接頭套零件沖壓成形工藝及模具設(shè)計
接頭套零件沖壓成形工藝及模具設(shè)計,接頭套零件沖壓成形工藝及模具設(shè)計,接頭,零件,沖壓,成形,工藝,模具設(shè)計
學 院中期檢查表學生姓名學 號指導教師董二婷選題情況課題名稱止動板的結(jié)構(gòu)工藝及模具設(shè)計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)書有無開題報告有無外文翻譯質(zhì)量優(yōu)良中差學習態(tài)度、出勤情況好一般差工作進度快按計劃進行慢中期工作匯報及解答問題情況優(yōu)良中差中期成績評定:所在專業(yè)意見: 負責人: 2017 年 3 月 16日 學院任務(wù)書系 部: 專 業(yè): 學生姓名: 學 號: 設(shè)計題目 : 接頭套零件沖壓成形工藝及模具設(shè)計 起 迄 日 期: 指 導 教 師: 2017 年 2 月 13 日 任 務(wù) 書1本設(shè)計課題來源及應(yīng)達到的目的:該題目來源于實際生產(chǎn)中零部件的設(shè)計。在完成設(shè)計之后,可以加強對模具設(shè)計工藝及生產(chǎn)的知識,能熟練掌握相關(guān)設(shè)計手冊的使用,能獨立完成一套模具的設(shè)計及模具工作零件加工工藝的編制,能夠運用模具設(shè)計軟件完成模具裝配圖及零件圖的繪制。2本設(shè)計課題任務(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): 材料為鋼,厚度為1 mm,未注公差均按IT13級精度制造(一)設(shè)計計算說明書部分1、零件的工藝性分析2、沖壓工藝方案的確定3、沖模類型及結(jié)構(gòu)形式的確定4、排樣設(shè)計及材料利用率計算5、沖壓力及壓力中心的計算6、沖壓設(shè)備類型及規(guī)格的選擇7、模具工作部件外形尺寸的設(shè)計與計算8、模具工作部件刃口尺寸的計算9、模具其它零件的選用或設(shè)計10、其他要說明的問題(二)設(shè)計繪圖部分 1、沖壓模具零件圖:要求繪制非標準的零件圖。零件圖的繪制和標注應(yīng)符合制圖標準。要注明全部尺寸,公差配合,形位公差,表面粗糙度,材料,熱處理要求及其它技術(shù)要求。圖幅為A4紙2、模具裝配圖:應(yīng)包括主視圖、俯視圖、制件圖、排樣圖、標題欄和零件明細表。圖幅為A3 紙上述零件圖和裝配圖可打印也可手繪。 所在專業(yè)審查意見:負責人: 年 月 日系部意見:系領(lǐng)導: 年 月 日 說 明 書題目:街頭套零件沖壓成型工藝及模具設(shè)計系 部: 專 業(yè): 班 級: 學生姓名: 學 號: 指導教師: 2017年 4月20日 機 械 加 工 工 藝 過 程 卡 零件號零 件 名 稱工序號工 序 名 稱工序內(nèi)容夾 具刀 具量 具1鍛造鍛造毛坯專用夾具游標卡尺2熱處理退火專用夾具游標卡尺3車粗車三抓卡盤車刀游標卡尺4車粗車(直徑55、60、65、70的圓)留有余量三抓卡盤車刀游標卡尺5車粗車(直徑176外援表面留有余量)三抓卡盤車刀游標卡尺6熱處理調(diào)制專用夾具游標卡尺7鉆鉆端面直徑30的孔普通夾具鉆頭游標卡尺8鉆鉆各種底面孔普通夾具鉆頭游標卡尺9鉸鉸孔并修復普通夾具鉸刀游標卡尺10銑粗銑凹模普通夾具銑刀游標卡尺11熱處理淬火專用夾具游標卡尺12車精加工三抓卡盤車刀游標卡尺13銑精加工普通夾具銑刀游標卡尺14去毛刺去除全部毛刺專用夾具游標卡尺15終撿檢查全部零件圖樣要求游標卡尺 編制 校對 審核 批準 學院評語學生姓名: 班級: 學號: 題 目: 接頭套零件沖壓成形工藝及模具設(shè)計 綜合成績: 指導者評語: 該生能照格式要求撰寫說明書,查閱了大量的文獻資料,模具圖形繪制基本符合國標要求,工作量適中,模具結(jié)構(gòu)較合理,可以進行答辯,建議成績及格。 指導者(簽字): 年 月 日評語評閱者評語:該生的設(shè)計說明書的撰寫符合格式要求,圖形繪制基本符合國標規(guī)定,工作量滿足畢業(yè)要求,可以進行答辯。建議成績及格。 評閱者(簽字): 年 月 日答辯委員會(小組)評語: 答辯委員會(小組)負責人(簽字): 年 月 日 1 緒論 目前,我國沖壓技術(shù)與工業(yè)發(fā)達國家相比還相當?shù)穆浜?,主要原因是我國在沖壓基礎(chǔ)理論及成形工藝、模具標準化、模具設(shè)計、模具制造工藝及設(shè)備等方面與工業(yè)發(fā)達的國家尚有相當大的差距,導致我國模具在壽命、效率、加工精度、生產(chǎn)周期等方面與工業(yè)發(fā)達國家的模具相比差距相當大。 1.1國內(nèi)模具的現(xiàn)狀和發(fā)展趨勢我國模具近年來發(fā)展很快,據(jù)不完全統(tǒng)計,2003年我國模具生產(chǎn)廠點約有2萬多家,從業(yè)人員約50多萬人,2004年模具行業(yè)的發(fā)展保持良好勢頭,模具企業(yè)總體上訂單充足,任務(wù)飽滿,2004年模具產(chǎn)值530億元。進口模具18.13億美元,出口模具4.91億美元,分別比2003年增長18%、32.4%和45.9%。進出口之比2004年為3.69:1,進出口相抵后的進凈口達13.2億美元,為凈進口量較大的國家。在2萬多家生產(chǎn)廠點中,有一半以上是自產(chǎn)自用的。在模具企業(yè)中,產(chǎn)值過億元的模具企業(yè)只有20多家,中型企業(yè)幾十家,其余都是小型企業(yè)。近年來,模具行業(yè)結(jié)構(gòu)調(diào)整和體制改革步伐加快,主要表現(xiàn)為:大型、精密、復雜、長壽命中高檔模具及模具標準件發(fā)展速度快于一般模具產(chǎn)品;專業(yè)模具廠數(shù)量增加,能力提高較快;三資及私營企業(yè)發(fā)展迅速;國企股份制改造步伐加快等。雖然說我國模具業(yè)發(fā)展迅速,但遠遠不能適應(yīng)國民經(jīng)濟發(fā)展的需要。我國尚存在以下幾方面的不足: 第一,體制不順,基礎(chǔ)薄弱。 “三資”企業(yè)雖然已經(jīng)對中國模具工業(yè)的發(fā)展起了積極的推動作用,私營企業(yè)近年來發(fā)展較快,國企改革也在進行之中,但總體來看,體制和機制尚不適應(yīng)市場經(jīng)濟,再加上國內(nèi)模具工業(yè)基礎(chǔ)薄弱,因此,行業(yè)發(fā)展還不盡如人意,特別是總體水平和高新技術(shù)方面。 第二,開發(fā)能力較差,經(jīng)濟效益欠佳.我國模具企業(yè)技術(shù)人員比例低,水平較低,且不重視產(chǎn)品開發(fā),在市場中經(jīng)常處于被動地位。我國每個模具職工平均年創(chuàng)造產(chǎn)值約合1萬美元,國外模具工業(yè)發(fā)達國家大多是1520萬美元,有的高達2530萬 美元,與之相對的是我國相當一部分模具企業(yè)還沿用過去作坊式管理,真正實現(xiàn)現(xiàn)代化企業(yè)管理的企業(yè)較少。 第三,工藝裝備水平低,且配套性不好,利用率低雖然國內(nèi)許多企業(yè)采用了先進的加工設(shè)備,但總的來看裝備水平仍比國外企業(yè)落后許多,特別是設(shè)備數(shù)控化率和CAD/CAM應(yīng)用覆蓋率要比國外企業(yè)低得多。由于體制和資金等原因,引進設(shè)備不配套,設(shè)備與附配件不配套現(xiàn)象十分普遍,設(shè)備利用率低的問題長期得不到較好解決。裝備水平低,帶來中國模具企業(yè)鉗工比例過高等問題。 第四,專業(yè)化、標準化、商品化的程度低、協(xié)作差 由于長期以來受“大而全”“小而全”影響,許多模具企業(yè)觀念落后,模具企業(yè)專業(yè)化生產(chǎn)水平低,專業(yè)化分工不細,商品化程度也低。目前國內(nèi)每年生產(chǎn)的模具,商品模具只占45%左右,其馀為自產(chǎn)自用。模具企業(yè)之間協(xié)作不好,難以完成較大規(guī)模的模具成套任務(wù),與國際水平相比要落后許多。模具標準化水平低,標準件使用覆蓋率低也對模具質(zhì)量、成本有較大影響,對模具制造周期影響尤甚。 第五,模具材料及模具相關(guān)技術(shù)落后模具材料性能、質(zhì)量和品種往往會影響模具質(zhì)量、壽命及成本,國產(chǎn)模具鋼與國外進口鋼相比,無論是質(zhì)量還是品種規(guī)格,都有較大差距。塑料、板材、設(shè)備等性能差,也直接影響模具水平的提高。 巨大的市場需求將推動中國模具的工業(yè)調(diào)整發(fā)展。雖然我國的模具工業(yè)和技術(shù)在過去的十多年得到了快速發(fā)展,但與國外工業(yè)發(fā)達國家相比仍存在較大差距,尚不能完全滿足國民經(jīng)濟高速發(fā)展的需求。未來的十年,中國模具工業(yè)和技術(shù)的主要發(fā)展方向包括以下幾方面: 1)模具日趨大型化; 2)在模具設(shè)計制造中廣泛應(yīng)用CAD/CAE/CAM技術(shù); 3)模具掃描及數(shù)字化系統(tǒng); 4)在塑料模具中推廣應(yīng)用熱流道技術(shù)和高壓注射成型技術(shù); 5)提高模具標準化水平和模具標準件的使用率;6)發(fā)展優(yōu)質(zhì)模具材料和先進的表面處理技術(shù);7)模具的精度將越來越高; 8)模具研磨拋光將自動化、智能化; 9)研究和應(yīng)用模具的高速測量技術(shù)與逆向工程;10)開發(fā)新的成形工藝和模具。1.2國外模具的現(xiàn)狀和發(fā)展趨勢模具是工業(yè)生產(chǎn)關(guān)鍵的工藝裝備,在電子、建材、汽車、電機、電器、儀器儀表、家電和通訊器材等產(chǎn)品中,6080的零部件都要依靠模具成型。用模具生產(chǎn)制作表現(xiàn)出的高效率、低成本、高精度、高一致性和清潔環(huán)保的特性,是其他加工制造方法所無法替代的。模具生產(chǎn)技術(shù)水平的高低,已成為衡量一個國家制造業(yè)水平高低的重要標志,并在很大程度上決定著產(chǎn)品的質(zhì)量、效益和新產(chǎn)品的開發(fā)能力。近幾年,全球模具市場呈現(xiàn)供不應(yīng)求的局面,世界模具市場年交易總額為600650億美元左右。美國、日本、法國、瑞士等國家年出口模具量約占本國模具年總產(chǎn)值的三分之一。國外模具總量中,大型、精密、復雜、長壽命模具的比例占到一半以上;國外模具企業(yè)的組織形式是大而專、大而精。2004年中國模協(xié)在德國訪問時,從德國工、模具行業(yè)組織-德國機械制造商聯(lián)合會(VDMA)工模具協(xié)會了解到,德國有模具企業(yè)約5000家2003年德國模具產(chǎn)值達48億歐元。其中(VDMA)會員模具企業(yè)有90家,這90家骨干模具企業(yè)的產(chǎn)值就占德國模具產(chǎn)值的90%,可見其規(guī)模效益。 隨著時代的進步和技術(shù)的發(fā)展,國外的一些掌握和能運用新技術(shù)的人才如模具結(jié)構(gòu)設(shè)計、模具工藝設(shè)計、高級鉗工及企業(yè)管理人才,他們的技術(shù)水平比較高故人均產(chǎn)值也較高我國每個職工平均每年創(chuàng)造模具產(chǎn)值約合1萬美元左右,而國外模具工業(yè)發(fā)達國家大多1520萬美元,有的達到 2530萬美元。國外先進國家模具標準件使用覆蓋率達70%以上,而我國才達到451.3 冷沖壓模具的分類冷沖壓模具主要用于金屬及非金屬板料的壓力加工,其加工方式可分為分離和成形兩大類。 分離:按一定輪廓線將工件與板料分開。冷沖壓模具是沖壓生產(chǎn)的主要工藝裝備。沖壓件的沖壓質(zhì)量、生產(chǎn)效率以及生產(chǎn)成本等,都與模具類型及其結(jié)構(gòu)設(shè)計有直接關(guān)系。沖壓件的品種、式樣很多,所以沖壓模具的類型也是多種多樣的。為了研究方便,將沖壓模具按照不同特征進行分類,一般有以下幾種分類方法。彎曲模具 彎曲模具又分為自由彎曲模具、校正彎曲模具、V型彎曲模具、U型彎曲模具等。拉深模具 拉深模具又可分為無凸緣筒形件拉深模具、有凸緣筒形件拉深模具、錐形件拉深模具、階梯形件拉深模具、球面件拉深模具、拋物面件拉深模具、盒形件拉深模具等。 成形模具 成形模具又可分為脹形模具、翻邊模具、縮口模具等。 單工序模 壓力機行程一次,只對板料完成一種沖壓工序的模具。例如:落料模具、沖孔模具、切邊模具、彎曲模具、拉深模具等。單工序模結(jié)構(gòu)簡單,造價低,生產(chǎn)效率低,形位精度低。 復合模 模具上僅有一個工位,安排有兩對或兩對以上的凸、凹模,壓力機行程一次,能對板料完成兩種(或兩種以上)的沖壓的模具。其結(jié)構(gòu)的主要特點是:具有復合形式的凸凹模,它既是落料的凸模,又是沖孔的凹模。復合模結(jié)構(gòu)復雜,造價高,生產(chǎn)率適中,形位精度高。 級進模 模具上有n個(n1)工位,在一直線上等距離安裝n對凸、凹模,條料送進一次,壓力機行程一次,模具對板料的不同(n個)位置完成n對沖壓,連續(xù)送進,連續(xù)沖壓。級進模結(jié)構(gòu)復雜,生產(chǎn)率高,產(chǎn)品形位精度適中。級進模又稱為級連續(xù)或跳步模。分為無導向的開式模具、有導向的導板模具和導柱模具等。分為固定導料銷模具、活動導料銷模具、導正銷模具、側(cè)刃定距模具等。此外,可以依據(jù)對沖裁件尺寸、精度等質(zhì)量的不同,把模具分為精密沖裁模具和普通沖裁模具;依據(jù)模具體積的大小,把模具分為小型模具、中型模具和大型模具等。有時還可以依據(jù)壓力機類型、送料方式、出件方式等對模具進行分類。 1.4接頭模具設(shè)計與制造方面 沖孔、落料、拉深是沖壓基本工序之一,它是利用沖裁模在壓力機作用下,將平板坯料進行沖孔或落料的加工方法。一般情況下,一般精度的工件IT8IT7級精度的普通沖裁模;較高精度的工件采用IT7IT6級精度的高級沖裁模。 翻邊是將工件的孔邊緣在模具的作用下,翻出豎直的或一定角度的邊。 只有加強沖裁件基礎(chǔ)理論的研究,才能提供更加準確、實用、方便的計算方法,才能正確地確定沖裁工藝參數(shù)和模具工作部分的幾何形狀與尺寸,解決沖裁中出現(xiàn)的各種實際問題,從而,進一步提高制件質(zhì)量。制件沖孔落料件是最典型的沖裁件,其工作過程很簡單就沖孔落料,可采用單工序模、復合模具或級進模具,根據(jù)計算的結(jié)果和選用的標準模架。為了保證制件的順利加工和順利取件,模具必須有足夠高度。要改變模具的高度,只有從改變導柱和導套的高度。導柱和導套的高度可根據(jù)凸模與凹模工作配合長度決定設(shè)計時可能高度出現(xiàn)誤差,應(yīng)當邊試沖邊修改高度。此設(shè)計分成兩部分,第一部分落料、拉深、沖孔復合模,第二部分翻邊模。在設(shè)計的過程中,將有一定的困難,但有指導老師的悉心指導和自己的努力,相信會完滿的完成畢業(yè)設(shè)計任務(wù)。由于學生水平有限,而且缺乏經(jīng)驗,設(shè)計中難免有不妥之處,肯請各位老師指正。 2. 沖壓工件的工藝分析 工件名稱:接頭套生產(chǎn)批量:中批量材料:08F鋼厚度:1mm對固定套翻邊件進行分析可知,處有內(nèi)孔直徑52翻邊成形,翻邊前應(yīng)預(yù)沖孔,是圓筒件拉深件直徑,經(jīng)計算可一次拉深成形。工序安排為落料,沖孔,拉深,翻邊。 該零件形狀簡單、對稱,是有圓弧組成的。沖裁件內(nèi)外形所能達到的經(jīng)濟精度為IT11 IT14,孔中心與邊緣距離尺寸公差為.將以上精度與零件的精度要求相比較,可認為該零件的精度要求能夠在沖裁加工中得到保證,其他尺寸標注、生產(chǎn)批量等情況,也均符合沖裁的要求,故決定采用沖壓方式可以得到落料、沖孔、拉深件,然后進行翻邊得到制件。2.1制件的總體分析圖示零件材料為08F號鋼板,能夠進行一般的沖壓加工,市場上也容易得到這種材料,價格適中。由工件圖可知:該工件既有落料、沖孔、拉深又有翻邊,但工件是圓形的對稱零件,總的來說加工起來是容易的。 由以上分析可知,圖示零件有比較好的沖壓工藝性,沖壓生產(chǎn)。2.2制件的外形分析該零件有08F號鋼板組成,具有良好的塑性、韌性、冷沖壓性能,能夠進行一般的沖壓加工。多處用圓角過度,以便于模具加工,減少熱處理開裂,減少沖裁時尖角處的崩刃和過快磨損,尺寸精度要求一般。 該零件對稱,只需要落料、拉深、沖孔工序,然后再翻邊。2.3 拉伸件的尺寸精度和表面粗糙度 沖裁件上的未注公差等級定為IT14級,查表確定工件尺寸如下: 尺寸的工件制造公差為0.62 尺寸的工件制造公差為0.75 尺寸的工件制造公差為0.43 尺寸的工件制造公差為0.43沖裁件的斷面粗糙度值與材料塑性、厚度,沖裁間隙,刃口銳鈍及沖模結(jié)構(gòu)相關(guān),工件厚度為1.5mm,其斷面粗糙度值為.2.4 工藝方案確定 該零件所需的基本沖壓工序為落料、拉深。 可擬訂出以下三種工藝方案。 方案一:用簡單模分四次加工,即落料拉深拉伸. 方案二:落料、沖孔復合模,拉深模、翻邊模。 方案三:落料沖孔級進模,再拉深,再翻邊。 采用方案一,生產(chǎn)率低,工件的累計誤差大,操作不方便,由于該工件為中批量生產(chǎn),方案二和方案三更具有優(yōu)越性。但復合模模具的行位精度和尺寸精度容易保證,且生產(chǎn)率也高。盡管模具結(jié)構(gòu)比較復雜但由于零件的幾何形狀簡單對稱,模具制造并不困難。級進模雖生產(chǎn)率也高,但零件的沖裁精度稍差。欲保證沖壓件的行位精度,需要在模具上設(shè)置導正銷導正,故模具制造、安裝較復合模復雜。 通過對上述三種方按的分析比較,該零件采用方案二最佳。 故應(yīng)采用三副模具來完成。 第一副模具為落料沖孔復合模。 第二副模具為單工序拉深模。 第三副模具為單工序翻邊模。3 必要的工藝計算3.1 毛坯尺寸計算 由最終制件從翻邊算起,毛坯的預(yù)沖孔直徑計算。 一次拉深成形。工序安排為落料、拉深、預(yù)沖孔、翻邊等。翻邊前為、髙為9.5mm的無凸緣圓筒形件,如圖2-2所示。計算預(yù)沖孔 D=41.5mm H=7mmH=H-r-t=7-2-1.5=3.5mm由式(5.1)計算翻邊前預(yù)沖孔直徑計算翻邊系數(shù) 由表5.1計算翻邊系數(shù)為 由查表5.2得知低碳鋼極限翻邊系數(shù)為0.65m,所以該零件能一次翻邊成形,預(yù)沖孔直徑。計算翻邊力 落料毛坯直徑計算 拉深件毛坯尺寸確定原則的依據(jù): 體積不變原則 相似原則 毛坯尺寸應(yīng)包括修邊余量因=1.5mm1mm,所以應(yīng)按中線尺寸計算。(1)確定修邊余量 根據(jù)拉深件尺寸,其相對高度為h/d=(9.5-0.75)/(68-1.5)=8.75/66.50.13查表4-1,得修邊余量h=1mm 則拉深件總的高度h為: h=9.5-0.75+1=9.75mm計算毛坯展開直徑 先判斷能否一次拉深出來,將圖4-53中提供的已知條件d =66.5mm r=2.75mm h=9.75mm 代入式(4-5)可求出毛坯的直徑D3.2排樣設(shè)計與計算設(shè)計復合模時,首先要設(shè)計條料排樣圖。根據(jù)工件的形狀選擇有廢料排樣,且為直排的形式,雖然材料的利用率低于少廢料和無廢料排樣,但工件的精度高,且易于保證工件外形的圓角。確定搭邊與搭肩值搭邊和搭肩值一般是由經(jīng)驗確定的,查表2.9可知搭邊值工件間 ,側(cè)面。確定零件的排樣方案設(shè)計模具時,條料的排樣很重要。分析零件形狀可知,確定排樣方案:條料從右至左送進,落料凸模的沖壓力比較均勻,零件形狀精度容易保證。條料的排樣如圖2-3所示。 計算送料步距和條料的寬度 按如上排樣方式,并根據(jù)工件的尺寸確定送料步距為83mm。 查表2.5.3可知條料寬度單向偏差為,由公式計算如下: 計算材料的利用率:根據(jù)一般的市場供應(yīng)情況,原材料選用的冷軋薄鋼板()。每塊可剪規(guī)格條料7條,材料剪切利用率達98%。計算沖壓件的面積:由文獻2 一個步距的材料利用率通用計算公式: 式中 一個步距內(nèi)零件實際面積; 一張步距內(nèi)所需毛坯面積; 條料寬度 ; 送料步距 ;得 3.3計算沖壓力和初選壓力機(1)落料力的計算 式中 落料力;沖裁件剪切周邊長度;沖裁件材料厚度;被沖材料的抗剪強度;系數(shù),一般取。落料力為: (2)沖孔力的計算 式中 工件內(nèi)輪廓周長() 則(3)卸料力的計算 式中卸料力系數(shù);查手冊知 則卸料力為: (4)推件力的計算: 按式計算 式中 推件力因數(shù),查表得; 卡在凹模內(nèi)的工件數(shù),查7得n=3; 則推件力為 故工序總力: 為保證沖壓力足夠,一般沖裁時壓力機噸位應(yīng)比計算的沖壓力大30%左右,即 (5)初選壓力機 查文獻4開式可傾壓力機參數(shù)初選壓力機型號為和,見下表型號公稱壓力滑塊行程最大封閉高度工作臺尺寸可傾斜角/。封閉高度調(diào)節(jié)量4008030046070030653.4壓力中心的確定 由于該零件是中心對稱圖形,故壓力中心位于零件輪廓圖形的幾何中心上。4 模具總體結(jié)構(gòu)設(shè)計 4.1 模具類型設(shè)計由沖壓工藝分析可知,零件材料為08F號鋼板,能夠進行一般的沖壓加工,市場上也容易得到這種材料,價格適中。該零件屬于中型尺寸零件,料厚1.5mm,外形簡單,尺寸精度要求一般,因此可采用落料工藝獲得。該零件有冷軋08號鋼組成,具有良好的塑性、韌性、冷沖壓性能,能夠進行一般的沖壓加工。多處用圓角過度,以便于模具加工,減少熱處理開裂,減少沖裁時尖角處的崩刃和過快磨損,尺寸精度要求一般。該零件左右對稱.所以模具類型為倒裝復合模模。4.2 模具具體結(jié)構(gòu)設(shè)計(1)正倒裝結(jié)構(gòu)的確定根據(jù)上述分析,采用倒裝復合模具可直接利用壓力機的打桿裝置進行推件,卸料可靠,便于操作。(2)送料方式的確定因是中批量生產(chǎn),采用手動送料方式。(3)定位裝置的確定因該制件采用的是倒裝復合模,所以直接用擋料銷和導料銷即可。(4)導向方式的選擇為確保零件的質(zhì)量及穩(wěn)定性,選用導柱、導套導向。由于該零件導尺寸不大,且精度要求不是太高,所以宜采用后側(cè)導柱模架。(5)卸料、壓料方式本模具采用倒裝結(jié)構(gòu),卡于凸凹模上的廢料可由卸料板推出,而沖孔廢料則可以在下模座中開設(shè)通槽,使廢料從孔洞中落下。頂件壓邊裝置安裝在下模妨礙了沖孔廢料的排出。5 主要工作零部件設(shè)計 因為材料為08鋼,厚度為,查表2.4得間隙值 , 由手冊表查得:尺寸的工件制造公差為0.62尺寸的工件制造公差為0.75尺寸的工件制造公差為0.43尺寸的工件制造公差為0.43已知尺寸公差如下:尺寸的工件制造公差為0.1尺寸的工件制造公差為0.125.1沖孔凸、凹模刃口尺寸的計算由于制件結(jié)構(gòu)簡單,精度要求不高,所以采用凸模和凹模分開加工的方法制作凸、凹模。以孔為基準加工凸模,計算公式如下:設(shè)孔尺寸為對于32.03mm的孔查表2.6得 由于零件為淺拉深,可按有壓邊圈的圓筒形件近似計算。按下式計算: 式中 拉深力(); 拉深件直徑,; 材料厚度; 材料的強度極限(),查手冊b=; 修正因數(shù)。 拉伸系數(shù) 查表得修正因數(shù) 則 . 5.2拉伸工作部分尺寸的計算 確定凸、凹模合理間隙的方法有理論法和查表法兩種。由于理論計算法在生產(chǎn)中使用不方便,常用查表法來確定間隙值。對于尺寸精度、斷面垂直度要求不高的板料的普通沖裁,以提高模具壽命為主,可采用大間隙值。查我國沖裁間隙指導性技術(shù)文件推薦的間隙值表可得:Zmin =0.040mm ,Zmax = 0.060mm ,根據(jù)凸凹模的加工方法的不同,刃口的計算方法也不同,基本上可分為兩類:凸模與凹模分別加工法,凸模與凹模配合加工法。凸凹模配合加工法就是先按設(shè)計尺寸制出一個基準件(凸模或凹模),然后根據(jù)基準件的實際尺寸按間隙配制另一件。因為這種加工方法的特點是模具的間隙由配置保證,工藝比較簡單,并且還可以適當放大基準件的制造公差,使得制造也容易。且精度要求不高,故采用此方法。目前,一般工廠也常常采用此方法。 5.3拉伸凹模的計算1. 制件分析下圖為制件剖視圖,厚度1mm,材料為08鋼 圖4 帶凸緣圓筒件為旋轉(zhuǎn)體,壁厚為1mm,整個結(jié)構(gòu)尺寸較小,適合沖壓成型。底部外直徑為70mm,筒深大約為16mm,材料為08鋼,拉深性能較好,適合于拉伸成型。2坯料拉伸次數(shù)的計算此根據(jù)冷沖模設(shè)計手冊,確定制件的拉深成型次數(shù)。已知,t=2mm,D=124mm,t/D*100%=1.6%(通過附表4.11,1.6介于1.5到2.0之間,不需要壓邊圈),查表2,可知各次的拉深系數(shù)介于坯料相對厚度為1.5到2.0之間,又通過嘗試的方法,確定各次的拉深系數(shù),最終確定出依次為0.6、0.77、0.83、0.84,一共需要4次拉深,滿足要求??芍?,第一次拉深后,𝑑1=0.6*124=74.4mm;第二次拉深后,3=0.83*57.29=47.55mm;最后依次拉深后,4=d=0.84*47.55=40mm。3拉伸深度的計算則第一次的拉深深度為1=0.2574.4(1242-74.42)+0.43*(6.4+8)+0.1474.4(82-6.42)=39.3mm??芍谝淮卫畹淖畲笙鄬Ω叨?=39.34.4=0.52,查附表4.9,0.750.52,滿足設(shè)計的要求,可以繼續(xù)設(shè)計此后的各次拉深深度。根據(jù)以上步驟,并且不斷調(diào)整凸凹模半徑,以后的拉深深度分別為10mm、6mm,最后根據(jù)剩余量得到最后一次的拉深深度。4拉伸凹模的圖如下 5.5拉伸凸模的計算1凸模局部圖,實線為沖裁該工件所用沖孔凸模刃口的輪廓線,圖中虛線表示凸模刃口磨損后尺寸的變化情況。凸模磨損后刃口尺寸有變大,變小和不變?nèi)N情況,由圖可知,此凸模刃口尺寸磨損后變小。按一般沖孔凸模尺寸計算公式計算,即: 相應(yīng)的凸模刃口尺寸; 工件孔的最大極限尺寸; 工件公差。凸摸制造偏差通常取 系數(shù),為了避免沖裁件尺寸都偏向極限尺寸,應(yīng)使沖裁件的實際尺寸盡量接近沖裁件公差帶的中間尺寸。x值在0.51之間,與沖裁件的精度等級有關(guān)。工件精度IT10以上 x=1工件精度IT x=0.75工件精度IT14 x=0.5 因工件精度IT14,所以取.x=0.5。 以上是沖孔凸摸刃口尺寸的計算方法。沖孔用的凹模刃口尺寸,按凸模實際尺寸配制,并保證最小間隙Zmin。故在凹模上只標注基本尺寸,不標注偏差,同時在圖樣技術(shù)要求上注明:“凹模刃口尺寸按凸模實際尺寸配制,保證雙面間隙為Zmin Zmax。”即保證最小雙面間隙為0.040 mm。凸模圖如下所示 5.6凹凸模的結(jié)構(gòu)設(shè)計 對于軟鋼材料來說,拉伸凸凹模的間隙值為:第一次拉伸為1.31.5;中間各次拉伸為1.21.3;最好拉伸為1.1 。對于黃銅、鋁的第一次拉伸的間隙值為:1.31.4;中間各次為1.151.2;最后拉伸為1.1 通過材料計算所需拉伸次數(shù)(一次拉伸還是多次拉伸),假設(shè)一次拉伸,典型拉伸模具包括 凹模 凸模 壓邊圈 和上下模板為了避免沖裁件尺寸都偏向極限尺寸,應(yīng)使沖裁件的實際尺寸盡量接近沖裁件公差帶的中間尺寸。X值在0.51之間,與沖裁件的精度等級有關(guān)。查表可得: =0.52.凹模磨損后不變的尺寸(圖中C1),其基本計算公式為。為方便使用,隨工件尺寸的標注方法不同,將其分為三種情況:而圖中C1是符合其第三種情況 即 相應(yīng)的凹模刃口尺寸; 工件的最小極限尺寸; 工件偏差 凹模制造偏差,通常取 以上是落料凹模刃口尺寸的計算方法。落料用的凸模刃口尺寸,按凹模實際尺寸配制,并保證最小間隙Zmin。故在凸模上只標注基本尺寸,不標注偏差,同時在圖樣技術(shù)要求上注明:“凸模刃口尺寸按凹模實際尺寸配制。 6卸料裝置的設(shè)計標記:圓柱頭卸料螺釘M 材料為35,熱處理硬度為28-38HRC 技術(shù)條件按2.橡膠彈簧具有重量輕,彈性大,變形不受限制,較高的內(nèi)阻,可吸收沖擊和高頻振動能量,工作平穩(wěn),噪聲小,安裝和調(diào)試方便,便于維護和保養(yǎng)等優(yōu)點。另外,橡膠彈簧可同時承受多向載荷,可使系統(tǒng)簡單。所以本設(shè)計采用橡膠彈簧。橡膠的選用和計算原則:1:保證橡膠正常工作應(yīng)使橡膠在預(yù)壓縮狀態(tài)下的預(yù)壓力滿足式中 橡膠在預(yù)壓縮狀態(tài)下的壓力 卸料力,取6.3.2:為保證橡膠不過早失效,其允許最大壓縮量不超過其自由高的45%,一般取式中 橡膠允許的總壓縮量 橡膠的自由高度所選橡膠彈簧必須滿足由于 ,故式中 一般取510mm取=5mm則。取則=28mm。取=28mm,=2.8mm式中 A橡膠橫截面積,;。 P橡膠產(chǎn)生的單位面積壓力 ,Mpa;取彈簧壓縮量為35% ,查表得 P=2.1Mpa所以校核:符合設(shè)計合理。 橡膠彈簧的安裝高度 7拉伸模裝配圖的設(shè)計繪制拉伸模采用倒裝結(jié)構(gòu),使用大圓角圓柱形翻邊凸模,工件預(yù)沖孔套在導正銷上定位,壓邊靠壓力機標準彈頂器壓邊,工件若留在上模由頂件器推出,選用對角滑動導向模架。根據(jù)固定板尺寸和閉合高度選用250KN雙柱可傾壓力機。選用JC23-35開式雙柱可傾壓力機。有關(guān)參數(shù)如下表所選擇壓力機的相關(guān)參數(shù):型號公稱壓力滑塊行程最大封閉高度工作臺尺寸可傾斜角/。封閉高度調(diào)節(jié)量55mm3.4拉伸模如圖所示。 結(jié) 束 語接頭屬于復雜的零件,分析其工藝性,并確定工藝方案。根據(jù)計算確定該制件的沖裁力及模具刃口尺寸,然后選取相應(yīng)的壓力機。本設(shè)計主要是沖孔凸、凹模以及拉深工藝的設(shè)計,需要計算凸凹模的間隙、工作零件的尺寸和公差。此外,還需要確定模具工藝零件和結(jié)構(gòu)零件以及模具的總體尺寸,然后根據(jù)上面的設(shè)計繪出模具的總裝圖。 由于在零件制造前進行了預(yù)測,分析了制件在生產(chǎn)過程中可能出現(xiàn)的缺陷,采取了相應(yīng)的工藝措施。因此,模具在生產(chǎn)零件的時候才可以減少廢品的產(chǎn)生。 接頭的形狀結(jié)構(gòu)一般,但是其尺寸相對較大不適合選用標準模架。要保證零件的順利加工和取件,模具必須有足夠的長度,因此需要改變上、下模座的長度,以達到要求。模具工作零件的結(jié)構(gòu)也較為簡單,它可以相應(yīng)的簡化模具結(jié)構(gòu)。便于以后的操作、調(diào)整和維護。接頭沖套成形工藝及模具的設(shè)計,是理論知識與實踐有機的結(jié)合,更加系統(tǒng)地對理論知識做了更深切貼實的闡述。也使我認識到,要想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),并不斷學習新知識新技術(shù),樹立終身學習的觀念,把理論知識應(yīng)用到實踐中去,并堅持科學、嚴謹、求實的精神,大膽創(chuàng)新,突破新技術(shù),為國民經(jīng)濟的騰飛做出應(yīng)有的貢獻。 致 謝時光如電,歲月如梭,三年的大學生活即將結(jié)束,而我也即將離開可敬的老師和熟悉的同學踏入不是很熟悉的社會中去。在這畢業(yè)之際,作為一名工科院校的學生,做畢業(yè)設(shè)計是一件必不可少的事情。畢業(yè)設(shè)計是一項非常繁雜的工作,它涉及的知識非常廣泛,很多都是書上沒有的東西,這就要靠自己去圖書館查找自己所需要的資料;還有很多設(shè)計計算,這些都要靠自己運用自己的思維能力去解決,可以說,沒有一定的毅力和耐心是很難完成這樣復雜的工作。在學校中,我主要學的是理論性的知識,而實踐性很欠缺,而畢業(yè)設(shè)計就相當于實戰(zhàn)前的一次總演練。畢業(yè)設(shè)計不但把我以前學的專業(yè)知識系統(tǒng)的連貫起來,也使我在溫習舊知識的同時也可以學習到很多新的知識;這不但提高了我們解決問題的能力,開闊了我們的視野,在一定程度上彌補我們實踐經(jīng)驗的不足,為以后的工作打下堅實的基礎(chǔ)。由于本人資質(zhì)有限,很多知識掌握的不是很牢固,因此在設(shè)計中難免要遇到很多難題,在有課程設(shè)計的經(jīng)驗及老師的不時指導和同學的熱心幫助下,克服了一個又一個的困難,使我的畢業(yè)設(shè)計日趨完善。畢業(yè)設(shè)計雖然很辛苦,但是在設(shè)計中不斷思考問題,研究問題,咨詢問題,一步步提高了自己,一步步完善了自己。同時也汲取了更完整的專業(yè)知識,鍛煉了自己獨立設(shè)計的能力,使我受益匪淺,我相信這些經(jīng)驗對我以后的工作一定有很大的幫助,而且也鍛煉我的吃苦耐勞的精神,讓我在這個競爭的社會里有立足之地。最后,我衷心感謝各位老師特別是我的指導老師蘇光老師在這一段時間給予我無私的幫助和指導,并向你們致意崇高的敬意,以后到社會上我一定努力工作,不辜負你們給予我的知識和對我寄予的厚望! 參 考 文 獻1薛彥成主編. 公差配合與技術(shù)測量。北京:機械工業(yè)出版社,1999.102中國模具設(shè)計大典編委會主編. 中國模具設(shè)計大典。南昌江西科學技術(shù)出版社, 2003.13郝濱海主編. 沖壓模具簡明設(shè)計手冊。北京:化學工業(yè)出版社,2004.114王樹勛主編. 模具實用技術(shù)設(shè)計手冊。華南理工大學出版社, 1995.65楊玉英主編. 實用沖壓工藝與模具設(shè)計手冊。北京:機械工業(yè)出版社,2004.76王孝培主編. 實用沖壓技術(shù)手冊。北京:機械工業(yè)出版社, 2001.37劉建超、張寶忠主編. 沖壓模具設(shè)計與制造。北京:高等教育出版社,2002.38吳伯杰編著. 沖壓工藝與模具。北京:電子工業(yè)出版社,2001.59周玲編著. 沖模設(shè)計實例詳解?;瘜W工業(yè)出版社,2003.410模具實用技術(shù)叢書編委會。沖模設(shè)計應(yīng)用實例。機械工業(yè)出版社,2001.811馬正元. 沖壓工藝與模具設(shè)計。機械工業(yè)出版社,2000.6 21 目錄 1 緒論11.1國內(nèi)模具的現(xiàn)狀和發(fā)展趨勢11.2國外模具的現(xiàn)狀和發(fā)展趨勢31.3 冷沖壓模具的分類41.4接頭模具設(shè)計與制造方面52. 沖壓工件的工藝分析62.1制件的總體分析62.2制件的外形分析72.3 拉伸件的尺寸精度和表面粗糙度72.4 工藝方案確定73 必要的工藝計算83.1 毛坯尺寸計算83.2排樣設(shè)計與計算93.3計算沖壓力和初選壓力機113.4壓力中心的確定134 模具總體結(jié)構(gòu)設(shè)計134.1 模具類型設(shè)計134.2 模具具體結(jié)構(gòu)設(shè)計145 主要工作零部件設(shè)計145.1沖孔凸、凹模刃口尺寸的計算155.2拉伸工作部分尺寸的計算165.3拉伸凹模的計算165.5拉伸凸模的計算185.6凹凸模的結(jié)構(gòu)設(shè)計196卸料裝置的設(shè)計207拉伸模裝配圖的設(shè)計繪制22結(jié) 束 語24致 謝25參 考 文 獻26 摘 要 近年來零件的使用范圍越來越廣泛,與之相應(yīng)的沖模設(shè)計也顯得尤為重要。盒形零件沖壓成形過程中坯料所受應(yīng)力和變形沿周邊不均勻分布,這給零件的沖模設(shè)計技術(shù)提出了新的要求。 本文首先對沖壓的發(fā)展應(yīng)用、工藝特點、成形原理等進行了綜述。然后對該盒形件展開工藝性分析,制定沖壓工藝方案,計算毛坯尺寸和相關(guān)工藝力。重點在于根據(jù)盒形零件的結(jié)構(gòu)特點設(shè)計沖模各零件結(jié)構(gòu)尺寸,繪制各零件圖和模具總裝圖。 該零件材料為08鋼,強度、硬度很低,而韌性和塑性極高,適合于制造拉深件。其直壁高度不大,可一次拉深成形,但與圓筒形拉深和沖孔部位距離較近。為了提高沖壓成形設(shè)備的壽命,便于模具設(shè)備的維護,保證零件質(zhì)量,本文采用正裝式落料拉深復合模、圓筒形拉深模和倒裝式?jīng)_孔模三套模具聯(lián)合加工該盒形零件,并針對可能出現(xiàn)的成形缺陷提出改進措施。 零件成形過程中坯料流動情況的復雜性決定了盒形零件試模過程的重要性。在盒形零件的實際生產(chǎn)中,可根據(jù)試模結(jié)果調(diào)整凸、凹模的圓角半徑、間隙大小和壓邊力,從而消除制件缺陷。關(guān)鍵詞: 拉深 模具設(shè)計 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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