[交通运输]GD&ampT 福特汽车形位公差培训资料.ppt
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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 descriptio
2、ns which 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. Genera
3、l Tolerancing and Principles,Definition Dimension 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。 External VC= MMC 尺寸 + Geom
4、etric Tolerance Internal 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 tolerance Note: No additional positional or form tolerance is available; no matter
5、 what the size. (形位公差与尺寸公差各自独立, 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
6、shall not extend a boundary of LMC. (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
7、.95,20, 0.0,MMC 最大实体原则:,The surface of the 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
8、大和最小实体极限边界),20 +0/-0.021,20.01,0.031,19.979,20,20.01,19.979,0.01,20, 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 M
9、MC Feature LMC Tolerance(max)=0.09,0, 50,25.04, 0.09,Datum LMC Feature LMC Tolerance(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
10、 parts from which a datum is established.,-A-,A,A,Datum Targets 基准目标 Due to manufacturing considerations, or inherent irregularities of some surfaces, the entire surface of some features are not used as a datum reference. Point datum target Line datum target Surface datum target Datum Targets Symbol
11、 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 translation direction X, Y, Z 3 Rotational orientation U, 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 par
12、t is placed in final assembly. 模拟装配形式 Datum must be recorded in a specific sequence called datum 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, ,Po
13、int as Primary Datum,Line as Primary Datum,Plane as Primary Datum,The Effect of Material Condition on a Datum 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 allowe
14、d 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 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-,-
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