法蘭盤(pán)(一)機(jī)械加工工藝及其鉆7-φ9孔的夾具設(shè)計(jì),法蘭盤(pán)(一)機(jī)械加工工藝及其鉆7-φ9孔的夾具設(shè)計(jì),法蘭盤(pán),機(jī)械,加工,工藝,及其,夾具,設(shè)計(jì) 機(jī)械制造技術(shù)課程設(shè)計(jì)說(shuō)明書(shū) 設(shè)計(jì)題目：設(shè)計(jì)法蘭盤(pán)零件的加工工藝 及鉆7-Φ9孔的鉆床夾具 專 業(yè)： 機(jī)械設(shè)計(jì)制造及其自動(dòng)化 班 級(jí)： 09-3 摘 要 本次設(shè)計(jì)內(nèi)容涉及了機(jī)械制造工藝及機(jī)床夾具設(shè)計(jì)、金屬切削機(jī)床、公差配合與測(cè)量等多方面的知識(shí)。 法蘭盤(pán)的加工工藝規(guī)程及其夾具設(shè)計(jì)是包括零件加工的工藝設(shè)計(jì)、工序設(shè)計(jì)以及專用夾具的設(shè)計(jì)三部分。在工藝設(shè)計(jì)中要首先對(duì)零件進(jìn)行分析，了解零件的工藝再設(shè)計(jì)出毛坯的結(jié)構(gòu)，并選擇好零件的加工基準(zhǔn)，設(shè)計(jì)出零件的工藝路線；接著對(duì)零件各個(gè)工步的工序進(jìn)行尺寸計(jì)算，關(guān)鍵是決定出各個(gè)工序的工藝裝備及切削用量；然后進(jìn)行專用夾具的設(shè)計(jì)，選擇設(shè)計(jì)出夾具的各個(gè)組成部件，如定位元件、夾緊元件、引導(dǎo)元件、夾具體與機(jī)床的連接部件以及其它部件；計(jì)算出夾具定位時(shí)產(chǎn)生的定位誤差，分析夾具結(jié)構(gòu)的合理性與不足之處，并在以后設(shè)計(jì)中注意改進(jìn)。 關(guān)鍵詞：工藝、工序、切削用量、夾緊、定位、誤差。 目 錄 一、序言 1 1.1 夾具的現(xiàn)狀及生產(chǎn)對(duì)其提出新的要求 1 1.2 現(xiàn)代夾具的發(fā)展方向 2 二、零件的分析 4 2.1零件的作用 4 2.2零件的工藝分析 4 三、工藝規(guī)程設(shè)計(jì) 5 3.1 確定毛坯的制造形式 5 3.2 基面的選擇 5 3.3 制定工藝路線 6 3.4 機(jī)械加工余量，工序尺寸及毛坯尺寸的確定 9 3.5 確定切削用量及基本尺寸 10 四、夾具設(shè)計(jì) 23 4.1問(wèn)題的提出 23 4.2定位基準(zhǔn)的選擇 23 4.3切削力及夾緊力計(jì)算 24 4.4定位誤差分析 24 4.5夾具設(shè)計(jì)及操作簡(jiǎn)要說(shuō)明 25 總結(jié) 28 致謝 29 參考文獻(xiàn) 30 29 一、 序 言 夾具最早出現(xiàn)在1787年，至今經(jīng)歷了三個(gè)發(fā)展階段。第一階段表現(xiàn)為夾具與人的結(jié)合。在工業(yè)發(fā)展初期。機(jī)械制造的精度較低，機(jī)械產(chǎn)品工件的制造質(zhì)量主要依賴勞動(dòng)者個(gè)人的經(jīng)驗(yàn)和手藝，而夾具僅僅作為加工工藝過(guò)程中的一種輔助工具；第二階段是隨著機(jī)床、汽車(chē)、飛機(jī)等制造業(yè)的發(fā)展，夾具的門(mén)類才逐步發(fā)展齊全。夾具的定位、夾緊、導(dǎo)向（或?qū)Φ叮┰慕Y(jié)構(gòu)也日趨完善，逐漸發(fā)展成為系統(tǒng)的主要工藝裝備之一；第三階段，即近代由于世界科學(xué)技術(shù)的進(jìn)步及社會(huì)生產(chǎn)力的迅速提高，夾具在系統(tǒng)中占據(jù)相當(dāng)重要的地位。這一階段的主要特征表現(xiàn)為夾具與機(jī)床的緊密結(jié)合。 1.1夾具的現(xiàn)狀及生產(chǎn)對(duì)其提出新的要求 現(xiàn)代生產(chǎn)要求企業(yè)制造的產(chǎn)品品種經(jīng)常更新?lián)Q代，以適應(yīng)市場(chǎng)激烈競(jìng)爭(zhēng)，企業(yè)中多品種生產(chǎn)的工件已占工件種類數(shù)的85%左右。然而目前，一般企業(yè)習(xí)慣與采用傳統(tǒng)的專用夾具，在一個(gè)具有大批量生產(chǎn)的能力工廠中約擁有13000~15000套專用夾具。另一方面，在多品種生產(chǎn)的企業(yè)中，約隔4年就要更新80%左右的專用夾具，而夾具的實(shí)際磨損量只有15%左右，特別最近年來(lái)柔性制造系統(tǒng)（FMS）、數(shù)控機(jī)床（NC），加工中心（MC）和成組加工（GT）等新技術(shù)被應(yīng)用和推廣，使中小批生產(chǎn)的生產(chǎn)率逐步趨近于大批量生產(chǎn)的水平。 綜上所述，現(xiàn)代生產(chǎn)對(duì)夾具提出了如下新的要求： 1. 能迅速方便地裝備新產(chǎn)品的投產(chǎn)以縮短生產(chǎn)準(zhǔn)備周期 2. 能裝夾一組相似性特征的工件 3. 適用于精密加工的高精度的機(jī)床 4. 適用于各種現(xiàn)代化制造技術(shù)的新型技術(shù) 5. 采用液壓汞站等為動(dòng)力源的高效夾緊裝置，進(jìn)一步提高勞動(dòng)生產(chǎn)率 1.2現(xiàn)代夾具的發(fā)展方向 現(xiàn)代夾具的發(fā)展方向表現(xiàn)為精密化、高效化、柔性化、標(biāo)準(zhǔn)化等四個(gè)方面： 1. 精密化 隨著機(jī)械產(chǎn)品精度的日益提高，勢(shì)必也相應(yīng)提高對(duì)其精度要求。精密化夾具的結(jié)構(gòu)類型很多，例如用于精密分度的多齒盤(pán)，其分度可達(dá)正負(fù)0.1，用于精密車(chē)削的高精度三爪卡盤(pán)，其定心精度為5um，又如用于軸承套圈磨削的電磁無(wú)心夾具，工件的圓讀可達(dá)0.2~0.5um。 2. 高效化 高效化夾具主要用來(lái)減少工件加工的機(jī)動(dòng)時(shí)的和輔助時(shí)的，以提高勞動(dòng)生產(chǎn)率，減少工人勞動(dòng)強(qiáng)度，常見(jiàn)的高效化夾具有：自動(dòng)化夾具、告訴化夾具、具有夾緊動(dòng)力模塊的夾具等。例如使用電動(dòng)虎鉗裝夾工件，可使工件效率比普通虎鉗提高了5倍左右；而高速卡盤(pán)則可保證卡爪在轉(zhuǎn)速9000r/min的條件下能正常夾緊工件，使切削速度大幅度提高。 3. 柔性化 夾具的柔性化與機(jī)床的柔性化相似，它是通過(guò)調(diào)組合等方式，以適應(yīng)工藝可變因素的能力。工藝的可變因素主要有：工序特征、生產(chǎn)批量、工件的形狀和尺寸等，具有柔性化特征的新型夾具種類主要有：組合夾具、通用可調(diào)夾具、成組夾具、模塊夾具、數(shù)控夾具等，在較長(zhǎng)時(shí)間內(nèi)，夾具的柔性化趨向?qū)⑹菉A具發(fā)展的主要方向。 4. 標(biāo)準(zhǔn)化 夾具的標(biāo)準(zhǔn)化與通用化是相互聯(lián)系的兩個(gè)方面，在制造典型夾具，結(jié)構(gòu)的基礎(chǔ)上，首先進(jìn)行夾具元件和部件的通用化，建立典型尺寸系列或變型，以減少功能用途相近的夾具元件和不見(jiàn)的形成：舍棄一些功能低劣的結(jié)構(gòu)，通用化方法包括：夾具、部件、元件、毛呸和材料的通用化夾具的標(biāo)準(zhǔn)化階段是通用化的深入并為工作圖的審查創(chuàng)造了良好的條件。目前，我國(guó)已有夾具零件、部件的國(guó)家標(biāo)準(zhǔn)：GB2148~2249-80，GB2262~2269-80以及通用夾具標(biāo)準(zhǔn)，組合夾具標(biāo)準(zhǔn)等。夾具的標(biāo)準(zhǔn)化也是夾具柔性化高效化的基礎(chǔ)，作為發(fā)展趨勢(shì)，這類夾具的標(biāo)準(zhǔn)化，有利于夾具的專業(yè)化生產(chǎn)和有利于縮短生產(chǎn)準(zhǔn)備周期，降低生產(chǎn)總成本。 二、 零 件 的 分 析 2.1零件的作用 題目所給定的零件是法蘭盤(pán)， 法蘭盤(pán)起聯(lián)接作用是車(chē)床上的重要零件。零件上精度要求較高的兩個(gè)平面用以裝配。 2.2零件的工藝分析 法蘭盤(pán)是一回轉(zhuǎn)體零件,有一組加工表面,這一組加工表面以Φ38，Φ50，Φ62為中心 ,包括:兩個(gè)左右端面,端面上面的7-Φ9和7-Φ15的階梯孔. 和M12孔和斜孔Φ6孔, 以及退刀槽。 這組加工表面是以右端面為中心,其余加工面都與它有位置關(guān)系,可以先加工它的一個(gè)端面,再借助專用夾具以這個(gè)端面為定位基準(zhǔn)加工另一端面,然后再加工其它加工表面. 三、 工 藝 規(guī) 程 設(shè) 計(jì) 3.1確定毛坯的制造形式 零件材料為HT150，由于零件年產(chǎn)量為20000件，已達(dá)到大批生產(chǎn)的水平，而且零件輪廓尺寸不大，故采用金屬模鑄造。這從提高生產(chǎn)率，保證加工精度上考慮也是應(yīng)該的。 3.2基面的選擇 3.2.1 粗基準(zhǔn)的選擇 粗基準(zhǔn)選擇應(yīng)當(dāng)滿足以下要求： （1）粗基準(zhǔn)的選擇應(yīng)以加工表面為粗基準(zhǔn)。目的是為了保證加工面與不加工面的相互位置關(guān)系精度。如果工件上表面上有好幾個(gè)不需加工的表面，則應(yīng)選擇其中與加工表面的相互位置精度要求較高的表面作為粗基準(zhǔn)。以求壁厚均勻、外形對(duì)稱、少裝夾等。 （2） 選擇加工余量要求均勻的重要表面作為粗基準(zhǔn)。例如：機(jī)床床身導(dǎo)軌面是其余量要求均勻的重要表面。因而在加工時(shí)選擇導(dǎo)軌面作為粗基準(zhǔn)，加工床身的底面，再以底面作為精基準(zhǔn)加工導(dǎo)軌面。這樣就能保證均勻地去掉較少的余量，使表層保留而細(xì)致的組織，以增加耐磨性。 （3） 應(yīng)選擇加工余量最小的表面作為粗基準(zhǔn)。這樣可以保證該面有足夠的加工余量。 （4） 應(yīng)盡可能選擇平整、光潔、面積足夠大的表面作為粗基準(zhǔn)，以保證定位準(zhǔn)確夾緊可靠。有澆口、冒口、飛邊、毛刺的表面不宜選作粗基準(zhǔn)，必要時(shí)需經(jīng)初加工。 （5） 粗基準(zhǔn)應(yīng)避免重復(fù)使用，因?yàn)榇只鶞?zhǔn)的表面大多數(shù)是粗糙不規(guī)則的。多次使用難以保證表面間的位置精度。 基準(zhǔn)的選擇是工藝規(guī)程設(shè)計(jì)中的重要工作之一，他對(duì)零件的生產(chǎn)是非常重要的。 3.2.2 精基準(zhǔn)的選擇 精基準(zhǔn)的選擇應(yīng)滿足以下原則： （1）“基準(zhǔn)重合”原則 應(yīng)盡量選擇加工表面的設(shè)計(jì)基準(zhǔn)為定位基準(zhǔn)，避免基準(zhǔn)不重合引起的誤差。 （2）“基準(zhǔn)統(tǒng)一”原則 盡可能在多數(shù)工序中采用同一組精基準(zhǔn)定位，以保證各表面的位置精度，避免因基準(zhǔn)變換產(chǎn)生的誤差，簡(jiǎn)化夾具設(shè)計(jì)與制造。 （3）“自為基準(zhǔn)”原則 某些精加工和光整加工工序要求加工余量小而均勻，應(yīng)選擇該加工表面本身為精基準(zhǔn)，該表面與其他表面之間的位置精度由先行工序保證。 （4）“互為基準(zhǔn)”原則 當(dāng)兩個(gè)表面相互位置精度及自身尺寸、形狀精度都要求較高時(shí)，可采用“互為基準(zhǔn)”方法，反復(fù)加工。 （5）所選的精基準(zhǔn) 應(yīng)能保證定位準(zhǔn)確、夾緊可靠、夾具簡(jiǎn)單、操作方便。 主要考慮精基準(zhǔn)重合的問(wèn)題，當(dāng)設(shè)計(jì)基準(zhǔn)與工序基準(zhǔn)不重合的時(shí)候，應(yīng)該進(jìn)行尺寸換算，這在以后還要進(jìn)行專門(mén)的計(jì)算，在此不再重復(fù)。 3.3制定工藝路線 制定工藝路線的出發(fā)點(diǎn)，應(yīng)當(dāng)是使零件的幾何形狀，尺寸精度及位置精度等技術(shù)要求能得到合理的保證。在生產(chǎn)綱領(lǐng)一確定為中批生產(chǎn)的條件下，可以考慮采用萬(wàn)能性的機(jī)床配以專用工夾具，并盡量使工序集中來(lái)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。 1、.工藝路線方案一： 1 鑄造 鑄造 2 時(shí)效處理 時(shí)效處理 3 車(chē) 粗車(chē)左端面和外圓 4 車(chē) 粗車(chē)右端面和外圓 5 車(chē) 粗車(chē)中心各孔 6 車(chē) 車(chē)3x1的退刀槽 7 車(chē) 精車(chē)各外圓和端面 8 車(chē) 車(chē)內(nèi)孔退刀槽3x2 9 車(chē) 精車(chē)內(nèi)孔 10 鉆 鉆7-Ф9階梯孔 11 鉆 鉆M12螺紋孔 12 鉆 鉆斜孔Ф6 13 檢驗(yàn) 檢驗(yàn) 14 入庫(kù) 入庫(kù) 2 、工藝方案二： 1 鑄造 鑄造 2 時(shí)效處理 時(shí)效處理 3 車(chē) 車(chē)左端面和外圓 4 車(chē) 車(chē)右端面和外圓 5 車(chē) 粗車(chē)中心各孔 6 車(chē) 車(chē)3x1的退刀槽 7 車(chē) 車(chē)內(nèi)孔退刀槽3x2 8 車(chē) 精車(chē)內(nèi)孔 9 鉆 鉆7-Ф9階梯孔 10 鉆 鉆M12螺紋孔 11 鉆 鉆斜孔Ф6 12 檢驗(yàn) 檢驗(yàn) 13 入庫(kù) 入庫(kù) 3、工藝方案的比較與分析： 上述兩個(gè)方案的特點(diǎn)在于：方案一采用粗精加工端面和外圓可以提高加工精度，而方案二直接車(chē)端面和外圓，效率雖高但精度不能保證，應(yīng)把保證精度放在首位，故選用方案一。 因此最后確定的加工工藝路線如下： 1 鑄造 鑄造 2 時(shí)效處理 時(shí)效處理 3 車(chē) 粗車(chē)左端面和外圓 4 車(chē) 粗車(chē)右端面和外圓 5 車(chē) 粗車(chē)中心各孔 6 車(chē) 車(chē)3x1的退刀槽 7 車(chē) 精車(chē)各外圓和端面 8 車(chē) 車(chē)內(nèi)孔退刀槽3x2 9 車(chē) 精車(chē)內(nèi)孔 10 鉆 鉆7-Ф9階梯孔 11 鉆 鉆M12螺紋孔 12 鉆 鉆斜孔Ф6 13 檢驗(yàn) 檢驗(yàn) 14 入庫(kù) 入庫(kù) 3.4機(jī)械加工余量，工序尺寸及毛坯尺寸的確定 法蘭盤(pán)零件材料為HT150，硬度200HBS，毛坯重量約為1.4KG，生產(chǎn)類型為大批生產(chǎn)，采用鑄造毛坯。 根據(jù)上述原始資料及加工工藝，分別確定各加工表面的機(jī)械加工余量，工序尺寸及毛坯尺寸下： 1.Φmm外圓表面 外圓表面為IT6級(jí)，參照《實(shí)用機(jī)械加工工藝手冊(cè)》確定各工序尺寸及加工余量 工序名稱 工序余量 工序基本尺寸 工序尺寸的公差 工序尺寸及公差 精車(chē)外圓 1 50 h6 Φ 粗車(chē)外圓 3 51 Φ 毛坯 4 54 Φ 2.外圓表面Φmm 參照《實(shí)用機(jī)械加工工藝手冊(cè)》確定各工序尺寸及加工余量 工序名稱 工序余量 工序基本尺寸 工序尺寸及公差 精車(chē)外圓 1 85 Φ 粗車(chē)外圓 3 86 Φ 毛坯 4 89 Φ 3．中心孔Φ38，Φ50，Φ62 參照《實(shí)用機(jī)械加工工藝手冊(cè)》確定各工序尺寸及加工余量 工序名稱 工序余量 工序基本尺寸 工序尺寸及公差 精車(chē)孔 1 38 Φ38 粗車(chē)孔 3 39 Φ39 毛坯 4 42 Φ40 工序名稱 工序余量 工序基本尺寸 工序尺寸及公差 精車(chē)孔 1 50 Φ50 粗車(chē)孔 3 51 Φ51 毛坯 4 54 Φ54 工序名稱 工序余量 工序基本尺寸 工序尺寸的公差 工序尺寸及公差 精車(chē)孔 1 62 K7 Φ62 粗車(chē)孔 3 63 Φ63 毛坯 4 66 Φ66 3.5確定切削用量及基本工時(shí) 工序3： 粗車(chē)左端面和外圓 工件材料：HT15-33 δb=220MPa 模鑄 加工要求：車(chē)左端面和外圓 機(jī)床：CA6140臥式車(chē)床 刀具：采用刀片的材料為YT15，刀桿尺寸16x25mm,=90,=15,=12,=0.5mm 1) 已知毛坯長(zhǎng)度方向的加工余量為3+0..8 -0。7mm,考慮的模鑄拔模斜度，=4mm 2) 進(jìn)給量f 根據(jù)《實(shí)用機(jī)械加工工藝手冊(cè)》中表2.4-3,當(dāng)?shù)稐U尺寸為16×25 mm >3~5mm,以及工件直徑為100時(shí)，f =0.7~1.0mm/r 按CA6140車(chē)床說(shuō)明書(shū)（見(jiàn)切削手冊(cè)）取 f =0.9mm/r 3) 計(jì)算切削速度，按《切削手冊(cè)》表1.27,切削速度的計(jì)算公式為(壽命T=60min) (m/min) 其中：=342, =0.15, =0.35, m=0.2。修正系數(shù)見(jiàn)《切削手冊(cè)》表1.28,即 =1.44 , =0.8 , =1.04 , =0.81 , =0.97。 所以 x1.44x0.8x1.04x0.81x0.97=158.6(m/min) 4)確定機(jī)的主軸轉(zhuǎn)速 ns== 1010r/min 按機(jī)床說(shuō)明書(shū)(見(jiàn)《工藝手冊(cè)》表4.2-8),與1010r/min相近的機(jī)床轉(zhuǎn)速為1050r/min及1200r/min?，F(xiàn)選取=1050r/min。 所以實(shí)際切削速度v=170r/min。 5) 切削工時(shí)，按《工藝手冊(cè)》表6.2-1 　　L==40mm , =2mm, =0, =0 tm===0.098(min) 工序 4：粗車(chē)右端面和外圓 機(jī)床：CA6140臥式車(chē)床 刀具：采用刀片的材料為YT15，刀桿尺寸1625mm,=90,=15, =12,=0.5mm 1) 切削深度。單邊余量Z=2mm 2) 計(jì)算切削速度　　 其中：=342, =0.15, =0.35, m=0.2。 =1.44 , =0.8 , =1.04 , =0.81 , =0.97。 所以 1.440.81.040.810.97=187m/min 3) 確定機(jī)床主軸轉(zhuǎn)速　 ns== 700r/min 與700r/min相近的機(jī)床轉(zhuǎn)速為750r/min?，F(xiàn)選取=750r/min。 所以實(shí)際切削速度== 4) 切削工時(shí)，按《工藝手冊(cè)》表6.2-1。 　　t=i ;其中l(wèi)=25mm; =4mm; =2mm; t=i=x1=0.06(min) 工序7：精車(chē)各外圓和端面 　　精車(chē)左端外圓 1) 切削深度 單邊余量為Z=0.7mm 2) 進(jìn)給量 根據(jù)《機(jī)械加工工藝手冊(cè)》取f=0.2mm/r 3) 計(jì)算切削速度　 其中：=342, =0.15, =0.35, m=0.2。即 =1.44 , =0.8 , =1.04 , =0.81 , =0.97。 所以 1.440.81.040.810.97=96m/min 4) 確定機(jī)床主軸轉(zhuǎn)速　 ns== 578r/min 與578r/min相近的機(jī)床轉(zhuǎn)速為600r/min?，F(xiàn)選取=600r/min。 所以實(shí)際切削速度 == 5)切削工時(shí)，按《工藝手冊(cè)》表6.2-1。 　　　　t=i ;其中l(wèi)=41mm; =4mm; =0mm; t=i==0.37(min) 精車(chē)左端面 1) 切削深度 單邊余量為Z=0.5mm 一次切除。 2) 進(jìn)給量 根據(jù)《機(jī)械加工工藝手冊(cè)》取f=0.2mm/r 3) 計(jì)算切削速度：　 其中：=342, =0.15, =0.35, m=0.2。 =1.44 , =0.8 , =1.04 , =0.81 , =0.97。 所以 1.440.81.040.810.97=134m/min 4)確定機(jī)床主軸轉(zhuǎn)速　　 ns== 458r/min 與458r/min相近的機(jī)床轉(zhuǎn)速為480r/min。現(xiàn)選取=480r/min。 所以實(shí)際切削速度== 5) 切削工時(shí)，按《工藝手冊(cè)》表6.2-1 t=i ;其中l(wèi)==22.5mm; =4mm; =0mm; t=i==0.28(min) 精車(chē)右端面： 1) 切削深度，單邊余量為Z=0.5mm 一次切除。 2) 進(jìn)給量，　根據(jù)《機(jī)械加工工藝手冊(cè)》取f=0.9mm/r 3)計(jì)算切削速度　?。?32m/min 4)確定機(jī)床主軸轉(zhuǎn)速　　 ns== 420r/min 與420r/min相近的機(jī)床轉(zhuǎn)速為480r/min現(xiàn)選取480r/min 所以實(shí)際切削速度　　== 5) 檢驗(yàn)機(jī)床功率　 　　　　　　　　?。? 　　　　　其中?。?985，＝1.0，＝0.65，＝-0.15， ===0.63 =0.61 =29851.00.51500.630.89=1122.4(N) 切削時(shí)消耗功率＝＝＝2.81(KW) CA6140主電機(jī)功率為7.5kw.轉(zhuǎn)速為480r/min時(shí)主軸傳遞的最大功率為4.5kw.所以機(jī)床功率足夠，可以正常加工。 　　6) 校驗(yàn)機(jī)床進(jìn)給系統(tǒng)強(qiáng)度　已知主切削力＝1122.4N.徑向切削力 ＝ 其中　＝1940，＝0.9，＝0.6，＝-0.3， ===0.59 =0.5 所以 =19401.50.51500.590.5=203(N) 而軸向切削力 ＝ 其中?。?880，＝1.0，＝0.5，＝-0.4， ===0.34 =1.17 軸向切削力 =28801.50.51500.341.17=442(N) 取機(jī)床導(dǎo)軌與床鞍之間的摩擦系數(shù)μ=0.1,則切削羅在縱向進(jìn)給方向?qū)M(jìn)給機(jī)構(gòu)的作用力為F=+μ (+)=442+0.1(1122.4+203)=442+132.5=574.5N 而機(jī)床縱向進(jìn)給機(jī)床可承受的最大縱向力為3530N(見(jiàn)《切削手冊(cè)》表1.30)故機(jī)床進(jìn)給系統(tǒng)可正常工作。 進(jìn)給量f 根據(jù)《實(shí)用機(jī)械加工工藝手冊(cè)》表2.4-2.取f＝0.2mm/r 機(jī)床主軸轉(zhuǎn)速＝480r/min 所以切削工時(shí)　tm==＝0.44（min） 精車(chē)右端外圓 　　粗精加工的切削用量除了進(jìn)給量和切削深度外都相同，故其余在此省略 進(jìn)給量f 根據(jù)《機(jī)械加工工藝手冊(cè)》表2.4-2 取f=0.2mm/r 主軸轉(zhuǎn)速 n=480r/min 所以切削工時(shí)　　t==0.33 min 工序9：精車(chē)各內(nèi)孔 1) 切削深度 單邊余量為Z=0.5mm 2) 進(jìn)給量　根據(jù)《機(jī)械加工工藝手冊(cè)》取f=0.2mm/r 3) 計(jì)算切削速度　　 其中：=342, =0.15, =0.35, m=0.2。即 =1.44 , =0.8 , =1.04 , =0.81 , =0.97。 所以 1.440.81.040.810.97=187m/min 4) 確定機(jī)床主軸轉(zhuǎn)速 ns== 553r/min 與553r/min相近的機(jī)床轉(zhuǎn)速為600r/min?，F(xiàn)選取=600r/min。 所以實(shí)際切削速度 == (1)精車(chē)Φ38內(nèi)孔 粗精加工的切削用量除了進(jìn)給量和切削深度外其它都相同，故在此省略。 .取f＝0.5mm/r 機(jī)床主軸轉(zhuǎn)速＝480r/min 所以切削工時(shí)　tm==＝0.44（min） (2)精車(chē)Φ50內(nèi)孔 　　粗精加工的切削用量除了進(jìn)給量和切削深度外都相同，故其余在此省略 　　進(jìn)給量f 根據(jù)《機(jī)械加工工藝手冊(cè)》表2.4-2 取f=0.2mm/r 主軸轉(zhuǎn)速 n=480r/min 所以切削工時(shí)　　t==0.17min (3)精車(chē)Φ62內(nèi)孔 5) 切削工時(shí)，按《工藝手冊(cè)》表6.2-1 　　　t=i ;其中l(wèi)=25mm; =4mm; =2mm; t=i=1=0.26(min) 工序10 鉆7-Ф9孔 機(jī)床：Z525立式鉆床 刀具：根據(jù)《機(jī)械加工工藝手冊(cè)》表10-61選取高速鋼麻花鉆Φ9. 1) 給量 查《機(jī)械加工工藝師手冊(cè)》表28-13，取f=0.13mm/r 2) 削速度　　根據(jù)《機(jī)械加工工藝手冊(cè)》表10-70,及10-66,查得 V=30m/min. 3) 定機(jī)床主軸轉(zhuǎn)速　　 ns== 1061r/min ,與1061r/min相近的機(jī)床轉(zhuǎn)速為1020r/min?，F(xiàn)選取=1020r/min。 所以實(shí)際切削速度 == 5) 削工時(shí)，按《工藝手冊(cè)》表6.2-1。 　 t=i ;其中l(wèi)=8mm; =4mm; =3mm; t= ==0.11(min) 工序11：锪孔7-Ф15孔 根據(jù)有關(guān)資料介紹，利用鉆頭進(jìn)行擴(kuò)鉆時(shí)，其進(jìn)給量與切削速度與鉆同樣尺寸的實(shí)心孔時(shí)的進(jìn)給量與切削速度之關(guān)系為 　　　 式中的、——加工實(shí)心孔進(jìn)的切削用量. 現(xiàn)已知 =0.36mm/r (《切削手冊(cè)》)表2.7 =42.25m/min (《切削手冊(cè)》)表2.13 　　　　　　　　 1) 給量 取f=1.5×0.36=0.51mm/r 按機(jī)床選取0.5mm/r 2) 削速度　　v=0.4×42.25=16.9m/min. 3) 定機(jī)床主軸轉(zhuǎn)速　　 ns== 358.5r/min 與358.5r/min相近的機(jī)床轉(zhuǎn)速為375r/min?，F(xiàn)選取=375r/min。 4) 所以實(shí)際切削速度 == 5) 削工時(shí)，按《工藝手冊(cè)》表6.2-1。 t=i ;其中l(wèi)=91mm; =10mm; =4mm; t= ==0.78(min) 工序12：鉆底孔，攻螺紋M12mm （1）鉆底孔 選用高速鋼錐柄麻花鉆（《工藝》表3.1－6） 由《切削》表2.7和《工藝》表4.2－16查得 （《切削》表2.15） 按機(jī)床選取 基本工時(shí)： min （2）攻螺紋M12mm： 選擇M12mm高速鋼機(jī)用絲錐 等于工件螺紋的螺距，即 按機(jī)床選取 基本工時(shí)： 工序13： 鉆斜孔Φ6的孔 刀具：根據(jù)《機(jī)械加工工藝手冊(cè)》表10-61選取高速鋼麻花鉆Φ6. 1) 進(jìn)給量 查《機(jī)械加工工藝師手冊(cè)》表28-13，取f=0.13mm/r 2) 切削速度　V=24~34m/min. 取V=30m/min 3) 確定機(jī)床主軸轉(zhuǎn)速　 ns== 1592r/min 與1592r/min相近的機(jī)床轉(zhuǎn)速為1592r/min。現(xiàn)選取=1426r/min。 所以實(shí)際切削速度 == 5) 切削工時(shí)，按《工藝手冊(cè)》表6.2-1 　 t=i ;其中l(wèi)=7mm; =4mm; =3mm; t= ==0.07(min) 四、 夾具設(shè)計(jì) 為了提高勞動(dòng)生產(chǎn)率，保證加工質(zhì)量，降低勞動(dòng)強(qiáng)度，需要設(shè)計(jì)專用夾具。 由指導(dǎo)老師的分配，決定設(shè)計(jì)第10道工序鉆7-Φ9孔。 4.1 問(wèn)題的提出 本夾具主要用于鉆7-Φ9孔，精度要求不高，為此，只考慮如何提高生產(chǎn)效率上，精度則不予考慮。因?yàn)镸12螺紋孔和Φ62K7中心孔有垂直度要求，因此我們要以已加工的Φ62K7孔為定位基準(zhǔn)。采用蓋板式鉆模板加工，用固定套定位，另外用一擋銷(xiāo)，即可實(shí)現(xiàn)完全定位。 4.2 定位基準(zhǔn)的選擇 擬定加工路線的第一步是選擇定位基準(zhǔn)。定位基準(zhǔn)的選擇必須合理，否則將直接影響所制定的零件加工工藝規(guī)程和最終加工出的零件質(zhì)量。基準(zhǔn)選擇不當(dāng)往往會(huì)增加工序或使工藝路線不合理，或是使夾具設(shè)計(jì)更加困難甚至達(dá)不到零件的加工精度（特別是位置精度）要求。因此我們應(yīng)該根據(jù)零件圖的技術(shù)要求，從保證零件的加工精度要求出發(fā)，合理選擇定位基準(zhǔn)。此零件圖沒(méi)有較高的技術(shù)要求，也沒(méi)有較高的平行度和對(duì)稱度要求，所以我們應(yīng)考慮如何提高勞動(dòng)效率，降低勞動(dòng)強(qiáng)度，提高加工精度。Φ62的孔已加工好，為了使定位誤差減小，選擇已加工好的Φ62孔和其端面作為定位基準(zhǔn)，來(lái)設(shè)計(jì)本道工序的夾具，以兩銷(xiāo)和已加工好的Φ62孔及其端面作為定位夾具。為了提高加工效率，縮短輔助時(shí)間，決定用簡(jiǎn)單的螺母作為夾緊機(jī)構(gòu)。 4.3切削力和夾緊力的計(jì)算 由于本道工序主要完成工藝孔的鉆孔加工，鉆削力。由《切削手冊(cè)》得： 鉆削力 式（5-2） 鉆削力矩 式（5-3） 式中： 代入公式（5-2）和（5-3）得 本道工序加工工藝孔時(shí)，夾緊力方向與鉆削力方向相同。因此進(jìn)行夾緊立計(jì)算無(wú)太大意義。只需定位夾緊部件的銷(xiāo)釘強(qiáng)度、剛度適當(dāng)即能滿足加工要求。 4.4定位誤差分析 本工序選用的工件以圓孔在定位銷(xiāo)上定位，定位銷(xiāo)為水平放置，由于定位副間存在徑向間隙，因此必將引起徑向基準(zhǔn)位移誤差。在重力作用下定位副只存在單邊間隙，即工件始終以孔壁與心軸上母線接觸，故此時(shí)的徑向基準(zhǔn)位移誤差僅存在Z軸方向，且向下，見(jiàn)下圖。 式中 ——定位副間的最小配合間隙（mm）； ——工件圓孔直徑公差（mm）； ——定位銷(xiāo)外圓直徑公差（mm）。 定位銷(xiāo)水平放置時(shí)定位分析圖 4.5 夾具設(shè)計(jì)及操作簡(jiǎn)要說(shuō)明 如前所述，在設(shè)計(jì)夾具時(shí)，應(yīng)該注意提高勞動(dòng)生產(chǎn)率避免干涉。應(yīng)使夾具結(jié)構(gòu)簡(jiǎn)單，便于操作，降低成本。提高夾具性價(jià)比。本道工序?yàn)殂@床夾具選擇了螺母夾緊方式。我們采用蓋板式鉆模板，本工序?yàn)殂@切削余量小，切削力小，所以一般的手動(dòng)夾緊就能達(dá)到本工序的要求。 本夾具的最大優(yōu)點(diǎn)就是結(jié)構(gòu)簡(jiǎn)單緊湊。夾具的夾緊力不大，故使用手動(dòng)夾緊。為了提高生產(chǎn)力，使用快速螺旋夾緊機(jī)構(gòu)。 裝配圖： 夾具體： 總 結(jié) 這次設(shè)計(jì)即將結(jié)束了，時(shí)間雖然短暫但是它對(duì)我們來(lái)說(shuō)受益菲淺的，通過(guò)這次的設(shè)計(jì)使我們不再是只知道書(shū)本上的空理論，不再是紙上談兵，而是將理論和實(shí)踐相結(jié)合進(jìn)行實(shí)實(shí)在在的設(shè)計(jì)，使我們不但鞏固了理論知識(shí)而且掌握了設(shè)計(jì)的步驟和要領(lǐng)，使我們更好的利用圖書(shū)館的資料，更好的更熟練的利用我們手中的各種設(shè)計(jì)手冊(cè)和AUTOCAD等制圖軟件，為我們踏入設(shè)計(jì)打下了好的基礎(chǔ)。 這次設(shè)計(jì)使我們認(rèn)識(shí)到了只努力的學(xué)好書(shū)本上的知識(shí)是不夠的，還應(yīng)該更好的做到理論和實(shí)踐的結(jié)合。因此同學(xué)們非常感謝老師給我們的辛勤指導(dǎo)，使我們學(xué)到了好多，也非常珍惜學(xué)院給我們的這次設(shè)計(jì)的機(jī)會(huì)，它將是我們畢業(yè)設(shè)計(jì)完成的更出色的關(guān)鍵一步。 致 謝 這次設(shè)計(jì)使我收益不小，為我今后的學(xué)習(xí)和工作打下了堅(jiān)實(shí)和良好的基礎(chǔ)。但是，查閱資料尤其是在查閱切削用量手冊(cè)時(shí)，數(shù)據(jù)存在大量的重復(fù)和重疊，由于經(jīng)驗(yàn)不足，在選取數(shù)據(jù)上存在一些問(wèn)題，不過(guò)我的指導(dǎo)老師每次都很有耐心地幫我提出寶貴的意見(jiàn)，在我遇到難題時(shí)給我指明了方向，最終我很順利的完成了畢業(yè)設(shè)計(jì)。 這次設(shè)計(jì)成績(jī)的取得，與指導(dǎo)老師的細(xì)心指導(dǎo)是分不開(kāi)的。在此，我衷心感謝我的指導(dǎo)老師，特別是每次都放下她的休息時(shí)間，耐心地幫助我解決技術(shù)上的一些難題，她嚴(yán)肅的科學(xué)態(tài)度，嚴(yán)謹(jǐn)?shù)闹螌W(xué)精神，精益求精的工作作風(fēng)，深深地感染和激勵(lì)著我。從課題的選擇到項(xiàng)目的最終完成，她都始終給予我細(xì)心的指導(dǎo)和不懈的支持。多少個(gè)日日夜夜，她不僅在學(xué)業(yè)上給我以精心指導(dǎo)，同時(shí)還在思想、生活上給我以無(wú)微不至的關(guān)懷，除了敬佩指導(dǎo)老師的專業(yè)水平外，她的治學(xué)嚴(yán)謹(jǐn)和科學(xué)研究的精神也是我永遠(yuǎn)學(xué)習(xí)的榜樣，并將積極影響我今后的學(xué)習(xí)和工作。在此謹(jǐn)向指導(dǎo)老師致以誠(chéng)摯的謝意和崇高的敬意。 參 考 文 獻(xiàn) 1. 切削用量簡(jiǎn)明手冊(cè),艾興、肖詩(shī)綱主編,機(jī)械工業(yè)出版社出版，1994年 2.機(jī)械制造工藝設(shè)計(jì)簡(jiǎn)明手冊(cè)，李益民主編，機(jī)械工業(yè)出版社出版，1994年 3.機(jī)床夾具設(shè)計(jì)，哈爾濱工業(yè)大學(xué)、上海工業(yè)大學(xué)主編，上海科學(xué)技術(shù)出版社出版，1983年 4.機(jī)床夾具設(shè)計(jì)手冊(cè)，東北重型機(jī)械學(xué)院、洛陽(yáng)工學(xué)院、一汽制造廠職工大學(xué)編，上?？茖W(xué)技術(shù)出版社出版，1990年 5.金屬機(jī)械加工工藝人員手冊(cè)，上?？茖W(xué)技術(shù)出版社，1981年10月 6.機(jī)械制造工藝學(xué)，郭宗連、秦寶榮主編，中國(guó)建材工業(yè)出版社出版，1997年 Proceedings ofthe2006 IEEE/RSJ International Conference on Intelligent Robots and Systems October9- 15, 2006, Beijing, China ANovelModularFixtureDesignandAssemblySystem BasedonVR PengGaoliang, LiuWenjian SchoolofMechatronicsEngineering HarbinInstituteofTechnology Harbin, 150001, China pgl7782a Abstract - Modular fixtures are one oftheimportant aspects ofmanufacturing. This paper presents a desktop VR system for modular fixture design. The virtual environmentis designed and the design procedure is proposed. It assists the designer to make the feasible design decisions effectively and efficiently. A hierarchical data model is proposed to represent the modular fixture assembly. Based on this structure, the user can manipulate the virtual models precisely in VE during the design and assembly processes. Moreover, the machining simulation for manufacturing interaction checking is discussed and implemented. Finally, the case study has demonstrated the functionality of the proposed system. Compared with the immersive VR system, the proposed system has offered an affordable andportable solutionformodularfixtures design. Index Terms - Modularfixture, desktop VR, assembly design, machiningsimlulation. I. INTRODUCTION Modular fixtures are one of the important aspects of manufacturing. Proper fixture design is crucial to product quality in terms of precision, accuracy, and finish of the machined part. Modular fixture is a system of interchange- eable and highly standardized components designed to securely and accurately position, hold, and support the workpiece throughout the machining process 1. Tradition- ally, fixture designers rely on experience or use trial-and- error methods to determine an appropriate fixturing scheme. With the advent of computer technology, computer aided design has been prevalent in the area of modular fixture design. In general, the associated fixture design activities, namely setup planning, fixture element design, and fixture layout design are often dealt with at the downstream end of the machine tool development life-cycle. These practices do not lend themselves well to the bridging of design and manufacturing activities. Forexample, very few systems have incorporated the functionality of detecting machining interference. This leads to a gap between the fixture design andmanufacturing operationswheretheaspectofcutterpaths is not considered during the design stage 2. As a result, re- designcannotbeavoidedwhenthecutterisfoundtointerfere with the fixture components in the manufactu- ring set-up. Therefore, in orderto bring machining fixture design into the arenaofflexiblemanufacturing, amoresystematicandnatural designenvironmentisrequired. As a synthetic, 3D, interactive environment typically generated by a computer, VR has been recognized as a very powerful human-computer interface for decades 4. VR holds great potential in manufacturing applications to solve problems before being employed in practical manufacturing thereby preventing costly mistakes. The advances in VR technology in the last decade have provided the impetus for applying VR to different engineering applications such as product design 5, assembly 6, machining simulation 7, andtraining 8. The goal ofthis paper is to develop a VR- basedmodular fixtures design system (VMJFDS). This is the firststepto develop anintegratedandimmersiveenvironment for modular fixture design. This application has the advantages of making the fixture design in a natural and instructive manner, providing better match to the working conditions, reducing lead-time, and generally providing a significantenhancementoffixtureproductivityandeconomy. II. OVERVIEWOFTHEPROPOSEDSYSTEM The system architecture of the proposed desktop VR systemismodularisedbasedonthefunctionalrequirements of thesystem,whichisshowninFig.1. Atthesystemlevel,three modules of proposed system, namely, Graphic interface (GUI), Virtual environment (VE) and Database modules are designed. For each ofthe modules, a set ofobjects has been identified to realize its functional requirements. The detailed objectdesignandimplementation are omittedfromthispaper. Instead, the briefdescription ofthese three modules is given below. 1) Graphic Interface (GUI): The GUI is basically a friendly graphic interface that is used to integrate the virtual environmentandmodularfixturedesignactions. 2) Virtual environment (VE): TheVEprovidestheusers with a 3D display for navigating and manipulating the models of modular fixture system and its components in the virtual environment. As shown in Fig. 1, the virtual environment module comprises two parts, namely assembly design environment andmachiningsimulationenvironment. Theuser selects appropriate elements andputs downthese elements on the desk in the assembly design area. Then he assembles the selected elements one by one to build up the final fixture systemwiththeguidanceofthesystem. 1-4244-0259-X/06/$20.00 C)2006IEEE 2650 Authorized licensed use limited to: Nanchang University. Downloaded on December 20, 2009 at 22:44 from IEEE Xplore. Restrictions apply. Fig.1.OverviewofthedesktopVRbasedmodularfixturedesignsystem. 3) Database: The database deposit all of the models of environment and modular fixture elements, as well as the domain knowledge and useful cases. There are 5 databases shown in Fig.1. Among them, knowledge & rule base governing all fixture planning principles forms the brains of thesystem. III. PROCEDUREOFMODULARFIXTUREDESIGN In this section, an instructive modular fixture design procedure within VE is presented. Besides the 3D depth that the users feel and the real-world like operation process, this procedure features intelligence and introduction. During the design process, some useful cases and suggestion will be presented to the user for reference based on intelligent inference method such as Case based reasoning (CBR) and Rule based reasoning (RBR). Further more, relative knowledge andrules arepresented ashelppages thattheuser caneasilybrowsedduringthedesignprocess. Overview of modular fixture design process is summarized in Fig. 2. After the VE environment is initialed andthe workpiece is loaded, the first step is fixtureplanning. Inthis step, theuserfirstdecides thefixturing scheme, thatis specifies the fixturing faces of the workpiece interactively. Forhelptheusersdecision-making, someusefulcasesaswell as their fixturing scheme will be presented via the automatic CBR retrieval method. Once the fixturing faces are selected, theusermaybepromptto specifythefixturingpoints. Inthis task, somesuggestions andrulesaregiven. After the fixturing planning, the next step is fixture FUs design stage. In this stage, the user may be to select suitable fixture elements andassembletheseindividualparts into FUs. According to the spatial information ofthe fixturingpoints in relation to the fixture base and the workpiece, some typical FUs and suggestions may be presented automatically. These willbehelpfulfortheuser. AftertheplanningandFUs design stage, the next stage is interactively assembling the designed fixtureFUstoconnecttheworkpiecetothebaseplate. When the fixture configuration is completed, the result will be checked and evaluated within the machining environment. The tasks executed in this environment including assembly planning, machining simulation, and fixture evaluation. Assemblyplanning isusedto gain optimal assembly sequence and assembly path of each component. Machining simulation is responsible for manufacturing interaction detection. Fixture evaluation will check and evaluate the design result. In conclusion, the whole design process isinanaturemannerforthebenefitofVE. Moreover, the presented information of suggestion and knowledge can advise the user on how to make decisions ofthe best design selection. IV. ASSEMBLYMODELINGOFMODULARFIXTURE A. Modularfixturestructureanalysis A functionalunit(FU) is acombination offixture elements to provide connectionbetweenthebaseplate and aworkpiece 11. Generally, modularfixture structuremaybe dividedinto three functional units according to its basic structure characteristics, namely locating unit, clamping unit, and supporting unit. The number offixture elements in aFU may consist ofone or more elements, in which only one element serves as a locator, support or clamp. The major task ofthe modularfixture assembly is to selectthe supporting, locating, clamping and accessory elements to generate the fixture FUs toconnecttheworkpiecetothebaseplate. By analyzing the practical application ofmodular fixtures, it is found that the assembly ofmodular fixtures begins by selecting the suitable fixture elements to construct FUs, then subsequentlymountingtheseFUs onthebaseplate. Therefore, the FUs can be regarded as subassemblies ofmodular fixture system.Further,thestructureofmodularfixturesystemcanbe representedasahierarchalstructureasshowninFig.3. 2651 Authorized licensed use limited to: Nanchang University. Downloaded on December 20, 2009 at 22:44 from IEEE Xplore. Restrictions apply. UsefTa6 *T- siikg&Sugge lr,l Fixtui e Elemenets rUetrieval i0 Tools rKetrieval 4 Fig.2Modularfixturedesignprocedureinproposedsystem B. Hierarchically structured data modelfor modularfixture representation in VE It is common that the corresponding virtual environment may contain millions ofgeometric polygon primitives. Over thepastyears, anumberofmodel sub-division schemes, such asBSP-tree 10 andOctrees,havebeenproposedto organize largepolygonalmodels.However, formodular Ba 1I_ 1 Hsreplalte Bansepla1nte Elements *Locatng ElementsL,cating Units AccessoryEllements ClamnpingElemnents !ClampingUnits SupportingElemntsSupporting Ufnits Accessory Elements Fig. 3Hierarchical structureofmodularfixture system design applications, the scene is also dynamically changing, due to interactions. For example, in design process, the part object may change its spatial position, orientation and assembly relations. This indicates that a static representation, such as BSP-tree, is not sufficient. Further more, the above models can only represent the topology structure of fixture system in the component level. However, to the assembly relationship among fixture components, which refers to the mating relationship between assembly features that is not concerned. In this section, we present a hierarchically structuredandconstraint-baseddatamodelformodularfixture system representation, real-time visualization and precise 3D manipulationinVE. As shown in Fig.4, the high-level component based model is used for interactive operations involving assemblies or disassembles. It provides both topological structure and link relationsbetweencomponents. Theinformationrepresent- ed in the high-level model can be divided into two types, i.e. component objects and assembly relationships. Component objects can be a subassembly or a part. A subassembly consists of individual parts and assembly relationships betweentheparts. Component Level (Pt Part S Subassembly Assembly relationship Feature Level Ft3 Feature Feature mating relationship t- -t Polygon Level FZ-ll. Polygon Fig.4ThehierarchicalstructuredatamodelinVE Themiddle-levelfeaturebasedmodelisbuiltuponfeatures and feature constraints. In general, the assembly relationship often treated as the mating relationships between assembly features. Thus the featurebasedmodel isusedto describethe assembly relationship andprovides necessary information for spatial relationship calculating during assembly operation. In this model, only the feature relationships between two different components are considered. The relationship between features ofone element will be discussed in feature basedmodularfixtureelementmodelingbelow. The low-level polygon based model corresponds to the above two level models for real-time visualization and interaction. It describes the entire surface as an inter- connected triangular surface mesh. More about how the polygons organized of a single element will be discussed is thenextsection. C. Modularfixtureelementsmodeling As we know, in VE, the part is only represented as a number ofpolygon primitives. This result in the topological 2652 Authorized licensed use limited to: Nanchang University. Downloaded on December 20, 2009 at 22:44 from IEEE Xplore. Restrictions apply. relations- hips and parametric information are lost during the translation process of models from CAD systems to VR systems. However, this important information is necessary in design and assembly process. In order to fulfill the requirements, we present a modeling scheme for fixture elementsrepresentationinthissection. The modular fixture elements are pre-manufactured parts withstandarddimensions. Afterthefixturingschemedesigned, the left job is to select suitable standard elements and assemblethese elements to formafixture systeminafeasible andeffectivemanner. Therefore, intheproposed system, only the assembly features of the fixture elements need to be considered. Inthispaperanassemblyfeature isdefinedas apropertyof afixture element, whichprovidesrelatedinformationrelevant to modular fixture design and assembly/disassembly. The following eight function faces are defined as assembly featuresoffixtureelements: supportingfaces, supportedfaces, locating holes, counterbore holes, screw holes, fixing slots, andscrewbolts. Besidestheinformation aboutthefeaturelike typeanddimension, otherparameters, i.e. therelativeposition andorientationofthe featureintheelements localcoordinate system are recorded with the geometric model in the fixture element database. When one element assembles with another, the information aboutthematedfeatures isretrieved andused to decide the spatial relationship ofthe two elements. More information about the assembly features and their mating relationship arediscusseddetailedinRef 1. D. Constraintbasedfixtureassemblyin VE 1)Assemblyrelationshipbetweenfixtureelements Mating relationships have been used to define assembly relationships between part components in the field of assembly. According to the assembly features summarized in the above section, there are fivetypes ofmating relationships between fixture elements. Namely against, fit, screw fit, across, andT-slotfit,which are illustrated inFig. 5. Based on these mating relationships, we can reason the possible assemblyrelationshipofanytwoassembledfixtureelements. 2)Assemblyrelationshipreasoning Ingeneral, the assemblyrelationship oftwo assembledpart isrepresented as thematedassembly featurepairs ofthem. In the above section, we defined five basic mating relationships between fixture elements. Therefore, it is enabled to decide the possible assembly relationships through finding the possible mating assembly feature pairs. These possible assembly relationships are saved in assembly relationships database(ARDB)forfixtureassemblyinnextstage. However, when the fixture is complicated and the numbers ofcomposite fixture elements is large, the possible assembly relationships are too much to take much time for reasoning andtreating. To avoidthis situation, wefirstdecide the possible assembled elements pairs. That is to avoid reasoning the assembly relationship between a clamp andthe baseplate, for they never were assembled together. In this stage, some rules are utilized to find the possible assembled elementspairs. The algorithm of assembly relationships reasoning is similar to what discussed in Ref 12. Thus the detailed descriptionofthealgorithmisomittedfromthispaper. (a) AIlai.ns .2 l.I.F LIi I7 F d) Asicmie 1f-isxkt Elmn Fig. 5Fivebasicmatingrelationshipsbetweenfixtureelements 3)Constraint-basedfixtureassembly Aftercarrying outthe assemblyrelationships reasoning, all possible assembly relationships ofthe selected elements are establishedandsavedinARDB. Basedontheserelationships, the trainee can assemble these individual parts to a fixture system. This section is about the discussion of interactive assembly operation in VE. The process ofa single assembly operation is presented in Fig.5 and illustrated by two simple partsassemblyasshowninFig.6. In general, the assembly operation process is divided into three steps, namely assembly relationship recognizing, constraint analysis and applying, constraint-based motion. Firstly, the trainee selects an element and moves it to the assembled component. Once an inference between the assembling and assembled component is detected during the moving,the inferredfeatures is checked. Ifthetwo features is one of the assembly relationships in ARDB, they will be highlighted and will await the users confirmation. Once it is confirmed, the recognized assembly relationship will be appliedby constraint analyzing and solving, that is adjustthe translationandorientationoftheassemblingelementtosatisfy the position relationship ofthese two components, as well as applythenew constrainttotheassemblingelement.Whenthe new constraint is applied, the motion of the assembling element will be mapped into a constraint space. This is done bytransferring 3Dmotiondatafromtheinputdevicesintothe allowable motions ofthe object. The constraint-based motion notonlyensuresthattheprecisepositionsofacomponentcan be obtained, but also guarantee that the existing constraints will not be violated during the future operations. The assembling element will reach to the final position through succession assembly relationship recognizing and constraint applying. 2653 Ii 1-11 4- (b) F.t Authorized licensed use limited to: Nanchang University. Downloaded on December 20, 2009 at 22:44 from IEEE Xplore. Restrictions apply. NO Assembly relationship Iis possible checking elatioohship? Fig. 6Processofassemblyconstraintestablishment No V. MACHINING SIMULATION A. Manufacturinginteractions During the machining process, there are many types of manufacturing interactions associated with the fixture may occur. These interactions can be divided into two broad categories illustrated below, namely static interactions and dynamicinteractions. 1) Static interactions refer to the interference between fixture components, the interference between fixture components and machine tool, and the interference between fixture components andmaching feature ofworkpiece during theworkpiecesetup. 2)Dynamicinteractionsrefertothetool-fixtureinteractions, which occur within a single operation when the tool and the fixtureusedinthatoperationmaycollideduringcutting. Generally, the aspects of machining process and cutter paths are not considered duringthe fixture design stage. As a result, these interactions may often occur during the practical manufacturing. Thus the human machinists have to spend muchoftheirtimeidentifyingtheseinteractions andresolving them. Itis oftenresults inmodification orre-designoffixture system. Thatistediousandtimecostly. B.Interferencedetection Although the currently commercial software, like VERICUT, can simulates NC machining to detect tool path errors and inefficient motion prior to machining an actual workpiece. It is available to eliminate errors that could ruin the part, damage the fixture, break the cutting tool, or crash the machine during the part programming stage. However, these software are expensive and oriented to NC program- mertherebynotsuitableforfixturedesigners. During the fixture design stage, it should be ensured that the associated fixture interactions can be avoided. In this system, after the fixture configuration is complete, the machining simulation module is presented to the user to identifytheinteractionsandresolvethem. Within the machining simulation environment, the 3D digitalmodelofmachinetoolispresented. The canassemble the fixture components on the work bench and setup the workpiece, just as what the machining engineers do in the actual site. During the setup, the fixture components and the workpiece are move to their assembly position under manipulation. Theinterferencecheckingmoduleiscarriedout. Ifinterference occurs, the inferred objectwill be highlight. It is p