Analysis of Causes of Broken Wires in High Speed ​​Wire Cutting Machines
High-speed wire cutting machine is suitable for processing various complex shapes of die and single-piece gears, splines, sharp corners and other narrow parts. It has the advantages of high speed, short cycle, etc. The application is very popular. The electrode wire of high-speed wire cutting wire-cutting machine tools is mainly made of molybdenum wire. The speed of the electrode wire is usually 8 to 12 meters/second, and it is a two-way round-trip cycle operation. Wire breakage is very likely to occur during processing. If you break the wire many times during the cutting process, it will not only cause a certain economic loss, but also bring about the trouble of rewinding the wire; not only will the time be lost, but also a broken wire mark will be produced on the workpiece, which will affect the quality of processing. The workpiece was scrapped. This article summarizes the causes and solutions of wire breakage often encountered in high-speed wire-cutting wire-cutting machines.
1 Molybdenum wire
The degree of tightness of the molybdenum wire. If the molybdenum wire is too loosely installed, the molybdenum wire will be extremely jittery, which will not only cause broken wires, but also will directly affect the surface roughness of the workpiece due to the jitter of the molybdenum wire. However, molybdenum wire can not be installed too tight, too tight internal stress, it will cause broken wire, so the molybdenum wire in the cutting process, its tightness should be appropriate, the new installation of molybdenum wire, first tighten the wire and then processing, Do not apply too much force when tightening the wire. After processing for a period of time, the molybdenum wire becomes loose due to its own stretching. When the elongation is large, the vibration of the molybdenum wire may be exacerbated or the molybdenum wire may overlap on the wire storage drum. Causes wire breakage and causes breakage. Always check the tightness of the molybdenum wire. If there is slack, tighten it in time.
Molybdenum wire installation. The molybdenum wire should be wound on the wire storage drum according to the specified direction while fixing both ends. When winding the wire, generally two ends of the tube are left 10mm, the middle is full and does not overlap, the width is not less than half of the length of the wire storage tube, so as to avoid frequent motor change and accelerate the damage of the parts, and also to prevent molybdenum wire from being involved in cutting frequently. Broken wire.
The molybdenum wire at the machine tool has a wire block. The wire block is a guide column made of two rubies. The block wire does not roll like a guide wheel. They directly contact the molybdenum wire and make sliding friction. Therefore, the wear is very fast, and deep groove will be formed in the place where the cylinder contacts with the molybdenum wire in the near future. It must be checked and turned over and replaced in time. Otherwise, the wire will break.
2 wire feeding mechanism
The wire feeding mechanism of the wire cutting machine is mainly composed of a wire storage tube, a wire holder and a guide wheel. When the accuracy of the wire feeding mechanism is reduced (mainly the transmission bearing), radial runout and axial turbulence of the yarn storage drum may occur. The radial runout of the yarn storage drum will reduce the tension of the wire electrode, causing the wire to loosen. In severe cases, the wire will break off from the guide wheel groove. Axial turbulence of the storage drum will cause the thread to be uneven, resulting in overlapping phenomenon. The parts of the shaft, bearings, etc. of the wire storage drum often cause gaps due to wear, and can easily cause wire chatter and breakage. Therefore, worn shafts and bearings must be replaced in time. When the storage drum changes direction, if the high-frequency power is not cut off, the molybdenum wire will be overheated in a short time and the molybdenum wire will be blown. Therefore, it is necessary to check whether the stroke switch at the rear end of the storage drum is out of order. It is necessary to keep the spinning tube and the guide wheel rotating flexibly, otherwise it will cause the wire feeding system to vibrate and break the wire when it is moving back and forth. Check the molybdenum wire for jitter after wire winding and check the cause if jitter occurs. The limit stopper of the rear end of the wire storage drum must be adjusted well to prevent the wire storage drum from breaking out of the limit stroke and breaking the wire. The stopper in the wire-blocking device is in contact with the rapidly moving molybdenum wire and frictionally, which easily creates a groove and causes the wire to break, so it also needs to be replaced in time. The wear of the guide wheel bearing will directly affect the precision of the guide wire. In addition, when the V groove of the guide wheel, the gemstone limiting block, and the conductive block wear, the groove will also cause the friction wire of the electrode wire to be too large and easy to use molybdenum. Pull off the wire. This phenomenon usually occurs when the machine tool is used for a long time, the workpiece is thick, and the wire feeding mechanism is not easy to clean. Therefore, during the use of the machine tool, the accuracy of the wire feeding mechanism should be regularly checked and the wear parts should be promptly replaced.
3 workpieces
Workpiece materials: For materials that have not been forged or quenched, it is best to use low-temperature tempering to eliminate the internal stress before inline cutting, because if the internal stress of the workpiece is not eliminated, some workpieces will crack when cutting, and the molybdenum wire will be cracked. Some of them will deform the gap and pinch or break the molybdenum wire. Such as after quenching T8 steel in the online processing and easy to cause broken wire as little as possible. When cutting thick aluminum materials, due to the difficulty of chip removal, the conductive block wears too much and attention should be paid to timely replacement.
Workpiece clamping: Although the workpiece is subjected to minimal force during the wire cutting process, it is still necessary to firmly clamp the workpiece to prevent wire breakage due to the position change during the machining process. At the same time to avoid the broken wire due to the workpiece's own weight and the elastic deformation of the workpiece material. When processing heavy workpieces, you can use the magnet to absorb the workpiece that will fall when the workpiece is about to finish, or manually protect the dropped workpiece so that it falls slowly in parallel to prevent wire breakage.
4 Electrical parameters
Improper selection of electrical parameters is also an important cause of wire breakage, so it is necessary to select reasonable electrical parameters according to the thickness of the workpiece, and to separate the pulse intervals to facilitate the discharge of molten metal particles. At the same time, the peak current and no-load voltage should not be too high. Otherwise, the energy of a single pulse becomes larger, the cutting speed is accelerated, concentrated discharge and arc drawing are easily generated, and broken wires are caused. The general no-load voltage is about 100V. In EDM, arc discharge is the main cause of corrosion damage of the negative electrode. In addition to improper clearance, it is easy to cause a certain pulse to form an arc discharge. As long as the arc discharge is concentrated in a certain section, wire breakage will occur.
According to the thickness of the workpiece to choose the appropriate discharge gap: discharge gap can not be too small, otherwise prone to short circuit, but also not conducive to the cooling and discharge of electrocorrosive; discharge gap is too large, will affect the surface roughness and processing speed. When cutting a workpiece with a large thickness, a large pulse width current should be used as much as possible. At the same time, the discharge gap should be larger and longer to enhance the chip removal effect and improve the cutting stability.
5 Conclusion:
The analysis of the causes of the broken wire in the high speed wire cutting machine and the mentioned solutions are summarized based on long-term work experience. In the actual operation process, due to equipment, processing technology, and materials, there are many reasons for broken wires, which need to be continuously summarized and improved in the work.
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