A new machining strategy for roughing deep pockets of magnesium-rare earth alloys

Plunge milling is an efficient machining process for roughing deep pockets. Its efficiency is mainly due to low radial forces on the cutter. This leads to reduced bendings and vibrations that allow one to improve cutting parameter values. The machining time can then be reduced with respect to machining processes with constant Z-level. Recently, another machining process has been introduced, called ”balancing of the transversal cutting force” (BotTCF), that is also characterized by a suitable distribution of forces on the cutter. It has been applied only to finishing operations on complex surfaces. In this paper, we present two main contributions. First, we extend the BotTCF concept to roughing open deep pockets and semi-open pockets opened from side to side. This is mainly based on successive parallel ramping trajectories, defined by an optimal angle which ensures a good balancing of the transversal cutting forces. This can be applied to 3-axis and 5-axis computer numerical control (CNC) machine tools. Second, we propose a new, hybrid methodology for roughing semi-open pockets (not opened from side to side) and closed pockets. It is based on the combination of ramping trajectories with BotTCF and plunge milling. The proposed methodology is developed for three-axis machining and can be extended to five-axis machining. Based on an identical criterion (identical maximum force acting on the cutters), we perform a fair machining-time comparison of plunge milling with the proposed hybrid method applied on a closed deep pocket: a simplified aeronautical housing made of magnesium-rare earth alloy. Results show a significant gain in machining time when the hybrid method is applied.