U型彎曲沖壓成形工藝及模具設(shè)計(jì)

U型彎曲沖壓成形工藝及模具設(shè)計(jì),U型彎曲沖壓成形工藝及模具設(shè)計(jì),彎曲,曲折,沖壓,成形,工藝,模具設(shè)計(jì) 中期檢查表學(xué)生姓名學(xué) 號(hào)指導(dǎo)教師選題情況課題名稱U型彎曲沖壓成形工藝及模具設(shè)計(jì)難易程度偏難適中偏易工作量較大合理較小符合規(guī)范化的要求任務(wù)書有無開題報(bào)告有無外文翻譯質(zhì)量?jī)?yōu)良中差學(xué)習(xí)態(tài)度、出勤情況好一般差工作進(jìn)度快按計(jì)劃進(jìn)行慢中期工作匯報(bào)及解答問題情況優(yōu)良中差中期成績(jī)?cè)u(píng)定：所在專業(yè)意見： 負(fù)責(zé)人： 2014年 2 月 22 日 設(shè)計(jì)任務(wù)書系 部： 專 業(yè)： 學(xué)生姓名: 學(xué) 號(hào): 設(shè)計(jì)題目： U型彎曲沖壓成形工藝及模具設(shè)計(jì)起迄日期: 指導(dǎo)教師: 2014 年 4月 13日畢 業(yè) 設(shè) 計(jì) 任 務(wù) 書1本畢業(yè)設(shè)計(jì)課題來源及應(yīng)達(dá)到的目的：本畢業(yè)設(shè)計(jì)課題來源于生產(chǎn)實(shí)踐，在完成該課題之后，應(yīng)對(duì)沖壓成形工藝較為熟悉，能熟練掌握相關(guān)設(shè)計(jì)手冊(cè)的使用，能獨(dú)立完成一套模具的設(shè)計(jì)及模具工作零件加工工藝的編制，能夠運(yùn)用繪圖軟件完成模具裝配圖及零件圖的繪制。2本畢業(yè)設(shè)計(jì)課題任務(wù)的內(nèi)容和要求（包括原始數(shù)據(jù)、技術(shù)要求、工作要求等）： 原始數(shù)據(jù)如圖材料：鋁大批量 工作要求: (1)完成模具的設(shè)計(jì),編寫設(shè)計(jì)說明書一份；(2)繪制模具裝配圖以及全套的模具零件圖； (3)編寫主要零件的加工工藝卡。 所在專業(yè)審查意見：負(fù)責(zé)人： 年 月 日系部意見：系領(lǐng)導(dǎo)： 年 月 日設(shè)計(jì)說明書 畢業(yè)設(shè)計(jì)題目： U型彎曲沖壓成形工藝及模具設(shè)計(jì)系 部 專 業(yè) 班 級(jí) 學(xué)生姓名 學(xué) 號(hào) 指導(dǎo)教師 2014年 4 月 16 日目 錄緒論1第一章 彎曲件成形工藝分析2 1.1彎曲件成形工藝性分析21.2彎曲件成形概述2第二章 彎曲工藝方案的確定32.1彎曲件成形方案32.2方案設(shè)計(jì)進(jìn)度5第三章 模具相關(guān)計(jì)算63.1 模具成形力的計(jì)算63.1.1 彎曲應(yīng)力計(jì)算63.1.2壓料力的計(jì)算63.1.3 初選壓力機(jī) 6 3.1.4 彎曲件毛坯坯料尺寸的計(jì)算73.2 彎曲模工作部分尺寸的設(shè)計(jì)83.2.1凸模圓角半徑的選取83.2.2凹模圓角半徑93.2.3凹模深度 93.2.4 凹凸模間隙計(jì)算103.3 U 形彎曲凸凹結(jié)構(gòu)尺寸的設(shè)計(jì)103.4 橡皮的選擇12第四章 彎曲模具的選擇134.1 模具結(jié)構(gòu)選擇134.2 定位方式的選擇144.3 卸料方式的設(shè)計(jì)14第五章 模具零件結(jié)構(gòu)的設(shè)計(jì)145.1 凸模零件的結(jié)構(gòu)設(shè)計(jì)145.1.1凸模的結(jié)構(gòu)圖145.1.2 凸模主要尺寸的計(jì)算155.2 凹模的結(jié)構(gòu)設(shè)計(jì)175.2.1 凹模主要尺寸的設(shè)計(jì)175.3 擺塊的結(jié)構(gòu)設(shè)計(jì)185.3.1 擺塊的結(jié)構(gòu)草圖18 5.3.2擺塊的主要尺寸的設(shè)計(jì)195.4 定位零件的設(shè)計(jì)205.4.1 限位釘?shù)脑O(shè)計(jì)205.5 定位塊的設(shè)計(jì)21 5.6 彈頂部件的設(shè)計(jì)225.6.1墊板的設(shè)計(jì)225.6.2 導(dǎo)板的設(shè)計(jì)22第六章 壓力機(jī)的參數(shù)及模具相關(guān)參數(shù)校核23第七章 模具零件的加工工藝247.1凸模的加工工藝過程 24 7.2凹模的加工工藝過程 25 第八章 模具的裝配26第九章 模具試沖27設(shè)計(jì)總結(jié)28致謝 29參考文獻(xiàn) 30評(píng)語學(xué)生姓名： 班級(jí): 學(xué)號(hào)： 題 目： U型彎曲沖壓成形工藝及模具設(shè)計(jì) 綜合成績(jī)： 指導(dǎo)者評(píng)語： 指導(dǎo)者(簽字)： 年 月 日畢業(yè)設(shè)計(jì)（論文）評(píng)語評(píng)閱者評(píng)語： 評(píng)閱者(簽字)： 年 月 日答辯委員會(huì)（小組）評(píng)語： 答辯委員會(huì)（小組）負(fù)責(zé)人(簽字)： 年 月 日 U型彎曲件沖壓工藝及模具設(shè)計(jì)畢業(yè)設(shè)計(jì)說明書第一章 彎曲件成形工藝分析1.1 彎曲件成形工藝性分析工件名稱：U型彎曲件工件簡(jiǎn)圖：如圖所示生產(chǎn)批量：大批量材料：鋁材料厚度：2 mm 制件圖由上圖可知,此工件為典型U型彎曲件。材料為鋁，具有良好的彎曲性能適合彎曲成型加工。工件結(jié)構(gòu)簡(jiǎn)單，除了裝配尺寸，公差等級(jí)IT14級(jí)有嚴(yán)格要求外其余尺寸均為自由公差，工件整體上看，尺寸精度較高，普通彎曲成型不能完全滿足要求,需要復(fù)合彎曲。1.2 彎曲件成形概述 本課題研究的思路: U型彎曲件模具的設(shè)計(jì). U型彎曲件是最典型的彎曲件，其工作過程很簡(jiǎn)單就一個(gè)彎曲，根據(jù)實(shí)際確定它不能一次彎曲成功.因此，需要兩次彎曲。從制件的成型原理和模具加工成本考慮，確定此次彎曲不采用標(biāo)準(zhǔn)的模架。為了保證制件的順利加工，模具必須有足夠精度。要保證模具的精度，特別要保證導(dǎo)柱和導(dǎo)套的配合精度,保證導(dǎo)柱和導(dǎo)套的配合精度的同時(shí),還要注意保證導(dǎo)柱和導(dǎo)套的剛度. 另外，模具的精度還和彎曲凸模與彎曲凹模工作配合精度有關(guān)設(shè)計(jì)時(shí)可能精度出現(xiàn)誤差，應(yīng)當(dāng)邊試沖邊修改調(diào)整。只有加強(qiáng)彎曲變形基礎(chǔ)理論的研究，才能提供更加準(zhǔn)確、實(shí)用、方便的計(jì)算方法，才能正確地確定彎曲工藝參數(shù)和模具工作部分的幾何形狀與尺寸，解決彎曲變形中出現(xiàn)的各種實(shí)際問題，從而，進(jìn)一步提高制件質(zhì)量。 本課題設(shè)計(jì)進(jìn)度的安排如下：1.了解目前國(guó)內(nèi)外沖壓模具的發(fā)展現(xiàn)狀，所用時(shí)間15天；2.確定加工方案，所用時(shí)間5天；3.模具的設(shè)計(jì)，所用時(shí)間30天； 4.模具的調(diào)試所用時(shí)間5天。第二章 彎曲工藝方案的確定2.1 彎曲件成形方案該工件彎曲成型，可以一次彎曲成型，也可以二次彎曲成型有以下三種方案供選擇：方案一：采用一次彎曲成型，單工序生產(chǎn)。如下圖所示： 圖2方案二：采用兩次彎曲成型，先彎U型，再彎 U型，采用兩套單工序模生產(chǎn)具體如下圖所示：圖a 為首次彎曲模具結(jié)構(gòu)圖；圖b為第二次彎曲模具結(jié)構(gòu)圖。 a)首次彎曲 b)二次彎曲圖3方案三：采用在一套模具上成型，復(fù)合模生產(chǎn)。 具體如下圖所示：圖42.2 方案設(shè)計(jì)進(jìn)度：方案一、模具結(jié)構(gòu)簡(jiǎn)單，生產(chǎn)制造成本低，但工件尺寸精度低，尤其是四個(gè)直角的精度難以得到保證。另外，在彎曲過程中，由于凸模肩部妨礙了坯料的轉(zhuǎn)動(dòng)，加大了坯料通過凹模圓角的摩擦力，使彎曲件側(cè)壁容易擦傷和變薄，成型后彎曲件兩肩部與底面不平行。方案二、模具結(jié)構(gòu)相對(duì)簡(jiǎn)單，生產(chǎn)成本較高，由于采用兩副模具進(jìn)行彎曲成形，從而可以避免了方案一中的缺陷，提高了彎曲件的質(zhì)量，但由于采用兩副模具進(jìn)行生產(chǎn)，生產(chǎn)效率低，另外，凹模的強(qiáng)度不易保證。方案三、模具結(jié)構(gòu)復(fù)雜，生產(chǎn)制造成本與方案二差不多，但是工件尺寸精度，位置精度容易保證，生產(chǎn)效率也高。綜上所述，經(jīng)過對(duì)三種方案的比較分析可見，該工件的彎曲成型生產(chǎn)采用方案三比較合理。第三章 模具相關(guān)計(jì)算3.1模具成形力的計(jì)算3.1.1 彎曲應(yīng)力的計(jì)算該模具工件屬于自由彎曲成型，所以U形件彎曲力： = 式中：自由彎曲在沖壓行程結(jié)束時(shí)的彎曲力(N); B彎曲件的寬度,B=10mm; t 彎曲材料的厚度(mm); r 彎曲件的內(nèi)彎曲半徑(mm); 材料的抗拉強(qiáng)度(MPa); K安全系數(shù),一般取K=1.3。 = =3276（N）；3.1.2 壓料力的計(jì)算據(jù)公式(3.5.4),如果彎曲模設(shè)有頂出裝置或壓料裝置時(shí),其頂出力可以近似取自由彎曲力的30% 80%即: =(0.3 0.8) 在此取: =0.6 =0.6 3276 =1965.6 N3.1.3 初壓力機(jī)根據(jù)公式(3.5.5)即: (1.2 1.3) (+)式中: -彎曲應(yīng)力 -壓料力考慮到彎曲工件板料較厚,而且板寬也較大,壓力機(jī)公稱壓力應(yīng)取值偏大為宜。在此取: 1.3(+) =1.3(3276+1965.6) =6814.08 N根據(jù)計(jì)算結(jié)果,查表2-3初選壓力機(jī)為：J23-31.5。3.1.4 彎曲件毛坯坯料尺寸的計(jì)算 因?yàn)閺澢膹澢鷪A角半徑較大（r0.5t）,應(yīng)根據(jù)中性層長(zhǎng)度不變?cè)碛?jì)算。中性層位置以曲率半徑表示，通用用下面經(jīng)驗(yàn)公式2.1確定 =r+xt (2.1) 式中 r彎曲件的內(nèi)彎曲半徑； t板料厚度； x中性層位移系數(shù)。相對(duì)彎曲半徑r1/t=1.5,、r2/t=2.25，由表3.4可查的中性層的位移系數(shù)x分別為0.44,、0.45。則：1=r+xt=3+0.442=3.882=r+xt=4.5+0.452=5.4 坯料的總長(zhǎng)度等于彎曲件直線部分長(zhǎng)度和彎曲圓角部分應(yīng)變中性層長(zhǎng)度之和，即=6.09 =8.48長(zhǎng)度方向的總長(zhǎng)度計(jì)算公式為：，又因?yàn)樵摴ぜ笥覍?duì)稱.則：=2（6.5+25.5）+30+2+2=94+29.14=123.14（mm）毛坯料的長(zhǎng)度尺寸二維圖如下圖：制件展開圖3.2 彎曲模工作部分尺寸的設(shè)計(jì)3.2.1 凸模圓角半徑由方案三可知,所設(shè)計(jì)的復(fù)合模整個(gè)工作原理可分為兩部分: U型彎曲和在U 型彎曲基礎(chǔ)上的 U型彎曲。歸根到底,其設(shè)計(jì)為U 型彎曲種類,所以,其設(shè)計(jì)可按U 型件設(shè)計(jì)方法設(shè)計(jì)因?yàn)?1.5、2.25, 值較小,所以取=r=3mm、4.5mm3.2.2 凹模圓角半徑根據(jù)實(shí)際生產(chǎn)經(jīng)驗(yàn)可知: 當(dāng)t = 2 4 mm 時(shí), =(2 3) t從保證制件精度要求考慮,特別是所設(shè)計(jì)的彎曲復(fù)合模值不宜取大值。在此?。? t2 24 mm 。3.2.3 凹模深度 圖6 凹模深度過小,則坯料兩端受壓部分太多,工件回彈大,而且不平直,影響工件質(zhì)量。如果過大,則浪費(fèi)模具鋼材,且需沖床有較大的工作行程。由前面計(jì)算可知彎曲件邊長(zhǎng)L=+ =25.5+6.5+8.48 =40.48 mm據(jù)邊長(zhǎng)L=40.48 mm 查表19.3-18得: = 20 mm3.2.4 凹凸模間隙計(jì)算查的U 型件彎曲的凸凹模單邊間隙可按下式計(jì)算: C = + x t = t + + x t 式中: C彎曲凹、凸模單邊間隙(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間隙系數(shù),查表19.3-19得 X = 0.05 ; 所以: C = 2 + 0.006 + 0.052 =2.106 mm3.3 U 形彎曲凸凹模尺寸的設(shè)計(jì) 圖7由工件圖上可知:工件是內(nèi)形標(biāo)注的彎曲件,設(shè)計(jì)時(shí)應(yīng)該以凸模為基準(zhǔn)先確定凹模尺寸。再利用凸凹間隙求出凹模的尺寸。根據(jù)教程公式(3.944)與(3.9.5)得: 凸模尺寸為: = ( + 0.75 式中: 凸模橫向尺寸(mm); 彎曲件橫向的最小極限尺寸(mm); 彎曲件的尺寸公差(mm); 凸模的制造公差,采用IT7級(jí)。 所以: =(36 + 0.75 0.62 =36.465查表1-6標(biāo)準(zhǔn)公差數(shù)值IT7級(jí)得: =36.465 mm凹模尺寸為: =( + Z 式中: 凹模橫向尺寸(mm); Z凹凸模雙面間隙(mm); 凹模的制造公差,取IT8級(jí)得: = (36.46 + 4.212 = 40.672查表1-6標(biāo)準(zhǔn)公差值IT 8級(jí)得: = 40.873.4 橡皮的選擇3.4.1 橡皮高度的選擇 為保證橡皮不致過早失去彈性而損壞，一般?。?(5.1)式中 橡皮自由狀態(tài)下高度，mm； 所需工作行程，mm。工作行程可知所需工作行程為25.5mm，則自由狀態(tài)下橡皮的高度選為85mm。3.4.2 橡皮外徑的選擇根據(jù)模具特點(diǎn)，選擇圓柱形橡皮。由沖壓手冊(cè)表10-6查得外徑的計(jì)算公式為5.2：D= (5.2)式中 F壓力，由上文知道F=6814.08N。 P與橡皮壓縮量有關(guān)的單位壓力。由表10-7查得壓縮量為30%的時(shí)候的單位壓力位1.52MPa。則D=75.45（mm）又有校驗(yàn)公式：，D為橡皮外徑，即是D170mm且D56.66mm。選橡皮外徑為60mm。3.4.3 橡皮的連接固定橡皮靠一個(gè)法蘭板固定在下模座上，并有螺釘連接，工作力通過頂桿傳遞給頂板，以保證在工作的時(shí)候頂板于凸模夾緊工件。第四章 彎曲模具的選擇4.1模具結(jié)構(gòu)選擇由彎曲工藝分析可知,采用復(fù)合模,所以模具類型為復(fù)合模。具體結(jié)構(gòu)如下土所示:圖8八字?jǐn)[塊復(fù)合模結(jié)構(gòu)模具上模部分主要由: 凹模、打桿、壓板、組成。卸料方式采用剛性打件裝置卸件,工作原理:上?；爻?壓力機(jī)限位裝置迫使打桿推動(dòng)壓板把彎曲件從凹模腔中推出。下模部分由凸模,限位釘(2個(gè)),擺塊(一對(duì)),銷軸(2個(gè)),導(dǎo)板,銷釘(2個(gè)),內(nèi)六方螺釘(4個(gè)),下模座,限位塊(2個(gè)),螺釘(2個(gè)),上墊板,下墊板,彈簧等零件組成。彎曲坯料由前一沖裁工序準(zhǔn)備尺寸為:123.14 mm x 10 mm ,板料由前方送進(jìn),送料方向定位由限位釘限位,左右方向由限位塊定位。板料定位后,上模下行,凸模壓入凹模同時(shí)把板料拉入模腔內(nèi),進(jìn)行首次U型彎曲動(dòng)作;當(dāng)凸模壓入凹模深度16 mm時(shí),首次U型彎曲完成,進(jìn)入二次彎曲動(dòng)作,這時(shí),在上模下行力的驅(qū)使下,擺塊被迫向左右擺動(dòng),同時(shí)板料發(fā)生二次彎曲動(dòng)作,最后工件成型為 U型件。由于彎曲回彈力的作用下,工件被卡在凹模腔內(nèi),隨著上?；爻?。當(dāng)上模的打桿觸動(dòng)壓力機(jī)的限位裝置時(shí),達(dá)桿推動(dòng)壓板迫使工件從凹模中頂出,卸下工件。在上?；爻掏瑫r(shí),下模的彈簧彈性勢(shì)能釋放,驅(qū)使凸模回程,從而完成整個(gè)工件的彎曲動(dòng)作。4.2定位方式的選擇因?yàn)槟＞卟捎玫氖乔耙还ば驔_裁好的板料,板料由模具前方送進(jìn),送進(jìn)方向在凸模的頂部設(shè)有兩個(gè)限位釘定位,左右方向采用一對(duì)定位塊定位。4.3出件方式的設(shè)計(jì) 彎曲成型后由于彎曲回彈力的作用下,工件回卡在凹模內(nèi),為此,在這里采用了上出現(xiàn)的方式,利用壓力機(jī)的限位裝置迫使打桿推動(dòng)壓板頂出工件。第五章 主要零件結(jié)構(gòu)的設(shè)計(jì)5.1工作零件的結(jié)構(gòu)設(shè)計(jì)5.1.1 凸模的結(jié)構(gòu)草圖如下所示: 圖9凸模的結(jié)構(gòu)草圖在凸模頂部鉆兩個(gè)的孔固定兩個(gè)限位釘,凸模與限位釘?shù)呐浜习碒7 / n6 配合。在底部鉆一螺孔用來與上墊板連接,另外在兩側(cè)各鉆兩個(gè)銷孔用以安裝擺塊,其中銷釘與銷孔采用H7 / m6 配合。5.1.2 凸模主要尺寸的計(jì)算 長(zhǎng)度方向: = = = 10 mm 式中: 擺塊的寬度(mm); 坯料寬度10 mm 。 L = + 2 t 式中: t凸模長(zhǎng)度方向上側(cè)壁厚度,綜合考慮到模具強(qiáng)度,剛度和生產(chǎn)成本,選t = 10 mm 。 L =10 + 2 15 = 40 mm 寬度方向: 由前面凸模橫向尺寸計(jì)算可知: B = = 36.465 mm; = B 2 P 式中: p 擺塊的厚度,由后面擺塊設(shè)計(jì)中可知, p =10mm。所以: = 36.465 2 10 = 16.465 mm d = + p / 2 = 16.465+ 10/ 2 = 21.465 mm從定位準(zhǔn)確和加工難易程度考慮,在此選R =5mm。 高度方向: = = 18 mm 式中: 首次彎曲時(shí),凸模進(jìn)入凹模的深度18 mm。 = + P / 2 = 18 +5 = 23 mm h = + + + 式中: 首次彎曲,凸模進(jìn)入凹模的深度(mm) ; 擺塊高度,由后面擺塊設(shè)計(jì)中可知 = 49.5mm 。 導(dǎo)板的高度8 mm,由后面的設(shè)計(jì)可知; 下模座的高度26 mm,由后面的設(shè)計(jì)可知。 所以: h = 18 +49.5 + 8 + 26 = 101.5mm凸模其余尺寸的設(shè)計(jì)和具體結(jié)構(gòu)的設(shè)計(jì)可參見后面的凸模零件圖所示。5.2 凹模的結(jié)構(gòu)設(shè)計(jì)考慮到凹模在彎曲時(shí)所受的彎曲力和左右張力都比較大,因此,對(duì)凹模的強(qiáng)度和剛度都要有較高的要求。為了保證凹模的強(qiáng)度和剛度,在此把凹模和模柄做成一個(gè)整體,其結(jié)構(gòu)草圖如下所示:圖105.2.1 凹模主要尺寸的設(shè)計(jì) 長(zhǎng)度方向: 由前面的計(jì)算可知: = = 36.465 mm 。 L = + 2 式中: 凹模側(cè)壁厚度,因?yàn)楣ぜ诘诙螐澢尚褪窃诎寄Ｅc擺塊的共同作用下成型的,所以凹模壁厚度應(yīng)略大于 U工件的凸緣外伸部分尺寸,即: + 由前面彎曲件坯料尺寸計(jì)算可知, =6.5mm , = 8.48 mm 。 所以: 6.5 + 8.48 =14.98 mm綜合考慮模具剛度和生產(chǎn)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: 首次彎曲凸模進(jìn)入凹模的深度 =18 mm ； 壓板高度（mm），= 23 mm 。所以： = 18 + 23 = 41 mm凹模其余尺寸的設(shè)計(jì)和凹模結(jié)構(gòu)的具體設(shè)計(jì)可參見后面的凹模結(jié)構(gòu)零件圖所示。5.3 擺塊的結(jié)構(gòu)的設(shè)計(jì)5.3.1 擺塊的結(jié)構(gòu)草圖如下所示：圖11擺塊草圖5.3.2 擺塊的主要尺寸的設(shè)計(jì)圓角半徑R：R = / 2 式中： 擺塊的厚度（mm），根據(jù)擺塊的工作受力情況和生產(chǎn)成本考慮在此選 = 10 mm 。 所以：R = 10 / 2 = 5 mm擺塊寬度B：B = = 10 mm 式中： 彎曲坯料的板寬10 mm。擺塊的工作原理圖如下所示：圖12擺塊工作原理 由上面擺塊工作原理得L的計(jì)算公式如下： L = + + 式中： 模側(cè)壁的厚度，= 25.5 mm； 坯料厚度，= 2 mm； 擺塊厚度，= 10 mm。 L =25.5 + 2 + 10 / 2 =32.5mm擺塊的其余尺寸設(shè)計(jì)與及具體結(jié)構(gòu)可參見后面擺塊零件圖所示。5.4 定位零件的設(shè)計(jì)坯料的定位采用限位釘前方定位和定位塊左右定位，限位釘與凸模頂孔采用H7 / n6配合固定,定位塊采用銷釘定位,螺桿固定在下模座上。5.4.1 限位釘?shù)脑O(shè)計(jì)限位釘?shù)慕Y(jié)構(gòu)草圖如下所示:圖13限位螺釘結(jié)構(gòu)草圖 由于限位釘只起限位作用,基本上不受過大的力作用,所以限位釘尺寸設(shè)計(jì)如下即可滿足使用要求: = 5 mm D = 8 mm h = 5 mm其余尺寸設(shè)計(jì)見后面限位釘零件圖所示。5.5 定位塊的設(shè)計(jì) 定位塊的結(jié)構(gòu)草圖如下所示:圖14定位塊結(jié)構(gòu)草圖定位塊主要工作尺寸H可按以下公式計(jì)算: H = + t + 式中: H 定位塊主要工作尺寸(mm); 凸模高度, = 101.5 mm ; t 坯料厚度, t = 2 mm ; 為定位可靠,設(shè)定的自由高度,在此選定= 5 mm。 所以: H = 101.5+ 2 + 5 =108.5 mm定位塊的其余尺寸設(shè)計(jì)及具體結(jié)構(gòu)可參見后面定位塊零件圖所示。5.6 彈頂部件的設(shè)計(jì)根據(jù)工件彎曲受力，在此采用橡膠作彈性元件，該模具采用4根彈簧，上下墊板中間，由4螺桿組成彈頂部件固定。5.6.1 墊板的設(shè)計(jì)由模具結(jié)構(gòu)所限，上下墊板均是圓形結(jié)構(gòu)，主要設(shè)計(jì)如下：上墊板： 直徑115 mm ,厚度12 mm ；下墊板： 直徑115 mm ,厚度12 mm ；上下墊板均采用45鋼制造，淬火硬度40 45 HRC 。其具體結(jié)構(gòu)見后面墊板零件圖所示。5.6.2 導(dǎo)板的設(shè)計(jì)導(dǎo)板主要起導(dǎo)向定位作用，選用材料T8A，淬火硬度58 60 HRC。制造尺寸：143 mm x 115 mm x 8 mm 。其具體結(jié)構(gòu)以及尺寸設(shè)計(jì)見后面墊板零件圖所示。第六章 壓力機(jī)的參數(shù)與校核 由前面壓力機(jī)公稱壓力計(jì)算初選的壓力機(jī)型號(hào)：J23-10，查模具實(shí)用技術(shù)手冊(cè)表2-3得壓力機(jī)主要技術(shù)參數(shù)如下：公稱壓力：100 KN ；滑塊行程：45 mm ；最大閉合高度：180 mm ；最大裝模高度：180 mm ；連桿調(diào)節(jié)長(zhǎng)度：35 mm ；工作臺(tái)尺寸（前后x左右）：130 mm x 200 mm ；墊板尺寸（厚度）：35 mm ；模柄孔尺寸：30 mm x 60 mm ；最大傾斜角度： 由上述技術(shù)參數(shù)可知，所選壓力機(jī)J23-10型號(hào)可用。第七章 模具零件的加工工藝 7.1 凸模的加工工藝過程表1凸模加工工藝卡工序號(hào)工序名稱工序內(nèi)容1備料鋸床下料60mm 60mm 2煅造煅成42mm x36mm x 120 mm3熱處理退火，硬度 229 HBS4刨刨六面，互為直角40mm x36mm x 120 mm5平磨磨六方91 mm x 55 mm x 115 mm 6數(shù)控銑銑出擺塊安裝槽和凸模邊倒角r=3mm7熱處理淬火硬度58 60 HRC8磨1、 磨外形至圖紙要求尺寸，90 mm x 54 mm x 114 mm 。2、 磨安裝槽至圖紙要求尺寸，70 mm x 16 mm x 84 mm 。9鉗1、 倒角去毛刺。2、 畫線、鉆孔、攻螺紋、精修等。3、 研磨銷孔。4、 精修全部達(dá)設(shè)計(jì)要求。 7.2 凹模的加工工藝過程表2凹模加工工藝卡工序號(hào)工序名稱工序內(nèi)容1下料鋸床下料80 mm x 60 mm 2鍛造煅成67 mm x40 mm x 86 mm 3熱處理退火,硬度退火，硬度229 HBS4刨刨外形與凹模腔，留2 mm 余量。5磨磨外形與凹模腔，留0.5 mm 余量。6銑樹控銑，銑20孔與16孔，留0.5余量。7熱處理淬火硬度58 60 HRC8磨磨至圖紙要求9鉗倒角、去毛刺、精修、研磨凹模腔，16孔。第八章 模具的裝配模具的裝配全過程如下表格所示：表3裝配工序卡序號(hào)工序工藝說明1凸凹模預(yù)配1、 裝配前仔細(xì)檢查凸模形狀、尺寸以及凹模的形狀與尺寸，是否符合圖紙要求尺寸精度，形狀精度。2、 將凸模與凹模相配，檢查加工是否均勻。不適合者，應(yīng)重新修磨或者更換。2凸模裝配以凸模為基準(zhǔn)，安裝好限位釘，擺塊。3裝配下模1、 把導(dǎo)板與下模座安裝好。2、 把彈頂部件安裝到下模座上。3、 安裝凸模，由上端把已經(jīng)安裝好的凸模部件壓入導(dǎo)板孔至上墊板接觸，用螺釘把凸模與上墊板連接擰緊。4、 安裝定位塊，把定位塊安裝到下模座上。4上模安裝把壓桿插入凹模后與壓板連接好，擰緊。5安裝模具分別把上模部分，下模部分安裝到壓力機(jī)工作臺(tái)上，并調(diào)出合理的間隙。6試沖與調(diào)整開機(jī)試沖并根據(jù)試沖的結(jié)果作出相應(yīng)的調(diào)整。第九章 模具試沖下表分別列出了模具在試沖時(shí)常見的故障，原因和調(diào)整方法：表4模具在試沖時(shí)常見的故障，原因和調(diào)整方法常見故障產(chǎn)生原因調(diào)整方法彎曲角度不夠1、 凸凹模的回彈角制造過小2、 凸模進(jìn)入凹模的深度太淺3、 凸、凹模間隙過大4、 試模材料不對(duì)5、 彈頂器的彈力太小1、 加大回彈角2、 調(diào)整沖模閉合高度3、 調(diào)整間隙值4、 更換試沖材料5、 加大彈頂器的彈頂力彎曲位置偏移1、 定位塊的位置不對(duì)2、 凹模兩側(cè)進(jìn)口圓角大小不等，材料滑動(dòng)不一致3、 沒有壓料裝置或者壓料裝置的壓力不足和壓板位置過低4、 凸模沒有對(duì)正凹模1、 調(diào)整定位板位移2、 修磨凹模圓角3、 加大壓料力4、 調(diào)整凸凹模位置沖件的尺寸過長(zhǎng)或者不足1、 凸凹模之間的間隙過小，材料被拉長(zhǎng)2、 壓料裝置壓力過大，將材料拉長(zhǎng)3、 設(shè)計(jì)時(shí)計(jì)算錯(cuò)誤或不正確1、 調(diào)整凸凹模間隙2、 減小壓料力3、 改變坯料尺寸沖件外部有光亮的凹陷1、 凹模的圓角半徑過小，沖件表面被劃痕2、 凸、凹模之間的間隙不均勻3、 凸、凹模表面粗糙度太大1、 加大圓角半徑2、 調(diào)整凸、凹模間隙3、 拋光凸、凹模表面設(shè)計(jì)總結(jié) 通過沖壓課程設(shè)計(jì)，我進(jìn)一步鞏固了沖裁理論知識(shí)。并且也加深了相關(guān)理論知識(shí)的認(rèn)識(shí)。同時(shí)熟練掌握了專業(yè)工具書的使用方法。在整個(gè)過程中，增強(qiáng)了自己的動(dòng)手能力及獨(dú)立思考解決問題的能力。當(dāng)然，由于本人水平有限及缺乏生產(chǎn)實(shí)際經(jīng)驗(yàn)，該設(shè)計(jì)難免存在不足之處。希望老師對(duì)此提出批評(píng)意見，在此表示萬分的感謝。 復(fù)合模具的設(shè)計(jì)，是理論知識(shí)與實(shí)踐有機(jī)的結(jié)合，更加系統(tǒng)地對(duì)理論知識(shí)做了更深切貼實(shí)的闡述。也使我認(rèn)識(shí)到，要想做為一名合理的模具設(shè)計(jì)人員，必須要有扎實(shí)的專業(yè)基礎(chǔ)，并不斷學(xué)習(xí)新知識(shí)新技術(shù)，樹立終身學(xué)習(xí)的觀念，把理論知識(shí)應(yīng)用到實(shí)踐中去，并堅(jiān)持科學(xué)、嚴(yán)謹(jǐn)、求實(shí)的精神，大膽創(chuàng)新，突破新技術(shù)，為國(guó)民經(jīng)濟(jì)的騰飛做出應(yīng)有的貢獻(xiàn)。致謝畢業(yè)設(shè)計(jì)是我們進(jìn)行完了三年的模具設(shè)計(jì)與制造專業(yè)課程后進(jìn)行的，它是對(duì)我們?nèi)陙硭鶎W(xué)課程的又一次深入、系統(tǒng)的綜合性的復(fù)習(xí)，也是一次理論聯(lián)系實(shí)踐的訓(xùn)練。它在我們的學(xué)習(xí)中占有重要的地位。通過這次畢業(yè)設(shè)計(jì)使我在溫習(xí)學(xué)過的知識(shí)的同時(shí)又學(xué)習(xí)了許多新知識(shí)，對(duì)一些原來一知半解的理論也有了進(jìn)一步的的認(rèn)識(shí)。特別是原來所學(xué)的一些專業(yè)基礎(chǔ)課：如機(jī)械制圖、模具材料、公差配合與技術(shù)測(cè)量、冷沖模具設(shè)計(jì)與制造等有了更深刻的理解，使我進(jìn)一步的了解了怎樣將這些知識(shí)運(yùn)用到實(shí)際的設(shè)計(jì)中。同時(shí)還使我更清楚了模具設(shè)計(jì)過程中要考慮的問題，如怎樣使制造的模具既能滿足使用要求又不浪費(fèi)材料，保證工件的經(jīng)濟(jì)性，加工工藝的合理性。在學(xué)校中，我們主要學(xué)的是理論性的知識(shí)，而實(shí)踐性很欠缺，而畢業(yè)設(shè)計(jì)就相當(dāng)于實(shí)戰(zhàn)前的一次演練。通過畢業(yè)設(shè)計(jì)可是把我們以前學(xué)的專業(yè)知識(shí)系統(tǒng)的連貫起來，使我們?cè)跍亓?xí)舊知識(shí)的同時(shí)也可以學(xué)習(xí)到很多新的知識(shí)；這不但提高了我們解決問題的能力，開闊了我們的視野，在一定程度上彌補(bǔ)我們實(shí)踐經(jīng)驗(yàn)的不足，為以后的工作打下堅(jiān)實(shí)的基礎(chǔ)。通過對(duì)彎曲冷沖模的設(shè)計(jì)，我對(duì)沖裁模、彎曲模有了更為深刻的認(rèn)識(shí)，特別是這種彎曲模具的設(shè)計(jì)。彎曲模的主要零件的加工一般比較復(fù)雜，多采用線切割進(jìn)行加工，彎曲回彈的影響因素多，不容易從純理論的角度精確的計(jì)算出來，多需要在試模后再進(jìn)行調(diào)整。在模具的設(shè)計(jì)過程中也遇到了一些難以處理的問題，雖然設(shè)計(jì)中對(duì)它們做出了解決 ，但還是感覺這些方案中還是不能盡如人意，如壓力計(jì)算時(shí)的公式的選用、凸凹模間隙的計(jì)算、卸件機(jī)構(gòu)選用、工作零件距離的調(diào)整，都可以進(jìn)行進(jìn)一步的完善，使生產(chǎn)效率提高。參考文獻(xiàn)1 劉建超，張寶忠主編.沖壓模具設(shè)計(jì)與制造.北京：高等出版社，2004.62 中國(guó)模具設(shè)計(jì)大典編委員會(huì).中國(guó)模具設(shè)計(jì)大典3.南昌：江西科學(xué)出版社，2003.13 任嘉卉主編.公差與配合手冊(cè). 北京：機(jī)械出版社，2000.44 馮炳光主編.模具設(shè)計(jì)與制造簡(jiǎn)明手冊(cè).上海：上?？茖W(xué)技術(shù)出版社，1998.55 中國(guó)標(biāo)準(zhǔn)出版社，全國(guó)彈簧標(biāo)準(zhǔn)化技術(shù)委員會(huì)編.中國(guó)機(jī)械工業(yè)標(biāo)準(zhǔn)匯編彈簧卷.北京：中國(guó)標(biāo)準(zhǔn)出版社，1999.66 中國(guó)輕工模具網(wǎng)模具新聞 中國(guó)模具工業(yè)特點(diǎn)基本狀況及情況 分析2006.4.117 太空模具網(wǎng). 未來10年的模具發(fā)展趨勢(shì). 2005.11.248 中國(guó)金屬加工網(wǎng).沖壓模具行業(yè)發(fā)展現(xiàn)狀及技術(shù)趨勢(shì).2005.69 彭建聲、秦曉剛編著.模具技術(shù)問答. 北京：機(jī)械工業(yè)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.