Investigation of Boring Bar Mode Shape Rotation by Experimental Modal Analysis in Correlation with Finite Element Modeling

摘要

Productivity degrading vibration problems are traditional in metal cutting, in particular in internal turning, when the boring bar is long and slender. The high levels of vibrations arise at the boring bar's natural frequencies corresponding to its fundamental bending modes. The vibrations are dominating at the boring bar's eigenfrequency in the cutting speed direction, since the cutting force has the largest component in this direction. The negative effects of vibrations, e.g. poor surface finish, reduced tool life, high sound pressure levels in the working environment etc., can be eliminated for instance by using passive tuned damper or active control. The level of success implementing any of these methods is dependent on the knowledge of the dynamic properties of tooling structure - the interface between the cutting tool or insert and the machine tool - involved. Results from experimental modal analysis on the boring bar clamped in a lathe reveal a rotation of the mode shapes with respect to the cutting speed and cutting depth direction. The paper addresses boring bar mode shape rotation phenomenon and discusses its possible sources based on results obtained from experimental modal analysis of two systems: boring bar with original boundary conditions and boring bar with linearized boundary conditions in correlation with results obtained from corresponding 3-D finite element models.