Abstract: The mechanical manufacturing industry is one of the main pillar industries of a country's national economy. As a relatively expensive precision equipment, CNC machine tools, if some faults occur in production, will have a direct or indirect impact on the accuracy of the product parts being processed. Meanwhile, in the process of producing and assembling CNC lathes, the spindle is a very important component that directly affects the dimensional accuracy of the processed parts. Therefore, effective accuracy adjustment and timely diagnosis and maintenance are crucial. Mastering some efficient methods for restoring spindle accuracy can provide assurance for the dimensional accuracy of turning parts and promote the healthy development of the processing and manufacturing industry.
Keywords: maintenance methods; Spindle accuracy adjustment; CNC machine tool maintenance
0 Introduction
The spindle components of CNC machine tools are composed of transmission components, bearings, flanges, etc. The main function is to support the transmission components, drive the workpiece and tool to rotate. The spindle stiffness and motion accuracy directly determine the machining quality and cutting efficiency. During operation, the spindle, as the main moving component of the machine tool, supports the torque during transmission, and drives other workpieces through the good and stable operation of the machine tool spindle, thereby forming stable forming motion on the surface of the machine tool spindle.
1. Method for Adjusting the Precision of CNC Lathe Spindle
The main function of the CK6140 lathe spindle is to support and clamp rotating parts, and its own accuracy plays a crucial role in the quality of the processed products. During the installation of the lathe spindle, the chuck and shaft sleeve frequently exceed the tolerance or wear, resulting in the spindle circular runout exceeding the tolerance, which directly affects the turning parts. Therefore, in the machining and manufacturing of CNC lathe spindles, it is necessary to effectively control the roundness and coaxiality of the machine tool spindle to not exceed 0.01mm.
The main structural parameters of the spindle include the diameters D1 and D2 of the front and rear journals of the spindle, the diameter d of the inner hole, the front overhang a, and the span L between the main supports, as shown in Figure 1.
Figure 1 Lathe Spindle Structure
The steps for adjusting the spindle accuracy are as follows:
① Spindle pre inspection: The step of accurately adjusting the spindle accuracy of a CNC lathe is to pre inspect the entire production process of the spindle and promptly identify any problems that may arise. The main content of pre inspection is to ensure the wear and runout frequency of the entire lathe spindle outer circle, and control the machining and production error of the lathe spindle within 0.005-0.01mm.
② Adjust the geometric accuracy before disassembling the spindle: the front end of the CK6140 machine tool spindle uses two groups of angular contact ball bearings, which are pre tightened through the front support sleeve and nuts. The rear end uses cylindrical roller bearings, and the radial clearance is adjusted through two nuts. If the spindle stiffness of the machine tool is good, cutting processing is guaranteed at this time. At the same time, in production practice, maintenance personnel will also timely adjust and control the moving direction and proper clearance of the lathe spindle to further improve the production efficiency and processing quality of the lathe spindle.
③ Testing the dynamic accuracy of the spindle: Doing a good job in the temperature rise test of the machine tool spindle can effectively avoid errors during actual measurement. By monitoring the temperature rise pattern of relevant bearing components during the idle operation of the spindle, appropriate lubrication schemes are adopted to reasonably allocate and adjust the distribution of the entire spindle temperature. The factors that affect the rotation accuracy of the machine tool spindle are spindle accuracy, bearing accuracy, and corresponding spindle hole accuracy. Therefore, before assembling the spindle unit, it is necessary to ensure the accuracy of the spindle, bearing, and spindle hole to ensure that the dynamic error of the spindle during operation is within the allowable value.
④ For lathes with large spindle errors, they need to be removed for maintenance. The specific maintenance process is shown in Figure 2.
2. Maintenance methods for CNC machine tool spindles
2.1 Maintenance method of spraying Hotfix
The spraying Hotfix method refers to the selection and spraying of corresponding materials by referring to relevant data and combining with the organization and structure of the machine tool spindle in order to ensure the quality of the whole spindle repair, in which metal material Z is commonly used. According to the thickness of the spindle, the thickness of the sprayed material should be reasonably controlled. Maintenance practice has shown that it is generally more appropriate to control the thickness of the repair material between 0.05 and 0.2mm. At the same time, in the spraying operation, in order to ensure that the work is always in a low temperature state, active measures should be taken to control the spindle temperature, and it is even more important to avoid spindle damage.
2.2 Scraping repair method
During the long-term operation of the CNC lathe spindle, there may be phenomena such as circular runout exceeding the tolerance. If the bearing components of the spindle contain a taper sleeve structure and the copper taper sleeve is found to be worn, the scraping and grinding repair method can be used. By scraping and repairing, the errors in the spindle can be eliminated, thereby ensuring that the dynamic accuracy of the CNC lathe spindle meets the requirements. When using this method for repair work, attention should be paid to eliminating significant internal stress during the repair process. This repair method requires selecting the appropriate size of the machine tool and the spindle.
2.3 Electroplating repair methods
When repairing the chrome coating on the lathe spindle, strictly control the relevant dimensional accuracy of the spindle components, carefully understand the technical requirements of the actual use of the machine tool, and strengthen the surface hardness of the spindle in a targeted manner to prevent rapid wear during operation after repair. When using electroplating method to repair the spindle, the thickness of the chromium plating layer should be controlled within 0.03mm. Electroplating operations can produce some toxic and harmful substances. While ensuring quality, chromium metal should be used as little as possible to minimize pollution to the surrounding environment.
2.4 Accuracy inspection of spindle components after maintenance
After completing the spindle inspection and maintenance work, in order to ensure the dynamic accuracy and stability requirements of the CNC machine tool spindle unit, professional maintenance personnel and operators cooperate to adjust the spindle? Inspect and track the technical status of the machine tool spindle unit. Detect static and dynamic accuracy separately. After completing the static and dynamic accuracy inspection of the machine tool spindle, it is necessary to fill out and improve the record form, and archive and manage the inspection form and record form for future maintenance and reference at any time.
3. Maintenance examples of common faults in the main transmission system
Fault phenomenon: A CK6140 CNC lathe spindle box has excessive noise.
Firstly, it is necessary to determine whether it is caused by a motor malfunction. Disconnect the transmission belt and run the motor separately, ensuring that the sound is normal.
Next, it is necessary to investigate one by one from the following aspects: the dynamic balance of the spindle components has not reached the predetermined value; Uneven gear meshing clearance or poor gear manufacturing accuracy; Bearing damage; The transmission shaft undergoes bending deformation; The length of the transmission belt is too long, loose, or worn; The lubrication is poor, and the main shaft transmission part is short of oil.
Troubleshooting method: For dynamic balancing issues, the spindle unit needs to be removed and re balanced; Adjust the gear meshing clearance or replace the gear; Replace with a new bearing; Replace the transmission shaft or grind it for correction; Adjust the tightness of the transmission belt or replace it with a new one; Replace lubricating grease and add lubricating oil to ensure smooth lubrication of the oil circuit.
The maintenance work of machine tools should not only be limited to troubleshooting and repairing worn and deformed parts when faults have occurred, but also pay attention to the standardized use of the machine tool, pay attention to daily maintenance, and persist in preventive maintenance work for a long time.
4. Systematic maintenance of CNC lathes
① Each shift of operators strictly follows the equipment operating procedures and specifications, and operators and maintenance personnel strictly adhere to the maintenance and repair system.
② Maintain the sealing of electrical cabinets and high voltage cabinets to prevent oil mist, dust, and metal powder in the air from adsorbing onto circuit boards or electronic components in the CNC system. Dust accumulation can reduce the insulation resistance between components and even cause circuit board damage. It is strictly prohibited to open the CNC cabinet door to dissipate heat in hot weather, and always maintain the good operation of the ventilation fan or air conditioning on the electric cabinet.
③ Regularly clean the heat dissipation and ventilation devices of the electrical cabinet, clean the dust pads and filter screens every month, and replace damaged filter screens and other dust prevention devices in a timely manner. To prevent excessive temperature inside the electrical cabinet caused by blocked heat dissipation and ventilation channels.
⑤ For the input/output devices of the CNC system, it is necessary to use appropriate force during daily use, and rough operation is prohibited. If the buttons become loose, they should be repaired and replaced in a timely manner, and operation should not be carried out with faults.
⑥ During the operation of CNC machine tools, pay attention to the sound of the running parts. If any abnormal noise is found, it should be promptly investigated. If the motor is running with excessive noise, it is necessary to check whether it is the wear transition of the DC motor brush, as the worn brush can affect the performance of the motor. Therefore, the electric brush of the CNC lathe motor should be inspected or replaced every year.
⑦ When the FANNUC system experiences a BAT alarm, it is necessary to replace the new battery when the system is powered on to prevent the loss of system parameters. When CNC machine tools are not in use for a long time, they should also be powered on frequently and run at least once or twice a month.
⑧ Pay attention to the Preventive maintenance of the main drive chain, and regularly check and adjust the tightness and wear of the main shaft drive belt to avoid spinning caused by belt drive slip.
⑨ Regularly inspect the lubrication of various parts of the CNC machine tool, replenish the lubricating oil tank, oil cup, etc. in a timely manner, replace with new oil, and clean the filter screen.
⑩ For occasions with high machining accuracy requirements, regular maintenance of the overall accuracy of CNC lathes should be carried out, which can be achieved through recalibration of the lathe level and restoration of mechanical accuracy inspection.
⑪ There are two methods for correcting the mechanical accuracy of CNC lathes: soft and hard. Among them, software methods are mainly carried out through system parameter compensation, such as reverse clearance compensation for ball screw transmission, compensation for correcting coordinate positioning errors, etc; The hardware correction method is carried out during the overhaul of the lathe, such as rail scraping, scraping, pre tightening adjustment of ball screw nut pairs, and replacement of inserts.
5 Conclusion
The spindle of a lathe is a crucial part of the structural components of a machine tool. The spindle has the characteristics of high speed, high precision, high efficiency, and low noise. Timely and effective preventive maintenance work, as well as standardized operation and maintenance by operators every shift, will directly or indirectly affect the overall accuracy of the machine tool. At the same time, scientific and standardized maintenance of CNC systems can greatly reduce the failure rate and shutdown rate of CNC machine tools.
In short, the good technical condition of machine tools requires operators, maintenance workers, and production managers to maintain coordination and teamwork in their daily work.
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2023-07-03