Construction of Machining Stability Domain and Trajectory Parameter Optimization for Five-Axis U-Pass Milling of Deep-Cavity Curved Parts

U-pass milling removes material under the condition of large cutting depth and small engagement angle, which renders it an ideal rough-machining approach for deep-cavity curved parts. Nevertheless, existing cutting stability characterization methods formulated in terms of spindle speed and cutting depth are poorly applicable to multivariable U-pass milling. Typical U-pass milling is performed at a constant spindle speed with variable cutting width. Its trajectory cycle number is governed by the trochoid step and trochoid circle radius, which further exerts an influence on machining efficiency. Accordingly, this paper investigates the effect of dynamic characteristics of low-rigidity systems on U-pass milling. The system frequency response function is obtained by averaging multiple hammer-impact tests. The eigenvalues of the state transition matrix are solved via the full-discretization method. Taking U-pass trajectory parameters as variables, the stability domain for five-axis U-pass milling is constructed. Subject to the guarantee of machining stability, trajectory parameter optimization for U-pass milling of integral impellers is accomplished. The optimized scheme reduces the machining time by 64.21%. This research provides a theoretical foundation for the practical implementation of U-pass milling.