Calculating an Assembly Dimension Chain

Contents

1 Introduction

2 Initial data

3 Creating a Dimension Chain

4 Calculation of assembly chain ensuring complete interchangeability of its assembled components during assembly of the article

5 Calculation of assembly dimension chain ensuring incomplete interchangeability of assembled components of the article during assembly

6 Comparison of results of linear dimension chain calculations ensuring complete interchangeability of the assembled component parts of the product during assembly and their incomplete interchangeability at the estimated value of Rrisk risk percentage

7 List of literature

Introduction

The need for calculations using assembly dimension chains arises both at the stage of product design and at the stage of its manufacture (in particular, at the stage of design of the process of its assembly).

The main purpose of dimensional chain calculation during the design phase is:

establishment of nominal dimensions of component parts of the article and their limit deviations ensuring the required accuracy of the corresponding assembly parameters of the article. These are the so-called "direct problems" solved using assembly dimensional chains;

assigning a method of assembly that ensures the required accuracy of each assembly parameter with a certain confidence probability.

At the design stage of the process of assembly of the product using assembly dimension chains, the following are produced:

check of correct assignment of dimensions of component parts of the article ensuring required accuracy of the corresponding assembly parameters. These are the so-called "inverse problems" solved using assembly dimensional chains.

selecting an assembly method (or checking the acceptability of an assembly method assigned by the designer) of a product that provides (with a certain confidence probability) the accuracy of the corresponding assembly parameter specified by the designer.

The accuracy specified by the designer of an assembly parameter (closing link) must be achieved at the lowest technological cost.

All other things being equal, it is recommended to assign the assembly first by means of full interchangeability. If the use of the full interchangeability method turns out to be economically impractical or technically impossible, then you should go either to assembly by the method of incomplete interchangeability or group interchangeability, or to the method of compensating for the excessive error of the closing link (fitting, adjustment, selection of the compensator).

The calculation of the assembly dimension chain (when solving the "direct problem") consists of the following stages:

A closing link is detected, which determines one or another parameter of normal operation of the assembly unit. Then the nominal value of the closing link and its limit deviations are set.

Components of links responsible for accuracy of closing link and forming closed dimension chain with it are detected.

Due to design considerations, the values ​ ​ of the memorial dimensions of the component links are assigned (if they are unknown).

By assigning an assembly method, the limit deviations of the component links are calculated.

Source Data

The starting point for the coursework is a fragment of the assembly drawing.

The specified size is clearance A∆zad, Ajzadshire of rolling bearings.

A∆= 0.3... 1.5 mm;

TA∆zad=1.2 mm;

Record the nominal value of the closing link in the form: A∆=0+0.3+1.5 mm.

Ajzad1 = 36 mm;

TAjzad1 = 150 mcm.

Ajzad2 = 36 mm;

TAjzad2 = 150 μm

To Create a Dimension Chain

Identification of component links

A1, A2, A3, A4, A5, A6 A7, A8, A9, A10, A11, A12, A∆.

The total number of constituent links: n = 12.

Number of component links whose tolerances are given: nback = 2.