<p>Thin-walled curved groove structures, widely used in aerospace applications, pose challenges for efficient multi-axis milling due to their complex geometry, extensive material removal, and thin-walled nature. Traditional plunge milling is mainly used for rough milling and machining of straight surface; in this paper, a new tool path generation method with continuous variable axis is proposed for the plunge milling of complex trajectories, and the radial strength of the tool is considered for the Ti-6Al-4&#xa0;V alloy leading edge protection cap in composite material fan blades. The strategy integrates '3 + 2' axis plunge milling for slotting with continuous variable-axis plunge milling for free-form surface machining, fully exploiting the axial rigidity of cylindrical tools to ensure efficient material removal while maintaining machining accuracy. Initially, the geometric model is used to construct a straight grain surface within the slot. Following this, the free-form surface is segmented along the unfolding direction using families of planes, with continuous variable-axis plunge milling cutter contact trajectories generated to control the residual height effectively. The process concludes by using the tool contact path to calculate tool axis vectors, subsequently deriving the tool position point paths. Experimental results demonstrate a reduction in wall thickness error by more than 70% and a decrease in residual material volume by more than 75%, compared to conventional plunge milling methods. This makes the plunge milling method more flexible in the tool path generation and will further improve the application range of the plunge milling process.</p>