Abstract: High-frequency impact drilling speed-up theories and its tools have rapid developed in recent year, and effectively solve the problem of the stick-slip, rebound and vibration of PDC (polycrystalline diamond compact) bit in complex wellbore. However, the failure of PDC teeth under impacting load remains serious. For this reason, a new type of drill bit combining of separated impact and cutting is proposed, this drill bit can effectively solve the adverse effect of impact load on the service life of PDC teeth. The rock breaking of the drill bit is totally different from that of traditional percussion tools, and the mechanism of the rock breaking is unclear, it is thus urgent to perform relevant study. Based on the new type of drill bit combining of separated impact and cutting, the rock breaking experiments under different combinations of unit tooth impact, cutting and their different combinations are carried out, and the corresponding numerical analysis is carried out. The results show that the rock with significant impact pit is damaged by the shock wave after the impact tooth loading, consequently, reducing the strength of the rock around impact pit. As a result, it also effectively reduces the cutting force of the cutting teeth during cutting, and increases the crushing volume. At the same time, based on the orthogonal experiment, the parameter sensitivity analysis is carried out considering the impact speed, the impact angle and the offset distance between the impact pit and the cutting tooth. The results show that the impact speed has the greatest influence on the cutting force of the cutting tooth. The above research reveals the mechanism of rock breaking under combining of separated impact and cutting and the best combination of impact tooth and cutting tooth. The present work has important reference value for the design and research of impact drilling tools.

Key words: percussion drilling, rock breaking mechanism, impacting-cutting combining, experimental study, numerical analysis