Abstract: The titanium alloy leading edge protection caps used in large composite fan blades for domestically produced commercial aircraft engines feature a complex thin-walled, deep, narrow V-shaped long slot structure. Its inner and outer profiles are formed through multi-axis precision machining processes. Residual stress introduced during machining exhibits mismatched distributions across the inner and outer profiles, readily inducing bending and torsional deformation that leads to dimensional deviations in the part. This paper addresses the deformation issue of TC4 titanium alloy leading edge protection caps caused by residual stress during milling. It proposes a method for controlling residual stress deformation in protection caps based on vector optimization of the machining tool axis during outer profile machining. This method achieves precise control over the bending and twisting deformation of the protection caps by optimizing the tool axis vector during multi-axis machining of the outer profile contour, thereby adjusting the residual stress distribution in the outer profile contour machining to match the residual stress in the inner contour. First, a hyperbolic tangent model was employed to characterize the residual stress gradient profile in multi-axis machining of titanium alloys. Second, using the Abaqus finite element simulation platform, machining residual stress was applied via the thin-shell stress-fitting method to establish a finite element simulation model for residual stress deformation of the protection cap. Third, a mapping relationship between the tool axis tilt angle and deformation was constructed to optimize the tool axis vector for multi-axis machining of the outer profile contour. Finally, the reliability of the method was validated through multiple sets of protection cap part machining experiments. Results demonstrated an average reduction of 23.41% in contour error for four protection caps. This method provides an effective technical solution for the deformation control of multi-axis machining of titanium alloy leading edge protection caps, which is of great engineering value for improving the manufacturing quality of composite fan blades and engine service performance.

Key words: Leading edge protection cap, TC4 titanium alloy, Multi-axis machining, Residual stress, Tool axis vector, Deformation control