Method and apparatus for the non-destructive checking of spot welds between metal sheets produced by electric welding
First Claim
1. A method for the non-destructive checking of a spot weld between metal sheets, produced by electric welding, in which an electrical direct current of predetermined constant strength is passed through a spot weld by means of a first pair of electrodes and the electrical potential difference between two points on the surface of one of the sheets, respectively upstream and downstream of the spot weld along the path of the current, is measured by means of a second pair of electrodes,the second pair of electrodes being used to make at least one first measurement before the application of the direct current and at least one second measurement during the application of the direct current, the first and second measurements being carried out at two instants separated by a time interval equal to or a whole multiple of the period of the main power voltage used for electric welding, the difference between the values measured in the first and second measurements providing an indication of the quality of the spot weld.
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Accused Products
Abstract
A electrical current of predetermined strength is passed through a spot weld by a first pair of electrodes. The electrical potential difference between two points, respectively upstream and downstream of the spot weld along the current path, is measured with a second pair of electrodes. In particular, this second pair of electrodes is used to carry out at least one first measurement before the application of the current, and at least one second measurement during the application of the current. These measurements are carried out at two instants separated by a time interval equal to or a whole multiple of the period of the main power voltage. The difference between the values measured in the first and second measurements provides an indication of the quality of the spot weld.
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Citations
7 Claims
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1. A method for the non-destructive checking of a spot weld between metal sheets, produced by electric welding, in which an electrical direct current of predetermined constant strength is passed through a spot weld by means of a first pair of electrodes and the electrical potential difference between two points on the surface of one of the sheets, respectively upstream and downstream of the spot weld along the path of the current, is measured by means of a second pair of electrodes,
the second pair of electrodes being used to make at least one first measurement before the application of the direct current and at least one second measurement during the application of the direct current, the first and second measurements being carried out at two instants separated by a time interval equal to or a whole multiple of the period of the main power voltage used for electric welding, the difference between the values measured in the first and second measurements providing an indication of the quality of the spot weld.
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5. An apparatus for the non-destructive checking of a spot weld between metal sheets, produced by electric welding, comprising
a direct current generator, a first pair of electrodes connected to the generator for passing an electrical current of predetermined strength through a spot weld in use, voltage measuring means, a second pair of electrodes connected to the measuring means for detecting the electrical potential difference between two points on the surface of one of the metal sheets, respectively upstream and downstream of the spot weld along the path of the current, an indicator device, and an electronic control unit connected to the current generator, the voltage measuring means and the indicator device, and arranged: -
to detect and store at least one value of the voltage detected by the measuring means between the two points at a first instant before the application of the current to the spot weld, to cause the application of the current produced by the generator through the first pair of electrodes for a predetermined period of time, to detect and memorize at least one value of the voltage measured by the measuring means during the application of the current, at a second instant separated from the first instant by a time interval equal to or a whole multiple of the period of the main power voltage used for the electric welding; to generate electrical signals indicative of the difference between the voltages detected at the first and second instants, and to activate the indicator device so as to provide a perceptible indication of the difference. - View Dependent Claims (6, 7)
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Specification