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沖壓模具畢業(yè)設(shè)計(jì)
1.緒論
1.1沖壓的概念、特點(diǎn)及應(yīng)用
沖壓是利用安裝在沖壓設(shè)備(主要是壓力機(jī))上的模具對材料施加壓力,使其產(chǎn)生分離或塑性變形,從而獲得所需零件(俗稱沖壓或沖壓件)的一種壓力加工方法。沖壓通常是在常溫下對材料進(jìn)行冷變形加工,且主要采用板料來加工成所需零件,所以也叫冷沖壓或板料沖壓。沖壓是材料壓力加工或塑性加工的主要方法之一,隸屬于材料成型工程術(shù)。
沖壓所使用的模具稱為沖壓模具,簡稱沖模。沖模是將材料(金屬或非金屬)批量加工成所需沖件的專用工具。沖模在沖壓中至關(guān)重要,沒有符合要求的沖模,批量沖壓生產(chǎn)就難以進(jìn)行;沒有先進(jìn)的沖模,先進(jìn)的沖壓工藝就無法實(shí)現(xiàn)。沖壓工藝與模具、沖壓設(shè)備和沖壓材料構(gòu)成沖壓加工的三要素,只有它們相互結(jié)合才能得出沖壓件。
與機(jī)械加工及塑性加工的其它方法相比,沖壓加工無論在技術(shù)方面還是經(jīng)濟(jì)方面都具有許多獨(dú)特的優(yōu)點(diǎn)。主要表現(xiàn)如下。
(1) 沖壓加工的生產(chǎn)效率高,且操作方便,易于實(shí)現(xiàn)機(jī)械化與自動(dòng)化。這是因?yàn)闆_壓是依靠沖模和沖壓設(shè)備來完成加工,普通壓力機(jī)的行程次數(shù)為每分鐘可達(dá)幾十次,高速壓力要每分鐘可達(dá)數(shù)百次甚至千次以上,而且每次沖壓行程就可能得到一個(gè)沖件。
(2)沖壓時(shí)由于模具保證了沖壓件的尺寸與形狀精度,且一般不破壞沖壓件的表面質(zhì)量,而模具的壽命一般較長,所以沖壓的質(zhì)量穩(wěn)定,互換性好,具有“一模一樣”的特征。
(3)沖壓可加工出尺寸范圍較大、形狀較復(fù)雜的零件,如小到鐘表的秒表,大到汽車縱梁、覆蓋件等,加上沖壓時(shí)材料的冷變形硬化效應(yīng),沖壓的強(qiáng)度和剛度均較高。
(4)沖壓一般沒有切屑碎料生成,材料的消耗較少,且不需其它加熱設(shè)備,因而是一種省料,節(jié)能的加工方法,沖壓件的成本較低。
但是,沖壓加工所使用的模具一般具有專用性,有時(shí)一個(gè)復(fù)雜零件需要數(shù)套模具才能加工成形,且模具 制造的精度高,技術(shù)要求高,是技術(shù)密集形產(chǎn)品。所以,只有在沖壓件生產(chǎn)批量較大的情況下,沖壓加工的優(yōu)點(diǎn)才能充分體現(xiàn),從而獲得較好的經(jīng)濟(jì)效益。
沖壓地、在現(xiàn)代工業(yè)生產(chǎn)中,尤其是大批量生產(chǎn)中應(yīng)用十分廣泛。相當(dāng)多的工業(yè)部門越來越多地采用沖壓法加工產(chǎn)品零部件,如汽車、農(nóng)機(jī)、儀器、儀表、電子、航空、航天、家電及輕工等行業(yè)。在這些工業(yè)部門中,沖壓件所占的比重都相當(dāng)?shù)拇?,少則60%以上,多則90%以上。不少過去用鍛造=鑄造和切削加工方法制造的零件,現(xiàn)在大多數(shù)也被質(zhì)量輕、剛度好的沖壓件所代替。因此可以說,如果生產(chǎn)中不諒采用沖壓工藝,許多工業(yè)部門要提高生產(chǎn)效率和產(chǎn)品質(zhì)量、降低生產(chǎn)成本、快速進(jìn)行產(chǎn)品更新?lián)Q代等都是難以實(shí)現(xiàn) 的。
1.2 沖壓的基本工序及模具
由于沖壓加工的零件種類繁多,各類零件的形狀、尺寸和精度要求又各不相同,因而生產(chǎn)中采用的沖壓工藝方法也是多種多樣的。概括起來,可分為分離工序和成形工序兩大類;分離工序是指使坯料沿一定的輪廓線分離而獲得一定形狀、尺寸和斷面質(zhì)量的沖壓(俗稱沖裁件)的工序;成形工序是指使坯料在不破裂的條件下產(chǎn)生塑性變形而獲得一定形狀和尺寸的沖壓件的工序。
上述兩類工序,按基本變形方式不同又可分為沖裁、彎曲、拉深和成形四種基本工序,每種基本工序還包含有多種單一工序。
在實(shí)際生產(chǎn)中,當(dāng)沖壓件的生產(chǎn)批量較大、尺寸較少而公差要求較小時(shí),若用分散的單一工序來沖壓是不經(jīng)濟(jì)甚至難于達(dá)到要求。這時(shí)在工藝上多采用集中的方案,即把兩種或兩種以上的單一工序集中在一副模具內(nèi)完成,稱為組合的方法不同,又可將其分為復(fù)合-級進(jìn)和復(fù)合-級進(jìn)三種組合方式。
復(fù)合沖壓——在壓力機(jī)的一次工作行程中,在模具的同一工位上同時(shí)完成兩種或兩種以上不同單一工序的一種組合方法式。
級進(jìn)沖壓——在壓力機(jī)上的一次工作行程中,按照一定的順序在同一模具的不同工位上完面兩種或兩種以上不同單一工序的一種組合方式。
復(fù)合-級進(jìn)——在一副沖模上包含復(fù)合和級進(jìn)兩種方式的組合工序。
沖模的結(jié)構(gòu)類型也很多。通常按工序性質(zhì)可分為沖裁模、彎曲模、拉深模和成形模等;按工序的組合方式可分為單工序模、復(fù)合模和級進(jìn)模等。但不論何種類型的沖模,都可看成是由上模和下模兩部分
組成,上模被固定在壓力機(jī)工作臺或墊板上,是沖模的固定部分。工作時(shí),坯料在下模面上通過定位零件定位,壓力機(jī)滑塊帶動(dòng)上模下壓,在模具工作零件(即凸模、凹模)的作用下坯料便產(chǎn)生分離或塑性變形,從而獲得所需形狀與尺寸的沖件。上?;厣龝r(shí),模具的卸料與出件裝置將沖件或廢料從凸、凹模上卸下或推、頂出來,以便進(jìn)行下一次沖壓循環(huán)。
1.3 沖壓技術(shù)的現(xiàn)狀及發(fā)展方向
隨著科學(xué)技術(shù)的不斷進(jìn)步和工業(yè)生產(chǎn)的迅速發(fā)展,許多新技術(shù)、新工藝、新設(shè)備、新材料不斷涌現(xiàn),因而促進(jìn)了沖壓技術(shù)的不斷革新和發(fā)展。其主要表現(xiàn)和發(fā)展方向如下。
(1).沖壓成形理論及沖壓工藝方面
沖壓成形理論的研究是提高沖壓技術(shù)的基礎(chǔ)。目前,國內(nèi)外對沖壓成形理論的研究非常重視,在材料沖壓性能研究、沖壓成形過程應(yīng)力應(yīng)變分析、板料變形規(guī)律研究及坯料與模具之間的相互作用研究等方面均取得了較大的進(jìn)展。特別是隨著計(jì)算機(jī)技術(shù)的飛躍發(fā)展和塑性變形理論的進(jìn)一步完善,近年來國內(nèi)外已開始應(yīng)用塑性成形過程的計(jì)算機(jī)模擬技術(shù),即利用有限元(FEM)等有值分析方法模擬金屬的塑性成形過程,根據(jù)分析結(jié)果,設(shè)計(jì)人員可預(yù)測某一工藝方案成形的可行性及可能出現(xiàn)的質(zhì)量問題,并通過在計(jì)算機(jī)上選擇修改相關(guān)參數(shù),可實(shí)現(xiàn)工藝及模具的優(yōu)化設(shè)計(jì)。這樣既節(jié)省了昂貴的試模費(fèi)用,也縮短了制模具周期。
研究推廣能提高生產(chǎn)率及產(chǎn)品質(zhì)量、降低成本和擴(kuò)大沖壓工藝應(yīng)用范圍的各種壓新工藝,也是沖壓技術(shù)的發(fā)展方向之一。目前,國內(nèi)外相繼涌現(xiàn)出精密沖壓工藝、軟模成形工藝、高能高速成形工藝及無模多點(diǎn)成形工藝等精密、高效、經(jīng)濟(jì)的沖壓新工藝。其中,精密沖裁是提高沖裁件質(zhì)量的有效方法,它擴(kuò)大了沖壓加工范圍,目前精密沖裁加工零件的厚度可達(dá)25mm,精度可達(dá)IT16~17級;用液體、橡膠、聚氨酯等作柔性凸?;虬寄5能浤3尚喂に?,能加工出用普通加工方法難以加工的材料和復(fù)雜形狀的零件,在特定生產(chǎn)條件下具有明顯的經(jīng)濟(jì)效果;采用爆炸等高能效成形方法對于加工各種尺寸在、形狀復(fù)雜、批量小、強(qiáng)度高和精度要求較高的板料零件,具有很重要的實(shí)用意義;利用金屬材料的超塑性進(jìn)行超塑成形,可以用一次成形代替多道普通的沖壓成形工序,這對于加工形狀復(fù)雜和大型板料零件具有突出的優(yōu)越性;無模多點(diǎn)成形工序是用高度可調(diào)的凸模群體代替?zhèn)鹘y(tǒng)模具進(jìn)行板料曲面成形的一種先進(jìn)技術(shù),我國已自主設(shè)計(jì)制造了具有國際領(lǐng)先水平的無模多點(diǎn)成形設(shè)備,解決了多點(diǎn)壓機(jī)成形法,從而可隨意改變變形路徑與受力狀態(tài),提高了材料的成形極限,同時(shí)利用反復(fù)成形技術(shù)可消除材料內(nèi)殘余應(yīng)力,實(shí)現(xiàn)無回彈成形。無模多點(diǎn)成形系統(tǒng)以CAD/CAM/CAE技術(shù)為主要手段,能快速經(jīng)濟(jì)地實(shí)現(xiàn)三維曲面的自動(dòng)化成形。
(2.)沖模是實(shí)現(xiàn)沖壓生產(chǎn)的基本條件.在沖模的設(shè)計(jì)制造上,目前正朝著以下兩方面發(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,與此相比適應(yīng)的新型模具材料及其熱處理技術(shù),各種高效、精密、數(shù)控自動(dòng)化的模具加工機(jī)床和檢測設(shè)備以及模具CAD/CAM技術(shù)也在迅速發(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,鋅基合金沖模、聚氨酯橡膠沖模、薄板沖模、鋼帶沖模、組合沖模等各種簡易沖模及其制造技術(shù)也得到了迅速發(fā)展。
精密、高效的多工位及多功能級進(jìn)模和大型復(fù)雜的汽車覆蓋件沖模代表了現(xiàn)代沖模的技術(shù)水平。目前,50個(gè)工位以上的級進(jìn)模進(jìn)距精度可達(dá)到2微米,多功能級進(jìn)模不僅可以完成沖壓全過程,還可完成焊接、裝配等工序。我國已能自行設(shè)計(jì)制造出達(dá)到國際水平的精度達(dá)2?~5微米,進(jìn)距精度2~3微米,總壽命達(dá)1億次。我國主要汽車模具企業(yè),已能生產(chǎn)成套轎車覆蓋件模具,在設(shè)計(jì)制造方法、手段方面已基本達(dá)到了國際水平,但在制造方法手段方面已基本達(dá)到了國際水平,模具結(jié)構(gòu)、功能方面也接近國際水平,但在制造質(zhì)量、精度、制造周期和成本方面與國外相比還存在一定差距。
模具制造技術(shù)現(xiàn)代化是模具工業(yè)發(fā)展的基礎(chǔ)。計(jì)算機(jī)技術(shù)、信息技術(shù)、自動(dòng)化技術(shù)等先進(jìn)技術(shù)正在不斷向傳統(tǒng)制造技術(shù)滲透、交叉、融合形成了現(xiàn)代模具制造技術(shù)。其中高速銑削加工、電火花銑削加工、慢走絲切割加工、精密磨削及拋光技術(shù)、數(shù)控測量等代表了現(xiàn)代沖模制造的技術(shù)水平。高速銑削加工不但具有加工速度高以及良好的加工精度和表面質(zhì)量(主軸轉(zhuǎn)速一般為15000~40000r/min),加工精度一般可達(dá)10微米,最好的表面粗糙度Ra≤1微米),而且與傳統(tǒng)切削加工相比具有溫升低(工件只升高3攝氏度)、切削力小,因而可加工熱敏材料和剛性差的零件,合理選擇刀具和切削用量還可實(shí)現(xiàn)硬材料(60HRC)加工;電火花銑削加工(又稱電火花創(chuàng)成加工)是以高速旋轉(zhuǎn)的簡單管狀電極作三維或二維輪廓加工(像數(shù)控銑一樣),因此不再需要制造昂貴的成形電極,如日本三菱公司生產(chǎn)的EDSCAN8E電火花銑削加工機(jī)床,配置有電極損耗自動(dòng)補(bǔ)償系統(tǒng)、CAD/CAM集成系統(tǒng)、在線自動(dòng)測量系統(tǒng)和動(dòng)態(tài)仿真系統(tǒng),體現(xiàn)了當(dāng)今電火花加工機(jī)床的技術(shù)水平;慢走絲線切割技術(shù)的發(fā)展水平已相當(dāng)高,功能也相當(dāng)完善,自動(dòng)化程度已達(dá)到無人看管運(yùn)行的程度,目前切割速度已達(dá)到300mm/min,加工精度可達(dá)±1.5微米,表面粗糙度達(dá)Ra=01~0.2微米;精度磨削及拋光已開始使用數(shù)控成形磨床、數(shù)控光學(xué)曲線磨床、數(shù)控連續(xù)軌跡坐標(biāo)磨床及自動(dòng)拋光等先進(jìn)設(shè)備和技術(shù);模具加工過程中的檢測技術(shù)也取得了很大的發(fā)展,現(xiàn)在三坐標(biāo)測量機(jī)除了能高精度地測量復(fù)雜曲面的數(shù)據(jù)外,其良好的溫度補(bǔ)償裝置、可靠的抗振保護(hù)能力、嚴(yán)密的除塵措施及簡單操作步驟,使得現(xiàn)場自動(dòng)化檢測成為可能。此外,激光快速成形技術(shù)(RPM)與樹脂澆注技術(shù)在快速經(jīng)濟(jì)制模技術(shù)中得到了成功的應(yīng)用。利用RPM技術(shù)快速成形三維原型后,通過陶瓷精鑄、電弧涂噴、消失模、熔模等技術(shù)可快速制造各種成形模。如清華大學(xué)開發(fā)研制的“M-RPMS-Ⅱ型多功能快速原型制造系統(tǒng)”是我國自主知識產(chǎn)權(quán)的世界惟一擁有兩種快速成形工藝(分層實(shí)體制造SSM和熔融擠壓成形MEM)的系統(tǒng),它基于“模塊化技術(shù)集成”之概念而設(shè)計(jì)和制造,具有較好的價(jià)格性能比。一汽模具制造公司在以CAD/CAM加工的主模型為基礎(chǔ),采用瑞士汽巴精化的高強(qiáng)度樹脂澆注成形的樹脂沖模應(yīng)用在國產(chǎn)轎車試制和小批量生產(chǎn)開辟了新的途徑。
(3) 沖壓設(shè)備和沖壓生產(chǎn)自動(dòng)化方面
性能良好的沖壓設(shè)備是提高沖壓生產(chǎn)技術(shù)水平的基本條件,高精度、高壽命、高效率的沖模需要高精度、高自動(dòng)化的沖壓設(shè)備相匹配。為了滿足大批量高速生產(chǎn)的需要,目前沖壓設(shè)備也由單工位、單功能、低速壓力機(jī)朝著多工位、多功能、高速和數(shù)控方向發(fā)展,加之機(jī)械乃至機(jī)器人的大量使用,使沖壓生產(chǎn)效率得到大幅度提高,各式各樣的沖壓自動(dòng)線和高速自動(dòng)壓力機(jī)紛紛投入使用。如在數(shù)控四邊折彎機(jī)中送入板料毛坯后,在計(jì)算機(jī)程序控制下便可依次完成四邊彎曲,從而大幅度提高精度和生產(chǎn)率;在高速自動(dòng)壓力機(jī)上沖壓電機(jī)定轉(zhuǎn)子沖片時(shí),一分鐘可沖幾百片,并能自動(dòng)疊成定、轉(zhuǎn)子鐵芯,生產(chǎn)效率比普通壓力機(jī)提高幾十倍,材料利用率高達(dá)97%;公稱壓力為250KN的高速壓力機(jī)的滑塊行程次數(shù)已達(dá)2000次/min以上。在多功能壓力機(jī)方面,日本田公司生產(chǎn)的2000KN“沖壓中心”采用CNC控制,只需5min時(shí)間就可完成自動(dòng)換模、換料和調(diào)整工藝參數(shù)等工作;美國惠特尼公司生產(chǎn)的CNC金屬板材加工中心,在相同的時(shí)間內(nèi),加工沖壓件的數(shù)量為普通壓力機(jī)的4~10倍,并能進(jìn)行沖孔、分段沖裁、彎曲和拉深等多種作業(yè)。
近年來,為了適應(yīng)市場的激烈競爭,對產(chǎn)品質(zhì)量的要求越來越高,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,無需設(shè)計(jì)專用模具、性能先進(jìn)的轉(zhuǎn)塔數(shù)控多工位壓力機(jī)、激光切割和成形機(jī)、CNC萬能折彎機(jī)等新設(shè)備已投入使用。特別是近幾年來在國外已經(jīng)發(fā)展起來、國內(nèi)亦開始使用的沖壓柔性制造單元(FMC)和沖壓柔性制造系統(tǒng)(FMS)代表了沖壓生產(chǎn)新的發(fā)展趨勢。FMS系統(tǒng)以數(shù)控沖壓設(shè)備為主體,包括板料、模具、沖壓件分類存放系統(tǒng)、自動(dòng)上料與下料系統(tǒng),生產(chǎn)過程完全由計(jì)算機(jī)控制,車間實(shí)現(xiàn)24小時(shí)無人控制生產(chǎn)。同時(shí),根據(jù)不同使用要求,可以完成各種沖壓工序,甚至焊接、裝配等工序,更換新產(chǎn)品方便迅速,沖壓件精度也高。
(4)沖壓標(biāo)準(zhǔn)化及專業(yè)化生產(chǎn)方面
模具的標(biāo)準(zhǔn)化及專業(yè)化生產(chǎn),已得到模具行業(yè)和廣泛重視。因?yàn)闆_模屬單件小批量生產(chǎn),沖模零件既具的一定的復(fù)雜性和精密性,又具有一定的結(jié)構(gòu)典型性。因此,只有實(shí)現(xiàn)了沖模的標(biāo)準(zhǔn)化,才能使沖模和沖模零件的生產(chǎn)實(shí)現(xiàn)專業(yè)化、商品化,從而降低模具的成本,提高模具的質(zhì)量和縮短制造周期。目前,國外先進(jìn)工業(yè)國家模具標(biāo)準(zhǔn)化生產(chǎn)程度已達(dá)70%~80%,模具廠只需設(shè)計(jì)制造工作零件,大部分模具零件均從標(biāo)準(zhǔn)件廠購買,使生產(chǎn)率大幅度提高。模具制造廠專業(yè)化程度越不定期越高,分工越來越細(xì),如目前有模架廠、頂桿廠、熱處理廠等,甚至某些模具廠僅專業(yè)化制造某類產(chǎn)品的沖裁?;驈澢#@樣更有利于制造水平的提高和制造周期的縮短。我國沖模標(biāo)準(zhǔn)化與專業(yè)化生產(chǎn)近年來也有較大發(fā)展,除反映在標(biāo)準(zhǔn)件專業(yè)化生產(chǎn)廠家有較多增加外,標(biāo)準(zhǔn)件品種也有擴(kuò)展,精度亦有提高。但總體情況還滿足不了模具工業(yè)發(fā)展的要求,主要體現(xiàn)在標(biāo)準(zhǔn)化程度還不高(一般在40%以下),標(biāo)準(zhǔn)件的品種和規(guī)格較少,大多數(shù)標(biāo)準(zhǔn)件廠家未形成規(guī)?;a(chǎn),標(biāo)準(zhǔn)件質(zhì)量也還存在較多問題。另外,標(biāo)準(zhǔn)件生產(chǎn)的銷售、供貨、服務(wù)等都還有待于進(jìn)一步提高。
蓋冒墊片設(shè)計(jì)說明書
一、工件工藝性分析
如右圖1所示:工件為有凸緣圓筒形零件,且在凸緣上均勻分布4個(gè)相同的孔。故可得知此工件為:落料拉深沖孔所得,其加工工藝過程為:落料-拉深-沖孔,各尺寸關(guān)系如圖1所示
一、 拉深工藝及拉深模有設(shè)計(jì)
1、 設(shè)計(jì)要點(diǎn)
設(shè)計(jì)確定拉深模結(jié)構(gòu)時(shí)為充分保證制件的質(zhì)量及尺寸的精度,應(yīng)注意以下幾點(diǎn)
1) 拉深高度應(yīng)計(jì)算準(zhǔn)確,且在模具結(jié)構(gòu)上要留有安全余量,以便工件稍高時(shí)仍能適應(yīng)。
2) 拉深凸模上必須設(shè)有出氣孔,并注意出氣孔不能被工件包住而失去作用。
3) 有凸緣拉深件的高度取決勝于上模行程,模具中要設(shè)計(jì)有限程器,以便于模具調(diào)整。
4) 對稱工件的模架要明顯不對稱,以防止上、下模位置裝錯(cuò),非旋轉(zhuǎn)工件的凸、凹模裝配位置必須準(zhǔn)確可行,發(fā)防松動(dòng)后發(fā)生旋轉(zhuǎn),偏移而影響工件質(zhì)量,甚至損壞模具。
5) 對于形狀復(fù)雜,需經(jīng)過多次拉深的零件,需先做拉深模,經(jīng)試壓確定合適的毛坯形狀和尺寸后再做落料模,并在拉深模上按已定形的毛坯,設(shè)計(jì)安裝定位裝置。
6) 彈性壓料設(shè)備必須有限位器,防止壓料力過大。
7) 模具結(jié)構(gòu)及材料要和制件批量相適應(yīng)。
8) 模架和模具零件,要盡是使用標(biāo)準(zhǔn)化。
9) 放入和取出工件,必須方便安全。
2、 有凸緣圓筒形件的拉深方法及工藝計(jì)算
有凸緣筒形件的拉深原理與一般圓筒形件是相同的,但由于帶有凸緣,其拉深方法及計(jì)算方法與一般圓筒形件有一定差別。
1) 在凸緣拉深件可以看成是一般圓筒形件在拉深未結(jié)束時(shí)的半成品,即只將毛坯外徑拉深到等于法蘭邊(即凸緣)直徑df時(shí)的拉深過程就結(jié)束。因此其變形區(qū)的壓力狀態(tài)和變形特點(diǎn)應(yīng)與圓筒形件相同。
根據(jù)凸緣的相對直徑df/d比值同有凸緣筒形件可分為:窄凸緣筒形件(df/d=1.1~1.4)和寬凸緣筒形件(df/d>1.4)。顯然此工件df/d=50/21=2.38>1.4為寬凸緣筒形件。下面著重對寬凸緣件的拉深進(jìn)行分析,主要介紹其與直壁筒形件的不同點(diǎn)。
當(dāng)rp=rd=r時(shí)(圖2),寬凸緣件毛坯直徑的計(jì)算公式為:
?。?)
根據(jù)拉深系數(shù)的定義寬凸緣件總拉深系數(shù)仍可表示為:
(2)
3、 寬凸緣圓筒形件的工藝計(jì)算要點(diǎn)
1)毛坯尺寸的計(jì)算,毛坯尺寸的計(jì)算仍按等面積原理進(jìn)行,參考無凸緣筒形件毛坯的計(jì)算方法計(jì)算,毛坯直徑的計(jì)算公式見式(1),其中df要考慮修邊余量,其值可從《沖壓工藝與模具設(shè)計(jì)》表4.22中查得=1.6mm即df=50+1.6=51.6mm
則D==54.75mm
根據(jù)拉深系數(shù)的定義,寬凸緣件總拉深系數(shù)仍可表示為:
M=
2)判斷工件是否一次拉成,這只須比較工件實(shí)際所需的總拉深系數(shù)和h/d與凸緣件第一次拉深系數(shù)和極限拉深系數(shù)的相對高度即可。m總>m1,當(dāng)1,h/d≤h1/d1時(shí)可以一次拉成,工序計(jì)算到此結(jié)束,否則應(yīng)進(jìn)行多次拉深。m總=0.38 h/d==0.33。由《沖壓工藝與模具設(shè)計(jì)》表4.2.6查得此凸緣件的第一次拉深系數(shù)m1=0.37。由表4.2.7查得此凸緣件的第一次拉深最大相對高度h1/d1=0.28~0.35之間,可知m總>m1,h/d≤h1/d1可一次拉成。
4、拉深凸模和凹模的間隙
拉深模間隙是指單面間隙,間隙的大小對拉深力,拉深件的質(zhì)量,拉深模的壽命都有影響,若c值大小,凸緣區(qū)變厚的材料通過間隙時(shí),校正和變形的阻力增加,與模具表面間的摩擦,磨損嚴(yán)重,使拉深力增加,需件變薄嚴(yán)重,甚至拉破,模具壽命降低。間隙小時(shí)得到的零件側(cè)壁平直而光滑,質(zhì)量較好,精度較高。
間隙過大時(shí),對毛坯的校直和擠壓作用減小,拉深力降低,模具的壽命提高,但零件的質(zhì)量變差,沖出的零件側(cè)壁不直。
因此拉深模的間隙值也應(yīng)合適,確定c時(shí)要考慮壓邊狀況,拉深次數(shù)和工件精度高。其原則是:即要考慮材料本身的公差,又要考慮板料的增厚現(xiàn)象,間隙一般都比毛坯厚度略大一些。不用壓邊圈時(shí),考慮到起皺的可能性取間隙值為:
C=(1~1.1)tmax
有壓邊圈時(shí),間隙數(shù)值也可按表4.6.3取值(《沖壓工藝與模具設(shè)計(jì)》),此工件的拉深間隙可取,
C=1.1t=1.1mm
4、拉深凸模,凹模的尺寸及公差
工件的尺寸精度由末次拉深的凸、凹模的尺寸及公差決定,因此除最后一道拉深模的尺寸公差需要考慮外,首次及中間各道次的模具尺寸公差和拉深半成品的尺寸公差沒有必要做嚴(yán)格限制。這是模具的尺寸只取等于毛坯的過渡尺寸即可。此工件內(nèi)形尺寸公差有要求,故以凸模為基準(zhǔn),先定凸模尺寸考慮到凸?;静荒p,(其尺寸關(guān)系如圖3所示)以及工件的回彈情況,凸模開始尺寸不要取得過大。其值為:
Dp=(d+0.4Δ)-δp
凸模尺寸為:Dd=(d+0.4Δ+2C)+ δd
凸、凹模的制造公差δp和δd可根據(jù)工件的公差來選定。工件公差為TT13級以上時(shí)δp和δd可按TT6~8級取,工件公差在IT14級以下時(shí),則δp和δd可按IT10級?。?
Dp=(20+0.4×0.2)0-0.021=20.080-0.021mm
Dd=(d+0.4Δ+2c)0+d
=(20+0.4×0.2+2×1.1)0+d=22.280+0.021mm
5、凹模圓角半徑?rd
拉深時(shí),材料在經(jīng)過凹模圓角時(shí)不僅因?yàn)榘l(fā)生彎曲變形需要克服彎曲阻力,還要克服因相對流動(dòng)引起的磨檫阻力,所以rd大小對拉伸工件的影響非常大。主要有以下影響:
1)拉伸力的大?。?)拉伸件的質(zhì)量;3)拉伸模的壽命。rd小時(shí)材料對凹模的壓力增加,磨檫力增大,磨損加劇,使磨具的壽命降低。所以rd的值即不能太大,也不能太小。在生產(chǎn)上一般應(yīng)盡量避免采用過小圓角半徑,在保證工件質(zhì)量的前提下盡量取大值,以滿足模具壽命要求。通??砂唇?jīng)驗(yàn)公式計(jì)算:
rd=
式中D為毛坯直徑或上道工序拉深件直徑;d為本道拉深后的直徑rd應(yīng)大于或等于2t,若其值小于2t,一般很難拉出,只能靠拉深后整形得到所需零件,故可取rd=2.5mm
6、凸模圓角半徑rp
凸模圓角半徑對拉深工序的影響沒有凹模圓角半徑大,但其值也必須合格,一般首次拉深時(shí)凸模圓角半徑為rp=(0.7~1.0)rd
這里取rp =1.0rd=2.5mm
三、沖裁工藝及沖裁模具的設(shè)計(jì)
1、凸模與凹模刃口尺寸的計(jì)算
沖裁件的尺寸精度主要決定于模具刃口的尺寸精度。模具的合理間隙也要靠模具刃口尺寸制造精度來保證。正確確定模具刃口尺寸及其制造公差,是設(shè)計(jì)沖裁模的主要任務(wù)之一。從生產(chǎn)實(shí)踐可發(fā)現(xiàn):由于凸凹模之間存在間隙,使落下的料或伸出的孔卻帶有錐度,且落料件的大端尺寸等于凹模尺寸,沖孔件的小端尺寸等于凸模尺寸;在測量于使用中,落料件以大端尺寸為基準(zhǔn),沖孔件以小端尺寸為基準(zhǔn)。
2、凸、凹模刃口尺寸的計(jì)算方法
由于加工模具的方法不同,凸模與凹模刃口部分尺寸的計(jì)算公式與制造公差的標(biāo)注也不同,刃口尺寸的計(jì)算方法可分為以下兩種情況:凹模與凸模分開加工,凸模和凹模配合加工,從此工件的結(jié)構(gòu)上分析,選擇凸模與凹模分開加工的制造方法:采用這種方法,凸模和凹模分別按圖紙加工至尺寸,要分別標(biāo)注凸模和凹模的刃口尺寸及制造公差(凸模δp、凹模δd),適用于圓形或簡單形狀的制件。為了保證初始間隙值小于最大合理間隙2Cmax,必須滿足下列條件:
或?。?
也就是說,新制造模具應(yīng)該是,否則制造的模具部隙已超過允許變動(dòng)范圍2Cmin~2Cmax,影響模具的使作壽命。
下面對落料和沖孔兩咱情況分別進(jìn)行討論。
1) 落料
高工件的尺寸為D-0Δ,根據(jù)計(jì)算原則,落料時(shí)以凹模為設(shè)計(jì)基準(zhǔn)。首先確定凹模尺寸,凹模的基本尺寸接近或等于制件輪廓的最小極限尺寸,再減小凸模尺寸以保證最小合理間隙值2Cmin。
名部分分配位置如圖5(a)所示。其計(jì)算公式如下
?。?)
(4)
代入數(shù)據(jù)得
校核;由此可知,只有縮小、,提高制造精度,才保證間隙在合理范圍內(nèi),此時(shí)可取、,放得:
2)沖孔
設(shè)沖孔尺寸為,根居以上原則,沖孔時(shí)以凸模設(shè)計(jì)為基準(zhǔn),首先確定凸模刃口尺寸,使凸?;境叽缃咏虻扔诠ぜ椎淖畲髽O限尺寸,再增大凹模尺寸,凸模制造偏差為負(fù)偏差,凹模取正偏差,名部分分配位置如圖5.b所示,其計(jì)算公式如下:
在同一工步制件上沖出兩個(gè)以上孔時(shí),凹模型孔中心距Ld按下式確定:
代入數(shù)據(jù)
校核
孔距尺寸:
3)凹模洞的類形
常用凹模洞口的類形如圖6所示:
圖 6
其中圖a、b、c為直筒式刃的凹模,其特點(diǎn)是制造方便,刃口強(qiáng)度高,刃磨后工作部分尺寸不變,廣泛用于沖裁公差要求較小,形狀復(fù)雜的精密制件。但因廢料(或制件的聚集而增大了推件力和凹模的脹裂力,給凸、凹模的強(qiáng)度都帶來了不利的影響。一般復(fù)合模上出件的沖裁模用圖a、c型,下出件的沖裁模用圖b或圖a型,圖d、e型是錐筒式刃口,在凹模內(nèi)不聚集材料,側(cè)壁磨損小,但刃口強(qiáng)度差,刃磨后刃口徑向尺寸略有增大(如α=300時(shí),刃磨0.1mm時(shí),其尺寸增大0.0017mm
凹模錐角α,后角β和洞高度h,均隨制件材料厚度增加而增大,一般取α=15'~30' β=20'~30' h=4-10mm綜上所述及其對工件孔分析,選擇B型凹模洞口,取h=6mm β=20'
4)凹模的外形尺寸
凹模的外形一般有矩形與圓形兩種。凹模的外形尺寸應(yīng)保證凹模有足夠的強(qiáng)度,剛度和修磨量,凹模的外形尺寸一般是根據(jù)被沖材料的厚度和沖裁件的最大外形尺寸來確定的如圖7所示
凹模的厚度為:
1+ kb (≥15)
凹模壁厚度為c=(1.5~2)H (≥30~40mm)
式中b為沖裁件的最大外形尺寸;K為系數(shù),是考慮板料厚度影響的系數(shù)可以《沖壓工藝與模具設(shè)計(jì)》表2.8.2中查得代入數(shù)據(jù)可得沖孔凹模
H=15mm c=30mm
落料凹模H=0.35×54.75=20mm c=40mm
四、模具的其它零件
1、模具除簡單沖模外,一般沖模多利用模架的結(jié)構(gòu)。模架的和種類很多,要根據(jù)模具的精度要求,模具的類別,模具的大小選擇合適的模架.
模架的選擇可從《實(shí)用模具技術(shù)手冊》P192頁選擇標(biāo)準(zhǔn)架。根據(jù)查閱的內(nèi)容及分析,此復(fù)合模可選用后側(cè)導(dǎo)柱模架導(dǎo)、導(dǎo)柱安裝在后側(cè),有偏心裁荷時(shí)容易歪斜,滑動(dòng)不夠平穩(wěn),可從左右前三個(gè)方向關(guān)料操作比較方便。常用于一般要求的小型工件的沖裁和拉深模。所選模架的結(jié)構(gòu)及尺寸關(guān)系如圖8所示:
L =250mm B=160mm 上模座:250×160×45 下模座250×160×50
導(dǎo)柱,32×190 導(dǎo)套 32×105×43 Hmax=210 Hmin=170mm 其余尺寸見上下模座零件圖,可以《沖壓手冊》沖壓模具常用標(biāo)準(zhǔn)件選擇。
2.模柄
模柄有多種形式,要根據(jù)模具的結(jié)構(gòu)特點(diǎn),選用模柄的形式模柄的直徑根據(jù)所選壓力機(jī)的模柄孔徑確定,模柄可根據(jù)《實(shí)用模具技術(shù)手冊》P201頁選擇,經(jīng)查閱各種
模柄的特點(diǎn),選用壓入式模柄,這種模柄應(yīng)用比較廣泛壓入模柄的結(jié)構(gòu)和尺寸,可參表11-10制造,表中B型模柄中間有孔可按裝打料桿,用壓力機(jī)的打料模桿進(jìn)行打料,模柄的結(jié)構(gòu)及尺寸關(guān)系如圖9所示。
圖 9
d=30
D=32
D1=42mm
h=78mm
h2=30mm
h1=5mm
b=2mm
a=0.5mm
d1(H7)=6+0.0120
d2=11mm
3、卸料板
卸料板的主要作用是將沖壓的料從凸模或凸、凹模上推下來,此外在進(jìn)模比較復(fù)雜的模具中,卸料板還具有保護(hù)小凸模作用,常用的卸料板結(jié)構(gòu)形式及適用范圍見表11-24和第八章級進(jìn)模表8-10《實(shí)用模具技術(shù)手冊》卸料板的尺寸可根據(jù)《實(shí)用模具技術(shù)手冊》表11-25查得,本模具選用彈壓式卸料板。卸料板的結(jié)構(gòu)與尺寸關(guān)系如圖10所示,
ho'=16mm
B=150mm
C'=(0.1~0.2)t=0.2mm)
4.彈頂和推出裝置
彈頂裝置由彈簧元件組成裝于模具的下面通過頂桿起到推料的作用,彈頂裝置通常在壓力機(jī)的工作臺孔中,彈頂裝置結(jié)構(gòu)形式見表11-26《實(shí)用模具技術(shù)手冊》,具體結(jié)構(gòu)及尺寸見裝配圖及零件圖所示,見圖表(10)設(shè)計(jì)模具時(shí)選用標(biāo)準(zhǔn)的彈簧。已知沖裁時(shí)卸料為 FQ=3.8 可選圓鋼絲螺壓縮彈簧,由表11-28查得d=8.0mm D2=50mm F=1990N. Dmax=38mm
Dmin=62mm; 節(jié)距P=14.9mm
5、導(dǎo)向裝置(導(dǎo)柱 導(dǎo)套)
導(dǎo)向裝置指得是模架上的導(dǎo)柱、導(dǎo)套。模具在開模,閉模過程中,導(dǎo)柱和導(dǎo)套起導(dǎo)向的作用,使得凸凹模正確的閉合,故此,導(dǎo)柱、導(dǎo)套需要有嚴(yán)格的配合精度及尺寸要求,導(dǎo)柱、導(dǎo)套的選擇可以《沖壓手冊》中選取,(取H7/h6配合)
如圖11 a導(dǎo)柱的具體尺寸為:
d=32 L=190mm
導(dǎo)套的具體尺寸為(圖11 .b)
圖11
D=32
D(r6)=45
L=105mm
h=43mm
L=25mm
油槽數(shù)為2
b=3;a=1
6、固定零件(固定板、墊板)
1)墊板的作用是承受凸模和凹模的壓力,防止過大的沖壓,在上下模座上壓出凹坑,影響模具的正常工作,墊板厚度根據(jù)壓力機(jī)的大小選擇,一般取5-12mm,外形與固定板相同,材料45鋼,熱處理后硬度為45-48HRC,如圖12a .b所示:
墊板在模具中的受力情況
2)固定板 固定板的作用起固定凸、凹模,防止其在沖壓過程中松動(dòng),造成模具的損壞,固定板的形狀要根據(jù)凸、凹模而定,而外形尺寸與墊板相似。固定板和具體形狀尺寸見零件圖所示。
7、連接零件
此類零件包括螺釘、銷釘?shù)?,主要作用是?lián)接其它零部伯,使之共同完成工件的制造,螺釘和銷釘可由《沖壓手冊》第十章、第七、八章查選,形狀及尺寸見七、八節(jié)圖所示現(xiàn)選螺釘M12 圓柱銷 d=8,則沖壓模上有關(guān)螺釘孔的尺寸見表10-28《沖壓手冊》D=27 d=17.5
卸料螺釘選M16,具體尺寸見表10-29《沖壓手冊》
五、壓力機(jī)的選擇
壓力機(jī)的選擇要考慮,沖裁力、拉深力以及卸料力、推件力、頂件力,壓力機(jī)的總噸位應(yīng)大于等以上所有力之和1.3倍,普通刃沖裁模,其沖裁力FP一般可按下式計(jì)算。
FP= KPtLτ
式中τ為材料的抗剪強(qiáng)度,L為沖裁周邊總長(mm),t為材料厚度,系數(shù)KP是考慮到?jīng)_裁模刃口的磨損,凸模與凹模間隙的波動(dòng)(數(shù)值的變化或分布不均勻)
潤滑情況,材料力學(xué)性能與厚度公差的變化等因素而設(shè)置的安全系數(shù),一般取1.3,當(dāng)查不到強(qiáng)度τ時(shí),可用強(qiáng)度,σb代替,而取KP=1的近似計(jì)算法計(jì)算,材料鋼的強(qiáng)度可以《沖壓工藝與模具設(shè)計(jì)》表1.4.1查得τ=260MPa~360MPa。 現(xiàn)取τ=340MPa
FP1=1.3×1×3.14×54.75×340=76KN
FP2=1.3×1×3.14×5×340=7KN
影響卸料力、推料力和頂件力的因素很多,要精確的計(jì)算出很困難,在實(shí)際生產(chǎn)采用經(jīng)驗(yàn)公式計(jì)算:
卸料力:FQ=KFp
推料力:FQ1=nK1Fp
頂件力:FQ2=K2Fp
式中:
卸料力系數(shù),其值為 0.02~0.06 (薄料取大值,厚料取小值)
推件力系數(shù),其值為0.03~0.07 (薄料取大值,厚料取小值)
頂件力系數(shù),其值為0.04~0.08 (薄料取大值,厚料取小值)
n為梗塞在凹模內(nèi)的制件或廢料數(shù)量,n=h/t,h為直刃口部分的高,t為材料的厚度,h取4~10mm , 現(xiàn)取h=6mm
本模具中只有卸料力和推件力即可則:
FQ=0.05×76=3.8KN
FQ1=6/1×0.06×7=2.52KN
2)拉深力
理論計(jì)算拉深力可以推導(dǎo),但它使用不便,生產(chǎn)中常利用經(jīng)驗(yàn)公式計(jì)算拉深力,第次拉深(一次拉深成形時(shí))
F1=πd1tσbk1
式中σb為材料的抗拉強(qiáng)度,K1為系數(shù),查表4.5.4(《沖壓工藝與模具設(shè)計(jì)》)代入數(shù)據(jù)可得F1=3.14×21×1×390×1=25.7KN
壓邊力: FQ=0.25×25.7=6.4KM
卸料力: FQ==KF=0.04×25.7=1.02KN
綜上所述:F總=76+7+3.8+2.25+25.7+6.4+1.02=123KN
F壓力=1.3 F總=1.3×123=160 KN
由《實(shí)用模具技術(shù)手冊》P22頁,應(yīng)用壓力機(jī)的選擇查表2-3可選擇J23—16型壓力機(jī),其參數(shù)可參考表2—3
六、 主要組件的裝配
1.模柄的裝配,因?yàn)樗灸>叩哪1菑囊陨夏W南露蛏蠅喝氲?,所以在安裝凸模固定板和墊板之前,應(yīng)先把模柄裝好。
模柄與上模座的配合要求是H7/m6.裝配時(shí),先在壓力機(jī)上將模柄壓入,再加工定儉銷孔或螺紋孔。然后把模柄端面突出部分銼平或磨平,安裝好模柄后,用角尺檢查模柄與上模座上平面的垂有度。
2、凸模和裝配,凸模與固定板的配合要求為H7/m6.。裝配時(shí),先在壓力機(jī)上將凸模固定板內(nèi),檢查凸模的垂直度,然后將固定板的上平面與凸模尾部一起磨平,為了保持凸模刀口鋒利還應(yīng)將凸模的端面磨平。
3、彈壓卸料板的裝配,彈壓卸料板起壓料和卸料的作用。裝配的保證它與凸模之間具有適當(dāng)?shù)拈g隙,其裝配方法是,將彈壓卸料板 裝入固定板的凸模內(nèi),在固定板與卸料板之間墊上平行墊塊,并用平等夾板將它們夾緊,然后按卸料板上的螺孔在固定板上抽窩,拆開后鉆固定板上的螺釘穿過孔。
4、模架的技術(shù)要求及裝配
組成模架的各零件均應(yīng)符合相應(yīng)的技術(shù)條件,其中特別重要的是每對導(dǎo)柱,導(dǎo)套的配合間隙應(yīng)符合要求。
裝配成套的模架,多項(xiàng)技術(shù)指標(biāo)(上模座上平面對下模座下平面的平行度)導(dǎo)柱軸心線對下模座下平面的垂直度和導(dǎo)套孔軸心線對上模座下面垂直度)應(yīng)符合相應(yīng)精度等級要求。
裝配后的模架,上模座沿導(dǎo)柱上、下移動(dòng)平穩(wěn)無阻滯現(xiàn)象,
壓入上、下模座的導(dǎo)柱導(dǎo)柱離其它裝表面應(yīng)有1—2mm距離,壓入后就牢固。裝配成套的模架,各零件的工作表不應(yīng)有碰傷,裂 以及其它機(jī)械損傷
模架的裝配主要指導(dǎo)柱導(dǎo)套的裝配,目前大多數(shù)導(dǎo)柱,導(dǎo)套與模座之間采用過盈配合,但也有少數(shù)采用粘 工藝的,即將上下模座孔擴(kuò)大,降低其加工要求,同時(shí)將導(dǎo)柱、導(dǎo)套之間冷入粘結(jié)劑,即可使用導(dǎo)柱,導(dǎo)套固定,滑動(dòng)導(dǎo)向模架常用的裝配工藝和檢驗(yàn)方法有壓入導(dǎo)套、壓入導(dǎo)套安、裝導(dǎo)套。
七、模具的工作過程
本模具是一套倒裝的落料拉深沖孔的復(fù)合模。前后送料,擋料銷19限位,導(dǎo)向銷20導(dǎo)正。上模下行凸凹模11與拉深凹模18接觸進(jìn)行拉深,工件成型后,上模上行,打桿1推動(dòng)打板12把工件從凸凹模11中打出。落料廢料有彈簧8推動(dòng)卸料板10推出。
體會
俗話說“凡事必親躬”,唯有自己親自去做的事,才懂得其過程的艱辛。通過做這次大作業(yè),我著實(shí)遇到了不少的困難,構(gòu)思、定數(shù)據(jù)、畫圖、寫論文等都得自己去做。每天泡在圖書館,找例證、查資料,個(gè)中自有不少困難,而這些難題都是課本中所不曾提到過的。開始時(shí),由于書本上沒有任何提示,我甚至不知道從何入手,只能與同學(xué)們相互切磋,這樣我慢慢地入了門,進(jìn)而也可以自己搞定了。這其中有一個(gè)習(xí)慣問題最需要克服。眾所周知,課堂、書本給我們的都是一種確切的數(shù)據(jù),但實(shí)際上你去做的時(shí)候就會發(fā)現(xiàn)它們都是經(jīng)驗(yàn)性的,也就是說需要你根據(jù)從資料上查得的范圍靠經(jīng)驗(yàn)自己去定,這就給習(xí)慣于接受確切數(shù)字的我?guī)砹撕艽蟮奶魬?zhàn)。幸而,最終我還是學(xué)會了怎樣去查找自己想要的資料,這應(yīng)該是這次作業(yè)的一大收獲吧。
第二大收獲就是學(xué)會了做一次設(shè)計(jì)項(xiàng)目的具體流程。從策劃構(gòu)思、總體設(shè)計(jì)到各個(gè)模塊的的具體設(shè)計(jì)及其組合,再到編寫需要提交的論文,這一切如今仍歷歷在目。我想,這種對整體設(shè)計(jì)流程的把握應(yīng)該是以后走上工作崗位所必需的技能,而這種技能卻只能通過自己的親身實(shí)踐才能獲得。這也是為什么我認(rèn)為機(jī)械設(shè)計(jì)大作業(yè)這種教學(xué)實(shí)踐模式值得推廣的原因。
畢業(yè)設(shè)計(jì)是我在大學(xué)生涯完成的最后一項(xiàng)內(nèi)容,此時(shí)此刻,我感覺自己有很多想要說的話,有很多需要感謝的人。首先感謝指導(dǎo)老師李波和唐宇老師給予的支持與指導(dǎo),但由于工作的原因和條件的限制,我在外面所做的畢業(yè)設(shè)計(jì)并不完善。自從回校之后,向老師們請教和指導(dǎo),他們都在百忙之中給予了我悉心的指導(dǎo)和幫助。師生之情無法言表,在此,謹(jǐn)向恩師們深表謝意!
也許,我的學(xué)生生涯從此就會結(jié)束,但是學(xué)習(xí)的道路卻還將持續(xù)下去,未來的人生路途中難免會遇到各種各樣的困難和挫折,使我始終能夠勇敢的迎接新的挑戰(zhàn)。
參考文獻(xiàn)
1;冷沖壓技術(shù) 翁其金主編 北京機(jī)械工業(yè)出版社 2000.11
2;公差配合與技術(shù)測量 薛彥成主編 北京機(jī)械工業(yè)出版社1999.10
3;機(jī)械制圖 李澄 聞百橋 吳天生主編 北京高等教育出版社2003..8
4;模具設(shè)計(jì)與制造簡明手冊 馮炳堯 韓泰來 蔣文森 主編 上海科學(xué)技術(shù)出版社 1998(第二版)
5;模具技術(shù)標(biāo)準(zhǔn)應(yīng)用 全國模具標(biāo)準(zhǔn)技術(shù)委員會秘書處四川省模具工業(yè)協(xié)會印 1992.8
25
Journal of Materials Processing Technology 151 (2004) 237241 Recent developments in sheet hydroforming technology S.H. Zhang a, , Z.R. Wang b ,Y.Xu a , Z.T. Wang a , L.X. Zhou a a Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, China b School of Materials Science and Engineering, Harbin Institute of Technology, Harbin 150001, China Abstract In this paper, recent developments in sheet hydroforming technology are summarized, several key technical problems to be solved for the development of sheet hydroforming technology are analyzed, and varied sheet hydroforming technologies are discussed. Compound deformation by drawing and bulging is the main direction for the development of sheet hydroforming technology, in which it is advantageous to increase the feeding of materials, and the ratio of drawing deformation (drawing in of the blank flange) to bulging, enabling the forming limit of a sheet blank to be increased. It is also advantageous to increase the local deformation capacity for sheet hydroforming, to increase the range of application of the process. Press capacity is one of the important factors restraining the range of applications. As one of the flexible forming technologies that is still under development, it has much potential for innovative applications. Its applications have been increasing remarkably, recently in automotive companies. A breakthrough in the technology will be obtained by the development of novel equipment. A new sheet hydroforming technology using a movable die is proposed in this paper, which has been developed recently by the authors. 2004 Elsevier B.V. All rights reserved. Keywords: Sheet hydroforming; Drawing in; Bulging; Flexible forming; Forming limit 1. Introduction Compared with conventional deep drawing, sheet hydro- forming technology possesses many remarkable advantages, such as a higher drawing ratio, better surface quality, less springback, better dimensional freezing and the capability of forming complicated-shaped sheet metal parts. For exam- ple a multi-pass forming process may be decreased to one pass for the forming parabolic parts. Sheet hydroforming technology has been applied to industries for the forming of automotive panels and aircraft skins 1. It is a soft-tool forming technology and as the development of this technol- ogy is imperfect compared with other rigid forming tech- nologies, there are more extensive demands and space for it to be improved with the development of modern industry. There are many demands for hydrofoming technology for use with some new materials, such as forming of magnesium alloy sheets, composite material sheets and sandwich sheets. Some new hydroforming processes have entered this area, such as viscous pressure forming technology, warm sheet hydroforming, the hydroforming of sheet metal pairs and the hydroforming of tailor-welded blanks. Through long-term Corresponding author. Tel.: +86-24-8397-8266/8721; fax: +86-24-2390-6831. E-mail address: (S.H. Zhang). investigation by the AP namely, the compound deformation of bulging and drawing due to the draw-in of blank flange area (blank feeding of the blank flange area), which compensates the materials for the stretch of the bulging area and avoids excessive thinning resulting from the increase of the blank area, thus assuring material strength and rigidity in the bulging area. It is very diffi- cult to realize the uniform distribution of thinning, the large local deformation of sheet the metal and the increasing of the forming limit of the blank without blank feeding and supplementation. Thus the advantages for the hydroforming of complicated-shaped parts from sheet cannot be revealed fully, although the breakthrough for tube hydroforming has been realized. A tubular component can be hydroformed if dealing with a high-pressure forming process with the simul- taneous feeding of the tube end 3, which increases the tube area and thus reduces little thinning. The requirements for the pressure of the tool in tube hydroforming are small. The internal pressure for the tube is closed and self-restrained, and the closing force involved is small. The material feeding of the tube end can be enforced without difficulty for this technology, compared with the difficulties of the feeding in of the material in hydroforming. As in tube hydroforming, a closing force is required for sheet hydroforming, but a difficulty is that the closing force for sheet hydroforming is far greater than that in tube hydro- forming, and requires a high press tonnage: this is an impor- tant factor restraining the application of sheet hydroforming. The closing pressure can be supplied by a hydraulic press, but the pressure for sheet hydroforming is no limits and not self-restrained. 2.1. Hydroforming with a rubber diaphragm A rubber membrane was employed as the diaphragm of the hydraulic chamber and the blankholder in the early form of sheet hydroforming. This process has been applied to small batch production of automotive panels and aircraft skins (Fig. 1). There are many advantages for this process: better surface quality and the forming of more complicated workpieces. It is suitable for small batch production. How- ever, it also has some disadvantages, such as low process efficiency and the requirement of heavy presses. In addition, it is easy to destroy the rubber membrane and difficult to control wrinkling. 2.2. The hydromechanical deep drawing process and the hydro-rim deep drawing process The hydromechanical deep drawing process has been de- veloped on the basis of rubber membrane hydroforming (Fig. 2(a). The pressure can be produced by the downwards movement of the punch into the fluid chamber, or supplied by a hydraulic system, because a rubber membrane is not used. Thus, it is very easy to obtain hydraulic pressure. The tool device is similar to a conventional tool. All these param- eters lead to high efficiency. The shape of the workpieces may be very complicated, and the drawing ratio may be in- creased, from 1.8 to 2.7, compared with that for conven- tional drawing processes. There are many applications for this process 1315. More local deformation and forming of complicated parts are realized by using this process. Forced feeding is difficult to practice in current sheet hy- droforming processes. To some extent, the radial hydrome- S.H. Zhang et al. / Journal of Materials Processing Technology 151 (2004) 237241 239 Fig. 1. Sheet hydroforming with a rubber membrane: (a) the process; (b) a hydroformed workpiece. chanical deep drawing (hydro-rim) process can realize some forced radial feeding (Fig. 2(b), which can significantly in- crease the forming limit of the sheet metal. According to the research results in 2, the drawing ratio can be increased, from 2.6 to 3.2, compared with that for the common hy- dromechanical deep drawing process. 2.3. Hydroforming of sheet metal pairs A special case is the hydroforming of welded-closing sheet metal pairs (Fig. 3(a). The hydroforming technology of sheet metal pairs was developed by Kleiner et al at. Dort- mund University in the early 1990s 46. In the first scheme the periphery of the sheet metal can be welded using laser welding. Then a liquid medium can be filled between the blanks, and pressurization can be effected by a hydraulic sys- tem. Plastic deformation starts in the blank under the pres- sure and then further deformation occurs sequentially in the zone contacting with the die. However, it is very difficult to realize radial feeding using this method, as it is essentially a pure bulging deformation. The advantage is that the pres- sure is a kind of self-restraining pressure. There is a low re- quirement for the closing force. A stainless steel automotive model was formed with the new press of 100,000 kN with hydroforming technology. To some extent, this technology is similar to tube hydroforming, however, it is very difficult to realize the radial feeding of the blank. Fig. 2. Showing: (a) hydromechanical deep drawing; (b) hydro-rim deep drawing. Another variation was proposed by Dortmund University (Fig. 3(b). The principle is that the tool system is made up of an upper and lower die and an intermediate plate. The intermediate plate can be applied on its own or together with the upper and lower blank, for hydroforming. The pressure pipeline may be connected or disconnected. Generally, the shape of the upper and lower workpieces is symmetrical when the pressure pipeline is connected, whilst the shapes of the upper and lower workpieces are independent when the pressure pipeline is not connected: infact, they may deform separately. This tool is for the realization of the compound deformation of drawing and bulging. 2.4. The compound deformation of drawing and bulging Sheet hydroforming with compound drawing and bulging has been investigated for many years. Since the early 1980s, the theory of hydroforming with draw-in has been studied by Shang at Singapore National University 7. He studied the reasonable match of draw-in and bulging, but it is still in the research stage and has not been applied. 2.5. The dieless integral hydro-bulge forming (IHBF) of spherical shells Another special case is the integral hydro-bulge forming (IHBF) of spherical shells. IHBF is a new dieless forming 240 S.H. Zhang et al. / Journal of Materials Processing Technology 151 (2004) 237241 Fig. 3. The hydroforming of sheet metal pairs with an intermediate plate. technology for sphere-inner-scribing polyhedral shell, that means, all the side inter-sections of the polyhedral shell sides are on the sphere; which was invented by Wang 8 at Harbin Institute of Technology in 1985. It realized the dieless IHBF of flat sheets. In fact, this technology is a pure bulging process as it is impossible to obtain the supplementation of materials. Moreover, it is a non-uniform bulging forming. The hydroforming of single curvature shells and the dieless IHBF of double spherical vessels, oblate spheroid shells, ellipsoidal shells and pairs of pressure vessel heads were developed later, which resulted in the full development of the dieless IHBF technology and secured wide applications. 3. A new sheet hydroforming technology: hydroforming with a movable die A sheet hydroforming technology with a movable female die was proposed by authors in 2001 (see Fig. 4) 11,12. Some hydroformed workpieces of stainless steel and magne- sium alloys are shown in Fig. 5. For sheet hydroforming with a movable die, a combined die is used, which consists of a fixed part and a movable part. As the technology can realize the compound deformation of drawing and bulging, it is suit- able for forming complicated-shaped parts and low-plasticity difficult-to-form materials. That part of the blank in the flange area is drawn in during the process, which may real- ize the compound deformation of deep drawing and bulging. Fig. 5. Some hydroformed workpieces of stainless steel and magnesium alloy. Blankholder plate Movable die Combination die Bolster plate O-ring sealing Blank Dies Fig. 4. Schematic of the new set-up for sheet hydroforming using a movable die. The movable die component keeps in touch with the blank during the early stage. Plastic deformation and then defor- mation of the blank in the die-contacting area take place. The movable die remains in contact with the blank under the friction force, which makes the deformation area spread to the non-contacting area. Preliminary research shows that the thinning of the sheet metal can be alleviated remark- ably if this innovative process is adopted 12 (see Fig. 6). The forming limit of the sheet metal is increased. This pro- cess is suitable for the forming of complicated-shaped parts such as aluminum alloy sheets, as well as low-plasticity and light-weight materials such as aluminum lithium alloy and magnesium alloys. S.H. Zhang et al. / Journal of Materials Processing Technology 151 (2004) 237241 241 Fig. 6. Comparison of the thinning ratio between hydroforming with and without a movable die. It is difficult for the tool to be damaged or worn because of the use of hydraulic pressure, so the tool life is improved. Moreover, it is very easy to modify the product because the blankholder has versatility and the punch is not required to be changed: it is only required to change the die for the form- ing of different parts. It can be shown that this process has many advantages over conventional processes: it makes the dies contact well, which results in better shape, dimensional accuracy, less springback and higher precision, remarkably lower tools cost and obviously shorter production periods for small batch production. This process is especially suit- able for the production of large-scale sheet metal parts with complicated shape, varied size and of small batch. It makes the production of complicated shape parts simple and flex- ible and realizes the quick production of workpieces. It is especially suitable for the development of new products in the aerospace industry and prototypes in the automotive in- dustry. If the deformation methods of conventional tools are adopted, because the production batch is not great, the de- sign cycle is long and the manufacturing cost is high, whilst if the presently described process is adopted, the cost for the tool will be decreased and the production periods and development cycle will be shortened. It is expected to apply this technology to many other area of manufacture, such as the production of prototype workpieces, which may save the cost of development, shorten the development cycle for the development of new models and improve competitive power for the business. 4. Conclusions In this paper, recent developments of sheet hydroforming technology are discussed systematically. With the realization of the compound deformation of drawing and bulging for further development of sheet hydroforming, more draw-in of blank flange (drawing deformation) and more capacity of local deformation, can be achieved. The forming limit of sheet metal can be significantly increased, and a wider range of part shape can be formed. Moreover, the multi-pass form- ing process for conventional complicated sheet parts can be decreased to one or two passes. Thus higher efficiency and lower costs can be achieved, which compensates for the low efficiency of the single pass procedure of hydroforming. The pre-requisite to the application for this process is a large tonnage for the equipment and high automation. The com- pound deformation of drawing and bulging can be realized if hydroforming with movable dies is adopted. Moreover, the distribution of wall thickness can be controlled. Thin- ning can be decreased and the forming limit of sheet metal can be increased. There are wide prospects for this technol- ogy, and the process can meet the developing direction of production requirements. References 1 S.H. Zhang, Developments in hydroforming, J. Mater. Process. Tech- nol. 91 (1991) 236244. 2 S.H. Zhang, J. Danckert, Development of hydromechanical deep drawing, J. Mater. Process. Technol. 83 (1998) 1425. 3 F. Dohmann, Ch. Hartl, Hydroforminga method to manufacture light-weight parts, J. Mater. Process. Technol. 60 (1996) 669676. 4 M. Kleiner, A. Gartzke, R. Kolleck, J. Ramer, T. Weidner, Finite element simulation for high pressure sheet metal forming (HBU process) and tool construction, Adv. Technol. Plast. 2 (1996) 975 983. 5 S. Novotny, P. Hein, Hydroforming of sheet metal pairs from alu- minum alloys, in: Proceedings of the SheMet99, 9 September 1999, pp. 591598. 6 P. Hein, F. Vollertsen, Hydroforming of sheet metal pairs, J. Mater. Process. Technol. 87 (1999) 154164. 7 H.M. Shang, F.S. Chau, C.J. Tay, S.L. Toh, J. Mech. Work. Technol. 13 (1986) 279289. 8 Z.R. Wang, T. Wang, D.C. Kang, S.H. Zhang, Y. Fang, The technol- ogy of the hydro-bulging of whole spherical vessels and experimental analysis, J. Mech. Work. Technol. 18 (1) (1989) 8594. 9 M.W. Fu, S.Q. Lu, M.H. Huang, High-precision sheet metal work- pieces manufactured by using a viscous-plastic pressure-carrying medium, J. Mater. Process. Technol. 62 (1996) 7075. 10 J. Liu, B. Westhoff, M. Ahmetoglu, T. Altan, Application of viscous pressure forming (VPF) to low volume stamping of difficult-to-form alloys, J. Mater. Process. Technol. 59 (1996) 4958. 11 S.H. Zhang, Y. Xu, Z.T. Wang, Sheet hydroforming tools, China Patent ZL01211437.5 (2001). 12 S.H. Zhang,Y. Xu, L.X. Zhou, Z.T. Wang, Computer simulation on sheet hydroforming with a movable female die, in: Proceedings of the NUMISHEET2002, 1525 October 2002, Jeju, Korea, pp. 391397. 13 L.H. Lang, J. Danckert, K.B. Nielsen, S.H. Zhang, D.C. Kang, About sheet hydroforming and hydromechanical deep drawing without draw die, J. Plast. Eng. 9 (4) (2002) 2934. 14 J. Zhao, R. Ma, Latest technology and its development trends in sheet metal forming, Met. Forming Technol. 20 (6) (2002) 14, 9. 15 Y.S. Wu, J.C. Xie, G.A. 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