氣門搖桿軸支座零件機(jī)械加工工藝過程及其銑φ32外圓端面工裝夾具設(shè)計(jì)
氣門搖桿軸支座零件機(jī)械加工工藝過程及其銑32外圓端面工裝夾具設(shè)計(jì),氣門搖桿軸支座零件機(jī)械加工工藝過程及其銑32外圓端面工裝夾具設(shè)計(jì),氣門,搖桿,支座,零件,機(jī)械,加工,工藝,過程,進(jìn)程,及其,32,端面,工裝,夾具,設(shè)計(jì)
廣西大學(xué)先進(jìn)制造專業(yè)機(jī)械加工工藝卡片工序名稱鑄造工序號I零件名稱氣門搖桿軸支座零件號零件重量3kg同時(shí)加工件數(shù)4材料毛坯牌號硬度型號重量HT200190225HBS鑄件3.2kg設(shè)備夾具輔助工具名稱型號專用夾具鍋爐安裝工步安裝及工步說明刀具量具走刀長度mm走刀次數(shù)切削深度mm進(jìn)給量mm/r主軸轉(zhuǎn)速r/min切削速度m/min基本工時(shí)min1備料52鑄造游標(biāo)卡尺15設(shè)計(jì)者指導(dǎo)老師共13 頁第 1 頁廣西大學(xué)先進(jìn)制造專業(yè)機(jī)械加工工藝卡片工序名稱時(shí)效工序號零件名稱氣門搖桿軸支座零件號零件重量3kg同時(shí)加工件數(shù)材料毛坯牌號硬度型號重量HT200190225HBS鑄件3.2kg設(shè)備夾具輔助工具名稱型號專用夾具數(shù)控車床C6161安裝工步安裝及工步說明刀具量具走刀長度mm走刀次數(shù)切削深度mm進(jìn)給量mm/r主軸轉(zhuǎn)速r/min切削速度m/min基本工時(shí)min480設(shè)計(jì)者指導(dǎo)老師共 1 3 頁第 2 頁廣西大學(xué)先進(jìn)制造專業(yè)機(jī)械加工工藝卡片工序名稱涂漆工序號III零件名稱氣門搖桿軸支座零件號零件重量3kg同時(shí)加工件數(shù)4材料毛坯牌號硬度型號重量HT200180207HB鑄件3.2kg設(shè)備夾具輔助工具名稱型號專用夾具毛刷數(shù)控車床C616-1安裝工步安裝及工步說明刀具量具走刀長度mm走刀次數(shù)切削深度mm進(jìn)給量mm/r主軸轉(zhuǎn)速r/min切削速度m/min基本工時(shí)min1涂漆52晾干360設(shè)計(jì)者指導(dǎo)老師共 1 3 頁第 3 頁廣西大學(xué)先進(jìn)制造專業(yè)機(jī)械加工工藝卡片工序名稱銑上端面工序號 零件名稱氣門搖桿軸支座零件號零件重量3kg同時(shí)加工件數(shù)1材料毛坯牌號硬度型號重量HT200180207HRC鑄件3.2kg設(shè)備夾具輔助工具名稱型號專用夾具立式銑床X1632安裝工步安裝及工步說明刀具量具走刀長度mm走刀次數(shù)切削深度mm進(jìn)給量mm/r主軸轉(zhuǎn)速r/min切削速度m/min基本工時(shí)min1安裝夾緊22銑上端平面至81尺寸硬質(zhì)合金立銑刀游標(biāo)卡尺48120.142554000.0設(shè)計(jì)者指導(dǎo)老師共 1 3 頁第 4 頁廣西大學(xué)先進(jìn)制造專業(yè)機(jī)械加工工藝卡片工序名稱粗,精銑下端面工序號零件名稱氣門搖桿軸支座零件號零件重量3kg同時(shí)加工件數(shù)1材料毛坯牌號硬度型號重量HT200180207HRC鑄件3.2kg設(shè)備夾具輔助工具名稱型號專用夾具立式銑床X1632安裝工步安裝及工步說明刀具量具走刀長度mm走刀次數(shù)切削深度mm進(jìn)給量mm/r主軸轉(zhuǎn)速r/min切削速度m/min基本工時(shí)min1裝夾22加工時(shí)保證78,mm尺寸硬質(zhì)合金立銑刀游標(biāo)卡尺50120.143804000.32 設(shè)計(jì)者指導(dǎo)老師共 1 3 頁第 5 頁廣西大學(xué)先進(jìn)制造專業(yè)機(jī)械加工工藝卡片工序名稱鉆兩13通孔工序號零件名稱氣門搖桿軸支座零件號零件重量3kg同時(shí)加工件數(shù)1材料毛坯牌號硬度型號重量HT200180207HRC鑄件3.2kg設(shè)備夾具輔助工具名稱型號專用夾具高速臺鉆Z3025安裝工步安裝及工步說明刀具量具走刀長度mm走刀次數(shù)切削深度mm進(jìn)給量mm/r主軸轉(zhuǎn)速r/min切削速度m/min基本工時(shí)min1安裝夾緊32鉆兩13孔高速鋼錐柄麻花鉆游標(biāo)卡尺7820.351951401.243設(shè)計(jì)者指導(dǎo)老師共 1 3 頁第 6 頁廣西大學(xué)先進(jìn)制造專業(yè)機(jī)械加工工藝卡片工序名稱銑右端面工序號零件名稱氣門搖桿軸支座零件號零件重量3kg同時(shí)加工件數(shù)1材料毛坯牌號硬度型號重量HT200180207HRC鑄件3.2kg設(shè)備夾具輔助工具名稱型號專用夾具立式銑床X1632安裝工步安裝及工步說明刀具量具走刀長度mm走刀次數(shù)切削深度mm進(jìn)給量mm/r主軸轉(zhuǎn)速r/min切削速度m/min基本工時(shí)min1安裝夾緊32銑右端面保證尺寸44硬質(zhì)合金立銑刀游標(biāo)卡尺32123804000.26設(shè)計(jì)者指導(dǎo)老師共 1 3 頁第 7 頁廣西大學(xué)先進(jìn)制造專業(yè)機(jī)械加工工藝卡片工序名稱鉆通孔18工序號零件名稱氣門搖桿軸支座零件號零件重量3kg同時(shí)加工件數(shù)1材料毛坯牌號硬度型號重量HT200180207HRC鑄件3.2kg設(shè)備夾具輔助工具名稱型號專用夾具高速臺鉆Z3025安裝工步安裝及工步說明刀具量具走刀長度mm走刀次數(shù)切削深度mm進(jìn)給量mm/r主軸轉(zhuǎn)速r/min切削速度m/min基本工時(shí)min1安裝夾緊32鉆通孔18高速鋼錐柄麻花鉆游標(biāo)卡尺441951401.10設(shè)計(jì)者指導(dǎo)老師共 1 3 頁第 8 頁廣西大學(xué)先進(jìn)制造專業(yè)機(jī)械加工工藝卡片工序名稱鏜孔到20，孔口倒角1*45度工序號零件名稱氣門搖桿軸支座零件號零件重量3kg同時(shí)加工件數(shù)1材料毛坯牌號硬度型號重量HT200180207HRC鑄件3.2kg設(shè)備夾具輔助工具名稱型號專用夾具臥式組合鏜床安裝工步安裝及工步說明刀具量具走刀長度mm走刀次數(shù)切削深度mm進(jìn)給量mm/r主軸轉(zhuǎn)速r/min切削速度m/min基本工時(shí)min1安裝夾緊32鏜孔到20，孔口倒角1*45度,保證位ITA20鏜削頭游標(biāo)卡尺44110.40380240.38置度要求1設(shè)計(jì)者指導(dǎo)老師共 1 3頁第 9 頁廣西大學(xué)先進(jìn)制造專業(yè)機(jī)械加工工藝卡片工序名稱銑左端面工序號零件名稱氣門搖桿軸支座零件號零件重量3kg同時(shí)加工件數(shù)1材料毛坯牌號硬度型號重量HT200180207HRC鑄件3.2kg設(shè)備夾具輔助工具名稱型號專用夾具立式銑床X1632安裝工步安裝及工步說明刀具量具走刀長度mm走刀次數(shù)切削深度mm進(jìn)給量mm/r主軸轉(zhuǎn)速r/min切削速度m/min基本工時(shí)min1安裝夾緊32銑左端面保證42硬質(zhì)合金立銑刀游標(biāo)卡尺32123804000.26設(shè)計(jì)者指導(dǎo)老師共 1 頁第 10 頁廣西大學(xué)先進(jìn)制造專業(yè)機(jī)械加工工藝卡片工序名稱銑軸向槽工序號零件名稱氣門搖桿軸支座零件號零件重量3kg同時(shí)加工件數(shù)1材料毛坯牌號硬度型號重量HT200180207HRC鑄件3.2kg設(shè)備夾具輔助工具名稱型號專用夾具立式銑床X1632安裝工步安裝及工步說明刀具量具走刀長度mm走刀次數(shù)切削深度mm進(jìn)給量mm/r主軸轉(zhuǎn)速r/min切削速度m/min基本工時(shí)min1定位夾緊22銑軸向槽保證尺寸3硬質(zhì)合金立銑刀游標(biāo)卡尺171100178200.18設(shè)計(jì)者指導(dǎo)老師共 1 3 頁第 11 頁廣西大學(xué)先進(jìn)制造專業(yè)機(jī)械加工工藝卡片工序名稱檢驗(yàn)工序號零件名稱氣門搖桿軸支座零件號零件重量3kg同時(shí)加工件數(shù)1材料毛坯牌號硬度型號重量HT200180207HRC鑄件3.2kg設(shè)備夾具輔助工具名稱型號專用夾具工作臺安裝工步安裝及工步說明刀具量具走刀長度mm走刀次數(shù)切削深度mm進(jìn)給量mm/r主軸轉(zhuǎn)速r/min切削速度m/min基本工時(shí)min1按產(chǎn)品圖要求對各尺寸進(jìn)行檢測5設(shè)計(jì)者指導(dǎo)老師共 13 頁第 12頁廣西大學(xué)先進(jìn)制造專業(yè)機(jī)械加工工藝卡片工序名稱入庫工序號零件名稱氣門搖桿軸支座零件號零件重量3kg同時(shí)加工件數(shù)1材料毛坯牌號硬度型號重量HT200180207HRC鑄件3.2kg設(shè)備夾具輔助工具名稱型號專用夾具安裝工步安裝及工步說明刀具量具走刀長度mm走刀次數(shù)切削深度mm進(jìn)給量mm/r主軸轉(zhuǎn)速r/min切削速度m/min基本工時(shí)min入庫進(jìn)行防銹處理擺放整齊,并進(jìn)行標(biāo)識6設(shè)計(jì)者指導(dǎo)老師共 1 3 頁第 13頁廣西大學(xué)先進(jìn)制造專業(yè)機(jī)械加工工藝過程卡片零件號零件名稱氣門搖桿軸支座工序號工序名稱設(shè)備夾具刀具量具機(jī)動工時(shí)（min）名稱型號名稱規(guī)格名稱規(guī)格名稱規(guī)格鑄造鍋爐專用夾具游標(biāo)卡尺01255時(shí)效鍋爐專用夾具游標(biāo)卡尺0125480涂漆毛刷 專用夾具游標(biāo)卡尺0125銑上端面立式銑床X1632專用夾具硬質(zhì)合金立銑刀80mm游標(biāo)卡尺01250.粗,精銑下端面立式銑床X1632專用夾具硬質(zhì)合金立銑刀80mm游標(biāo)卡尺01250.32鉆兩13通孔高速臺鉆Z3025專用夾具高速鋼錐柄麻花鉆13mm游標(biāo)卡尺01251.88銑右端面立式銑床X1632專用夾具硬質(zhì)合金立銑刀80mm游標(biāo)卡尺01250.26鉆通孔18高速臺鉆Z3025專用夾具高速鋼錐柄麻花鉆18mm游標(biāo)卡尺01251.10鏜孔到20，孔口倒角1*45度臥式組合鏜床專用夾具ITA20鏜削頭1.5KM游標(biāo)卡尺01250.38銑左端面立式銑床X1632專用夾具硬質(zhì)合金立銑刀80mm游標(biāo)卡尺01250.26銑軸向槽立式銑床X1632專用夾具硬質(zhì)合金立銑刀80mm游標(biāo)卡尺01250.18檢驗(yàn)工作臺自制游標(biāo)卡尺0125入庫工作臺自制0125機(jī)械制造工藝學(xué)課程設(shè)計(jì)任務(wù)書題目：設(shè)計(jì)氣門搖桿軸支座零件的機(jī)械加工工藝規(guī)程及專用夾具內(nèi)容：（1）零件一毛坯合圖 1張（2）機(jī)械加工工藝規(guī)程卡片 12張（3）夾具裝配總圖 1張（4）夾具零件圖 一張（5）課程設(shè)計(jì)說明書 一份原始資料：該零件圖樣一張；生產(chǎn)綱領(lǐng)6000件/年。 班級： 學(xué)生： 指導(dǎo)老師： 2008年9月20日目錄第一部分：序言 2一 設(shè)計(jì)目的 2二 設(shè)計(jì)感想與體會 2第二部分：工藝規(guī)程與夾具設(shè)計(jì)過程工藝規(guī)程與夾具設(shè)計(jì)過程 4一、設(shè)計(jì)題目,計(jì)算生產(chǎn)綱領(lǐng)及生產(chǎn)型 4二、零件的分析5 (一) 零件的作 5(二) 零件的工藝分析 5三、確定毛坯的制造方法，初步確定毛坯 6四、工藝規(guī)程設(shè)計(jì) 6 (一) 定位基準(zhǔn)的選擇 6（二）零件表面加工方法的選擇 7（三）制定加工工藝路線 8（四）選擇加工設(shè)備及刀、夾、量具 10五、加工工序設(shè)計(jì) 11(一) 確定切削用量及基本工時(shí) 11六、填寫機(jī)械加工工藝卡和機(jī)械加工工序卡 17 七、夾具設(shè)計(jì)17（一）問題的提出17（二）夾具設(shè)計(jì)的有關(guān)計(jì)算17（三）夾具結(jié)構(gòu)設(shè)計(jì)及操作簡要說明20八、主要參考文獻(xiàn)21序 言一、設(shè)計(jì)目的：現(xiàn)代機(jī)械制造工藝設(shè)計(jì)是機(jī)械類專業(yè)學(xué)生在學(xué)完了機(jī)械制造技術(shù)基礎(chǔ)等技術(shù)基礎(chǔ)和專業(yè)課理論之后進(jìn)行的一個(gè)實(shí)踐教學(xué)環(huán)節(jié)。其目的是鞏固和加深理論教學(xué)內(nèi)容，培養(yǎng)學(xué)生綜合運(yùn)用所學(xué)理論，解決現(xiàn)代實(shí)際工藝設(shè)計(jì)問題的能力。通過工藝規(guī)程及工藝裝備設(shè)計(jì)，學(xué)生應(yīng)達(dá)到：1、掌握零件機(jī)械加工工藝規(guī)程設(shè)計(jì)的能力；2、掌握加工方法及其機(jī)床、刀具及切削用量等的選擇應(yīng)用能力；3、掌握機(jī)床專用夾具等工藝裝備的設(shè)計(jì)能力；4、學(xué)會使用、查閱各種設(shè)計(jì)資料、手冊和國家標(biāo)準(zhǔn)等，以及學(xué)會繪制工序圖、夾具總裝圖，標(biāo)注必要的技術(shù)條件等。二、設(shè)計(jì)感想與體會：三周的課程設(shè)計(jì)就是一個(gè)團(tuán)隊(duì)合作的過程。所謂1+12，一個(gè)團(tuán)隊(duì)的合作，使我們的設(shè)計(jì)成果不到三周時(shí)間就漸漸呈現(xiàn)在我們的眼前?？粗矍暗氖止D紙、CAD圖和設(shè)計(jì)計(jì)算的手稿，三周的設(shè)計(jì)過程一幕幕浮現(xiàn)在眼前。三周的設(shè)計(jì)讓我們學(xué)到了很多東西。這次設(shè)計(jì)可以說是三年的課程學(xué)習(xí)所掌握的所有機(jī)械工程學(xué)科的基礎(chǔ)知識的融會貫通，因?yàn)槲覀円郧霸?jīng)學(xué)得很好，但是都是理論的東西，學(xué)習(xí)了馬克思主義哲學(xué)之后，終于知道理論聯(lián)系實(shí)際才使我們有了更進(jìn)一步的體會。在這次設(shè)計(jì)中，我學(xué)會的如何設(shè)計(jì)、如何計(jì)算，更重要的是我學(xué)會了合作，我懂得了團(tuán)隊(duì)合作的重要性。我們以前做的設(shè)計(jì)都是一個(gè)人的，而且規(guī)模小，不需要什么規(guī)劃，這次可以說是綜合了我們的所有智慧。同時(shí)，得到了我們的指導(dǎo)老師的大力支持。由于我們水平所限，設(shè)計(jì)中難免有錯(cuò)誤和不妥之處，在此還誠請指導(dǎo)老師批評指正。工藝規(guī)程與夾具設(shè)計(jì)過程一、根據(jù)生產(chǎn)綱領(lǐng)，確定生產(chǎn)類型：該零件是柴油機(jī)上的氣門搖桿軸支座，按照指導(dǎo)老師的要求，設(shè)計(jì)此零件為大批量生產(chǎn)。二 零件的分析 （一） 零件的作用氣門搖桿軸支座是柴油機(jī)一個(gè)主要零件。是柴油機(jī)搖桿座的結(jié)合部，20孔裝搖桿軸，軸上兩端各裝一進(jìn)氣門搖桿，搖桿座通過兩個(gè)13mm孔用M12螺桿與汽缸蓋相連，3mm軸向槽用于鎖緊搖桿軸，使之不轉(zhuǎn)動。（二） 零件的工藝分析 由附圖1得知，其材料為HT200。該材料具有較高的強(qiáng)度，耐磨性，耐熱性及減振性，適用于承受較大應(yīng)力，要求耐磨的零件。 該零件上主要加工面為上端面、下端面，左、右端面，2-13mm孔和20mm以及3mm軸向槽的加工。20mm孔的尺寸精度與下端面0.05mm的平行度與左右兩端面孔的尺寸精度，直接影響到進(jìn)氣門與排氣門的傳動精度及密封，213mm孔的尺寸精度，以上下兩端面的平行度0.05mm。因此，需要先以下端面為粗基準(zhǔn)加工上端面，再以上端面為粗基準(zhǔn)加工下端面，再把下端面作為精基準(zhǔn)，最后加工20mm孔與左右兩端面時(shí)以下端面為定位基準(zhǔn)，以保證孔軸線與兩端面相對下端面的位置精度。由參考文獻(xiàn)（1）中有關(guān)孔的加工的經(jīng)濟(jì)精度機(jī)床能達(dá)到的位置精度可知上述要求可以達(dá)到的零件的結(jié)構(gòu)的工藝性也是可行的。三 確定毛坯的制造方法，初步確定毛坯形狀，（附圖2）根據(jù)零件的用途及其結(jié)構(gòu)，材料確定為HT200，毛坯為鑄件，零件形狀簡單，因此毛坯形狀需與零件的形狀盡量接近，又因內(nèi)孔很小，不可鑄出。已知零件的生產(chǎn)綱領(lǐng)為6000件/年，通過計(jì)算，該零件質(zhì)量約為3Kg，由參考文獻(xiàn)（5）表14、表13可知，其生產(chǎn)類型為大批生產(chǎn)，毛坯的鑄造方法選用砂型機(jī)器造型。此外，為消除殘余應(yīng)力，鑄造后安排人工時(shí)效處理。參考文獻(xiàn)（1）表2.312；該種鑄造公差等級為CT1011，MA-H級。參考文獻(xiàn)（1）表2.3-12，用查表方法確定各表面的加工余量如下表所示：表1加工表面基本尺寸加工余量等級加工余量數(shù)值說明上端面82mmH2mm單側(cè)加工下端面82mmH2mm單側(cè)加工左端面46mmH2mm單側(cè)加工右端面46mmH2mm單側(cè)加工四工藝規(guī)程設(shè)計(jì)（一） 定位基準(zhǔn)的選擇：定位基準(zhǔn)的選擇是工藝規(guī)程設(shè)計(jì)中的重要工作之一，定位基準(zhǔn)選擇得正確與合理，可以使加工質(zhì)量得到保證，生產(chǎn)率得以提高，否則，加工工藝過程中會問題百出，更有甚者，還會造成零件大批報(bào)廢，使生產(chǎn)無法正常進(jìn)行。粗基準(zhǔn)的選擇：考慮到以下幾點(diǎn)要求，選擇零件的重要面和重要孔做基準(zhǔn)。在保證各加工面均有加工余量的前提下，使重要孔或面的加工余量盡量均勻，此外，還要保證定位夾緊的可靠性，裝夾的方便性，減少輔助時(shí)間，所以粗基準(zhǔn)為上端面。加工左右兩端平面時(shí),為了保證位置度求,采用一面兩孔定位,限制六個(gè)自由度,用下端面與兩13孔作為定位基準(zhǔn). 鏜削20mm孔的定位夾緊方案為：用一菱形銷加一圓柱銷定位兩個(gè)13mm的孔，再加上底面定位實(shí)現(xiàn)，兩孔一面完全定位，這種方案適合于大批生產(chǎn)類型中。精基準(zhǔn)的選擇：主要考慮基準(zhǔn)重合問題，氣門搖桿軸支座的下端面既是裝配基準(zhǔn)又是設(shè)計(jì)基準(zhǔn)，用它作為精基準(zhǔn)，能使加工遵循基準(zhǔn)重合的原則。20孔及左右兩端面都采用底面做基準(zhǔn)，這使得工藝路線又遵循“基準(zhǔn)統(tǒng)一”的原則，下端面的面積比較大，定位比較穩(wěn)定，夾緊方案也比較簡單，可靠，操作方便。（二）零件表面加工方法的選擇：本零件的加工面有端面、內(nèi)孔、槽等，材料為HT200灰鑄鐵，參考機(jī)械制造工藝設(shè)計(jì)簡明手冊（以下簡稱工藝手冊）表1.4-7、表1.4-8及表1.4-17其加工方法選擇如下：上端面：粗銑。 下端面：精銑左端面：粗銑精銑 右端面：粗銑精銑213mm孔：鉆孔。 3mm 軸向槽精銑20mm：鉆孔粗鏜精鏜（三）制定加工工藝路線制定工藝路線的出發(fā)點(diǎn)，應(yīng)當(dāng)是使零件的加工精度（尺寸精度、形狀精度、位置精度）和表面質(zhì)量等技術(shù)要求能得到合理的保證。在生產(chǎn)綱領(lǐng)已經(jīng)確定為中批量生產(chǎn)的條件下，可以考慮采用通用機(jī)床配以專用夾具并盡量使工序集中來提高生產(chǎn)率。除此以外，還應(yīng)當(dāng)考慮經(jīng)濟(jì)效果，以便使生產(chǎn)成本盡量下降。方案一：表2工序號工序內(nèi)容01鑄造02時(shí)效03涂漆04車上端面05鉆兩13通孔06精銑下端面07銑右端面08鉆通孔18mm09鏜孔20mm，孔口角*度10銑左端面11銑軸向槽12檢驗(yàn)13入庫方案二：表3序號工序內(nèi)容簡要說明01020304050607080910111213鑄造時(shí)效涂漆銑上端面粗,精銑下端面鉆兩13通孔銑右端面鉆通孔18鏜孔到20，孔口倒角1*45度銑左端面銑軸向槽檢驗(yàn)入庫消除內(nèi)應(yīng)力防止生銹先加工粗基準(zhǔn)面加工經(jīng)基準(zhǔn)先面后孔先面后孔后鏜削余量次要工序后加工工藝方案的比較與分析：因左右兩端面均對20mm孔有較高的位置要求，故它們的加工宜采用工序集中原則，減少裝次數(shù)，提高加工精度。根據(jù)先面后孔，先主要表面后次要表面和先粗加工后精加工的原則，將端面的精銑和下端面的粗銑放在前面，下端面的精銑放在后面，每一階段要首先加工上端面后鉆孔，左右端面上20mm孔放后面加工。初步擬訂加工路線方案一。方案一遵循了工藝路線擬訂的一般原則，但某些工序還有一些問題還值得進(jìn)一步討論。如車上端面，因工件和夾具的尺寸較大，在臥式車床上加工時(shí)，它們慣性力較大，平衡困難；又由上端面不是連續(xù)的圓環(huán)面，車削中出現(xiàn)斷續(xù)切削容易引起工藝系統(tǒng)的震動，故改動銑削加工。工序05應(yīng)在工序06前完成，使上端面在加工后有較多的時(shí)間進(jìn)行自然時(shí)效，減少受力變形和受熱變形對213mm通孔加工精度的影響。通過以上的兩工藝路線的優(yōu)、缺點(diǎn)分析，最后確定工藝路線方案一為該零件的加工路線。該工藝過程詳見附表和附表2，機(jī)械加工工藝過程卡片和機(jī)械加工工序卡片。（四） 選擇加工設(shè)備及刀、夾、量具由于生產(chǎn)類型為大批生產(chǎn)，故加工設(shè)備適宜通用機(jī)床為主，輔以少量專用機(jī)床的流水生產(chǎn)線，工件在各機(jī)床上的裝卸及各機(jī)床間的傳動均由人工完成。銑上端面：考慮到工件的定位夾緊方案及夾具結(jié)構(gòu)設(shè)計(jì)等問題，采用立銑選擇X1632立式銑床。（參考文獻(xiàn)（1）表6-18），選擇直徑D為80mm立銑刀，參考文獻(xiàn)（1）表7-88，通用夾具和游標(biāo)卡尺。粗銑下端面：采用上述相同的機(jī)床與銑刀，通用夾具游標(biāo)卡尺。精銑下端面：采用上述相同的機(jī)床與銑刀，通用夾具游標(biāo)卡尺。粗銑左端面：采用立式銑床X1632，參考文獻(xiàn)（1）表621，采用以前的刀具，專用夾具游標(biāo)卡尺。精銑左端面：采用臥式銑床X1632,參考文獻(xiàn)（1）表621，專用夾具及游標(biāo)卡尺。鉆2-13mm孔：采用Z3025，參考文獻(xiàn)（1）表626，通用夾具。刀具為d為13mm的直柄麻花鉆，參考文獻(xiàn)（1）表7111。鉆18mm孔：鉆孔直行為18mm，選擇搖臂鉆床Z3025參考文獻(xiàn)（1）表626，采用錐柄麻花鉆，通用夾具及量具。鏜20mm孔：粗鏜：采用臥式組合鏜床，選擇功率為1.5KM的ITA20鏜削頭，參考文獻(xiàn)（1）白喔88。選擇鏜通孔鏜刀及鏜桿，專用夾具，游標(biāo)卡尺。五 加工工序設(shè)計(jì)(一)確定切削用量及基本工時(shí)（機(jī)動時(shí)間）在工藝文件中還要確定每一工步的切削用量。(1)切削用量指：背吃刀量asp(即切削深度ap)、進(jìn)給量f及切削速度Vc 。(2)確定方法是：確定切削深度確定進(jìn)給量確定切削速度(3)具體要求是：由工序或工步余量確定切削深度：精、半精加工全部余量在一次走刀中去除；在中等功率機(jī)床上一次走刀ap可達(dá)810mm。按本工序或工步加工表面粗糙度確定進(jìn)給量：對粗加工工序或工步按加工表面粗糙度初選進(jìn)給量后還要校驗(yàn)機(jī)床進(jìn)給機(jī)構(gòu)強(qiáng)度：可用查表法或計(jì)算法得出切削速度Vc查，用公式 換算出查表或計(jì)算法所得的轉(zhuǎn)速nc查，根據(jù)Vc查在選擇機(jī)床實(shí)有的主軸轉(zhuǎn)速表中選取接近的主軸轉(zhuǎn)速n機(jī)作為實(shí)際的轉(zhuǎn)速，再用 換算出實(shí)際的切削速度Vc機(jī)填入工藝文件中。對粗加工，選取實(shí)際切削速度Vc機(jī)、實(shí)際進(jìn)給量f機(jī)和背吃刀量asp之后，還要校驗(yàn)機(jī)床功率是否足夠等，才能作為最后的切削用量填入工藝文件中。工序鉆個(gè)mm孔(1)、加工條件工件材料：HT200正火，b=220MPa，190220HBS 加工要求：鉆擴(kuò)孔mm 機(jī)床選擇：選用立式鉆床Z525（見工藝手冊表4.2-14）(2)、確定切削用量及基本工時(shí)選擇mm高速鋼錐柄標(biāo)準(zhǔn)麻花鉆（見工藝手冊P84）d=13 L=238mm L1=140mmf機(jī)=0.48mm/r (見切削手冊表2.7和工藝手冊表4.2-16)Vc查=13m/min （見切削手冊表2.15）按機(jī)床選取n機(jī)=195r/min（按工藝手冊表4.2-15）所以實(shí)際切削速度： m/min.基本工時(shí)： l=80mm ) l2=(14)mm(取4mm)按工藝手冊表6.2-5公式計(jì)算1.24（min）工序 粗、精銑左右端面（） 粗銑1）、選擇刀具：根據(jù)工藝手冊表3.1-27，選擇用一把YG6硬質(zhì)合金端銑刀，其參數(shù)為：銑刀外徑d0=100mm，銑刀齒數(shù)Z=10。2）、確定銑削深度a p：單邊加工余量Z=0.27，余量不大，一次走刀內(nèi)切完，則：a p=mm3）、確定每齒進(jìn)給量fz:根據(jù)切削手冊表3.5，用硬質(zhì)合金銑刀在功率為4.5kw的X51銑床加工時(shí)，選擇每齒進(jìn)給量fz=0.140.24mm/z，由于是粗銑，取較大的值?，F(xiàn)?。篺z=0.18mm/z4）、選擇銑刀磨鈍標(biāo)準(zhǔn)及刀具耐用度：根據(jù)切削手冊表3.7，銑刀刀齒后刀面最大磨損量為1.01.5mm，現(xiàn)取1.2mm，根據(jù)切削手冊表3.8銑刀直徑d0=100mm的硬質(zhì)合金端銑刀的耐用度T=180min。5）、確定切削速度Vc：根據(jù)切削手冊表3.16可以查Vc：由 ap=mm fz=0.18mm/z，查得Vc=77mm/z n=245mm/z V=385mm/z根據(jù)X1632型立銑床說明書（表4.2-35）nc=255 r/min Vc=400 mm/min (橫向)6）、計(jì)算基本工時(shí)：l=47mm l2=2 T=0. min（）精銑1）、選擇刀具：根據(jù)工藝手冊表3.1-27，選擇用一把YG6硬質(zhì)合金端銑刀，銑刀外徑d0=100mm，銑刀齒數(shù)Z=102）、確定銑削深度ap：由于單邊加工余量Z=1，故一次走刀內(nèi)切完，則：a p= 1 mm3）、確定每齒進(jìn)給量fz:由切削手冊表3.5，用硬質(zhì)合金銑刀在功率為4.5kw的X51銑床加工時(shí)，選擇每齒進(jìn)給量fz=0.140.24mm/z，半精銑取較小的值。現(xiàn)?。篺z=0.14mm/z4）、選擇銑刀磨鈍標(biāo)準(zhǔn)及刀具耐用度：根據(jù)切削手冊表3.7，銑刀刀齒后刀面最大磨損量為1.01.5mm，現(xiàn)取1.2mm，根據(jù)切削手冊表3.8銑刀直徑d0=100mm的硬質(zhì)合金端銑刀的耐用度T=180min。5）、確定切削速度Vc：根據(jù)切削手冊表3.16可以查Vc：由 ap4mm z=0.14mm/z，查得：Vc=110mm/z n=352mm/z V=394mm/z根據(jù)X1632型立銑床說明書（表4.2-35）nc=380 r/min Vc=400 mm/min (橫向)6）、計(jì)算基本工時(shí)：l=40 mm l2 =2 所以本工序的基本時(shí)間為： T=t1+t2=0.14+0.12=0.26min（）工序粗鏜工序粗鏜余量參考文獻(xiàn)表取粗鏜為.mm，粗鏜切削余量為0.2mm,鉸孔后尺寸為20H8,各工部余量和工序尺寸公差列于表加工表面加工方法余量公差等級工序尺寸及公差18粗鏜1.8_19.819.2精鏜0.2H820H8孔軸線到底面位置尺寸為0mm，精鏜后工序尺寸為20.020.08mm，與下底面的位置精度為0.05mm,與左右端面的位置精度為0.06mm,且定位夾緊時(shí)基準(zhǔn)重合，故不需保證。0.06mm跳動公差由機(jī)床保證。(2.1) 鉆孔18mm選擇18mm高速鋼錐柄標(biāo)準(zhǔn)麻花鉆（見工藝手冊P84）d=18 L=238mm L1=140mmf機(jī)=0.48mm/r (見切削手冊表2.7和工藝手冊表4.2-16)Vc查=13m/min （見切削手冊表2.15）按機(jī)床選取n機(jī)=195r/min（按工藝手冊表4.2-15）所以實(shí)際切削速度：基本工時(shí)：l=80mm ) l2=(14)mm(取4mm)按工藝手冊表6.2-5公式計(jì)算 1.10min粗鏜孔時(shí)因余量為1mm,故ap=1mm,查文獻(xiàn)表. 4-8取V=0.4m/s=24m/min去進(jìn)給量為f=002mm/rn=1000V/d=1000*24/3.14*20=380r/min查文獻(xiàn)的Fz=9.81*60nFzCFzapXFzVnFzKFzpm=FzV*10-3CF2=180, XFz=1Yfz=0.75nFz=0Rfz=9.81*60*180*2.75*0.20.75*0.4*1 =1452 NP=0.58 kw 取機(jī)床效率為.0.78*0.85=0.89kw0.58kw故機(jī)床的功率足夠。下面計(jì)算工序09的時(shí)間定額（） 機(jī)動時(shí)間粗鏜時(shí)：L/(f*n)=45/0.2*380=7.5s精鏜時(shí)：f取0.1mm/s L/(f*n)=45/0.1*380=15s總機(jī)動時(shí)間:T=7.5+15=0.38min六 填寫機(jī)械加工工藝卡和機(jī)械加工工序卡工藝文件詳見附表。七 夾具設(shè)計(jì)為了提高勞動生產(chǎn)率，保證加工質(zhì)量，降低勞動成本，需要設(shè)計(jì)專用夾具。按指導(dǎo)老師的布置，設(shè)計(jì)第07與道工序粗，精銑mm左右兩端面銑床夾具。本夾具將用于X51立式銑床，刀具為YG6硬質(zhì)合金端銑刀，對工件mm端面。（一）問題的提出：本夾具主要用于銑mm端面，由于該端面精度要求高，所以，在本道工序加工時(shí)，應(yīng)該考慮其精度要求，同時(shí)也要考慮如何提高勞動生產(chǎn)率。（二）夾具設(shè)計(jì)的有關(guān)計(jì)算：、定位基準(zhǔn)的選擇：由零件圖可知，mm端面應(yīng)對下端面有垂直度要求，并且左右兩端面有平行度要求。為了使定位誤差為零，應(yīng)該選擇以20孔定位的定心夾具。但這種定心夾具在結(jié)構(gòu)上將過于復(fù)雜，因此這里只選用以13和下端面為主要定位基面。、切削力及夾緊力計(jì)算：刀具：YG6硬質(zhì)合金端銑刀(見切削手冊表3.28)其中：CF=54.5，ap=4.5，XF=0.9，fZ=0.18，YF=0.74，ae=28，UF=1.0，d0=100，qF=1.0，n=255，WF=0，Z=10F=54.54.50.90.180.742810/(1002550)166.1(N)水平分力：FH=1.1F實(shí)182.7(N)垂直分力：FV=0.3F實(shí)49.8(N)在計(jì)算切削力時(shí)，必須安全系數(shù)考慮在內(nèi)。安全系數(shù): K=K1K2K3K4。其中：K1=1.5 K2=1.1 K3=1.1 K4=1.1F=KFH=（1.51.11.11.1）182.7=364.8 (N)實(shí)際加緊力為F加= KFH/（U1*U2）=364.8/0.5=729.6 (N)其中U1和U2為夾具定位面及加緊面上的磨擦系數(shù)，U1=U2=0.025螺母選用M16X1.5細(xì)牙三角螺紋，產(chǎn)生的加緊力為W=2M/D2tg(a+6055)+0.66(D3- d3 )/（D2- d2)其中： M=19000 N.M D2=14.8mm a=2029， D=23mm d=16mm解得： W=1O405 (N)此時(shí)螺母的加緊力W已大于所需的729.6的加緊力F加，故本夾具可安全工作。1. 心軸取材料為Q2352. 查表得Q235的許用彎曲應(yīng)力為： 158Mpa3. 彎曲應(yīng)力=M/Wz=32FL/ 3.14 d3=99.4X32X0.028/3.14X(0.022)24. =2.67 許用彎曲應(yīng)力158Mpa (3)定位誤差分析由于基準(zhǔn)重合,故軸,徑向尺寸無極限偏差、形狀和位置公差，故徑向尺寸無基準(zhǔn)不重合度誤差。即不必考慮定位誤差，只需保證夾具的心軸的制造精度和安裝精度。且工件是以內(nèi)孔在心軸上定位，下端面靠在定位塊上，該定位心軸的尺寸及公差現(xiàn)規(guī)定為與零件內(nèi)孔有公差相同。因?yàn)閵A緊與原定位達(dá)到了重合，能較好地保證了銑mm端面所得到的尺寸和下端面形位公差要求。（三）夾具結(jié)構(gòu)設(shè)計(jì)及操作簡要說明：如前所述，在設(shè)計(jì)夾具時(shí)，應(yīng)該注意提高勞動率。為此，在螺母夾緊時(shí)采用活動手柄，以便裝卸，夾具體底面上的一對定位槽可使整個(gè)夾具在機(jī)床工作臺上有正確的安裝位置，以利于銑削加工。結(jié)果，本夾具總體的感覺還比較緊湊。為了保證零件加工精度，我們采用可換定位銷來進(jìn)行定心加緊。夾具體底面上的一對定位槽與銑床工作臺的T型槽相連接，保證夾具與銑床縱向進(jìn)給方向相平行的位置，使夾具在機(jī)床工作臺上占有一正確加工位置。此外，為了把夾具緊固在銑床工作臺上，夾具體兩端設(shè)置供T型螺栓穿過夾具用的兩個(gè)U型耳座。夾具上裝有對刀塊裝置，可使夾具在一批零件的加工之前很好的對刀（與塞尺配合使用）；同時(shí)，夾具體底面上的一對定位鍵可使整個(gè)夾具在機(jī)床工作臺上有一正確的安裝位置，以有利于銑削加工。銑床夾具的裝配圖及夾具體零件圖分別見附圖3附圖4。主要參考文獻(xiàn)1段明揚(yáng)主編.現(xiàn)代機(jī)械制造工藝設(shè)計(jì)實(shí)訓(xùn)教程.桂林:廣西師范大學(xué)出版社,20072段明揚(yáng)主編.現(xiàn)代制造工藝設(shè)計(jì)方法.桂林:廣西師范大學(xué)出版社,20073. 李益民主編.機(jī)械制造工藝設(shè)計(jì)簡明手冊.北京:機(jī)械工業(yè)出版社,20034. 艾 興等編.切削用量簡明手冊.北京:機(jī)械工業(yè)出版社,20025. 東北重型機(jī)械學(xué)院等編.機(jī)床夾具設(shè)計(jì)手冊.上海:上?？萍汲霭嫔?19906華楚生主編.機(jī)械制造技術(shù)基礎(chǔ)（第二版）.重慶:重慶大學(xué)出版社,20037互換性及測量技術(shù)(東南大學(xué)出版社 2000)8朱冬梅等編.畫法幾何及機(jī)械制圖.北京:高等大學(xué)出版社,2000 22ORIGINAL ARTICLE Fast collision detection approach to facilitate interactive modular fixture assembly design in a virtual environment Gaoliang Peng the objects not Int J Adv Manuf Technol (2010) 46:315328 DOI 10.1007/s00170-009-2073-0 G. Peng (*) : X. Hou : T. Jin : X. Zhang School of Mechanical and Electrical Engineering, Harbin Institute of Technology, Harbin, China e-mail: C. Wu School of Management, Harbin Institute of Technology, Harbin, China penetrating into others must be guaranteed. Therefore, a fast interactive collision detection (CD) algorithm is fundamen- tal in such a VR system. However, collision checking for a complex VE is computationally intensive. Researchers have addressed some “universal” algorithms to reduce the computational costs. But these algorithms often need auxiliary data structures and require intensive preprocessing time cost. In addition, the implementation of such algorithm is very complicated. Therefore, based on the well study of modular fixture characteristics and practical requirements, we develop a “special” CD algorithm to keep the associated costs as low as possible for VR-based modular fixture assembly design. The paper is organized as follows. A review of related work of the existing CD algorithms is presented in Section 2. Section 3 gives an overview of our proposed algorithm. In Section 4, we describe the space subdivision model used in our algorithm. Section 5 provides the details about the broad phase of our proposed algorithm, in which irrelevant objects are discarded and a set of objects that can possibly collide are determined. The narrow phase for exact polygon based overlap tests is described in Section 6. Section 7 presents some experimental results of our algorithm, and finally, in Section 8, we give concluding remarks and outline directions for future extensions of this work. 2 Related work During the past few years, a great deal of effort has been made to solve the CD problem for various types of interactive 3D graphics and scenarios. For a workspace filled with n objects, the most obvious problem is the O(n 2 ) problem of detecting collisions between all objects, which is time consuming and not bearable if the number n is large. Thus, some necessary techniques are needed to reduce the computational costs. Generally, a CD algorithm consists of two main steps, namely broad phase and narrow phase 9. The first phase aims to filter out pairs of objects which are impossible to interact and determine which objects in the entire workspace potentially interact. The second phase is to perform a more accurate test to identify collision between those selected object parts in the first phase, moreover if necessary, to find the pairs of contacting primitive geometric elements (polygons), and to calculate the overlapping distance. For a CD algorithm, it is critical to reduce the number of pairs of objects or primitives that need to be checked. Therefore, a number of different techniques have been used to make coarse grain detection, among which space decomposition and bounding volumes is most popular. In space decomposition methods, the environment is subdivided into space grids using hierarchical space subdivision. Objects in the environment are clustered hierarchically according to the regions that they fall into. These objects are then checked for intersection by testing for overlapping grid cells exploiting spatial partitioning methods like Octrees 10, 11, BSP-trees 12, k-d trees 13, etc. Using such decompositions in a hierarchical manner can further speed up the collision detection process but leads to extremely high storage requirements. Bounding volume (BV) approach is used in previous computer graphics algorithms to speed up computation and rendering process. The BVof a geometric object is a simple volume enclosing the object. Typically, BV types are axis- aligned boxes (AABBs) 14, spheres 15, and oriented bounding boxes (OBB) 16. Since AABBs method is simple to compute and allows efficient overlap queries, it is often used in hierarchy, but it also may be a particularly poor approximation of the set that they bound, leaving large “empty corners.” The systems utilizing AABBS include I-COLLIDE 17, Q- COLLIDE 18, and SOLID 19, etc. Bounding sphere is another natural choice to approxi- mate an object as it is particularly simple to test pairs for overlap, and the update for a moving object is trivial. However, spheres are similar to AABBs as they can be poor approximations to the convex hull of contained objects. In comparison, an OBB is a rectangular bounding box at arbitrary orientations in 3D space. In an ideal case, the OBB can be repositioned such that it is able to enclose an object as tightly as possible. In other words, the OBB is the smallest possible bounding box of arbitrary orientation that can enclose the geometry in question. This approach is very good at performing fast rejection tests. A system called RAPID 20 for interference detection based on OBB has been built, which approximates geometry better than AABBs. The shortcomings of OBB-tree against sphere tree lie in its slowness to update and orientation sensitive 9. Most CD-related researches are involved in “universal” algorithms, and few literatures are found to develop CD approach in a special application like virtual assembly. Actually, a fast and interactive collision detection algorithm is fundamental to a virtual assembly environment, which allows designers to move parts or components to perform assembly and disassembly operations. Figueiredo 21 presented a faster algorithm for the broad and narrow phases of the collision detection algorithm of determining precise collisions between surfa- ces of 3D assembly models in virtual prototype environ- ments. The algorithm used the overlapping AABB and the R-tree data structure to improve performance in both the broad and narrow phases of the collision detection. This approach is for such a VE with objects dispersed in the 316 Int J Adv Manuf Technol (2010) 46:315328 space. In addition, the R-tree data structure is very memory intensive. Stephane 22 worked on continuous collision detection methods and constraints to deal with rigid polyhedral objects for desktop virtual prototyping. Whereas such a 4D method is only useful for handling the path of known moving objects. Especially, the algorithm is so computa- tionally intensive that it has to run on high-end computers. Collision detection is a critical problem in multi-axis numerical control (NC) machining with complex machining environments. There has been much previous work on interference detection and avoidance in NC machining simulation. Wang 23 developed a graphics-assisted collision detection approach for multi-axis NC machining. In this method, a combination of machining environment culling and a two-phase collision detection strategy was used. Researches surveyed above provided various efficient techniques to carry out collision detection for polygonal models. However, these popular algorithms aimed at general polygonal models, most of which need expensive pretreatments or large system memory or both of them in order to improve the performance and meet real-time requirements. Therefore, when these algorithms are utilized in desktop VR application system such as modular fixture design, the requirement of real time cannot be well guaranteed. Few CD researches can be found in the area of computer-aided fixture design. Hu 24presentedan algorithm of fast interference checking between the machining tool and fixture units, as well as between fixture units, to replace the visually checked method. Moreover, in Kumars work 25, in order to automate interference-free modular fixture assembly design, the machining interference detection is accomplished through the use of cutter-swept solid based on cutter-swept volume approach. However, these algorithms are only capable of static interference checking and applied in CAD software packages. The research presented in this paper makes a solution to these issues by addressing a “special” collision detection algorithm for VR-based modular fixture design. The proposed algorithm uses the hybrid approach of space decomposition and bounding volume method to get high performance. 3 Algorithm overview 3.1 Requirements for proposed algorithm We aimed to develop a desktop VR-based modular fixture assembly design system, in which the designer can select suitable fixture elements and put them together to generate a fixture structure, like “building blocks.” Without physical fixture elements, he/she can test different structure schemes and finally design a feasible fixture configuration that meets the fixturing function requirements. In order to retain high degree of “reality” in engineering application, there are three main requirements for a CD algorithm to perform modular fixture configuration design: 1. Precise and fast: During the simulation of assembly and disassembly operations, finding precise collisions is an important task for achieving realistic behavior 26. When the user interactively assembles a part or a component, the “flying” object may collide with static models, thus the system must find out the “colliding” event immediately. The interval between two checking points should be near enough to achieve better performance. Otherwise, when objects move very fast, they may appear before checking, which will reduce the immersive feelings. Therefore, the proposed system carries out a CD checking task in each rendering loop of VE. In addition, in modular fixture assembly design process, the designer selects elements and assembles them to right position or disassembles them to change the fixture configuration. Once an element is assembled or disassembled, the “static” environment models are updated. Accordingly, the CD checking model needs restructure. So the preprocess should not take too long; otherwise, the performance of proposed system will be impaired severely for certain “smooth feel” cannot be achieved. 2. Low system requirements: Finding collisions in a 3D environment is time-consuming. In some cases, it can easily consume up to 50% of the total run time 21. However, in modular fixture design workspace, there are some other time-consuming tasks, such as design process control and reasoning, automatic geometric constraints recognition and solving, etc. In spite of the complexity of the 3D virtual prototypes due to thousands of polygons, the designed CD checking procedure must be done in real time with relatively low system resource demands. 3. Low hardware cost: In order to achieve wider engi- neering applications, the proposed modular fixture assembly system is designed to run on common PC like popular CAD commercial software. Although much research has engaged in developing hardware- accelerated CD algorithms, which utilize special graph- ic hardware, like graphics processing unit, to deal with the computing collisions, thus the systems CPU can be freed. Nevertheless, we did not plan to adopt this kind of method and optimize performance only from software implementation. The objective of this research is to develop a CD algorithm Int J Adv Manuf Technol (2010) 46:315328 317 Taking into account all above requirements, unfortunate- ly, these objectives usually are in conflict. To meet the precise demand, we must increase checking frequency which will enormously increase the computational com- plexity and the memory bandwidth requirement. So, how can a balance be reached with regard to these? In other words, how can the utilization of system resources be minimized yet the performance optimized without the help of extra hardware? It is the start point of our algorithm. 3.2 Modular fixture analysis The objective of this research is to develop a CD algorithm for assisting in modular fixture assembly design operations in VE. To simplify the algorithm and to gain high performance, the characteristics of modular fixture should be well studied. 1. Process of modular fixture assembly design: The tasks of modular fixture assembly design are to select the proper fixture elements and assemble them to a configuration one by one according to the designed fixturing plan. Thus, the CD problem in VR-based modular fixture assembly design can be stated as: the intersection checking between one moving object (assembling element or unit) with the static environ- ment objects (assembled elements) at discrete time. 2. Fixture element shape: Modular fixture elements with regular shape can be classified into three types, namely, block, cylinder, and block-cylinder 27. Other compli- cated assembly units can be regarded as compositions of these three meta-elements. It is well known that the OBB is tighter than the AABB and sphere. Moreover, when an object changes its position and orientation in VE, its OBB does not need to rebuild. Therefore, we can construct OBBs of modular fixture elements off- line and store them as attributes of element models. During the assembly design process, such attributes can be retrieved directly; thus, complex work for construct- ing bounding volume in run time can be avoided. 3. Fixture element layout: A modular fixture system often consists of supporting units, locating units, and clamp- ing units. These units lie out on the base plate and provide corresponding functions at certain positions. As Fig. 1 shows, in the projection view parallel to the base plate, the units are arranged in some kind of “regions.” In addition, to meet the height requirement of fixturing point, a unit often utilizes a number of supporting elements severed as blocking up objects. Therefore, at the direction perpendicular to the baseplate, the elements lay out hierarchically. Accordingly, we can decompose the space with regard to elements layout feature. 3.3 Algorithm flowchart According to the above characteristics of modular fixture, the proposed algorithm is designed to decrease the complexity and meet the requirements of VR-based modular fixture assembly design. As Fig. 2 shows, at the preprocessing stage, once an element or component is assembled or disassembled, the Layer-based Projection Model (LPM) is established in terms of OBBs of those assembled elements. Such an LPM is used for the CD checking when a new object is assembled. Just like the traditional CD method, proposed algorithm consists of two steps, namely, broad phase and narrow phase. The broad phase is responsible for filtering pairs of objects that cannot intersect. At this stage, it determines pairs of objects in the same subspace, whose silhouettes in LPM overlap and their OBBs intersect. These pairs of objects are candidates for exact polygon-based collision tests in the next narrow phase. During the broad phase, the (a)default view (b)downtown view Fig. 1 Modular fixture structure 318 Int J Adv Manuf Technol (2010) 46:315328 test may cease at any time if no intersection is found, which helps to reject many noncollision or trivial collision cases. In the narrow phase, the collision detection algorithm will calculate detailed intersection between geometrical meshes of the objects. If no intersection polygons are found, the collide will not occur, and the active object can keep on moving. Otherwise, whenever overlaps are detected, related reactions (for proposed system, it highlights objects and does back-tracking) may arise. 4 Space decomposition for identifying neighboring objects Considering the fact that most regions of the “universe” are occupied by only a few objects or left empty, it means that collision only happens among objects that are close enough. So we can use this phenomenon to filter out most of “far- away” objects. Space decomposition is the common approach to be used for this intention. It first splits the “universe” into cells and then does further collision tests for objects in the same cell. In order to keep generality, most of existing space subdivision approaches are based on a set of polygons. Such a “polygon-oriented” approach is so computationally intensive to deal with large number of polygons. Since standard components are almost with relatively regular shapes, we plan to develop an “object- oriented” space decomposition method. 4.1 Space decomposition model After the baseplate is arranged, the remaining work is to assemble the fixture elements or units onto the baseplate. As the assembling elements or units move to the assembled position, collisions may happen between active object and the assembled elements that have been fixed in the space around the baseplate. Hence, the CD checking process needs start-up only after the active object enters into this space. Firstly, as Fig. 3a shows, we define a valid collision space noted as , which is a cuboid whose bottom face is decided by the baseplate, and its height would change along with the assembling operation. The top of is determined by the vertex coordinates of OBBs. is defined to guarantee that all the assembled elements are inside. After the checking space is identified, we need to decompose the space into a number of cells. How can we organize these cells into proper structure and represent the relevant information to facilitate interaction checking? In literature, some kinds of hierarchical data structure, like R- tree structure 21, have been used to help find neighbors. In complex environment with lots of dispersed objects, this complicated data structure is useful. For modular fixture assembly design, the element models are relatively central- ized, and the number of objects is not so much. Conse- quently, the complex data structure is not needed as constructing such a model is time-consuming. We propose a novel data model to represent partition of the checking space. The model gets the advantages of easy intersection tests and simple information representation. As Fig. 3b shows, the checking space is decomposed into several layers along the axis vertical to the baseplate. Each layer can be represented as a 4-turple L i =h 1 , h 2 , V, B, where h 1 is the start height, h 2 is the end height, V is the grid information of this layer, and B describes the projection of elements OBBs belonging to this layer. For each layer, the stored information is illustrated in Fig. 3c. Easy to overlap checking, we orthogonally project the bounding box onto the x, y axis (convenient for illustration and does not lose universality). Then, with these projections, intervals are formed on each axis for each object. We construct one list for each axis. Each list contains the coordinate value of the endpoints of the interval on the corresponding axis. By comparing the endpoints, the corresponding pair of objects that are in contact may be determined. If the intervals do not overlap, the corresponding two objects are not in contact and can be discarded. Fig. 2 Overview of collision detection algorithm Int J Adv Manuf Technol (2010) 46:315328 319 4.2 Space decomposition model construction The above section gives the representation of our space decomposition model; this section will discuss how to construct and reconstruct this model. Most existing space partition methods decompose an entire space into cells in terms of primitive geometric elements (polygons), by computing the position of each polygon and assigning them into corresponding cells, which are often organized into a hierarchical data structure. Despite the data structure remarkably speeding up the CD checking procedure, the establishment of such structure is a complex process and time-consuming. In a situation that the objects in an environment are uniform or the environment models do not change frequently, the cost for preprocessing may be bearable. However, during the modular fixture virtual assembly process, objects within the checking space are changed with time. Therefore, the space composition model must be rebuilt once a fixture element is assembled. To reduce preprocessing time, we
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