小孔E形硅鋼片沖壓工藝及級進模設計-沖壓模具【含12張CAD圖紙+PDF圖】

喜歡就充值下載吧。資源目錄里展示的全都有，下載后全都有,請放心下載，原稿可自行編輯修改【QQ：1304139763 或 414951605 可咨詢交流】= 喜歡就充值下載吧。資源目錄里展示的全都有，下載后全都有,請放心下載，原稿可自行編輯修改【QQ：1304139763 或 414951605 可咨詢交流】= 目 錄2.1 設計課題要達到的設計目的22.2 調研結論22.2.1 硅鋼材料性能22.2.2 沖壓模具發展趨勢22.3 方案設計32.3.1 工藝性分析42.3.2 選擇模具的結構形式42.3.3 排樣設計與計算42.3.4 設計方案擬定62.4 設計方案論證62.4.1技術方面62.4.2設計制造方面62.4.3現有的知識儲備方面72.4.4經濟性方面82.4.5結論8參考文獻92.1 設計課題要達到的設計目的本次畢業設計題目：E字硅鋼片沖壓模具設計目的及意義：通過E字硅鋼片沖壓模具設計的沖壓模具設計，能熟練使用PROE、CAD等繪圖軟件，并且可以進行模具各個部件的設計及強度校核，同時掌握基本的沖壓模具設計的知識，了解模具設計的整個過程，在結構設計、工藝分析、模具數字化設計等方面得到綜合訓練。硅鋼片的應用廣泛、結構較簡單且典型。并且隨著沖壓制品在機械、電子、交通、建筑、國防、農業等各行業廣泛應用，對沖壓模具的需求日益增加，沖壓模具在經濟中的重要性日益突出，因此，研究沖壓模具對了解沖壓產品的生產過程和提高產品質量有很大意義。2.2 調研結論硅鋼片材料本身性能優異，適合沖片。此外，由于硅鋼片應用廣泛，市場需求量巨大。2.2.1 硅鋼片材料性能硅鋼片，英文名稱是siliconsteelsheets，它是一種含碳極低的硅鐵軟磁合金,一般含硅量為0.54.5。加入硅可提高鐵的電阻率和最大磁導率,降低矯頑力、鐵芯損耗（鐵損）和磁時效。硅鋼片主要用來制作各種變壓器、電動機和發電機的鐵芯。世界硅鋼片產量約占鋼材總量的1%。對硅鋼性能的要求主要是：鐵損低，這是硅鋼片質量的最重要指標。各國都根據鐵損值劃分牌號，鐵損愈低，牌號愈高。較強磁場下磁感應強度（磁感）高，這使電機和變壓器的鐵芯體積與重量減小，節約硅鋼片、銅線和絕緣材料等。表面光滑、平整和厚度均勻，可以提高鐵芯的填充系數。沖片性好，對制造微型、小型電動機更為重要。表面絕緣膜的附著性和焊接性良好，能防蝕和改善沖片性?；緹o磁時效。2.2.2 沖壓模具發展趨勢以汽車覆蓋件為代表的大型、復雜、精密沖壓模具, 采用CAD/CAM/CAE軟件進行三維設計和模擬, 減少試模時間和縮短周期。借助高速、精密的加工設備加工生產, 獲得良好的尺寸精度和表面粗糙度, 用新型的研磨或拋光方法代替傳統的手工研磨拋光, 提高模具質量。沖壓模具發展的趨勢總結為以下六點：（1）全面推廣CAD/CAM/ CAE 技術；（2）模具檢測設備向精密、高效和多功能方向發展；（3）模具加工設備向高速、一體化方向發展；（4）一體化加工中心是目前正在發展的新技術；（5）模具材料及表面處理技術發展迅速；（6）模具工業新工藝、新理念和新模式逐步得到認同。2.3 方案設計課程設計題目是E字硅鋼片沖壓模具設計，硅鋼片的結構形狀及尺寸大小如圖1所示。圖1 硅鋼片二維結構圖2.3.1 工藝性分析該材料是低碳硅合金材料，用途是電器鐵芯放電片材料。該制件形狀簡單其工序內容只有落料和沖孔，尺寸較小厚度適中，屬于普通沖壓件，但是有幾點應該注意：1.由于尺寸較小，制件上要沖的小孔相對而言要多一些，因此孔的位置要準確，應該選擇正確的定位方法。2.制件較小，從安全考慮要采取適當的取件方式。3.有一定的批量，應重視模具材料和模具結構的選擇，保證一定的模具壽命。2.3.2 選擇模具的結構形式因為這個制件的材料較薄，尺寸比較小，為保證制件平整，這副模具用自動送料裝置，毛坯為卷料。因此模具上不用設初定位用的始用擋料銷與粗定位作用的擋料銷，由自動送料機構保證而精定位是用導正銷保證送料步距的。為方便操作和取件選用雙柱可傾壓力機，橫向送料。2.3.3 排樣設計與計算排樣是重要的步驟，它決定材料的利用率。硅鋼片呈山形，有如下排樣形式，如圖2所示。 第一種 第二種 第三種 第四種 圖2 排樣形式第一種方案卷料寬度適中，不至于太窄，且可使模具的寬度不至于較長。第二種方案和第三種方案，會使模具結構復雜，且使步距增大，從而降低生產率。三種材料的利用率相當，但重要的是后兩種方案的板料軋向不符合零件圖的要求。而第四種方案，會使模具的結構復雜，無形中又增加一個方向相反的沖模結構。所以，優先考慮零件加工質量，選用第一種方案。（1）搭邊值的確定1：通過查表可知工件間的距離mm，側面mm；（2）送料步距與條料寬度：送料步距式中為平行于送料方向的沖裁件寬度，mm；（3）沖裁件之間的搭邊值取26（4）條料寬度式中沖裁件與送料方向垂直的最大尺寸，mm；沖裁件與條料側邊之間的搭邊，mm；板料剪裁的下偏差，mm；取58（5）材料利用率的計算：材料利用率 硅鋼片排樣圖如圖3所示。 圖3 硅鋼片排樣圖2.3.4 設計方案擬定根據制件工藝性分析，其基本工序只有落料和沖孔兩種，由于制件尺寸較小且孔的數量較多，因此為了使沖孔的位置準確,應沖兩個工藝孔。按照先后順序組合可以有如下幾種方案：A.落料-沖兩個工藝孔及五個小孔-沖四個缺口；B.沖五個小孔-沖四個缺口及兩個工藝孔-落料；C.沖四個缺口及兩個工藝孔-沖五個小孔-落料。2.4 設計方案論證2.4.1技術方面A方案為先落料再沖兩個工藝孔和五個較小的孔，最后再沖四個方形缺口。如果先沖孔勢必影響大大沖件精度，而且先沖大孔再沖小孔，定位是很困難的。這樣增加了模具的設計難度，提高了成本，且有安全隱患，操作不便。B方案先沖五個小孔，再沖四個方形缺口和兩個工藝孔，最后落料。五個小孔精度要求較高，先進行沖壓不易保證精度。如果最后沖兩個工藝孔的話，起不到保證小孔位置準確的作用，故而沒有意義。C方案先沖四個方形缺口和兩個較大工藝孔，再沖五個小孔，最后落料。此方案能夠保證制件精度，將外形上容易磨損的四個缺口與整個形分開來，先行沖出，有利于提高模具壽命。2.4.2設計制造方面A方案：工序繁瑣，定位困難，涉及結構較多，設計制造難度大，成本高。B方案：兩個工藝孔沒有發揮其作用，提高了成本。C方案：工序合理，操作簡便，制件精度高，且模具壽命長。C方案示意圖如圖4所示。 圖4 C方案模具示意圖2.4.3現有的知識儲備方面模具CAD/CAM系統是計算機輔助某一種類型的模具設計、計算、分析、繪圖和數控加工自動編程等的有機集成。這種一體化技術是在模具CAD和CAM分別發展的基礎上出現的，是計算機技術綜合應用的一個飛躍。這種一體化技術能夠構建模具型芯和型腔的三維實體，并能夠生成刀具軌跡和數控加工代碼，進行計算機仿真等。1、現階段的設計能力能根據產品的特性和產品的市場需求量，沖裁力等標準選取合適的壓力機，確定沖裁方案，確定模具結構以及凸凹模的基本類型 。2、設計步驟第一步：確定沖裁件的工藝方法；第二部：選擇模具的結構形式；第二步：進行必要的工藝計算；第四步：選擇與確定模具的重要零部件的結構尺寸； 第五步：導向與定位系統的設計。 3、設計手段在設定參數、整理完說明書后，利用CAD軟件進行裝配設計、用PRO/E進行建模及裝配仿真。 2.4.4經濟性方面 硅鋼片（亦稱電工鋼）是電力、電子和軍事工業不可缺少的重要軟磁合金，亦是產量最大的金屬功能材料，主要用作各種電機、發電機和變壓器的鐵心。全世界的總產量約700萬噸。近年來，特別這幾年隨著中國電力、電器工業的迅猛發展，中國的硅鋼片需求量快速增加，2004年的消費量幾乎已占全世界硅鋼片產量的一半，導致中國的硅鋼產量進入了一個快速發展時期，但仍然無法滿足國內需求，2004年進口硅鋼片164萬噸，可見其具有良好的經濟性。2.4.5結論在進行可行性分析過程中，對硅鋼片沖壓模具設計的經濟可行性和制造可行性有所了解，并且硅鋼片價格較低，應用廣泛，可見市場需求量大。綜合考慮，選擇C方案較好，既可以保證成型塑件的質量要求，其模具制造成本合理，加工容易，其經濟效益比其他方案要好，綜上所述，采用C方案。參考文獻1馬朝興.沖壓模具設計手冊M.北京:化學工業出版社,2009.2王燕.沖壓模具精加工分析J.科技資訊,2012,(18):119119.3王都.堅持與時俱進抓好技術創新J.模具工業,2002(8):2324.4馬思臣.現代模具工業發展述評J.機械工程師,2006(3):2324.5周永泰.我國沖壓模具的現狀與發展(下)J.鍛造與沖壓,2005(4):1820.6翟崇琳.沖壓模具零件的制造工藝J.新技術新工藝,2011,(10):2324.7馮炳堯,韓泰榮,蔣文森.模具設計與制造簡明手冊M.上海:上?？茖W技術出版社,2008.8牟林,魏崢.冷沖壓工藝及模具設計M.北京:清華大學出版社,2009.9許炳鑫.模具材料與熱處理M.北京:機械工業出版社.2007.10陳勇.模具材料及表面處理M.北京:機械工業出版社.2007.11勞動和社會保障部教材辦公室.模具安裝調試及維修M.北京:中國勞動社會保障出版社.2006.12翁其金.沖壓工藝與沖模設計M.北京:機械工業出版社.2004.13唐博雅，王權聰，常志良多孔定位片沖壓工藝分析及其模具設J.黑龍江大學工程學報,2014,5(1):74779Int J Adv Manuf Technol(2002)19:253259 2002 Springer-Verlag London LimitedAn Analysis of Draw-Wall Wrinkling in a Stamping Die DesignF.-K.Chen and Y.-C.LiaoDepartment of Mechanical Engineering,National Taiwan University,Taipei,TaiwanWrinkling that occurs in the stamping of tapered square cupsand stepped rectangular cups is investigated.A commoncharacteristic of these two types of wrinkling is that thewrinkles are found at the draw wall that is relatively unsup-ported.In the stamping of a tapered square cup,the effect ofprocess parameters,such as the die gap and blank-holderforce,on the occurrence of wrinkling is examined using finite-element simulations.The simulation results show that the largerthe die gap,the more severe is the wrinkling,and suchwrinkling cannot be suppressed by increasing the blank-holderforce.In the analysis of wrinkling that occurred in the stampingof a stepped rectangular cup,an actual production part thathas a similar type of geometry was examined.The wrinklesfound at the draw wall are attributed to the unbalancedstretching of the sheet metal between the punch head and thestep edge.An optimum die design for the purpose of eliminatingthe wrinkles is determined using finite-element analysis.Thegood agreement between the simulation results and thoseobserved in the wrinkle-free production part validates theaccuracy of the finite-element analysis,and demonstrates theadvantage of using finite-element analysis for stamping diedesign.Keywords:Draw-wall wrinkle;Stamping die;Stepped rec-tangular cup;Tapered square cups1.IntroductionWrinkling is one of the major defects that occur in the sheetmetal forming process.For both functional and visual reasons,wrinkles are usually not acceptable in a finished part.Thereare three types of wrinkle which frequently occur in the sheetmetal forming process:flange wrinkling,wall wrinkling,andelastic buckling of the undeformed area owing to residualelastic compressive stresses.In the forming operation of stamp-ing a complex shape,draw-wall wrinkling means the occurrenceCorrespondence and offprint requests to:Professor F.-K.Chen,Depart-ment of Mechanical Engineering,National Taiwan University,No.1Roosevelt Road,Sec.4,Taipei,Taiwan 10617.E-mail:fkchen?w3.me.ntu.edu.twof wrinkles in the die cavity.Since the sheet metal in the wallarea is relatively unsupported by the tool,the elimination ofwall wrinkles is more difficult than the suppression of flangewrinkles.It is well known that additional stretching of thematerial 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 stressesleads to failure by tearing.Hence,the blank-holder force mustlie within a narrow range,above that necessary to suppresswrinkles on the one hand,and below that which producesfracture on the other.This narrow range of blank-holder forceis difficult to determine.For wrinkles occurring in the centralarea of a stamped part with a complex shape,a workablerange of blank-holder force does not even exist.In order to examine the mechanics of the formation ofwrinkles,Yoshida et al.1 developed a test in which a thinplate was non-uniformly stretched along one of its diagonals.They also proposed an approximate theoretical model in whichthe onset of wrinkling is due to elastic buckling resulting fromthe compressive lateral stresses developed in the non-uniformstress field.Yu et al.2,3 investigated the wrinkling problemboth experimentally and analytically.They found that wrinklingcould occur having two circumferential waves according totheir theoretical analysis,whereas the experimental results indi-cated four to six wrinkles.Narayanasamy and Sowerby 4examined the wrinkling of sheet metal when drawing it througha conical die using flat-bottomed and hemispherical-endedpunches.They also attempted to rank the properties thatappeared to suppress wrinkling.These efforts are focused on the wrinkling problems associa-ted with the forming operations of simple shapes only,suchas a circular cup.In the early 1990s,the successful applicationof the 3D dynamic/explicit finite-element method to the sheet-metal forming process made it possible to analyse the wrinklingproblem involved in stamping complex shapes.In the presentstudy,the 3D finite-element method was employed to analysethe effects of the process parameters on the metal flow causingwrinkles at the draw wall in the stamping of a tapered squarecup,and of a stepped rectangular part.A tapered square cup,as shown in Fig.1(a),has an inclineddraw wall on each side of the cup,similar to that existing ina conical cup.During the stamping process,the sheet metalon the draw wall is relatively unsupported,and is therefore254F.-K.Chen and Y.-C.LiaoFig.1.Sketches of(a)a tapered square cup and(b)a steppedrectangular cup.prone to wrinkling.In the present study,the effect of variousprocess parameters on the wrinkling was investigated.In thecase of a stepped rectangular part,as shown in Fig.1(b),another type of wrinkling is observed.In order to estimate theeffectiveness of the analysis,an actual production part withstepped geometry was examined in the present study.Thecause of the wrinkling was determined using finite-elementanalysis,and an optimum die design was proposed to eliminatethe wrinkles.The die design obtained from finite-element analy-sis was validated by observations on an actual production part.2.Finite-Element ModelThe tooling geometry,including the punch,die and blank-holder,weredesignedusingtheCADprogramPRO/ENGINEER.Both the 3-node and 4-node shell elements wereadopted to generate the mesh systems for the above toolingusing 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 andFig.2.Finite-element mesh.are not for stress analysis.The same CAD program using 4-node shell elements was employed to construct the meshsystem for the sheet blank.Figure 2 shows the mesh systemfor the complete set of tooling and the sheet-blank used in thestamping of a tapered square cup.Owing to the symmetricconditions,only a quarter of the square cup is analysed.Inthe simulation,the sheet blank is put on the blank-holder andthe die is moved down to clamp the sheet blank against theblank-holder.The punch is then moved up to draw the sheetmetal into the die cavity.In order to perform an accurate finite-element analysis,theactual stressstrain relationship of the sheet metal is requiredas part of the input data.In the present study,sheet metalwith deep-drawing quality is used in the simulations.A tensiletest has been conducted for the specimens cut along planescoinciding with the rolling direction(0)and at angles of 45and 90 to the rolling direction.The average flow stress?,calculated from the equation?(?0?2?45?90)/4,for eachmeasured true strain,as shown in Fig.3,is used for thesimulations for the stampings of the tapered square cup andalso for the stepped rectangular cup.All the simulations performed in the present study were runon an SGI Indigo 2 workstation using the finite-element pro-gram PAMFSTAMP.To complete the set of input data requiredFig.3.The stressstrain relationship for the sheet metal.Draw-Wall Wrinkling in a Stamping Die Design255for the simulations,the punch speed is set to 10 m s?1and acoefficient of Coulomb friction equal to 0.1 is assumed.3.Wrinkling in a Tapered Square CupA sketch indicating some relevant dimensions of the taperedsquare cup is shown in Fig.1(a).As seen in Fig.1(a),thelength of each side of the square punch head(2Wp),the diecavity opening(2Wd),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 cavityopening and the punch head is termed the die gap(G)in thepresent study,i.e.G?Wd?Wp.The extent of the relativelyunsupported sheet metal at the draw wall is presumably dueto the die gap,and the wrinkles are supposed to be suppressedby increasing the blank-holder force.The effects of both thedie gap and the blank-holder force in relation to the occurrenceof wrinkling in the stamping of a tapered square cup areinvestigated in the following sections.3.1Effect of Die GapIn order to examine the effect of die gap on the wrinkling,the stamping of a tapered square cup with three different diegaps of 20 mm,30 mm,and 50 mm was simulated.In eachsimulation,the die cavity opening is fixed at 200 mm,and thecup is drawn to the same height of 100 mm.The sheet metalused in all three simulations is a 380 mm?380 mm squaresheet with thickness of 0.7 mm,the stressstrain curve for thematerial is shown in Fig.3.The simulation results show that wrinkling occurred in allthree tapered square cups,and the simulated shape of thedrawn cup for a die gap of 50 mm is shown in Fig.4.It isseen in Fig.4 that the wrinkling is distributed on the drawwall and is particularly obvious at the corner between adjacentwalls.It is suggested that the wrinkling is due to the largeunsupported area at the draw wall during the stamping process,also,the side length of the punch head and the die cavityFig.4.Wrinkling in a tapered square cup(G?50 mm).opening are different owing to the die gap.The sheet metalstretched between the punch head and the die cavity shoulderbecomes unstable owing to the presence of compressive trans-verse stresses.The unconstrained stretching of the sheet metalunder compression seems to be the main cause for the wrink-ling at the draw wall.In order to compare the results for thethree different die gaps,the ratio?of the two principal strainsis introduced,?being?min/?max,where?maxand?minare themajor and the minor principal strains,respectively.Hosfordand Caddell 5 have shown that if the absolute value of?isgreater than a critical value,wrinkling is supposed to occur,and the larger the absolute value of?,the greater is thepossibility of wrinkling.The?values along the cross-section MN at the samedrawing height for the three simulated shapes with differentdie gaps,as marked in Fig.4,are plotted in Fig.5.It is notedfrom Fig.5 that severe wrinkles are located close to the cornerand fewer wrinkles occur in the middle of the draw wall forall three different die gaps.It is also noted that the bigger thedie gap,the larger is the absolute value of?.Consequently,increasing the die gap will increase the possibility of wrinklingoccurring at the draw wall of the tapered square cup.3.2Effect of the Blank-Holder ForceIt is well known that increasing the blank-holder force canhelp to eliminate wrinkling in the stamping process.In orderto study the effectiveness of increased blank-holder force,thestamping of a tapered square cup with die gap of 50 mm,which is associated with severe wrinkling as stated above,wassimulated with different values of blank-holder force.Theblank-holder force was increased from 100 kN to 600 kN,which yielded a blank-holder pressure of 0.33 MPa and 1.98MPa,respectively.The remaining simulation conditions aremaintained the same as those specified in the previous section.An intermediate blank-holder force of 300 kN was also usedin the simulation.The simulation results show that an increase in the blank-holder force does not help to eliminate the wrinkling thatoccurs at the draw wall.The?values along the cross-sectionFig.5.?-value along the cross-section MN for different die gaps.256F.-K.Chen and Y.-C.LiaoMN,as marked in Fig.4,are compared with one another forthe stamping processes with blank-holder force of 100 kN and600 kN.The simulation results indicate that the?values alongthe cross-section MN are almost identical in both cases.Inorder to examine the difference of the wrinkle shape for thetwo different blank-holder forces,five cross-sections of thedraw wall at different heights from the bottom to the line MN,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-sectionsfor both cases is similar.This indicates that the blank-holderforce does not affect the occurrence of wrinkling in the stamp-ing of a tapered square cup,because the formation of wrinklesis mainly due to the large unsupported area at the draw wallwhere large compressive transverse stresses exist.The blank-holder force has no influence on the instability mode of thematerial between the punch head and the die cavity shoulder.4.Stepped Rectangular CupIn the stamping of a stepped rectangular cup,wrinkling occursat the draw wall even though the die gaps are not so significant.Figure 1(b)shows a sketch of a punch shape used for stampinga stepped rectangular cup in which the draw wall C is followedby a step DE.An actual production part that has this typeof geometry was examined in the present study.The materialused for this production part was 0.7 mm thick,and the stressstrain relation obtained from tensile tests is shown in Fig.3.The procedure in the press shop for the production of thisstamping part consists of deep drawing followed by trimming.In the deep drawing process,no draw bead is employed onthe die surface to facilitate the metal flow.However,owingto the small punch corner radius and complex geometry,asplit occurred at the top edge of the punch and wrinkles werefound to occur at the draw wall of the actual production part,as shown in Fig.7.It is seen from Fig.7 that wrinkles aredistributed on the draw wall,but are more severe at the corneredges 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 simulationwas first performed for the original design.The simulatedshape 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 stretchedFig.6.Cross-section lines at different heights of the draw wall fordifferent 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 edgeAB,and the radius of the punch corner A,as marked in Fig.1(b),are considered to be the major reasons for the wallbreakage.However,according to the results of the finite-element analysis,splitting can be avoided by increasing theabove-mentioned radii.This concept was validated by theactual 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 originalvalue.However,just as for the results obtained in the previoussection for the drawing of tapered square cup,the effect ofblank-holder force on the elimination of wrinkling was notfound to be significant.The same results are also obtained byincreasing the friction or increasing the blank size.We concludethat this kind of wrinkling cannot be suppressed by increasingthe stretching force.Since wrinkles are formed because of excessive metal flowin certain regions,where the sheet is subjected to large com-pressive stresses,a straightforward method of eliminating thewrinkles is to add drawbars in the wrinkled area to absorb theredundant material.The drawbars should be added parallel tothe direction of the wrinkles so that the redundant metal canbe absorbed effectively.Based on this concept,two drawbarsare added to the adjacent walls,as shown in Fig.9,to absorbthe excessive material.The simulation results show that theDraw-Wall Wrinkling in a Stamping Die Design257Fig.9.Drawbars added to the draw walls.wrinkles at the corner of the step are absorbed by the drawbarsas expected,however some wrinkles still appear at the remain-ing wall.This indicates the need to put more drawbars at thedraw 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 forthe stamping process is that the deformed shape of the sheetblank can be monitored throughout the stamping process,whichis not possible in the actual production process.A close lookat the metal flow during the stamping process reveals that thesheet blank is first drawn into the die cavity by the punchhead and the wrinkles are not formed until the sheet blanktouches the step edge DE marked in Fig.1(b).The wrinkledshape is shown in Fig.10.This provides valuable informationfor 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 punchcorner radius A and the step corner radius D,as indicated inFig.1(b).Therefore a modification of die design was carriedout in which the step corner was cut off,as shown in Fig.11,so that the stretch condition is changed favourably,whichallows more stretch to be applied by increasing the step edges.However,wrinkles were still found at the draw wall of thecup.This result implies that wrinkles are introduced becauseof the uneven stretch between the whole punch head edge andthe whole step edge,not merely between the punch corner andFig.10.Wrinkle formed when the sheet blank touches the steppededge.Fig.11.Cut-off of the stepped corner.the step corner.In order to verify this idea,two modificationsof the die design were suggested:one is to cut the whole stepoff,and the other is to add one more drawing operation,thatis,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 isquite similar to that of a rectangular cup drawing,as shown inFig.12.It is seen in Fig.12 that the wrinkles were eliminated.In the two-operation drawing process,the sheet blank wasfirst drawn to the deeper step,as shown in Fig.13(a).Sub-sequently,the lower step was formed in the second drawingoperation,and the desired shape was then obtained,as shownin Fig.13(b).It is seen clearly in Fig.13(b)that the steppedrectangular cup can be manufactured without wrinkling,by atwo-operation drawing process.It should also be noted that inthe two-operation drawing process,if an opposite sequence isapplied,that is,the lower step is formed first and is followedby 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 themetal cannot easily flow over the lower step into the die cavity.The finite-element simulations have indicated that the diedesign for stamping the desired stepped rectangular cup usingone single draw operation is barely achieved.However,themanufacturing cost is expected to be much higher for the two-operation drawing process owing to the additional die cost andoperation cost.In order to maintain a lower manufacturingcost,the part design engineer made suitable shape changes,and modified the die design according to the finite-elementFig.12.Simulated shape for the modified die design.258F.-K.Chen and Y.-C.LiaoFig.13.(a)First operation and(b)second operation in the two-operation drawing process.simulation result to cut off the lower step,as shown in Fig.12.With the modified die design,the actual stamping die forproduction was manufactured and the production part wasfound to be free from wrinkles,as shown in Fig.14.The partshape also agreed well with that obtained from the finite-element simulation.In order to further validate the finite-element simulationresults,the thickness distribution along the cross-section GHobtained from the simulation result as indicated in Fig.14,Fig.14.The defect-free production part.was compared with those measured from the production part.The comparison is shown in Fig.15.It can be seen in Fig.15 that the predicted thickness distribution by fin