Wed Jun 08 15:34:39 CST 2022
1. The fast-moving wire-cutting machine tool is basically an open-loop control device. Because the repeated positioning accuracy is difficult to control, frequent wire breaks will deteriorate the processing accuracy and even cause waste.
2. If the wire is broken, the wire needs to be re-wound and threaded. Because there are dirt formed after discharge in the cutting seam of the workpiece, or the material deformation after processing makes the cutting seam narrow, the threading work becomes difficult, and a lot of time is wasted when cutting from the beginning.
In short, reasonable control of the wire breakage rate can achieve the purpose of improving processing accuracy and processing efficiency. In today's article, I will tell you about the control methods of wire cutting machine broken wires.
Frequent broken wire failures of fast-moving wire cutting machines are closely related to several reasons, such as the quality of molybdenum wire, wire conveying system, coolant and liquid supply system, pulse power supply, pulse processing regulations, etc. By controlling these factors, frequent failures can be reduced. Broken wire fault.
Fast-moving wire cutting machines mostly use cold drawn molybdenum wires with a diameter of 0.12~0.2mm as wire cutting molybdenum wires. Regarding the issue of molybdenum wire, first of all I would like to advise all friends to buy genuine molybdenum wire. At present, there are too many fake molybdenum wires on the market. You can consult major molybdenum wire manufacturers to find local regular dealers to buy. When buying molybdenum wire, pay attention to the weight and be careful. It is silk that is not enough rice, and not enough rice often means that this is a fake.
In addition, everyone should pay attention to the storage of molybdenum wire, and pay attention to whether the vacuum-sealed packaging is intact to avoid oxidation problems during storage. The surface of molybdenum wire will break easily after being oxidized, and the tensile properties will deteriorate. The wire is easily broken during electrical discharge machining, and the stable machining time of the machine tool becomes shorter. I bought a new molybdenum wire and looked at the color. The black and shiny metallic luster is the new wire, and the dark and grayish molybdenum wire is the oxidized molybdenum wire. For the second fold, grab a piece of wire and bend it repeatedly at the same point, insisting that the more the number of bends, the better the quality.
The reliability of the wire transport system is embodied in several aspects such as uniform wire discharge in the wire storage drum, slight vibration of the molybdenum wire in the processing area, and reliable commutation.
1. For the wire storage barrel, each forward or reverse rotation, the molybdenum wire can travel more than 0.2mm along the axis of the wire barrel to ensure sufficient distance for the wire. At the same time, when the wire is in and out, it is generally clamped by the gem guide post. Wire-cutting molybdenum wire prevents wire-cutting molybdenum wire from stacking and breaking the wire due to the axial movement of the wire-cutting molybdenum wire. Generally, check the transmission of the wire barrel and the jewel guide post when the wire is overlapped: ① The wire barrel has no axial movement and radial runout. ②The carriage moves more than 0.2mm along the axis of the wire barrel every time the wire barrel rotates. The gem guide post will wear out due to frequent friction with the molybdenum wire. Adjust the gem guide post so that it can hold the key wire.
2. Molybdenum wire jitter is a more complicated and difficult problem to solve. The wire-cut molybdenum wire has a relatively large jitter in the processing area, which will cause the wire-cut molybdenum wire to be too close to the workpiece locally, causing the discharge current to be too large or drawing arcs to burn the molybdenum wire. At the same time, the surface quality of the cut surface will deteriorate. The current consensus is to reduce the number of guiding links as much as possible, that is, reduce the number of transmission guide wheels to reduce vibration, and at the same time improve the consistency of the positive and negative commutation of the wire transport system on the wire-cut molybdenum wire tension. For example, as shown in the figure below:
F is an automatic tightening weight counterweight, D, E, G, and H are unilateral guide wheels, and B and C are bilateral guide wheels. When the storage drum rotates clockwise, A and B are the take-up systems, and I, H, G, F, E, D, and C are thread-feeding systems. When the silk tube rotates counterclockwise, A and B are thread-feeding systems, and the rest are thread-receiving systems. It can be seen that the pulling force of the key wire is different during forward and reverse rotation. Due to the different pulling force, the wire wound in the storage drum is tightened in one direction and loosened in the other direction. It is easy to cause the transmission parts of the wire drum, carriage, and guide wheel system to wear and the accuracy changes. Poor, aggravate the jitter of the wire. In the early use process, the automatic thread tightening counterweight F was added, and it was found that the thread was often taken up (mainly due to the stretching of the thread) and the thread was easily broken. After the thread was tightened, the F was removed, and the thread was tightened every 4 hours or so. There is no significant improvement in the fluttering condition.
Research has found that in the I, H, G, F, E, D, and C systems, the influence of H is more pronounced except for F. Change the wire path to I, G, E, D, C, B, and A. After opening holes in the corresponding parts of the machine tool and taking certain anti-splash measures, the jitter of the molybdenum wire has been significantly improved. At the same time, the wear of the wire storage cylinder and the guide wheel is reduced, the wire breakage failure during processing is significantly reduced, and the surface quality of the workpiece is improved. In daily maintenance, if there is any trembling or abnormal response, check the guide wheels of the yarn storage drum as soon as possible, and replace the worn parts in time. Under normal circumstances, the guide wheel must be replaced every 3 months of full load operation; the wire barrel bearing shall be replaced every 1.5 to 2 years; the wire storage barrel shall be precisely rounded and the static balance test shall be performed at the same time. In actual operation, if the constant tension wire tightening system is unreliable, it can be used in processing. Instead, the processing will be stopped after each segment is cut and the wire will be tightened. This is because the wire-cut molybdenum wire will stretch and become longer and longer during processing. If it is thin, the discharge will also cause the molybdenum wire to wear out. In order to avoid the wire cutting molybdenum wire jitter caused by insufficient tension, the wire is generally tightened every 4 hours or so. The exception is for processing pure copper materials. As the copper cooling quickly will splash back on the molybdenum wire, the wire-cut molybdenum wire will become thicker and the tension will increase, which will increase the load of the wire transport system and cause the accuracy of the transmission parts such as bearings to deteriorate rapidly. It is recommended that each processing About 2h to loosen the silk about 10mm.
3. The reliability of the commutation includes that the wire storage drum can stop suddenly and start in the reverse direction at high speed when it runs to the positioning stroke. During this period, the pulse power supply must be able to reliably stop processing, and resume processing when the molybdenum wire is cut online to a certain speed. In old-fashioned machine tools, bumpers, travel switches, relay sets, etc. are generally used to complete the process. Due to frequent mechanical collisions during processing, the bumpers and travel switches are often damaged, and unreliable commutation will break the wire and burn the wire. To solve these problems, it is recommended to use a magnetic switch without mechanical contact. Generally, a magnetic switch can directly control a 24V relay, so the machine tool will not be changed too much. There should be multiple sampling control points when the high frequency is disconnected during commutation, such as the current of the motor starting and running, the contacts on the contactor of the wire drum motor relay, etc., to ensure that the commutation breaking pulse and the processing conditions are not reliable and the pulse is not sent. Sex.