(V) Submerged Bobbin Tool (SBT) Tunneling Technology
Submerged bobbin tools, or SBTs, are specially designed to form integral sub‐surface channels (tunnels) within components. Like a conventional bobbin tool (BT) used in friction stir welding (FSW), an SBT has two opposing shoulders spaced apart along the bobbin or probe section of the tool. Unlike a conventional BT, however, an SBT is used to form enclosed internal channels by the distal shoulder – the one located at the terminal end of the bobbin – being submerged within the workpiece while the opposite shoulder rides along on an outer surface of the workpiece during processing.
Similar to other BT designs, the opposing shoulders of SBT designs serve to contain a substantial portion of stirred material generated throughout the progression of the process. As a result, process forces produced parallel to the tool’s axis of rotation are reacted between the opposing shoulders. Compared to single‐sided tool designs having one shoulder, SBT tools therefore produce relatively lower out‐of‐plane forces that must be supported by the fabrication equipment. In turn, fabrication equipment for internal channel production by SBTs have reduced force and stiffness requirements compared to equipment for single‐sided channeling methods.
Preliminary studies show that this innovation can be deployed on CNC machining centers, FSP purpose-built equipment and industrial robots to produce 3‐D curvilinear subsurface integral channels in complex‐shaped parts.