0125-拉鉤的冷沖模設計【全套5張CAD圖+文獻翻譯+說明書】
0125-拉鉤的冷沖模設計【全套5張CAD圖+文獻翻譯+說明書】,全套5張CAD圖+文獻翻譯+說明書,拉鉤,沖模,設計,全套,cad,文獻,翻譯,說明書,仿單
文獻綜述
題 目： 拉鉤的冷沖模設計
一、模具工業(yè)的分類
我國模具設計與制造技術的發(fā)展經(jīng)歷了手工作坊制造階段、工業(yè)化生產(chǎn)階段和現(xiàn)代化生產(chǎn)階段。伴隨著計算機技術的快速發(fā)展, 數(shù)字化、信息化CADCAE/CAM技術和數(shù)控加工機床已普遍采用, 模具產(chǎn)業(yè)正處于高速發(fā)展階段。
模具是制造業(yè)的重要基礎工藝裝備。模具總體上可分為兩大類: 金屬材料制件成形模具，如沖壓模具、鍛造模具、壓鑄模具、擠壓模具、拉絲模具、粉末冶金模具等; 非金屬材料制件成形模具, 如塑料注射模具、壓鑄模具、擠出模具, 橡膠制件、玻璃制件和陶瓷制件成形模具等。模具的具體分類方法很多, 如按模具結構形式分, 沖壓模具可分為簡單模、連續(xù)模和復合模, 注塑模具可分為單分型面和雙分型面注塑模具等; 按工藝性質分, 沖壓模具可分為沖孔模、落料模、拉深模、彎曲模，塑模具可分為壓塑模、傳遞模、注射模等。[1]
其中沖壓模具、塑料模具、鑄造模具、鍛壓模具、橡膠模具、粉末冶金模具、拉絲模具、無機材料成形模具等是最主要的八大類, 用于制造業(yè)中的幾乎所有產(chǎn)品的生產(chǎn)。[7]
二、模具工業(yè)的地位
模具是以其特定的形狀通過一定的方式使原材料成型。隨著社會的發(fā)展和科技的進步， 模具行業(yè)越來越被重視，模具技術在國民經(jīng)濟各個部門都得到廣泛的應用，它不僅與整個機械行業(yè)密切相關，而且與人們的生活密切相關。模具工業(yè)是國民經(jīng)濟的基礎產(chǎn)業(yè)，是“百
業(yè)之母”，是永不衰亡的行業(yè)，模具工業(yè)的發(fā)展水平標志著一個國家的工業(yè)水平及產(chǎn)品開發(fā)的能力。“十五” 規(guī)劃指出，模具是生產(chǎn)各種工業(yè)產(chǎn)品的重要基礎工藝裝備，國民經(jīng)濟的五大支柱產(chǎn)業(yè)—機械、電子、汽車、石化、建筑等都要求模具工業(yè)的發(fā)展與之相適應。
模具因其生產(chǎn)效率高、產(chǎn)品質量好、材料消耗低、操作簡單、生產(chǎn)過程易于實現(xiàn)機械化與自動化、生產(chǎn)成本低而獲得廣泛應用，利用模具可以加工出薄壁、重量輕、剛性好、形狀復雜的零件；產(chǎn)品質量有模具保證，具有一模一樣的的特點；這是其它加工制造業(yè)所無法完成的；模具是現(xiàn)代工業(yè)，特別是汽車、摩托車、航空、儀表、儀器、醫(yī)療器械、電子通信、兵器、家用電器、五金工具、日用品等工業(yè)必不可少的工藝裝備。據(jù)資料統(tǒng)計，利用模具制造的零件數(shù)量，在飛機、汽車、摩托車、拖拉機、電機、電器、儀器儀表等機電產(chǎn)品中占80%以上；在電腦、電視機、攝像機、照相機、錄像機等電子產(chǎn)品中占85%以上；在電冰箱、洗衣機、空調、電風扇、自行車、手表等輕工業(yè)產(chǎn)品中占90%以上；在子彈、槍支等兵器產(chǎn)品中占95%以上；在日用金屬產(chǎn)品中占95%以上。可見，研究和發(fā)展模具技術，對于促進國民經(jīng)濟的發(fā)展具有特別重要的意義。目前，模具技術已成為衡量一個國家產(chǎn)品制造水平的重要標志之一。[2]
起步到現(xiàn)在，我國模具工業(yè)經(jīng)歷了半個多世紀的發(fā)展，已有了較大的提高，與國外的差距正在進一步縮小。而中國模具對世界的影響也在不斷擴大, 主要表現(xiàn)在以下幾點:
1、ISTMA 和FADMA 及其他國家的模協(xié)和有關國際組織已越來越重視中國模協(xié), 他們邀請中國模協(xié)出席國際會議和參加國際行業(yè)活動越來越多, 他們到中國來考察和交流也越來越多, 中國模具已經(jīng)成為國際模具中的一個不可忽視的力量。
2、隨著國際交往的日益增多和外資(包括港資、合資) 在中國模具行業(yè)的投入日漸增加, 中國模具正表現(xiàn)得越來越融入世界, 并已逐步與國際接軌, 三資企業(yè)已對中國模具的發(fā)展作出了很大貢獻,中國模具和世界模具已越來越密不可分。
3、無論是出口還是在中國國內使用, 中國模具已經(jīng)為境外企業(yè)和境內三資企業(yè)降低了不少生產(chǎn)成本, 也就是說, 為世界的進步做出了一些貢獻,而且這一貢獻將隨著中國模具的進一步發(fā)展而不斷增大。中國模具與世界正在實現(xiàn)共贏。
4、由于中國的過去、現(xiàn)在和不久的將來一直有較為優(yōu)秀且豐富和廉價的人力資源、龐大的市場及其他許多有利條件, 外資在中國模具中已經(jīng)并且將進一步占據(jù)越來越重要的地位, 中國已成為承接工業(yè)發(fā)達國家模具業(yè)轉移的良好目的地, 確實加速了世界模具產(chǎn)業(yè)的轉移, 從而也為通過這種轉移而使工業(yè)發(fā)達國家向更高層次發(fā)展做出了貢獻。
5、中國龐大的模具市場促進了世界模具的發(fā)展。
從上述情況來看, 中國模具確實已經(jīng)與世界模具密不可分, 而且中國模具在世界模具中的地位將會越來越重要, 其影響也會越來越大。中國模具加速融入世界并實現(xiàn)國際共贏的局面將會進一步發(fā)展下去。在當今的信息社會和世界經(jīng)濟進一步全球化的發(fā)展過程中,世界在促進中國模具的發(fā)展,中國模具也正在并將進一步促進世界的發(fā)展。[9]
三、我國模具工業(yè)的現(xiàn)狀
模具屬于邊緣科學，它涉及機械設計制造、塑性加工、鑄造、金屬材料及其熱處理、高分子材料、金屬物理、凝固理論、粉末冶金、塑料、橡膠、玻璃等諸多學科、領域和行業(yè)。
從中國模具工業(yè)協(xié)會獲悉, 近年來在國民經(jīng)濟中占有重要地位的模具工業(yè)得到了迅速發(fā)展。模具是工業(yè)生產(chǎn)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(chǎn)品中, 一般的零部件都依靠模具成型。國民經(jīng)濟的五大支柱產(chǎn)業(yè), 機械, 電子、汽車、石化、建筑都要求模具工業(yè)的發(fā)展與之相適應, 模具是“ 效益放大器”, 用模具生產(chǎn)的最終產(chǎn)品價值, 往往是模具自身價值的幾十倍、上百倍。模具生產(chǎn)水平的高低, 己成為衡量一個國家產(chǎn)品制造水平高低的重要標志, 在很大程度上決定著產(chǎn)品的質量、效益和新產(chǎn)品的開發(fā)能力。因此, 振興和發(fā)展我國的模具工業(yè),日益受到人們的重視和關注國務院頒布的《關于當前產(chǎn)業(yè)政策要點的丸定》也把模具列為機械工業(yè)改造序列的第一位、生產(chǎn)和基本建設序列的第二位。由于我國模具工業(yè)發(fā)展迅速, 前景廣闊, 國內外模具及模具加工設備廠商已普遍看好中國市場。縱觀我國的模具工業(yè)，既有高速發(fā)展的良好勢頭，又存在精度低、結構欠合理、壽命短等一系列不足，無法滿足整個工業(yè)迅速發(fā)展的迫切要求。[3]
近年來，我國模具工業(yè)的迅速發(fā)展是大家有目共睹的，中國模具工業(yè)的現(xiàn)狀大致可以從以下3個方面來講：
1、模具的產(chǎn)值與出口量增長明顯。從整體情況來看，我國已經(jīng)步入模具工業(yè)大國之列，但是距模具強國還有相當差距。
2、模具制造水平不斷提高。近幾年，以大型、精密、復雜、長壽命模具為代表的、技術含量較高的中高檔模具的比重進一步提高，現(xiàn)在中高檔模具所占比重已經(jīng)達到35% 以上。模具的設計和制造水平也有了很大的發(fā)展，很多先進的模具設計與制造技術在我國的模具企業(yè)中得到應用，如CAD/CAE/CAM 等計算機輔助技術、高速加工技術、熱流道技術、氣輔技術、逆向工程等新技術得到廣泛應用，E R P、P D M 等信息化管理技術正得到積極推廣，這些先進技術的應用和信息化管理的實施極大地提高了模具企業(yè)的生產(chǎn)效率，縮短了生產(chǎn)周期。
3、我國模具行業(yè)已經(jīng)形成了自己的骨干隊伍。目前，我國約有模具生產(chǎn)廠點3 萬余家，從業(yè)人員100余萬人，在各個模具行業(yè)的骨干企業(yè)隊伍中也涌現(xiàn)出了本行業(yè)的龍頭企業(yè)。他們的生產(chǎn)裝備先進，生產(chǎn)達到了一定規(guī)模，技術水平較高，而且產(chǎn)品具有自己的特點。[10]
目前，中國約有模具生產(chǎn)廠2萬余家，從業(yè)人員50多萬人，全年模具產(chǎn)值達450億元人民幣以上。近年來，模具行業(yè)結構調整步伐加快，主要表現(xiàn)為大型、精密、復雜、長壽命模具和模具標準件發(fā)展速度高于行業(yè)的總體發(fā)展速度；塑料模和壓鑄模比例增大；面向市場的專業(yè)模具廠家數(shù)量及能力增加較快。隨著經(jīng)濟體制改革的不斷深入，“三資”及民營企業(yè)的發(fā)展很快。[5]
在模具產(chǎn)值產(chǎn)量和進出口迅速發(fā)展的同時, 近年來中國在模具行業(yè)技術進步和模具水平的提高方面也取得了可喜的成績?，F(xiàn)在, 我國已能生產(chǎn)精度達到詳?shù)亩喙の患夁M模, 壽命可達億沖次以上。個別企業(yè)生產(chǎn)的多工位級進模已可在次的高速沖床上使用, 精度可達林。在大型塑料模具方面, 我國已能生產(chǎn)英寸大屏幕彩電和英寸背投式電視的塑殼模具、大容量洗衣機全套塑料件模具以及汽車保險杠、整體儀表板塑料模具等。在精密塑料模具方面, 我國已能生產(chǎn)照相機和手機塑料件模具、多型腔小模數(shù)齒輪模具及精度達林的腔塑封模具等,精度達到林的光盤模也已能夠生產(chǎn)了。塑料模具的熱流道和氣輔等技術水平不斷提高。在大型精密復雜壓鑄模方面, 國內已能生產(chǎn)自動扶梯整體踏板壓鑄模、汽車后橋齒輪箱壓鑄模以及汽車發(fā)動機殼體的鑄造模具等。在汽車覆蓋件模具方面,國內已能生產(chǎn)中檔新型轎車的覆蓋件模具, 高檔轎車的部分覆蓋件模具也已能夠生產(chǎn)了。子午線輪胎活絡模具、鋁合金和塑料門窗異型材擠出成形模、精鑄或樹脂快速成型拉延模等, 也已達到相當高的水平, 制造出來的模具可與進口模具媲美。國內生產(chǎn)的最大模具單套重量已超過100t我國模具企業(yè)CAD、CAM、CAE、CAPP、PDM、PLM、ERP等數(shù)字、化信息化技術的使用面正在不斷擴大, 水平也在不斷提高。
中國模具工業(yè)產(chǎn)值僅次于日本和美國, 排在世界前三位。中國經(jīng)濟的高速發(fā)展同樣對模具工業(yè)提出了越來越高的要求, 也為其發(fā)展提供了巨大的空間。現(xiàn)今, 國內的模具生產(chǎn)廠家已增至2 萬余家, 模具制造從業(yè)人員已超過50 多萬人, 模具的年產(chǎn)值達到534 億元人民幣。近10 年來, 國內模具在數(shù)量、質量、技術等方面有了很大的跨躍; 現(xiàn)正以每年15 %左右的增長速度穩(wěn)步發(fā)展。[4]
四、現(xiàn)代模具設計與制造方法
現(xiàn)代模具制造業(yè)已成為技術密集型和資金密集型的產(chǎn)業(yè), 它與高新技術已形成相互依托的關系。一方面, 模具是直接為高新技術產(chǎn)業(yè)化服務的不可缺少的裝備另一方面, 模具生產(chǎn)本身又大量采用高新技術及裝備, 因此, 模具制造已成為高新技術產(chǎn)業(yè)的重要組成部分。模具成形零件時實現(xiàn)快速、優(yōu)質、低耗是國家可持續(xù)發(fā)展戰(zhàn)略的要求。[7]
我國模具制造技術發(fā)展迅速，逐漸由單一、具體、細節(jié)的設計及各道工序的加工過程向設計、制造技術的系統(tǒng)化、集成化過程轉變，已成為現(xiàn)代先進制造技術的重要組成部分。
1、模具CAD/CAE/CAM技術：以三維造型為主的模具設計、制造、工藝信息的數(shù)字化傳遞及轉換所形成的CAD/CAE/CAM一體化技術在我國已大量推廣應用。例如，汽車大型覆蓋件模具已普遍應用CAD/CAM技術，實現(xiàn)了模具設計、制造、沖壓一體化、數(shù)控編程和數(shù)控加工實現(xiàn)了DNC，計算機軟硬件配置已接近國際水平；在塑料模具方面也已廣泛應用CAD/CAE/CAM技術，多項國內自主開發(fā)的軟件推廣之中，如北航華正的CAXA軟件系列和華中理工大學的HSC2.0等；在壓鑄模方面，CAD/CAM同樣得到了廣泛應用，并已開始應用CAE軟件進行澆道系統(tǒng)和工藝參數(shù)等方面的優(yōu)化分析。
2、模具先進制造工藝及裝備：模具由功能件和支持件組成。在塑料模和壓鑄模中，功能件為型腔和型芯，在鍛模中為型腔，在沖壓模具中為型孔和沖頭，支持件一般為標準件，因此，模具加工的主要部件可分為兩類，即型腔，型芯加工和型孔加工。
（1）高速銑削加工
高速銑削加工在模具制造中具有以下特點：高效，高速銑削加工的主軸轉速一般為15000-40000r/min,最高可達100000r/min。切削鋼時，其切削速度約為400m/min，比傳統(tǒng)的銑削加工高5~10倍；在加工型腔模時與傳統(tǒng)的加工方法相比起效率提高4-5倍；與完全采用EDM加工相比，其加工速度提高了4-8倍；高精度，一般加工精度為10m，有的精度更高；高表面質量，由于高速銑削的工具溫度小，姑表面沒有變質層及微裂紋，熱變形也小。最好的表面粗糙度R小于1m；可加工高硬材料，可銑削50~54HRC。
（2）NCEDM加工
NCEDM的多軸聯(lián)動控制、電極自動交換、C軸加工、數(shù)控擺動等功能能完成各種復雜型腔的精密加工，采用自適應控制、模糊控制、各種專家系統(tǒng)、新型脈沖電源燈優(yōu)化加工狀態(tài)，自動完成全部加工過程。NCEDM在中小型腔模、復雜精密型腔模等加工方面發(fā)揮著越來越重要的作用。
（3）虛擬軸數(shù)控加工
在模具復雜型腔銑削加工中采用五軸數(shù)控銑床可提高加工質量和效率。五軸數(shù)控加工還可在三軸聯(lián)動加工不易接近的地方進行加工，以避免銑刀中心銑削工作帶來的弊端，并能在一次裝夾中完成五面加工，因此更適合于模具制造。虛擬軸五軸數(shù)控機床突破了傳統(tǒng)的串聯(lián)式床身滑臺結構，由于采用了高級軟件、降低了傳統(tǒng)五軸數(shù)控銑床結構的復雜性，因此，結構簡單，成本低。虛擬軸五軸數(shù)控機床也可實現(xiàn)高速加工，尤其適合復雜型腔的銑削、磨削和測量，是我國模具制造工藝及裝備的重要發(fā)展方向。
（4）復合加工
復合加工時指在一臺機床上進行兩種或兩種以上不同加工工藝的復合，以實現(xiàn)不同加工工藝優(yōu)勢互補的作用。其發(fā)展方向又可分為兩個方向：銑削加工與激光加工復合技術，銑削加工與EDM復合技術。
（5）型孔加工工藝及裝備
沖壓模等型孔加工主要依靠磨削加工及數(shù)控電火花線切割加工（WEDM）。在磨削加工中，成形磨、坐標磨、光曲磨等精密加工工藝及裝備在我國已廣泛應用。WEDM在沖壓模等型孔加工中已起到不可替代的作用。國內外沖壓模等加工都離不開WEDM。主要方向有：磨削加工、WEDM加工。[6]
五、我國模具行業(yè)存在的問題
目前, 我國模具總量雖然已達到相當大的規(guī)模, 模具水平也已有了很大提高, 但在總體上, 我國模具生產(chǎn)的商品化、專業(yè)化、標淮化程度還較低, 商品化模具只占左右, 模具標準件使用覆蓋率還不到, 專業(yè)模具企業(yè)只占模具生產(chǎn)廠點的少數(shù), 而且裝備也比較落后。由于資金缺乏, 我國的模具企業(yè)大都只能購買較低檔的國產(chǎn)設備和來自我國臺灣的設備, 而少用歐美和日本的高檔設備, 設備數(shù)控化程度遠低于國際水平。我國模具設計制造水平在總體上要比工業(yè)發(fā)達國家落后許多。
主要存在以下幾點問題：
1、產(chǎn)品質量不高：當前我國模具生產(chǎn)廠中多數(shù)是“大而全”、“小而全”，國外模具企業(yè)大多是“小而專”、“小而精”。國內模具總量中屬大型、精密、復雜、長壽命模具的比例只有30% 左右，國外在50%以上。國內模具生產(chǎn)廠家，工藝條件參差不齊，差距很大?，F(xiàn)代模具工業(yè)早已走出以前手工制模的時代，進入了數(shù)字化時代，實現(xiàn)了無圖化生產(chǎn)，通過電腦輸入數(shù)據(jù)加工制作模具。我國不少廠家由于設備不配套很多工作依賴手工完成，嚴重影響了精度和質量。
2、標準化水平不高：模具是專用成形工具產(chǎn)品，雖然個性化強，但也是工業(yè)產(chǎn)品，所以標準化工作十分重要。模具標準化工作主要包括模具技術標準的制訂和執(zhí)行、模具標準件的生產(chǎn)和應用以及有關標準的宣傳、貫徹和推廣等工作。中國模具標準化工作起步較晚，因此模具標準化落后于生產(chǎn)，更落后于世界上許多工業(yè)發(fā)達的國家。由于中國模具標準化工作起步較晚，模具標準件生產(chǎn)、銷售、推廣和應用工作也比較落后，因此，模具標準件品種規(guī)格少、供應不及時、配套性差等問題長期存在，從而使模具標準件使用覆蓋率一直較低。
3、CAD/CAE/CAM 技術剛起步：CAD/CAE/CAM 是面向制造的工程設計技術群中的核心技術，是提高企業(yè)產(chǎn)品自主開發(fā)能力和產(chǎn)品檔次的重要手段，也是提高企業(yè)對市場的應變能力和快速響應能力的重要途徑，是現(xiàn)階段應大力推廣應用的關鍵共性技術，是模具設計的發(fā)展方向。
4、缺乏相關人才：當今世界正進行著新一輪的產(chǎn)業(yè)調整，一些模具制造逐漸向發(fā)展中國家轉移，中國正成為世界模具大國，但我國模具行業(yè)人才緊缺成為一個迫在眉睫的問題。模具行業(yè)是一個需長期積累經(jīng)驗的行業(yè)，現(xiàn)在的年輕人能堅持下來而有所成就的很少。由于最初的學習非常枯燥，因此許多初學者常半途而廢。此外，我國傳統(tǒng)教育方式對模具人才的培養(yǎng)存在不足。一些高校盡管在近幾年內設立了模具專業(yè)，但由于受軟硬件設施限制，培養(yǎng)出的學員實際技能不夠。而社會上各種各樣的模具培訓班，由于缺乏規(guī)范的職業(yè)標準，因此學員質量良莠不齊。
5、受到外資的挑戰(zhàn)：目前世界制造業(yè)生產(chǎn)基地加速向中國轉移，中國制造業(yè)又正邁向更高的發(fā)展階段，對優(yōu)質精密模具的需求不斷上升。國際模具工業(yè)巨頭繼20世紀90 年代中期進入中國后，再掀投資熱潮，目的正為搶占先機，中國本土模具工業(yè)面臨國外先進技術與高質量制品的挑戰(zhàn)，生存空間受擠壓。
6、缺乏自有品牌：企業(yè)開發(fā)能力弱、沒有品牌，導致了經(jīng)濟效益欠佳，在市場中常處于被動地位。[8]
六、參考文獻
[1]馬忠臣等.現(xiàn)代模具工業(yè)發(fā)展述評[J].模具技術，2006,03
[2]蔣桂芝.模具技術在國民經(jīng)濟中的地位[J].機電產(chǎn)品開發(fā)與創(chuàng)新，2009,05
[3]洪慎章.現(xiàn)代模具技術的現(xiàn)狀及發(fā)展趨勢[J].航空制造技術，2006,06
[4]吳存雷.淺談模具產(chǎn)業(yè)的發(fā)展[J].塑料工業(yè)，2006,10
[5]曹延安.中國模具工業(yè)現(xiàn)狀[J].現(xiàn)代零部件，2009,03
[6]陳德忠.我國模具先進制造技術的發(fā)展[J].發(fā)展前沿，2000,09
[7]周永泰.中國模具工業(yè)的現(xiàn)狀與發(fā)展[J].行業(yè)展望，2007,12
[8]屈偉平.我國模具制造業(yè)發(fā)展現(xiàn)狀、存在的問題及對策[J].模具技術，2006,05
[9]周永泰.中國模具正在加速融入世界并實現(xiàn)國際共贏[J].模具工業(yè)，2006,04
[10]曉霏等.中國模具工業(yè)發(fā)展現(xiàn)狀與展望[J].航空制造技術，2008,08
[11] A. Y. C. Nee and M. W. Fu, “Determination of optimal parting directions in plastic injection mold design”, Annals CIRP, 46(1),pp. 429–432, 1997.
9
冷沖模設計-拉鉤
一、前言部分
模具是機械制造業(yè)中技術先進、影響深遠的重要工藝裝備,具有生產(chǎn)效率高、材料利用率高、制件質量優(yōu)良、工藝適應性好等特點,被廣泛應用于汽車、機械、航天、航空、輕工、電子、電器、儀表等行業(yè)。2005年中國模具工業(yè)產(chǎn)值達到610億元,增長率保持在25%的高水平,行業(yè)的生產(chǎn)能力約占世界總量的10%,僅次于日本、美國而位列世界第三[2]。當前，我國模具制造方面與工業(yè)發(fā)達國家相比，差距較大主要表現(xiàn)在[3]：
（1）標準化程度低。
（2）模具制造精度低、周期長。
提高勞動生產(chǎn)率、產(chǎn)品質量、降低成本、擴大沖壓工藝應用范圍；提高沖壓零件精度、減少制造周期、提高模具壽命；模具的標準化及專業(yè)化、管理的統(tǒng)一化及等級化；提高專業(yè)人員的技術水平。
沖壓是利用安裝在沖壓設備上的模具對材料施加壓力，使其產(chǎn)生分離或塑性變形，從而獲得所需零件的一種壓力加工方法[5]。由于沖壓加工具有許多突出的優(yōu)點，因此在工業(yè)生產(chǎn)中，尤其是大批量生產(chǎn)中得到廣泛應用。從精細的電子元件、儀表指針到汽車的覆蓋件、高壓容器封頭以及航空航天器的蒙皮、機身等均需沖壓加工。隨著工業(yè)產(chǎn)品的不斷發(fā)展和生產(chǎn)技術水平不斷提高，不少過去用鑄造、鍛造、切削加工方法制造的零件，已被質量輕、剛度好的沖壓件所代替[6]。
我國沖壓模具無論在數(shù)量上，還是在質量、技術和能力等方面都已有了很大發(fā)展，但與國民經(jīng)濟需求和世界先進水平相比，差距仍很大，一些大型、精密、復雜、長壽命的高檔模具每年仍大量進口，特別是中高檔轎車的覆蓋件模具，目前仍主要依靠進口。一些低檔次的簡單沖模，已趨供過于求，市場競爭激烈[7]。我國沖壓模具產(chǎn)品質量水平低主要表現(xiàn)在精度、表面粗糙度、壽命及模具的復雜程度上；生產(chǎn)工藝水平低則主要表現(xiàn)在加工工藝、加工裝備等方面[8]。
雖然近年來我國模具行業(yè)發(fā)展迅速，但是離國內的需要和國際水平還有很大的差距。制造產(chǎn)業(yè)是一個國家的綜合國力及技術水平的體現(xiàn)，而模具行業(yè)的發(fā)展是制造產(chǎn)業(yè)的關鍵。針對這種情況，國家出臺了相應的政策，正積極發(fā)展模具制造產(chǎn)業(yè)。
二 、主題部分
1 、冷沖模具工業(yè)在歷史上的背景
冷沖壓加工工藝，在我國已有悠久的歷史。據(jù)文獻記載：我國勞動人民遠在青銅時期就發(fā)現(xiàn)了金屬具有錘擊變形的性能；到了戰(zhàn)國時代（公元前403-221年）已經(jīng)能煉劍淬火?？梢钥隙?，我們的祖先，在2300年前已掌握了錘擊金屬制造兵器和各種日用品技術。在漫長的封建社會時期，我國勞動在金、銀、銅裝飾品和日用品的制作中，顯示出精巧的工藝技術和高超的藝術水平[9]。
2、冷沖模具工業(yè)的現(xiàn)狀
由于沖壓工藝具有生產(chǎn)率、生產(chǎn)成本低、材料利用率高、能成形復雜零件、適合大批量生產(chǎn)等優(yōu)點，在某些領域已取代機械加工，并正逐步擴大其應用范圍。據(jù)國際生產(chǎn)技術協(xié)會預測，到本世紀中，機械零部件中60%的粗加工、80%的精加工要由模具來完成。因此，沖壓技術對發(fā)展生產(chǎn)、增加效益、更新產(chǎn)品等方面具有重要作用[10]。在近半個世紀以來，我國的冷沖壓工藝和其它生產(chǎn)工藝一樣，得到了迅速的發(fā)展。在一些工廠中，建立了具有現(xiàn)代規(guī)模和技術先進的冷沖壓生產(chǎn)車間，并建立了專門研究冷沖壓技術的科研機構及專業(yè)性工廠，培養(yǎng)了大批從事冷沖壓生產(chǎn)的科技人員，廣泛地開展了冷沖壓生產(chǎn)的科技及學術活動，編輯出版了各種冷沖壓技術資料，從而使冷沖壓生產(chǎn)技術得到了迅速發(fā)展。在冷沖壓生產(chǎn)中，出現(xiàn)了很多可喜的高科技成果。沖壓加工的工藝和設備正在不斷地發(fā)展，例如精密沖裁、冷擠壓、多工位自動沖壓、高速成形、液壓成形、超塑沖壓等，把冷沖壓生產(chǎn)技術提高到了新的水平。為了適應冷沖壓工藝水平的提高，我國對沖模的研制也在不斷加強。近年來，出現(xiàn)了很多制造周期短、使用壽命長的新型沖模結構。并且，模具加工工藝及模具材料也相應地在不斷革新，例如采用鋼結硬質合金、硬質合金或低熔點合金澆注模具、采用電加工技術及計算機制造沖模等以適用于不同的生產(chǎn)條件。從而使沖壓生產(chǎn)的產(chǎn)品質量、勞動生產(chǎn)率大大提高，成本也大幅度下降，有利地推動了我國社會主義經(jīng)濟建設和發(fā)展[11]。
我國的模具工業(yè)的發(fā)展，日益受到人們的重視和關注，在電子、汽車、電機、電器、儀器、儀表、家電和通信等產(chǎn)品中，60%-80%的零部件都要依靠模具成形（型）。用模具生產(chǎn)制件所具備的高精度、高復雜程度、高一致性、高生產(chǎn)率和代消耗，是其它加工制造方法所不能比擬的。近幾年，我國模具工業(yè)一直以每年15%左右的增長速度發(fā)展，2003年，我國模具總產(chǎn)值超過400億元人民幣[12]。模具工業(yè)的發(fā)展和進步，在很大程度上取決于模具加工設備、軟件及切削刀具的制造水平。如今，人們對手機、電腦、汽車、手表、數(shù)碼電子等商品的要求一點也不低于發(fā)達國家。但另一方面，我國生產(chǎn)這些商品所需模具的工作母機即模具加工設備的制造水準，從總體上來說還是比較低的。這就出現(xiàn)了一個奇怪的現(xiàn)象，這些年我國模具生產(chǎn)所需的先進加工設備、制造軟件及切削刀具進口越來越多。去年，我國機床進口約60億美元，其中用于模具生產(chǎn)的就占十分之一；去年我國模具生產(chǎn)所需超硬質合金和陶瓷等超硬刀具銷售額約12億元，其中90%依賴進口[13]。
隨著計算機軟件的發(fā)展和進步，CAD/CAE/CAM 技術也日臻成熟，其現(xiàn)代模具中的應用將越來越廣泛?？梢灶A料不久的將來，模具制造業(yè)將從機械制造業(yè)中分離出來，而獨立成為國民經(jīng)濟中不可缺少的支柱產(chǎn)業(yè)，與此同時，也進一步促進了模具制造技術向集成化、智能化、益人化、高效化方向發(fā)展。因此，大力發(fā)展模具工業(yè)可以促進我國更快的走向工業(yè)化國家。
3、冷沖模具的發(fā)展方向
發(fā)展模具工業(yè)的關鍵是制造模具的技術和相關人才以及模具材料。
模具技術的發(fā)展應該為適應模具產(chǎn)品“交貨期短”、“精度高”、“質量好”、“價格低”的要求服務。達到這一要求急需發(fā)展如下幾項[14]：
(1) 全面推廣CAD/CAM/CAE技術：模具CAD/CAM/CAE技術是模具設計制造的發(fā)展方向。隨著微機軟件發(fā)展和進步，普及CAD/CAM/CAE技術的條件已基本成熟，各企業(yè)將加大CAD/CAM技術培訓和技術服務的力度；進一步擴大CAE技術的應用范圍。計算機和網(wǎng)絡的發(fā)展正使CAD/CAM/CAE技術跨地區(qū)、跨企業(yè)、跨院所地在整個行業(yè)中推廣成為可能，實現(xiàn)技術資源重新整合，使虛擬制造成為可能[15]。
(2) 高速銑削加工：國外近年來發(fā)展的高速銑削加工，大幅度提高了加工效率，并可獲得極高的表面光潔度[16]。
(3) 模具掃描及數(shù)字化系統(tǒng)：高速掃描機和模具掃描系統(tǒng)提供了從模型或實物掃描到加工出期望的模型所需的諸多功能，大大縮短了模具的在研制制造周期。有些快速掃描系統(tǒng)，可快速安裝在已有的數(shù)控銑床及加工中心上，實現(xiàn)快速數(shù)據(jù)采集、自動生成各種不同數(shù)控系統(tǒng)的加工程序、不同格式的CAD數(shù)據(jù)，用于模具制造業(yè)的“逆向工程” [17]。?
(4) 電火花銑削加工。
(5) 提高模具標準化程度：我國模具標準化程度正在不斷提高，估計目前我國模具標準件使用覆蓋率已達到30%左右。國外發(fā)達國家一般為80%左右。
(6) 優(yōu)質材料及先進表面處理技術：選用優(yōu)質鋼材和應用相應的表面處理技術來提高模具的壽命就顯得十分必要。
(7) 模具研磨拋光將自動化、智能化：模具表面的質量對模具使用壽命、制件外觀質量等方面均有較大的影響，研究自動化、智能化的研磨與拋光方法替代現(xiàn)有手工操作，以提高模具表面質量是重要的發(fā)展趨勢[18]。
(8) 模具自動加工系統(tǒng)的發(fā)展
雖然近年來我國模具行業(yè)職工隊伍發(fā)展迅速，估計目前已達近百萬人，但由于模具企業(yè)數(shù)量的急劇膨脹、傳統(tǒng)教育的力不從心以及模具技師的老齡化，模具人才遠遠跟不上行業(yè)的發(fā)展需求，主要表現(xiàn)在總量不足。對中國的模具企業(yè)來說，如何更好地管理人才，如何留住人才，如何為人才提供足夠的平臺和發(fā)展空間是擺在眼前的一個嚴峻的、迫切需要解決的課題，否則，人才緊缺問題將成為中國模具工業(yè)繼續(xù)高速發(fā)展的一個重要障礙[19]。
因選材和用材不當，致使模具過早失效，大約占失效模具的45%以上。在整個模具價格構成中，材料所占比重不大，一般在20% ～30% 。因此，選用優(yōu)質鋼材和應用表面處理技術來提高模具的壽命就顯得十分必要。對于模具鋼來說，要采用電渣重熔工藝，如采用粉末冶金工藝制造的粉末高速鋼等。模具鋼品種規(guī)格多樣化、產(chǎn)品精細化、制品化，盡量縮短供貨時間亦是重要發(fā)展趨勢。
這只是發(fā)展模具工業(yè)的三個重要部分，要向使模具工業(yè)在我國經(jīng)濟建設中發(fā)揮更大的作用，需要國家更大的關注與投入，帶動相關人員研究和發(fā)展。
三、總結部分
目前我國模具工業(yè)的發(fā)展步伐日益加快，但在整個模具設計制造水平和標準化程度上，與德國、美國、日本的發(fā)達國家相比還存在相當大的差距。存在的問題和差距主要表現(xiàn)在下列5個方面：（1）總量供不應求。（2）企業(yè)組織結構、產(chǎn)品結構、技術結構和進出口結構都不合理。（3）模具產(chǎn)品水平低很多，生產(chǎn)周期長。（4）開發(fā)能力較差，經(jīng)濟效益較差。（5）與國際水平相比，模具企業(yè)的管理落后[20]。
由此可得，我國模具制造，應該向以下所述的幾點進行實行。這樣對我國的模具行業(yè)有巨大的歷史意義，這影響著我國能不能走到世界的前列和引領模具技術潮流。1.CAD/CAE/CAM計算機輔助設計、模擬、制造一體化2.先進設備在現(xiàn)代模具制造中的作用3.模具材料及表面處理技術。模具技術未來發(fā)展趨勢主要是朝信息化、高速化生產(chǎn)與高精度化發(fā)展。(1)使計算機輔助設計/加工/工程技術得到廣泛使用。(2)讓大型模具企業(yè)擁有高速數(shù)控加工/加工中心/數(shù)控機床等先進的加工工藝與裝備,可以開展RP/RT或模具逆向工程工作,使硬件裝備站在與世界基本同步的水平線上。(3)在沖模的表面精整加工技術方面,要開展積極探索、積累經(jīng)驗。借助高速、精密的加工設備加工生產(chǎn),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?zhèn)鹘y(tǒng)的手工研磨拋光,提高模具質量。與前面的雷同！
在模具制造的方法中，冷沖壓與其他加工方法相比，具有獨到的特點：操作工藝方便，便于組織生產(chǎn)，是一種高效低耗的加工方法，適合大批量生產(chǎn)。而且沖壓出的零件制品一般不需要進一步機械加工，互換性好，在耗費不大的情況下能獲得強度高、剛度大而重量輕的零件。所以在工業(yè)生產(chǎn)中，尤其在大批量生產(chǎn)中應用十分廣泛。相當多的工業(yè)部門都越來越多地次采用冷沖壓加工產(chǎn)品零部件，如機械制造、車輛生產(chǎn)、航空航天、電子、電器、輕工、儀表及日用品等行業(yè)。在這些工業(yè)部門中，沖壓件所占的比重都相當大，不少過去用鑄造、鍛造、切削加工方法制造的零件，現(xiàn)在已被質量輕、剛度好的沖壓件所代替[21]。通過沖壓加工，大大提高了生產(chǎn)率，降低了成本?？梢哉f，如果在生產(chǎn)中不廣泛采用沖壓工藝，許多工業(yè)部門的產(chǎn)品要提高生產(chǎn)率、提高質量、降低成本，進行產(chǎn)品的更新?lián)Q代是難以實現(xiàn)的。
我國沖壓模具產(chǎn)品的質量和生產(chǎn)工藝水平,總體上比國際先進水平低許多,而模具生產(chǎn)周期卻要比國際先進水平長許多。產(chǎn)品質量水平低主要表現(xiàn)在精度、表面粗糙度、壽命及模具的復雜程度上;生產(chǎn)工藝水平低則主要表現(xiàn)在加工工藝、加工裝備等方面。在模具壽命上，合理選擇模具材料是非常重要的[22]。壓力容器作為沖壓模具的產(chǎn)品之一，其分析標準一定要與國際相符合。為此，國內較有實力的壓力容器制造廠為了使生產(chǎn)的壓力容器產(chǎn)品能順利進入國際市場,陸續(xù)取得ASME認證證書[23]。
模具制造產(chǎn)業(yè)是制造產(chǎn)業(yè)之一，而制造產(chǎn)業(yè)標志著一個國家的綜合國力及技術水平。因此大力發(fā)展模具制造產(chǎn)業(yè)是國家經(jīng)濟建設中所必須計劃到的。本次設計壓力容器模具雖然不能為整個行業(yè)做出什么貢獻，但我希望能夠通過本次的設計制作有所體會和認識，發(fā)現(xiàn)一些問題，提供一些有用的資料。
參考文獻：
[1] 鄭津洋等.壓力容器設計技術進展及我國應采取的對策.2001,29
[2] Liu Shengguo.The Current Situation and Development of Stamping Die Technology in China.[J] Vo.l 23 No. 1Feb 2007
[3] 徐政坤.沖壓模具設計與制造. 北京：化學工業(yè)出版社，2005，7
[4] 余銀柱、趙躍文.沖壓工藝與模具設計.北京：北京大學出版社2005，10
[5] 徐政坤.沖壓模具與設備. 北京：機械工業(yè)出版社，2004，1
[6] 余銀柱、趙躍文.沖壓工藝與模具設計.北京：北京大學出版社2005，1
[7] 張春水.國內外冷沖模技術現(xiàn)狀及發(fā)展趨勢. 模具工業(yè).2001
[8] Liu Shengguo.The Current Situation and Development of Stamping Die Technology in China.[J] Vo.l 23 No. 1Feb 2007
[9] 溫燦華. 汽車工業(yè)與模具工業(yè)的發(fā)展[J]. 模具制造 , 2005,(02)
[10]?付宏生.冷沖壓成形工藝與模具設計制造[M].北京：化學工業(yè)出版社，2004，前言
[11] 薛啓翔.冷沖壓實用技術. 北京：機械工業(yè)出版社，2006,1
[12] 李和平、吳霞.現(xiàn)代模具行業(yè)現(xiàn)狀與發(fā)展趨勢綜述[J].
[13] 趙昌盛.實用模具材料應用手冊[M]. 北京：機械工業(yè)出版社，2005，6
[14] 余銀柱.沖壓工藝與模具設計.北京：北京大學出版社，2005，11
[15] Koric, Seid. Journal of Materials Processing Technology. Feb2008, Vol.
[16] 張六玲. 國內外模具工業(yè)的基本現(xiàn)狀與市場預測[J]. 模具制造 , 2002,(01)
[17] Jae Yeo Lee and Kwangsoo Kim.A feature-based approach to extracting machining features[J].Computer-Aided Design, Vol.30,No.13, pp.101959-1035, 1998
[18] 胡興軍. 我國模具業(yè)的發(fā)展及改進措施[J]. 世界制造技術與裝備市場 , 2005,(01)
[19] 洪慎章. 現(xiàn)代模具工業(yè)的發(fā)展趨勢及企業(yè)特征[J]. 航空制造技術 , 2003,(06)
[20] 周永泰. 模具設計和加工技術的發(fā)展方向[J]. 制造技術與機床 , 2003,(05)
[21] 李雙義.冷沖模具設計.清華大學出版社[J]
[22] 林承全.論沖壓模具設計制造與模具壽命的關系[J]
[23] 黃安庭.國壓力容器標準和ASME規(guī)范的比較分析[J]
8
文 獻 翻 譯
外文原文
Design and thermal analysis of plastic injection mould
S.H. Tang ?, Y.M. Kong, S.M. Sapuan, R. Samin, S. Sulaiman
Department of Mechanical and Manufacturing Engineering, Universiti Putra Malaysia, 43400 Serdang, Selangor, Malaysia Received 3 September 2004; accepted 21 June 2005
Abstract
This paper presents the design of a plastic injection mould for producing warpage testing specimen and performing thermal analysis for the mould to access on the effect of thermal residual stress in the mould. The technique, theory, methods as well as consideration needed in designing of plastic injection mould are presented. Design of mould was carried out using commercial computer aided design software Unigraphics, Version 13.0. The model for thermal residual stress analysis due to uneven cooling of the specimen was developed and solved using a commercial finite element analysis software called LUSAS Analyst, Version 13.5. The software provides contour plot of temperature distribution for the model and also temperature variation through the plastic injection molding cycle by plotting time response curves. The results show that shrinkage is likely to occur in the region near the cooling channels as compared to other regions. This uneven cooling effect at different regions of mould contributed to warpage.
Keywords: Plastic Injection mould; Design; Thermal analysis
1. Introduction
Plastic industry is one of the world’s fastest growing industries, ranked as one of the few billion-dollar industries. Almost every product that is used in daily life involves the usage of plastic and most of these products can be produced by plastic injection molding method [1]. Plastic injection molding process is well known as the manufacturing process to create products with various shapes and complex geometry at low cost [2].
The plastic injection molding process is a cyclic process. There are four significant stages in the process. These stages are filling, packing, cooling and ejection. The plastic injection molding process begins with feeding the resin and the appropriate additives from the hopper to the heating/injection system of the injection plastic injection molding machine [3]. This is the “filling stage” in which the mould cavity is filled with hot polymer melt at injection temperature. After the cavity is filled, in the “packing stage”, additional polymer melt is packed into the cavity at a higher pressure to compensate the expected shrinkage as the polymer solidifies. This is followed by “cooling stage” where the mould is cooled until the part is sufficiently rigid to be ejected. The last step is the “ejection stage” in which the mould is opened and the part is ejected, after which the mould is closed again to begin the next cycle [4].
The design and manufacture of injection molded polymeric parts with desired properties is a costly process dominated by empiricism, including the repeated modification of actual tooling. Among the task of mould design, designing the mould specific supplementary geometry, usually on the core side, is quite complicated by the inclusion of projection and depression [5].
In order to design a mould, many important designing factors must be taken into consideration. These factors are mould size, number of cavity, cavity layouts, runner systems, gating systems, shrinkage and ejection system [6].
In thermal analysis of the mould, the main objective is to analyze the effect of thermal residual stress or molded-in stresses on product dimension. Thermally induced stresses develop principally during the cooling stage of an injection molded part, mainly as a consequence of its low thermal conductivity and the difference in temperature between the molten resin and the mould. An uneven temperature field exists around product cavity during cooling [7].
During cooling, location near the cooling channel experiences more cooling than location far away from the cooling channel. This different temperature causes the material to experience differential shrinkage causing thermal stresses. Significant thermal stress can cause warpage problem. Therefore, it is important to simulate the thermal residual stress field of the injection-molded part during the cooling stage [8]. By understanding the characteristics of thermal stress distribution, deformation caused by the thermal residual stress can be predicted.
In this paper the design of a plastic injection mould for producing warpage testing specimen and for performing thermal analysis for the mould to access on the effect of thermal residual stress in the mould is presented.
2. Methodology
2.1. Design of warpage testing specimen
This section illustrates the design of the warpage testing specimen to be used in plastic injection mould. It is clear that warpage is the main problem that exists in product with thin shell feature. Therefore, the main purpose of the product development is to design a plastic part for determining the effective factors in the warpage problem of an injectionmoulded part with a thin shell.
The warpage testing specimen is developed from thin shell plastics. The overall dimensions of the specimen were 120mmin length, 50mmin width and 1mmin thickness. The material used for producing the warpage testing specimen was acrylonitrile butadiene stylene (ABS) and the injection
temperature, time and pressure were 210 ?C, 3 s and 60MPa, respectively. Fig. 1 shows the warpage testing specimen produced.
2.2. Design of plastic injection mould for warpage testing specimen
This section describes the design aspects and other considerations involved in designing the mould to produce warpage testing specimen. The material used for producing the plastic injection mould for warpage testing specimen was AISI 1050 carbon steel.
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Fig. 1. Warpage testing specimen produced.
Four design concepts had been considered in designing of the mould including:
i. Three-plate mould (Concept 1) having two parting line with single cavity. Not applicable due to high cost.
ii. Two-plate mould (Concept 2) having one parting line with single cavity without gating system. Not applicable due to low production quantity per injection.
iii. Two-plate mould (Concept 3) having one parting line with double cavities with gating and ejection system. Not applicable as ejector pins might damage the product as the product is too thin.
iv. Two-plate mould (Concept 4) having one parting line with double cavities with gating system, only used sprue puller act as ejector to avoid product damage during ejection.
In designing of the mould for the warpage testing specimen, the fourth design concept had been applied. Various design considerations had been applied in the design.
Firstly, the mouldwas designed based on the platen dimension of the plastic injection machine used (BOY 22D). There is a limitation of the machine, which is the maximum area of machine platen is given by the distance between two tie bars. The distance between tie bars of the machine is 254 mm. Therefore, the maximum width of the mould plate should not exceed this distance. Furthermore, 4mm space had been reserved between the two tie bars and the mould for mould setting-up and handling purposes. This gives the final maximum width of the mould as 250 mm. The standard mould base with 250mm×250mmis employed. The mould base is fitted to the machine using Matex clamp at the upper right and lower left corner of the mould base or mould platen. Dimensions of other related mould plates are shown in Table 1.
Table 1
Mould plates dimensions.
The mould had been designed with clamping pressure having clamping force higher than the internal cavity force (reaction force) to avoid flashing from happening.
Based on the dimensions provided by standard mould set, the width and the height of the core plate are 200 and 250 mm, respectively. These dimensions enabled design of two cavities on core plate to be placed horizontally as there is enough space while the cavity plate is left empty and it is only fixed with sprue bushing for the purpose of feeding molten plastics. Therefore, it is only one standard parting line was designed at the surface of the product. The product and the runner were released in a plane through the parting line during mould opening.
Standard or side gate was designed for this mould. The gate is located between the runner and the product. The bottom land of the gate was designed to have 20? slanting and has only 0.5mm thickness for easy de-gating purpose. The gate was also designed to have 4mm width and 0.5mm thickness for the entrance of molten plastic.
In the mould design, the parabolic cross section type of runner was selected as it has the advantage of simpler machining in one mould half only, which is the core plate in this case. However, this type of runner has disadvantages such as more heat loss and scrap compared with circular cross section type. This might cause the molten plastic to solidify faster.
This problem was reduced by designing in such a way that the runner is short and has larger diameter, which is 6mm in diameter.
It is important that the runner designed distributes material or molten plastic into cavities at the same time under the same pressure and with the same temperature. Due to this, the cavity layout had been designed in symmetrical form.
Another design aspect that is taken into consideration was air vent design. The mating surface between the core plate and the cavity plate has very fine finishing in order to prevent flashing from taking place. However, this can cause air to trap in the cavity when the mould is closed and cause short shot or incomplete part. Sufficient air vent was designed to ensure that air trap can be released to avoid incomplete part from occurring.
The cooling system was drilled along the length of the cavities and was located horizontally to the mould to allow even cooling. These cooling channels were drilled on both cavity and core plates. The cooling channels provided sufficient cooling of the mould in the case of turbulent flow. Fig. 2 shows cavity layout with air vents and cooling channels on core plate.
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Fig. 2. Cavity layout with air vents and cooling channels.
In this mould design, the ejection system only consists of the ejector retainer plate, sprue puller and also the ejector plate. The sprue puller located at the center of core plate not only functions as the puller to hold the product in position when the mould is opened but it also acts as ejector to push the product out of the mould during ejection stage. No additional ejector is used or located at product cavities because the product produced is very thin, i.e. 1 mm. Additional ejector in the product cavity area might create hole and damage to the product during ejection.
Finally, enough tolerance of dimensions is given consideration to compensate for shrinkage of materials.
Fig. 3 shows 3D solid modeling as well as the wire frame modeling of the mould developed using Unigraphics.
Fig. 3. 3D solid modeling and wireframe modeling of the mould.
3. Results and discussion
3.1. Results of product production and modification
From the mould designed and fabricated, the warpage testing specimens produced have some defects during trial run. The defects are short shot, flashing and warpage. The short shot is subsequently eliminated by milling of additional air vents at corners of the cavities to allow air trapped to escape. Meanwhile, flashing was reduced by reducing the packing pressure of the machine. Warpage can be controlled by controlling various parameters such as the injection time, injection temperature and melting temperature.
After these modifications, the mould produced high quality warpage testing specimen with low cost and required little finishing by de-gating. Fig. 4 shows modifications of the mould, which is machining of extra air vents that can eliminate short shot.
Fig. 4. Extra air vents to avoid short shot.
3.2. Detail analysis of mould and product
After the mould and products were developed, the analysis of mould and the product was carried out. In the plastic injection moulding process, molten ABS at 210 ?C is injected into the mould through the sprue bushing on the cavity plate and directed into the product cavity. After cooling takes place, the product is formed. One cycle of the product takes about 35 s including 20 s of cooling time.
The material used for producing warpage testing specimen was ABS and the injection temperature, time and pressure were 210 ?C, 3 s and 60MPa respectively. The material selected for the mould was AISI 1050 carbon steel. Properties of these materials were important in determining temperature distribution in the mould carried out using finite element analysis. Table 2 shows the properties for ABS and AISI 1050 carbon steel.
Table 2
Material properties for mould and product
The critical part of analysis for mould is on the cavity and core plate because these are the place where the product is formed. Therefore, thermal analysis to study the temperature distribution and temperature at through different times are performed using commercial finite element analysis software called LUSAS Analyst, Version 13.5. A two-dimensional (2D) thermal analysis is carried out for to study the effect of thermal residual stress on the mould at different regions.
Due to symmetry, the thermal analysis was performed by modeling only the top half of the vertical cross section or side view of both the cavity and core plate that were clamped together during injection. Fig. 5 shows the model of thermal analysis analyzed with irregular meshing.
Modeling for the model also involves assigning properties and process or cycle time to the model. This allowed the finite element solver to analyze the mould modeled and plot time response graphs to show temperature variation over a certain duration and at different regions.
For the product analysis, a two dimensional tensile stress analysis was carried using LUSAS Analyst, Version 13.5. Basically the product was loaded in tension on one end while the other end is clamped. Load increments were applied until the model reaches plasticity. Fig. 6 shows loaded model of the analysis.
Fig. 5. Model for thermal analysis. Fig. 6. Loaded model for analysis of product.
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3.3. Result and discussion for mould and product analysis
For mould analysis, the thermal distribution at different time intervals was observed. Fig. 7 shows the 2D analysis contour plots of thermal or heat distribution at different time?intervals in one complete cycle of plastic injection molding.
Fig. 7. Contour plots of heat distribution at different time intervals.
For the 2D analysis of the mould, time response graphs are plotted to analyze the effect of thermal residual stress on the products. Fig. 8 shows nodes selected for plotting time response graphs.
Figs. 9–17 show temperature distribution curves for different nodes as indicated in Fig. 8.
From the temperature distribution graphs plotted in Figs. 9–17, it is clear that every node selected for the graph plotted experiencing increased in temperature, i.e. from the ambient temperature to a certain temperature higher than the ambient temperature and then remained constant at this temperature for a certain period of time. This increase in temperature was caused by the injection of molten plastic into the cavity of the product.
After a certain period of time, the temperature is then further increased to achieve the highest temperature and remained constant at that temperature. Increase in temperature was due to packing stages that involved high pressure, which caused the temperature to increase. This temperature remains constant until the cooling stage starts, which causes reduction in mould temperature to a lower value and remains at this value. The graphs plotted were not smooth due to the absence of function of inputting filling rate of the molten plastic as well as the cooling rate of the coolant. The graphs plotted only show maximum value of temperature that can be achieved in the cycle.
The most critical stage in the thermal residual stress analysis is during the cooling stage. This is because the cooling stage causes the material to cool from above to below the glass transition temperature. The material experiences differential shrinkage that causes thermal stress that might result in warpage.
From the temperature after the cooling stage as shown in Figs. 9–17, it is clear that the area (node) located near the cooling channel experienced more cooling effect due to further decreasing in temperature and the region away from the cooling channel experienced less cooling effect. More cooling effect with quite fast cooling rate means more shrinkage is occurring at the region. However, the farthest region , Node 284 experience more cooling although far away from cooling channel due to heat loss to environment.
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Fig. 8. Selected nodals near product region for time response graph plots. Fig. 9. Temperature distribution graph for Node 284.
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Fig. 10. Temperature distribution graph for Node 213. Fig. 11. Temperature distribution graph for Node 302.
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Fig. 12. Temperature distribution graph for Node 290. Fig. 13. Temperature distribution graph for Node 278.
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Fig. 14. Temperature distribution graph for Node 1838. Fig. 15. Temperature distribution graph for Node 1904.
Fig. 16. Temperature distribution graph for Node 1853. Fig. 17. Temperature distribution graph for Node 1866.
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As a result, the cooling channel located at the center of the product cavity caused the temperature difference around the middle of the part higher than other locations. Compressive stress was developed at the middle area of the part due to more shrinkage and caused warpage due to uneven shrinkage that happened. However, the temperature differences after cooling for different nodes are small and the warpage effect is not very significant. It is important for a designer to design a mould that has less thermal residual stress effect with efficient cooling system.
For the product analysis, from the steps being carried out to analyze the plastic injection product, the stress distribution on product at different load factor is observed in the two dimensional analysis.
A critical point, Node 127, where the product experiences maximum tensile stress was selected for analysis.
From the load case versus stress curves at this point plotted in Fig. 23, it is clear that the product experiencing increased in tensile load until it reached the load factor of 23, which is 1150 N. This means that the product can withstand tensile load until 1150 N. Load higher than this value causes failure to the product. Based on Fig. 23, the failure is likely to occur at the region near to the fixed end of the product with maximum stress of 3.27×107 Pa.
The product stress analysis reveals very limited information since the product produced was for warpage testing purposes and had no relation with tensile loading analysis.
In future, however, it is suggested that the product service condition should be determined so that further analysis may be carried out for other behaviors under various other loading. that affect warpage. The testing specimen was produced at?low cost and involves only little finishing that is de-gating.
The thermal analysis of plastic injection mould has provided an understanding of the effect of thermal residual stress on deformed shape of the specimen and the tensile stress analysis of product managed to predict the tensile load that the warpage testing specimen can withstand before experiencing failure.
Acknowledgement
The authors wish to thank the Faculty of Engineering, Universiti Putra Malaysia for initiating the publication o
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