ELECTRICAL DISCHARGE MACHINING EFFICIENCY AND SAFETY MONITORING SYSTEM

• US 3,816,692 A
• Filed: 03/02/1972
• Issued: 06/11/1974
• Est. Priority Date: 03/02/1972
• Status: Expired due to Term

• Current Assignee: Samuel C. Ratmansky
• Original Assignee: Samuel C. Ratmansky
• Inventors: Ratmansky, Samuel C.
• Primary Examiner(s): Truhe, J. V.
• Assistant Examiner(s): Jaeger, Hugh D.
• Application Number:
  US05/231,215
• Time in Patent Office: 831 Days
• Field of Search: 219/69C,69G,69P,69S
• US Class Current: 219/69.13
• CPC Class Codes: B23H 1/02 Electric circuits specially adapted therefor, e.g. power supply, control, preventing short circuits or other abnormal discharges

Abstract

An electrical discharge machine efficiency and safety monitoring system in which the energy dissipated or charge flow across the cutting gap of individual spark pulses, the output pulse frequency of the electrical discharge machine and the percentage of pulses of the electrical discharge machine which actually cause conduction across the cutting gap are in process measured and displayed. The results of these three measurements indicate the metal removal rate efficiency of the settings on the EDM machines, RMS surface finish of the work, size of the spark gap or overcut, depth of pitting on work, recast layer on work, size of micro-cracks on work, and may also be multiplied together manually or by means of hardware to obtain a product called the metal removal rate factor. This is indicative of the actual amount of metal removed by the EDM machining process when correlated with a reference chart, and will indicate the highest cutting efficiency possible at a given RMS finish, when compared with other settings. An alarm may also be provided to provide a signal in response to the percentage of pulses crossing the gap dropping below a predetermined minimum. Safety means in the monitoring system are provided to detect incipient and steady state arcing or burning conditions in order to signal the EDM operator to take corrective action to avoid ruining the workpiece.

Claims

1. Apparatus for monitoring the efficiency of an electrical discharge machining operation in which pulses of electrical energy are applied to an electrode through a lead, said electrode being spaced from a work piece to form a gap between said electrode and said work piece, comprising:

transducer means coupled to said lead, said transducer providing an output in response to current flow through said leads;

electrical connections connected across said gap to provide an output to enable measurement of gap voltage;

gating means connected to said output of said transducer means, said gating means passing the output of said transducer only when an output is provided by said transducer in response to current flow through said leads;

integrating means for integrating the output of said transducer passed by said gating means and providing an output;

means for indicating the value of the output of said integrating means;

a switch means for selecting either the output of said transducer means or the output of said eLectrical connections;

a frequency meter, said frequency meter receiving a signal from said switch means, said frequency meter indicating the frequency of the pulses of electrical energy applied to said electrode when the switch means is selecting the output of said electrical connections;

a calibration means, said calibration means receiving a signal from said switch means; and

an indicator means, said calibration means being adjustable to cause said indicator means to read a predetermined value corresponding to 100 percent when said switch means is selecting the output of said electrical connections, said indicator means indicating the percentage of pulses of electrical energy applied to said electrode upon which conduction across said gap occurs, whereby the electrical charge measurement, the frequency indicated by said frequency meter and the percentage indicated by said indicator means may be multiplied together to obtain an indication of the efficiency of the electrical discharge machining operation.

2. Apparatus in accordance with claim 1 including means for multiplying together the electrical charge measurement, frequency indicated by said frequency meter and percentage indicated by said indicator means and means for indicating the product of said multiplication.

3. Apparatus in accordance with claim 1 including a switch operated by said indicating means when said indicating means indicates a percentage below a predetermined percentage, and an alarm actuated in response to operation of said switch.

4. Apparatus in accordance with claim 1 including means to compare the magnitude of the voltage of the electrical energy pulse appearing at the output of said electrical connections connected across said gap with a predetermined voltage only during periods of conduction across said gap and providing an output only if the magnitude of the electrical voltage pulse across said gap is less than the predetermined voltage during said periods of conduction.

5. Apparatus in accordance with claim 1 including a Schmitt trigger circuit for receiving the output of said switch means, said Schmitt trigger circuit providing a shaped output pulse to said frequency meter and said calibration means.

6. Apparatus for monitoring the efficiency of an electrical discharge machining operation in which electrical voltage pulses are applied across a gap formed between an electrode and a work piece, comprising:

means for monitoring the pulse voltage applied across said gap, said monitoring means having an output at which appears a pulse for each voltage pulse applied across said gap;

means for detecting current flow through said electrode in response to conduction across said gap, said current detecting means producing an output pulse in response to each voltage pulse applied across said gap upon which conduction occurs;

means to select the output of said monitoring means or said current detection means;

calibration means, said calibration means receiving the selected output of said selector means, said calibration means including means to adjust the signal level output of said calibration means; and

indicator means, said indicator means receiving the output of said calibration means and providing a percentage indication in response to the signal received from said calibration means, said indicator means being caused to read a predetermined value corresponding to a maximum by adjustment of said adjusting means of said calibration means when said selector means is selecting the output of said monitoring means, and said indicator means reading a value equal to or less than said predetermined value when said selector means is selecting the output of said current detection means to indicate the efficiency of the machining operation in terms of percentage of electrical voltage pulse upon which machining occurs.

7. Apparatus in accordance with claim 6 including means to compare the magnitude of the output of said monitoring means with a first, a second and a third predetermined voltage, respectively, means to gate the output of said comparator means only during periods of conduction across said gap, means to provide an alarm if the output of said monitoring means is less than said first predetermined voltage, means for counting the number of times the output of said monitoring means is less than said second predetermined voltage in order to provide an indication of the steady state arcing condition, and means to count the number of times the output of said monitoring means is less than said third predetermined voltage in order to provide an indication of the incipient arcing condition.

8. Apparatus for monitoring the efficiency of an electrical discharge machining operation in which electrical voltage pulses are applied across a gap formed between an electrode and a work piece, comprising:

means for measuring the electrical charge flowing across said gap during each electrical voltage pulse, said electrical charge measuring means including transducer means for producing an output responsive to current flow to said electrode, means for gating the output of said transducer only during periods of current flow to said electrode, and integrator means for integrating the gated transducer output from said gating means to produce an output signal proportional to the integrated value of current flow to said electrode; and

means for measuring the actual number of pulses per unit of time in which conduction across said gap occurs whereby the electrical charge measurement may be multiplied by the number of pulses per unit time measurement in order to obtain an indication of the metal removal rate efficiency of the electrical discharge machining operation.

9. Apparatus in accordance with claim 8 including means for detecting a predetermined percentage decrease in magnitude of the voltage pulse appearing across said gap.

10. Apparatus in accordance with claim 8 including indicator means for indicating the value of the output of said integrator means.

11. Apparatus in accordance with claim 10 wherein said indicator means is a meter.

12. Apparatus for monitoring the efficiency of an electrical discharge machining operation in which electrical voltage pulses are applied across a gap formed between an electrode and a work piece, comprising:

means for measuring the electrical charge flowing across said gap during each electrical voltage pulse; and

means for measuring the actual number of pulses per unit of time in which conduction across said gap occurs, said measuring means including transducer means for producing an output in response to current flow to said electrode, means for producing a single output pulse in response to each output pulse of said transducer means and a frequency meter for counting the output pulses of said pulse producing means whereby the electrical charge measurement may be multiplied by the number of pulses per unit time measurement in order to obtain an indication of the metal removal rate efficiency of the electrical discharge machining operation.

13. Apparatus for monitoring the efficiency of an electrical discharge machining operation in which pulses of electrical energy are applied to an electrode through a conductor, said electrode being spaced from a work piece to form a gap between said electrode and said work piece, comprising:

means for measuring the electrical charge flowing across said gap during each electrical energy pulse, said electrical charge measuring means including transducer means for producing an output responsive to current flow to said electrode, means for gating the output of said transducer only during periods of current flow to said electrode and integrator means for integrating the transducer output of said gating means to produce a signal proportional to the energy flow to said electrode during each current pulse to said electrode;

means for measuring the rate at which pulses of electrical energy are applied tO said electrode; and

means for measuring the percentage of pulses of electrical energy applied across said gap upon which conduction across said gap occurs whereby the electrical charge measurement, the pulse rate measurement and the percentage on which conduction occurs measurement may be multiplied in order to obtain an indication of the efficiency of the electrical discharge machining operation.

14. Apparatus in accordance with claim 13 including indicator means for indicating the value of the output of said integrator means.

15. Apparatus in accordance with claim 13 including means to compare the magnitude of the voltage of the electrical energy pulse across said gap with a predetermined voltage and providing an output only if the magnitude of the electrical voltage pulse across said gap is less than the predetermined voltage during periods of conduction across said gap.

16. Apparatus in accordance with claim 14 wherein said indicator means is a meter.

17. Apparatus in accordance with claim 13 including means for multiplying together the electrical charge measurement, the pulse rate measurement and the percentage on which conduction occurs measurement and means for indicating the product of said multiplication.