Optimization and application of unequally spaced milling cutters

Abstract

Milling, the most efficient material removal process, is an interrupted cutting operation whose high power is concentrated at a few discrete frequencies (tooth impact harmonics). The following presentation focuses on the dynamics of the cutting process as a primary source of vibration. The behavior of multitooth cutters is first reconstructed from the individual force pulse and continuous spectrum of one single tooth. This procedure is readily extended to unequally spaced cutters which break the regular rhythm of successive cuts and randomize the excitation by spreading its energy over more frequencies (spindle speed harmonics). The analysis leads to the frequency response function of the cutter. Properties of such cutter signatures are discussed (periodicity, symmetry, influence of tooth number, sensitivity to out-of-roundness errors, etc.). Optimization criteria, strategies, and procedures are then derived and evaluated. The presentation concludes with potential applications of unequally spaced cutters. The most promising one, besides reduction of forced and self-excited vibrations, is testing of operating milling machines with cepstral and/or spectral averaging methods in order to validate model data obtained by artificial excitation at standstill.