Less interference tool-path planning method for quarter revolution penetration and retraction trajectories in internal cylindrical thread helical milling

Critical interference error can be mostly resulted from illogical tool-path generations in the penetration and retraction segments of internal cylindrical thread helical milling. Therefore, a less interference tool-path planning method is proposed for the quarter revolution penetration and retraction trajectories in internal cylindrical thread helical milling. Firstly, the parametric expression of the complete tool path of internal cylindrical thread helical milling is established; after that, a definition of eccentricity parameter m is given to adjust the radius of the penetration and retraction trajectories, and Z-axis coordinate of any point on the tool path is defined as a function of the θ; thus, the planned penetration and retraction trajectories in internal cylindrical thread helical milling with the m are derived; finally, the proper eccentricity parameter m is decided to improve the machining accuracy of thread by exploring the influence of the m on the interference error. Taking the experimental of milling, an M20 × 1.5 thread using a φ8 × 1.5 cutter as one of the examples that indicate the maximum interference error of the planning method (m = 0.4) can be reduced by 30.93%, compared with the original trajectory, and can dramatically improve the precision of internal cylindrical thread helical milling.