Tolerance and Cooperation Plan 1

Teaching Plan on tolerances and cooperation

1. Concept of interchangeable

Definition of interchangeable

Swapping refers to the process of selecting one part from a batch of identical parts, which can be assembled into machines or parts without Configuration Modification and meet the performance requirements of products.

Interchangeable meaning

Interchangeable parts are conducive to organizational collaboration and professional production. It is of great significance to ensure product quality, reduce costs and facilitate assembly and maintenance.

Terms and definitions of Dimensional Tolerances

1)Basic Size-- Design the given size. Ø 30mm in.
2)Actual Size-- After the parts are made, the size obtained through measurement is obtained.
3)Maximum Size-- Two boundary values that allow the actual size change of a part. The larger one is called the maximum limit size, and the smaller one is called the minimum limit size.

B shows that the maximum and maximum sizes of the shaft ø 30mm are ø 29. 993mm and the minimum limit sizes are ø 29. 980mm. The actual size must be between the two limit sizes.

)Dimensional Deviation(AbbreviationDeviation) -- Returns the algebraic difference between a dimension and a basic dimension. The maximum deviation, the lower deviation (hereinafter referred to as the limit deviation), and the actual deviation.

Upper deviation = maximum limit size-Basic Size
Lower deviation = minimum limit size-Basic Size

Shows the axis:

Upper deviation = (29.993-30) mm =-0.007mm
Lower deviation = (29.980-30) mm =-0.020mm

National standardsRules: CodeESAndEsRepresentHoleAndAxisOffset; CodeEIAndEiRepresentHoleAndAxis
. The deviation can be positive, negative, or zero.

The algebraic difference between the actual size and the basic size is calledActual deviation. The actual deviation of the Part Size is between the above and below.

5)Dimensional Tolerances(AbbreviationTolerances) -- The amount of size changes allowed.

That is: Tolerances = maximum limit size-minimum limit size
Or: Tolerances = upper deviation-lower Deviation

As shown in

Tolerances = (29.993-29.980) mm = 0.013mm
Or: Tolerances = [-0.007-(-0.020)] mm = 0.013

Since the maximum limit size is always greater than the minimum limit size, the tolerances are always positive and cannot be zero.

InPart DrawingGenerally, dimensions with tolerances are not labeled with two limit dimensions, butBasic SizeAndUpper and lower deviations, See.

6)Size Difference band(AbbreviationPublic difference band) -- The Public difference is an area that represents the tolerances and the position relative to the zero line.

A Represents the relationship between a pair of Combined Holes and the basic dimensions, limit sizes, deviations, and tolerances of the shaft. For the sake of simplification, we generally only draw a simplified diagram of the upper and lower deviations of the holes and axes.Public difference band chart, See B.

In the public difference band diagram,Zero LineIs a straight line indicating the basic size. When the zero line is drawn as a horizontal line, the positive deviation is located on the zero line
The negative deviation is located below the zero line, and the unit of the deviation is micron.

 

 

Standard tolerances and basic deviations

The national standard tolerances and Cooperation sets outPublic difference bandByStandard tolerancesAndBasic DeviationIt consists of two elements.

Standard tolerancesOKSize of the Public difference band,

WhileBasic DeviationOKLocation of the Public difference band, See.

1)Standard tolerances (it)

The value of the standard tolerances is determined by the basic dimensions and tolerances. The tolerances are used to determine the dimension accuracy. Standard public
The difference is classified into 20 levels, namely, it01, it0, it1 ,..., Iti8. The size accuracy decreases from it01 to iti8. The specific values of the standard tolerances can be queried.

2) Basic Deviation

The Basic Deviation generally refers to the deviation close to the zero line between the upper and lower deviations. That is, when the public difference is above the zero line, the basic deviation is the lower deviation. When the public difference is below the zero line, the basic deviation is the upper deviation, see.

The national standards set 28 different basic deviations for both holes and shafts. The Basic Deviation code is represented by a Latin letter, an uppercase letter represents a hole, and a lowercase letter represents a axis. It is a series of 28 basic deviations between holes and shafts.

From the Basic Deviation series, we can see that the Basic Deviation of the axis is from A to H, and is a negative value, and its absolute value decreases in turn; from J to 2C is the lower deviation (EI), and is a positive value, and its absolute value increases sequentially.

The Basic Deviation from A to H of a hole is the lower deviation (E1), and is a positive value, and its absolute value decreases sequentially. From J to ZC is the upper deviation (es), and it is a negative value, the absolute values increase sequentially. The Basic Deviation between H and H is zero. JS and JS are symmetric on the zero line and there is no basic deviation. The top and bottom deviations are + It/2 and-it/2 respectively.

The Basic Deviation series diagram only represents the locations of the Public difference band. Therefore, only one end of the basic deviation is drawn, and the other end is open, that is, the other end of the Public difference band depends on the standard tolerances (it).

Public difference band code

The common difference band code of the hole and shaft consists of the Basic Deviation code and the tolerances class code.

For example, explain the meanings of ø 50h8 and ø 50f7.

Cooperation

The relationship between the holes with the same basic size and the Public difference of the shaft is called cooperation. According to different requirements, the combination between the hole and the shaft is relaxed and tight. Therefore, the national standard stipulates that the combination should be divided into three types: Gap cooperation, interference cooperation, and transitional cooperation (see ).

Gap cooperation

When the hole and the shaft are assembled, there is a gap (including the minimum gap is equal to zero. As shown in, the public difference band of the hole is above the public difference band of the axis.

 

 

Transitional cooperation

There may be a gap or interference when assembling the hole and the shaft. As shown in, the public difference bands of holes overlap with those of uranium.

 

Interference sharing

There is a surplus between the hole and the shaft assembly (including the Minimum Surplus is equal to zero. C shows that the public difference of the hole is under the Public difference of the axis.

 

The National Standard specifies two benchmark systems: base hole and base axis.

Base hole System

The basic deviation is the public difference band of a certain hole, and the public difference band of the shaft with different basic deviations forms a system of various combinations (). The lower deviation of the reference hole is zero and is indicated by the serial number H.

 

 

 

Base axis

The basic deviation is the public difference band of a certain axis, and the public difference band of the holes with different basic deviations forms a system of various combinations (B ). The vertical deviation of the reference axis is zero and is indicated by the Code h.

Codename

The codename consists of the Public difference band code of the hole and the axis. It is written as the score form. The numerator is the public difference band code of the hole, and the denominator is the public difference band code of the axis. Base-hole-based coordination of H contained in molecules and base-axis coordination of h contained in denominator.

The meaning of the sample description.

The basic size of the fit isØ 25mmAnd the gap matching of the base hole. The public difference band of the reference hole isH7, (The Basic Deviation is H. the tolerance level is 7 .)G6(The Basic Deviation is g, and the tolerance level is 6 ).