Development of a micro/meso-tool clamp using a shape memory alloy for applications in micro-spindle units

Abstract

In developing micro-spindle units, a critical problem is miniaturization of the tool clamp. Approaches for scaling down conventional tool clamps, such as the collet-chuck, hydraulic chuck, and shrink-fit methods may be limited by their inherently complicated mechanisms. This study developed a novel tool clamp based on shape memory alloy (SMA), which allows further miniaturization. The tool clamp can be simplified by using an SMA ring, which is all that is needed for clamping. The SMA-based tool clamp does not require any collet, and its structural configuration is axisymmetric. Furthermore, the SMA makes it possible to switch between the clamped and unclamped states by using a simple device to regulate small changes in temperature. This paper first describes the operating principle of the SMA-based tool clamp. Second, it presents the finite element method (FEM) analyses that were conducted to investigate the characteristics of the clamping/unclamping operations and the effect of centrifugal force. Third, it describes a prototype of the SMA-based tool clamp, which was designed and built for applications in micro-spindle units. Fourth, it presents an evaluation of the time needed for the clamping/unclamping operations and the tool-clamping force, which were both evaluated experimentally. Finally, it describes a mill-machining test conducted with the prototype, which confirmed that the tool clamp is little affected by centrifugal force at high rotational speeds. The experimental results confirm that the proposed SMA-based tool clamp can be successfully applied to micro-machining.