Process Monitoring with a Force Sensitive Axis-slide for Machine Tools

Previous publications regarding the project “Gentelligent Components for Machine Tools” presented the design of a new sensory z-slide for a 5-axis machining center. Equipped with several strain sensors, the new slide is able to “feel” the machining process by measuring the process forces and vibrations. Here, a challenge is the detection of mechanical strains in the slide without degrading its high global stiffness. The application of micro strain gauges in small notches on the slide represents a promising approach for the improvement of the sensitivity as well as the integration of sensors into the slide. This paper presents the utilization of the sensing axis-slide in a manufacturing environment. For this purpose, a first prototype of the slide is integrated into a milling center DMG HSC 55 linear. In this test machine, the dynamic characteristics of the integrated slide are identified with frequency response function measurements. Based on force measurements with a dynamometer, force calibration matrices are computed to calculate the forces at the tool center point from the measured strain signals during milling processes. The force sensing with the slide allows furthermore the identification of tool characteristics such as the static tool stiffness. This parameter is estimated from the ratio of the measured contact forces and the set colliding distance when moving the tool smoothly into the work piece. The known tool stiffness enables the detection of the static tool deflection from the force signals during a milling process. In order to compare the detected tool deflection with the real tool deflection, reference measurements on the work piece are performed using a perthometer.