1 Introduction The machine tool should ensure that the processed parts meet the specified accuracy and surface roughness. The accuracy and surface roughness of the workpiece are determined by many aspects such as machine tools, tools, fixtures, cutting conditions, and operators. However, as far as the machine tool is concerned, the accuracy of the machine tool is gradually reduced due to the wear deformation and vibration of some moving parts of the machine tool. Therefore, the machine tool itself must have a certain precision, and the accuracy of the machine tool reflects the comprehensive technical state of the machine tool to a certain extent. The accuracy of the machine tool can be measured by the accuracy index.
Method: The accuracy index is the measured value (Tp) and the specified tolerance value (Ts) of the accuracy of the equipment. It is calculated by the following formula in the number of items (n): where: T-accuracy index n― The measured item Tp—the single measured value Ts of the machine tool—the single item allowable value accuracy index of the machine tool is an important data for evaluating the positional change between the components caused by the physical wear of the machine tool. The smaller the T value, the higher the accuracy. Based on years of practical experience, the author summarizes: <0.5, it can be used as one of the new equipment acceptance conditions; when T<1, it can be accepted as an overhaul and key repair.
2 Geometric accuracy Geometric accuracy is the shape accuracy and positional accuracy of the main parts of the parts when the machine is not running. Mainly include: 1 straightness of the guide rail; 2 parallelism of the work surface; verticality between the guide rail and the component; 4 radial runout and axial sway of the spindle center line; 5 spindle center and other corresponding component center Axis; 6 indexing accuracy of rotary table.
The geometric accuracy of the machine tool has a direct impact on the geometric accuracy of the machined part. Therefore, it is the main indicator for assessing the accuracy of machine tools. For the general inspection standards of the general machine tool countries, such as the national standard for the geometric accuracy of ordinary lathes, fifteen inspection standards are specified. The main inspection items are as follows: 21 radial runout of the spindle cone axis. Insert the inspection rod with the taper shank into the spindle cone. In the hole, the dial indicator is fixed on the slide plate so that the probe of the dial indicator is placed on the surface of the test rod, and the rotating main shaft is respectively measured at the ends a and b of the length L, when the measurement length L=300 mm, The allowable difference is a=001mm high, and the life is high. The aif times saves the amount of the publishingHouse.Allrights and reduces the inventory backlog. It is a good way to solve the lack of spare parts in the mining area.
For the matching of the spare parts, reinforcement measures should be taken during the manufacture to improve the process and increase the wear resistance of the mating pair by 1-2 times.
4 Conclusion About 16% of the equipment parts of our company are matched, but it is the key to the possession of equipment. Their wear occurs at the relative movement of the inner and outer surfaces. Therefore, the repair or manufacture according to the wear condition should be strengthened by the surface strengthening process. During the use process, it is necessary to strengthen the quality evaluation work, timely and accurately adjust the matching auxiliary gap, rationally lubricate, and maintain the seal, so that it can always be in a high performance state.
This has laid a good material foundation for the company to achieve better economic returns, and opened up a new way for increasing production and reducing consumption.
(English) HH Doroshkin is waiting. A new method for repairing maple parts.
Machine maple design manual. Machine Maple Industry Press - edited by Yan Liangui. Maple parts - electroplating and finishing. Tianjin total issued in 1985.
22 Parallelism of the spindle axis to the movement of the slide plate The inspection rod with the taper shank is inserted into the spindle taper hole, and the square meter is used to check the upper bus bar a and the side bus bar b when moving the slide.
When the measured length L = 300mm, the tolerance values ​​are a = 0.03mm (only upward bias), b = 0.015mm (only forward bias).
23 spindle axial rotation Insert a short inspection rod into the spindle cone hole, put a steel ball in the center of the inspection rod, and then touch the steel ball on the flat head dial fixed to the slide, turn the spindle Carry out inspections. The maximum difference in dial gauge readings is the error value for axial turbulence. The allowable difference is 0. When the parallelism of the axis of the taper hole of the tailstock sleeve is 300 mm, the tolerance value is a=0. 03mm (only upward), b=0.03mm (only forward) Partial).
5 bed head and tailstock two tip height and other height between the main shaft and the tailstock tip into the test rod, the dial indicator is fixed on the slide, move the slide, the dial indicator at the ends of the test rod, the reading difference is the bed The height of the head and tailstock are the same. The tolerance value is 0.04mm (only the tailstock height is allowed).
Working precision The working precision of the machine tool is 1/8 of the maximum turning diameter of the workpiece under dynamic conditions, and the actual length is three times the diameter of the medium carbon steel, clamped by the chuck, and the outer circle of the finished car. Check the roundness and cylindricity of the test piece after finishing the car. The tolerance of the roundness is 0.01 mm, the cylindricity is 0.03 mm over the measured length of 300 mm, and the surface roughness is 3.22. Take a disc-shaped cast iron test piece with a diameter not less than 1/2 of the maximum turning diameter of the bed, and clamp it with a chuck to finish the end of the car. Flatness error of the test piece after finishing the car. The tolerance is 300mm and the diameter is 0.02mm (only concave). The surface roughness Ra is not more than 2. 3.23 precision thread pitch error. Hold a steel test piece with the same diameter of the lead screw and a length of not less than 300mm in the middle of the two tops. The 60°C ordinary thread with the same pitch of the lathe and the turning of the lathe is tested to check the pitch error. The tolerance value is 0.04mm in the measurement length of 300mm, and the measurement length in any 500mm is 0.015mm.4 Conclusion There are many precision items in the machine tool. As long as there is one tolerance, it will involve the overall machine tool. Therefore, the accuracy of the machine tool can be used to evaluate the accuracy of the machine tool. For example, the accessory factory has performed an accuracy check on a lathe. The allowable values ​​and measured values ​​of each inspection item are shown in the following table. This makes it possible to find the accuracy index of the lathe. Thereby determining whether the machine tool continues to be used. The specific method is shown in the table below.
Machine tool accuracy reflected by working hours. The actual geometric parameters (size, geometry and surface mutual position) of the workpiece after machining through the machine are in good agreement with the ideal geometric parameters. If the machine tool has high precision and the degree of conformity is poor, the machine tool has low working precision.
The main factors affecting the accuracy of machine tools are: machine tool deformation. There are many reasons for the machine tool's working accuracy due to machine tool deformation. Machine tool stiffness and thermal deformation are the main factors affecting machine tool deformation.
Machine tool stiffness refers to the ability of the machine tool to resist deformation under external force. The stiffness includes the stiffness of the machine tool component itself and the contact stiffness between the components. The greater the stiffness, the higher the accuracy.
Thermal deformation of the machine tool. Due to the influence of external heat sources (including changes in sunlight and ambient temperature) and internal heat sources (such as motors, gearboxes, bearings, hydraulic systems, and cutting heat), the temperature of various parts of the machine has changed. Since the temperature of each part is not the same, the thermal expansion coefficients of various materials are different, which causes different deformation and relative displacement of various parts of the machine tool. This phenomenon is called thermal deformation of the machine tool. According to statistics, the error caused by thermal deformation of machine tools in long-term work can account for up to 70% of all errors. Especially for precision machine tools, large machine tools and automated machine tools, the effects of thermal deformation can not be ignored.
1.2 Machine vibration. The vibrations appearing on the machine tool can be divided into two types: forced vibration and self-excited vibration. The vibration of the machine tool during the cutting process seriously affects the performance of the machine tool. Vibration can affect the machining accuracy of the machine tool, the quality of the machined surface and noise, reduce productivity, shorten the life of the tool and even damage the moving parts of the machine.
The vibration resistance of the machine tool and the stiffness, damping characteristics of the machine tool, and the evaluation of the working frequency of the natural frequency 2 machine tool. There is no uniform standard for the evaluation of the machine tool working accuracy, mainly the precision of the machine tool indirectly through the precision achieved by cutting typical parts. Make a comprehensive evaluation. For example, the accuracy of ordinary lathe work can be as follows: 2.1 Roundness and cylindricity of the outer circle of the fine car. Take the diameter of not less than the standard accuracy value of the inspection items of a lathe CA6140 and the measured value. The project name tolerance value (mm) measured value The radial runout of the spindle cone axis is 0.010. 02 The parallelism of the main axis to the movement of the slide is 0.030 .02He axis of the spindle is tilted 0.010. 01 degree tailstock sleeve cone hole axis parallelism of the movement of the slide box 0.030. 02 bed head and tailstock two tip heights 0.040.03 finishing car outer cylindrical temperament 0 Finishing car end face flatness 0.020. 02 degree precision thread pitch error 0.040.04 In the computer bed accuracy index, first calculate the geometric accuracy and working precision, respectively, using the arithmetic mean of the two as the machine tool's accuracy index T. T A few = work accuracy index T = 1.13 < 2, so it can be judged that the lathe can continue to use, but must pay attention to adjustment. Therefore, through the above analysis, it is known that the accuracy of the machine tool is evaluated by measuring various indexes of machine tool precision and computer bed precision index. Therefore, it is determined how the state of use of the machine tool is, and the machine tool is maintained and repaired in time. Further improve the use of machine tools. Practice has proved that it is very effective to use the accuracy index method to identify and test the machine tool.
13 Improvement of sealing conditions A better sealing form prevents the abrasive particles from entering the lubricating parts and improves the life of the mating pair.
The above is a necessary measure to improve the sub-life, but it is not the main measure. It should start from the material and the surface quality of the copy body to improve its life. The research results of contact-abrasive wear made by MM Chammu and AM Farneb pointed out the law of the influence of different surface hardness ratio on the wear of the friction pair components: when the hardness value of the pin (or sleeve) is larger, The lower the wear of the pin (or sleeve); the lowest wear value of the pin (or sleeve) is the lowest, while the higher hardness part is always more wearable due to the extrusion scraping effect. The reason. It can be seen that selecting a material with high strength and wear resistance is the key to prolonging the life of the sub-joint. However, engineering materials often require comprehensive properties such as wear resistance, corrosion resistance, temperature resistance, good heat conductivity, abrasion resistance, good plasticity and high strength. According to this requirement, it is most desirable to increase the reinforcing layer on the surface based on the above high performance.
In the author's investigation, it is economical and practical to use the iron plating process to repair the worn joints. Jian'an Headquarters Xinyi Iron Plating Plant will strengthen the nitrogen plating of the nitrogen cylinders after the 75B and other vehicles, improving the condition of the mating surface.
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