Low-frequency vibration-assisted gun drilling for surface damage regulation mechanisms in the ultra-deep hole of high-strength steel

High-strength steel possesses high strength and hardness, which makes it prone to generating significant thermal stresses and cutting forces during deep-hole gun drilling. This can lead to surface damage on the hole wall and rapid tool failure. However, research on the regulation of surface damage in ultra-deep hole machining of high-strength steel materials under the constraint of gun drills with weak rigidity has rarely been reported, resulting in a lack of clarity in this field. To address this, this paper proposes a low-frequency vibration-assisted gun drilling (LFVGD) method. This study conducted experiments on LFVGD, elucidating the influence mechanisms of process parameters on surface roughness and residual stress fields, as well as the tool wear behavior. The results indicate that LFVGD can reduce the hole wall surface roughness by 30 % compared to conventional drilling (CD). An excessive feed rate of 40 mm/min in LFVGD will induce a coupling effect between vibration-dynamics instability and material nonlinear response, resulting in undesirable fibrous textures on the hole wall. It is recommended to use a low feed rate (≤30 mm/min) and high rotational speed (＞1200 rev/min) to reduce the surface roughness of the hole wall. LFVGD can reduce the residual stress on the hole wall surface by 40 % compared to CD. Residual compressive stress with layer-depth exhibits approximately “uniform decay” under a high feed rate of 40 mm/min, whereas under a low feed rate of 10 mm/min, it shows a dual-stage “steep drop-gradual release” characteristic, with residual stress attenuating faster. The findings provide insights into surface damage regulation mechanisms of LFVGD for ultra-deep hole manufacturing.