A. Relating to the electrode wires

Wire tension and cutting speed may affect the result of finish surface of workpieces. For high speed wire cut EDM machining, molybdenum wire of 0.06mm to 0.25mm is widely used due to the good wear resistance, high tensile strength, less molybdenum wire brittleness and less molybdenum wire breakage.

Increasing the tension of electrode wires can reduce the influence of molybdenum wire vibration, thereby improving the accuracy and cutting speed of high speed wire cut EDM machines. The fluctuation of molybdenum wire tension has a great influence on the processing stability in the wire EDM machine adjustment. The reason for the fluctuation is that the tension of the electrode molybdenum wire on the wire storage is different when it moves forward and backward. After cutting a period of time, the electrode molybdenum wire will stretch again, causing the reduction of wire tension. Normally it is considered that the molybdenum wire tension is suitable between 12 and 15N. The vibration of molybdenum wire soars to cause the wire breakage easily.

Along with the advancement of molybdenum wire feeding speed, the cutting speed of wire EDM machine will increase within a certain range. At the same time, the improvement of wire feeding speed will be conducive for electrode molybdenum wire to carry the working fluid into the discharging gap of a larger thick workpiece. It is also beneficial to the elimination of electrical corrosion products and the stability of electrical discharge machining.

However, haste makes waste. You have got to do it step by step. The molybdenum wire feeding speed is too high and the electrode wire shakes seriously, which destroys the processing stability. This not only reduces the processing speed of high speed wire cut EDM machines, but also deteriorates the processing accuracy and surface roughness, and easily causes the molybdenum wire breakage. But the wire speed should not be too low, otherwise the wire will break easily due to high loss during wire processing. Generally, it is better to be less than 10m/s.

The selection of electrode wires

The choice of electrode wire is nothing more than the type and diameter of the electrode wire for high speed EDM machines. Generally, the wire electrode material used in wire EDM should have good conductivity, small electron overflow, high tensile strength, and good electrical corrosion resistance. The electrode wire itself must not be bent or knotted. The materials usually include molybdenum wire, tungsten wire, tungsten molybdenum wire, brass wire, copper tungsten wire, etc. Among them, molybdenum wire and brass wire are most used. The use of tungsten wire processing can obtain a higher processing speed, but the wire becomes brittle and easy to break after discharge, which is less used. Therefore, The tungsten wire is generally used when the wire speed is slow and the weak current gauge is punctual. Molybdenum wire has low melting point and tensile strength, but good toughness. In the frequent changes of rapid cooling and heating during the machine processing, the wire quality is not easy to become brittle and break the wire. Therefore, although some properties are not as good as tungsten wire, it is still the most widely used as the popular electrode wire. Tungsten-molybdenum wire (50% of tungsten and molybdenum each have a better processing effect than the first two), so the service life and processing speed are higher than that of molybdenum wire, but they are expensive. Copper wire has high processing speed, stable processing, but poor tensile strength , The loss is also large, generally used in low-speed wire cutting processing. In summary, the type of electrode wire should be determined according to the processing conditions. Otherwise, it will often cause wire breakage.

For high speed wire cut EDM machining, the diameter of electrode wire is normally between Φ0.06～Φ0.25mm, and the commonly used diameter is between Φ0.12～Φ0.18mm. When you need to obtain a fine shape and a small fillet radius, please choose an electrode wire of Φ0.04mm. Proper selection of electrode wire will greatly reduce the occurrence of wire breakage.

New molybdenum wire and automatical molybdenum wire breakage

There is a layer of black oxide on the surface of the new molybdenum wire. The cutting speed is fast during processing, and the surface of the workpiece is thick and black. At this time, if the power source energy is too large, the wire will be easy to break. Therefore, for the new molybdenum wire, the processing current needs to be appropriately reduced, and the normal electrical parameters can be restored after the electrode wire is basically white.

When the high speed wire cut EDM machine has not been used for a long period of time, when it is to be used, it is found that the molybdenum wire is broken. This is because the temperature difference causes the material to expand and contract with heat, coupled with the tension of the molybdenum wire itself and break. If the wire EDM machine is out of service, please shake the wire storage tube to the end and loosen the molybdenum wire.