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畢業(yè)設(shè)計(jì)(論文)外文資料翻譯
系 別： 機(jī)電信息系
專 業(yè)： 機(jī)械設(shè)計(jì)制造及其自動(dòng)化專業(yè)
班 級(jí)：
姓 名：
學(xué) 號(hào)：
外文出處： 塑料注塑模具并行設(shè)計(jì)
21（2005）368-378
附 件： 1. 原文； 2. 譯文
2013年3月
塑料注塑模具并行設(shè)計(jì)
Assist.Prof.Dr. A. YAYLA /Prof.Dr. Pa? a YAYLA
摘要
塑料制品制造業(yè)近年迅速成長(zhǎng)。其中最受歡迎的制作過程是注塑塑料零件。注塑模具的設(shè)計(jì)對(duì)產(chǎn)品質(zhì)量和效率的產(chǎn)品加工非常重要。模具公司想保持競(jìng)爭(zhēng)優(yōu)勢(shì),就必須縮短模具設(shè)計(jì)和制造的周期。
模具是工業(yè)的一個(gè)重要支持行業(yè)，在產(chǎn)品開發(fā)過程中作為一個(gè)重要產(chǎn)品設(shè)計(jì)師和制造商之間的聯(lián)系。產(chǎn)品開發(fā)經(jīng)歷了從傳統(tǒng)的串行開發(fā)設(shè)計(jì)制造到有組織的并行設(shè)計(jì)和制造過程中,被認(rèn)為是在非常早期的階段的設(shè)計(jì)。并行工程的概念(CE)不再是新的,但它仍然是適用于當(dāng)今的相關(guān)環(huán)境。團(tuán)隊(duì)合作精神、管理參與、總體設(shè)計(jì)過程和整合IT工具仍然是并行工程的本質(zhì)。CE過程的應(yīng)用設(shè)計(jì)的注射過程包括同時(shí)考慮塑件設(shè)計(jì)、模具設(shè)計(jì)和注塑成型機(jī)的選擇、生產(chǎn)調(diào)度和成本中盡快設(shè)計(jì)階段。
介紹了注射模具的基本結(jié)構(gòu)設(shè)計(jì)。在該系統(tǒng)的基礎(chǔ)上,模具設(shè)計(jì)公司分析注塑模具設(shè)計(jì)過程。該注射模設(shè)計(jì)系統(tǒng)包括模具設(shè)計(jì)過程及模具知識(shí)管理。最后的原則概述了塑料注射模并行工程過程并對(duì)其原理應(yīng)用到設(shè)計(jì)。
關(guān)鍵詞:塑料注射模設(shè)計(jì)、并行工程、計(jì)算機(jī)輔助工程、成型條件、塑料注塑、流動(dòng)模擬
1、簡(jiǎn)介
注塑模具總是昂貴的,不幸的是沒有模具就不可能生產(chǎn)模具制品。每一個(gè)模具制造商都有他/她自己的方法來(lái)設(shè)計(jì)模具,有許多不同的設(shè)計(jì)與建造模具。當(dāng)然最關(guān)鍵的參數(shù)之一,要考慮到模具設(shè)計(jì)階段是大量的計(jì)算、注射的方法,澆注的的方法、研究注射成型機(jī)容量和特點(diǎn)。模具的成本、模具的質(zhì)量和制件質(zhì)量是分不開的
在針對(duì)今天的計(jì)算機(jī)輔助充型模擬軟件包能準(zhǔn)確地預(yù)測(cè)任何部分充填模式環(huán)境中。這允許快速模擬實(shí)習(xí),幫助找到模具的最佳位置。工程師可以在電腦上執(zhí)行成型試驗(yàn)前完成零件設(shè)計(jì)。工程師可以預(yù)測(cè)過程系統(tǒng)設(shè)計(jì)和加工窗口,并能獲得信息累積所帶來(lái)的影響,如部分過程變量影響性能、成本、外觀等。
2、注射成型法
注塑成型是最有效的方法之一,將塑料最好的一面呈現(xiàn)。這是普遍用于制造復(fù)雜的制件,優(yōu)點(diǎn)是簡(jiǎn)單、經(jīng)濟(jì)、準(zhǔn)確與少浪費(fèi)。塑料零件的批量生產(chǎn)主要采用模具。產(chǎn)品設(shè)計(jì)制造過程包括模具的結(jié)構(gòu)必須經(jīng)過外觀評(píng)價(jià)和結(jié)構(gòu)優(yōu)化。當(dāng)設(shè)計(jì)師創(chuàng)造注射模具組件時(shí)，他們面臨一個(gè)巨大的多種選擇，并行工程需要一個(gè)工程師考慮制產(chǎn)品在發(fā)展階段時(shí)的過程設(shè)計(jì)。一個(gè)好的產(chǎn)品設(shè)計(jì)為了滿足市場(chǎng)其制造過程是不可能太貴的。CAD/CAM整合了過程仿真、快速成形制造能減少風(fēng)險(xiǎn),進(jìn)一步提高產(chǎn)品開發(fā)的有效性。
3、注塑模具設(shè)計(jì)重要的計(jì)算機(jī)輔助
注射模具設(shè)計(jì)任務(wù)是相當(dāng)復(fù)雜的。計(jì)算機(jī)輔助工程(CAE)分析工具提供了巨大的優(yōu)勢(shì)讓設(shè)計(jì)工程師考慮幾乎所有模具、注塑參數(shù)沒有真正利用的地方。在可能性的設(shè)計(jì)、理念設(shè)計(jì)師，給工程師們機(jī)會(huì)去消除潛在的問題,開始真正的生產(chǎn)。此外,在虛擬環(huán)境中,設(shè)計(jì)師可以快速而方便地評(píng)估特定的成型參數(shù)敏感性的質(zhì)量和生產(chǎn)最終產(chǎn)品。所有這些分析工具使所有模具設(shè)計(jì)將在一天甚至數(shù)小時(shí)完成,而不需要幾周或幾個(gè)月來(lái)做真正的實(shí)驗(yàn)反復(fù)試驗(yàn)。CAE用于早期設(shè)計(jì)的部分,模具和注塑模具參數(shù)、節(jié)約成本是實(shí)質(zhì)功能不僅是最好的部分,而且還能節(jié)省和縮短開發(fā)產(chǎn)品推向市場(chǎng)的時(shí)間。
在所有方面的成型過程中需要滿足塑料部分設(shè)置的公差,包括零件的尺寸和形狀,樹脂的化學(xué)結(jié)構(gòu)、填料使用,模具型腔布置、澆注、模具冷卻并釋放機(jī)制使用。面對(duì)這復(fù)雜性,設(shè)計(jì)師經(jīng)常使用電腦設(shè)計(jì)工具,如有限元分析(FEA)和充型分析(MFA),減少開發(fā)時(shí)間和成本。有限元分析確定部分結(jié)構(gòu)的應(yīng)變、應(yīng)力和撓度,在那里這些參數(shù)可以很好地被定義。沖型分析位置和大小進(jìn)行優(yōu)化樹脂流動(dòng)。它還定義了焊縫的位置、面積過大的壓力,以及如何影響墻壁和肋厚度流動(dòng)。其它有限元分析設(shè)計(jì)工具包括模具冷卻溫度分布,分析周期時(shí)間和收縮為空間控制和預(yù)測(cè)凍結(jié)應(yīng)力、翹曲變形等情況。
采用CAE分析部分壓縮模如圖1所示。分析周期始于創(chuàng)造一個(gè)CAD模型和有限元網(wǎng)格的模具腔。在注入條件規(guī)定,充型、纖維取向、固化和熱歷史、收縮和翹曲變形等情況進(jìn)行仿真。該材料的性能計(jì)算模型模擬可用于結(jié)構(gòu)的行為的一部分。如果需要部分設(shè)計(jì)澆口位置及加工條件可以在電腦上修改,直到一個(gè)可接受的零件的表達(dá)式。摘要分析了一個(gè)優(yōu)化完成部分可采用降低weldline(亦即也knitline),優(yōu)化力量、控制溫度和固化、最小收縮和翹曲變形等情況。
模具加工的前身是手工制作,如檢查每一剪機(jī)床維修工。自動(dòng)化的增長(zhǎng)和普遍使用的電腦數(shù)值控制或CNC加工中心使這過程變得更加簡(jiǎn)便。設(shè)計(jì)的時(shí)間也被大大降低通過使用特殊的軟件能夠產(chǎn)生刀具路徑直接從CAD數(shù)據(jù)文件提取。主軸速度高達(dá)100000每分鐘轉(zhuǎn)速提一步提出了高速加工。切削材料已經(jīng)證明了驚人的表現(xiàn)而不使用任何的剪切/冷卻液,什么都沒有。作為一個(gè)結(jié)果,加工過程復(fù)雜的型心和型腔已經(jīng)加快了。
這是一個(gè)好消息,產(chǎn)生一個(gè)模具所花費(fèi)的時(shí)間不斷的被減少。壞消息是,另一方面,甚至所有這些進(jìn)步、設(shè)計(jì)和制造的模具仍然要花很長(zhǎng)時(shí)間,是非常昂貴的。
圖1的注射模CAE分析部分
許多公司的經(jīng)理人現(xiàn)在體會(huì)部署新產(chǎn)品推向市場(chǎng)迅速發(fā)展是多么的重要。企業(yè)的繁榮關(guān)鍵在于新產(chǎn)品。他們推動(dòng)企業(yè)的收入、市場(chǎng)份額、底線和股票價(jià)格。一個(gè)公司能夠發(fā)明優(yōu)質(zhì)的產(chǎn)品和合理的價(jià)格領(lǐng)先其競(jìng)爭(zhēng)不僅實(shí)現(xiàn)了100%的打敗市場(chǎng)競(jìng)爭(zhēng)對(duì)手的產(chǎn)品,但之前到達(dá)也傾向于保持主導(dǎo)地位甚至幾年之后終于宣布競(jìng)爭(zhēng)產(chǎn)品(史密斯,1991)。對(duì)大多數(shù)產(chǎn)品來(lái)說(shuō),這兩個(gè)優(yōu)勢(shì)是戲劇性的?，F(xiàn)在產(chǎn)品快速發(fā)展的一個(gè)關(guān)鍵方面的競(jìng)爭(zhēng)成功。圖2顯示,只有3 - 7%的產(chǎn)品結(jié)構(gòu)與一般的工業(yè)或電子公司是小于5歲。公司在第一四分位,這個(gè)數(shù)字增加到15 - 25%。一流的公司,它是60 - 80%(湯普森,1996)。最好的公司在不斷開發(fā)新產(chǎn)品。在惠普,超過80%的利潤(rùn)結(jié)果從產(chǎn)品小于2歲!(Neel,1997)
圖2重要的新產(chǎn)品(雅克布,2000)
以先進(jìn)的計(jì)算機(jī)技術(shù)和人工智能,努力已經(jīng)被指向降低成本和交貨時(shí)間在設(shè)計(jì)和制造注塑模具。注塑模具設(shè)計(jì)主要感興趣的地區(qū),因?yàn)樗且粋€(gè)復(fù)雜的過程涉及到很多表面設(shè)計(jì)等各零件的模具,每個(gè)都需要專家的知識(shí)和經(jīng)驗(yàn)。李et.艾爾。(1997)提出了一種系統(tǒng)的方法關(guān)于注塑模具設(shè)計(jì)的知識(shí)庫(kù)和并行工程環(huán)境。
4并行工程在模具設(shè)計(jì)中
并行工程(CE)是一個(gè)系統(tǒng)性的方法來(lái)集成產(chǎn)品開發(fā)過程。它代表了團(tuán)隊(duì)合作的價(jià)值觀、信任和分享,以這樣的方式,決策是通過協(xié)商一致,包括視角并聯(lián),從一開始就產(chǎn)品的整個(gè)生命周期(埃文斯,1998)。從本質(zhì)上講,CE提供合作、合作、集體和同步工程的工作環(huán)境。一個(gè)并行工程的方法是基于五個(gè)關(guān)鍵要素:
1、過程
2、多學(xué)科小組
3、綜合設(shè)計(jì)模型
4、設(shè)施
5、軟件基礎(chǔ)設(shè)施
圖3的方法對(duì)塑料注射模設(shè)計(jì),工程b)串并行工程
在塑料模具制造業(yè)、CE是很重要的,由于高成本加工和長(zhǎng)交貨期。通常,CE利用制造原型模具在設(shè)計(jì)之初相位分析和調(diào)整設(shè)計(jì)。生產(chǎn)制造模具是作為最后一步。制造過程,包括模具的結(jié)構(gòu)必須經(jīng)過外觀評(píng)價(jià)和結(jié)構(gòu)優(yōu)化的產(chǎn)品設(shè)計(jì)。CE要求工程師考慮生產(chǎn)過程中產(chǎn)品設(shè)計(jì)的發(fā)展階段。一個(gè)好的設(shè)計(jì)產(chǎn)品是滿足市場(chǎng)如果其制造過程是不可能的。CAD/CAM整合過程模擬、快速成形制造能減少風(fēng)險(xiǎn),從效率和進(jìn)一步提高產(chǎn)品開發(fā)的有效性。
多年來(lái),設(shè)計(jì)師已經(jīng)被限制在他們可以產(chǎn)出通常必須設(shè)計(jì)制造(DFM)——那就是,調(diào)整他們的設(shè)計(jì)意圖,使元件(或總成)生產(chǎn)使用一個(gè)特定的進(jìn)程或程序。此外,如果一個(gè)模具用于產(chǎn)生一個(gè)項(xiàng)目,而因此自動(dòng)設(shè)計(jì)對(duì)固有限制在一開始就相處得很好。以注塑為例,以處理一個(gè)組件成功,即使在最小程度上,下面的設(shè)計(jì)元素需要考慮的內(nèi)容:
1、.幾何
.拔模斜度
.非內(nèi)角形狀
.近恒壁厚
.復(fù)雜性
.分裂線位置
.表面拋光
材料選擇
元件的合理化(減少組件)
成本
在注塑、生產(chǎn)的模具生產(chǎn)注射模具元件通常是最長(zhǎng)的部分產(chǎn)品開發(fā)過程。當(dāng)利用快速造型、CAD需要長(zhǎng)時(shí)間,因此成為瓶頸。
廢水處理工程的工藝設(shè)計(jì)和注塑塑料涉及相當(dāng)復(fù)雜且耗時(shí)的活動(dòng),包括零件設(shè)計(jì)、模具設(shè)計(jì)、注塑成型機(jī)的選擇、生產(chǎn)排程、工裝和成本估算。所有這些活動(dòng)是傳統(tǒng)上由部分設(shè)計(jì)和模具制作人員按注射模順序的方式完成后塑料部件的設(shè)計(jì)。很明顯的,這些序列階段可能會(huì)導(dǎo)致長(zhǎng)的產(chǎn)品開發(fā)時(shí)間。但隨著社會(huì)的過程中實(shí)施并行工程所有參數(shù)影響產(chǎn)品設(shè)計(jì)、模具設(shè)計(jì)、機(jī)械的選擇、生產(chǎn)排程、模具和加工成本被認(rèn)為是盡早塑料部件的設(shè)計(jì)。
使用時(shí)有效,CAE方法節(jié)省了部分設(shè)計(jì)及制造巨大的成本和時(shí)間。這些工具幾乎讓工程師測(cè)試部分處理它在其正常使用壽命表現(xiàn)怎樣。材料供應(yīng)商,設(shè)計(jì)師和制造商應(yīng)該運(yùn)用這些工具同時(shí)在設(shè)計(jì)之初階段利用CAE增加塑料成本效益。CAE技術(shù)使人們有可能取代傳統(tǒng),順序決策程序和并行設(shè)計(jì)過程,其中各方之間是如何產(chǎn)生互動(dòng)和分享信息,圖3塑料注塑、CAE及相關(guān)設(shè)計(jì)數(shù)據(jù)提供一個(gè)綜合的環(huán)境,為便于并行工程的設(shè)計(jì)、制造和模具部分,以及材料的選擇和模擬優(yōu)化工藝控制參數(shù)。
定性費(fèi)用有關(guān)的部分比較設(shè)計(jì)上的變化被顯示在圖4，顯示出一個(gè)事實(shí),那就是當(dāng)設(shè)計(jì)已經(jīng)改好了在早期階段在計(jì)算機(jī)屏幕上時(shí),與成本有關(guān)的順序的10.000倍,如果低于部分生產(chǎn)。這些改變可能發(fā)生在塑料部件模具的改變,如澆口位置、厚度變化、生產(chǎn)延遲,質(zhì)量成本、機(jī)械安裝時(shí)間,或是設(shè)計(jì)變更在塑料部件。
圖4的成本在部分改變?cè)O(shè)計(jì)產(chǎn)品開發(fā)周期(張志剛,2001年版)
在早期設(shè)計(jì)階段,設(shè)計(jì)師設(shè)計(jì)模具部分必須完成零件設(shè)計(jì)基于各自的經(jīng)驗(yàn)相似的部分。但是隨著部分變得更為復(fù)雜,它變得相當(dāng)困難的加工性能預(yù)測(cè)及部分不使用計(jì)算機(jī)輔助工具。因此,即使是相對(duì)復(fù)雜的部分,使用計(jì)算機(jī)輔助工具,防止變化和昂貴的設(shè)計(jì)過程中出現(xiàn)的問題,可以注射后。為成功實(shí)施并行工程,必須有歸屬感從人人參與。
5個(gè)案研究
圖5顯示初始CAD(計(jì)算機(jī)輔助設(shè)計(jì))塑料部分用于噴灌消防栓的腿。一個(gè)基本特征,部分的部分保持平注射后,在注射操作原因變形問題。
另一個(gè)重要特點(diǎn)的塑料部件必須是一種高效的抗彎剛度。一批料中加入了不同取向的部分如圖5 b。這些應(yīng)設(shè)計(jì)成一種方式,它有貢獻(xiàn)的重量最小部分的,而且是可行的。
在模具的設(shè)計(jì)流程,分析了塑料部分進(jìn)行了模具仿真分析軟件讓選拔的最佳澆口位置圖6。這個(gè)數(shù)字表明最好的點(diǎn)澆口位置的中間饋線的中心部分。作為失真和陶瓷注射后的部分,至關(guān)重要的是,從功能的角度,它必須被保持在最低水平,同樣也使用軟件里面分析。圖5 b顯示結(jié)果暗示了事實(shí)后殘留在陶瓷注射預(yù)定義的尺寸公差。
6總結(jié)
在塑料注塑、CAD模型所得的塑料部分商業(yè)的3 D程序可用于部分性能和注塑工藝分析。借助于CEA技術(shù)和并行工程方法的使用,不僅注塑模具的設(shè)計(jì)和制造可以在很短的一段時(shí)間完成,而且它可能在開始時(shí)的模具設(shè)計(jì)把出現(xiàn)的所有潛在的問題從部分設(shè)計(jì)、模具設(shè)計(jì)和工藝參數(shù)消除。這兩個(gè)工具幫助設(shè)計(jì)師和模具制造商生產(chǎn)良好的產(chǎn)品,更好的交付和更快的模具用較少的時(shí)間和金錢。
【原文一】
CONCURRENT DESIGN OF PLASTICS INJECTION MOULDS
Assist.Prof.Dr. A. YAYLA /Prof.Dr. Pa? a YAYLA
Abstract
The plastic product manufacturing industry has been growing rapidly in recent years. One of the most popular processes for making plastic parts is injection moulding. The design of injection mould is critically important to product quality and efficient product processing. Mould-making companies, who wish to maintain the competitive edge, desire to shorten both design and manufacturing leading times of the by applying a systematic mould design process.
The mould industry is an important support industry during the product development process, serving as an important link between the product designer and manufacturer. Product development has changed from the traditional serial process of design, followed by manufacture, to a more organized concurrent process where design and manufacture are considered at a very early stage of design. The concept of concurrent engineering (CE) is no longer new and yet it is still applicable and relevant in today’s manuf acturing environment. Team working spirit, management involvement, total design process and integration of IT tools are still the essence of CE. The application of The CE process to the design of an injection process involves the simultaneous consideration of plastic part design, mould design and injection moulding machine selection, production scheduling and cost as early as possible in the design stage.
This paper presents the basic structure of an injection mould design. The basis of this system arises from an analysis of the injection mould design process for mould design companies. This injection mould design system covers both the mould design process and mould knowledge management. Finally the principle of concurrent engineering process is outlined and then its principle is applied to the design of a plastic injection mould.
Keywords :Plastic injection mould design, Concurrent engineering, Computer aided engineering, Moulding conditions, Plastic injection moulding, Flow simulation
1. Introduction
Injection moulds are always expensive to make, unfortunately without a mould it can not be possible ho have a moulded product. Every mould maker has his/her own approach to design a mould and there are many different ways of designing and building a mould. Surely one of the most critical parameters to be considered in the design stage of the mould is the number of cavities, methods of injection, types of runners, methods of gating, methods of ejection, capacity and features of the injection moulding machines. Mould cost, mould quality and cost of mould product are inseparable
In today’s completive environment, computer aided mould filling simulation packages can accurately predict the fill patterns of any part. This allows for quick simulations of gate placements and helps finding the optimal location. Engineers can perform moulding trials on the computer before the part design is completed. Process engineers can systematically predict a design and process window, and can obtain information about the cumulative effect of the process variables that influence part performance, cost, and appearance.
2. Injection Moulding
Injection moulding is one of the most effective ways to bring out the best in plastics. It is universally used to make complex, finished parts, often in a single step, economically, precisely and with little waste. Mass production of plastic parts mostly utilizes moulds. The manufacturing process and involving moulds must be designed after passing through the appearance evaluation and the structure optimization of the product design. Designers face a huge number of options when they create injection-moulded components. Concurrent engineering requires an engineer to consider the manufacturing process of the designed product in the development phase. A good design of the product is unable to go to the market if its manufacturing process is impossible or too expensive. Integration of process simulation, rapid prototyping and manufacturing can reduce the risk associated with moving from CAD to CAM and further enhance the validity of the product development.
3. Importance of Computer Aided Injection Mould Design
The injection moulding design task can be highly complex. Computer Aided Engineering (CAE) analysis tools provide enormous advantages of enabling design engineers to consider virtually and part, mould and injection parameters without the real use of any manufacturing and time. The possibility of trying alternative designs or concepts on the computer screen gives the engineers the opportunity to eliminate potential problems before beginning the real production. Moreover, in virtual environment, designers can quickly and easily asses the sensitivity of specific moulding parameters on the quality and manufacturability of the final product. All theseCAE tools enable all these analysis to be completed in a meter of days or even hours, rather than weeks or months needed for the real experimental trial and error cycles. As CAE is used in the early design of part, mould and moulding parameters, the cost savings are substantial not only because of best functioning part and time savings but also the shortens the time needed to launch the product to the market.
The need to meet set tolerances of plastic part ties in to all aspects of the moulding process, including part size and shape, resin chemical structure, the fillers used, mould cavity layout, gating, mould cooling and the release mechanisms used. Given this complexity, designers often use computer design tools, such as finite element analysis (FEA) and mould filling analysis (MFA), to reduce development time and cost. FEA determines strain, stress and deflection in a part by dividing the structure into small elements where these parameters can be well defined. MFA evaluates gate position and size to optimize resin flow. It also defines placement of weld lines, areas of excessive stress, and how wall and rib thickness affect flow. Other finite element design tools include mould cooling analysis for temperature distribution, and cycle time and shrinkage analysis for dimensional control and prediction of frozen stress and warpage.
The CAE analysis of compression moulded parts is shown in Figure 1. The analysis cycle starts with the creation of a CAD model and a finite element mesh of the mould cavity. After the injection conditions are specified, mould filling, fiber orientation, curing and thermal history, shrinkage and warpage can be simulated. The material properties calculated by the simulation can be used to model the structural behaviour of the part. If required, part design, gate location and processing conditions can be modified in the computer until an acceptable part is obtained. After the analysis is finished an optimized part can be produced with reduced weldline (known also knitline), optimized strength, controlled temperatures and curing, minimized shrinkage and warpage.
Machining of the moulds was formerly done manually, with a toolmaker checking each cut. This process became more automated with the growth and widespread use of computer numerically controlled or CNC machining centres. Setup time has also been significantly reduced through the use of special software capable of generating cutter paths directly from a CAD data file. Spindle speeds as high as 100,000 rpm provide further advances in high speed machining. Cutting materials have demonstrated phenomenal performance without the use of any cutting/coolant fluid whatsoever. As a result, the process of machining complex cores and cavities has been accelerated.
It is good news that the time it takes to generate a mould is constantly being reduced. The bad news, on the other hand, is that even with all these advances, designing and manufacturing of the mould can still take a long time and can be extremely expensive.
Figure 1 CAE analysis of injection moulded parts
Many company executives now realize how vital it is to deploy new products to market rapidly. New products are the key to corporate prosperity. They drive corporate revenues, market shares, bottom lines and share prices. A company able to launch good quality products with reasonable prices ahead of their competition not only realizes 100% of the market before rival products arrive but also tends to maintain a dominant position for a few years even after competitive products have finally been announced (Smith, 1991). For most products, these two advantages are dramatic. Rapid product development is now a key aspect of competitive success. Figure 2 shows that only 3–7% of the product mix from the average industrial or electronics company is less than 5 years old. For companies in the top quartile, the number increases to 15–25%. For world-class firms, it is 60–80% (Thompson, 1996). The best companies continuously develop new products. At Hewlett-Packard, over 80% of the profits result from products less than 2 years old! (Neel, 1997)
Figure 2. Importance of new product (Jacobs, 2000)
With the advances in computer technology and artificial intelligence, efforts have been directed to reduce the cost and lead time in the design and manufacture of an injection mould. Injection mould design has been the main area of interest since it is a complex process involving several sub-designs related to various components of the mould, each requiring expert knowledge and experience. Lee et. al. (1997) proposed a systematic methodology and knowledge base for injection mould design in a concurrent engineering environment.
4. Concurrent Engineering in Mould Design
Concurrent Engineering (CE) is a systematic approach to integrated product development process. It represents team values of co-operation, trust and sharing in such a manner that decision making is by consensus, involving all per spectives in parallel, from the very beginning of the product life-cycle (Evans, 1998). Essentially, CE provides a collaborative, co-operative, collective and simultaneous engineering working environment. A concurrent engineering approach is based on five key elements:
1. process
2. multidisciplinary team
3. integrated design model
4. facility
5. software infrastructure
Figure 3 Methodologies in plastic injection mould design, a) Serial engineering b) Concurrent engineering
In the plastics and mould industry, CE is very important due to the high cost tooling and long lead times. Typically, CE is utilized by manufacturing prototype tooling early in the design phase to analyze and adjust the design. Production tooling is manufactured as the final step. The manufacturing process and involving moulds must be designed after passing through the appearance evaluation and the structure optimization of the product design. CE requires an engineer to consider the manufacturing process of the designed product in the development phase. A good design of the product is unable to go to the market if its manufacturing process is impossible. Integration of process simulation and rapid prototyping and manufacturing can reduce the risk associated with moving from CAD to CAM and further enhance the validity of the product development.
For years, designers have been restricted in what they can produce as they generally have to design for manufacture (DFM) – that is, adjust their design intent to enable the component (or assembly) to be manufactured using a particular process or processes. In addition, if a mould is used to produce an item, there are therefore automatically inherent restrictions to the design imposed at the very beginning. Taking injection moulding as an example, in order to process a component successfully, at a minimum, the following design elements need to be taken into account:
1. . geometry;
. draft angles,
. Non re-entrants shapes,
. near constant wall thickness,
. complexity,
. split line location, and
. surface finish,
2. material choice;
3. rationalisation of components (reducing assemblies);
4. cost.
In injection moulding, the manufacture of the mould to produce the injection-moulded components is usually the longest part of the product development process. When utilising rapid modelling, the CAD takes the longer time and therefore becomes the bottleneck.
The process design and injection moulding of plastics involves rather complicated and time consuming activities including part design, mould design, injection moulding machine selection, production scheduling, tooling and cost estimation. Traditionally all these activities are done by part designers and mould making personnel in a sequential manner after completing injection moulded plastic part design. Obviously these sequential stages could lead to long product development time. However with the implementation of concurrent engineering process in the all parameters effecting product design, mould design, machine selection, production scheduling, tooling and processing cost are considered as early as possible in the design of the plastic part.
When used effectively, CAE methods provide enormous cost and time savings for the part design and manufacturing. These tools allow engineers to virtually test how the part will be processed and how it performs during its normal operating life. The material supplier, designer, moulder and manufacturer should apply these tools concurrently early in the design stage of the plastic parts in order to exploit the cost benefit of CAE. CAE makes it possible to replace traditional, sequential decision-making procedures with a concurrent design process, in which all parties can interact and share information, Figure 3. For plastic injection moulding, CAE and related design data provide an integrated environment that facilitates concurrent engineering for the design and manufacture of the part and mould, as well as material selection and simulation of optimal process control parameters.
Qualitative expense comparison associated with the part design changes is shown in Figure 4 , showing the fact that when design changes are done at an early stages on the computer screen, the cost associated with is an order of 10.000 times lower than that if the part is in production. These modifications in plastic parts could arise fr om mould modifications, such as gate location, thickness changes, production delays, quality costs, machine setup times, or design change in plastic parts.
Figure 4 Cost of design changes during part product development cycle (Rios et.al, 2001)
At the early design stage, part designers and moulders have to finalise part design based on their experiences with similar parts. However as the parts become more complex, it gets rather difficult to predict processing and part performance without the use of CAE tools. Thus for even relatively complex parts, the use of CAE tools to prevent the late and expe