A Model for Bending, Torsional, and Axial Vibrations of Micro- and Macro-Drills Including Actual Drill Geometry—Part II: Model Validation and Application

Abstract

In Part II of this work, an experimental study is conducted to validate the three-dimensional (3D-ST) drill dynamics model. Modal experiments on macro- and micro-drills are performed by exciting the drills with small piezoelectric elements directly attached to the drill body. The response measurements are conducted in a noncontact manner using a laser Doppler vibrometer system. In addition, to perform the comparison on a complete frequency response function, rather than on only natural frequencies and mode shapes, an impact hammer test with a miniature hammer and a small accelerometer was conducted on one of the macro-drills. In the validation study, five macro-drills and three micro-drills with different geometric parameters are used. It was concluded that the 3D-ST model can capture both bending and torsional-axial natural frequencies and mode shapes of macro-drills (up to 15 kHz) and micro-drills (up to 90 kHz) with better than 4.5% accuracy, and with an average absolute error of 1.5%. For each case, the natural frequencies are also compared with those from detailed solid-element finite-elements (FEs) model to gain further insight about the 3D-ST model. The natural frequencies from the FE and 3D-ST models are seen to match with better than 1.5% accuracy. Subsequently, the effects of tool geometry (diameter, aspect ratio, helix angle, and web-taper) and axial (thrust) force on dynamics of macro- and micro-drills are analyzed.