Incorporating Additively Manufactured Triply Periodic Minimum Surface Lattice Structures in Langevin Ultrasonic...

Bolt-clamped Langevin transducers (BLTs) are widely used in power ultrasonic applications. Opportunities to tailor the vibrational response of BLTs are limited, particularly the achievable vibration displacement and the displacement field that enables complexity of the mode shape at resonance. Common solutions are based on geometric modifications of the BLT front mass, which include diameter reductions along the profile and engineered cuts. Herein we leverage the design freedom of metal additive manufacturing to tailor the vibrational response of BLTs through incorporation of porous lattices. Specifically, triply periodic minimal surface (TPMS) lattice structures, created using laser powder bed fusion (LPBF), are introduced into the front mass and the BLTs are characterised to understand the ability to tune the vibrational response. For the first time, this study investigates BLTs with a range of TPMS configurations of Ti-6Al-4V front masses. We explore different lengths (20 - 50%) and locations of gyroid lattice in the front mass. The vibrational response enhancements achieved include a more than 95% increase in displacement amplitude of the output face when driven at 60 V_rms compared to a BLT with a solid front mass driven at the same excitation level. Incorporating gyroid TPMS lattice also enables excitation of hybrid modes. In this case, BLTs with longitudinal-bending (L-B) mode resonance responses are created, with different ratios of L to B displacement depending on the configuration of the gyroid lattice. The vibrational response of different lattice structures in BLTs is also investigated, including different TPMS lattices and simple cubic lattice structures. The displacement amplitude gain of all the BLTs is significantly higher (3.7 - 4.5) compared to a BLT with solid front mass (1.7). Comparing the maximum cyclic stress under ultrasonic excitation, TPMS lattices exhibited lower stress than strut-based cubic lattices, with gyroid TPMS exhibiting the lowest maximum cyclic stress. Localised stress concentrations appear in the lattice and maximum cyclic stress is higher closer to the nodal region of the vibration mode. We demonstrate the significant flexibility that TPMS lattice structures offer for controlling the vibration behaviour of BLTs and in significantly increasing the design space for BLTs, showing promise for many power ultrasonic applications.