SSCK20A数控车床主轴及主轴箱的数控加工及数控编程设计【说明书+CAD】
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摘 要随着社会的进步,制造业的发展越来越迅速,数控技术和数控装备是制造工业现代化的重要基础。这个基础是否牢固直接影响到一个国家的经济发展和综合国力,关系到一个国家的战略地位。因此,世界上各工业发达国家均采取重大措施来发展自己的数控技术及其产业。在我国,数控技术与装备的发展亦得到了高度重视,近年来取得了相当大的进步。数控机床发展很快,作为数控机床的重要部分,主轴箱的设计更新也越来越快。我设计的是SSCK20A数控机床主轴和主轴箱箱体加工工艺以及数控编程,其中涉及了主轴和箱体加工中刀具、量具、毛坯、定位基准等的选择。设计图为两张零号图纸,一张一号图纸,两张二号图纸。关键词:数控加工工艺 、数控编程、定位基准、主轴箱、工艺编程。AbstractOre and Along with the advance of society, the development of manufacturing industry is mmore quick, the technical equipment of numerical control of numerical control is to make industrial modern important foundation. Whether directly affect a economy of country strongly develop this foundation with the countrys comprehensive power, concern a strategic position of country. Therefore on world, each industrial developed countries adopts significant measure to develop the own technical and its estate of numerical control. in recent years, have gotten fairly big advance. The development of numerical control of machine tool is very rapid , is the important part of the machine tool of numerical control, the design of the case of main shaft update also more and more rapid. What I design is that the case casing processing technology as well as programming of numerical control of machine tool of main shaft have in which been concerned with the option of cutting tool, measuring tool, blank and location standard etc. in casing processing. Design drawing is the two blueprints No. 0 and a blueprint No. 1 and two blueprints No. 2 .Keyword: Number control to process the craft、count to control to weave the distance、fixed position basis、 principal axis box、craft plait distance。目 录摘要:1Abstract2第一章 绪论5第二章 数控加工概念62.1高速、高效、高精度、高可靠性8第三章 数控车床93.1数控车床的组成93.2数控车床的特点 113.3数控车床的适用范围及工作原理12第四章 数控加工工艺分析154.1 毛坯的选择184.2确定数控加工内容184.3数控加工零件的工艺性分析18 4.4定位基准的选择19 4.4.1精基准的选择19 4.4.2粗基准的选择19 4.5加工方法的选择20 4.6刀具的选择21 4.6.1数控车刀的类型与刀片选择214.7夹具的选择214.8量具的选择224.9数控加工工艺路线设计22 4.9.1外圆表面的加工方法的选择22第五章 工序的划分245.1加工顺序的安排255.1.1切削加工工序安排255.1.2热处理工序安排255.1.3辅助工序安排26 5.2数控加工工序设计265.3走刀路线和工步顺序的确定265.4主轴机械加工工艺规程卡片275.5主轴的工艺分析275.6箱体机械加工工艺规程卡片275.7箱体的工艺分析28第六章 数控加工程序296.1主轴数控加工程序29 6.2箱体数控加工部分的程序31 6.2.1安装面的数控加工31 6.2.2主轴孔的数控加工程序33第七章 毕业设计总结377.1成本分析37 7.2经济效益分析377.3前景预测37结论38参考文献39致谢40附录1专题41附录2外文翻译(外文部分)49附录3外文翻译(中文部分)62附录4主轴机械加工工艺卡片69附录5主轴箱机械加工工艺卡片70第一章绪论随着社会的进步,制造业的发展越来越迅速,数控技术和数控装备是制造工业现代化的重要基础。这个基础是否牢固直接影响到一个国家的经济发展和综合国力,关系到一个国家的战略地位。因此,世界上各工业发达国家均采取重大措施来发展自己的数控技术及其产业。 在我国,数控技术与装备的发展亦得到了高度重视,近年来取得了相当大的进步。现在不仅能够生产车、钻、镗、铣类及磨削和其它类型的数控机床,而且还可以生产各种加工中心、车削中心、柔性制造单元、组合柔性制造单元等高性能、高自动化的数控机床和柔性制造系统。我国数控机床的品种已有200多个,产量已达到年产10000台的水平。特别是在通用微机数控领域,以PC平台为基础的国产数控系统,已经走在了世界前列。但是,我国在数控技术研究和产业发展方面亦存在不少问题,特别是在技术创新能力、商品化进程、市场占有率等方面情况尤为突出。我的设计题目为SSCK20A数控机床主轴和主轴箱箱体数控加工工艺分析及数控加工程序编制,通过对数控机床的箱体设计来加深自己对数控机床的了解,为以后自己进入机械厂这样的工作单位打下基础。由于我所了解的知识有限,所以我的设计难免有缺陷。在本次设计中,有导师,同学的很大帮助,对此非常感谢。第二章数控加工概念数控加工就是泛指在数控机床上进行零件加工的工艺过程。数控机床是一种用计算机来控制的机床,用来控制机床的计算机不管是专用计算机,还是通用计算机都统称为数控系统。数控机床的运动和辅助动作均受控于数控系统发出的指令。在数控机床上加工零件与在普通机床上加工零件,其加工方法并无多大差异,但是在机床的运动控制上却有很大的区别。在普通机床加工时,机床的运动受控于操作工人。如机床的开启、主轴转速的变换、走刀路径、运动部件的位移量,以及机床的停止等都是依靠操作工人来控制的。在数控机床上加工零件时,机床的运动和辅助动作的实现均受控于数控系统发出的指令。而数控系统的指令是由程序员根据工件的材质、加工要求、机床的特性和系统所规定的指令格式编制的。编写加工指令的过程就称为编程。所谓编程,就是把加工零件的工艺过程、工参数、运动要求用数字指令形式记录在介质上,并输入数控系统。数控系统根据程序指令向伺服装置和其它功能部件发出运动或终断信息来控制机床的各种运动。当零件的加工程序结束时,机床便会自动停止。任何一种数控机床,在其数控系统中若没有输入程序指令,数控机床不能工作。2.1、高速、高效、高精度、高可靠性 要提高加工效率,首先必须提高切削和进给速度,同时,还要缩短加工时间;要确保加工质量,必须提高机床部件运动轨迹的精度,而可靠性则是上述目标的基本保证。为此,必须要有高性能的数控装置作保证。 1)高速、高效 机床向高速化方向发展,可充分发挥现代刀具材料的性能,不但可大幅度提高加工效率、降低加工成本,而且还可提高零件的表面加工质量和精度。超高速加工技术对制造业实现高效、优质、低成本生产有广泛的适用性。 新一代数控机床(含加工中心)只有通过高速化大幅度缩短切削工时才可能进一步提高其生产率。超高速加工特别是超高速铣削与新一代高速数控机床特别是高速加工中心的开发应用紧密相关。90年代以来,欧、美、日各国争相开发应用新一代高速数控机床,加快机床高速化发展步伐。高速主轴单元(电主轴,转速15000100000r/min)、高速且高加/减速度的进给运动部件(快移速度60120m/min,切削进给速度高达60m/min)、高性能数控和伺服系统以及数控工具系统都出现了新的突破,达到了新的技术水平。随着超高速切削机理、超硬耐磨长寿命刀具材料和磨料磨具,大功率高速电主轴、高加/减速度直线电机驱动进给部件以及高性能控制系统(含监控系统)和防护装置等一系列技术领域中关键技术的解决,应不失时机地开发应用新一代高速数控机床。 依靠快速、准确的数字量传递技术对高性能的机床执行部件进行高精密度、高响应速度的实时处理,由于采用了新型刀具,车削和铣削的切削速度已达到5000米8000米/分以上;主轴转数在30000转/分(有的高达10万转/分)以上;工作台的移动速度:(进给速度),在分辨率为1微米时,在100米/分(有的到200米/分)以上,在分辨率为0.1微米时,在24米/分以上;自动换刀速度在1秒以内;小线段插补进给速度达到12米/分。根据高效率、大批量生产需求和电子驱动技术的飞速发展,高速直线电机的推广应用,开发出一批高速、高效的高速响应的数控机床以满足汽车、农机等行业的需求。还由于新产品更新换代周期加快,模具、航空、军事等工业的加工零件不但复杂而且品种增多。我们学校的数控加工中心引进的先进数控加工中心设备就是高速的切削,在我国这样转速的加工中心很少,因此,大力发展高速的数控机床是未来的发展方向。2)高精度 从精密加工发展到超精密加工(特高精度加工),是世界各工业强国致力发展的方向。其精度从微米级到亚微米级,乃至纳米级(90的刀具;而副偏角的选择要考虑是否已加工表面轮廓产生干涉。刀具选择是数控加工的工序设计的重要内容之一,它不仅影响机床的加工效率,而且直接影响加工质量。另外数控机床主轴转速比不同机床高12倍,且输出功率大,因此与传统的加工方法相比,数控加工对刀具的要求更高,不仅要求精度高、强度大、刚度好、耐用度高,而且要求尺寸稳定、安装方便。参考机械加工工艺师手册选用微调镗刀。刀具材料采用高速钢。4.7夹具的选择数控加工的特点对夹具提出了两个基本要求:一是保证夹具的坐标方向与机床的坐标方向相对固定:二是能协调零件与机床坐标系的尺寸/除此之外,重点考虑以下几点。1) 单件小批量生产时,优先选用组合夹具,可调夹具和其他通用夹具,以缩短生产准备时间和节省生产费用。2) 在成批生产时,才考虑采用专用夹具,并力求结构简单。3) 零件的装卸要快速、方便、可靠,以缩短机床的停顿时间。4) 夹具上各零部件应不妨碍机床对零件各表面的加工,既夹具要敞开,其定位、夹紧机构元件不能影响加工中的走刀。5) 为提高数控机床的效率,批量较大的零件加工可采用多工位、气动或液压夹具。4.8量具的选择数控加工主要用于单件小批量生产,一般采用通用量具,如游标卡尺、百分表等。查机械加工工艺师手册表55-7我选择杠杆千分表,游标卡尺4.9数控加工工艺路线设计工艺路线的拟定是制定工艺规程的重要内容之一,其主要内容包括:选择各加工表面的加工方法、划分加工阶段、划分工序以及安排工序的先后顺序等。设计者应根据从生产实践中总结出来的一些综合性工艺原则,结合本厂的实际生产条件,提出几种方案,通过对比分析,从中选择最佳方案。选择机械零件的结构形状是多种多样的,但它们都是由平面、外圆柱面、内圆柱面或曲面、成形面等基本表面组成的。每一种表面都有多种加工方法,具体选择时应根据零件的加工精度、表面粗糙、材料、结构形状、尺寸及生产类型等因素,选用相应的加工方法和加工方案。4.9.1外圆表面的加工方法的选择外圆表面的主要加工方法是车小和磨削。当表面粗糙度要求较高时,还要经光整加工。 最终工序为车削的加工方案,适用与淬火钢以外的各种金属。 最终工序为磨削的加工方案,适用与淬火钢,未淬火钢和铸铁,不适用于有色金属,因为有色金属韧性大,磨削时易堵塞砂轮。 最终工序为精细车和金刚车的加工方案,适用于要求较高的有色金属的精加工 最终工序为光整加工,如研磨、超精磨及超精加工等,为提高生产率和加工质量,一般在光整加工前进行精磨。 对表面粗糙度要求高而尺寸精度要求不高的外圆,可采用滚压或抛光。在数控机床上加工的零件,一般按工序集中原则划分工序,划分方法如下。1)按所用的刀具划分 以同一把刀具完成的那一部分工艺过程为一道工序,这种方法适用于工件的待加工表面较多、机床连续工作时间过长、加工程序的编制和检查难道较大等情况。加工中心常用这种方法划分。2)按安装次数划分 以同一把刀具完成的那一部分工艺过程为一道工序。这种方法适用于工件的加工内容不多工件,加工完成后就能达到后达到待检状态。第五章加工工艺规程的编制(1)工序划分的原则工序划分可以采用两种不同的原则,即工序集中原则和工序分散原则。 工序集中原则 是指每道工序包括尽可能多的加工内容,从而使工序的总数减少。如果箱体加工采用工序集中原则,可以高效的专用设备和数控机床,提高生产率;减少工序数目,缩短工艺路线,简化生产计划和生产组织工作;减少机床的数量、操作工人数和占地面积;减少工件装夹次数,不仅保证了个加工表面间的相互位置精度,而且减少夹具数量和装夹工件的辅助时间。缺点是专用设备和工艺装备投资达、调整维修比较麻烦、生产准备周期长,不利于转产。 序分散原则 就是将工件的加工分散在较多的工序内进行,每道工序的加工内容较少,。采用工序分散原则的优点是:加工设备和装备结构简单,调整和维修方便,操作简单,转产容易;有利于选择合理的切削用量,减少机动时间。缺点是工艺路线较长,所需设备和工人较多,占地面积较大。(2)工序的划分方法 工序的划分主要考虑生产纲领、所用设备及零件本身的结构和技术要求等。大批大量生产时,若使用多轴、多刀的高效加工中心,可按工序集中原则组织生产;若在由组合机床组成的自动线上加工,供需一般按分散原则划分。随着现代数控技术的发展,特备是加工中心的应用,工艺路线的安排更多地趋向于工序集中。单件小批生产时,通常采用工序集中原则。成批生产时,可按工序集中原则划分,也可按工序分散原则划分,应视具体情况而定。对于结构尺寸和重量都很大的重型零件,应采用工序集中原则,以减少装夹次数和运输量。对于刚性差、精度高的零件,应按工序需分散原则划分工序。(3)工序集中的划分方法在数控机床上加工的零件,一般按工序集中原则划分工序,划分方法如下: 按所用刀具划分 以同一把刀具完成的那一部份工艺过程维一道工序,这种方法适用于工件的待加工表面较多、机床连续工作时间过长、加工工序的变成和检查难度较大等情况。 按安装次数划分 以一次安装完成的那一部分工艺过程维一道工序。这种方法适用于工件的加工内容不多的工件,加工完成后就能达到待检状态。 按粗、精加工划分 即粗加工中完成的那一部分工艺过程称为一道工序,精加工中完成的那一部分工艺过程称为一道工序。这种划分方法适用于加工后的变形较大,需粗、精加工分开的零。 按加工部位划分 即以完成相同型面的那一部分工艺过程为一道工序,对于加工表面多而复杂的零件,可按其结构特点划分成多道工序。5.1零件加工顺序的安排在选定加工方法、划分工序后,我们要对加工顺序进行安排。零件的加工工序包括切削加工工序、热处理工序、辅助工序(包括表面处理、清洗和检验等),这些工序直接影响到零件的加工质量、生产效率和加工成本。因此我们要合理安排好箱体的切削加工、热处理和辅助工序顺序。5.1.1切削加工工序安排 切削加工工序安排原则包括基面先行原则、先粗后精原则、先主后次原则和先面后孔原则。根据以上的原则,对于主轴我们应该先加工端面,然后一端面作为定位基准再加工台阶轴的各部分外圆面。对于箱体我们首先要把B面先铣好,因为它他是后面加工的定位基准,但我们不采用数控机床加工,可以在普通的铣床上加工。接着我们要根据先粗后精原则和先主后次原则来加工个行孔,为了避免基准不重合引起的误差,我们先加工4650.2,接着先后加工加工150H7行孔,接着先后铣面350、面320、面380、然后镗140行孔、141.5行孔。但是要粗、精分开,粗镗半精镗精镗。5.1.2热处理工序安排 为了提高材料的力学性能、改善材料的切削加工性和消除工件的内应力,箱体在加工之前要进行正火热处理,可以消除在毛坯制造时产生的残余应力,第1页共2页机械加工工艺卡片产品型号零件图号产品名称SSCK20A零件名称主轴序号工序工 序 内 容车间设备工 艺 装 备工等工时单件备注夹具刃具量具辅具0备料10精锻立式精锻机20热处理正火30锯头40铣端面专用机床50粗车车各外圆面卧式车床60热处理调质220240HBS70车大端面卧式车床80粗车仿形车小端各部仿形车床90钻钻打断各孔摇臂钻床第2页共2页机械加工工艺卡片产品型号零件图号产品名称SSCK20A零件名称主轴序号工序工 序 内 容车间设备工 艺 装 备工等工时单件备注夹具刃具量具辅具100热处理高频感应加热淬火110数车精车各外圆并车槽数控车床120粗磨粗磨个外圆万能外圆磨床130精铣铣键槽铣床140精车加工三段螺纹卧式车床150粗精磨粗精磨各外圆万能外圆磨床第1页共6页机械加工工艺卡片产品型号零件图号产品名称SSCK20A零件名称主轴箱体序号工序工 序 内 容车间设备工 艺 装 备工等工时单件备注夹具刃具量具辅具0铸造正火10划线照顾毛坯各部划立车加工线20立车车4650.2两面,各面均留量3mm30划线划镗序加工线40卧镗镗铣A面,B面留量3mm以A面为基面,B面为导向粗镗150(-0.008,+0.002)140(-0.007,+0.003)各孔留量半径3mm过孔留量半径3mm050二次正火060划线划车序加工线第2页共6页机械加工工艺卡片产品型号零件图号产品名称SSCK20A零件名称主轴箱序号工序工 序 内 容车间设备工 艺 装 备工等工时单件备注夹具刃具量具辅具070立车车4650.2尺寸两面,至4650.1mm,两面平行0.1mm080划线划刨、镗序加工线090卧镗1)镗铣A面、B面各留量0.50.6mm铣30尺寸下面达图铣5尺寸空刀至尺寸2)按线铣右视图上部两处135度斜面达图铣:1500.2尺寸上面留量0.5mm钻:2M12底孔 X8(起吊孔)钻:2M12底孔(右上图局部剖)按线钻攻:左、右视图4M16(装配起吊孔)3)以A面为基面、 B面导向粗镗150(-0.008,+0.002)140(-0.007,+0.003)各孔留量半径11.2 mm过孔留量半径 11.2 mm第3页共6页机械加工工艺卡片产品型号零件图号产品名称SSCK20A零件名称主轴箱序号工序工 序 内 容车间设备工 艺 装 备工等工时单件备注夹具刃具量具辅具100数镗以465尺寸左面为基面; 工件压在工作台一角位置, 找正A面在0.1以内, 精铣A、B面(B面精加工用30立铣刀侧刃加工,不许有接刀痕,吃刀深度0.2mm)粗糙度达Ra3.2,平面度达0.05mm110卧镗 1)以465尺寸左面为基面;工件压在工作台一角位置找正A面在0.1以内,铣3X2空刀(根据刀具情况可加工至5X3)2)工作太转90度,包拯350尺寸,铣350尺寸左面达 Ra6.3。3)铣320尺寸两面:左面粗糙度达Ra3.2。4)铣380尺寸右6.3 面。5)钻4M6、2M8底孔。120卧镗以A面为基面,B面导向,上等高垫铁、位置公差军达图纸要求第4页共6页机械加工工艺卡片产品型号零件图号产品名称SSCK20A零件名称 主轴箱序号工序工 序 内 容车间设备工 艺 装 备工等工时单件备注夹具刃具量具辅具半精镗:150(-0.008,+0.002)140(-0.007,+0.003)、141.5孔留量,半径0.50.6mm。半精划:底面留量0.2mm精铣:280范围内,240范围内达Ra1.64650.2至465(+0.2,+0.3)130卧镗1、以465尺寸左面为基面,找正A面。在0.05以内实测140孔尺寸,按实际尺寸计算;精铣 1500.2尺寸上面。要求上面与C、D平行0.03mm。钻4M10底孔2、保证250.2,80尺寸自划线,钻划622X36140装配钳刮研A、B面。25MMX25MM范围内不少于8个点。B A达0.02MM150数镗以A面为基面、B面导向、第5页共6页机械加工工艺卡片产品型号零件图号产品名称SSCK20A零件名称主轴箱序号工序工 序 内 容车间设备工 艺 装 备工等工时单件备注夹具刃具量具辅具保证B面与主轴孔平行0.02上等高垫铁,300(0,+0.1)至300(0,+0.05)。500.1尺寸达500.05mm。保证深度尺寸115(-0.2,-0.1)。精镗141.5过孔至尺寸,精镗:140、150孔。孔径公差按轴承尺寸配镗;160卧镗1)精划Ra1.6底面。精铣:280、240(检查范围)。2)引窝:左视:6M8。 右视:6M10。在右视图125度左侧斜面打编号3) 三坐标检测:按图纸技术要求检测, 孔径用比较仪测量。170钻按窝钻攻:6M8、6M10180钳工各锐角倒钝、去刺第6页共6页机械加工工艺卡片产品型号零件图号产品名称SSCK20A零件名称主轴箱序号工序工 序 内 容车间设备工 艺 装 备工等工时单件备注夹具刃具量具辅具攻丝:4M6、4M12、2M84M10。190喷漆姓名: 任务下达日期: 年月日设计(论文)开始日期: 年 月 日设计(论文)完成日期: 年 月 日一、设计(论文)题目:SSCK20A数控车床主轴及主轴箱的数控加工及数控编程 二、专题题目: 数控五轴技术及数控编程 三、设计的目的和意义:随着社会的进步,制造业的发展越来越迅速,数控技术和数控装备是制造工业现代化的重要基础。这个基础是否牢固直接影响到一个国家的经济发展和综合国力,关系到一个国家的战略地位。因此,世界上各工业发达国家均采取重大措施来发展自己的数控技术及其产业。在我国,数控技术与装备的发展亦得到了高度重视,近年来取得了相当大的进步。数控机床发展很快,作为数控机床的重要部分,主轴箱的设计更新也越来越快。四、设计(论文)主要内容:(1)SSCK20A数控车床的主轴箱展开图(1张0号)、主轴零件图(1张1号)、箱体零件图(1张0号)、带轮零件图(1张2号)、前端盖零件图(1张2号);(2)主轴及主轴箱的加工工艺规程;(3)主轴及主轴箱的部分加工工艺的数控程序;五、设计目标:主要完成对SSCK20A数控车床的主轴及主轴箱加工工艺规程设计以及部分加工工艺数控程序的编制。六、进度计划: 2007年3月13日至3月31日进行为期3周的生产实习;4月1日至4月10日完成对设计题目的资料收集与查询;4月11日至5月10日完成对设计图纸的绘制;5月11日至6月10日完成毕业设计说明书的编写;6月11日至6月20日最后的审稿及说明书和图纸的打印。 七、参考文献资料:许镇宇.机械零件.北京:高等教育出版社,1983;孔庆复.计算机辅助设计与制造.哈尔滨:哈尔滨工业大学出版社,1994;雷宏.机械工程基础.哈尔滨:黑龙江出版社 2002;王中发.实用机械设计.北京:北京理工大学出版社 1998; 唐宗军.机械制造基础.大连:机械工业出版社 1997;吴祖育,秦鹏飞.数控机床.上海:上海科学技术出版社 2003;许翔泰,刘艳芳. 数控加工编程实用技术.北京:机械工业出版社2000;吴明友.数控机床加工技术 东南大学出版社.江苏:2000;王宝成.现代数控机床.天津:天津科学技术出版社,2000;廖效果,朱启俅.数字控制机床.江西:华中科技大学出版社,2002;王卫兵.数控编程100例.机械工业出版社,2004;张树森.机械工程学.辽宁;东北大学出版社,2001;应云天.俄文翻译手册.北京:高等教育出版社,1999;金蓓.数控加工的编程技巧.航空精密制造技术.成都:2002,2;邓星钟. 机电传动控制(第三版). 武汉: 华中科技大学出版社, 2001; 指 导 教 师: 院(系)主管领导: 年 月 日附录2 外文翻译(外文部分)ADVANCED MACHINING PROCESSES As the hardware of an advanced technology becomes more complex, new and visionary approaches to the processing of materials into useful products come into common use. 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 vari
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