Weak stiffness region identification and optimization of a high-precision heavy-duty gantry machining center based on the modal mass distribution matrix

Abstract

Insufficient structural stiffness in high-precision, heavy-duty gantry machining centers can directly affect machining accuracy and operational stability. To address this issue, the identification and optimization of structurally weak-stiffness regions are investigated. A finite element model of the entire machine tool is established, and modal analysis is conducted to obtain vibration mode data, thereby enabling preliminary identification of weak-stiffness components. A modal mass distribution matrix is then constructed, and the weak regions are further identified based on the squared values of the maximum normalized modal shape coefficients. The results indicate that the ram structure is the primary weak stiffness component of the machine tool. Subsequently, structural optimization is performed by adjusting key parameters, such as the wall and rib thicknesses of the ram. The results show that the optimized structure increases the low-order natural frequencies, with the first natural frequency rising from 157.44 Hz to 159.89 Hz (a 1.6% increase), thereby significantly improving the overall stiffness of the machine tool.