Device and control process for EDM machining with an electrode-wire

• US 5,410,117 A
• Filed: 05/19/1993
• Issued: 04/25/1995
• Est. Priority Date: 01/13/1989
• Status: Expired due to Term

• Current Assignee: Charmilles Technologies SA (Georg Fischer AG)
• Original Assignee: Charmilles Technologies SA (Georg Fischer AG)
• Inventors: Crivelli, Lorenzo, Bosson, Jean-Michel, Reynier, Alain
• Primary Examiner(s): Evans, Geoffrey S.
• Application Number:
  US08/064,784
• Time in Patent Office: 706 Days
• Field of Search: 219/69.12, 219/69.13, 219/69.17, 219/69.18, 219/69.14
• US Class Current: 219/69.12
• CPC Class Codes: B23H 7/04 Apparatus for supplying current to working gap; Electric circuits specially adapted therefor
• CPC Class Codes: B23H 7/065 Electric circuits specially adapted therefor

Abstract

At least one machining parameter of an electrode-wire EDM machine, cutting according to a predetermined trajectory, is varied when the electrode-wire reaches the apex of an angle or approaches an arc. The strategy consists of the following stages:

1) calculation of the locations along the trajectory or path at which these variations must be started;

2) stopping of relative electrode-wire movement and the work-piece, when the wire reaches one of these points;

3) gradual and stepped variations of the parameter up to a final designated value or until a predetermined number of steps have been performed;

4) resumption of wire-part relative movement, with the new parameter value over a computer predetermined distance, and

5) variation of the parameter in the opposite direction so as to return it to its initial value.

The step durations are slaved to changes of a factor giving an image of the conditions existing in the machining slot, around a predetermined threshold.

Claims

1. A device for an EDM machine, said EDM machine cutting an electrode-workpiece along a predetermined trajectory with a wire-electrode and having

a generator connected between the workpiece and the wire and emitting voltage pulses;

a numerical control unit for controlling the relative movements between the workpiece and the wire and for controlling machining parameters;

a programmed computing unit

1) to calculate the points on the trajectory at which the wire-electrode reaches the apex of an angle or approaches an arc and to detect that the wire reaches one of these points;

2) to send corresponding signals to the numerical control unit for stopping the relative movement between the wire-electrode and the workpiece, and for initiating the variation of at least one machining parameter from its initial value V to a predetermined final value V'"'"';

3) to send further signals to the numerical control unit for restarting the relative movement between the wire-electrode and the workpiece and controlling said parameter by maintaining it at said final scheduled value V'"'"';

4) to detect that a predetermined distance lo of said trajectory has been run while said parameter remaining at said final value V'"'"' and to send corresponding signals to the numerical control unit for initiating the return of said machining parameter to its initial value V;

said device comprising;

means connected to said programmed computing unit and numerical control unit for performing stepped variations of said at least one machining parameter in a manner that the durations of these steps are slaved to the fluctuations of a pilot factor which gives an image of the machining gap, said means for performing stepped variations comprising;

a data processing element memorizing a predetermined number of steps and the predetermined values of each elementary variation;

a measurement circuit controlling and determining continuously the fluctuations of said pilot factor; and

a comparison circuit connected to said measurement circuit and data processing element, comparing continuously the value of said pilot factor to a predetermined reference threshold and sending corresponding signals to the numerical control unit and to the programmed computing unit for either starting an elementary variation of said at least one machining parameter or for stopping said variation when said at least one machining parameter has reached its final value V'"'"' or has returned again to its initial value V or when a predetermined number of steps have been performed.

2. The device according to claim 1, in which said at least one machining parameter is the frequency of the voltage pulses emitted by the generator.

3. The device according to claim 2, wherein said means for providing stepped variations of at least one machining parameter comprises an injection pressure at which the machining fluid is injected into the machining gap.

4. The device according to claim 3, which further comprises a bank of solenoid valves connected to the numerical control unit as actuators to activate variations of said injection pressure by predetermined elementary quantities.

5. The device according to claim 1, in which the elementary variations of said at least one machining parameter which are memorized by said data processing element have a constant value.

6. The device according to claim 1, in which said measurement circuit to control and determine continuously the fluctuations of said pilot factor is a circuit to measure the machining voltage Um existing between the workpiece and the wire-electrode.

7. The device according to claim 6, in which said measurement circuit is further provided with means for determining a mean value Um for the machining voltage and for calculating a difference Usa between said mean value and an average reference voltage Umr, said difference Usa being said pilot factor.

8. The device according to claim 7, in which said measurement circuit further comprises means for integrating the value of said difference Usa over a predetermined period of time.

9. A control process for an EDM machine which is cutting an electrode-workpiece along a predetermined trajectory with a wire-electrode, so as to vary in a first direction at least one machining parameter from its initial value up to a predetermined final value when the wire-electrode reaches the apex of an angle or approaches an arc, said at least one machining parameter returning from said final value to its initial value V at the end of cutting of the angle or arc, said variation being stepped variations performed in a manner that the durations of the steps are slaved to the fluctuations of a pilot factor which gives an image of the machining gap, said control process comprising the stages of:

calculating the points of said trajectory at which the wire-electrode reaches the apex of an angle or approaches an arc;

stopping the relative movement between the wire-electrode and the workpiece and initiating the variation of said at least one machining parameter from its initial value to said predetermined final value when the wire reaches one of these points;

continuously determining the fluctuations of said pilot factor and comparing continuously its value to a predetermined reference threshold;

when said value of said pilot factor reaches said reference threshold, varying the value of said at last one machining parameter by a predetermined elementary quantity, said elementary variation step causing in turn a further variation of said pilot factor;

further varying in steps said at least one machining parameter by predetermined elementary quantities until it is detected either that it has reached its final scheduled value or that a predetermined number of steps have been performed;

restarting the relative movement between the wire-electrode and the workpiece and maintaining said parameter at said final scheduled value;

when a predetermined distance lo of said trajectory has been run while said parameter is at said final value, initiating the variation in opposite direction of said machining parameter anew by successive elementary variation steps, the durations of which are slaved to the fluctuations of said pilot factor, until it is detected either that said parameter has returned again to its initial value or that a predetermined number of steps have been performed.

10. The process according to claim 9, in which the successive stepped variations by elementary quantities or increments and decrements, applied to said at least one machining parameter are all equal.

11. The process according to claim 9, in which the predetermined reference threshold to which is continuously compared said pilot factor, is the value of said factor corresponding to machining along a straight line.

12. The process according to claim 9, in which said machining parameters which are made to vary are the frequency of the voltage pulses emitted by the generator and the injection pressure at which the reechoing fluid is injected into the gap.

13. The process according to claim 9, in which said pilot factor which is continuously determined and compared to a reference threshold is the difference Usa between an average reference voltage Umr and a mean value of the machining voltage Um existing between the workpiece and the wire-electrode, said machining voltage being continuously measured.

14. The process according to claim 9, in Which said predetermined distance lo of said trajectory which is to be run while said machining parameter remains at said final value is equal to:

##EQU3## where r is the radius of the wire, g the sparking distance, α

the value of the angle to be cut.

15. The process according to claim 9, in which said predetermined distance lo of said trajectory which is to be run while said machining parameter remains at said final value is equal to:

space="preserve" listing-type="equation">lo=γ

r,

where y is the value in radians of the angle corresponding to the arc to be cut, and r being the radius of curvature of this arc.