Dynamic Disturbances in BTA Deep-Hole Drilling: Modelling Chatter and Spiralling as Regenerative Effects

Abstract

The BTA deep-hole drilling process is a process that very often is one of the final steps in the production of expensive workpieces. For example axial bores in turbines or compressor shafts are produced with this process. A serious problem in deep-hole drilling is the formation of dynamic disturbances that may be subdivided into the most common disturbance types chatter and spiralling. Chatter shows in self-excited rotational vibrations which lead to an increased tool-wear while spiralling is governed by bending vibrations and causes holes with several lobes. Since such lobes are a severe impairment of the bore hole the formation of spiralling has to be prevented. One common explanation for the occurrence of spiralling is the intersection of time varying bending eigenfrequencies with multiples of the tool’s rotational frequency. Little is known about which specific eigenfrequencies are crucial. Furthermore an underlying assumption of this explanation is, that the resulting holes in cross-sectional view are appearing as a curve with constant width. This assumption implies that spiralling results from a parallel displacement of the drill head. We disprove this assumption and show a way how stability charts for the classification between stable and unstable processes can be computed by means of simulations. These simulations result from statistical–physical models which model the disturbances chatter and spiralling as regenerative effects.