Experimental Investigation into Mixed Tool Cutting of Granite with Stinger PDC Cutters and Conventional PDC Cutters

The Stinger PDC cutter has superior impact resistance, wear resistance, and rock-breaking efficiency compared to the conventional PDC cutter. Thus, hybrid PDC bits that combine conventional and Stinger PDC cutters have significant advantages in drilling hard, interbedded, and highly abrasive rocks. Although the hybrid PDC bit has demonstrated outstanding performance in improving the rate of penetration and prolonging the life of PDC bits, the arrangement of mixed cutters still awaits a thorough understanding and optimization. In this research, 14 groups of mixed cutting granite experiments were carried out with the Stinger and conventional PDC cutters. The influences of the cutting sequence, spacing, and depth difference of mixed cutters on the cutting force, broken rock volume, and mechanical specific energy (MSE) were compared and analyzed. The results show that the Stinger PDC cutter followed by the conventional PDC cutter can provide a higher rock-breaking efficiency. Additionally, the total rock breaking efficiency increases with the increase of cutter depth difference for single-track cutting. For multi-track cutting, the cutting force and mechanical specific energy (MSE) first decreases and then increases with an increase in the Stinger PDC cutter spacing. The optimal Stinger PDC cutter spacing is 18 mm for the tested granite. With the increase of cutter depth difference, the rock broken volume gradually increases, the cutting force and MSE first decrease and then rise rapidly. The optimal cutter depth difference is 0.5 mm. The characteristics of the cracks around the cutting groove of the Stinger PDC cutter were observed by optical microscope and the experimental results were further explained from the point of cracks and damage. This work explains the mixed cutting mechanism and provides experimental and theoretical guidance for the design of hybrid PDC bits.