GBOU SPO "NATK"
APPROVED Deputy Director for NGOs __________ G.B. Korotysh
METHODOLOGICAL INSTRUCTIONS
for conducting laboratory and practical classes
in discipline: Technical measurements.
Developed Reviewed and approved at the meeting
Subject (cycle) commission
Teacher Protocol No.___ dated ____________
M.S. Lobanova Chairman ______L.N. Veselova
2014
Preview:
State budgetary educational institution
secondary vocational education
"NIZHNY NOVGOROD AVIATION TECHNICAL COLLEGE"
(GBOU SPO "NATK")
I approve
Deputy Director for Open Source Education
T.V.Afanasyeva
"___"_______2013
Set
test materials
for intermediate certification By academic discipline
OP.01 Technical measurements
code and name
basic professional educational program
by profession/specialty
01/15/25 Machine operator (metalworking)
code and name
Nizhny Novgorod
2013
Developers: Teacher Lobanova M.S.
Reviewed by PCC "Mechanical Engineering"
Protocol No.____ dated “___”________2013.
Chairman of the PCC Veselova.L.N ______
Testing and measuring materials are intended for monitoring and assessing the educational achievements of students who have mastered the academic discipline programTechnical measurements
CMMs include control materials for intermediate certification in the form oral on tickets.
2. Results of mastering the discipline to be tested
(the results of mastering the discipline are indicated in accordance with work program academic discipline)
Mastered skills | Learned knowledge |
|
|
3. Measuring materials for assessing the results of mastering an academic discipline Technical measurements
3.1 Form of differentiated credit - oral on tickets
3.2 Tasks for differentiated credit:
Ticket No. 1
1. Define tolerance, maximum dimensions, deviations
2. Surface roughness and its parameters
Ticket No. 2
1. Interchangeability, measurement error
2. Total tolerances, their definition
Ticket No. 3
1.Draw a diagram of the location of tolerance fields in the hole and shaft system
2.Roughness parameters
Ticket No. 4
Ticket No. 5
1. The procedure for selecting and assigning accuracy grades and choosing landings
2. Designation of roughness in the drawings
Ticket No. 6
1. Classification of landings
Ticket No. 7
2.Smooth micrometer device
Ticket No. 8
1.Table symbols tolerances of shape and location
2. Control of calibers and their devices
Ticket No. 9
1. The influence of roughness on the operational properties of components and mechanisms
2.Automatic controls
Ticket No. 10
1.Name the basic principles of constructing tolerances and fits
2. Test rulers and plates
Ticket No. 11
1.The concept of error and size accuracy
2.Measurements and control of linear quantities
Ticket No. 12
1.Measuring rulers
2. Limit dimensions and deviations
Ticket No. 13
1.Tolerances and fits of conical connections
2.Surface roughness. Basic terms and definitions
Ticket No. 14
1. Designation of landings on the drawings
2. Design of the ShTs-2 caliper
Ticket No. 15
1. Caliber control
2.Characteristics of fastening threads
Ticket No. 16
1. Roughness sign. Designation of roughness in drawings
2. Tolerances and fits of threads with clearance
Ticket No. 17
1.Tolerances and interference fits of threads
2. Design of the ShTs-1 caliper
Ticket No. 18
1. Tolerances and fits of key connections
2.Micrometer instrument
Ticket No. 19
1.Methods and means of thread inspection
2. Deviations in the shape of cylindrical surfaces
Ticket No. 20
1.Classification of calibers
2. Determination of maximum deviations
Criteria for assessing assignments
"5" 2 ticket questions + additional task
"4" 2 ticket questions
"3" 1 ticket question
"2" No response to ticket
Conditions for completing the task
1. Place, conditions for completing the task - class
2. Maximum task completion time: 2 hours
3. Sources of information permitted for use during the exam, equipment -textbook Zaitsev.S.A., posters, stands, reference book
The item(s) corresponding to the results (objects) and certification types specified in section 1 are filled in. The rest are deleted.
Preview:
Laboratory work No. 1
Average diameter measurement and control external thread thread gauges
Goal of the work:
Study methods of measuring and controlling the average diameter of external threads using working and control gauges
1.Working and control gauges for bolts
2.Threaded go and no-go rings
3.Threaded brackets
4. Part - bolt for measuring threads
5.Thread micrometers
6.Delays
Work order:
1.Repeat general information about threads: thread elements, working surfaces
2. Familiarize yourself with the provided control gauges in the form KPR-HE, U-PR, U-NE, K-I, KI-NE KHE-PR, KHE-HE
3.Measure the average diameter using the three-wire thread method and gauge
4.Draw up a report
Report generation algorithm:
1. Record the measured size H (based on the outer diameter of the wires)
2.According to the formula d 2 = M - 3d + 0.866Р the average diameter of the thread is calculated d – the diameter of the wires
3. Using a special table, knowing the size M, thread pitch and wire diameter, we find the values of the average diameter of the external thread d 2
Control questions:
1.List the main parameters of cylindrical threads and draw their sketch
2.What is meant by the given average thread diameter?
3.What working gauges are used to control bolt threads?
Preview:
Laboratory work No. 2
Measuring size and shape deviation with a smooth micrometer
Goal of the work:
Study micrometric measuring instruments and their main characteristics, learn how to measure dimensions with permissible error
Material and technical equipment:
1. Micrometer
2. Depth gauge
3. Bore gauge for a cylindrical part
Work order:
1.Repeat the purpose of the main means of measuring and monitoring linear dimensions, measurement techniques, basic tools, measurement accuracy, main characteristics of tools
2. Familiarize yourself with the device of the micrometer and its measurement limits
3. Take measurements of the proposed parts
4.Draw up a report
Report generation algorithms:
1.Make measurements of the parts yourself with a smooth micrometer
2. Determine the reading value using the formula l=S x n
3.Summarize the data into a table
Control questions:
1.What is the commonly used thread angle when measuring with a micrometer?
2.What are the characteristics of micrometer instruments
3.What is the measurement limit of the micrometer?
Laboratory work is designed for 2 hours
Preview:
Laboratory work No. 3
Tolerance as the difference between maximum deviations from the nominal size
Goal of the work:
Teach the student to determine the maximum deviations, arithmetically calculate the upper deviation, lower deviation, the largest maximum size, the smallest maximum size, tolerance on the shaft and hole
Material and technical equipment:
1.Calculators
2.Posters of tolerance fields in the hole system and in the shaft system
3.Tables
4.Reference books
5. Stand “Scheme of tolerance fields and allowances for machining holes and shafts”
Execution order:
1.Repeat the basic definitions (nominal size, tolerance, actual size)
2.Look at the approval poster
3.Study the definition of VO, BUT
4.Familiarize yourself with the tolerance diagram for parts: shaft, hole
5.Draw up a report
Report generation algorithm:
1.Draw a schematic sketch of the hole shaft according to the given assignment
2.Independently select tolerances for shaft dimensions and holes according to the table
4. Draw a diagram of tolerance fields yourself
5.Summarize the data into a table
Given | Solution | Result |
Dmax Dmin D valid d max dmin | ES=D max – D es = d max – d EI = D min - D ei = d min – d TD= D max - D min = l ES-EI l Td = d max - d min = l es – ei l | ES, es- ? EI, ei - ? D action, d action - ? TD - ? Td - ? |
Control questions:
1.What are the largest and smallest limit sizes?
2.What is measurement error?
4.What is the actual size?
Laboratory work is designed for 4 hours
Preview:
Laboratory work No. 4
Determination of the maximum dimensions of holes and shafts, clearance and interference tolerances
Goal of the work:
1. Learn to draw a diagram of the location of tolerance fields for fits and interferences
2. Learn to determine the maximum tolerance dimensions for clearances and interference
Exercise:
1.Draw a diagram of the location of tolerance fields based on the initial data
Selection of measuring instruments
Goal of the work:
1. Teach the student how to choose measuring instruments to control parts
2. Teach the student to control dimensions using measuring instruments with an acceptable error
Material and technical equipment:
1.Measuring rulers
2.Smooth micrometer
3. Vernier caliper
4.Details
5.Drawings
6.Tutorial
7.Posters
Exercise:
1.Study the detail drawing
2. Select a measuring tool according to the dimensions of the drawing with an acceptable error
3.Measure the proposed part with a measuring tool
4.Draw up a report
Performance:
1.Study the design and metrological characteristics of measuring instruments
2.Draw a sketch of the part, putting down all the dimensions
3.Draw sketches of the selected measuring instruments
4.Measure the dimensions of the part
5.Summarize the data into a table
Conclusion:
Laboratory work is designed for 2 hours
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Tolerances and technical measurements
Processing accuracy
Machining accuracy is understood as the compliance of the sizes, shapes and relative positions of sections of the machined surfaces with a given accuracy, as well as the cleanliness of the surface treatment of the part with the requirements of the drawing and technical specifications.
The durability of machines operating at high speeds and loads depends largely on the quality of the surface of the rubbing parts. Despite the great accuracy and high perfection of modern metal-cutting equipment, it is impossible to obtain absolutely accurate dimensions or shapes of the part in accordance with the dimensional tolerance specified in the drawing. Therefore, all manufactured parts will have some deviations (errors).
Magnitude errors in the manufacture of parts depends on the following reasons:
Accuracy of machine tools and cutting tools (machines cannot be absolutely accurate, but cutting tool may have wear);
Temperature of the part being tested. As the temperature of the part increases, its size will differ from the size measured at normal temperature(20°C);
Serviceability measuring tool;
Ability of a motor mechanic and mechanic to use measuring instruments.
The concept of tolerances
In the connection of two parts that fit into one another, a hole and a shaft are distinguished (Fig. 210). Hole and shaft are terms used to denote, respectively, internal (female) 1 and external (covered) 2 elements of parts are not only cylindrical (Fig. 210, a), but also flat with parallel planes - groove, key, etc. (Fig. 210, b).
Fig. 210 Connection of two parts:
a) cylindrical; b) flat
Modern technology is unthinkable without the interchangeability of parts. Interchangeable These are parts that exactly, without any adjustment, fit the installation site and can replace the part being replaced. It is clear that parts can be interchangeable only when their dimensions and material properties are within strictly specified limits. Therefore, when designing interchangeable parts, in addition to nominal size (determined by calculation) indicate the permissible value of deviations at which their reliable operation and interchangeability.
Admission size is the difference between the largest and smallest limit sizes. The tolerance value is indicated in tenths or even hundredths of a millimeter (microns - 0.001mm).
The tolerance is determined in the form of two deviations from the nominal: upper and lower dimensions. The deviation can be positive if the limit size is greater than the nominal size, and negative if the limit size is less than the nominal size.
Proper tolerance selection is critical to cost-effective part manufacturing. The smaller the tolerance, the more difficult to manufacture parts, the cost of machines and tools for their processing and control is higher. Tolerances are chosen so that, in addition, there is reliable operation of the part.
Fig. 211 Designation of tolerance fields.
For example, Fig. 211 shows a shaft with a nominal diameter d=55mm and the deviations are indicated: at the top - upper +0.03 and lower - 0.02. The upper deviation (+0.03) for the shaft is considered when the maximum size is larger than the nominal one. The lower deviation (-0.02) is considered when the maximum size is less than the nominal size.
When one of the maximum dimensions is equal to the nominal one, then the deviation is not indicated in the drawing. If the upper and lower deviations are equal in magnitude, but have different signs, then the total number with the ± sign is indicated in the drawing. drawing detail tolerance
Landings
Landing called the nature of the connection of two parts inserted into one another. There are movable (with clearance), fixed (with interference) and transitional landings.
Movable are called landings that provide a gap in the connection, characterizing greater or less freedom of relative movement of parts.
GapS is the positive difference between the hole diameter and the shaft diameter S = D - d
Due to fluctuations in the actual dimensions of the mating parts within the specified tolerances, the gaps will also fluctuate from the largest to the smallest value.
By interference N called the difference between the diameters of the shaft and the diameter of the hole before assembly, i.e. N = d - D. The interference can also vary from greatest to least. Maximum interference Nh is the difference between the largest maximum shaft size and the smallest
The immobility of interference fits is ensured by friction forces.
Transitional fits are those in which it is possible to obtain both a gap and an interference fit. When graphically depicting a transitional fit, the tolerance fields of the hole and shaft overlap completely or partially. The immobility of transitional fits is ensured both by friction forces and by the use of additional fastening devices in the form of keys, splines, etc.
ConceptaboutdeviationfromformsAndlocationsurfaces.
When processing parts, not only deviations from the specified dimensions are observed, but also deviations from the specified geometric shape and correct relative position of surfaces.
Deviation from the shape and correct relative position of surfaces includes deviation from straightness (Fig. 212, a), which is defined as a deviation from a straight line of the surface of a part in a given direction.
Deviation from the shape of parts in the form of a cylinder is characterized by a deviation from cylindricity. A special case of deviation from cylindricity is ovality (ellipse) (Fig. 213, b) .
Deviations from the profile of the longitudinal section of the cylinders are: taper (Fig. 213, A), barrel-shaped (Fig. 213, b) and her corsetry (Fig. 213, c)
Fig. 212 Deviations from shape Rice. 213 Deviations from the longitudinal section profile
a) deviations from straightness; a) taper; b) barrel-shaped; c) corsetry
b) deviations from forms
The main deviations from the location are: deviation from parallelism (Fig. 214, a), referred to as deviation from perpendicularity (Fig. 214.6), deviation from coaxiality (Fig. 214, c).
Rice. 214 Deviations from the location of surfaces:
a) deviation from parallelism; b) deviation from perpendicularity; c) deviation from alignment.
Roughnesssurfaces
Surface roughness- a set of surface irregularities with relatively small steps along the base length. Measured in micrometers (µm). Roughness refers to microgeometry solid and determines its most important performance qualities. First of all, wear resistance from abrasion, strength, density (tightness) of connections, chemical resistance, appearance. Depending on the operating conditions of the surface, a roughness parameter is assigned when designing machine parts, and there is also a relationship between the maximum size deviation and roughness.
Fig.215Surface roughness
where: - base length; - midline of the profile; - average pitch of profile irregularities; - average pitch of local profile protrusions; - deviation of the five largest profile maxima; - deviation of the five largest profile minima; - the distance from the highest points of the five largest maxima to a line parallel to the average and not intersecting the profile; - the distance from the lowest points of the five largest minima to a line parallel to the average and not intersecting the profile; - maximum profile height; - deviation of the profile from the line; - profile section level; - the length of the segments cut off at the level.
Basics of technical measurements
When repairing internal combustion engines and other ship mechanisms, accurate measurements are required. For this, various tools and devices are used.
Yardstick manufactured in lengths of 150-1000 mm, used for measuring linear dimensions. Measurement accuracy 0.5 mm.
Folding meter consists of thin elastic steel rulers, hingedly connected. Measurement accuracy 0.5 mm.
Vernier caliper b Designed for precise measurements of length, thickness, outer and inner diameters, as well as for measuring the depth of holes, recesses and heights.
Rice. 216 Vernier caliper:
1 - rod; 2 - movable jaws; 3 - fixed jaws;
4 - fixation screw; 5 - rod; 6- vernier.
The caliper (Fig. 216) is a rod 1 with millimeter divisions of double-sided jaws - fixed 2 and mobile 3. A movable double-sided jaw moves along the rod 3, having a slot with beveled edges. There are divisions on one of the beveled sides. This part of the caliper is called the vernier 6. Screw 4 serves to fix the position of the frame, rod 5 - for measuring depths.
More accurate measurements are made with a caliper with a vernier division size 0.02 mm smaller than each division marked on the rod scale. This achieves a measurement accuracy of 0.02 mm.
Micrometer(Fig. 217) has bracket 1 and stop 2. The scale of whole and half millimeters is marked on the fixed sleeve 5. Movable rod 3 has an exact one at the other end metric thread in increments of 0.5 mm. This means that in one revolution the rod will move 0.5 mm. Circumference of movable bushing 6, fixed on a rod, divided into 50 equal divisions. This means that if in one full revolution the movable sleeve together with the rod moves by 0.5 mm, then when the sleeve is turned by only one division, the rod will move only 0.5:50 = 0.01 mm.
Fig.217 Vernier
Fig. 218 Micrometer for determining sizes up to 25 mm
Fig. 219. Sizing Fig.220. Micrometric gauge By micrometer
Let us assume (Fig. 219) that 13.5 mm is visible on the fixed scale of the micrometer, and the vernier mark number 45 coincides with the mark of the fixed rod. Then the micrometer reading is 13.50 + (45* 0.01) = 13.5 + 0.45 = 13.95 mm.
The ratchet (see Fig. 218) is used to create a constant force when screwing the micrometer screw. Retainer 4 designed to fix the position of the screw after measurement.
The micrometer is a tool high precision and is only used for precise measurements.
Micrometric gauge (Fig. 220) are used to measure the internal diameters of cylinders and other holes. It consists of a micrometer head and a set of extensions. The design of the micrometer head is the same as that of a micrometer. Measurement accuracy 0.01 mm. To measure a hole, for example 350 mm, take a 75 mm head, 25 mm and 250 mm extensions. Having collected the micromass from the indicated elements, they begin to measure the holes.
When measuring with a micro-piece, the extension must be stationary, and the point of contact should be looked for with the head. By shaking the end of the micro-piece with a micrometer head along the axis of the product and increasing or decreasing the size of the head, the size of the hole is found.
Indicator - a lever-mechanical device with which deviations in the sizes and shapes of parts are determined. The indicator is also used to check the parallelism of the planes, the engagement of the journals of the crankshafts and other shafts, the excavation of the crankshafts, etc.
The indicator mechanism (Fig. 221) consists of gears and a rack enclosed in a housing 1 and connected to the measuring rod 2 and tip 3. On the front of the case there is a scale divided into 100 equal parts, the size of each part is 0.01 mm. When taking measurements, the indicator is mounted on a tripod (stand) so that its tip touches the surface of the part being measured. When moving the indicator or part, all changes in the shape of the surface (protrusions, depressions, breaks) will immediately be reflected on the indicator rod, which, moving, will set the scale arrow in motion. If the rod moves 0.01 mm, the indicator needle will deviate by one scale division.
Dipstick (Fig. 222) serves to determine the gap between the surfaces of parts. It is a set of calibrated plates made of high-quality steel and ground in thickness with an accuracy of 0.001 mm. A typical plumbing probe includes plates of the following thicknesses: 0.03; 0.05; 0.10; 0.15; 0.20; 0.25; 0.30; 0.40; 0.50; 0.75; 1.00.
Rice. 221 Indicator Rice. 222 Dipstick
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The mechanisms of machines and devices consist of parts that perform certain relative movements during operation or are connected motionlessly. Parts that, to one degree or another, interact with each other in a mechanism are called conjugated.
Production experience has shown that the problem of choosing optimal accuracy can be solved by establishing for each part size (especially for its mating dimensions) the limits within which its actual size can fluctuate; At the same time, it is assumed that the assembly into which the part is included must correspond to its purpose and not lose its functionality under the required operating conditions with the required resource.
Recommendations for the selection of maximum deviations in the dimensions of parts were developed based on many years of experience in the manufacture and operation of various mechanisms and devices and scientific research, and are set out in the unified system of admissions and landings (USDP CMEA). Tolerances and fits established by the ESDP CMEA can be carried out using hole or shaft systems.
Basic terms and definitions are established by GOST 25346-89 “Basic standards of interchangeability. ESDP. General provisions, series of tolerances and main deviations.”
Dimensions – the numerical value of linear quantities (diameters, lengths, etc.) in mechanical engineering and instrument making; dimensions are indicated in millimeters (mm). All sizes are divided into nominal, actual and limit.
Nominal size - the size that is indicated in the drawing on the basis of engineering calculations, design experience, ensuring constructive perfection or ease of manufacture of the part (product). The maximum dimensions are determined relative to the nominal size; it also serves as the starting point for deviations. To reduce the variety of sizes assigned by designers with all the ensuing advantages (narrowing the range of materials, the range of measuring cutting and measuring tools, reducing the standard sizes of products and spare parts for them, etc.), as well as for the purpose of using scientifically based, most rationally constructed series of numbers , when designing, you should be guided by GOST 6636 - 69 for normal linear dimensions. In standardization, series of numbers are used, the members of which are members of geometric progressions.
Product quality is one of the most important indicators of production economic activity enterprises. The economic characteristics of the enterprise, its competitiveness, and position in the market for goods and services largely depend on the level of quality of manufactured products.Underproduct quality is understood as a set of characteristics and properties of a product that determine its ability to satisfy certain needs.
There are two groups of indicators that reflect product quality.
Performance indicators , which reflect product quality properties related to meeting needs in accordance with the purpose of the products. Such indicators, in relation to mechanical engineering products, include: specifications machines and devices, their reliability and durability, design, resistance to impact environment and others, as well as the price of the product and the costs of its operation.
Production and technological indicators characterizing a machine or device as an object of production in the conditions of the manufacturer.These indicators indicate the compliance of the quality of manufactured products with the requirements of standards or technical specifications, the degree of their manufacturability, the labor intensity and cost of products in production, etc.
Each enterprise is called upon to produce products of proper quality that can satisfy all consumer requirements. . The production of high-quality products determines the need to provide the enterprise with a complex of technical, organizational and managerial measures aimed at producing products of appropriate quality. International standard ISO 8402 series interprets the concept of quality assurance as follows:
"Quality assurance “are all planned and systematically carried out activities within the quality system, as well as confirmed (if required), necessary to create sufficient confidence that the facility will meet quality requirements.”
Ensuring the quality of products – one of the important functions of organizing production at an enterprise. To implement this function, the enterprise is forming a product quality assurance system, which is a set of organizational measures aimed at creating necessary conditions to produce products of the required quality.
GOST - state standard – is being developed for products of cross-industry significance.Unlike technical specifications, GOST requirements are developed not by the manufacturer, but by government industry structures, approved at top level Interstate Council for Standardization, Metrology and Certification.
Each GOST undergoes serious tests and inspections in certified laboratories, is evaluated by industry scientists, undergoes interdepartmental approvals, and only after that is allowed for publication.
Many institutes, enterprises, and experts are involved in the creation and approval of GOST. GOSTs are approved by the Federal Agency for Technical Regulation and Metrology (abbreviated name in 2004-2010 - Rostekhregulirovanie; since June 2010 - Rosstandart) - a federal executive body that carries out the functions of providing public services, state property management in the field of technical regulation and metrology. Administered by the Ministry of Industry and Trade Russian Federation. In other countries (CIS) - similarly.
Specifications
THAT - technical specifications- is developed by the manufacturing enterprise and approved by the sectoral ministry with minimal formalities. Therefore, specifications can be softer compared to GOST, or they can be more stringent when the standard is outdated and does not meet the requirements of a particular production, for example, in terms of manufacturing accuracy, the amount of impurities, etc. Businesses to avoid extra costs, often develop their own specifications to certify their products.
GOST establishes technical requirements to products, safety requirements, methods of analysis, scope and methods of application. GOST requirements must be followed by everyone government agencies management and business entities. If GOST is at the very top of the pyramid of standards, then TU is at the very bottom: technical conditions are mostly developed by manufacturers independently, based on their own ideas about how this or that product should be made and what properties it should have.
Industry standard
OST – industry standard – developed for products of industry significance.
Industry Standard (OST) - established for those types of products, norms, rules, requirements, concepts and designations, the regulation of which is necessary to ensure the quality of products in this industry.
Objects of industry standardization in particular, there may be certain types of products of limited use, technological equipment and tools intended for use in a given area, raw materials, materials, semi-finished products for intra-industry use, certain types of consumer goods. Also, the objects can be technical standards and standard technological processes industry-specific norms, requirements and methods in the field of design organization; production and operation of industrial products and consumer goods.
Industry standards are approved by the ministry (department), which is the head (leading) in the production of this type of product. The degree of mandatory compliance with the requirements of an industry standard is determined by the enterprise that applies it, or by agreement between the manufacturer and the consumer. Monitoring the implementation of mandatory requirements is organized by the agency that adopted this standard.
Size
Nominal size
Actual size
Limit dimensions
The larger one is Dmax and dmax, and the smaller one is Dmin and dmin.
Limit dimensions make it possible to determine the accuracy of processing; using them, parts are rejected.
In modern mechanical engineering, machine parts are madeinterchangeable . This means that during assembly, any part from the entire mass of identical parts can be connected to the parts mating to it without additional processing (adjustment), and the required type of connection (fit) is obtained. Only under this condition is it possible to assemble machines using the in-line method.
It is impossible to perfectly accurately process parts; there will always be small deviations from the required dimensions due to the inaccuracy of the machines on which the parts were processed, the inaccuracy of the measuring instruments used to measure, etc. Therefore, in order for the parts to meet the requirements of interchangeability, it is necessary to indicate acceptable values on the drawings deviations from nominal dimensions for this type of connection of parts
The largest permissible size for the required connection (fitting) of parts is calledlargest size limit ;
The smallest permissible size to achieve the required connection (fit) is calledsmallest size limit (Fig. 626).
The difference between the largest and smallest limit sizes is calledadmission .
The difference between the largest limit size and the nominal size is calledupper limit deviation .
The difference between the smallest limit size and the nominal size is calledlower limit deviation.
In fig. Figure 1 shows the upper positive deviation (with a + sign) and the negative lower one (with a - sign).
However, the largest limit size is not always larger, and the smallest limit size is less than the nominal size. Typically, in the case of a fixed fit, the largest and smallest maximum dimensions of the shaft must be larger than the nominal size (Fig. 1).
With a movable fit, the largest and smallest maximum dimensions of the shaft must be less than the nominal size (Fig. 627). In this case, a gap is formed between the parts being connected, the size of which is determined by the positive difference between the diameter of the hole and the diameter of the shaft. In this case, a gap is formed between the parts being connected, the size of which is determined by the positive difference between the diameter of the hole and the diameter of the shaft.
Size tolerance is called the difference between the largest and smallest limit sizes or the algebraic difference between the upper and lower deviations.
Nominal size , relative to which the maximum dimensions and deviations are determined. The nominal size is common to connections.Actual size established by measurement with permissible error.
Limit dimensions - these are two maximum permissible sizes, between which the actual size must be, or to which the actual size can be equal.
Validity condition for actual parts: The usable actual size must be no more than the maximum and no less than the minimum or be equal to them.
Hole validity condition:
Dmin< Dd < Dmax
Shaft validity conditions:
dmin< dd < dmax
The validity condition must be supplemented with a characteristic of the defect: the defect is correctable, the defect is incorrigible.
Example : The designer, based on strength conditions, determined the nominal shaft size to be 54 mm. But, depending on the purpose, size 54 may deviate from the nominal within the following limits: largest size dmax = 54.2 mm, smallest size dmin = 53.7 mm. These dimensions are limiting, and the actual size of a suitable part can have dimensions between them, that is, from 54.2 to 53.7 mm.
However, it is inconvenient to specify two sizes in the drawing, therefore, in addition to the nominal size, its upper and lower maximum deviations are indicated in the drawing.
The upper limit deviation is the algebraic difference between the largest limit and nominal sizes.
The lower limit deviation is the algebraic difference between the smallest limit and nominal sizes.
In the drawing, the maximum deviations of dimensions are indicated on the right immediately after the nominal size: the upper deviation is above the lower one, and the numerical values of the deviations are written in a smaller font (the exception is a symmetrical two-sided tolerance field, in this case the numerical value of the deviation is written in the same font as the nominal size) . The nominal size and deviations are indicated on the drawing in mm.A + or - sign is indicated before the maximum deviation value; if one of the deviations is not indicated, this means that it is equal to zero.
There is no such thing as a negative tolerance; it is always a positive value.
A size does not exist without a drawing; it must be correlated with the surface whose processing is determined by it.
For convenience and simplification of handling drawing data, the whole variety of specific elements of parts is usually reduced to two elements:
external (male) elements - shaft,
internal (encompassing) elements – hole.
At the same time, the accepted term “shaft” should not be identified with the name of a typical part. The variety of elements such as “shaft” and “hole” is in no way connected with a specific geometric shape, which is usually associated with the word “cylinder”. Specific structural elements parts can have the shape of smooth cylinders or be limited by smooth parallel planes. Only the generalized type of part element is important: if the element is external (male) it is a “shaft”, if internal (male) it is a “hole”.
A part is considered acceptable if:
Dmin ≤ DD ≤ Dmax (for hole)
dmin ≤ dД ≤ dmax (for shaft)
We will fix the marriage if:
DD< Dmin (для отверстия)
dД > dmax (for shaft)
The specified image is constructed as follows. First, draw a zero line, which corresponds to the nominal size and serves as the starting point for measuring dimensional deviations.
When the zero line is horizontal, positive deviations are laid up from it, and negative deviations are laid down. Next, the values of the upper and lower deviations of the hole and shaft are noted, and horizontal lines of arbitrary length are drawn from them, which are connected by vertical straight lines. The tolerance field obtained in the form of a rectangle is shaded (the tolerance field of the hole and the tolerance field of the shaft, as well as adjacent parts, are shaded in different sides). Such a scheme makes it possible to directly determine the size of gaps, maximum dimensions, tolerances; interference
Schematic graphic representation of tolerance fields
Landing - the nature of the connection of two parts, determined by the difference in their sizes before assembly. The fit characterizes the freedom of relative movement of the parts being connected or the degree of resistance to their mutual displacement.There are three types of plantings: with clearance, interference fit and transitional fits.
Landings with clearance
Gap S
Preference fits
Preload N - positive difference between the dimensions of the shaft and hole before assembly. The tension ensures the mutual immobility of the parts after their assembly.
Transitional landings . A transitional fit is a fit in which it is possible to obtain both a gap and an interference, depending on the actual dimensions of the hole and shaft.
Transitional fits are used for fixed connections in cases where during operation it is necessary to disassemble and assemble, and also when increased demands are placed on the centering of parts.
Transitional fits, as a rule, require additional fastening of the mating parts to ensure the immobility of the joints (dowels, pins, cotter pins and other fasteners).
Fit tolerance – the sum of the tolerances of the hole and shaft that make up the connection.
Rice. 2. Scheme of pairing the hole and shaft with a gap
There are also fits in the hole system and fits in the shaft system.
Landings in the hole system – fits in which the required clearances and interferences are obtained by combining various shaft tolerance fields with the tolerance field of the main hole, designated by the letter H. The main hole is a hole whose lower deviation is zero.
Fittings in the shaft system – fits in which the required clearances and interferences are obtained by combining different tolerance fields of the holes with the tolerance field of the main shaft, designated by the letter h. The main shaft is a shaft whose upper deviation is zero.
The system of tolerances and fits provides for fits in the hole system and in the shaft system.Landings in the hole system – landings in which various clearances and tensions are obtained by connecting different shafts to the main hole, which is designated by the letter H.
Fittings in the shaft system – landings in which various gaps and interferences are obtained by connecting various holes with the main shaft, which is designated by the letter h.
Landings with clearance . A clearance fit is a fit that always ensures a gap in the connection, i.e. the smallest limit size of the hole is greater than or equal to the largest limit size of the shaft (the tolerance field of the hole is located above the tolerance field of the shaft).
Gap S - positive difference between the sizes of the hole and the shaft. The gap allows relative movement of mating parts.
Preference fits . An interference fit is a fit in which interference is always ensured in the connection, i.e. the largest limit size of the hole is less than or equal to the smallest limit size of the shaft (the tolerance field of the hole is located under the tolerance field of the shaft).
How to determine the type of landing?
Example.
Nominal shaft size 122 mm
lower shaft deflectionei = -40 μ (-0.04 mm)
upper shaft deflectiones = 0 μ (0 mm). Ø122H7/h7
Nominal hole size 122 mm,
lower hole deviationEI = 0 μ (0 mm),
upper hole deviationES = +40 µm (+0.040 mm).
Solution.
1. Maximum shaft size limitd max
d max = d + es = 122 + 0 = 122 mm.
2. Smallest maximum shaft sized min
d min =d+ei= 122 + (-0.04) = 121.96 mm.
3. Shaft tolerance
ITd = d max - d min = 122 – 121.96 = 0.04 mm
orITd = es - ei = 0- (-0.04) = 0.04 mm.
4. Largest hole size limit
D max = D+ES = 122 + 0.04 = 122.04 mm.
5. Smallest hole size limit
D min = D + E1 = 122 + 0 = 122 mm.
6. Hole tolerance
ITD = D max - D min = 122.04 - 122 = 0.04 mm
orITD = ES - E1 = 0.04 - 0 = 0.04 mm.
7. Maximum joint clearance
S max = D max - d mia = 122.04 - 122.96 = 0.08 mm
orS max=ES-ei= 0.04 - (-0.04) = 0.08 mm.
8. Minimum gap in connection
S mia = D mia - d max= 122 - 122 = 0 mm
orS min =EI-es= 0 – 0 = 0 mm.
9. Fit tolerance (clearance)
ITS = S max - S min = 0.08 - 0 = 0.08 mm
orITS = ITd + ITD = 0,04 + 0,04 = 0,08 mm.
It should be understood that S= - N and N= -S.
Conclusion: landing with clearance.
Lesson #17TOLERANCES AND DEVIATIONS IN THE ARRANGEMENT OF SURFACES
Deviation of EP location is the deviation of the actual location of the element in question from its nominal location. Undernominal refers to the location determined by the nominal linear and angular dimensions.
To assess the accuracy of the location of surfaces, bases are assigned (an element of the part in relation to which the location tolerance is set and the corresponding deviation is determined).
Admission location is called a limit that limits the permissible deviation of the location of surfaces.
TR location tolerance field – an area in space or a given plane, within which there must be an adjacent element or axis, center, plane of symmetry within the normalized area, the width or diameter of which is determined by the tolerance value, and the location relative to the bases is determined by the nominal location of the element in question.
Table 2 - Examples of applying shape tolerances in the drawing
The standard establishes 7 types of surface location deviations:
from parallelism;
from perpendicularity;
tilt;
from alignment;
from symmetry;
positional;
from the intersection of the axes.
Deviation from parallelism – the difference ∆ of the largest and smallest distances between planes (axis and plane, straight lines in a plane, axes in space, etc.) within the normalized area.
Deviation from perpendicularity – deviation of the angle between planes (plane and axis, axes, etc.) from right angle, expressed in linear units ∆, over the length of the standardized section.
Tilt deviation – deviation of the angle between planes (axes, straight lines, plane and axis, etc.), expressed in linear units ∆, over the length of the standardized section.
Deviation from symmetry – the greatest distance ∆ between the plane (axis) of the element (or elements) under consideration and the plane of symmetry base element(or common plane symmetry of two or more elements) within the normalized area.
Deviation from alignment – the greatest distance ∆ between the axis of the surface of revolution under consideration and the axis of the base surface (or the axis of two or more surfaces) along the length of the standardized section.
Deviation from intersection of axes – the smallest distance ∆ between axes that nominally intersect.
Positional deviation – the greatest distance ∆ between the actual location of the element (center, axis or plane of symmetry) and its nominal location within the normalized area.
Table 3 - Types of location tolerances
The working drawings of the parts provide precise indications of the surface roughness acceptable for normal normal operation these details.
Undersurface roughness is understood as a set of surface microroughnesses measured at a certain length, which is called the base.
The amount of roughness on the surface of a part is measured in micrometers (mKm). 1 mKm = 0.001 mm.
Surface roughness parameters.
Altitude parameters.
Rz, mKm – average height of micro-irregularities at 10 points (1 mKm = 0.001 mm).
We draw any line. In relation to it, the distances of up to 5 protrusions and up to 5 depressions are the average distance between five located within the base length l highest points protrusions and the five lowest points of the depressions, numbered from a line parallel midline.
Ra, mKm – arithmetic mean deviation of the profile – average conclusion, within the base length l, the distance of the points of protrusions and points of depressions from the center line:
Roughness classes.
GOST establishes 14 classes of surface cleanliness.
Classification of surface roughness is carried out according to the numerical values of the parameters Ra and Rz with normalized basic data in accordance with the table.
The higher the class (smaller numerical value of the parameter), the smoother (cleaner) the surface. Roughness classes from 1 – 5, from 13 – 14 are determined by the Rz parameter, all others from 6 to 12 – by the Ra parameter.
The surface roughness of the part is specified during design, based on functional purpose details, i.e. from the conditions of her work, or for aesthetic reasons.
The required cleanliness class is ensured by the manufacturing technology of the part.
Roughness designation
Designation
Processed surfaces
R z 20
Non-working surfaces gear wheels
Internal surface of the piston skirt
Inner non-working surface of the bushing
R A 2,5
End surfaces that serve as a support for gear hubs.
Side surface teeth of large modules of slotted and planed wheels
Outer surface of the ring gear
Inner surface housings for rolling bearings
R A 1,25
Non-working surfaces of bronze wheels
Block cover reference plane
Support scraped plane of the control tool ruler
Ground rod for studs
R A 0,63
Mating surfaces of bronze wheels
Non-working crankshaft and camshaft journals
Sockets for crankshaft bearings
Cylindrical surface of power studs
Working surfaces of lead screws
Shaft surfaces for rolling bearings
R A 0,32
Outer surface of the piston crown
Piston boss holes finger to finger
The surface of the connecting rod flanges. Working surfaces of centers
Shaft surfaces for rolling bearings of classes B, A and C
R A 0,16
Working journals of the crankshaft of a high-speed engine. Working camshaft journals. Valve working plane. The outer surface of the piston skirt. Supercharger impeller blade surface
R A 0,08
Valve master plate. The outer surface of the piston pin. Mirror of a cylindrical sleeve. Balls and rollers of rolling bearings. Working journals of precision high-speed machines.
R A 0,04
Measuring surfaces of limit gauges for 4th and 5th accuracy classes.
Working surfaces of parts measuring instruments in moving joints of medium precision Balls and rollers of high-speed critical transmissions.
R a 0,1
Measuring surfaces of high precision instruments and gauges (classes 1, 2 and 3). Working surfaces of parts in moving joints of medium precision.
R z 0,05
Measuring surfaces of tiles. The measuring surfaces of measuring instruments are of very high precision. Measuring surfaces for high class tiles. Surfaces of extremely critical precision instruments
Measuring instrument (MI) - This technical means or a set of means used to carry out measurements and having standardized metrological characteristics. Using measuring instruments physical quantity can not only be detected, but also measured.In the scientific literature, technical measuring instruments are divided into three large groups. This:measures , calibers Anduniversal facilities measurements , which include measuring instruments, instrumentation (instrumentation), and systems.
Calibers are called scale-free control instruments designed to limit deviations in size, shape and relative position of product surfaces. With the help of gauges it is impossible to determine the actual deviations in the dimensions of a product, but their use makes it possible to determine whether or not the deviations in the dimensions of a product are within specified limits.
Calibersserve not to determine the actual size of the parts, but tosorting them into suitable and two groups of rejects (from which not all of the allowance has been removed and from which excess allowance has been removed).
Sometimes, using gauges, parts are sorted into several groups suitable for subsequent selective assembly.
Depending on the type of products being controlled, calibers are distinguished for:
checking smooth cylindrical products (shafts and holes),
smooth cones,
cylindrical external and internal threads,
tapered threads,
linear dimensions,
gear (spline) connections,
location of holes, profiles, etc.
Limit calibers are divided into pass and non-pass.
When inspecting a passable part, the pass gauge (PR) must be included in the passable product, and the no pass gauge (NOT) must not be included in the passable product. The product is considered suitable if a pass-through gauge is included, but a non-go-through gauge is not. A pass gauge separates usable parts from correctable defects (these are parts from which not all of the allowance has been removed), and a pass-through gauge separates usable parts from irreparable defects (these are parts from which excess allowance has been removed).
According to their technological purpose, gauges are divided into working gauges used to control products during the manufacturing process and acceptance of finished products by quality control department workers and control gauges (counter gauges) to check working gauges.
Basic requirements for calibers
1. Precision manufacturing. The working dimensions of the caliber must be made in accordance with the tolerances for its manufacture.
2. High rigidity with low weight . Rigidity is necessary to reduce errors from deformation of gauges (especially large staples) during measurement. Light weight is required to increase the sensitivity of the control and facilitate the work of the inspector when checking medium and large sizes.
3. Wear resistance . To reduce production costs and periodic check calibers, measures must be taken to increase their wear resistance. The measuring surfaces of the gauges are made of alloy steel, hardened to high hardness and covered with a wear-resistant coating (for example, chrome-plated). They also produce calibers small sizes, made of hard alloy.
4. Performance Control ensured by rational design of calibers; Where possible, one-sided limit gauges should be used.
5. Stability of working dimensions achieved by appropriate heat treatment (artificial aging).
6. Corrosion resistance , necessary to ensure the safety of calibers, is achieved by using anti-corrosion coatings and choosing materials that are less susceptible to corrosion.
Vernier tools are common types of measuring instruments in mechanical engineering. They are used to measure external and internal diameters, lengths, thicknesses, depths, etc.Three types of calipers are used: ShTs-I, ShTs-I and ShTs-Sh.
Caliper ShTs – I: 1- rod, 2, 7 - jaws, 3- movable frame, 4- clamp, 5- vernier scale, 6- depth gauge ruler
The ShTs-I caliper is used to measure external, internal dimensions and depths with a vernier reading of 0.1 mm. The caliper (Figure 1.8) has a rod 1, on which there is a scale with millimeter divisions. At one end of this rod there are fixed measuring jaws 2 and 7, and at the other end there is a ruler 6 for measuring depths. A movable frame 3 with jaws 2 and 7 moves along the rod.
During the measurement process, the frame is fixed to the rod with clamp 4.
The lower jaws 7 are used to measure external dimensions, and the upper 2 - for internal dimensions. On the beveled edge of the frame 3 there is a scale 5, called a vernier. The vernier is designed to determine the fractional value of the bar division, i.e. to determine the fraction of a millimeter. The vernier scale, 10 mm long, is divided into 10 equal parts; therefore, each vernier division is equal to 19:10 = 1.9 mm, i.e. it is shorter than the distance between every two divisions marked on the rod scale by 0.1 mm (2.0-1.9 = 0.1) . With the jaws closed, the initial division of the vernier coincides with the zero stroke of the caliper scale, and the last 10th stroke of the vernier coincides with the 19th stroke of the scale.
Before measuring with the jaws closed, the zero strokes of the vernier and the rod must coincide. If there is no clearance between the jaws for external measurements or with a small clearance (up to 0.012 mm), the zero strokes of the vernier and the rod must coincide.
When measuring, the part is taken in the left hand, which should be behind the jaws and grasp the part not far from the jaws, the right hand should support the bar, while thumb This hand moves the frame until it comes into contact with the surface being tested, avoiding distortion of the jaws and achieving normal measuring force.
The frame is secured with a clamp using the thumb and forefinger. right hand, supporting the barbell with the remaining fingers of this hand; left hand at the same time, it should support the lower lip of the rod. When reading the readings, the caliper is held directly in front of the eyes. An integer number of millimeters is counted on the rod scale from left to right by the zero stroke of the vernier. The fractional value (the number of tenths of a millimeter) is determined by multiplying the reading value (0.1 mm) by the serial number of the vernier stroke, not counting the zero, which coincides with the rod stroke. Sample readings are shown in the figure below.
39+0,1*7= 39,7; 61+0,1*4=61,4
Height gauges designed for measuring heights from flat surfaces and precise markings, manufactured in accordance with GOST 164-90.
Thickness gauges are designed as follows: they have a base with a rod with a scale rigidly attached to it, a movable frame with a vernier and a locking screw, a micrometric feed device, which consists of a slider, a screw, a nut and a locking screw, which allows you to install replaceable legs with a marking point (applying marks).
List of recommended literature:
Zaitsev S. A. Tolerances and technical measurements. / S.A. Zaitsev, A. D. Kuranov, A. N. Tolstvo. – M.: Academy, 2017. – 304 p.
Taratina E.P. Tolerances, fits and technical measurements. Tutorial–M.: Academbook \ Textbook, 2014
Zaitsev, S.A. Tolerances, fits and technical measurements in mechanical engineering / S.A. Zaitsev, A.D. Kuranov, A.K. Tolstoy. – M.: Academy, 2016. – 238 p.
Internet resources:
https://studfiles.net/
Compiled by: D. A. Mogilnaya
In modern mechanical engineering and instrument making, one of the main prerequisites for organizing mass production with conveyor assembly is the interchangeability of parts.
Thanks to interchangeability it is possible to provide high quality products at low cost.
Interchangeability can be complete or partial. With complete interchangeability, there should be no fitting or adjustment operations during the assembly process. This, as a rule, requires the manufacture of parts with very tight dimensional tolerances, as a result of which the cost of the product slightly increases. Therefore, they often prefer to move to partial interchangeability. In this case, during assembly it is necessary to use compensators (washers, gaskets, adjusting screws, etc.) and even perform some adjustment operations. Reducing the cost of processing parts due to expanded tolerances, as a rule, fully compensates for the additional time spent during assembly on adjustment and fitting.
In the production of parts, interchangeability is ensured by the choice of processing methods in which the variation in the dimensions of parts would fit within the tolerance zone, and during control - by the most rational choice of measuring instruments (in terms of accuracy) and their correct use in the work.
Due to the fact that when processing a batch of identical parts, their dimensions will inevitably fluctuate (size variation), the concept of tolerance is introduced.
Tolerance is the permissible, legalized range of variation, i.e., the amount of variation in the sizes of parts. It is defined as the maximum difference in size
δ = dmax - dmin.
The location of the tolerance relative to the size of the parts (its relationship with the size) is determined by the so-called deviations. Deviations can be likened to errors, since both are counted (measured) from some value, have a direction (are vectors) and, therefore, a plus or minus sign.
Size deviation is the algebraic difference between the size and its nominal value. Deviations are considered positive if the size is larger than the nominal one, and negative if the size is smaller than the nominal one.
The tolerance field is determined by the size of the tolerance and its location relative to the nominal size. The upper limit of the tolerance field corresponds to the largest limit size, and the lower limit corresponds to the smallest.
Tolerances in drawings of parts and assemblies are indicated in the form of deviations after the designation of the nominal size. Moreover, the upper deviation is applied above the lower one, for example 100+0.03-0.20. A deviation equal to zero is not indicated. If the tolerance field is symmetrically located, the deviation value is marked with a “±” sign, for example 100 ± 0.2.
In order to assemble a mechanism or machine from individual parts, these parts must be connected to each other in a certain sequence, ensuring their contact and interaction, i.e., mutual interfacing. There are two types of conjugations: complete and incomplete. Complete mating presupposes the presence of a male and a female part, so that the latter is somehow seated on the first. This is where the term landing came from. Depending on whether it is necessary to maintain mutual immobility between the parts being connected or to provide them with freedom of movement relative to each other, two types of landings are distinguished - movable and fixed.
A typical and common case of mating is the fitting of a round bushing hole on a round shaft.
In case of incomplete mating, one part moves not in another, but along another; Thus, the conjugation conditions in this case are always variable.
Complete couplings, as noted above, include movable and fixed landings.
Movable fits are characterized by a gap, and fixed fits are characterized by interference.
The gap is usually called the positive difference between the diameter of the hole dA and the shaft dB.
The interference is considered to be the positive difference between the shaft diameter dв and the hole diameter dA before assembling the parts.
During assembly, under the influence of force applied in the axial direction, the shaft bigger size fits into the smaller hole in the bushing. In this case, the shaft compresses and the bushing expands. The resulting deformations create stresses that ensure a tight fit.
Currently, the system of tolerances and fits of shafts and holes is a large regulatory material containing standardized tolerances (accuracy classes), the location of the tolerance field (fits) and a series of normal diameters ranging from 0.1 to 31,500 mm.
Ten accuracy classes (or gradations of tolerances in magnitude) have been established from 1 - the most accurate to 9 - the least accurate.
The tolerance for manufacturing inaccuracy increases with the increase in the processed size of the part using the same processing method.
Measurement is a comparison, a juxtaposition of two quantities: an object that requires definition, with some measure, that is, with a materialized (materialized) unit of measurement, its multiples or submultiples.
Measurement as a process can occur continuously (in dynamics) and be periodic or discrete (in statics).
Discrete measurements, i.e. measurements of objects that do not change their size and position in time and space, are mainly reduced to two types:
1) repeated measurements of the same quantity;
2) repeated measurements of different, but close to each other in size quantities (for example, a batch of parts).
Measurement requires the presence of a measured object or process, a materialized unit of measurement (measure) or a system of units, as well as a means by which or through which the measurement is made.
The set of measures, means and techniques of measurement is called a measurement method.
The dimensions of machine parts and devices are measured only in linear and angular units.
A distinction is made between direct measurement, in which the measured value is obtained as a result of direct readings, and indirect measurement, when the measured value is obtained by measuring other quantities associated with the known functional relationship being measured.
Two measurement methods are possible:
absolute - direct measurement of the entire value (for example, using a metal meter or caliper);
relative - determination of the deviation of the measured value from that taken as the original (from the measure).
The measurement results depend on the accuracy of the instruments used.
The error of a measuring device is the algebraic difference between the reading of the device and the nominal value of the measured value. The permissible error is the largest error allowed by the standards.
The accuracy of measuring instruments is checked periodically using standard standards or reference measuring instruments and must correspond to the required accuracy of the part or structure being measured.
When choosing the type of measuring instrument, it is usually based on the condition that the maximum (permissible) error of the measurement method should not exceed 0.3 of the tolerance field of the controlled size.
Currently used in technology big number various measuring and control equipment.
