The present invention relates to a wire electrode for use in a wire-cut electrical discharge machining process.
Wire electrodes for wire-cut electrical discharge machining are generally in the form of a wire of copper, brass, tungsten or the like and have a diameter in a range of from 0.05 to 0.3 mm. FIG. 1 of the accompanying drawings is illustrative of the manner in which electrical discharge machining is carried out with such a wire electrode. The wire electrode, designated at 1, is tensioned and fed along at a constant speed in the direction of the arrow A while being held in a confronting relation to a workpiece 2. Then, a machining solution 3 is applied in a direction coaxial with the wire electrode 1 while a pushed voltage is impressed between the wire electrode 1 and the workpiece 2. An electrical discharge is now repeatedly produced through the medium of the machining solution 3 across a small gap between the wire electrode 1 and the workpiece 2 to melt and scatter away an amount of material of the workpiece 2 by heat energy generated upon the electrical discharge. An XY crosstable (not shown) coupled to the workpiece 2 is numerically controlled to achieve desired relative movement between the wire electrode 1 and the workpiece 2 while keeping the electrode-to-workpiece gap constant at all times and ensuring continuous electrical discharge.
By repeating the electrical discharge and controlling the XY crosstable in the above manner, a groove 4 can be continuously cut in the workpiece 2 to machine the workpiece 2 to a desired contour. Such wire-cut electrical discharge machining has been widely used in blanking and cutting general dies, for example.
The speed of wire-cut machining is dependent on the degree of tension applied to the wire electrode 1, as shown in FIG. 2 where the abscissa indicates the tension T (g) and the ordinate the cutting speed F (mm/minute). FIG. 2 shows a characteristic curve which progressively rises as it goes to the right, the indication being that the cutting speed is higher as the tension is larger. It has been confirmed that as the tension is made larger, the wire electrode 1 is subjected to smaller vibrations and the electrode-to-workpiece gap can be controlled more uniformly for stabler electrical discharge repetitions, resulting in a higher cutting speed.
Wire electrodes of copper, brass or steel, for example, having conventional crystalline structures suffer a limitation on the tensile strength thereof, and it is not possible to achieve a higher cutting speed through an increase in tensile strength.
When a conventional wire electrode 1 of copper, brass or steel is fed along upwardly or downwardly with respect to a workpiece during machining as shown in FIG. 3, portions of the wire electrode 1 are often scattered and deposited on an upper or lower end of a groove 4 cut in the workpiece 2. The deposited material 5 is mainly composed of copper or steel, and it has been observed that the material is deposited behind the wire electrode 1 as it cuts into the workpiece 2 as illustrated in FIGS. 3A. The deposit 5 on the machined surface tends to impair the dimensional accuracy of the cut groove 4. Such a deposited layer 5 has a thickness in the range of about 10 to 100 microns in areas where large machining energy is applied. As the machining energy is increased, the cut groove 4 is sometimes filled with the deposited material as shown in FIG. 4.
This undesirable phenomenon results in various drawbacks. The workpiece having been machined cannot be removed from the wire electrode. During machining, the machining solution 3 ejected coaxially with the wire electrode 1 does not enter the electrode-to-workpiece gap, causing a gaseous electrical discharge to lower the cutting speed and resulting in a danger of breaking the wire electrode 1. The deposit 5, mainly of copper, iron or the like, can only be removed with a dangerous chemical such as fuming nitric acid, a procedure which is tedious, time-consuming, and dangerous.
Therefore, conventional wire electrodes have suffered from many drawbacks and have proven unsatisfactory.