U型弯曲冲压成形工艺及模具设计
U型弯曲冲压成形工艺及模具设计,U型弯曲冲压成形工艺及模具设计,弯曲,曲折,冲压,成形,工艺,模具设计
中期检查表学生姓名学 号指导教师选题情况课题名称U型弯曲冲压成形工艺及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: 学生姓名: 学 号: 设计题目: U型弯曲冲压成形工艺及模具设计起迄日期: 指导教师: 2014 年 4月 13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:本毕业设计课题来源于生产实践,在完成该课题之后,应对冲压成形工艺较为熟悉,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,能够运用绘图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): 原始数据如图材料:铝大批量 工作要求: (1)完成模具的设计,编写设计说明书一份;(2)绘制模具装配图以及全套的模具零件图; (3)编写主要零件的加工工艺卡。 所在专业审查意见:负责人: 年 月 日系部意见:系领导: 年 月 日设计说明书 毕业设计题目: U型弯曲冲压成形工艺及模具设计系 部 专 业 班 级 学生姓名 学 号 指导教师 2014年 4 月 16 日目 录绪论1第一章 弯曲件成形工艺分析2 1.1弯曲件成形工艺性分析21.2弯曲件成形概述2第二章 弯曲工艺方案的确定32.1弯曲件成形方案32.2方案设计进度5第三章 模具相关计算63.1 模具成形力的计算63.1.1 弯曲应力计算63.1.2压料力的计算63.1.3 初选压力机 6 3.1.4 弯曲件毛坯坯料尺寸的计算73.2 弯曲模工作部分尺寸的设计83.2.1凸模圆角半径的选取83.2.2凹模圆角半径93.2.3凹模深度 93.2.4 凹凸模间隙计算103.3 U 形弯曲凸凹结构尺寸的设计103.4 橡皮的选择12第四章 弯曲模具的选择134.1 模具结构选择134.2 定位方式的选择144.3 卸料方式的设计14第五章 模具零件结构的设计145.1 凸模零件的结构设计145.1.1凸模的结构图145.1.2 凸模主要尺寸的计算155.2 凹模的结构设计175.2.1 凹模主要尺寸的设计175.3 摆块的结构设计185.3.1 摆块的结构草图18 5.3.2摆块的主要尺寸的设计195.4 定位零件的设计205.4.1 限位钉的设计205.5 定位块的设计21 5.6 弹顶部件的设计225.6.1垫板的设计225.6.2 导板的设计22第六章 压力机的参数及模具相关参数校核23第七章 模具零件的加工工艺247.1凸模的加工工艺过程 24 7.2凹模的加工工艺过程 25 第八章 模具的装配26第九章 模具试冲27设计总结28致谢 29参考文献 30评语学生姓名: 班级: 学号: 题 目: U型弯曲冲压成形工艺及模具设计 综合成绩: 指导者评语: 指导者(签字): 年 月 日毕业设计(论文)评语评阅者评语: 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 U型弯曲件冲压工艺及模具设计毕业设计说明书第一章 弯曲件成形工艺分析1.1 弯曲件成形工艺性分析工件名称:U型弯曲件工件简图:如图所示生产批量:大批量材料:铝材料厚度:2 mm 制件图由上图可知,此工件为典型U型弯曲件。材料为铝,具有良好的弯曲性能适合弯曲成型加工。工件结构简单,除了装配尺寸,公差等级IT14级有严格要求外其余尺寸均为自由公差,工件整体上看,尺寸精度较高,普通弯曲成型不能完全满足要求,需要复合弯曲。1.2 弯曲件成形概述 本课题研究的思路: U型弯曲件模具的设计. U型弯曲件是最典型的弯曲件,其工作过程很简单就一个弯曲,根据实际确定它不能一次弯曲成功.因此,需要两次弯曲。从制件的成型原理和模具加工成本考虑,确定此次弯曲不采用标准的模架。为了保证制件的顺利加工,模具必须有足够精度。要保证模具的精度,特别要保证导柱和导套的配合精度,保证导柱和导套的配合精度的同时,还要注意保证导柱和导套的刚度. 另外,模具的精度还和弯曲凸模与弯曲凹模工作配合精度有关设计时可能精度出现误差,应当边试冲边修改调整。只有加强弯曲变形基础理论的研究,才能提供更加准确、实用、方便的计算方法,才能正确地确定弯曲工艺参数和模具工作部分的几何形状与尺寸,解决弯曲变形中出现的各种实际问题,从而,进一步提高制件质量。 本课题设计进度的安排如下:1.了解目前国内外冲压模具的发展现状,所用时间15天;2.确定加工方案,所用时间5天;3.模具的设计,所用时间30天; 4.模具的调试所用时间5天。第二章 弯曲工艺方案的确定2.1 弯曲件成形方案该工件弯曲成型,可以一次弯曲成型,也可以二次弯曲成型有以下三种方案供选择:方案一:采用一次弯曲成型,单工序生产。如下图所示: 图2方案二:采用两次弯曲成型,先弯U型,再弯 U型,采用两套单工序模生产具体如下图所示:图a 为首次弯曲模具结构图;图b为第二次弯曲模具结构图。 a)首次弯曲 b)二次弯曲图3方案三:采用在一套模具上成型,复合模生产。 具体如下图所示:图42.2 方案设计进度:方案一、模具结构简单,生产制造成本低,但工件尺寸精度低,尤其是四个直角的精度难以得到保证。另外,在弯曲过程中,由于凸模肩部妨碍了坯料的转动,加大了坯料通过凹模圆角的摩擦力,使弯曲件侧壁容易擦伤和变薄,成型后弯曲件两肩部与底面不平行。方案二、模具结构相对简单,生产成本较高,由于采用两副模具进行弯曲成形,从而可以避免了方案一中的缺陷,提高了弯曲件的质量,但由于采用两副模具进行生产,生产效率低,另外,凹模的强度不易保证。方案三、模具结构复杂,生产制造成本与方案二差不多,但是工件尺寸精度,位置精度容易保证,生产效率也高。综上所述,经过对三种方案的比较分析可见,该工件的弯曲成型生产采用方案三比较合理。第三章 模具相关计算3.1模具成形力的计算3.1.1 弯曲应力的计算该模具工件属于自由弯曲成型,所以U形件弯曲力: = 式中:自由弯曲在冲压行程结束时的弯曲力(N); B弯曲件的宽度,B=10mm; t 弯曲材料的厚度(mm); r 弯曲件的内弯曲半径(mm); 材料的抗拉强度(MPa); K安全系数,一般取K=1.3。 = =3276(N);3.1.2 压料力的计算据公式(3.5.4),如果弯曲模设有顶出装置或压料装置时,其顶出力可以近似取自由弯曲力的30% 80%即: =(0.3 0.8) 在此取: =0.6 =0.6 3276 =1965.6 N3.1.3 初压力机根据公式(3.5.5)即: (1.2 1.3) (+)式中: -弯曲应力 -压料力考虑到弯曲工件板料较厚,而且板宽也较大,压力机公称压力应取值偏大为宜。在此取: 1.3(+) =1.3(3276+1965.6) =6814.08 N根据计算结果,查表2-3初选压力机为:J23-31.5。3.1.4 弯曲件毛坯坯料尺寸的计算 因为弯曲件的弯曲圆角半径较大(r0.5t),应根据中性层长度不变原理计算。中性层位置以曲率半径表示,通用用下面经验公式2.1确定 =r+xt (2.1) 式中 r弯曲件的内弯曲半径; t板料厚度; x中性层位移系数。相对弯曲半径r1/t=1.5,、r2/t=2.25,由表3.4可查的中性层的位移系数x分别为0.44,、0.45。则:1=r+xt=3+0.442=3.882=r+xt=4.5+0.452=5.4 坯料的总长度等于弯曲件直线部分长度和弯曲圆角部分应变中性层长度之和,即=6.09 =8.48长度方向的总长度计算公式为:,又因为该工件左右对称.则:=2(6.5+25.5)+30+2+2=94+29.14=123.14(mm)毛坯料的长度尺寸二维图如下图:制件展开图3.2 弯曲模工作部分尺寸的设计3.2.1 凸模圆角半径由方案三可知,所设计的复合模整个工作原理可分为两部分: U型弯曲和在U 型弯曲基础上的 U型弯曲。归根到底,其设计为U 型弯曲种类,所以,其设计可按U 型件设计方法设计因为=1.5、2.25, 值较小,所以取=r=3mm、4.5mm3.2.2 凹模圆角半径根据实际生产经验可知: 当t = 2 4 mm 时, =(2 3) t从保证制件精度要求考虑,特别是所设计的弯曲复合模值不宜取大值。在此取:2 t2 24 mm 。3.2.3 凹模深度 图6 凹模深度过小,则坯料两端受压部分太多,工件回弹大,而且不平直,影响工件质量。如果过大,则浪费模具钢材,且需冲床有较大的工作行程。由前面计算可知弯曲件边长L=+ =25.5+6.5+8.48 =40.48 mm据边长L=40.48 mm 查表19.3-18得: = 20 mm3.2.4 凹凸模间隙计算查的U 型件弯曲的凸凹模单边间隙可按下式计算: C = + x t = t + + x t 式中: C弯曲凹、凸模单边间隙(mm); t工件材料厚度(基本尺寸) (mm); 工件材料厚度的正偏差(mm); X间隙系数,查表19.3-19得 X = 0.05 ; 所以: C = 2 + 0.006 + 0.052 =2.106 mm3.3 U 形弯曲凸凹模尺寸的设计 图7由工件图上可知:工件是内形标注的弯曲件,设计时应该以凸模为基准先确定凹模尺寸。再利用凸凹间隙求出凹模的尺寸。根据教程公式(3.944)与(3.9.5)得: 凸模尺寸为: = ( + 0.75 式中: 凸模横向尺寸(mm); 弯曲件横向的最小极限尺寸(mm); 弯曲件的尺寸公差(mm); 凸模的制造公差,采用IT7级。 所以: =(36 + 0.75 0.62 =36.465查表1-6标准公差数值IT7级得: =36.465 mm凹模尺寸为: =( + Z 式中: 凹模横向尺寸(mm); Z凹凸模双面间隙(mm); 凹模的制造公差,取IT8级得: = (36.46 + 4.212 = 40.672查表1-6标准公差值IT 8级得: = 40.873.4 橡皮的选择3.4.1 橡皮高度的选择 为保证橡皮不致过早失去弹性而损坏,一般取: (5.1)式中 橡皮自由状态下高度,mm; 所需工作行程,mm。工作行程可知所需工作行程为25.5mm,则自由状态下橡皮的高度选为85mm。3.4.2 橡皮外径的选择根据模具特点,选择圆柱形橡皮。由冲压手册表10-6查得外径的计算公式为5.2:D= (5.2)式中 F压力,由上文知道F=6814.08N。 P与橡皮压缩量有关的单位压力。由表10-7查得压缩量为30%的时候的单位压力位1.52MPa。则D=75.45(mm)又有校验公式:,D为橡皮外径,即是D170mm且D56.66mm。选橡皮外径为60mm。3.4.3 橡皮的连接固定橡皮靠一个法兰板固定在下模座上,并有螺钉连接,工作力通过顶杆传递给顶板,以保证在工作的时候顶板于凸模夹紧工件。第四章 弯曲模具的选择4.1模具结构选择由弯曲工艺分析可知,采用复合模,所以模具类型为复合模。具体结构如下土所示:图8八字摆块复合模结构模具上模部分主要由: 凹模、打杆、压板、组成。卸料方式采用刚性打件装置卸件,工作原理:上模回程,压力机限位装置迫使打杆推动压板把弯曲件从凹模腔中推出。下模部分由凸模,限位钉(2个),摆块(一对),销轴(2个),导板,销钉(2个),内六方螺钉(4个),下模座,限位块(2个),螺钉(2个),上垫板,下垫板,弹簧等零件组成。弯曲坯料由前一冲裁工序准备尺寸为:123.14 mm x 10 mm ,板料由前方送进,送料方向定位由限位钉限位,左右方向由限位块定位。板料定位后,上模下行,凸模压入凹模同时把板料拉入模腔内,进行首次U型弯曲动作;当凸模压入凹模深度16 mm时,首次U型弯曲完成,进入二次弯曲动作,这时,在上模下行力的驱使下,摆块被迫向左右摆动,同时板料发生二次弯曲动作,最后工件成型为 U型件。由于弯曲回弹力的作用下,工件被卡在凹模腔内,随着上模回程。当上模的打杆触动压力机的限位装置时,达杆推动压板迫使工件从凹模中顶出,卸下工件。在上模回程同时,下模的弹簧弹性势能释放,驱使凸模回程,从而完成整个工件的弯曲动作。4.2定位方式的选择因为模具采用的是前一工序冲裁好的板料,板料由模具前方送进,送进方向在凸模的顶部设有两个限位钉定位,左右方向采用一对定位块定位。4.3出件方式的设计 弯曲成型后由于弯曲回弹力的作用下,工件回卡在凹模内,为此,在这里采用了上出现的方式,利用压力机的限位装置迫使打杆推动压板顶出工件。第五章 主要零件结构的设计5.1工作零件的结构设计5.1.1 凸模的结构草图如下所示: 图9凸模的结构草图在凸模顶部钻两个的孔固定两个限位钉,凸模与限位钉的配合按H7 / n6 配合。在底部钻一螺孔用来与上垫板连接,另外在两侧各钻两个销孔用以安装摆块,其中销钉与销孔采用H7 / m6 配合。5.1.2 凸模主要尺寸的计算 长度方向: = = = 10 mm 式中: 摆块的宽度(mm); 坯料宽度10 mm 。 L = + 2 t 式中: t凸模长度方向上侧壁厚度,综合考虑到模具强度,刚度和生产成本,选t = 10 mm 。 L =10 + 2 15 = 40 mm 宽度方向: 由前面凸模横向尺寸计算可知: B = = 36.465 mm; = B 2 P 式中: p 摆块的厚度,由后面摆块设计中可知, p =10mm。所以: = 36.465 2 10 = 16.465 mm d = + p / 2 = 16.465+ 10/ 2 = 21.465 mm从定位准确和加工难易程度考虑,在此选R =5mm。 高度方向: = = 18 mm 式中: 首次弯曲时,凸模进入凹模的深度18 mm。 = + P / 2 = 18 +5 = 23 mm h = + + + 式中: 首次弯曲,凸模进入凹模的深度(mm) ; 摆块高度,由后面摆块设计中可知 = 49.5mm 。 导板的高度8 mm,由后面的设计可知; 下模座的高度26 mm,由后面的设计可知。 所以: h = 18 +49.5 + 8 + 26 = 101.5mm凸模其余尺寸的设计和具体结构的设计可参见后面的凸模零件图所示。5.2 凹模的结构设计考虑到凹模在弯曲时所受的弯曲力和左右张力都比较大,因此,对凹模的强度和刚度都要有较高的要求。为了保证凹模的强度和刚度,在此把凹模和模柄做成一个整体,其结构草图如下所示:图105.2.1 凹模主要尺寸的设计 长度方向: 由前面的计算可知: = = 36.465 mm 。 L = + 2 式中: 凹模侧壁厚度,因为工件在第二次弯曲成型是在凹模与摆块的共同作用下成型的,所以凹模壁厚度应略大于 U工件的凸缘外伸部分尺寸,即: + 由前面弯曲件坯料尺寸计算可知, =6.5mm , = 8.48 mm 。 所以: 6.5 + 8.48 =14.98 mm综合考虑模具刚度和生产成本,在此取 = 15 mm 。 所以: L = 36.465 + 2 x 15 = 66.465 mm 在此,取L = 67 mm 。 高度方向: = + 式中: 首次弯曲凸模进入凹模的深度 =18 mm ; 压板高度(mm),= 23 mm 。所以: = 18 + 23 = 41 mm凹模其余尺寸的设计和凹模结构的具体设计可参见后面的凹模结构零件图所示。5.3 摆块的结构的设计5.3.1 摆块的结构草图如下所示:图11摆块草图5.3.2 摆块的主要尺寸的设计圆角半径R:R = / 2 式中: 摆块的厚度(mm),根据摆块的工作受力情况和生产成本考虑在此选 = 10 mm 。 所以:R = 10 / 2 = 5 mm摆块宽度B:B = = 10 mm 式中: 弯曲坯料的板宽10 mm。摆块的工作原理图如下所示:图12摆块工作原理 由上面摆块工作原理得L的计算公式如下: L = + + 式中: 模侧壁的厚度,= 25.5 mm; 坯料厚度,= 2 mm; 摆块厚度,= 10 mm。 L =25.5 + 2 + 10 / 2 =32.5mm摆块的其余尺寸设计与及具体结构可参见后面摆块零件图所示。5.4 定位零件的设计坯料的定位采用限位钉前方定位和定位块左右定位,限位钉与凸模顶孔采用H7 / n6配合固定,定位块采用销钉定位,螺杆固定在下模座上。5.4.1 限位钉的设计限位钉的结构草图如下所示:图13限位螺钉结构草图 由于限位钉只起限位作用,基本上不受过大的力作用,所以限位钉尺寸设计如下即可满足使用要求: = 5 mm D = 8 mm h = 5 mm其余尺寸设计见后面限位钉零件图所示。5.5 定位块的设计 定位块的结构草图如下所示:图14定位块结构草图定位块主要工作尺寸H可按以下公式计算: H = + t + 式中: H 定位块主要工作尺寸(mm); 凸模高度, = 101.5 mm ; t 坯料厚度, t = 2 mm ; 为定位可靠,设定的自由高度,在此选定= 5 mm。 所以: H = 101.5+ 2 + 5 =108.5 mm定位块的其余尺寸设计及具体结构可参见后面定位块零件图所示。5.6 弹顶部件的设计根据工件弯曲受力,在此采用橡胶作弹性元件,该模具采用4根弹簧,上下垫板中间,由4螺杆组成弹顶部件固定。5.6.1 垫板的设计由模具结构所限,上下垫板均是圆形结构,主要设计如下:上垫板: 直径115 mm ,厚度12 mm ;下垫板: 直径115 mm ,厚度12 mm ;上下垫板均采用45钢制造,淬火硬度40 45 HRC 。其具体结构见后面垫板零件图所示。5.6.2 导板的设计导板主要起导向定位作用,选用材料T8A,淬火硬度58 60 HRC。制造尺寸:143 mm x 115 mm x 8 mm 。其具体结构以及尺寸设计见后面垫板零件图所示。第六章 压力机的参数与校核 由前面压力机公称压力计算初选的压力机型号:J23-10,查模具实用技术手册表2-3得压力机主要技术参数如下:公称压力:100 KN ;滑块行程:45 mm ;最大闭合高度:180 mm ;最大装模高度:180 mm ;连杆调节长度:35 mm ;工作台尺寸(前后x左右):130 mm x 200 mm ;垫板尺寸(厚度):35 mm ;模柄孔尺寸:30 mm x 60 mm ;最大倾斜角度: 由上述技术参数可知,所选压力机J23-10型号可用。第七章 模具零件的加工工艺 7.1 凸模的加工工艺过程表1凸模加工工艺卡工序号工序名称工序内容1备料锯床下料60mm 60mm 2煅造煅成42mm x36mm x 120 mm3热处理退火,硬度 229 HBS4刨刨六面,互为直角40mm x36mm x 120 mm5平磨磨六方91 mm x 55 mm x 115 mm 6数控铣铣出摆块安装槽和凸模边倒角r=3mm7热处理淬火硬度58 60 HRC8磨1、 磨外形至图纸要求尺寸,90 mm x 54 mm x 114 mm 。2、 磨安装槽至图纸要求尺寸,70 mm x 16 mm x 84 mm 。9钳1、 倒角去毛刺。2、 画线、钻孔、攻螺纹、精修等。3、 研磨销孔。4、 精修全部达设计要求。 7.2 凹模的加工工艺过程表2凹模加工工艺卡工序号工序名称工序内容1下料锯床下料80 mm x 60 mm 2锻造煅成67 mm x40 mm x 86 mm 3热处理退火,硬度退火,硬度229 HBS4刨刨外形与凹模腔,留2 mm 余量。5磨磨外形与凹模腔,留0.5 mm 余量。6铣树控铣,铣20孔与16孔,留0.5余量。7热处理淬火硬度58 60 HRC8磨磨至图纸要求9钳倒角、去毛刺、精修、研磨凹模腔,16孔。第八章 模具的装配模具的装配全过程如下表格所示:表3装配工序卡序号工序工艺说明1凸凹模预配1、 装配前仔细检查凸模形状、尺寸以及凹模的形状与尺寸,是否符合图纸要求尺寸精度,形状精度。2、 将凸模与凹模相配,检查加工是否均匀。不适合者,应重新修磨或者更换。2凸模装配以凸模为基准,安装好限位钉,摆块。3装配下模1、 把导板与下模座安装好。2、 把弹顶部件安装到下模座上。3、 安装凸模,由上端把已经安装好的凸模部件压入导板孔至上垫板接触,用螺钉把凸模与上垫板连接拧紧。4、 安装定位块,把定位块安装到下模座上。4上模安装把压杆插入凹模后与压板连接好,拧紧。5安装模具分别把上模部分,下模部分安装到压力机工作台上,并调出合理的间隙。6试冲与调整开机试冲并根据试冲的结果作出相应的调整。第九章 模具试冲下表分别列出了模具在试冲时常见的故障,原因和调整方法:表4模具在试冲时常见的故障,原因和调整方法常见故障产生原因调整方法弯曲角度不够1、 凸凹模的回弹角制造过小2、 凸模进入凹模的深度太浅3、 凸、凹模间隙过大4、 试模材料不对5、 弹顶器的弹力太小1、 加大回弹角2、 调整冲模闭合高度3、 调整间隙值4、 更换试冲材料5、 加大弹顶器的弹顶力弯曲位置偏移1、 定位块的位置不对2、 凹模两侧进口圆角大小不等,材料滑动不一致3、 没有压料装置或者压料装置的压力不足和压板位置过低4、 凸模没有对正凹模1、 调整定位板位移2、 修磨凹模圆角3、 加大压料力4、 调整凸凹模位置冲件的尺寸过长或者不足1、 凸凹模之间的间隙过小,材料被拉长2、 压料装置压力过大,将材料拉长3、 设计时计算错误或不正确1、 调整凸凹模间隙2、 减小压料力3、 改变坯料尺寸冲件外部有光亮的凹陷1、 凹模的圆角半径过小,冲件表面被划痕2、 凸、凹模之间的间隙不均匀3、 凸、凹模表面粗糙度太大1、 加大圆角半径2、 调整凸、凹模间隙3、 抛光凸、凹模表面设计总结 通过冲压课程设计,我进一步巩固了冲裁理论知识。并且也加深了相关理论知识的认识。同时熟练掌握了专业工具书的使用方法。在整个过程中,增强了自己的动手能力及独立思考解决问题的能力。当然,由于本人水平有限及缺乏生产实际经验,该设计难免存在不足之处。希望老师对此提出批评意见,在此表示万分的感谢。 复合模具的设计,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,要想做为一名合理的模具设计人员,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。致谢毕业设计是我们进行完了三年的模具设计与制造专业课程后进行的,它是对我们三年来所学课程的又一次深入、系统的综合性的复习,也是一次理论联系实践的训练。它在我们的学习中占有重要的地位。通过这次毕业设计使我在温习学过的知识的同时又学习了许多新知识,对一些原来一知半解的理论也有了进一步的的认识。特别是原来所学的一些专业基础课:如机械制图、模具材料、公差配合与技术测量、冷冲模具设计与制造等有了更深刻的理解,使我进一步的了解了怎样将这些知识运用到实际的设计中。同时还使我更清楚了模具设计过程中要考虑的问题,如怎样使制造的模具既能满足使用要求又不浪费材料,保证工件的经济性,加工工艺的合理性。在学校中,我们主要学的是理论性的知识,而实践性很欠缺,而毕业设计就相当于实战前的一次演练。通过毕业设计可是把我们以前学的专业知识系统的连贯起来,使我们在温习旧知识的同时也可以学习到很多新的知识;这不但提高了我们解决问题的能力,开阔了我们的视野,在一定程度上弥补我们实践经验的不足,为以后的工作打下坚实的基础。通过对弯曲冷冲模的设计,我对冲裁模、弯曲模有了更为深刻的认识,特别是这种弯曲模具的设计。弯曲模的主要零件的加工一般比较复杂,多采用线切割进行加工,弯曲回弹的影响因素多,不容易从纯理论的角度精确的计算出来,多需要在试模后再进行调整。在模具的设计过程中也遇到了一些难以处理的问题,虽然设计中对它们做出了解决 ,但还是感觉这些方案中还是不能尽如人意,如压力计算时的公式的选用、凸凹模间隙的计算、卸件机构选用、工作零件距离的调整,都可以进行进一步的完善,使生产效率提高。参考文献1 刘建超,张宝忠主编.冲压模具设计与制造.北京:高等出版社,2004.62 中国模具设计大典编委员会.中国模具设计大典3.南昌:江西科学出版社,2003.13 任嘉卉主编.公差与配合手册. 北京:机械出版社,2000.44 冯炳光主编.模具设计与制造简明手册.上海:上海科学技术出版社,1998.55 中国标准出版社,全国弹簧标准化技术委员会编.中国机械工业标准汇编弹簧卷.北京:中国标准出版社,1999.66 中国轻工模具网模具新闻 中国模具工业特点基本状况及情况 分析2006.4.117 太空模具网. 未来10年的模具发展趋势. 2005.11.248 中国金属加工网.冲压模具行业发展现状及技术趋势.2005.69 彭建声、秦晓刚编著.模具技术问答. 北京:机械工业出版社,199610 Kondo K.Parametric and Interactive Geometric Modeler Formechanical.Computer-Aeded Design.1990(10)28 Int 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.
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