Rock Breaking Mechanism of Saddle PDC Cutters and Analysis of Mixed Cutter Layouts

The surface geometry of polycrystalline diamond compact (PDC) cutters has a considerable influence on their rock-cutting mechanism. In the study reported here, to study the mechanism for rock crushing by saddle PDC cutters, two-dimensional and three-dimensional finite-element models of such cutters cutting granite were established. The two-dimensional simulation results were used to analyze the crack generation and expansion forms when a saddle PDC cutter cuts rock, and the results show that it mainly crushes the rock via joint tensile and shear action. Next, the wear resistance and cutting performance of saddle PDC cutters were analyzed by simulation and experiment, and both were better than those of conventional PDC cutters. The residual stresses on the surface of a notch cut by a saddle PDC cutter were extracted from the 3D model, and it is concluded that they are mainly compressive stresses. Cutting models for mixed arrangements of saddle and conventional PDC cutters were established, and analyses were conducted of how the cutting-depth difference between the front and rear cutters in the same-track cutting scheme and the spacing of the front cutters in the different-track cutting scheme affect the cutting force of the rear cutters, the mechanical specific energy, and the cutting stability. The results show that for the same-track cutting scheme, the optimum cutting depth difference between the front and rear cutters is 0.1–0.2 mm, and for the different-track cutting scheme, the optimum spacing between the front cutters is 17 mm. Finally, the characteristics of the cutting damage areas of different types of PDC cutters are discussed. The present results help in revealing the rock-breaking mechanism of saddle PDC cutters and provide theoretical support for designing hybrid PDC bits.