What are 11 and 5 qualifications. Accuracy qualifications in mechanical engineering. Linear dimensions, angles, surface quality, material properties, technical characteristics

Initially, production was a one-man business. One person made any mechanism from start to finish, without resorting to outside help. The connections were adjusted individually. It was impossible to find 2 identical parts in one factory. This continued until the middle of the 18th century, when people realized the effectiveness of the division of labor. This gave great performance, but then the question arose about the interchangeability of products. For this, a system for standardizing the levels of precision in the manufacture of parts has been developed. The ESDP has established qualifications (otherwise, the degree of accuracy).

Standardization of levels of accuracy

The development of methods for standardizing production - this includes tolerances, fit, accuracy qualifications - is carried out by metrological services. Before proceeding directly to their study, you need to understand the meaning of the word "interchangeability". What is hidden under this definition?

Interchangeability is the property of parts to be assembled into a single unit and perform their functions without mechanical processing. Relatively speaking, one part is manufactured at one plant, the other at the second, and at the same time they can be assembled at the third and fit together.

The purpose of this separation is to increase productivity, which is formed for the following reasons:

Development of cooperation and specialization. The more varied the range of production, the more time it takes to set up equipment for each specific detail.
Reducing the varieties of the instrument. Fewer types of tools also increase the efficiency of making mechanisms. This is due to the reduction in the time for its replacement in the production process.

The concept of admission and quality

It is difficult to understand the physical meaning of the tolerance without introducing the term “size”. Size is a physical quantity that characterizes the distance between two points lying on the same surface. In metrology, there are the following varieties:

The actual size is obtained by direct measurement of the part: with a ruler, caliper and other measuring tool.
The nominal size is shown directly in the drawing. It is ideal in terms of accuracy, so getting it in reality is impossible due to the presence of a certain equipment error.
Deviation is the difference between nominal and actual dimensions.
The lower limit deviation shows the difference between the smallest and the nominal size.
The upper limit deviation indicates the difference between the largest and the nominal dimensions.

For clarity, we will consider these parameters using an example. Let's imagine there is a shaft with a diameter of 14 mm. It is technically determined that it will not lose its performance if the accuracy of its manufacture is from 15 to 13 mm. In the design documentation, this is denoted 〖∅14〗 _ (- 1) ^ (+ 1).

Diameter 14 is the nominal size, "+1" is the upper limit deviation, and "-1" is the lower limit deviation. Then subtracting from the upper limit deviation of the lower one will give us the value of the shaft tolerance. That is, in our case, it will be + 1- (-1) = 2.

All sizes of tolerances are standardized and combined into groups - qualifications. In other words, quality shows the accuracy of the part being manufactured. There are 19 such groups or classes in total. Their designation scheme is represented by a certain sequence of numbers: 01, 00, 1, 2, 3 ... 17. The more accurate the size, the less quality it has.

Accuracy grade table

Interval nominal sizes mm		Quality
Numerical values of tolerances
Interval nominal sizes mm		01	0	1	2	3	4	5	6	7	8	9	10	11	12	13	14	15	16	17	18
St.	Before	micron													mm
	3	0.3	0.5	0.8	1.2	2	3	4	6	10	14	25	40	60	0.10	0.14	0.25	0.40	0.60	1.00	1.40
3	6	0.4	0.6	1	1.5	2.5	4	5	8	12	18	30	48	75	0.12	0.18	0.30	0.48	0.75	1.20	1.80
6	10	0.4	0.6	1	1.5	2.5	4	6	9	15	22	36	58	90	0.15	0.22	0.36	0.58	0.90	1.50	2.20
10	18	0.5	0.8	1.2	2	3	5	8	11	18	27	43	70	110	0.18	0.27	0.43	0.70	1.10	1.80	2.70
18	30	0.6	1	1.5	2.5	4	6	9	13	21	33	52	84	130	0.21	0.33	0.52	0.84	1.30	2.10	3.30
30	50	0.6	1	1.5	2.5	4	7	11	16	25	39	62	100	160	0.25	0.39	0.62	1.00	1.60	2.50	3.90
50	80	0.8	1.2	2	3	5	8	13	19	30	46	74	120	190	0.30	0.46	0.74	1.20	1.90	3.00	4.60
80	120	1	1.5	2.5	4	6	10	15	22	35	54	87	140	220	0.35	0.54	0.87	1.40	2.20	3.50	5.40
120	180	1.2	2	3.5	5	8	12	18	25	40	63	100	160	250	0.40	0.63	1.00	1.60	2.50	4.00	6.30
180	250	2	3	4.5	7	10	14	20	29	46	72	115	185	290	0.46	0.72	1.15	1.85	2.90	4.60	7.20
250	315	2.5	4	6	8	12	16	23	32	52	81	130	210	320	0.52	0.81	1.30	2.10	3.20	5.20	8.10
315	400	3	5	7	9	13	18	25	36	57	89	140	230	360	0.57	0.89	1.40	2.30	3.60	5.70	8.90
400	500	4	6	8	10	15	20	27	40	63	97	155	250	400	0.63	0.97	1.55	2.50	4.00	6.30	9.70
500	630	4.5	6	9	11	16	22	30	44	70	110	175	280	440	0.70	1.10	1.75	2.80	4.40	7.00	11.00
630	800	5	7	10	13	18	25	35	50	80	125	200	320	500	0.80	1.25	2.00	3.20	5.00	8.00	12.50
800	1000	5.5	8	11	15	21	29	40	56	90	140	230	360	560	0.90	1.40	2.30	3.60	5.60	9.00	14.00
1000	1250	6.5	9	13	18	24	34	46	66	105	165	260	420	660	1.05	1.65	2.60	4.20	6.60	10.50	16.50
1250	1600	8	11	15	21	29	40	54	78	125	195	310	500	780	1.25	1.95	3.10	5.00	7.80	12.50	19.50
1600	2000	9	13	18	25	35	48	65	92	150	230	370	600	920	1.50	2.30	3.70	6.00	9.20	15.00	23.00
2000	2500	11	15	22	30	41	57	77	110	175	280	440	700	1100	1.75	2.80	4.40	7.00	11.00	17.50	28.00
2500	3150	13	18	26	36	50	69	93	135	210	330	540	860	1350	2.10	3.30	5.40	8.60	13.50	21.00	33.00

Landing concept

Before that, we considered the accuracy of one part, which was set only by the tolerance. And what will happen with accuracy when connecting several parts into one unit? How will they interact with each other? And so, here it is necessary to introduce a new term "fit", which will characterize the location of the tolerances of the parts relative to each other.

The selection of landings is made in the shaft and hole system

Shaft system - a set of landings in which the size of the gap and interference is selected by changing the size of the hole, and the shaft tolerance remains unchanged. In the hole system, the opposite is true. The nature of the connection is determined by the selection of the shaft dimensions, the hole tolerance is considered constant.

In mechanical engineering, 90% of production is produced in the hole system. The reason for this is the more complex process of making a hole from a technological point of view, compared to a shaft. The shaft system is used when there are difficulties in processing the outer surface of the part. Balls in rolling bearings are a prime example of this.

All types of fittings are regulated by standards and also have accuracy qualifications. The purpose of this division of plantings into groups is to increase productivity by increasing the efficiency of interchangeability.

Landing types

The type of fit and its quality of accuracy are selected based on the operating conditions and the assembly method of the unit. In mechanical engineering, the following varieties are divided:

Clearance fits are joints that are guaranteed to form a clearance between the surface of the shaft and the bore. They are designated by Latin letters: A, B… H. They are used in nodes in which parts "move" relative to each other and when centering surfaces.
Interference fits are joints where the shaft tolerance overlaps the hole tolerance, resulting in additional compressive stresses. Interference fit refers to non-collapsible connection types. They are used in highly loaded assemblies, the main parameter of which is strength. This is the fastening of metal sealing rings and valve seats of the cylinder head to the shaft, the installation of large couplings and keys for gears, etc., etc. Fitting the shaft to the hole with an interference fit is done in two ways. The simplest of these is pressing. The shaft is centered over the hole and then placed under a press. With a greater interference, the properties of metals are used to expand when exposed to elevated temperatures and lend when the temperature drops. This method is more accurate for mating surfaces. Immediately before joining, the shaft is pre-cooled and the hole is heated. Next, the parts are installed, which, after some time, return to their previous dimensions, thereby forming the desired fit with a gap.
Transitional landings. Designed for fixed connections that are often subject to disassembly and assembly (for example, during repairs). In terms of their density, they occupy an intermediate position among the varieties of landings. These fits have an optimal balance of precision and bond strength. In the drawing are designated by the letters k, m, n, j. A striking example of their application is the fit of the inner rings of the bearing on the shaft.

Usually, the use of a particular fit is indicated in the special technical literature. We simply determine the type of connection and select the type of fit and quality of accuracy we need. But it is worth noting that in especially critical cases, the standard provides for an individual selection of the tolerance of the mating parts. This is done using special calculations specified in the relevant methodological manuals.

Qualities form the basis of the current system of tolerances and fits. Quality is a kind of set of tolerances that, for all nominal dimensions, correspond to the same degree of accuracy.

Thus, we can say that it is precisely the qualifications that determine how accurately the product as a whole or its individual parts is made. The name of this technical term comes from the word “ qualitas", Which in Latin means" quality».

The set of those tolerances that correspond to the same level of accuracy for all nominal sizes is called the quality system.

The standard established 20 qualifications - 01, 0, 1, 2...18 ... With an increase in the quality number, the tolerance increases, that is, the accuracy decreases. Qualities from 01 to 5 are intended primarily for calibers. For landings, qualifications from the 5th to the 12th are provided.

Interval nominal sizes mm		Quality

Numerical values of tolerances
Interval nominal sizes mm		01	0	1	2	3	4	5	6	7	8	9	10	11	12	13	14	15	16	17	18
St.	Before	micron													mm
	3	0.3	0.5	0.8	1.2	2	3	4	6	10	14	25	40	60	0.10	0.14	0.25	0.40	0.60	1.00	1.40
3	6	0.4	0.6	1	1.5	2.5	4	5	8	12	18	30	48	75	0.12	0.18	0.30	0.48	0.75	1.20	1.80
6	10	0.4	0.6	1	1.5	2.5	4	6	9	15	22	36	58	90	0.15	0.22	0.36	0.58	0.90	1.50	2.20
10	18	0.5	0.8	1.2	2	3	5	8	11	18	27	43	70	110	0.18	0.27	0.43	0.70	1.10	1.80	2.70
18	30	0.6	1	1.5	2.5	4	6	9	13	21	33	52	84	130	0.21	0.33	0.52	0.84	1.30	2.10	3.30
30	50	0.6	1	1.5	2.5	4	7	11	16	25	39	62	100	160	0.25	0.39	0.62	1.00	1.60	2.50	3.90
50	80	0.8	1.2	2	3	5	8	13	19	30	46	74	120	190	0.30	0.46	0.74	1.20	1.90	3.00	4.60
80	120	1	1.5	2.5	4	6	10	15	22	35	54	87	140	220	0.35	0.54	0.87	1.40	2.20	3.50	5.40
120	180	1.2	2	3.5	5	8	12	18	25	40	63	100	160	250	0.40	0.63	1.00	1.60	2.50	4.00	6.30
180	250	2	3	4.5	7	10	14	20	29	46	72	115	185	290	0.46	0.72	1.15	1.85	2.90	4.60	7.20
250	315	2.5	4	6	8	12	16	23	32	52	81	130	210	320	0.52	0.81	1.30	2.10	3.20	5.20	8.10
315	400	3	5	7	9	13	18	25	36	57	89	140	230	360	0.57	0.89	1.40	2.30	3.60	5.70	8.90
400	500	4	6	8	10	15	20	27	40	63	97	155	250	400	0.63	0.97	1.55	2.50	4.00	6.30	9.70
500	630	4.5	6	9	11	16	22	30	44	70	110	175	280	440	0.70	1.10	1.75	2.80	4.40	7.00	11.00
630	800	5	7	10	13	18	25	35	50	80	125	200	320	500	0.80	1.25	2.00	3.20	5.00	8.00	12.50
800	1000	5.5	8	11	15	21	29	40	56	90	140	230	360	560	0.90	1.40	2.30	3.60	5.60	9.00	14.00
1000	1250	6.5	9	13	18	24	34	46	66	105	165	260	420	660	1.05	1.65	2.60	4.20	6.60	10.50	16.50
1250	1600	8	11	15	21	29	40	54	78	125	195	310	500	780	1.25	1.95	3.10	5.00	7.80	12.50	19.50
1600	2000	9	13	18	25	35	48	65	92	150	230	370	600	920	1.50	2.30	3.70	6.00	9.20	15.00	23.00
2000	2500	11	15	22	30	41	57	77	110	175	280	440	700	1100	1.75	2.80	4.40	7.00	11.00	17.50	28.00
2500	3150	13	18	26	36	50	69	93	135	210	330	540	860	1350	2.10	3.30	5.40	8.60	13.50	21.00	33.00

System of tolerances and fits

The set of tolerances and fits, which was created on the basis of theoretical research and experimental research, and also built on the basis of practical experience, is called the system of tolerances and fits. Its main purpose is to select such options for tolerances and fits for typical joints of various parts of machinery and equipment, which are minimally necessary, but completely sufficient.

The basis for the standardization of measuring tools and cutting tools is precisely the most optimal gradation of tolerances and fits. In addition, thanks to them, the interchangeability of various parts of machinery and equipment is achieved, as well as an increase in the quality of finished products.

To design a unified system of tolerances and landings, tables are used. They indicate the reasonable values of the maximum deviations for various nominal sizes.

Interchangeability

When designing various machines and mechanisms, the developers proceed from the fact that all parts must meet the requirements of repeatability, applicability and interchangeability, as well as be unified and comply with accepted standards. One of the most rational ways to fulfill all these conditions is to use at the design stage the largest possible number of such components, the release of which has already been mastered by the industry. This allows, among other things, to significantly reduce development time and costs. At the same time, it is necessary to ensure high accuracy of interchangeable components, assemblies and parts in terms of their compliance with geometric parameters.

With the help of such a technical method as modular layout, which is one of the methods of standardization, it is possible to effectively ensure the interchangeability of units, parts and assemblies. In addition, it greatly facilitates repairs, which greatly simplifies the work of the relevant personnel (especially in difficult conditions), and allows you to organize the supply of spare parts.

Modern industrial production is focused mainly on mass production of products. One of its prerequisites is the timely arrival on the assembly line of such components of finished products that do not require additional adjustment for their installation. In addition, such interchangeability must be ensured that does not affect the functional and other characteristics of the finished product.

When manufacturing parts that will be mated with each other, the designer takes into account the fact that these parts will have errors and will not fit perfectly to each other. The designer determines in advance in what range the errors are allowed. Set in 2 sizes for each mating part, minimum and maximum value. The size of the part must be within this range. The difference between the largest and smallest limiting dimensions is called tolerance.

Especially critical tolerances manifest themselves in the design of the dimensions of the seats for the shafts and the dimensions of the shafts themselves.

Maximum part size or upper deviation ES, es- the difference between the largest and the nominal size.

Minimum size or lower deviation EI, ei- the difference between the smallest and the nominal size.

Landings are divided into 3 groups depending on the selected tolerance fields for the shaft and hole:

With a gap. Example:

With interference... Example:

Transitional... Example:

Tolerance fields for landings

For each group described above, there are a number of tolerance fields in accordance with which a shaft-hole interface group is made. Each separately taken tolerance zone solves its specific problem in a specific area of industry, which is why there are so many of them. Below is a picture of the types of tolerance fields:

The main deviations of the holes are indicated by capital letters, and the shafts are indicated by lowercase letters.

There is a rule for the formation of a landing shaft - hole. The meaning of this rule is as follows - the main deviations of the holes are equal in magnitude and opposite in sign to the main deviations of the shafts, indicated by the same letter.

An exception is made for joints intended for pressing or riveting. In this case, the closest value of the hole tolerance field is selected for the shaft tolerance field.

Set of tolerances or quality

Quality- a set of tolerances considered as corresponding to the same level of accuracy for all nominal dimensions.

Quality implies that the processed parts fall into the same accuracy class, regardless of their size, provided that the manufacture of different parts is carried out on the same machine, and under the same technological conditions, with the same cutting tools.

There are 20 qualifications (01, 0 - 18).

The most accurate grades are used to make samples of measures and calibers - 01, 0, 1, 2, 3, 4.

Qualities used for the manufacture of mating surfaces must be accurate enough, but under normal conditions, special accuracy is not required, therefore, for these purposes, grades 5 to 11 are used.

From 11 to 18, grades are not particularly accurate and their use is limited in the manufacture of non-mating parts.

Below is a table of accuracy by grade.

Difference between tolerances and qualifications

There are still differences. Tolerances- these are theoretical deviations, margin of error within which it is necessary to make a shaft - a hole, depending on the purpose, the size of the shaft and the hole. Quality same is the degree precision manufacturing of the mating surfaces the shaft is the hole, this is the actual deviation depending on the machine tool or the method of bringing the surface of the mating parts to the final stage.

For example. It is necessary to make a shaft and a seat for it - a hole with a tolerance field of H8 and h8, respectively, taking into account all factors such as the diameter of the shaft and hole, working conditions, material of the products. We take the diameter of the shaft and the hole 21mm. With H8 tolerance, the tolerance field is 0 + 33μm and h8 + -33μm. in order to get into this tolerance field, you need to select the quality or class of manufacturing accuracy. Let us take into account that when manufacturing on a machine, the unevenness of the production of a part can deviate both in the positive and in the negative direction, therefore, taking into account the tolerance field H8 and h8, it was 33/2 = 16.5 μm. All qualifications of 6, inclusive, correspond to this value. Therefore, we choose a machine and a processing method that allows us to achieve an accuracy class corresponding to quality 6.

Quality is a set of tolerances corresponding to the same degree of accuracy for all nominal sizes.

In total, there are 19 qualifications (01 is the highest and 17 is the lowest). The aforementioned CMEA standards contain a number of figures, but they do not give instructions in what cases, what quality is required. Similar instructions are given by designers in the drawings in the form of a numerical size and a symbol for the tolerance field, consisting of a letter and a number (sometimes two letters and numbers).

The size for which the tolerance field is indicated is indicated by a number, followed by a letter of the Latin alphabet (uppercase for holes and lowercase for shafts) indicating the position of the tolerance field relative to the zero line, and a number (two digits) that determines the quality. For example,

30h6, ZON7, ZOK10... The fit designation includes the nominal size common to the mating surfaces (hole and shaft) and the tolerance fields for each element, starting from the hole. For example, ZONE7 / g6 , or

ЗОH7 = g6, or 40 Н7 / g6 .

For irrelevant non-mating surfaces, the location of the tolerance fields is assigned: for holes - in plus (denoted by the letter H); for shafts - in minus (denoted by the letter h); for dimensions not identified by holes and shafts - symmetrically (denoted ± IT / 2). Instead of symbols, the tolerance field in the drawings is often used to limit deviations of dimensions, for example, 36 + 0.02;

18 -0,036 -0,072 .

Qualities

Classes (levels, degrees) of accuracy in the ESDP are called qualifications, which distinguishes them from the accuracy classes in the OST system. Quality (degree of accuracy) - the level of gradation of the values of the system tolerances.

The tolerances in each grade increase with the increase in nominal sizes, but they correspond to the same level of accuracy determined by the grade (its serial number).

For a given nominal size, the tolerance for different qualities is not the same, since each quality determines the need to use certain methods and means of processing products.

The ESDP has 19 qualifications, indicated by the serial number: 01; 0; 1; 2; 3; 4; 5; 6; 7; eight; nine; ten; eleven; 12; 13; fourteen; 15; 16 and 17. The highest accuracy corresponds to the quality of 01, and the lowest - the 17th quality. Accuracy decreases from grade 01 to grade 17.

The quality tolerance is conventionally denoted in capital Latin letters IT with the quality number, for example, IT6 - the 6th quality tolerance. In what follows, the word tolerance means the tolerance of the system. Grades 01, 0 and 1 are provided for evaluating the accuracy of plane-parallel gage blocks, and grades 2, 3 and 4 are intended for evaluating smooth plug gauges and staple gauges. The dimensions of parts of high-precision critical joints, for example, rolling bearings, crankshaft journals, parts connected to rolling bearings of high accuracy classes, spindles of precision and precision metal-cutting machines and others are performed according to the 5th and 6th qualifications. Grades 7 and 8 are the most common. They are designed for the dimensions of precise critical connections in instrument making and mechanical engineering, for example, parts of internal combustion engines, automobiles, airplanes, metal-cutting machines, measuring instruments. The dimensions of parts for diesel locomotives, steam engines, hoisting and transport mechanisms, printing, textile and agricultural machines are mainly performed according to the 9th grade. Quality 10 is intended for the dimensions of non-critical connections, for example, for the dimensions of parts of agricultural machines, tractors and wagons. The dimensions of parts that form irrelevant joints, in which large gaps and their fluctuations are permissible, for example, the dimensions of covers, flanges, parts obtained by casting or stamping, are assigned according to the 11th and 12th qualifications.

Qualities 13-17 are intended for irresponsible sizes of parts that are not connected with other parts, i.e. for free sizes, as well as for interoperational sizes.

Tolerances in grades 5-17 are determined by the general formula:

1Тq = аі, (1)

where q is the quality number; a is a dimensionless coefficient set for each grade and not depending on the nominal size (it is called the “number of tolerance units”); і - tolerance unit (μm) - multiplier depending on the nominal size;

for sizes 1-500 microns

for the sizes of St. 500 to 10,000 mm

(3)

where D c is the geometric mean of the boundary values

(4)

where D min and D max are the smallest and largest boundary value of the range of nominal dimensions, mm.

For a given quality and range of nominal sizes, the tolerance value is constant for shafts and holes (their tolerance fields are the same). Starting from the 5th grade, the tolerances when moving to the neighboring less accurate grade increase by 60% (the denominator of the geometric progression is 1.6). For every five qualifications, the tolerances increase 10 times. For example, for parts of nominal sizes St. 1 to 3 mm tolerance of the 5th grade ІТ5 = 4 microns; after five qualifications, it increases 10 times, i.e. IT1O = .40 microns, etc.

Intervals of nominal sizes in the ranges of St. 3 to 180 and St. 500 to 10000 mm in the OST and ESDP systems are the same.

In the OST system up to 3 mm, the following size intervals are set: up to 0.01; St. 0.01 to 0.03; St. 0.03 to 0.06; St. 0.06 to 0.1 (exception); 0.1 to 0.3; St. 0.3 to 0.6; St. 0.6 to 1 (exception) and 1 to 3 mm. St. 180 to 260 mm is divided into two intermediate intervals: St. 180 to 220 and St. 220 to 260 mm. The interval St.-260 to 360 mm is divided into intervals: St. 260 to 310 and St. 310 to 360 mm. St. 360 to 500 mm divided into intervals: St. 360 to 440 and St. 440 to 500 mm.

When converting accuracy classes according to OST to those according to ESDP, you need to know the following. Since in the OST system, the tolerances were calculated using formulas that differ from formulas (2) and (3), there is no exact coincidence of tolerances in accuracy classes and qualifications. Initially, accuracy classes were established in the OST system: 1; 2; 2a; 3; 3a; 4; 5; 7; eight; and 9. Later, the OST system was supplemented with more accurate classes 10 and 11. In the OST system, the tolerances of shafts 1, 2 and 2a of accuracy classes are set smaller than for holes of the same accuracy classes. This is due to the difficulty of machining holes in comparison with shafts.

SURFACES OF HOLE AND SHAFT IN THE HOLE SYSTEM DEPENDING ON ACCURACY CLASS

Accuracy class (quality)

Designation of tolerance fields

DIMENSIONS, mm

1…3

3…6

6…10

10…18

18…30

30…50

50…80

80…120

120…180

180…260

260…360

360…500

500…630

630…1000

(6-7)

HOLE

Ra = = 0.63

Ra = 1.25

Ra = 2.5

Rz = 20

Rz = 40

SHAFT

Ra = 2.5

Rz = 20

r6, s6

Ra = 2.5

Rz = 40

Ra = 0.63

Ra = 1.25

Ra = 2.5

Rz = 20

js6

WITH

Ra = 2.5

Rz = 20

Rz = 40

Ra = 0.63

Ra = 1.25

Ra = 2.5

Rz = 20

2a (7-8)

HOLE

A2a

Ra = 1.25

Ra = 2.5

Rz = 20

Rz = 40

SHAFT

Pr 2a

s7, u8

Ra = = 0.63

Ra = 1.25

Ra = 2.5

Rz = 20

Rz = 40

(8-9)

HOLE

H8, H9

Ra = = 1.25

Ra = 2.5

Rz = 20

Rz = 40

Rz = 80

SHAFT

Ex2 3

Ra = 2.5

Rz = 20

Rz = 40

Rz = 80

Ex1 3

x8, u8, s8

Ra = 2.5

Rz = 20

Rz = 40

Rz = 80

h8, h9

Ra = = 1.25

Ra = 2.5

Rz = 20

Rz = 40

Rz = 80

f9, e9, e8

Ra = 2.5

Ш3

Ra = 2.5

Rz = 20

Rz = 40

(11)

HOLE

H11

Rz = 20

Rz = 40

Rz = 80

SHAFT

h11

d11

b11, c11

Rz = 20

Rz = 40

Rz = 80

Ш4

a11

(12)

HOLE

H12

Rz = 40

Rz = 80

Rz = 160

SHAFT

h12

Rz = 40

Rz = 80

Rz = 160

b12

7 (14)

HOLE

H14

Rz = 80

Rz = 160

Rz = 320

Roughness parameters and criteria surfaces of metals, plastics and other materials are established by GOST 2789-73. The standard specifies six parameters of surface roughness. Most often, only two are used:

Ra - arithmetic mean deviation of the profile, mainly in the range Ra = 2.5 - 0.04 μm (6 - 12th roughness grades), and

Rz - the height of the profile irregularities at ten points, mainly in the intervals Rz = 320 - 20 μm

(1st and 5th roughness grades) and Rz= 0.1-g 0.05 microns (13-14 roughness grades). Roughness is indicated in the drawing as follows: \/ - for the surface formed by the removal of material, for example, turning, milling, etching, etc.; \/ - for a surface formed without removing material, such as casting, forging, pressing, drawing, etc.; \/ - for a surface, the method of formation of which is not established. For parameterRa indicate only the numerical value of the roughness without the letter designation of the parameter. The roughness value common for a number of surfaces of the part is set in the upper right corner of the drawing.

Surface roughness with mechanical processing methods

Surfaces to be treated

Processing methods

Roughness parameters

2,5

1,25

0,63

0,32

0,160

0,080

0,040

0,100

External cylindrical

Turning

Preliminary

Finishing

Thin

Grinding

Preliminary

Finishing

Thin

Lapping

Rough

Average

Thin

Finishing with abrasive cloth

Roller rolling

Grinding Superfinishing

Internal cylindrical

Boring

Preliminary

Finishing

Thin

Drilling

Countersinking

Rough (on a crust)

Finishing

Deployment

Normal

Exact

Thin

Broaching

Internal grinding

Preliminary

Finishing

Ball calibration

Lapping

Rough

Average

Thin

Grinding Lapping Honing

Normal

Mirrored

Planes

Planing

Preliminary

Finishing

Thin

Cylindrical milling

Preliminary

Finishing

Thin

Face milling

Preliminary

Finishing

Thin

Face turning

Preliminary

Finishing

Thin

Surface grinding

Preliminary

Finishing

Lapping

Rough

Average

Thin

Limit deviations of the shape and location of surfaces set only when the accuracy requirements for these parameters are higher than the dimensional accuracy requirements. In other cases, for deviations in shape and location, the technologist has the right to spend half of the size tolerance. Deviations according to GOST 24642-81, GOST 24643-81 are indicated on the drawings with symbols according to GOST 2.308-79. Data on maximum deviations of the shape and location of surfaces are indicated in a rectangular frame divided into two or three parts: the tolerance mark is placed in the first field; in the second - the numerical value of the tolerance in millimeters and in the third - the letter designation of the base (s), for example: | / | 0,01 I A | - the radial runout of this surface relative to the axis of the surface A (base) is not more than 0.01 mm.

Deviations in the shape and location of surfaces

Shape deviation real surface or real profile from the shape of the nominal (specified by the drawing) surface (profile)

is estimated by the largest distance D from the points of the real surface (profile) to the adjacent surface (profile) along the normal to it.

An adjacent surface (profile) is a surface (profile) that has the shape of a nominal surface (profile), in contact with a real surface (profile) and located outside the material of the part so that the deviation from

from the most distant point of the real surface (profile) within the normalized area had a minimum value.

GOST 24642-81 establishes the following deviations in the shape of surfaces

Deviation from straightness in plane t and. Convexity and concavity are particular types of this deviation.

Convex - deviation from straightness, at which the distance of the points of the real profile from the adjacent straight line decreases from the edge to the middle (Fig. 6, a) \

Concavity - deviation from straightness, at which the distance of the points of the real profile from the adjacent straight line increases from the edge to the middle (Fig. 6b).

Convexity Concavity

Roundness deviation ... Ovality and cut are particular types of this deviation.

Ovality - deviation from roundness, in which the real profile is an oval-shaped figure, the largest d m 3 X and the smallest d mla diameters of which are in mutually perpendicular directions

Cut - deviation from roundness, in which the real profile is a multifaceted figure "(Fig. 6, e).

Deflection of the profile of the longitudinal section characterizes the deviation from the straightness and parallelism of the generatrices. Particular types of this deviation are cone-shaped, barrel-shaped and saddle-shaped.

Taper - the deviation of the profile of the longitudinal section, at which the generatrices are rectilinear, but not parallel (Fig. 7, a).

Barrel- the deviation of the profile of the longitudinal section, in which the generatrices are non-rectilinear and the diameters increase from the edges to the middle of the section (Fig. 7, b).

Saddle-like - deviation of the profile of the longitudinal section, at which the generatrices are non-rectilinear and the diameters decrease from the edges to the middle of the section (Fig. 7, c).

Location deviation characterizes the deviation of the actual location of the element under consideration (surface, line, point) from its nominal (specified by the drawing) location. There are the following location deviations.

Deviation from plane parallelism - the difference AB (Fig. 8, a) of the largest and smallest distances between adjacent planes on a given area or length.

Deviation from parallelism of straight lines in the plane - the difference A-B (Fig. 8, b) of the largest and smallest distances between adjacent straight lines at a given length.

Deviation from parallelism of axes of surfaces of revolution (or straight lines in space) - deviation Yes; (Fig. 8, c) on the parallelism of the projections of the axes on their common theoretical plane passing through one axis and one of the points of the other axis.

Axle misalignment (or straight lines in space) - deviation of Du (Fig. 8, c) from the parallelism of the projections of the axes on a plane perpendicular to the general theoretical plane and passing through one of the axes.

Deviation from the parallelism of the axis of the surface of revolution and the plane - the difference A-B (Fig. 8, d) of the largest and smallest distances between the adjacent plane and the axis of the surface of revolution at a given length.

Deviation from perpendicularity of planes, axes or axis and plane - deviation D (Fig. 8, d) of the angle between planes, axes or axis and plane from a right angle, expressed in linear units at a given length L.

Face runout - the difference D (Fig. 8, e) of the largest and smallest distances from the points of the real end surface, located on a circle of a given diameter, to a plane perpendicular to the base axis of rotation. If no diameter is specified, then face runout is determined at the largest diameter of the face.

Deviation from coaxiality with respect to the base surface - the largest distance D (Fig. 8, g) between the axis of the considered surface and the axis of the base surface and the entire length of the considered surface or the distance between these axes in a given section.

Deviation from alignment with respect to the common axis - the greatest distance D x; D 2 (Fig. 8, h) from the axis of the considered surface to the common axis of two or more nominally coaxial surfaces of revolution within the length of the considered surface. The common axis of the two surfaces is taken as a straight line passing through these axes in the middle sections of the surfaces under consideration.

Radial runout - the difference D = L max -y4 min (Fig. 8, i) of the largest and smallest distances from the points of the real surface to the base axis of rotation in the section perpendicular to this axis.

Deviation from intersection - the shortest distance D (Fig. 8, k) between the axes, nominally intersecting.

Departure from symmetry - the greatest distance (Fig. 8, l) between the plane of symmetry (axis of symmetry) of the surface under consideration and the plane of symmetry (axis of symmetry) of the base surface.

Axis offset (or plane of symmetry) from the nominal location - the greatest distance D (Fig. 8, m) between the actual and nominal locations of the axis (or plane of symmetry) along the entire length of the surface under consideration.

Limit deviations of the shape and location of surfaces are indicated on the drawings or in the technical requirements. When designating in the drawing, data on the maximum deviations of the shape and location of surfaces are indicated in a rectangular frame divided into two or three parts: in the first part, the symbol for the deviation is placed, in the second, the maximum deviation in millimeters, and in the third, the letter designation of the base or other plane, to which the deviation belongs.

The accuracy standards of metal-cutting machines are characterized by the greatest permissible deviations in the shape and location of the surfaces of the workpieces being processed. The norm of machine accuracy should be understood as the maximum achievable accuracy of manufacturing a part when performing finishing operations on a new machine or on a machine that has been in operation for a short time. Accuracy indicators obtained with various types of processing, taking into account the wear of equipment and fixtures, positioning errors and other factors, are usually below these limits and characterize the economically achievable processing accuracy. The economically achievable accuracy of surface treatment is determined by the amount of costs required for the application of this processing method, which should not exceed the costs for any other method suitable for processing the same surface. As examples, we can cite data on the degree of accuracy of the geometric shape of parts when machining on various machines (Table 1).

The accuracy of the shape and location of surfaces is characterized by maximum deviations assigned in accordance with GOST 24643-81 in the presence of special requirements arising from the working conditions, manufacture or measurement of parts. In other cases, deviations in the shape and location of surfaces should be within the tolerance range of the corresponding size.

GOST 24643-81 establishes 16 degrees of accuracy and the corresponding to these degrees (depending on the nominal lengths and diameters), the dimensions of the maximum deviations of the shape and location of the surface. So, the maximum deviations from flatness and straightness for lengths from 25 to 40 mm are for the 1st degree of accuracy 0.5 microns, and for the 10th - 30 microns; the limiting values of deviations in the shape of cylindrical surfaces for diameters from 18 to 30 mm are 0.6 μm for the 1st degree of accuracy, 40 μm for the 10th degree of accuracy, and the limiting values of the radial runout for the same diameters and degrees of accuracy are 1, respectively, 6 and 100 microns. The accuracy of dimensions, shape and roughness are interdependent: it is impossible to make an exact surface if it has a large roughness, it is impossible to ensure the accuracy of measuring such a surface, etc.Rz = 10 - 0.2 μm, the following relationships between size tolerance and average roughness height have proven themselves:

- symmetrical surfaces mated by press fits,

- Rz = (0.1-0.12) T;

- transitional landings -Rz = (0.084 - 0.10) T ;

- landing movements -Rz = (0.05 - g 0.07) T.

Dimensional tolerance also interacts with the accuracy of the shape and position of surfaces. There are corresponding tables in the reference literature.

Factors affecting machining accuracy.

In the process of manufacturing parts, as a result of the action of a large number of production factors (fluctuations in workpiece allowances, cutting forces, tool wear, etc.), errors arise in all operations and transitions (size, shape, location of surfaces relative to each other, mechanical properties, etc.). ). Therefore, products made according to the same TP inevitably differ from each other and from the design "ideal" prototype in all quality characteristics. This phenomenon is called quality scattering. The scattering of any quality parameter is characterized by the scattering field w, which is the difference between the maximum and minimum values of a given characteristic from a batch of products, and the practical distribution (scattering) curve of the values of this characteristic.

Some production factors in their effect on the dispersion of the quality characteristic (on the formation of the total error) are comparable with each other, and their influence individually is small. They are difficult to identify and determine; therefore, the contribution of such factors to the error of the product (operation) is determined statistically (scattering field and distribution curve). Errors formed under the influence of such production factors are called random.

If on the coordinate grid on the abscissa axis the numbers of the parts to be processed are plotted, and on the ordinate axis - the corresponding values of the quality characteristic, for example, size, then the resulting set of points will represent a scatter diagram. Random errors form the scattering field w, Fig. 3.2, a. The practical curve of the size distribution in this field, as will be shown in § 3.2, is close to the Gaussian curve, the normal distribution law.

Along with randomly manifested factors, there are those that stand out from the total mass of production factors by their dominant influence. Such factors form permanent systematic errors in quality characteristics, which have the same value for each product in a batch or variables. systematic errors, the values of which are different on the parts, but changes from part to part are subject to a certain law.

The influence of the cumulative effect of random and systematic dominant factors leads to practical curves, which are compositions of the corresponding distribution curves, Fig. 3.2c. In this case, the magnitude of the stray field is equal to the sum of the magnitudes of the stray fields: w = w1 + w2 .

The cumulative effect of a large number of independent factors of the same order of magnitude, forming random errors (scattering fields), is studied only on the basis of statistical laws by summarizing experimental data, compiling appropriate tables, diagrams, etc. errors due to their action to warn when debugging TO. It is important to note that the division of errors into systematic and random is rather arbitrary. So, for example, if the entire batch of workpieces is processed with one cutter, then the error in setting the cutter is a systematic error. If, during the processing of a batch of blanks, several cutters have changed, then the error in the installation of the cutter becomes random and must be investigated statistically.

The fundamental relationship between the accuracy of manufacturing parts and their cost is shown in Fig. 1.4. High precision corresponds to significant processing costs. As the requirements for machining accuracy decrease, the costs, and therefore the cost, decrease (curve).

Rice. 1.4. Determination of the optimal precision of manufacturing parts.

õ - the size of the tolerance; õ 6ort - optimal tolerance; WITH- cost price, rub. / 1- the cost of manufacturing operations of parts; 2 - the cost of assembly operations; 3 - the resulting cost curve.