Abstract: The tool center fluctuation problem commonly exists in the current machining strip-width maximization methods for 5-axis finish machining of complex surfaces with abrupt curvature change by using a torus cutter. This has negative impact on machining efficiency and quality improvement. After analyzing the tool position adjusting process of those strip-width maximization machining methods, the reasons for fluctuation caused by cutting strip-width (FCCS) and fluctuation caused by tool axis (FCTA) are decomposed. FCCS is the tool center fluctuation caused by the different machining strip-widths between two adjacent tool positions, and FCTA is the tool center fluctuation caused by tool freedom resulted from surface curvature variation. Although the influences by FCCS and FCTA may counteract with each other, the tool center fluctuation may be aggravated when they are both positive and both negative. A mid-point-error-control method (MPEC) for tool position optimization which can eliminate FCCS is proposed. Thus, FCTA is the only causation of the tool center fluctuation in this method. The torus cutter is firstly positioned by the mid-point on the effective-character-curve-segment (ECCS), and the other 2 degrees of freedom (DOF) are adjusted to obtain the maximum strip-width. The corresponding program of this method for an airscrew part is developed and the cutting experiment is conducted. Through comparison among the proposed method, the Sturz algorithm and the multi-point method, the effectiveness of MPEC in tool path smoothing and machining efficiency improvement for complex surface machining is validated.

Key words: Complex surface, Middle-point-error-control, Strip-width maximization machining, Tool center’s fluctuation