Tool Condition Monitoring of Turning Inserts Using an Eddy Current Sensor

Manufacturing industry is becoming increasingly automated, which causes demands to improve tool condition monitoring. Especially automated machining processes require rigorous tool condition monitoring due to rapid tool wear and high cost of machine downtime. The present study investigated wear measurement for turning operations by utilizing a custom eddy current sensor design. Typically, eddy current sensors are used in high accuracy applications such as displacement measurement and nondestructive testing. However, the present study demonstrates an application of these sensors to tool wear measurement. The sensor used in this study was an air-cored coil wound to shape resembling a L-letter. 3 turning inserts were measured with the sensor. The inserts had different wear states: no wear, cutting edge chipping, and cutting edge fracture. The wear measurement were performed on a CNC-lathe. An impedance analyzer was used to record the sensor impedance response. Inserts with different wear states had significant differences in the impedance responses, which progressively decreased as the wear increased. The impedance response decrease caused by wear was interpreted to have three potential causes: increased distance between the sensor and insert, increased surface irregularity, and wear on the coating of the insert. The results suggest that the presented eddy current sensor could be used for condition monitoring in turning applications. It should be noted however that the sample size in this study is small. Hence, the results should be further validated for example by investigating wear measurements on different types of inserts and other applications.