Abstract

A weld monitoring and evaluating circuit (10) for non-destructively determining if a just-completed weld is a satisfactory or an unsatisfactory weld. The circuit is used to derive the temperature at the weld zone in real time by determining the total power input to the weld zone, taking into account losses experienced at the weld zone, and dividing the result by the thermal mass of the weld zone. The predicted temperature at the weld zone is compared against an electrical signal representing at least a minimum desired welding temperature needed to be attained at the weld zone to produce a satisfactory weld at the time that the stud (16) contacts the weld pool (18a) (e.g., the "plunge event"). If the derived weld temperature signal has exceeded the reference signal at the time the plunge event occurs, then it is assumed that a satisfactory weld has occurred. If the electrical signal representing the derived weld temperature does not exceed the reference signal at the time the plunge event occurs, then it is assumed that an unsatisfactory weld has occurred. In an alternative preferred embodiment, a comparator window circuit (138) is used to ensure that the derived weld temperature at the time of the plunge event falls between predetermined upper and lower temperature limits before a satisfactory weld is indicated. A further embodiment uses the derived weld temperature signal to dynamically control the drop point of the stud and thereby control the total weld time. Weld repeatability and quality are thereby improved.

Other References

• Morgan-Warren, "The Control of Arc Stud Welding", Advances in Welding Processes 3rd International Conference, vol. 1, May 1974, pp. 1-