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Automatic stepper for resistance welding

  • US 4,885,451 A
  • Filed: 05/09/1988
  • Issued: 12/05/1989
  • Est. Priority Date: 05/09/1988
  • Status: Expired due to Term
First Claim
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1. For use in a resistance welding process in which an alternating electrical current is delivered to a metal workpiece through a circuit including electrodes to produce a weld caused by localized melting of the workpiece, wherein the application of an excessive amount of said current results in expulsion of molten metal from said weld thereby diminishing the quality of said weld, a method of controlling the magnitude of current delivered to said workpiece through said electrodes, comprising the steps of:

  • (A) determining the time interval t1 between the application of voltage to said electrodes and the following zero crossover of said voltage;

    (B) determining the time interval t2 between said zero crossover point of said voltage and the following zero point of the current resulting from said application of voltage;

    (C) determining the value of the power factor of said circuit using the time intervals t1, t2 determined in steps (A) and (B), the expulsion of molten metal from said weld being a function of the value of the power factor determined in step (B); and

    (D) changing the magnitude of said current based at least in part on the value of the power factor determined in step (C).

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