The effect of spindle dynamics on tool-tip radial throw in micromachining

Abstract

In this work, we present a model to predict the speed-dependent radial throw at the tool-tip during micromachining with ultra-high-speed (UHS) spindles. This speed-dependent nature of the radial throw arises from the interaction between the quasi-static radial throw (tool attachment errors, tool geometric errors, and spindle error motions) and the dynamic response of the tool-collet-spindle system. The radial throw causes the cutting edge trajectory to deviate from the ideal trajectory, critically affecting the attainable dimensional accuracy and surface quality, as well as the micromachining forces. Hence, accurate determination of radial throw at the micro-tool tip is important for both practical applications and process-modeling efforts. In the current work, the proposed model describes the radial throw of the tool-axis as a dynamic response to excitation from rotating unbalance of the spindle assembly. The model parameters are first calibrated using experimentally obtained spindle dynamics and the radial throw measurements, both at two speeds. The calibrated model is then used to predict the radial throw for any spindle speed. The presented model is used to predict radial throw at two different axial locations (microtool's shaft at 2 mm and its tool-tip at 15 mm). For both the axial locations, the spindle dynamics measured at 2 mm is used for model calibration. The average error is observed to be less than 2.4% at the tool-tip (15 mm). It is concluded that the speed-dependent spindle dynamics can be used in an analytical formulation to determine tool-tip radial throw at any speed.

Topics & Concepts