ADVANCED MATERIALS & PROCESSES | SEPTEMBER 2023 22 speeds as high as 890 mm/min were achieved in the same alloy. TESTING As noted in the original SBT study, it was anticipated that this new approach would be capable of producing curvilinear internal path- ways for a range of existing and new uses, including pathways for wiring, gases, fluids, and tubing, as well as reservoirs for powders and solid materials such as composites. Targeted components include heat exchangers, cooling plates, and vacuum tools. Other potential uses are in electric vehicle battery trays and in structural components having integral pathways for embedded sensor wiring, pneumatic actuator lines, and engineered designs for weight reduction and stiffness tuning of structural components. Following the initial development phase, a program for testing the transferability of SBT tunneling was carried out. For this second phase, several series of coupon-level tests were completed on two pieces of equipment located on the Discovery Park campus of the University of North Texas (UNT), a purpose-built FSP machine and an FSP-capable industrial robot. Results from the transferability phase and the prior developmental phase demonstrated that this new technology was indeed adaptable to a range of industry equipment[3]. As part of documenting the quality of SBT channels in the technology transfer study, test coupons were examined visually, metallographically, and with an x-ray microscope (XRM)[3]. The XRM proved valuable for documenting the nature of the SBT channel surfaces, providing 3D images like the one shown in Fig. 2 for characterizing surface roughness for high-rate SBT tunneling. As can be seen, the surface has a regular texture, which can aid in heat transfer. In turn, slower travel speeds were found to produce closer spacings in the surface roughness periodicity. Figure 3 shows one of several complex processing paths that were designed and tested. This particular coupon was machined from AA6061- T6511 extruded stock. Following machining, the test part was then processed as part of an industry-sponsored development program to establish a repeatable SBT tunneling process. The CT images from XRM examinations show a well-formed 3D EIP throughout its length. Another example, shown in Fig. 4, illustrates the variation in the cross- sectional area from a set of EIPs produced in a 2000 series aluminum alloy. The shape of the cross-sections reflects the asymmetry in metal flow from the advancing to the retreating side of the SBT toolset. Shapes other than trapezoidal or rectangular may be produced for various applications by controlling the toolset design, the pre-processed part geometry, and processing parameters. CONCLUSION SBT tunneling holds promise as an emerging green fabrication innovation that promotes sustainable manufacturing. This goal is achieved through efficiently forming EIPs in malleable components in many industries and for multiple uses, Fig. 2 – Surface model built from x-ray microscope test data results for an EIP produced at 635 mm/min (25 ipm) and 750 rpm[3,4]. Fig. 3 – XRM CT images from an AA 6061-T6511 3-D EIP sample. The pathway followed a sine wave pattern in both the transverse and out-of-plane directions relative to the primary direction of travel[4].
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