Accuracy rationing

Contents

Contents

Introduction

Description of assembly unit (assembly)

Defining Gaps and Interference in a Smooth Cylindrical Joint

Calculation of limit gauges

Calculation and selection of joint fits with rolling bearings

Calculation and selection of fits on splined joints with straight-sided profile

Calculation of threaded joint fits

Conclusion

List of literature

Introduction

Mechanical engineering is the most important leading industry. But engineering plays an equal role in other areas such as science, culture, education, public utilities and housing. Humanity is growing and developing, thereby giving food for the development of mechanical engineering and the expansion of its nomenclature. The main emphasis nowadays is on electrification, as well as mechanization and automation of production and labor, in general everything is being done to facilitate physical work of a person.

Course work on the course "Normalization of Accuracy in Mechanical Engineering" allows you to consolidate the theoretical provisions of the course set out in lectures, instills skills in using reference material, ESKD standards, introduces students to the main types of calculations.

An important place in the course work is occupied by issues related to ensuring the accuracy of interchangeable parts of assembly units. The standards of accuracy of interchangeability of all types of connections are regulated by a unified system of tolerances and fits (ERP).

The purpose of the course work is to instill the skills of assigning accuracy of parts and assemblies and the skills of designating it in drawings.

During the course work, the main standards for tolerances and fits of standard joints are worked out, the issues of size control and technical requirements are touched upon.

Description of assembly unit (assembly)

Accessories for tooth-cutting machines.

The installation and clamping of gears when cutting teeth on them are carried out on various devices. The method of tooth processing determines the type of accessory to tooth processing machines. Depending on the group of the machine, these devices are divided into types: toothfreezer, toothfreezing, toothostrogal, toothoschewing, tooth-grinding, etc. The design of the gear machine adaptor also depends on the overall dimensions of the gears, the degree of accuracy of their manufacture, the shape and size of the base surfaces, and the mounting positions of the table or spindle of the machine on which the tool is mounted.

Depending on the shape of the gear and the length of the hub, the main mounting base may be a hole or a flat end surface of the hub or rim of the wheel.

When cutting gears with a low degree of accuracy, as well as during preliminary cutting of teeth, gears are installed on rigid mandrels (fit A/C, A/D) with a small gap. When cutting gears with a higher degree of accuracy, installation - centering is carried out on mandrels without a gap.

Device with collet pneumatic clamp for milling teeth of cylindrical gears by worm cutter is installed on toothed-cutter table of machine and fixed with screws. When the distribution valve is switched over, compressed air is supplied through the connector to the upper cavity of the pneumatic cylinder built in the accessory housing and moves the piston with the rod and push-pull rod down. At that tie-rod with its upper conical end spreads collet, which clamps the treated wheel. After cutting the teeth on the wheel, the distribution valve switches over, and compressed air through the connector and air channels in the pneumatic cylinder and its cover enters the lower cavity of the pneumatic cylinder and moves the piston with the rod and the rod upwards. The upper conical end of the tie rod leaves the collet hole, which is compressed under the action of elastic forces, and the treated wheel is released from the clamp. When the piston moves upwards, the bushing moves with it and removes the wheel from the collet mandrel with rods. The gear cycle is then repeated.

The introduction of the device improves the accuracy of the installation, increases the service life of the replaceable mandrels and increases the maintenance culture.

Description of fits:

⌀55H11/h11 - Fit with clearance, in the hole system. Often used for elements between which structural clearances are provided in the units, for example, the height of the keys, non-centering diameters of splined shafts and bushings, diameters of through holes for fasteners with high assembly accuracy, etc.

⌀60H10/h10 - Fit with clearance, in the hole system. is mainly used instead of landing H9/h9, if the economical manufacturing conditions require some expansion of tolerances, and the working conditions of the connection allow some reduction in accuracy.

⌀265F8/h7 - Fit with clearance, in the hole system. Preferred and most often used in precise connections (Examples of applications: shaft bearings in gearboxes, main shafts of turning, milling and drilling machines).

⌀50H7/r6 - Interference fit in the hole system. They are used in connections without fasteners at low loads (Examples of applications: bushing in the head of the connecting rod of the pneumatic engine) and with fasteners at high loads (fitting on the key of gears and couplings in rolling mills, oil drilling equipment, etc.).

Conclusion

Modern mechanical engineering is based on the interchangeability of parts, assemblies and mechanisms, has high productivity, accuracy and high quality of manufacture.

In this course work, all necessary calculations were carried out, which are required on assignment. Design features of the mechanism and working conditions are taken into account. The method of calculation of permissible values of maximum and minimum tension in fit was studied and standard fit with interference, seat of bearing rings with shaft and housing are calculated, deviations of shape of mounting surfaces and roughness are assigned to mating parts, as well as selection of mounts of rolling bearings on shafts and holes of housings, scheme of tolerance fields and calculation of gaps and tension in connection are justified. The fit of the threaded connection, the calculation of gaps or interference, the scheme of tolerance fields are justified. The degrees of accuracy and the type of coupling of the gear wheel, the choice of a complex of controlled parameters for it, are justified.