Development of contact detection method between tool cutting edge and workpiece (Influence of contact state onto vibration characteristics and contact detection during milling operation)

Abstract

The contact between a tool and workpiece during machining has a significant effect on the vibration characteristics of machine tools. This study proposes a method for detecting contact between a tool and workpiece, and demonstrates applications of the detection. To detect the contact between the tool and workpiece, this study used the change in the contact electrical resistance in a metal-to-metal contact corresponding to the true contact area. The contact resistance between the tool and workpiece was connected in series with a buffer resistance, and the degree of separation was defined based on the change in the ratio of a voltage applied to the circuit under a constant current flow. Two types of applications were demonstrated in this study; one was an analysis of the influences of the contact state on the vibration characteristics, and the other was contact detection during milling operations. In the first demonstration, a contacting ratio was defined based on the contact time per unit time and degree of separation based on the tool-workpiece contact as detected during an excitation test, and the relationship between the contacting ratio and vibration characteristics was examined. It was confirmed that the natural frequency increases significantly when the contacting ratio exceeds 90%, and that the damping characteristics increase significantly when the contacting ratio is in the range of 0–10%. For the second demonstration, a milling test using a face mill with the same detection circuit confirmed that the system could detect contact during intermittent cutting and the changes in contact conditions associated with the occurrence of chattering vibration. It is expected that the developed method can be used to monitor machining conditions.