Summary Almost all previous cutter-force models assumed that cutting force was proportional to cutting area. Cutting-area-based single-cutter-force models were extensively used in polycrystalline-diamond-compact (PDC) -bit design optimization. This paper explains why cutting-area-based bit models failed to predict bit forces. A new cutter force model and a new bit model were developed and are discussed in the paper. In the new cutter force model, cutting force is a function of the shape of the cutting area. A common force model is developed for three types of cutting shapes. In the new bit model, 3D rock chips created in front of cutting face are modeled, meshed, and removed from the hole bottom by updating the hole bottom at each timestep. To validate the new model, four different PDC bits were designed, manufactured, and laboratory-tested under controlled conditions. Details from laboratory testing and field-test results are presented.

Almost all previous cutter force models assumed that cutting force was proportional to cutting area. Cutting-area-based single cutter force models have been extensively used in polycrystalline diamond compact (PDC) bit design optimization. This paper explains why cutting-area-based bit models failed to predict bit forces. A new cutter force model and a new bit model have been developed and are discussed in the paper. In the new cutter force model, cutting force is a function of the shape of the cutting area. Three types of cutting shapes are respectively modeled. In the new bit model, three-dimensional (3D) rock chips created in front of cutting face are modeled, meshed, and removed from the hole bottom by updating the hole bottom at each time step. To validate the new model, six different PDC bits were designed, manufactured, lab tested under controlled conditions, and field tested. Details from laboratory testing and field-test results are presented.