Contact Stiffness Determination of High-Speed Double-Locking Toolholder-Spindle Joint based on a Macro-Micro Scale Hybrid Method

The stiffness of toolholder-spindle joint at high speeds plays an important role in the cutting efficiency and the machining accuracy. A double-locking toolholder (BTF type) is designed to improve the stiffness of joint. This paper presents a macro-micro scale hybrid method to determine the stiffness of double-locking toolholder-spindle joint at high speeds. In this method the finite element method and the three-dimensional fractal method are combined. It is assumed flat in macro-scale for the contact surfaces of joint. The finite element method is introduced to obtain the pressure distribution with the influence of centrifugal force at high speeds. In micro-scale, the contact surfaces are fractal featured and the three-dimensional fractal method is used to compute the stiffness based on the pressure. Experiments with BTF40-type toolholder are conducted to verify the efficiency of the proposed model in zero-speed case. The relationship between the stiffness and the technological parameters of the system can be derived based on the presented model. The upper limit of speed, the optimized range of each technological parameter are determined for obtaining the higher stiffness of joint. The results can provide theoretical basis for improving the cutting efficiency and the machining accuracy of high-speed machine tool.