Overhang structures are essential geometries in metal additive manufacturing for realizing complex shapes. However, achieving stable, support-free overhang structures requires precise control of process parameters, and securing shape fidelity becomes particularly challenging as overhang length increases due to thermal deformation. To address this challenge, this study proposed a Bayesian optimization framework for efficiently identifying optimal process parameters to fabricate high-difficulty overhang structures. An image-based scoring method was developed to quantitatively evaluate shape defects. Experimental data were collected by fabricating 3, 6, and 9 mm overhang structures with various process parameters. Based on collected data, Gaussian Process Regression (GPR) models were trained. A physics-informed soft penalty term based on energy density was incorporated to construct a surrogate model capable of making physically plausible predictions even in extrapolated regions. Using this model, Bayesian optimization was applied to overhang lengths of 12, 15, and 18 mm, for which no prior experimental data existed. Recommended parameters enabled stable, support-free fabrication of overhang structures. This study demonstrates that reliable optimization of process parameters for complex geometries can be achieved by combining minimal experimental data with physics-informed modeling, highlighting the framework’s potential extension to a wider range of geometries and processes

Boring depth is limited by the overhang on which the vibration frequency depends. To improve the process, a passive boring bar with dynamic vibration absorber has been used, but is effective only for a limited length of overhangs. In this study, a tunable damped boring bar was devised to cope with a variable length of overhangs. Vibration parameters arising from the various overhangs were analyzed using Euler’s beam theory. The proposed bar contains a cantilever-type dynamic vibration absorber to suppress the vibration amplitudes of the overhangs. The absorber adjusts the natural frequency of the bar by adjusting the spring stiffness. The proposed bar was fabricated and tested by impact excitation and its capability to suppress vibration was demonstrated.