FREQUENCY AND TIME-DOMAIN ANALYSES OF SENSOR SIGNALS IN DRILLING .1. CORRELATION WITH DRILL WEAR

Results of an investigation on a multisensor approach to drill wear mo nitoring are reported. Four sensors, namely, thrust, torque, and strai ns in two orthogonal directions of the machine table, were used in thi s study. A strategy involving the use of a combination of accelerated testing at high cutting speed to obtain different states of;drill wear and testing at the recommended speed to obtain data pertinent to conv entional drilling conditions was adopted. The wear on the outer corner of the drill bit was used as the performance index. The sensor signal s were investigated in both the time and frequency domains. In the tim e domain, no significant difference was observed between the signals f or a sharp drill and a worn drill, and the correlation between the sen sor signals and drill wear was found to be rather poor. Consequently, the power spectral densities of the sensor signals were calculated to obtain information in the frequency domain. The power spectral densiti es of thrust, torque, and strain in the X-direction showed good correl ation with drill wear.