1790_汽车锁座零件冲压工艺分析及模具设计
1790_汽车锁座零件冲压工艺分析及模具设计,汽车,零件,冲压,工艺,分析,模具设计
汽车锁座零件冲压工艺分析及模具设计学生姓名:杨飞明 班级:0781053指导老师:罗海泉摘要:模具是现代工业生产中的重要工艺装备,本论文主要涉及冲压模具工艺设计和弯曲模具工艺设计,整个过程包括工艺方案、工序安排、工序尺寸、使用的设备及模具类型,并根据设计出的冲裁凸凹模的尺寸及技术要求制定其机加工工艺规程,最终绘制出正确的冲裁模具装备图和弯曲模具装备图。根据零件的技术要求,确定工艺方案为:先进行冲裁然后弯曲。在冲裁工艺阶段,拟定两种落料与冲孔方案:一种是落料与冲孔复合;一种是先落料在冲孔。通过各方面计算与比较,确定第一种方案更优。在弯曲阶段,由于孔接近变形区,弯曲后需要钳工修磨,以达到工艺要求。在凸凹模的制造过程中,由于模具制造与一般机械制造相比较,有着特殊的技术要求和明显的特点,必须区别对待, (1)单件生产:每种模具一般生产 12 副,普遍采用修锉、修配方法加工,工序组合相对集中对工人技术水平要求较高。 (2)制造质量高:一般地,模具工作零件的制造精度比产品零件高 24 级,需采用坐标磨床、数控机床加工。 (3)形状复杂:一般加工难度大,有时需要特种加工或专门化机床。 (4)材料硬度高:一般采用工具钢淬火、低温回火,需要采用特种加工方法。关键词:模具 冲裁 弯曲 工艺指导老师签名:Block lock parts of car stamping prodess and die design Student name: Yang Feiming Class: 0781053Supervisor: Luo HaiquanAbstract: Mold is an important technique and equipment in modern industrial production, In this paper, the main process involved in design of stamping die and design of bending mold,the entire process including planning of process, organization of process, size of process, use of equipment and types of mold. And in accordance to the size of convex and concave mold and the its technical requirements complete the development of its machining process planning, eventually draw the correct assembling drawing of blanking dies and bending .According to the technical requirements of parts, Technology program is determined to blanking firstly and then bending. In the Stage of blanking process, The development of blanking and punching two programs: one is the composite blanking and punching; anther is blank firstly then punch. Through calculation and comparison of various aspects, the first program was to identify better.In the Stage of bending. As the deformation zone be in near of the hole, it need to bending fitter after grinding in order to meet the technical requirements.In the manufacturing process of Bump of Blanking Die, mold manufacturing is compared with the general machinery manufacturing, as a result of its special technical requirements and it clear features,wo Must be treated differently.(1) One-piece production:Generlly,each mold product for 12, Widely used processing of file repair, repair methods, combination of the process of relative concentration and demand the workers of higher skill levels; (2)the Manufacturing of high-quality: In general, the manufacturing of mold parts products are more precision than 2 to 4 high by the general parts, need to the use of coordinate grinding machines and CNC machining;(3) Complex shape: General the processing is more difficult, and sometimes it need for special processing or specialized tools;(4) Material hardness:In general tool steel need to hardening, low temperature tempering, it need to use the methods of special processing.Keywords: Mold Blanking Bending TechnologySignature of Supervisor:毕业设计(论文)任务书I、毕业设计(论文)题目:汽车锁座零件冲 压 工 艺 分 析 及 模具设计II、 毕 业设计(论文)使用的原始资料(数据)及设计技术要求:设计原始资料:1零件图;2零件材料牌号及厚度:Q235,2.0;设计技术要求:1年生产纲领:80000 件;2. 要求外文资料翻译忠实原文;3. 要求编制的冲压工艺规程合理;4. 要求设计的冲压模具满足加工要求;5. 要求图纸设计规范,符合制图标准;6. 要求毕业论文叙述条理清楚,设计计算正确,论文格式规范。III、 毕 业设计(论文)工作内容及完成时间:1绘制零件图,收集、查阅有关资料,外文资料翻译(6000 字符),撰写开题报告; 第 1 周第 4 周2对零件进行冲压工艺分析,确定工艺方案; 第 5 周第 6周 3计算、确定冲压力模具工作部分尺寸及公差,选取模具结构; 第 7 周第 9周4设计专用模具, 绘制装配图,拆绘主要零件图; 第 10 周第 13 周 5撰写毕业论文、毕业设计审查、毕业答辩。 第 14 周第 17周 、 主 要参考资料:1姜奎华主编. 冲压工艺与模具设计. 北京:机械工业出版社,2003.6 2解汝升. 冲压模具设计与制造技术. 北京:中国标准出版社,19973许发樾主编. 实用模具设计与制造手册. 北京:机械工业出版社,2001.24廖念钊等主编 . 互换性与技术测量. 北京:中国计量出版社,2011.2第 5 版5. Wilson,F.W .Die design handbook MaGraw Hill 1990.6航空与机械工程 系 机械设计制造及其自动化 专业类 0781053 班学生(签名):填写日期: 2011 年 1 月 3 日指导教师(签名):助理指导教师(并指出所负责的部分):机械设计制造及其自动化 系(室)主任(签名):附注:任务书应该在已完成的毕业 说明书首页。1学士学位论文原创性声明本人声明,所呈交的论文是本人在导师的指导下独立完成的研究成果。除了文中特别加以标注引用的内容外,本论文不包含法律意义上已属于他人的任何形式的研究成果,也不包含本人已用于其他学位申请的论文或成果。对本文的研究作出重要贡献的个人和集体,均已在文中以明确方式表明。本人完全意识到本声明的法律后果由本人承担。作者签名: 日期:2011-03-29学位论文版权使用授权书本学位论文作者完全了解学校有关保留、使用学位论文的规定,同意学校保留并向国家有关部门或机构送交论文的复印件和电子版,允许论文被查阅和借阅。本人授权南昌航空工业学院可以将本论文的全部或部分内容编入有关数据库进行检索,可以采用影印、缩印或扫描等复制手段保存和汇编本学位论文。作者签名: 日期:2011-03-29导师签名: 日期:1毕业设计(论文)开题报告题目 汽车锁座零件冲压工艺分析及模具设计专 业 名 称 机械设计制造及其自动化班 级 学 号 078105334学 生 姓 名 杨 飞 明指 导 教 师 罗 海 泉填 表 日 期 2011 年 3 月 30 日2说 明开题报告应结合自己课题而作,一般包括:课题依据及课题的意义、国内外研究概况及发展趋势(含文献综述) 、研究内容及实验方案、目标、主要特色及工作进度、参考文献等内容。以下填写内容 各专业 可根据具体情况适当 修改 。但每个专业填写内容应保持一致。3一、选题的依据及意义:模具是成形金属、塑料、橡胶、玻璃、陶瓷等制件的基础工艺装备,是工业生产中发展和实现少切屑加工技术中不可缺少的工具。如汽车、拖拉机、电器、仪器仪表、电子等行业有 60%80%的零件需用模具加工。包括航空工业中许多钣金件,零件的成形工艺也要用到模具。由此可知,模具是工业生产中使用极为广泛的主要工艺装备之一。模具是一种高效率的工艺装备,用模具进行各种材料的成形可实现高速度的大批量生产,并能在大量生产下稳定的保证制件的质量以及节约原材料。因此,在现代工业生产中,模具的应用日益广泛,是当代工业生产的重要手段和工艺发展方向。许多现代工业的发展和技术水平的提高,在很大程度上取决于模具工业的发展水平。模具工业的水平和发展状况已被认为是衡量一个国家工业水平的重要标志之一。做为一个机械行业的毕业生,经过四年的专业学习和工程教育,初步掌握了一些机械方面的基础知识,希望在最后一次专业设计中,在指导老师的指点下对模具特别是冲模的设计与制造有大致的了解,培养踏实,严谨的工程意识,为以后参加工作做准备。二、国内外研究概况及发展趋势(含文献综述):模具发展日新月异,今后其发展趋势大致包括以下方面:1. 发展高效模具 对于大批量生产用模具,应向高效率发展。如为了适应当前高速压力机的使用,应发展多工位级进模以提高生产效率。2. 发展简易模具 对于小批量生产用模具,为降低成本,缩短模具制造周期,尽量发展薄板冲模,锌合金、低熔点合金,环氧树脂等简易模。3. 发展多功能模具 为了提高效率和保证制品的质量,要采用多工位级进模及具有组合功能的双色,多色塑料注射模等。4. 发展高寿命模具 高效率必然需要高寿命,为了达到高寿命,除模具本身结构优化外,还要对材料的选用和热处理,表面强化技术予以开发和创新。5. 发展高精度模具 要实现模具的高精度,在模具的设计与加工中必然要使用高精度加工设备和高技术加工工艺。要进一步发展数控机床和加工中心的使用,要发展 CAD,CAE,CIM 等高新技术。目前,我国的模具工业与国外发达国家相比,精密加工设备在模具加工设备中的比重还比较低,CAD/CAE/CAM 技术的普及度不高,许多先进技术应用还不够广泛,4特别是在大型,精密,复杂和长寿命模具技术上存在着明显的差距。三、研究内容及实验方案: 本次毕业设计的课题锁座模具设计着重研究的是冲模,冲模是冲压生产中必不可少的工艺装备。冲模大致可分为工作零件,定位零件,卸料装置零件,压料装置及零件,导向零件,推件装置与零件,支承及支持零件,紧固零件以及缓冲零件。其中,工作零件,定位零件,卸,推料零件称为模具的工艺零件,而导向零件,支承及支持零件,紧固零件,缓冲零件称为模具的辅助零件。实际上,对于每一套冲模,它们都会必然形成完整的独立整体,是由各种不同零部件结合而成的。目前,我国对冲压模具已经制定了国家标准,其中包括:模架,典型零件,模架技术条件,典型组合技术条件等。这对简化模具设计与制造,提高模具寿命,降低成本,缩短模具制造周期都有十分重要的意义。具体到本次模具设计时,可选用标准零部件,其已经规定了轮廓尺寸,精度,表面粗糙度,配合精度,材料, ,热处理及技术条件等。在设计时,只需要把主要精力集中在非标准零件的设计和一些板类标准件的工作型孔等设计方面。同时还要考虑到工程实际中模具零件的工艺性问题。零件工艺性对生产影响很大。一般说来,工艺性良好的零件,所需的加工设备数目少,容易加工,同时节省材料。另外,工艺性良好的模具零件,产品质量稳定,出现的废品少,工艺操作简单,还能使技术准备工作及生产管理做到经济合理。因此,在模具零件的设计中一定要满足工艺性要求。总的说来,本次冲模设计所研究的内容主要包括冲压工艺性分析,工艺方案制定,排样图设计,总的冲压力计算及压力中心的计算,刃口尺寸计算,弹簧、橡胶件的计算与选用,凸模、凹模或凸凹模结构设计以及其他冲模零件的结构设计,绘制模具装配图和工作零件图,编写设计说明书,填写冲压工艺卡和工作零件的机械加工工艺过程卡等。三个孔的边缘与弯曲中心的距离分别为:1.5mm2.0t(4mm)6.5mm2.0t(4mm)弯曲时会引起 b 边上小孔的变形,可以在弯曲后修正,所以可以先冲孔在弯曲.方案一:落料与冲孔复合。方案二:先落料再冲孔。5分析冲压工艺方案:方案一:模具结构简单,模具寿命长、制造周期短、投产快。能利用一个侧面定位,操作比较简单方便。方案二:模具结构简单,投产快寿命长,尺寸和形状不精确。综上所述,考虑到该零件的批量为中批量,作为保证各项技术要求,选用方案一。工序如下:1. 下料。2. 落料和冲孔。四、目标、主要特色及工作进度本次毕业设计所设计的模具结构要求满足冲压生产的要求,(即大批量生产),不仅要冲压出合格的零件制品,而且要适应大批量生产的需要,操作要方便,使用寿命要长,安全可靠,成本低廉,并能容易制造和维修。另外还希望通过这次毕业设计初步掌握模具,特别是冲模的设计的一般步骤与方法,并能综合运用四年所学的工程技术知识,通过查阅相关资料,请教老师来解决这次设计中的实际问题,锻炼实事求是,科学严谨的工程意识和工作态度。毕业设计的进度安排参照指导老师给出的时间表进行分配:1绘制零件图,收集、查阅有关资料,外文资料翻译(6000字符),撰写开题报告; 第1周-第4周2对零件进行冲压工艺分析,确定工艺方案; 第5周-第6周3计算、确定冲压力模具工作部分尺寸及公差,选取模具结构; 第7周-第9周4设计专用模具,绘制装配图,拆绘主要零件图; 第10周-第13周5撰写毕业论文、毕业设计审查、毕业答辩。 第14周-第17周五、参考文献1姜奎华主编 . 冲压工艺与模具设计. 北京:机械工业出版社,2003.62解汝升. 冲压模具设计与制造技术. 北京:中国标准出版社,19973许发樾主编. 实用模具设计与制造手册. 北京:机械工业出版社,2001.24廖念钊等主编. 互换性与技术测量. 北京:中国计量出版社,2011.2第5版5. Wilson,F.W .Die design handbook MaGraw Hill 1990.6拉中拉深壁起皱的分深模设计析FKChen and YCLiao台湾大学机械设计研究所在带有斜度的方形盒和带有阶梯的方形盒的拉深中发生的起皱现象一直在被研究。这两中类型的起皱现象有一个共同的特征:全都发生在相对无支撑、无压边的拉深壁处。在带有斜度的方形盒的拉深中,常受到工序参数的影响,例如:模具的间隙值和压边力等,所以常用有限元模拟的方法来研究分析起皱的发生。模拟的结果表明模具的间隙值越大,起皱现象就越严重,而且增加压边力也不能抑制和消除起皱现象的发生。在带有阶梯的方形盒拉深的起皱现象分析中,常通过实际生产中一种近似的几何结构来研究、试验。当凸模与阶梯边缘之间的金属板料在拉深时分布并不均衡,就会在侧壁发生起皱现象。为了消除起皱现象的发生,一个最优的模具设计常采用有限元的方法进行分析。模拟的结果和起皱试验论证了有限元分析的准确性,并且表明了在拉深模具设计中使用有限元方法分析的优越性。关键词:侧壁起皱;拉深模;带有阶梯的方形盒;带有斜度的方形盒一、介绍:起皱是金属板料成形中常见的失效形式之一。由于功能和视觉效果的原因,起皱通常是不能为零件制品所能接受的。在金属板料成形加工中通常存在三种类型的起皱现象:法兰起皱;侧壁起皱和由于残余压应力在未变形区产生的弹性变形。在冲压复杂形状的时候,拉深壁起皱就是在模具型腔中形成的褶皱。由于金属板料在拉深壁区域内相对无支撑,因此,消除拉深壁起皱比抑制法兰起皱要难得多。我们知道在不被支撑的拉深壁区域中材料的外力拉深可以防止起皱,这可以在实践中通过增加压边力而实现,但是运用过大的拉深力会引起破裂失效。因此,压边力必须控制在一定的范围内,一方面可以抑制起皱,另一方面也可以防止破裂失效。合适的压边力范围是很难确定的,因为起皱在拉深零件的中心区域以一个复杂的形状形成,甚至根本不存在一个合适的压边力范围。为了研究起皱的原因,Yoshida et al.发明了一个试验,即:一张薄板延着对角的一个方向进行不均匀拉深。他们还提出了一个近似的理论模型,起皱的初始是由于弹性变形导致横向压力发展成为不均匀的压力场。Yu et al.用试验和理论分析的方法来研究起皱问题。他们发现根据他们的理论分析,起皱发生在两个环形的起伏处,而且试验结果指出了46 处起皱。Narayanasamy 和 Sowerby 通过圆锥形凸模和半球形凸模的拉深来研究金属板料的起皱。同时,他们也试图整理防止发生起皱的特性参数。这些试验都仅仅围绕在与简单形状成形有关的起皱问题上,例如:一个圆形的盒件等等。在 20 世纪 90 年代初期,3D 动态有限元方法的应用成功,使得解决金属板料成形复杂形状的起皱现象的分析变成了可能。目前,研究人员都使用 3D 有限元方法来分析带有斜度的方形盒和带有阶梯的方形盒零件拉深时在拉深壁处由于金属板料流动引起的褶皱以及在成形过程中的参数的影响因素。一个有斜度的方形盒,如图 1(a)所示,盒形件的每一个倾斜的拉深壁都与圆锥盒形件相似。拉深成形过程中,在拉深壁处的金属板料是相对无支撑的,因此,褶皱是倾斜的。在目前的研究中,各种关于起皱的成型过程参数都被研究。在带有阶梯的方形盒件的研究中,如图 1(b)所示,观察到了另一种类型的起皱。在当前的研究中,为了得出分析的效果,实际生产用阶梯形结构的零件来研究。使用有限元方法可以分析出起皱的原因,并且可以使一个最优的模具设计消除起皱现象。有限元分析使得模具设计在实际生产中更为合理化。(a)带有斜度的方形盒件(b)带有阶梯的方形盒件图 1二、有限元模型模具的几何结构(包括凸模、凹模、压边装置等等),通过使用 CAD 和 PRO/ENGINEER 来设计。使用 CAD 将 3 个节点或 4 个节点形成壳形的单体,进而在模型上形成网格体系。使用有限元模拟,模型被视为是刚性的,并且相对应的网格仅仅可以定义模型的几何形状,不能对压力进行分析。使用 CAD 所建立的 4 个节点的壳形单体可以为板料创建网格体系。图 2 给出了模型完全建立时的网格体系和用以成形带有斜度的方形盒件的金属板料。由于对称的原因,仅仅分析了零件的 1/4。在模拟过程中,金属板料放在压边装置上,凹模向下移动,夹紧板料。凸模向上移动,拉深板料至模具型腔。 为了精确的完成有限元分析,金属板料的实际压力拉力的关系需要输入相关的数据。从目前的研究来看,金属板料的深拉深的特性参数已经用于模拟。一个拉深的实验已经用于样品的生产,并且沿着压延方向和与压延方向成 45和 90的方向切断。平均的流动压力 可以通过公式 =(0+245+90)/4,计算出来,进而准确测量出实际拉力,如图 3 所示,以用于带有斜度的方形盒件和带有阶梯的方形盒件的拉深。目前研究中的所有模拟都在 SGI Indigo2 工作站使用有限元可调拉深程序完成。完成了用于模拟所需数据的输入(假定凹模速度为 10m /s,并且平均摩擦系数为 0.1)。图 2 有限元模拟的网格体系实际压力(GPa)图 3 金属板料的实际压力拉力的关系实际拉力(mm/mm)三、带有斜度的方形盒件的起皱一个带有斜度的方形盒可以给出草图的相关尺寸,如图 1(a)所示。从图 1(a)可以看出方形凸模顶部每边的长度为 2Wp,凹模口部长度为 2Wd 以及拉深高度 H影响起皱所考虑的关键性尺寸。凹模的口部尺寸与凸模顶部尺寸差值的一半为凸模的间隙,即:G=WdWp。拉深壁处金属板料相对无支撑的程度可能取决于凸模的间隙,并且增加压边力也有可能抑制起皱现象的发生。在有斜度的方形盒拉深中,与发生起皱有关系的两个参数凸模间隙和压边力,他们对起皱的影响也正在研究之中。1.凸模间隙的影响为了研究凸模间隙对起皱的影响,现在分别用凸模间隙为 20mm,30mm 和 50mm 的带有斜度的方形盒进行拉深模拟。在每次模拟拉深中,凹模口部尺寸为 200mm 固定不变,并且拉深高度均为 100mm。在 3 次模拟中,均使用尺寸为 380mm380mm 的方形板料,且板料厚度均为 0.7mm,凹模对板料的压力拉力关系,如图 3 所示。图 4 带有斜度的方形盒件的褶皱模拟图(G=50mm)模拟结果表明:三个有斜度的方形盒均发生了起皱现象,图 4 给出了凸模间隙为 50mm的方形盒的形状。从图 4 可以看出,起皱分布在拉深壁处,并且拉深壁邻近的拐角处起皱现象尤为严重。经分析,在拉深过程中,起皱是由于拉深壁处存在过大的无支撑区域,而且凸模顶部和凹模口部长度的不同是由于凸模间隙的存在。在凸模顶部与凹模之间的金属板料的延伸变得不稳定,是由于断面压力的存在。在压力作用下,金属板料的无约束拉深是在拉深壁处形成褶皱的主要原因。为了比较三个不同凸模间隙的试验结果,需要引入两个主应力的比值 , 为 min/max, min/max 是主应力相对的最小值和最大值。Hosford 和 Caddell 指出, 值比临界值更重要,如果起皱发生,那么 值越大,起皱现象就可能越严重。如图 4 和图 5 的曲线所示,三次不同凸模间隙的拉深模拟,沿 MN 截面的相同拉深高度处的 值。从图 5 可以看出,在 3 次模拟中位于拉深壁的拐角处起皱比较严重,在拉深壁的中间起皱比较弱。还可以看出,凸模间隙越大,比值 就越大。因此,增加凸模间隙将可能增加带有斜度的方形盒件在拉深壁处起皱的可能性。2.压边力的影响众所周知,增加压边力可以帮助削弱拉深过程中发生的褶皱。为了研究增加压边力的影响,采用凸模间隙为 50mm,不同的压边力数值来对有斜度的方形盒进行拉深起皱的模拟。压边力从 100KN 增加到 600KN,以提供压边力 0.33Mpa 到 1.98Mpa。其他模拟条件和先前的规定保持一致(在模拟当中采用了 300KN 的压边力)。 模拟结果表明:增加压边力并不能消除拉深壁处起皱现象的发生。如图 4 所示,在MN 截面处的 值,和压边力分别为 100KN、600KN 的拉深相比较,模拟结果指出,在MN 截面处的 值都是相同的。为了分析两次不同压边力时出现起皱的不同,从拉深壁顶部到直线 MN 处,对 5 处不同高度截面进行了分析,如图 4 所示,图 6 给出了所有情况的曲线。从图 6 可以看出,几种情况截面处的波度是相似的。这就证明压边力与有斜度的方形盒件拉深中的起皱现象无关,因为褶皱的形成主要是由于拉深壁处大面积无支撑区域存在较大的横断面压力,所以压边力并不影响凸模顶部与凹模肩部之间的制件形状的不稳定状况。距离(mm)图 5 对于不同凸模间隙在 MN 截面处的 值图 6 在不同的压边力状态下,拉深壁不同高度处的横断面线。(a)100KN.(b)600KN.四、带有阶梯的方形盒件在带有阶梯的方形盒件的拉深中,即使凸模间隙不是这样重要,而在拉深壁处仍然会发生起皱。图 1(b)所示为带有阶梯的方形盒件拉深用的凸模,图 1(b)给出了拉深壁 C和阶梯处 D、E。目前,实际生产中一直在研究这种类型的几何结构。生产中,板料的厚度为 0.7mm,压力拉力关系从应力试验中获得,如图 3 所示。这种拉深件的生产是通过深拉深和整形两个工序组成的。由于凸模拐角处的小圆角半径和复杂的几何结构,导致在盒形件的顶部边缘发生破裂,在盒形件的拉深壁处发生褶皱,如图 7 所示。从图 7 中可以看出,褶皱分布在拉深壁处,尤其在阶梯边缘的拐角处更为严重,如图 1(b)所示的 AD 和 BE 处。金属板料在凸模顶部的边缘开裂,进而形成破裂,如图 7 所示。图 7 产品上的褶皱和破裂情况图 8 模拟产品起皱和破裂的盒形件外形图为了对拉深过程中金属板料出现的变形现象有更进一步的了解,生产中仍然采用了有限元分析方法。最初的设计已经用有限元模拟完成。模拟的盒形件外形如图 8 所示。从图8 可以看出,盒形件顶部边缘的网络拉深比较严重,褶皱分布在拉深壁处,这与实际生产中的状况是一致的。小的凸模圆角,例如 AB 边缘的圆角和凸模拐角 A 处的圆角,如图 1(b)所示,是拉深壁处破裂的主要原因。然而,根据有限元分析的结果,通过加大上述两处圆角可以避免破裂的产生。较大的拐角圆角这种想法通过实际生产加工被验证是可行的。还有一些试验也是模拟褶皱的。最初时将压边力增加到初始值的 2 倍。然而,正如和有斜度的方形盒件拉深时获得的结论是一样的,压边力对起皱的影响并不是最主要的。相同的结论是增大摩擦或者增加坯料的尺寸。因此我们得出的结论是:通过增加压边力是不能抑制起皱现象的发生的。起皱的形成是由于在某些区域发生多余的金属板料流动,所以应在起皱的区域增加压杆装置来控制多余的金属料流。压杆应加到平行于起皱的方向,以便能有效的控制多余的金属料流。在这种理论分析下,两个压杆应加到拉深壁的临近处,如图 9 所示以便能控制多余的金属料流。模拟的结果表明:正如所期望的那样,通过压杆的作用,阶梯拐角处的起皱被控制住了,但是一些褶皱还是存在于拉深壁处。这就表明:需要在拉深壁处设置更多的压杆,以控制多余的金属料流。但是从结构设计的角度考虑,这种结构是不可行的。图 9 在拉深壁处增加的压杆在拉深工序中采用有限元分析的优点之一就是可以通过拉深模拟来监视、控制金属板料的形状变形,而这些在实际生产中是不可能做到的。在拉深过程中,仔细地看金属板料的流动,可以看出金属板料首先由凸模拉深进凹模腔内,直到金属板料到阶梯边缘 DE处时,褶皱才开始形成。褶皱的形状如图 10 所示。有限元分析还可以为模具设计的改进提供相关的数据信息。 图 10 金属板料接触阶梯边缘时形成褶皱图 11 切断阶梯拐角后的外形图图 12 凸模设计修改后的外形模拟图最初推断发生起皱的原因是由于凸模拐角圆角 A 处和阶梯拐角圆角 D 处的金属板料不均匀、不稳定拉深形成的。因此,模具应设计成在阶梯拐角处切断一部分,如图 11 所示,以有利于改善拉深条件。通过增加阶梯边缘而使板料均匀、稳定的拉深。然而在拉深壁处还是存在起皱现象。结果指出:起皱的原因是由于凸模顶部边缘和整个阶梯边缘的板料不均匀、不稳定的拉深,这与凸模拐角和阶梯拐角不同。毫无疑问,模具的设计结构应有两处需要调整,一处是切断整个阶梯;另一处是增加拉深工序,使用 2 次拉深可以获得期望的形状。如图 12 所示,是这种成形方法模拟出的外形。如果较低的台阶被切断去除,那么这种盒形件的拉深就与矩形盒件的拉深十分相似,详见图 12。从图 12 可以看出,褶皱被去除了。在两次拉深过程中,金属板料首先拉深成较深的台阶,如图 13(a)所示。因此,较低的阶梯是在第二次拉深工序中形成的,此时,可以获得我们所期望的外形,如图13(b)所示。从图 13(b)中可以清楚地看出,带有阶梯的方形盒件通过两次拉深被制作出来,而且没有褶皱。在两次拉深工序中,如果假想使用相反的顺序拉深,较低的阶梯首先成形,然后再拉深成较高的台阶,那么在较深台阶的边缘处,如图 1(b)AB 处,容易形成破裂现象,因为凹模中在较低阶梯处的金属板料很难流动。有限元模拟分析指出要想获得理想的带有阶梯的方形盒件,使用一次拉深几乎是不可能成功的。然而,使用两次拉深则增加了生产成本,因为模具成本和制造成本增加了。为了维持较低的生产成本,设计师对盒形件外形做了适当的修改,并且根据有限元模拟的结果,修改了模具,切断去除了较低的阶梯,如图 12 所示。修改之后,拉深模制造出来了,并且盒形件消除了褶皱问题,如图 14 所示。盒形件的外形也与用有限元模拟所获得的外形效果一样好。图 13 (a)第一次拉深工序 (b)第二次拉深工序图 14 消除褶皱后的产品图为了更进一步验证有限元模拟的结论,将从模拟的结果中获得的截面 GH 处的板料厚度的分布情况与实际生产中的情况进行比较。比较情况如图 15 所示。从图 15 的比较情况可以断定:通过有限元模拟的厚度分布与实际生产的情况基本上一致。这就证明了有限元分析方法的有效性。厚度(mm)距离(mm)图 15 模拟与实际生产中,GH 截面处的板料厚度分布比较图五、简要论点及结束语在拉深过程中发生的两种类型的褶皱通过有限元分析研究以及对起皱原因做的试验,最终发现了抑制起皱的方法。第一种类型的起皱出现在带有斜度的方形盒件的拉深壁处。在凹模口部的高度尺寸和凸模顶部的高度尺寸等因素中,起皱的发生归因于较大的凸模间隙。较大的凸模间隙会导致拉深到凸模顶部与凹模肩部的金属板料处产生较大的无支撑区域,而金属板料较大的无支撑区域是形成起皱的最终原因。有限元模拟表明这种类型的起皱是不能通过增加压边力而抑制的。另一种类型的起皱发生在实际生产中带有阶梯的几何结构的方形盒件中。研究发现即使凸模间隙影响不是很重要,起皱还是会发生在阶梯上面的拉深壁处。根据有限元分析,起皱的原因主要是由于凸模顶部和台阶边缘之间的不均匀拉深造成的。为了避免起皱,在模具设计中使用有限元模拟做了一些试验,试验最终确定的最优设计就是将阶梯去除。修改后的模具设计生产出了无缺陷的盒形零件。模具分析的结果和实际生产所获得的结论证明了有限元分析的准确性和使用有限元模拟的有效性。因此可以说:有限元方法可以取代传统的实际生产试验的昂贵的方法。An Analysis of Draw-Wall Wrinkling in a Stamping Die DesignF.-K. Chen and Y.-C. LiaoWrinkling 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 unsupported.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 finiteelement 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 rectangular cup; Tapered square cups1. IntroductionWrinkling 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 stamping a complex shape, draw-wall wrinkling means the occurrence Correspondence and offprint requests to: Professor F.-K. Chen, Department of Mechanical Engineering, National Taiwan University, No. 1 Roosevelt Road, Sec. 4, Taipei, Taiwan 10617. E-mail: fkchen 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 blankholder 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 indicated four to six wrinkles. Narayanasamy and Sowerby 4examined 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 associated 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 sheetmetal 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 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 analysis was validated by observations on an actual production part.2. Finite-Element ModelThe tooling geometry, including the punch, die and blankholder,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 simulation,the tooling is considered to be rigid, and the corresponding meshes are used only to define the tooling geometry and 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 45and 90to the rolling direction. The average flow stress,calculated from the equation (0 245 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 program 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 s1 and a coefficient of Coulomb friction equal to 0.1 is assumed.3. Wrinkling in a Tapered Square CupA 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 (2Wp), the die cavity opening (2Wd), and the drawing height (H) are consideredas 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 Wd Wp. 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 GapIn 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 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 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 transverse stresses. The unconstrained stretching of the sheet metal under compression seems to be the main cause for the wrinkling at the draw wall. In order to compare the results for the three different die gaps, the ratio of the two principal strains is introduced, being min/max, where max and min are the major and the minor principal strains, respectively. Hosford and Caddell 5 have shown that if the absolute value of is greater than a critical value, wrinkling is supposed to occur,and the larger the absolute value of , the greater is the possibility of wrinkling.The 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 . 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 ForceIt 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 usedin the simulation.The simulation results show that an increase in the blankholder force does not help to eliminate the wrinkling that occurs at the draw wall. The values along the cross-section Fig. 5. -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 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 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-holder force does not affect the occurrence of wrinkling in the stamping 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 blankholderforce has no influence on the instability mode of the material between the punch head and the die cavity shoulder.4. Stepped Rectangular CupIn 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 followedby 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 stressstrain 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 deformation of the sheet-blank during the stamping process, a finiteelement analysis was conducted. The finite-element simulation was 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 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 finiteelementanalysis, 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 compressive stresses, a straightforward method of eliminating the wrinkles is to add drawbars in the wrinkled area to absorb theredundant 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 absorbthe 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 remaining 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 lookat 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 wrinkling 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). Subsequently,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 isapplied, 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 twooperation 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-elementFig. 12. Simulated shape for the modified die design.Fig. 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 for production was manufactured and the production part was found to be free from wrinkles, as shown in Fig. 14. The part shape also agreed well with that obtained from the finiteelement simulation.In order to further validate the finite-element simulati
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