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目 录前 言11 工艺规程制定21.1机械加工工艺规程制订21.2机械加工工艺规程的组成21.3制订机械加工工艺规程的原始资料22 零件的分析32.1零件的作用32.2零件的工艺分析33 工艺规程设计43.1基准面的选择43.1.1 粗基准的选择原则43.1.2 精基准的选择原则43.2 制定工艺路线53.3 确定各工序的加工余量、计算工序尺寸及公差63.4 基本工时的确立84 钻夹具设计194.1定位基准的选择194.2定位元件的设计194.3切削力及夹紧力计算194.5夹紧力的确定204.5钻套设计214.6夹具设计及操作简要说明23结 论24前 言 机械制造业是制造具有一定形状位置和尺寸的零件和产品，并把它们装备成机械装备的行业。机械制造业的产品既可以直接供人们使用，也可以为其它行业的生产提供装备，社会上有着各种各样的机械或机械制造业的产品。我们的生活离不开制造业，因此制造业是国民经济发展的重要行业，是一个国家或地区发展的重要基础及有力支柱。从某中意义上讲，机械制造水平的高低是衡量一个国家国民经济综合实力和科学技术水平的重要指标。锥齿轮座的加工工艺规程及其钻、攻4-M8螺纹孔的夹具是在学完了机械制图、机械制造技术基础、机械设计、机械工程材料等进行毕业设计之后的下一个教学环节。正确地解决一个零件在加工中的定位，夹紧以及工艺路线安排，工艺尺寸确定等问题，并设计出专用夹具，保证零件的加工质量。本次设计也要培养自己的自学与创新能力。因此本次设计综合性和实践性强、涉及知识面广。所以在设计中既要注意基本概念、基本理论，又要注意生产实践的需要，只有将各种理论与生产实践相结合，才能很好的完成本次设计。本设计选用锥齿轮座来进行工艺编制与夹具设计，以说明书、绘图为主，设计手册与国家标准为附来进行详细说明。1 工艺规程制定1.1机械加工工艺规程制订1、工艺规程 规定产品或零部件制造工艺过程和操作方法等的工艺文件。2、制订工艺规程的原则 保证图样上规定的各项技术要求，有较高的生产效率，技术先进，经济效益高，劳动条件良好。3、制订工艺规程的原始资料 4、制订工艺规程的程序 计算生产纲领，确定生产类型；分析产品装配图，对零件图样进行工艺审查；确定毛坯的种类、形状、尺寸及精度；拟订工艺路线（划分工艺过程的组成、选择定位基准、选择零件表面的加工方法、安排加工顺序、选择机床设备等）；进行工序设计（确定各工序加工余量、工序尺寸及公差，选择工艺装备，计算时间定额等；确定工序的技术要求及检验方法，填写工艺文件。1.2机械加工工艺规程的组成工艺过程由若干个按着一定顺序排列的工序组成。工序是工艺过程的基本单元，也是生产组织和计划的基本单元。工序又可细分为若干个安装、工位及工步等。1、 工序 一个或一组人，在一个工作地对同一个或同时对几个工件所连续完成的一部分工艺过程。2、 安装 工件经一次装夹后所完成的那一部分工序3、 工位 为了完成一定的工序部分，一次装夹工件后，工件与夹具或设备的可动部分相对刀具或设备的固定部分占据每一位置所完成的那部分工序。4、 工步 在加工表面和加工工具不变的情况下所连续完成的那一部分工序5、 走刀 在一个工步内当被加工表面的切削余量较大，需分几次切削时，则每进行一次切削称为一次走刀。1.3制订机械加工工艺规程的原始资料产品装配图及零件图；产品质量的验收标准；产品的生产纲领及生产类型；原材料及毛坯的生产水平；现场生产条件（机床设备与工艺装备、工人技术水平等）；国内外有关工艺、技术发展状况。2 零件的分析2.1零件的作用 锥齿轮座是一个典型的交叉孔零件，主要应用在混凝土拖泵中导向轮部件上，其上要安装两个配对锥齿轮座，因此主要的工作表面为90mm和52mm的两个孔。 2.2零件的工艺分析对该零件的平面、孔和螺纹进行加工，具体要求如下：155下端面 粗糙度Ra6.373孔 粗糙度Ra6.390孔 粗糙度Ra1.6155上端面 粗糙度Ra3.2100端面 粗糙度Ra6.3100外圆 粗糙度Ra1.680沉孔 粗糙度Ra6.382端面 粗糙度Ra6.352孔 粗糙度Ra1.64-M8螺纹 粗糙度Ra12.5M3螺纹 粗糙度Ra12.53-M6螺纹 粗糙度Ra12.54-M5螺纹 粗糙度Ra12.52-8锥孔 粗糙度Ra6.3 3 工艺规程设计3.1基准面的选择基面的选择是工艺规程设计中的重要工作之一。基面选择的正确、合理，可以保证质量，提高生产效率。否则，就会使加工工艺过程问题百出，严重的还会造成零件大批报废，使生产无法进行。3.1.1 粗基准的选择原则1）如果必须首先保证工件上加工表面与不加工表面 之间的位置要求，应以不加工表面作为粗基准。如果在工件上有很多不需加工的表面，则应以其中与加工面位置精度要求较高的表面作粗基准。2）如果必须首先保证工件某重要表面的加工余量均匀，应选择该表面作精基准。3）如需保证各加工表面都有足够的加工余量，应选加工余量较小的表面作粗基准。4）选作粗基准的表面应平整，没有浇口、冒口、飞边等缺陷，以便定位可靠。5）粗基准一般只能使用一次，特别是主要定位基准，以免产生较大的位置误差。3.1.2 精基准的选择原则选择精基准时要考虑的主要问题是如何保证设计技术要求的实现以及装夹准确、可靠、方便。精基准选择应当满足以下要求：1）用设计基准作为定位基准，实现“基准重合”，以免产生基准不重合误差。2）当工件以某一组精基准定位可以较方便地加工很多表面时，应尽可能采用此组精基准定位，实现“基准统一”，以免生产基准转换误差。3）当精加工或光整加工工序要求加工余量尽量小而均匀时，应选择加工表面本身作为精基准，即遵循“自为基准”原则。该加工表面与其他表面间的位置精度要求由先行工序保证。4）为获得均匀的加工余量或较高 的位置精度，可遵循“互为基准”、反复加工的原则。5）有多种方案可供选择时应选择定位准确、稳定、夹紧可靠，可使夹具结构简单的表面作为精基准。 3.2 制定工艺路线制定工艺路线的出发点，应当是使零件的几何形状、尺寸精度及位置精度等技术要求能得到合理的保证。在生产纲领以确定为大批生产的条件下，可采用通用机床配以专用工夹具，并尽量使工序集中来提高生产效率。除此以外，还应考虑经济效果，以便降低生产成本。最终工艺方案如下：工序01：金属型浇注工序02：时效处理以消除内应力工序03：以155外圆作为定位基准，粗车155下端面、73孔、90孔、半精车90孔工序04：以90孔作为定位基准，粗车155上端面、100端面、100外圆、80沉孔 、半精车155上端面、100外圆、精车100外圆、洁角工序05：以155外圆作为定位基准，精车90孔、车槽工序06：以90孔作为定位基准，粗车82端面、52孔、半精车、精车52孔工序07：以90孔作为定位基准，钻4-M8螺纹底孔6.8深21、攻4-M8深18螺纹工序08：以90孔作为定位基准，钻M3螺纹底孔2.55深8、攻M3深6螺纹工序09：以90孔作为定位基准，钻3-M6螺纹底孔5.1深15、攻M6深12螺纹工序10：以73孔作为定位基准，钻4-M5螺纹底孔4.25深15、攻M5深12螺纹工序11：以90孔作为定位基准，配作2-8锥孔工序12：钳工去毛刺工序13：检验至图纸要求工序14：包装、入库3.3 确定各工序的加工余量、计算工序尺寸及公差 1. 155下端面的加工余量查机械制造工艺设计简明手册表2.2-4，得铸件的单边加工余量Z=2.5mm,铸件尺寸公差为CT8级，表面粗糙度Ra为6.3。根据机械制造工艺设计简明手册表1.4-8，一步车削（即粗车、半精车）方可满足其精度要求。2. 73孔的加工余量查机械制造工艺设计简明手册表2.2-4，得铸件的单边加工余量Z=1.5mm,铸件尺寸公差为CT8级，表面粗糙度Ra为6.3。根据机械制造工艺设计简明手册表1.4-8，一步车削（即粗车、半精车）方可满足其精度要求。3. 90孔 的加工余量查机械制造工艺设计简明手册表2.2-4，得铸件的单边加工余量Z=8.5mm,铸件尺寸公差为CT8级，表面粗糙度Ra为1.6。根据机械制造工艺设计简明手册表1.4-8，三步车削（即粗车、半精车、精车）方可满足其精度要求。粗车 单边余量Z=8.0mm半精车 单边余量Z=0.4mm精车 单边余量Z=0.1mm4. 155上端面的加工余量查机械制造工艺设计简明手册表2.2-4，得铸件的单边加工余量Z=2.5mm,铸件尺寸公差为CT8级，表面粗糙度Ra为3.2。根据机械制造工艺设计简明手册表1.4-8，两步车削（即粗车、半精车）方可满足其精度要求。粗车 单边余量Z=2.0mm半精车 单边余量Z=0.5mm5. 100端面 的加工余量查机械制造工艺设计简明手册表2.2-4，得铸件的单边加工余量Z=2.0mm,铸件尺寸公差为CT8级，表面粗糙度Ra为6.3。根据机械制造工艺设计简明手册表1.4-8，一步车削（即粗车）方可满足其精度要求。6. 100外圆的加工余量查机械制造工艺设计简明手册表2.2-4，得铸件的单边加工余量Z=1.5mm,铸件尺寸公差为CT8级，表面粗糙度Ra为1.6。根据机械制造工艺设计简明手册表1.4-8，三步车削（即粗车、半精车、精车）方可满足其精度要求。粗车 单边余量Z=1.0mm半精车 单边余量Z=0.4mm精车 单边余量Z=0.1mm 7.80沉孔 的加工余量查机械制造工艺设计简明手册表2.2-4，得铸件的单边加工余量Z=3.5mm,铸件尺寸公差为CT8级，表面粗糙度Ra为6.3。根据机械制造工艺设计简明手册表1.4-8，一步车削（即粗车）方可满足其精度要求。8.82端面加工余量查机械制造工艺设计简明手册表2.2-4，得铸件的单边加工余量Z=2.0mm,铸件尺寸公差为CT8级，表面粗糙度Ra为6.3。根据机械制造工艺设计简明手册表1.4-8，一步车削（即粗车）方可满足其精度要求。9.52孔加工余量查机械制造工艺设计简明手册表2.2-4，得铸件的单边加工余量Z=1.5mm,铸件尺寸公差为CT8级，表面粗糙度Ra为1.6。根据机械制造工艺设计简明手册表1.4-8，三步车削（即粗车、半精车、精车）方可满足其精度要求。粗车 单边余量Z=1.0mm半精车 单边余量Z=0.4mm精车 单边余量Z=0.1mm10. 4-M8螺纹的加工余量查机械制造工艺设计简明手册表2.2-4，因其加工螺纹的尺寸不大故采用实心铸造，铸件尺寸公差为CT8级，表面粗糙度Ra为12.5。根据机械制造工艺设计简明手册表1.4-8，钻.攻即可方可满足其精度要求。钻 单边余量Z=3.4mm攻 单边余量Z=0.6mm11. M3螺纹的加工余量查机械制造工艺设计简明手册表2.2-4，因其加工螺纹的尺寸不大故采用实心铸造，铸件尺寸公差为CT8级，表面粗糙度Ra为12.5。根据机械制造工艺设计简明手册表1.4-8，钻.攻即可方可满足其精度要求。钻 单边余量Z=1.275mm攻 单边余量Z=0.225mm12. 3-M6螺纹的加工余量查机械制造工艺设计简明手册表2.2-4，因其加工螺纹的尺寸不大故采用实心铸造，铸件尺寸公差为CT8级，表面粗糙度Ra为12.5。根据机械制造工艺设计简明手册表1.4-8，钻.攻即可方可满足其精度要求。钻 单边余量Z=2.55mm攻 单边余量Z=0.45mm13. 4-M5螺纹的加工余量查机械制造工艺设计简明手册表2.2-4，因其加工螺纹的尺寸不大故采用实心铸造，铸件尺寸公差为CT8级，表面粗糙度Ra为12.5。根据机械制造工艺设计简明手册表1.4-8，钻.攻即可方可满足其精度要求。钻 单边余量Z=2.125mm攻 单边余量Z=0.375mm14. 2-8锥孔的加工余量查机械制造工艺设计简明手册表2.2-4，因其加工表面的尺寸不大故采用实心铸造,铸件尺寸公差为CT8级，表面粗糙度Ra为6.3。根据机械制造工艺设计简明手册表1.4-8，一步钻削方可满足其精度要求。 3.4 基本工时的确立工序01：金属型浇注工序02：时效处理以消除内应力工序03：以155外圆作为定位基准，粗车155下端面、73孔、90孔、半精车90孔工步一：粗车155下端面 1、 切削用量机床为C620-1型卧式车床， 所选刀具为YT5硬质合金端面车刀。根据切削用量简明手册第一部分表1.1，由于C620-1型卧式车床的中心高度为200mm（表1.30），故选刀杆尺寸BH=16mm25mm，刀片厚度为4.5mm。根据表1.3，选择车刀几何形状为卷屑槽带倒棱型前刀面，前角，后角，主偏角，副偏角，刃倾角，刀尖圆弧半径。1） 确定切削深度由于单边余量为2.5mm，可在1次走刀内切完。2） 确定进给量根据表1.4，在粗车QT500-7、刀杆尺寸为16mm25mm、3mm、工件直径为0100mm时，=0.10.6mm/r按C620-1型卧式车床的进给量（表4.2-9），选择=0.27mm/r确定的进给量尚需满足机床进给机构强度的要求，故需进行校验。根据表1.30，C620-1机床进给机构允许的进给力=3530N。根据表1.21，当2mm,0.35mm/r，=450m/min(预计)时，进给力=760N。的修正系数为=0.1，=1.17（表1.29-2），故实际进给力为 =7601.17N=889.2N 由于切削时的进给力小于机床进给机构允许的进给力，故所选=0.27mm/r可用。3） 选择车刀磨钝标准及耐用度 根据表1.9，车刀后刀面最大磨损量取为1mm，可转位车刀耐用度T=30min。4） 确定切削速度切削速度可根据公式计算，也可直接由表中查出。现采用查表法确定切削速度。根据表1.10，当用YT15硬质合金车刀加工铸件，3mm，0.25mm/r，切削速度=450m/min。切削速度的修正系数为=0.8，=0.65，=0.81,=1.15,=1.0(均见表1.28），故=4500.80.650.811.15m/min218m/min 448r/min 按C620-1机床的转速(表4.2-8），选择=460r/min 则实际切削速度=218m/min5） 校验机床功率由表1.24，3mm，0.27mm/r，46m/min时，=1.7KW。切削功率的修正系数=1.17，=1.13，=0.8，=0.65（表1.28），故实际切削时的功率为=0.72KW根据表1.30，当=460r/min时，机床主轴允许功率=5.9KW。 F所以,时工件不会转动,故本夹具可安全工作。根据工件受力切削力、夹紧力的作用情况，找出在加工过程中对夹紧最不利的瞬间状态，按静力平衡原理计算出理论夹紧力。最后为保证夹紧可靠，再乘以安全系数作为实际所需夹紧力的数值。即：安全系数K可按下式计算有：式中：为各种因素的安全系数，查参考文献5表可得： 所以有： 该孔的设计基准为中心轴，故以回转面做定位基准，实现“基准重合”原则；参考文献，因夹具的夹紧力与切削力方向相反，实际所需夹紧力F夹与切削力之间的关系F夹KF轴向力：F夹KF （N）扭距：Nm在计算切削力时必须把安全系数考虑在内，安全系数由资料机床夹具设计手册查表可得：切削力公式： 式（2.17）式中 查表得： 即：实际所需夹紧力：由参考文献16机床夹具设计手册表得： 安全系数K可按下式计算，由式（2.5）有：式中：为各种因素的安全系数，见参考文献16机床夹具设计手册表 可得： 所以 由计算可知所需实际夹紧力不是很大，为了使其夹具结构简单、操作方便，决定选用螺旋夹紧机构。1.1.4 4.4 钻孔与工件之间的切屑间隙钻套的类型和特点:1、固定钻套：钻套直接压入钻模板或夹具体的孔中，钻模板或夹具体的孔与钻套外圆一般采用H7/n6配合，主要用于加工量不大，磨损教小的中小批生产或加工孔径甚小，孔距离精度要求较高的小孔。2、可换钻套：主要用在大批量生产中，由于钻套磨损大，因此在可换钻套和钻模板之间加一个衬套，衬套直接压入钻模板的孔内，钻套以F7/m6或F7/k6配合装入衬套中。3、快换钻套：当对孔进行钻铰等加工时，由于刀径不断增大，需要不同的导套引导刀具，为便于快速更换采用快换钻套。4、特殊钻套：尺寸或形状与标准钻套不同的钻套统称特殊钻套。钻套下端面与工件表面之间应留一定的空隙C，使开始钻孔时，钻头切屑刃不位于钻套的孔中，以免刮伤钻套内孔，如图4.3。图4.3 切屑间隙 C=(0.31.2)d。在本次夹具钻模设计中考虑了多方面的因素，确定了设计方案后，选择了C=8。因为此钻的材料是铸件，所以C可以取较小的值。1.1.5 4.5 钻模板在导向装置中，导套通常是安装在钻模板上，因此钻模板必须具有足够的刚度和强度，以防变形而影响钻孔精度。钻模板按其与夹具体连接的方式，可分为固定式钻模板、铰链式钻模板、可卸式钻模板、滑柱式钻模板和活动钻模板等。在此套钻模夹具中选用的是可卸式钻模板，在装卸工件时需从夹具体上装上或卸下，钻螺栓紧固，钻模精度较高。41.1.6 4.6定位误差的分析3) 夹具安装误差因夹具在机床上的安装不精确而造成的加工误差，称为夹具的安装误差。1.1.7 图5-2中夹具的安装基面为平面，因而没有安装误差，=0.4) 夹具误差因夹具上定位元件、对刀或导向元件、分度装置及安装基准之间的位置不精确而造成的加工误差，称为夹具误差。夹具误差主要包括定位元件相对于安装基准的尺寸或位置误差；定位元件相对于对刀或导向元件（包含导向元件之间）的尺寸或位置误差；导向元件相对于安装基准的尺寸或位置误差；若有分度装置时，还存在分度误差。以上几项共同组成夹具误差。5) 加工方法误差因机床精度、刀具精度、刀具与机床的位置精度、工艺系统的受力变形和受热变形等因素造成的加工误差，统称为加工方法误差。因该项误差影响因素多，又不便于计算，所以常根据经验为它留出工件公差的1/3.计算时可设。2. 保证加工精度的条件工件在夹具中加工时，总加工误差为上述各项误差之和。由于上述误差均为独立随机变量，应用概率法叠加。因此保证工件加工精度的条件是即工件的总加工误差应不大于工件的加工尺寸。为保证夹具有一定和夹具总图上各项公差值确定得是否合理。知此方案可行。在分析计算工件加工精度时，需留出一定的精度储备量。因此将上式改写为或 当时，夹具能满足工件的加工要求。值的大小还表示了夹具使用寿命的长短和夹具总图上各项公差值确定得是否合理。知此方案可行。4.7 钻套、衬套、钻模板设计与选用工艺孔的加工只需钻切削就能满足加工要求。故选用可换钻套（其结构如下图所示）以减少更换钻套的辅助时间。为了减少辅助时间采用可换钻套，以来满足达到孔的加工的要求。表dDD1Ht基本极限偏差F7基本极限偏差D601+0.016+0.0063+0.010+0.004669-0.00811.84+0.016+0.00871.82.6582.63698121633.3+0.022+0.0103.347+0.019+0.010104581156101110162068+0.028+0.01112+0.023+0.0121581015181220251012+0.034+0.0161822121522+0.028+0.01526162836151826300.0121822+0.041+0.02030342036HT200222635+0.033+0.017392630424625HT200563035+0.050+0.0254852354255+0.039+0.02059305667424811066485070740.040钻模板选用固定钻模板，用沉头螺钉锥销定位于夹具体上。1.1.8 4.8 确定夹具体结构和总体结构对夹具体的设计的基本要求（1）应该保持精度和稳定性在夹具体表面重要的面，如安装接触位置，安装表面的刀块夹紧安装特定的，足够的精度，之间的位置精度稳定夹具体，夹具体应该采用铸造，时效处理，退火等处理方式。（2）应具有足够的强度和刚度保证在加工过程中不因夹紧力，切削力等外力变形和振动是不允许的，夹具应有足够的厚度，刚度可以适当加固。（3）结构的方法和使用应该不错夹较大的工件的外观，更复杂的结构，之间的相互位置精度与每个表面的要求高，所以应特别注意结构的过程中，应处理的工件，夹具，维修方便。再满足功能性要求（刚度和强度）前提下，应能减小体积减轻重量，结构应该简单。（4）应便于铁屑去除在加工过程中，该铁屑将继续在夹在积累，如果不及时清除，切削热的积累会破坏夹具定位精度，铁屑投掷可能绕组定位元件，也会破坏的定位精度，甚至发生事故。因此，在这个过程中的铁屑不多，可适当增加定位装置和夹紧表面之间的距离增加的铁屑空间：对切削过程中产生更多的，一般应在夹具体上面。（5）安装应牢固、可靠夹具安装在所有通过夹安装表面和相应的表面接触或实现的。当夹安装在重力的中心，夹具应尽可能低，支撑面积应足够大，以安装精度要高，以确保稳定和可靠的安装。夹具底部通常是中空的，识别特定的文件夹结构，然后绘制夹具布局。图中所示的夹具装配。加工过程中，夹具必承受大的夹紧力切削力，产生冲击和振动，夹具的形状，取决于夹具布局和夹具和连接，在因此夹具必须有足够的强度和刚度。在加工过程中的切屑形成的有一部分会落在夹具，积累太多会影响工件的定位与夹紧可靠，所以夹具设计，必须考虑结构应便于铁屑。此外，夹点技术，经济的具体结构和操作、安装方便等特点，在设计中还应考虑。在加工过程中的切屑形成的有一部分会落在夹具，切割积累太多会影响工件的定位与夹紧可靠，所以夹具设计，必须考虑结构应便排出铁屑。 结 论课程设计即将结束了，时间虽然短暂但是它对我们来说受益菲浅的，通过这次的课程设计使我们不再是只知道书本上的空理论，不再是纸上谈兵，而是将理论和实践相结合进行实实在在的设计，使我们不但巩固了理论知识而且掌握了设计的步骤和要领，使我们更好的利用图书馆的资料，更好的更熟练的利用我们手中的各种设计手册和AUTOCAD等制图软件，为我们进行毕业设计打下了良好的基础。课程设计使我们认识到了只努力的学好书本上的知识是不够的，还应该更好的做到理论和实践的结合。因此同学们非常感谢老师给我们的辛勤指导，使我们学到了好多，也非常珍惜学院给我们的这次设计的机会。致 谢这次课程设计使我收益不小，为我今后的学习和工作打下了坚实和良好的基础。但是，查阅资料尤其是在查阅切削用量手册时，数据存在大量的重复和重叠，由于经验不足，在选取数据上存在一些问题，不过我的指导老师每次都很有耐心地帮我提出宝贵的意见，在我遇到难题时给我指明了方向，最终我很顺利的完成了课程设计。这次课程设计成绩的取得，与指导老师的细心指导是分不开的。在此，我衷心感谢我的指导老师，特别是每次都放下她的休息时间，耐心地帮助我解决技术上的一些难题，她严肃的科学态度，严谨的治学精神，精益求精的工作作风，深深地感染和激励着我。从课题的选择到项目的最终完成，她都始终给予我细心的指导和不懈的支持。多少个日日夜夜，她不仅在学业上给我以精心指导，同时还在思想、生活上给我以无微不至的关怀，除了敬佩指导老师的专业水平外，她的治学严谨和科学研究的精神也是我永远学习的榜样，并将积极影响我今后的学习和工作。在此谨向指导老师致以诚挚的谢意和崇高的敬意。 参 考 文 献1， 邹青 主编 机械制造技术基础课程设计指导教程 北京： 机械工业出版社 2004，8 2， 赵志修 主编 机械制造工艺学 北京： 机械工业出版社 1984，23， 孙丽媛 主编 机械制造工艺及专用夹具设计指导 北京：冶金工业出版社 2002，12 4， 李洪 主编 机械加工工艺手册 北京： 北京出版社 1990，125， 邓文英 主编 金属工艺学 北京： 高等教育出版社 20006， 黄茂林 主编 机械原理 重庆： 重庆大学出版社 2002，77， 丘宣怀 主编 机械设计 北京： 高等教育出版社 19978， 储凯 许斌 等主编 机械工程材料 重庆： 重庆大学出版社 1997，129， 廖念钊 主编 互换性与技术测量 北京： 中国计量出版社 2000，110，乐兑谦 主编 金属切削刀具 北京： 机械工业出版社 1992，1211，李庆寿 主编 机床夹具设计 北京： 机械工业出版社 1983，412，陶济贤 主编 机床夹具设计 北京： 机械工业出版社 1986，413， 机床夹具结构图册 贵州：贵州人民出版社 1983，714，龚定安 主编 机床夹具设计原理 陕西：陕西科技出版社，1981,715，李益民 主编 机械制造工艺学习题集 黑龙江： 哈儿滨工业大学出版社 1984, 716, 周永强等 主编 高等学校毕业设计指导 北京： 中国建材工业出版社 2002,1217，李益民等 主编 机械制造工艺设计简明手册 北京： 机械工业出版社 1992，1218，徐鸿本等 主编 切削手册 北京： 机械工业出版社 2003，1130A functional approach for the formalization of the fixture design processR. Huntera, J. Riosb,*, J.M. Pereza, A. VizanaaDepartment of Mechanical and Manufacturing Engineering, Escuela Tecnica Superior de Ingenieros Industriales, Universidad Politecnica de Madrid,Jose Gutierrez Abascal, 2, 28006 Madrid, SpainbCurrently in Enterprise Integration (Bldg 53), Cranfield University, Cranfield, MK43 0AL, UKReceived 14 January 2005; accepted 14 April 2005Available online 26 August 2005AbstractThe design of machining fixtures is a highly complex process that relies on designer experience and his/her implicit knowledge to achievea good design. In order to facilitate its automation by the development of a knowledge-based application, the explicit definition of the fixturedesign process and the knowledge involved is a prior and a fundamental task to undertake. Additionally, a fundamental and well-knownengineering principle shouldbe considered: the functional requirements and their associated constraints should be the first input toany designprocess. Considering these two main ideas, this paper presents the development undertaken to facilitate the automation of the fixture designprocess based on a functional approach.In this context, the MOKA methodology has been used to elicit fixtures knowledge. IDEF0 and UML have been used to represent thefixture design process. A methodology based on the function concept and aiming to formalize such design process is proposed. Fixturefunctional requirements have beendefined and formalized. Functional fixtures elements havebeen used tocreate a functionaldesign solution,the link of these elements with the functional requirements and with typical commercial fixture components has been defined via tables andrules mapping. And finally, a prototype knowledge-based application has been developed in order to make an initial validation of theproposed methodology.q 2005 Elsevier Ltd. All rights reserved.Keywords: Fixture design process; Fixture knowledge modelling, Fixture functional requirements1. IntroductionThe main objective of any design theory is to provide asuitable framework and methodology for the definition ofa sequence of activities that conform the design process of aproduct or system 1. In general, all of them identifyrequirements as the starting point in the design process. Infact, the engineering discipline dealing with product designcan be defined as the one that considers scientific andengineering knowledge to create product definitions anddesign solutions based on ideas and concepts derived fromrequirements and constraints 24.For this research, a relevant issue when consideringrequirements, taking this as a general concept, is to makeexplicit the meaning of two main terms: FunctionalRequirement (FR) and Constraint (C). A functionalrequirement, as it stated by different authors, representswhat the product has to or must do independently of anypossible solution, 2,4. A FR is a kind of requirement, andconsidering some basic principles widely recognized in thefield of Requirements Engineering, we could add it is aunique and unambiguous statement in natural language of asingle functionality, written in a way that it can be ranked,traced, measured, verified, and validated. A constraintcan be defined as a restriction that in general affects somekind of requirement, and it limits the range of possiblesolutions while satisfying the requirements. So, a constraintshould be always linked to a requirement, and its purpose isto narrow the design outcome to acceptable solutions.Considering the Theory of Axiomatic Design 4,functional requirements should be defined in the functionaldomain, which brings on the scene the issue of how to defineand represent the functionality of a product. The way used torepresent it will affect the reasoning process of the designer,and in that sense, the mapping between the functionalInternational Journal of Machine Tools & Manufacture 46 (2006) 683697/locate/ijmactool0890-6955/$ - see front matter q 2005 Elsevier Ltd. All rights reserved.doi:10.1016/j.ijmachtools.2005.04.018*Corresponding author. Tel.: C44 1234 754936; fax.: C44 1234750852.E-mail address: j.rioscranfield.ac.uk (J. Rios).and the physical domains, being the later the one where thedesign solutions are developed. Several authors haveinvestigated the concept of functionality and functionalrepresentation 2,58. Their design approach provides aview based on the Function-Behaviour-Structure frame-work, where function is defined using structure andbehaviour 6. The objective is to fill the gap that allowsa designer to progress from FRs to physical designsolutions. The approach is that product functions areachieved by means of its structure, which seems to lead toan iterative causal approach, where solutions are soughtuntil the selected structure causes the intended functionality.The approach adopted in the research presented in this paperis based on the definition of Fixture Functional Components(FFC), which can satisfy the fixture functionality, and on themapping between such FFC and fixture commercialelements.An advanced approach to the definition of requirementsand functions comes from the creation of ontologies. Theontological approach pursues the definition of the meaningof terms making use of some kind of logic, and the definitionof axioms to enable automatic deduction and reasoning 9.The ontological approach has got a higher relevance sincethe representation of knowledge is considered the key factorin whatever engineering process, and it has been recognizedas a way to facilitate the integration of engineeringapplications 10, to describe functional design knowledge7, and to define requirements 11. Considering a puristapproach, if an ontology does not include axioms to enablereasoning then it could be considered more like aninformation model, and in this sense, this is the approachdeveloped in the work presented in this paper.When considering the methodologies developed for thedesign of fixtures, it can be stated that in general they arerational and propose a series of steps to follow. For example,the methodologies proposed by Scallan and Henriksen 12,13, make use of this approach to describe in general termsthe information needed in each stage of the fixture designprocess. Basically, the importance of modelling in detailsuch information, which mainly is related to fixturerequirements, fixture functionality, fixture components,manufacturing resources, manufacturing processes, anddesign rules; resides on the possibility to automate thedesign process through the development of a knowledge-based application or system. It is relevant to mention thatseveral authors have already aimed to develop knowledge-based applications for fixture design, none of them based ona functional approach, some of the most recently publishedworks can be found in the Refs. 1419.Inthefollowingsections,thispaperpresentsamethodology to formalize the design process of machin-ingfixturesbasedontheengineeringconceptsoffunctional requirements and fixture functions 20. Theformalization of the functional requirements is achievedthrough the application of a structured way of specifica-tion via natural language. Additionally, IDEF0, MOKAmethodology, and UML diagrams are used to capture,represent and formalize knowledge, being the ultimategoal to facilitate the automation of the fixture designprocess.The IDEF0 method is used to create an activity model ofthe fixture design process, allowing the identification of theinformation used in each one of the different tasks itcomprises. UML has been used to complement the IDEF0model by representing the interaction between the activitiesof the process. The MOKA methodology together withUML, are used to capture and represent knowledge involvedin the fixture design process. Finally, to validate theproposed methodology, partial results obtained from thedevelopment of a prototype knowledge-based applicationare presented.2. Analysis of machining fixtures requirementsIn Section 1, two terms have been defined: functionalrequirement and constraint. Requirements have alwaysexisted, the way in which they are expressed, and howthey are integrated in the product design process, are aspectsthat are addressed from different disciplines, for example:product design engineering and requirements engineeringamong others. In general, Requirements Engineering refersto the discipline dealing with the capture, formalization,representation, analysis, management and verification ofrequirements fulfilment. However, all these aspects need tobe integrated in the product design process, and require-ments should lead to the definition of the possible productdesign solutions, which in general demands an integratedview of the requirements issue. It is important to keep inmind that the development of such discipline is stronglyrelated to Software Engineering and Systems Engineering,and in fact much of the research related to requirementscome from authors from these engineering areas 2123.When considering the analysis of requirements, prob-ably, the first aspect to think about is how the requirementsare represented or declared. As it has been previouslymentioned, the way of expressing requirements definitivelyaffects their interpretation and the creation of a designsolution. In this sense, it is widely accepted, that the use ofnatural language is the most common way of expressingrequirements and in consequence, their writing becomes animportant issue. The anatomy proposed by Alexander et al.24 to write requirements in a semi-structured way is usedas basis to declare the functional requirements andconstraints of fixtures 20.In machining, work holding is a key aspect, and fixturesare the elements responsible to satisfy this general goal. Intheir design process, the starting point is the definition of themachining fixtures functional requirements and constraints.Usually, a fixture solution is made of one or several physicalelements, as a whole the designed fixture solution mustsatisfy all the FRs and the associated Cs. Centring, locating,R. Hunter et al. / International Journal of Machine Tools & Manufacture 46 (2006) 683697684orientating, clamping, and supporting, can be considered thefunctional requirements of fixtures, what a fixture must doindependently of any particular solution. In terms ofconstraints, what limits the range of possible solutions,there are many factors to be considered, mainly dealingwith: shape and dimensions of the part to be machined,tolerances, sequence of operations, machining strategies,cutting forces, number of set-ups, set-up times, volume ofmaterial to be removed, batch size, production rate, machinemorphology, machine capacity, cost, etc. At the end, thesolution can be characterized by its: simplicity, rigidity,accuracy, reliability, and economy.2.1. Functional requirementsFrom the literature review 2527, and from theinterview with designers of machining fixtures 28, it canbe concluded that basic functional requirements that anyfixture solution must satisfy are related to: centring,locating, orientating, clamping, and supporting.However, the way that designers deal with these FRs isfar from being independent of the solution they areconsidering, and in general the FRs are not explicit butimplicit in the design process. Chakrabarti et al. 29 pointout some of the problems that appear in relation torequirements during the design process, for examplerequirements during conceptual and embodiment designsresult mainly from analysis of proposed designs, which infact it is in contradiction with the basic principle, presentedby different authors, of functional definition prior to anydesign solution identification. Adopting the ideas ofToyotas Set-based Concurrent Engineering 30 andAxiomatic Design Theory 4, it seems logical to statethat the FRs should be clearly identified and defined prior toselecting any possible design solution and as the designprogresses the different constraints linked to the FRs shouldbe refined to narrow the set of possible solutions.Chakrabarti et al. 29 also conclude that in order forrequirements to be adequately fulfilled by the final design,they must be identified, understood, remembered and used.Thisconclusion is not new, and in this sense, it demonstrateshow actual and relevant this issue is. It also reinforces acouple of ideas widely recognized in engineering design,one is the need to capture, formalize and documentknowledge, and the second is to make use of it in thedevelopment of Knowledge-Based Engineering (KBE)applications that could help the designers to carry outtheir job and make use in an automatic way of as muchscientific knowledge as possible 31. In this particular caseapplied to the design of machining fixtures.When addressing the development of a KBE application,there are two different sorts of FRs that need to be identifiedand documented. One kind is the functional requirements ofthe application itself; in this case a KBE application forthe design of machining fixtures; and the second one is thefunctional requirements of the components subject of theapplication; in this case machining fixtures. An example ofthe former ones for an application developed in collabor-ation with an industrial partner is presented by Rios et al.28. For this kind of FRs specification, UML seems to beFig. 1. MOKA Entity form for fixture FRs.R. Hunter et al. / International Journal of Machine Tools & Manufacture 46 (2006) 683697685a good methodology: activity, component, and use casediagrams help to specify and give a view of the system.However, when getting into the logical view where classand interaction diagrams have to be defined, it is needed tohave a complete understanding of the object of theapplication: machining fixtures. With this objective, andconsidering that the design of machining fixtures based onfunctional requirements would be the aim of a KBEapplication, the capture and documentation of the machin-ing fixtures FRs is part of the subject of the work developed20, and it is commented next.In this context, the approach adopted was to use part ofthe tools provided by the MOKA methodology 31, thenamed: Illustrations, Constraints, Activities, Rules andEntities forms, to elicit knowledge about machiningfixtures as a first step in the formalization of the FRs andCs. Based on these forms, it is possible to represent themain components linked with the fixture design process:non-functional requirements, functional requirements,constraints, design rules, fixture functional elements,fixture commercial components, etc. 20. Figs. 1 and 2present an example of application to the definition offixture FRs and Cs.After this first phase, the requirements capture iscompleted with the formalization of the functionalrequirements syntax. At this point, it is important toremember that the declaration of a FR is a sentence writtenin a way that allows the FR to be measured, verified, andvalidated. The structure proposed is based on Alexandersanatomy 24, and it has similarities with the functionrepresentation presented by Takeda et al. 6, where it isstated that a function is a combination of a function body(verb), an objective entity (on which the function occurs onor to), and functional modifiers (adverb). The structureproposed in this research is made up of four maincomponents: action, object, resource, and qualifiers(Fig. 3). And unlike with the Takeda approach, all themodal adverbs (i.e.: firmly, precisely, in general allInside the working area of the table:X = 200 mmY = 400 mmZ = 400 mmTolerance for all the dimensions: 1 mmObjectResourcePart A in vertical ma chining center DM T50 ActionQualifierSupport Fig. 3. Functional requirement structure.MOKA ICARE: ENTITYNameReferenceEntity TypeFunctionBehaviourContext, Information,ValidityDescriptionManagementAuthorDateVersionStatusConstraints Functional Requirements for the FixtureConstraints Functional Requirements (CFR)StructureDefine constrains to Functional Requirements for the fixtureNot ApplicableDefine constraints that support the functional requirementsThe constraints will be structured thinking on the functional requirements structureWith this target it has been defined a group of constraints associated with eachfunctional requirement of the fixture, such as:OrientationSupportLocateClampMachiningResourcesRenato Hunter03-07-041.0In progressFig. 2. MOKA Entity form for fixture Cs.R. Hunter et al. / International Journal of Machine Tools & Manufacture 46 (2006) 683697686the adverbs ending with the suffix y) are not considered as amodifier, since they do not have a quantitative value, and inconsequence they cannot be measured neither validated.The Action component is expressed by an active verb thatrefers to the function of the fixture. As named previously,these functions are: centre, position, orientate, clamp, andsupport. A noun expresses the Object component, and refersto the physical object on which the action is performed. Inthe first level of fixture FRs definition, Object will be thepart to be machined. A noun expresses the Resourcecomponent, and it refers to where the action will beperformed. In the first level of fixture FRs definition,part_requirementscost_requirementsprocess_requirementsorientation_requirements-identificacion : char-nombre : char-descripcion : char-accion : char-que : char-recurso : char-calificador : chardocumentation_requirementFixture_requirementslocate_requirementssupport_requirementsclamp_requirements-Requirements1-Documentation1.*accesibility_requirements-Process1.*-Part1formal_representation_requirements-identificador : char-nombre : char-descripcion : char-accion : char-que : char-recurso : char-calificador : charfunctional_requirements-identificador : char-nombre : char-descripcion : char-accion : char-que : char-recurso : char-cualificador : charno_functional_requirements-identificador : char-nombre : char-descripcion : char-accion : char-que : char-recurso : char-calificador : charstructure_requirementscentre_requirementsmachine_tool_requirementsmachining_feature_requirements-Part1-feature1.*-Process1-Feature1.*-Identificator: char-name: char-description: char-action: char-object: char-resource: char-qualifier: char-Identificator: char-name: char-description: char-action: char-object: char-resource: char-qualifier: char-Identificator: char-name: char-description: char-action: char-object: char-resource: char-qualifier: char-Identificator: char-name: char-description: char-action: char-object: char-resource: char-qualifier: charFig. 4. UML model of the fixture functional requirements.Table 1Instances of fixture FRsActionObjectQualifiersQualifier typeOrientatePartIn the machine tool (M0)(Resource)Respect to the coordinated system of thepart (M1)(How)On the orientation part activity (M2)(When/Where)Modifier (M0)Respect to system axis of machine toolModifier (M0)In a vertical milling machineModifier (M1)Respect to the tool pathConstraintsMachine tool type (Vertical or horizontalmill)Work area: lengths in X, Y, ZSupportPartIn machine tool (M0)(Resource)On static equilibrium (M1)(How)On the support part activity (M2)(When/Where)Modifier (M0)In a vertical milling machineModifier (M1)When the sum of forces is equal to zeroModifier (M2.1)Vertical degree of freedom of the partModifier (M2.2)When the orient activity propose a resultConstraintsWork area: lengths in X, Y, Z Shape andsize of the base plateR. Hunter et al. / International Journal of Machine Tools & Manufacture 46 (2006) 683697687Resource will be the machine tool on which the machiningis performed. A quantitative adjective group or noun groupexpresses a Qualifier for the action. The Qualifierscomponents refer to limits of the FRs, and allowrepresenting the constraints (Cs) associated with them.Each quantitative qualifier must have at least a nominalnumerical value, a unit of measure, and a tolerance. Each FRmust have at least one quantitative qualifier. Considering theprevious concept of constraints refinement to narrow the setof possible solutions, the specification of the qualifiers maynot have numerical values when they are initially defined,but in the final stage, when the constraints have to beconsidered to select a candidate solution the numericalvalues need to be declared. The proposed structure of thefixture FR was then modelled in UML (Fig. 4).The class functional_requirements has as attributes thefour components previously defined: Action, Object,Resource and Qualifier. Considering an Object Orientedimplementation, each instance of the class will have aunique identifier that allows tracing that particular FR. Withthis capability, it is possible to modify and update any of theattributes of such FR at any time during the design process.As an example, instances of fixture FRs for orientating andsupporting are represented in the Table 1.3. Proposed methodology for the formalizationof the fixtures design processThe methodology proposed in this research for thefixtures design process is based on five main design phases(numbered 15), named: Functional Requirements develop-ment (FR), definition of Fixture design Functions (FF),Functional Design fixture solution (FD), Detailed Designfixture solution (DD) and Fixture final design solutionValidation (FV). These stages aims to define a process withcontinuous feedback, which allows developing the fixturedesign in a systematic, structured and concurrent way(Fig. 5).Phase 1: The first phase, development of functionalrequirements (FR), comprises the capture of the knowledgeneeded to perform the design process formachining fixtures.It has two main tasks, first filling in the MOKA forms, andsecond formalization of the functional requirementsaccording to the structure defined in Section 2.Phase 2: The secondphase, definition offixture functions(FF), is aimed to complete a set of high level softwarefunction templates that implemented in a knowledge-basedapplication allows to generate fixture solutions which arecompliant with the functional requirements defined in theprevious phase. The fixture functions have been definedgraphically using a method based on the IDEF0 modelling.The representation notation permits to embody graphicallythe attributes and operations needed for the implementationof a function. Fig. 6 shows an example. The proposedrepresentation is a high-level function definition; it isindependent of the knowledge representation to be used inthe implementation, and it does not require from the fixturedesigner a deep knowledge of any software modellingtechnique.Thedefinitionofthesefixturefunctionsisafirststepinthemodelling needed for a KBE application development. Forexample, considering stability as one of the main constraintsaffecting the fixture FRs, any fixture functional solutionshould satisfy this constraint. To achieve that, it would benecessary to define a fixture function (FF) for stabilityFig. 5. Fixture design process methodology.R. Hunter et al. / International Journal of Machine Tools & Manufacture 46 (2006) 683697688evaluation, and this function could be called from the fixturefunction clamp (clamp_FF) presented as example in theFig.6.From ahighlevelperspective,thestability_FF wouldneed as input: part information (i.e.: material mechanicalproperties, shape, dimensions and tolerances), machiningprocess information (i.e.: machining operations, machiningstrategies, volumes to remove, cutting parameters, cuttingtool parameters), and fixture functional element information(i.e.: function, constraints, rules, containing volume, pointand vector of application). Part of this information will havetobeusedtodetermine somederived parameterslikecuttingand allowed clamping forces. Making use of such infor-mation together with an analysis model, for example the oneproposed by Liao et al. 32, and optimization methods, forexample the one proposed by Pelinescu et al. 33, suchstability_FF could be developed and implemented. Thecomplexity in the detailed specification of such stability_FFis extremely high, and demands its own research by itself32,34,35, but the definition of a high level function whereall the information needed for its development could berepresented,isoneoftheobjectivesoftheresearchpresentedin this paper.Phase 3: The third phase, functional design (FD), isaimed to create a set of functional solutions for the fixturedesign. A functional solution is independent of anyparticular commercial fixture component, and it is rep-resented by means of a set of fixture functional elements. Afixture functional element satisfies at least one of thefunctions identified as inherent to a fixture, i.e.: centre,position, orientate, clamp, and support. These elements arerepresented by means of graphical symbols, also calledfunctional symbols, which apart from the functionality alsorepresent some qualifiers that affect them. Such fixturefunctional symbols are based on the technological elementsdefined in the AFNOR standard NF E 04-013 - 1985 36.Fig. 7 presents their structure, which comprises: kind ofPart machining:operationsstrategiescutting parameterscutting tool parametersvolume to removeFixture functional elements:functionconstraintsrulescontaining volumeOptimization methodAnalysis modelConstraints:DeformationStabilityInterferenceFunction Clamp(clamp_FF)F4Part orientationPart support:support pointssupport vectorssupport surfacesPart location:locating pointslocating vectorslocating surfacesPart information:mechanical propertiesfriction coefficientraw material shape and dimensionspart shape and dimensionstolerancesDetermine cutting forcesDetermine clamping surfaceDetermine clamping pointsDetermine clamping orientationDetermine clamping forcesDetermine clamping elementsFig. 6. High-level function template representation.Fig. 7. Structure of the AFNOR fixture technological elements.R. Hunter et al. / International Journal of Machine Tools & Manufacture 46 (2006) 683697689technology, state of the part surface, function of thetechnological element, and the kind of contact betweenthe part surface and the fixture element.In order to progress from the functional design to thedetailed one, which is the next phase, it has been defined amapping table between functional symbols and commercialfixture elements 20, Table 2 represents an example.For the creation of the possible functional solutions a setof input information, analysis models, optimization func-tions, and rules has to be included in the software functionspreviously defined in the second phase. Basically, the inputsdefined are: Part information: material mechanical properties, shapeand dimensions of the part to be machined, and theassociated tolerances. Functional element information: functions, associatedrestrictions, orientation, containing volume, contactparameters, and location point. Part manufacturing process: sequence of operations, andfor each operation: machining strategy, cutting para-meters, cutting tool, and volume to remove. Production estimation of: number of set-ups, set-uptimes, batch size, production rate, and target cost. Resource information: machine morphology, andmachine capacity.Functional design brings benefits to design environmentswhere the solution is mainly driven by the satisfaction ofquantitative functions, as opposite to environments wheresubjective aspects like aesthetics has a major relevance. Inparticular, in the fixture design environment, the advantageof creating a functional solution derives from not using afull library of commercial fixture elements but a reducednumber of basic functional elements, which can betransformed into the former ones in a second designphase. And this is particularly relevant when some kind ofartificial intelligence technique is going to be applied in theimplementation phase, since many of these techniques arebased on the initial generation of a complete design spacewhere the possible solutions are contained, if the designspace can be reduced then the determination of the solutionscan be done more efficiently. And with the functional designapproach the design space is divided in two subsets, onesubset dealing with the functional solution and other dealingwith the physical one.Phase 4: The fourth phase, detailed design (DD)comprises the creation of detailed solutions from afunctional one. To undertake this phase the mapping tablespreviously mentioned and the corresponding interpretationrules have to be used. To mention as well, that the fixturesoftware functions apply in a similar way, but with adifferent input, which basically is the geometry (containingvolume) associated with the fixture element, this isparticularly relevant for the interference checking. How-ever, in this case the space of possible solutions is reducedby the fact that only those commercial elements that can bemapped to the functional ones can be used, and that a pointof application and an orientation vector for the elements tobe used are data as well. A detailed solution contains thefinal fixture commercial elements to be used in themachining of the part and their set-up.Finally, the fifth phase, validation of the design (FV), isaimed to make a final evaluation and validation of thefunctional requirements and their associated constraintsdefinedinthefirstphase.However,itisimportanttomentionthat in addition to a final validation, the functional approach,with the separation of the design spaces in two parts, allowsimplementing the validation in two prior stages. First in thefunctional design phase, so the possible functional designsolutions fulfil the imposed requirements, and second in thedetailed design phase. This can be made by means of theoptimization method that can be included in the FixtureFunction(FF),asitwaspreviouslymentionedinthePhase3.Based on this methodology, a detailed definition of thefixture functional design process is presented in the nextsection.4. Fixture functional design process modelAs it was mentioned in the introduction, the functionalapproach to design has drawn the attention of severalresearchers 2,5,6,7,8. However, as it is pointed out byTable 2Relation between AFNOR elements and fixture commercial componentsFixture functionFunctional representationCommercial elements selected typeClamp function*Type technology: Clamp(Attribute)Type technologySurface ClassType FunctionType contact surface*Surface class: Machined*Type technology*Type contact surface: Punctual*Surface class*Type function: Machining Fixture*Type contact surface*Type functionR. Hunter et al. / International Journal of Machine Tools & Manufacture 46 (2006) 683697690Kitamura 7, in general, the functional knowledge is leftimplicit, there are not clear definitions of the functionalconcepts, and the generic functions proposed in theliterature are too generic to be used by designers. In thissense, the ontological approach is an interesting contri-bution to formalize the functional design knowledge. Theapproach adopted in this research deals with the definitionof what would be the first step in a fixture ontologydevelopment, which is the modelling of the fixtureinformation.The functional approach to fixture design, based on aninformation model definition, has some characteristics thatcan be deduced from the facts presented in the previoussections, that is: a reduced number offunctions that a fixturehas to perform, the possibility of formalizing the FRsspecification with quantitative qualifiers, and the reductionof the design space by using functional elements. However,prior to the definition of any fixture information model, it isnecessary to define the fixture design process and theinformation flow along it.Following is the activity model developed in thisresearch to represent the fixture design process. Themodel is represented using the IDEF0 technique andUML, and it allows identifying the knowledge unitsneeded during such process, and the interaction amongthe activities. The development of this model is based onthe findings from the literature review, and on thefindings from a development conducted in collaborationwith an industrial partner 28. Some authors have alsoused modelling techniques to represent the process andpart of the information related to the fixture designprocess 37,38, but without taking a functional approachto it.Starting with the input knowledge units related to partgeometry,manufacturingprocessplan,machiningresources, and following the IDEF0 methodology, the firststep is to create a context diagram or highest-level diagram,of the fixture design process. The knowledge units thatconstitute the final output to the process are the fixturedetailed design, and the fixture assembly plan. The resourceknowledge units are the machine-tool unit and the modularfixture elements one.The IDEF0 methodology is based on the definition of ahierarchical break down of activities, each of them isdefined by an active verb, together with a set of inputs toand outputs from each activity, resources needed for itscompletion, and elements can be used as control in itsundertaking. Following are the main diagrams developedduring the research.From the root diagram, the first level diagram is created.As it presented in the Fig. 8, it comprises the activitiesdealing with the analysis and definition of the three maininformation units defined: part geometrical information,manufacturing process plan, and fixture design plan. It isrelevant to mention, that the performance of these activitiesis highly concurrent and iterative.Activity A1: The fixture designer analyse the partgeometrical features, shape and dimensions, tolerances,C2M2FixtureDesignerO1Fixture Assemby PlanC4Principles of Fixture DesignC3Manufacturing ConditionsO3FixtureDesignANALYSEFEATURES OF THE PARTANALYSE MACHINING PROCESSDETAIL FIXTURE DESIGN PLANPart FeaturesMachining operations and tool pathDesign RulesI3Part Information:GeometryI1Defined Phaseand SubphasesC1and SubphaseM1ManufacturingResourcesI2Machining OperationsA1A2A3P.3P.4P.5State of resourcesDefined PhaseFig. 8. Node A0: design machining fixture.R. Hunter et al. / International Journal of Machine Tools & Manufacture 46 (2006) 683697691and surface finish. The output is the set of part technologicalfeatures to be considered in the fixture design process.Activity A2: The fixture designer analyse the partmanufacturing process plan, machining operations, volumesto remove, cutting tool, cutting conditions, machiningstrategy, and machine tool morphology. The output is anunderstanding of the correspondence between the parttechnological features and the machining operations.Activity A3: Using the outputs from the two otheractivities, plus the production information, the designerdefines the functional requirements and the constraints ofthe fixture. After that, he starts with the identification ofpossible functional solutions to fulfil such requirements.Each of these solutions has to be evaluated in order toguarantee that the requirements are satisfied. The followingstage is to define for each functional solution the feasibledetailed ones, those including commercial fixture elements.The second level of break down is presented in threedifferent diagrams, Fig. 9 for the A1 node, Fig. 10 for the A2node, and Fig. 11 for the A3 node.The activity A1 has been divided into four sub activities(Fig. 9). The activity A11 creates a list of geometricinformation defining the volumes to machine. The activityA12 deals with the dimensional, tolerances and surfacefinish analysis. The Activity A13 defines the starting rawmaterial, in case that the part is not shaped in a primarymanufacturing process. And finally, the Activity A14focuses on the definition of the technological features ofthe machining to be performed on the part. It comprisesthe input of the results from the previous three activitiesand it creates a list of machining features with theirassociated dimensions and tolerances.The activity A2 has been divided into three sub activities(Fig. 10). The activity A21 deals with the productioninformation, and the analysis of the machine tool to be used,for example: machining working space dimensions, speedspindle rates, feed rates, and table dimensions. The activityA22 focus on the analysis of the machining operations,possible operation sequences, identification of possibleorientations for the part. Finally, the activity A23 combinesthe output of the Activity A14, machining features, with theoutput of the activity A22, machining process analysis, todefine a set of machining subphases, set of operationsperformed with the same cutting tool, with all theinformation needed for their execution.The activity A3, elaborate detailed fixture design plan,has been broken down into four sub activities, all of themrelated to the methodology proposed in the Section 3,Fig. 11 shows the diagram. The activity A31 comprisesthe definition of the fixture requirements and constraintsaccording to description previously presented in theSection 2.1. The activity A32 requires the use of a setof predefined fixture functions (FF), presented in themethodology section. The final objective would be toimplement these functions in a knowledge-based appli-cation, so the functional design solution would fulfil therequirements defined. In this case, a first level objectivewas addressed in this research, to make these functionsand the information needed for their development explicit,in a way that any fixture designer could understand themC1M1FixtureDesignerANALYSE GEOMETRY TO MACHINING ANALYSE DIMENSIONS AND TOLERANCES OF THE PART DEFINE PART MATERIALDEFINE TECHNOLOGICAL FEATURES OF THE PARTTolerance Analysis CriterionsConstraints TolerancesMaterial of thePartI1Part Information:GeometryO1PartGeometricFeatures of the A11A12A13A14 FeaturesDesign RulesFig. 9. Node A1: analyse part characteristics.R. Hunter et al. / International Journal of Machine Tools & Manufacture 46 (2006) 683697692and decide which actions to undertake to get a functionalsolution. Additionally, the description proposed for the FFmakes them independent of any deployment environment,and any programmer could use them as a starting point todevelop such fixture design knowledge-based application.Making use of the FFs, the activity A33 focus onthe definition of the fixture functional design, which isrepresented using the functional elements based on theAFNOR standard presented in the Section 3 36. Finally,the activity A34 deals with the fixture detailed design.Making use of the fixture functional design, functionalelements-commercialelementsmappingtables,O2Machining operations and tool pathsM1FixtureDesignerC4Manufacturing ConditionsC3State of resourcesO1Fixture Assemply PlanANALYSE MACHINING PHASE AND SUBPHASESANALYSE MACHINING OPERATIONSANALYSE MACHINETOOLOperations ListTolerances ConstraintsI4Part Information:GeometryM2ManufacturingResourcesI2Machining OperationsC2Defined Phaseand SubphasesI3Defined Phaseand SubphasesI1Part FeaturesC1Part FeaturesMachine-ToolConditionsA21A22A23Fig. 10. Node A2: analyse machining process.C1Machining operations and tool pathsM1FixtureDesignerC3Principles of Fixture DesignO1Fixture Assemby PlanO3FixtureDesignI1Machining operations and tool pathsC2Manufacturing ConditionsDEVELOPFIXTURE REQUIREMENTSDEVELOP FIXTURE FUNCTION ELABORATE FUNCTIONAL DESIGNELABORATE DETAILED DESIGNRepresentationFormatFunctional RepresentationFixture RequirementsFixture FunctionsFunctionalFixture DesignFunctionalElementsProgrammerModification of RequirementsFixture ModificationsI2Part Information:GeometryM2ManufacturingResourcesA33A34A32A31Fig. 11. Node A3: detail fixture design plan.R. Hunter et al. / International Journal of Machine Tools & Manufacture 46 (2006) 683697693and the corresponding FFs, the final fixture design can beobtained.The diagrams presented so far need a complementaryview to show the temporal interaction among the high levelactivities that constitute the fixture design process. TheUML sequence diagram presented in the Fig. 12 providesthis view.5. Information model, instantiation, and methodologyvalidationFollowing the modelling of the fixture design process,the identified knowledge units: fixture requirements, fixturefunctions, part definition, machining operations, functionaldesign rules, detail design rules, fixture resources, andfixture validation, have been modelled in an object-orientedstructure, and UML has been used for its representation20. For some of these knowledge units, specifically forpart definition and machining operations, prior develop-ments have been used 39,40.Following is an example to show a partial instantiation ofsuch model, and the results obtained from a prototypeknowledge-based application, which has been developed ina commercial CAD/CAM system to validate the method-ology proposed in this research 20.As starting point, the Table 3 presents initial geometricand machining data used as input to initiate the fixturedesign process for a particular part to be machined in a CNCvertical milling machine.Following the methodology proposed in the Section 3,the process starts with the analysis of the part geometricalinformation and machining plan. As a consequence, thefixture functional requirements have to be defined. Theseactivities are part of the phase 1 (FR). Then the fixturefunctions have to be defined and represented (phase 2) (FF).Fig. 13 depicts a sample of these two design phases.Specifically, Fig. 13a presents an instance of the functionalrequirement support, with the attributes: action (support),object (part), resource (vertical milling machine), andqualifier (machining subphase 10, Table 3). Keeping thestructure proposed in the section 2.1. These attributes areused as input in the fixture function support_FF, the linesgoing from the Fig. 13a to the Fig. 13b represent the link.functional requirementsfixture functionsfunctionaldesigndetailed designvalidate design1: 3: establish value2: define functions8: validate design4: validate design5: check design7: establish correspondence13: Verification functional requirements6: establish value14: approve design Fig. 12. Fixture design sequence diagram.Table 3Geometric and machining part dataInformationFeature for fixture design processInitial shape geometryMachining operations listMachining subphase 10:Pocket_milling :24 mmPocket_milling :26 mmPocket_milling :30 mmDrilling :8 mm (2 Holes)Counterboring :36 mm, 5 mmCounterboring :40 mm, 8 mmMachining subphase 20:Manufacturing resourcesVertical milling machineModular fixture elementsFinal shape geometryR. Hunter et al. / International Journal of Machine Tools & Manufacture 46 (2006) 683697694The Fig. 13b represents the function support_FF usingUML, and its instantiation in CCC is presented in theFig. 13c.The functional design phase (FD) makes use of the FFsdefined in the previous phase, which directly correspondto the functional requirements (FRs): support_FF,clamp_FF,centre_FF,orientate_FF,position_FF,together with a set of design rules. In Fig. 14c, it isshown the raw material part, in Fig. 14b the volumes ofmaterial to be removed, and in Fig. 14a, the correspond-ing attributes for the support function. In the example, therules defined have relation with the determination of:surfaceandpointofsupport,kind,locationandorientation of the functional element (Fig. 14d). TheFig. 14e represents a result of the application of thefunctions and the associated rules.Finally, the detailed design phase (DD) should determinethe commercial standard fixture elements to use inthe machining of the part. To achieve this objective, themapping tables between functional elements and thecommercial fixture elements have to be used. Followingwith the example, according to the mapping presented in theTable 2, the Fig. 15 represents a detailed solution to thefunctional one presented in the Fig. 14. -machining_geometry : void = Subphase_10 information -initial_geometry : void = Case1.CATPart resource - machine_type : char = Vertical_milling resource - support_element : char = AFNOR_support constrains -machining_operation : char = Subphase_10 constrains -tool_path : charsupport_function_part+determine_support_surface() : void+determine_support_point() : void- identificator : char = iFunction_support_1- name : char = Function_support_1 information -machining_geometry : void = Subphase_10 information -initial_geometry : void = Case1.CATPart resource - machine_type : char = Vertical_milling resource - support_element : char = AFNOR_support constrains -machining_operation : char = Subphase_10 constrains -tool_path : charsupport_function_part- identificator : char = iRequerement_support - name : char = Requirement_support - description : char - action : char = support - what : char = Part Case1. CATPart - resource : char = vertical milling - qualifier : char = subphase machining 10 support_requirement - identificator : char = iRequerement_support - name : char = Requirement_support - description : char - action : char = support - object char = Part Case1. CATPart - resource : char = vertical milling - qualifier : char = subphase machining 10 support_requirement #include support_function_part.h“support_function_part: support_function_part (): Function_fixture (), m_identificator(iFunction_support _1), m_name(Function_support _1), m_machining_geometry(Subphase 10), m_initial_geometry(Case _1. CATPart ), m_machine_type(Vertical_milling ), m_support_element(support_element_AFNOR ) Information Group Functional Requirement Information Group Fixture FunctionsInstantiationFunctions C+ (a) (b)(c)Fig. 13. Functional requirements interpretation and fixture functions.Fig. 14. Functional design solution example.Fig. 15. Detailed design solution example.R. Hunter et al. / International Journal of Machine Tools & Manufacture 46 (2006) 6836976956. ConclusionsAn integrated approach to the design process ofmachining fixtures has been adopted in this research.The basic aim was to formalize a methodology tofacilitate the automation of such design process. Basedon the findings and conclusions obtained from theliterature review and the interaction with fixture designers,some principles were considered to guide the research.Following are these principles and how they were takeninto consideration: The starting step is the definition of the fixturefunctional requirements. This principle led to theformalization of such requirements, based on someapproaches from Requirements Engineering, and to thefunctional representation of fixture design solutions,based on the standard AFNOR NF E 04-013 - 1985.This approach allows validating the design solutionsagainst the specified requirements. There is a need to capture and formalize machiningfixture knowledge. This principle led to the use of anestablished methodology, in this case MOKA, and tothe ontology, and information modelling approachfinally adopted. UML was used for its representation. There is a need to define and represent the machiningfixture design process. This principle led to itsdefinition and representation using IDEF0 and UML. There is a need to define software fixture functions,whose objective is to create solutions that fulfil thefixture functional requirements. And the definition hasto be independent of any implementation system. Thisprinciple led to the study of some of the solutionsalready done in this area, in particular optimizationworks, and to the conclusion that only a high leveldescription of such functions, where the informationand the basic rules needed for their implementationwere specified, was possible to address. The analysisof the MOKA modelling language was also analyzed,however the high level of complexity of the fixturefunctions, demands a further investigation in order todefine how to break them down into lower levels ofdetail while keeping the representation independent ofthe implementation level.From the research conducted, it can be concluded that theformalization of the fixture design process based onfunctional requirements allows developing a more inte-grated approach to the problem offixtures design. The basicsteps, and fundamental input to any implementation aimingto automate such process, start with the Fixture DesignProcess, and continue with the definition of the FixtureKnowledge Units: fixture requirements, fixture functions