Electrode wire quality, installation, preservation and other factors are directly related to the quality of the workpiece after processing. Check whether the electrode wire is properly selected, the processing of thick workpieces should be selected thicker electrode wire, which is conducive to chip removal, but also to improve its tension; check the degree of tightness of the electrode wire installation, too loose, the electrode wire jitter is strong, easy to break the wire, too tight, the internal stress increases, but also prone to break the wire; check the electrode wire installation position is not deviated from the center of the position is not in the same plane, such as, the electrode wire is very easy to be stuck or pinched off Check whether the electrode wire is stored in a standardized way, such as moisture, oxidation, sun exposure during storage, then the electrode wire will also become brittle and easy to break.
1. EDM wire cutting machine common failure diagnosis
1.2 Mechanical and then electrical
EDM machine tools are most prone to mechanical failures, and these failures are often not easy to be found, wear parts caused by the failure is a typical example. Therefore, the maintenance personnel should target the local scope of the occurrence of faults, first from the mechanical part of the start, careful observation, careful troubleshooting, such as whether there are cracks, loose, broken, cut, etc.. Instead of immediately checking whether the circuit is broken, short-circuited, whether the components are damaged and other electrical faults.
1.3 Theory before practice
The control circuits of EDM machine tools are relatively not too complex, which makes some maintenance personnel do not look at the schematic diagrams provided by the manufacturer, do not analyze the root cause of the failure to blindly carry out maintenance operations with electricity, which will lead to further expansion of the fault. Maintenance personnel should be based on an understanding of the fault, carefully analyze the causes of the failure, from the theory to figure out how to solve the problem, and then put into practice.
1.4 First simple and then complex
Some failures are caused by a variety of factors. At this time, should follow the first simple and then complex procedures, the first to solve the difficulty of small faults, properly deal with these hidden problems, and then solve the difficult faults. When solving difficult faults, it should also be reduced to zero, the first to solve its simple part, and then deal with the complex part. Often simple problems solved, difficult problems may also be solved.
2 EDM wire cutting machine troubleshooting methods
2.1 Routine inspection method
Routine inspection method refers to the routine inspection carried out by the maintenance personnel before the start of the equipment. Specifically, it includes the following aspects:
(1) Power supply
Check the incoming power supply of the EDM wire cutting machine, whether the voltage fluctuation is within the range of ± 10%, whether the high harmonics are serious, the magnitude of the power factor, and whether it is necessary to install a voltage stabilized power supply.
(2) wire cutting fluid
Wire cutting fluid is cooling, washing, chip removal, etc., so the wire cutting fluid is qualified directly related to the quality of the workpiece after processing. Check whether the wire cutting processing fluid is too black, whether there is a strange odor, if so, then its comprehensive performance will be worse, easily lead to broken wire.
(3) electrode wire (molybdenum wire)
Electrode wire quality, installation, preservation and other factors are directly related to the quality of the workpiece after processing. Check whether the electrode wire is properly selected, the processing of thick workpieces should be selected thicker electrode wire, which is conducive to chip removal, but also to improve its tension; check the tightness of the electrode wire installation, too loose, the electrode wire jitter is strong, easy to break the wire, too tight, the internal stress increases, but also prone to break the wire; check whether the electrode wire installed position is not centered on whether not in the same plane, such as, the electrode wire is very easy to get stuck or pinched off; check the electrode wire installation of the position of the center is not the same plane, such as, the electrode wire is very easy to get stuck or broken! Check whether the electrode wire is stored in a standardized way, such as moisture, oxidation, sun exposure during storage, then the electrode wire will become brittle and easy to break.
(4) Control cabinet
Dust is easily accumulated in the control cabinet due to static electricity. This dust will corrode the circuit boards when they are damp, causing short-circuit or disconnection conditions, which in turn will damage electronic components, etc., and even render the entire circuit board obsolete, so be sure to check before repairing.
Example 1: A wire cutter breaks the wire irregularly every once in a while. Sometimes can run a day without breaking the wire, sometimes a day break a few wire. Inspection found wire cutting processing fluid black, but there is no odor. After careful observation, found that too many impurities in the wire cutting fluid, resulting in insulation degree is not good, ultimately leading to irregular wire breakage, replacement of the new processing fluid, the fault is eliminated.
2.2 Vulnerable parts inspection method
Vulnerable parts inspection refers to the equipment after the start, maintenance personnel for the emergence of faults to be checked parts. After a long period of equipment operation, most of the failures are caused by the damage of wearing parts. Vulnerable parts are mainly guide wheels, wire stopping devices, wire breakage protection block body, conductive blocks, buffer pads, travel switches and so on. The following is a brief introduction to the maintenance staff how to carry out the inspection of wearing parts.
(1) guide wheel
The main role of the guide wheel is to reduce friction and the molybdenum wire positioning. If the guide wheel is not in the right position, the guide wheel does not rotate, the guide wheel surface has grooves and other problems, it will lead to a variety of difficult failures. If the position of the guide wheel is not correct, it is impossible to process qualified workpieces; if the guide wheel does not rotate, the surface wear will increase and the surface of the guide wheel will soon be cut into grooves by the molybdenum wire. If the groove is shallow, when the molybdenum wire has a large jitter, will make the molybdenum wire localized excessively close to the workpiece, so that the discharge current is too large or due to the arc and burn off the molybdenum wire, while the cutting surface surface surface quality deterioration; if the groove is deeper, high-speed movement of molybdenum wire in the slight jitter, will be the groove of the two walls of the clip off. Therefore, maintenance personnel must carefully check the guide wheel on the surface in contact with the molybdenum wire.
(2) Wire stopping device
The main function of the wire stopping device is to locate the molybdenum wire. When checking, be sure to pay attention to the wire stopping device in the row of wire column is close to the molybdenum wire, row of wire column has been cut into grooves. In addition, you should also carefully observe whether there is any superposition of silk on the storage cylinder.
(3) break wire protection retainer
The main function of the break wire protection retainer is to break the wire protection, to prevent the electrode wire from being stirred up because of the break wire. When checking, measure whether the break wire protection switch is normally closed, if not, should adjust the position of the break wire protection stopper body, so that the break wire protection switch is normally closed.
(4) conductive block
The main role of the conductive block is to conduct electricity. And the conductive block is extremely easy to damage, such as being cut into deep grooves, the surface is oxidized, etc., which will lead to poor contact between the conductive block and the molybdenum wire. When the contact is poor, it may result in little or no high-frequency pulse current output.
(5) buffer pad
The buffer pad plays the role of buffer when changing direction. When checking, listen to the sound that occurs in the wire-walking mechanism, especially the sound when changing direction. If the sound is abnormal, accompanied by a lot of vibration, generally speaking, is the buffer pad has been damaged.
(6) travel switch
The main function of the travel switch is to change direction or break high frequency.
Operating silk motor can not change direction; change direction can not break high frequency. Travel switches are easily damaged or poor contact after frequent extrusion. When the travel switch is faulty, the contactor can not be disconnected, thus causing the wire motor can not be reversed. Some wire cutting machines use the other pair of contacts of the travel switch as the control signal for breaking high frequency. When the travel switch contact is poor or damaged, the phenomenon of commutation can not break the high-frequency phenomenon.
Example 2: a wire cutting machine commutation without high frequency. Inspection found that the break wire protection block wire body has been cut into a deep groove, because the break wire protection control circuit does not control the function of the total power supply, only to control the break high-frequency circuit. So when the blocking body was cut into a deep groove, micro-switch due to the sagging of the iron block from a normally closed state into a normally open state, which can not turn off the high-frequency circuit. Replace the wire body, the fault is eliminated.
2.3 Principle analysis method
Principle analysis method refers to a detailed understanding of the fault, according to the working principle of the EDM wire cutting machine, analyze the causes of failure, and try to find a solution to the problem. These methods are varied, the most commonly used are the following:
(1) the whole into zero
The schematic diagram according to different functions, divided into the main circuit, control circuit. The main circuit mainly includes the silk transport motor, pump motor circuit. Control circuits mainly include trigger circuits, adjustment circuits, drive circuits, single board control circuits. When a fault occurs, according to the fault phenomenon analysis, the fault should belong to which part, so that gradually narrow the scope of the fault, can be faster troubleshooting.
(2) reverse analysis
When basically determined that a small range of failures, you can use the reverse analysis method. That is, assuming that a circuit does not work, or a circuit short circuit, what will happen, from the theoretical simulation of the failure should be shown when the state, so as to determine the cause of the failure.
(3) circuit simulation
When a large electronic circuit failure, the usual practice is to use an oscilloscope to check the output signals of important links, such as voltage and waveform, so as to determine whether the component has been damaged. But often through simple measurements, can not determine whether the output signal is correct, then the use of electronic circuit simulation software is the best choice. Through the circuit simulation, can help us faster to determine whether the electronic circuit components have been damaged.
(4) Spare parts replacement
For a variety of reasons, it is often difficult for maintenance personnel to get a complete electronic circuit diagram. When a large failure, can only analyze the general cause of the failure, maintenance personnel can use spare printed circuit boards, fragile electronic components, etc. for replacement, so that the equipment as soon as possible into operation.
Example 3: a wire cutting machine to increase the multiplier frequency, high-frequency current shows no change, wire cutting processing speed is very slow. According to the whole to zero can be known, is to adjust the circuit problem. Open the control cabinet inspection found that the frequency multiplier circuit input signal contact has been false, no matter what position is adjusted to, the output voltage is always zero. After re-soldering, the fault is eliminated
Electro discharge machining in the common problems
1. emulsified oil flushing liquid does not emulsify how to do?
In the production process of emulsified oil will generally add some volatile stabilizers, if in the production process can not be operated in accordance with the process requirements or the use of poor-quality base oils as raw materials may produce this phenomenon, to deal with the problem of the simplest way is to add some emulsified emulsified oil can be emulsified, stirring can be made to emulsify, or to add some alcohol, the proportion of control at 1 The proportion is controlled at about 1-2%.
2. Workpiece cutting does not move how to do?
In the actual cutting process will often encounter the workpiece cutting does not move, and sometimes can not cut, this situation generally occurs in the high thickness cutting or cutting of stainless steel and other difficult to process materials, the fundamental reason is that the working fluid does not have a good shot in addition to the characteristics of the erosion of the product, the emergency approach is to add some detergent essence or increase the concentration of the working fluid, but the most fundamental way is to change the working fluid to a good. But the most fundamental solution is to change to a good working fluid. (In some areas due to the use of hard water flushing fluid can also produce cut the problem)
3. molybdenum wire cutting speed is inconsistent when cutting forward and reverse, or even a direction does not go how to do?
This situation is often encountered in high thickness cutting, the root cause is still the problem of the working fluid, of course, but also with other factors such as: frequency tracking speed, molybdenum wire tension uniformity consistency and so on. By the way, in the cutting of high thickness workpieces, it is best to frequency tracking to play a little faster, because in the over-tracking will not break the basic wire, but in the under-tracking often leads to processing instability, causing broken wire.
4. How to reduce the chances of molybdenum wire breakage at both ends of the barrel
High-speed wire cutting molybdenum wire at both ends of the barrel to frequently change direction, so the two ends of the molybdenum wire will be repeatedly received by the impact of the pulling force, so the two ends of the molybdenum wire by fatigue damage, so in order to extend the service life of molybdenum wire should be every other shift (about 8 hours) will be reversed to the travel switch to move a little inward. This method is especially important in high current and high efficiency processing.
5. How to extend the service life of the molybdenum wire
The molybdenum wire will be damaged every time it discharges with the workpiece, but only to a small extent, so it is best to use small energy processing parameters for cutting (so that the damage is small), and wait until the color of molybdenum wire is basically white, and then switch to the normal high current for cutting. Of course, before changing the molybdenum wire for cutting, it is best to let the molybdenum wire empty run for 5-10 minutes, so that its original internal stress is released.
6. How to reduce the molybdenum wire at the starting point of the wire breakage
Generally, the use of automatic frequency tracking machine tools from the outside of the cut into the workpiece can reduce the molybdenum wire at the starting point of the breakage of the wire, and at the same time, to ensure a good supply of coolant to absorb the discharge of explosive force to the molybdenum wire produced by the perturbation of the workpiece is best away from the upper and lower jets of the mouth of the 5-10mm, so that the coolant can be better wrapped around the coolant, so the coolant can be better. So that the coolant can better wrap the molybdenum wire.
7. How to adjust the frequency tracking speed
Adjusting the frequency tracking speed itself does not have the ability to increase the machining speed, its role is to ensure the stability of the process. When the tracking speed is not adjusted properly, it will significantly affect the process indicators and cutting surface quality, and may produce broken wires. The best frequency tracking speed adjustment can refer to the following two bases:
First of all, the best processing current should be about 80% of the short-circuit current (in the beginning of processing can be pressed with molybdenum wire on the side of the workpiece and then open the high-frequency, at this time, the ammeter shows that is the short-circuit current value), this law can be used to determine whether the feed speed adjustment is appropriate; Secondly, can be judged by the ammeter pointer swing, the normal processing of the ammeter pointer should be used to judge the quality of the cutting surface, and may produce broken wires. Normal processing ammeter needle should be basically immobile. If often downward swing, it is not tracking, tracking speed should be adjusted faster; such as often upward swing is often short-circuit, belonging to the state of tracking, tracking speed should be adjusted slower; such as the needle back and forth more substantial swing is that the processing is not stable, should be judged to be the cause of good parameter adjustments (such as adjusting the pulse energy, the flow of working fluids, the wire walking system, including the state of the guide wheel, the bearings) and then processed, or else prone to cause breakage of the wire.
With the development of new materials, new technologies, EDM wire cutting machine applications are becoming increasingly popular, its good flexibility, stable machining accuracy for users to bring great benefits. However, the high failure rate of EDM wire cutting machine, especially the downtime and maintenance costs bring great inconvenience and waste of resources to users. Usually small faults can be solved by reading the manual in detail, now I 7725-2 type wire cutting machine, for example, on its often difficult faults and their causes, solutions for an analysis.
1 Fault (1): In the automatic processing process, many times the phenomenon of automatic shutdown of the storage cylinder.
After careful inspection and detailed study of the instruction manual, found that the problem in the KA4, in the automatic processing of power loss caused by the normally open contacts disconnected, so that the control circuit is de-energized. After further inspection, boot observation, the relay KA4 many times the phenomenon of ignition, unloading KA4 feel the red circle of heat, but did not find obvious faults. Unpacked with a multimeter check, found that one end of the coil wire head false connection, re-soldered, mounted after use, help troubleshooting.
2 Trouble (2): molybdenum wire in the automatic processing, there is a stacked wire, through to the many times the broken wire, resulting in scrap processing.
In accordance with the instruction manual and consult the machine tool manufacturer, the requirements to check the storage cylinder slide plate air travel clearance is not excessive, according to its requirements to eliminate the axial clearance is still no clear industry to change the present.
After reviewing the information and many on-site tests, and finally found that the reason for the lower end of the wire frame under the guide wheel, carefully adjusted the position of the guide wheel to find a little effect. Further inspection, found that the guide wheel due to long-term abnormal operation (when turning and stopping) and the emergence of different depths of the groove. When running will cause radial runout, resulting in molybdenum wire runout, so that the molybdenum wire stacked wire. After replacing the new guide wheel, use a few days later, and the above situation, found that this is due to the vice guide wheel does not turn the treatment method, the effect is very good, is now used for about a year, no stacked wire failure.
3 Fault (3): the machine tool running longitudinal, transverse feeding at the same time, can not feed according to program requirements, in the automatic feeding lock can not be, with the hand can be rotated.
After checking, there are two reasons for this type of failure: (1) the spare two 5V battery contact is poor, replace the new battery or battery unloading and reloading, the fault is eliminated. (2) stepper motor into the line wire off or poor contact, re-connected after the fault is lifted. Through the above analysis, it can be seen that the electric wire cutting machine repair, maintenance is a very important and detailed work, must be equipped with experienced maintenance personnel, detailed maintenance of machine tools, repair and troubleshooting files in order to do to minimize the loss caused by machine tool failure.
CNC EDM wire cutting electrode wire should have the performance
CNC EDM wire cutting processing of high-performance electrode wire must be a variety of useful features of the organic combination of the electrode wire, then what are the useful features of the electrode wire?
1, electrical characteristics
Modern wire cutting power supply on the electrode wire puts forward strict requirements. It has to be able to withstand large cutting currents with peaks in excess of 700 amperes or average values in excess of 45 amperes, and the transfer of energy has to be very efficient in order to provide the high-frequency pulsed currents required to achieve a high surface finish (0.2Ra or more). This depends on the resistance or conductivity of the electrode wire. Copper has one of the highest conductivities and is used as a benchmark against which other materials are measured. The conductivity of purple copper is labeled as 100% IACS (International Annealed Copper Standard), while brass has a conductivity of 20%.
2. Mechanical Properties
Tensile Strength:
Tensile strength is a measure of a material's ability to resist fracture when subjected to a radial load. It is scaled by the weight that can be withstood per unit of cross-sectional area, such as PSI (pounds per square inch) in the British system or N/mm2 (Newtons per square millimeter) in the metric system. Copper is among the materials with the lowest tensile strength (245N/mm2), while molybdenum has the highest (1930N/mm2). The tensile strength of electrode wires depends on the choice of material and the various heat and tensile treatment processes. Electrode wires are sometimes categorized as "soft" or "hard", each having its own strengths for different equipment and applications.
Memory Effect:
This is directly related to whether the electrode wire is "soft" or "hard". Soft wires do not have the memory to return to a straight line when they are drawn off the spool, so they cannot be used for automatic threading, but this has no effect on the cutting because the electrode wire is tensioned during processing. Soft wires are suitable for large inclination cuts of more than 7 degrees in equipment where the upper and lower guide nozzles cannot be tilted. Hard wire, on the other hand, is the best choice for automatic threading machines, and because of its high tensile strength, its ability to resist jittering of the wire due to the current and flushing force during cutting is stronger.
Elongation:
Elongation is the percentage change in the length of the electrode wire due to tension and heat during the cutting process. Soft wires can have elongation as large as 20%, while hard wires are less than 2%. When soft wires are used in beveled processing, electrode wires with high elongation ensure more geometric accuracy of the bevel, and softer wires produce less vibration when sliding in the wire guide nozzle. However, the soft wire jerks more than the hard wire when the electrode wire enters the cutting zone, so there is still a compromise to be made.
3, geometric characteristics
In the early days of the development of wire cutting technology (1969 to the mid-1970s), the electrode wire almost no research was done, using off-the-shelf motors and cables on the purple copper wire. Today, high-efficiency, high-precision wire-cutting machines require electrode wires with geometrical characteristics that are subject to very small errors. The final stage of wire manufacturing is the use of multiple jeweled wire drawing dies to obtain a smooth, perfectly rounded finished product with a wire diameter tolerance of +/-0.001mm. On the other hand, there are other electrode wires that are purposely designed to have a relatively rough surface, which can increase cutting speed.
4, thermophysical properties
The thermophysical properties of the electrode wire are the key to improving cutting efficiency. These characteristics are determined by the ratio of alloy composition or the choice of base core material.
Melting point:
The melting point of the electrode wire is an important indicator. Due to the mechanical movement of the electrode wire as it passes through the wire guide nozzle, as well as factors such as flushing force and discharge, the electrode wire is jittery when cutting. This causes numerous very small short circuits, slowing down the cutting process. If the electrode wire works with some loss in the outer diameter, so that it has a gap in the direction of facing the cut can prevent or reduce the short-circuit effect. At the same time, its clearance in the direction of the back to the kerf helps to improve the flushing effect, which can better remove the processing waste chips. The loss of the outer diameter of the electrode wire does not affect the machining accuracy because new electrode wire is constantly being fed. This is one of the two properties of materials that metallurgists consider when studying the flushing properties of electrode wires.