四角墊片沖壓模具設計【說明書+CAD+UG】

四角墊片沖壓模具設計【說明書+CAD+UG】,說明書+CAD+UG,四角墊片沖壓模具設計【說明書+CAD+UG】,四角,墊片,沖壓,模具設計,說明書,仿單,cad,ug 畢 業(yè) 設 計 說 明 書 四角墊片沖壓模具設計 年 4 月 22 日 目 錄 第1章 零件的工藝分析 2 1.1 材料分析 4 1.2 工件結(jié)構(gòu)分析 4 1.3 精度分析 4 1.4 批量 4 第2章 工藝方案的確定 4 2.1 沖裁工藝方案的確定 4 2.2 沖裁工藝方法的選擇 4 2.3 沖裁順序的安排 4 第3章 模具整體結(jié)構(gòu)的設計 5 3.1 送料方式的確定 5 3.2 定位方式的選擇 5 3.3 卸料、出件方式的選擇 5 3.4 導向方式的選擇 5 第4章 零件工藝計算 6 4.1 制件圖 6 4.2 材料利用率 6 第5章 凸、凹模刃口尺寸計算 6 5.1 模具刃口尺寸的計算方法 6 5.2 模具刃口尺寸的計算 7 第6章 模具主要零部件 7 6.1 上模板模板 7 6.2 定位塊 9 6.3 導柱 9 6.4 上模 10 6.5 導套 11 6.6 組合下模 12 6.7 定位墊塊 13 6.8 裝配圖 13 結(jié) 論 14 致 謝 15 參考文獻 17 引言 科技行業(yè)的一個重要領(lǐng)域,其技術(shù)水平已成為一個國家制造業(yè)水平的重要標志。目前我國模具年度總產(chǎn)量有世界上第三大,包括總額百分之四十以上的沖壓模具。中國已經(jīng)可以生產(chǎn)一些關(guān)于汽車的模具。汽車的一些模具制造起來是飛車昂困難的，質(zhì)量要求高是評價的一部分 隨著科技的進步和發(fā)展，發(fā)現(xiàn)了許多新材料和新工藝。 第1章 零件工藝分析 圖1.1 1.1 材料分析 08f是沸騰鋼，它有比較低的強度和硬度，可塑性比較高，有很好的韌性，有良好的冷變形能力，焊接，切割后正火，退火后的高磁導率、低殘留。 最好選用08f材料 表1.1 部分碳素鋼抗剪性能 表1.2碳素結(jié)構(gòu)鋼的化學成分，性能及用途 由圖表得08F的鋼材是優(yōu)質(zhì)結(jié)構(gòu)鋼，厚0.6mm，有許多良好的性能 1.2 工件的結(jié)構(gòu)分析 結(jié)構(gòu)相對比較簡易,矩形薄板的切割邊90度角。長度281毫米,適用于切削加工、模具架形狀是對稱的,由導套,導柱,其適合H7 /h6間隙配合。單從左到右,定位塊的定位。 1.3 精度分析 經(jīng)濟公差等級的沖裁件通常需要12 ~ 13級,通常把IT12水平。 1.4 批量生產(chǎn) 因為零件結(jié)構(gòu)比較的簡單，但是因為矩形的切角很容易損壞，可以單一的批量生產(chǎn) 第2章 方案設計 2.1 方案的確定 過程由沖裁和消隱的組合順序安排 2.2 方法的選擇 沖裁是一個單一的過程中按下一個旅行不僅完成落料沖孔過程。 復沖裁件級進沖壓工藝的消隱是一個數(shù),安排在特定的順序,在新聞訪問條目在沖孔模的不同位置,都必須完成工件的過程。 復合模由于部分生產(chǎn)要求的小批量生產(chǎn),大的組件和結(jié)構(gòu)簡單,制造相對簡單,生產(chǎn)率低,根據(jù)上述方案分析,比較,根據(jù)上面的分析,這個問題簡單的部分是對稱的,宜采用單一的消隱技術(shù)解決方案。 2.3 沖裁順序的安排 計劃1:第一次落料,沖孔后。用兩個模具進行生產(chǎn) 計劃2第一次落料后用沖孔復合沖壓。用 復合模具生產(chǎn) 方案1模具的結(jié)構(gòu)比較簡單，但是要用兩個工藝兩套模具，所以生產(chǎn)效率很低，并且 零件的精確度還不高，不太適合大量生產(chǎn)。 方案2 沖壓制件的形狀精確度和尺寸都較好，生產(chǎn)效率也很高。 計劃3還需要一副模具,生產(chǎn)效率高,但相比之下,方案2的生產(chǎn)精密零件有點可憐。為了確保沖壓形成的準確性,需要設置導料銷指南在模具上,模具制造、裝配組合模具稍微復雜。 相比之下,只需要一個簡單的過程。 第3章 模具整體結(jié)構(gòu)的設計 3.1 送料方式的確定 當然,這取決于類型的部分生產(chǎn)批次和模具可以使用人工送料方式。 3.2 定位方式的選擇 包含控制供給到距離擋料和垂直進給,等。由于選擇空白的文章預計,部分結(jié)構(gòu)簡單,定位塊可用于定位。 3.3 卸料、出件方式的選擇 常用于硬,厚和準確性不高,卸載后的工件切割。 彈性卸載流量和壓力的雙重角色,主要用于材料厚度2毫米以下的鈑金沖壓,由于材料的壓力,相對平坦的沖裁件。精致卸料板和彈性元件,卸料螺旋壓力設備。 因為零件是單個進程死,死框架很簡單,你只需要用手的部分。 3.4 導向方式 方案1:可以用斜列模板。因為導銷裝在模具的壓力中心，所以可以滑動到小、導銷 方案2:可以用側(cè)導板列模板。導銷在后面,操作員可以看到模具的材料轉(zhuǎn)化為行動。但不能使用浮動模處理。 方案3:四列模板。具有光滑的定位、準確、可靠和良好的剛性的優(yōu)點。解決方案4:導料銷模組在中間。如圖3 - 1所示,導桿安裝模具的對稱的線條,光滑的和準確的。只有一個方向。 1-下模座 2-導柱 3-導套 4-上模座 圖3.1 通過對上述方案的比較，方案2較好 第4章 零件工藝計算 4.1 制件圖 圖4-1 排樣圖 4.2 材料利用率 關(guān)于材料利用率，可用下式表示： 第5章 凸、凹模刃口尺寸計算 5.1 模具刃口尺寸 邊緣尺寸計算加的工方法大致分為兩類。 分別沖壓和模具。該方法適用于簡單的形狀沖壓。用這個方法，分別制造公差，同時，可以保證有一些間隙，制造公差必須符合一些條件 打孔和處理。首先處理基準零件,然后按基準基準零件,加工打孔和死后不可以互換。選擇死亡作為基準模型通常材料下降和沖孔沖頭作為基準模型。大部分用在形狀復雜，需要切割部分比較小的零件。 5.2 模具的刃口的尺寸 1,凸模與凹模配合加工 凸模與凹模配合加工是首先根據(jù)的大小設計基準模型,再根據(jù)實際大小配合處理穿孔或模切邊緣維度,首先應根據(jù)穿孔或剖面正確確定后葉片的模具每個維度的變化過程中磨損較大,較小的或不變,然后分別根據(jù)不同的公式。 第一種大小、穿孔或死后穿得到更大的尺寸 沖裁?；虼蚩状虼┖蟪叽鐣黾硬糠值拇笮?相當于一個簡單的形狀沖裁凹 模具尺寸因此基本尺寸和制造公差。第一類尺寸-凸或凹模磨損會成為大尺寸的沖裁?；驔_孔模磨損大小會增加沖裁的大小相當于一個簡單的形狀，方法是： （2）第二類尺寸：凸，凹模因為磨損而減小的尺寸 沖裁?；虼┛缀蟠蚩状┏叽绲拇笮p少部分,等于一個基本形狀沖壓沖頭，所以它的計算方法如下 （3）凸，凹模的基本尺寸及制造公差的確定方法如下： 因為這個凸凹模具的設計不是圓形的，而是長方形，所以只需要定下上下模的定位尺寸就可以了 第6章 模具的主要零件 6.1 上模板 模具的下積分凹模板(圖6.2)是需要開放的下模孔和螺絲針直接固定在模具基地,凹模板尺寸標準和標準固定板時，使用板和模具設計輪廓尺寸選擇根據(jù)模具的計算。使用模具基礎(chǔ)的螺絲和錐形銷，以保證螺釘孔和銷孔之間的螺釘和螺釘或銷孔和下邊緣的模具是不是太接近，否則會影響模具的強度。通用螺孔和螺釘孔和銷孔和銷孔之間的低模切邊緣維度 表6-1下模厚度系數(shù)k 表6-2 圖6-1 6.2定位塊 圖6.2 6.3導柱 圖6.3 6.4 上模 用兩個直徑為17mm的上模（如圖6.4）用壓入法 6.5導套 圖6.5 6.6組合下模 圖6.6 6.7定位墊塊 圖6.7 6.8 裝配圖 經(jīng)過計算所有尺寸，將所有組件完成，然后裝成裝配圖，如圖 圖6.8 1.導柱,導套,柔性裝配相對運動后,沒有滯后現(xiàn)象; 2.處理成模具的模架模柄軸基準平面直線度公差,范圍內(nèi)的總長度不超過0.2毫米; 3.裝配后凸、凹模周邊間隙應均勻； 結(jié)束語 窗體底端 這個設計是大規(guī)模生產(chǎn)的墊片模具設計。沖孔模設計的兩周后,我們將在課程研究中進行使用，提高我們的專業(yè)能力， 計算模具工藝的可行性，然后確定處理計劃,準備和沖裁模設計;先根據(jù)模具結(jié)構(gòu)以及,其工件等的大小和位置設計;然后再繪制模具裝配圖和凸、凹模圖等。在畫圖的過程中,主要是使用AutoCAD繪圖軟件,更好的使用這個繪圖能力，并且提供了一個更好的環(huán)境。這能讓我們更好的體驗實踐并且更深刻的理解了理論知識，雖然在這個過程中有很多困難我們不知道如何解決，但是通過我們的努力還是可以克服，希望以后我們能得到更多的這類機會，來鍛煉我們自己，提高我們自己的設計能力，因為我們只是停留在書本知識中，缺少實踐經(jīng)驗，并且我們的水平有限，很多的困難是由同學們和老師一起共同努力才得以解決的，我們經(jīng)常需要借用學校的圖書館中的書本和網(wǎng)絡查詢來解決疑惑，但是依舊很難避免所有的錯誤，還需要老師和同學們一起檢查分析。我畢業(yè)設計的完成首先要感謝我們的高老師給我們細心的講解和教導，在圖紙的繪畫中給我檢查出了許多的問題所在，在模具設計中也給了我許多的建議，為我檢查出了許多的錯誤，并且感謝所有的老師教會了我在完成畢業(yè)設計中使用的所有技能，感謝同學們一起幫助我完成畢業(yè)設計 參考文獻 [1] 王樹勛.高廣升冷沖壓模具結(jié)構(gòu)圖冊大全..華南理工大學出版社,1999.9. [2] 朱冬梅.胥北瀾 畫法幾何及機械制圖.高等教育出版.2002.12.第五版. [3] 虞全寶.冷沖壓及塑料成型工藝與模具設計資料.機械工業(yè)出版社,1992.10. [4] 夏巨諶.李志剛.中國模具設計大典數(shù)據(jù)庫（電子版）. 中國機械工程學會. [5] 朱冬梅.胥北瀾標準技術(shù)網(wǎng):http://www.bzjsw.com 畫法幾何及機械制圖..高等教育出版.2002.12.第五版. [6]翁其金.徐新成.沖壓工藝及沖模設計. 普通高等教育規(guī)劃教材,2004.7. [7]姜勇.高薇嘉.AutoCAD2004中文版基礎(chǔ)教程.人民郵電出版社.2005.2. [8]沈蓮.機械工程材料,機械工業(yè)出版社.2005.1. [9葉邦彥.陳統(tǒng)堅.]機械工程英語.機械工業(yè)出版社.2007.1.第2版. 15 Int J Adv Manuf Technol (2002) 19:253259 2002 Springer-Verlag London Limited An Analysis of Draw-Wall Wrinkling in a Stamping Die Design F.-K. Chen and Y.-C. Liao Department of Mechanical Engineering, National Taiwan University, Taipei, Taiwan Wrinkling that occurs in the stamping of tapered square cups and stepped rectangular cups is investigated. A common characteristic of these two types of wrinkling is that the wrinkles are found at the draw wall that is relatively unsup- ported. In the stamping of a tapered square cup, the effect of process parameters, such as the die gap and blank-holder force, on the occurrence of wrinkling is examined using finite- element simulations. The simulation results show that the larger the die gap, the more severe is the wrinkling, and such wrinkling cannot be suppressed by increasing the blank-holder force. In the analysis of wrinkling that occurred in the stamping of a stepped rectangular cup, an actual production part that has a similar type of geometry was examined. The wrinkles found at the draw wall are attributed to the unbalanced stretching of the sheet metal between the punch head and the step edge. An optimum die design for the purpose of eliminating the wrinkles is determined using finite-element analysis. The good agreement between the simulation results and those observed in the wrinkle-free production part validates the accuracy of the finite-element analysis, and demonstrates the advantage of using finite-element analysis for stamping die design. Keywords: Draw-wall wrinkle; Stamping die; Stepped rec- tangular cup; Tapered square cups 1. Introduction Wrinkling is one of the major defects that occur in the sheet metal forming process. For both functional and visual reasons, wrinkles are usually not acceptable in a finished part. There are three types of wrinkle which frequently occur in the sheet metal forming process: flange wrinkling, wall wrinkling, and elastic buckling of the undeformed area owing to residual elastic compressive stresses. In the forming operation of stamp- ing a complex shape, draw-wall wrinkling means the occurrence Correspondence and offprint requests to: Professor F.-K. Chen, Depart- ment of Mechanical Engineering, National Taiwan University, No. 1 Roosevelt Road, Sec. 4, Taipei, Taiwan 10617. E-mail: fkchenL50560 w3.me.ntu.edu.tw of wrinkles in the die cavity. Since the sheet metal in the wall area is relatively unsupported by the tool, the elimination of wall wrinkles is more difficult than the suppression of flange wrinkles. It is well known that additional stretching of the material in the unsupported wall area may prevent wrinkling, and this can be achieved in practice by increasing the blank- holder force; but the application of excessive tensile stresses leads to failure by tearing. Hence, the blank-holder force must lie within a narrow range, above that necessary to suppress wrinkles on the one hand, and below that which produces fracture on the other. This narrow range of blank-holder force is difficult to determine. For wrinkles occurring in the central area of a stamped part with a complex shape, a workable range of blank-holder force does not even exist. In order to examine the mechanics of the formation of wrinkles, Yoshida et al. 1 developed a test in which a thin plate was non-uniformly stretched along one of its diagonals. They also proposed an approximate theoretical model in which the onset of wrinkling is due to elastic buckling resulting from the compressive lateral stresses developed in the non-uniform stress field. Yu et al. 2,3 investigated the wrinkling problem both experimentally and analytically. They found that wrinkling could occur having two circumferential waves according to their theoretical analysis, whereas the experimental results indi- cated four to six wrinkles. Narayanasamy and Sowerby 4 examined the wrinkling of sheet metal when drawing it through a conical die using flat-bottomed and hemispherical-ended punches. They also attempted to rank the properties that appeared to suppress wrinkling. These efforts are focused on the wrinkling problems associa- ted with the forming operations of simple shapes only, such as a circular cup. In the early 1990s, the successful application of the 3D dynamic/explicit finite-element method to the sheet- metal forming process made it possible to analyse the wrinkling problem involved in stamping complex shapes. In the present study, the 3D finite-element method was employed to analyse the effects of the process parameters on the metal flow causing wrinkles at the draw wall in the stamping of a tapered square cup, and of a stepped rectangular part. A tapered square cup, as shown in Fig. 1(a), has an inclined draw wall on each side of the cup, similar to that existing in a conical cup. During the stamping process, the sheet metal on the draw wall is relatively unsupported, and is therefore 254 F.-K. Chen and Y.-C. Liao Fig. 1. Sketches of (a) a tapered square cup and (b) a stepped rectangular cup. prone to wrinkling. In the present study, the effect of various process parameters on the wrinkling was investigated. In the case of a stepped rectangular part, as shown in Fig. 1(b), another type of wrinkling is observed. In order to estimate the effectiveness of the analysis, an actual production part with stepped geometry was examined in the present study. The cause of the wrinkling was determined using finite-element analysis, and an optimum die design was proposed to eliminate the wrinkles. The die design obtained from finite-element analy- sis was validated by observations on an actual production part. 2. Finite-Element Model The tooling geometry, including the punch, die and blank- holder, were designed using the CAD program PRO/ ENGINEER. Both the 3-node and 4-node shell elements were adopted to generate the mesh systems for the above tooling using the same CAD program. For the finite-element simul- ation, the tooling is considered to be rigid, and the correspond- ing meshes are used only to define the tooling geometry and Fig. 2. Finite-element mesh. are not for stress analysis. The same CAD program using 4- node shell elements was employed to construct the mesh system for the sheet blank. Figure 2 shows the mesh system for the complete set of tooling and the sheet-blank used in the stamping of a tapered square cup. Owing to the symmetric conditions, only a quarter of the square cup is analysed. In the simulation, the sheet blank is put on the blank-holder and the die is moved down to clamp the sheet blank against the blank-holder. The punch is then moved up to draw the sheet metal into the die cavity. In order to perform an accurate finite-element analysis, the actual stressstrain relationship of the sheet metal is required as part of the input data. In the present study, sheet metal with deep-drawing quality is used in the simulations. A tensile test has been conducted for the specimens cut along planes coinciding with the rolling direction (0) and at angles of 45 and 90 to the rolling direction. The average flow stress H9268, calculated from the equation H9268H11005(H9268 0 H11001 2H9268 45 H11001H9268 90 )/4, for each measured true strain, as shown in Fig. 3, is used for the simulations for the stampings of the tapered square cup and also for the stepped rectangular cup. All the simulations performed in the present study were run on an SGI Indigo 2 workstation using the finite-element pro- gram PAMFSTAMP. To complete the set of input data required Fig. 3. The stressstrain relationship for the sheet metal. Draw-Wall Wrinkling in a Stamping Die Design 255 for the simulations, the punch speed is set to 10 m s H110021 and a coefficient of Coulomb friction equal to 0.1 is assumed. 3. Wrinkling in a Tapered Square Cup A sketch indicating some relevant dimensions of the tapered square cup is shown in Fig. 1(a). As seen in Fig. 1(a), the length of each side of the square punch head (2W p ), the die cavity opening (2W d ), and the drawing height (H) are con- sidered as the crucial dimensions that affect the wrinkling. Half of the difference between the dimensions of the die cavity opening and the punch head is termed the die gap (G) in the present study, i.e. G H11005 W d H11002 W p . The extent of the relatively unsupported sheet metal at the draw wall is presumably due to the die gap, and the wrinkles are supposed to be suppressed by increasing the blank-holder force. The effects of both the die gap and the blank-holder force in relation to the occurrence of wrinkling in the stamping of a tapered square cup are investigated in the following sections. 3.1 Effect of Die Gap In order to examine the effect of die gap on the wrinkling, the stamping of a tapered square cup with three different die gaps of 20 mm, 30 mm, and 50 mm was simulated. In each simulation, the die cavity opening is fixed at 200 mm, and the cup is drawn to the same height of 100 mm. The sheet metal used in all three simulations is a 380 mm H11003 380 mm square sheet with thickness of 0.7 mm, the stressstrain curve for the material is shown in Fig. 3. The simulation results show that wrinkling occurred in all three tapered square cups, and the simulated shape of the drawn cup for a die gap of 50 mm is shown in Fig. 4. It is seen in Fig. 4 that the wrinkling is distributed on the draw wall and is particularly obvious at the corner between adjacent walls. It is suggested that the wrinkling is due to the large unsupported area at the draw wall during the stamping process, also, the side length of the punch head and the die cavity Fig. 4. Wrinkling in a tapered square cup (G H11005 50 mm). opening are different owing to the die gap. The sheet metal stretched between the punch head and the die cavity shoulder becomes unstable owing to the presence of compressive trans- verse stresses. The unconstrained stretching of the sheet metal under compression seems to be the main cause for the wrink- ling at the draw wall. In order to compare the results for the three different die gaps, the ratio H9252 of the two principal strains is introduced, H9252 being H9280 min /H9280 max , where H9280 max and H9280 min are the major and the minor principal strains, respectively. Hosford and Caddell 5 have shown that if the absolute value of H9252 is greater than a critical value, wrinkling is supposed to occur, and the larger the absolute value of H9252, the greater is the possibility of wrinkling. The H9252 values along the cross-section MN at the same drawing height for the three simulated shapes with different die gaps, as marked in Fig. 4, are plotted in Fig. 5. It is noted from Fig. 5 that severe wrinkles are located close to the corner and fewer wrinkles occur in the middle of the draw wall for all three different die gaps. It is also noted that the bigger the die gap, the larger is the absolute value of H9252. Consequently, increasing the die gap will increase the possibility of wrinkling occurring at the draw wall of the tapered square cup. 3.2 Effect of the Blank-Holder Force It is well known that increasing the blank-holder force can help to eliminate wrinkling in the stamping process. In order to study the effectiveness of increased blank-holder force, the stamping of a tapered square cup with die gap of 50 mm, which is associated with severe wrinkling as stated above, was simulated with different values of blank-holder force. The blank-holder force was increased from 100 kN to 600 kN, which yielded a blank-holder pressure of 0.33 MPa and 1.98 MPa, respectively. The remaining simulation conditions are maintained the same as those specified in the previous section. An intermediate blank-holder force of 300 kN was also used in the simulation. The simulation results show that an increase in the blank- holder force does not help to eliminate the wrinkling that occurs at the draw wall. The H9252 values along the cross-section Fig. 5. H9252-value along the cross-section MN for different die gaps. 256 F.-K. Chen and Y.-C. Liao MN, as marked in Fig. 4, are compared with one another for the stamping processes with blank-holder force of 100 kN and 600 kN. The simulation results indicate that the H9252 values along the cross-section MN are almost identical in both cases. In order to examine the difference of the wrinkle shape for the two different blank-holder forces, five cross-sections of the draw wall at different heights from the bottom to the line M N, as marked in Fig. 4, are plotted in Fig. 6 for both cases. It is noted from Fig. 6 that the waviness of the cross-sections for both cases is similar. This indicates that the blank-holder force does not affect the occurrence of wrinkling in the stamp- ing of a tapered square cup, because the formation of wrinkles is mainly due to the large unsupported area at the draw wall where large compressive transverse stresses exist. The blank- holder force has no influence on the instability mode of the material between the punch head and the die cavity shoulder. 4. Stepped Rectangular Cup In the stamping of a stepped rectangular cup, wrinkling occurs at the draw wall even though the die gaps are not so significant. Figure 1(b) shows a sketch of a punch shape used for stamping a stepped rectangular cup in which the draw wall C is followed by a step DE. An actual production part that has this type of geometry was examined in the present study. The material used for this production part was 0.7 mm thick, and the stress strain relation obtained from tensile tests is shown in Fig. 3. The procedure in the press shop for the production of this stamping part consists of deep drawing followed by trimming. In the deep drawing process, no draw bead is employed on the die surface to facilitate the metal flow. However, owing to the small punch corner radius and complex geometry, a split occurred at the top edge of the punch and wrinkles were found to occur at the draw wall of the actual production part, as shown in Fig. 7. It is seen from Fig. 7 that wrinkles are distributed on the draw wall, but are more severe at the corner edges of the step, as marked by AD and BE in Fig. 1(b). The metal is torn apart along the whole top edge of the punch, as shown in Fig. 7, to form a split. In order to provide a further understanding of the defor- mation of the sheet-blank during the stamping process, a finite- element analysis was conducted. The finite-element simulation was first performed for the original design. The simulated shape of the part is shown from Fig. 8. It is noted from Fig. 8 that the mesh at the top edge of the part is stretched Fig. 6. Cross-section lines at different heights of the draw wall for different blank-holder forces. (a) 100 kN. (b) 600 kN. Fig. 7. Split and wrinkles in the production part. Fig. 8. Simulated shape for the production part with split and wrinkles. significantly, and that wrinkles are distributed at the draw wall, similar to those observed in the actual part. The small punch radius, such as the radius along the edge AB, and the radius of the punch corner A, as marked in Fig. 1(b), are considered to be the major reasons for the wall breakage. However, according to the results of the finite- element analysis, splitting can be avoided by increasing the above-mentioned radii. This concept was validated by the actual production part manufactured with larger corner radii. Several attempts were also made to eliminate the wrinkling. First, the blank-holder force was increased to twice the original value. However, just as for the results obtained in the previous section for the drawing of tapered square cup, the effect of blank-holder force on the elimination of wrinkling was not found to be significant. The same results are also obtained by increasing the friction or increasing the blank size. We conclude that this kind of wrinkling cannot be suppressed by increasing the stretching force. Since wrinkles are formed because of excessive metal flow in certain regions, where the sheet is subjected to large com- pressive stresses, a straightforward method of eliminating the wrinkles is to add drawbars in the wrinkled area to absorb the redundant material. The drawbars should be added parallel to the direction of the wrinkles so that the redundant metal can be absorbed effectively. Based on this concept, two drawbars are added to the adjacent walls, as shown in Fig. 9, to absorb the excessive material. The simulation results show that the Draw-Wall Wrinkling in a Stamping Die Design 257 Fig. 9. Drawbars added to the draw walls. wrinkles at the corner of the step are absorbed by the drawbars as expected, however some wrinkles still appear at the remain- ing wall. This indicates the need to put more drawbars at the draw wall to absorb all the excess material. This is, however, not permissible from considerations of the part design. One of the advantages of using finite-element analysis for the stamping process is that the deformed shape of the sheet blank can be monitored throughout the stamping process, which is not possible in the actual production process. A close look at the metal flow during the stamping process reveals that the sheet blank is first drawn into the die cavity by the punch head and the wrinkles are not formed until the sheet blank touches the step edge DE marked in Fig. 1(b). The wrinkled shape is shown in Fig. 10. This provides valuable information for a possible modification of die design. An initial surmise for the cause of the occurrence of wrink- ling is the uneven stretch of the sheet metal between the punch corner radius A and the step corner radius D, as indicated in Fig. 1(b). Therefore a modification of die design was carried out in which the step corner was cut off, as shown in Fig. 11, so that the stretch condition is changed favourably, which allows more stretch to be applied by increasing the step edges. However, wrinkles were still found at the draw wall of the cup. This result implies that wrinkles are introduced because of the uneven stretch between the whole punch head edge and the whole step edge, not merely between the punch corner and Fig. 10. Wrinkle formed when the sheet blank touches the stepped edge. Fig. 11. Cut-off of the stepped corner. the step corner. In order to verify this idea, two modifications of the die design were suggested: one is to cut the whole step off, and the other is to add one more drawing operation, that is, to draw the desired shape using two drawing operations. The simulated shape for the former method is shown in Fig. 12. Since the lower step is cut off, the drawing process is quite similar to that of a rectangular cup drawing, as shown in Fig. 12. It is seen in Fig. 12 that the wrinkles were eliminated. In the two-operation drawing process, the sheet blank was first drawn to the deeper step, as shown in Fig. 13(a). Sub- sequently, the lower step was formed in the second drawing operation, and the desired shape was then obtained, as shown in Fig. 13(b). It is seen clearly in Fig. 13(b) that the stepped rectangular cup can be manufactured without wrinkling, by a two-operation drawing process. It should also be noted that in the two-operation drawing process, if an opposite sequence is applied, that is, the lower step is formed first and is followed by the drawing of the deeper step, the edge of the deeper step, as shown by AB in Fig. 1(b), is prone to tearing because the metal cannot easily flow over the lower step into the die cavity. The finite-element simulations have indicated that the die design for stamping the desired stepped rectangular cup using one single draw operation is barely achieved. However, the manufacturing cost is expected to be much higher for the two- operation drawing process owing to the additional die cost and operation cost. In order to maintain a lower manufacturing cost, the part design engineer made suitable shape changes, and modified the die design according to the finite-element Fig. 12.