CA6140车床主轴的钻4×φ23孔夹具设计及加工工艺装备含3张CAD图
收藏
资源目录
压缩包内文档预览：(预览前20页/共35页)
编号：145732874
类型：共享资源
大小：5.77MB
格式：ZIP
上传时间：2021-09-28
上传人：QQ14****9609
认证信息
个人认证
郭**（实名认证）
陕西
IP属地：陕西
20
积分
- 关 键 词：
-
CA6140
车床
主轴
23
夹具
设计
加工
工艺
装备
CAD
- 资源描述：
-
CA6140车床主轴的钻4×φ23孔夹具设计及加工工艺装备含3张CAD图,CA6140,车床,主轴,23,夹具,设计,加工,工艺,装备,CAD
- 内容简介：
-
摘 要机械制造业的发展对世界经济起着非常重要的作用，也是一个国家技术进步和社会发展的支柱产业之一，无论是传统产业，还是现代化科技，都离不开各式各样的机械装备。而机械加工的编制是机械制造技术的重要组成部分和关键工作。近些年来，随着现代化技术的广泛应用，使得传统机械加工制造方法发生了重大的变革，夹具的功能已经从传统意义上的装夹、定位、引导刀具上脱离出来，向着更加广阔的意义上发展，来满足不断发展的机械加工产业。关键词：制造；设计；分类；夹具AbstractThe development of machinery manufacturing industry plays a very important role in the world economy, and it is also one of the pillar industries of a countrys technological progress and social development. Both traditional industries and modern science and technology cannot be separated from all kinds of machinery and equipment. The compilation of machining is an important part and key work of mechanical manufacturing technology. In recent years, with the wide application of modern technology, great changes have taken place in traditional machining and manufacturing methods. The functions of jigs have been separated from the traditional clamping, positioning and guiding tools, and developed in a broader sense to meet the growing machining industry.Key words：Manufacturing; Design; Classification; fixture1 机械加工工艺的现状和发展趋势随着机械制造工艺的飞速发展。比如，应用人工智能选择零件的工艺规程。因为特种加工的微观物理过程非常复杂，往往涉及电磁场、热力学、流体力学、电化学等诸多领域，其加工机理的理论研究极其困难，通常很难用简单的解析式来表达。近年来，虽然各国学者采用各种理论对不同的特种加工技术进行了深入的研究，并取得了卓越的理论成就，但离定量的实际应用尚有一定的距离。然而采用一种特种加工方法所获得的加工精度和表面质量与加工条件参数间都有其规律。因此，目前常采用研究传统切削加工机理的实验统计方法来了解特种加工的工艺规律，以便实际应用，但还缺乏系统性。为了能具体确切的说明过程，使工件能按照零件图的技术要求加工出来，就得制定复杂的机械加工工艺规程来作为生产的指导性技术文件，学习研究制定机械加工工艺规程的意义与作用就是本课题研究目的。学习研究制 定机械加工工艺规程的意义与作用就是本课题研究目的。1.世界各国都把发展机械制造业作为发展本国经济的战略重点之一，机械制造业已成为我国工业种产品门类比较齐全，具有相当规模和一定技术基础的最大的产业之一。2.但与工业发达国家相比仍存在着阶段性的差距，反映了制造技术的落后一是技术开发能力和技术基础薄弱。二是全员劳动生产率低。三是产品质量不高并且能耗高，国际竞争乏力，尽管机械产品的出口增长迅速但进出口逆差仍然很大。3.机械工艺为质量，生产率和经济性：保证和提高产品质量，提高劳动生产率，降低成本。4. 工艺过程的典型化和工艺规程的编制方法。5.加工精度的理论。6.机械加工的表面质量。7.机械零件间及其加工过程中的尺寸联系和尺寸链。8.机床夹具的设计原理和方法。2 机械加工工艺的相关知识2.1 机械生产过程和工艺过程生产过程是指产品由原材料到成品之间的各个相互联系的劳动过程的总和。对于机器生产而言，它包括：原材料的运输和保管，生产的技术准备工作，毛坯的制造，零件的机械加工和热处理，部件和产品的装配、检验、油漆和包装等。在机械产品的生产过程中，对于那些与原材料变成产品直接有关的过程，如毛坯制造、机械加工等，称为工艺过程。采用机械加工方法，直接改变毛坯的形状、尺寸和表面质量，使之称为产品零件的过程称为机械加工工艺过程。2.2 机械加工工艺过程及其组成机械加工工艺过程由一个或若干个顺次排列的工序组成，每一个工序可分为若干个安装、工位和工步。(1) 工序工序是一个或一组工人，在一个工作地对同一个或同时对几个工件所连续完成的那一部分工艺过程，称为工序。它是组成工艺过程的基本单元。(2) 安装在同一个工序中，工件在工作位置可能只装夹一次，也可能要装夹几次，工件经一次装夹后所完成的那一部分工艺过程。(3) 工位工件在一次安装中，工件相对于机床或刀具每占据一个确切位置所完成的那一部分工艺过程称为工位。(4) 工步工步，即在加工表面（或装配时的连接面）和加工（或装配）工具、主轴转速及进给量不变的情况下，所连续完成的那一部分作业。在同一个工位上，要完成不同的表面加工时，其中加工表面、切削速度、进给量和加工工具都不变的情况下，所连续完成的那一部分工序内容，称为一个工步。(5) 走刀 在一个工步内，若被加工表面需切去的材料很厚，就可分几次切削，每一次切削就是一次走刀。3 CA6140车床主轴加工工艺及夹具设计1.根据零件图，对零件进行工艺分析；2.确定零件生产类型3.确定毛坯种类及制造方法，绘制毛坯图；4.拟订零件的机械加工工艺路线，确定加工余量和工序尺寸，选择各工序加工设备及工艺装备（刀具、夹具、量具、辅具），确定各工序切削用量，计算工序的工时定额；5.填写工艺文件：工艺过程卡片、工序卡片；6.设计指定工序的专用夹具，绘制夹具配图；7.结合本课题查阅并翻译不少于8000个印刷符号的英文资料；8.编写设计说明书。4 零件加工工艺分析4.1 轴类零件的功用、分类和结构特点轴类零件是机器中经常遇到的典型零件之一。轴类零件的功用为支承传动零件（齿轮、皮带轮等）、转动扭矩、承受载荷，以及保证装在主轴上的工件（或刀具）具有一定的回转精度。本课题所设计的CA6140车床主轴，该轴既是阶梯轴又是空心轴，并且是长径比小于12的刚性轴。根据其结构和精度要求，在加工过程中对这种轴的定位基准面选择、深孔加工和热处理变形等方面，为技术难点。4.2 定位基准的选择（1）基面的选择基面选择是工艺规程设计中的重要工作之一。基面选择得正确与合理，可以使加工质量得到保证，生产率得以提高。否则，加工工艺过程中会问题百出，更有甚者，还会造成零件大批报废，使生产无法正常进行。（2）粗基准的选择选择粗基准主要是选择第一道机械加工工序的定位基准，以便为后续的工序提供精基准。选择粗基准的出发点是：一要考虑如何分配各加工表面的余量。二要考虑怎样保证不加工面与加工面间的尺寸及相互位置要求。这两个要求常常是不能兼顾的，但对于一般的轴类零件来说，以外圆作为粗基准是完全合理的。对本零件而言，由于每个表面都要求加工，为保证各表面都有足够的余量，应选加工余量最小的面为粗基准（3）精基准的选择主要应该考虑基准重合的问题。当设计基准与工序基准不重合时，应该进行尺寸换算，还要专门计算。该零件为小型零件，加工的部位较多且互相之间有较高的位置精度，故选择精基准时首先考虑基准统一的方案。4.3 主轴加工工艺过程(1) 毛坯处理(2) 毛坯，备料，锻造，正火(3) 粗加工(4) 锯除多余部分，铣端面、钻中心孔和粗车外圆等。(5) 该阶段的主要目的：用大的切削量切除大部分余量，把毛坯加工至接近工件的最终形状和尺寸，只留少量余量。还可以及时发现锻件裂纹等缺陷，采取相应措施。(6) 半精加工阶段(7) 半加工前热处理；半精车外圆端面。(8) 精加工阶段(9) 精加工前先热处理：局部高频淬火。(10) 精磨外圆和内外锥面以保证主轴最重要的表面精度。(11) 去毛刺，检查(12) 这个阶段的主要目的是把每个表面都加工到规定的要求。4.4 工艺规程设计的目的对机械加工工艺规程基本要求可归结为质量、生产率和经济性。虽然有时互相矛盾，但只要把它们处理好，就会成为一个统一体。在三个要求中，质量是首要的。质量表现在机械产品的各项技术性能指标，质量不能保证，根本谈不上数量；质量和生产率之间是密切联系的，在保证质量的前提下，应该不断地最大限度地提高生产率，满足生产量的要求。如果两者矛盾，则生产率要服从于质量，应在保证质量的前提下解决生产率问题。在保证质量的前提下，应尽可能的节约耗费，减少投资，降低制造成本，这就是经济性。因此，工艺规程设计应该体现质量、生产率和经济性的统一，达到经济合理及可行的目的。5 设计的难点在这个设计过程中，我们还必须考虑工件的安装和夹紧，安装的正确与否直接影响工件加工精度, 安装是否方便和迅速，又会影响辅助时间的长短, 从而影响生产率，夹具是加工工件时，为完成某道工序，用来正确迅速安装工件的装置，它对保证加工精度、提高生产率和减轻工韧动量有很大作用。这是整个设计的重点,也是一个难点。受其限制，目前一些加工的工艺参数只能凭经验选取，还难以实现最优化和自动化，例如，电火花成形电极的沉入式加工工艺，它在占电火花成形机床总数95%以上的非数控电火花成形加工机床和较大尺寸的模具型腔加工中得到广泛应用。虽然已有学者对其CAD、CAPP和 CAM原理开展了一些研究，并取得了一些成果，但由于工艺数据的缺乏，仍未有成熟的商品化的CAD/CAM 系统问世。通常只能采用手工的方法或部分借助于CAD造型、部分生成复杂电极的三维型面数据。随着模糊数学、神经元网络及专家系统等多种人工智能技术的成熟发展，人们开始尝试利用这一技术来建立加工效果和加工条件之间的定量化的精度、效率、经济性等实验模型，并得到了初步的成果。因此，通过实验建模，将典型加工实例和加工经验作为知识存储起来，建立描述加工工艺规律的可扩展性开放系统的条件已经成熟。并为进一步开展特种加工加工工艺过程的计算机模拟，应用人工智能选择零件的工艺规程和虚拟加工奠定基础。6 总结在整个设计过程中,通过CA6140车床主轴装配图的绘制、工艺分析（制订工艺规程、确定加工余量、工艺尺寸计算、工时定额计算、定位误差分析）以及对专用夹具的设计，将会增强分析零件图、独立识图、运用软件、工艺分析的能力。工艺是使各种原材料，半成品成为产品的方法和过程；机械制造工艺是各种机械的制造方法和过程。机械制造工艺基础内容广泛包括零件的毛坯制造，机械加工，热处理，产品的装配以及先进制造技术等。主要研究机械加工和产品装配。机械制造工艺研究的问题：保证和提高产品的质量，提高劳动生产率，价低成本。夹具是一种装夹工件的工艺设备他的主要功用是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。世界各国都把发展机械制造业作为发展本国经济的战略重点之一，机械制造业已成为我国工业种产品门类比较齐全，具有相当规模和一定技术基础的最大的产业之一。但与工业发达国家相比仍存在着阶段性的差距，反映了制造技术的落后一是技术开发能力和技术基础薄弱。二是全员劳动生产率低。三是产品质量不高并且能耗高，国际竞争乏力。尽管机械产品的出口增长迅速但进出口逆差仍然很大机械工艺为质量，生产率和经济性：保证和提高产品质量，提高劳动生产率，降低成本。工艺过程的典型化和工艺规程的编制方法。加工精度的理论。机械加工的表面质量，机械零件间及其加工过程中的尺寸联系和尺寸链。机床夹具的设计原理和方法因此，在以后的学习工作中，我要从以下方面来提高自己，解决设计中存在的问题。多学习相关的知识，关注前沿的科学技术，拓宽知识面，尽量进行实践，以便设计时能够在保证成本的前提下，较好地利用其本身。参考文献1 王绍俊.机械制造工艺设计手册.哈尔滨：哈尔滨工业大学出版社，1981 2 刘文剑曹天河.夹具工程师手册.哈尔滨：黑龙江科学技术出版社，1987 3 艾兴，肖诗纲 . 切削用量简明手册（第三版）.北京：机械工业出版社，2004 4 吴宗泽.机械设计课程设计手册（第二版）.北京:高等教育出版社，19995 李益民.机械制造工艺设计简明手册.北京: 机械工业出版社，19946 赵家齐.机械制造工艺学课程设计指导书.北京：机械工业出版社，20047 艾兴.切削用量简明手册S.北京:机械工业出版社,1999.8 哈尔滨工业大学.机床夹具设计手册S.北京:机械工业出版社,2002.9 陈立德.工装设计M.上海:上海交通大学出版社,1999.10 孙本绪,熊万武.机械加工余量手册S.北京:国防工业出版社,1999.11 冯辛安.机械制造装备设计M.北京:机械工业出版社,2008.12 教育部高等教育司.画法几何及机械制图M.北京:高等教育出版社,1999.13 毛平淮.互换性与测量技术基础M.北京:机械工业出版社,2007.14 李宏.机械加工工艺手册.北京.北京出版社，2004.15 徐宏海.机械制造工艺.化学工业出版社，2004.16 弈继昌.机械制造工艺学及夹具设计.中国人民出版社，2003.17 吕明.机械制造技术基础（第3版）M.武汉:武汉理工大学出版社,2015.18 水根.机械制造工艺学（第二版）M.北京:清华大学出版社,2004.19 杨叔子.机械加工工艺师手册S.北京:机械工业出版社,2002.20 贺毅.如何设计车床夹具J.科技创新导报,2013.10 译文：材料的可机加工性一种材料的可机加工性通常以四种因素的方式定义：（1）、良好的的表面光洁性和表面完整性。（2）、刀具的寿命。（3）、切削力和功率的需求。（4）、切屑控制。好的可机加工性指的是指好的表面光洁性和完整性，因为剪切工序的复杂属性，所以很难建立定量地释义材料的可机加工性的关系。在制造厂里，刀具寿命和表面粗糙度通常被认为是可机加工性中最重要的因 素。尽管已不再大量的被使用，近乎准确的机加工率在以下的例子中能够被看到。1. 钢的可机加工性因为钢是最重要的工程材料之一，所以他们的可机加工性已经被广泛地研究过。通过铅和硫磺，钢的可机加工性已经大大地提高了。从而得到了所谓的易切削钢。二次硫化钢和二次磷化钢硫在钢中形成硫化锰夹杂物硒，其化学性质与硫类似，在二次硫化钢中起夹杂物改性作用。钢中的磷有两个主要的影响。它加强铁素体，增加硬度。越硬的钢，形成更好的切屑形成和表面光洁性。需要注意的是软钢不适合用于有积屑瘤形成和很差的表面光洁性的机器。第二个影响是增加的硬度引起短切屑而不是不断的细长的切屑的形成，因此需要提高可加工性。含铅的钢中高含量的铅在硫化锰夹杂物尖端析出。在非二次硫化钢中，铅呈细小而分散的颗粒。铅在铁、铜、铝和它们的合金中是不能溶解的。因为它的低抗剪强度。因此，铅充当固体润滑剂并且在切削时，被涂在刀具和切屑的接口处。这一特性已经被在机加工铅钢时，在切屑的刀具面表面有高浓度的铅的存在所证实。当温度足够高时例如，在高的切削速度和进刀速度下铅在刀具前直接熔化，并且充当液体润滑剂。除了这个作用，铅降低第一剪切区中的剪应力，减小切削力和功率消耗。铅能用于各种钢号，例如10XX，11XX，12XX，41XX等等。铅钢被第二和第三数码中的字母L 所识别（例如，10L45）。（需要注意的是在不锈钢中，字母L 的相同用法指的是低碳，提高它们的耐蚀性的条件）。然而，因为铅是有名的毒素和污染物，因此在钢的使用中存在着严重的环境隐患（在钢产品中每年大约有4500 吨的铅消耗）。结果，对于估算钢中含铅量的使用存在一个持续的趋势。铋和锡现正作为钢中的铅最可能的替代物而被人们所研究。脱氧钙钢一个重要的发展是脱氧钙钢，在脱氧钙钢中矽酸钙盐中的氧化物片的形成。 这些片状，依次减小第二剪切区中的力量，降低刀具和切屑接口处的摩擦和磨损。温度也相应地降低。结果，这些钢产生更小的月牙洼磨损，特别是在高切削速度时更是如此。根据它们的构成，碳和锰钢在钢的可机加工性方面有不同的影响。低碳素钢（少于0.15%的碳）通过形成一个积屑瘤能生成很差的表面光洁性。尽管铸钢的可机加工性和锻钢的大致相同，但铸钢具有更大的磨蚀性。刀具和模具钢很难用于机加工，他们通常再煅烧后再机加工。大多数钢的可机加工性在冷加工后都有所提高，冷加工能使材料变硬并且减少积屑瘤的形成。其它合金元素，例如镍、铬、钳和钒，能提高钢的特性，减小可机加工性。硼的影响可以忽视。气态元素比如氢和氮在钢的特性方面能有特别的有害影响。 氧已经被证明了在硫化锰夹杂物的纵横比方面有很强的影响。越高的含氧量，就产生越低的纵横比和越高的可机加工性。选择各种元素以改善可加工性，我们应该考虑到这些元素对已加工零件在使用中的性能和强度的不利影响。例如，当温度升高时，铝会使钢变脆（液体金属脆化，热脆化），尽管其在室温下对力学性能没有影响。因为硫化铁的构成，硫能严重的减少钢的热加工性，除非有足够的锰来防止这种结构的形成。在室温下，二次磷化钢的机械性能依赖于变形的硫化锰夹杂物的定位（各向异性）。二次磷化钢具有更小的延展性，被单独生成来提高机加工性。2. 其它不同金属的机加工性尽管越软的品种易于生成积屑瘤，但铝通常很容易被机加工，导致了很差的表面光洁性。 高的切削速度，高的前角和高的后角都被推荐了。有高含量的矽的 锻铝合金铸铝合金也许具有磨蚀性，它们要求更硬的刀具材料。尺寸公差控制也 工铝时会成为一个问题，因为它有膨胀的高导热系数和相对低的弹性模 数。铍和铸铁相同。因为它更具磨蚀性和毒性，尽管它要求在可控人工环境下进行机加工。灰铸铁普遍地可加工，但也有磨蚀性。铸造无中的游离碳化物降它们的可机加工性，引起刀具切屑或裂口。它需要具有强韧性的工具。具有坚硬的刀具材 料的球墨铸铁和韧性铁是可加工的。钴基合金有磨蚀性且高度加工硬化的。它们要求尖的且具有耐蚀性的刀具材料并且有低的走刀和速度。尽管铸铜合金很容易机加工，但因为锻铜的积屑瘤形成因而锻铜很难机加工。黄铜很容易机加工，特别是有添加的铅更容易。青铜比黄铜更难机加工。镁很容易机加工，镁既有很好的表面光洁性和长久的刀具寿命。然而，因高的氧化速度和火种的危险（这种元素易燃），因此我们应该特别小心使用它。钳易拉长且加工硬化，因此它生成很差的表面光洁性。尖的刀具是很必要的。镍基合金加工硬化，具有磨蚀性，且在高温下非常坚硬。它的可机加工性和不锈钢相同。钽非常的加工硬化，具有可延性且柔软。它生成很差的表面光洁性且刀具磨损非常大。钛和它的合金导热性(的确，是所有金属中最低的)，因此引起明显的温度升高和积屑瘤。它们是难机加工的。钨易脆，坚硬，且具有磨蚀性，因此尽管它的性能在高温下能大大提高，但它的机加工性仍很低。锆有很好的机加工性。然而，因为有爆炸和火种的危险性，它要求有一个冷却性质好的切削液。3. 各种材料的机加工性 石墨具有磨蚀性它要求硬的、尖的，具有耐蚀性的刀具。塑性塑料通常有低的导热性，低的弹性模数和低的软化温度。因此，机加工热塑性塑料要求有正前角的刀具（以此降低切削力），还要求有大的后角，小的切削和走刀深的，相对高的速度和工件的正确支承。刀具应该很尖。热固性塑料易脆，并且在切削时对热梯度很敏感。它的机加工性和热塑性塑料的相同。因为纤维的存在，加强塑料具有磨蚀性，且很难机加工。纤维的撕裂、拉出和边界分层是非常严重的问题。它们能导致构成要素的承载能力大大下降。这些材料的机加工要求对加工残片仔细切除，以此来避免接触和吸进纤维。随着纳米陶瓷的发展和适当的参数处理的选择，例如塑性切削。金属基复合材料和陶瓷基复合材料很能机加工，它们依赖于单独的成分的特性，比如说增强纤维或金属须和基体材料。4. 热辅助加工在室温下很难机加工的金属和合金在高温下能更容易地机加工。在热辅助加工时（高温切削），热源一个火把，感应线圈，高能束流（例如雷射或电子束），或等离子弧被集中在切削刀具前的一块区域内。好处是：（a）低的切削力。（b）增加的刀具寿命。（c）便宜的切削刀具材料的使用。（d）更高的材料切除率。（e）减少振动。也许很难在工件内加热和保持一个不变的温度分布。而且，工件的最初微观结构也许被高温影响，且这种影响是相当有害的。尽管实验在进行中，以此来机加工陶瓷器如氮化矽，但高温切削仍大多数应用在高强度金属和高温度合金的车削中。小结通常，零件的可机加工性能是根据以下因素来定义的：表面粗糙度，刀具的寿命， 切削力和功率的需求以及切屑的控制。材料的可机加工性能不仅取决于起内在特性和微观结构，而且也依赖于工艺参数的适当选择与控制。6外文原文：The machinability ofmaterialThe machinability of a material usually defined in terms of four factors: (1). Surface finish and integrity of the machined part;(2).Tool life obtained;(3).Force and power requirements; (4). Chip control.Thus, good machinability good surface finish and integrity, long tool life, and low force And power requirements. As for chip control, long and thin (stringy) cured chips, if not broken up, can severely interfere with the cutting operation by becoming entangled in the cutting zone.Because of the complex nature of cutting operations, it is difficult to establish relationships that quantitatively define the machinability of a material. In manufacturing plants, tool life and surface roughness are generally considered to be the most important factors in machinability. Although not used much any more, approximate machinability ratings are available in the example below.1. Machinability Of SteelsBecause steels are among the most importantengineering materials , their machinabilityhas been studied extensively. The machinabilityof steels has been mainly improved by adding lead and sulfur to obtain so-called free-machining steels. Resulfurized and Rephosphorized steels.Sulfurin steels forms manganese sulfide inclusions (second-phase particles), which act as stress raisers in the primary.Shear zone. As a result, the chips produced break up easily and are small; this improves machinability. The size, shape, distribution, and concentration of these inclusions significantly influence machinability. Elements such as tellurium and selenium, which are both chemically similar to sulfur, act as inclusion modifiers in resulfurized steels.Phosphorus in steels has two major effects. It strengthens the ferrite, causing increased hardness.Harder steels result in better chip formation and surface finish. Note that soft steels can be difficult to machine, withbuilt-up edge formation and poor surface finish. The second effect is that increased hardness causes the formation of short chips instead of continuous stringy ones, thereby improving machinability.Leaded Steels. A high percentage of lead in steels solidifies at the tip of manganese sulfide inclusions. In non-resulfurized grades of steel, lead takes the form of dispersed fine particles. Lead is insoluble in iron, copper, and aluminum and their alloys. Because of its low shear strength, therefore, lead acts as a solid lubricant and is smeared over the tool-chip interface during cutting. This behavior has been verified by the presence of high concentrations of lead on the tool-side face of chips when machining leaded steels.When the temperature is sufficiently high-for instance, at high cutting speeds and feeds the lead melts directly in front of the tool, acting as a liquid lubricant. In addition to this effect, lead lowers the shear stress in the primary shear zone, reducing cutting forces and power consumption. Lead can be used in every grade of steel, such as 10xx, 11xx, 12xx, 41xx, etc. Leaded steels are identified by the letter L between the second and third numerals (for example, 10L45). (Note that in stainless steels, similar use of the letter L means“low carbon,”a condition that improves their corrosion resistance.)However, because lead is a well-known toxin and a pollutant, there are serious environmental concerns about its use in steels (estimated at 4500 tons of lead consumption every year in the production of steels ).Consequently, there is a continuing trend toward eliminating the use of lead in steels (lead-free steels). Bismuth and tin are now being investigated as possible substitutes for lead in steels. Calcium-Deoxidized Steels. An important development is calcium-deoxidized steels, in which oxide flakes of calcium silicates (CaSo) are formed. These flakes, in turn, reduce the strength of the secondary shear zone, decreasing tool-chip interface and wear.Temperature is correspondingly reduced.Consequently,these steels produce less crater wear, especially at high cutting speeds.Stainless Steels. Austenitic (300 series) steels are generally difficult to machine. Chatter can be s problem, necessitating machine tools with high stiffness. However, ferritic stainless steels (also 300 series) have good machinability.Martensitic (400 series) steels are abrasive, tend to form a built-up edge, and require tool materials with high hot hardness and crater-wear resistance. Precipitation-hardening stainless steels are strong and abrasive, requiring hard and abrasion-resistant tool materials.He Effects of Other Elements in Steels on Machinability. The presence of aluminum and silicon in steels is always harmful because these elements combine with oxygen to form aluminum oxide and silicates, which are hard and abrasive. These compounds increase tool wear and reduce machinability. It is essential to produce and use clean steels.Carbon and manganese have various effects on the machinability of teels, depending on their composition. Plain low-carbon steels (less than 0.15% C) can produce poor surface finish by forming a built-up edge. Cast steels are more abrasive, although their machinability is similar to that of wrought steels. Tool and die steels are very difficult to machine and usually require annealing prior to machining.Machinability of most steels is improved by cold working, which hardens the material and reduces the tendency for built-up edge formation.Other alloying elements, such as nickel, chromium,molybdenum, and vanadium,which improve the properties of steels, generally reduce machinability. The effect of boron is negligible.Gaseous elements such as hydrogen and nitrogen can have particularly detrimental effects on the properties of steel. Oxygen has been shown to have a strong effect on the aspect ratio of the manganese sulfide inclusions; the higher the oxygen content, the lower the aspect ratio and the higher the machinability.In selecting various elements to improve machinability, we should consider the possible detrimental effects of these elements on the properties and strength of the machined part in service. At elevated temperatures, for example,lead causes embrittlement of steels (liquid-metal embrittlement, hot shortness), although at room temperature it has no effect on mechanical properties.Sulfur can severely reduce the hot workability of steels, because of the formation of iron sulfide, unless sufficient manganese is present to prevent such formation. At room temperature, the mechanical properties of resulfurized steels depend on the orientation of the deformed manganese sulfide inclusions (anisotropy).Rephosphorized steels are significantly less ductile, and are produced solely to improve machinability.2. Machinability of Various Other MetalsAluminum is generally very easy to machine, although the softer grades tend to form a built-up edge, resulting in poor surface finish. High cutting speeds, high rake angles, and high relief angles are recommended. Wrought aluminum alloys with high silicon content and cast aluminum alloys may be abrasive; they require harder tool materials. Dimensional tolerance control may be a problem in machining aluminum, since it has a high thermal coefficient of expansion and a relatively low elastic modulus.Beryllium is similar to cast irons. Because it is more abrasive and toxic, though, it requires machining in a controlled environment.Cast gray irons are generally machinable but are. Free carbides in castings reduce their machinability and cause tool chipping or fracture, necessitating tools with high toughness. Nodular and malleable irons are machinable with hard tool materials.Cobalt-based alloys are abrasive and highly work-hardening. They require sharp, abrasion-resistant tool materials and low feeds and speeds.Wrought copper can be difficult to machine because of built-up edge formation, although cast copper alloys are easy to machine. Brasses are easy to machine,especially with the addition pf lead (leaded free-machining brass). Bronzes are more difficult to machine than brass.Magnesium is very easy to machine, with good surface finish and prolonged tool life. However care should be exercised because of its high rate of oxidation and the danger of fire (the element is pyrophoric).Molybdenum is ductile and work-hardening,so it can produce poor surface finish. Sharp tools are necessary.Nickel-based alloys are work-hardening,abrasive, and strong at high temperatures. Their machinability is similar to that of stainless steels.Tantalum is very work-hardening, ductile, and soft. It producesa poor surface finish; tool wear is high.Titanium and its alloys have poor thermal conductivity (indeed, the lowest of all metals), causing significant temperature rise and built-up edge; they can be difficult to machine.Tungsten is brittle,strong,and very abrasive, so its machinability is low, although it greatly improves at elevated temperatures.Zirconium has good machinability. It requires a coolant-type cutting fluid, however, because of the explosion and fire.3. Machinability of Various MaterialsGraphite is abrasive; it requires hard, abrasion-resistant, sharp tools. Thermoplastics generally have low thermal conductivity, low and low softening temperature. Consequently, machining them requires tools with positive rake angles (to reduce cutting forces), large relief angles, small depths of cut and feed, relatively high speeds, and proper support of the work piece. Tools should be sharp.Thermosetting plastics are brittle and sensitive to thermal gradients during cutting. Their machinability is generally similar to that of thermoplastics.Because of the fibers present, reinforced plastics are very abrasive and are difficult to machine. Fiber tearing, pulling, and edge delamination are significant problems; they can lead to severe reduction in the load-carrying capacity of the component. Furthermore, machining of these materials requires careful removal of machining debris to avoid contact with and inhaling of the fibers.The machinability of ceramics has improved steadily with the development of nanoceramicsand with the selection of appropriate processing parameters, such as ductile-regime cutting .Metal-matrix and ceramic-matrix composites can be difficult to machine, depending on the properties of the individual components, i.e., reinforcing or whiskers, as well as the matrix material.4. Thermally Assisted MachiningMetals and alloys that are difficultto machine at room temperature can be machined more easily at elevated temperatures. In thermally assisted machining (hot machining), the source of heat a torch, induction coil,high-energy beam (such as laser or electron beam), or plasma arcis forces, (b) increased tool life, (c) use of inexpensive cutting-tool materials, (d) higher material-removal rates, and (e) reduced tendency for vibration and chatter.It may be difficult to heat and maintain a uniform temperature distribution within the work piece. Also, the original microstructure of the work piece may be adversely affected by elevated temperatures. Most applications of hot machining are in the turning of high-strength metals and alloys, although experiments are in progress to machine ceramics such as silicon nitride.SUMMARYMachinability is usually defined in terms of surface finish, tool life, force and power requirements, and chip control. Machinability of materials depends not only on their intrinsic properties and microstructure, but also on proper selection and control of process variables.The machinability ofmaterialThe machinability of a material usually defined in terms of four factors: (1). Surface finish and integrity of the machined part;(2).Tool life obtained;(3).Force and power requirements; (4). Chip control.Thus, good machinability good surface finish and integrity, long tool life, and low force And power requirements. As for chip control, long and thin (stringy) cured chips, if not broken up, can severely interfere with the cutting operation by becoming entangled in the cutting zone.Because of the complex nature of cutting operations, it is difficult to establish relationships that quantitatively define the machinability of a material. In manufacturing plants, tool life and surface roughness are generally considered to be the most important factors in machinability. Although not used much any more, approximate machinability ratings are available in the example below.1. Machinability Of SteelsBecause steels are among the most importantengineering materials , their machinabilityhas been studied extensively. The machinabilityof steels has been mainly improved by adding lead and sulfur to obtain so-called free-machining steels. Resulfurized and Rephosphorized steels.Sulfurin steels forms manganese sulfide inclusions (second-phase particles), which act as stress raisers in the primary.Shear zone. As a result, the chips produced break up easily and are small; this improves machinability. The size, shape, distribution, and concentration of these inclusions significantly influence machinability. Elements such as tellurium and selenium, which are both chemically similar to sulfur, act as inclusion modifiers in resulfurized steels.Phosphorus in steels has two major effects. It strengthens the ferrite, causing increased hardness.Harder steels result in better chip formation and surface finish. Note that soft steels can be difficult to machine, withbuilt-up edge formation and poor surface finish. The second effect is that increased hardness causes the formation of short chips instead of continuous stringy ones, thereby improving machinability.Leaded Steels. A high percentage of lead in steels solidifies at the tip of manganese sulfide inclusions. In non-resulfurized grades of steel, lead takes the form of dispersed fine particles. Lead is insoluble in iron, copper, and aluminum and their alloys. Because of its low shear strength, therefore, lead acts as a solid lubricant and is smeared over the tool-chip interface during cutting. This behavior has been verified by the presence of high concentrations of lead on the tool-side face of chips when machining leaded steels.When the temperature is sufficiently high-for instance, at high cutting speeds and feeds the lead melts directly in front of the tool, acting as a liquid lubricant. In addition to this effect, lead lowers the shear stress in the primary shear zone, reducing cutting forces and power consumption. Lead can be used in every grade of steel, such as 10xx, 11xx, 12xx, 41xx, etc. Leaded steels are identified by the letter L between the second and third numerals (for example, 10L45). (Note that in stainless steels, similar use of the letter L means“low carbon,”a condition that improves their corrosion resistance.)However, because lead is a well-known toxin and a pollutant, there are serious environmental concerns about its use in steels (estimated at 4500 tons of lead consumption every year in the production of steels ).Consequently, there is a continuing trend toward eliminating the use of lead in steels (lead-free steels). Bismuth and tin are now being investigated as possible substitutes for lead in steels. Calcium-Deoxidized Steels. An important development is calcium-deoxidized steels, in which oxide flakes of calcium silicates (CaSo) are formed. These flakes, in turn, reduce the strength of the secondary shear zone, decreasing tool-chip interface and wear.Temperature is correspondingly reduced.Consequently,these steels produce less crater wear, especially at high cutting speeds.Stainless Steels. Austenitic (300 series) steels are generally difficult to machine. Chatter can be s problem, necessitating machine tools with high stiffness. However, ferritic stainless steels (also 300 series) have good machinability.Martensitic (400 series) steels are abrasive, tend to form a built-up edge, and require tool materials with high hot hardness and crater-wear resistance. Precipitation-hardening stainless steels are strong and abrasive, requiring hard and abrasion-resistant tool materials.He Effects of Other Elements in Steels on Machinability. The presence of aluminum and silicon in steels is always harmful because these elements combine with oxygen to form aluminum oxide and silicates, which are hard and abrasive. These compounds increase tool wear and reduce machinability. It is essential to produce and use clean steels.Carbon and manganese have various effects on the machinability of teels, depending on their composition. Plain low-carbon steels (less than 0.15% C) can produce poor surface finish by forming a built-up edge. Cast steels are more abrasive, although their machinability is similar to that of wrought steels. Tool and die steels are very difficult to machine and usually require annealing prior to machining.Machinability of most steels is improved by cold working, which hardens the material and reduces the tendency for built-up edge formation.Other alloying elements, such as nickel, chromium,molybdenum, and vanadium,which improve the properties of steels, generally reduce machinability. The effect of boron is negligible.Gaseous elements such as hydrogen and nitrogen can have particularly detrimental effects on the properties of steel. Oxygen has been shown to have a strong effect on the aspect ratio of the manganese sulfide inclusions; the higher the oxygen content, the lower the aspect ratio and the higher the machinability.In selecting various elements to improve machinability, we should consider the possible detrimental effects of these elements on the properties and strength of the machined part in service. At elevated temperatures, for example,lead causes embrittlement of steels (liquid-metal embrittlement, hot shortness), although at room temperature it has no effect on mechanical properties.Sulfur can severely reduce the hot workability of steels, because of the formation of iron sulfide, unless sufficient manganese is present to prevent such formation. At room temperature, the mechanical properties of resulfurized steels depend on the orientation of the deformed manganese sulfide inclusions (anisotropy).Rephosphorized steels are significantly less ductile, and are produced solely to improve machinability.2. Machinability of Various Other MetalsAluminum is generally very easy to machine, although the softer grades tend to form a built-up edge, resulting in poor surface finish. High cutting speeds, high rake angles, and high relief angles are recommended. Wrought aluminum alloys with high silicon content and cast aluminum alloys may be abrasive; they require harder tool materials. Dimensional tolerance control may be a problem in machining aluminum, since it has a high thermal coefficient of expansion and a relatively low elastic modulus.Beryllium is similar to cast irons. Because it is more abrasive and toxic, though, it requires machining in a controlled environment.Cast gray irons are generally machinable but are. Free carbides in castings reduce their machinability and cause tool chipping or fracture, necessitating tools with high toughness. Nodular and malleable irons are machinable with hard tool materials.Cobalt-based alloys are abrasive and highly work-hardening. They require sharp, abrasion-resistant tool materials and low feeds and speeds.Wrought copper can be difficult to machine because of built-up edge formation, although cast copper alloys are easy to machine. Brasses are easy to machine,especially with the addition pf lead (leaded free-machining brass). Bronzes are more difficult to machine than brass.Magnesium is very easy to machine, with good surface finish and prolonged tool life. However care should be exercised because of its high rate of oxidation and the danger of fire (the element is pyrophoric).Molybdenum is ductile and work-hardening,so it can produce poor surface finish. Sharp tools
- 温馨提示:
1: 本站所有资源如无特殊说明，都需要本地电脑安装OFFICE2007和PDF阅读器。图纸软件为CAD,CAXA,PROE,UG,SolidWorks等.压缩文件请下载最新的WinRAR软件解压。
2: 本站的文档不包含任何第三方提供的附件图纸等，如果需要附件，请联系上传者。文件的所有权益归上传用户所有。
3.本站RAR压缩包中若带图纸，网页内容里面会有图纸预览，若没有图纸预览就没有图纸。
4. 未经权益所有人同意不得将文件中的内容挪作商业或盈利用途。
5. 人人文库网仅提供信息存储空间，仅对用户上传内容的表现方式做保护处理，对用户上传分享的文档内容本身不做任何修改或编辑，并不能对任何下载内容负责。
6. 下载文件中如有侵权或不适当内容，请与我们联系，我们立即纠正。
7. 本站不保证下载资源的准确性、安全性和完整性, 同时也不承担用户因使用这些下载资源对自己和他人造成任何形式的伤害或损失。
人人文库网所有资源均是用户自行上传分享，仅供网友学习交流，未经上传用户书面授权，请勿作他用。
川公网安备: 51019002004831号