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防止活塞銷冷擠壓工藝中出現(xiàn)流動缺陷的新方法
D.J.Lee ,D.J.Kim, B.M.Kim
精密機(jī)械工程系，研究生院，釜山國家大學(xué)，釜山，韓國
機(jī)械設(shè)計工程部門，研究生院，釜山國家大學(xué)，釜山，韓國
機(jī)械工程系，工程研究中心，釜山國家大學(xué)，釜山，韓國編號3
Janjeon-董，Kumjeong-顧，釜山609-735，韓國
摘要：
這份報告主要研究的是作為汽車零部件之一的活塞銷的流動缺陷。在聯(lián)合冷擠壓制活塞銷的工藝中，起皺就是一種流動缺陷，它是由死金屬區(qū)引起的。具有這種缺陷的部件帶有很明顯的外部特征，特征是被一微小而且厚的塊狀物嵌入材料中，這種缺陷對保證尺寸精度和降低材料損失是不利的，活塞銷的這種缺陷對于其強(qiáng)度和疲勞壽命也有不利的影響。因此，在工藝設(shè)計的早期預(yù)測并防止這種缺陷是非常重要的。防止其產(chǎn)生的最好方法就是通過控制材料流動來限制或減少死金屬區(qū)。有限元模擬分析方法被應(yīng)用于流動缺陷研究分析當(dāng)中，這份研究報告提出了通過去除死金屬區(qū)防止產(chǎn)生流動缺陷的新工藝方法——有限元分析法。將有限元分析的結(jié)果與實(shí)驗(yàn)結(jié)果做比較，結(jié)果表明有限元分析的結(jié)果與實(shí)驗(yàn)結(jié)果相符合。
關(guān)鍵詞：
流動缺陷；活塞銷釘；材料流動控制；前后雙向冷擠壓；死金屬區(qū)；有限元分析
1、序言
冷加工是一種及其重要而且經(jīng)濟(jì)的加工方法，尤其對于大批量制件的加工，其優(yōu)點(diǎn)更為突出。由于冷加工具有高的成品率、精確的尺寸精度、良好的表面光潔度，優(yōu)良的機(jī)械加工性和冶金工藝性等優(yōu)點(diǎn)，因此冷加工是工業(yè)生產(chǎn)當(dāng)中應(yīng)用最為廣泛的零件加工工藝。
冷鍛制件廣泛應(yīng)用于飛機(jī)制造、摩托車、螺母和螺栓等生產(chǎn)制造。但是，冷鍛制件也有可能產(chǎn)生缺陷，這主要取決于金屬材料的變形過程、成形加工的外部條件和材料的流動方式等?？裳由斓牧鸭y缺陷是由材料的引應(yīng)力狀態(tài)和變形過程引起的；流動缺陷是由不穩(wěn)定的材料流動引起的；低的尺寸精度是由低的模具尺寸精度和摩擦情況引起的，總之，鍛壓制件的缺陷主要包括兩類，分別是內(nèi)部缺陷和外部缺陷。
這些缺陷危害到產(chǎn)品的質(zhì)量和制造成本，因此，在工藝設(shè)計中的早期預(yù)防是非常重要的。利用有限元分析法中的不同可用標(biāo)準(zhǔn)來研究大型鍛件的可延伸裂紋缺陷。KIM和KIM對兩道加強(qiáng)筋進(jìn)行冷擠壓件的內(nèi)部和外部缺陷研究，并還在進(jìn)行一種防止產(chǎn)生這些缺陷的加工工藝設(shè)計。
這份報告是一份關(guān)于汽車活塞銷產(chǎn)生的缺陷的測試報告，而這種活塞銷是采用前后雙向聯(lián)合擠壓的方式支撐的。這份報告中也提出了新的工藝方法可在工藝設(shè)計的早期防止產(chǎn)生流動缺陷，而這些新工藝方案是通過有限元分析研究得出的，實(shí)驗(yàn)證明，這些新工藝方案是可行的。
2、成形工藝與缺陷形成分析
2.1、成形工藝
活塞銷是汽車零部件當(dāng)中用來連接活塞與曲軸的并傳遞動力的部件，當(dāng)采用冷沖壓制活塞銷時，設(shè)計要求必須保證前后雙向沖壓時具有相同的高度并且不能出現(xiàn)鍛壓缺陷，因?yàn)榛钊N在周期性大載荷作用下工作。制作活塞銷的材料是AISI-4135H合金鋼，它具有如下材料流動性 σ＝768.06*ε0.139 ，潤滑措施是采用潤滑油類的磷鍍在活塞銷表面進(jìn)行潤滑，經(jīng)試驗(yàn)測試摩擦系數(shù)M為0.1。
加工活塞銷釘以前用的是多步驟加工法（如圖3所示），前兩步通過導(dǎo)圓角和沖出非圓形的基準(zhǔn)孔等預(yù)處理工序來減少缺陷的產(chǎn)生，從而可以提高尺寸精度和模具壽命，第三步和第四步相同，分別是從前后雙向沖出圓形的腹板，最后一步是修整工序，從而得到活塞銷的形狀，然而，用普通加工方法加工的結(jié)果顯示：第三步的早期會在腹板部位形成缺陷，更嚴(yán)重的是在缺陷產(chǎn)生的部位出現(xiàn)了一種不一致的流動形式，這種形式是一種非常壞的流動形式的延伸
圖1 活塞銷釘?shù)男螤詈统叽? 圖2 活塞銷釘?shù)牧鲃尤毕?
圖3活塞銷釘傳統(tǒng)的形成過程
2.2用有限元分析預(yù)測缺陷的產(chǎn)生
塑性變形組織分布和有效應(yīng)力對比圖的應(yīng)用，暗示著有限元精密塑造程序在成形與缺陷分析領(lǐng)域中的商業(yè)價值。最初的坯料直徑為30mm，深度為61mm，最終成品的體積為43.118，這種成形工藝看上去類似于普通加工結(jié)果。
最大的裂縫值可以結(jié)算出斷裂缺陷產(chǎn)生的可能性，在這個沖壓過程中，其大小只有0.08mm，而且分布在坯料和沖床活塞沖頭接觸的端部。因此，可以避免流動缺陷的產(chǎn)生，因此這種缺陷并不能產(chǎn)生可延展的裂紋。金屬流動的流線圖是由Altan和Knoerr提出的，他們正在從事這種缺陷的分析研究，隨著沖頭沖壓深度的增加，劇烈變動的流線出現(xiàn)了不同的流動速度，從而導(dǎo)致實(shí)驗(yàn)中缺陷的產(chǎn)生（如圖5所示）。
所以金屬流動只出現(xiàn)在第四步的反向沖壓而不出現(xiàn)在正向沖壓，并且在靠近腹板處的金屬被拔起形成一條筋，很像是重疊缺陷，因此，活塞銷的流動缺陷產(chǎn)生并發(fā)展的原因是：正反沖壓時由于死金屬區(qū)域產(chǎn)生而造成的金屬流動速度的不同，這種現(xiàn)象在像活塞銷這種薄壁件沖出尺寸精度高，材料損耗少的孔的制件中是非常明顯的。對于活塞銷這類工作溫度高，載荷大而且為交變載荷的零件來說，這種流動缺陷的產(chǎn)生會對其強(qiáng)度和疲勞壽命產(chǎn)生有害的影響。因此，有必要研究一種新工藝來防止產(chǎn)生流動缺陷。
圖4有效的負(fù)荷和裂縫價值的關(guān)系
圖5金屬流動和速度的關(guān)系
3.防止缺陷的工藝分析與設(shè)計
流動缺陷產(chǎn)生的原因是金屬限制死金屬區(qū)域的流動。為了在傳統(tǒng)工藝中早期的沖壓部位(第三步)消除死金屬區(qū)，正沖壓或反沖壓工藝被改為聯(lián)合正反沖壓工藝，這種工藝在兩個完全相反的方向上同時進(jìn)行同樣地動作。由于正反兩向不同的沖壓率和沖壓長度，要使兩個方向上同時完成材料流動是很困難的，因此在提前完成材料流動就會出現(xiàn)傳統(tǒng)工藝一樣出現(xiàn)的死金屬區(qū)。
因此，在活塞銷成形這種情況下，兩個方向的沖壓率和沖壓長度都是1.89和51mm。目前，一項關(guān)于活塞銷的沖壓長度的調(diào)查研究正在進(jìn)行開模正反沖壓工藝的分析，兩個方向上的沖壓長度是不同的，正向沖壓長度長為24.9mm，反向沖壓長度如圖6所示要比正向的短。
反向金屬流動必須強(qiáng)制性的被限制才能滿足設(shè)計要求，而這就意為著死金屬區(qū)會產(chǎn)生。因此，要想在兩個方向上得到相同的沖壓長度，提出了三種控制金屬流動的方法，這三種方法都不同程度的強(qiáng)制限制金屬流動。
圖6反向沖壓長度
3.1 改變初加工的形狀
在正反雙向沖壓之前，為了保證從腹板中心處起正反兩個方向的沖壓長度相等，就得要求初加工要將反向沖壓筋的長度設(shè)計與雙向沖壓長度24.9mm有所不同。圖7展示了這種改進(jìn)的工藝的結(jié)果，圖8展示了在這種情況下采用正反雙向沖壓工藝時最后一步中金屬的流動。從模擬實(shí)驗(yàn)的結(jié)果可以得出，兩個方向的沖壓筋的長度都是51mm，這恰好滿足設(shè)計要求和活塞銷的尺寸要求。另外，死金屬區(qū)的金屬流動形式相同，而不像采用普通加工時會產(chǎn)生流動缺陷，而且在兩個方向上的流動速度也是連續(xù)變化的，這就意為著金屬流動在整個過程中是一致的，不會出現(xiàn)限制其流動的死金屬區(qū)。
圖七 多級樣板的修改過程 圖八金屬網(wǎng)的流動
3.2 驅(qū)動沖壓模膛
驅(qū)動模膛工藝被用來控制金屬流動從而滿足設(shè)計要求，這種設(shè)備采用向相反方向運(yùn)動的模膛先與已經(jīng)沖壓成形的一側(cè)接觸（如圖9所示），這樣就有助于加快后沖壓方向上的金屬流動而減慢先沖壓方向上的金屬流動速度，采用這種工藝制作的活塞銷，由于反方向沖壓提前完成，而此時活塞正沿著這個方向移動從而增加了金屬沿著這個方向的流動，這個工藝的首要變化因素是沖頭與活塞的相對速率和金屬材料與活塞之間的摩擦條件。
在這個研究中，由于摩擦系數(shù)m＝0.1（在毛胚材料和模膛之間），模擬實(shí)驗(yàn)只與相對速率這一變量有關(guān)。如果相對速率小于滿足同時成型最合適的速率，則在反向方向上的沖壓過程就會比正向沖壓提前完成，這樣的話就會像采用普通加工一樣在相同部位產(chǎn)生流動缺陷，相反，如果相對速率大于最適宜的速率，則正向沖壓過程就會比反向沖壓過程提前完成，這樣就會在相反地部位產(chǎn)生缺陷。
因此，為了滿足設(shè)計要求，采用半分法可以找出最佳的相對速率，從結(jié)果來看，最佳的相對速率是0.48，圖10和11顯示了相對速率分別為0.1 、0.48、1.0時采用一次沖壓變形過程和金屬流動情況。圖11（c）顯示了當(dāng)采用最佳相對速率0.48時的金屬流動形式，它記錄了一個可以防止缺陷產(chǎn)生的流動形式。
圖9軸向移動的箱體示意圖
圖10根據(jù)相對速度比率變化的活塞銷釘形態(tài)
圖11根據(jù)相對速度比率比較的金屬
3.3 修改模具結(jié)構(gòu)
這種被提出的修改模具結(jié)構(gòu)的工藝可以限制金屬在反方向上的流動，而在這個方向上容易提前完成變形，從而可以實(shí)現(xiàn)在兩個方向上同時完成變形，采用這種工藝時，為了能在兩個方向上同時完成變形過程而得到相同的變形長度，卸料器又被設(shè)計者重新采用，它是一種使沖頭從制件中抽出的裝置。如果采用普通加工工藝中的固定式卸料器，則由于材料流動受到限制，會出現(xiàn)死金屬區(qū)，而此時產(chǎn)生的部位與采用雙向沖壓時產(chǎn)生在中間位置不同。
因此，一種利用彈簧彈力的結(jié)構(gòu)可以推遲金屬材料沿反方向的流動。圖12顯示了這種模具結(jié)構(gòu)，采用這種方法，選用合適的彈簧彈力對于滿足變形同時完成的要求來講是很重要的，因而有限元模擬可以計算出這種必要地彈力。從模擬結(jié)果來看，需要給卸料器施加5噸的彈力。圖13展示了這種工藝下金屬流動形式，與其它改進(jìn)的工藝方法相比，這種工藝在死金屬區(qū)沒有出現(xiàn)不連續(xù)的流動速度，此處的金屬流動形式是相同的。
圖12使用沖壓模板的凹模模子結(jié)構(gòu)示意圖 圖13使用沖壓模板的金屬流動
4.結(jié)果和實(shí)驗(yàn)
通過有限元分析法分析出的三種方法中是適合防止金屬的流動缺陷。每個方法的情況如下。第一種方法是初步加工的產(chǎn)品需要三級過程(預(yù)制， 正反壓擠，穿孔)并且有一個簡單的模具結(jié)構(gòu)；第二方法是使用沿軸方向移動的沖孔模板；第三種方法是軸向移動的箱體需要二級過程(前后壓擠，穿孔)并且有一個復(fù)雜的模具結(jié)構(gòu)。關(guān)于在里面形成的負(fù)荷，這三個方法都非常相似。
特別是在沿軸方向移動的大約10噸的箱體情況下形成最大的負(fù)荷比其他方法小，因?yàn)樵诖┛走^程中沿軸方向移動的箱體會增加材料的流動。通過表1分析出的方法為形成做出了比較。在這項研究過程中，一個用在初步加工產(chǎn)品的實(shí)驗(yàn)被進(jìn)行，并且為了證實(shí)模擬結(jié)果所以使用一個250噸能力的多級樣板。在穿孔之前，為了金屬的觀察蝕刻流動能夠正常被進(jìn)行，所以必須為活塞銷做一個流動缺陷檢查。圖14就是表示這個實(shí)驗(yàn)結(jié)果，這種方法改變了初步加工的產(chǎn)品。實(shí)驗(yàn)結(jié)果證明了在缺陷區(qū)域內(nèi)金屬流動的缺陷是相同的，并且滿足形成同時完成和在兩個擠壓方向長度相同。這種過程和模擬的結(jié)果相符。
傳統(tǒng)方法
初步加工的產(chǎn)品的使用
沖壓模板的使用
移動箱體的用途
最大負(fù)荷（噸）
97.2
96.3
96.1
84.0
擠壓的過程
2個階段
2個階段
1個階段
1個階段
缺陷
存在
不存在
不存在
不存在
表1 各個方法的比較
圖14 對流動缺陷的消除
5.結(jié)論
在這項研究過程中，流動缺陷過程和預(yù)防缺陷的過程都已經(jīng)被有限元分析重新設(shè)計。，缺陷的原因已經(jīng)被分析，并且通過分析已經(jīng)模擬出了結(jié)果。從模擬結(jié)果中可以看出，有限元分析方法是可以防止流動缺陷并且滿足生產(chǎn)過程中控制材料的流動狀態(tài)。通過有限元分析的結(jié)果和實(shí)驗(yàn)的結(jié)果做比較，可以得出以下幾個結(jié)論：
（1）活塞銷里存在流動缺陷的原因是材料限制死金屬區(qū)域的流動。消除這個區(qū)域最重要的是控制材料的流動。
（2）初步加工的產(chǎn)品設(shè)計和改變模具結(jié)構(gòu)是使用軸向運(yùn)動的擠壓箱來消除擠壓過程中出現(xiàn)的流動缺陷。
（3）被提出的方法滿足了工藝的要求，向前擠壓的長度部分和落后的部分都是相同的，這些已經(jīng)由實(shí)驗(yàn)所證實(shí)。
參考文獻(xiàn)：
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[2] T. Okamoto，T. Fukuda，H. Hagita，Source Book on Cold Forming，ASTM，1997，pp. 216–226.
[3] S.W.Oh，T.H.Kim，B.M.Kim，J.C.Choi，KSME 19 (12) (1995) 3121–3129.
[4] R.C.Batra，N.V.Nechitailo，Int.J.Plast. 13 (4) (1997) 291–306.
[5] A.S. Wifi，A.Abdel-Hamid，N. El-Abbasi， J. Mater. Process. Technol.
77 (1998) 285–293.
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[7] D.C. Ko，Pusan National University Dissertation，1998.
[8] T. Altan，M. Knoerr，J. Mater. Process. Technol. 35 (1992) 275–302.
[9] K. Osakata，X. Wang，S. Hanami，J. Mater. Process. Technol. 71 (1997) 105–112.
10
學(xué)生實(shí)習(xí)報告
（限1500字以上）
院（系）：機(jī)械工程 專業(yè)：機(jī)械設(shè)計制造及其自動化 班級：0304姓名：葉明飛
一、實(shí)習(xí)的主要內(nèi)容
生產(chǎn)實(shí)習(xí)是機(jī)械類專業(yè)教學(xué)中的一項重要實(shí)踐環(huán)節(jié)。其目的是使學(xué)生了解和掌握本專業(yè)基本生產(chǎn)實(shí)際知識，培養(yǎng)學(xué)生理論聯(lián)系實(shí)際及初步的獨(dú)立工作能力，為后續(xù)有關(guān)課程的學(xué)習(xí)打下基礎(chǔ)。實(shí)習(xí)可分為兩個階段：第一階段為見習(xí)實(shí)習(xí)；第二階段為結(jié)合專業(yè)方向的生產(chǎn)實(shí)習(xí)。實(shí)習(xí)內(nèi)容是使學(xué)生接觸和了解機(jī)械制造的生產(chǎn)過程，學(xué)習(xí)到有關(guān)主要工種加工方法的基本知識，為學(xué)好金屬工藝學(xué)、機(jī)械制造基礎(chǔ)奠定必要的感性知識基礎(chǔ)，同時也為學(xué)習(xí)其他技術(shù)基礎(chǔ)課建立一些實(shí)踐基礎(chǔ)。
實(shí)習(xí)目的是使學(xué)生了解各類機(jī)械的運(yùn)轉(zhuǎn)和工作原理，并結(jié)合本專業(yè)的需要和目的，了解和觀察本專業(yè)涉及到的各類機(jī)械的組成結(jié)構(gòu)、運(yùn)轉(zhuǎn)機(jī)構(gòu)和工作原理以及生產(chǎn)過程，為課程設(shè)計和畢業(yè)設(shè)計打下基礎(chǔ)。結(jié)合專業(yè)方向的生產(chǎn)實(shí)習(xí)應(yīng)根據(jù)專業(yè)特點(diǎn)，有針對性的到一些工礦企業(yè)單位進(jìn)行。
2006年初我在衡陽冶金機(jī)械廠實(shí)習(xí)：
1參加由公司組織的理論知識的學(xué)習(xí)，由有經(jīng)驗(yàn)的領(lǐng)導(dǎo)、工程師授課，學(xué)習(xí)公司的文化、以及公司的發(fā)展前景、主要產(chǎn)品的生產(chǎn)流程和必要的技術(shù)要求以及一些改進(jìn)方向、公司必須保留和更新發(fā)展的技術(shù)核心等等。
2在有經(jīng)驗(yàn)的師傅的指導(dǎo)下，親自動手拆裝模具、維修模具以及學(xué)習(xí)模具的結(jié)構(gòu)組成以及工藝技術(shù)要求、模具的裝拆的方法和技巧、同時也要求設(shè)計一些簡單實(shí)用的模具，為以后設(shè)計或改進(jìn)大型模具做準(zhǔn)備。
3參加由公司有經(jīng)驗(yàn)的技術(shù)員指導(dǎo)的模具設(shè)計，學(xué)習(xí)如何根據(jù)模具的用途設(shè)計一些實(shí)用的模具，以及設(shè)計制造模具時應(yīng)該注意的主要問題和細(xì)節(jié)。
二、實(shí)習(xí)取得的經(jīng)驗(yàn)及收獲
畢業(yè)實(shí)習(xí)是一門專業(yè)實(shí)踐課，是機(jī)械類各專業(yè)學(xué)生學(xué)習(xí)了各門專業(yè)課程之后，在進(jìn)行畢業(yè)設(shè)計或畢業(yè)論文時必不可少的實(shí)踐教學(xué)環(huán)節(jié)。它對于培養(yǎng)我們的動手能力有很大的意義，而且可以使我們了解傳統(tǒng)的機(jī)械制造工藝和現(xiàn)代機(jī)械制造技術(shù)。我國現(xiàn)行的教育體制，使得通過高考而進(jìn)入大學(xué)的大學(xué)生的動手實(shí)踐能力比較薄弱。因此，處于學(xué)校和社會過渡階段的大學(xué)就承擔(dān)了培養(yǎng)學(xué)生實(shí)踐能力的任務(wù)。畢業(yè)實(shí)習(xí)就是培養(yǎng)學(xué)生實(shí)踐能力的有效途徑。通過實(shí)習(xí)掌握了模具的一些基本知識，如模具的組成結(jié)構(gòu)、如何根據(jù)用戶的需要去設(shè)計一些簡單的模具、在模具設(shè)計時的工藝、公差、粗造度、等如何選擇和應(yīng)用有了初步的理解。
我們機(jī)械制造及自動化專業(yè)所學(xué)習(xí)的重點(diǎn)在于各種機(jī)械成型設(shè)備，本次實(shí)習(xí)就是為了讓我們能夠?qū)τ谖覀兯鶎W(xué)過的各種儀器、設(shè)備有一個感性的直觀的認(rèn)識，從而把書本上的理論和現(xiàn)實(shí)中的傳統(tǒng)技術(shù)和已經(jīng)被應(yīng)用于實(shí)際的最新發(fā)展的高新技術(shù)聯(lián)系與結(jié)合起來，進(jìn)一步鞏固和深化所學(xué)的理論知識，彌補(bǔ)以前單一理論教學(xué)的不足,為后續(xù)專業(yè)課學(xué)習(xí)和畢業(yè)設(shè)計打好基礎(chǔ)。
三、存在的不足及建議
通過實(shí)習(xí)我本人感覺到還有很多不足的地方：
1、專業(yè)知識還不是很扎實(shí)，特別是公差方面的，為了讓設(shè)計出來的產(chǎn)品達(dá)到要求而一味的加大精度，給制造帶來了難度；
2、實(shí)際操作能力不夠，現(xiàn)在是技術(shù)更新的時候，公司都引進(jìn)了很多先進(jìn)的生產(chǎn)設(shè)備，但自己對這些高新設(shè)備束手無策；
3、初到公司缺乏工作經(jīng)驗(yàn)，很多的工作感到無從下手，沒有一個完整的頭緒，很難單獨(dú)去接受一個實(shí)際的課題。
通過實(shí)習(xí)我想對學(xué)校一點(diǎn)建議：
雖然自己只工作了兩個月，但還是感覺到了學(xué)校和公司之間有很大的差距。如果能縮小這種差距的話，對以后學(xué)校就業(yè)將有很大優(yōu)勢，更對學(xué)生能夠很快融入工作環(huán)境打下堅實(shí)的基礎(chǔ)。我就以過來人的身份建議學(xué)校能夠更加注重學(xué)生的實(shí)際動手能力，加強(qiáng)學(xué)生的實(shí)踐能力的培養(yǎng)，如增加學(xué)生的在校實(shí)習(xí)的機(jī)會和延長學(xué)生的實(shí)踐活動的時間，更加注重在老師的指導(dǎo)下讓學(xué)生真正的參與到實(shí)踐中去。畢業(yè)設(shè)計期間學(xué)校是否能考慮組織學(xué)生到生產(chǎn)現(xiàn)場去參觀實(shí)習(xí)，讓學(xué)生接受最為直接的設(shè)計基本知識，比憑空去設(shè)想更有效果。
畢業(yè)設(shè)計說明書
玻璃升降器復(fù)合拉伸模的設(shè)計
年 月 日
目 錄
第1章 前言 1
第2章 沖裁工藝設(shè)計 2
2.1 沖裁工藝計算 2
2.1.1 工藝力和功的計算 2
2.1.2 壓力機(jī)的選擇 4
2.2 模具總體設(shè)計 5
2.2.1 模具類型的確定 5
2.2.2 操作方式的確定 5
2.2.3 定位、聯(lián)接型式的確定 5
2.2.4 模具壓力中心的確定 6
2.2.5 模具精度的確定 6
2.2.6模具閉合高度的初定 6
2.3 定位裝置 6
2.4 卸料裝置 7
2.4.1 卸料裝置的選擇 8
2.4.2 彈性元件的設(shè)計 8
2.5 落料凹凸模的設(shè)計 9
2.5.1 凸模結(jié)構(gòu)的確定 9
2.5.2 凹模結(jié)構(gòu)確定 10
2.5.3 凹凸模工作部分尺寸設(shè)計 10
2.5.4 凸凹模工作表面技術(shù)要求 12
2.5.5 凸凹模材料 12
2.6 導(dǎo)向裝置 13
2.6.1 導(dǎo)向裝置的選擇 13
2.6.2 導(dǎo)向裝置尺寸確定 13
2.7 模具其它主要零部件的設(shè)計 14
2.7.1 板料定位裝置的設(shè)計 14
2.7.2螺栓和銷釘?shù)倪x用 15
第三章 工藝方案選擇 17
3.1 沖壓件的工藝確定 17
3.1.1 沖壓件的工藝分析 17
3.1.2 零件材料的分析 19
3.1.3 確定工藝方案和模具形式 20
3.1.4 落料尺寸的計算 22
3.2確定排樣方案 22
3.2.1確定排樣、裁板方案 22
3.3 計算拉深次數(shù) 25
2.4拉深沖壓力的計算 26
3.4.1落料過程 26
3.4.2、拉深過程 27
3.4.3成型過程 28
3.5沖壓設(shè)備的選擇 29
3.6 分析比較和確定工藝方案 30
第四章 主要工藝參數(shù)的計算 36
4.1 確定各中間工序尺寸 36
4.2 計算各工序壓力，選用壓力機(jī) 37
第五章 模具設(shè)計 42
5.1 模具結(jié)構(gòu)形式選擇 42
5.2 卸料彈簧的選擇 42
5.3 模具工作部分尺寸和公差計算 43
5.4 模具其它零件的結(jié)構(gòu)尺寸計算 44
5.5 工作原理 45
第六章 沖壓工藝過程卡的編寫 47
結(jié) 論 49
致 謝 50
第1章 前言
現(xiàn)在許多轎車門窗玻璃的升降(關(guān)閉和開啟)已經(jīng)拋棄了搖把式的手動升降方式，一般都改用按鈕式的電動升降方式，即使用電動玻璃升降器來控制，也就是常說的“電動門窗”。轎車用的電動玻璃升降器多是由電動機(jī)、減速器、導(dǎo)繩、導(dǎo)向板、玻璃安裝托架等組成。因?qū)ЮK的材料或制作工藝方式不同，又分為繩輪式、軟軸式和塑料帶式三種電動玻璃升降器。前二種是用鋼絲繩做為導(dǎo)繩，后一種是用塑料帶做為導(dǎo)繩。
以普遍使用的繩輪式電動玻璃升降器為例，它是由電動機(jī)、減速器、鋼絲繩、導(dǎo)向板和玻璃安裝托架等零部件組成，安裝時門窗玻璃固定在玻璃安裝托架上，玻璃導(dǎo)向槽與鋼絲繩導(dǎo)向板平行。
開啟電動機(jī)，由電動機(jī)帶動減速器輸出動力，拉動鋼絲繩移動玻璃安裝托架，迫使門窗玻璃作上升或下降的直線運(yùn)動。而塑料帶式電動玻璃升降器的導(dǎo)繩采用塑料帶，帶上有孔，用來移動和定位塑料帶，控制門窗玻璃的升降。
電動玻璃升降器結(jié)構(gòu)的關(guān)鍵是電動機(jī)和減速器，這兩者是組裝成一體的，其中電動機(jī)采用可逆性永磁直流電動機(jī)，電動機(jī)內(nèi)有兩組繞向不同的磁場線圈，通過開關(guān)的控制可做正轉(zhuǎn)和反轉(zhuǎn)，也就是說可以控制門窗玻璃的上升或下降。
電動機(jī)是由雙聯(lián)開關(guān)按鈕控制，設(shè)有升、降、關(guān)等三個工作狀態(tài)，不操縱時開關(guān)自動停在“關(guān)”的位置上。操縱電路設(shè)有總開關(guān)（中央控制）和分開關(guān)，兩者線路并聯(lián)?？傞_關(guān)由駕車者，控制全部門窗玻璃的開閉，而各車門內(nèi)把手上的分開關(guān)由乘員分別控制各個門窗玻璃的開閉，操作十分便利。
電動機(jī)的質(zhì)量直接關(guān)系到電動玻璃升降器的正常工作，它一定要具有體積小、重量輕、防護(hù)等級高、噪聲低、電磁干擾小、運(yùn)行可靠等特點(diǎn)?，F(xiàn)代轎車已廣泛應(yīng)用微電子技術(shù)，電機(jī)工作會發(fā)射電磁波干擾其它電器件的工作；前幾年通用汽車公司一篇售后分析報告顯示，近40%的電動玻璃升降器故障是由電動機(jī)密封性差引起的。因此，減少電磁干擾和解決電機(jī)密封性問題巳成為近年汽車電機(jī)技術(shù)的熱門話題。
90年代中期以來，電動玻璃升降器的控制機(jī)構(gòu)技術(shù)發(fā)展很快，電子模塊控制形式大量應(yīng)用于批量裝車，并設(shè)有安全保護(hù)裝置。例如博世公司生產(chǎn)的電動玻璃升降器系統(tǒng)，在電動機(jī)中埋植磁環(huán)，感應(yīng)電機(jī)轉(zhuǎn)速，在電子模塊中埋植霍爾元件，感應(yīng)電流，并通過電子模塊控制對電動機(jī)的過流、過壓及過熱保護(hù)，而且當(dāng)玻璃上升途中遇到人力障礙時會自動識別而反向運(yùn)行，防止乘員夾傷。
1
第2章 沖裁工藝設(shè)計
2.1 沖裁工藝計算
2.1.1 工藝力和功的計算
沖裁力是指沖裁過程中的最大抗力，它是合理地選用沖壓設(shè)備噸位和校檢模具強(qiáng)度的重要依據(jù)。影響沖裁力的因素很多，主要有材料的機(jī)械性能、厚度、沖裁件周邊長度、模具間隙以及刃口鋒利程度等。
Journal of Materials Processing Technology 139 (2003) 422427 New processes to prevent a flow defect in the combined forwardbackward cold extrusion of a piston-pin D.J. Lee a , D.J. Kim b , B.M. Kim c, a Department of Precision Mechanical Engineering, Graduate School, Pusan National University, Pusan, South Korea b Department of Mechanical Design Engineering, Graduate School, Pusan National University, Pusan, South Korea c Department of Mechanical Engineering, Engineering Research Center for Net Shape and Die Manufacturing, Pusan National University, No. 3, Janjeon-Dong, Kumjeong-Ku, Pusan 609-735, South Korea Abstract A flow defect of a piston-pin for automobile parts are investigated in this study. In the combined cold extrusion of a piston-pin, a lapping defect, which is a kind of flow defect, appears by the dead metal zone. This defect is evident in products with a small thickness to be pierced and is detrimental to dimensional accuracy and decrease of material loss. The flow defect that occurs in the piston-pin has bad effects on the strength and the fatigue life of the piston-pin. Therefore, it is important to predict and prevent the defect in the early stage of process design. The best method that can prevent the flow defect is removing or reducing dead metal zone through the control of material flow. Finite element simulations are applied to analyze the flow defect. This study proposes new processes which can prevent the flow defect by removing the dead metal zone. Then the results are compared with the results of experiments for verification. These FE simulation results are in good agreement with the experimental results. 2003 Elsevier Science B.V. All rights reserved. Keywords: Flow defect; Piston-pin; Material flow control; Forwardbackward extrusion; Dead metal zone; FE simulation 1. Introduction Cold forming is extremely important and economical pro- cesses, especially for producing parts in large quantities. Because of advantages of cold forming such as high pro- duction rates, excellent dimensional tolerances and surface finish, mechanical and metallurgical properties, cold form- ing is by far the largest application of industry for producing parts. However, cold forged parts are also used in manufactur- ing aircraft, motorcycles, nuts and bolts 1, but it is possible for defects to occur in forged parts, depending on the de- formation history, forming conditions and material flow pat- tern, etc. The kind of defects are ductile fracture caused by the state of stress and the deformation history, flow defects caused by unstable material flow, and poor dimensional tol- erances caused by inferiority of the die and friction condi- tion. Further, defects in forged parts are classified as internal defects and external defects 24. These defects have harmful effects on the quality of the product and an increase in the cost of production. Therefore, Corresponding author. Tel.: +82-51-510-3074; fax: +82-51-514-7640. E-mail address: bmkimpusan.ac.kr (B.M. Kim). it is important to predict and prevent defects in the early stage of process design. Wifietal.5 studied ductile fracture in bulk formed parts, using different workability criteria by the finite ele- ment method. Kim and Kim 6 studied internal and exter- nal defects of cold extruded products with double ribs and performed process design to prevent these defects. In this study is examined a defect which occurs in produc- ing a forwardbackward extrusion product, a piston-pin for an automobile part, and new processes are designed to pre- vent the defect by finite element method in the early stage of process design. Then the results are compared with the results of experiments for verification. 2. Forming and defect-occurrence analysis 2.1. Forming process The piston-pin is an automobile components used in the transmission of power between the connecting rod and the crankshaft. In the cold extrusion of a piston-pin, the design requirements are to keep the same height of the forward extruded part and the backward part (Fig. 1) without any defect in the forged product, for use under high and repeated 0924-0136/03/$ see front matter 2003 Elsevier Science B.V. All rights reserved. doi:10.1016/S0924-0136(03)00515-6 D.J. Lee et al. / Journal of Materials Processing Technology 139 (2003) 422427 423 Fig. 1. Shape and dimension of the piston-pin. Fig. 2. Photograph of a flow defect of a piston-pin. load. The material used for the piston-pin is AISI-4135H (Fig. 2) alloy steel, with the following flow stress behavior: = 768.06 0.139 (MPa) Fig. 4. Distribution of effective strain and fracture value. Fig. 3. Conventional forming process for a piston-pin. The lubricant used is phosphate coating and bond lube. The friction factor, m, is assumed to be 0.1, which is confirmed by the ring compression test. The sequence of the conventional process for the piston-pin is performed using a multi-stage former (Fig. 3). The first and second stages are pre-upsetting to eliminate defects by the cropping process such as ovality and ec- centricity of the billet for improvement of dimensional tolerances and die life whilst the third and forth stages are forward or backward extrusion for the forming of one di- rection from the web, and final stage is the piercing process for the pin shape. However, the results of experiment for the conventional process displayed a defect in the web part formed early in the third process (Fig. 3). Especially, a nonuniform flow pattern is observed in part of the defect occurrence, which looks like a flow defect similar to lapping with an undesirable flow pattern. 2.2. Prediction of defects by FE analysis DEFORM is used, which is commercial code of a rigid-plastic FE program for forming and defect analy- sis. The diameter of the initial billet is 30 mm and the height is 61 mm, the whole volume of final product being 424 D.J. Lee et al. / Journal of Materials Processing Technology 139 (2003) 422427 Fig. 5. Metal flow and velocity distribution, where a defect occurs according to stroke. 43,118 mm 3 . The forming is simulated with a conventional process sequence. The maximum fracture value that can estimate the occur- rence of a crack 7 is small at 0.08 and is distributed in a position within the head part of the punch, so that a de- fect does not occur. Thus this defect is not one due to duc- tile fracture (Fig. 4). Then flow line-tracking scheme that was proposed by Altan and Knoerr 8 is performed for de- fect analysis. According to the progress of the punch stroke, severe variation of flow lines appears and discontinuity of velocity occurs in the part that a defect occurred in the ex- periment (Fig. 5). Consequently, the metal flows only in the backward di- rection without flow to the forward direction in the fourth process and metal near the web part is pulled up in the rib part like a lapping defect. Therefore, the cause of the ini- tiation and development of the flow defect that occurred in piston-pin is the velocity discontinuity between backward and forward direction by the formation of a dead metal zone. This appearance evidently occurs in products like a piston-pin with a low thickness to be pierced for the dimen- sional accuracy and the decrease of material loss. A flow defect occurring in a piston-pin has harmful effects on the strength and the fatigue life of a piston-pin that has high and repeated load at high temperature. Therefore, it is necessary for a new process to prevent the flow defect. 3. Process redesign and analysis for the prevention of defect The cause of the initiation and development of the flow defect is the restriction of metal flow by the dead metal zone. For the elimination of the dead metal zone in the early extruded part (3rd process) in the conventional process, the forward or backward extrusion process is modified to combined forwardbackward extrusion, which is performed simultaneously in the two directions. Because of the variety of extrusion ratios and lengths in the forward and backward directions, the simultaneous completion of the material flow in the both directions is very difficult. Consequently, one of the directions is completed early, then material flow stopped and dead metal zone appears in this part just like that in the conventional process. Therefore, in the case of piston-pin forming, the extrusion ratio and the length of both directions are the same at 1.89 and 51 mm. First, analysis of open die forwardbackward ex- trusion is performed for an investigation of extrusion lengths of the piston-pin. The difference of two extruded ribs is 24.9 mm and the backward extruded rib is shorter than the forward extruded rib as shown in Fig. 6. The metal flow of backward direction must be restricted compulsorily for the satisfaction of the design conditions and this means the occurrence of a dead metal zone. There- fore, for the same extrusion length in both directions, three Fig. 6. Extrusion length in forwardbackward extrusion. D.J. Lee et al. / Journal of Materials Processing Technology 139 (2003) 422427 425 Fig. 7. Modified process sequence for a multi-stage former. methods are proposed to control the metal flow without the compulsory restriction of metal flow 3.1. Change of preform shape To secure the same length of both directions from the center of web, it is required that the backward extruded rib is performed by preform design as the difference of both-direction lengths at 24.9 mm from the above results, before forwardbackward extrusion. Fig. 7 shows the mod- ified process sequence, and Fig. 8 shows the metal flow of the final stage of forwardbackward extrusion in this case. From the results of simulation, the lengths of two extruded ribs are 51 mm, which is the dimension of the piston-pin and satisfied the design condition. In addition, the metal flow is uniform in the defect zone where the flow defect occurred in the conventional process, and there is not a discontinu- ity of velocity in both extrusion directions. This means that metal flows uniformly in the whole process without a dead metal zone by restriction of metal flow. Fig. 8. Metal flow of web in case of using preform. Fig. 9. Schematic diagram of the axially moving container die structure. 3.2. Driving of extrusion container The driving extrusion container method 9 is used for metal flow control for the satisfying of the design condi- tion. This structure is that the extrusion container is moved in the counter direction to the early extruded one (Fig. 9). This has the effect of increasing the metal flow in the late extruded direction and restricting metal flow in the early ex- truded direction. In the case of the piston-pin, because of the early completion of backward extrusion, the extrusion container is moved in the forward direction for the increase of metal flow to this direction. In this process, the princi- pal process variables are the relative velocity ratio of the punch and the moving extrusion container, and the friction condition between the material and the moving extrusion container. In this study, because the friction factor, m, is 0.1 be- tween the material and container, simulation is performed only according to the variation of the relative velocity ratio (V C /V P = 0.1, 0.25, 0.5, 0.75, 1.0). If the relative velocity ratio is smaller than the optimum which can complete form- ing simultaneously, extrusion in the backward direction is completed earlier than in the forward direction and a flow defect occur in the same part as in the conventional process. Otherwise, if the relative velocity ratio is larger than the op- timum one, extrusion in the forward direction is complete earlier than backward direction and a flow defect occurs in the opposite part to where a defect occurs in the conven- tional process. Therefore, for satisfaction of the design conditions, the optimum relative velocity ratio is searched for by an opti- mization technique, the bisection method. From the result, the optimum relative velocity ratio is 0.48. Figs. 10 and 11 show the deformation modality and metal flow according to the relative velocity ratio (0.1, 0.48, 1.0) for a punch stroke of 42.7 mm, respectively. Fig. 11(c) shows the metal flow 426 D.J. Lee et al. / Journal of Materials Processing Technology 139 (2003) 422427 Fig. 10. Deformation modality of the piston-pin according to the relative velocity ratio. Fig. 11. Comparisons of metal flow according to the relative velocity ratio. at the optimum relative velocity (0.48) where an improved flow pattern without a flow defect can be noted. 3.3. Modification of die structure A modification of the die structure is proposed which can restrict the metal flow of backward direction, which is deformed early, for simultaneous completion of extrusion in both directions. In this case, for simultaneous completion and the same length in both directions, the stripper, which is Fig. 12. Schematic diagram of die structure using stripper. equipment for punch extraction from products, is redesigned. If a fixed stripper of conventional type is used, a dead metal zone appears from the middle stage of backwardforward extrusion by the restriction of material flow. Therefore, a structure is used that can delay the metal flow in the backward direction by spring force. Fig. 12 shows the die structure. For this method, it is very important to decide the proper spring force for simultaneous completion of forming. Therefore, the necessary spring force for this is calculated by FE simulation. From the simulation result, it was 5 t to be applied load to stripper. Fig. 13 shows metal flow in this case. The metal flow is similarly uniform at the defect zone without discontinuity of velocity in comparison with other modification methods. Fig. 13. Metal flow of web in case of using stripper. D.J. Lee et al. / Journal of Materials Processing Technology 139 (2003) 422427 427 Table 1 Comparison process for each of the proposed method Conventional method Use of preform Use of stripper Use of moving container Maximum load (t) 97.2 96.3 96.1 84.0 Process of extrusion 2 stage 2 stage 1 stage 1 stage Defect Exist None None None 4. Results and experiment From the FE simulation, the three proposed methods are proper to prevent a flow defect by metal flow control. The characteristics of each process are as follows. The first method that uses a preform needs three stage processes (pre- forming, forwardbackward extrusion, piercing) and has a simple die structure; however, the second method that uses a stripper and the third method that uses an axially mov- ing container need two-stage processes (forwardbackward extrusion, piercing) and have a complex die structure. In respect of the forming load, the processes are similar to each other. Especially, the maximum forming load is smaller than that of other processes by about 10 t in the case of the axially moving container, because the axially moving container in- creases material flow in the direction punch movement. It is compared with the proposed method for forming by a press in Table 1. In this study, an experiment using a preform is performed and uses a multi-stage former having 250 t ca- pacity for the verification of simulation. Etching for obser- vation of metal flow is performed to examine for a flow defect for the piston-pin before piercing. Fig. 14 shows the experiment result, based on the first proposed method, changing the preform. The experiment result shows that metal flow is uniform in the defect zone where the flow de- fect had occurred, and satisfied the simultaneous completion of forming and the same length in both extrusion directions. This tendency is in good agreement with the simulation result. Fig. 14. The elimination of the flow defect by the first proposed method. 5. Conclusions In this study, the flow defect that occurs in the manu- facturing process of the piston-pin is examined and a new process to prevent the defect is redesigned by FE analysis. First, the cause of the defect is investigated, and the analyti- cal approach is verified by comparison of experimental and simulation results. From these results, it is possible to de- sign processes that can prevent the flow defect and satisfy the design condition to control the material flow. Comparing the experiment and FE analysis for the pro- posed new processes, several conclusions can be drawn: (1) The cause of the flow defect that occurs in the piston-pin forming is a dead metal zone by restriction of material flow, and it is very important to control the material flow for eliminating this zone. (2) Design of the preform and change of the die structure and the use of an axially moving extrusion container are proposed to secure simultaneous filling for elimination of the flow defect in the combined forwardbackward extrusion process. (3) The proposed methods satisfy the requirements of pro- cess design, i.e. the same length of the forward extru- sion part and the backward one, and these are verified by experiment. Acknowledgements The authors wish to thank the Engineering Research Cen- ter for Net Shape and Die Manufacturing, located in Pusan National University, Pusan, South Korea, for the support of this research. References 1 T. Altan, S.I. Oh, L. Gegel, Metal forming, ASM (1983). 2 T. Okamoto, T. Fukuda, H. Hagita, Source Book on Cold Forming, ASTM, 1997, pp. 216226. 3 S.W. Oh, T.H. Kim, B.M. Kim, J.C. Choi, KSME 19 (12) (1995) 31213129. 4 R.C. Batra, N.V. Nechitailo, Int. J. Plast. 13 (4) (1997) 291306. 5 A.S. Wifi, A. Abdel-Hamid, N. El-Abbasi, J. Mater. Process. Technol. 77 (1998) 285293. 6 D.J. Kim, B.M. Kim, J. KSTP 8 (6) (1999) 612619. 7 D.C. Ko, Pusan National University Dissertation, 1998. 8 T. Altan, M. Knoerr, J. Mater. Process. Technol. 35 (1992) 275302. 9 K. Osakata, X. Wang, S. Hanami, J. Mater. 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