Method and apparatus for evaluating quality of resistance welds
First Claim
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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Abstract
A method for evaluating quality of a resistance weld is provided, in which a nugget generation state during a welding process is evaluated by observable numerical values based on physical phenomena, and which can afford a wide application range in welding material as well as a capability of accurate knowledge as to the nugget generation state of the weld. Based on that a specific resistance value of a metal material to be welded has a temperature dependency in a conduction state of AC or current-pulsated welding current, a rate of change of inter-chip dynamic resistance instantaneous value during a current changing period is determined, a changing state of the dynamic resistance instantaneous value is further calculated, and a heat-generating state of a weld zone, i.e., a nugget formation state is estimated. Thus, a quality evaluation of a weld is performed accurately.
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Citations
5 Claims
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1. A method for evaluating quality of a resistance weld, comprising:
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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. - View Dependent Claims (3)
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2. An apparatus for evaluating quality of a resistance weld, comprising:
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a welding current measuring circuit that continuously detects an instantaneous value of welding current; an inter-chip voltage detecting circuit that continuously detects an instantaneous value of inter-electrode voltage; an inter-chip dynamic resistance instantaneous value calculating circuit that continuously calculates an instantaneous value of an apparent inter-electrode dynamic resistance from detected values of the measuring circuit and the detecting circuit; a rate of change of dynamic resistance instantaneous value calculating circuit that calculates a rate of change of dynamic resistance instantaneous value of the inter-electrode dynamic resistance instantaneous value during a current changing period during which the instantaneous value of the welding current in a welding process is changing; a storage circuit that stores the inter-electrode dynamic resistance instantaneous value and the rate of change of dynamic resistance instantaneous value one after another; and an arithmetic processing circuit that performs an arithmetic process for judgement of welding quality by using the stored rates of change of dynamic resistance instantaneous value. - View Dependent Claims (4, 5)
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Specification