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Method and apparatus for evaluating quality of resistance welds

  • US 6,140,825 A
  • Filed: 05/12/1998
  • Issued: 10/31/2000
  • Est. Priority Date: 05/14/1997
  • Status: Expired due to Term
First Claim
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1. A method for evaluating quality of a resistance weld, comprising:

  • continuously detecting instantaneous values of welding current and inter-electrode voltage during a current changing period during which instantaneous value of the welding current is changing;

    continuously calculating an instantaneous value of an apparent inter-electrode dynamic resistance from both detected values;

    obtaining a series of the calculated instantaneous values, and calculating a differential coefficient, representative of an approximate waveform formed from the obtained series of calculated instantaneous values, as a rate of change of the dynamic resistance instantaneous value during an arbitrary time period; and

    evaluating welding quality by using a change characteristic of the calculated rate of change of dynamic resistance instantaneous value.

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