<p>The blisk is a critical load-bearing component in aero-engines, featuring complex geometry and stringent machining accuracy requirements. Cutting forces in five-axis ball-end milling have a significant influence on machining quality and process stability. To improve the prediction accuracy of milling forces for the blisk, this study proposes an analytical modeling approach for five-axis ball-end milling, considering the geometric and mechanical variations caused by tool orientation changes. First, cutter–workpiece engagement (CWE) is extracted efficiently and accurately using GPU-accelerated mesh Boolean operations, providing realistic cutting boundaries. Then, the effect of tool inclination angles on uncut chip thickness is examined, and a new instantaneous uncut chip thickness (UCT) model is developed to describe the dynamic chip thickness under varying postures. Finally, an analytical milling force model that incorporates both edge effects and size effects is established for blisk machining. Simulation and cutting experiments validate the proposed model, showing good agreement between predicted and measured forces, with an overall average error below 10%. The study demonstrates that the method can effectively capture the combined influence of tool posture and micro-scale cutting effects on milling forces, providing reliable theoretical support for the optimization of machining parameters and tool design in five-axis ball-end milling of blisks.</p>