Method and apparatus for spark-erosion machining of a workpiece

• US 9,844,825 B2
• Filed: 09/11/2014
• Issued: 12/19/2017
• Est. Priority Date: 09/12/2013
• Status: Active Grant

• Current Assignee: Agie Charmilles SA (Georg Fischer AG)
• Original Assignee: Agie Charmilles SA (Georg Fischer AG)
• Inventors: Boccadoro, Marco, Bonini, Stefano
• Primary Examiner(s): Hall, Arthur O
• Assistant Examiner(s): Greenlund, Joseph A
• Application Number:
  US14/483,566
• Publication Number:
  US 20150069023A1
• Time in Patent Office: 1,195 Days
• Field of Search: 219 6913, 219 6917, 219 6918
• CPC Class Codes: B23H 1/022 for shaping the discharge pulse train B23H1/024 takes precedence
• CPC Class Codes: B23H 1/024 Detection of, and response to, abnormal gap conditions, e.g. short circuits preventing short circuits or other abnormal discharges by altering machining parameters using adaptive control B23H7/16
• CPC Class Codes: B23H 7/04 Apparatus for supplying current to working gap; 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
• CPC Class Codes: B23H 7/20 for programme-control, e.g. adaptive programme-control systems in general G05B19/00
• CPC Class Codes: B23H 9/14 Making holes

Abstract

The invention relates to a method for electrical discharge machining of workpieces by electrical discharge pulses generated by a power module of an electrical discharge machine. The invention is characterized in that firstly the discharge voltage of a number N1 of electrical discharge pulses is acquired and stored, secondly a front discharge voltage (63) is determined out of this amount of N1 acquired discharge voltages and thirdly, the voltage Uhps (64) of the electrical discharge pulses produced by the power module for machining the workpiece (17) is adjusted in function of the determined front discharge voltage (63).

Claims

1. A method for the electrical discharge machining of workpieces by electrical discharge pulses generated by an output voltage generated by a power module of an electrical discharge machine, said electrical discharge pulses including front discharge pulses extending from a front of tool electrode and having a front discharge voltage, and side discharge pulses extending from a side of the tool electrode and having a side discharge voltage, said method comprising,

a.) acquiring and storing a number of front and side discharge voltages;

and

b.) adjusting the output voltage generated by the power module as a function of an analysis of the discharge pulses in step a.) to provide front discharge pulses while minimizing the occurrence of side discharge pulses; and

wherein step b.) comprises averaging an amount N2 of the lowest stored discharge voltages out of a total amount N1 of stored discharge voltages and wherein the output voltage (Uhps) generated by the power module of the generator is calculated according to the following formula

Uhps=Ubr,front+Ucab+Udiode+Us

Where

Ubr,front is the front voltage

Ucab is the voltage drop on the electrode cables

Udiode is the voltage drop on the power module blocking the diode

Us is a safety margin.

2. The method for electrical discharge machining of workpieces according to claim 1, wherein,

step a.) occurs during the entire electrical discharge machining of the workpiece or in determinable intervals during the electrical discharge machining of the workpiece.

3. The method for electrical discharge machining of workpieces according to claim 1, wherein,

step a.) is performed by moving the tool electrode used in the electrical discharge machining process in such a spatial position in respect of the workpiece, that only front discharge pulses can occur between the workpiece and the tool electrode, and wherein step b.) includes generating an amount N3 of electrical discharge pulses and by averaging the N3 measured discharge voltages of the produced electrical discharge pulses to determine therewith the front discharge voltage Ubr,front.

4. The method for electrical discharge machining of workpieces according to claim 1, wherein,

step a.) comprises moving the tool electrode used in the electrical discharge machining process in such a spatial position in respect of the workpiece, that only side discharges can occur between the workpiece and the tool electrodes, and wherein step b.) includes generating an amount N4 of electrical discharge pulses and by averaging the measured discharge voltages of the N4 produced electrical discharge pulses to determine therewith the side discharge voltage Ubr,side.

5. The method for electrical discharge machining of workpieces according to claim 4, wherein,

the output voltage Uhps of the power module is calculated by the determined side discharge voltage Ubr,side and the formula

Uhps=Ubr,side−

Us;

where

Us is a safety margin.

6. The method for electrical discharge machining of workpieces according to claim 1, wherein every time the output voltage Uhps of the power module is adjusted, additionally an energy-equivalent discharge pulse is chosen, either from a pre-computed database or by calculating it.

7. The method for electrical discharge machining of workpieces according to claim 1, wherein the front discharge pulses are generated in isofrequency mode, and the current shape of the front discharge pulses has a current amplitude increasing with the pulse duration.

8. The method for electrical discharge machining of workpieces according to claim 1, wherein the slope of the front discharge pulses is changed in one of the following ways

a) by programming an internal current reference of the generator, and/or

b) by adapting the Uhps power supply.

9. An apparatus for electrical discharge machining of workpieces by electrical discharge pulses, comprising

at least an ignition module for producing an ignition voltage Uign;

at least one power module for producing generator pulses at a programmable current amplitude, shape, duration and voltage Uhps,

a programmable voltage power supply,

a gap voltage acquisition module,

a generator controller with

a control system for the power module of the generator for determining the voltage Uhps of the electrical discharge pulses produced by the power module of the generator in accordance with claim 1.