Structural optimization of eccentric fastening screws for small-sized indexable milling tools through finite element analysis

The clamping safety problem of indexable milling tools, consisted by the tool body, the cutter and the fastening screws, has been widely observed in the field of milling operations. For a class of small-sized indexable milling tools, the eccentric fastening screw is easy to loosen under cyclic milling forces due to its compact dimensions. In this work, the dynamic behavior of eccentric fastening screws during preloading and the loosening behavior during milling processes are investigated by the finite element analysis. The structure of the eccentric fastening screw is optimized to enhance its clamping reliability, in which three structural parameters, including the eccentric distance, the eccentric angle, and the pitch diameter, are included. Firstly, through the finite element analysis of the physical model, the relationship between the rotation angle of the eccentric fastening screw and the clamping force is established. A suitable preload is determined according to the distributions of the elastic strain, the plastic strain and the surface contact. Then, a simplified physical model is built, in which the repetitive simulation of preloading processes can be avoided with improved computing efficiency, while high accuracies can be maintained. It is found that the considered structural parameters make unpredictable influences on the loosening behavior of eccentric fastening screws. Optimal combinations of structural parameters are obtained by the joint optimization. According to milling experiments, the clamping force is decreased only by 4.107% of the initial preload for the milling length up to 60 m, indicating good anti-loosening performances after the structural optimization of eccentric fastening screws.