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1、GD&T Introduction,2,Slide 2,1.Definition,GD&T:Geometric Dimensioning and Tolerancing GD&T is a method for precisely defining the geometry of mechanical parts.It introduces tools which allow mechanical designers,fabricators,and inspectors to effectively communicate complex geometrical descriptions wh
2、ich are not otherwise able to be described in a defined language.,Customer 用户,Manufacturing Including.Supplier 制造包括供应商,Product&Tool Design产品/模具设计,Engineering Drawing工程图纸,Geometric Characteristic,Material Condition symbol,Primary Datum,Second Datum,Tertiary Datum,Geometric Tolerance,2.General Toleran
3、cing and Principles,DefinitionDimension Tolerance 公差:尺寸变化允许范围，等于最大极限和最小极限的差。Geometric Tolerance 形位公差：与部件的几何特征相关的公差 形状、轮廓、定向、定位、跳动 Reference Dimension 参考尺寸：没有公差的尺寸，仅供参考，加括号或跟随REF。,Virtual Condition(实效状态）：指实际要素具有最大实体尺寸且相应中心要素的形位误差等于形位公差时的状态。以控制匹配部件的间隙或建立量具的要素尺寸。ExternalVC=MMC 尺寸+Geometric Tolerance In
4、ternal VC=MMC 尺寸 Geometric Tolerance,2)Material Conditions,Regardless of Feature 独立原则（RFS):A geometric tolerance or datum reference applies at any increment of size of the feature within its size toleranceNote:No additional positional or form tolerance is available;no matter what the size.(形位公差与尺寸公差
5、各自独立，彼此无关，分别满足各自的公差原则。,Envelope Principle(包容原则):用最大/小实体来限定被测要素的实体。The surface of the feature shall not extend beyond a boundary of MMC.If the feature is produced at its MMC limit of size.No form variation is permitted.(被测要素实体不得超越最大实体理想边界）The surface of the feature shall not extend a boundary of LMC.
6、（被测要素实体不得超越最小实体理想边界）Where it is desire to permit a surface of a feature to exceed the boundary of MMC,a local note is directed to a specific dimension as“Perfect form at MMC not required”.（当需要容许被测要素实体超出最大实体边界，须加注释于特定尺寸：“不需MMC时的理想形状”）,20+0/-0.05,20,20,0.05,19.95,20,0.0,MMC 最大实体原则：,The surface of the
7、feature shall not extend beyond a boundary at virtual condition.If the feature is produced at its MMC limit of size.No form variation is permitted.(被测要素实体不得超越实效边界）The surface of the feature shall not extend beyond a boundary of MMC and LMC.(被测要素实体不得超越最大和最小实体极限边界）,20+0/-0.021,20.01,0.031,19.979,20,20
8、.01,19.979,0.01,20,49.92,50,49.92,49.92,0.08,49.92,50.13,49.92,49.92,0.21,0.021,50.13,50,0.08,Virtual condition boundary,0.08,A,A,0.12,0.012,50.13,50,0.08,50.04,0.04,A,50,25.04,0.09,Virtual condition boundary,24.95,Drawing Callout,Datum MMCFeature LMCTolerance(max)=0.09,0,50,25.04,0.09,Datum LMCFeat
9、ure LMCTolerance(max)=0.14,0.05,49.95,3）Datum 基准,Datum Feature 基准:A datum(theoretical)is a plane,axis,or point derived from the true geometric counterpart of a specified datum feature.Datum Feature:基准要素Actual feature on a parts from which a datum is established.,-A-,A,A,Datum Targets 基准目标 Due to man
10、ufacturing considerations,or inherent irregularities of some surfaces,the entire surface of some features are not used as a datum reference.Point datum targetLine datum target Surface datum target Datum Targets Symbol 基准目标符号,A3,A3,A3,15,20,The datum reference Frame(基准参考体系）,Degree of Freedom 3 transl
11、ation directionX,Y,Z 3 Rotational orientationU,V,W,Specifying Datums in an Order of Precedence按顺序来规定基准,Based on the functional and three dimentsional requirements.根据功能和三维要求 Simulate the Manner in which a part is placed in final assembly.模拟装配形式Datum must be recorded in a specific sequence called datu
12、m precedence.按特定的基准优先次序来记录,The datum precedence and minimun contact with a part is基准优先次序和与部件的最小接触为 Primary datum three points第一基准点Secondary datum two points第二基准点 Tertiary datum one point第三基准点,Point as Primary Datum,Line as Primary Datum,Plane as Primary Datum,The Effect of Material Condition on a Da
13、tum Feature,Effect of MMC/LMC 最大/小实体的影响The datum is the axis or center plane of the feature at the MMC limit.Where the actual size of the datum feature departed from MMC.A variation is allowed between its axis or center plane and those of the datum.Effect of RFS 独立原则的影响Referencing a datum feature of
14、 size on an RFS basis means the a centering about its axis or center plane is necessary,regardless of the actual size of the feature.,Effect of Datum Sequence and Material Condition.,-A-,-C-,Datum Axis B,Note:1.Datum B-最大内接圆且垂直于基准A.,Datum center plane C,2.Datum C-最大内接两平面且垂直于A和B一致,Effect of Datum Seq
15、uence and Material Condition.,-A-,-C-,Datum Axis B,Note:1.Datum B-实效状态且垂直于基准A.,Datum center plane C,2.Datum C-实效状态且垂直于A又和B一致,3.Geometric Characteristic Symbols,1)Geometric Characteristic Symbols,Straightness is the condition where an element of a surface or an axis is a straight line,Flatness is the
16、 condition of a surface having all elements in one plane,Circularity is a condition of a surface of revolution as cylinder,cone and sphere.,Cylindricity is a condition of a surface of revolution in which all points of the surface are equidistant from a common axis.,Form tolerance（形状公差）control straig
17、htness,flatness,circularity and cylindricity.,Straightness is the condition where an element of a flat surface or cylindrical surface is a straight line An axis or a center plane is a straight line.,Straightness,Specifying straightness of an Axis-RFS,轴线必须在0.04圆柱公差带内，于尺寸公差无关 每个圆形单元必须在15.9816.02 尺寸范围之
18、内。,Specifying straightness of an Axis Per Unit,轴线必须在0.5圆柱公差带内 轴线在任何25mm长度内必须位于0.1mm 圆柱公差带内。每个圆形单元必须在15.816.02 尺寸范围之内。,Flatness,Flatness is the condition of a surface having all elements in one plane 面上所有的点必须位于两个平行平面之间。他们分开的量即为规定的平面度公差 RFS is implied.,Specifying flatness of an surface,平面度公差必须小于尺寸公差 表
19、面在间距0.25两平面之间尺寸必须在45.046.0之间,Circularity,Circularity is a condition of a surface of revolution as cylinder,cone and sphere.圆度为旋转表面的一个状态,圆柱体或锥体面上所有的与垂直中心轴线任何平面截得的圆单元上的点与中心轴线等距离 表面上所有的圆单元必须位于两同心圆之间。同心圆的距离即为规定公差的量,Specifying Circularity of an cylinder or Cone,圆度公差必须小于尺寸公差 必须在14.014.3 尺寸范围之内 表面的每个圆单元必须在
20、两个间距为0.5的同心圆内,Cylindricity is a condition of a surface of revolution in which all points of the surface are equidistant from a common axis.圆柱面是当表面上所有的点都与一公共轴线等距离的旋转表面的状态。,Cylindricity,表面必须位于两个同心圆柱之间。同心圆柱之间的距离即为规定公差 RFS Implied 不能超出MMC 边界。,Note:圆柱度是圆度，锥度和直线度的组合。,Specifying Cylindricity of an Cylinder
21、,圆柱度公差必须小于尺寸公差 必须在23.024.0 尺寸范围之内 表面的每个圆单元必须在两个间距为0.25的同心圆内,The profile tolerance(轮廓度)specifies a uniform boundary along the true profile within which the elements of the surface must lie.It may be applied to an entire surface or to individual profiles taken at various cross sections through the par
22、t.,Profile of a line 线轮廓度,Profile of a Surface 面轮廓度,Profile of a line 线轮廓度 是一种状态，此时：表面的单元为一种轮廓线。他由弧线、曲线、直线或不规则线或他们组合而成。理论尺寸用于定义公差带轮廓。表面上所有线单元必须在沿理论轮廓的均匀公差带内。RFS implied.,Profile of a line,Specifying Profile of a Line,全公差带是3 mm 宽，沿理论轮廓不均匀分布,Profile of a Surface,Profile of a Surface线轮廓度 是一种状态，此时：表面的单元
23、为一种轮廓面。他由弧线、曲线、直线或不规则线或他们组合而成。理论尺寸用于定义公差带轮廓。公差带是三维的 表面上所有点必须在沿理论轮廓的均匀公差带内。RFS implied.,Specifying Profile of a Surface,Orientation(定向)The tolerances control the orientation of the features to one-anther.,Angularity 倾斜度,Perpendicularity 垂直度,Parallelism 平行度,一个表面、轴线或中心平面与以基准暗示垂直关系。与两个垂直于基准平面或轴线的两个平行平面所
24、规定的公差带内。当用于平面表面时，公差同样控制平面度。RFS implied.,Perpendicularity 垂直度,Perpendicularity,表面位于0.12间距的两平行平面内，该二平面垂直与基准A。表面必须位于MMC尺寸内。该公差必须小于尺寸公差,Specifying Perpendicularity for a Plane,公差带形状与基准相关,基准为直线，则公差带有方向性垂直与基准轴线。如基准为平面，特征为线，则公差带为一圆柱形,Angularity 倾斜度一个表面或轴线与一个基准平面或轴线成一个规定的理论正确角度,Angularity,表面必须位于两个与基准成规定角度的平
25、行平面内，给平行平面距离即为公差带 用于平面时，公差同样控制平面度。RFS Implied.,Specifying Angularity for a Plane,表面必须位于两个平行平面的公差带内表面必须在尺寸极限内。既右端在3.5 4.5范围内。,Parallelism 平行度表面所有点与一个基准平面等距离或一根轴线与一基准轴线等距离 公差带形状：基准为面：两平行平面内基准为线：圆柱面内 用于平面时，公差同样控制平面度 RFS Implied.,Parallelism,Specifying Parallelism for a Axis,轴心线位于两平行平面内。,Location(定位)：Lo
26、cation tolerance are used to control relationship of 1)center distance;2)Location from datums;3)Coaxiality of symmetry;4)Equally disposed center distances.,Position 位置度：center,axis,center plan of a feature.,Concentricity 同轴度：revolution feature,Symmetry 对称度,Position 位置度：精确控制单一要素或成组要素在基准体系中的位置.位置度公差带与
27、基准体系密切相关。位置度公差带内，允许中心，轴线或其他尺寸要素偏离理论位置在同一范围内控制垂直度或平行度。,Position,该位置度控制的垂直度与S 基准相关。公差带为圆柱面内。,Concentricity 同轴度：revolution feature一个旋转表面所有的剖面单元的轴线与基准要素的轴线共线,Concentricity,Note:不管表面状态如何，要求检测轴线难以测量，经济性较差3。建议用跳动公差来取代。,50,25.04,0.09,0.05,49.95,Symmetry 对称度两个或多个要素表面的所有相对或对应位置的中点与基准轴线或中心平面一致,Symmetry,公差带为以中心
28、平面为中心的两个平行平面 规定的公差和基准适用于 RFS.,公差带为两平行平面,Runout 跳动:Runout is a composite tolerance used to control the functional relationship of one or more features of a part to a datum axis.,Circular Runout 圆跳动,Total Runout 全跳动,Circular Runout 圆跳动控制单一圆单元围绕一基准轴线的表面的圆度和同轴度的累积变化与一基准轴线成直角关系的平面上所有圆单元的控制。,Circular Runo
29、ut,Total Runout 全跳动,Total Runout,控制围绕一个基准轴线构成的表面所有单元由以下公差积累的状态 圆度直线度同轴度 倾斜度面轮廓度平面度,控制所有单元围绕一基准轴线的表面的圆度和同轴度的累积变化与一基准轴线成直角关系的平面上所有单元的控制。,0.05,所有测量必须垂直于中心轴线,4.Reference Documents,ASME Y14.5 1994 Dimensioning and TolerancingASME Y 14.5-1-1994 Mathematical Definition of Dimensioning and Tolerancing Principle.,
