Causes and prevention methods of high-speed wire-cut EDM wire cutting

Abstract: In view of the common broken wire phenomenon of high-speed wire cutting machine, the six factors of electrode wire breakability are analyzed in detail: the factor of wire electrode, the factor of wire feeding mechanism, the factor of workpiece, the factor of electrical parameter, the factor of working fluid. The factors of operation and use, etc., propose corresponding prevention methods, which can be used as reference for improving the surface quality and precision of the workpiece and improving the processing efficiency.

According to the running speed of the electrode, the WEDM machine is generally divided into two categories: one is a high-speed wire-cut EDM machine, and the wire of this type of machine is used for high-speed reciprocating motion. The general wire speed is 6-11m/s. The other type is a low-speed wire-cut EDM machine. The wire of this type of machine is used for low-speed one-way movement. The wire speed is generally less than 0.2m/s. At present, high-speed wire-cut EDM wire cutting machine tools are still the main types of production and use in China.

Broken wire is a common problem due to the high speed wire cutting process and the single bidirectional reciprocating motion. This paper makes a comprehensive analysis and research on the reasons of high-speed wire breakage, and proposes corresponding prevention and resolution measures.

1 Causes and prevention of broken wire 1.1 Factors of wire electrode (1) Material of wire electrode. In the high-speed wire-cut wire-cutting process, the wire is usually made of molybdenum wire and requires good electrical conductivity and toughness. Because of good electrical conductivity, the resistance per unit length is small. Otherwise, the energy on the filament resistance is much, the energy delivered to the gap by the processing power source is small, the energy consumed on the electrode wire is much, the wire is heated, and the wire is easy to break; Poor, it is also easy to break the wire in frequent hot and cold changes. In addition, the quality of the electrode wire should be guaranteed, such as small surface roughness and high dimensional accuracy. Otherwise, the wire is easily broken during processing.

(2) The diameter of the wire. The thickness of the wire is an important factor influencing the wire breakage. Generally, the wire electrode is selected to be thicker as much as possible under the processing requirements. If the wire diameter is too small, the current is small and the slit 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 increase the tension of the wire, reduce the jitter of the wire, and is not easy to break. Therefore, when the wire wear loss is to a certain extent, the electrode wire should be replaced in time to prevent the wire from being too thin and broken.

1.2 Factors of wire feeding mechanism The wire breakage caused by the wire feeding mechanism is mainly caused by improper installation or wear of the guide wheel, conductive block, wire block and other components in the wire feeding mechanism and the tightness of the wire.

(1) The components such as the guide wheel, conductive block and wire block should be installed correctly, the clearance should be suitable, the rotation should be flexible, the guide wheel is not allowed to have large radial runout or axial turbulence, and the electrode wire is not allowed to be wound. Or wire, to reduce the wire wire jitter, improve the wire wire movement accuracy, otherwise, it is easy to cause the wire break. In addition, it is necessary to clean the relevant parts frequently to eliminate dirt; when the parts such as the guide wheel and the conductive block are worn to a certain extent, care should be taken to replace them.

(2) The tightness of the wire is extremely easy to cause broken wire. The wire and tight wire on the wire are an important part of the wire cutting, which directly affects the tension of the wire, too loose, the wire tension is too small, the jitter is too large, the wire is easy to break, and the workpiece quality and cutting speed are affected; If the wire tension is too large, it is also easy to break. Therefore, the tightness of the wire should be suitable. When the hole or the end face is processed, the wire is easily broken at the initial discharge position, and the tension at this time can be slightly smaller. After working for a while, the wire is tight. Make adjustments and bring the tension to a steady state.

1.3 Factors of the workpiece The high-speed wire-cut EDM wire cutting process has certain requirements on the material and size of the workpiece.

(1) Materials with good forging performance, good hardenability, small heat treatment deformation and good surface quality are suitable for wire cutting. If there are interlayers and workpieces with a rough or cut surface, the oxidized residue is not conductive, and the unevenness may cause broken wire, burnt wire or deep marks on the surface of the workpiece. In severe cases, the workpiece may be scrapped. Therefore, before the online cutting process, the residual material should be removed, the surface of the workpiece should be flattened with oil stone, and the appropriate electrical parameters should be selected to avoid broken wire.

(2) The workpiece is too thin or the sheet is superimposed on the workpiece, which is easy to break. The workpiece is thin, the working fluid is easy to enter and fills the discharge gap, which is advantageous for chip removal and stable processing, but the electrode wire is easy to produce jitter, or the wire is broken due to the dislocation deformation of the cut portion of the workpiece, so that the wire is broken. Therefore, if you want to cut the thin plate workpiece, you should use a thicker wire or choose reasonable electrical parameters, such as increasing the power pulse amplitude, increasing the pulse width, etc., so that the spark gap is increased to prevent broken wire. In addition, if the workpiece is too thick, the chip evacuation condition is deteriorated, and the electrode is easily broken.

1.4 Factors of electrical parameters In high-speed wire-cut EDM wire-cutting, the reasonable selection of electrical parameters is very important.

(1) When selecting, it is necessary to take into account the processing speed, surface roughness and stability. Generally, the parameters are strong, the processing speed is fast, but the surface roughness is large, and it is easy to break the wire. Therefore, when selecting electrical parameters, it is necessary to comprehensively consider the process requirements, processing accuracy, roughness and workpiece thickness of the workpiece to obtain a satisfactory processing result.