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Abstract: This article analyzes three common faults that occur during the precision machining process of 3MZ3220B ultrasound, including end face support damage, high failure rates of electric motors and frequency converters, and oil stone fracture. Targeted solutions are proposed.
Keywords: ball bearings; Ultra precision machine; Frequency converter; PLC; Oil stone
1. Existing problems
The 3MZ3220B bearing outer ring ultra precision machine is mainly used for ultra precision machining of the outer ring grooves of deep groove ball bearings and angular contact ball bearings with an outer diameter of 130-200 mm and a width of 22-42 mm. The main purpose is to reduce surface roughness, improve groove roundness and waviness, and meet the production needs of low-noise and high-precision bearings. The (fully automatic) processing steps of the machine tool are: workpiece rotation → feeding → pressing the workpiece with the pressure wheel → placing the swing frame box in the processing position → pressing the workpiece channel with the oil stone → (swinging the swing head) ultra precision channel → lifting the oil stone → retracting the swing frame box → retracting the pressure wheel → discharging. Repeat this process repeatedly to achieve ultra precision in the workpiece channel. However, due to the unreasonable electrical and structural parts of the original machine tool, end face support damage, high failure rates of electric motors and frequency converters, and oil stone fractures often occur during the machining process. It is urgent to find effective solutions.
2. Fault analysis and improvement measures
2.1 End face support alloy ring damage
During the ultra precision process, there is a phenomenon where the alloy ring supporting the front end face of the workpiece shaft is broken by collision. Observation shows that when processing lightweight products (with small workpiece thickness), the stroke of the pressure wheel design is relatively large, and the pressure wheel device does not have a front limit function. When the pressure wheel presses the workpiece and the end face support in automatic processing, the workpiece is in surface contact with the end face support, and the end face support is not easily damaged; When there is no workpiece, the pressure wheel will directly press onto the end face support. Due to the automatic adjustment of the rotation allowance of the pressure wheel, the contact between the pressure wheel and the end face support is often a linear contact at one end, and the pressure is high, resulting in the fracture and breakage of the brittle alloy ring on the end face support. In addition, when there is no workpiece, the machine tool will automatically circulate empty, resulting in energy waste. To solve the above problems, a material free electrical protection device has been added, a proximity switch has been installed in the feeding tank, integrated into the PLC (Figure 1), and the program has been changed. When there is material in the hopper, the proximity switch senses and sends a signal to the PLC, which controls the program to run downwards; When there is no material in the hopper, the proximity switch does not sense or send a signal, and the automatic cycle does not start until there is material in the hopper before continuing the cycle action. After improvement, it can effectively protect the end face support from damage caused by subsequent actions when there is no material, and effectively control the machine tool's idle cycle when there is no material, saving energy consumption during the waiting process.
Figure 1 Electrical schematic diagram after adding material detection
2.2 High failure rate of electric motors and control frequency converters
The original machine tool was designed to rotate the workpiece shaft continuously after startup. Improper adjustment can easily cause the workpiece to be biased or fly out when the pressure wheel is pressed, and also affect the service life of the motor and frequency converter.
Therefore, the control method of the automatic machining motor is improved by changing the original workpiece shaft to rotate continuously to start rotating when the pressure wheel presses the workpiece; When the ultra precision is completed and the swing box returns to its original position, the workpiece stops rotating, and this cycle repeats (Figure 2). Install a proximity switch at the lower seat of the pressure wheel and adjust its position. When the pressure wheel presses the workpiece, the upper seat of the pressure wheel and the proximity switch sense each other. The intermediate relay is controlled through the sensing switch, and the frequency converter is turned on to control the rotation of the workpiece shaft; When the ultra precision is completed and the roller seat retracts, the proximity switch controls the intermediate relay to disconnect, the relay controls the frequency converter to interrupt, and the workpiece shaft stops rotating. After the transformation, the automatic processing of the equipment is normal, the safety is improved, and the service life of the motor and frequency converter is extended.
Figure 2 Schematic diagram of improved motor control
2.3 Oil stone fracture
The original machine tool oil stone pressing and lifting part adopts the principle of hydraulic lever to control the pressing and lifting of the oil stone, and the lever part is often severely worn; The lifting of the oil stone and the retraction of the swing frame box are basically synchronized. The hydraulic diversion causes the lifting of the oil stone to be slightly slower than the retraction of the swing frame box, which can easily interfere and cause the oil stone to not completely detach from the workpiece channel and be pulled apart by the retraction of the swing frame box.
After improvement, the oil stone pressing and lifting will be changed to pneumatic control, using a cylinder to drive a small guide rail pair to control the oil stone pressing and lifting, so that the oil stone pressing and lifting action and the swing frame box retraction action are controlled by air pressure and hydraulic pressure respectively, without interfering with each other; Add a delay function to the program to ensure that the oil stone is lifted for 2 seconds before the controller controls the swing box to retract. After the transformation, the problem of easy wear of the original lever part was completely solved, effectively avoiding the problem of oil stone fracture.
3. Conclusion
By adding electrical protection devices to the machine tool, improving motor control methods, and improving local unreasonable structures, the failure rate of the machine tool has been effectively reduced and costs have been saved.
2024 September 1st Week KYOCM Product Recommendation:
Composite bearing is a kind of roller bearing which can bear both radial load and axial load. The structure of the corrugated ined bearing is axial and radial bearing running at 900 °, the main load is borne by the radial bearing, and the axial bearing bears the lateral thrust.
Corrugated ination bearing is used together with profile guide rail or channel steel. There are two main types of profiles, I and C profiles. The corrugated ined bearing slides into the profile guide rail to generate the required linear movement. The corrugated ined bearing is welded with the flange plate for installation according to the application requirements. The assembly is mainly used for precise heavy vertical and horizontal movement.
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2024-09-09