1、Fundamentals of GD&T基础几何尺寸与公差概述 CH1 Introduction to the GD&T Hierarchy 介绍GD&T组成层级GOAL 目标Understand what an engineering drawing is.懂得什么是工程图纸Understand why geometric tolerancing is superior to coordinate tolerance.懂得为什么几何公差优于坐标共差Understand the modifiers and symbols used in geometric tolerancing.懂得几何公差
2、修饰符和符号Remember:Tolerances should be as large as possible to keep manufacturing cost low.记住:为了降低制造成本，公差应该越大越好。CH1 Introduction to the GD&T Hierarchy 介绍GD&T组成层级ENGINEERING DRAWINGS 工程图纸The Need for Precise Communications 精确交流的需要Engineering drawings are a communications tools.Engineering drawings affec
3、t many parts of an organization.They have major impact on costs.工程图纸是精确交流的工具，对机构许多部门和成本构成重大影响。Consequences of Poor Drawings 品质差图纸后果(Cost in four ways:Money,Time,Material,Unhappy customers)（4 种成本：钱、时间、材料、不满意的客户）Cost of a Drawing Error 图纸错误的成本When discovered by the Design Dept.设计 Model shop 样件 Product
4、ion Group 生产 Customer 客户$1-10$100-500$2,000-100,000$50,000-$1,000,000Figure 1-1CH1 Introduction to the GD&T Hierarchy 介绍GD&T组成层级Types of Tolerances 公差的类型-A limit tolerance 极限公差(12.0-12.5)-A plus-minus tolerance 正负公差(12.250.25 equal bilateral tolerance)-A unilateral tolerance 单项公差(12+0.50)-An unequal
5、 bilateral tolerance 双向不等公差(12.2+0.3-0.2)(Where limit or bilateral tolerancing is used,each tolerance value should have the same number of decimal places,using zeros where necessary.)当使用极限或双向公差时，每个公差值小数点后应该有同样多位数，必要时用零)CH1 Introduction to the GD&T Hierarchy 介绍GD&T组成层级Interpreting Dimensional Limits
6、解读尺寸极限 All dimensional limits are absolute.A dimension is considered to be followed by zeros after the last specified digit.所有极限尺寸都是绝对精确值，其最后一个数字后面都是零。26.02 means 26.020026 means 26.0016.54 means 16.540016.5 means 16.500For this dimension 26.0-26.2A part measuring26.201would be rejectedAnd 25.999 wo
7、uld be rejectedGD&T in the United States GD&T在美国ASME(American Society of Mechanical Engineers)Y14.5(the standard number)M(Metric)-2009(the year the standard was approved)is a revision of ASME Y14.5M-1994 ASME（美国机械工程师协会）Y14.5（标准编号）M（公制）-2009（标准批准年份）是ASME Y14.5M-1994标准的升级版The ISO and ASME Y14.5M dimen
8、sioning standards are currently 80-90%common.ISO标准和ASME Y14.5M标准目前有80-90%相同。CH1 Introduction to the GD&T Hierarchy 介绍GD&T组成层级ASME and ISO Dimensioning Standard Comparison ASME和ISO标准比较ISOASME Y14.5Approach to dimensioning 编写方式Theoretical definition 理论性强Function of product功能性强Level of explanation 解释方式
9、Few words/many figures文字少/图表多Thorough explanation解释透彻Cost of standards 标准售价Over$1000Less than$200Number of standards 标准数目10-151CH1 Introduction to the GD&T Hierarchy 介绍GD&T组成层级CH1 Introduction to the GD&T Hierarchy 介绍GD&T组成层级FUNDAMENTAL DIMENSIONING RULES(Rule#6)(ASME Y14.5M-1994)基本尺寸规则（6号规则）(ASME Y
10、14.5M-1994)1.Each dimension shall have a tolerance,except those dimensions specifically identified as reference,maximum,minimum,or stock(commercial stock)size.每个尺寸都应该有一个公差，但是，参考、最大/最小或型钢尺寸除外。2.Dimensioning and tolerancing shall be complete so there is full definition of each part feature.尺寸和公差应完整，才能
11、完全定义零件形体。3.Dimensions shall be selected and arranged to suit the function and mating relationship of a part and shall not be subject to more than one interpretation.尺寸选择和布置，要适合零件功能和装配关系，而且只能有一种解释。4.The drawing should define a part without specifying manufacturing methods.图纸只定义零件，不要注明生产工艺。5.A 900 ang
12、le applies where centerlines and lines depicting features are shown on a drawing at right angles,and no dimension is shown.900角在图纸上不标出。CH1 Introduction to the GD&T Hierarchy 介绍GD&T组成层级6.Implied basic 900 angles-A 900 basic angle applies where centerlines of features in a pattern(or surfaces shown at
13、 right angles on a drawing)are located and defined by basic dimensions and no angle is specified.基本900角在图纸上不标出。Implied basic zero dimension Where a centerline or centerplane of a FOS is shown in line with a datum axis or centerplane,the distance between the centerlines or centerplanes is an implied
14、basic zero.基本0尺寸在图纸上不标出。7.Unless otherwise specified,all dimensions are applicable at 200 C.零件常温200 C8.All dimensions and tolerances apply in the free-state condition.零件自由状态。9.Unless otherwise specified,all geometric tolerances apply to the full depth,length,and width of the feature.除非另有说明，几何公差应用全部形
15、体长、宽、高。10.Dimensions and tolerances apply only at the drawing level where they are specified.A dimension specified on a detail drawing is not mandatory for that feature on the assembly drawing.尺寸公差应用于它标明的层级，装配图尺寸公差不能强制该层级尺寸公差。CH1 Introduction to the GD&T Hierarchy 介绍GD&T组成层级THE COORDINATE TOLERANCIL
16、NG SYSTEM 坐标公差Definition 定义 Coordinate tolerancing is a dimensioning system where a part feature is located(or defined)by means of rectangular dimensions with given tolerances.用直角坐标系尺寸和公差定义零件位置或用尺寸和公差定义形体。SHORTCOMINGS OF COORDINATE TOLERANCING 坐标公差缺点Square Tolerance Zones 方形公差带(Figure 1-2)Fixed-Size
17、 Tolerance Zones 固定尺寸公差带(Figure1-2)Figure 1-2 Cylindrical vs.Square tolerance zone 圆柱对比方形公差带Square tolerance zone that results from coordinate tolerances坐标公差方形公差带Cylindrical tolerance zone that results from geometric tolerancing 几何公差圆柱形公差带(57%additional tolerance 增加公差带57%)CH1 Introduction to the GD&
18、T Hierarchy介绍GD&T组成层级Ambiguous instructions for Inspection 检测指导不明确(Figure 1-3)Should the hole location be measured as shown in setup A or B 应该用A或B方法测孔的位置 A BFigure 1-3 Method of Inspection 检测方法Surface Plate(Datum feature simulator)Surface Plate(Datum feature simulator)CH1 Introduction to the GD&T Hi
19、erarchy 介绍GD&T组成层级Appropriate uses for coordinate tolerancing 正确使用坐标公差-Plus/minus tolerancing is basically a caliper or micrometer type measurement.It works very well for individual feature of size(Rule#1 Taylor Principle)but does not control the relationship between individual feature very well.Thi
20、s does not mean that limit tolerancing cannot be used.It is just important that we realize its limitations and problems.坐标（正负）公差基本上就是卡尺或千分尺类型测量，它可很好的测量单个形体尺寸（规则#1）但不能控制两个形体之间的关系。这并不意味着坐标公差不能用，但我们要知道它的局限性和问题。Coordinate Dimension Usage 坐标公差使用Type of Dimension 尺寸类型Appropriate Use 好Poor Use 不好Size 尺寸XCh
21、amfer 倒角XRadius 半径XLocating Part Features 位置XControlling Angular Relationships 角度XDefining the Form of Part Features 形状XCH1 Introduction to the GD&T Hierarchy介绍GD&T组成层级THE GEOMETRIC DIMENSIONING AND TOLERANCEING SYSTEM 几何尺寸和公差系统Definition and Philosophy 定义和哲学 GD&T is an international language that i
22、s used on engineering drawings to accurately describe a part.Geometric tolerancing encourages a dimensioning philosophy called“functional dimensioning.”which is a dimensioning philosophy that defines a part based on how it functions in the final product.GD&T是一个在工程图纸上精确描述零件的国际语言。几何公差鼓励一个“功能尺寸”的哲学，就是以
23、零件的功能来确定如何定义零件。GD&T BENEFITS 优点 Improves Communication 改善交流Provides Better Product Design 提供更好的产品设计Increases Production Tolerances 增加生产公差CH1 Introduction to the GD&T Hierarchy 介绍GD&T组成层级 CONPARISON BETWEEN GD&T AND COORDINATE TOLERANCING 几何与坐标公差比较Drawing ConceptCoordinate Tolerancing 坐标公差 Geometric
24、Tolerancing 几何公差Tolerance Zone Shape公差带形状孔公差带是方形或长方形-孔公差带较小-制造成本更高公差带是圆形，可使用直径符号-增加公差带57%-制造成本更低Tolerance Zone Flexibility公差带灵活性公差带尺寸固定-好零件被废弃-生产成本更高使用MMC修饰符使公差带在一定条件下增加-好零件被使用-生产成本更低Ease of Inspection方便检测检测可以得到不同的检测结果-好零件被废弃-坏零件被接受基准系统可以统一检测设置-清楚指导检测-消除是否接受零件的争议CH2 Features,Rules and Concepts of GD
25、&T 形体、规则和概念GOAL 目标Understand key terms and how they affect the interpretation of a drawing.懂得影响解读图纸的关键术语Understand Rule#1 and Rule#2.懂得规则#1和规则#2Understand the concepts of basic dimensions,virtual condition,inner and outer boundary and bonus tolerance.懂得：基本尺寸、实效状况、内部边界、外部边界、奖励公差。FEATURES 形体Definition
26、 定义 A feature is a general term applied to a physical portion of a part,such as a surface,hole,or slot.(Figure 2-1)形体就是一个零件上的一部分，如：表面、孔或槽。(A feature is any surface on a part.形体就是零件的任何一个表面。）Figure 2-1 Examples of Features (This part has seven features 这个零件有7个形体)Left sideHole surfaceRight sideFrontTop
27、BackBottomCH2 Features,Rules and Concepts of GD&T 形体、规则和概念Features of Size 尺寸形体 -A feature of size(FOS)is one cylindrical or spherical surfaces,or a set of two opposed elements or opposed parallel surfaces associated with a size dimension,such as,the diameter of hole,or shaft.一个尺寸形体是一个圆柱面、球面、或一组两个相对
28、的平行的元素或表面，且由一个尺寸连接。如：孔径或轴径。-Contains opposing elements or surfaces.包含相对元素或表面。-Can be used to establish an axis,median plane,or centerpoint.能被用来建立轴心线、中心面或中心点。-Is associated with a size dimension.用一个尺寸连接。-Every feature of size contains one or more features surface(s)within it.A cylindrical FOS contain
29、s one feature:the cylindrical surface.A planar FOS is a FOS that contains two feature:the two parallel plane surfaces.每个尺寸形体包含一个或两个形体（表面）。一个圆柱尺寸形体包括一个表面。一个平面尺寸形体包括两个形体：两个平行平面表面。-Usually(99%of the time),the opposing elements will both be the same type,for example,two opposing surfaces or two opposing
30、 line elements.通常（99%情况下），两个相对的元素是相同类型的，如两个表面或两条线。CH2 Features,Rules and Concepts of GD&T 形体、规则和概念CH2 Features,Rules and Concepts of GD&T 形体、规则和概念Figure 2-2 Examples of feature of size and non-feature of size(This part has four feature of size dimensions and three non-feature of size dimensions)（这个零
31、件有4个尺寸形体尺寸和3个非尺寸形体尺寸）R514.2-4.82.0-2.6EG36-3824-2545036-37Internal and External Features of size 内部和外部尺寸形体In Figure 2-2,the 4.2-4.8 is internal 是内部 FOS;36-38,24-25 and 36-37 are external 是外部 FOS.CH2 Features,Rules and Concepts of GD&T 形体、规则和概念Actual Local Size(ALS)实际局部尺寸 Actual local size is the val
32、ue of any individual distance at any cross section of a FOS.A two-point measurement is often considered an actual local size.一个实际局部尺寸是尺寸形体任何一个截面间的距离。两点测量通常被认为是一个实际局部尺寸。Actual Mating Envelope(AME)实际包容体 For an external feature of size;a similar perfect feature counterpart of the smallest size which su
33、rrounds the feature so it contacts the high points of the surface(s).For an internal feature of size;a similar perfect feature counterpart of the largest size which fits inside the feature so it contacts the high points of the surface(s)对外部尺寸形体：就是一个最小尺寸包在该形体上的一个与其相似的完美形体。对内部尺寸形体：就是一个最大尺寸膨胀在该形体上的一个与其
34、相似的完美形体。(Actual mating envelope is a variable value,derived from an actual part)（实际包容体是一个由实际零件得来的变值）CH2 Features,Rules and Concepts of GD&T 形体、规则和概念MATERIAL CONDITIONS 材料状况Maximum Material Condition(MMC)最大实体状况 The condition in which a feature of size contains the most amount of material everywhere w
35、ithin the stated limits of size.For example,the largest shaft diameter,the smallest hole diameter.尺寸形体包含有最多的材料，但仍然在尺寸范围内。如：最大的轴径，最小的孔径。Least Material Condition(LMC)最小实体状况 The condition in which a feature of size contains the least amount of material everywhere within the stated limits of size.For ex
36、ample,the smallest shaft diameter,the largest hole diameter.尺寸形体包含有最少的材料，但仍然在尺寸范围内。如：最小的轴径，最大的孔径。(The MMC and LMC concepts can only be used when referring to a FOS)（MMC和LMC 概念只能应用于尺寸形体）Regardless of Feature Size(RFS)(ANSI Y14.5M-1982)不管形体尺寸 A term that indicates a geometric tolerance applies at any
37、increment of size of the feature within its size tolerance,in-other-word,a geometric tolerance applies at whatever size the part feature is produced.几何公差应用于尺寸形体在尺寸范围内任何尺寸。CH2 Features,Rules and Concepts of GD&T 形体、规则和概念RULES 规则Rule#1 规则#1(Individual Feature of Size Rule 单个尺寸形体规则)-Often referred as t
38、he“envelope principle”or“perfect form at MMC”Rule#1 states where only a tolerance of size is specified,the limits of size also control the limits of form.经常被称为“包容原则”或“MMC理想形状”。规则#1规定一个尺寸公差控制尺寸极限，还控制形状极限。(Rule#1 is a dimensioning rule used to ensure that features of size will assemble with one anothe
39、r.规则#1保证尺寸形体能相互装配。)-For features of size,where only a tolerance of size is specified,the surfaces shall not extend beyond a boundary(envelope)of perfect form at MMC.尺寸形体公差指定后，形体表面将不能突出MMC理想形状边界。CH2 Features,Rules and Concepts of GD&T 形体、规则和概念-When the actual local size of a FOS has departed from MMC
40、 toward LMC,the form is allowed to vary by the same amount.当尺寸形体实际局部尺寸从MMC向LMC变化，形体形状被允许相同量变形。-The actual local size of an individual feature of size must be within the specified tolerance of size.单个尺寸形体实际局部尺寸必须在规定的尺寸公差范围内。-There is no requirement for a boundary of perfect form at LMC.If a feature o
41、f size is produced at LMC,it can vary from true form by the amount allowed by the MMC boundary.没有 LMC理想形状边界要求。CH2 Features,Rules and Concepts of GD&T 形体、规则和概念How to Override Rule#1(Figure 2-3)怎样能否掉规则#1-Rule#1 applies whenever a feature of size is specified on a drawing.There are two ways Rule#1 can
42、be overridden.规则#1应用于任何尺寸形体，但有两种方法可否掉规则#1：-A straightness control applied to a FOS.直线度应用在尺寸形体。-A special note applied to a FOS.一个说明应用在尺寸形体。Rule#1 Limitation 规则#1 局限性 -Does not control the location,orientation,or relationship between features of size(i.e.angle E,G).(Figure 2-2)规则#1 不能控制位置度、方向度或尺寸形体之间
43、的关系。Rule#1 Exceptions 规则#1 例外 -A FOS on a non-rigid part 非刚性尺寸形体 -Stock sizes,such as bar stock,sheets,tubing or structural shapes etc.型钢尺寸，如：棒料、薄板、管材、结构钢材等。CH2 Features,Rules and Concepts of GD&T 形体、规则和概念Figure 2-3 Feature control frame（FCF）placement 形体控制框放置 0.02 12.2-12.7 12.2-12.7 0.02A:形体控制框（FCF
44、）应用在形体 B:形体控制框（FCF）应用在尺寸形体OB=12.7Rule#1 applies.规则#1应用 OB=12.72Rule#1 overridden.规则#1失效CH2 Features,Rules and Concepts of GD&T 形体、规则和概念Inspecting a Feature of Size 检测尺寸形体 -The MMC size and the Rule#1 envelope can be verified with a Go gage.A Go gage is a gage that is intended to fit into(for a inter
45、nal FOS)or fit over(for an external FOS)the FOS.A Go gage is made to the MMC limit of the FOS and has perfect form.To fully verify the Rule#1 effects,a Go gage must be at least as long as the FOS it is verifying.通规可测量尺寸形体MMC尺寸和规则#1 包容体。通规就是尺寸形体MMC理想形状形体，至少要与被测形体一样长，能完全通过为合格。-The minimum size(LMC)of
46、a FOS can be measured with a No-Go gage.A No-Go gage is a gage that is not intended to fit into or over a FOS.A No-Go gage is made to the LMC limit of the FOS.A No-Go gage makes a two-point check;a caliper or snap could be used as a No-Go gage.Multiple two-point checks are required.止规可测量尺寸形体LMC尺寸。止规
47、就是尺寸形体LMC尺寸，要做许多位置两点检测，不能通过为合格。CH2 Features,Rules and Concepts of GD&T 形体、规则和概念Rule#2 规则#2 RFS applies,with respect to the individual tolerance,datum reference,or both,where no modifying symbol is specified.MMC or LMC must be specified on the drawing where required.(RFS-from Y14.5M-1982)不管形体尺寸（RFS）应
48、用在单个公差、基准系或同时在两者，RFS不出现。MMC和LMC就必须在应用处出现。INTRODUCTION TO BASIC DIMENSIONS 介绍基本公差Basic Dimension 基本尺寸 -A basic dimension is a numerical value which have two uses on the engineering drawing.One is to define the theoretically exact location,size,orientation,or true profile of a part feature,Basic dimen
49、sion is the goal,and a geometric tolerance specifies the amount of acceptable variation from the goal;the other is to define gage information(example:datum target):基本尺寸在图纸上有两个基本用途：一是定义理论精确位置、尺寸、方向或真实轮廓；基本尺寸是目标，必须伴有几何公差表示允许偏离目标的范围。二是定义测量基准目标。CH2 Features,Rules and Concepts of GD&T 形体、规则和概念-Titleblock
50、 tolerance do not apply to basic dimension.Basic dimensions must get their tolerances from a geometric tolerance or from a special note.标题栏公差不能应用在基本尺寸。基本尺寸必须从别处得到它自己的公差。-Basic Dimension are theoretically exact,but gage-makers tolerances do apply.Gages should have no tolerances,but in industry gages
