Development of SMA-based tool clamping device and its applications

Generally the traditional tool-clamping devices in small-sized spindle system use taper collets. However, since the collets lead to further stack-up tolerance, the accuracy of rotating runout is decreased and due to additional components such as collet nuts and springs the structure of spindle rotor becomes complicated. In this paper, a tool-clamping mechanism based on shape memory effect is proposed to simplify structures of a tool-clamping part. Thus, the structure of the developed tool-clamping device is just the tool holder where a ring-type shape memory alloy(SMA) is inserted with a specific amount of interference. In principle, tool-clamping force results from the recovery stress caused by the SMA ring. Especially, in order to transform from clamping state to unclamping state, the mechanism using the inherent elastic force of the tool holder instead of employing the SMA exhibiting the two-way shape memory effect is introduced. Also, considering the fact that the proposed tool clamping device can alternate between clamping and unclamping through temperature control, available cooling/heating methods are suggested in practice. According to the methods respective responses for clamping/unclamping operation were investigated experimentally. Finally, the prototype of the small-sized spindle system equipped with the SMA-based tool clamping device was demonstrated. Considering effect of the centrifugal force, it is confirmed that the spindle system is capable of speed up to 300,000 rpm under clamping a tool securely.