Power source for electric discharge machining

A power source for electric discharge machining in which voltage is applied across an electrode and a workpiece to be machined to cause electric discharge in an interelectrode gap formed between said electrode and said workpiece to thereby machine said workpiece comprising:

• an AC source for applying AC voltage to an interelectrode gap;
• an output detecting unit for detecting an output of said Ac source and for performing impedance matching with said interelectrode gap;
• and
• a frequency control circuit for automatically changing the frequency of said AC source according to a detection value provided by said output detecting unit,
• wherein a high frequency signal applied to said output detecting unit by said AC source is subjected to impedance-matching in response to variation in impedance of said interelectrode gap prior to being applied to said interelectrode gap.

A power source for electric discharge machining in which voltage is applied across an electrode and a workpiece to be machined to cause electric discharge in an interelectrode gap formed between said electrode and said workpiece thereby to machine said workpiece, comprising:

• an AC source for applying AC voltage to an interelectrode gap;
• and
• an automatic impedance-matching unit provided between said AC source and said interelectrode gap,
• wherein an electric discharge machining operation is carried out while impedance matching is automatically effected in response to variations in an impedance of said interelectrode gap.

An apparatus for use in electric discharge machining by providing a voltage across an interelectrode gap formed between an electrode and a workpiece to be machined, the interelectrode gap having a capacitance, said apparatus comprising:

• power source means for producing an Ac voltage having a frequency;
• output detection means for detecting a travelling wave signal level and a reflected wave signal level;
• impedance matching means for use in matching impedance of said apparatus with a capacitance of an interelectrode gap;
• and
• frequency control means for changing the frequency of the AC voltage in response to a change in impedance of said interelectrode gap to maintain said apparatus in resonance based on the travelling wave signal level and the reflected wave signal level detected by said output detection means.