Gating methods for use in weld inspection systems

1. A method for characterizing a spot weld, comprising:

(a) providing an acoustic probe, wherein the acoustic probe includes:

(i) a plurality of ultrasonic transducer elements arranged in a curved phased array at one end of the acoustic probe, wherein the transducer elements are operative to both generate ultrasonic signals and receive reflections thereof, and

(ii) a combination of materials for allowing the probe to conform to a contoured surface of the spot weld while enabling sound energy to be transferred directly into the spot weld under test conditions;

(b) providing a phased array excitation unit in electrical communication with the array of the transducer elements for ultrasonically exciting the transducer elements in a phased manner;

(c) providing a computerized controller in electrical communication with the phased array excitation unit for controlling an operation of the phased array excitation unit, and gathering and processing information from the transducer elements;

(d) acquiring a sequence of A-scans from the phased array, wherein the A-scans describe individual portions of a field of view of the phased array,

(e) defining an interface gate offset and length for an interface gate, and a flaw gate offset and length for a flaw gate, with respect to a known total material thickness for each individual A-scan within the sequence of A-scans;

(f) calculating a gate ratio between a maximum amplitude under the interface gate and a maximum amplitude under the flaw gate for each individual A-scan within the sequence of A-scans;

(g) plotting the gate ratio for each individual A-scan as a function of a location within the field of view of the phased array to generate a weld fusion map;

(h) using a predetermined threshold to differentiate fused locations from unfused locations on the weld fusion map; and

(i) calculating predetermined weld metrics, wherein the predetermined weld metrics include area, diameter, width, length, percent fused, or combinations thereof.

2. The method of claim 1 , further comprising providing at least two sheets of material that have been joined together by resistance welding, and wherein the resistance welding has generated at least one spot weld to be characterized.

3. The method of claim 1 , wherein the combination of materials further includes a flexible membrane mounted on the one end of the acoustic probe and a fluid filled chamber or solid sound delay material disposed between the membrane and the array.

4. The method of claim 1 , wherein the transducer elements are further arranged into discrete subgroups, and wherein each subgroup may be activated independently of the other subgroups and at different time intervals.

5. The method of claim 4 , wherein activating each subgroup independently of the other subgroups and at different time intervals for each transducer element in the subgroup provides signal focusing and steering capability.

6. The method of claim 1 , wherein the interface gate offset and the flaw gate offset are adjusted according to a position of a first front surface refection position for each individual A-scan within the sequence of A-scans.

7. The method of claim 1 , wherein the flaw gate offset and length are adjusted according to a measured position of the maximum amplitude under the interface gate for each individual A-scan within the sequence of A-scans.