彎鉤形零件彎曲模結(jié)構(gòu)與設(shè)計【說明書+CAD】,說明書+CAD,彎鉤形零件彎曲模結(jié)構(gòu)與設(shè)計【說明書+CAD】,彎鉤形,零件,彎曲,曲折,結(jié)構(gòu),設(shè)計,說明書,仿單,cad 河南機(jī)電高等?？茖W(xué)校 畢業(yè)設(shè)計論文 設(shè)計題目：彎鉤形零件 彎鉤模設(shè)計 設(shè) 計 者：張 磊 指 導(dǎo) 教 師：楊 占 堯 材 料 工 程 系 模 具 專 業(yè) 0 3 5 班 2006.05.10 畢業(yè)設(shè)計任務(wù)書 設(shè)計題目：彎鉤形零件彎曲模的設(shè)計 設(shè)計時間：10周 設(shè)計任務(wù)：1.完成工件彎曲工藝分析及模具設(shè)計工藝過程 2．繪制模具裝配圖及各零件圖 3．編寫設(shè)計說明書 目錄 1 工件的工藝性分析…………………………………………………1 2 工藝方案的確定……………………………………………………1 3 模具結(jié)構(gòu)形式的確定………………………………………………1 4 工藝設(shè)計……………………………………………………………1 ⑴ 毛坯尺寸的計算……………………………………………1 ⑵ 彎曲力的計算………………………………………………2 ⑶ 彎曲凸、凹模的間隙………………………………………2 ⑷ 彎曲模工作部分尺寸計算…………………………………2 15 模具的總體設(shè)計……………………………………………………3 6 模具主要零件的設(shè)計………………………………………………4 ⑴ 凸模部分………………………………………………4 ⑵ 凹模部分………………………………………………4 7 模具其他主要零件設(shè)計及選用……………………………………5 ⑴ 頂件裝置的設(shè)計………………………………………………5 ① 彈簧的選用………………………………………………5 ② 頂桿的設(shè)計………………………………………………6 ③ 頂件板的設(shè)計……………………………………………6 ⑵ 斜楔、滑塊設(shè)計………………………………………………7 ① 滑塊之間的行程關(guān)系……………………………………7 ② 斜楔、滑塊的尺寸設(shè)計…………………………………7 ⑶ 應(yīng)有可靠的當(dāng)塊………………………………………………7 ⑷ 斜楔與滑塊的結(jié)構(gòu)、尺寸……………………………………7 8選定設(shè)備………………………………………………………………8 9校核壓力安裝尺寸……………………………………………………9 10畫裝配圖和零件圖……………………………………………………9 11編寫技術(shù)文件…………………………………………………………9 12模具的制造和裝配……………………………………………………9 13 彎曲模試沖時出現(xiàn)的缺陷…………………………………………10 總結(jié) ……………………………………………………………………12 致謝 ……………………………………………………………………13 參考文獻(xiàn) ………………………………………………………………14 工件工藝卡 ……………………………………………………………15 凸模加工工藝過程卡 …………………………………………………16 活動凹模加工工藝卡 …………………………………………………17 彎鉤形零件彎曲模結(jié)構(gòu)與設(shè)計 1 工件的工藝性分析： 該工件零件圖如上所示，由零件圖可知。該制件形狀簡單，尺寸不大，厚度適中，一般批量，屬普通彎曲件，但零件上端口處有兩個45°的內(nèi)彎，且長度確定，在設(shè)計模具時應(yīng)注意并控制回彈。由于制件時內(nèi)彎，要考慮合適的取件方案。因有一定的批量，應(yīng)注意模具材料和結(jié)構(gòu)的選擇。 2 工藝方案的確定： 根據(jù)制件的工藝性分析，其有兩道工序，有彎曲和內(nèi)彎，因為此工件是上端內(nèi)彎，因此合理的工藝方案是彎曲——折彎。先將平板毛坯彎曲成“ U”形，再對上端進(jìn)行彎鉤內(nèi)彎。零件成形后，由于工件內(nèi)彎，可縱向取出，此方案是較為合理。 3 模具結(jié)構(gòu)形式的確定： 因工件材料較薄，彎曲中為保證工件平整，采用彈性頂尖裝置。由于零件是內(nèi)彎，需采用活動凹模，斜楔，靠斜楔與滑塊作用使工件內(nèi)彎，活動凹模上設(shè)有彈性回復(fù)裝置。 4 工藝設(shè)計： （1）：毛坯尺寸的計算 計算毛坯尺寸，相對彎曲半徑為 K/t=4/2=2<5 式中：K——彎曲半徑(mm) t——料后（mm） 可見，制件屬于圓角半徑較大的彎曲件，應(yīng)先求彎曲變形區(qū)中性層曲率半徑 ρ（mm） ρ=ν+Kt 由文獻(xiàn)《冷沖壓工藝及模具設(shè)計》中表3－2查得K＝0.39L， r——彎曲半徑 K——中性層系數(shù) ρ＝（4＋0.39x2）mm =4.78 mm 由表3－5查得，最小彎曲半徑rmin＝0.5t＝1mm L考慮到工件的質(zhì)量問題及彎曲工藝要求，取彎鉤處彎曲半徑為r＝t＝2 mm 。 毛坯長度L＝48＋16＋6.5＝70.5mm 考慮工件的誤差，取L＝72mm，b＝22±1.1mm 。 （2）彎曲力的計算 為有效控制回彈，采用校正彎曲，F(xiàn)核＝PA P——材料單位彎曲校正力 A——校正部分投影面積 查得材料15的單位校正力為50mpa. F=50[(48+6.5)*22] =50*54.5*22 =59950N ≈60KN （3）彎曲凸、凹模的間隙 C=t+Δ+k*t C——彎曲凸、凹模單邊間隙 t——料厚 Δ——材料厚度正偏差 k ——系數(shù) 由表查得k ＝0.05 c =t+Δ+kt =2+0.05x2 =2.1mm 2c=4.2mm （4）彎曲模工作部分尺寸計算 （由于制件精度不高，凸、凹模制造公差均采用IT9級） 由于工件外形尺寸要求相對精度高，計算尺寸時，要先計算凹模的尺寸，然后根據(jù)凹模尺寸萊計算凸模尺寸。 由手冊查得沖壓件未注尺寸的極限偏差 L1=48±2.2 L2=16±1.1 L3=6.5±0.8 凹模尺寸 bd=(L-1/2Δ) =46.9 圓角半徑Vd=3t=6mm (查表)t≤2mm時，Vd＝（3-6）t 深度由表3-17得，L=16mm 則凸模尺寸，（bd-2c） =(46.9-4.2) =42.7 Vp=V=4mm 考慮到本工件精度要求不同，取凹模尺寸為48 ，凸模43.8 ，Vp=4mm, Vd=6mm。 5 模具的總體設(shè)計 根據(jù)所需壓彎力的大小，初步考慮使用160KN的壓力機(jī)，模具結(jié)構(gòu)草圖如下，只要有上模板、凸模、凹模、活動凹模、下模板、墊板等組成。 初步設(shè)計模具閉合高度196mm 支撐板外輪廓尺寸為210X210mm 下模板外輪廓尺寸為270X100mm （上面為便于視圖清晰，留有一定尺寸，實際為閉合狀態(tài)） 6 模具主要零件的設(shè)計 ⑴凸模部分 由于該工件的端面是額“ ”形 的，該工件是先彎成 “ ”，后再“ ”形頂端內(nèi)彎，因此，可把凸模設(shè)計成整體式，結(jié)構(gòu)如下： 由于該工件 毛坯式矩形，工件是內(nèi)彎，所以，當(dāng)工件成形后，可縱向取出工件，（取工件時需注意安全）。 ⑵凹模部分 凹模是活動凹模，設(shè)計成滑塊式，左右兩件相對稱，斜面與工件斜面相配合，結(jié)構(gòu)簡單，便于機(jī)械加工。 模具開啟時 模具閉合時 凹模設(shè)計成活動滑塊，靠斜楔作用力使工件內(nèi)彎，斜楔見裝配圖。 7 模具其他主要零件的設(shè)計及選用 (1）頂件裝置的設(shè)計 考慮到工件的工藝結(jié)構(gòu)及制件精度，采用彈性頂件裝置是設(shè)計時，根據(jù)所需的頂件力選擇合適的彈簧。 ② 彈簧的選用：由頂件力選擇彈簧 由于頂件力校大，選用強(qiáng)力彈簧。 外徑D＝30.5mm，內(nèi)徑d＝17.5mm，自由高度h＝63mm。 ② 頂桿的設(shè)計 由于彈簧內(nèi)徑D=17.5mm,取頂桿直徑D=16mm，長度L＝121mm。 結(jié)構(gòu)如圖所示： 上端部長度為 2mm，起定位作用。 ③ 頂件板設(shè)計： 頂件板與凸模一起壓緊工件，尺寸應(yīng)比工件大，其結(jié)構(gòu)如圖所示： 彈性裝置結(jié)構(gòu)如圖所示： ⑵ 斜楔、滑塊的設(shè)計　 在工件內(nèi)彎過程中，需有較大的側(cè)向力，則應(yīng)采用斜楔結(jié)構(gòu)，通過斜楔機(jī)構(gòu)將滑塊的垂直運(yùn)動轉(zhuǎn)化為凸凹模的運(yùn)動方式傾斜運(yùn)動，提供側(cè)向力進(jìn)行內(nèi)彎曲。 ① 斜楔、滑塊之間的行程關(guān)系 確定斜楔的角度主要考慮到機(jī)械效率，行程和受力狀態(tài)。這里取斜楔角為40度。 為使滑塊平穩(wěn)可靠工作 S/S1=0.8391 S——滑塊行程 S1——斜楔行程 S=4.6mm S1=5.478mm 與滑塊接觸長度，b≥斜面斜度/5 b≥1.3mm 則滑塊斜面L ≥1.3+5.478/cos40°=8.45mm,為使滑塊有可靠長度，取L=10mm。 ② 斜楔、滑塊尺寸設(shè)計： 滑塊長度?。?～1）H2,因此是凹模增大，保證其斜面長度， 由工件工藝 可知，滑塊高度H2=16mm，L2=60～50mm，取55mm。 為保證滑塊運(yùn)動的平穩(wěn)，滑塊寬度滿足B2≤2.5L2. B2=40mm L2≥B2/2.5＝40/2.5＝16mm。 L2＝55滿足上式。 ⑶ 應(yīng)有可靠的當(dāng)塊　 擋塊與支撐板設(shè)計成一體，如裝配圖所示： 斜楔與滑塊采用橡皮復(fù)位。 ⑷ 斜楔與滑塊結(jié)構(gòu)、尺寸 如圖所示。 滑動模塊結(jié)構(gòu)圖： 斜楔滑塊工作圖如裝配圖所示。 8 選定設(shè)備： 由所得的彎曲力出算設(shè)備 該零件所需的彎曲力為F=60KN。 模具閉合高度H=196mm 模具外廓尺寸為270X100mm 現(xiàn)有160KN壓力機(jī)，其型號為J23-16F，其主要參數(shù)如下： 公稱壓力：160KN 滑塊行程：80mm 最大裝模高度：205mm 最大封閉高度調(diào)節(jié)量：45mm 臺面尺寸：300mmX450mm 模柄尺寸（孔）：Φ40mm 根據(jù)模具閉合高度，彎曲力，外輪廓尺寸等數(shù)據(jù)選擇此設(shè)備是合適的。 9 校核壓力機(jī)安裝尺寸： 模座外形尺寸為270X100mm，閉合高度為196mm，而J23-16F型壓力機(jī)工作臺尺寸為450X300mm，最大閉合高度為205mm，調(diào)節(jié)量為45mm，故在工作臺上可以安裝；模柄孔尺寸也與本副模具所選模柄尺寸相符。 10 裝配圖和零件圖：見附圖。 11 編寫技術(shù)文件：見工藝卡。 12 模具的制造和裝配： 模具的制造： 彎曲凸、凹模、斜楔均采用T8A，淬硬58-62HRC，在淬火前應(yīng)先試模，在加工凸、凹模時，先加工凹模，凸模按加工出的凹模來配制加工，要保證雙面間隙。凸、凹模圓角半徑加工應(yīng)一致，工作部分表面進(jìn)行拋光。斜楔，滑塊滑動面采用銑刨，淬硬后磨平。 模具的裝配： 在裝配前，檢查模具零件的加工質(zhì)量。 主要組件裝配： 裝配：模柄3是從上模板的下面向上壓入的，在安裝凸模固定板的墊板之前，先把模柄裝好。 模柄與上橫板之間的配合要求是H7/m6，先在壓力機(jī)上將模柄壓入，再加工定位銷孔和螺紋孔，然后把模柄端面突出部分銼平或磨平。安裝好模柄后，用角尺檢查模柄與上模座上平面的垂直度。 凸模、斜楔裝配：凸模、斜楔與固定板的配合要求為H7/m6，裝配時，先在壓力機(jī)上將凸模、斜楔壓入固定板內(nèi)，檢查凸模、斜楔的垂直度，然后將固定板的上平面與凸模、斜楔一齊磨平。 總裝配： 模具的主要組件裝配完畢后開始進(jìn)行總裝配。因為此模具為無導(dǎo)柱模具，凸、凹模間隙在模具安裝到機(jī)床上時進(jìn)行調(diào)整，上、下模裝配次序沒有特別要求，則對上、下模分別安裝。 上模安裝：上述已安裝好了模柄、凸模、斜楔，安裝墊板后，找正位置，裝入銷釘，擰緊螺釘即可安裝上模完成。 下模： （1）把活動凹模裝入固定板中，磨平底面，側(cè)面，安裝滑塊回復(fù)裝置，如圖中所示。 （2）在凹模上安裝定位板，然后在支撐板上安裝好蓋板。 （3）把固定板安裝在下模座上，找正位置后，先在下模座上投窩，加工螺紋孔，然后加工銷釘孔，裝入銷釘（注：要限位銷的安裝），擰緊螺釘，然后安裝好頂件裝置。 （4）把分別安裝好的上、下模進(jìn)行檢查，然后把已裝入固定板的凸模，插入凹模中，檢查是否完全閉合，如有，檢查安裝并進(jìn)行調(diào)整。 （5）凸凹模的間隙調(diào)整：當(dāng)裝配完成后，采用塞尺法來測凸、凹模之間的間隙是否均勻，如不均勻進(jìn)行調(diào)整，也可在裝配完成后進(jìn)行試彎，檢查零件是否合格及表面質(zhì)量。 （6）在生產(chǎn)條件下進(jìn)行試彎，彎曲成形的工件按零件產(chǎn)品圖或試樣進(jìn)行檢查驗收。在驗收過程中，如發(fā)現(xiàn)產(chǎn)品有各種缺陷，則要仔細(xì)分析。找出原因，并對模具進(jìn)行適當(dāng)?shù)恼{(diào)整和修理，然后再進(jìn)行試彎，直到模具正常工作并得到合格的彎曲件為止。然后打標(biāo)記交付生產(chǎn)使用。 13 彎曲模試沖時出現(xiàn)的缺陷，原因及調(diào)整 ⑴ 沖件的彎曲角度不夠 原因： ① 凸凹模的彎曲回彈角制造小。 ② 凸模進(jìn)入凹模深度太淺。 ③ 凸模之間間隙過大。 ④ 校正彎曲的實際單位校正力過小。 調(diào)整方法： ① 修正凸凹模，使彎曲角度達(dá)到要求。 ② 加深凹模深度，增大沖件的有效彎曲變形區(qū)域。 ③ 按實際情況采取措施，減小凸凹模的配合間隙。 ④ 增大校正力或修整凸凹模形狀，使校正力幾種在變形部位。 ⑵ 工件的彎曲位置不合要求 原因：① 定位板位置不正。 ②曲件兩側(cè)受力不平衡產(chǎn)生便移。 ③壓料力不足 方法：①重裝定位板，保證其位置正確 ⑶ 分析方法： ①據(jù)實際情況修正凸、凹模，增大間隙值。 ②取措施減小壓料力。 ③在試模后確定。 ⑷ 表面擦傷： 原因：①凹模圓角半徑過小，表面粗糙度不合要求。 ②潤滑不良使坯料粘附于凹模。 ③凸、凹模之間間隙不均勻。 方法：①增大凹模圓角半徑，降低表面粗糙度值。 ②合理潤滑。 ③修正凸、凹模，使間隙均勻。 ⑸ 彎曲部位產(chǎn)生裂紋： 原因：①材料的塑性差。 ②彎曲線與板料的纖維方向平行。 方法：①將坯料退火后彎曲。 ②使彎曲線與板料的纖維方向成一定的彎曲角度。 總 結(jié) 隨著產(chǎn)品向精密化和復(fù)雜化的發(fā)展，產(chǎn)品零件也日益復(fù)雜，級進(jìn)模的工位數(shù)隨之增加，精度要求提高，壽命要求更高，這對級進(jìn)模的設(shè)計就提出了新的要求。由于級進(jìn)模沖壓生產(chǎn)效率高，操作簡單安全，模具壽命長，產(chǎn)品質(zhì)量高，生產(chǎn)成本較低等特點，現(xiàn)國民經(jīng)濟(jì)發(fā)展的同時，各種家用電器、儀表電器、汽車等也越來越多的走進(jìn)了千家萬戶，而家用電器的生產(chǎn)也隨著生產(chǎn)技術(shù)的發(fā)展越來越多地采用多工位級進(jìn)模生產(chǎn)。 彎鉤形零件彎鉤模設(shè)計，是理論知識與實踐有機(jī)的結(jié)合，更加系統(tǒng)地對理論知識做了更深切貼實的闡述。也使我認(rèn)識到，要向做為一名合格的模具設(shè)計人員，必須要有扎實的專業(yè)基礎(chǔ)，并不斷學(xué)習(xí)新知識新技術(shù)，樹立終身學(xué)習(xí)的觀念，把理論知識應(yīng)用到實踐中去，并堅持科學(xué)、嚴(yán)謹(jǐn)、求實的精神，大膽創(chuàng)新，突破新技術(shù)，為國民經(jīng)濟(jì)的騰飛做出應(yīng)有的貢獻(xiàn)。 致 謝 涼風(fēng)習(xí)習(xí)，綠樹成蔭，在這大地萬物都吸足了養(yǎng)分拼命抽枝成長的季節(jié)，我們也將帶著多年學(xué)習(xí)所吸取的養(yǎng)分投入到社會實踐中去，去體現(xiàn)自身的人生價值，實現(xiàn)人生的理想。當(dāng)然，這一切都離不開老師對我們的精心培養(yǎng)和澆灌，而這次的畢業(yè)設(shè)計，更系統(tǒng)地把所學(xué)專業(yè)知識運(yùn)用到實踐中去，使我們所學(xué)專業(yè)知識更加牢固，更加系統(tǒng)化，能順利地完成畢業(yè)設(shè)計，這和指導(dǎo)老師的精心指導(dǎo)和諄諄教誨是分不開的，在這里我衷心地感謝原老師、楊老師、翟老師、程老師、余老師對我的指導(dǎo)和幫助，是你們不辭勞苦地為我們講解了學(xué)習(xí)中遇到的各種問題，使我掌握了模具設(shè)計在這個現(xiàn)代化工業(yè)生產(chǎn)中充當(dāng)生力軍的技能知識，使你們?yōu)槲覍崿F(xiàn)了自身的人生理想插上了堅實的翅膀。我會帶著你們殷切的期望和百倍的熱情投入到以后的工作和生活中去，去實現(xiàn)自身的人生價值，為社會的發(fā)展做出最大的貢獻(xiàn)。 此致 敬禮 參考文獻(xiàn)： １ 《冷沖模設(shè)計與制造》 　高鴻庭主編 機(jī)械工業(yè)出版社 ２ 《冷沖壓模具設(shè)計指導(dǎo)》 　王芳主編 機(jī)械工業(yè)出版社 ３ 《冷沖模設(shè)計指導(dǎo)》 　史鐵梁主編 機(jī)械工業(yè)出版社 ４ 《沖壓工藝與模具設(shè)計》 王芳主編 機(jī)械工業(yè)出版社 ５ 《冷沖模設(shè)計與制造》 姜奎華主編 機(jī)械工業(yè)出版社 ６ 《沖壓工藝學(xué)》 　　姜奎華、肖景容主編 機(jī)械工業(yè)出版社 ７ 《模具設(shè)計與制造簡明手冊》 馮丙堯主編 上?？茖W(xué)技術(shù)出版社 ８ 《沖模設(shè)計應(yīng)用實例》 模具實用技術(shù)手冊 機(jī)械工業(yè)出版社 ９ 《沖壓模具圖冊》 　　　楊占堯主編 機(jī)械工業(yè)出版社 １０ 《模具制造技術(shù)》 　　　羅大金主編 機(jī)械工業(yè)出版社 工件工藝卡 產(chǎn)品名稱：彎鉤形零件 材料牌號：15 規(guī)格71*22*2mm 毛坯尺寸：板料71*22mm 工序：“U”形彎曲——內(nèi)彎 設(shè)備：J23——16F 工藝裝配：彎曲模 檢驗：按產(chǎn)品圖紙檢驗 14 目錄 1． 工件的工藝性分析………………………………………………………………1 2． 工藝方案的確定…………………………………………………………………1 3． 模具結(jié)構(gòu)形式的確定……………………………………………………………1 4． 工藝設(shè)計…………………………………………………………………………1 ⑴ 毛坯尺寸的計算……………………………………………………………1 ⑵ 彎曲力的計算………………………………………………………………2 ⑶ 彎曲凸、凹模的間隙………………………………………………………2 ⑷ 彎曲模工作部分尺寸計算…………………………………………………2 5． 模具的總體設(shè)計…………………………………………………………………3 6． 模具主要零件的設(shè)計……………………………………………………………3 ⑴ 凸模部分………………………………………………………………3 ⑵ 凹模部分………………………………………………………………3 7． 模具其他主要零件設(shè)計及選用…………………………………………………4 ⑴ 頂件裝置的設(shè)計……………………………………………………………5 ① 彈簧的選用……………………………………………………………5 ② 頂桿的設(shè)計……………………………………………………………5 ③ 頂件板的設(shè)計…………………………………………………………5⑵ 斜楔、滑塊的設(shè)計…………………………………………………………7 ① 滑塊之間的行程關(guān)系…………………………………………………7② 斜楔、滑塊的尺寸設(shè)計………………………………………………7 ⑶ 應(yīng)有可靠的當(dāng)塊……………………………………………………………7 ⑷ 斜楔與滑塊的結(jié)構(gòu)、尺寸…………………………………………………7 8． 選定設(shè)備…………………………………………………………………………8 9． 校核壓力安裝尺寸………………………………………………………………9 10. 畫裝配圖和零件圖………………………………………………………………9 11. 編寫技術(shù)文件……………………………………………………………………9 12. 模具的制造和裝配………………………………………………………………9 13 彎曲模試沖時出現(xiàn)的缺陷………………………………………………………10 總結(jié)……………………………………………………………………………………11 致謝……………………………………………………………………………………12 參考文獻(xiàn)………………………………………………………………………………13 工件工藝卡……………………………………………………………………………14 凸模加工工藝過程卡…………………………………………………………………15 活動凹模加工工藝卡…………………………………………………………………16 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.