GD&T_福特汽车形位公差培训资料.pdf

GD&T Introduction
e !
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 plex geometrical
descriptions which are not otherwise able to be
described in a defined language.
2
Slide 2
Customer 用户
Engineering
Drawing
工程图纸
Product&Tool Design Manufacturing Including. Supplier
产品/模具设计制造包括供应商
Geometric Characteristic
Geometric Tolerance
Ф M A B M C M
Tertiary Datum
Material Condition Second Datum
symbol
Primary Datum
2. General Tolerancing and
Principles
1) 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+ Geometric Tolerance
. Internal
VC= MMC 尺寸– Geometric Tolerance
2) Material Conditions
Material Conditions Symbol
Maximum Material Condition M
Least Material Condition L
Regardless of Feature None
• 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 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 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 r