圓筒冷沖模具設(shè)計(jì)【無(wú)凸緣圓筒件】【說(shuō)明書(shū)+CAD】

圓筒冷沖模具設(shè)計(jì)【無(wú)凸緣圓筒件】【說(shuō)明書(shū)+CAD】,無(wú)凸緣圓筒件,說(shuō)明書(shū)+CAD,圓筒冷沖模具設(shè)計(jì)【無(wú)凸緣圓筒件】【說(shuō)明書(shū)+CAD】,圓筒,模具設(shè)計(jì),凸緣,說(shuō)明書(shū),仿單,cad 畢業(yè)設(shè)計(jì)(論文)外文資料翻譯 系 別 機(jī)電信息系 專(zhuān) 業(yè) 機(jī)械設(shè)計(jì)制造及其自動(dòng)化 班 級(jí) B070203 姓 名 張瑞 學(xué) 號(hào) B07020336 外文出處 附 件 1. 原文； 2. 譯文 2011年3月 熱沖壓模具冷卻系統(tǒng)的設(shè)計(jì) 摘要： 熱沖壓和高強(qiáng)度鋼材在汽車(chē)行業(yè)正越來(lái)越受歡迎。熱沖壓是通過(guò)加熱和按下推進(jìn)器水冷工具來(lái)實(shí)現(xiàn)鋼板高強(qiáng)度的一種工藝，冷卻系統(tǒng)對(duì)該工藝的影響很大。本文提出了一種對(duì)冷卻管道系統(tǒng)進(jìn)行優(yōu)化的設(shè)計(jì)過(guò)程,介紹一種在冷卻系統(tǒng)上進(jìn)行有限元分析與一個(gè)特定的進(jìn)化算法的優(yōu)化程序。通過(guò)對(duì)每個(gè)單獨(dú)程序組件進(jìn)行了優(yōu)化設(shè)計(jì),然后讓熱沖壓工藝和thermo-mechanically熱模擬相結(jié)合的優(yōu)化方案。 關(guān)鍵詞: 熱沖壓、有限元法(FEM),優(yōu)化 1概述 近年來(lái),在不降低安全標(biāo)準(zhǔn)的前提下減輕重量已成為汽車(chē)工業(yè)的研究重點(diǎn)。熱沖壓、高強(qiáng)度鋼對(duì)此提供了可能性,不但降低重量而且提高了乘車(chē)的安全系數(shù)。為了達(dá)到高強(qiáng)度，利用熱沖壓將高強(qiáng)度鋼加熱奧氏體溫度范圍，然后對(duì)其進(jìn)行迅速冷卻，馬氏體轉(zhuǎn)變發(fā)生。在熱沖壓工藝中,工件的溫度必須保持在200°C以上，實(shí)現(xiàn)高強(qiáng)度。到目前為止,很少有對(duì)冷卻系統(tǒng)進(jìn)行研究的熱沖壓模具。 本文介紹了一種系統(tǒng)化的設(shè)計(jì)方法,熱沖壓工具與冷卻系統(tǒng)達(dá)到最佳而快速。在這個(gè)例子中,冷卻系統(tǒng)進(jìn)行了優(yōu)化幫助進(jìn)行有限元分析與一個(gè)特定的進(jìn)化算法，隨后一系列的熱成形過(guò)程的數(shù)值thermo-mechanically熱模擬以及觀察傳熱和冷卻速率來(lái)優(yōu)化冷卻系統(tǒng)，在高溫的沖壓工刀具運(yùn)動(dòng)需要的時(shí)間相對(duì)整個(gè)過(guò)程的時(shí)間較短。因此,熱沖壓過(guò)程必須有足夠的工具、合理的準(zhǔn)確性計(jì)算與短時(shí)間的快速設(shè)計(jì)。 模具的冷卻系統(tǒng)分析了包括這項(xiàng)議案的一項(xiàng)形成過(guò)程是很有必要的,可以提高預(yù)測(cè)精度。在本文中，第2章介紹了一輛汽車(chē)和其相應(yīng)的熱沖壓原件，第3章中介紹了優(yōu)化有限元分析的程序及進(jìn)化算法。隨后,結(jié)果通過(guò)熱分析與熱、光的優(yōu)化為熱沖壓模具設(shè)計(jì)提供了科學(xué)依據(jù)。 2熱沖壓模具的冷卻 2.1動(dòng)機(jī) 提高了工藝流程的經(jīng)濟(jì)性和優(yōu)化了成形零件的特點(diǎn)、熱沖壓才能達(dá)到設(shè)計(jì)最佳狀況。因此,本研究的主要目的是優(yōu)化設(shè)計(jì)一種在經(jīng)濟(jì)冷卻系統(tǒng)熱沖壓工具才能獲得有效的冷卻速率的工具。到目前為止,只有很少數(shù)的人進(jìn)行了有關(guān)冷卻系統(tǒng)在熱沖壓工具的應(yīng)用。因此,先進(jìn)的設(shè)計(jì)方法配以適當(dāng)?shù)姆抡婺Ｐ屯瓿梢蟮膬?yōu)化調(diào)查，達(dá)到工具和產(chǎn)品的快速完成和盡可能的精確。 2.2熱沖壓和模具冷卻的工藝特點(diǎn) 在直接熱成形工藝中,quenchable boronmanganese合金鋼熱沖壓和模具冷卻是常用。同時(shí),熱沖壓和模具冷卻是其中的一個(gè)具有代表意義的材料超高強(qiáng)度鋼。因此,在此研究中,熱沖壓和模具冷卻的鋁預(yù)表(阿塞洛USIBOR)被認(rèn)為是空白的材料。材料熱沖壓和模具冷卻的拉伸強(qiáng)度600MPa在臨界狀態(tài),材料的拉伸強(qiáng)度通過(guò)熱沖壓工藝顯著增加。更高的抗拉強(qiáng)度達(dá)到了熱沖壓工藝是通過(guò)快速冷卻至少27°的速度C / s[2]。作為在奧氏體冷卻淬火過(guò)程非常快馬氏體相變將發(fā)生。該微結(jié)構(gòu)提供與馬氏體與硬化的最終產(chǎn)品較高的抗拉強(qiáng)度達(dá)到1500兆帕。 2.3工具組件和檢驗(yàn) 原型的組成及其熱沖壓工具運(yùn)動(dòng)學(xué)是如圖1所示,最初的空白，該試驗(yàn)的一部分,在圖2。最初的空白的430mm尺寸x 1.75mm x 170mm和抽簽儀式提出了一種深度的檢驗(yàn)的一部分是30毫米。 2.4沖壓模具冷卻系統(tǒng) 該工具設(shè)計(jì)必須考慮能夠達(dá)到的最大的降溫速率和熱沖壓零件的溫度分布均勻性。因此,冷卻系統(tǒng)需要被整合到工具。這冷卻系統(tǒng)冷卻管靠近工具輪廓目前認(rèn)為是一種有效的解決方案。然而,冷卻管的幾何形狀限制因在鉆井和約束也應(yīng)放置導(dǎo)管盡可能在盡可能的靠近但足以有效的冷卻遠(yuǎn)離工具輪廓,以避免任何塑性變形在熱成形工藝的工具。保證滿(mǎn)意繪制部分的特點(diǎn),整個(gè)活躍部位，該工具(沖壓、模具、壓邊及解決沖床)需要設(shè)計(jì)冷卻充分。 3冷卻系統(tǒng)的設(shè)計(jì) 3.1優(yōu)化的進(jìn)化算法 圖3為每個(gè)工具的優(yōu)化程序。為優(yōu)化程序設(shè)計(jì)的冷卻系統(tǒng)呈現(xiàn)在圖3。在這個(gè)過(guò)程中,冷卻在每個(gè)通道可優(yōu)化工具通過(guò)具體的進(jìn)化算法(EA),這是在發(fā)達(dá)的ISF(Institut Fertigung皮毛Spannende多特蒙德,大學(xué)德國(guó)),為優(yōu)化注塑工具適用于設(shè)計(jì)和冷卻系統(tǒng)在熱沖壓件工具[3、4]。作為約束條件進(jìn)行優(yōu)化,可得到的大小的連接器和插座,最低的墻以及nonintersection厚度的鉆孔因素也被考慮在內(nèi)。反推最小距離冷卻風(fēng)管和卸之間/裝載工具輪廓(a / x)和最小距離冷卻管(s)通過(guò)有限元分析確定。參數(shù)的冷卻系統(tǒng)如通道的數(shù)量(一根鏈條上的序貫孔),鉆孔每通道和直徑的孔洞每個(gè)工具組件也提供作為神經(jīng)網(wǎng)絡(luò)的輸入?yún)?shù)的優(yōu)化。這些輸入?yún)?shù)可從現(xiàn)有的設(shè)計(jì)通過(guò)有限元模擬指南或?；谳斎氤跏冀馍呻S機(jī)參數(shù)通過(guò)EA或手動(dòng),由用戶(hù)。從初始解,EA創(chuàng)造新的解決方案經(jīng)過(guò)重組的電流修改他們的解決方案和隨機(jī)的。定義了隨后被用于約束的校正生成的解決方案和消除作廢的解決方案。所有的生成方案最優(yōu)標(biāo)準(zhǔn)等進(jìn)行有效的冷卻率和均勻冷卻。最后,最好的解決辦法為優(yōu)化冷卻通道選擇對(duì)選定的工具組件 3.2冷卻通道的優(yōu)化 在我們的研究,選定的管的直徑對(duì)8毫米和12mm 8毫米,12mm沖床、毫米到16毫米之間死亡,8毫米和10毫米反凸模和8毫米為空白持有人。EA是用于儲(chǔ)放冷卻通道根據(jù)給定的輸入翻案和約束條件每個(gè)工具組件。優(yōu)化后的型材的8毫米直徑的渠道,為管道在圖4。 4最佳冷卻系統(tǒng)的評(píng)價(jià) 冷卻通道的渠道設(shè)計(jì)產(chǎn)生EA每個(gè)工具組件以不同的孔直徑和其冷卻性能進(jìn)行了評(píng)估,采用鐵模擬。 4.1熱學(xué)分析 在設(shè)計(jì)和開(kāi)發(fā)階段的熱沖壓件工具,這是很重要的,估計(jì)熱沖壓工藝定性和定量地在很短的時(shí)間經(jīng)濟(jì)制造的工具。為了這個(gè)目的,兩個(gè)瞬態(tài)熱模擬的基礎(chǔ)上進(jìn)行利用ABAQUS /標(biāo)準(zhǔn),一個(gè)隱式方法。在這個(gè)分析1.2379曾被選為鋼的刀具材料。這仿真模型包含4工具組件:沖床,死亡,壓邊和反拳。如表1所,選擇與優(yōu)化組合的零件冷卻通道的方法。V1是這種變體組合優(yōu)化工具和小冷卻風(fēng)管直徑大,而變種冷卻風(fēng)管。V2直徑。表1:設(shè)計(jì)工具的組合進(jìn)行有限元分析。摘要為了代表一系列生產(chǎn)流程,一個(gè)循環(huán)數(shù)的熱沖壓的過(guò)程模擬為一個(gè)周期傳熱分析。圖5的表明有限元模型包括邊界conditionsFigure 5:有限元模型和邊界條件。這種熱成形工藝的部分的樣機(jī)這樣的設(shè)計(jì)周期時(shí)間是30秒。在一個(gè)周期內(nèi),沖壓運(yùn)動(dòng)的形成需要3秒,這種工具關(guān)閉了17秒的空白,它可以使淬火另一個(gè)10秒開(kāi)發(fā)工具和定位的下一步空白的工具。然而,在這種熱分析運(yùn)動(dòng)和變形工具坯料的卻沒(méi)有考慮到減少了計(jì)算量。因此,只有進(jìn)行了傳熱分析是在一個(gè)封閉的工具。在熱分析、淬火過(guò)程耗時(shí)的地方2017秒秒來(lái)代替,因?yàn)檫\(yùn)動(dòng)沖壓不考慮。假定空白有一個(gè)最初的穩(wěn)態(tài)溫度(Tb,0°C)由于850從950°C冷卻免費(fèi)在轉(zhuǎn)運(yùn)環(huán)境。最初的工具的溫度(Tt,0)假設(shè)為20°C在第一個(gè)周期和變化周期周期。冷卻介質(zhì)的溫度(Tc)假設(shè)為室溫。邊界的旁邊條件、材料性能的熱沖壓和模具冷卻的工藝要求從熱拉伸試驗(yàn),獲得了LFT舉辦(Lehrstuhl皮毛Fertigungstechnologie,大學(xué)Erlangen-Nurnberg、德國(guó)),和他在一起共同研究在熱沖壓被帶領(lǐng)[2]。在分析中,對(duì)流從空白和工具的環(huán)境(他),辦理在每一個(gè)工具,對(duì)流從工具融入到冷卻通道(hc)和傳熱熱空白是considered. c)工具(Here,􀁄c,是the(CHTC接觸傳熱系數(shù)),描述了熱通量的數(shù)量從毛坯到工具。這通常取決于系數(shù)之間的差距的工具和d空白和接觸壓力p .它增加通常是作為接觸壓力的增加而增加。然而,在熱分析了CHTC壓力是無(wú)效的,依賴(lài)但是差距是使用相關(guān)系數(shù)。CHTC是假設(shè)為5000W°C / m2在零距離之間的空白和工具(缺口)和保持常數(shù),直到差距的增加而增加超越批判價(jià)值。 4.2 機(jī)械分析 仿真與傳統(tǒng)熱成形是不同的板料成形過(guò)程模擬,其中的分布規(guī)律在溫度或壓力的工具被忽視。為快速又簡(jiǎn)單的方法去分析熱成形工藝的工具與空白被建成有殼單元在其他的研究[5,6]。在這些研究中,研究溫度可能是分布式沿厚度的殼元素和用戶(hù)自定義函數(shù)的溫度,但這件工具是內(nèi)溫度不考慮。同時(shí),在仿真模型的加熱,在一系列的工具熱沖壓過(guò)程不被考慮。此外,殼模型,對(duì)接觸熱的問(wèn)題只是足夠于相對(duì)較短的接觸時(shí)間[6]。因此,我們?cè)谘芯抗ぞ吆涂瞻着c體積元模擬仿制的順序的在一系列的傳熱過(guò)程。熱力的進(jìn)行仿真是ABAQUS /顯性。在熱分析、比較,整個(gè)形成和淬火工藝是仿制,而動(dòng)態(tài)溫度和應(yīng)力響應(yīng)的工具進(jìn)行了模擬接觸熱利用空白time-temperature依賴(lài)流動(dòng)應(yīng)力曲線(xiàn)。熱更準(zhǔn)確地表達(dá)了轉(zhuǎn)會(huì)應(yīng)該使用在接觸壓力CHTC場(chǎng)所依賴(lài)改變?cè)谛纬蛇^(guò)程。此外,氣溫依賴(lài)的熱導(dǎo)率和比熱也會(huì)考慮。然而,在通過(guò)熱分析,為號(hào)元素的增加,鐵的復(fù)雜性問(wèn)題顯著的增加。在傳統(tǒng)的成形有限元模擬提出了一種自適應(yīng)網(wǎng)格可以通常用來(lái)閑了仿真時(shí)間,來(lái)獲得更多的精確解接觸面積。然而,自適應(yīng)網(wǎng)格細(xì)化在計(jì)算在熱力不穩(wěn)定的原因分析。因此,一個(gè)雅致的網(wǎng)格更高的沖壓速度被認(rèn)為是減少模擬時(shí)間。傳熱系數(shù)的結(jié)垢因此,獲得相同的熱通量[7]。 圓筒冷沖模設(shè)計(jì) 產(chǎn)品圖 如圖1所示 生產(chǎn)批量：中批量 材料：10鋼 材料厚度：0.8mm 圖1 一．工藝分析: 工藝性是指沖壓件對(duì)沖壓工藝的適應(yīng)性。 工件:此工件只有落料和拉深兩個(gè)工序.工件形狀簡(jiǎn)單,并且工件為無(wú)凸緣圓筒件,要求內(nèi)形尺寸,拉深時(shí)厚度不變,因此工件能滿(mǎn)足落料拉深要求.工件的底部圓角半徑r=2mm≥t,滿(mǎn)足再次拉深圓角半徑要求.尺寸φ55.5 0+0.4mm為IT13級(jí),也滿(mǎn)足拉深工序?qū)ぜ墓畹燃?jí)要求。 材料:10鋼為低碳鋼,由于強(qiáng)度低,塑性好,適用于制造受力不大的沖壓件和拉深件,并有利于沖壓成形和制件質(zhì)量的提高,還具有良好的沖壓成形性能,即有良好的抗破裂性,良好的貼模和定形性,所以具有良好的沖壓性能。 一. 工藝方案的確定: 1． 先確定拉深次數(shù)： 確定拉深次數(shù),先判斷能否一次拉出總拉糸數(shù)m總=dn/D中的, dn實(shí)際上是零件所要求的直徑.當(dāng)m總> m1時(shí),則該零件只需要一次拉出,否則就要進(jìn)行多次拉深 計(jì)算毛坯尺寸： 查[1]中表6-2得修邊余量△h, h/d=43.6/56.3=0.77,取△h=2mm 毛坯直徑公式D= d2+4dh-1.72rd-0.56r2 參數(shù):d = 56.3mm 參數(shù):h = 43.6+2=45.6mm 參數(shù):r = 2mm 計(jì)算結(jié)果D=114.9mm 查[1]中表6-6得,取m1=0.53~0.55,取m1=0.55；取m2=0.76~0.78,取m2=0.78 總拉深糸數(shù): m總=dn/D=56.3/114.9=0.49Hmax，則該壓力機(jī)不能用，若H模具< Hmin，則可以加墊板。 實(shí)際算得H模具=301mm 則滿(mǎn)足Hmin+10mm≤H模具≤Hmax-5mm的要求。 二次拉深模： 根據(jù)F總查《冷沖模設(shè)計(jì)》中表1-3選型號(hào)為J23-25的壓力機(jī) 其基本參數(shù)：標(biāo)稱(chēng)壓力（kN）——250 滑塊行程（mm）——65 行程次數(shù)( 次/min)——50/105 連桿調(diào)節(jié)長(zhǎng)度（mm）——55 最大裝模高度（mm）——270 工作臺(tái)尺寸 前后×左右（mm×mm）——370×560 模柄孔尺寸 直徑×深度（mm）——φ50×70 電動(dòng)機(jī)功率（kW）——2.2 模具的閉合高度H模具應(yīng)介于壓力機(jī)的最大裝模高度Hmax與最小裝模高度Hmin之間，否則就不能保證下常的安裝與工作。其關(guān)系為： Hmin+10mm≤H模具≤Hmax-5mm 若模具的閉合高度H模具>Hmax，則該壓力機(jī)不能用，若H模具< Hmin，則可以加墊板。 實(shí)際算得H模具=209.8mm 則滿(mǎn)足Hmin+10mm≤H模具≤Hmax-5mm的要求。 七．對(duì)二次拉深件進(jìn)入切邊： 主要通過(guò)切邊模具對(duì)二次拉深件進(jìn)切邊，而達(dá)到所需要的產(chǎn)品尺寸?？梢圆捎脦уF形口的拉深凹?；驇A角的拉深凹模設(shè)計(jì)進(jìn)行切邊，由于切邊凹模沒(méi)有鋒利的刃口，所以切下的廢料拖有較大的毛刺，也有將這種切邊方法稱(chēng)為擠邊。用這種方法對(duì)筒形件切邊由于其結(jié)構(gòu)簡(jiǎn)單，使用方便，并可用復(fù)合模的結(jié)構(gòu)與拉深同時(shí)進(jìn)行，所以使用十分廣泛。切邊的工序圖如下所示： 八.結(jié)束語(yǔ) 由于編寫(xiě)者水平有限,設(shè)計(jì)書(shū)中難免有缺點(diǎn)和錯(cuò)誤,敬請(qǐng)讀者批評(píng)指正.同時(shí)也多謝指導(dǎo)老師吳裕農(nóng)在本人的設(shè)計(jì)中的指導(dǎo). 九.參考文獻(xiàn) [1].丁松聚主編 . 冷沖模設(shè)計(jì).北京:機(jī)械工業(yè)出版社,2001 [2]《沖壓設(shè)計(jì)手冊(cè)》編寫(xiě)組編寫(xiě). 沖壓設(shè)計(jì)手冊(cè).北京:機(jī)械工業(yè)出版社,1999 [3]楊玉英主編. 實(shí)用沖壓工藝及模具設(shè)計(jì)手冊(cè). 北京:機(jī)械工業(yè)出版社,2004 [4]王樹(shù)勛主編. 典型模具結(jié)構(gòu)圖冊(cè). 廣州:華南理工大學(xué)出版社,2005 [5]孫鳳勤、閻亞林主編. 沖壓與塑壓成形設(shè)備. 北京:高等教育出版社,2003 Annals of the CIRP Vol. 56/1/2007 -269- doi:10.1016/j.cirp.2007.05.062 Design of Hot Stamping Tools with Cooling System H. Hoffmann 1 (2), H. So 1 , H. Steinbeiss 1 1 Institute of Metal Forming and Casting, Technische Universitt Mnchen, Garching, Germany Abstract Hot stamping with high strength steel is becoming more popular in automotive industry. In hot stamping, blanks are hot formed and press hardened in a water-cooled tool to achieve high strength. Hence, design of the tool with necessary cooling significantly influences the final properties of the blank and the process time. In this paper a new method based on systematic optimization to design cooling ducts in tool is introduced. The optimization procedure was coupled with FE analysis and a specific evolutionary algorithm. Through this procedure each tool component was separately optimized. Subsequently, the hot stamping process was simulated both thermally and thermo-mechanically with the combination of optimized solutions. Keywords: Hot Stamping, Finite element method (FEM), Optimization 1 INTRODUCTION In recent years, weight reduction while maintaining safety standards has been strongly emphasized in the automotive industry for building new models. Hot stamping of high strength steels for automotive inner body panels offers the possibility of fuel saving by weight reduction and enhances passenger safety due to its higher strength. In order to achieve high strength by hot stamping with high strength steels, blanks should be heated above austenitic temperature and then cooled rapidly such that the martensitic transformation will occur. Normally, the tools are heated up to 200C without active cooling systems in serial production 1. However, in hot forming processes, the tool temperature must maintain below 200C to achieve high strength. So far, very few studies have been conducted regarding the design of cooling systems in a hot stamping tool. This paper presents a systematic method to design hot stamping tools with cooling systems in optimal and fast manners, in which the cooling system is optimized with the help of FE analysis and a specific evolutionary algorithm. Subsequently, a series of hot forming processes was simulated thermally as well as thermo-mechanically to observe the heat transfer and the cooling rate through the optimized cooling system. In the hot stamping process the tool motion requires relatively short time compared to the whole process time. Therefore, thermal analysis of a series of hot stamping processes without considering the tool motion could be sufficient with reasonable accuracy and shorter computation time for quick design of the hot stamping tools with cooling system. However, thermo- mechanical analyses that include the motion of the punch and the forming process are necessary to enhance the accuracy of the predictions. In this paper, a crash relevant hot stamped component of a vehicle and its corresponding prototype of hot stamping tool are introduced in chapter 2. And the optimization procedure with FE analysis and evolutionary algorithm is introduced in chapter 3. Subsequently, the results of thermal and thermo-mechanical analyses with the optimized hot stamping tool are presented. 2 COOLING OF HOT STAMPING TOOL 2.1 Motivation To enhance the economical production procedure and good characteristics of the formed parts, hot stamping tools need to be designed optimally. Therefore, the main objective of this study is the optimal designing of an economical cooling system in hot stamping tools to obtain efficient cooling rate in the tool. So far, very few researches have been conducted regarding the design of cooling systems in hot stamping tools. Therefore, an advanced design method is required. Also, an adequate simulation model is required to perform the optimization and investigation of tools and products as fast and accurate as possible. 2.2 Characteristics of 22MnB5 In direct hot forming process, the quenchable boron- manganese alloyed steel 22MnB5 is commonly used. Also, 22MnB5 is one of the representative materials of ultra high strength steels. Therefore, in this study, aluminium pre-coated 22MnB5 sheet (Arcelors USIBOR) was considered as the blank material. The material 22MnB5 has a tensile strength of 600MPa approximately at the delivery state, and the tensile strength can be significantly increased by hot stamping process. Higher tensile strength is achieved in the hot stamping process by a rapid cooling at least at the rate of 27C/s 2. The initial sheet of 22MnB5 consisting of ferritic-perlitic microstructure must be austenitized before forming process in order to achieve a ductility of blank sheet. As the austenite cools very fast during quenching process martensite transformation will occur. This microstructure with martensite provides the hardened final product with a high tensile strength up to 1500 MPa. 2.3 Tool component and test part The components of the prototype hot stamping tool and its kinematics are shown in Figure 1 and the initial blank and the proposed test part in Figure 2. The initial blank has the dimension of 170mm x 430mm x 1.75mm and the draw depth of the proposed test part is 30mm. -270- faceplate counter punch blank holder punch faceplate table table blank distance bolts die barells plunger Figure 1: Schematic of a test hot stamping tool. Initial thickness: 1.75mm 4 3 0 m m1 7 0 m m 4 0 0 m m 1 0 0 m m Draw depth: 30mm Figure 2: Initial blank and drawn part. 2.4 Cooling systems in stamping tools The tool must be designed to cool efficiently in order to achieve maximum cooling rate and homogeneous temperature distribution of the hot stamped part. Hence, a cooling system needs to be integrated into the tools. The cooling system with cooling ducts near to the tool contour is currently well known as an efficient solution. However, the geometry of cooling ducts is restricted due to constraints in drilling and also the ducts should be placed as near as possible for efficient cooling but sufficiently away form the tool contour to avoid any deformation in the tool during the hot forming process. To guarantee good characteristics of the drawn part, the whole active parts of the tool (punch, die, blank holder and counter punch) need to be designed to cool sufficiently. 3 DESIGNING OF COOLING SYSTEMS 3.1 Optimization with Evolutionary Algorithm x s a boring position minimum distance between loaded contour and cooling duct (x) between unloaded contour and cooling duct (a) between cooling ducts (s) loaded contour unloaded contour coolant bore Constraints sealing plug input parameters of cooling system number of cooling channels and coolant bores diameter of cooling duct evaluation criteria cooling intensity and uniform cooling Optimization (Evolutionary Algorithm) 1 solution per given input separate optimization Solution Figure 3: Optimization procedure for each tool. The optimization procedure for design of a cooling system is presented in Figure 3. In this procedure, cooling channels can be optimized in each tool by a specific Evolutionary Algorithm (EA), which was developed at ISF (Institut fr Spannende Fertigung, Universitt Dortmund, Germany) for the optimization of injection molding tools and adapted for design of cooling systems in hot stamping tools 3,4. As constraints for optimization, the available sizes of connectors and plugs, the minimum wall thicknesses as well as the nonintersection of drill holes were considered. The admissible minimal distance between cooling duct and unloaded/loaded tool contour (a/x) and the minimal distance between cooling ducts (s) were determined through FE analyses. Parameters of the cooling system such as the number of channels (a chain of sequential drill holes), drill holes per channel and the diameter of the holes for each tool component were also provided as input parameters to the optimization. These input parameters can be obtained from existing design guidelines or through FE simulations. Based on the input parameters initial solution is generated randomly by EA or manually by the user. From the initial solution, the EA generates new solutions by recombination of current solutions and modifying them randomly. The defined constraints were subsequently used for the correction of the generated solutions and the elimination of inadmissible solutions. All the generated solutions were evaluated by optimum criteria such as efficient cooling rate and uniform cooling. Finally, the best solution was selected as optimized cooling channels for a selected tool component. 3.2 Optimized cooling channels In our research, the selected diameters of ducts were 8mm and 12mm for punch, 8mm, 12mm and 16mm for die, 8mm and 10mm for counter punch and 8mm for blank holder. EA was used to place the cooling channels optimally according to the given input and constraints for each tool component. The optimized profiles of the channels for duct diameter of 8mm are shown in Figure 4. c a b 4 0 0 m m 100mm 145 mm pu n c h cou n ter p un ch die b l an k h o ld er a b a b c a b 5 1 0 m m 260 mm a b c 70mm 510mm ab 260 mm a 110mm cooling medium plug 380mm a 70mm 250 mm b c b direction of cut view Figure 4: Optimized cooling channels with 8mm duct diameter. 4 EVALUATION OF THE OPTIMUM COOLING CHANNEL DESIGNS The design of cooling channels was generated by EA for each tool component with different bore diameters and their cooling performances were evaluated by using FE simulations. 4.1 Thermal analysis In the design and development phase of hot stamping tools, it is important to estimate the hot stamping process qualitatively and quantitatively within a short time for -271- economic manufacturing of tools. For this purpose, two transient thermal simulations were carried out with ABAQUS/standard, which uses an implicit method. In this analysis steel 1.2379 was selected as a tool material. The simulation model comprises 4 tool components: punch, die, blank holder and counter punch. In Table 1, the selected combinations of tool components with optimized cooling channels are presented. The variant V1 is the combination of optimized tools with small cooling duct diameters, whereas variant V2 with large cooling duct diameters. V1 V2 punch counter punch blank holder 8mm 8mm 8mm 8mm 12mm 10mm 16mm 8mm diameter of cooling duct die Table 1: Combinations of designed tools for FE analysis. In order to represent a series of production processes, a number of cycles of the hot stamping processes were simulated as a cycle heat transfer analysis. The Figure 5 shows the FE model including boundary conditions. cooling duct (c) T c = 20C h c = 4700W/m 2 C tool (t) T t,0 = 20C environment (e) T e = 20C h e = 3.6W/m 2 C counter punch blank holder punch blank die blank (b) T b,0 = 850C blank - tool D c = f (d,P) Figure 5: FE model and boundary conditions. This hot forming process for the prototype part was designed such that the cycle time is 30 sec. In a cycle, the punch movement for forming requires 3 sec, the tool is closed for 17 sec for quenching the blank and it takes another 10 sec for opening the tool and locating the next blank on the tool. However, in this thermal analysis, the tool motion and deformation of the blank was not considered to reduce the computation time. Hence, only heat transfer analysis was performed in a closed tool. In thermal analysis, the quenching process takes places 20 sec instead of 17 sec, because the motion of punch was not considered. It was assumed that the blank has an initial homogeneous temperature (T b,0 ) of 850C due to free cooling from 950C during the transfer in environment. The initial tool temperature (T t,0 ) was assumed as 20C at the first cycle and changes from cycle to cycle. The temperature of the cooling medium (T c ) was assumed as room temperature. Beside the boundary conditions, the required material properties of 22MnB5 were obtained from hot tensile test conducted at LFT (Lehrstuhl fr Fertigungstechnologie, Universitt Erlangen-Nrnberg, Germany), with whom a joint research on hot stamping is being conducted 2. In this analysis, convection from blank and tools to the environment (h e ), conduction within each tool, convection from tool into cooling channels (h c ) and heat transfer from hot blank to tool (D c ) were considered. Here, D c , is the contact heat transfer coefficient (CHTC) which describes the amount of heat flux from blank into tools. This coefficient usually depends on the gap d between tool and blank and the contact pressure P. It increases usually as the contact pressure increases. However, in thermal analysis the pressure dependent CHTC was not available, but a gap dependent coefficient was used. CHTC was assumed as 5000W/m 2 C at zero distance between blank and tool (gap) and keeps constant until the gap increases beyond critical value. 4.2 Thermo-mechanical analysis Simulation of hot forming is different from conventional sheet metal forming simulation, in which the distribution of temperatures or stresses in tools is neglected. For fast and easy way to analyze the hot forming process the tool and the blank were modelled with shell elements as in other studies 5,6. In these studies, the temperatures could be distributed along the thickness of the shell element with the user-defined function of temperature, but the temperature within the tool was not considered. Also, in this simulation model the heating of tools in a series of hot stamping processes were not considered. Furthermore, the shell model for thermal contact problems is just adequate for relatively short contact time 6. Therefore, in our studies the tools and the blank were modelled with volume elements to simulate the sequential heat transfer in a series of processes. The thermo- mechanical simulation was conducted with ABAQUS/explicit. In comparison to the thermal analysis, the whole forming and quenching process were modelled and the dynamic temperature and stress responses of tools in contact with hot blank were simulated by using time-temperature dependent flow stress curves. The heat transfer could be more accurately expressed using pressure dependent CHTC at contact places which change during forming process. In addition, temperature dependent thermal conductivity and specific heat were also considered. However, in thermo-mechanical analysis, as the number of elements increases, the complexity of the FE problem significantly increases. In conventional forming simulation an adaptive mesh can be normally used to spare the simulation time and to obtain a more accurate solution in the contact area. However, adaptive mesh refinement causes instability during computation in thermo- mechanical analysis. Therefore, a refined mesh with higher punch velocity was considered to reduce the simulation time. The heat transfer coefficients were scaled accordingly to obtain the same heat flux 7. 5 SIMULATION RESULTS AND DISCUSSION 5.1 Thermal analysis Figure 6 shows the temperature changes in the tool components for 10 cycles at tool combination V1 and V2. T C 400 300 100 0 030100 0 300100 die punch t s t s V1 V2 Figure 6: Temperature changes in heat transfer analysis. The results show that the hottest temperatures of the tools at the end of each cycle do not change almost after some cycles. The obtained cooling rates of the blank at the hottest point from 850C to 170C are 40C/s with V1 and 33C/s with V2 at 10th cycle and these are greater than the required minimum cooling rate of 27C/s. Furthermore, V1 leads to a more efficient cooling performance than V2. Better cooling performance for V1 compared to V2 can be explained with the geometric restrictions and the minimal wall thickness. A cooling duct with small diameter can be placed closer to the tool surface in a convex area and the amount of the cooling channels can be increased additionally. Usually, the heat dissipation in the convex area is slower than in concave area 6. The result shows also that the temperature of convex area in the punch -272- cools down slower than the concave areas in the die. Due to this fact, it can be concluded that the efficient cooling is most desired at convex area. 5.2 Thermo-mechanical analysis The heat transfer with optimized tool components was simulated thermally at first. However, there was a simplification of a hot stamping process in thermal analysis. Therefore, a thermo-mechanical analysis for V1 was performed to observe the differences and the significance of modelling the punch movement. Temperature change curves at the hottest point from the end of the first cycle in the blank, die and punch are shown in Figure 7. The tool cooled further 10 sec after quenching and the temperature changes in the die and punch were presented for 30 sec. A coupled thermo- mechanical analysis was done using gap-pressure dependent CHTC. The results from thermal analysis shows a cooling rate of 92C/s from 850C to 170C in comparison to 75C/s from thermo-mechanical analysis. 400 300 100 0 die punch 05 20 1000 800 400 T C 200 Thermal analysis Thermo-mechanical analysis t s 15 blank 0 0 5 30 0 5 25 30t s10 202510 20t s T C Figure 7: Temperature changes in thermal and thermo- mechanical analysis (1th cycle). To verify the accuracy of a thermal analysis or to predict a serial production process more accurately a series of thermo-mechanical analysis was done. For this analysis the punch velocity was increased 10 times and 10 hot stamping processes were simulated. In Figure 8, the temperature change curves at the hottest point of the die and punch from a thermal and thermo-mechanical analysis are compared for 10 cycles. Finally, the temperature distributions in the blank at the end of the 10th cycle are shown in Figure 9. 400 300 100 0 TC 030ts100 030ts100 die punch thermal thermo-mechanical Figure 8: Temperature changes for 10 cycles. (b) T C (a) 130 60 102 74 88 116 T C 140 70 112 84 98 126 Figure 9: Temperature fields of blanks at the end of 10th cycle: (a) thermal and (b) thermo-mechanical analysis. In Figure 8, the temperature differences at the end of 10th cycle between the thermal and thermo-mechanical analyses were 7C in the die and 3C in the punch. Subsequently, the Figure 9 indicates that the maximum temperature of the blank from the thermal analysis is slightly greater than that of the thermo-mechanical about 10C. Nonetheless, the temperature fields of blanks from both analyses are very similar. As a consequence, the thermal analysis for a series of hot stamping processes is relatively accurate compared to the thermo-mechanical analysis. Furthermore, a thermal heat transfer analysis could be used to design and develop the hot stamping tools in the early phase due to its timesaving computation. 6 CONCLUSION AND FUTURE WORK A systematic method has been developed for optimizing the geometrical design of the cooling systems of hot stamping tools. This methodology was successfully applied to design of cooling channels in a prototype tool for efficient cooling performance. This indicates that the method can be used for designing cooling systems in other stamping tools as well. This paper presented both thermal and thermo- mechanical simulations to represent a series of hot stamping processes. The thermal analysis could be used for an optimization and investigation of hot stamping processes especially in the developing stage. However, a thermo-mechanical analysis is needed to predict more accurately but it is still time consuming to analyze the processes within adequate time period. To resolve this problem, an alternative simulation model will be further studied. Also, a more accurate contact condition for thermo-mechanical analysis remains to be studied. To validate this proposed method and its corresponding FE model, a prototype tool is currently being built and experiments will be carried out for validation. 7 ACKNOWLEDGMENTS We extend our sincere thanks to all joint project researchers of LFT and ISF. 8 REFERENCES 1 Sik