側(cè)板固定卡沖壓模具設(shè)計(jì)【說(shuō)明書(shū)+CAD】

側(cè)板固定卡沖壓模具設(shè)計(jì)【說(shuō)明書(shū)+CAD】,說(shuō)明書(shū)+CAD,側(cè)板固定卡沖壓模具設(shè)計(jì)【說(shuō)明書(shū)+CAD】,固定,沖壓,模具設(shè)計(jì),說(shuō)明書(shū),仿單,cad 紫瑯職業(yè)技術(shù)學(xué)院 畢業(yè)設(shè)計(jì) 課 題： 側(cè)板固定卡 院 系： 紫瑯職業(yè)技術(shù)學(xué)院 班 級(jí)： 模具3081 學(xué)科專(zhuān)業(yè)： 模具設(shè)計(jì)與制造 學(xué) 生： 王明園 學(xué) 號(hào)： 080140105 指導(dǎo)教師： 錢(qián) 軍 摘 要 目錄 1、課題…………………………………………………………………………....1 2、原始數(shù)據(jù)………………………………………………………………………1 3、工藝分析……………………………………………………………………....1 4、沖裁工藝方案的確定…………………………………………………………1 4.1方案的種類(lèi)……………………………………………………………………1 4.2方案的比較……………………………………………………………………1 4.3方案的確定…………………………………………………………………….2 5、模具結(jié)構(gòu)形式的確定…………………………………………………………2 6、工藝尺寸的計(jì)算………………………………………………………………2 6.1排樣的設(shè)計(jì)…………………………………………………………………….2 6.2沖裁力的計(jì)算………………………………………………………………….3 6.3壓力機(jī)公稱(chēng)力的確定………………………………………………………….4 6.4沖裁壓力中心的確定………………………………………………………….4 6.5刃口尺寸的計(jì)算……………………………………………………………….4 7、模具總體結(jié)構(gòu)設(shè)計(jì)…………………………………………………………….6 8、主要零部件的結(jié)構(gòu)設(shè)計(jì)……………………………………………………….6 9、模具總裝圖…………………………………………………………………… 8 致謝………………………………………………………………………………..9 參考文獻(xiàn)…………………………………………………………………………..10 后附：模具零件圖 摘 要 沖壓模是實(shí)現(xiàn)沖壓生產(chǎn)的基本條件。在沖壓模的設(shè)計(jì)和制造上，目前正朝著以下的兩個(gè)方面發(fā)展：一方面，為了適應(yīng)高速、自動(dòng)、精密、安全等大批量現(xiàn)代生產(chǎn)的需要，沖模正向高效率、高精度、高壽命及多工位、多功能方向發(fā)展，為此相適應(yīng)的新型模具材料及其熱表面處理技術(shù)也在迅速的發(fā)展；另一方面，為了適應(yīng)產(chǎn)品更新?lián)Q代和試制或小批量生產(chǎn)的需要，鋅基合金模、聚氨脂橡膠沖模、薄板沖模、組合沖模等各種簡(jiǎn)易沖模及其制造也得到了迅速的發(fā)展。 近年來(lái)，為了適應(yīng)市場(chǎng)的激烈競(jìng)爭(zhēng)，對(duì)產(chǎn)品質(zhì)量的要求越來(lái)越高，且其更新?lián)Q代的周期大為縮短。沖壓生產(chǎn)為適應(yīng)這一新的要求，開(kāi)發(fā)了多種適合不同批量生產(chǎn)的工藝、設(shè)備和模具。其中，無(wú)需設(shè)計(jì)專(zhuān)用模具、性能先進(jìn)的轉(zhuǎn)塔數(shù)控多工位壓力機(jī)、激光等新設(shè)備的使用。特別是近近幾年來(lái)國(guó)外已經(jīng)發(fā)展起來(lái)、國(guó)外亦開(kāi)始使用的沖壓柔性制造單元和沖壓柔性制造系統(tǒng)代表了沖壓生產(chǎn)的發(fā)展趨勢(shì) 關(guān)鍵詞： 模具 沖壓 發(fā)展趨 紫瑯職業(yè)技術(shù)學(xué)院畢業(yè)設(shè)計(jì) 1、題目：側(cè)板固定卡 2、原始數(shù)據(jù) 如圖所示，大批量生產(chǎn)、材料ST12、t=1mm 3、工藝分析 此工件既有沖孔，又有落料兩個(gè)工序。材料為ST12 t=1mm的碳素結(jié)構(gòu)鋼，具有良好的沖壓性能適合沖裁，工件結(jié)構(gòu)中等復(fù)雜，涉及尺寸比較多，有兩個(gè)直徑為4.5mm的圓孔。周?chē)幱辛鶄€(gè)R=2mm的1/4半圓。此工件滿(mǎn)足沖裁的加工要求，工件的尺寸落料按IT11級(jí)，沖孔按10級(jí)計(jì)算，尺寸精度一般，普通沖裁完全能滿(mǎn)足要求。 4、沖裁工藝方案的確定 （1）方案的種類(lèi) 該工件包括落料、沖孔兩道基本工序，可以有以下三種工藝方案。 方案一：先沖孔后落料。采用單工序模生產(chǎn)。 方案二：沖孔—落料級(jí)進(jìn)沖壓。采用級(jí)進(jìn)模生產(chǎn)。 方案三：采用落料—沖孔同時(shí)進(jìn)行的復(fù)合模生產(chǎn)。 （2）方案的比較各方案的特點(diǎn)及比較如下 方案一：模具結(jié)構(gòu)簡(jiǎn)單，制造方便，但需要兩道工序，兩副模具，成本相對(duì)較高，生產(chǎn)效率低，且更重要的是在第一道工序完成后，進(jìn)入第二道工序必然會(huì)增大誤差，使工件精度、質(zhì)量大打折扣，達(dá)不到所需的要求，故不選此方案。 方案二：級(jí)進(jìn)模是一種多工位，效率高的加工方法，一般適用于大批量、小型沖壓件，但級(jí)模輪廓尺寸較大，制造復(fù)雜，成本較高，故不選用此方案。 方案三：只需要一副模具，工件的精度及生產(chǎn)效率都能都能達(dá)到滿(mǎn)足，模具輪廓較小、模具制造成本不高。故選用此方案。 （3）方案的確定 綜上所述本副模具采用落料—沖孔復(fù)合模 5、模具結(jié)構(gòu)形式的確定 復(fù)合模有兩種結(jié)構(gòu)形式，正裝式復(fù)合模和倒裝式復(fù)合模。分析該工件成行后脫落方便性，正裝式復(fù)合模成形后工件留在下模，需向上推出該工件，取出不方便。倒裝式復(fù)合模成形后工件留在上模，只需在上模裝一副推件裝置，從效率上講，倒裝式復(fù)合模比正裝式復(fù)合模的生產(chǎn)效率高，故采用倒裝式復(fù)合模。 6、工藝尺寸計(jì)算 （1）排樣設(shè)計(jì) a、排樣方法的確定 根據(jù)工件的形狀，確定采用無(wú)廢料排樣的方法不可能做到，但能采用有廢料和少?gòu)U料的排樣方法，經(jīng)多次排樣計(jì)算決定采用直對(duì)排法如圖所示。 b、確定搭邊值，取最小搭邊值 工件a1=1.5側(cè)面a=2 c、確定條料步距 步距：35.8mm 寬度：70 +2+2=7 4 d、條料的利用率 η = = ×100％ = 62.21％Error! No bookmark name given. e、畫(huà)出排樣圖 （2）沖裁力的計(jì)算 a、沖裁力F 材料ST12的抗拉強(qiáng)度 σb=350MPa 由 F≈Ltσb 已知L= 66＋10×2＋20.4×2＋10×2＋20＋10.2×2＋3×2＋11.1×2＋6π＋4.5π×2 =262.5 所以 F=262.5×1×350N = 91875N = 91.875KN b、卸料力Fx 由Fx=KxF，已知Kx=0.05 Fx=KxF=0.05×91.875KN = 4.59KN C、推件力FT 由FT=nKTF ，n = 4 KT=0.055 FT=nKTF=3×0.055×91.875=15.16KN d、頂件力FD 由FD=KDF,已知 KD=0.06 FD=KDF=0.06×91.875=5.5KN (3)壓力機(jī)公稱(chēng)壓力的確定 本副模具采用剛性卸料和下出料方式 FZ=F＋FT≈107.KN 根據(jù)以上計(jì)算結(jié)果，沖壓設(shè)備擬選J23—40 （4）沖裁壓力中心的確定 由于沖壓件基本為對(duì)稱(chēng)件故壓力中心為排樣圖中坐標(biāo)值（35，17.15） （5） 刃口尺寸的計(jì)算 a、加工方法的確定，結(jié)合模具及工件的形狀特點(diǎn)，此模具制造宜采用配作法。落料時(shí)選凹模為設(shè)計(jì)基準(zhǔn)件，只需要計(jì)算落料凹模刃口尺寸及制造公差，凸模刃口尺寸由凹模實(shí)際尺寸進(jìn)行配作加工。沖孔時(shí)需要計(jì)算凸模刃口尺寸及制造公差。凹模刃口尺寸由凸模實(shí)際尺寸按要求配作，保證在配作時(shí)最小雙面合理間隙值Zmin=0.1mm b、采用配作法 先判斷模具各個(gè)尺寸在模具磨損后的變化情況，分三種情況，分別統(tǒng)計(jì)如下: 第一種尺寸（增大）70 20 34.3 12 46 60 21.2 31.4 A1d =﹙Α1－ΧΔ﹚ ＝(70－0.75×0.19)＝69.86 A2d =﹙ A2－ΧΔ﹚ ＝(20－0.75×0.13)＝19.90 A3d =﹙ A3－ΧΔ﹚ ＝(34.3－0.75×0.16)＝34.18 A4d =﹙ A4－ΧΔ﹚ ＝(12－0.75×0.11)＝11.92 A5d =﹙ A5－ΧΔ﹚ ＝﹙46－0.75×0.16﹚ ＝45.88 A6d =﹙ A6－ΧΔ﹚ ＝ ﹙60－0.75×0.19﹚ ＝59.86 A7d＝﹙A7－ΧΔ﹚ ＝﹙21.2－0.75×0.13﹚ ＝21.1 A8d＝﹙A8－ΧΔ﹚ ＝﹙31.4－0.75×0.16﹚ ＝31.28 第二種尺寸（減?。?3 4.5 2 B1d＝﹙B1＋χΔ﹚ ＝﹙3﹢0.75×0.06﹚ ＝3.045 B2d＝﹙B2＋χΔ﹚ ＝﹙4.5＋0.75×0.075﹚ ＝4.556 B3d＝﹙B3＋χΔ﹚ ＝﹙2＋0.75×0.06﹚ ＝2.045 第三種尺寸（不變）： 60 Cd＝C±＝60±＝60±0.015 C、按入體原則，查表確定沖裁件內(nèi)形與內(nèi)形尺寸公差。 d、畫(huà)出落料凸凹模尺寸 (落料凹模) 凸凹模 e、卸料裝置的設(shè)計(jì) 已知沖裁板厚t=1mm沖裁力為Fx=4.59KN 故選用四個(gè)彈簧、 每個(gè)彈簧的預(yù)壓力為： F0>Fx/n=1.1475KN 7、模具總體結(jié)構(gòu)設(shè)計(jì) a、模具類(lèi)型的選擇 由沖壓工藝分析可知，采用復(fù)合模沖壓。所以本套模具類(lèi)型為復(fù)合模。 b、定位方式的選擇 因?yàn)樵撃＞卟捎玫氖菞l料控制條料的送向采用彈性擋料銷(xiāo)來(lái)定步距。 c、卸料、出件方式的選擇 根據(jù)模具的運(yùn)動(dòng)特點(diǎn)，該模具采用剛性卸料方式比較好，取出工件方便。 d、導(dǎo)柱、導(dǎo)套位置的確定，為了提高模具的壽命和質(zhì)量，方便安裝、調(diào)整、維修模具，該復(fù)合模采用后側(cè)導(dǎo)柱模架。 8、主要零部件的結(jié)構(gòu)設(shè)計(jì) a、落料凹模 凹模采用整體凹模，輪廓全部采用數(shù)控線切割機(jī)床即可，一次成形，安排凹模在模架上的位置時(shí)，要依據(jù)壓力中心數(shù)據(jù)盡量保證壓力中心與模柄中心一致。 b、 輪廓尺寸的計(jì)算 凹模厚度 H=KB 凹模壁厚 C=(1.2-2)H 取凹模厚度H=30mm 壁厚C=30mm 凹模寬度B=b+2c=140 凹模長(zhǎng)度L=170 根據(jù)工件圖樣，在分析受力情況及保證壁厚強(qiáng)度的前提下，取凹模長(zhǎng)度為170 mm寬度為 140 mm，所以凹模輪廓尺寸為 170mm ×140mm×30mm c、沖孔凸模 根據(jù)圖樣：工件中有兩個(gè)孔且相等，因此需設(shè)計(jì)一支凸模長(zhǎng)度為L(zhǎng)=凹模+固定板+T=48㎜ 落料凹模 卸料板+凹模+凹模墊板 凸凹模設(shè)計(jì)時(shí)保證最小間隙0.05㎜ d、定位零件的設(shè)計(jì) 結(jié)合本套模具的具體結(jié)構(gòu)?？紤]到工件的形狀，設(shè)置一個(gè)彈性當(dāng)料銷(xiāo)﹙起定距的作用﹚ ﹙ 彈性當(dāng)料銷(xiāo)﹚ 卸料板設(shè)計(jì) 卸料板的周界尺寸與凹模周界尺寸相同。厚度為15mm，材料為Q235鋼、淬火硬度為40—45HRC。 卸料螺釘?shù)倪x用 卸料板采用4個(gè)M10的螺釘固定，長(zhǎng)度50㎜ 模架均采用標(biāo)準(zhǔn)模架 H閉＝H＋H＋H＋L＋H－h(huán)＝209㎜ 式中：L―凸模高度，㎜ H―凸凹模高度，㎜ h― 凸模沖裁后進(jìn)入凸凹模的深度，㎜ 可見(jiàn)該模具的閉合高度小于所選壓力機(jī)J23—40的最大裝模高度330mm，因此該壓力機(jī)可以滿(mǎn)足使用要求。 9、模具裝配圖 通過(guò)以上設(shè)計(jì)，可以看到，模具上模部分由上模座、墊板、沖孔凸模、沖孔凸模固定板、凹模板組成。下模板由下模座板、固定板、卸料板等組成。 致謝 此次畢業(yè)設(shè)計(jì)，對(duì)我來(lái)說(shuō)是對(duì)三年所學(xué)知識(shí)的綜合運(yùn)用，是解決實(shí)際問(wèn)題的綜合訓(xùn)練。再設(shè)計(jì)過(guò)程中，不可避免的我遇到了許多問(wèn)題，得到了老師和同學(xué)們以及我實(shí)習(xí)單位“蘇州三電精密零件有限公司”模具設(shè)計(jì)課人員的真誠(chéng)幫助，在此表示真心感謝。 另外，我要特別感謝我的指導(dǎo)老師錢(qián)軍老師。他工作認(rèn)真，嚴(yán)謹(jǐn)負(fù)責(zé)的態(tài)度，在設(shè)計(jì)過(guò)程中幫我完成了一個(gè)又一個(gè)大大小小的錯(cuò)誤，給予我正確的指導(dǎo)，使我模糊的思路漸漸清晰起來(lái)。 參考文獻(xiàn) [1 ] 沖壓模具課程設(shè)計(jì)指導(dǎo)與范例／林承全，胡紹平主編. 北京：化學(xué)工業(yè)出版社，2008.1 [2 ] 沖壓工藝與模具設(shè)計(jì)／馬朝興主編. －北京：化學(xué)工業(yè)出版社，2006.2 [3 ] 公差配合與技術(shù)測(cè)量／徐茂功主編. －3版. －北京：機(jī)械工業(yè)出版社，2008.1（2009.1重?。? [4 ] 模具制造技術(shù)／劉航主編. －西安：西安電子科技大學(xué)出版社，2006.1 [5 ] 模具材料及表面處理／吳兆祥．北京：機(jī)械工業(yè)出版社，2008 9 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