The objective of this research is to (1) confirm that it is possible to introduce auxiliary forces to detach the droplet of melted wire in gas metal arc welding while still maintaining the required arc stability, and (2) confirm that metal transfer variables, including droplet mass/diameter, impact speed, and trajectory, can be fully controlled by adjusting the power and application time of the auxiliary forces. The approach is to (1) aim two lasers of relatively low power to the droplet to apply auxiliary forces from opposite directions, (2) establish a model to correlate metal transfer variables with laser powers, arc variables, and droplet state, (3) apply the model to adaptively determine the power and firing timing of the lasers based on droplet state and arc variables to achieve the desired metal transfer variables, and (4) monitor the resultant metal transfer variables to improve the model.
Gas metal arc welding is the most widely used process in automatic welding. The completion of the research will be of significant help in better understanding and controlling this complex but important process. Possible transfer of this technology will help our industry maintain its manufacturing technology leadership and compete with countries where the labor cost is relatively low. The multi-disciplinary nature of the proposed research and possible collaboration with national lab, industry and international institution will provide a variety of opportunities to train next generation academic and manufacturing experts/researchers in a wide range of levels in forms of hands-on design course, undergraduate research experience, thesis/dissertation research, application-oriented case study, knowledge dissemination and possible commercialization with industry partners.
Gas Metal Arc Welding (GMAW) is the most widely used welding process. Its consumable electrode brings it advantages over another widely used welding process - gas tungsten arc welding (GTAW) - in productivity. However, the liquid metal melted from this consumable electrode must be transferred into the work-piece. For successful transfer in the desired mode, a high current is typically needed despite the actual requirement from the application. Next generation manufacturing requires the highly productive GMAW be operated at any current, in a reasonable range, as determined by the application. To this end, an innovative method is needed to achieve the desired transfer mode at any given current (arc variables). This project aims at applying a laser to the liquid metal to reach this goal resulting in the laser-enhanced GMAW. The research team has experimentally confirmed that the application of a laser can indeed effectively reduce the amperage of the welding current needed to successfully achieve the desired transfer mode. The research team has also extended the arc physics theory into the laser enhanced GMAW for modeling and analysis and found that all physical phenomena can be explained by the extended arc physics. However, a large laser beam has been continuously applied in order to assure that the laser be applied at the needed time and needed location. The laser energy has been wasted causing extra fumes and overheats. To resolve this issue, the research team has established a real-time machine vision system to monitor the metal transfer process at 1,000 frames per second. As a result, a real-time control system has been established based on vision feedback to apply a pulsed small laser spot at the right time and right location. The laser energy waste and side effect are minimized. As for the broader impact, this research established part of the foundation for the development of the next generation welding machines that help US manufacturing industry to compete with other manufacturing industries that enjoy relatively low labor costs. In education, this research yielded two high quality PhD dissertation research projects and provided challenging topics to train a post-doctoral researcher and two undergraduate researchers both from under-represented groups. The peer-reviewed journal publications from this research received two prestigious awards from the American Welding Society. A PhD student graduated with dissertation research from this project won the prestigious Henry Granjon award in 2012 from the International Institute of Welding (IIW) for Category A - Welding technology representing the US through competition among other IIW member countries.
