Experimental study of impregnated diamond bit part 2: Effect of the bit wear state on the drilling response

Impregnated diamond bits are widely used in hard rock drilling due to their robust structure and self-sharpening nature. In the companion study, we showed how the depth of cut and the rock properties (Mohs hardness) control the dominant wear mechanisms and proposed a method to select operating parameters that balance productivity with bit wear. This sequel paper develops quantitative relationships between the bit wear state and the drilling response — that is, the relationship between the bit kinematics (feed rate and angular velocity) and the forces acting on the bit (axial thrust and torque). These relations yield a relation between the performance (feed rate) and the energy or power required to achieve the performance, which is essential to improve drilling efficiency. These relations provide also the framework to analyse drilling data in real time to assess the bit state of wear and identify optimum drilling parameters. A laboratory experimental methodology was developed to (i) measure the bit wear state and (ii) construct the drilling response. Controlled drilling experiments were conducted on a high-precision rig using three sizes of impregnated diamond tools across a wide range of wear states, characterized by diamond wear flats, matrix wear flats, and average diamond protrusion. Bit wear was measured before and after each test using an optical microscope. Experiments were performed under varying operating conditions, including different rock types, drilling fluids, flow rates, and rotation speeds. • Simplified the bit’s cutting face geometry into three measurable lengths. • Developed an experimental workflow to track drill bit wear and drilling responses. • Established quantitative relationships between bit wear state and drilling responses. • Diamond protrusion controls three-body contact between the bit, rock, and cuttings. • Proposed a workflow to track bit wear state using real-time drilling responses.