Machine precision. Testing and verification of machine tools for accuracy
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MACHINE PRECISION. TESTING AND VERIFICATION OF MACHINE TOOLS FOR ACCURACY Tadjibayev Rasul Karimovich Candidate of Technical Sciences, associate professor at Ferghana Polytechnic Institute tojiboyev55@mail.ru Homidjonov Ma`murjon Ma`rufjon o`g`li Master's student at Fergana Polytechnic Institute Annotation Testing machine tools for accuracy is one of the main sections of the test program for the acceptance of serial machines and prototypes of new models. Measuring the geometric accuracy of machine tools belongs to the field of metrological work. The geometric accuracy of the machine, which characterizes the quality of its manufacture and installation, is understood as: 1. the degree of approximation of the surfaces basing the workpiece and the tool to geometrically correct surfaces; 2. compliance of movements in the guide supports of the main units of the machine, carrying the workpiece and tool, with the calculated geometric movements; 3. the accuracy of the location of the basing surfaces relative to each other and relative to the guide supports, which determine the main movements and determine the shaping of the processed surfaces; 4. accuracy of installation of linear and angular dimensions and accuracy of kinematic transmission chains. Keywords: precision, control, processing, detail, measurement, surface, orientation, machine tool, accuracy, direction, bench,16K20F3, ZMM CU500M/1000 bench Introduction Before testing for accuracy, the machine is installed on a test bench or on a foundation on the supports provided for by the design of the machine. This must be done very carefully, since the geometric accuracy of the machine in some cases depends on the accuracy of its installation. There are the following types of installation of machines during testing: 1. Three-point machine mounting is generally used for small-sized precision machine tools with a rigid bed, working without additional strengthening of its rigidity by the foundation. The machine is set in a horizontal position by adjusting the supports. Alignment is carried out by levels set in the longitudinal and transverse directions. When installing the machine, all its moving parts (tables, carriages, calipers, stocks, etc.) must occupy the middle positions. Consideration should be given to the possibility of changing the position of the machine on the supports during the test; to eliminate errors, it is necessary to control the position of the bed with an additional level. 2. Installing the machine (during operation) on the number of supports more than three is the most common way. In this case, the machine bed is rigidly connected to the foundation with bolts, which increases its rigidity. When such a machine is installed for testing on a stand or foundation by alignment with wedges or shoes, the machine bed, which does not have sufficient rigidity, is deformed under the action of its own weight and the weight of the units mounted on it. Therefore, the installation of the machine on many supports is carried out by measuring the levels of deformations of the bed in its individual parts. By adjusting the supports, the frame is set to a position in which its deformations will be the smallest. In the process of testing the machine for accuracy, additional adjustment of the supports can take place within the limits of the permissible deformations of the frame with a check of the relative position of the individual parts of the machine. When testing machine tools, the beds of which have sufficient rigidity and operate without fixing them with foundation bolts or on vibration-isolating supports, additional adjustment of the supports during the accuracy test is not allowed. The installation of the machine before testing must be carried out according to the installation drawing, but without tightening the foundation bolts. The accuracy of the machine setting before testing is specified in each section of the accuracy standards below.
Measurement of straightness and flatness of guide surfaces of machine tools Rectilinear movement in metal-cutting machines, along with circular ones, is the main and most common type of movement and rearrangement of the moving parts of the machine relative to its basic parts (bed, racks, traverses, etc.) and is carried out using guide surfaces. The straightness of movement determines the accuracy of the form and the relative position of the surfaces processed on the machine, the accuracy of coordinate and calculated movements, the accuracy of the installation of rearranged parts, assemblies and mechanisms, the interaction of mechanisms connecting the moving and fixed parts of the machine. In turn, the accuracy of rectilinear motion is determined by the accuracy of manufacturing and installation of the guide surfaces of the base part, i.e., the degree of their approximation in shape and relative position to the given geometric shapes. Measuring the straightness of a guide system includes: checking the straightness of individual guide surfaces or traces of their intersection;
The measurement of the straightness of the guide surface is aimed at establishing its actual shape using coordinates expressed in linear terms and determining the deviation of the guide surface from the original geometric plane or the trace of the intersection of the surfaces from the geometric line. Methods and means of measuring straightness are based on two types of measurements: measurement of linear quantities that determine the coordinates of the elementary areas of the surface of the guide relative to the original straight line; measurement of angular values that determine the angles of inclination of individual sections of the guide, limited by elementary platforms relative to the original straight line Instruments for measuring the accuracy of machine tools Devices and general purpose tools used for most tests of the accuracy of machine tools (control rulers and squares, levels, probes, end blocks, control mandrels, indicators and microcators, etc.) are quite simple and do not require special instructions for their use. All measuring instruments used to check the accuracy of machine tools must be properly checked and certified, and their errors taken into account when measuring. It must be borne in mind that in some cases, the errors of measuring instruments and tools can be automatically excluded from the measurement results by methods known in measuring technology, for example: rearrangement of control mandrels with their rotation by 180 °, » a square when checking perpendicularity, measuring straightness with two faces of a test ruler, taking into account their non-parallelism, etc. Such measurement techniques provide high accuracy of checks and should be used in all cases where it is possible. A relatively small number of critical checks that characterize the accuracy of the machine require the use of special measuring instruments. The use of these devices requires the presence of qualified personnel who have the skills to work with such devices. Specialized measuring devices include: optical instruments for measuring the straightness of guides - collimating and autocollimating instruments, sighting tubes, also used for checking alignment and other purposes; optical instruments for measuring angles - theodolites and collimators, dividing disks with reading microscopes used to check the dividing chains of machine tools, dividing mechanisms, etc.; reference screws and special measuring and self-recording devices for checking the accuracy of screw-cutting chains of screw-cutting, thread-cutting, and thread-grinding machines; precision line measures and reference microscopes for measuring the accuracy of movements of coordinate systems of precision coordinate boring machines and some other machines; devices for continuous checking of dividing chains of gear-cutting machines. When carrying out measurements with special devices and when processing the measurement results, it is necessary to follow the instructions and manuals for these devices. The verification methods and measuring instruments specified in the standards for the accuracy of machine tools are mandatory; the use of other methods and measuring instruments is allowed provided that they fully ensure the determination of the accuracy of machine tools required by the standards. When checking machines for accuracy (without cutting), the movements of the machine components are made by hand, and in the absence of a manual drive, mechanically at the lowest speed. If the design features of the machine do not allow measurement at the length to which the tolerance is related, the latter is recalculated to the largest length at which the measurement can be made. For lengths that are significantly different from the length for which the tolerance is specified, the tolerance proportionality rule does not apply.
In terms of the number and range of machine tools covered by the standards for accuracy standards (about 65 current GOSTs), the USSR occupies a leading position. The scope of testing machine tools for accuracy, regulated in GOST, basically corresponds to that adopted in most foreign standards. The difference mainly concerns the checks of individual parts (frames, lead screws, dividing disks), which are controlled during their manufacture and assembly and, as a rule, are not included in GOST. The values of permissible deviations of the parameters given in GOST for accuracy standards also basically correspond to those adopted in most foreign standards. The increased demands of the industry for the quality of manufactured machine tools, especially for their accuracy, reliability and durability, as well as the conditions for the supply of machine tools for export, pose the problem of ensuring a sufficient duration of operation of machine tools with a given accuracy before the machine-tool industry of the Soviet Union. In particular, in the manufacture of machines supplied for export, it is allowed to use only part of the tolerance field for the accuracy of machines. It seems necessary in some cases, where appropriate, to impose more stringent requirements on accuracy and to introduce verification of new parameters. In the near future, new and revised GOSTs will be issued with higher requirements for a number of machine tool accuracy indicators and the addition of increased accuracy classes in accordance with the developed classification. It should be borne in mind that in some cases the tolerances specified in foreign standards are unreasonably high and therefore, when comparing them with the GOST accuracy standards, it is necessary to check the feasibility of this overestimation, as well as analyze the effect of reduced requirements for the accuracy of individual parameters on the accuracy of the machine in accordance with with his appointment. In the above tables of comparison of the accuracy standards of GOST and foreign standards (Tables 172-192), completely identical checks are not always given both in terms of the methodology for their implementation and the control equipment used, and in terms of lengths, to which accuracy tolerances are assigned. In such cases, the relevant disclaimers are given in the tables. Tolerances are recalculated depending on the lengths to which they are related. It should also be taken into account that different standards have adopted their own system of interconnection of individual checks, and a literal comparison of their accuracy without taking into account this interconnection does not always make it possible to judge the actual accuracy of the machines. In these cases, a deeper analysis of the compared accuracy indicators is required, as well as verification of the accuracy of the machines in exactly the same conditions. When comparing permissible deviations according to GOST and foreign standards, it should be borne in mind that in the manufacture of machine tools supplied by factories of the Soviet Union for export, it is allowed to use only part of the accuracy tolerance field according to GOST: 0.6 - from the tolerance value - for machines of normal and increased accuracy; 0.8 - from the tolerance value - for machine tools of high and very high accuracy. Download 83.06 Kb. Do'stlaringiz bilan baham: 
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