Chapter 1 Interchangeability 1 1 Parts Interchangeability 1

Chapter 1 Interchangeability 互 换性 1. 1 Parts Interchangeability 零件的互换性 1. 2 Series of Preferred Values 优先数系 1. 3 Dimensioning Tolerance 尺寸公差的基本概念

1. 1 Parts interchangeability 零件的互换 性 In modern production, it is required that randomly selected parts from the same lot shall be successfully mounted to the machine and fulfill their functions without repairing. Such a property is called the compatibility of parts. 在现代化机械生产中, 要求制造出来的相同规格的零 件, 不经挑选和修配, 任取一件就能顺利地装到机器上去, 并满足机器性能的要求, 零件的这种性能称为互换性。 Limit and fits standards have been defined. Such standards ensure the compatibility and precision of parts. 国家制定了极限与配合的标准, 这些标准保证了零件 的互换性和制造精度。

1. 2 Series of Preferred Values优先数系 • Series of preferred values are the decimal geometric series and their common ratio can be calculated as • 优先数系是十进制等比数列

Application Examples应用实例 • If our design constraints tell us that the two screws in our gadget should be placed between 32 mm and 55 mm apart, we make it 40 mm, because 4 is in the R 5 series of preferred numbers.

1. 3 Dimensioning Tolerance尺寸公差 • Tolerance is the total amount that a specific dimension is permitted to vary; • It is the difference between the maximum and the minimum limits for the dimension. • For Example a dimension given as 1. 625 ±. 002 means that the manufactured part may be 1. 627” or 1. 623”, or anywhere between these limit dimensions.

Dimensioning Tolerance • Why is dimensioning tolerance necessary? 为什么 需要尺寸公差？ • It is impossible to manufacture a part to an exact size or geometry • Since variation from the drawing is inevitable the acceptable degree of variation must be specified • Large variation may affect the functionality of the part • Small variation will effect the cost of the part • requires precise manufacturing • requires inspection and the rejection of parts

Tolerance Examples公差实例 The Tolerance is 0. 001” for the Hole as well as for the Shaft

Tolerance examples公差实例