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Reasons and solutions for broken wire in high speed wire cutting machine:
1. Reasons and solutions for wire breakage related to electrode wire:
(1) Wire tension and wire speed. For high speed wire cutting, widely used? 0.06 ~ 0.25mm molybdenum wire, because it is resistant to loss, high tensile strength, silk is not easy to become brittle and less broken wire. Increasing the tension of the electrode wire can reduce the influence of the wire vibration, thereby increasing the accuracy and cutting speed. The fluctuation of wire tension has a great influence on the processing stability. The reason for the fluctuation is that the tension on the wire electrode is not the same when the electrode wire on the wire storage drum moves forward and backward; after a certain period of time, the wire electrode will be elongated, resulting in a decrease in the tension. (It is generally believed that the tension is lower than the proper tension of 12 to 15 N. It is aggravated by vibrating wire, and it is easy to break the wire.With the increase of the wire speed, the processing speed will be increased within a certain range, and at the same time, the wire speed will increase, which will help the electrode wire to discharge the working fluid with a large thickness of the workpiece. In the gap, it is beneficial to the elimination of the electric erosion product and the stability of the electric discharge machining, but the desire is not reached, the threading speed is too high, the electrode wire jitter is severe, and the processing stability is damaged, which not only reduces the processing speed, but also The processing accuracy and surface roughness will be degraded, and it is easy to cause broken wires, but the wire-drawing speed should not be too low, otherwise, the loss during processing is large and it is easy to break the wire. Generally, the experience is less than 10m/s.
(2) Selection of electrode wire. The choice of electrode wire is nothing more than the type and diameter of the electrode wire. The wire electrode material used for wire-cut electric discharge machining should have good conductivity, low electron discharge power, high tensile strength, and good resistance to electric corrosion. The wire itself must not be bent or knotted. The material is usually molybdenum wire, tungsten wire, tungsten molybdenum wire, brass wire, copper tungsten wire and so on. Among them, molybdenum wire and brass wire are used most. With tungsten wire processing, higher processing speeds can be obtained, but after the discharge, the wire becomes brittle and easy to break, and the application is less. Therefore, it is generally used when the wire drawing speed is slow and the weak power standard is used. Molybdenum wire has a low melting point and tensile strength, but has good toughness. In the frequent changes of quenching and rapid heating, the silk is not easy to become brittle and broken. Therefore, although some properties are not as good as tungsten, it is still the most widely used at present. An electrode wire. Tungsten and molybdenum wire (50% tungsten and molybdenum each have better processing efficiency than the former two, so their service life and processing speed are higher than those of molybdenum wire, but they are expensive. The copper wire has a high processing speed, a stable process, but poor tensile strength. The loss is also large, generally used in the low-speed wire cutting process.In summary, the type of electrode wire should be determined according to the processing conditions. Otherwise it will often cause broken wire. For high-speed wire cutting, general electrode wire The diameter is between 0.06 and 0.25mm, and is usually between 0.12 and 0.18mm. When a fine shape and a small fillet radius are required, the 0.04-mm electrode wire is selected. The wire electrode is selected properly. Greatly reduce the occurrence of broken wire.
(3) New molybdenum wire and molybdenum wire self-break. There is a layer of black oxide on the surface of the new molybdenum wire. The cutting speed during processing is fast, and the surface of the workpiece is rough black. At this time, the power supply is too much energy and it is easy to break the wire. Therefore, for the new molybdenum wire, the processing current needs to be properly reduced. After the electrode wire is basically white, the normal electrical parameters can be restored. When the machine tool is not used for a long time, it is found that the molybdenum wire has been broken when it is used. This is the temperature difference that causes the material to expand and contract, and the tension of the molybdenum wire itself. If the machine is out of service, the drum should be shaken to the end and the molybdenum wire loosened.
2. Broken wire causes and solutions related to the workpiece:
(1) Broken wire when machining thin workpieces. Thin workpieces generally have a thickness of 3 mm or less. The main reason for the broken wire is that the opening distance of the upper and lower guide wire wheels is fixed, generally about 70mm. When the thin workpiece is cut, the wire electrode loses the damping effect of the cooling liquid produced when the workpiece is processed at a high speed, and the silver wire is easily shaken due to the effect of the spark discharge. The solution is that the processing voltage can be adjusted to about 50V; adjust the processing current is about 0.3A, adjust the pulse width to less than 10μm; reduce the wire jitter, such as the storage tube is a DC motor drag, can be changed Armature voltage, reduce the speed; if the AC motor is dragged, then connect a 10-15, 7 5W wire-wound resistor in any two-phase three-phase, reduce the phase voltage, make the commutation transition time slightly Long, to achieve soft commutation, can effectively reduce the jitter; the use of thickening of auxiliary materials between the upper and lower guide wheels, increase the thickness, increase the damping, can also prevent the molybdenum wire jitter. This method is relatively simple and does not require adjustment of processing electrical parameters.
(2) Broken wire when machining thick workpieces. Thick workpieces generally refer to workpieces larger than 100 mm. The broken wire when cutting thick workpieces may occur when the spark is just fed or when the workpiece is cut and when the workpiece is cut. The main reasons for broken wire are: 1 Broken wire from cutting. Cutting the wire just from the outside of the workpiece and cutting the spark. This is because the initial cutting, the molybdenum wire outside the workpiece, the upper and lower guide wire from the large distance, because the molybdenum wire is not damped and jitter, so that the gap between the molybdenum wire and the workpiece is in a poor state, or an excessive amount of emulsion, The insulation resistance is reduced and the arc extinguishing performance is not good, so that arc discharge is included in the discharge gap and the copper wire burns. In EDM, arc discharge is the main factor that causes negative electrode corrosion damage. In addition, the gap is poor and arc discharge is easily formed. As long as the arc is concentrated in a certain section, it will cause broken wires. Also, the greater the short-circuit current, the more severe the arc burns the molybdenum wire, and the greater the possibility of wire breakage. 2 Broken wire during cutting. When the molybdenum wire cuts the workpiece, due to the narrow slit, the emulsion penetrates difficultly, and the electric corrosion material in the slit (when the carbon black and the metal do not come out, the processing condition is deteriorated, and is often discharged twice in the slit and three times. Processing, resulting in widening of the kerf, as in the cutting of thin workpieces, the gap is in a poor state, so that the pulse to form an arc discharge.If the arc discharge is concentrated in a certain section, then the molybdenum wire will be blown soon. In addition to the above reasons, there are also the weight of the workpiece, the deformation caused by the internal stress of the workpiece material, and the resulting clip. The method of solving the problem is to make a simple and easy-to-use fixture and to perform the necessary heat treatment before processing.
(3) Broken wires caused by non-conductive substances in the workpiece. When a normal-looking material is viewed normally, a "short-circuit" phenomenon suddenly occurs, and no matter how it is excluded, it does not work. In this case, impurities are mostly trapped in the forged or smelted material. These impurities do not have good conductivity, resulting in continuous short-circuit in the process and eventually breaking the steel wire. The solution is to compile a program that steps back from 0.5 to 1 mm per 0.05 to 0.1 mm. Repeated use during processing and increased coolant flow can generally flush away impurities and restore normal cutting.
(4) Most of the workpieces for wire-cutting are after flat grinding, and they should be demagnetized after grinding. If the workpiece is not demagnetized, the electrocorrosive particles produced in the wire cutting process are likely to be absorbed in the slits. Particularly when the workpiece is thick, the non-removable magnets easily cause uneven cutting and the surface roughness increases to cause short circuits and broken filaments.
(5) Wire cutting automatically breaks the center. This is because there are oil stains, burrs, or some non-conducting substances on the wall of the process hole. When the electrode wire moves to the hole wall, no spark discharge occurs, so that the machine tool cannot automatically reverse the direction, the work piece bends the molybdenum wire, and finally breaks the steel wire. Therefore, the process hole must be cleaned before processing.
3. Causes of broken wires related to pulse power supply and solutions:
(1) The processing current is large and the spark discharge is abnormal, resulting in broken wires. Most of these faults are caused by the output of the pulsed power supply has become a DC output. The waveform is examined from the output stage of the pulsed power supply to the multivibrator in a step-by-step manner, and the defective component is replaced so that the output can be put into use in response to the desired pulse waveform.
(2) The output current exceeds the limit broken wire. During the processing, the spark discharge suddenly turns into a blue arc discharge, and the current exceeds the limit and the molybdenum wire is blown. With the oscilloscope, there is no waveform output at the input end and at the oscillation section. It can be judged that the fault is in the oscillation part. Inspection found that there are triodes. The meritorious internal space is open and the interior of the middle pole is broken down. Replace the tube and the high frequency power supply returns to normal. Another condition is that during the processing, the wire breaks suddenly and the current is above the limit. With an oscilloscope to measure the output of high-frequency power, its waveform amplitude is reduced, and there is a negative wave, and the pulse width meets the requirements, and the frequency, pulse width, and amplitude of the push-level waveform are all in line with the requirements. Determine the fault in the amplifier section. Examine the power tube and measure the internal breakdown of the ce pole of one of the tubes so that the final current is directly applied between the wire and the workpiece to cause the arc to burn off the molybdenum wire. Change the tube and return to normal. Imported pump (3) Broken wires on the molybdenum wire occurred at the burn point. Once the molybdenum wire has a "birth"-like burn spot, wire breakage can easily occur. It is generally believed that this is due to the processing debris (anode material) adhering to the wire electrode. This adhesion material serves to concentrate the electric discharge on the electrode wire. In this case, if the cooling and heat radiation conditions are poor, it is likely to cause the The temperature rises at the site, so that in the continuous discharge it may continue to have other processing swarf adhering near this point, thus creating a vicious circle that eventually leads to burns. As to the problem of why the machining chips stick to the electrode wire, the main reason is related to the pulse parameters and the cooling conditions of the discharge gap. The solution is to increase the no-load voltage amplitude of the pulsed power supply, or use a double-pulse approach similar to what is commonly referred to as a grouping pulse), which reduces the likelihood of machining debris sticking to the electrode wire; Flow rate improves cooling conditions.
(4) Broken filaments appear on the molybdenum wire at the point of ablation. In the amount of wire, there is an ablation point at intervals (about 10mm or so). Slightly like a mildew, severely visible spots of molybdenum wire erosion. This is caused by the arc between the electrode wire and the workpiece. For some reason, the A point on the workpiece and the B point on the molybdenum wire are arced. The electrode wire is moving. The arc between A and B is longer and longer. At point A, the arc starts to pull at the nearest point B'. This repeated cycle begins to form regularly spaced pits, which greatly reduces the strength of the electrode wire. The main reason for this phenomenon is the unbalanced output of the final stage of the feed system. Adjusting the feed system can eliminate this phenomenon.
4. Reasons and solutions for broken wires related to wire drawing device and working fluid:
(1) The broken wire related to the wire drawing device is the root cause of the deterioration of the precision of the device, especially the wear of the different wheels, which will increase the jitter of the molybdenum wire, destroy the normal gap of the spark discharge, and easily cause a large current concentrated discharge. This increases the chance of broken wires. The precision of the guide wheel mechanism can be checked from 3 aspects: 1 The V-groove of the guide wheel is widened. This will cause the wire electrode to reciprocate in the Y-axis direction. This phenomenon occurs when the wire spool is reversed or reversed. The bottom diameter of the guide wheel V-shaped groove is not round. This is because the bearing supporting the guide wheel is damaged, the molybdenum wire does not enter into the V-shaped groove of the guide wheel or the guide wheel is jammed when there is dirt, and the molybdenum wire is pulled out of the deep groove. When the storage sleeve is shaken by hand, It will be found that the wire is displaced back and forth in the direction of the X-axis; 3 the wire is broken due to poor contact between the conductive shaft and the conductive wheel. During the machining, the current meter pointer was found to oscillate from side to side, the feed rate was uneven, and sometimes the current meter pointer was returned to zero. The console feed rate was very fast. Because there was no discharge, the molybdenum wire was finally broken. At this time, replace the new conductive wheel and the conductive shaft.
(2) For workpieces requiring high cutting speed or large thickness, the ratio of the working fluid can be appropriately lightened to a concentration of about 5% to 8%, so that the processing is relatively stable and is not easy to break.
(3) The working fluid is dirty, and the deterioration of the overall performance after a long time is an important cause of broken wires. In practice, it can be used to measure whether the working fluid is degraded: When the processing current is about 2A, the cutting speed is about 40mm2/min, and the working time is 8 hours per day. The best results are obtained after two days of use, and it is easy to break after using for 8 to 10 days. Wire, must be replaced with new working fluid.
(4) It has been considered that the working fluid configured with high purity water is stable and less broken during processing. The reason is that it is estimated that high-purity water removes some ions harmful to electrolytic etching during the ion exchange purification process, such as calcium ions, magnesium ions, etc., resulting in that during the processing, although there is an intermediary of the electrolytic corrosion products, the working fluid Various ions are mixed in, but the processing is stabilized due to the removal of harmful ions.
5. Reasons and solutions for broken wires related to materials:
(1) Metals that are not subjected to forging, quenching, and tempering are generally considered to be easy to break. This is due to the uneven distribution of carbides in the steel, resulting in arc machining caused by unstable electrical machining and broken wires. The carbide particles contained in the steel are large and aggregate into clusters, and the distribution is not uniform. Such materials are susceptible to cracking and deformation during processing, resulting in broken wires. Especially the quenched parts, after quenching, there are about 500-800 MP in the non-carbon alloy. The internal stress can reach up to 1600 MPa internal stress in high carbon steel. If it is ground, it can also cause 70 ~ 80MP. The internal stress, and the electrical discharge machining will form a white electrical discharge degradation layer on its processing surface, and produce about 800MPa tensile stress. Stress stress, grinding stress, and EDM stress caused by stress and concentration are the direct causes of cracking in the quenching process. Therefore, in order to reduce the broken wire caused by the material, good forging performance and good hardenability should be selected. The heat treatment of the deformed material promotes the uniform distribution of the carbides contained in the steel, thereby enhancing the processing stability. For example, the cold punching die with wire cutting as the main process; CrWMn, Cr12Mo, GCr15 and other alloy tool steels are used as far as possible, and the heat processing method and the heat treatment specification are strictly selected.
6| Other broken wire causes and solutions:
(1) When removing the wire, the old wire on the storage tube is often cut with scissors to form a lot of short heads. If it is not noticed, it will be mixed in the electrical part or caught in the wire drawing device, causing a short circuit, resulting in broken wire. .
(2) After the processing is completed, the processing power supply should be turned off first, then the working fluid should be turned off, and the wire should be stopped after running for a period of time. If the working fluid is first shut off, it will cause discharge in the air and form a burning wire; if the yarn is first shut off, the wire speed will be too slow or even stop running, the wire will be cooled poorly, and the lack of working fluid in the interval will also cause burning.
(3) When manual cutting is required at certain times (refers to hand-cranked cross-slide), the visual ammeter should not exceed the frequency conversion speed during normal cutting, otherwise it is easy to break the wire.
(4) In practice, there is a broken filament due to dirt, and this phenomenon often occurs after the workpiece has been processed. During the inspection, electrical resistance of the multimeter was used to measure the resistance between the steel wire and the machine tool shell, which was about 30kΩ, and the replacement pen was charged and discharged. Further inspections revealed that there was a lot of liquid-sludge fouling between the mo- wire block stopper screw and the wire frame, and between the broken wire detection block and the screw on the fixed frame.
After the stopper and the detection block are removed, the charge/discharge phenomenon disappears and the resistance value rises. This is because the liquid residue dirt makes a resistance capacitance between the steel wire and the machine tool shell, and is connected to the output end of the power amplifier tube (due to equal potential of the shell and the power amplifier tube), so that the bottom of the output waveform becomes wider and the DC component increases. When the workpiece is finished quickly, the gap between the molybdenum wire and the workpiece is increased, so that the sampling potential is increased and the feeding speed is increased. This causes the molybdenum wire to be easily broken when it is processed. After cleaning the dirt, the machine is back to normal. Only think of it, you can't do it. Change your style from now on. Opening the Chinese cutting machine trading network is equivalent to opening up your wealth road, come and click on the website now! 】

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