Numerical Modelling of Clamping Condition Effects on Contact Behavior and Structural Stability in Toolholder Systems during External Cylindrical Turning

Abstract

The mechanical stability of tool-clamping systems is governed by contact conditions at the tool holder–tool post interface, which are directly controlled by bolt-induced preload forces. In external turning operations on universal lathes, manual tightening of clamping bolts may introduce preload asymmetry, resulting in non-uniform contact pressure distributions. This study presents a numerical modeling framework to investigate the relationship between clamping conditions, contact behavior, and structural stability in a bolted toolholder system. A pre-stressed finite element model was developed to simulate bolt tightening and subsequent cutting-force application, enabling the evaluation of contact-state evolution. The effects of total tightening torque, torque ratio between clamping bolts, and mounting orientation were examined for right-hand (RH) and left-hand (LH) configurations under light, medium, and hard cutting regimes. Static stiffness and the first three natural frequencies were used to characterize the structural response. Regression-based analysis of variance was performed to identify statistically significant parameters, and significant responses were modeled using Response Surface Methodology (RSM). Model predictions were verified through additional finite element simulations. The results showed that preload-induced contact behavior strongly influences system response, with static stiffness and the second natural frequency exhibiting the highest sensitivity to clamping parameters. In addition, mounting orientation generated directional asymmetry relative to the tangential cutting force, leading to configuration-dependent dynamic characteristics. The findings demonstrate that tightening torque magnitude alone is insufficient to evaluate toolholder behavior; preload distribution, contact mechanics, and mounting configuration must be considered together to accurately describe clamped interfaces.