Acoustic resonance diagnostics for process monitoring during vibratory stress relief of grey cast iron components

Residual stress management remains a major challenge in the manufacturing of cast iron components because conventional assessment techniques are typically localized, time-consuming, and difficult to integrate into production environments. This study introduces a process-integrated acoustic diagnostic approach for monitoring changes in the dynamic response of components during machining and vibratory stress relief (VSR). The methodology was developed for direct industrial application and investigated under real manufacturing conditions. The approach combines acoustic resonance monitoring with complementary X-ray diffraction (XRD) measurements to establish a practical workflow for evaluating component response throughout the manufacturing sequence. Rather than replacing established residual stress characterization techniques, acoustic measurements provide rapid diagnostic information that can support assessment at different manufacturing stages and during vibration treatment. Experiments showed measurable changes in the acoustic response between successive machining stages and during stepwise VSR. Complementary XRD measurements provided local near-surface residual-stress information that helped contextualize the acoustic observations and, together with the acoustic results, supported consideration of the intermediate machining stage as a promising condition for VSR under the investigated conditions. No direct quantitative correlation between XRD residual stress and natural frequency was established. The combined approach therefore illustrates the potential of acoustic resonance for process monitoring while complementing localized residual-stress measurements. The principal contribution is a process-integrated framework for applying acoustic diagnostics under industrial manufacturing conditions. The results provide a basis for further investigation of the approach in other materials and manufacturing conditions.