局部尺寸在功能公差设计中的应用和替代标注研究

Study on Local Size in Functional Tolerancing and Its Alternative Annotation

为了更好地运用现行公差标准中局部尺寸的定义进行尺寸公差设计,首先以一种自动上料机构为例介绍了ASME Y14.5和ISO/GPS公差标准中局部尺寸的概念及不同之处,分析了在两个不同标准体系下设定局部尺寸、采用公差原则和附加符号来实现几何功能的差异;随后,以电机轴的几何规范为例,分析了当采用两点测量法无法检测局部尺寸的情况下,在保证几何功能的同时采用几何公差项目进行替代标注,以规避检测局部尺寸。正确理解局部尺寸的概念、相关符号及其检测特点,避免歧义性的标注,对合理保证零件的功能、可装配性和控制制造成本有积极意义。

In order to make better use of the definition local size for the design of mechanical tolerance under current tolerance standards. The concepts of local size in ASME Y14.5 and ISO/GPS were introduced. The differences in the use of local size in ASME Y14.5 and ISO/GPS were analyzed with the application of local size in an automatic feeding mechanism. The two tolerance standards differ in setting the local size, using tolerance principle and adding symbols to realize geometrical functions. Then, the geometrical specifications of the motor shaft were analyzed when using two-point measurement methods can’t detect the local size. The geometric tolerances items were used to replace the dimensioning of sector-cylinder to avoid the detection of local size. It is of positive significance to correctly understand the concept of the local size, relevant symbols and its detection characteristics, and to avoid ambiguous dimensioning, which can guarantee the functionality and assemblability of parts, and can improve the economy.