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1.1 first outside the inside
With the continuous improvement of the EDM machine control system, the probability of failure in the control part is getting smaller and smaller, and most of the failures are not caused by single-board machines or other core control and trigger circuits, but due to the external Damaged circuit or device. Therefore, maintenance personnel should start from the outside to conduct inspections step by step. Do not disassemble the trigger circuit board, change the system parameter settings, adjust the operation mode, etc., as this may cause new faults to occur.
1.2 Mechanical and Electrical
EDM machine tools are most likely to experience mechanical failures, and these failures are often not easily discovered. Failures caused by wearing parts are a typical example. Therefore, the maintenance personnel should start with the mechanical part to observe the local area where the failure occurred, and carefully observe and carefully investigate the failure, such as whether there are cracks, looseness, fractures, and cracks. Instead of immediately checking whether the circuit is open circuited, short circuited, and whether the components are damaged or not, electrical faults are detected.
1.3 First Practice After Theory
The control circuit of the EDM machine tool is relatively not very complicated, which makes some maintenance personnel not look at the schematic diagram provided by the manufacturer, do not analyze the root cause of the fault, blindly carry out live maintenance operations, which will lead to further expansion of the fault . The maintenance personnel should carefully analyze the cause of the fault on the basis of the understanding of the fault condition, understand the method of solving the fault theoretically, and then put it into practice.
1.4 simple and complicated
Some failures are caused by a variety of factors. At this time, we should follow simple and complicated procedures first, solve the difficult problems first, properly handle these hidden dangers, and then solve difficult problems. When solving difficult problems, they should also be reduced to zero. The simple part should be solved first and the complicated parts should be dealt with. After simple problems are solved, difficult problems may also be resolved.
2 Wire EDM Cutting Machine Troubleshooting Methods
2.1 routine inspection method
Routine inspection refers to routine inspections performed by maintenance personnel before the equipment is started. Specifically include the following aspects:
(1) Power supply
View the power supply of the wire-cut electric discharge machine, whether the voltage fluctuation is in the range of ±10%, whether the high-order harmonic is serious, the size of the power factor, whether to install a regulated power supply, and so on.
(2) Wire cutting fluid
The role of wire cutting fluid is cooling, washing, chip removal, etc. Therefore, whether the wire cutting fluid is qualified is directly related to the quality of the processed workpiece. Check if the wire cutting fluid is too dark and if there is any odor. If it is, then its overall performance will be poor and it will easily lead to broken wires.
(3) Electrode wire (molybdenum wire)
The quality of the electrode wire, installation, preservation and other factors are directly related to the quality of the processed workpiece. Check whether the electrode wire is properly selected. Thicker workpiece wire should be selected to be thicker, which is beneficial to chip removal and also can increase its tension. Check the tightness of the electrode wire installation. When the wire is too loose, the electrode wire is very jittery and easy to break. , Too tight, the internal stress increases, it is easy to break the wire; Check whether the position of the electrode wire is not in the same plane from the center position. If yes, the electrode wire is easily broken or pinched; check whether the electrode wire is preserved. Specifications, such as moisture, oxidation, and exposure to light during storage, can result in the electrode wire becoming brittle and brittle.
(4) Control cabinet
Due to static electricity, etc., the control cabinet is susceptible to dust. When these dusts are exposed to moisture, they will corrode circuit boards, cause short circuits or open circuits, damage electronic components, etc. Even the entire circuit board will be scrapped. Therefore, it must be checked before maintenance.
Example 1: A wire cutter intermittently breaks the wire at regular intervals. Sometimes it can run for one day and sometimes it breaks several times a day. It was found that the wire cutting fluid was black but there was no odor. After careful observation, it was found that there were too many impurities in the wire cutting fluid, resulting in poor insulation, and eventually resulting in irregular broken wires. After the replacement of the new machining fluid, the troubleshooting was eliminated.
2.2 Consumables inspection method
Consumables inspection refers to the location where the maintenance personnel will check for faults after the equipment is started. After the equipment is operated for a long time, most of the failures are caused by the damage of the wearing parts. The wearing parts mainly include a guide wheel, a wire blocking device, a broken wire protection block body, a conductive block, a cushion, a travel switch and the like. The following is a brief introduction of how maintenance personnel will perform consumable inspections.
(1) Guide wheel
The main role of the guide wheel is to reduce friction and position the molybdenum wire. If there are problems such as misaligned guide wheels, non-rotating guide rollers, and grooves on the surface of guide rollers, many difficult problems will be caused. The position of the guide wheel is not correct, it is impossible to machine a qualified workpiece; the guide wheel does not turn, the surface wear is intensified, and the surface of the guide wheel will be quickly cut into grooves by the molybdenum wire. If the groove is shallow, when the molybdenum wire has a large jitter, the molybdenum wire will be locally excessively close to the workpiece, so that the discharge current is too large or the molybdenum wire is burned due to arc drawing, and the surface quality of the cut surface becomes worse; The groove is deeper and the molybdenum wire moving at high speed will be pinched off by both walls of the groove under slight shaking. Therefore, maintenance personnel must carefully check the surface of the guide roller that is in contact with the molybdenum wire.
(2) Wire blocking device
The main function of the wire blocking device is to position the molybdenum wire. When checking, be sure to pay attention to whether the wire column in the wire block device is close to molybdenum wire and whether the wire column has been cut into grooves. In addition, it is necessary to carefully observe whether there is any overlap on the storage drum.
(3) broken wire protection block body
Broken wire protection The main function of the blocking wire is broken wire protection to prevent the electrode wire from being disturbed due to broken wire. During the inspection, it is measured whether the broken wire protection switch is in the normally closed state. If not, the position of the broken wire protection and blocking wire body should be adjusted so that the broken wire protection switch is normally closed.
(4) Conductive blocks
The main role of the conductive block is electrical conduction. The conductive block is easily damaged, such as being cut into deep grooves, the surface is oxidized, etc., which can lead to poor contact between the conductive block and the molybdenum wire. When the contact is poor, it may cause high-frequency pulse current is very small, even without high-frequency pulse current output.
(5) cushion
The cushion acts as a buffer when reversing. During the inspection, listen to the sound produced by the wire removal mechanism, especially when changing direction. If the sound is abnormal and the vibration is large, generally speaking, the cushion is damaged.
(6) Travel switch
The main function of the travel switch is to reverse or break the high frequency.
Winding motor can not be reversing; reversing can not cut high frequency. The trip switch is easily damaged or badly contacted after frequent squeezing. When the trip switch malfunctions, the contactor cannot be de-energized, thus causing the wire feeder motor not to switch. Some wire cutters use the other contact of the travel switch as a control signal to cut off the high frequency. When the contact switch is in poor contact or damaged, the commutation cannot be cut off at high frequencies.
Example 2: A wire cutting machine reversing constantly high frequency. It was found that the broken wire protection block has been cut into a deep groove. Since the broken wire protection control circuit does not control the function of the main power supply, only the high-frequency circuit is controlled and cut off. Therefore, when the block body is cut into a deep groove, the micro switch is turned from the normally closed state to the normally open state due to the sag of the iron block, so that the high frequency circuit cannot be turned off. Replace the block, the fault is eliminated.
2.3 Principle Analysis
The principle analysis method refers to the detailed understanding of the fault, according to the working principle of the WEDM, analyze the cause of the fault, and try to find a solution to the problem. There are many kinds of such methods, the most commonly used are the following:
(1) Divide to zero
According to different functions in the schematic diagram, it is divided into main circuit and control circuit. The main circuit mainly includes wire feeding motor and water pump motor circuit. The control circuit mainly includes a trigger circuit, an adjustment circuit, a drive circuit, a single board machine control circuit, and the like. When a fault occurs, according to the analysis of the fault phenomenon, which part should be the fault, so that the scope of the fault is gradually narrowed down, and the fault can be quickly eliminated.
(2) Reverse Analysis
When it is basically determined that a certain range has failed, reverse analysis can be used. That is, it is assumed that a circuit somewhere is not connected, or when a circuit is short-circuited somewhere, what kind of situation occurs, and the state that should be represented when the fault occurs is theoretically simulated to determine the cause of the fault.
(3) Circuit Simulation
When the electronic circuit has a large fault, it is a common practice to use an oscilloscope to check the output signals of important links, such as voltage and waveform, to determine whether the component is damaged. However, after a simple measurement, it is impossible to judge whether the output signal is correct. Therefore, using electronic circuit simulation software is the best choice. Through circuit simulation, we can help us to determine more quickly if the electronic circuit component is damaged.
(4) Replacement of spare parts
For various reasons, maintenance personnel often have difficulty obtaining a complete electronic circuit diagram. When a major fault occurs, the general cause of the fault can only be analyzed. The maintenance personnel can use spare printed circuit boards, vulnerable electronic components, etc. to replace it, and the equipment can be put into operation as soon as possible.
Example 3: A wire cutter increases the frequency, the high-frequency current shows no change, and the speed of the wire cutting process is very slow. According to the integerization, it can be seen that the adjustment circuit has a problem. Check the open control cabinet and found that the input signal of the frequency multiplication circuit has been virtually connected. No matter what the position is adjusted, the output voltage is always zero. After re-welding, the fault is eliminated.
1 EDM cutting machine fault diagnosis principle