車床組合夾具的設(shè)計(jì)

資源目錄里展示的全都有，所見即所得。下載后全都有,請放心下載。原稿可自行編輯修改=【QQ：401339828 或11970985 有疑問可加】 畢業(yè)設(shè)計(jì)(論文)開題報(bào)告 題目：車床組合夾具的設(shè)計(jì) 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 班 級 姓 名 學(xué) 號 導(dǎo) 師 2012年12月20日 1.畢業(yè)設(shè)計(jì)（論文）綜述（題目背景、研究意義及國內(nèi)外相關(guān)研究情況） 題目背景: 機(jī)械制造離不開金屬切削機(jī)床，而機(jī)床夾具則是保證機(jī)械加工質(zhì)量、提高生產(chǎn)效率、減輕勞動(dòng)強(qiáng)度、降低對工人技術(shù)的過高要求、實(shí)現(xiàn)生產(chǎn)過程自動(dòng)化不可或缺的重要工藝裝備之一。機(jī)床夾具被廣泛用于制造業(yè)中，大量專用機(jī)床夾具的使用為大批量生產(chǎn)提供了必要條件。 夾具是工藝裝備的主要組合部分,在機(jī)械制造中占有重要地位。目前,單件、小批量生產(chǎn)正逐漸成為現(xiàn)代機(jī)械制造業(yè)新的生產(chǎn)模式。在這種模式中,要求加工機(jī)床和夾具裝備具有更好的柔性,以縮短生產(chǎn)準(zhǔn)備時(shí)間、降低生產(chǎn)成本,所以,按單一品種設(shè)計(jì)專用夾具的方法已不能滿足生產(chǎn)發(fā)展的要求,而組合夾具正是適應(yīng)這一生產(chǎn)模式的柔性工裝設(shè)備。它對縮短工藝裝備的設(shè)計(jì)、制造周期,以及產(chǎn)品換型后對原有工裝夾具延續(xù)使用起到至關(guān)重要的作用。國外為了適應(yīng)這種生產(chǎn)模式,也把柔性制造系統(tǒng)作為開發(fā)新產(chǎn)品的有效手段,并將其作為機(jī)械制造業(yè)的主要發(fā)展。 研究意義： 組合夾具是一種先進(jìn)的工藝裝備，它是由一套預(yù)先制造好的各種不同的形狀、不同規(guī)格、不同尺寸、具有互換性、高耐磨性和高精度的標(biāo)準(zhǔn)元件組成，其結(jié)構(gòu)靈活多變，適應(yīng)性廣，元件可長期循環(huán)使用。組合夾具的元件精度高、耐磨，并且實(shí)現(xiàn)了完全互換，元件精度一般為IT6-IT7級。用組合夾具加工的工件，位置精度一般可達(dá)IT8-IT9級，若精心調(diào)整，可以達(dá)到IT7級。由于組合夾具有很多優(yōu)點(diǎn)，又特別適用于新產(chǎn)品試制和多品種小批量生產(chǎn)，所以近年來發(fā)展迅速應(yīng)用較廣。組合夾具的主要缺點(diǎn)是體積較大，剛度較差，一次投資多，成本高，這使組合夾具的推廣應(yīng)用受到一定限制。隨著機(jī)械制造業(yè)的飛速發(fā)展，產(chǎn)品的更新?lián)Q代越來越快，傳統(tǒng)的大批量生產(chǎn)模式逐步被中小批量生產(chǎn)模式所取代，機(jī)械制造系統(tǒng)欲適應(yīng)這種變化需具備較高的柔性。國外己把柔性制造系統(tǒng)(FMS)作為開發(fā)新產(chǎn)品的有效手段，并將其作為機(jī)械制造業(yè)的主要發(fā)展方向。柔性化的著眼點(diǎn)主要在機(jī)床和工裝兩個(gè)方面，組合夾具是工裝柔性化的重點(diǎn)。組合夾具是一種標(biāo)準(zhǔn)化、系列化、通用化程度很高的工藝裝備，它是由一套預(yù)先制造好的各種不同形狀、不同規(guī)格、不同尺寸、具有完全互換性的標(biāo)準(zhǔn)元件和組合件，按工件的加工要求組裝而成的夾具。它可以拆卸、清洗，并可重新組裝成新的夾具，其應(yīng)用非常普遍，尤其適合于多品種、中小批量的生產(chǎn)。由于組合夾具的平均設(shè)計(jì)和組裝時(shí)間是專用夾具所花時(shí)間的5%-20%，可以認(rèn)為組合夾具就是柔性夾具的代名詞。 一個(gè)優(yōu)良的組合夾具必須滿足下列基本要求： （1）保證工件的加工精度，穩(wěn)定加工質(zhì)量 保證加工精度的關(guān)鍵，首先在于正確地選定定位基準(zhǔn)、定位方法和定位元件，必要時(shí)還要進(jìn)行定位誤差分析，還要注意夾具中其它零部件的結(jié)構(gòu)對加工精度的影響，確保組合夾具能滿足工件的加工精度要求。 （2）提高生產(chǎn)效率，降低成本 組合夾具的復(fù)雜程度應(yīng)與生產(chǎn)綱領(lǐng)相適應(yīng)，應(yīng)盡量采用各種快速高效的裝夾機(jī)構(gòu)，保證操作方便，縮短輔助時(shí)間，提高生產(chǎn)效率。 （3）良好的強(qiáng)度、剛度和結(jié)構(gòu)工藝性能 組合夾具的結(jié)構(gòu)應(yīng)力簡單、合理，便于制造、裝配、調(diào)整、檢驗(yàn)、維修等，有利于提高組合夾具的制造精度。 （4）操作性能好 組合夾具的操作方便、省力、安全可靠。在客觀條件允許及又經(jīng)濟(jì)適用的前提下，應(yīng)盡可能采用氣動(dòng)、液壓等機(jī)械化夾緊裝置，以減輕操作者的勞動(dòng)強(qiáng)度。 （5）經(jīng)濟(jì)性好 組合夾具應(yīng)盡量采用標(biāo)準(zhǔn)件和標(biāo)準(zhǔn)結(jié)構(gòu)，力求結(jié)構(gòu)簡單、制造容易，以降低組合夾具的成本。因此，設(shè)計(jì)時(shí)應(yīng)根據(jù)生產(chǎn)綱領(lǐng)對組合夾具方案進(jìn)行必要的技術(shù)經(jīng)濟(jì)分析，以提高組合夾具在生產(chǎn)中的經(jīng)濟(jì)效益。 （6）擴(kuò)大機(jī)床的使用范圍 使用組合夾具可以改變原機(jī)床的用途和使用范圍，實(shí)現(xiàn)一機(jī)多能。 （7）排屑順暢 組合夾具中積集切削會影響到工件的定位精度，切削的熱量使工件和夾具產(chǎn)生熱變形，影響加工精度。清理切削將曾加輔助時(shí)間，降低生產(chǎn)率。因此組合夾具設(shè)計(jì)中要給予排屑問題充分的重視。 國外的研究現(xiàn)狀: 夾具的設(shè)計(jì)包括三個(gè)步驟:設(shè)備規(guī)劃、夾具規(guī)劃和夾具結(jié)構(gòu)設(shè)計(jì)。目前,Joneja以及Ferreira等人在進(jìn)行CAPP方面的研究中對設(shè)備規(guī)劃有詳細(xì)論述。計(jì)算機(jī)輔助夾具設(shè)計(jì)(CAFD)就夾具方面也作了一些工作:Chou YC ,Chandru V等人提出的自動(dòng)夾具定位和夾緊的一種方法；De Meter EC提出的利用機(jī)械杠桿原理進(jìn)行定位和夾緊位置選擇的一種算法；Markus A等人提出的針對棱柱形工件進(jìn)行組合夾具設(shè)計(jì)的基于規(guī)則的系統(tǒng)。目前,關(guān)于工件夾具的自動(dòng)化配置方面的工作,自動(dòng)夾具結(jié)構(gòu)設(shè)計(jì)(AFCD)中很少提及。TrappeyAJC等人提出了一個(gè)二維組合夾具元件的配置算法。幾乎所有的AFCD研究者都承認(rèn),在一個(gè)成功的AFCD系統(tǒng)中, 工件的幾何形狀是一個(gè)關(guān)鍵因素。Nnaji B ,Alladin S等人也對具有復(fù)雜幾何形狀的工件進(jìn)行嘗試研究。然而其結(jié)果也僅僅適用于特定的幾 何體,比如多邊形棱柱。Brost和Goldberg提出了一個(gè)“完整”的算法用來分析多邊形工件的組合夾具設(shè)計(jì)。并開發(fā)出一個(gè)組合夾具設(shè)計(jì)系統(tǒng),針對一個(gè)任意存在的工件,能自動(dòng)產(chǎn)生所有可行的夾具設(shè)計(jì)。并且采用力球分析的方法對產(chǎn)生的方案進(jìn)行優(yōu)化。以后的許多研究者大多借鑒了Brost 和Goldberg的算法。組合夾具在動(dòng)力學(xué)方面的研究也取得了一定的進(jìn)步,Yu and Goldberg的夾具加載規(guī)劃方案是把夾具的加載問題看作基于傳感器的集成問題并給了一個(gè)規(guī)劃算法。Cai等提出了一種指導(dǎo)夾具設(shè)計(jì)的方法,此方法是縮小由于工件表面與夾具安裝誤差所帶來的定位誤差。Hockenberger與DeMter提出的模式是在工件加工期間工件的靜態(tài)分析,這種方法是一種定性分析并且是在抓緊或夾緊物體的最壞的情況下的偏差,這種情況是由于在單位扭球的干涉扭矩。 國內(nèi)的研究現(xiàn)狀: 我國于80年代末開始對組合夾具元件的設(shè)計(jì)與管理進(jìn)行了研究和開發(fā),在總結(jié)和吸取我國應(yīng)用和發(fā)展槽系夾具經(jīng)驗(yàn)的基礎(chǔ)上,根據(jù)現(xiàn)代機(jī)械加工特征及夾具的發(fā)展趨勢,研制了新一代孔系組合夾具系統(tǒng)。此系統(tǒng)發(fā)揮了槽系平移可調(diào)性和孔的旋轉(zhuǎn)可調(diào)性的優(yōu)勢,可直接組裝獲得任何直線尺寸和角度尺寸。此系統(tǒng)把大中小三個(gè)系列的元件有機(jī)融為一體,可在一塊多夾具基礎(chǔ)板上,既能組裝單個(gè)大工件夾具,又能組裝多個(gè)中小零件夾具,有利于裝夾具基礎(chǔ)板長期固定在機(jī)床工作臺上,此系統(tǒng)還設(shè)有孔系和槽系過渡元件,便于實(shí)現(xiàn)孔、槽系夾具元件混合使用。北京工商大學(xué)麻建東和劉璇開發(fā)的組合夾具元件庫,元件庫模塊的核心程序用ObjectARX SDK2. 02工具包開發(fā),界面程序用AUTOCAD 提供的對話框控制語言DCL (Dialog Control Language)語言開發(fā),在VC + + 6.0下編譯和聯(lián)接,生成的ARX可執(zhí)行程序在AU TOCADR14下直接加載運(yùn)行。元件庫可為使用者提供7類組合夾具元件三維圖形的瀏覽以及交互設(shè)計(jì)功能,并生成三維組合夾具構(gòu)形圖,在CAD環(huán)境中可進(jìn)行修改或刪除山東工業(yè)大學(xué)的徐志剛在“廣義映射原理”的指導(dǎo)下,開發(fā)了支持“top - down”風(fēng)范的夾具設(shè)計(jì)軟件自動(dòng)化系統(tǒng)。吳玉光博士在這個(gè)領(lǐng)域取得了較大的突破。提出孔系基礎(chǔ)板組合夾具設(shè)計(jì)的系統(tǒng)方法。該方法利用連桿機(jī)構(gòu)原理自動(dòng)確定由直線和圓弧組成定位邊界的零件的全部候選定位方案。并提出定位銷可見錐概念和定位銷轉(zhuǎn)動(dòng)支點(diǎn)的概念,進(jìn)行定位方案的裝卸方便性分析。進(jìn)一步提出瞬心三角形和同向邊的概念,對工件進(jìn)行可夾緊性分析,確定工件邊界的可夾緊范圍。其理論水平在國內(nèi)外相關(guān)領(lǐng)域內(nèi)開拓了新的局面。 2.本課題研究的主要內(nèi)容和擬采用的研究方案、研究方法或措施 主要內(nèi)容：設(shè)計(jì)一種車床的組合夾具，加工零件為三通接頭，對其進(jìn)行車孔。同時(shí)，設(shè)計(jì)出來的車床組合夾具可以經(jīng)過簡單拆卸、調(diào)整，能夠加工同一系列不同大小的三通接頭。 擬采用的研究方案：定位裝置采用兩個(gè)大小不一的定位塊，組合成類似于V形塊，夾緊裝置采用擋鐵和三個(gè)長螺釘?shù)慕M合裝置。由于加工的工件為90度的三通接頭，因此，要進(jìn)行所有管內(nèi)內(nèi)孔的加工，一次加工是無法完成，需要兩次裝夾兩次加工過程。而這樣的設(shè)計(jì)方案減少了夾緊元件的頻繁拆換，節(jié)省了時(shí)間。 研究方法： 1）繪制零件圖，認(rèn)真分析、研究零件圖及其加工工藝，根據(jù)要求選用孔 系組合夾具。 2）確定切削用量及參數(shù)要求，進(jìn)行組合夾具的定位、夾緊、支承、基礎(chǔ) 板部件設(shè)計(jì)。 3）繪制組合夾具裝配圖、繪制組合夾具重要部件的零件圖 3.本課題研究的重點(diǎn)及難點(diǎn)，前期已開展工作 課題研究的重點(diǎn)： 夾具設(shè)計(jì)本質(zhì)上是一種經(jīng)驗(yàn)設(shè)計(jì)，且夾具分類比較多，夾具參數(shù)比較復(fù)雜，夾具設(shè)計(jì)和工件形狀、加工條件、加工工藝等很多因素有關(guān)。組合夾具的設(shè)計(jì)主要是針對所要加工的零件進(jìn)行夾緊、定位等部件的設(shè)計(jì)，使之能適應(yīng)系列化零件的合理裝夾。 課題研究的難點(diǎn)： a、異型零件的工藝分析，對零件的工藝分析要求對該零件有相當(dāng)熟悉的了解，由于條件有限使得對零件不熟悉，可能導(dǎo)致工藝分析不到位。 b、組合夾具的設(shè)計(jì)，目前組合夾具的設(shè)計(jì)跟個(gè)人的經(jīng)驗(yàn)有直接關(guān)系，所以本課題的設(shè)計(jì)可能不夠成熟。 前期已經(jīng)開展的工作： 查閱有關(guān)組合夾具資料，了解國內(nèi)外組合夾具的發(fā)展及其新技術(shù)，積極與導(dǎo)師進(jìn)行交流，確定研究方案及其研究方法。 4.完成本課題的工作方案及進(jìn)度計(jì)劃（按周次填寫） （1）分析題目，做好開題報(bào)告，準(zhǔn)備好開題答辯。（1周） （2）根據(jù)設(shè)計(jì)內(nèi)容的要求，查閱相關(guān)資料，明確設(shè)計(jì)方向，對存在的疑問咨詢指導(dǎo)老師。（2～5周） （3）檢查、閱讀及完善設(shè)計(jì)內(nèi)容準(zhǔn)備中期答辯。（6周） （4）進(jìn)行畢業(yè)設(shè)計(jì)，包括：相關(guān)方面的計(jì)算、確定參數(shù)，繪制相關(guān)圖紙并建立圖庫，對資料進(jìn)行整理。（7～11周） （5）對畢業(yè)設(shè)計(jì)進(jìn)行整理，與老師進(jìn)行討論修改，校核定稿。（12～13周） （6）審查、閱讀設(shè)計(jì)內(nèi)容準(zhǔn)備答辯。（14～15周） （7）進(jìn)行畢業(yè)答辯。(16周) 5.指導(dǎo)教師意見（對課題的深度、廣度及工作量的意見） 指導(dǎo)老師： 年 月 日 6.所在系審查意見： 系主管領(lǐng)導(dǎo)： 年 月 日 參考文獻(xiàn) [1] 薛源順.機(jī)床夾具設(shè)計(jì). 北京:機(jī)械工業(yè)出版社,2000 [2] 楊黎明.機(jī)床夾具設(shè)計(jì)手冊. 北京：國防工業(yè)出版社,1996 [3] 東北重型機(jī)械學(xué)院.機(jī)床夾具設(shè)計(jì)手冊. 上海：上?？萍汲霭嫔?1988 [4] 胡家秀主編.機(jī)械零件設(shè)計(jì)實(shí)用手冊. 北京:機(jī)械工業(yè)出版社,1999 [5] 李益民主編.機(jī)械制造工藝設(shè)計(jì)手冊. 北京:機(jī)械工業(yè)出版社,1995 [6] 孟憲椅等主編.機(jī)床夾具圖冊. 北京:機(jī)械工業(yè)出版社,1991 [7] 謝家瀛主編.車床設(shè)計(jì)簡明手冊.北京:機(jī)械工業(yè)出版社,1999 [8] 楊培元等主編.液壓系統(tǒng)設(shè)計(jì)手冊. 北京:機(jī)械工業(yè)出版社,1995 [9] 李云.機(jī)械制造工藝及設(shè)備設(shè)計(jì)指導(dǎo)手冊. 北京:機(jī)械工業(yè)出版社,1996 [10] 李益民.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,1993 [11] 周開勤.機(jī)械零件手冊.第五版. 北京：高等教育出版社,2002 [12] 姚永明.非標(biāo)準(zhǔn)設(shè)備設(shè)計(jì). 上海：上海交通大學(xué)出版社,1999 [13] 張樹有.圖學(xué)基礎(chǔ)教程. 北京：高等教育出版社,1999 [14] 陳秀寧.機(jī)械設(shè)計(jì)課程設(shè)計(jì). 浙江：浙江大學(xué)出版社,2002 [15] Ashley S., High – speed machining goes mainstream, Mechanical Engineering, May 1995, (56 – 61). [16] Cai-HuaXionga,YouFuLib,Kevin Rongc,You-LunXionga.Qualitative Analysis and Quantitive Evaluation of Fixturing [J].Robotics and Computer Integrated Manufacturing,002,18：335-342. [17] Diana M Pelinescu,Michael Yu Wang.Multi-objective Optimal Fuxture Layout Design[J].Rob Otics and Computer Integrated Manufacturing,2002,18：365-372. [18] Brost RC Goldberg K Y.A Complete Algorithm for Designing Planar Fixtures Using Modular Components [J] IEEE Transactions on Robotics and Automation,1996,1 (1)：31-46. Int J Adv Manuf Technol (2001) 18:784789 2001 Springer-Verlag London LimitedA Clamping Design Approach for Automated Fixture DesignJ. CecilVirtual Enterprise Engineering Lab (VEEL), Industrial Engineering Department, New Mexico State University, Las Cruces, USAIn this paper, an innovative clamping design approach isdescribed in the context of computer-aided fixture design activi-ties. The clamping design approach involves identification ofclamping surfaces and clamp points on a given workpiece.This approach can be applied in conjunction with a locatordesign approach to hold and support the workpiece duringmachining and to position the workpiece correctly with respectto the cutting tool. Detailed steps are given for automatedclamp design. Geometric reasoning techniques are used todetermine feasible clamp faces and positions. The requiredinputs include CAD model specifications, features identified onthe finished workpiece, locator points and elements.Keywords: Clamping; Fixture design1.Motivation and ObjectivesFixture design is an important task, which is an integration linkbetween design and manufacturing activities. The automation offixture design activities and the development of computer-aidedfixture design (CAFD) methodologies are key objectives to beaddressed for the successful realisation of next generationmanufacturing systems. In this paper, a clamp design approachis discussed, which facilitates automation in the context of anintegrated fixture design methodology.Clamp design approaches have been the focus of severalresearch efforts. The work of Chou 1 focused on the twincriteria of workpiece stability and total restraint requirement.The use of artificial intelligence (AI) approaches as well asexpert system applications in fixture design has been widelyreported 2,3. Part geometry information from a CAD modelhas also been used to drive the fixture design task. Bidanda4 described a rule-based expert system to identify the locatingand clamping faces for rotational parts. The clamping mech-anism is used to perform both the locating and clampingCorrespondence and offprint requests to: Dr J. Cecil, Virtual EnterpriseEngineering Lab (VEEL), Industrial Engineering Department, NewMexico State University, Las Cruces, NM 88003, USA. E-mail:jcecil?nmsu.edufunctions. Other researchers (e.g. DeVor et al. 5,6) haveanalysed the cutting forces and built mechanistic models fordrilling, and other metal cutting processes. Kang et al. 2defined assembly constraints to model spatial relationshipsbetween modular fixture elements. Several researchers haveemployed modular fixturing principles to generate fixturedesigns 2,711.Other fixturedesign effortshave beenreported in 1,3,9,1223. An extensive review of fixture designrelated work can be found in 21,24.In Section 2, the various steps in the overall approach toautomate the clamping design task are outlined. Section 3describes the determination of the clamp size to hold a work-piece during machining and in Section 4, the automatic determi-nation of the clamping surface or face region on a workpieceis detailed. Section 5 discusses the determination of the clamp-ing points on a workpiece.2.Overall Approach to Clamp DesignIn this section, the overall clamping design approach isdescribed. Clamping is usually carried out to hold the part ina desired position and to resist the effects of cutting forces.Clamping and locating problems in fixture design are highlyrelated. Often, the clamping and locating can be accomplishedby the same mechanism. However, failure to understand thatthese two tasks are separate aspects of fixture design may leadto infeasible fixture designs. Human process planners generallyresolve the locating problem first. The approach developed canwork in conjunction with a locator design strategy. However,the overall locator and support design approach is beyond thescope of this paper.CAD models of the part design (for which the clamp designhas to be developed), the tolerance specifications, processsequence, locator points and design, among other factors, arethe inputs to the clamp design approach. The purpose ofclamping is to hold the parts against locators and supports.The guiding theme used is to try not to resist the cutting ormachining forces involved during a machining operation.Rather, the clamps should be positioned such that the cuttingforces are in the direction that will assist in holding the partsecurely during a specific machining operation. By directingA Clamping Design Approach785the cutting forces towards the locators, the part (or workpiece)is forced against solid, fixed locating points and so cannotmove away from the locators.The clamp design approach discussed here must be viewedin the context of the overall fixture design approach. Priorto performing locator/support and clamp design, a prelimi-nary phase involving analysis and identification of features,associated tolerances and other specifications is necessary.Based on the outcome of this preliminary evaluation anddetermination, the locator/support design and clamp design canbe carried out. The clamp design approach described in thispaper is discussed based on the assumption that locator/supportdesign attributes have been determined earlier (this includesdetermination of appropriate locator and support faces on aworkpiece as well as identification of locator and supportfixturing elements such as V-blocks, base plates, locatingpins, etc).2.1Inputs to Clamp DesignThe inputs include the winged-edge model of the given productdesign, the tolerance information, the extracted features, theprocess sequence and the machining directions for each of theassociated features in the given part design, the location facesand locator devices, and the machining forces for the variousprocesses required to produce each corresponding feature.2.2Clamp Design StrategyThe main steps in the automation of the clamping design taskare summarised in Fig. 1. An overview of these steps isas follows:Step 1. Consider the set-up SUi in the set-up configuration listalong with the associated process ? feature entries.Step 2. Identify the direction and type of clamping. The inputsrequiredarethemachiningdirectionvectorsmdv1,mdv2,. . .,mdvn and identified normal vectors of support face nvs. Ifthe machining directions are downward (which correspond tothe direction vector 0, 0, 1), and the normal vector of thesupport face is parallel to the machining direction, then thedirection of clamping is parallel to the downward machiningdirection 0, 0, 1. If sideways clamping is required, and ifthere are no feasible regions at which to position a clamp fordownward clamping, then a side-clamp direction is obtainedas follows. Let sv and tv be the normal vectors of the secondary(sv) and tertiary (tv) locating faces. Then, the direction ofclamping used by a side-clamping mechanism such as a v-block should be parallel to both these normal vectors, i.e. thenormal vectors of the each of the v-surfaces in the v-blockwill be parallel to sv and tv, respectively. The side clampingface should be a pair of faces parallel to the faces sv andtv, respectively.Step 3. Determine the highest machining force from the mach-ining forces list (for each feature) MFi (i = 1, . . .,n). This willbe the effective force FE that must be balanced while designingthe clamp for this set-up SUi.Step 4. Using the value of the calculated highest machiningforce FE, the dimensions of the clamp to be used to hold theFig. 1. The clamp design activities.workpiece can be determined (for example, a strap clamp canbe used as a clamping mechanism). The approach for this taskis explained in Section 3.Step 5. Determine the clamping face on a given workpiece.This step can be automated as described in Section 4.Step 6. The actual position of the clamp on the clampingface is determined in an automated manner as explained inSection 5.Consider next set-up SU(i + 1) and proceed to step 1.3.Determination of the Clamp SizeIn this work, the clamps used belong to the family of clampsreferred to as strap clamps. A strap clamp is based on thesame principle as that of the lever (see Fig. 2). In this section,the automated design of a strap clamp is described. Theclamping force required is related to the size of the screw ora threaded device that holds the clamp in place. The clampingforce should balance the machining force to hold the workpiecein position. Let the clamping force be W and the screwdiameter be d. The dimensions of the various screw sizes forvarious clamping forces can be determined in the followingmanner. Initially, the ultimate tensile strength (UTS) of thematerial of the clamp (depending on availability) can beretrieved from a data library. Various materials have differenttensile strengths. The selection of the clamp material can alsobe performed directly using heuristic rules. For example, if thepart material is mild steel, then the clamp material can be low786J. CecilFig. 2. The strap clamp.carbon steel or machine steel. To determine the design stress,the UTS value can be divided by a safety factor (such as 4or 5). The root area A1 of the screw (for a clamp such asa screw clamp) can then be determined: Clamping forcerequired/Design Stress DS. Subsequently, the full area FA ofthe bolt cross-section can be computed as equal to A1/(65%)(since the root area of the screw where shearing can occur isapproximately 65% of the total area of the bolt). The diameterof the screw d can then be determined by equating FA to(3.14 d2/4). Another equation which can be used involvesrelating the width B, height H and span L of the clamp to thescrew diameter d (B, H, and L can be computed for variousvalues of d): d2= 4/3 BH2/L.4.The Determination of the ClampingFaceThe required inputs to determine the clamping region includethe CAD model of the product, the extracted features infor-mation, the feature dimensions and faces on which they occur,the locating faces and locators selected. Consider a potentialclamping face PCF as shown in Fig. 3. The crucial criterionto be satisfied is that the clamping surface should not overlapor intersect with the features on that face, as shown in Fig. 4.The clamping surface area, which is in contact with theworkpiece surface (or PCF) is a 2D profile consisting of linesegments (see Fig. 6). By using line segment intersection tests,it can be determined whether the potential clamping area ofcontact overlaps any of the features on the given PCF.The determination of clamping faces can be automated as fol-lows:Fig. 3. Potential clamping face and feature profiles.Fig. 4. Potential clamping face and clamp box profile.Step 1. Identify faces that are parallel to the secondary andtertiary locator faces (lf1 and lf2) and at the farthest distancefrom lf1 and tcj, respectively. This is performed as shownbelow:(a)Identify faces tci, tcj such that tci is parallel to lf1 andtcj is parallel to lf2.(b)Insert candidate faces tci in list TCF.(c)By examining all faces tci listed in TCF, determine facestci and tcj that are farthest from face lf1 and lf2, respect-ively, and discard all other faces from list TCF.Step 2. Identify the face that is parallel to the location facesbut not adjacent to the additional locator faces. It is preferableto select a clamp face that does not have to share the adjacentperpendicular face with a locator. This step can be automatedas shown below:(a)Consider each face tci in list TCF and obtain correspond-ing faces fci that are adjacent and perpendicular to eachtci. Then, insert each face fci in list FCF.(b)Examine each fci and perform the following test:If fci is adjacent, perpendicular to lf1 or lf2,then discard it from list FCF and insert it in list NTCF.Step 3. Determine the clamping faces, based on the availabilityof potential clamping faces, as described below.Case (a). If there are no entries in list NTCF, then use thefaces in list TCF and proceed to step 4. If any faces werefound that were perpendicular to the secondary and tertiarylocation faces lf1 and lf2, such faces are the next feasiblechoices to be used for clamping.In this case, the only remaining choice is to re-examine thefaces in list NTCF.Case (b). If the number of entries in list NTCF is 1, thefeasible clamping face is fci. The normal vector of thecorresponding adjacent, perpendicular face tci is the axis ofclamping.Case (c). If number of entries in list NTCF is greater than 1,determine the face tci with larger area and proceed to step 4.Step 4. Depending on the direction of clamping which is either(+ or )1, 0, 0 or (+ or ) 0, 1, 0, the clamp can bepositioned along the centre of the face tci. The candidategeometrical positions of the clamp can be determined usingpart geometry and topological information, which is describedin the next section.A Clamping Design Approach787Fig. 5. Determination of the clamp profile dimensions.5.Determination of the Clamping Pointson a Clamping FaceAfter the clamp face has been determined, the actual clampingpositions on that face must be determined. The inputs are theclamp profile dimensions, clamp directions x, y, z, and poten-tial clamping face CF. The clamp profile dimensions areobtained (as in case (g) using CF geometry as follows.The first step is to determine a box size, which is tested todetermine whether it contains any features inside it. Profileintersection tests can also be performed using the methoddescribed earlier. If the intersection test returns a negativeresult, then no feature intersects with the clamp box profile,as shown in Fig. 4. If the intersection test returns a positiveresult, the following steps can be performed:1. Divide the clamp box profile into smaller rectangular stripsof size (1 w) (Figs 5 and 6).2. Perform the intersection tests with the feature profiles offeatures that occur on the face CF for the given part design.Fig. 6. Profiles intersection test of feature and clamp regions.3. The rectangular strips, where no feature intersection occurs,are feasible clamping regions. If there is more than onecandidate rectangle for clamping, the rectangle profile thatis toward the mid-point of the CF face along the clampingaxis is the clamp profile (and clamp points).If no profile Pi can be found that does not intersect with thefeature profiles, clamp width can be reduced by half and thenumber of clamps increased to two on that face. Using thesemodified clamp dimensions, perform the feature intersectiontest described earlier. If this test also fails, then the side faceadjacent to the PCF can be used as the clamping surface toperform side clamping. The side face then becomes the PCFand the feature intersection test can be repeated.5.1The Intersection of Profiles TestThe required inputs include the 2D profile P1 another 2Dprofile P2. The intersection of profiles can be determined inan automated manner using the following approach. Each inputprofile Pi consists of a closed loop of line segments Lij. Thesteps in this profile test are as follows:(T1) Consider a line segment L(i,1) in P1 and another linesegment L(2, j) in P2.(T2) For inputs L(i,1) and L(2, j), the intersection of edgescan be employed. If the edge intersection test returns a positivevalue, then the feature profile intersects with the candidate orpotential clamp profile under evaluation. If it returns a negativevalue, proceed to step 3.(T3) Repeat step (T1) for the same segment or edge (Li,1) inP1 with all remaining segments (L2, j+1) till j = n1 in P2.(T4) Repeat steps (T1) and (T2) for the remaining edges orsegments L12, L13,. . .,L1n in profile P1.If the feature profiles overlap the clamping profiles, the lineintersection tests will determine that occurrence. The inter-section of edges test can be performed automatically to detectwhether two edges intersect with each other. The inputsrequired for this test are the line segments L12 connecting(x1, y1) and (x2, y2) and L34 connecting (x3, y3) and(x4, y4).Let the equation of L12 be represented by:F(x,y) = 0(1)and that of L34 by:H(x,y) = 0(2)Step 1. Using Eq. (1) compute r3 = F(x3, y3) by substitutingx3 and y3 for x and y and compute r4 = F(x4, y4) by substitut-ing x4 and y4 for x and y.Step 2. If r3 is not equal to 0, r4 is not equal to 0, and thesigns of r3 and r4 are the same, (which indicate r1 and r2lie on same side), then the edges L12 and L34 do not intersect.If this is not satisfied, then step (3) is performed.Step 3. Using Eq. (2), compute r1 = H(x1, y1). Then, computer2 = G(x2, y2) and proceed to step 4.Step 4. If r1 is not equal to zero, r2 is not equal to zero, andthe signs of both r1 and r2 are the same , then r1, r2 lie on788J. CecilFig. 7. Sample part to illustrate the clamping design approach.the same side and the input line segments do not intersect.Else, if this condition is not satisfied, proceed to step 5.Step 5. The given line segments do intersect. This completesthe test.Consider the same sample part shown in Fig. 7. The featuresto be produced are a step and hole. Initially, the locator designis completed. The support locator (or primary locator) is abase plate (placed against face f4) and the secondary andtertiary locators are placed against faces f6 and f5 (whichcorrespond to the locator faces lf1 and lf2 discussed in Section4). An ancillary locator is also used, which is a v-block(positioned against the ancillary faces f3 and f5), shown inFig. 8. Based on the steps outlined in the clamp designFig. 8. Fixture design for the sample part in Fig. 7.approach discussed earlier, the candidate faces (which areparallel and at the farthest distance from lf1 and lf2) are facef3 and f5. There are no faces which are parallel to the locatorfaces but not adjacent to them. Using the priority rules in suchcases (as discussed in step 3 of Section 4), the remainingcandidate face is face f2. The clamp direction is downward;the v-block radial locator and other locators provide therequired location with the clamp holding the workpiece down-ward against the baseplate.The position of the clamp is determined based on the stepsdescribed in Section 5. As there are no feaures occurring onface f2, there is no need for feature intersection tests todetermine collision-free clamping. The position of the clampshould be away from the v-locator (which is positioned alongthe ancillary location faces) as the clamping face is adjacentto the ancillary location faces (this ensures better access forquick clamping). The final location and clamping design isshown in Fig. 8.The method discussed in this paper compares favourablywith the other clamp design methods discussed in the literature.The uniqueness of the discussed approach is the systematicidentification of the clamping faces based on part geometry,topology, and the occurrence of features to be machined. Whileother approaches have not exploited the position of the locatorsadequately, the proposed method uses the locators to hold theworkpiece during machining against the primary, secondary,and tertiary locators. Another advantage of this approach isthe determination of candidate feasible locations on clampfaces using the detection of profile intersections test (describedearlier), which quickly and efficiently identifies potential down-stream problems which may occur during clamping and mach-ining of features.6.ConclusionIn this paper, the clamping design aspects in the overall contextof a fixture design methodology was discussed. The locatordesign, the part design specifications, and other inputs areconsidered in identifying the clamping faces and directions.The various steps to automate this approach are also discussed.References1. Y. C. Chou, V. Chandru and B. Barash, “A mathematical approachto automatic configuration of machining fixtures: analysis andsynthesis”, Transactions ASME, Journal of Engineering for Indus-try, 111(4), pp. 299306, 1989.2. Y. Kang, Y. Rong and M. Sun, “Constraint based modular fixtureassembly modelling and automated design”, Proceedings of theASMEManufacturingScienceandEngineeringDivisio