High Frequency Correction of Dynamometer for Cutting Force Observation in Milling

Piezoelectric dynamometers are widely used for cutting force measurements. Indeed, this device has the largest bandwidth for this kind of measurement. Nevertheless, the behavior of this device is not very well-known and its use is sometimes inappropriate for static and high frequency dynamic measurements. In this paper, a piezoelectric dynamometer is used for cutting force measurements in a milling case. Cutting forces in milling are discontinuous by nature due to successive inward and outward movements of tool-teeth on the workpiece. As a result, a bandwidth criterion based on cutting parameters is defined in order to permit clear observation of the mean oscillation of the cutting force. The frequency response of a dynamometer is then analyzed over a wide frequency range. A 2 kHz bandwidth can be defined for an efficient correction of cutting force. The dynamometer appears to be exploitable for higher frequencies up to at least 16 kHz though a large number of factors must be taken into account in the analysis. Finally, several lateral milling tests are performed by changing cutting speed, feed rate, and lubricant conditions. The correction of measurements permits highlighting certain particularities in the cutting force signals, such as the effect of shock of inward tool-teeth strokes on the workpiece, the specific behavior for outward tool-teeth strokes, and the effect of a lubricant on the variation in cutting forces.