As indicated by the title, this project seeks to investigate the homopolar pulsed welding process in two areas: characterization and real-time quality assurance. The goal of the characterization was to define the existing homopolar generator based welding system sufficiently so that its performance could be predicted with simple mathematical models. In addition, characterization of the system led to a methodology for quickly identifying optimum welding parameters in new materials and geometries. With a good characterization of the system performance, various parameters were measured and evaluated during controlled welding tests in order to quantify dependable weld quality indicators. These in-process weld quality indicators are expected to form the basis of a real-time quality assurance system for homopolar welding.
Homopolar welding systems and some of the baseline calculations used to describe the process are defined. The experimental procedure and investigations used to characterize the welding system and evaluate various weld quality indicators is presented. Generalized methodology for initiating a homopolar welding program with a new material and weld geometry different from that investigated in this research is summarized.
Homopolar welding was found to be amenable to in-process monitoring of weld quality, primarily using three measurable parameters as weld strength indicators: electrical energy deposited into the bulk material of the workpieces around the interface, thermal expansion of the workpiece due to the rapid temperature rise at the interface, and the final displacement due to forging of the workpieces. The energy deposition into the workpiece bulk material and the final displacement due to forging are both evaluated after the weld is made and are best suited for post-process nondestructive evaluation of weld quality. However, the thermal expansion due to interface heating (or, back-off displacement), is well suited to real-time quality control since it is fully evaluated prior to upset.