Progenero Products

Nondestructive testing using ultrasonic NDT systems with gates help to determine the integrity of a spot weld and whether a spot weld has any cracks or other flaws.  Gates are an electronic means of selecting a segment of the time for monitoring.  They can be used to focus the analysis of a spot weld at a certain time frame, which translates to depth, to better determine the integrity of the weld nugget.  The amplitude of the signals being read at that time frame can be compared to a standard or relative amplitudes of signals at another time frame to determine if that portion of the weld nugget is good or not.

Because the ultrasonic waves travel at a consistent rate through the spot weld nugget, the NDT system can focus on the expected time frame, or depth, of the nugget to see if the signals reflected back are greater than a determined threshold which would be considered acceptable for a good weld.  If the amplitude of the signals in this time frame are greater than the threshold, it suggests that either the sheets are not sufficiently welded at this dept or there is a crack or some other type of flaw that is reflecting the ultrasonic signals.  The gate is usually positioned between the front echo (reflected on the upper surface of the first sheet) and the back echo (reflected on the bottom surface of the last sheet).  On an A-scan, the signals coming through in this time frame are usually weak as there should not be much to reflect the ultrasonic signals.  Minor reflections are expected as the grain structure of the material provides small amount of interference to the signals.

Because of the slight movements in the ultrasonic transducer, the distance between the ultrasonic transducer and the upper surface of the first sheet can change, which can lead to signal time shift and require the position of the gate needs to be adjusted in real time. In an ultrasonic C-scan, the above problem can be solved by tracking the front echo peak and keeping the relative distance between the gate and the front echo peak constant.  When gates are used properly, the C-scan image should provide a meaningful data and visual representation of size of the nugget as well as flaws that are present in the nugget.