法兰盘斜孔和径向孔回转分度钻床夹具的设计【含CAD图纸、文档全套】【GJ系列】
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系主任批准日期茂 名 学 院毕 业 设 计(论 文)任 务 书 机电工程 系 机械设计制造及其自动化 专业 机电042 班 学生 廖志华 一、毕业设计(论文)课题 法兰盘斜孔和径向孔加工回转分度钻床夹具设计 二、毕业设计(论文)工作自 2008年 3 月 17日起至 2008 年 6 月 15 日止三、毕业设计(论文)进行地点 茂名学院机电工程学院 四、毕业设计(论文)的内容要求 (一)、已知条件 (1)、被加工的零件的零件图 (2)、成批生产 (二)、主要内容及要求 (1)、按要求写出开题报告 (2)、结合课题到工厂进行毕业实习 (3)、收集国内外有关情报资料,查阅文献资料15篇以上 (4)、翻译不少于5000字的英语科技文献 (5)、研究形成总体方案 (6)、设计绘制出夹具的总装工作图 (7)、绘制出主要零件图 (8)、按学校规定格式编写出不少于20000字的设计计算说明书(含文献综述) (9)、准备和参加毕业答辩。 (三)、主要参考资料: (1)机床夹具图册P1819 孟宪栋等主编 机械工业出版社 (2)巧改机床 陈榕林 张磊 编著中国农业机械化出版社 (3)金属切屑机床 上、下册 顾熙赏等主编 上海科技出版社 (4)组合机床设计手册 机械工业出版社 (5)机电传动与控制 邓星钟等 华中理工大学出版社 (6)新编机械设计手册 徐生 机械工业出版社 (7)机械可靠性设计 刘信主编 机械工业出版社 (8)机械设计手册 机械工业出版社 (9)机床夹具设计 龚定安等 西安交通大学出版社 (10)机床夹具设计 李庆寿 机械工业出版社 (11)机床设计图册 华东五高校编 华东科技大学出版社 (12)机电一体化系统设计手册 杨黎明 主编 国防工业出版社 教研室负责人 指导教师 王安民(教授) 接受设计论文任务开始执行日期 2008 年 3 月 17 日学生签名 廖志华 茂 名 学 院毕业设计说明书题 目: 法兰盘斜孔和径向孔加工卧、斜轴 回转分度钻床夹具的设计 英文并列题目: The Design of the Rotary-Drilling Fixture of the Horizontal and Inclined Shaft about Flange of the Slanting-Holes and Radial Holes Machining 学院 机电工程学院 专业 机械设计制造及其自动化班级 机电04-2班 学生 廖志华 指导教师(职称) 王安民 (教授) 完成时间 2008年 3月 17日至 2008年 6月 15日毕业设计(论文)开题报告题 目法兰盘斜孔和径向孔加工卧、斜轴回转分度钻床夹具的设计The Design of the Rotary-Drilling Fixture of the Horizontal and Inclined Shaft about Flange of the Slanting-Holes and Horizontal Radial Holes Machining学 院茂名学院年 级2004级专 业机械设计制造及自动化学 号04024020214姓 名廖志华 指导教师王安民(教授)2008年 3 月 17日毕业设计(论文)开题报告题目法兰盘斜孔和径向孔加工卧、斜轴回转分度钻床夹具的设计时 间2008年 3月 17日至 2008年 6月 15 日本课题的目的意义(含国内外的研究现状分析)机床夹具是机械制造工艺系统重要的组成部分,其实现工件定位和夹紧; 使工件加工时相对于机床刀具有正确的位置; 以保证工件的加工精度。其质量的高低直接影响到零件制造的质量、工人的劳动强度、产品成本和生产率。通过机床夹具的设计,提高设计、计算、分析问题和解决问题的能力,综合运用计算机绘图能力、表达技术问题的能力以及开拓创新的能力等。通过本夹紧机构的设计进而掌握一般机床夹具的一般方法、步骤和技巧,从而达到掌握一般机械的设计方法和技巧,综合运用所学的知识来解决工程实际问题。机床夹具是用以装夹工件和引导刀具的附加装置。主要用于金属切削加工,在机床与工件、刀具之间起桥梁作用,是工艺系统中的一个重要环节。它可准确地确定工件与刀具、机床的相对位置,确保加工质量;它可以提高生产效率,确保劳动强度;它可以扩大或改变机床的使用范围等。因此,机床夹具是保证机械加工工艺过程正常进行的技术硬件之一。综上所诉,需要对零件进行夹具设计。设计(论文)的基本条件及设计(论文)依据零件图1张,材料为45钢设计夹具的主要依据 (1) 根据给定的生产量大小来确定夹具类型。 (2) 根据本单位的先有生产条件,注意充分发挥现场技术条件手段和技术力量的潜力来设计夹具。本课题的主要内容、重点解决的问题主要内容: (1)设计该零件钻孔的专用夹具 (2)绘制毛坯图1张 (3)绘制装配图1张及零件图若干张 (4)完成设计说明书一份,书写格式符合茂名学院本科生毕业设计格式规范 (5)完成外文翻译一份,内容与毕业设计相关,且不少于5000字符重点解决问题:在保证零件加工质量前提下,提高生产效率,降低消耗,以取得较好的经济效益和社会效益.本课题欲达到的目的或预期研究的结果毕业设计是学生完成本专业教学计划的最后一个极为重要的实践性教学环节,是使学生综合运用所学过的基本理论、基本知识与基本技能去解决专业范围内的工程技术问题而进行的一次基本训练。这对学生即将从事的相关技术工作和未来事业的开拓都具有一定意义。其主要目的:一、 培养学生综合分析和解决本专业的一般工程技术问题的独立工作能力,拓宽和深化学生的知识。 二、 培养学生树立正确的设计思想,设计构思和创新思维,掌握工程设计的一般程序规范和方法。三、 培养学生树立正确的设计思想和使用技术资料、国家标准等手册、图册工具书进行设计计算,数据处理,编写技术文件等方面的工作能力。四、 培养学生进行调查研究,面向实际,面向生产,向工人和技术人员学习的基本工作态度,工作作风和工作方法。计 划 进 度时 间工 作 内 容备 注2008.3.202008.4.62008.4.72008.4.202008.4.212008.5.42008.552008.5.182008.5212008.6.8课题资料收集、写开题报告夹具的方案设计工序设计与夹具方案的确定夹具设计与绘制装配图及零件图毕业论文的撰写整理及排版打印指导教师意见指导教师签名: 年 月 日先进制造与自动化技术的发展1我国制造业面临的挑战世纪之交,世界的政治、经济和技术发生了前所未有的巨大变化,经济全球化正在形成。信息技术对制造业产生了极其深刻和全面的影响,使制造业的发展打上了明显的信息化烙印。经济全球化和信息化使制造业的竞争环境、发展模式及运行效率与活动空间等发生了深刻变化,这些变化对我国制造业提出了严峻的挑战,同时也为实现我国制造业的跨越式发展提供了有利条件和机遇。1.1制造业竞争环境的变化随着经济全球化进程的加快,出现了新的国际分工格局:发达国家主要发展知识密集型的高新技术产业和服务业,而把劳动和资源密集型的产业向发展中国家转移。经济全球化的浪潮和我国加入WTO,使我国正在逐步成为世界的重要制造基地。跨国公司纷纷在我国投资建立企业和技术中心,国外产品大举进入中国。这使产品的市场竞争更加激烈,也使得我国制造企业必须直接同跨国公司在技术、资源、人才等方面进行正面竞争。面对如此严峻的挑战,我国制造业只能背水一战,加快技术升级的步伐,提高企业综合竞争能力。1.2制造业发展模式的变化信息化提高了生产要素的信息属性,促使企业竞争模式从自然资源和人力的竞争转向创新能力和创造高附加值产品的竞争;信息化使得知识的重要性凸显,人才成为竞争优势的重要因素;信息化促使企业管理由金字塔型结构向扁平型结构转变。经营思想由粗放型向集约型转变,出现了各种先进制造模式,如并行工程、敏捷制造、网络化制造和虚拟制造等,为我国企业向先进制造模式转变、提升我国制造企业的水平和能力提供了可以借鉴的模式。1.3制造企业运行效率与活动空间的变化信息化促进了国际金融市场的快速发展,不仅保障了跨国经济活动的正常运行,而且提高了资金在全球的流动速度;信息化可以大大缩短产品上市时间,提高产品质量,降低生产消耗和交易成本,提高资源利用率,从而大幅度提高制造企业的效率;信息化使企业在规模、经济实力和创新能力等方面得到了空前的发展,跨国公司的力量进一步加强;信息化和经济全球化打破了国界的阻隔,跨国经营日益普遍,国际贸易高速增长,国际投资日趋活跃,为企业发展创造了广阔空间。我国的制造业在国民经济中占有重要的地位,在工业化的进程中又同时面;临着信息化的艰巨任务。中共中央提出的“用信息化带动制造业现代化,用高新技术改造制造业,以实现制造业跨越发展”战略,为我国发展先进制造与自动化技术指明了方向。2我国制造业存在的主要差距由于我国工业化进程起步较晚,与国际先进水平相比,我国的制造业和制造技术还存在着阶段性差距。为了迎接经济全球化和信息化的挑战,迫切需要解决以下几方面的问题。a产品创新能力较差,开发周期较长。我国机械制造业的新产品贡献率约为18.09(20O0年),而美国已经达到52左右(1995年)。我国大中型企业生产的 2 000多种主导产品的平均生命周期为105年,是美国同类产品生命周期的35倍。我国有8O以上的企业生产能力利用不足或严重不足,但同时每年还要进口数以千亿美元国内短缺的产品。b制造工艺装备落后,成套能力不强。我国大多数企业目前还采用较落后的制造工艺与技术装备进行生产,优质高效低耗工艺的普及率不足10,数控机床、精密设备不足 5,配有国产数控系统的中档数控机床不超过 25,高档数控机床的90以上依赖进口;我国在大型成套装备技术方面严重落后, 100的光纤制造装备、85的集成电路(IC)制造装备、 80的石化装备、 70的轿车工业装备都依赖进口。C生产自动化和优化水平不高,资源综合利用率低。我国平均劳动生产率为0263万美元,而美国、日本和印度分别为9.37万美元、10.47万美元和0.34万美元;我国的能源综合利用率仅为32左右,比国外的先进水平低IO多个百分点;我国每万元国民生产总值的能耗比发达国家高4倍多,主要产品单位能耗比发达国家高3090,工业排放的污染物超过发达国家1O倍以上。d企业管理粗放,协作能力较差,国际市场开拓能力弱。我国多数企业缺少现代化管理的概念、方法和手段,众多的企业尚处于经验管理阶段,企业机构臃肿,富裕人员一般多达 3O 4O。我国机械工业的专业化水平仅为1530,而美国、西欧诸国、日本企业的专业化水平已经达到7595,小而全、大而全的“庄园式企业”缺乏快速响应市场需求的能力。经过20多年的努力,我国出口商品占世界市场份额从0.5提高到目前的35,但是根据近3年的统计数据分析,高附加值和高技术含量的出口商品仅占我国出口商品总量的10左右。e战略必争装备和竞争前核心技术的开发相对薄弱。战略必争装备涉及国家安全和经济命脉,对国民经济有重大影响。竞争前核心技术在未来的国际竞争中有可能开拓新的广阔市场或成为新的重大关键技术。例如:用于海洋资源开发的水下作业装备,用于高精尖设备制造的超精密加工装备,面向IT等产业的集成电路制造关键装备,对未来许多行业将产生重大影响的微机电系统(MEMS)以及集高技术于一身的仿人形机器人等。由于国外的技术封锁,这些装备和技术是花钱也很难买到的,必须靠自己的力量加以解决。综上所述,我国的制造业和制造技术还不能很好满足国民经济发展和参与国际竞争的需要。不解决上述问题,中国的制造业就不能在激烈的竞争中生存和发展。为了使我国制造业在国内、国际市场竞争中立于不败之地,为了尽快形成我国自主创新和跨越发展的先进制造技术体系,积极发展和应用先进制造与自动化技术刻不容缓,势在必行。3 先进制造与自动化技术发展现状世界各国十分重视发展先进制造与自动化技术,许多跨国公司应用先进制造与自动化技术实现了设计、制造后理和经营的一体化,加强了在国际市场的垄断地位。例如,美国波音公司在波音777客机的研制中,由于使用了先进的产品开发设计技术,使开发周期从过去的89年缩短到45年,缩短了40以上。成本降低25,出错返工率降低75,用户满意度也大幅度提高。美国通用汽车公司应用现代集成制造系统技术,将轿车的开发周期由原来的48个月缩短到了24个月,碰撞试验的次数由原来的几百次降到几十次,应用电子商务技术降低销售成本 10;美国 Exxon Mobil石油公司应用先进的综合自动化技术后,使企业的效益提高58,劳动生产率提高例15;机器人技术与自动化工艺装备的核心技术一直受到世界各国的重视,面向未来服务的水下机器人、微机器人。医用机器人、仿人形机器人等特种机器人,面向国防、航空、航天等方面的超精密加工装备,面向基础设施建设的智能化大型工程机械,面向制造业的高精度、高效率、低成本和高柔性基础制造装备等已成为目前的研究开发重点。先进制造与自动化技术已经成为带动制造业发展的重要推动力。为了占领先进制造与自动化技术的制高点,许多国家提出了跨世纪的研究计划。例如,美国政府提出了美国国家关键技术、先进制造技术计划、敏捷制造与制造技术计划和下一代制造(NGM)等计划;在欧共体的尤里卡计划(EUREKA)、信息技术研究发展战略计划(ESPRIT)和第五届框架研究计划中,与先进制造技术有关的项目占有相当大的比重;德国政府提出了制造2000计划、微系统2000计划和面向未来的生产等计划;日本的智能制造系统计划、极限作业机器人研究计划、微机器研究计划和仿人形机器人研究计划;英国的国家纳米技术计划(NION);韩国的高级先进技术国家计划(G7计划)等。这些国家均将先进制造与自动化技术列为重要研究内容。通过政府、企业、大学和科研院所的合作实施,这些计划大大促进了先进制造与自动化技术的发展。近10多年来,我国有关部门有计划地部署了一系列国家级重点科技项目,有效地促进了我国先进制造与自动化技术的研究与应用推广,如。科技部组织实施的863计划的CIMS主题、智能机器人主题,“九五”国家科技攻关计划的CAD应用工程、精密制造技术开发与应用、数控技术与装备、现场总线控制技术开发与应用、工业机器人应用、激光技术应用等重点项目;总装备部(原国防科工委)在“九五”期间,组织实施了我国武器装备先进制造技术的发展项目;航空。航天、兵器和机械等许多行业和部门在“九五”期间组织实施了行业先进制造技术项目;国家计委、经贸委等部委在用高技术改造传统产业方面也推行了一系列计划。上述计划和项目极大地推动了我国先进制造与自动化技术的发展。综观各国先进制造与自动化技术计划的制定和实施情况可以看到,先进制造和自动化技术的发展有其深刻的国际经济竞争背景。这些先进制造与自动化技术计划提出时,即以提高本国制造业的国际竞争能力、促进经济增长和提高国家综合实力为目标,既注重技术的超前性,更重视来自产业界的实际需求;在关键技术的选择上注重系统集成技术与工艺装备研究开发并重,通过系统技术、信息技术和自动化技术的引入,提高制造企业的竞争能力;同时也可以看到,各国在发展先进制造与自动化技术的过程中,政府通过若干计划的实施起到了关键的引导和调控作用,并形成了一套有效的研究开发及推广应用的管理机制和创新机制。4 先进制造与自动化技术重大发展方向目前制造业正在从以机器为特征的传统技术时代向着以信息为特征的系统技术时代迈进,进入了一个能够增强企业在不可预见的多变环境中生存能力的全球化敏捷制造阶段。合理开发利用资源、保护生态环境、实现经济一社会相互协调的可持续发展战略和绿色制造成为全社会的共识。今后15年制造技术的发展将超过以往的75年。当前先进制造与自动化技术发展的主要特点是产品设计制造和企业管理的信息化、生产过程控制的智能化、生产装备的数字化和机器人的与人和谐化。4.1产品设计制造和企业管理的信息化信息技术在制造业中的广泛应用,促进了产品设计制造和企业管理信息化程度的提高,改变了现代制造企业的产品设计、产品制造和管理模式。以并行工程、虚拟制造为代表的信息技术的应用提高了创新产品的设计制造水平,以敏捷制造、动态联盟、企业电子商务为代表的企业管理技术的应用促进了新型制造企业的迅速发展,形成了新型的跨国企业和基于供应链的战略企业联盟。42生产过程控制的智能化生产过程的控制是典型的复杂大系统问题,提高生产过程的控制水平和生产效率是工业界急待解决的具有挑战性的问题,采用智能化方法进行生产过程控制是一个有前途的发展方向。采用智能化技术可以解决生产过程控制中存在的强耦合、非线性和不确定性问题,从而显著提高生产效率和产品质量。研制开发智能化的生产过程控制设备也是发展高新技术产业的重要基础。43生产装备的数字化信息技术的广泛采用,提高了生产装备的数字化程度,从而显著提高了产品的高技术附加值。生产装备的数字化不仅增强了产品的功能和集成能力,提高了产品的市场竞争力和经济效益,还显著提高了产品的可操作性、可维护性,降低了产品的运行和维护成本。发展高度数字化的生产装备是制造企业赢得市场竞争的主要手段之一。44机器人的与人和谐化机器人集当代众多高技术于一身,特别强调人机和谐共存。人机和谐共存是机器人进入人类未来工作和生活的基础,已经成为公认的21世纪前沿高技术。目前重点研究的特种机器人有仿人形机器人、水下机器人、医用机器人、服务机器人、网络机器人、军用机器人、农林与农副产品加工机器人等等,在航空、航天、能源、交通、海洋、生物、医疗、服务、农业、军事和娱乐等领域具有非常广阔的应用前景。5先进制造与自动化技术领域拟解决的问题“十五”863计划先进制造与自动化技术领域针对我国国民经济建设的主战场的重大需求,瞄准国际先进制造与自动化技术前沿,拟有重点地选择能够主导21世纪初期我国制造业发展和升级的关键技术和装备,促进形成我国先进制造与自动化技术产业的群体优势,提升我国制造业综合竞争能力,实现制造业的跨跃式发展;拟有重点地选择若干涉及国家安全的战略必争装备和竞争前核心技术,实现局部领域的突破和跨越式发展,打破国外的技术封锁,在国际相关高技术领域占有一席之地。5.1制造业信息化工程关键技术的研究开发和集成应用面对经济全球化和信息化对我国制造业的挑战和机遇,为了增强我国制造业的综合竞争能力,“十五”期间,本领域拟在科技部开展的“制造业信息化工程”专项行动中发挥关键作用。重点解决制造业信息化急需的关键技术及支撑系统平台,主要包括:基于三维产品模型的CADCAE/CAPP/CAM/PDM系统,流程工业MESPCS系统,基于中国先进管理模式的ERP和电子商务系统,支持整体解决方案的PLM系统,支持制造协同、资源共享与集成服务的区域制造网络系统等。通过支持技术产品的开发和典型示范应用,促进相关软件产品的产业化,为制造业信息化工程提供技术支撑。52战略必争装备和竞争前核心技术的研究开发“十五”期间,本领域拟选择若干迫切需要解决的战略必争技术与装备和竞争前核心技术进行重点开发,主要包括:开发拥有自主知识产权的7 000m深海载人潜器,提供深海勘察作业技术装备,为使我国赢得“蓝色圈地运动”的主动权做出贡献;突破数据库管理系统(DBM)关键技术,形成自主产权的、能与主流产品相抗衡的DBM核心系统与应用套件,为我国信息化工程和信息安全提供支撑;掌握一批微机电系统(MEM)的关键技术,取得自主知识产权,并开发出若干MEMS器件及微系统,为MEMS在未来形成产业打下良好的基础;突破伤人形机器人系统中的关键技术,研制具有自主知识产权的国际先进水平的仿人形机器人,奠定仿人形机器人应用的基础,促进人工智能、传感等技术的发展。53基础制造装备与成套装备的研究开发“十五”期间,本领域拟重点选择若干基础制造装备和成套装备进行开发,实现产业化,主要包括:以中档精切类数控机床装备的产业化作为切人点,掌握数控装备关键技术,塑造中国数控机床品牌,提高市场占有率;根据国防工业的具体需求,设计制造高精尖精密加工装备,打破国外封锁;通过整机带动相关的机床设计技术,系统与伺服、高附加值关键部件以及配套工具的技术创新,全面提升国家基础制造装备的核心竞争力;支持典型的成套工程机械产品的信息化、智能化研究开发和示范应用,促进我国工程机械产品的升级换代,提高国际竞争力;研制适应我国典型土层的63m全断面隧道掘进机,进行实际应用,掌握自主知识产权的全断面隧道掘进机关键技术,制定相关的标准和规范体系,提高国产全断面隧道掘进机的市场占有率。54先进制造与自动化前沿创新技术的研究“十五”期间,本领域拟支持一批以原始创新和取得具有自主知识产权为目的的前沿创新技术课题研究。拟在数字化设计与制造、过程自动化、企业管理与电子商务、现代集成制造系统平台、制造工艺与装备、特种机器人、基础部件与系统等7个方面推进前沿创新技术的研究,为先进制造与自动化技术的可持续发展与创新跨越奠定技术基础。6先进制造与自动化技术领域总体战略目标与布6.1总体战略目标总体战略目标包括:(1)面向国民经济建设主战场和先进制造与自动化技术发展前沿,结合重大工程和产品,积极推进具有椰沿性。前瞻性和战晗性的高技术研究,形成有原始创新的理论方法、有知识产权的成果和技术储备,取得发明专利、专利受理和软件著作权登记500项以上;(2)力争在制造业信息化、深海载人潜器微机电系统(MEMS)、数据库管理系统(EBMS)。仿人形特种机器人、智能化工程机械和全断面隧道掘进机(盾构)等对提升我国制造业竞争力有重大影响的共性技术与装备以及战略必争装备和竞争前核心技术方面研发出一批具有自主知识产权的创新产品:(3)在重点行业、典型区域、试点省市和骨干企业进行集成示范应用,产生显著的经济效益,提高我国制造业竞争力;(4)仿委立先进制造与自动化技术战略研究体系、咨询服务体系和研究开发基地,培养一批高水平拔尖人才,全面实施人才战略、专利战略与标准战略。6.2战略布局a先进制造与自动化技术领域由现代集成制造系统技术和机器人技术2个主题组成。现代集成制造系统技术主题的主要任务是:突破一批战略性、前沿性和前瞻性的现代集成制造技术,开发一批具有自主知识产权的应用软件系统,以若干重大行业和典型区域的集成应用为突破口,推进制造业信息化工程。机器人技术主题的主要任务是:研究开发具有战略性、前沿性和前瞻性的机器人和自动化工艺装备中的核心技术,在深海载人潜器、微机电系统和特种机器人等方面取得突破,为我国的可持续发展做出贡献,促进中高档数控装备和大型工程机械等关键基础装备的产业化,提高制造企业的生产能力和市场竞争力。b先进制造与自动化技术领域的研究发展工作在内容上可分成前沿创新技术研究、产品研发与产业化、集成应用示范Xi程3个层次。前沿创新技术研究以探索技术前沿为主要目标,鼓励原始创新,取得具有自主知识产权的技术成果;产品研发与产业化以关键产品的研发与产业化为重要目标,开发一批对提高我国企业竞争力有重大作用的技术和装备,以及战略必争装备和竞争前核心技术;集成应用示范工程面向我国重点行业和典型区域,利用先进制造与自动化技术领域研发的关键技术和产品,实施重大集成应用,取得显著的经济效益和社会效益。 C先进制造与自动化技术领域的发展战略目标充分体现了“创新跨越,精简聚焦”的精神。在2O01年8月第一次战略目标论证会后,先进制造与自动化技术领域先后召开了2次有地方、部门。行业及领域、主题专家参加的战略目标研讨会,逐步明确了先进制造与自动化技术领域以信息化带动工业化,推进制造业信息化的工作主线,并将先进制造与自动化技术领域的主要工作内容整合到科技部“制造业信息化关键技术研究及应用示范工程”(简称“制造业信息化工程”)重大专项中。制造业信息化工程将通过信息技术、自动化技术、现代管理技术等与制造技术相结合,带动产品的设计制造方法和工具创新、企业管理模式的创新、企业间协作关系的创新,实现产品设计制造和企业管理的信息化、生产过程控制的智能化、生产装备的数字化、社会服务和咨询的网络化,实现用信息技术改造我国传统产业和以信息化带动工业化,促进提升我国制造业的综合竞争能力。d先进制造与自动化技术领域将根据国际先进制造与自动化技术的最新发展动向和国家的实际需求,动态地调整领域的布局和研究内容。为此先进制造与自动化技术领域将发展战略研究作为一项长期的任务来抓,组织专门的战略研究小组,不断调整先进制造与自动化技术领域规划,本领域的布局和课题的设置更切合实际。科技译文Improved Workpiece Location Accuracy Through Fixture Layout OptimizationAbstractInaccuracies in workpiece location lead to errors in position and orientation of a machined feature on the workpiece. The ability to accurately locate a workpiece in a machining fixture is strongly influenced by rigid body displacements of the workpiece caused by elastic deformation of loaded fixture-workpiece contacts. This paper presents a model for improving workpiece location accuracy in fixturing. A discrete elastic contact model is used to represent each fixture-workpiece contact. Reduction in workpiece locating error due to rigid body displacements is achieved through optimal placement of locators and clamps around the workpiece. The layout optimization model is also shown to improve the overall workpiece deflection and reaction force characteristics.1.IntroductionThe accuracy of location of a machined feature depends on the machining fixtures ability to precisely locate the workpiece relative to the machine tool axes. Workpiece location in a fixture is significantly influenced by localized elastic deformation of the workpiece at the fixturing points. These deformations are caused by the clamping force(s) applied to the workpiece. For a relatively rigid workpiece the localized elastic deformations cause it to undergo rigid body translations and rotations which alter its location with respect to the cutting tool. It is therefore important to minimize such effects through optimal design of the fixture layout.Previous work in fixture layout optimization has focused on the use of finite element and rigid body models. Menassa and DeVries 1, Rearick et al. 2, Trappey et al. 3, and Cai et al 4 used finite element models of the fixture-workpiece system as input to the layout optimization. In these works the fixture layout design is formulated as a constrained nonlinear optimization problem. The goal is to determine the positions of locator-clamp pairs that will minimize a nonlinear function of the elastic deformation at selected points on the workpiece. Such a formulation requires solution of the complete finite element model during each iteration of the optimization process. Hence, the technique is computationally intensive.DeMeter 5 presented a min-max algorithm to determine the optimal fixture layout and clamping force intensity that minimizes the maximum contact force. In this study the workpiece and fixture were assumed to be perfectly rigid. Such a formulation does not allow the effect of workpiece displacement on locating errors to be minimized directly. Recently, Gui et al 6 reported a model for improving workpiece location accuracy by optimizing the clamping force. They model the elasticity of fixtureworkpiece contacts using linear springs of known stiffness. However, methods for determining the contact stiffness are not addressed. In addition, the fixture layout is assumed fixed for a given workpiece and cutting force system. This paper presents a method that directly minimizes workpiece location errors due to localized elastic deformation of the workpiece at the fixturing points by optimally placing the locators and clamps around the workpiece. The method considers the fixtureworkpiece contact to be linearly elastic and uses closed-form contact stiffness models derived from well-known contact mechanics problems. Also, the method outlined here is computationally less intensive than the finite element approach. The following sections give details of the underlying models and constraints used to formulate the fixture layout optimization procedure. Model simulations are presented to demonstrate the ability of the method to minimize workpiece location errors through optimal arrangement of locators and clamps.2.Fixture Layout Optimization Fixture layout optimization requires formulation of an objective function and constraints. In this paper our objective is to minimize the effect of localized elastic deformation of the workpiece at the fixturing points on workpiece location. As stated earlier, the elastic deformations cause the workpiece to undergo a rigid body motion, which in turn shifts the workpiece location. The objective function for optimization is constructed as follows. Objective Function Formulation. Consider a solid rectangular workpiece held in a fixture consisting of several locators and clamps (see Figure 1). The fixture is typically very rigid compared to the workpiece. It can hence be assumed that the locators do not undergo any rigid body displacement. In contrast, forces acting on the workpiece at the locating and clamping points cause the workpiece to translate and rotate in the global coordinate system. Assume that the rigid body motion of the workpiece due to normal and tangential elastic deformations at the ith fixturing point is given by vector i= xiyizi T . Note that the components of i are expressed in the local coordinate system fixed to the ith point. Geometric transformations are applied so that the rigid bodymotion due to deformation at the ith fixturing point is expressed in the global coordinatesystem as: where Tgi is a general rotation matrix that transforms quantities expressed in the ith local coordinate system into the global coordinate system. Thus, the total rigid body motion ofthe workpiece due to elastic deformations at all the fixturing points is: where N is the total number of locators and clamps.In order to minimize the effect of rigid body motion on workpiece location, a quadratic objective function for fixture layout optimization can now be formulated as follows:Note that the above expression is not an explicit function of the fixture element positions.But the rigid body motion i , and therefore , is dependent on the fixturing forces which are in turn uniquely determined by the layout of fixturing points and elastic contact properties. Hence, changing the fixture layout changes the value of the objective function indirectly.Fixture-Workpiece Contact Constraints. The fixture-workpiece system is subject toseveral contact constraints that the optimum fixture layout must also satisfy. In particular, constraints specifying the geometric compatibility of elastic deformation andfrictional resistance are needed. These constraints are developed using a discrete elasticcontact modeling approach similar to that of Conry and Seireg 7, and Sinha and Abel8.The workpiece is assumed to be elastic in the contact region and rigid elsewhere.The fixture is assumed to be completely rigid. At each fixturing point a square contact surface tangent to the fixture and workpiece surfaces is assumed. The contact surface isdiscretized into a grid containing M square elements as shown in Figure 2. A distributed normal force of intensity p ji and a distributed friction force of intensity (q) (q) xjiyj2 i 2 +are assumed to act across an arbitrary element j of the ith contact surface. The total normal ( Pi ) and friction (Qi ) forces acting at the ith fixturing point are then given by:The localized deformation at a fixturing point causes distant points in the workpiece to undergo a rigid body motion in the normal direction given by zi . If s ji isthe initial separation of the fixture and workpiece surfaces for the jth element at the ith fixturing point, the normal deformation, wji , must satisfy the following contact condition9:The equality sign applies to points that lie inside the equilibrium contact area and theinequality sign for outside points.Orthogonal components of tangential deformation, uji and v ji , produced by the frictional forces acting at a fixturing point lead to tangential rigid body motions xiy, i ,respectively. The deformation and rigid body motion should satisfy the following geometric compatibility conditions 9:where the equality and inequality signs apply for slip and no slip cases, respectively.Contact Deformation Model.The workpiece is assumed to be a linear elastic solid in the vicinity of the fixturing points. Hence, by linear superposition, the normal deformation in the jth element of the ith contact region can be written as: where e e e jknjkxjk, , y are the flexibility influence coefficients for deformation in the normal direction due to fixturing forces in the normal (n) and tangential directions (x, y).Similarly, the x and y components of tangential deformation are given by: where are the normal and tangential flexibility influence coefficients for workpiece deformation in the local x and y directions at the ith fixturing point, respectively.In this paper the influence coefficients are derived from closed-form solutions forthe contact compliance of an elastic half-space subjected to distributed normal and tangential loads. Details of the influence coefficient models may be found in 8, 9.Contact Friction Constraint. Coulomb friction is assumed to apply at each fixturing point. This implies a nonlinear relation between the normal and frictional forces acting at a fixturing point, i.e., (q) (q) p xj where s is the coefficient of static friction for the fixture-workpiece material pair. For simplicity, a linearized version of this constraint is used: Static Equilibrium Constraint. The workpiece must be in static equilibrium after application of fixturing forces at the selected points. This constraint is given by the following force and moment equilibrium equations: F = 0 (12) M = 0 (13)where the forces and moments are expressed in terms of the elemental normal ( p ji ) and tangential forces ( qxji , qyji ) acting at the contact surface for each fixturing point.Clamping Force Constraint. When the clamping force applied by the clamps isspecified, it is necessary that the sum of the elemental normal forces at the clampingpoint equal the specified force. This constraint is expressed as follows: where C is the number of clamps in the fixture. In this paper the clamping force isassumed to be known. In general however the clamping force could be treated as adesign variable in the layout optimization process 5.Fixture Element Position Constraints. The fixture layout optimization procedure seeksto find the optimal locations of the fixturing points. In general, fixture element positionson a workpiece datum surface cannot be chosen randomly and are often constrained bythe geometric complexity of the workpiece surfaces, size and location of the features tobe machined, and other process related issues. Hence, the position of a fixture element isrestricted to a bounded region on the datum surface. In this paper each fixture elementposition is constrained to lie inside a convex polygonal region. A sequence of orderedstraight edges represents each convex polygon. Mathematically, the system of linearinequalities constructed from the line equations for all ordered edges (for N fixturingpoints) is used to specify the bounded region:A X C p p p (15)WhereAndThe elements of Ai and ci are coefficients of the line equations of the polygon edges usedto specify the polygon boundary for the ith point, xi is the position vector (global) to the ithpoint on the workpiece surface, and li is the number of ordered edges making up thebounding polygon for the ith point.The above inequalities can now be used to easily establish the location of afixturing point relative to its polygon boundary. Points inside or on the boundarycompletely satisfy the above inequalities whereas points outside the bounded region do not 10.Layout Optimization Model. The complete fixture layout optimization problem cannow be formally stated as follows:Minimize :Subject to:Bounds: pji 0i = 1, , N; j = 1, , M; k = 1, , CNote that the normal compatibility constraint has been multiplied by -1 to convert it intoa type inequality. Also, by definition, the friction force components qxji and qxji lie inthe contact surface plane, and p ji is assumed to be positive when directed into the9workpiece surface.3.Solution MethodA nonlinear programming method is used to solve the above layout optimizationproblem. Specifically, Zoutendijks method of feasible direction 11 is used. Thismethod is similar to that used by DeMeter 5 and involves the solution of the followinggeneral nonlinear program:Minimize f(x)Subject to Gx b (linear inequality constraint)H(x) = 0 (nonlinear equality constraint)Ex = e (linear equality constraint)where x is the feasible solution. For the nonlinear program given in equation (16) thesolution x =F X pT where:Note that in addition to position of the fixturing points, Xp, the solution procedure treatsthe fixturing forces F and rigid body motion also as design variables during theoptimization process. This is because the fixturing forces and rigid body motion dependon the fixture layout and are determined uniquely for each layout by the physics of theproblem.The first linear inequality constraint is constructed by combining all the inequality constraints given in equation (16). The second nonlinear constraint arises from themoment equilibrium equation in (16). Finally, the linear equality constraint equation isconstructed by combining all the equality constraints listed in (16). For the problem athand, G, H, and E result in matrices with the following sizes: (4MN+N liiN= 1) x(3MN+6N), 3 x (3MN+6N), and (3+C) x (3MN+6N). Note that x is a (3MN+6N) x1 column vector.The method of feasible directions solves the nonlinear program by moving from a initial feasible solution to an improved feasible solution. This is accomplished in four steps: a) find initial feasible solution, b) determine line search direction, c) determine step size, d) solve quadratic program. By iterating between steps (b) and (d) furtherimprovements in the feasible solution can be obtained. Mathematical details of step (b)through (d) can be found in reference 11.The initial feasible solution x is obtained by solving the elastic fixture-workpiececontact model for the initial layout. This is done by minimizing the total complementaryenergy for the fixture-workpiece system. Details of the solution procedure andexperimental validation can be found in 7, 8, 12. Note that the contact model needs tobe solved only once at the beginning to obtain the initial feasible solution. Thereafter,the layout optimization model relies on the contact constraints and the contactdeformation model to compute valid rigid body displacements and fixturing forces.4.Results and DiscussionThe fixture layout optimization model and solution algorithm has been implemented in MATLAB (version 5.0). The capability of the model is illustrated through an example. Consider the initial fixture layout shown in Figure 3. This layout uses a 4-2-1 location scheme with two simultaneously actuated hydraulic clamps to hold the workpiece against the locators. Table 1 lists the positions and orientations of thefixture elements in the initial layout. Locators L1-L4 and clamps C1-C2 have sphericaltips while locators L5-L7 have small area planar tips (area = 63 mm2). A clamping forceof 703 N is assumed to act at each clamping point. The workpiece is a 127mm x 127mmx 382 mm block of Aluminum 7075-T6. The Youngs modulus (E) and Poissons ratio() for the workpiece are 70.3 GPa and 0.354 respectively, and 201 GPa and 0.296respectively for the fixture elements.The initial feasible solution vector x is computed by solving the fixture-workpiececontact model for the initial fixture layout using the minimum complementary energymethod. The layout optimization problem is then solved using the four step iterationprocedure outlined in the previous section. The fixture element position constraints usedfor this problem are given in Table 2. The improved fixture layout that minimizes the11effects of rigid body motion is given in Table 1. The objective function value is reducedfrom 528 m2 to 426 m2.The impact of the optimization process on the fixture layout is shown in Figure 4.The initial fixture layout was intentionally designed to violate well-known empirical“locating rules” 13. For instance, it is standard practice to position the locators on adatum surface as far apart as possible. This is done to ensure the best possible locationalstability of the workpiece. In the initial layout, locators L1-L2 and L4-L7 clearly do notsatisfy this rule. Also, the initial position of clamps C1 and C2 do not provide adequateclamping stability. It is clear from Figure 4 and Table 1 that the layout optimizationmodel gives a solution that supports the empirical rules. Specifically, L1 and L2 arepushed as far apart as possible. Also, locators L4-L7 are spread out on the primarydatum plane so as to include the projected center of gravity of the workpiece inside thebounding polygon formed by joining L4-L7. This improves workpiece stability in thefixture. The new position of clamp C1 is approximately half-way between locators L1and L2. Similarly, clamp C2 and locator L3 directly oppose each other in the improved lay out.If, for simplicity, only the normal component of rigid body motion ( z ) isconsidered, it can be shown through suitable geometric transformations that the locationerror, Ep, of a point P on the workpiece is reduced by the optimization process surface(see Figure 5). For instance, the location error of the point (30, 100, 19.1) decreases from15.3 m for the initial fixture layout to 11.7 m for the improved layout. Thus, thefixture layout optimization model and solution procedure described above improve workpiece location accuracy by minimizing the effect of workpiece rigid bodydisplacement.Finite Element Analysis. In order to further analyze the effect of the fixturelayout optimization process on overall workpiece deformation a finite element model wasconstructed using ANSYS (version 5.3). The locators were modeled as displacementconstraints that prevent workpiece translation in the normal direction. The clampingforce was modeled as a uniformly distributed force acting over the workpiece-clampcontact area.The deflection of the top surface of the workpiece (i.e., the surface to bemachined) is shown for the initial and improved fixture layouts in Figures 6 and 7,respectively. The initial fixture layout shows a significant deflection gradient across thetop surface of the workpiece. Deflection magnitudes range from 0.25 x 10-4 mm to 0.76 x10-2 mm. In general a large variation in deflection magnitudes is not desirable. On theother hand, the improved fixture layout produces a relatively uniform distribution ofdeflections that range from 0.10 x 10-2 mm to 0.19 x 10-2 mm. The maximum deflectionof the top surface is much less for the improved layout (0.19 x 10-2 mm compared to 0.76x 10-2 mm). Also, the reaction forces at L1 and L2 are 638.05 N and 65.31 Nrespectively for the initial layout, and 327.20 N and 376.16 N respectively for theimproved layout. Thus reaction forces in the improved layout are more uniformlydistributed than the initial layout.Therefore the optimization process produces a fixture layout that improves theoverall workpiece deflection and reaction force characteristics in addition to improvingworkpiece location accuracy.5.ConclusionsThe paper presented a fixture layout optimization model for improving thelocation accuracy of the workpiece when clamped in a machining fixture. Theinaccuracy in workpiece location was due to rigid body motion of the workpieceproduced by the localized elastic deformation at the fixturing points. A discretizedelastic contact model of the fixture-workpiece interaction was used to develop t
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