Z形彎曲件沖壓工藝及模具設計【沖孔落料復合?!俊緩澢!俊?套】
Z形彎曲件沖壓工藝及模具設計【沖孔落料復合?!俊緩澢!俊?套】,沖孔落料復合模,彎曲模,2套,彎曲,曲折,沖壓,工藝,模具設計,沖孔,復合
廣西科技大學鹿山學院
畢業(yè)設計(論文)開題報告
題 目: Z形彎曲件沖壓工藝及模具
系 別:
專業(yè)班級:
姓 名:
學 號:
指導教師:
二〇 年 月 日
一、選題的背景和意義(所選課題的歷史背景、國內外研究現(xiàn)狀和發(fā)展趨勢)
模具是制造業(yè)的重要基礎工藝裝備,工業(yè)產品大批量生產和新產品開發(fā)都離不開模具,用模具生產制件所達到的(四高二低)高精度,高復雜程度,高一致性,高生產率和低耗能、低耗材,使模具工業(yè)在制造業(yè)中的地位越來越重要。模具品種繁多,共有10大類,包括沖壓、塑料、橡膠、鑄造、鍛壓等,用于制造業(yè)中幾乎所有產品的生產,可見模具的服務范圍已包括國民經濟的許多方面,現(xiàn)在模具技術已成為衡量一個國家產品制造水平的重要標志之一,沒有高水平的模具就沒有高水平的產品已成為共識。因而,設計制造出高質量的模具已勢在必行。
模具設計和制造技術水平的高低,是衡量一個國家產品制造水平高低的重要標志之一,在很大程度上決定著產品的質量、效益和新產品的開發(fā)能力。本課題旨在鍛煉畢業(yè)生的思維,熟練掌握和運用大學四年所學知識,能夠進行獨立的設計作業(yè)。
針對題目使畢業(yè)生得到機械原理、機械零件設計、機械制造技術基礎及模具設計與制造的綜合訓練。針對題目使學生獲得沖壓工藝規(guī)程、模具設計與制造加工基礎知識,工藝參數(shù)及加工設備的選取,計算機輔助繪圖及資料、手冊的查閱。 培養(yǎng)綜合運用所學知識分析問題和解決實際問題的能力、探求真理的創(chuàng)新精神和創(chuàng)新能力并受到工程設計與科學理論結合的初步訓練等方面的能力。鞏固所學的專業(yè)知識,鍛煉動手能力,培養(yǎng)工程意識,強化工程應用能力,為未來的工作打下良好的基礎 。
近幾年,我國模具制造水平大幅度提高。一個國家的模具技術水平,已成為衡量國家制造業(yè)水平的一個重要標志,也是保持這些國家的產品在國際市場上優(yōu)勢的核心競爭力。中國模具行業(yè)加快了體制改革和機制轉換步伐,產業(yè)結構日趨合理。相關機構預測到2018年,中國將一躍成為全球最大的模具制造業(yè)基地之一。據(jù)國際模協(xié)秘書長羅百輝介紹,這幾年全球58%的模具是由德國等國家生產制造的,中國等亞洲國家的比例只占到1%,但今后東歐國家的模具將會有較大幅度的增長,而亞洲國家的生產比例將提高至22%左右。
模具,是工業(yè)生產的基礎工藝裝備,在電子、汽車、電機、電器、儀表、家電和通訊等產品中,60%—80%的零部件都依靠模具成形,模具質量的高低決定著產品質量的高低,因此,模具被稱之為“百業(yè)之母”。模具又是“效益放大器”,用模具生產的最終產品的價值,往往是模具自身價值的幾十倍、上百倍。由于現(xiàn)代模具企業(yè)大多體現(xiàn)出技術密集、資金密集和高素質勞動力密集以及高社會效益的特點,模具制造業(yè)已成為高新技術制造產業(yè)的一部分。近年來,伴隨著國產設備水平的不斷提升,也有不少模具企業(yè)開始選擇了國產機床。超精密鏡面銑床、納米級車銑復合中心、超精密數(shù)控車床等也已用于模具制造。不過有些高端設備主要還是靠國外進口。但現(xiàn)階段我國模具制造業(yè)確實取得了顯著的成功。據(jù)國際模協(xié)秘書長羅百輝介紹,我國以大型、精密、復雜、長壽命模具為代表的高水平的模具的比例已經達到了三分之一以上。
我們要想成為世界制造業(yè)大國,沒有先進的模具工業(yè)是不行的。在這方面我們還有很長的路要走,還有很多東西要學。首要的一條是要重視模具行業(yè)的發(fā)展,不但要有先進的技術,更要重視模具行業(yè)的商品化,讓模具行業(yè)從企業(yè)中走出來,成為一個具有市場競爭力的新興行業(yè)。據(jù)國際模協(xié)秘書長羅百輝調查,歐洲模具設計和生產的時間要比中國快,但因中國的勞動力成本低,對部分國外客戶有著很強的吸引力。同時,歐洲及世界各國之間的模具競爭也相應加劇。當前,越來越多的外資制造企業(yè)看到日益發(fā)展的中國模具,紛紛加入到中國的模具市場,許多國際知名品牌的汽車模具、沖壓模具、注塑模具企業(yè)也都進入中國,且進入中國市場的力度非常迅猛,速度也非??臁S绕涫窃谖覈娜A南地區(qū)廣東一帶,港資、臺資和外資制造企業(yè)規(guī)模已經發(fā)展很大,模具的銷售總量成為中國最多的地區(qū)。國際模協(xié)秘書長羅百輝表示,外資企業(yè)進入中國市場,不僅將資金帶到中國市場,而且?guī)砹讼冗M的技術、設備和工廠管理。國外模具企業(yè)已越來越感受到來自中國同行所帶來的影響和壓力。
很多新興的模具企業(yè)善于總結整個中國模具行業(yè)發(fā)展歷程,從中吸取有價值的經驗教訓,并將其消化吸收在企業(yè)的設計規(guī)劃和發(fā)展戰(zhàn)略中。國際模協(xié)秘書長羅百輝表示,很多模具制造企業(yè)還很注重企業(yè)的品牌建設,注重企業(yè)的信息化建設,注重企業(yè)的國際化市場的開拓,并實現(xiàn)了模具的專業(yè)化生產。
我國模具行業(yè)前路該怎樣走?據(jù)不完全統(tǒng)計,2004年國內模具進口總值達到600多億,同時,有近200個億的出口,如果我們把進口這一塊吃下來,這將是很大的一塊市場需求。國內模具企業(yè)要想獲得良性的發(fā)展,體制轉變和技術創(chuàng)新是提高模具行業(yè)水平的關鍵,同時也要解決好規(guī)模和效益的問題。
如何把模具行業(yè)的規(guī)模和效益做大 ?對于我國模具業(yè),且拋開技術研發(fā)層面的問題不談,我們先探討一下如何通過行業(yè)內的分工合作、策略聯(lián)盟共同把行業(yè)規(guī)模和效益做大。國內模具企業(yè)要想獲得良性的發(fā)展,必須要解決好規(guī)模和效益的問題。
專家分析模具業(yè)將向多功能方向發(fā)展,國際模協(xié)秘書長羅百輝認為,我國模具行業(yè)將向大型、精密、復雜、高效、長壽命和多功能方向發(fā)展。隨著車輛和電機等產品向輕量化方向發(fā)展,對壓鑄模的數(shù)量、壽命和復雜程度將提出越來越高的要求。隨著以塑料代鋼、以塑代木的發(fā)展和產品零件的精度和復雜程度的不斷提高,塑料模的比例將不斷提高,其精度和復雜程度也將隨著相應提高。
采用高新技術提升我國模具工業(yè)水平,發(fā)展我國的模具工業(yè),必須結合我國國情和提升模具工業(yè)實際,走新型工業(yè)化道路。從技術的發(fā)展來看,高精度、低成本、交貨期短是今后模具發(fā)展的一個趨勢,而我們要想趕上國際先進水平,技術創(chuàng)新是至關重要的一個環(huán)節(jié)。
信息化—中國未來模具企業(yè)競爭焦點,眾所周知,電子商務是代表著未來貿易發(fā)展的方向,也是經濟發(fā)展和進步的一個必然趨勢。在市場競爭逐步深入的時期,企業(yè)創(chuàng)新能力越來越成為企業(yè)競爭力的重要組成部分,信息資源也越來越成為企業(yè)的戰(zhàn)略資源。
結語:目前,我國經濟仍處于高速發(fā)展階段,國際上經濟全球化發(fā)展趨勢日趨明顯,這為我國模具工業(yè)高速發(fā)展提供了良好的條件和機遇?!笆晃濉逼陂g中國模具工業(yè)發(fā)展迅速,產需兩旺,漸入佳境。但也要看到我國模具行業(yè)綜合水平落后的面貌未得到根本性的改變,一些深層次的問題尚待解決。現(xiàn)在,中國可以說是世界模具生產大國之一,但還遠遠不是生產強國?!笆濉逼陂g,應該向生產強國這目標邁進。
本課題要求對給定的零件進行沖壓模設計,通過對零件進行詳細的工藝分析確定零件的沖壓工藝方案工藝。通過課題讓我們能夠掌握中等復雜程度零件的沖壓模具設計和制造的一般方法,對零件沖壓工藝方案的確定、工藝計算及模具設計有更深層次的認識,并學會對模具設計資料的檢索與整合以及對已有資料的充分合理的使用,該實踐性課題是對學生理論學習水平的實踐和檢驗,可對以后從事類似的工作有一定的指導性和實踐性意義。
二、研究的基本內容和擬解決的主要問題
本課題研究的主要內容
(1)對給定零件進行工藝分析并確定工藝方案
(2)模具總體結構設計及相關工藝計算
(3)進行模具零部件的設計
(4)繪制模具裝配圖和非標準件的零件圖
(5)編寫設計說明書
課題研究的主要內容
該零件的材料為20鋼,較軟的碳素鋼,強度硬度很低,而韌性較高,有好的深沖、彎曲等冷加工性能性能。且該零件形狀簡單,彎曲半徑大于材料允許的最小彎曲半徑,可以考慮采用復合沖壓的形式。該零件尺寸較小,因此加工精度較高,但一般沖壓都能滿足其尺寸精度的要求。綜合以上分析,得出的結論是:該零件工藝性能較好,適于沖壓。
1)方案對比
該工件包括落料、沖孔、彎曲三個基本工序可以采用以下三種工藝方案:
方案一:落料沖孔復合----彎曲--- ---彎曲;
方案二:落料沖孔復合—一次彎曲;
方案三:落料---彎曲---沖孔。
2)方案分析
方案一:該方案工序合理,步驟符合工件形狀要求,生產效率不高,模具的兩次彎曲操作復雜
方案二:該方案經計算可沖孔落料復合完成,且不會致使彎曲過程中孔變形、生產效率高,且易于操作
方案三:該方案在生產過程中需要三副模具,在后來工序中一步一步操作需要時間較多,且三副模具制作也不方便。
3)方案確定
比較上述三種工藝方案,方案二最佳。方案一、三均不能達到零件要求,
(1) 通過對工件的工藝分析,確定工作的重點主要集中在模具工作部分零件的設計(例凸模,凹模,凸凹模),各種固定板的設計和相關尺寸的計算和校核。
(2) 設計前后工序的關聯(lián)性以及模具的關聯(lián)性,合理安排工序,盡量使模具的結構更緊密,同時在模具的設計過程中還要考慮到所設計的零件的課加工性,要盡量多的選用標準件,達到規(guī)范化設計的要求成為此畢業(yè)設計的難點。
針對此次模具設計工作量大,工作難度大的特點,擬采用計算機輔助設計AutoCAD、UG等相關軟件來完成模具的設計,從而節(jié)省時間和精力;收集相關文獻、期刊論文來加以輔助設計;針對自身理論方面的不足將更多的向輔導老師請教學習;當然,子啊具體的設計中也要不斷的去實踐設計的模具的實用性與經濟性,使設計更趨于精確化,規(guī)范化,系統(tǒng)化。
三、研究方法及措施
(二)研究方法:?
1.文獻資料法:通過查閱和收集關于沖壓模具相關的文獻材料。?
2.問卷調查法和實地考察:通過到工廠實際了解加工工藝方式,掌握研究的第一手資料。?
3.數(shù)理統(tǒng)計法:對獲得的材料進行整理。?
(三)技術路線?
查閱及收集相關的文獻資料→實地走訪企業(yè)工廠→資料整理→撰寫論文
四、研究工作的步驟、進度
第一周 1、熟悉課題,查閱并收集有關資料,為寫開題報告做準備;
2、繪制產品零件圖;
3、完成工藝性分析,提出設計方案
4、寫出開題報告,并完成其修改
第二周 1、模具總體結構設計,及工藝結構計算
2、完成模具零件結構形式確定及設計,選擇設備
3、繪制模具裝配圖和非標準零件零件圖,
第三周 1、擬定主要零件的制造工藝
2、編寫畢業(yè)設計說明書,完成初稿并交與輔導老師指導
第四周 1、針對畢業(yè)設計所出現(xiàn)問題有目的的修改確定終稿
2、準備畢業(yè)答辯
五、主要參考文獻(其中外文文獻不少于2篇)
[1]劉建超、張寶忠 主編. 沖壓模具設計與制造[M]. 北京:高等教育出版社,2010
[2]夏琴香主編. 沖壓成形工藝及模具設計[M].廣州:華南理工大學出版社,2004
[3]吳詩惇,李淼泉. 沖壓工藝及模具設計[M].西安:西北工業(yè)大學出版社,2002
[4]沖模設計手冊編寫組.沖模設計手冊[M].機械工業(yè)出版社,1999.6
[5]王孝培主編. 沖壓設計資料[M] . 北京:機械工業(yè)出版社,1983
[6]李天佑主編. 沖模圖冊[M]. 北京:機械工業(yè)出版社,1990
[7]盧險峰編著.沖壓工藝模具學[M].北京:機械工業(yè)出版社,2003
[8]陳文彬,塑性成形工藝與模具設計[M],北京,機械工業(yè)出版社,2001
[9]陳錦昌.計算機工程制圖[M].廣州:華南理工大學出版社,2004
[10]鐘翔山.冷沖模設計案例剖析[M].北京:機械工業(yè)出版社,2009.
[11]二代龍震工作室.沖壓模具基礎教程[M].北京:清華大學出版社,2010
[12]張正修.沖模結構設計方法、要點及實例[M].北京:機械工業(yè)出版社,2007
[13]鄧明,呂琳.沖壓成形工藝及模具[M].北京:化學工業(yè)出版社,2007.
[14]王鵬駒,成虹.沖壓模具設計師手冊[M].北京:機械工業(yè)出版社2009.
[15]牟林,胡建華.沖壓工藝及模具設計[M].北京:中國林業(yè)出版社,2006,
[16]??Rajput?R?K.?Elements?of?Mechanical?Engineering.Katson?
Publ.House,1985
? [17]?Wang,?C.T.?An?Industrial?Outlook?for?Springback?Predictability,?Measurement?Reliability,
?and?Compensation?Technology,?Proc.?Numisheet?2002,?Oct.?21-25,?200,?Jeju?Island,?Koera?
[18]?R.D.JiangB.T.Lauw?,?A.Y.C.Nee?.?Insert?design?automation?for?progressive?dies?.?
Singapore:?Institute?of?High?Performance?Computing?,2004.06
六、導師評語:
簽字: 年 月 日
外文翻譯
專 業(yè) 名 稱 機械設計制造及其自動化
班 級 學 號 078105232
學 生 姓 名 冼 振 源
指 導 教 師 陳 為 國
填 表 日 期 2011 年 1 月 17 日
General all-steel punching die’s punching accuracy
Accuracy of panel punching part is display the press accuracy of the die exactly. But the accuracy of any punching parts’ linear dimension and positional accuracy almost depend on the blanking and blanking accuracy,. So that the compound mould of compound punching’s accuracy, is typicalness and representation in the majority.
Analyse of the die’s accuracy
For the analyse of pracyicable inaccuracy during production of dies to inactivation, we could get the tendency when it is augmentation in most time. From this we could analyse the elements. When the new punch dies pt into production to the first cutter grinding, the inaccuracy produced called initial error; if the die grinding more than twenty times, until it’s discard, the inaccuracy called conventional error; and before the dies discard, the largest error of the last batch permit, called limiting error. at job site, the evidence to confirm life of sharpening is the higher of the blanking, punched hole or punched parts. Because all finished parts had been blanked ,so it is especially for the compound dies. Therefore, the analyse of burr and measurement is especially important when do them as enterprise standardization or checked with <>.
The initial error usually is the minimal through the whole life of die. Its magnitude depend on the accuracy of manufacture, quality, measure of the punching part, thickness of panel, magnitude of gap and degree of homogeneity. The accuracy of manufacture depend on the manufacture process. For the 1 mm thicked compound punching part made in medium steel, the experimental result and productive practice all prove that the burr of dies which produced by spark cutting are higher 25%~~30% than produced by grinder ,NC or CNC. The reason is that not only the latter have more exact machining accuracy but also the value of roughness Ra is less one order than the formmer, it can be reached 0.025μm. Therefore, the die’s initial blanked accuracy depends on the accuracy of manufacture, quality and so on.
The normal error of the punch die is the practicable error when the fist cutter grinding and the last cutter grinding before the die produce the last qualified product. As the increase of cutter grinding, caused the measure the nature wear of the dies are gradual increasing, the error of punching part increase also, so the parts are blew proof. And the die will be unused. The hole on the part and inner because the measure of wear will be small and small gradually, and its outside form will be lager in the same reason. Therefore, the hole and inner form in the part will be made mould according to one-way positive deviation or nearly equal to the limit max measure. In like manner, the punching part’s appearance will be made mould according to one-way negative deviation or nearly equal to limit mini measure. For this will be broaden the normal error, and the cutter grinding times will be increased, the life will be long.
The limit error in punching parts are the max dimension error which practicable allowed in the parts with limit error. This kind of parts usually are the last qualified products before the die discard.
For the all classes of dies, if we analyse the fluctuate, tendency of increase and decrease and law which appeared in the die’s whole life, we will find that the master of the error are changeless; the error that because the abrade of the cutter and impression will be as the cutter grinding times increased at the same time. And that will cause the error oversize gradually; and also have another part error are unconventional , unforeseen. Therefore, every die’ s error are composed of fixed error, system error, accident error and so on.
1. fixed error
At the whole process when the New punching die between just input production to discard, the changeless master error that in qualified part are called fixed error. It’s magnitude is the deviation when the die production qualified products before the first cutter grinding. Also is the initial error, but the die have initial punching accuracy at this time. Because of the abrade of parts, the die after grinding will be change the dimension error. And the increment of deviation will oversize as the times of cutter grinding. So the punching accuracy after cutter grinding also called “grinding accuracy” and lower tan initial accuracy. The fixed error depend on the elements factor as followed :
(1) the material , sorts, structure, (form) dimension, and thick of panel
the magnitude of punching gap and degree of homogeneity are have a important effect for the dimension accuracy. Different punching process, material, thick of panel, have completely different gap and punching accuracy. A gear H62 which made in yellow brass with the same mode number m=0.34, 2mm thick and had a center hole, when the gap get C=0.5%t (single edge) , and punched with compound punching die, and the dimension accuracy reached IT7, the part have a flat surface ,the verticality of tangent plane reached 89.5°, its roughness Ra magnitude are 12.5μm, height of burr are 0.10mm; and the punching part are punched with progressive die, the gap C=7%t (single edge) , initial accuracy are IT11, and have an more rough surface, even can see the gap with eyes. In the usual situation, flushes a material and its thickness t is theselection punching gap main basis. Once the designation gap haddetermined flushes the plane size the fixed error main body; Flushesthe structure rigidity and the three-dimensional shape affects itsshape position precision.
(2) punching craft and molder structure type
Uses the different ramming craft, flushes a precision and the fixederror difference is really big. Except that the above piece gearexample showed, the essence flushes the craft and ordinary punching flushes a precision and the fixed error differs outside a magnitude,even if in ordinary punching center, uses the different gap punching, thefixed error difference very is also big. For example material thickt=1.5mm H62 brass punching, selects C <= the 40%t unilateral I kind ofsmall gap punching compared to select C <= 8%t (unilaterally) III kindof big gap punching, will flush a fixed error to enlarge 40% ~ 60%, theprecision at least will fall a level. Side in addition, whether thereis picks builds a row of type side, flushes a error to have far to bebigger than has builds a row of type to flush. Side not builds a rowof type to flush. Side not builds a row of type to flush a precisionto be lower than the IT12 level side, but most has builds a row oftype to flush a precision in IT11 between ~ IT9 level, material thickt > 4mm flushes, the size precision can lower some. Different die’s structure type, because is suitable the rammingmaterial to be thick and the manufacture precision difference, causesto flush a fixed error to have leaves. Compound die center, multi-locations continuous type compound die because flushes continuously toduplicate the localization to add on the pattern making error to bebigger, therefore it flushes a fixed error compound punching die to wantcompared to the single location Big 1 ~ 2 levels
(3) the craft of punching die’s manufacture
the main work of punching die namely are raised, the concave moldprocessing procedure, to operates on the specification not to behigh, can time form a more complex cavity. But its processing surfaceapproximately is thick > 0.03 ~ 0.05mm is the high temperatureablation remaining furcated austenite organization, degree ofhardness may reach as high as HRC67 ~ 70, has the micro crack, easilywhen punching appears broke the cutter or flaking. The Italian CorradaCorporation''s related memoir called "the line cut the processing contruction to have the disadvantageous influence to the superficialgold, in fact already changed the gold contruction. We must use theJin''gang stone powder to grind or the numerical control continual pathcoordinates rub truncate (cut to line) to make the precision work ". In recent years country and so on Switzerland and Japan, has conductedthe thorough research to the electrical finishing equipment and abigger improvement, makes function complete high accuracy NC and theCNC line cutter, the processing precision may reach ±0.005 ~ 0.001mm,even is smaller. The processing surface roughness Ra value can achieve0.4 mu m. According to the recent years to the domestic 12 productionlines cutter factory investigation and study, the domesticallyproduced line cutter processing precision different factory differentmodel line cutter might reach ±0.008 ~ ±0.005mm, generally all in±0.01mm or bigger somewhat, was individual also can achieve±0.005mm, the processing surface roughness Ra value was bigger than1.6μm. However, the electrical finishing ablation metal surface thus the change and the damage machined surface mental structure character can not change, only if with rubs truncates or other ways removes this harmful level. Therefore, merely uses electricity machining, including the spark cutting and the electricity perforation, achieves with difficulty punching, especially high accuracy, high life punching die to size precision and work components surface roughness Ra value request.
With precisely rubs truncates the law manufacture punching die, specially makes the high accuracy, the high life punching die, such as: Thin material small gap compound punching die, multi- locations continuous type compound die and so on, has the size precision high, the work component smachined surface roughness Ra value is small, the mold life higher characteristic. Its processing craft at present changed the electrical fire by the past ordinary engine bed rough machining spark cutting or the electricity puncher rough machining, finally precisely rubs truncates, also from takes shape rubs, optics curve rubs, the manual grid reference rubs gradually filters the continual path grid reference to rub and NC and the CNC continual path grid reference rubs, Processing coarseness may reach ±0.001 ~ 0.0005mm, the processing surface roughness Ra value may reach 0.1 ~ 0.025 mu m. Therefore, with this craft manufacture the die , regardless of the size precision, the work components surface roughness, all can satisfy die, each kind of compound request, the die is especially higher than the electrical finishing craft manufacture scale.
(4) gap size and degree of homogeneity
the flange and other sheet forming sgene rally all must first punching (fall material) the plate to launch the semi finished materials, after also has the forming to fall the material, the incision obtains the single end product to flush. Therefore punching the work, including is commonly used punching hole, the margin, cut side and so on, regarding each kind of sheet pressing partall is necessary. Therefore punching the gap to flushes a out form in chprecision to have the decisive influence. punching the gap small and is even, may cause punching the size gain high accuracy. Regarding drawability, is curving and so on mould, the gap greatly will decide increases flushes the oral area size error and the snapping back. The gapnon-uniformity can cause to flush a burr enlarges and incurs cutting edge the non-uniform attrition.
(5) ramming equipment elastic deformation In the ramming process
After the punch press load bearing can have the certain elastic deformation. Although this kind of distortion quantity according to flushes the pressure the size to change also to have the obvious directivity, but on the pressing part, mainly is to has the volume ramming archery target stamping, embosses, the equalization, the pressure is raised, the wave, flushes crowds, the shape, the flange, hits flatly, thinly changes draw ability and so on the craft work punching forming flushes, has the significant influence to its ramming aspect size precision
普通全鋼沖模的沖壓精度分析
板料沖壓件的精度準確顯示出其沖模的沖壓精度。而任何沖件的線性尺寸精度與形位精度主要取決于沖模沖裁和立體成形沖壓件展開平毛坯的落料精度。因此,多工步復合沖壓的單工位復合模、多工位連續(xù)模的沖壓精度,在普通沖壓的眾多種類與不同結構的沖模中,最具典型性和代表性。
沖模的沖壓精度分析
對沖模投產至失效報廢各個時期沖件的實際誤差分析,可以看出其增大的時期及趨向,從而分析其增大的因素。新沖模投產至第一次刃磨前沖制沖件的誤差即所謂的初始誤差;沖模經過20次左右刃磨至失效報廢前沖制的沖件誤差稱之為常規(guī)誤差;而沖模失效報廢前沖制的最后一批合格沖件的允許最大誤差稱之為極限誤差。在現(xiàn)場,確定沖模刃磨壽命的依據(jù)是沖件沖孔與落料的毛刺高度。由于任何成形件都具有沖裁作業(yè)(毛坯落料或沖孔),對于復合模尤為如此。所以,沖件毛刺高度的觸模檢查和測量并按企業(yè)標準或JB4129-85《沖壓件毛刺高度》對照檢測就顯得十分重要。
沖模的初始誤差通常是沖模整個壽命中沖件誤差最小的。其大小主要取決于沖模的制造精度與質量及沖件尺寸、料厚以及間隙值大小與均勻度。沖模的制造精度及質量又取決于制模工藝。對于料厚t≤1mm的中碳鋼復合沖裁模沖件,實驗結果與生產實踐都證明,電火花線切割制造的沖模沖件毛刺高度比用成型磨或NC與CNC連續(xù)軌跡座標磨即精密磨削工藝制造的沖模沖件要高25%~30%。這是因為后者不僅加工精度高,而且加工面粗糙度Ra值要比前者小一個數(shù)量級,可達到0.025μm。因此,沖模的制造精度與質量等因素決定了沖模的初始沖壓精度,也造就了沖件的初始誤差。
沖件的常規(guī)誤差是沖模經第一次刃磨到最后一次刃磨后沖出最后一個合格沖件為止,沖件實際具有的誤差。隨著刃磨次數(shù)的增加,刃口的自然磨損而造成的尺寸增量逐漸加大,沖件的誤差也隨之加大。當其誤差超過極限偏差時,沖件就不合格,沖模也就失效報廢。///////沖件上孔與內形因凸模磨損尺寸會逐漸變?。黄渫庑温淞铣叽鐣虬寄Dp而逐漸增大。所以,沖件上孔與內形按單向正偏差標允差并依接近或幾乎等于極限最大尺寸制模。同理,沖件外形落料按單向負偏差標注允差并依接近或幾乎等于極限最小尺寸制模。這樣就使沖件的常規(guī)誤差范圍擴大,沖??扇心ゴ螖?shù)增加,模具壽命提高。
沖件的極限誤差是具有極限偏差的沖件所具有的實際允許的最大尺寸誤差。這類沖件通常是在沖模失效報廢前沖制的最后一批合格沖件。
對各類沖模沖件誤差在沖模整個壽命中出現(xiàn)的波動、增減趨向及規(guī)律等進行全面分析便可發(fā)現(xiàn):沖件誤差的主導部分是不變的;因刃口或型腔的自然磨損而出現(xiàn)的誤差增量隨沖模刃磨沖數(shù)增加而使這部分誤差逐漸加大;還有部分誤差的增量是非常規(guī)的、不可預見的。所以,各類沖模沖件誤差是由因定誤差、漸增誤差、系統(tǒng)誤差及偶發(fā)誤差等幾部分綜合構成。
1、固定誤差
新沖模在指定的沖壓設備上投入使用至失效報廢的整個(總)壽命過程中,其合格沖件誤差的主導部分固定不變即所謂固定誤差。其大小就是新沖模第一次刃磨前沖制的合格沖件的偏差,也即沖模的初始誤差,而此時的沖模具有初始沖壓精度。刃磨后的沖模,因其工作零件(凸、凹模)磨損而改變尺寸誤差,使沖件識差增量隨刃磨次數(shù)增加而逐漸加大,故沖模刃磨后的沖壓精度亦稱“刃磨精度”比其初始精度要低。沖模沖件的固定誤差取決于以下各要素:
(1)沖件的材料種類、結構(形狀)尺寸及料厚
沖裁間隙的大小及其均勻度對沖裁件的尺寸精度有決定性的影響。不同沖裁工藝、不同材料種類與不等料厚,間隙相差懸殊,沖壓精度差異很大。同一種模數(shù)m=0.34的2mm的料厚、中心有孔的H62黃銅材料片齒輪復合模沖件,當取間隙C=0.5%t(單邊),用復合精沖模沖制,沖件尺寸精度達到IT7級,沖件平直無拱彎,沖切面垂直度可達89.5°,其表面粗糙Ra值為0.2μm;而用普通復合模沖制,間隙C=5%t(單邊),沖件初始誤差亦即沖模的初始沖壓精度為1T9級,沖切面粗糙度Ra值為12.5μm,毛刺高度為0.10mm;還是這個沖件用連續(xù)模沖制,間隙C=7%t(單邊),初始沖件精度為IT11級,沖切面更粗糙,甚至有肉眼可見的臺階。通常情況下,沖件材料及其厚度t是選取沖裁間隙的主要依據(jù)。一旦選定間隙就確定了沖件的平面尺寸的固定誤差的主體;沖件結構剛度及立體形狀則影響其形位精度。
(2)沖壓工藝及沖模結構類型
采用不同的沖壓工藝,沖件的精度及固定誤差相差甚大。除上述片齒輪實例說明,精沖工藝與普通沖裁的沖件精度與固定誤差相差一個數(shù)量級之外,即便在普通沖裁中,采用不同間隙沖裁,固定誤差相差也很大。例如料厚t=1.5mm的H62黃銅沖裁件,選用C≤40%t單邊Ⅰ類小間隙沖裁比選用C≤8%t(單邊)Ⅲ類大間隙沖裁,沖件固定誤差將加大40%~60%,精度至少降一級。此外,采有無搭邊排樣,沖件的誤差要遠大于有搭邊排樣沖件。無搭邊排樣沖件。無搭邊排樣沖件的精度低于IT12級,而多數(shù)有搭邊排樣的沖件精度在IT11~IT9級之間,料厚t>4mm的沖件,尺寸精度會更低一些。
不同沖模結構類型,由于適用沖壓料厚及制造精度的差異,導致沖件的固定誤差有別。復合模中,多工位連續(xù)式復合模由于沖件連續(xù)重復定位加上制模誤差較大,故其沖件的固定誤差比單工位復合沖裁模要
大1~2級。
(3)沖模制造工藝
沖模主要工作零件即凸、凹模的加工程序,對操作上的技術要求不高,能夠一次成形較復雜的模腔。但其加工表面約厚>0.03~0.05mm為高溫燒蝕的殘余樹枝狀奧氏體組織,硬度可高達HRC67~70,有顯微裂紋,容易在沖裁時出現(xiàn)崩刃或剝落。意大利Corrada公司的有關研究報告稱“線切割加工對表面金相結構產生不利的影響,實際上已經改變了金相結構。我們必須用金剛石粉研磨或數(shù)控連續(xù)軌跡坐標磨削(對線切割件)作精加工”。近年來瑞士和日本等國,對電加工設備進行了深入的研究和較大的改進,制造出功能齊全的高精度NC和CNC線切割機,加工精度可達±0.005~0.001mm,甚至更小。加工表面粗糙度Ra值能達到0.4μm。根據(jù)近年對國內12家生產線切割機工廠的調研,國產線切割機加工精度各別廠家的各別型號線切割機可達±0.008~±0.005mm,一般都在±0.01mm或更大一些,個別也能達到±0.005mm,加工表面粗糙度Ra值均大于1.6μm。然而,電加工燒蝕金屬表面從而改變和損壞加工面金相結構的特性不會改變,除非用磨削或其他加工法去除這一有害層。所以,僅僅用電加工法,包括電火花線切割與電穿孔,難以達到沖模,尤其高精度、高壽命沖模對尺寸精度與工作零件表面粗糙度Ra值要求。
用精密磨削法制造沖模,特別是制造高精度、高壽命沖模,諸如:薄料小間隙復合沖裁模、多工位連續(xù)式復合模等,具有尺寸精度高、工作零件加工面粗糙度Ra值小、模具壽命高等特點。其加工工藝目前已由過去的普通機床粗加工改為電火花線切割或電穿孔機粗加工,最后精密磨削,也由成型磨、光學曲線磨、手動座標磨逐步過濾到連續(xù)軌跡座標磨及NC與CNC連續(xù)軌跡座標磨,加工粗度可達±0.001~0.0005mm,加工表面粗糙度Ra值可達0.1~0.025μm。所以,用該工藝制造的沖模,無論尺寸精度、工作零件表面粗糙度,都能滿足沖模,尤其各種復合模的要求,比電加工工藝制造的沖模高一個檔次。
(4)間隙的大小與均勻度
拉深、彎曲、翻邊及其他板料成形件一般都要先沖裁(落料)出平板展開毛坯,也有成形后落料、切開得到單個成品沖件。故沖裁作業(yè),包括常用的沖孔、切口、切邊等,對于每種板料沖壓件都是必要的。所以沖裁間隙對沖件的外廓尺寸精度有決定性的影響。沖裁間隙小而均勻,可使沖裁尺寸獲取更高精度。對于拉深、彎曲等成形模,間隙大定將增大沖件口部尺寸誤差及回彈。間隙不均勻會使沖件毛刺加大并招致刃口的不均勻磨損。
(5)沖壓設備的彈性變形
在沖壓過程中,沖床承載后會產生一定的彈性變形。雖然這種變形量依沖壓力的大小變化且具有明顯的方向性,但就沖壓件,主要是對具有體積沖壓性質的壓印、壓花、校平、壓凸、起波、沖擠、鐓形、翻邊、鐓粗、打扁、變薄拉深等工藝作業(yè)沖制成形的沖件,對其沖壓方面的尺寸精度有重大影響。
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