Displacement-based dynamometer for milling force measurement

This project will study the design and testing of a low-cost dynamometer for milling dynamic force measurement. The monolithic design is based on constrained-motion/flexure-based kinematics, where force is inferred from displacement measured using a low-cost optical interrupter (i.e., a knife edge that partially interrupts the light beam in an emitter-detector pair). The time-dependent displacement of the dynamometer’s moving platform caused by the milling force is converted to the frequency domain, multiplied by the inverse of the dynamometer’s ideally single degree of freedom (SDOF) frequency response function (FRF), and converted back into the time-domain to obtain the time-dependent cutting force. The basic science to be examined is the process dynamics and vibration behavior of the innovative dynamometer design and the ability to measure dynamic cutting forces by applying a structural deconvolution technique. A vibration transducer with high resolution, signal-to-noise ratio, and linearity is therefore able to accurately deconvolve dynamic forces from the measured displacement using the dynamometer’s FRF. This dynamometer will enable accurate and repeatable static and dynamic force measurement for milling operations; however, this approach can be extended to turning, grinding, and drilling as well. A SDOF constrained-motion dynamometer will be designed, manufactured, and evaluated against a commercially available, piezoelectric dynamometer system to validate the displacement-based cutting force approach. A milling process model will be implemented through the solution of second-order, time-delay differential equations of motion that describe the milling behavior [1]. Experiments will be performed to identify the critical stability limit for the various dynamometer systems and mechanistic cutting force coefficients

The sensor selection, monolithic constrained-motion design, and companion structural deconvolution technique will provide an innovative, low-cost, high fidelity cutting force dynamometer for use in both production and research environments This approach offers the potential for reduced uncertainty cutting force measurement and significant advancement of metrology for machining operations including the in-process assessment of tool wear and the corresponding machining process health.