In-process monitoring of tool wear in small-diameter end-milling using an image photographing system

摘要

Because tool wear, tool deflection and cutting heat are the significant factors influencing machining accuracy, monitoring, and measurement and evaluation techniques, they are exceedingly important in a machining process. To monitor tool wear, methods based on changes in the measurement of cutting force and on indirect estimation of acoustic emission signals have been used, but direct measurement is considered relatively easy for the quantitative evaluation of wear and the analysis of measurement data. This study describes a system that uses images obtained using a charge-coupled device (CCD) camera in a machining process to recognize the state of the tools on a machining center and enable the measurement of tool wear. The proposed system consists of two CCD cameras, an image processing device, and a machining center with an open computer numerical control. The monitoring technique of tool deflection is based on the analysis of the tool projection image obtained using the CCD camera, as shown in our previous study. In this experiment, tool wear in end-milling was measured based on the projection image and actual image obtained using two CCD cameras without removal of the tool from a machine tool spindle. Slotting was conducted on a steel plate using a small-diameter tool under certain cutting conditions; changes in tool wear were obtained during processing. Moreover, the relation between tool wear and tool deflection in cutting was examined. As a result, the measurement of the cutting edge based on CCD image in a machining process enabled this system to monitor the tool wear. In addition, a correlation was demonstrated between the measured tool wear and tool deflection.