An experimental technique to detect tool–workpiece contact in micromilling

There is a need for simple, accurate, and low-cost techniques to detect tool–workpiece contact (or tool touch-off) in micromilling operations. This paper presents a method that is based on monitoring changes in the power spectral characteristics of the spindle vibration signal. The accuracy of this contact detection method is evaluated under different conditions by measuring the overshoot of the tool into the workpiece surface. Specifically, the effects of tool geometry, workpiece surface roughness and hardness, tool wear, step size, and contact detection threshold on the overshoot are analyzed through experiments carried out on a 3-axis micromilling machine. The results show that the method is capable of sub-micron contact detection accuracy depending on the workpiece hardness, roughness, and contact detection threshold.