Development of variable preload system for machine tool spindle using giant magnetostrictive material Terfenol-D actuator

Applying a bearing preload of machine tool spindle produces positive effects, including increased stiffness, rotation noise reduction, increase in shaft precision, position adjustment during operation, and prevention of rolling element resonance and rotating slip, along with a significant extension of the bearing lifespan. A variable preload technique is a method that improves the bearing performance by appropriately varying the preload applied to the bearing according to the spindle rotation speed and machining condition. In this study, a novel variable preload method utilizing a Terfenol-D actuator has greater power and more displacement and force than those of other transducer materials such as piezo elements or nickel alloys. Terfenol-D has greater power and more displacement and more force. A prototype of a spindle for the variable preload system using Terfenol-D was fabricated, and the axial force and displacement of the bearing were measured during a running experiment. In order to assess whether the proposed variable preload device can effectively apply preloading to the bearing, a comparative analysis was conducted between the theoretical and empirically obtained values of the bearing axial direction displacement. Through the comparative analysis, the real applicability of the proposed structure was confirmed.