Method and apparatus for fine machining with spark erosion using a wire electrode

• US 5,852,268 A
• Filed: 05/09/1996
• Issued: 12/22/1998
• Est. Priority Date: 05/09/1995
• Status: Expired due to Term

• Current Assignee: AGI (Meadwestvaco Corporation)
• Original Assignee: AGI (Meadwestvaco Corporation)
• Inventors: Angelella, Stefano, Mazzolini, Livio, Locati, Pierangelo, Gironi, Adriano, Buhler, Ernst, Boccadoro, Marco
• Primary Examiner(s): Evans, Geoffrey S.
• Application Number:
  US08/647,238
• Time in Patent Office: 957 Days
• Field of Search: 219/69.12, 219/69.17, 219/69.13, 219/69.16
• 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
• CPC Class Codes: B23H 7/16 for preventing short circuits or other abnormal discharges by altering machining parameters using adaptive control

Abstract

A method of and a spark erosion apparatus for fine machining by spark erosion of a workpiece (2) with a wire electrode (1) eliminates very efficiently process interruptions caused by short circuits, such that at least one gap parameter is continuously monitored for the purpose of detecting a short circuit; when a short circuit is detected, the forward motion of the electrode (1) is arrested at the point (K) where the short circuit occurred; if the short circuit persists, the electrode (1) is moved away from the workpiece (2) to an intervention point (M)--in a direction perpendicular to the path (6) used for trim cutting; at the intervention point (M), one or several measures to eliminate the short circuit are executed once or several times; and after it has been detected that the short circuit is eliminated, the electrode (1) is moved back to the point (K) where the short circuit occurred, whereafter normal machining continues.

Claims

1. A method for trim cutting by fine machining with spark erosion of a workpiece with a wire electrode, comprising the steps of:

a) continuously monitoring at least one gap parameter for detecting a short circuit;

b) arresting the forward motion of the wire electrode upon detecting a short circuit at a point (K) where the short circuit occurred;

c) moving the electrode away from the workpiece to an intervention point (M) upon persisting of the short circuit, in the direction perpendicular to a trim cutting path;

d) carrying out at least a first measure to eliminate the short circuit at the intervention point (M) at least one time;

e) upon detecting the elimination of the short circuit, moving the electrode back to the point (K) where the short circuit occurred; and

continuing machining.

2. The method according to claim 1, further comprising a step of applying at the intervention point (M) a flushing pulse having at least one of an increased pressure and flow for providing the first measure for short circuit elimination.

3. The method according to claim 1, further comprising a step of applying at the intervention point (M) a current pulse having an increased amplitude for melting down the short circuit for providing the first measure for short circuit elimination.

4. The method according to claim 1, further comprising a step of moving at the intervention point (M) the wire electrode parallel to the trim cutting path, from the intervention point (M) back to a stop point (H) and then again forward to the intervention point (M), for providing the first measure for short circuit elimination.

5. The method according to claim 1, further comprising a step of increasing for a period of time at least one of tension and speed of the wire at the intervention point (M), for providing the first measure for short circuit elimination.

6. The method according to claim 1, further comprising a step of discontinuing for a certain period of time at the intervention point (M) the processing pulse, for providing the first measure for short circuit elimination.

7. The method according to claim 1, further comprising a step of reversing for a period of time at the intervention point (M) the polarity of the processing pulses, for providing the first measure for short circuit elimination.

8. The method according to claim 1, further comprising a step of moving at the intervention point (M) the wire electrode parallel to the trim cutting path from the intervention point (M) forward to a cleaning point (R) and then back again to the intervention point (M), for providing the first measure for short circuit elimination.

9. A method according to claim 1, further comprising a step of selecting a variable for the path between the short circuit point (K) and the intervention point (M), the intervention point (M) and a stop point (H), and at least one of the intervention point (M) and a cleaning point (R).

10. A method according to claim 1, further comprising a step of locating the intervention point (M), at least one of a stop point (H), and a cleaning point (R) on a path for conducting a full thickness cut.

11. A method according to claim 1, further comprising a step of preselecting at least one of the following measures for short circuit elimination:

applying at the intervention point (M) a flushing pulse having at least one of an increased pressure and flow;

applying at the intervention point (M) a current pulse having an increased amplitude for melting down the short circuit;

moving at the intervention point (M) the wire electrode parallel to the trim cutting path, from the intervention point (M) back to a stop point (H) and then again forward to the intervention point (M);

increasing for a period of time at least one of the tension and the speed of the wire at the intervention (M);

discontinuing for a certain period of time at the intervention point (M) the processing pulses;

reversing for a period of time at the intervention point (M) the polarity of the processing pulses;

moving at the intervention point (M) the wire electrode parallel to the trim cutting path from the intervention point (M) forward to a cleaning point (R) and then back again to the intervention point (M).

12. The method according to claim 11, further comprising a step of

a) applying at least one of the measures as a first measure for short circuit elimination;

b) determining and saving at least one of the success ratios as given by the short circuit duration and the number of successful short circuit eliminations;

c) sorting at least one of the sequence and combination according to the success ratios; and

d) applying, during subsequent occurrences of short circuits, measures for short circuit elimination based on the sorted data of step c).

13. The method according to claim 12, wherein the most probable causes for short circuits are determined based on the distribution of the success ratios of the various measures for short circuit elimination, and the measures to eliminate the causes for short circuits are implemented based on the results of the determination of the success ratios.

14. The method according to claim 13, further comprising a step of changing the rate of speed for the elimination of the causes for short circuits for providing the first measure for the elimination of causes.

15. The method according to claim 13, further comprising a step of changing the nominal controller setting for the servo speed (S) for the elimination of the causes for short circuits for providing the first measure for the elimination of causes.

16. The method according to claim 13, further comprising a step of changing the offset value of the trim cutting path for the elimination of the causes for short circuits for providing the first measure for the elimination of causes.

17. The method according to claim 13, further comprising a step of changing at least one of the wire tension and the wire speed for providing the first measure for the elimination of the causes for short circuits.

18. The method according to claim 13, further comprising a step of changing at least one of the pressure and flow of the flushing agent for the elimination of the causes for short circuits for providing the first measure for the elimination of causes.

19. The method according to claim 13, further comprising a step of activating at least one of a wire cleaning device and a wire alignment device for the elimination of the causes for short circuits for providing the first measure for the elimination of causes.

20. The method according to claim 13, further comprising the steps of:

interrupting the erosion machining process; and

servicing the spark erosion apparatus based on the observed causes for the elimination of these causes for short circuits for providing the first measure for the elimination of causes.

21. A spark erosion apparatus for trim cutting by fine machining with spark erosion of a workpiece with a wire electrode, comprising

a) a monitor for continuously monitoring one gap parameter for the detecting a short circuit, the monitor having

b) control means connected to the monitor, said control means comprises:

b.1) arrest means, which after receiving an output signal from the monitor indicating that a short circuit has been detected, arrest the forward motion of the electrode at the point (K) where the short circuit occurred;

b.2) first moving means, which if the short circuit persists, move the electrode away from the workpiece to an intervention point (M)--in a direction perpendicular to the path used for trim cutting;

b.3) execution means which at the intervention point (M) executes at least once at least one measure to eliminate the short circuit; and

b.4) second moving means, which, after detecting that the short circuit is eliminated, moves the electrode back to the point (K) where the short circuit occurred, whereafter machining continues.

22. The spark erosion apparatus, according to claim 21, wherein the control means is programmed with a first algorithm which

a) applies, in the event of a short circuit, measures for short circuit eliminations;

b) determines success ratios as given by at least one of the short circuit duration and the number of successful short circuit eliminations;

c) sorts at least one of the sequence and combination according to the success ratios; and

d) induces, during subsequent occurrences of short circuits, measures for short circuit elimination based on newly sorted data.

23. The spark erosion apparatus, according to claim 22, wherein the control means is programmed with a second algorithm for pattern recognition which determines the most probable causes for short circuits based on the distribution of the success ratios of the various measures for short circuit elimination, and indicates the existence of short circuits and the most likely causes based on the results of this determination.

24. The spark erosion apparatus, according to claim 23, further comprising means, implementing the second algorithm, for displaying recommendations for eliminating the causes of short circuits.

25. The spark erosion apparatus, according to claim 23, wherein

the control means is programmed with a third algorithm which determines the frequency of short circuits based on the results of the second algorithm;

and

the control means initiates at least one measure to eliminate the causes of the short circuits if the frequency of short circuits is higher than a first limit, and cancels the measures again after at least one of a time and a frequency of short circuits is lower than a second limit.

26. The spark erosion apparatus, according to claim 25, wherein the control means activates a transverse servo system to adjust the offset value of the trim cutting path if a short circuit is present.

27. The spark erosion apparatus according to claim 25, wherein, in the design of at least one of the first, second and third algorithms, fuzzy logic is utilized.