There is known a wire cut electrical discharge machining apparatus which includes a device for feeding an electrode wire automatically through the material to be machined.

This invention relates to a wire cut electrical discharge machining apparatus. More particularly, it provides an improved wire cut electrical discharge machining apparatus including a tubular guide for guiding an electrode wire in a machining area in which the wire faces the material to be machined, and in its vicinity.

The wire cut electrical discharge machining apparatus constructed as shown in FIG. 1, and adapted for operation as hereinabove described with reference to FIGS. 2 and 3 has a number of disadvantages. It is necessary to move the electricity feeders 24 away from each other to enable the vertical movement of the tubular guide 16, and toward each other to supply electricity to the wire 10 when the material 12 to be machined is machined. A separate mechanism is required for moving the feeders24, and fine control is required for bringing the feeders 24 into proper contact with the wire 10. The strength of the tubular guide 16 is reduced by the presence of the openings 28 provided for enabling the supply of electricity from the exterior of the guide 16 to the wire 10. When the apparatus is set for the machining operation, it is impossible to move the tubular guide 16 vertically to its optimum position suited for any possible variation in the thickness of the material 12 to be machined, since the feeders 24 are not vertically movable.

Under these circumstances, this invention provides a wire cut edm electrical discharge machining apparatus having electricity feeders for an electrode wire disposed in a tubular guide through which the wire extends. The feeders are vertically movable with the tubular guide, and no mechanism is required for moving the feeders to or away from the tubular guide. The tubular guide is improved in rigidity. Improved reliability is obtained in the supply of electricity to the wire. The vertical position of the tubular guide is adjustable to suit variation in the thickness of the material to be machined.

In a wire cut edm electrical discharge machining apparatus having an automatic wire feeder which feeds an electrode wire 10 through the material 12 to be machined automatically, electricity feeders 70 for supplying electrical energy for the machining operation to the wire 10 are disposed within a tubular guide 64 through which the wire 10 extends. The tubular guide 64 is improved in rigidity, and improved reliability is achieved in the supply of electricity to the wire.

A wire cut electrical discharge machining apparatus comprising a tubular guide through which an electrode wire supplied from a wire supply reel extends, a system for moving saidtubular guide vertically relative to an initial hole in the conductive material to be machined, an upper guide die provided at the lower end of said tubular guide for supporting said wire, a lower guide facing said upper guide die and provided below saidconductive material for guiding said wire, a wire cut edm operable to cut said wire when said tubular guide is raised to a cutting position, and a plurality of feeders disposed in said tubular guide for supplying electricity to said wire.

A wire cut electrical discharge machining apparatus comprising a tubular guide having an axial bore through which an electrode wire supplied from a wire supply reel extends, said tubular guide being provided in its sidewall with an inlet fora working fluid leading to said axial bore, an insulating pipe which is threadedly connected to said tubular guide, and through which said wire extends, a system connected to said pipe for moving said tubular guide vertically relative to an initial holein the conductive material to be machined, an upper guide die provided at the lower end of said tubular guide below said inlet for supporting said wire, a lower guide facing said upper guide die and provided below said conductive material for guidingsaid wire, a wire cutter operable to cut said wire when said tubular guide is raised to a cutting position, a plurality of feeders disposed in said tubular guide for supplying electricity to said wire, a wire holder provided in said tubular guide andhaving an axial hole extending eccentrically relative to said axial bore of said tubular guide to hold said wire in contact with said feeders, and an upper nozzle having a bearing by which said tubular guide is guided when it is vertically moved throughsaid nozzle.

Referring to FIG. 1, conventional wire cut electrical discharge machine(EDM) as disclosed in Taiwan Utility Model Patent Publication No. 82108873, as shown in FIG. 1, comprises a power source 1, a capacitor 2, electrode wires 3 including lines L1~Ln combined with point "a" line of a loop circuit, a wire electrode 4 of the wire cut EDM and a workpiece 5. To maintain a stable electrical discharge state, the wire cut EDM controls the discharging conditions by sending the voltage condition of discharge gap 6 to an electrical discharge detecting circuit 7 to judge whether it is in one of the normal discharge or the arc discharge conditions, then deciding the pulse width of discharging duration through a timing controller circuit 8, driving a set of switches 10 by a driver circuit 9 which receives the output of the timing controller circuit 8 to control the turn-on time of SW-1~SW-n of switches 10 respectively so that the pulse width of the normal discharge is twice that of the arc discharge. The main discharge loop circuit of the conventional wire cut EDM has no current-limited resistor, and its machining current slope which is constant after finishing configuration is determined by the inductance of the electrode wire 3. A large machining current slope will obtain a faster machining rate and therefore can be more efficient, but it is more possible to cause wire electrode breakage is excess current peak and current density of arc discharge arc provided. The method of detecting electrical discharge of the conventional wire cut EDM is to provide a detecting voltage between the wire electrode 4 and the workpiece 5, and checking the gap voltage between the wire electrode 4 and the workpiece 5 alter a period of time to see whether the gap voltage is larger than a predetermined reference voltage or not. If the gap voltage is larger than the reference voltage, it means there is a proper gap between the wire electrode 4 and the workpiece 5, so that it will be deemed as normal discharge when it discharges next time. Otherwise, if the detected voltage is smaller than the reference voltage, it means that the distance between the wire electrode 4 and the workpiece 5 (gap) is too small, and it would be deemed as are discharge next time.

The wire cut electrical discharge machine(EDM) as above-mentioned judges first, whether the electrical discharge (of next time is normal discharge or, arc discharge by electrical discharge detecting circuit 7 alter initiating machining, then controls the driver circuit 9, by the timing signals produced by the discharge timing controller circuit 8 to control the turn-on of the set of switches 10 SW-1~SW-n for pulse width modulation, making the pulse width of normal discharge to be twice that of the arc discharge, so as to obtain a differert discharging energy for maintaining a stable machining. The discharging current signal waveform at point "a" of the circuitry is shown in FIG. 2, wherein T1 is the half cycle pulse width controlled by normal discharge and T2 is the half cycle pulse width controlled by arc discharge; the slopses of both discharge states are the same, S1; the provided energy ratio of normal discharge and arc discharge equals (T1/T2)², the energy variance during electrical discharge, therefore, is nonlinear and the wire electrode 4 breakage occurs easily due to the same large discharging slope of normal discharge and arc discharge, affecting the machining quality and speed.

The present invention has been accomplished to solve the above said problem. In one aspect the present invention offers a novel method for controlling a wire cut EDM such that the discharge current of the wire cut EDM is controlled within a predetermined range and also the processing speed is improved. In another aspect the present invention offers a novel device for controlling a wire cut EDM such that said device comprises a main circuit for supplying the discharge current to the wire electrode and a testing circuit for supplying a testing voltage to the wire electrode and workpiece. The main circuit includes a high voltage power source and a first switching transistor operated by a control unit containing a pulse generator [hereinafter simply as a control unit], and the testing circuit includes a low voltage power source, a second switching transistor, a resistor, and a diode, wherein the second switching transistor is also operated by the same control unit. The control unit is used to detect the voltage drop between the wire electrode and the workpiece to determine whether the gap between the wire electrode and the workpiece is within a predetermined range suitable for discharging operation. If it is within the predetermined range, the first switching transistor is turned on to allow a large amount of current to be supplied to the wire electrode from the high voltage power source, and at the same time the second switching transistor is turned off for a period of time to cut off the supply of the test voltage from the low voltage power source, and then turned on to test the voltage drop in the gap between the wire electrode and the workpiece again. The device of the invention thus eliminates the capacitor and the current limiting resistor used in the conventional wire cut EDM, and as a result the possibility of breakage of the wire electrode by an overcurrent is minimized, and the processing speed is improved. Only a small amount of current passes through the resistor employed in the testing circuit, and therefore the resistor employed in the device of this invention does not present any problem.

The method of the present invention comprises the following steps:

i) applying a testing voltage between the wire electrode of a wire cut EDM and the workpiece to be processed;

ii) detecting the voltage between the wire electrode and the workpiece after a period of time after the application of the detection voltage, so as to determine the next discharge as a normal discharge when the detected voltage is higher than a predetermined reference voltage, or an arc discharge when the detected voltage is lower than the predetermined reference voltage;

iii) giving a different discharging time (ON TIME) according to predetermined different discharge conditions when the detection voltage between the wire electrode and the workpiece has dropped;

iv) giving a different length of OFF TIME according to different conditions between the wire electrode and the workpiece, permitting the wire electrode to be insulated from the workpiece;

v) regarding the circuit as short circuited if the detection voltage applied between the wire electrode and the workpiece is always below the predetermined reference voltage;

vi) stopping from sending out discharge energy and directly entering a period of off time when a short-circuit occurs; and

vii) regarding the circuit still at the condition of short circuit if an arc discharge is detected before the testing voltage is turned on again; or regarding the short-circuit eliminated if a normal discharge is detected before the testing voltage is turned on again.