Radial Throw at the Cutting Edges of Micro-Tools When Using Ultra-High-Speed Micromachining Spindles

摘要

In this paper, we present an approach to determine the trajectory of the cutting edges of a micro-tool in the presence of radial throw when using ultra-high-speed (UHS) micromachining spindles. When micro tools are rotated, inaccuracies and dynamic response of the tool-collet-spindle assembly cause the microtool axis to displace radially from the average axis of rotation. This displacement is referred to as the radial throw of the axis of rotation. Unlike runout, which defines the total radial displacement of a surface within one cycle of rotation, radial throw depends on the angle of rotation (and thus, the time). The radial throw reflected at each culling edge causes the cutting edge trajectory to vary from the ideal trajectory, which is a circle with a diameter equal to the tool diameter. As such, the radial throw at the cutting edges critically affects the attainable dimensional accuracy and surface quality, as well as the micromachining forces. For this reason, accurate determination of effective radial throw of micro-tools is important for practical applications and process-modeling efforts. This paper devises an approach for accurate measurement of radial throw at the cutting edges of micro-tools when using UHS spindles. The approach involves (1) a mathematical framework to determine the trajectory of the cutting edges from measurements of the radial throw at two locations on the tool shank, and (2) an experimental method, based on non-contact displacement measurements, for simultaneous radial throw measurements on the tool shank at two mutually-perpendicular radial directions. The approach is experimentally validated by comparing the predicted and measured radial throw at the tool tip using a micro-tool blank rotated on an UHS spindle at 120,000 rpm. The results indicate that the deviations between the predicted and measured radial throw magnitude and orientation are less than 1% and 0.1 deg., respectively. Subsequently, the validated approach is used to determine tool-tip radial throw of a commercially-available micro-endmill rotated on the same spindle at different spindle speeds. It is concluded that the presented approach provides an effective means for accurate determination of the speed-dependent radial throw at the cutting edges of micro tools towards enhancing the process performance.