Chapter7 Dimensional Chain尺寸链 7.1 Definition 尺寸链的定义 7.2 Calculation Method of Dimensional Chain 尺寸链的算法 Example1 Example2

A dimensional chain is a set of independent parallel dimensions which continue each other to create a geometrically closed circuit. They can be dimensions specifying the mutual position of components on one part or dimensions of several parts in an assembly unit

Terms and Types of the Dimensional Chain A dimensional chain consists of separate component link (input dimensions) and ends with a closed link (resulting dimension). Component Link (A1, B1, C1,…) : are dimensions either directly dimensioned in the drawing or following from previous manufacturing, possibly assembly operations. Closed Link(A0, B0, C0): in the given chain, it represents the resulting manufacturing or assembly dimension and is the result of combining partial dimensions as a scaled manufacturing dimension, possibly assembly clearance or interference of a component.

Increasing link: is the component link, the increase of which results in an increase of the closed link. Decreasing link: is the component link, the increase of which results in a decrease of the closed component. 

Dimensional chains can be divided into several types: assembly dimension chain (a) component dimension chain (b) process dimension chain (c)

spatial location linear dimension chain (a) planar dimension chain (b) spatial dimension chain (c)

Geometric Feature length dimension chain (a) angle dimension chain (b)

7.2 Calculation Method of Dimensional Chain Tolerance analysis - direct tasks, control Using known limit deviations of all partial components, the limit deviation of the closed link is set. Direct tasks are unambiguous in calculation and are usually used for checking components and assembly units manufactured according to the specific drawing.  Tolerance synthesis - indirect tasks, designing Using known limit deviations of a closed link given by the functional demands, limit deviations of partial components are designed. Indirect tasks are solved when designing functional groups and assemblies.

Maximum - Minimum Calculation Method (1) basic size A0:

Upper Deviation ES0

Lower Deviation EI0

The Maximum Limit of Size

The Minimum Limit of Size

Tolerance of Closing Link

Example1 A structure is shown in Figure and part sizes are known which are A1=30mm, A2=A5=5mm, A3=43mm, and A4=3mm. Calculate the basic size and limit deviations of the clearance A0.

Example2