Experimental Measurement of NC Machine Tool Milling Cutting Forces

Experimental measurement of the cutting forces in milling processes can be a useful tool to validate standard and non-conventional milling models to be adopted in most industrial applications. As an example, such models can be used to design the machine tool components and fixtures, to choose the technological process parameters and to define process monitoring and diagnostic tools such as monitoring of tool wear and surface quality, diagnosis of critical cutting conditions. With respect to the latter case, high speed machining may exhibit self-excited chattering vibrations, which can be hard to predict using conventional theoretical cutting models. In this paper an experimental technique for cutting force measurement estimate is proposed. A system composed of a mechanical fixture with 4 piezoelectric tri-axial force transducers was designed, to be installed on the machine tool working table. During the milling operation on a workpiece mounted on this fixture, the 12 signals from transducers may be used to estimate the cutting force resultant. A filtering technique is proposed here to reduce error in cutting force experimental measurement estimation. Details of this technique are given, and some application examples are discussed by means of a numerical simulation in the frequency domain. An experimental application on an instrumented 3-axis laboratory machine tool is then illustrated and discussed in detail. NOMENCLATURE (bold) array notation ( ) transpose operator ( ) 1 − matrix inversion operator ( ) ( ) , ⋅ ⋅ ⋅ first and second time derivative operator , ⋅ × scalar (dot) and vector (cross) product { } , , T x y z v v v = v column vector of Cartesian global components { } ' ' , ' , ' T x y z v v v = v column vector of Cartesian local components ( ) ~ vector operator: ~ 0 0 0 x z y