Wear law and design of assembling diamond bit based on finite element analysis

In addition to coring drilling, full (non-coring) drilling also occupies a large proportion in the energy exploration and development. Non-coring drilling can reduce the high time cost of lifting and lowering work required for coring, thereby increasing the net drilling time, improving the drilling efficiency and reducing the drilling costs. The traditional non-coring drill bits are prone to uneven wear on the bit surface during the drilling process. To identify and improve this law of uneven wear, it was herein proposed to use the assembling non-coring bit to improve the eccentric wear of bit. For this reason, numerical simulation analysis was conducted on the drilling of granite with a combination of stage-1 and stage-2 non-coring impregnated diamond bits at first. The simulation results show that the stress and wear on the bit are decreased gradually from the outer edge to the center. Definitely, the stress and wear of bit matrix have the maximal value on the outer edge of the bit close to the water outlet, which are 282.14 MPa and 1.1×10⁻⁵ mm respectively, while the minimum value near the center of the drill bit, which are 0.002 MPa and 1.3×10⁻⁶ mm, respectively. When the radius of the bit lip is 55 mm, the bit wear speed changes. Then, a two-stage assembling non-coring drill bit was designed based on the numerical simulation results, consisting of an outer ring drill bit, a center drill bit, and a waterway system. The outer ring drill bit is in the size of ø95/48 mm, the center drill bit is sized ø46/16 mm, and the waterway system consists of a center hole, 4 main waterways, 4 auxiliary waterways and an annular gap waterway. Meanwhile, the bit matrix formula, diamond parameters and sintering process were designed based on the common drillability of 7‒8 grade rocks. To improve the wear resistance of the outer ring bit matrix, the diamond concentration, the proportion of small diamond particles, the sintering temperature and the sintering pressure were increased to a certain degree, thereby reducing the wear of the outer bit and ensuring the wearing consistency between the outer and inner bits. Besides, laboratory drilling test was carried out on the granite of grade-8 drillability with the designed ø75/16 mm two-stage assembling non-coring bit. The experiment results indicate that the bit is worn evenly, the rate of penetration is about 1.84 m/h, and the matrix consumption height is about 1 mm, which can meet the needs of full drilling in hard rocks. Generally, this research provides reference for the design, development and construction of non-coring impregnated diamond bit.