1, electrical characteristics
Modern wire-cutting power supplies place stringent demands on the electrode wire. It has to be able to withstand high cutting currents with peaks in excess of 700 amperes or averages in excess of 45 amperes, and the transfer of energy has to be very efficient in order to provide the high-frequency pulsed currents required to achieve a high surface finish (0.2Ra or more). This depends on the resistance or conductivity of the electrode wire. Copper has one of the highest conductivities and is used as a benchmark against which other materials are measured. The conductivity of copper is labeled as 100% IACS (International Annealed Copper Standard), while brass has a conductivity of 20%. 2, mechanical properties
Tensile strength: tensile strength is a measure of the ability of a material to resist fracture when subjected to radial loads. It is measured in terms of the weight that can be withstood per unit of cross-sectional area, such as PSI (pounds/square inch) in the British system or N/mm2 (Newtons/square millimeter) in the metric system. Copper is among the materials with the lowest tensile strength (245N/mm2), while molybdenum has the highest (1930N/mm2). The tensile strength of electrode wires depends on the choice of material and the various heat and tensile treatment processes. Electrode wires are sometimes categorized as "soft" and "hard", each having its own advantages for different equipment and applications. Memory effect: This is directly related to whether the electrode wire is "soft" or "hard". Soft wires do not have the memory to return to a straight line when withdrawn from the spool, so they cannot be used for automatic threading, but this has no effect on the cut because the electrode wire is tensioned during processing. Soft wires are suitable for large inclination cuts of more than 7 degrees in equipment where the upper and lower guide nozzles cannot be tilted. Hard wires, on the other hand, are the best choice for automatic threading machines. Also, because of the high tensile strength, their ability to resist jittering of the wire due to the current and flushing force during cutting is stronger. Elongation: Elongation is the percentage change in the length of the electrode wire due to tension and heat during the cutting process. Soft wires can have elongations as large as 20%, while hard wires are less than 2%. When soft wires are used in beveled processing, electrode wires with high elongation ensure more geometric accuracy of the bevel, and softer wires produce less vibration when sliding in the wire guide nozzle. However, the soft wire jerks more than the hard wire when the electrode wire enters the cutting zone, so there is still a compromise to be made.
3, geometric characteristics
In the early days of the development of wire cutting technology (1969 to the mid-1970s), the electrode wire almost no research was done, using off-the-shelf motors and cables on the purple copper wire. Today, high-efficiency, high-precision wire-cutting machines require electrode wires with geometrical characteristics that are subject to very small errors. The final stage of wire manufacturing is the use of multiple jeweled wire drawing dies to obtain a smooth, perfectly rounded finished product with a wire diameter tolerance of +/-0.001mm. On the other hand, there are other electrode wires that are purposely designed to have a relatively rough surface, which can increase cutting speed.
4, thermophysical properties
The thermophysical properties of the electrode wire are the key to improving cutting efficiency. These characteristics are determined by the ratio of alloy composition or the choice of base core material. Melting point: The melting point of the electrode wire is an important indicator. Due to the mechanical movement of the electrode wire as it passes through the wire guide nozzle, as well as factors such as flushing force and discharge, the electrode wire is jittery when cutting. This causes numerous very small short-circuits and slows down the cutting process. If the electrode wire can lose some of its outer diameter when working, so that its gap in the direction of facing the cut can prevent or reduce the short-circuit effect. At the same time, its clearance in the direction of the back to the kerf helps to improve the flushing effect, which can better remove the processing waste chips. The loss of the outer diameter of the electrode wire does not affect the machining accuracy because new electrode wire is constantly being fed. This is one of two properties of materials that metallurgists consider when studying the flushing properties of electrode wires. Vaporization pressure: EDM cutting generates a lot of heat, some of which is absorbed by the electrode wire, which can reduce cutting efficiency. If too much heat is lost to the electrode wire, the wire will melt due to overheating. Therefore, it is necessary for the surface of the electrode wire to vaporize quickly, releasing heat energy to the workpiece while the wire is cooled. When a material is heated to its melting point, it vaporizes, generating vapor pressure. Materials with a low melting point are easier to vaporize. Another characteristic that an electrode wire should have is a low melting point and a high vaporization pressure, which helps blow the slag away from the slit. This is another characteristic of a good flushing electrode wire. When the electrode wire and workpiece are vaporized rather than melted at the cutting surface, gas is produced rather than molten metal particles. This in turn improves the flushing process because there are fewer particles to flush away.