 坯牌 号硬 度种 类重 量Cr1248-52HRC锻 件设 备夹 具名 称辅 助工 具名 称型 号铣床虎钳垫块安 装工 步安装及工步说明刀 具量 具走 刀长 度走 刀次 数切 削 深 度进给量主 轴转 速切 削速 度基 本工 时二次2铣上、下平面30面铣刀游标卡尺50.2mm200/ min2000r/min二次1铣四周面10立铣刀游标卡尺20.5mm60/ min2000r/mi设 计 者指 导 教 师共 页第 页设计说明书毕业设计题目：铜垫片冲压成形工艺与模具设计系 部 专 业 班 级 学生姓名 学 号 指导教师 2014年4月16日铜垫片冲压成形工艺与模具设计摘要：本设计题目为垫片冲裁模，体现了典型冲裁模的设计要求、内容及方向，有一定的设计意义。通过对该模具的设计，加强了设计者对冲裁模设计基础知识的理解和运用，为设计更复杂的冲裁模具做好了铺垫。本设计运用冲裁工艺及模具设计的基础知识，首先分析了板材的性能要求，为选取模具的类型做好了准备；然后计算了冲裁件的冲裁力，便于选取压力机吨位及确定压力机型号；最后分析了冲裁件的特征，便于确定模具的设计参数、设计要点及卸件装置。本设计采用了冲孔落料复合模成形垫片。成形原理可划分为三个阶段：首先冲孔凸模与凹模共同作用先冲出四个5mm，而后利用第一步冲出的四个5mm孔做精确定位使外形凸模与凹模共同作用使工件落料成形，最后一步是进行折弯。关键词：冲孔落料复合模 冲孔凸模 凹模 压力机吨位 Abstract：The topic for the design is pad blanking die design,It has manifested the typical blanking dies design request, the content and the direction, has certain design significance.Through the design of the component mold, strengthens the designers understand and utilize to the blanking die design basical knowledge,has prepareed for designing more complex blanking die.The design has utilize blanking craft and the basical knowledge of the mold design, has first analyzed the property requirement of the plate , has prepared for selecting the mold type；then has calculated the blanking strength,has advantaged to select the press tonnage and determine press model; Finally has analyzed the characteristic of the products, has advantaged to finite the mold design variable,the design main point and shedder. This design used piercing and blanking progressive die to form the products.The forming principle can be divided to two stages: First, piercing punch and die affect together and pierce four holes of3.2mm and one hole of8.5mm,then use the four holes and the one hole as pinpoint to make the product formed.Key word: Piercing and blanking progressive die Piercing punch Press TonnageII设计评语学生姓名： 班级: 学号: 题 目： 铜垫片冲压成形工艺与模具设计 综合成绩： 指导者评语：1）该同学工作态度不够认真，能基本完成毕业设计任务；2）该同学制订出了较合理的冲压模具结构；3）该同学设计说明书内容比较完整，计算较正确，格式一般；4）该同学装配图、零件图设计比较合理，视图表达正确；5）可以提交答辩。 指导者(签字)： 年 月 日毕业设计评语评阅者评语：该同学毕业设计任务来自生产实际，工作量大小适中，能够按照要求完成设计说明书的撰写，零件图上存在较多问题，建议成绩评定为及格，可以提交答辩。 评阅者(签字)： 年 月 日答辩委员会（小组）评语： 答辩委员会（小组）负责人(签字)： 年 月 日 1 绪论1.1国内模具的现状我国模具近年来发展很快，据不完全统计，2003年我国模具生产厂点约有2万多家，从业人员约50多万人，2004年模具行业的发展保持良好势头，模具企业总体上订单充足，任务饱满，2004年模具产值530亿元。进口模具18.13亿美元，出口模具4.91亿美元，分别比2003年增长18%、32.4%和45.9%。进出口之比2004年为3.69:1，进出口相抵后的进净口达13.2亿美元，为净进口量较大的国家。在2万多家生产厂点中，有一半以上是自产自用的。在模具企业中，产值过亿元的模具企业只有20多家，中型企业几十家，其余都是小型企业。近年来，模具行业结构调整和体制改革步伐加快，主要表现为：大型、精密、复杂、长寿命中高档模具及模具标准件发展速度快于一般模具产品；专业模具厂数量增加，能力提高较快；三资及私营企业发展迅速；国企股份制改造步伐加快等。1.2国内模具的发展趋势 巨大的市场需求将推动中国模具的工业调整发展。虽然我国的模具工业和技术在过去的十多年得到了快速发展，但与国外工业发达国家相比仍存在较大差距，尚不能完全满足国民经济高速发展的需求。未来的十年，中国模具工业和技术的主要发展方向包括以下几方面: 1） 模具日趋大型化； 2）在模具设计制造中广泛应用CAD/CAE/CAM技术； 3）模具扫描及数字化系统； 4）在塑料模具中推广应用热流道技术、气辅注射成型和高压注射成型技术；5）提高模具标准化水平和模具标准件的使用率； 6）发展优质模具材料和先进的表面处理技术； 7）模具的精度将越来越高； 8）模具研磨抛光将自动化、智能化；9）研究和应用模具的高速测量技术与逆向工程；10）开发新的成形工艺和模具。1.3国外模具的现状和发展趋势模具是工业生产关键的工艺装备，在电子、建材、汽车、电机、电器、仪器仪表、家电和通讯器材等产品中，6080的零部件都要依靠模具成型。用模具生产制作表现出的高效率、低成本、高精度、高一致性和清洁环保的特性，是其他加工制造方法所无法替代的。模具生产技术水平的高低，已成为衡量一个国家制造业水平高低的重要标志，并在很大程度上决定着产品的质量、效益和新产品的开发能力。近几年，全球模具市场呈现供不应求的局面，世界模具市场年交易总额为600650亿美元左右。美国、日本、法国、瑞士等国家年出口模具量约占本国模具年总产值的三分之一。国外模具总量中,大型、精密、复杂、长寿命模具的比例占到50%以上；国外模具企业的组织形式是大而专、大而精。2004年中国模协在德国访问时，从德国工、模具行业组织-德国机械制造商联合会（VDMA）工模具协会了解到，德国有模具企业约5000家。2003年德国模具产值达48亿欧元。其中（VDMA）会员模具企业有90家，这90家骨干模具企业的产值就占德国模具产值的90%，可见其规模效益。 随着时代的进步和技术的发展，国外的一些掌握和能运用新技术的人才如模具结构设计、模具工艺设计、高级钳工及企业管理人才，他们的技术水平比较高故人均产值也较高我国每个职工平均每年创造模具产值约合1万美元左右，而国外模具工业发达国家大多1520万美元，有的达到 2530万美元。 2 冲孔落料的模具设计 2.1工件图及技术要求1.零件名称：铜垫片2.材 料：H623.材料厚度：0.5mm4.未注公差按14级5.批量生产2.2 任务要求1 完成制件工艺性分析，确定制件成形工艺方案。2 完成模具装配图设计，绘制模具总装图。3 完成模具零件图设计，绘制模具零件图。4 撰写毕业设计说明书。 2.3冲压件工艺性分析： 2.3.1结构工艺性分析 1.）该工件形状简单，规则，使用单次冲裁 2.)该冲件处有尖角，但图纸上无特殊要求，用圆角过渡 3.)冲件无悬臂和狭槽 4.)最小孔边距为（4-1.5）/2=1.251.5t，孔与孔之间的距离3.3-0.75-0.5=2.05t,合理 5.)冲裁件端部带圆弧，因为该材料比较软，所以不会出现台阶 6.)受凸模强度和刚度限制，冲裁件上的孔不能太小。因为最小孔d=10.9t,所以合理 2.3.2公差和表面粗糙分析1.) 该工件最小公差尺寸为1，上公差为+0.12,下公差为0，查的精度等级为IT12级，复合模冲孔能达到9级，落料能达到10级。2.) 表面粗糙度，图纸未作特殊要求3.) 冲裁材料H62，冲裁性能比较好，适合冲裁2.4工艺方案制定 1. 采用单冲模，分别做两副模具，冲孔模与落料模，但这样操作制件两次定位精度低，两副模具经济成本不高但模具寿命相对也较低，但需要劳动力多，管理成本多，分摊在单件上的成本较高，生产操作不安全。 2. 采用级进模即将冲孔和落料分成两个不同工位但装在同一副模具上同时完成不同工序冲裁，这种方法能使冲件精度较高，但是不适合批量生产，而且制造成本比较高。 3.采用复合模即冲孔和落料同时进行，一次定位能提高冲件精度且模具结构相对简单，制作费用较低，劳动力需求少，适合批量生产，制造成本一般。结论：综合以上的比较，选择复合模工艺方案比较可行，符合各方面要求 3 冲压零件主要参数的计算3.1搭边值的确定和条料宽度的确定查课本表格2-6得普通冲裁的塔边值，材料厚0.5mm，弹压卸料，工件宽度L小于50毫米，即a=1.0,a1=1.2 由表2-7得剪料公差为0.4，条料宽度为27.9mm,材料利用率87%3.2 压力中心及冲压力计算a.)冲裁力：Fp=1.3*68.01*0.5*225=9946.5Nb.)卸料力：FQ=0.04*9946.5=397.86Nc.)推件力：查表2-10得凹模刃口高h=4 FQ1=0.05*9946.5*4/0.5=3978.6N 采用弹压卸料和下出件装置： F=9946.5+397.86+3978.6=14322.96N d.)压力中心计算：冲孔 O 0 (0, 0) L0=4.71O 2 (3.3,0) L2=3.14落料 O 1 (2.3,0) L1=6.28O3 (7.4 ,2 ) L3=15.5O4 (7.4 ,-2) L4=15.5O5 (19.2,2.7) L5=5O6 (19.2,-2.7) L6=5O7 (22.5,2.4) L7=1.6O8 (22.5, 1.8) L8=1.6 O9 (22.5,-1.8) L9=1.6O10 (22.5,-2.4) L10=1.6X0=4.71*0+3.14*3.3+6.28*2.3+15.5*7.4+15.5*7.4+5*19.2+5*19.2+1.6*22.5+1.6*22.5+1.6*22.5+1.6*22.5/61.5313Y0=0即压力中心为（13，0）3.3压力机标准公称压力确定 P大于等于（1.11.3）F总=（1.11.3）*14KN=(15.418.2)KN根据表2-2得选择压力机为开式压力机，公称压力为100KN，压力机型号为J-23-10主要技术参数为：3.4凹模周界尺寸计算和模具典型结构选择1.）计算凹模周界L*B：外形尺寸按下式计算：L=2(L1+L2)式中，L1为压力中心到最远型孔的壁距离，按照孔型的布置，凹模的外形尺寸L1分别为L1（平行）=12.75垂直与送料方向的凹模外形最远壁间距L2（垂直）=2.7由表2-9查得L2=20垂直送料方向的凹模外形尺寸L垂直=2*（12.75+20）=65.5平行送料方向的凹模外形尺寸L平行=2* (2.7+20)=58L（垂直）=65.5大于L（平行）=58 所以该模具送料方向为纵向送料由从向送料，弹压卸料而选择典型组合，查手册的L*B=80*80g.冲裁凸凹模刃口尺寸计算凸凹模考虑用配作法 查表2-13 : =0.09t=0.09*0.5=0.045mm =0.12t=0.12*0.5=0.06mm Z=-=0.06-0.045=0.015mm =/4尺寸：1.5冲孔磨后变小 IT14 =0.25 x=0.5 =0.25/4=0.0625b凸=(1.5+0.5*0.25)0-0.06=1.63 0-0.06冲孔凹模按照凸模在最小间隙与最大间隙制件配做尺寸：1 0+0.12 冲孔磨后变小 IT12 =0.12 x=0.75 =0.12/4=0.03b凸=(1+0.75*0.12)0-0.03 =1.09 0-0.03冲孔凹模按照凸模在最小间隙与最大间隙制件配做尺寸：R2 落料后变大 IT14 =0.25 x=0.5 =0.25/4=0.06 B凹=(2-0.5*0.25) 0+0.06 =1.88 0+0.06落料凸模按照凹模在最小间隙与最大间隙之间配做尺寸：4 0-0.16 落料后变大 IT12 =0.16 x=0.75 =0.16/4=0.04 B凹=（4-0.75*0.16）0+0.04 =3.88 0+0.04落料凸模按照凹模在最小间隙与最大间隙之间配做尺寸：19 0-0.24 落料磨后变大 IT12 =0.24 x=0.75 =0.24/4=0.06 B凹=(19-0.75*0.24) 0+0.06 =18.82 0+0.06 落料凸模按照凹模在最小间隙与最大间隙之间配做尺寸： 6.5 0-0.2 落料后变大 IT12 =0.2 x=0.75 =0.2/4=0.05 B凹=(6.5-0.75*0.2) 0+0.05 =6.35 0+0.05落料凸模按照凹模在最小间隙与最大间隙之间配做尺寸：5 0-0.16 落料后变大 IT12 =0.16 x=0.75 =0.16/4=0.04 B凹=(5-0.75*0.16) 0+0.04 =4.88 0+0.04 落料凸模按照凹模在最小间隙与最大间隙之间配做尺寸：5.4 0-0.1 落料后变大 IT12 =0.1 x=0.75 =0.1/4=0.03 B凹=(5.4-0.75*0.1) 0+0.03 =5.33 0+0.03 落料凸模按照凹模在最小间隙与最大间隙之间配做尺寸：2.3 落料后变大 IT14 =0.25 x=0.5 =0.25/4=0.06 B凹=(2.3-0.5*0.25) 0+0.06 =2.18 0+0.06 落料凸模按照凹模在最小间隙与最大间隙之间配做尺寸：30+0.12 落料后变小 IT12 =0.12 x=0.75 =0.12/4=0.03 B凹=(3+0.75*0.12)0-0.03 =3.09 0-0.03 落料凸模按照凹模在最小间隙与最大间隙之间配做尺寸: 4.20.1 磨后尺寸不变 IT13 =0.2 x=0.75 =0.2/4=0.05 C凸=C凹=(4.1+0.1) 0.2/8=4.20.03尺寸：3.3 磨后尺寸不变 IT14 =0.3 x=0.5 =0.3/4=0.08 C凸=C凹=(3.3+0.15)0.3/8=3.450.043.5选择标准模架 由于冲件精度要求不高，选择对角到导柱的模架，该模架适合横，纵送料方向h.弹簧选择F卸/4=P *Fx 398/4=p *Fx根据手册查表1的取矩形界面符合弹簧即，选择25*90的规格1导柱 2下模座 3下固定板 4凸凹模 5弹压卸料板 6挡料销 7上模座 8上垫板9 浮动模柄 10 调节螺钉 11 压板 12 橡胶 13 螺钉 14 上固定板 15 中垫板 16 落料凹模17 导套 18顶杆 19 推板 20 冲孔凸模结构特点：模具导向：制件精度不高，采用对角导柱，用导柱12滑动导套8导向定位卸料：卸料板5不仅起卸料作用，同时可导向凸模的作用。卸料板材料为45钢，不热处理仍符合各项要求模具结构小，凹模采用整体结构；凸模用铆接式固定凸模选用Cr12MoV制作，热处理5862HRC，耐磨损 制件精度不高，对模具定位精度也不高，挡料销定位挡料，正确，方便 凸模固定板采用Q235，凹模采用Cr12Mov热处理6064HRC，上、下模用HT250制作，经调质 导柱、导套，采用20钢热处理5864（渗碳）凸模，固定板型腔，凹模，卸料板，采用快丝切割冲模工作过程将条料校平送入工作范围，挡料销定位，压力机滑块下行上模座向下运动卸料板将条料压平至凹模上，然后模具向上运动条料被卸料板卸下，推板推料，顺利完成冲压工序设计小结此课题来的比较晚，本来想放弃做毕业设计，因为我是委培生，原因很多，毕业证书不能拿到，工作的忙碌，路途的遥远，但后来想想，以上的原因也不能成为什么，大学三年，也应该有所成就，最后决定还是给自己一个交代，认认真真完成这样一生只有一次的毕业设计。拿到课题，分析之后发现，将要设计的是一副复合冲裁模，这样一来，在公司实习的东西，就只能用到一点点，我是学级进模的，相对来说，复合模应该是在这之前所需要经过的一个阶段，而在公司我没去学过单冲模，所以所需的一切我必须从以前的课本和记忆中寻找。参看典型毕业设计，让我对设计的步骤有了一定的了解，翻阅参考书，利用一段时间进行了各类工艺分析和各个尺寸的计算，由于有一定的基础，这些方面做起来也比较轻松，接下来才进入正题模具图的绘制我们公司主要用的软件是AutoCAD，所以一个设计员对CAD的操作熟练度是不可忽视的，由于经过一个月的强化练习，我对CAD的熟练度达到了一个很高的程度，所以绘制这样的模具的是难不到我的，我参阅课本的典型倒装复合模，对自己的工件进行总装图的设计。手册中查阅出了典型的模座布置，然后配上了各个板的大小，并且对各板的连接配上了销钉和螺钉，我选择的是弹簧弹压卸料，因为我认为用弹簧卸料要比其他方式都要好，用圆挡料销定位，推板通过顶杆推件，凸模凹模均采用Cr12Mov材料，有利于磨损。整个模具结构简单，模具寿命好，适合批量生产。此次毕业设计，我运用了公司与学校所学知识结合，利用工作空出时间，参考各类书籍独立完成的，由于对复合模的知识有所欠缺，难免出现错误，今后也会一一改正。然而在学习过程中，首先我明白了做学问要一丝不苟，对于出现的任何问题和偏差都不要轻视，要通过正确的途径去解决，在做事情的过程中要有耐心和毅力，不要一遇到困难就打退堂鼓，只要坚持下去就可以找到思路去解决问题的。在工作中要学会与人合作的态度，认真听取别人的意见，这样做起事情来就可以事倍功半。毕业设计的完成既为大学三年划上了一个完美的句号，也为将来的人生之路做好了一个很好的铺垫。 致谢三年一晃而过，校园生活已成回忆。在学校里，同学老师都很照顾我。我深表感谢。这次毕业设计做的很冲忙，有太多的纰漏，请老师多多包容。虽然我不是学校真正的学生，也不敢说为学校争光，但我也不会替学校摸黑。这三年，在学校学到很多专业知识，这可能就是我以后的衣食父母，我很感激。这是在学校交的最后一份作业了，主观上还是希望能完美结束，做到善始善终。但走出社会后，好多事情超出了自己能掌握的范围，与本意相违背了。考虑的不够好的希望给予指正。 参考文献 1韩森和主编.冷冲压工艺及模具设计制造.M 高等教育出版社.2006.22冯炳尧等.模具设计与制造简明手册.M上海科学技术出版社.2008.6 3金大鹰主编。机械制图。M机械工业出版设2006.811Int J Adv Manuf Technol (2002) 19:253259 2002 Springer-Verlag London Limited An Analysis of Draw-Wall Wrinkling in a Stamping Die Design F.-K. Chen and Y.-C. Liao Department of Mechanical Engineering, National Taiwan University, Taipei, Taiwan Wrinkling that occurs in the stamping of tapered square cups and stepped rectangular cups is investigated. A common characteristic of these two types of wrinkling is that the wrinkles are found at the draw wall that is relatively unsup- ported. In the stamping of a tapered square cup, the effect of process parameters, such as the die gap and blank-holder force, on the occurrence of wrinkling is examined using finite- element simulations. The simulation results show that the larger the die gap, the more severe is the wrinkling, and such wrinkling cannot be suppressed by increasing the blank-holder force. In the analysis of wrinkling that occurred in the stamping of a stepped rectangular cup, an actual production part that has a similar type of geometry was examined. The wrinkles found at the draw wall are attributed to the unbalanced stretching of the sheet metal between the punch head and the step edge. An optimum die design for the purpose of eliminating the wrinkles is determined using finite-element analysis. The good agreement between the simulation results and those observed in the wrinkle-free production part validates the accuracy of the finite-element analysis, and demonstrates the advantage of using finite-element analysis for stamping die design. Keywords: Draw-wall wrinkle; Stamping die; Stepped rec- tangular cup; Tapered square cups 1. Introduction Wrinkling is one of the major defects that occur in the sheet metal forming process. For both functional and visual reasons, wrinkles are usually not acceptable in a finished part. There are three types of wrinkle which frequently occur in the sheet metal forming process: flange wrinkling, wall wrinkling, and elastic buckling of the undeformed area owing to residual elastic compressive stresses. In the forming operation of stamp- ing a complex shape, draw-wall wrinkling means the occurrence Correspondence and offprint requests to: Professor F.-K. Chen, Depart- ment of Mechanical Engineering, National Taiwan University, No. 1 Roosevelt Road, Sec. 4, Taipei, Taiwan 10617. E-mail: fkchenL50560 w3.me.ntu.edu.tw of wrinkles in the die cavity. Since the sheet metal in the wall area is relatively unsupported by the tool, the elimination of wall wrinkles is more difficult than the suppression of flange wrinkles. It is well known that additional stretching of the material 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 stresses leads to failure by tearing. Hence, the blank-holder force must lie within a narrow range, above that necessary to suppress wrinkles on the one hand, and below that which produces fracture on the other. This narrow range of blank-holder force is difficult to determine. For wrinkles occurring in the central area of a stamped part with a complex shape, a workable range of blank-holder force does not even exist. In order to examine the mechanics of the formation of wrinkles, Yoshida et al. 1 developed a test in which a thin plate was non-uniformly stretched along one of its diagonals. They also proposed an approximate theoretical model in which the onset of wrinkling is due to elastic buckling resulting from the compressive lateral stresses developed in the non-uniform stress field. Yu et al. 2,3 investigated the wrinkling problem both experimentally and analytically. They found that wrinkling could occur having two circumferential waves according to their theoretical analysis, whereas the experimental results indi- cated four to six wrinkles. Narayanasamy and Sowerby 4 examined the wrinkling of sheet metal when drawing it through a conical die using flat-bottomed and hemispherical-ended punches. They also attempted to rank the properties that appeared to suppress wrinkling. These efforts are focused on the wrinkling problems associa- ted with the forming operations of simple shapes only, such as a circular cup. In the early 1990s, the successful application of the 3D dynamic/explicit finite-element method to the sheet- metal forming process made it possible to analyse the wrinkling problem involved in stamping complex shapes. In the present study, the 3D finite-element method was employed to analyse the effects of the process parameters on the metal flow causing wrinkles at the draw wall in the stamping of a tapered square cup, and of a stepped rectangular part. A tapered square cup, as shown in Fig. 1(a), has an inclined draw wall on each side of the cup, similar to that existing in a conical cup. During the stamping process, the sheet metal on the draw wall is relatively unsupported, and is therefore 254 F.-K. Chen and Y.-C. Liao Fig. 1. Sketches of (a) a tapered square cup and (b) a stepped rectangular cup. prone to wrinkling. In the present study, the effect of various process parameters on the wrinkling was investigated. In the case of a stepped rectangular part, as shown in Fig. 1(b), another type of wrinkling is observed. In order to estimate the effectiveness of the analysis, an actual production part with stepped geometry was examined in the present study. The cause of the wrinkling was determined using finite-element analysis, and an optimum die design was proposed to eliminate the wrinkles. The die design obtained from finite-element analy- sis was validated by observations on an actual production part. 2. Finite-Element Model The tooling geometry, including the punch, die and blank- holder, were designed using the CAD program PRO/ ENGINEER. Both the 3-node and 4-node shell elements were adopted to generate the mesh systems for the above tooling using 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 and Fig. 2. Finite-element mesh. are not for stress analysis. The same CAD program using 4- node shell elements was employed to construct the mesh system for the sheet blank. Figure 2 shows the mesh system for the complete set of tooling and the sheet-blank used in the stamping of a tapered square cup. Owing to the symmetric conditions, only a quarter of the square cup is analysed. In the simulation, the sheet blank is put on the blank-holder and the die is moved down to clamp the sheet blank against the blank-holder. The punch is then moved up to draw the sheet metal into the die cavity. In order to perform an accurate finite-element analysis, the actual stressstrain relationship of the sheet metal is required as part of the input data. In the present study, sheet metal with deep-drawing quality is used in the simulations. A tensile test has been conducted for the specimens cut along planes coinciding with the rolling direction (0) and at angles of 45 and 90 to the rolling direction. The average flow stress H9268, calculated from the equation H9268H11005(H9268 0 H11001 2H9268 45 H11001H9268 90 )/4, for each measured true strain, as shown in Fig. 3, is used for the simulations for the stampings of the tapered square cup and also for the stepped rectangular cup. All the simulations performed in the present study were run on an SGI Indigo 2 workstation using the finite-element pro- gram PAMFSTAMP. To complete the set of input data required Fig. 3. The stressstrain relationship for the sheet metal. Draw-Wall Wrinkling in a Stamping Die Design 255 for the simulations, the punch speed is set to 10 m s H110021 and a coefficient of Coulomb friction equal to 0.1 is assumed. 3. Wrinkling in a Tapered Square Cup A sketch indicating some relevant dimensions of the tapered square cup is shown in Fig. 1(a). As seen in Fig. 1(a), the length of each side of the square punch head (2W p ), the die cavity opening (2W d ), 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 cavity opening and the punch head is termed the die gap (G) in the present study, i.e. G H11005 W d H11002 W p . The extent of the relatively unsupported sheet metal at the draw wall is presumably due to the die gap, and the wrinkles are supposed to be suppressed by increasing the blank-holder force. The effects of both the die gap and the blank-holder force in relation to the occurrence of wrinkling in the stamping of a tapered square cup are investigated in the following sections. 3.1 Effect of Die Gap In order to examine the effect of die gap on the wrinkling, the stamping of a tapered square cup with three different die gaps of 20 mm, 30 mm, and 50 mm was simulated. In each simulation, the die cavity opening is fixed at 200 mm, and the cup is drawn to the same height of 100 mm. The sheet metal used in all three simulations is a 380 mm H11003 380 mm square sheet with thickness of 0.7 mm, the stressstrain curve for the material is shown in Fig. 3. The simulation results show that wrinkling occurred in all three tapered square cups, and the simulated shape of the drawn cup for a die gap of 50 mm is shown in Fig. 4. It is seen in Fig. 4 that the wrinkling is distributed on the draw wall and is particularly obvious at the corner between adjacent walls. It is suggested that the wrinkling is due to the large unsupported area at the draw wall during the stamping process, also, the side length of the punch head and the die cavity Fig. 4. Wrinkling in a tapered square cup (G H11005 50 mm). opening are different owing to the die gap. The sheet metal stretched between the punch head and the die cavity shoulder becomes unstable owing to the presence of compressive trans- verse stresses. The unconstrained stretching of the sheet metal under compression seems to be the main cause for the wrink- ling at the draw wall. In order to compare the results for the three different die gaps, the ratio H9252 of the two principal strains is introduced, H9252 being H9280 min /H9280 max , where H9280 max and H9280 min are the major and the minor principal strains, respectively. Hosford and Caddell 5 have shown that if the absolute value of H9252 is greater than a critical value, wrinkling is supposed to occur, and the larger the absolute value of H9252, the greater is the possibility of wrinkling. The H9252 values along the cross-section MN at the same drawing height for the three simulated shapes with different die gaps, as marked in Fig. 4, are plotted in Fig. 5. It is noted from Fig. 5 that severe wrinkles are located close to the corner and fewer wrinkles occur in the middle of the draw wall for all three different die gaps. It is also noted that the bigger the die gap, the larger is the absolute value of H9252. Consequently, increasing the die gap will increase the possibility of wrinkling occurring at the draw wall of the tapered square cup. 3.2 Effect of the Blank-Holder Force It is well known that increasing the blank-holder force can help to eliminate wrinkling in the stamping process. In order to study the effectiveness of increased blank-holder force, the stamping of a tapered square cup with die gap of 50 mm, which is associated with severe wrinkling as stated above, was simulated with different values of blank-holder force. The blank-holder force was increased from 100 kN to 600 kN, which yielded a blank-holder pressure of 0.33 MPa and 1.98 MPa, respectively. The remaining simulation conditions are maintained the same as those specified in the previous section. An intermediate blank-holder force of 300 kN was also used in the simulation. The simulation results show that an increase in the blank- holder force does not help to eliminate the wrinkling that occurs at the draw wall. The H9252 values along the cross-section Fig. 5. H9252-value along the cross-section MN for different die gaps. 256 F.-K. Chen and Y.-C. Liao MN, as marked in Fig. 4, are compared with one another for the stamping processes with blank-holder force of 100 kN and 600 kN. The simulation results indicate that the H9252 values along the cross-section MN are almost identical in both cases. In order to examine the difference of the wrinkle shape for the two different blank-holder forces, five cross-sections of the draw wall at different heights from the bottom to the line M N, 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-sections for both cases is similar. This indicates that the blank-holder force does not affect the occurrence of wrinkling in the stamp- ing of a tapered square cup, because the formation of wrinkles is mainly due to the large unsupported area at the draw wall where large compressive transverse stresses exist. The blank- holder force has no influence on the instability mode of the material between the punch head and the die cavity shoulder. 4. Stepped Rectangular Cup In the stamping of a stepped rectangular cup, wrinkling occurs at the draw wall even though the die gaps are not so significant. Figure 1(b) shows a sketch of a punch shape used for stamping a stepped rectangular cup in which the draw wall C is followed by a step DE. An actual production part that has this type of geometry was examined in the present study. The material used for this production part was 0.7 mm thick, and the stress strain relation obtained from tensile tests is shown in Fig. 3. The procedure in the press shop for the production of this stamping part consists of deep drawing followed by trimming. In the deep drawing process, no draw bead is employed on the die surface to facilitate the metal flow. However, owing to the small punch corner radius and complex geometry, a split occurred at the top edge of the punch and wrinkles were found to occur at the draw wall of the actual production part, as shown in Fig. 7. It is seen from Fig. 7 that wrinkles are distributed on the draw wall, but are more severe at the corner edges 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 simulation was first performed for the original design. The simulated shape 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 stretched Fig. 6. Cross-section lines at different heights of the draw wall for different 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 edge AB, and the radius of the punch corner A, as marked in Fig. 1(b), are considered to be the major reasons for the wall breakage. However, according to the results of the finite- element analysis, splitting can be avoided by increasing the above-mentioned radii. This concept was validated by the actual 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 original value. However, just as for the results obtained in the previous section for the drawing of tapered square cup, the effect of blank-holder force on the elimination of wrinkling was not found to be significant. The same results are also obtained by increasing the friction or increasing the blank size. We conclude that this kind of wrinkling cannot be suppressed by increasing the stretching force. Since wrinkles are formed because of excessive metal flow in certain regions, where the sheet is subjected to large com- pressive stresses, a straightforward method of eliminating the wrinkles is to add drawbars in the wrinkled area to absorb the redundant material. The drawbars should be added parallel to the direction of the wrinkles so that the redundant metal can be absorbed effectively. Based on this concept, two drawbars are added to the adjacent walls, as shown in Fig. 9, to absorb the excessive material. The simulation results show that the Draw-Wall Wrinkling in a Stamping Die Design 257 Fig. 9. Drawbars added to the draw walls. wrinkles at the corner of the step are absorbed by the drawbars as expected, however some wrinkles still appear at the remain- ing wall. This indicates the need to put more drawbars at the draw 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 for the stamping process is that the deformed shape of the sheet blank can be monitored throughout the stamping process, which is not possible in the actual production process. A close look at the metal flow during the stamping process reveals that the sheet blank is first drawn into the die cavity by the punch head and the wrinkles are not formed until the sheet blank touches the step edge DE marked in Fig. 1(b). The wrinkled shape is shown in Fig. 10. This provides valuable information for 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 punch corner radius A and the step corner radius D, as indicated in Fig. 1(b). Therefore a modification of die design was carried out in which the step corner was cut off, as shown in Fig. 11, so that the stretch condition is changed favourably, which allows more stretch to be applied by increasing the step edges. However, wrinkles were still found at the draw wall of the cup. This result implies that wrinkles are introduced because of the uneven stretch between the whole punch head edge and the whole step edge, not merely between the punch corner and Fig. 10. Wrinkle formed when the sheet blank touches the stepped edge. Fig. 11. Cut-off of the stepped corner. the step corner. In order to verify this idea, two modifications of the die design were suggested: one is to cut the whole step off, and the other is to add one more drawing operation, that is, 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 is quite similar to that of a rectangular cup drawing, as shown in Fig. 12. It is seen in Fig. 12 that the wrinkles were eliminated. In the two-operation drawing process, the sheet blank was first drawn to the deeper step, as shown in Fig. 13(a). Sub- sequently, the lower step was formed in the second drawing operation, and the desired shape was then obtained, as shown in Fig. 13(b). It is seen clearly in Fig. 13(b) that the stepped rectangular cup can be manufactured without wrinkling, by a two-operation drawing process. It should also be noted that in the two-operation drawing process, if an opposite sequence is applied, that is, the lower step is formed first and is followed by 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 the metal cannot easily flow over the lower step into the die cavity. The finite-element simulations have indicated that the die design for stamping the desired stepped rectangular cup using one single draw operation is barely achieved. However, the manufacturing cost is expected to be much higher for the two- operation drawing process owing to the additional die cost and operation cost. In order to maintain a lower manufacturing cost, the part design engineer made suitable shape changes, and modified the die design according to the finite-element Fig. 12.