Study on the Structural Design and Dynamic Performance of a Bottom-Hole Self-Renewal PDC Drill Bit

Progressive wear of the cutting structure degrades the performance of polycrystalline diamond compact (PDC) drill bits during deep and ultradeep drilling. Current designs primarily delay wear through improved material wear resistance and structural optimization, but provide limited capability for active downhole restoration after wear. This study proposes a rotary self-renewing PDC drill bit driven by drilling-fluid pressure through a worm gear transmission. The design allows active renewal of the cutting structure downhole. The overall bit structure was developed around four modules for pressure actuation, motion conversion and transmission, cutting-structure renewal, and position limiting. Kinematic and dynamic models were established to assess the required driving force and transmission characteristics. Computational fluid dynamics (CFD) simulations were used to evaluate the effect of piston clearance on pressure transmission, and Adams simulations were used to examine the motion and dynamic response of the mechanism. The total resisting torque of the renewal modules, including transmission resistance, was 3.84 N·m, corresponding to a theoretical driving force of approximately 115 N. In the Adams simulation, the renewal modules began moving at 120 N, a deviation of 4.3% from the theoretical value. A proof-of-concept prototype was then tested to verify the renewal function. At a water pressure of 0.8 MPa, the piston traveled 67 mm and rotated the renewal modules by approximately 114°, achieving one cutting-structure renewal. The results indicate that the proposed mechanism can use drilling-fluid pressure to achieve stable adjustment of the cutting structure. This design provides a structural approach to active downhole renewal of worn PDC cutting structures.