dimensional analysis of constructive units (methods for accuracy is achieved of closing links)...
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DIMENSIONAL ANALYSIS OF DIMENSIONAL ANALYSIS OF CONSTRUCTIVE UNITSCONSTRUCTIVE UNITS
(Methods for accuracy is achieved of (Methods for accuracy is achieved of closing links)closing links)
LecturerLecturerEgor Egor EfremenkovEfremenkov
TomskTomsk - 20 - 201515
Methods for accuracy is achieved of closing links
Achievement accuracy task may be solved by following 5-th methods:
full interchangeability; not-full interchangeability; sectional interchangeability; trueing; adjustment.
Describing of Methods
1. Full interchangeability method
The required accuracy of closing link is achieved any cases as a dimension chain include formative links without choice, selection or change mining of them
Let’s consider how the task is been solved at example next dimension chain.
Dimension chain of mechanism
Advantages: •Simply assembly;•Widely collaboration between deferent factories; •Possibility to us the workers without high qualification for assembly;•Simplicity of rate setting for technological process of assembly
Describing of Methods
Full interchangeability method
1. Closing link tolerance is divided between tolerances of formative links (using equation 4, lecture 2);
2. For the formative links are designated limit deviations except one;
3. Firstly middle coordinate of tolerance zone are found for remaining link by equation 6 (lecture 2). Then the limit deviations of last link may be calculated.
Tolerance and limit deviations of closing link are calculated by the method of maximums and minimums.Calculation make by following way:
Describing of Methods
Full interchangeability method
The formative links tolerances can be choose by manner of equal tolerances more often, like
Describing of Methods
Full interchangeability method
The full interchangeability method lead to uneconomical tolerances of formative links very often.
We us this method for short chains with less number of links (п + р ≤ 4).
The method essence consists in dimension chain is included formative links without choice, selection or change mining of these links for requirement closing link tolerance is achieved with some risk which was chosen earlier.
Describing of Methods
Not-full interchangeability
The aforethought risk is for meanings of closing links which can go out of tolerance zone. The risk is not big usually. By not-full interchangeability method the formative links tolerances are calculated at the statements of The theory of probability:
(1)
Direct task is solved for this method by the following way:
Meanings of the risk factor t and relative standard deviation λi are chose. Then middle tolerance of formative links is calculated;The formative links tolerance may be chose by equation (1);For the formative links are designated limit deviations except one;Firstly middle coordinate of tolerance zone are found for remaining link by equation 6 (lecture 2). Then the limit deviations of last link may be calculated.
Describing of Methods
Not-full interchangeability
This method allow for short dimension chain formative links tolerance are grate increased in comparison with previous method
We us the not-full interchangeability method when closing link tolerance is less but number of chain’s links increase in comparison with previous method.
Describing of Methods
Not-full interchangeability
By The Sectional interchangeability method the closing link tolerance is achieved due to dimension chain including formative links, which divided by the sections (groups) preliminary
Describing of Methods
Sectional interchangeability
Usually The Sectional interchangeability method is using when tolerance of closing link is small very much and it is obtained impossible by not-full interchangeability method
For the Sectional interchangeability method the closing link tolerance ТА is increased at N points (N – integer value). It called like expend tolerance
Т'А = ТАN
The expend tolerance is using for obtained formative links tolerances of dimension chain
Describing of Methods
Sectional interchangeability
The details is produced with the expend tolerance it’s sort by N groups.
For the Sectional interchangeability method is been using that following terms are accomplished
1. Tolerance of forms and surface location mustn’t be more then tolerances dimensions of them in group;
2. For expend tolerance of closing link is distributed between formative links by equation
Describing of Methods
Sectional interchangeability
3. Important requirement it equality allocation of dimensions in tolerance zone
Diagram of closing link tolerance achievement by the Sectional interchangeability method
Describing of Methods
Sectional interchangeability
The Sectional interchangeability method is more useful (economic) for large-scale manufacturing and mass production in high quality assembly
Describing of Methods
Sectional interchangeability
Describing of Methods
Trueing
In this case the closing link tolerance may be more then required tolerance
Describing of Methods
Trueing
And its difference called Maximum calculation compensation
This value should be delated from compensation link.Revision:
When we choose the compensation link very important:1.Like compensator we should choose detail which is measured with minimum expenses by trueing;2.The using is prohibited for detail including in tow or more chains.
Describing of Methods
Trueing
Main advantage: There is achievement of closing link high accuracy with relative low detail accuracy.
Disadvantages:1.Needs using workers with high quality;2.Big oscillations of time spend during the process.
Describing of Methods
Trueing
We can change compensator dimension without delete material and achieved accuracy of closing link.
Compensator dimension may be changed by tow ways:•Position of compensator can be changed;•Special detail is imputed in the chain. For example like gasket. It has needs dimension.
Describing of Methods
Adjustment
We can change the gap А by the sleeve move.
Describing of Methods
Adjustment
Example of gap accuracy is obtained by adjustment method with motion way
If tolerances Т'Аi and center coordinates '0Аi are knew then for closing link:
Describing of Methods
AdjustmentWhen we used motionless compensator it needs remember that it can't compensate itself tolerance.
Where п+p-1 means that compensator tolerance Т'Аk and it’s center coordinate А'0Аk
are not taken into account.
Maximum possible compensation:
Describing of Methods
Adjustment
Number of steps compensators
Advantages of the adjustment method:Any degree of tolerance is able to achieved for closing link;Spend time not so big for making adjustment;We may support of needs tolerance for closing link during the exploitation of units.
Describing of Methods
Adjustment
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