【正文】 s ratio is .In order to analyze the principal stress concentration area in the region of Crack I, different cases are studied. Let the models shown in Fig. 3a and b be Case 1. A new 3D model (Case 2) is used as shown in Fig. 3c. The die is separated into three parts. The Abaqus mand *CONTACT PAIR, TIED is used to tie separate surfaces together for joining dissimilar meshes. The advantage of this model is its convenience in changing the mesh of the halfmoon pattern and its position. First, the halfmoon pattern is moved 6 mm towards the center (Case 3) as shown in Fig. 3d. Second, the fillet radius of the halfmoon pattern is changed from 0 to mm (Case4) as shown in Fig. 3e.. Results and discussionFor the two meshes used in Case 1. The maximum principal shear stress (S12) distribution at the region of fillet are shown in Fig. 4a and b. The results show that the stress distribution patterns are the same for the two different meshes, and therefore, the convergence of the solutions is established.Altan and coworkers [14] have presented the stress analysis of an axisymmetric upper die. In their work, when the material of the workpiece flows to fill the volume between the dies and collar, the contact surface of the die is stretched. At the area of the transition radius, the principal stresses change direction and reach high tensile values.According to their analysis, the fatigue failure is due to two factors: (i) when the stress exceeds the yield strength of the die material, a localized plastic zone generally forms during the first load cycle and undergoes plastic cycling during subsequent unloading and reloading, ＸＸＸ：蓋板零件的沖壓工藝及模具設(shè)計(jì) 28 thus microscopic cracks initiate。 Die failure1. IntroductionIn metal forming processes, die failure analysis is one of the most important problems. Before the beginning of this decade, most research focused on the development of the oretical and numerical methods. Upper bound techniques [1,2], contactimpact procedures [3] and the finite element method (FEM) [4,5] are the main techniques for analyzing stamping problems. With the development of puter technology, the FEM bees the dominant technique [612].Altan and coworkers [13,14] discussed the causes of failure in fing tooling and presented a fatigue analysis concept that can be applied during process and tool design to analyze the stresses in tools. In these two papers, they used the punching load as the boundary force to analyze the stress states that exist in the inserts during the forming process and determined the causes of the failures. Based on these concepts, they also gave some suggestions to improve die design.In this paper, linear stress analysis of a threedimensional (3D) die model is presented. The stress patterns are then analyzed to explain the causes of the crack initiation. Some suggestions about optimization of the die to reduce the stress concentration are presented. In order to optimize the design of the die, the effects of geometry and fillet radius are discussed based on a simplified axisymmetric model.2. Problem definitionThis study focuses on the linear elastic stress analysis of the die in a typical metal forming situation (Fig. 1). The die (Fig. 2) with a halfmoon shaped ingot on the top surface is punched down towards the workpiece which is held inside the collar, and the pattern is made onto the workpiece. Cracks were found in the die after repeated operation: (i) when the die punched the workpiece, there is crack initiation between the tip of the moon shaped pattern and one of the edges (Crack I)。在此我向他們表示深深的感謝。雖然該設(shè)計(jì)可能還存在種種不足之處，但我覺(jué)得，該模具設(shè)計(jì)整體來(lái)說(shuō)還算巧妙，尤其是彎曲凸模的固定方式以及它與沖孔凸模固定板之間的配合都是經(jīng)過(guò)深思熟慮的，只要將上述所提到的一些不足之處加以改進(jìn)，還是有它的價(jià)值的。凸、凹模刃口尺寸的計(jì)算也是很重要的，還要通過(guò)壓力機(jī)的最大最小閉合高度來(lái)選擇模架，接下來(lái)進(jìn)行模具結(jié)構(gòu)與尺寸的設(shè)計(jì)，并且還需要確定模具的總體尺寸和模具零件的結(jié)構(gòu)，查詢(xún)并確定模具安裝和調(diào)試的要求及注意事項(xiàng)，整套模具組件的裝配技術(shù)要求，和一些重要的配合尺寸。開(kāi)始工作的順序?yàn)椋簭澢鷽_孔，即圖中下模中彎曲凸模、沖孔凹模上平面下齊時(shí)，上模沖孔凸模下作面最高，彎曲凸模成形部分次之，卸料部分經(jīng)試模調(diào)整應(yīng)保證壓邊及卸料力適當(dāng)，動(dòng)作順暢，功能滿(mǎn)足模具工作要求。開(kāi)模時(shí)，彈性卸料板降零件卸下，完成該模具的所有工序。壓入上、下模座的導(dǎo)柱、導(dǎo)柱離其它安裝表面應(yīng)有 12 mm 的距離，壓入后就應(yīng)牢固。 主要組件的裝配1．模柄的裝配，在安裝凸模固定板和墊板之前，應(yīng)先把模柄裝好,用角尺檢查模柄與上模座上平面的垂直度。,其封閉高度應(yīng)符合圖樣規(guī)定的要求。11．沖模的裝配必須符合模具裝配圖、明細(xì)表及技術(shù)條件規(guī)定。7．各緊固用的螺釘、鎖釘不得松動(dòng)，并保證螺釘和銷(xiāo)釘?shù)亩嗣娌煌怀錾?、下模座平面?裝配技術(shù)要求1．裝配時(shí)應(yīng)保證凸、凹模之間的間隙均勻一致，配合間隙符合設(shè)計(jì)要注，不允許采用使凸、凹模變形的方法來(lái)修正間隙。6．零件圖中未注公差尺寸的極限偏差按 GB/T1804 的規(guī)定。2．沖模各零件的材料和熱處理硬度應(yīng)優(yōu)先按模具設(shè)計(jì)手冊(cè)中標(biāo)準(zhǔn)選用，允許采用性能高于兩表規(guī)定的其他鋼種。整套模具中的彎曲沖孔凹模加工也比較難，特別是彎曲凹模，因?yàn)橛屑庸ぞ纫?，加工需要特別注意。A 型滑動(dòng)導(dǎo)套、導(dǎo)柱采用 20 鋼。墊板、凸模固定板、推板、打料桿、定位銷(xiāo)、卸料板、均采用 45 鋼。由于沖裁模主要用于各種板料的沖切成形,其刃口在工作過(guò)程中受到強(qiáng)烈的摩擦和沖擊,所以要求模具工作材料具有高的耐磨性、沖擊韌性以及耐疲勞斷裂性能。 模具材料的選用選擇模具材料應(yīng)遵循如下原則：1. 根據(jù)模具種類(lèi)及其工作條件，選用材料要滿(mǎn)足使用要求，應(yīng)具有較高的強(qiáng)度、硬度、耐磨性、耐沖擊、耐疲勞性等；2. 根據(jù)沖壓材料和沖壓件生產(chǎn)批量選用材料；3. 滿(mǎn)足加工要求，應(yīng)具有良好的加工工藝性能，便于切削加工，淬透性好、熱處理變形?。?4. 滿(mǎn)足經(jīng)濟(jì)性要求。如圖 36安徽工程大學(xué)機(jī)電學(xué)院畢業(yè)設(shè)計(jì)( 論文) 19 圖 36 下模座上模座的尺寸與形狀與下模座基本相同。圖 35 模柄 連接件與緊固件的選取下模座與下凸模固定板的固定選用 M1256 的內(nèi)六角螺釘，定位銷(xiāo)選用公稱(chēng)直徑d=8mm、長(zhǎng)度 l=60mm 的圓柱銷(xiāo)。送進(jìn)導(dǎo)向的定位零件有導(dǎo)正銷(xiāo)、導(dǎo)料板、側(cè)壓板等；送料定距的定位零件有用擋料銷(xiāo)、側(cè)刃等；在本次設(shè)計(jì)中使用的是定位銷(xiāo)。材料采用 45 號(hào)鋼。 墊板的設(shè)計(jì)在設(shè)計(jì)沖模時(shí)，由模板所承受壓力的大小來(lái)判斷是否加裝墊板。其結(jié)構(gòu)及尺寸如圖 3－3 所示：安徽工程大學(xué)機(jī)電學(xué)院畢業(yè)設(shè)計(jì)( 論文) 17 圖 33 沖孔凸模 凸凹模的設(shè)計(jì)該凸凹模為沖孔凹模、彎曲凸模。 H 模具各零部件的設(shè)計(jì)與計(jì)算ＸＸＸ：蓋板零件的沖壓工藝及模具設(shè)計(jì) 16 彎曲凹模設(shè)計(jì)由于每種制件的形狀和尺寸不同，因此沖模的加工以及裝配工藝等實(shí)際條件也有許多不同，所以在實(shí)際生產(chǎn)中使用的凹模結(jié)構(gòu)形式很多。 （39）maxmin5+10??式中 、 ——壓力機(jī)的最大和最小裝模高度；i ——模具的閉合高度。再按其標(biāo)準(zhǔn)選擇具體結(jié)構(gòu)，尺寸見(jiàn)表 32。凸 凹、 ——凸、凹模的制造公差；?凸 凹——最小沖裁間隙；minZ——磨損系數(shù),與沖件精度有關(guān)；x——沖裁件的公差，未注公差的毛坯尺寸按照 IT14 設(shè)計(jì)；?——落料件公稱(chēng)尺寸（mm）；D所以落料（）: mx 5)) ??? ???????（（ 凹凹 ?ＸＸＸ：蓋板零件的沖壓工藝及模具設(shè)計(jì) 12 mZxD 59)) ??? ?????（（ 凸凸 ?式中 x 查《實(shí)用沖壓設(shè)計(jì)技術(shù)》表 317 得，x=； 查附錄表 D， =??落料（26mm）: 745)) ??? ???????（（ 凹凹 ?Z 85)6..) ???（（ 凸凸 ?式中 x 查《實(shí)用沖壓設(shè)計(jì)技術(shù)》表 317 得，x=； 查附錄表 D， =??落料（40mm）: 693)) ??? ???????（（ 凹凹 ?Z 3)4..) ???（（ 凸凸 ?式中 x 查《實(shí)用沖壓設(shè)計(jì)技術(shù)》表 317 得，x=； 查附錄表 D， =??落料（161mm）: 516)) ??????????（（ 凹凹 ?Z 16).