Real-Time Adaptive Control for Conduction Mode EB Welding of Niobium Cavities

Sciaky’s experience developing and operating advanced electron beam welding (EBW) and additive manufacturing (EBAM®) systems is being utilized to develop sensing and control techniques to improve the quality and reduce risk when performing conduction mode electron beam welding of highly engineered niobium radio frequency cavities. Collaborating with the radio frequency cavity design and fabrication experts at Michigan State University’s Facility for Rare Isotope Beams (FRIB) has continued to provide direct insight into the types of structures and observed issues that are associated with this type of welding application. Leveraging Sciaky’s existing patented IRISS® Interlayer Realtime Imaging & Sensing System developed for closed loop process control of additive manufacturing applications our initial testing has shown the potential to sense changes in the melt pool during conduction mode welding. Modifying the image analysis technique has allowed for changes in thermal conditions to be correlated with potential changes in the material / joint configuration. Common sources of variation such as raw material tolerances, joint fit up, and general manufacturing tolerance stack-ups have been observed to cause thermal changes during the welding operation. A common defect referred to as “blow thru,” which can result in expensive rework and project delays, is considered a result of these potential variations and that by actively responding to thermal changes during welding these occurrences can be minimized or eliminated. Developments produced during the Phase I program have shown the capability to observe and record melt pool changes during welding. Data obtained from our trials has also been incorporated into a process control feedback algorithm that can adjust parameters during welding to compensate for measured changes. Our Phase II proposal intends to build upon these learnings in such a way as to transition what is considered a functioning prototype to a more calibrated and robust control system. This would also include additional weld testing that moves from simple joint configurations to applications representing real world radio frequency cavities. Our collaboration with Michigan State will allow us to produce realistic niobium coupons with custom defects intended to represent typical fabrication scenarios found in production assemblies. Implementing our advanced melt pool imaging and beam deflection system, we have noted additional areas that could be explored that may also further improve the control capabilities of the process leading to generally improved processing parameters for conduction mode welding applications.