Drill Bit Self-oscillation in Cutting

The paper analyzes the dynamics of drilling done with twist drill bits, and its dependency on the feed rate and rotation speed of the cutter. The analysis enables us to find the fundamental rules of how to control metal machining process systems. Depending on what such control might be needed for, study results could be used to make such control algorithms that help achieve and maintain the required drilling system quality. The analysis has revealed the regions of various tool motion types in the plane of cutting parameters (drill bit feed rate and rotation speed). We have found out that in a dynamic drilling system, the tool has three regions of motion: stable motion, unstable motion, and self-oscillatory motion. By choosing such cutter feed rate and rotation frequency values that belong to this or that region, one can control the drilling process parameters. High quality of machined hole surfaces is ensured as long as the feed rate and the rotation frequency are in the region of stable motion. Both values being in the region of self-oscillatory motion results in the fragmentation of chips, which makes the entire process more efficient for preparatory operations. Of course, the entire drilling process becomes more reliable as long as the feed rate and the rotation speed of the drill bit do not go to the unstable motion region. For more complete results, drilling dynamics analysis was complemented with analytical methodology and computer simulation.