Control of Metal Transfer at Given Arc Variables

This project aims at establishing the foundation to build the next generation gas metal arc welding (GMAW) machines so that the highly productive GMAW process can be fully controlled to compete with the much slower gas tungsten arc welding (GTAW) for critical applications. The proposed method decouples the control of metal transfer from that of arc variables and provides an improved heat-force balance needed for producing high quality welds. In particular, low power laser spots are applied onto the droplet to detach it and the laser powers are adaptively adjusted to achieve the desired metal transfer variables at whatever given/desired arc heat and force variables. The resultant metal transfer variables are monitored through an array of are light sensors for feedback control and adaptive modeling. The fiber optics for lasers and arc light sensor array are effectively integrated into the torch without reducing torch's accessibility. To determine the laser application timing, needed force from the lasers, and needed laser powers to achieve the needed force, three models will be established using numerical modeling and experiments combined approach. Once the models and integrated torch are available, the research team will demonstrate the fully controlled GMAW process and its capability to make full penetration weld meeting GTAW soundness and mechanical property requirements at higher production rates. - Intellectual Merit: The proposed research includes challenging issues related to numerical analysis of the GMAW process, modification of free droplet numerical models, establishment of models for process control purpose, modeling the laser pressure based on numerical analysis and experimental observation combined, establishing an adaptive model which modifies its parameters based on feedback measurements, building an integrated sensor torch which can deliver the laser spots as well as collect arc lights, integrating models and sensors into control system to demonstrate the fully controlled GMAW and its capability to make full penetration welds. The completion of the proposed multi-disciplinary exploratory research requires the use of knowledge in a broad range of areas including optics, laser, arc, metal transfer, numerical analysis, imaging devices, image processing/computer vision, high speed image systems, process modeling, process control. It will not only establish the foundation for building next generation capable GMAW machines, it will also provide tools to realize higher control goals such as three- dimensional weld pool surface control and weld joint penetration control in the most widely used robotic arc welding process. Broader Impact: Welding is typically the last operation during fabrication of high value added product. GTAW has historically used because of the high quality weld produced and ability to control the process while producing the desired properties. The ability to improve productivity without compromising quality is essential to sustaining high value-added manufacturing competency that currently exists in the US today. Possible future transition of the proposed technology will help US 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 needed to maintain such competency in a wide range of levels from high school, undergraduate, through PhD in forms of hands-on design course, research experience, exploratory thesis/dissertation research, application-oriented case study, knowledge dissemination and possible commercialization with industry partners.