Milling force monitoring with thin-film sensors integrated into fixtures

Cutting force measurement is a crucial task aimed at improving process performance, since the cutting force contains important information about the condition of the process, such as tool condition and vibration. In the machining process of aircraft structural parts, the cutting force becomes a key factor which influences the qualified rate of product due to the low rigidity of aircraft structural parts. In order to monitor the cutting force, a novel force-sensing element integrated into the fixture system for aircraft structural parts machining is proposed. Accordingly, a cutting force measuring model of a force-sensing fixture system consisting of a set of the force-sensing elements is developed, enabling the estimations of not only overall cutting forces but also dynamic contact forces caused by the cutting forces at different locating/clamping points. To validate the effectiveness of the force-sensing element, a series of milling tests are conducted under both up and down milling with different cutting parameters, and the measured cutting forces are compared with a commercial dynamometer. Then, a series of analyses is carried out, and from the results, a satisfactory agreement with the forces measured by the dynamometer is achieved. Moreover, the median errors of the average resultant force are less than 6% compared with the dynamometer.