ADVANCED MATERIALS & PROCESSES | SEPTEMBER 2023 20 Submerged bobbin tool (SBT) tunneling is an emerging green fabrication innovation that promotes sustainable manufacturing. This goal is achieved through efficiently forming engineered integral pathways (EIPs) in malleable components with SBTs for transportation vehicles, aerospace structures, and fabrication equipment. EIPs are defined here as subsurface channels (tunnels) integrated within a component’s design. Adding a cover plate or assembling parts is not needed to enclose a single EIP or even a complex network of EIPs because they are formed within a given part during fabrication. EIPs may be used as conduit for wiring, plumbing for heating oils and coolants, and piping for vacuum lines and pneumatic systems[1,2]. Advanced uses of EIPs may involve utilizing internal pathways for inspection and service in structural health monitoring. Another potential use is lightweighting cavities for weight reduction and/or redistributing mass within structures. They are also envisioned as a means for preparing tailored lattices for designing hybrid materials[3,4]. ENGINEERED INTEGRAL PATHWAYS Castings, forgings, extrusions, machined parts, and components made by additive manufacturing (AM) all have well-established manufacturing methods for integrating EIPs in a part’s design[5]. As depicted in Table 1, they are conventionally produced in castings via cores. Forgings may undergo direct piecing (shown) and rotary piercing (not shown) or another forging operation. With proper die design, a limitless number of linear extruded product forms are possible by way of common extrusion methods. Rivaling castings, forgings, and machined parts, AM parts now offer virtually unrestricted flexibility in designs with internal pathways[7]. While AM holds great promise, it should be noted that AM specifications for the aerospace industry—those pertaining to the qualification of AM processes and the certification of individual AM parts—are still in development by the respective stakeholders, including government regulators, professional organizations, and industry trade TECHNICAL SPOTLIGHT ADVANCEMENT IN ENGINEERED INTEGRAL PATHWAYS FOR MANUFACTURED STRUCTURES A new friction stir processing method creates subsurface integral pathways in components that can be used for wiring, gases, fluids, powders, or as a lightweighting technique. Dwight Burford* Advanced Materials & Manufacturing Processes Institute, University of North Texas *Member of ASM International TABLE 1 — ENGINEERED INTEGRAL PATHWAYS IN VARIOUS PRODUCT FORMS[4,6] Castings Forgings Extrusions AM Wrought plate Core design and placement in the mold cavity Piercing operations, e.g., direct piercing Die designs for specified crosssections CAD models for varied design complexity Submerged bobbin tool friction stir processing
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