Chatter stability of boring bars incorporating fine particle dampers: effects of particle diameter and filling ratio on the maximum chatter-free length–diameter ratio

Abstract Deep-hole boring requires a small shank diameter relative to the bore and a long overhang, which reduces boring-bar stiffness and often induces chatter, degrading surface roughness and tool life. Previous studies on boring bars incorporating particle dampers (PDs) have mainly examined relatively coarse particles. In the fine-particle regime, the effects of particle diameter and filling ratio on chatter stability in high- L / D (length–diameter ratio) boring have not yet been systematically clarified. To clarify these effects, PD boring bars were fabricated by drilling a blind hole in the rear end of a solid steel boring bar (shank diameter, 16 mm) and filling it with zirconia particles of nominal diameters 0.05, 0.10, 0.20, or 0.40 mm at prescribed filling ratios. Cutting tests were conducted, and the maximum chatter-free L / D was determined from machined surface observations. At a filling ratio of 58%, the maximum chatter-free L / D increased with decreasing particle diameter, reaching 7 for 0.05 mm particles, while solid steel and solid carbide boring bars of the same shank diameter yielded 4 and 5, respectively. For 0.05-mm particles, chatter-free cutting at L / D = 7 was achieved at filling ratios of 58% or higher while maintaining a non-compacted particle state. These results suggest a practical starting guideline under the investigated conditions: 0.05-mm-class particles with a filling ratio of at least 58%, while maintaining a non-compacted state. The feasibility of implementing this guideline via in-process powder encapsulation by laser powder bed fusion is also discussed.