Kinematic Model for Ultrasonic-Assisted Manufacturing of Bore Holes with Undefined Cutting Edges

Abstract

Hybrid machining represents a possibility for technological progress in production. As a part of hybrid machining processes, ultrasonic-assisted machining is often used to manufacture materials that are difficult to machine since process forces can be significantly reduced and the material removal rate (MRR) can be increased. This paper describes an approach for a model for ultrasonic-assisted drilling with undefined cutting edges. The ultrasonic vibration can theoretically be applied in axial, tangential or radial direction or it can be superimposed. An axial excitation, parallel to the feed direction, is selected in the presented model. Since the drilling is superimposed with a high-frequency vibration, the trajectories of the grains are modified. Therefore, an analytical-kinematic model is established, which is characterised by a periodical contact loss of tool and workpiece. Due to the modified kinematics, process-specific parameters, such as impact velocity or the ratio between vibration and cutting speed, are important, in addition to conventional cutting parameters. Such process parameters are useful to describe dominant material removal mechanisms in ultrasonic-assisted machining. Moreover, two models on tool topography are presented in this paper. Based on an analytical approach, the material removal rate, established by adding up the individual grain removals, is calculated. The quality of the developed models is validated by the standard calculation of the material removal rate by feed rate and tool cross section. The results show, that it must be taken into account that the grains do not hit an even surface. The grain distribution is also an important aspect.