圓筒件落料拉深復(fù)合模設(shè)計(jì)【說(shuō)明書+CAD】
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湖 南 農(nóng) 業(yè) 大 學(xué)全日制普通本科生畢業(yè)設(shè)計(jì) 落料拉深復(fù)合模設(shè)計(jì) DESIGN OF BLANKING DRAWING DIE COMPOSITE MOLD 學(xué)生姓名: 學(xué) 號(hào): 年級(jí)專業(yè)及班級(jí): 指導(dǎo)老師及職稱: 學(xué) 院: 湖南長(zhǎng)沙提交日期:2013 年 05 月湖南農(nóng)業(yè)大學(xué)全日制普通本科生畢業(yè)設(shè)計(jì)誠(chéng) 信 聲 明本人鄭重聲明:所呈交的本科畢業(yè)設(shè)計(jì)是本人在指導(dǎo)老師的指導(dǎo)下,進(jìn)行研究工作所取得的成果,成果不存在知識(shí)產(chǎn)權(quán)爭(zhēng)議。除文中已經(jīng)注明引用的內(nèi)容外,本論文不含任何其他個(gè)人或集體已經(jīng)發(fā)表或撰寫過(guò)的作品成果。對(duì)本文的研究做出重要貢獻(xiàn)的個(gè)人和集體在文中均作了明確的說(shuō)明并表示了謝意。本人完全意識(shí)到本聲明的法律結(jié)果由本人承擔(dān)。 畢業(yè)設(shè)計(jì)作者簽名: 年 月 日目 錄 摘要 4關(guān)鍵詞 41 前言41.1 沖模的優(yōu)勢(shì)51.2 研究目的和意義51.3 國(guó)內(nèi)外研究現(xiàn)狀61.4 沖壓模具三維CAD設(shè)計(jì)62 工件工藝性的分析62.1 零件要求62.2 材料的工藝性分析材料72.3 沖壓工藝方案的確定82.3.1 方案的制定82.3.2 論述方案特點(diǎn)83 主要涉及尺寸的計(jì)算93.1 毛坯尺寸的確定93.2 排樣的設(shè)計(jì)10 3.3 材料利用率103.4 壓力中心的確定103.5 沖壓工藝力的設(shè)計(jì)103.6 沖裁間隙114 零件的設(shè)計(jì)114.1 沖裁凸模、凹模的尺寸計(jì)算114.2 沖裁模凹模124.2.1 凹模的類型確定124.2.2 凹模厚度計(jì)算124.2.3 螺孔與銷孔的定位134.2.4 凹模設(shè)計(jì)134.2.5 凹模的強(qiáng)度校核144.3 導(dǎo)料和擋料方式的確定144.3.1 擋料方式144.3.2 導(dǎo)料方式154.3.3 卸料版與凸模單邊間隙的確定154.3.4 卸料板設(shè)計(jì)圖154.4 拉深相關(guān)計(jì)算164.4.1 拉深相關(guān)系數(shù)的計(jì)算164.4.2 拉深模的間隙164.4.3 凸、凹模的尺寸計(jì)算164.5 拉深凸模174.6 固定板設(shè)計(jì)184.7 凸凹模的計(jì)算194.8 模座的確定和選擇214.9 導(dǎo)套及導(dǎo)柱確定214.10 壓力機(jī)的確定 214.10.1 拉深力的計(jì)算 214.10.2 壓邊力的計(jì)算 224.11 壓邊圈確定 224.12 壓力機(jī)的公稱壓力的選擇 234.13 模柄的確定 234.14 彈簧的確定 234.15 頂件塊的設(shè)計(jì) 235 模具的總裝圖25 6 結(jié)束語(yǔ)27 參考文獻(xiàn) 27 致謝 29落料拉深復(fù)合模設(shè)計(jì)學(xué) 生:譚 巍指導(dǎo)老師: 周光永(湖南農(nóng)業(yè)大學(xué)工學(xué)院 長(zhǎng)沙 410128) 摘 要:本文介紹了模具設(shè)計(jì)的步驟,對(duì)模具的一些結(jié)構(gòu)作了相應(yīng)的介紹。對(duì)在模具設(shè)計(jì)時(shí),一些相關(guān)零件的設(shè)計(jì)的問(wèn)題也作了一點(diǎn)解釋;文章涉及了拉深模具設(shè)計(jì)時(shí)應(yīng)該考慮的方面以及影響模具設(shè)計(jì)的參數(shù)。具體內(nèi)容有以下幾點(diǎn):工件的工藝性分析;沖壓工藝方案的確定;模具的尺寸的計(jì)算校核,以及材料的選用;確定零件的工藝。本模具設(shè)計(jì)采用復(fù)合模設(shè)計(jì)方案,對(duì)零件排樣、凹凸模間隙、刃口尺寸、凹凸模外形尺寸進(jìn)行了設(shè)計(jì),選擇合適的其他零件。 關(guān)鍵詞:落料;拉深;復(fù)合模; Design of blanking drawing die composite mold Student: Tan Wei Tutor: Zhou Guangyong(College of Engineering, Hunan Agricultural University, Changsha 410128,China) Abstract: This article describes the steps of the mold design, made the introduction of mold structure. In the mold design, there also made a little explanation of some parts of the design problem; The articles should consider some aspects when drawing die design and the mold design parameters. The specific content is as follows: the analysis of the process of the workpiece; stamping process to determine the program; check of the calculation of the dimensions of the mold, as well as the selection of materials; determine the parts of the process. The mold design using composite mold design, nesting of parts, the bump die gap, the tip size bump mode Dimensions design, choose the right parts. Key words: blanking;drawing;composite mold 1 前言沖壓是使板料經(jīng)分離或成形而得到制件的工件加工方法。沖壓利用沖壓模具對(duì)板料進(jìn)行加工。沖模根據(jù)用途分為:?jiǎn)喂ば蚰?、?jí)進(jìn)沖模、復(fù)合沖模、精沖模、通用與經(jīng)濟(jì)沖模1.1 沖模的優(yōu)勢(shì)CAD、CAM、CAE的大量應(yīng)用,大大減化了模具的設(shè)計(jì)、制造。大大提升了模具制造質(zhì)量、效率。沖壓設(shè)備自動(dòng)化、高速化。高速?zèng)_床達(dá)到上萬(wàn)次/每分鐘,大大提高了效率,確保了生產(chǎn)的安全。模具的標(biāo)準(zhǔn)化、專業(yè)化。使得模具的設(shè)計(jì)和制造主要圍繞成形零件展開。新材料、新技術(shù)的大量使用。使得模具的性能提高、加工快速簡(jiǎn)便。我國(guó)沖壓模具產(chǎn)品均出口較大幅度的增長(zhǎng)。國(guó)際采購(gòu)商通過(guò)國(guó)內(nèi)某網(wǎng)站采購(gòu)沖壓模具的數(shù)量仍逆勢(shì)上揚(yáng)。我國(guó)沖壓模具的國(guó)際競(jìng)爭(zhēng)力正在不斷提升。隨著汽車工業(yè)近年以超過(guò)20的增幅發(fā)展,以及車型改款加速等等因素的刺激,進(jìn)入汽車領(lǐng)域的沖壓模具企業(yè)和模具產(chǎn)品比前幾年有大幅增加。汽車企業(yè)也對(duì)模具產(chǎn)品的質(zhì)量提出了更高要求,促使模具企業(yè)加緊改進(jìn),不斷提高水平。這些都促使沖壓模具企業(yè)的競(jìng)爭(zhēng)力不斷提升。模具技術(shù)水平的高低是衡量一個(gè)國(guó)家制造業(yè)水平的重要標(biāo)志之一。我國(guó)工業(yè)的進(jìn)一步發(fā)展要求模具行業(yè)向大型、精密、復(fù)雜、高效、長(zhǎng)壽命和多功能方向發(fā)展。隨著我國(guó)工業(yè)的崛起,模具工業(yè)得到迅猛的發(fā)展。模具設(shè)計(jì)與制造已成為一個(gè)行業(yè),越來(lái)越引起人們的重視。而被大量應(yīng)用到工業(yè)生產(chǎn)中來(lái)。沖壓模具可以大大的提高勞動(dòng)生產(chǎn)效率,減輕工人負(fù)擔(dān),具有重要的技術(shù)進(jìn)步意義和經(jīng)濟(jì)價(jià)值。整個(gè)行業(yè)處于青春期,行業(yè)所呈現(xiàn)的良好的發(fā)展趨勢(shì)是前所未有的。1.2 研究目的和意義模具是工業(yè)生產(chǎn)上用以注塑、吹塑、擠出、鑄壓或鍛壓成型、冶煉、沖壓、拉伸等方法得到所需產(chǎn)品的各種模子和工具。 簡(jiǎn)而言之,模具是用來(lái)成型物品的工具,這種工具由各種零件構(gòu)成,不同的模具由不同的零件構(gòu)成。它主要通過(guò)所成型材料物理狀態(tài)的改變來(lái)實(shí)現(xiàn)物品外形的加工。在外力作用下使坯料成為有特定形狀和尺寸的制件的工具。廣泛用于沖裁、成形、沖壓、模鍛、擠壓、粉末冶金件壓制、壓力鑄造,以及工程塑料、橡膠、陶瓷等制品的壓塑或注塑的成形加工中。模具具有搞的生產(chǎn)效率,低的加工成本,而且材料利用率高,產(chǎn)品尺寸精確穩(wěn)定,操作簡(jiǎn)單容易實(shí)現(xiàn)機(jī)械化和自動(dòng)化等一些列優(yōu)點(diǎn),適合于大批量生產(chǎn)。所以研究模具,使模具簡(jiǎn)單,耐用,高效,精確,經(jīng)濟(jì)的意義非凡。1.3 國(guó)內(nèi)外研究現(xiàn)狀在國(guó)家產(chǎn)業(yè)政策的正確引導(dǎo)下,經(jīng)過(guò)幾十年努力,現(xiàn)在我國(guó)沖壓模具的設(shè)計(jì)與制造能力已達(dá)到較高水平,包括信息工程和虛擬技術(shù)等許多現(xiàn)代設(shè)計(jì)制造技術(shù)已在很多模具企業(yè)得到應(yīng)用。雖然如此,我國(guó)的沖壓模具設(shè)計(jì)制造能力與市場(chǎng)需要和國(guó)際先進(jìn)水平相比仍有較大差距。這一些主要表現(xiàn)在高檔轎車和大中型汽車覆蓋件模具及高精度沖模方面,無(wú)論在設(shè)計(jì)還是加工工藝和能力方面,都有較大差距。轎車覆蓋件模具,具有設(shè)計(jì)和制造難度大,質(zhì)量和精度要求高的特點(diǎn),可代表覆蓋件模具的水平。雖然在設(shè)計(jì)制造方法和手段方面基本達(dá)到了國(guó)際水平,模具結(jié)構(gòu)周期等方面,與國(guó)外相比還存在一定的差距。標(biāo)志沖模技術(shù)先進(jìn)水平的多工位級(jí)進(jìn)模和多功能模具,是我國(guó)重點(diǎn)發(fā)展的精密模具品種。有代表性的是集機(jī)電一體化的鐵芯精密自動(dòng)閥片多功能模具,已基本達(dá)到國(guó)際水平。但總體上和國(guó)外多工位級(jí)進(jìn)模相比,在制造精度、使用壽命、模具結(jié)構(gòu)和功能上,仍存在一定差距。汽車覆蓋件模具制造技術(shù)正在不斷地提高和完美,高精度、高效益加工設(shè)備的使用越來(lái)越廣泛。高性能的五軸高速銑床和三軸的高速銑床的應(yīng)用已越來(lái)越多。NC、DNC技術(shù)的應(yīng)用越來(lái)越成熟,可以進(jìn)行傾角加工超精加工。這些都提高了模具面加工精度,提高了模具的質(zhì)量,縮短了模具的制造周期。模具表面強(qiáng)化技術(shù)也得到廣泛應(yīng)用。工藝成熟、無(wú)污染、成本適中的離子滲氮技術(shù)越來(lái)越被認(rèn)可,碳化物被覆處理(TD處理)及許多鍍(涂)層技術(shù)在沖壓模具上的應(yīng)用日益增多。真空處理技術(shù)、實(shí)型鑄造技術(shù)、刃口堆焊技術(shù)等日趨成熟。激光切割和激光焊技術(shù)也得到了應(yīng)用在傳統(tǒng)的工業(yè)生產(chǎn)中,工人生產(chǎn)的勞動(dòng)強(qiáng)度大、勞動(dòng)量大,嚴(yán)重影響生產(chǎn)效率的提高。 1.4 沖壓模具三維CAD設(shè)計(jì)三維CAD技術(shù)的出現(xiàn),使零件設(shè)計(jì)及模具結(jié)構(gòu)的設(shè)計(jì)可以直接在非常直觀的三維環(huán)境下進(jìn)行,模具設(shè)計(jì)完成后,可直接根據(jù)投影關(guān)系自動(dòng)生成工程圖,徹底解決了傳統(tǒng)二維設(shè)計(jì)的弊端。目前,三維CAD技術(shù)已廣泛地應(yīng)用于模具的設(shè)計(jì),縮短了新產(chǎn)品的開發(fā)周期和產(chǎn)品的更新周期,使得開發(fā)新產(chǎn)品達(dá)到“高質(zhì)量、低成本、上市快”的目標(biāo)成為可能。2 工件工藝性的分析2.1 零件要求圖1所示為目標(biāo)零件,材料:10鋼; 厚度:1mm 圖1 零件圖Fig 1 Part drawing2.2 材料的工藝性分析材料:材料:10鋼,抗剪強(qiáng)度=250333MPa,抗拉強(qiáng)度=294432MPa,屈服強(qiáng)度:=206MPa,厚度為1mm,該零件是圓筒件,可以保證彎曲時(shí)毛坯不會(huì)產(chǎn)生側(cè)向滑動(dòng)。綜合性能較好,強(qiáng)度、塑性等性能得到較好配合,其沖裁、拉深加工性較好,適于大批量生產(chǎn)。拉深變形過(guò)程大致是直徑為D的圓形平板毛坯被凸模拉入凸凹模的間隙里,形成直徑為d,高為H 的空心圓柱。在這一過(guò)程中,板料金屬是如何流動(dòng)的呢?把直徑為D的圓板料分成兩部分:一部分是直徑為d的圓板,另一部分直徑為(Dd)的圓環(huán)部分,把這塊料拉深成直徑為d的空心圓筒。在這個(gè)拉深實(shí)驗(yàn)完成后,發(fā)現(xiàn)板料的第一部分變化不大,即直徑為d的圓板仍然保持原形狀作為空心圓筒的底,板料的圓環(huán)部分變化相當(dāng)大,變成了圓柱的筒壁,這一部分的金屬發(fā)生了流動(dòng)。扇形chef是從板料圓環(huán)上截取的單元,經(jīng)過(guò)拉深后變成了矩形chef。扇形單元體變形是切線方向受壓縮,徑向受拉深,材料向凹??诹鲃?dòng)。設(shè)扇形面積為,拉深后矩形面積為,由于拉深使厚度變化很小,可認(rèn)為拉深前后面積相等,即所以。綜合起來(lái)看,平板毛坯的環(huán)形區(qū)的金屬在凸模壓力的作用下,要受到拉應(yīng)力和壓應(yīng)力的作用,徑向伸長(zhǎng)、切向縮短,依次流入凸、凹模的間隙里成為筒壁,最后使平板毛坯完全變成圓筒形工件。拉伸時(shí)的應(yīng)力狀態(tài)和形變情況。拉伸的變形區(qū)比較大,金屬流動(dòng)性比較大,拉深過(guò)程容易起皺、拉裂而失敗。因此,有必要分析拉深時(shí)的應(yīng)力狀態(tài)和變形特點(diǎn),找出發(fā)生起皺、拉裂的根本原因,在制定工藝和設(shè)計(jì)模具時(shí)注意它,以提高拉深件的質(zhì)量。設(shè)在拉深件的某一時(shí)刻,分析各部分的應(yīng)力狀態(tài)。平面凸緣部分-主變形區(qū) 由于凸模向下壓,迫使板料進(jìn)入凹模,故在凸緣產(chǎn)生徑向拉應(yīng)力,小單元體互相擠壓產(chǎn)生切向壓應(yīng)力,由于壓邊圈提供的壓邊力產(chǎn)生法向壓應(yīng)力,在這3個(gè)主應(yīng)力中的絕對(duì)值比、絕對(duì)值小得多,凸緣上、是變化的,由凸緣外到內(nèi),是由小變大,而的絕對(duì)值是由大變小的,凸緣最外緣的壓應(yīng)力是最大的,則材料在切向上必然是壓縮變形。如果被拉深的材料厚度較薄壓邊力太小,就有可能使凸緣部分的材料失穩(wěn)而產(chǎn)生起皺現(xiàn)象。筒壁部分-傳力區(qū) 該部分受到凸模傳來(lái)的拉應(yīng)力和凸模阻礙材料切向自由壓縮而產(chǎn)生的拉應(yīng)力,顯然的絕對(duì)值大,徑向是拉深變形,徑向的拉深是靠壁厚的變薄來(lái)實(shí)現(xiàn)的,故筒壁上厚下薄。底部圓角部分-過(guò)渡區(qū) 該部分受到徑向拉應(yīng)力和切向拉應(yīng)力的作用,厚度方向上受到凸模的彎曲作用而產(chǎn)生壓應(yīng)力。材料變形為平面應(yīng)變狀態(tài),徑向拉深變形,是靠壁厚變薄來(lái)實(shí)現(xiàn)的,這部分材料變薄最為嚴(yán)重,最容易出現(xiàn)拉裂,此處稱為危險(xiǎn)斷面。圓筒的底部-不變形區(qū) 這部分材料一開始就被拉入凹模中,始終保持平面狀態(tài),它受兩向拉應(yīng)力和的作用。變形是三向的,是拉深,是壓縮。由于拉深變形受到凸模摩擦力的阻止,故變薄很小,可忽略不計(jì)。2.3 沖壓工藝方案的確定2.3.1 方案的制定該零件包括需落料、拉深成形兩道工序,可以采用的工藝方案有方案一:先落料,后拉深,采用單工序模制造方案二:先落料,后拉深,采用復(fù)合模制造 方案一結(jié)構(gòu)簡(jiǎn)單,但需兩道工序、兩副模具才能完成,效率較低,且精度不易保證。如此浪費(fèi)了人力,物力,財(cái)力。從經(jīng)濟(jì)角度考慮不妥當(dāng),難以滿足大批量生產(chǎn)要求。方案二結(jié)構(gòu)較復(fù)雜,需一副模具即可成型,且精度易保證??紤]人力成本,材料節(jié)約,工件精度等因素故采用方案二2.3.2 論述方案特點(diǎn)(1) 模具采用了導(dǎo)柱和導(dǎo)套組成導(dǎo)向機(jī)構(gòu),從而提高了沖模的沖裁精度。(2) 模具落料凹模和沖孔凸模固定在下模上,凸凹模固定在上模上,模具結(jié)構(gòu)緊湊,在壓力機(jī)的一次行程下,可以同時(shí)完成沖孔與落料工序。(3) 卸料器安裝在上模上。同時(shí)有頂桿作用可使其上、下移動(dòng)。而下模安裝有卸料板組成的卸料機(jī)構(gòu),從而沖裁后零件容易落下,條料也很容易恢復(fù)到原位。(4) 凸凹模的內(nèi)孔作為拉深的凹模,而外援作為落料的凸模。同一個(gè)部件幷起兩種功能作用(5) 條料在送進(jìn)過(guò)程中,采用定位銷定位。3 主要涉及尺寸的計(jì)算3.1 毛坯尺寸的確定根據(jù)毛坯尺寸的確定原則可知有兩種方法來(lái)計(jì)算毛坯的計(jì)算原則:面積相等原則:由于拉深前和拉深后材料的體積不變,對(duì)于不變薄拉深,假設(shè)材料厚度拉深前后不變,拉深毛坯的尺寸按“拉深前后的表面積相等”來(lái)確定。圖2 毛坯尺寸工藝圖Fig2 Blank dimensions artwork (1) (2) (3) mm (4) (5) (6) (7) (8) (9) (10) (11) (12)3.2 排樣的設(shè)計(jì) 根據(jù)沖件的圖形,所以設(shè)計(jì)單排排列是最方便且最省材料的方法。 圖3 排樣圖形設(shè)計(jì)Fig3 Layout of graphic design由課本表2.8(沖裁金屬材料的搭邊值)查得 側(cè)搭邊值 正搭邊值 由課本表2.9(裁剪公差及條料與導(dǎo)料板之間的間隙) 條料寬度公差 條料與導(dǎo)料板間的間隙 (13)3.3 材料利用率 (14)3.4 壓力中心的確定對(duì)稱形狀的沖裁件,其壓力中心位于輪廓圖形的幾何中心點(diǎn),所以該零件的壓力中心點(diǎn)是圓心O點(diǎn)3.5 沖裁工藝力的計(jì)算 沖裁力的大小主要與材料力學(xué)性能、厚度及沖裁件分離的輪廓長(zhǎng)度有關(guān)。考慮到成本和沖裁件的質(zhì)量要求,此用平刃口模具沖裁,沖裁力F(N): (15)式中 L沖裁件周邊長(zhǎng)度(mm); t材料厚度(mm); 材料抗剪強(qiáng)度(MPa); K系數(shù),一般取值為1.3;3.6 沖裁間隙 沖裁間隙對(duì)沖裁斷面有極大的影響,還影響模具壽命和沖裁件的尺寸精度。合理的沖裁間隙能使斷面較好,所需沖裁力小,模具壽命長(zhǎng)。 (16)式中: 單邊間隙; t材料厚度; 光亮帶寬度,即產(chǎn)生裂紋時(shí)凸模擠入的深度; 產(chǎn)生裂紋時(shí)凸模擠入材料的相對(duì)深度; 剪裂紋與垂線間的夾角。也可查課本表2.12(落料、沖孔模刃口使用間隙) 最小間隙 最大間隙 4 零件的設(shè)計(jì)4.1 沖裁凸模、凹模的尺寸計(jì)算表1 凸凹模分別加工的工作部分尺寸的計(jì)算公式Table 1 Intensive processing work part of the size of the calculation formula, respectively工序性質(zhì)工作尺寸凸模尺寸凹模尺寸落 料沖孔凸凹模采用分開加工,采用這種方法,要分別澆筑凸模凹模的刃口尺寸與制造公差,它適用于圓形和簡(jiǎn)單形狀的公件式中:、分別為沖孔凸、凹模刃口尺寸,mm;分別為落料凸、凹模的刃口尺寸,mm;工件制造公差,mm;X磨損系數(shù);最小合理間隙值(雙面),mm;、凸、凹模制造公差,mm;D、d 分別為落料件外徑和內(nèi)徑的基本尺寸,mm;由課本表2.17 (磨損系數(shù))查的 由課本表7.18(沖裁和拉深件未標(biāo)注公差尺寸的偏差) 由表2.14(規(guī)則形狀的沖裁時(shí),凸、凹模的制造公差)查的 由以上數(shù)據(jù)計(jì)算出; 4.2 沖裁模凹模4.2.1 凹模的類型確定由于該零件有凸緣部分,所以要選用壓邊圈,考略壓邊圈的運(yùn)動(dòng),選用階梯型直壁凹模。這種類型凹模刃口強(qiáng)度高,制造方便,刃磨后型孔尺寸基本不變,對(duì)沖裁間隙無(wú)明顯影響。凹模的錐角和后角和刃口直壁高h(yuǎn)均和材料有關(guān)。通常;凹模外形為筒件,由于尺寸較大,采用銷釘和螺栓緊固在模座上;鑲塊與凹模采用H7/n6過(guò)渡配合4.2.2 凹模的厚度計(jì)算 (1) 厚度 (17)式中: b垂直送料方向凹模型孔壁間最大距離,mm; K由b和材料厚度t決定的凹模厚度系數(shù);由課本表2.20(凹模厚度系數(shù)K值): 故凹模的厚度大于24.5mm即可; (2)凹模壁厚計(jì)算 (18)取故凹模壁厚大于49mm即可;(3)凹模寬度計(jì)算 (19) ?。?)凹模的長(zhǎng)度計(jì)算 (20)式中:沿送料方向凹模型孔壁間最大距離,mm; 沿送料方向凹模型孔壁至凹模邊緣的最小距離,mm;由課本表2.21(凹模型孔壁至凹模邊緣的最小距離)查的: =50 mm =122.5 mm 4.2.3 螺孔與銷孔的定位 由表2.22(螺孔與銷孔間及至刃口邊的最小距離)查的: 刃口與螺紋孔的距離要大于11mm;刃口與銷孔的距離要大于10mm.4.2.4 凹模設(shè)計(jì)圖綜上的結(jié)果,確定凹模的A=212 mm, B=220 mm ,H=60 mm;材料選擇:Cr12MoV 確定圖形如下,二維圖4,三維圖圖5圖4 凹模設(shè)計(jì)圖Fig4 Punch design圖5 凹模設(shè)計(jì)圖(三維)Fig 5 Punch design(There-dimensional)4.2.5 凹模的強(qiáng)度校核 (21)式中: F沖裁力,N; 彎曲應(yīng)力的計(jì)算值,MPa; H凹模厚度; d凹模直徑; 下模座的直徑; 許用彎曲應(yīng)力,MPa; 對(duì)于材料Cr12MoVde,取300500 MPa 所以凹模的強(qiáng)度符合條件。4.3 導(dǎo)料和擋料方式的確定4.3.1 擋料方式 常見的限定條料送進(jìn)距離的方式有:用銷釘?shù)謸醮钸吇蚬ぜ喞薅l料送進(jìn)距離的擋料銷釘定距;用側(cè)刃在條料側(cè)邊沖切各種形狀的缺口,限定條料送進(jìn)的距離的側(cè)刃定距。 考慮到材料的節(jié)約,模具的儉約,在此選用擋料銷定距。數(shù)據(jù)選用查表 表2 定位板或定位銷的工作部分高度 h mmTable 2 Positioning plate or working part of the locating pin height h毛坯厚度11335ht+2t+1t板料的厚度 t=1,所以銷釘?shù)暮穸葹?mm4.3.2 導(dǎo)料方式 該模具需用卸料板,可以用卸料板附帶導(dǎo)向裝置。查課本表2.26(固定卸料板的厚度)選用h=9,H=12.54.3.3 卸料板與凸模單邊間隙的確定 表3 卸料板空與凸模的單邊間隙 mm Table 3 Stripper plate empty and punch the unilateral clearance板厚11335Z/20.20.30.5板料的厚度 t=1,所以單邊間隙為0.2 mm;4.3.4 卸料板設(shè)計(jì)圖 結(jié)合以上的有關(guān)數(shù)據(jù),設(shè)計(jì)卸料板,材料為Q235,輪廓如下圖圖6 卸料板設(shè)計(jì)圖(三維)Fig 6 Stripper plate design(There-dimensional)圖7 卸料板設(shè)計(jì)圖Fig 7 Stripper plate design卸料板緊固在凹模上,緊固件選用M8和8的銷釘;配合選用H7/n64.4 拉深相關(guān)計(jì)算4.4.1 拉深相關(guān)系數(shù)的計(jì)算 拉深系數(shù) (22)式中:m有凸緣圓筒件的拉深系數(shù); d工件圓筒部分直徑; D毛坯直徑。 (2)毛坯相對(duì)厚度 t/D=1/122.5=0.0081 (3)凸緣的而相對(duì)直徑(注凸緣的外徑 ,凸緣的內(nèi)徑)由表4.12(有凸緣圓筒形件第一拉深的最小拉深系數(shù))查的=0.550100100200200出氣孔直徑56.589.5數(shù)量按圓周直徑均布47個(gè)一組 凸模緊固在下模座上,緊固件選用M8和8的銷釘;配合選用H7/n6材料選擇:Cr12MoV凸模的圓角半徑大于t,考慮工件要求,取值r=3.5mm.具體設(shè)計(jì)如圖7和圖8圖9 拉深凸模設(shè)計(jì)圖(三維)Fig 9 Drawing punch design(There-dimensional)4.6 固定板設(shè)計(jì) 圖10 固定板設(shè)計(jì)圖Fig 10 Fixed plate design可以看出凸模的橫截面積較大,且該凸模也是拉深的凹模,所以確定該凸凹模為整體式。用固定板固定。 由于,設(shè)計(jì)固定板為邊長(zhǎng)200mm的正方形。固定板緊固在上模座上,緊固件選用M8和8的銷釘;配合選用H7/n6;如圖9,圖10;圖11 固定板設(shè)計(jì)圖(三維)Fig 11 Fixed plate design(There-dimensional)4.7 凸凹模的計(jì)算 復(fù)合模中的凸凹模,其最小壁厚受強(qiáng)度的限制。確定凸凹模的最小壁厚由課本表2.23查得:最小壁厚a=2.7 mm最小直徑 D=18 mm mm用于凹模部分的人口圓角半徑,查下表 表5 首次拉深凹模的圓角半徑 mmTable 5 Deep drawing die radius for the first time拉深形式毛坯相對(duì)厚度2.01.01.00.3固定板的長(zhǎng)度。確定上(下)模座:上(下)模座25025045 GB2855.5-81(GB2855.6-81)HT200模具的閉合高度: (26)4.9 導(dǎo)套及導(dǎo)柱確定由D=50 mm, d=35mm,確定導(dǎo)套為A35H611548 GB2861.6-81由d=35 mm,確定導(dǎo)柱為A35h5200 GB2861.1-814.10 壓力機(jī)的確定4.10.1 拉深力的計(jì)算由課本表4.17(計(jì)算拉深力實(shí)用公式)查的該零件的拉深力公式為 (27)式中:拉深力,mm; 圓筒拉深的額直徑,mm; 材料抗拉強(qiáng)度,MPa; 系數(shù);查課本表4.20(寬凸圓筒形件第一次拉深時(shí)的系數(shù)值)得=1.10=440 MPa4.10.2 壓邊力的計(jì)算 拉深過(guò)程中,壓邊圈的作用是用來(lái)防止工件邊壁或者凸緣起皺。隨著拉深深度的增加而需要的壓邊力應(yīng)減少。圓筒形件第一次拉深的壓邊力 (28)式中:p單位單位壓邊力,MPa;由表4.26查的p=2.7D平板毛坯直徑,mmm;d拉深的直徑,mm;r拉深凹模圓角半徑,mm;4.11 壓邊圈的確定根據(jù)凸模、凹模形狀的要求設(shè)計(jì)如下圖圖14 壓邊圈設(shè)計(jì)Fig 14 Blankholder design圖15 壓邊圈設(shè)計(jì)Fig 15 Blankholder design(There-dimensional)4.12 壓力機(jī)的公稱壓力的選擇拉深深度只有22mm,屬于淺拉深, (29), 壓力選擇開式可傾壓力機(jī),根據(jù)壓力,選擇J23-25該壓力機(jī)的基本數(shù)據(jù):公稱壓力 250KN滑塊行程65mm最大封閉高度270mm模柄孔尺寸:直徑40 mm ,深度60 mm 4.13 模柄的確定由于模炳孔的直徑40 mm,確定模柄為A4085 GB2862.3-81. Q2354.14 彈簧的確定 壓邊力F=10601 N,應(yīng)用五個(gè)彈簧,每個(gè)彈簧受力為2120 N;由于壓邊圈的行程是25mm,所以選擇1060130 GB2083-80;4.15 頂件塊的設(shè)計(jì)零件被壓入凸凹模后,卡在凸凹模中,需頂件塊,零件是一次拉深,無(wú)整形,可把頂件塊按,零件形狀設(shè)計(jì)制造。如圖圖16 頂件塊Fig 16 Push block圖17 頂件塊Fig 17 Push block(There-dimensional)4.16 支架的設(shè)計(jì)零件加工中,需要前后定位,設(shè)計(jì)一個(gè)擋料快,擋料快固定在支架上。圖18 支架Fig 18 Stand圖19 支架Fig 19 Stand(There-dimensional)4.17 擋料元件t=1 mm,所以選擇h=3 mm的擋料快,固定在支架上5. 模具的總裝圖圖20 模具總裝圖Fig 20 Mold assembly drawing圖21 模具總裝圖Fig 21 Mold assembly drawing(There-dimensional)為了實(shí)現(xiàn)先落料,后拉深,應(yīng)保證模具裝配后,拉深凸模的端面比落料凹模端面低。模具總裝配圖是裝配、安裝及拆繪模具零件圖的依據(jù),能更清楚的表達(dá)模具的主要結(jié)構(gòu)形狀、工作原理、各零件之間的裝配關(guān)系及固定連接方式。模具視圖一般為主視圖和俯視圖,主視圖應(yīng)標(biāo)明模具的閉合高度.6 結(jié)束語(yǔ)經(jīng)過(guò)近兩個(gè)月忙碌又緊張地設(shè)計(jì),我終于完成了老師布置的題目:落料拉深件的設(shè)計(jì)。在設(shè)計(jì)的過(guò)程中,我遇到了許多的困難。首先是計(jì)算的復(fù)雜,計(jì)算毛坯直徑時(shí),涉及的尺寸很多而且還帶根號(hào),計(jì)算量很大;還有計(jì)算拉深力、壓邊力時(shí)得查閱大量的表。其次是知識(shí)的完美結(jié)合,在設(shè)計(jì)模具時(shí),很多知識(shí)以前都沒有學(xué)過(guò),這就需要我查閱手冊(cè)、資料,然后與我們平常所學(xué)結(jié)合到一塊,做到融會(huì)貫通。同時(shí)在設(shè)計(jì)中,我也總結(jié)了許多: 1.選擇模具結(jié)構(gòu)(根據(jù)零件圖樣及計(jì)算要求,結(jié)合生產(chǎn)實(shí)際情況,提出模具結(jié)構(gòu)方案分析比較,選擇最佳結(jié)構(gòu))2.采用標(biāo)準(zhǔn)零部件(應(yīng)盡量選用國(guó)家標(biāo)準(zhǔn)及工廠沖模標(biāo)準(zhǔn)件,便模具設(shè)計(jì)典型化及制造簡(jiǎn)單化,縮短設(shè)計(jì)制造周期,降低成本)參考文獻(xiàn)1 王樹勛,高廣升. 冷沖壓模具結(jié)構(gòu)圖冊(cè)大全M. 廣州:華南理工大學(xué)出版社,2 鄭家賢. 沖壓工藝模具設(shè)計(jì)實(shí)用技術(shù)M. 北京:機(jī)械工業(yè)出版社,19993 成虹. 沖壓工藝與模具設(shè)計(jì)M. 成都:電子科技大學(xué)出版社,20004 杜東福. 冷沖壓工藝及模具設(shè)計(jì)M. 長(zhǎng)沙:湖南科學(xué)技術(shù)出版社,19905 盧險(xiǎn)峰. 沖壓工藝模具學(xué)M. 北京:機(jī)械工業(yè)出版社,20006 梁柄文. 實(shí)用板金沖壓工藝圖集M. 北京:機(jī)械工業(yè)出版社,19997 馮柄堯. 模具設(shè)計(jì)與制造簡(jiǎn)明手冊(cè)M. 上海:上??茖W(xué)技術(shù)出版社,19988 模具實(shí)用技術(shù)叢書編委會(huì). 沖模設(shè)計(jì)應(yīng)用實(shí)例M. 北京:機(jī)械工業(yè)出版社9 劉心冶. 冷沖壓工藝及模具設(shè)計(jì)M. 重慶:重慶大學(xué)出版社,199810 溫松民.互換性與技術(shù)測(cè)量基礎(chǔ).M長(zhǎng)沙:湖南農(nóng)業(yè)大學(xué)出版社200年10月.11 王世彤.機(jī)械原理與零件.M北京:高等教育出版社2004年3月.12 孫恒 陳作模.機(jī)械原理.M北京:高等教育出版社1996年5月.13 齊衛(wèi)東.冷沖壓模具圖集M.北京理工大學(xué)出版社,2007.14 王秀鳳,張永春.冷沖壓模具設(shè)計(jì)與制造(第二版)M.北京航空航天大學(xué)出版社,2010.15 毛衛(wèi)平 肖愛民 袁鐵軍.Pro/E沖壓模具設(shè)計(jì)與制造.M北京:化工工業(yè)出版社,2008.16 歐陽(yáng)波儀.現(xiàn)代冷沖模設(shè)計(jì)應(yīng)用實(shí)例M.北京:化工工業(yè)出版社,2003.17 周玲.沖模設(shè)計(jì)實(shí)例詳解M.化學(xué)工業(yè)出版社,200718 薛啟翔.沖壓模具設(shè)計(jì)結(jié)構(gòu)圖冊(cè)M. 北京:化工工業(yè)出版社,2008.19 郭克希,王建國(guó).機(jī)械制圖M.北京:機(jī)械工業(yè)出版社,2009.20 溫松民.互換性與技術(shù)測(cè)量基礎(chǔ).M長(zhǎng)沙:湖南農(nóng)業(yè)大學(xué)出版社200年10月.21 王世彤.機(jī)械原理與零件.M北京:高等教育出版社2004年3月.22 孫恒 陳作模.機(jī)械原理.M北京:高等教育出版社1996年5月.23 Solberg J J,Kashyap R L。ERC Research in Intelligent Manufacturing systems.Proc.of IEEE,1993,81(4):2541.致 謝 為期一個(gè)學(xué)期的畢業(yè)設(shè)計(jì)已接近尾聲了,我的四年大學(xué)生涯也即將圈上一個(gè)句號(hào)。此刻我的心中卻有些悵然若失,因?yàn)槟切┦煜さ臋C(jī)械設(shè)計(jì)制造及其自動(dòng)化系各位可愛的同學(xué)們,我們也即將揮手告別了。四年間,無(wú)論是學(xué)習(xí)、工作生活上的問(wèn)題,恩師們都會(huì)悉心給以指導(dǎo)解答,讓我倍受感動(dòng)。也就是在這里,給我的大學(xué)生涯設(shè)計(jì)點(diǎn)上了第一個(gè)逗號(hào)。我的學(xué)術(shù)論文創(chuàng)作的開始,也是從這里起步的。從某種意義上可以說(shuō),今日的畢業(yè)設(shè)計(jì)其實(shí)從大一時(shí)已經(jīng)開始了。工學(xué)院的老師們,給我四年的學(xué)習(xí)、成長(zhǎng)創(chuàng)造了一個(gè)良好的環(huán)境,引導(dǎo)我充分利用學(xué)校的學(xué)習(xí)資源,去發(fā)展、充實(shí)自我,而不曾虛度光陰。在此,我真誠(chéng)的向你們道一聲:“謝謝!”。讓我愧疚的是,個(gè)人能力有限,沒能為整個(gè)機(jī)械系的學(xué)生做出太多貢獻(xiàn),在此深表感謝和歉意。湯興初老師是我的制圖學(xué)入門老師,給我的專業(yè)方向打下了良好的基礎(chǔ),他是“師父送上馬”的那樣一位恩師。而周光永老師現(xiàn)在又是我畢業(yè)設(shè)計(jì)的指導(dǎo)老師,在畢業(yè)設(shè)計(jì)期間,沒少費(fèi)心思。從論文創(chuàng)作的選題、結(jié)構(gòu)、內(nèi)容、甚至是編排格式上都悉心指導(dǎo),提出了寶貴意見,讓我在專業(yè)論文創(chuàng)作上又進(jìn)了一步。就整個(gè)大學(xué)而言,周老師可以說(shuō)是“扶我下馬”的過(guò)程。在他這里,我學(xué)到了許多以前沒有學(xué)到的東西,包括做人方式。周老師,謝謝你!由于篇幅所限,不便把各位恩師一一列舉出來(lái),表達(dá)我的感激之情,在此對(duì)機(jī)械系所有專業(yè)課老師表示感謝。盡管由于年級(jí)原因,各位老師可能離我漸漸遠(yuǎn)去,但他們四年期間對(duì)我的幫助與教誨,我永遠(yuǎn)不會(huì)忘記,他們的音容笑貌仍舊不時(shí)浮現(xiàn)在我的眼前。各位老師鮮明地個(gè)性特點(diǎn)和人格魅力將是我回憶中的大學(xué)生涯重要的組成部分?!安环e跬步無(wú)以至千里”,這次畢業(yè)論文能夠最終順利完成,歸功于各位老師四年間的認(rèn)真負(fù)責(zé),使我能夠很好的掌握專業(yè)知識(shí),并在畢業(yè)論文中得以體現(xiàn)。也正是你們長(zhǎng)期不懈的支持和幫助才使得我的畢業(yè)論文最終順利完成。最后,我向湖南農(nóng)業(yè)大學(xué)機(jī)械系的全體老師們?cè)俅伪硎局孕母兄x:謝謝你們,謝謝你們四年的辛勤栽培!29 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
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