Dynamic characterization and finite element model refinement for a boring bar under varying overhang lengths using experimental modal analysis

Boring bars used in internal turning are sensitive to vibration at large overhang lengths because the resulting reduction in bending stiffness increases dynamic compliance and affects the dynamic response of the tool system. This study investigates the dynamic characteristics of a boring bar under five overhang conditions through a combined experimental and numerical framework. Experimentally, impact-hammer modal testing was performed using an instrumented hammer, an accelerometer, and a data acquisition system, and the measured signals were processed in Python to obtain frequency response functions (FRFs), natural frequencies, and damping ratios. Numerically, a three-dimensional finite element model was developed in ANSYS and analyzed using the Block Lanczos method. The initial model, based on ideal fixed boundary conditions, produced natural-frequency prediction errors greater than 20%. By introducing realistic circumferential clamping conditions to represent the actual holder restraint, the error was reduced below 10%. Further improvement was achieved through material sensitivity analysis by reducing the initially assumed Young’s modulus within an acceptable range and applying the finalized value consistently to all overhang conditions; for the largest overhang, the final prediction error was reduced to below 3%. Harmonic response analysis was performed using experimentally identified damping ratios, and the resulting numerical FRFs showed good agreement with the experimental FRFs in terms of resonance frequency and response magnitude. The study demonstrates that physically realistic boundary condition representation, supported by staged finite element model refinement and FRF based validation, is essential for reliable prediction of boring bar dynamics and provides a validated framework for future investigations of vibration-related machining behavior.