Cause and prevention of wire breakage in the most

2022-08-02
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Causes and prevention of wire breakage in high-speed WEDM

Abstract: in view of the common wire breakage phenomenon of high-speed WEDM machine, this paper analyzes in detail the six factors that are easy to break the electrode wire: electrode wire factor, wire feeding mechanism factor, workpiece factor, electrical parameter factor, working fluid factor, operation and use factor, and puts forward the corresponding prevention methods to improve the surface quality and accuracy of the workpiece, It can be used for reference to improve machining efficiency

key words: high speed wire EDM; Electrode wire; Cause of wire breakage; Prevention

WEDM tools are usually divided into two categories according to the operating speed of electrodes: one is high-speed WEDM machine tools. The electrode wires of this kind of machine tools move back and forth at a high speed, generally with a wire walking speed of M/s, and the other is low-speed WEDM machine tools. The electrode wires of this kind of machine tools move in a low-speed unidirectional direction, generally with a wire walking speed of less than 0.2m/s. At present, high-speed WEDM is still the main machine type produced and used in China

wire breakage is a common problem in high-speed wire cutting because of its high wire speed and single and two-way reciprocating motion. This paper makes a comprehensive analysis and Research on the causes of wire breakage in high-speed wire walking, and puts forward corresponding preventive and solving measures

1 causes of wire breakage and prevention

1.1 factors of electrode wire

(1) material of electrode wire. In high-speed WEDM, molybdenum wire is usually used as electrode wire, and good conductivity and toughness are required. Because of good conductivity, the resistance per unit length is small. Otherwise, more energy is consumed on the electrode wire resistance, less energy is transmitted from the processing power supply to the gap, more energy is consumed on the electrode wire, and the electrode wire is heated and easy to break; If the toughness is poor, the wire is also easy to break in frequent rapid heating and cooling changes. In addition, the quality of the electrode wire should be guaranteed. For example, the surface roughness is small and the dimensional accuracy is high. Otherwise, the electrode wire is easy to break during processing

(2) diameter of electrode wire. The thickness of electrode wire is an important reason for wire breakage. Generally, the thicker electrode wire is selected as far as possible under the condition of meeting the processing requirements. If the diameter of electrode wire is too small, the current bearing is small and the cutting seam is narrow, which is not conducive to chip removal and stable processing, and the possibility of wire breakage is large. In addition, the thicker electrode wire can improve the tension of the electrode wire, reduce the jitter of the electrode wire, and it is not easy to break the wire. Therefore, when the use loss of the electrode wire reaches a certain degree, the electrode wire shall be replaced in time to prevent the electrode wire from being too thin and breaking

1.2 environmental protection is related to the survival and development of Anyang industry. The wire breakage of electrode wire caused by wire feeding mechanism is mainly caused by improper installation or wear of guide wheel, conductive block, wire stopper block and other parts in wire feeding mechanism, as well as improper tightness of electrode wire

(1) the guide wheel, conductive block, stop wire block and other parts shall be installed correctly, with appropriate clearance and flexible rotation. The guide wheel shall not have large radial runout or axial movement. The electrode wire shall not be overlapped or clamped. The electrode wire jitter shall be reduced and the motion accuracy of the electrode wire shall be improved. Otherwise, the electrode wire may be broken. In addition, relevant parts shall be cleaned frequently to eliminate dirt; When the guide wheel, conductive block and other parts are worn to a certain extent, pay attention to replacement

(2) wire breakage is easily caused by improper tightness of electrode wire. Wire loading and tightening of electrode wire is an important part of wire cutting, which directly affects the tension of electrode wire. If the tension of electrode wire is too loose, the tension of electrode wire is too small, and the jitter is too large, the wire is easy to break, and the quality of workpiece and cutting speed are affected; If it is too tight, the tension of the electrode wire is too large, and it is easy to break the wire. Therefore, the tightness of the electrode wire should be appropriate. When the hole or end face is processed, it is easy to break the wire at the initial discharge position. At this time, the tension can be slightly smaller. After working for a period of time, adjust the tightness of the electrode wire and make the tension reach a stable state

1.3 workpiece factors

high speed WEDM process has certain requirements for workpiece material and size

(1) materials with good forging performance, good hardenability, small heat treatment deformation and good surface quality are suitable for wire cutting. For workpieces with interlayer, slag inclusion or rough cutting surface, due to the non-conductive and uneven oxidation residue, it will lead to wire breakage, wire burning or deep marks on the surface of the workpieces. In serious cases, the workpieces will be scrapped. Therefore, before cutting, the residues shall be removed, the surface of the workpiece shall be filed with an oilstone, and appropriate electrical parameters shall be selected to avoid wire breakage

(2) if the workpiece is too thin or the thin plate is superimposed, it is easy to break the wire. The workpiece is thin, and the working fluid is easy to enter and fill the discharge gap, which is beneficial to chip removal and stable processing. However, the electrode wire is easy to shake, or the cutting part of the workpiece is misaligned and deformed, resulting in wire clamping and wire breakage. Therefore, if you want to cut a thin plate workpiece, you should use a thicker electrode wire or select reasonable electrical parameters, such as increasing the power pulse amplitude, increasing the pulse width and other methods to increase the spark gap, so as to prevent wire breakage. In addition, if the workpiece is too thick, the durable part used by the chip removal strip to evaluate the adhesion of the tape becomes worse, which is also easy to cause wire breakage of the electrode

1.4 factors of electrical parameters

in high-speed WEDM, the reasonable selection of electrical parameters is very important

(1) when selecting, the processing speed, surface roughness and stability shall be considered. Generally, the parameters are strong and the processing speed is fast, but the surface roughness is large and the wire is easy to break. Therefore, when selecting electrical parameters, it is necessary to comprehensively consider the process requirements, machining accuracy, roughness and workpiece thickness, so as to obtain satisfactory machining results

(2) the adjustment of cutting preset feed speed has a great impact on cutting speed, machining accuracy and surface quality. If the preset feed speed is adjusted too fast, it will exceed the possible etching speed of the workpiece, and frequent short circuits will occur. Instead, the cutting speed will be slow, and the surface roughness will be poor. The cutting seams of the upper and lower sections will be burnt yellow, and even the wire may be broken; On the contrary, if the feed speed is adjusted too slowly, it will greatly lag behind the etching speed of the workpiece, and the poles will be open circuited, sometimes open circuited, sometimes short circuited, the machined surface will be scorched and light brown, and the upper and lower end faces of the workpiece will also be burned. Therefore, the preset feed speed should be appropriate, that is, the etching speed of the workpiece is equivalent to the feed speed. In this way, the machined surface is fine and bright, the silk lines are uniform, the surface roughness is good, and the precision is high

(3) improper frequency conversion tracking adjustment is also an important reason for wire breakage, because too fast tracking is easy to form short circuit and increase the tension of electrode wire, resulting in wire breakage. The actual adjustment can be judged by the stability of the ammeter pointer. The more stable the pointer swings, the better. If the pointer is not stable, try to make the pointer fluctuate in the direction of 0 bit

1.5 factors of working fluid

in high-speed WEDM, working fluid is the medium of pulse discharge, which has a great impact on machining. The working fluid is generally required to have certain insulation performance, good washing performance, good cooling performance, no pollution to the environment and no harm to human body. The configuration of working fluid is also very important. If it is too thick or too thin, it will cause wire breakage. Generally, the concentration ratio of water to liquid is in the range of 1:10-1:20. When the cutting speed is required to be high or the workpiece with large thickness is cut, the concentration should be appropriately low, so that the processing is relatively stable and the wire is not easy to break. However, the working fluid concentration should not be too low, otherwise the insulation performance of the working fluid will be reduced, the resistivity will be reduced, and the cooling capacity will be enhanced, thus reducing the lubrication effect on the workpiece, which is not conducive to chip removal and wire breakage. In order to ensure that the working fluid channel is not blocked, the flow of the working fluid should also be properly controlled. Generally, when the cutting is completed, the cutting section of the workpiece will sag under the hydraulic action of the working fluid, the cutting part will fall off, and the electrode wire is very easy to be clamped off. At this time, the working fluid should maintain a certain pressure and flow, and the corrosive substances should be discharged in time, so as to prevent wire breakage. When cutting aluminum, copper and other soft materials, especially when the cutting material is thick, in order to improve the processing efficiency and surface finish and reduce wire breakage, some special coolants can be used, which is also conducive to environmental protection

1.6 operating factors

in high-speed WEDM, in order to efficiently process qualified workpieces, there are certain requirements for operators. Operators shall correctly understand the technical requirements of the drawings. The working fluid shall be replaced in time to maintain a certain cleanliness and ensure that the upper and lower nozzles are not blocked and the flow is appropriate. Electrode 2. Energy saving: the original digital control wire is calibrated vertically and the workpiece is clamped correctly. The parameters of pulse power supply shall be selected reasonably, and the variable frequency feed speed shall be adjusted in time when the processing is unstable. Do not switch the function keys during the processing process, so as to avoid short circuit caused by poor switch contact or electrode wire burn, and even wire breakage. When the cutting is completed, the cut part will fall under the action of gravity, and the electrode wire is very easy to be clamped, so the magnet adsorption, splint clamping and other methods can be used to fix it in time to avoid wire breakage

2 conclusion

there are many factors that affect electrode wire breakage in high-speed WEDM, among which the effects of various factors are often interdependent and mutually restrictive. The above has analyzed and studied some phenomena of wire interruption in high-speed WEDM, and put forward corresponding preventive measures. This paper is summarized based on long-term work experience and consulting a large number of data. It is believed that it can be used for reference to improve the surface quality and accuracy of workpiece and improve machining efficiency

references

[1] Jin Dichen, song Fangzhi. Modern mold manufacturing technology [m] Beijing: China Machine Press, 2001.

[2] zhaowansheng, liujinchun, et al. Practical EDM technology [m] Beijing: China Machine Press, 2002

[3] Ma Mingjun, jianghengshun, guojiemin. Application of EDM Technology in mold manufacturing [m] Beijing: Chemical Industry Press, 2004.

[4] Cao Fengguo. EDM technology [m] Beijing: Chemical Industry Press, 2005

Author: dingmingming, wangtieliu (end), Zhejiang water conservancy and Hydropower College

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