锥齿轮减速器箱体的加工工艺规程及专用夹具设计
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锥齿轮减速器箱体的加工工艺规程及专用夹具设计,齿轮,减速器,箱体,加工,工艺,规程,专用,夹具,设计
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徐州工程学院毕业设计(论文)图书分类号：密 级：摘要蜗杆减速器箱体零件是减速器箱体的一种。它把减速器箱体中的轴和齿轮等有关零件和机构联接为一整体，使这些零件和机构保持正确的相对位置，以便其上各个机构和零件能正确、协调一致地工作，减速器箱体的加工质量直接影响减速器的装配质量，进而影响机器的使用性能和寿命。本课题要完成的内容有： （1）蜗杆减速器箱体的加工工艺设计根据给定的生产纲领60000台/年和零件的结构特点及加工精度要求，制定工艺方案，进行工艺计算，绘制并填写加工工艺综合卡。（2）钻孔专用夹具设计根据该孔系的尺寸精度和位置精度的要求，确定定位基准和定位方式，设计夹紧机构、导向机构、绘制夹具总装图，并拆画夹具的主要零件图。关键词：工艺；减速器；专用夹具AbstractWorm reducer box bodys are one of reducer box bodys。It links relevant parts and organizations such as the axle in the gearbox and gear wheel as a whole , ake these parts and organizations keep the correct relative position, and then influence serviceability and life-span of the machine.The content that this subject should be finished is as follows:(1) Process technological design with worm reducer box bodysAnd structural characteristic and machining accuracy of part require according to designated production 60000 of guiding principle one year, make the craft scheme, carry on the craft to calculate, draw and fill in the comprehensive card of the preparation method.(2) The special-purpose jig of precise bore hole is designedAccording to the request of size precision that this hole is and precision of position, fix the basis of orienting and orient the way, design and clamp the organization , lead the organization , control system, draw the assembly of jig to pursue, dismantle the major part picture of the picture jig .Keyword: gear box reducer box unit clampII徐州工程学院毕业设计(论文)目 录1绪论 111机床夹具的概述 1 111机床夹具的概述及其组成 1 112机床夹具的分类 1 113机床夹具的功用 212工件在夹具中的定位 2 121工件的装夹方法及获得尺寸精度的方法 3 122常用定位方法及其所用的定位元件 313国外先进机床的夹具介绍 414机床夹具的发展 42零件的工艺规程 5 21零件的分析 5 22零件的工艺分析 5 23工艺规程的设计 5231确定毛坯的制造形式 5232基准的选择 5233制定工艺路线 63机械加工余量及工序尺寸的确定 8 31毛坯的外廓尺寸确定 8 32主要平面加工的工序尺寸及加工余量 8 33加工的工序尺寸及加工余量 84确定切削用量及基本工时 9 41工序50铣180120上端面 9 42工序60钻攻螺纹6-M6-7H 10 43工序70铣结合面 11 44工序8012 441钻8-17的孔12 442锪平35凸台13 443钻圆销孔10 13 444钻攻螺纹4-M16-7H14 4 5工序90铣床机盖两端面16 46工序100 17 461粗镗 17 462精镗 18 47工序110钻攻螺纹6-M12 185专用夹具设计 21 51钻床专用夹具的主要类型 21 52钻床专用夹具的设计要点 21 53问题的提出 22 54定位基准的选择 22 55定位元件的设计 22 56定位误差的分析 235. 7切削力及夹紧力计算 23 571切削力计算 23 572夹紧力计算 2458主要零件的设计 25 581支承体的设计 25 582底座的设计 26 583钻模板的设计 27 584支承板的设计 285.9操作的简要说明 28结 论 29致 谢 30参考文献 31翻译部分 32 英文部分 32 中文部分 39431绪论机床夹具是机械加工工艺系统的一个重要组成部分。为保证工件某工序的加工要求，必须使工件在机床上相对刀具的切削或成形运动处于准确的相对位置。当用夹具装夹加工一批工件时，是通过夹具来实现这一要求的。而要实现这一要求，又必须满足三个条件：一批工件在夹具中占有正确的加工位置；夹具装夹在机床上的准确位置；刀具相对夹具的准确位置。这里涉及了三层关系：零件相对夹具，夹具相对于机床，零件相对于机床。工件的最终精度是由零件相对于机床获得的。所以“定位”也涉及到三层关系：工件在夹具上的定位，夹具相对于机床的定位，而工件相对于机床的定位是间接通 过夹具来保证的。工件定位以后必须通过一定的装置产生夹紧力把工件固定，使工件保持在准确定位的位置上，否则，在加工过程中因受切削力，惯性力等力的作用而发生位置变化或引起振动，破坏了原来的准 确定位，无法保证加工要求。这种产生夹紧力的装置便是夹紧装置。目前，机床的夹具设计对于机械工件的加工是很有必要的，也是必须要搞的研究项目，如果工件在加工的过程中不能定位的话，则工件会成为废品或根本不能达到预期加工的效果。再者，为了提高劳动生产率，保证加工质量，降低劳动强度，需要设计组合机床夹具。1.1机床夹具的概述1.1.1 机床夹具的概述及其组成机床夹具是在机床上将工件定位、夹紧，将刀具进行导向的一种装置，简称“夹具”。其作用是使工件相对于机床或刀具有一个正确的位置，并在加工过程中保持这个位置不变。如卡盘、平口钳和各种钻模等。辅助工具是将刀具在机床上进行定位、夹紧的装置，如钻夹头、铣刀杆及镗刀杆等。工艺装备是指在加工过程中，使用的刀具、夹具、量具及其他辅助工具的总称。机床夹具根据功用一般可以分为：定位元件、夹紧元件或装置、对刀及导向元件、夹具体、连接元件、其他元件和装置。1.1.2 机床夹具的分类机床夹具可按以下几种方法进行分类：1.按专门化程度分类 （1）通用夹具 通用夹具是指已经标准化的，在一定范围内可用于加工不同工件的夹具。例如，车床上三爪卡盘和四爪单动卡盘，铣床上的平口钳、分度头和回转工作台等。这类夹具一般由专业工厂生产，常作为机床附件提供给用户。其特点是适应性广，生产效率低，主要适用于单件、小批量的生产中。 （2）专用夹具 专用夹具是指专为某一工件的某道工序而专门设计的夹具。其特点是结构紧凑，操作迅速、方便、省力，可以保证较高的加工精度和生产效率，但设计制造周期较长、制造费用也较高。当产品变更时，夹具将由于无法再使用而报废。只适用于产品固定且批量较大的生产中。 （3）通用可调夹具和成组夹具 其特点是夹具的部分元件可以更换，部分装置可以调整，以适应不同零件的加工。用于相似零件的成组加工所用的夹具，称为成组夹具。通用可调夹具与成组夹具相比，加工对象不很明确，适用范围更广一些。 （4）组合夹具 组合夹具是指按零件的加工要求，由一套事先制造好的标准元件和部件组装而成的夹具。由专业厂家制造，其特点是灵活多变，万能性强，制造周期短、元件能反复使用，特别适用于新产品的试制和单件小批生产。 （5）随行夹具 随行夹具是一种在自动线上使用的夹具。该夹具既要起到装夹工件的作用，又要与工件成为一体沿着自动线从一个工位移到下一个工位，进行不同工序的加工。 2.按使用的机床分类 由于各类机床自身工作特点和结构形式各不相同，对所用夹具的结构也相应地提出了不同的要求。按所使用的机床不同，夹具又可分为：车床夹具、铣床夹具、钻床夹具、镗床夹具、磨床夹具、齿轮机床夹具和其他机床夹具等。 3.按夹紧动力源分类根据夹具所采用的夹紧动力源不同，可分为：手动夹具、气动夹具、液压夹具、气液夹具、电动夹具、磁力夹具、真空夹具等。1.1.3 机床夹具的功用1.能稳定地保证工件的加工精度 用夹具装夹工件时，工件相对于刀具及机床的位置精度由夹具保证，不受工人技术水平的影响，使一批工件的加工精度趋于一致。 2.能减少辅助工时，提高劳动生产率 使用夹具装夹工件方便、快速，工件不需要划线找正，可显著地减少辅助工时；工件在夹具中装夹后提高了工件的刚性，可加大切削用量；可使用多件、多工位装夹工件的夹具，并可采用高效夹紧机构，进一步提高劳动生产率。3.能扩大机床的使用范围，实现一机多能 根据加工机床的成形运动，附以不同类型的夹具，即可扩大机床原有的工艺范围。例如在车床的溜板上或摇臂钻床工作台上装上镗模，就可以进行箱体零件的镗孔加工。1.2工件在夹具中的定位1.2.1 工件的装夹方法及获得尺寸精度的方法1.工件的装夹方法将工件在机床或夹具中的定位、夹紧的过程称为装夹。定位就是确定工件在机床上或夹具中具有正确的位置。夹紧就是工件定位后将其压紧、夹牢的过程，使其在加工过程中保持定位不变的操作，能保持定位时已获得正确的位置不变。工件的装夹，可根据工件加工的不同技术要求，采取先定位后夹紧或在夹紧的过程中同时实现定位这两种方式，其目的都是为了保证工件在加工时相对刀具及成形运动具有正确的位置。一般有如下的几种装夹方法：（1）直接装夹。（2）找正装夹。（3）夹具装夹。2.获得尺寸精度的方法装夹的方法解决了被加工表面间的位置精度，尺寸精度可由以下方法获得。（1）试切法。（2）定尺寸刀具法。（3）调整法。（4）自动获得尺寸法。1.2.2 常用定位方法及其所用的定位元件1.工件以平面定位时可以分为主要支承和辅助支承。其中主要支承包括：（1）固定支承。（2）可调支承。（3）自位支承。2.工件以圆柱孔定位（1）定位销。（2）刚性心轴。（3）小锥度心轴。3.工件以外圆柱面定位（1）定位套。（2）支承板。（3）V型块。4.工件以圆锥孔定位工件以圆锥孔定位时，最常用的定位方式是用圆锥心轴，限制工件的五个自由度。作为圆锥孔定位的特例是用顶尖定位，固定顶尖限制工件的三个自由度。5.组合定位（1）一个平面及与其垂直的两个孔的组合。（2）一个平面及与其垂直的孔的组合。1.3国外先进机床夹具的介绍1.MF薄膜卡盘：带有HSK型快速可更换卡爪，重复夹持精度小于0.005mm，特别适合于精加工，如精车或磨削。 2.KUBFN轴向后拉力型卡盘/浮动卡盘：带有球形杠杆式夹紧机构，使卡盘具备轴向后拉力，能够更好地固定夹紧各种轴类，盘类零件，特别是曲轴的粗加工，或带有锥度的盘状零件。最大后拉行程为0.5mm，并且可以根据实际需要，分5档调整后拉力大小。 3.HTF曲轴分度卡盘：用于加工曲轴连杆颈的分度卡盘,适合于数控车拉床，磨床。 4.DURO-NCES快换卡爪卡盘：可以用扳手快速拆装单独任何一只卡爪，或同时拆装3只卡爪。带有离心力平衡机构，具备特别高的极限转速，具备很高的回转精度。 5.KFD立式车床专用卡盘，最大外径2000：卡盘自身带有防水密封机构，有效隔离外部流体，灰尘进入卡盘，能长期保持原有精度和更长的使用寿命。 6.HSF改进型翻转卡盘：适合十字轴，传动轴等多边加工的自动翻转卡盘，翻转精度达0.01mm，翻转速度更快。1.4机床夹具的发展回顾夹具的历史，它是来源于以大量生产为基础的互换性零件的加工。夹具最早出现于1988年，当时作为大量生产方式的创造者而名利前茅的“惠特尼”公司接受了美国政府订购的三年间制造一万支步枪的合同，把原来告手工操作的步枪枪管锻件，有一个人从头到尾制造下来的方式改为雇用不熟练工人进行简单操作、制造，使用了一系列夹具，使步枪按时交货。继而在1853年“科尔特”根据互换性方式建造了大型兵工厂，据说把涉及1400台机床的大部分作为了专用机床，并花费与机械设备的数量相同的费用，消耗在制造刀具和夹具上。这样通过使用刀具和夹具才使制造有互换性的零件成为可能。同时也简化了操作，为后来向大量生产的发展准备了条件。第二次世界大战时期，世界机床技术的发展在很大程度上受军火生产所影响，战前用于生产汽车、无线电、民用产品的大量技术，在战时广泛移用于军需品的生产。为了提高生产率，应付熟练技术工人的不足，机床夹具得到了更大的发展。1920年，世界上第一部介绍夹具的书籍在德国出版。在近几十年中，夹具的基本组成部分并无明显变化，但随着机械行业的迅速发展，对产品品种和生产率提出了愈来愈高的要求，使多品种、中小批生产成为机械工业生产的主流，为了适应机械工业这种发展的趋势，必然对机床夹具提出了更高的要求。2零件的工艺规程2.1零件的分析零件类箱体是机器式部件的基础零件，它把有关零件联结成一个整体，使这些零件正确的相对位置，因此能协调的工作，因此箱体零件的制造精度将直接影响机器的装配质量，进而影响机器的使用性能和寿命，因此箱体具有较高的技术要求。题目所给的零件是蜗杆的减速器的上机盖，机盖与机座相连接，使传动部分密封，且具有良好的润滑性。2.2零件的工艺分析1 以6-M6-7H为中心的加工表面。这一组加工表面包括机盖的上端面和M6的6个螺纹孔。2 以160为中心的加工表面。这一组表面包括以机座相联接的结合面，粗糙度为1.6，尺寸为18的4个孔，并且锪平35的凸台，还有2个10的圆销孔，4个17的孔。3 以下底面为加工的表面，加工机盖160的2端面，以机座配合加工尺寸为140的孔并倒角，12的6个螺纹孔并攻丝。2.3工艺规程的设计2.3.1确定毛坯的制造形式由于铸铁容易成型，切削性能好，价格低廉，且抗震性和耐磨性也较好，因此该机盖的材料选用的是牌号HT200，由于零件的年销量较多，达到大批量生产，采用金属机器造型，这对提高生产率，保证加工质量也是有利的。2.3.2基准的选择定位基准有粗基准和精基准之分，通常先确定粗基准，然后确定精基准。a)粗基准的选择粗基准的选择主要影响不加工表面与加工表面的相互位置精度，以及加工表面的余量分配。选择粗基准时必须注意以下几个问题：1. 如果必须首先保证工件上加工表面与不加工表面之间的位置精度要求，应以不加工表面作为粗基准。如果工件上由很多不需加工的表面，则应以其中与加工表面的位置精度要求较高的表面作为粗基准。2. 必须首先保证工件上的某种要表面的加工余量均匀，则应选择该表面作为粗基准。3. 选作粗基准的表面应尽量平整光洁，不应有飞边、浇口、冒口等缺陷。4. 粗基准一般只能使用一次。对于一般的轴类零件而言，以外圆做为粗基准，是完全合理的。但对本零件来说，以机盖的下底面作为粗基准b) 精基准的选择精基准的选择应重保证零件的加工精度，特别是加工表面的相互位置精度来考虑，同时也要考虑到装夹方便，夹具结构方便。选择精基准应遵循下列原则：1.“基准重合”原则 即应尽可能选用设计基准作为精基准。这样可以避免由于基准不重合而引起的误差。2.“基准统一”原则 即应尽可能选择加工工件的多个表面时都能使用的一组定位基准作为精基准。这样就便于保证各加工表面的相互位置精度，避免基准变换说产生的误差，并能简化夹具的设计制造。3.“互为基准”原则 当两个表面相互位置精度以及他们自身的尺寸与形状精度都要求很高时，可以采取互为基准的原则，反复多次进行加工。4.“自为基准”原则 有些精加工或光整加工工序要求加工余量小而均匀，再加工时就应尽量选择加工表面本身作为精基准，而该表面与其他表面之间的位置精度则有先行工序保证。精基准的选择主要应该考虑基准重合问题，当设计基准与工序基准不重合时，应该进行尺寸换算2.3.3制定工艺路线拟定机械加工工序，要依照“先粗后精，先主后次，先面后孔”加工箱体零件的原则。必要的热处理，检验等辅导工序安排在各加工段之间。加工工序的方案如（表1.1）工序号工序名称工序内容工艺装备10铸造毛坯铸成形20清砂清除浇注系统，冒口，型砂，飞边，飞刺等30热处理人工时效处理40涂漆非加工面涂防锈漆50粗铣以底面及孔为定位，按线找正，装夹工件，铣面留余量0.5-0.8mm立式铣床精铣60钻钻攻6-M6-7H摇臂钻床攻70粗铣以顶面为定位并用钻用液压装置夹紧，分三部铣底面立式铣床半精铣精铣80钻钻8-17的孔摇臂钻床锪锪平35凸台摇臂钻床钻钻圆销孔10摇臂钻床攻攻丝M16-7H摇臂钻床90粗铣铣160两端面，分为粗铣和精铣两部分立式铣床精铣100粗镗粗镗140的孔加工中心倒角倒角245精镗精镗140的孔110钻钻孔6-12的孔加工中心攻攻丝6M12表1.13机械加工余量及工序尺寸的确定根据上述原始资料及加工工艺，分析确定各加工表面的机械加工余量，工序尺寸及毛坯的尺寸如下：3.1毛坯的外廓尺寸确定考虑其加工外廓尺寸为500290185mm，铸件的材料为HT200。根据机械加工工艺手册中查得公差等级CT,机械加工余量RMA。由公式 得毛坯长：宽：高：则毛坯的外轮廓尺寸为：3.2主要平面加工的工序尺寸及加工余量为了保证加工后的工件的尺寸，在铣削工面时，工序4和工序7的铣削深度为3mm工序9的铣削深度为3.85mm3.3加工的工序尺寸及加工余量1攻钻6-M6-7H孔 钻孔6 2Z=6 攻丝M62. 钻孔锪平4-孔 钻孔 2Z=17 锪平 2Z=35 3. 钻孔锪平4-孔 钻孔 2Z= 锪平 2Z= 4. 攻钻6-M12-7H孔 钻孔 2Z= 攻丝M12 4确定切削用量及基本工时4.1工序50铣180120上端面（1）加工条件工件材料：灰铸铁加工条件：粗铣机盖上端面，保证尺寸刀具：采用高速钢镶齿三面铣刀，齿数，则量具：卡尺（2）计算铣削用量确定进给量：根据机械加工工艺手册，确定 切削速度：参考有关手册，确定，即27，采用X63卧式铣床，根据机床使用说明书（见工艺手册）取故实际切削速度为当时，工作台的每分钟进给量应为：在机床说明书中刚好有，故直接选用该值。由于是粗铣，故整个铣刀刀盘不必经过整个工件，用作图法，可得行程故机动工时为：=540s辅助时间为：其他时间计算：故工序50时间：4.2工序60钻攻螺纹6-M6-7H工件材料：灰铸铁加工要求：攻钻6个公制螺纹M6mm攻钻6M6mm的孔 机床：摇臂钻床刀具：5mm的麻花钻M6丝锥a)钻6-6mm的孔：根据切削手册，查得切削速度为故 根据机床说明书取故实际切削速度为 =37s辅助时间为：其他时间计算：故单件时间：b)攻6-M6mm 孔 按机床选取，则利用作图法得，辅助时间为：其他时间计算：故单件时间：所以总时间T=69.5+45=114.5s4.3工序70铣结合面（1）加工条件工件材料：灰铸铁加工条件：粗铣机盖底面，保证尺寸505mm刀具：采用高速钢镶齿三面铣刀，齿数，则量具：卡尺（2）计算铣削用量确定进给量：根据机械加工工艺手册，确定 切削速度：参考有关手册，确定，即27，采用X63卧式铣床，根据机床使用说明书（见工艺手册）取故实际切削速度为当时，工作台的每分钟进给量应为：在机床说明书中刚好有，故直接选用该值。由于是粗铣，故整个铣刀刀盘不必经过整个工件，用作图法，可得行程故机动工时为：=798s辅助时间为：其他时间计算：故工序70时间：4.4工序804.4.1钻8-孔工件材料：灰铸铁加工要求：钻8个直径为17mm的孔 机床：摇臂钻床I3025 刀具：采用13-17mm的麻花钻头走刀两次， 扩孔钻17mm走一次量具：内径百分表确定进给量：根据切削手册，由于本零件在加工低刚度零件，故进给量应乘系数0.75，则：根据钻床Z535机床说明书现取根据切削手册，查得切削速度为故 根据机床说明书取故实际切削速度为因为，故 以上为钻一孔的加工时间，故机动工时为： 辅助时间为：其他时间计算：故单件时间：4.4.2锪平35凸台（1）加工条件工件材料：灰铸铁加工要求：用带有锥度90度的锪钻锪轴承孔内边缘，倒角445度 机床：摇臂钻床刀具：32-35的锪刀（2）计算钻削用量为了缩短辅助时间，取倒角时的主轴转速与钻孔时相同， =195r/min确定进给量： f=0.25mm/r（工艺手册）故机动加工时间：根据切削手册查得切削速度为所以 故实际切削速度为因为 ，机动工时： 辅助时间为： =0.15tm=0.154.2=0.6s其他时间计算： + =6%(4.2+0.6)=0.3s由于要锪4个凸台，故单件生产时间： =4（+ + ） =4（4.2+0.6+0.3）=20.4s4.4.3钻圆销孔工件材料：灰铸铁 加工要求：钻2个直径为11mm的孔 机床：摇臂钻床 刀具：采用10mm的麻花钻头走刀两次 量具：内径百分表10mm的麻花钻：确定进给量：根据切削手册根据切削手册查得切削速度为所以 故实际切削速度为因为 ，故 以上为钻一孔的加工时间，故机动工时为：辅助时间为：其他时间计算：故单件时间：4.4.4钻攻螺纹4-M16-7H工件材料：灰铸铁加工要求：攻钻4个公制螺纹M16mm（1） 攻钻6M16mm的孔 机床：摇臂钻床刀具：15mm的麻花钻M16丝锥a) 钻4-16mm的孔：确定进给量：根据切削手册根据切削手册，查得切削速度为故 根据机床说明书取故实际切削速度为因为 ， 以上为钻一孔的加工时间，故机动工时为;辅助时间为：其他时间计算：故单件时间：b)攻6-M16mm 孔 按机床选取，则利用作图法得，辅助时间为：其他时间计算：故单件时间：故工序80总时间： T=372+2.8+12.1+20.4=407s4.5工序90铣机盖两端面（1）加工条件工件材料：灰铸铁加工条件：粗铣机盖上端面，保证尺寸刀具：采用高速钢镶齿三面铣刀，齿数，则量具：卡尺（2）计算铣削用量确定进给量：根据机械加工工艺手册，确定 切削速度：参考有关手册，确定，即27，采用X63卧式铣床，根据机床使用说明书（见工艺手册）取故实际切削速度为当时，工作台的每分钟进给量应为：在机床说明书中刚好有，故直接选用该值。由于是粗铣，故整个铣刀刀盘不必经过整个工件，用作图法，可得行程故机动工时为：=125s辅助时间为：其他时间计算：故工序90时间：4.6工序1004.6.1粗镗（1）加工条件 工件材料：灰铸铁 加工要求：粗镗140mm轴孔，留加工余量0.5mm，加工2mm 机床：加工中心 刀具：YT30镗刀 量具：内径百分表（2）计算镗削用量粗镗孔至139.5mm单边余量Z=0.5mm，切削深度，走刀长度分别为l=140mm。确定进给量f：根据工艺手册确定 参考有关手册，确定 根据资料，取 故加工轴孔机动时间为： 辅助时间为： 其他时间计算： 则单件时间为： 4.6.2精镗（1）加工条件 工件材料：灰铸铁 加工要求：粗镗140mm轴孔，留加工余量0.5mm，加工2mm 机床：加工中心 刀具：YT30镗刀 量具：塞规（2）计算镗削用量粗镗孔至140mm，切削深度，走刀长度分别为l=140mm。确定进给量f：根据工艺手册确定 参考有关手册，确定 根据资料，取 故加工轴孔机动时间为： 辅助时间为： 其他时间计算： 则单件总时间为： 故工序100总时间： T=0.146+4.39=4.536min4.7工序110钻攻螺纹6-M12工件材料：灰铸铁加工要求：钻6个直径为12mm的孔 机床：加工中心刀具：12的麻花钻头，M6丝锥量具：内径百分表a)钻6-12mm的孔确定进给量：根据机械加工工艺手册，确定根据切削手册，查得切削速度为故 根据机床说明书取 故实际切削速度为因为，故 以上为钻一孔的加工时间，故机动工时为： =49.7s辅助时间为：其他时间计算：故单件时间：b)攻6-M12mm 孔 按机床选取，则利用作图法得 ，辅助时间为：其他时间计算：故单件时间：所以工序110总时间： T=1.8+60.6=62.4s5专用夹具的设计5.1钻床专用夹具的主要类型钻床专用夹具一般通称为“钻模”。钻模的结构类型很多。可按钻模有无夹具体，以及夹具体是否可动，可分为以下五类：1.固定式钻模这种钻模在使用时，是被固定在钻床工作台上的。用于在立轴式钻床上加工较大的单孔或在摇臂钻床上加工平行孔系。如果要在立式钻床上使用固定式钻模加工平行空系，则需要在机床主轴上安装多轴传动头。这种钻模的夹具体上，设有专供夹压用的凸缘和凸边。在立式钻床上安装钻模时，一般应先将装在主轴上的定尺寸刀具（精度要求高时用心轴）伸入钻套中，以确定钻模的位置，然后将其紧固。这种加工方式的钻孔精度比较高。2.回转式钻模回转式钻模主要用于加工同一圆周上的平行空系，或分布在圆周上的径向孔。有立轴，卧轴和斜轴回转等三中基本模式。由于回转台已标准化，并作为机床附件由专门厂生产供应，固回转式钻模的设计，大多数情况是设计专用的工作夹具和标准的回转台联合使用。3.翻转式钻模翻转式钻模主要用于加工小型工件分布在不同表面上的孔。使用翻转式钻模可减少工件装夹次数，提高各孔上工件的位置精度。4.盖板式钻模这类钻模没有夹具体，实际上是一块钻模板，但其上除钻套外，一般还装用定位元件和夹紧机构，将它覆盖在工件上定位夹紧后即可进行加工。盖板式钻模的主要特点是结构简单轻巧，清除切削方便；但每次需从工件上拆装，比较费事。对于大而笨重的工件，采用盖板式钻模尤为适宜。也适用于中小批生产工件钻孔后立即进行倒角，锪面，攻丝等工步的情况。工件钻铰孔后，即可取下盖板式钻模进行上述后序工布的加工。5.滑柱式钻模滑柱式钻模的结构已标准化和规格化了，具有不同的系列。使用时，只要根据工件的形状，尺寸和加工要求等具体情况，专门设计制造相应的定位，夹紧装置和钻套等，装在夹具体的平台或钻模板上的适当位置，即可进行加工。5.2钻床专用夹具设计要点1.钻模类型的选择钻模类型很多，在设计钻模时，首先要根据工件的形状尺寸，重量和加工要求和批量来选择钻模的结构类型。选择时要注意以下几点：（1）被钻孔直径大于10mm时（特别是加工钢件），宜采用固定式钻模。（2）翻转式钻模适用于加工中小件，包括工件在内的总重量不宜超过10kg。（3）当加工分布不在同心圆周上的平行空系时，如工件和夹具的总重量超过15 kg，宜采用固定钻模和摇臂钻床加工。如生产批量大，则可在立式钻床上采用多轴传动轴加工。（4）对于孔的垂直度和孔心距要求不高的中小型工件，宜优先采用滑柱钻模。如孔的垂直度公差小于0.1mm，孔距位置公差小于0.15mm时，一般不宜采用这类钻模。（5）钻模板和夹具体为焊接式的钻模，因焊接应力不能彻底消除，精度不能长期保持，故一般在工件孔距公差要求不高（0.15）时采用。（6）孔距与孔和基面公差小于0.05mm时采用固定式钻模。2.钻套的选择和设计根据钻套的结构有固定钻套，可换钻套，快换钻套及特殊钻套四种类型，分别适用不同情况。3.钻模板的设计钻模板是供安装钻套用的，钻模板多装配在夹具体或支架上，与夹具上的其他元件相连接或与夹具体铸成一体。设计钻模板时应注意以下几点：（1）钻模板上安装钻套的孔之间及孔与定位元件的位置应有足够的精度。（2）钻模板应具有足够的刚度，以保证钻套位置的准确性，但又不能做的太厚太重。注意布置加强筋以提高钻模板的刚性。钻模板一般不承受夹紧力。（3）为保证加工的稳定性，悬挂式钻模板导杆上的弹簧力必须足够，使钻模板在夹具上能维持足够的定位应力。如钻模板本身重量超过80kg时，导杆上可不装弹簧。5.3问题的提出本夹具主要用来钻分布在面上的六个直径为M6-7H的孔。由零件图可知这六个螺纹孔的精度要求是相当高的。这六个孔的位置度要求是我们首要解决的问题。5.4 定位基准的选择由零件图可知，B面有平面度要求,设计基准是中心轴线。为了使定位误差为零，应选择以中心轴线为定位的自动定心夹具，以端面定位。但这种自动定心夹具在结构上将过于复杂。考虑到我们的生产要求，这种夹具不适用。因此，我们为本道工序设计了专用夹具，如图（钻孔夹具装配图），是以底面和两个支承块定位的5.5 定位元件的设计本工序选用的定位基准为三面定位，所以相应的夹具上的定位元件应是三个支承板。因此进行定位元件的设计主要是对三个支承板的设计。由加工工艺孔工序简图可计算出两支承板中心距。 由于两支承板有位置度公差，所以其尺寸公差为： 所以两支承板的中心距为，根据机床夹具的设计手册三支承板的设计计算过程如下：（1） 确定两支承板中心距尺寸及其偏差 （2） 确定支撑板尺寸及其公差 长 宽D5.6定位误差分析本夹具选用的定位元件为三面定位。其定位误差主要为：（1）、移动时基准位移误差 =0.009+0.027+0.016 =0.052mm（2）、转角误差 其中： 5.7 切削力及夹紧力的计算5.7.1 切削力的计算刀具：高速钢镶齿三面刃铣刀，225mm,Z=20,则 （见切削手册）式中：，,，（在加工面上测量的近似值），,Z=20,所以 当用两把刀铣削时， 水平分力: 垂直分力：在计算切削力时，必须考虑安全系数，安全系数为： 式中：基本安全系数，1.5； 加工性质系数，1.1； 刀具钝化系数，1.1； 断续切削系数，1.1。 则 为克服水平切削力，实际夹紧力N应为： 所以 其中及为夹具定位面及夹紧面上的摩擦系数，=0.25，则 5.7.2 夹紧力的计算螺旋面可视为绕在圆柱体上斜契，当加给螺杆以原始力矩时，螺纹中径处将受到夹具体的摩擦，反作用力矩，而螺杆末端将受到工件的摩擦反作用力矩，且,根据上述契块的受力分析可得螺旋的夹紧力W为： = 式中： 螺纹中径的半径； 螺纹的升角； 螺杆末端与工件（或压块）间的当量摩擦半径； 螺杆与螺母间的摩擦角，上式按矩形螺纹求得：对于梯形或三角形螺纹应以当量摩擦角 代入， 为螺纹半角； 螺杆末端与工件（或压块）间的摩擦角。 的数值视螺杆末端的形状而定，若末端为球面，=0；若为平面=；若为环形端面或螺母夹紧；因为本设计所选用的螺杆末端的形状为球面，所以。通常采用标准的夹紧螺钉，很小，故自锁可靠。因为W=12817.2N大于所需的12790N的切削力，故本夹具可安全工作。因此选用M18的夹紧螺钉即可。5.8主要零件的设计钻模板支架和底座多为铸铁件（一般为HT200），常分开制造，这对于夹具的加工、装配和铸件的时效处理都有利。要求支架与底座有足够的强度和刚度以及保持尺寸的稳定性，为了增强支架的刚度，支架和底座的装配连接要牢固。一般采用圆柱销和螺钉紧固，尽量避免采用焊接结构。要注意不允许钻模板支架承受夹紧反力作用，防止支架变形，影响加工精度。钻模板底座要承受安装在其上面的各种装置、元件、工件的重力、切削力及夹紧力。为了提高其刚度，除选取适当的壁厚外，合理设置加强筋是重要的措施。常采用十字形筋条，这样可以减少交接处面积，使铸件应力均匀，减少变形。如使加强筋的底面与底座周边的底面在同一平面上，则可以提高底座在机床工作台上的安装刚性。此外，可适当增加底座高度一般与夹具总高度之比推荐取，其最小高度应大于150160，壁厚或筋厚等具体结构见机床夹具设计，表7-4。5.8.1支承体设计支承体如下：该零件毛坯采用铸造方法获得，所用材料是HT200，上面的连接件是M16的双头螺柱，下面的连接件是M20的双头螺柱。根据机械设计得。5.8.2底座的设计机盖零件和底座底面的平行度应小于0.01，零件毛坯采用铸造方法获得，所用材料也是HT200。为了减轻重量及方便排屑，中间有部分应挖空，详见底座零件图可得。5.8.3钻模板的设计（1）钻套的选择及尺寸因为钻套是标准件，所以根据夹具设计手册选择固定钻套。钻套尺寸：a)钻套内经及偏差应根据所引导的刀具尺寸来确定，通常取刀具的最大极限尺寸为引导孔的基本尺寸，采用基轴制间隙配合，孔径公差依加工精度来确定。钻孔和扩孔时取F7，粗铰孔时取G7，精铰孔时取G6.若钻套引导的不是刀具的切削部分，而是导向部分，常取配合为H7/f7,H7/n6,H6/g5。本夹具应取H7/n6。b)钻套高度直接影响钻套的导向性能，高度较大时，导向性好，刀具与钻套间可能产生的偏斜量很小，加工精度高，但会加快刀具与钻套的磨损。因此，常取H=（1-2.5）d。d为刀具直径。加工精度要求较高，加工孔径较小，刀具刚性较差时应取大值，反之去小值。c)钻套与工件间一般应有排屑间隙h,并要求钻头的两个刃角都在钻套之外。一般取h为（0.3-1.2）d。故根据上述要求设计的钻套如图所示。（2）钻模板应于安装钻套，并确保钻套在转模板是的正确位置，要求具有一定的强度和刚度，以防变形而影响钻套的位置精度和导向精度。转模板通常装配在夹具体上或支架上。常用的有固定式转模板、铰链式转模板和可卸式转模板。为了保证钻套位置的准确性和加工稳定性，转模板必须具有足够的刚性，但又不能做的太重太厚。在实际使用中，厚度往往根据钻套的高度H确定，一般在15mm-30mm之间。如果钻套较长，可将模板局部加厚，加强模板的周边和设置强筋，以提高钻模板的支撑刚性。故根据上述要求设计的钻模板如图所示。此模板厚度为25mm。零件毛坯采用铸造方法获得，所用材料是HT200。5.8.4支承板的设计支承板主要用来定位，因上述已计算出采用三面定位定位误差较小，所以采用三面定位法，支承板设计如下：5.9 操作的简要说明为了提高生产效率，缩短加工中的辅助时间。因此夹紧装置采用方头紧固螺钉夹紧装置。工件在夹具上安装好后，螺钉从上往下顺时针旋转夹紧工件。本夹具用于减速器箱体机盖上端面钻孔。夹具的定位采用支承板定位，定位可靠，定位误差较小。其夹紧采用的是螺钉夹紧，夹紧简单、快速、可靠，有利于提高生产率。工件在夹具体上安装好后，螺钉从上往下顺时针旋转夹紧工件。当孔钻完后，螺钉随即逆时针旋转松开工件，即可取下工件。结论通过本次设计，可以说我熟练的掌握了机床夹具的设计方法和设计顺序，以及对机床的选择等。整个设计的创新性在于改变以往的定位方法，同时整个设计过程比较简洁，使读者一目了然。在设计钻床夹具的时候采用的夹具十分轻巧简便，简单易用，节省了劳动时间，提高了效率。设计的可行性在于可用于中小批量生产，设计周期较短，很快可以投入生产，经济性较好。同时,在设计的过程中，围绕保证加工精度的要求展开的，通过对比几套方案的优缺点，最后定下了本篇论文的设计方案，该方案不但比较经济，而且可以提高加工效率，使整个生产周期大大缩短。在设计的过程中遇到了不少的问题，经过自己的努力和指导老师的细心指导，终于完成了该项设计任务，并且对产品进行了经济分析，较为合理的阐述了自己的设计思路与创新点，我感觉自己在设计的过程中学会了不少的知识，不但温习了曾经学习的专业课知识，而且还学会了好多新的机械专业的知识，总的来说收获是很大的。致谢通过两个多月来的专心设计，通过史月英老师耐心、细致的辅导，和其他老师的热心帮助，我设计出了一套相对完整的箱体加工工艺流程，完成了蜗杆减速器箱体的机械加工工艺和专用夹具设计。由于本人能力有限，设计中难免会出现诸多譬如设计思想不成熟、设计不周到、不完善以及一些错误等不足之处，还请老师给予批评指正，在这里我将非常感谢！首先衷心感谢我的指导老师史月英老师对我毕业设计的指导与热情的帮助。无论是在论文的选题还是定稿、研究的方法、技术路线以及本文的撰写都得到老师的严格要求和精心指导，史老师花费了大量的精力，在各个环节中给了我许多宝贵的意见。在几个月的毕业设计中，史老师严谨的学术作风、治学态度，求实的工作作风和孜孜不倦的探索创新精神，深深地影响了我，这些使我受益匪浅。在此，谨向史月英老师的培育之恩表示最诚挚的谢意!感谢所有关心和帮助过我的老师们、同学们、朋友们! 200806.02主要参考文献 1 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This has been the trend in machining processes in recent years. Advanced methods of machine control as well as completely different methods of shaping materials have permitted the mechanical designer to proceed in directions that would have been totally impossible only a few years ago. Parallel development in other technologies such as electronics and computers have made available to the machine tool designer methods and processes that can permit a machine tool to far exceed the capabilities of the most experienced machinist. In this section we will look at CNC machining using chip-making cutting tools. CNC controllers are used to drive and control a great variety of machines and mechanisms, Some examples would be routers in wood working; lasers, plasma-arc, flame cutting, and waterjets for cutting of steel plate; and controlling of robots in manufacturing and assembly. This section is only an overview and cannot take the place of a programming manual for a specific machine tool. Because of the tremendous growth in numbers and capability of computers ,changes in machine controls are rapidly and constantly taking place. The exciting part of this evolution in machine controls is that programming becomeseasier with each new advanced in this technology.Advantages of Numerical Control A manually operated machine tool may have the same physical characteristics as a CNC machine, such as size and horsepower. The principles of metal removal are the same. The big gain comes from the computer controlling the machining axes movements. CNC-controlled machine tools can be as simple as a 2-axis drilling machining center (Figure O-1). With a dual spindle machining center, the low RPM, high horsepower spindle gives high metal removal rates. The high RPM spindle allows the efficient use of high cutting speed tools such as diamonds and small diameter cutters (Figure O-2). The cutting tools that remove materials are standard tools such as milling cutters, drills, boring tools, or lathe tools depending on the type of machine used. Cutting speeds and feeds need to be correct as in any other machining operation. The greatest advantage in CNC machining comes from the unerring and rapid positioning movements possible. A CNC machine does dot stop at the end of a cut to plan its next move; it does not get fatigued; it is capable of uninterrupted machining error free, hour after hour. A machine tool is productive only while it is making chips. Since the chip-making process is controlled by the proper feeds and speeds, time savings can be achieved by faster rapid feed rates. Rapid feeds have increased from 60 to 200 to 400 and are now often approaching 1000 inches per minute (IPM). These high feed rates can pose a safety hazard to anyone within the working envelope of the machine tool. Complex contoured shapes were extremely difficult to product prior to CNC machining .CNC has made the machining of these shapes economically feasible. Design changes on a part are relatively easy to make by changing the program that directs the machine tool. A CNC machine produces parts with high dimensional accuracy and close tolerances without taking extra time or special precautions, CNC machines generally need less complex work-holding fixtures, which saves time by getting the parts machined sooner. Once a program is ready and production parts, each part will take exactly the same amount of time as the previous one. This repeatability allows for a very precise control of production costs. Another advantage of CNC machining is the elimination of large inventories; parts can be machined as needs .In conventional production often a great number of parts must be made at the same time to be cost effective. With CNC even one piece can be machined economically .In many instances, a CNC machine can perform in one setup the same operations that would require several conventional machines. With modern CNC machine tools a trained machinist can program and product even a single part economically .CNC machine tools are used in small and large machining facilities and range in size from tabletop models to huge machining centers. In a facility with many CNC tools, programming is usually done by CNC programmers away from the CNC tools. The machine control unit (MCU) on the machine is then used mostly for small program changes or corrections. Manufacturing with CNC tools usually requires three categories of persons. The first is the programmer, who is responsible for developing machine-ready code. The next person involved is the setup person, who loads the raw stork into the MCU, checks that the correct tools are loaded, and makes the first part. The third person is the machine and unloads the finished parts. In a small company, one person is expected to perform all three of these tasks. CNC controls are generally divided into two basic categories. One uses a ward address format with coded inputs such as G and M codes. The other users a conversational input; conversational input is also called user-friendly or prompted input. Later in this section examples of each of these programming formats in machining applications will be describes.CAM and CNC CAM systems have changed the job of the CNC programmer from one manually producing CNC code to one maximizing the output of CNC machines. Since CNC machine tools are made by a great number of manufacturers, many different CNC control units are in use. Control units from different manufacturers use a variety of program formats and codes. Many CNC code words are identical for different controllers, but a great number vary from one to another. To produce an identical part on CNC machine tools with different controllers such as one by FANCU, OKUMA or DYNAPATH, would require completely different CNC codes. Each manufacturer is constantly improving and updating its CNC controllers. These improvements often include additional code words plus changes in how the existing code works. A CAM systems allows the CNC programmer to concentrate on the creation of an efficient machining process, rather then relearning changed code formats. A CNC programmer looks at the print of a part and then plans the sequence of machining operations necessary to make it (Figure O-3). This plan includes everything, from the selection of possible CNC machine tools, to which tooling to use, to how the part is held while machining takes place. The CNC programmer has to have a thorough understanding of all the capacities and limitations of the CNC machine tools that a program is to be made for. Machine specifications such as horsepower, maximum spindle speeds, workpiece weight and size limitations, and tool changer capacity are just some of the considerations that affect programming. Another area of major importance to the programmer is the knowledge of machining processes. An example would be the selection of the surface finish requirement specified in the part print. The sequence of machining processes is critical to obtain acceptable results. Cutting tool limitations have to be considered and this requires knowledge of cutting tool materials, tool types, and application recommendations. A good programmer will spend a considerable amount of time in researching the rapidly growing volume of new and improved tools and tool materials. Often the tool that was on the cutting edge of technology just two years ago is now obsolete. Information on new tools can come from catalogs or tool manufacturers tooling engineers. Help in tool selection or optimum tool working conditions can also be obtained from tool manufacturer software. Examples would be Kennametals TOOLPRO, software designed to help select the best tool grade, speed, and feed rates for different work materials in turning application. Another very important feature of TOOLPRO is the display of the horsepower requirement for each machining selection. This allow the programmer to select a combination of cutting speed, feed rate, and depth of cut that equals the machines maximum horsepower for roughing cuts. For a finishing cut, the smallest diameter of the part being machined is selected and then the cutting speed varied until the RPM is equal to the maximum RPM of the machine. This helps in maximizing machining efficiency. Knowing the horsepower requirement for a cut is critical if more than one tool is cutting at the same time. Software for a machining center application would be Ingersoll Tool Companys Actual Chip Thickness, a program used to calculate the chip thickness in relation to feed-per-tooth for a milling cutter, especially during a shallow finishing cut. Ingersolls Rigidity Analysis software ealculates tool deflection for end mills as a function of tool stiffness and tool force. To this point we looked at some general qualifications that a programmer should possess. Now we examine how a CAM system works. Point Control Companys SmartCam system uses the following approach. First, the programmer makes a mental model of the part to be machined. This includes the kind of machining to be performed-turning or milling. Then the part print is studied to develop a machining sequence, roughing and finishing cuts, drilling, tapping, and boring operations. What work-holding device is to be used, a vise or fixture or clamps? After these considerations, computer input can be started. First comes the creation of a JOBPLAN. This JOBPLAN consists of entries such as inch or metric units, machine type, part ID, type of workpiece material, setup notes, and a description of the required tools. This line of information describes the tool by number, type, and size and includes the appropriate cutting speed and feed rate. After all the selected tools are entered, the file is saved. The second programming step is the making of the part. This represents a graphic modeling of the projected machining operation. After selecting a tool from the prepared JOBPLAN, parameters for the cutting operation are entered. For a drill, once the coordinate location of the hole and the depth are given, a circle appears on that spot. If the location is incorrect, the UNDO command erases this entry and allows you to give new values for this operation. When an end mill is being used, cutting movements (toolpath) are usually defined as lines and arcs. As a line is programmed, the toolpath is graphically displayed and errors can be corrected instantly. At any time during programming, the command SHOWPATH will show the actual toolpath for each of the programmed tools. The tools will be displayed in the sequence in which they will be used during actual machining. If the sequence of a tool movement needs to be changed, a few keystrokes will to that. Sometimes in CAM the programming sequence is different from the actual machining order. An example would be the machining of a pocket in a part. With CAM, the finished pocket outline is programmed first, then this outline is used to define the roughing cuts to machine the pocket. The roughing cuts are computer generated from inputs such as depth and width of cut and how much material to leave for the finish cut. Different roughing patterns can be tried out to allow the programmer to select the most efllcient one for the actual machining cuts. Since each tool is represented by a different color, it is easy to observe the toolpath made by each one. A CAM system lets the programmer view the graphics model from varying angles, such as a top, front, side, or isometric view. A toolpath that looks correct from a top view, may show from a front view that the depth of the cutting tool is incorrect. Changes can easily be made and seen immediately. When the toolpath and the sequence of operations are satisfactory, machine ready code has to be made. This is as easy as specifying the CNC machine that is to be used to machine the part. The code generator for that specific CNC machine during processing accesses four different files. The JOBPLAN file for the tool information and the GRAPHICE file for the toolpath and cutting sequence. It also uses the MACHINE DEFINE file which defines the CNC code words for that specific machine. This file also supplies data for maximum feed rates, RPM, toolchange times, and so on. The fourth file taking part in the code generating process is the TEMPLATE file. This file acts like a ruler that produces the CNC code with all of its parts in the right place and sequence. When the code generation is complete, a projected machining time is displayed. This time is calculated from values such as feed rates and distances traveled, noncutting movements at maximum feed rates between points, tool change times, and so on. The projected machining time can be revised by changing tooling to allow for higher metal removal rates or creating a more efficient toolpath. This display of total time required can also be used to estimate production costs. If more then one CNC machine tool is available to machine this part, making code and comparing the machining time may show that one machine is more efficient than the others.CAD/CAM Another method of creating toolpath is with the use of a Computer-aided Drafting (CAD) file. Most machine drawings are created using computers with the description and part geometry stored in the computer database. SmartCAM, though its CAM CONNECTION, will read a CAD file and transfer its geometry represents the part profile, holes, and so on. The programmer still needs to prepare a JOBPLAN with all the necessary tools, but instead of programming a profile line by line, now only a tool has to be assigned to an existing profile. Again, using the SHOWPATH function will display the toolpath for each tool and their sequence. Constant research and developments in CAD/CAM interaction will change how they work with each other. Some CAD and CAM programs, if loaded on the same computer, make it possible to switch between the two with a few keystrokes, designing and programming at the same time. The work area around the machine needs to be kept clean and clear of obstructions to prevent slipping or tripping. Machine surfaces should not be used as worktables. Use proper lifting methods to handle heavy workpieces, fixtures, or heavy cutting tools. Make measurements only when the spindle has come to a complete standstill. Chips should never be handled with bare hands. Before starting the machine make sure that the work-holding device and the workpiece are securely fastened. When changing cutting tools, protect the workpiece being machined from damage, and protect your hands from sharp cutting edges. Use only sharp cutting tools. Check that cutting tools are installed correctly and securely. Do not operate any machine controls unless you understand their function and what they will do.The Early Development Of Numerically Controlled Machine Tools The highly sophisticated CNC machine tools of today, in the vast and diverse range found throughout the field of manufacturing processing, started from very humble beginnings in a number of the major industrialized countries. Some of the earliest research and development work in this field was completed in USA and a mention will be made of the UKs contribution to this numerical control development. A major problem occurred just after the Second World War, in that progress in all areas of military and commercial development had been so rapid that the levels of automation and accuracy required by the modern industrialized world could not be attained from the lab our intensive machines in use at that time. The question was how to overcome the disadvantages of conventional plant and current manning levels. It is generally ackonwledged that the earliest work into numerical control was the study commissioned in 1947 by the US government. The studys conclusion was that the metal cutting industry throughout the entire country could not copy with the demands of the American Air Force, let alone the rest of industry! As a direct result of the survey, the US Air Force contracted the Persons Corporation to see if they could develop a flexible, dynamic, manufacturing system which would maximize productivity. The Massachusetts Institute of Technology (MIT) was sub-contracted into this research and development by the Parsons Corporation, during the period 1949-1951,and jointly they developed the first control system which could be adapted to a wide range of machine tools. The Cincinnati Machine Tool Company converted one of their standard 28 inch Hydro-Tel milling machines or a three-axis automatic milling made use of a servo-mechanism for the drive system on the axes. This machine made use of a servomechanism for the drive system on the axes, which controlled the table positioning, cross-slide and spindle head. The machine cab be classified as the first truly three axis continuous path machine tool and it was able to generate a required shape, or curve, by simultaneous slide way motions, if necessary. At about the same times as these American advances in machine tool control were taking Place, Alfred Herbert Limited in the United Kingdom had their first Mutinous path control system which became available in 1956.Over the next few years in both the USA and Europe, further development work occurred. These early numerical control developments were principally for the aerospace industry, where it was necessary to cut complex geometric shapes such as airframe components and turbine blades. In parallel with this development of sophisticated control systems for aerospace requirements, a point-to-point controller was developed for more general machining applications. These less sophisticated point-to-point machines were considerably cheaper than their more complex continuous path cousins and were used when only positional accuracy was necessary. As an example of point-to-point motion on a machine tool for drilling operations, the typical movement might be fast traverse of the work piece under the drills position-after drilling the hole, anther rapid move takes place to the next holes position-after retraction of the drill. Of course, the rapid motion of the slideways could be achieved by each axis in a sequential and independent manner, or simultaneously. If a separate control was utilisec for each axis, the former method of table travel was less essential to avoid any backlash in the system to obtain the required degree of positional accuracy and so it was necessary that the approach direction to the next point was always the same.The earliest examples of these cheaper point-to-point machines usually did not use recalculating ball screws; this meant that the motions would be sluggish, and sliderways would inevitably suffer from backlash, but more will be said about this topic later in the chapter. The early NC machines were, in the main, based upon a modified milling machine with this concept of control being utilized on turning, punching, grinding and a whole host of other machine tools later. Towards the end of the 1950s,hydrostatic slideways were often incorporated for machine tools of highly precision, which to sonic extent overcame the section problem associated with conventional slideway response, whiles averaging-out slideway inaccuracy brought about a much increased preasion in the machine tool and improved their control characteristics allows concept of the machining center was the product of this early work, as it allowed the machine to manufacture a range of components using a wide variety of machining processes at a single set-up, without transfer of workpieces to other variety machine tools. A machining center differed conceptually in its design from that of a milling machine, In that the cutting tools could be changed automatically by the transfer machanism, or selector, from the magazine to spindle, or vice versa.In this ductively and the automatic tool changing feature enabled the machining center to productively and efficiently machine a range of components, by replacing old tools for new, or reselecting the next cutter whilst the current machining process is in cycle. In the mid 1960s,a UK company, Molins, introduced their unique System 24 which was meant represent the ability of a system to machine for 24 hours per day. It could be thought of as a machining complex which allowed a series of NC single purpose machine tools to be linked by a computerized conveyor system. This conveyor allowed the work pieces to be palletized and then directed to as machine tool as necessary. This was an early, but admirable, attempt at a form of Flexible manufacturing System concept, but was unfortunately doomed to failure. Its principal weakness was that only a small proportion of component varieties could be machine at any instant and that even fewer work pieces required the same operations to be performed on them. These factors meant that the utilization level was low, coupled to the fact that the machine tools were expensive and allowed frequent production bottlenecks of work-in-progress to arise, which further slowed down the whole operation. The early to mid-1970s was a time of revolutionary in the area of machine tool controller development, when the term computerized numerical control (CNC) became a reality. This new breed of controllers gave a company the ability to change work piece geometries, together with programs, easily with the minimum of development and lead time, allowing it to be economically viable to machine small batches, or even one-off successfully. The dream of allowing a computerized numerical controller the flexibility and ease of program editing in a production environment became a reality when two ralated factors occurred.These were:the development of integrated circuits, which reduces electronics circuit size, giving better maintenance and allowing more standardization of desing; that general purpose computers were reduced in size coupled to the fact that their cost of production had fallen considerably. The multipie benefits of cheaper electorics with greater reliability have result in the CNC fitted to the machine tools today, with the power and sophistication progtessing considerably in the last few years, allowing an almost artificial intelligence(AI) to the latest systems. Over the years, the machine tools builders have produced a large diversity in the range of applications of CNC and just some of those development will be reviewed in Volume 。With any capital cost item, such as a CNC machine tool, it is necessary for a company to undergo a feasibility study in order to ascertain whether the purchase of new plant is necessary and can be justified over a relatively short pay-back period. These thoughts and other circial decisions will be the subject of the next section which is concerned with the economic justification for CNC.中文部分机床实践随着先进科技的硬件变得复杂化，把原料加工成为有用产品的理想的、新的加工手段得到了普遍应用。这已经成为近几年机床加工的发展趋势。先进的机床控制方法和完全不同的材料成形方法还迫使机械设计人员进行前几年还完全没有进行的方向（研究）。其他科技如电子技术和计算机技术的并行发展，使机床设计者有办法让机床具有超过绝大多数经验丰富的机械师（在普通机床上）所具有的加工能力。在这个部分我们来看数控机床切削使用的工具。CNC控制器能被用来驱动和控制多种机床和机构。举几个例子，如刳刨机进行木料加工；激光、离子弧、火焰切削、喷水切削钢板；在制造和装配中机器人的控制等。本书的这个部分仅是一般介绍而不能作为专业机床的设计手册。由于计算机能力和容量的巨大增长，机床的控制技术很频繁地发生着变化。在机床控制发展中的精彩部分是在每个先进技术上的使用变得很容易了。NC的优势人工操作机床可能有和CNC机床一样的物理特性，例如马力和尺寸，其金属切削原理也是一样的。CNC最大的好处是通过计算机控制机床刀具的运动，CNC控制的机床可能简单得象2刀钻床或复杂得象5刀的加工中心（如图O-1）。两轴的加工机床，其特点是低转速、高马力轴有高进给率，高转速轴允许高效的高速切削刀具如钻石和小直径的刀具的使用（如图O-2）。它的切削刀具是标准的刀具如磨床的刀具、钻子、钻探工具或车刀，这些刀具依赖于所使用的机床型号。切削速度和进给量要象在其他操作机床中一样是正确的。CNC机床的最大优势来自无错的和快速的可能运动的控制。数控机床不会在一次加工完成后停下来计划下一次的运动，它不会疲劳，它是不中断的机床，机床只有在它切削的时候才有生产性。当切削过程被适当的进给量和切削速度控制时，时间的节约可以通过快速的进给率来完成。快速进给从60发展到200到400到现在已接近每分1000英寸了。这样高的进给率对在机床工作区的任何人构成了安全威胁。在CNC机床之前，复杂形状的加工是极困难的。CNC使这些形状的加工制造在经济上是可行的。零件的设计变化通过改变控制机床的程序而相对容易实现。CNC机床不需要额外的时间和特别的预防就可生产高精度的严格公差的零件。CNC使机床不需要复杂的夹具，这使零件很快被加工从而节约了时间。一旦程序准备好并加工零件，每个零件都将花与第一个一样的时间。这个一致性允许很精确地控制加工成本。数控机床的另一个优势是大量存货的减少，零件可以在需要时再被加工。在传统制造中，为了增加效率，通常一大批零件被同时加工。有了CNC即使一件也能够被经济地加工。在很多情况下，一个CNC机床完成了要建立几台相同传统机床才能做的操作。CAM和CNCCAM系统改变了CNC程序员的工作，
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