Method and apparatus for machining a workpiece in a travelling wire EDM apparatus

• US 4,598,190 A
• Filed: 04/19/1983
• Issued: 07/01/1986
• Est. Priority Date: 04/22/1982
• Status: Expired due to Term

• Current Assignee: Charmilles Technologies SA (Georg Fischer AG)
• Original Assignee: Charmilles Technologies SA (Georg Fischer AG)
• Inventors: Balleys, Francois
• Primary Examiner(s): Albritton, Clarence L.
• Assistant Examiner(s): Evans, Geoffrey S.
• Application Number:
  US06/486,381
• Time in Patent Office: 1,169 Days
• Field of Search: 219/69 W, 219/69 P, 219/69 V, 219/69 M, 219/69 C, 219/69 G, 204/129.7, 204/222
• US Class Current: 219/69.12
• CPC Class Codes: B23H 7/04 Apparatus for supplying current to working gap; Electric circuits specially adapted therefor

Abstract

A travelling wire EDM apparatus wherein a workpiece is cut by electrical discharges by a travelling wire electrode, relative motion of the workpiece and the wire electrode being controlled by a numerical control unit which, in addition, controls transverse oscillations of the electrode wire relative to the workpiece along the cutting path. The energy of the electrical discharges is varied as a function of the amplitude of the transverse oscillations of the electrode wire relative to the workpiece such as to obtain maximum electrical discharge energy when the amplitude of vibration of the electrode wire is at a minimum and minimum energy when the amplitude of vibration of the electrode wire is at a maximum. The invention permits to achieve a good surface finish on the machined surface of the workpiece corresponding to the peak of the transverse electrode wire oscillation displacement being reached simultaneously with minimum electrical discharge energy, and thus achieves rough cutting and finish cutting of the workpiece in a single pass.

Claims

1. In a method for effecting a cut in a conductive workpiece by electrical discharges of controllable energy by means of an electrode wire in a travelling wire EDM apparatus wherein the electrode wire and the workpiece are displaced relative to each other according to a cutting path of predetermined centerline, the improvement comprising oscillating said electrode wire and said workpiece relative to each other at a predetermined amplitude of oscillation on both sides of said centerline in a direction transverse to the cutting path centerline, monitoring the instantaneous value of the amplitude of each transverse oscillation, and automatically varying the energy of the electrical discharges as an inverse function of the instantaneous value of said amplitude such that rough machining of the cut in the workpiece is effected at a maximum value of said energy corresponding to a minimum instantaneous value of said amplitude and finish machining of at least one lateral wall of said cut in the workpiece is effected at a minimum value of said energy corresponding to a maximum instantaneous value of said amplitude, whereby rough machining of the workpiece and finish machining of at least said lateral wall of the cut in the workpiece are effected in a single pass.

2. The improvement of claim 1 wherein said varying of the energy of the electrical discharges to said minimum value corresponding to a maximum instantaneous value of said amplitude is effected in the course of a transverse oscillation on both sides of the centerline of the cut in said workpiece, whereby rough machining of the workpiece and finish machining of both lateral walls of the cut are effected in a single pass.

3. The improvement of claim 1 wherein said transverse oscillation is effected along substantially semi-circular paths centered on the centerline of the cutting path.

4. In a travelling wire EDM apparatus for effecting a cut by electrical discharges of controllable energy in a conductive workpiece by means of an electrode wire wherein the electrode wire and the workpiece are displaced relative to each other according to a cutting path of predetermined centerline, the improvement comprising means for oscillating said electrode wire and said workpiece relative to each other on both sides of said centerline at a predetermined amplitude of oscillation in a direction transverse to the cutting path centerline, means for monitoring the instantaneous value of the amplitude of each transverse oscillation, and means for automatically varying the energy of the electrical discharges as an inverse function of the instantaneous value of said amplitude such that rough machining of the cut in the workpiece is effected at a maximum value of said energy corresponding to a minimum instantaneous value of said amplitude and finish machining of at least one lateral wall of said cut in the workpiece is effected at a minimum value of said energy corresponding to a maximum instantaneous value of said amplitude, whereby rough machining of the workpiece and finish machining of at least said lateral wall of the cut in the workpiece are effected in a single pass.

5. The improvement of claim 4 wherein said varying of the energy of the electrical discharges of said minimum value corresponding to a maximum instantaneous value of said amplitude is effected in the course of a transverse oscillation on both sides of the centerline of the cut in said workpiece, whereby rough machining of the workpiece and finish machining of both lateral walls of the cut are effected in a single pass.

6. The improvement of claim 4 wherein said transverse oscilltion is effected along substantially semi-circular paths centered on the centerline of the cutting path.

7. In an EDM apparatus for effecting a cut by electrical discharges in a conductive workpiece by means of a travelling wire electrode, said apparatus comprising a numerical control unit for controlling a relative displacement between the workpiece and the wire electrode according to a programmed cutting path of predetermined centerline and a pulse generator providing electrical discharges at a machining zone between said workpiece and said wire electrode, the improvement comprising a data input and computation unit accepting information data representing relative oscillation of said wire electrode and said workpiece at a predetermined constant amplitude of oscillation in a direction transverse to the cutting path centerline, said data input and computation unit providing a signal representation of the instantaneous value of the amplitude of said tranverse oscillation, and a function generator circuit co-operating with said data input and computation unit for varying the energy of the electrical discharges provided by said pulse generator according to a function of the instantaneous value of the amplitude of said transverse oscillation such that maximum electrical discharge energy corresponds to the minimum instantaneous value of said amplitude of transverse oscillation and minimum electrical discharge energy corresponds to the maximum instantaneous value of said amplitude of transverse oscillation on at least one side of said path centerline, whereby said cut is rough machined in said workpiece and at least one corresponding lateral wall of the cut in said workpiece is finish machined in a single cut pass.

8. The improvement of claim 7 further comprising a pair of electrode wire guide members one disposed above and the other below said workpiece, means for displacing one of said electrode wire guide members relative to the other at predetermined amplitudes, and means for controlling the displacement of said one of said guide members such as to maintain a predetermined ratio between the amplitudes of displacement of said two electrode wire guide members.

9. The improvement of claim 7 wherein said function generator decreases the energy of said electrical discharges at each maximum instantaneous value of said transverse oscillation amplitude, whereby rough machining of the workpiece and finish machining of both lateral walls of the cut are effected in a single pass.