Abstract: Aiming at the rock-breaking problems of drill bits and characteristics of bottom hole model, a new type of drill bit that breaks rock with rotary-cutting motion was proposed. Based on the structure and the kinematics principles of rotary-cutting drill bit, its dynamics was analyzed, and the vibration displacement and speed of the cutter on different gear rings were obtained by establishing the vibration equation of the cutters. After that, rock-breaking properties of the rotary-cutting drill bit were researched. On the basis of an analysis model for the rock-breaking characteristics of the cutters on different gear rings, the cutters impact force, shear force and rock-breaking volume were obtained and compared. The results showed that compared with the existing drilling technology, the rotary-cutting drill bit breaks rock with shock and shear together and the largest gear ring through the center, which can improve the rock-breaking efficiency of the drill bit center effectively; the bottom hole model is tornado-like which can make all gear rings cut the wall and achieve bit gauge function in the rock-breaking process. At the same time, the analysis model can also be used for other types of bits like composite drill bits by changing corresponding parameters.

Key words: drill bit, drilling, rotary cutting, vibration, rock breaking, rate of penetration