WIRE ELECTRIC DISCHARGE MACHINE INCLUDING AVERAGE DISCHARGE DELAY TIME CALCULATING UNIT

• US 20150027992A1
• Filed: 07/23/2014
• Published: 01/29/2015
• Est. Priority Date: 07/24/2013
• Status: Active Grant

• Current Assignee: Fanuc Corporation
• Original Assignee: Fanuc Corporation
• Inventors: FURUTA, Tomoyuki
• Granted Patent: US 9,833,853 B2
• Time in Patent Office: Days
• US Class Current: 219/69.16
• CPC Class Codes: B23H 1/022 for shaping the discharge pulse train B23H1/024 takes precedence
• CPC Class Codes: B23H 7/04 Apparatus for supplying current to working gap; Electric circuits specially adapted therefor
• CPC Class Codes: B23H 7/18 for maintaining or controlling the desired spacing between electrode and workpiece
• CPC Class Codes: B23H 7/20 for programme-control, e.g. adaptive programme-control systems in general G05B19/00

Abstract

Provided is a wire electric discharge machine in which time from application of a voltage to a machining gap between a workpiece and a wire electrode until occurrence of electric discharge is measured as a discharge delay time, and the measured discharge delay time is integrated over a predetermined measurement period to calculate a discharge delay integrated time. Further, the number of times of the voltage application in the measurement period is counted. An average discharge delay time per voltage application in the measurement period is calculated from the discharge delay integrated time and the number of times of voltage application. The movement of the wire electrode with respect to the workpiece is controlled on the basis of the average discharge delay time.

Claims

1. A wire electric discharge machine that applies, while moving a relative position of a table with respect to a wire electrode, a voltage to a machining gap between the wire electrode and a workpiece arranged on the table to generate electric discharge and machines the workpiece, the wire electric discharge machine comprising:

a measuring unit configured to measure, as a discharge delay time, a no-load time from the application of the voltage to the machining gap until occurrence of the electric discharge, and integrate the measured discharge delay time over a predetermined measurement period to calculate a discharge delay integrated time;

a counting unit configured to count the number of times of the voltage application in the predetermined measurement period; and

an average discharge delay time calculating unit configured to calculate an average discharge delay time per voltage application in the predetermined measurement period from the discharge delay integrated time calculated by the measuring unit and the number of times of voltage application calculated by the counting unit.

2. The wire electric discharge machine according to claim 1, wherein

the wire electric discharge machine calculates, with the measuring unit and the counting unit, the discharge delay integrated time in the predetermined measurement period and the number of times of the voltage application for both or any one of polarities in each of a case in which a machining gap voltage is positive and a case in which the machining gap voltage is negative, and

the wire electric discharge machine calculates, with the average discharge delay time calculating unit, the average discharge delay time corresponding to the polarity in each predetermined measurement period.

3. The wire electric discharge machine according to claim 1, wherein the discharge delay integrated time is an integrated value of time in which a waveform obtained by full-wave rectifying a machining gap voltage in the predetermined measurement period or a waveform obtained by half-wave rectifying any one of a positive voltage and a negative voltage is equal to or larger than a predetermined reference voltage value.

4. The wire electric discharge machine according to claim 1, wherein the discharge delay integrated time is an integrated value of time from a point when a waveform obtained by full-wave rectifying a machining gap voltage in the predetermined measurement period or a waveform obtained by half-wave rectifying any one of a positive voltage and a negative voltage is equal to or larger than a predetermined first reference voltage value to a point when the waveform is equal to or smaller than a predetermined second reference voltage value.

5. The wire electric discharge machine according to claim 1, wherein a relative position between the workpiece and the wire electrode is controlled such that the average discharge delay time coincides with a target value set in advance.

6. The wire electric discharge machine according to claim 1, wherein, when the average discharge delay time is smaller than a predetermined reference value, the voltage application is not performed on the machining gap for a predetermined time.

7. The wire electric discharge machine according to claim 1, wherein, when the average discharge delay time is smaller than a predetermined reference value, at least one of deceleration, a stop, and receding is applied to a relative speed between the workpiece and the wire electrode.

8. The wire electric discharge machine according to claim 1, wherein

time from a start of the voltage application until the voltage application is discontinued when electric discharge does not occur, or time from the start of the voltage application until next voltage application is started, is set as a machining gap voltage residual time,

a rate of the average discharge delay time to the machining gap voltage residual time is calculated from an average discharge delay time in every predetermined measurement period output from the average discharge delay time calculating unit, and

a machining gap voltage value based on the average discharge delay time is calculated by multiplying the calculated rate by a predetermined reference voltage.

9. The wire electric discharge machine according to claim 8, wherein a relative position between the workpiece and the wire electrode is controlled such that a machining gap voltage based on the average discharge delay time coincides with a target value set in advance.

10. The wire electric discharge machine according to claim 8, wherein, when a machining gap voltage value based on the average discharge delay time is smaller than a predetermined reference value, the voltage application is not performed on the machining gap for a predetermined time.

11. The wire electric discharge machine according to claim 8, wherein, when a machining gap voltage value based on the average discharge delay time is smaller than a predetermined reference value, at least one of deceleration, a stop, and receding is applied to a relative speed between the workpiece and the wire electrode.

12. The wire electric discharge machine according to claim 1, further comprising a machining gap average voltage measuring unit configured to calculate a machining gap average voltage by full-wave rectifying and averaging a voltage waveform of the machining gap, or averaging a voltage waveform that is half-wave rectified for each of polarities to calculate an average voltage for each of the polarities, and adding up average voltages.

13. The wire electric discharge machine according to claim 12, wherein, when the average discharge delay time calculated by the average discharge delay time calculating unit is smaller than a predetermined reference value, the voltage application is not performed on the machining gap for a predetermined time while servo feed control is performed to control the machining gap average voltage calculated by the machining gap average voltage measuring unit to be constant.

14. The wire electric discharge machine according to claim 12, wherein, when the average discharge delay time calculated by the average discharge delay time calculating unit is smaller than a predetermined reference value, at least one of deceleration, a stop, and receding is applied to a relative speed between the workpiece and the wire electro while servo feed control is performed to control the machining gap average voltage calculated by the machining gap average voltage measuring unit to be constant.

15. The wire electric discharge machine according to claim 1, further comprising:

a state signal output unit configured to discriminate a voltage waveform applied to the machining gap as any one state of opening, electric discharge, and short circuit, and output a state signal; and

a state counting unit configured to count at least two or more of the number of times of opening, the number of times of electric discharge, and the number of times of short circuit in the measurement period by counting the state signal output from the state signal output unit every time a voltage is applied to the machining gap.

16. The wire electric discharge machine according to claim 15, wherein, when the average discharge delay time calculated by the average discharge delay time calculating unit is smaller than a predetermined reference value, the voltage application is not performed on the machining gap for a predetermined time while servo feed speed is calculated using at least one of the number of times of opening, the number of times of electric discharge, and the number of times of short circuit calculated by the state counting unit and servo feed control is performed.

17. The wire electric discharge machine according to claim 15, wherein, when the average discharge delay time calculated by the average discharge delay time calculating unit is smaller than a predetermined reference value, at least one of deceleration, a stop, and receding is applied to a relative speed between the workpiece and the wire electrode while servo feed speed is calculated using at least one of the number of times of opening, the number of times of electric discharge, and the number of times of short circuit calculated by the state counting unit and servo feed control is performed.

18. The wire electric discharge machine according to claim 1, wherein voltage application is performed by providing, between respective voltage applications to the machining gap, a quiescent time equal to or longer than the application time, such that a voltage waveform is formed in a trapezoidal shape.