Compact core drilling in basalt rock using PCD tool inserts: Wear characteristics and cutting forces

The hardest component of the Martian surface is believed to be basalt rock, which is highly abrasive in nature. It will be important to operate a Martian drill under conditions that are conducive to minimal tool wear. In preparation for a Mars drilling project, this paper reports results of an experimental study of dry drilling in basalt and related tool wear. It also reports the effect of the tool wear on increasing the forces and torques required when drilling in basalt rock (on earth) using polycrystalline diamond (PCD) compact core drill inserts. Force and torque data measured for a variety of cutting conditions are shown along with experimental wear data obtained while drilling in basalt rock having different strengths. It is found that flank wear, VB, and cutting edge radius, CER, wear rates increase with rock strength, VB-wear rates and CER-wear rates exhibit opposite trends in their dependence on the remainder of the cutting parameters. For example, while VB-wear rates decrease with an increase in tool feed and spindle speed values, CER-wear rates increase with increases in tool feed and remains unchanged with increases in spindle speed. VB-wear rates decrease as the rake angle becomes more negative, while CER-wear rates increase as this occurs. It is found that basalt rock strength manifests itself via larger (smaller) generated forces/torques for rocks of harder (softer) composition. Strong correlations are found between both modes of tool wear (VB and CER) and the measured values of thrust force and torque. Equations for progressive tool wear as functions of the process variables are developed. A model for the changing drill forces and torques required by the progressive tool wear is developed for drilling in basalt.