Voltage- and Current-Measurement Based Force Estimation in Broaching Using Synchronous Motor Drive

Abstract

Monitoring the cutting force in broaching provides valuable information about the tool condition as well as the effect of the process on the workpiece surface integrity. This study uses a synchronous-motor-drive broaching machine and deals with the motor-current based indirect-measurement of the cutting force, which is based on detecting the variation of the motor torque during cutting. Most current-based methods need to model the relationship between the motor current and the cutting force. However, when the feed drive mechanism is modeled to obtain this relationship, modeling errors occur. For accurate modeling, a calibration test using a force sensor is necessary before performing the indirect-force measurement. Therefore, this study focuses on the energy conversion from electrical power to mechanical power, and it identifies this relationship based on the voltage equation of the drive motor by using not only current measurement but also voltage measurement. Then, a developed model with the identified relationship calculates the cutting force, excluding electrical and mechanical losses that do not contribute to the process. By conducting a tool-wear test in broaching of Inconel 718, a possible application of the indirect force measurement system was demonstrated.

Keywords: process monitoring; indirect-force measurement; broaching; tool-wear