Position Dependent FRF Identification without Force Measurement in Milling Process

Abstract

Frequency Response Functions (FRF) are one of the most useful methods of representation of machine-tool dynamics under force excitation. FRFs are usually obtained empirically through output measurements and force excitations are controlled by an external device such as hammers or shakers. This study offers an operational identification method which utilizes calculation of force applied during the process as an input for FRF identification. Force excitation is provided through face milling of a thin walled workpiece and acceleration measurements are taken during the process. FRF is calculated at a designated position by sampling workpiece-cutting tool contacts as individual tap tests and substituting a force calculation as input. Force coefficients need to be known for the force calculation. An experimental force coefficient identification method is proposed. In that case, a similar thin walled workpiece at a point with known FRF and acceleration measurements are utilized. Results are confirmed with FRF obtained in the same location for both identification of FRF and identification of force coefficients approaches.