Application of the S-curve algorithm to modify drill bit movement speed on Gundrill machines

This paper presents a third-order jerk-limited S-curve feed strategy implemented through G-code modification for Gundrill machining. A customized G-code converter was developed to generate the corresponding feedrate and displacement commands and was experimentally implemented on an industrial MIROKU MEG-600 Gundrill machine using a D8 × 800 mm carbide drill (CHUNG JIN) and a C45 steel workpiece. Two S-curve feed-transition strategies were investigated and compared with conventional G-code under the same machining conditions. The vibration measurements showed that the S-curve strategies generally produced lower vibration amplitudes than conventional G-code, with the most pronounced reduction occurring in the 0–30 Hz frequency range. Surface-roughness measurements further showed that the first S-curve strategy achieved Ra = 1.1096 µm, Rz = 7.0540 µm, and Rt = 9.6292 µm, compared with Ra = 2.2915 µm, Rz = 14.8393 µm, and Rt = 22.9306 µm for conventional G-code, corresponding to reductions of approximately 51.6%, 52.5%, and 58.0%, respectively. The second S-curve strategy also improved the overall surface roughness. These results demonstrate that S-curve-based feed modulation can reduce measured vibration and improve bore-surface quality under the investigated machining conditions. The reduction in vibration also decrease dynamic loading on the long and slender Gundrill, lowering the risk of drill breakage during machining. The proposed approach provides a practical G-code-based method that can be implemented without modifying the internal CNC controller.