Abstract: During multi-axis machining process, complex surface can be machined flexibly while cutter’s posture is changeable in available workspace, which directly affects general stiffness characteristics of multi-axis machining system and also machining performance. By establishing general stiffness model related to cutter posture, the distribution of stiffness performance of whole machining system is analyzed. Based on multi-body small deflection theory, a semi-analytic method about closed-loop stiffness modeling for multi-axis machining system is proposed, in which Jacobi matrix method, point transformation matrix method and finite element method are applied. The force ellipsoid corresponding to the decoupling stiffness model is established in 3D space. Stiffness index is derived from force ellipsoid, which is used to plot isolines of general stiffness performance of multi-axis machining system. The result of analysis about the distribution of stiffness performance can help direct tool motion planning.

Key words: Force ellipsoid, Multi-axis machining, Stiffness, Tool motion planning