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Tolerance and cooperation problems in mechanical machining process
Dec 27, 2017

1.Q: What is called tolerance?

A: The allowable variations in part size and geometry parameters are called tolerances.
2. Q: What is the size?

A: The number of length values in a specific unit.
3.Q: What is the basic size?

A: Make the design a given size.
4.Q: What is the actual size?

A: The size obtained by the measurement.
5. Q: What is the limit size?

A: The two limits that allow dimensional changes.
6.Q: What is the maximum physical state (MMC) and the maximum physical size?

A: The maximum physical state refers to the state where the hole or the shaft has the largest amount of material within the dimensional tolerances. The size in this state, called the largest physical size, is the collective name for the minimum hole size limit and the maximum shaft size limit.
7. Q: What is the smallest entity state (LMC) and the smallest entity size?

A: The minimum physical state refers to the hole or the shaft within the size tolerance, with the least material state. The size in this state, called the smallest physical size, is the general term for the maximum hole size limit and the minimum shaft size limit.
8.Q: What is the role of size?

A: The length of the mating surface, with the actual hole connected to the maximum ideal axis size, known as the role of the hole size. The size of the smallest ideal hole circumscribed with the actual shaft is called the working size of the shaft.
9. Q: What is the size deviation?

A: It refers to a certain size minus the basic size of the algebraic difference.
10.Q: What is the size tolerance?

A: It refers to the allowable size variation.
11.Q: What is called zero line?

A: In the tolerance and cooperation diagram (referred to as tolerance band diagram), to determine a baseline deviation of the deviation, that is, zero deviation line.
12.Q: What is the tolerance zone?

A: In the tolerance band diagram, an area defined by two straight lines representing the upper and lower deviations.
13.Q: What is the basic deviation?

A: It is used to determine the tolerance zone relative to the zero line position of the upper or lower deviation, the generally deviation to the zero line ; when it is below the zero line, the basic deviation is the upper deviation.

14.Q: What is the standard tolerance?

A: The national standard, used to determine the size of any tolerance.
15.Q: What is called cooperation?

A: refers to the basic size of the same, combined with the hole and shaft tolerance between the relationship.
16.Q: What is called the base hole system?

A: It is the tolerance zone of the hole with the basic deviation, and the tolerance band of the shaft with different basic deviation forms

A system of cooperation.
17.Q: What is the base axis system?

A: Is the basic deviation of a certain shaft tolerance zone, with the basic deviation of the hole tolerance zone to form a system with a variety of cooperation.
18.Q: What is called mating tolerance?

A: It is the allowable variation of the gap, which is equal to the absolute value of the algebraic difference between the maximum gap and the minimum gap, which is also equal to the sum of the tolerance holes for the holes and the shaft tolerances.
19.Q: What is the gap?

A: The tolerance zone of the hole is completely above the tolerance zone of the shaft, ie the one with clearance (including the minimum clearance equal to zero).
20.Q: What is called interference fit?

A: The tolerance zone of the hole is completely below the tolerance band of the shaft, ie the interference fit (including the minimum interference equal to zero).
21.Q: What is called transitional cooperation?

A: In the cooperation of hole and shaft, the tolerance zone of hole and shaft overlap with each other. If one pair of holes and shaft are matched, there may be gap or interference fit.
22.Q: Base hole with the system for the H11 / c11 or base-shaft system for the hole with C11 / h11, the priority with what is the characteristic?

A: The gap is large, for very loose, slow moving with a dynamic fit; require large tolerances and exposed components of the large gap; requires easy assembly with a loose fit.
23.Q: With the base hole with H9 / d9 or base shaft base system with D9 / h9, the priority with what is the characteristic?

A: The gap is a great freewheeling fit, for non-precision requirements, or when there is a large temperature change, high speed or large journal pressure.
24.Q: Base hole with H8 / f7 or base-hole system with the base for the F8 / h7, the priority with what is the nature?

A: The small gap with the rotation, for medium-speed and medium-pressure neck rotation accuracy; also used to assemble more easily with the positioning.
25.Q: Base hole system with H7 / g6 or base-shaft base system with G7 / h6, the priority with what is the characteristic?

A: A very small clearance fit for unwanted freewheeling but free to move and slide and requires precision positioning, can also be used to require a clear alignment.
26.Q: H7 / h6; H8 / h7; H9 / h9; H11 / h11 or base-shaft mesoporous with H7 / h6; H8 / h7; H9 / h9; H11 / h11, what?

A: The positioning of the gap with the parts can be freely assembled and disassembled, while the work is generally relatively stationary. The gap under the maximum physical condition is zero, and the gap under the minimum physical condition is determined by the tolerance level.

27.Q: With the base hole with H7 / h6 or base shaft base hole with K7 / h6, the priority with what is the nature?

A: The transition fit for precision positioning.
28.Q: Base hole with the system for the H7 / n6 or base-shaft system with the hole for the N7 / h6, the priority with what is the characteristic?

A: The transition fit, allowing a more precise positioning of a larger surplus.
29.Q: Base hole with the system for the H7 / p6 or base-shaft system with a hole P7 / h6, the priority with what is the nature?

A: The interference with positioning, that is, a small interference fit, for positioning accuracy is particularly important, with the best positioning accuracy of parts to meet the rigidity and neutral requirements, and the pressure with the hole no special requirements, do not rely on Tight fit with friction load.
30.Q: Base hole system with H7 / s6 or base-shaft system with the base for the S7 / h6, the priority with what is the characteristic?

A: medium pressure with the fit, for general steel; or shrink fit with thin-walled parts for cast iron parts can get the most tight match,
31.Q: Base hole system with H7 / u6 or base shaft base system with U7 / h6, the priority with what is the characteristic?

A: Press fit, suitable for parts that can be pressed with a large pressure or not with a large force into the shrink fit.
32.Q: Axis of the basic deviation of a; b, with the characteristics of what?

A: It is a clearance fit, can get a particularly large gap, rarely used.
33.Q: When the basic deviation of the shaft is c, what is the fitting characteristic?

A: It is a clearance fit, get a lot of clearance, generally suitable for slow, loose with the action. For poor working conditions (such as agricultural machinery), the force deformation, or in order to facilitate the assembly, the surface must ensure that there is a large gap. Recommended with H11 / c11, its higher level with, such as H8 / c7 for a shaft work closely with the high temperature, such as the internal combustion engine exhaust valves and catheters.
34.Q: Axis of the basic deviation of d, with the characteristics of what?

A: It is with the gap, with the general for IT7 ~ IT11 level, through the loose rotation with the match, such as sealing cap, pulley, idler pulley with the shaft and so on. People apply to large diameter plain bearings, such as turbine, ball mill, roll forming and heavy bending machines and other heavy machinery in some sliding bearings.
35.Q: When the basic deviation of the shaft is e, what is the fitting characteristic?

A: With clearance fit, used for IT7 ~ IT9 level, usually suitable for requiring obvious clearance, easy to rotate with the support and cooperation, such as the large span, multi-fulcrum support, high-grade e-axis for large, Support and cooperation, such as worm gear generators, large motors, internal combustion engines, camshaft and rocker arm bearings.
36.Q: When the basic deviation of the shaft is f, what is the fitting characteristic?

A: The gap with, used for general IT6 ~ IT8 level with the rotation. When the temperature is not affected, it is widely used in the lubrication of ordinary lubricants (grease), such as gear boxes, small motors, pumps and other shaft and sliding support.
37.Q: What is the fitting characteristic when the basic deviation of the shaft is g?

A: The clearance fit, with the gap is small, high manufacturing costs, in addition to very light load of precision devices, is not recommended for rotating with. Used for IT5 ~ IT7 level, the most suitable non-rotating precision sliding fit, but also for latches and other positioning and coordination, such as precision connecting rod bearings, piston, slide valve and connecting rod and so on.
38.Q: When the basic deviation of shaft is h, what is the fitting characteristic?

A: The gap with, and more for IT4 ~ IT11 level. Widely used in non-rotating parts, as a general positioning with, if there is no temperature deformation, but also for precision sliding fit.
39.Q: When the basic deviation of the shaft is js, what is the fitting characteristic?

A: It is a transition fit, it is completely symmetrical deviation (+ IT / 2). Average with a slight gap with the more used for IT4-7 level, requiring less than the h-axis clearance, and allows a slight interference with the positioning (such as coupling), can be equipped with hand or wooden hammer.
40.Q: When the basic deviation of shaft is k, what is the fitting characteristic?

A: A transitional fit, with an average of no gaps for the IT4-IT7 level. , Recommended for a little interference positioning cooperation, down in order to eliminate the vibration with the positioning and cooperation. General assembly with wooden hammer.
41.Q: When the basic deviation of the shaft is m, what is the fitting characteristic?

A: The transition with the average, with a small transition with. For IT4I-T7 grade, with a hammer or press assembly, usually recommended for close with the components. H6 / n5 with interference fit.
42.Q: When the basic deviation of the shaft is n, what is the fitting characteristic?

A: The transition fit, the average torque slightly larger than the m-axis, rarely get the gap for IT4-IT7 level, with a hammer or press assembly, usually recommended for close with the components. H6 / n5 with interference fit.
43.Q: When the basic deviation of shaft is p, what is the fitting characteristic?

A: An interference fit, with H6 or H7 is interference fit, and H8 hole with the transition when the match. For non-ferrous parts, for light press fit, easy to disassemble when needed. For steel, cast iron or copper, steel components are standard press-fit.
44.Q: When the basic deviation of the shaft is r, what is the fitting characteristic?

A: An interference fit, the iron parts for the medium into the match, for non-ferrous parts, light into the match, when needed, can be demolished. H8 hole with the diameter of more than 100mm for the interference fit, when the diameter of the transition fit.
45.Q: When the basic deviation of the shaft is s, what is the fitting characteristic?

A: An interference fit for permanent and semi-permanent assembly of steel and iron parts. Can produce a considerable bond. When using an elastic material, such as a light alloy, the mating properties are comparable to the P-axis of ferrous parts. For example, the collar is press-fitted on the shaft, the valve seat and the like. Larger size, in order to avoid damage to the mating surface, the need for thermal expansion or shrinkage assembly.
46.Q: Axis of the basic deviation of t; u; v; x; y; z, with the characteristics of what?

A: It is an interference fit, in turn increase the amount of interference, generally not recommended.
47.Q: Under what circumstances the choice of base axis system?

A: The use of direct tolerance with the reference axis to create a tolerance level (- usually 8 to 11) and no longer machined cold drawn steel axis. At this time, different hole tolerance band positions can be selected to create various mating requirements. In agricultural machinery and textile machinery, this situation is more.

Machining precision shafts smaller than 1 mm is much more difficult than machining holes of the same level, so in instrumentation, clock and watch manufacturing, radio and electronics, shafts are usually made using thin steel wires that have been light-formed, Shaft with the base system than the economic efficiency.

48.Q: How to work with standard parts?

A: If with standard parts, should be based on standard parts to determine with the system.

For example, in the rolling bearing support structure, the outer race of the rolling bearing and the bore of the box should be made of the basic shaft. The inner ring of the bearing and the journal should be made of base hole. The box hole should be made of J7 and the journal should be made of k6.
49.Q: Grinding processing methods, should take what level of tolerance level?

A: It should take IT1 ~ IT5.
50.Q: Grinding processing method, should take what tolerance range?

A: It should take IT4 ~ IT7.

51.Q: Diamond car processing methods, should take what level of tolerance level?

A: It should take IT5 ~ IT7.
52.Q: Diamond boring process, what should be the scope of tolerance?

A: It should take IT5 ~ IT7.
53.Q: Grinding processing methods, should take what level of tolerance levels?

A: IT5 ~ IT8 should be taken.
54.Q: Flat grinding processing methods, should take what tolerance range?

A: IT5 ~ IT8 should be taken.
55.Q: Broaching processing method, should take what level of tolerance level?

A: IT5 ~ IT8 should be taken.
56.Q: Fine car fine boring processing methods, should take the tolerance level of what range?

A: It should take IT7 ~ IT9.
57.Q: Reaming processing methods, should take what level of tolerance levels?

A: IT6 ~ IT10 should be taken.
58.Q: Milling method, what level of tolerance should be taken?

A: It should take IT8 ~ IT11.
59.Q: Planing, insertion processing methods, should take the tolerance level of what extent?

A: It should take IT10 ~ IT11.
60.Q: Rolling, extrusion processing methods, what level should be taken tolerance level?

A: It should take IT10 ~ IT11.
61.Q: Roughing machining methods, should take what level of tolerance level?

A: It should take IT10 ~ IT12.
62.Q: Rough boring process, what should be taken tolerance level?

A: It should take IT10 ~ IT12.
63.Q: Drilling methods, what should be the scope of tolerance?

A: It should take IT10 ~ IT13.
64.Q: Stamping methods, what level of tolerance should be taken?

A: It should take IT10 ~ IT14.
65.Q: Sand casting processing methods, should take what level of tolerance levels?

A: It should take IT14 ~ IT15.
66.Q: Metal casting processing methods, should take what level of tolerance levels?

A: It should take IT14 ~ IT15.
67.Q: Forging processing methods, should take what level of tolerance level?

A: It should take IT15 ~ IT16.
68.Q: Gas cutting processing method, should take what level of tolerance level?

A: IT15 ~ IT18 should be taken.
69.Q: There are several ways to determine the basic deviation?

A: There are three ways to determine the basic deviation: test method, calculation method and analogy method.
70.Q: What is called test method?

A: The test method is the application of experimental methods to determine the type of cooperation to meet the performance of the product, mainly used in aerospace, aviation, defense, nuclear industry and some key institutions in the railway transportation industry, the impact on product performance and lack of experience The important and crucial cooperation. This method is more reliable. The disadvantage is the need for testing, high cost, long cycle. Less application.
71.Q: What is the calculation method?

A: The calculation method is based on the use of theoretical calculations to determine the type of cooperation. The advantage is that the theoretical basis is sufficient and the cost is lower than that of the test method. However, since the theoretical calculation can not take all practical factors of the working environment of the machine and equipment into consideration, the design scheme is not as accurate as the test method. For example, when calculating the type of mating with the clearance fit of a plain bearing, the minimum allowable clearance according to the fluid lubrication theory can be calculated from which the proper fit type is selected from the standards; With the type of surplus fit, according to the size of the load to be transmitted, according to the elastic deformation theory, the minimum required interference can be calculated. Based on this, the appropriate type of interference fit is selected and the strength of the part material can be checked at the same time The maximum interference generated. Due to the impact with the gap, a lot of interference, the theoretical calculation can only be approximate.
72.Q: What is analogy?

A: Analogy is based on the same type of design tasks with the production of machinery or agencies through the cooperation as a reference, combined with the design requirements of the product and application conditions to determine the actual situation. The method is the most widely used, but requires designers to have full reference and have considerable experience. The factors that should be considered when using analogy to determine cooperation are as follows:

 

Force size. When the force is greater, the tendency to tighten the choice of cooperation, that is, should be appropriate to increase the interference with interference, reduce the amount of clearance with the gap, the choice of transition probability with a large transition fit.

 

Disassembly situation and structural characteristics. Often with disassembly with the task of disassembly and disassembly than the same with the match, the match should be loosened. Assembly difficulties with, should be slightly loose.

 

Combination of length and shape error. The longer the mating length, the more tight the actually formed fit is due to the presence of the shape error compared to the shorter combined length. Therefore, it is appropriate to use appropriate loose some of the cooperation.

 

Material, temperature. When the phase material with different parts (a large difference between the linear expansion coefficient) and the working temperature and the standard temperature difference of 20 , consider the impact of thermal deformation. The impact of the deformation of the assembly.

73.Q: Tolerance level of 5, the application in what occasions?

A: Mainly used in conjunction with tolerances, shape and position tolerances require very small occasions, with the nature of stability, generally in machine tools, engines, instruments and other important parts of the application. Such as with D-class rolling bearing box hole; and E-class rolling bearing with the machine tool spindle, the machine tailstock and sleeve, precision machinery and high-speed machinery in the journal, precision screw diameter.
74.Q: Tolerance level of 6, the application in what occasions?

A: With the nature to achieve a higher uniformity, such as with the E-class rolling bearings matched holes, journals; and gear, worm gear, couplings, pulleys, cams, etc. connected to the shaft diameter, Rocker drilling column; Machine tool fixture in the guide outer diameter size; 6 precision gear reference hole, 7,8 gear reference axis.
75.Q: Tolerance level of 7, the application in what occasions?

A: The accuracy of level 7 is slightly lower than that of level 6, the application conditions are basically similar to level 6, and the application is more common in general machinery manufacturing. Such as couplings, pulleys, cams and other apertures; machine chuck seat hole, fixture fixed drill sleeve, drill sleeve can change; 7,8 gear reference hole, 9,10 gear reference axis.
76.Q: Tolerance level of 8, the application in what occasions?

A: Medium precision in machine construction. Such as the bearing bushing along the width direction size, 9 to 12 gear reference hole; 11 to 12 gear reference axis.
77.Q: Tolerance level of 9 to 10, the application in what occasions?

A: It is mainly used in machinery manufacturing in the outer diameter and bore sleeve; manipulator and shaft; hollow shaft pulley and shaft; single and spline.
78.Q: Tolerance level of 11 to 12, the application in what occasions?

A: With low accuracy, the assembly may have a lot of gaps, suitable for basically no requirements with the occasion. Such as the flange on the machine tool and the mouth; slippery and slippery gear; the size of the process in the process; with the stamping parts; machine tool manufacturing wrench hole and wrench seat connection
79.Q: Tolerance level of 11 to 12, the application in what occasions?

A: With low accuracy, the assembly may have a lot of gaps, suitable for basically no requirements with the occasion. Such as the flange on the machine tool and the mouth; slippery and slippery gear; the size of the process in the process; with the stamping parts; machine tool manufacturing wrench hole and wrench seat connection

80.Q:  How to use transitional design in practical design?

A: The top sleeve of the lathe tailstock is matched with the pulley and shaft,Rigid coupling with the bronze wheel rim and spokes with the cooperation.

85.Q: What are the requirements for linear dimension tolerances?

A: The tolerance code and the basic size of the same number.

When using the limit deviation to mark the linear dimension tolerance, the upper and lower deviation numbers are smaller than the basic size numbers, and the upper and lower deviation decimal places must be aligned with the sign.

One of the deviations is zero, which can be marked with "0" and aligned with another single digit of deviation.

Bottom deviation bottom line with the basic size Note on the same bottom line.

When the upper and lower deviation values are equal, the deviation is written only once, and the "+/-" sign is placed between the deviation and the basic size, and the two letters are the same in size.

86.Q: What is called a cone?

A: The basic cone of the same, the outer cone diameter, due to the combination of the formation of the relationship between. The mating feature of the cone is to provide clearance or interference through the axial position defined by the inner and outer cones in combination with each other. Gaps or interferences act perpendicular to the surface of the cone but are given and measured perpendicular to the axis of the cone; for a cone of taper less than or equal to 1: 3, perpendicular to the surface of the cone and to a value normal to the cone axis The difference between is negligible. According to determine the combination of the different methods of the inner and outer conical axial position, the cone is divided into two types of conical and displacement conical.
87.Q: What is called structural cone with?

A: From the structure itself or the size of the structure to determine the inner and outer cones relative to the axial position and get the match.
88.Q: What is called displacement cone?

A: The provisions of the axial displacement or the axial displacement of the axial force to determine the size of the outer cone relative to the axial position of the resulting engagement.
89.Q: Standard tolerance series which three elements of the composition?

A: The tolerance level, tolerance units and basic dimensions of the sub-paragraph.
90.Q: What is the general tolerance?

A: Refers to the general process equipment under the conditions of the general processing equipment can reach the tolerance.
91.Q: GB / T1804-1992 for the general size of the linear tolerance What is defined?

A: The provisions of f, m, c and v a total of four tolerance levels, the letter f that level, m said the level, c said the rough level, v that the most coarse level. Tolerance levels f, m, c and v correspond to IT12, IT14, lt16 and IT17, respectively.

94.Q: Gap with what should pay attention to?

A: The reference hole H (or reference shaft h) forms a clearance fit with the shafts a ~ h (or holes A ~ H) of the corresponding tolerance class, of which 11

H / a (or A / h) the largest gap, H / h with the smallest gap.

H / a (A / h), H / b (B / h), H / c (C / h) with the gap between the three kinds of cooperation, not often used. Generally used in poor working conditions, requiring flexible action on the machine, or for large deformation, shaft work under high temperature to ensure that there is a larger gap of the occasion.

H / d (D / h), H / e (E / h) with the gap between the two larger, for less demanding easy to rotate the support. Which H / d (D / h) for loose drive with, such as the sealing cap, pulley and idler pulley and shaft with the cooperation. Also suitable for large diameter plain bearings, such as ball mill, rolling mill and other heavy machinery, sliding bearings for IT7 ~ IT11 level. For example, the pulley and shaft with.

H / f (F / h) with the gap with the moderate, and more for IT7 ~ IT9 general transmission with, such as gear boxes, small motors, pumps and other shaft and sliding support with.

H / g (G / h) with the small gap with this, in addition to the light load of precision machinery, the general do not do with the rotation, used for IT5 ~ IT7 level, suitable for reciprocating swing and sliding precision. For example, drill sleeve and bushings.

H / h with the minimum clearance of this cooperation is zero, for IT4 ~ IT11 level, suitable for non-relative rotation and positioning with the requirements of the centering, if no temperature, deformation, but also for sliding with the recommended With H6 / h5, H7 / h6, H8 / h7, H9 / h9 and H11 / h11.

95.Q: What should you pay attention to when transitioning?

A: The basic hole H and the corresponding tolerance grade axis deviation code j ~ n form a transition fit (n and high-precision hole interference fit).

H / j, H / js cooperation, the transition of these two transitions with more opportunities for space, and more for IT4 ~ IT7 level, suitable for clearance requirements than h small and allow a slight interference with the positioning, such as coupling, Ring gear and steel wheels and rolling bearings and the box with the cooperation.

H / k. The average clearance obtained by this kind of fitting is close to zero, the centering is better, the contact stress after the assembly is small, and the utility model can be disassembled, and the utility model is suitable for IT4 ~ IT7, such as the rigid coupling.

H / m, H / n with the two opportunities for interference with more, good centering, assembly tight, suitable for IT4 ~ IT7.

96.Q: What to pay attention when interference fit?

A: The reference hole H forms an interference fit with the basic deviation code p ~ zc of the corresponding tolerance class shaft (p, r forms a transition fit with a lower accuracy H hole).

H / p, H / r with these two kinds of interference in the high tolerance level with the interference can be hammer or press assembly, should only be demolished when overhauling. Mainly used for high centering accuracy, parts are rigid enough, by the impact of load positioning with, and more for IT6 ~ IT8 level.

H / s, H / t with these two kinds of cooperation with moderate interference fit, and more use of IT6, IT7 level. For the permanent or semi-permanent combination of steel parts. No auxiliary parts, rely on the binding force generated by the surplus, you can directly pass the medium load. General pressure method assembly, but also useful cold shaft or heat sleeve assembly, such as cast iron wheels and shaft assembly, columns, pins, shafts, sets and other pressed into the hole with.

H / U, H / H, H / H, H / Y and H / z. These types of interferences are large interference fit, the interference increases in turn, the ratio of interference to diameter is above 0.001. They are suitable for transmitting large torques or large impact loads and rely firmly on the resulting bonding force to ensure a secure connection, usually with a thermowell or a cold shaft method. Train wheels and high manganese steel wheels to use H7 / u6 or H6 / u5 with. Due to large interference, the requirements of parts material is good, high strength, otherwise the parts will be cracked, so the time to be careful, generally go through the test to put into production. Before the assembly also often have to choose, so that a number of parts of the interference tend to be more in line, more modest.

97.Q: Why preferred base hole system?

A: Because the hole is difficult to process the shaft, changing the size of the hole need to change the number of tools, measuring tools. And change the size of the shaft will not change the number of tools, measuring tools.
99.Q: How to determine the type of cooperation?

A: When the hole, shaft relative movement or rotation, you must choose the gap fit. Select the relative movement of the smaller gap with the relative rotation to select a larger gap with the match.

When the hole, no key between the shaft, pins, screws and other connections, can only rely on the hole, the shaft between the drive to achieve cooperation, we must choose the interference fit.

The characteristics of the transition fit may be generated gap may also produce interference, but the amount of clearance or interference is relatively small. Therefore, when there is no relative movement between parts, concentricity requirements are high, and do not rely on the transmission of power, often choose transition fit.
100.Q: What is the principle of dimensional tolerance and cooperation?

A: The principle of choice is to get the best technical and economic benefits while meeting the requirements of use.