Method and apparatus for non-destructive quality testing of spot welds

Abstract

A method of non-destructive quality testing of spot welds resides in that in the test weld nugget region there is produced a primary electromagnetic field inducing eddy currents in that region. Thereupon, the primary electromagnetic field is displaced in a direction parallel to the surface of contact of the welded parts. The phase angle between the resultant and primary magnetic fields is measured at the points characterized by the maximum of the primary electromagnetic field intensity lying on the same line parallel to the surface of the test weld and located in the zone disposed between the points located on either side of the test weld zone wherein the weld nugget is disposed, the weld nugget thickness is evaluated from the difference between the maximum phase value of the intensity measured in the test weld zone wherein the weld nugget is absent and the minimum phase value of the intensity measured in the test weld zone wherein the weld nugget is disposed. The weld nugget diameter is evaluated from the length of the zone within the limits where the phase of the intensity has its minimum value. An apparatus for non-destructive quality testing of spot welds includes a sinusoidal voltage generator with a phase shifter and an unbalanced bridge circuit having a superimposed eddy current transducer included into one of its branches, which are connected to the output thereof, and the outputs of the phase shifter and unbalanced bridge circuit being connected with the respective inputs of a phase meter, the superimposed eddy current transducer being complete with an attachment for its mechanical displacement in the plane parallel to the surface of contact of welded parts.