Embedded Force Sensing at the Cutter

Cutting and friction forces have been widely studied for PDC bits. Rock/bit interaction models are currently verified with a single cutter experiment and the utilization of multi-axis load cells. This paper aims to demonstrate an innovative method that experimentally validates the embedded cutter sensing on a laboratory scaled-drill bit to measure the forces acting on a single cutter. A unique two-cutter drill bit design allows the integration of a sensor measuring the applied force on a cutter while drilling. A fully instrumented mini-rig is a key criterion to recreate the drilling environment. Control of the system and data analysis are performed while drilling, allowing continuous assessment of the drilled formations. Experiments are performed with new and worn cutters to independently evaluate the cutting and frictional components of the total measured force and compare them to the literature models. The high-frequency measurements at the cutter downscale the understanding that industry has on the bit-rock interaction and bring it to the cutter scale. The effective cutting area changes dynamically depending on the position of the cutters in three dimensions and axial speed. The architecture of the mini-rig control system allows accurate control of depth of cut and interactive graphs of the acquired data. The cutter sensing enables spatial monitoring distribution of the cutting forces over the face of the scaled-drill bit. Cutter/rock interaction models are validated with the acquired data from the cutter force sensing, enabling the evaluation of drilling efficiency while drilling different layers of rocks. Each cutter contributes to the weight-on-bit and torque-on-bit; thus, force sensing on a single cutter allows comprehensive performance evaluation for known drill bit design. The study of new and worn cutters provides insightful information on the drilling process in the cutter scale. In perspective, cutter force sensing might enable monitoring the wear evolution of individual cutters, which is impossible to detect with existing at-the-bit sensors. The present work assesses the potential of integrating a force sensor at the cutter. The development of this work built the foundation for up-scaling research on cutter force monitoring.