Stiffness optimization for high-speed double-locking toolholder-spindle joint using fractal theory

The higher contact stiffness of the double-locking toolholder-spindle (BTF40-type) joint is helpful in improving the machining accuracy and cutting stability of high-speed machining center. In this article, an optimization technique is introduced to obtain the high contact stiffness of BTF40 toolholder-spindle joint at the high speed. The torsional and radial stiffness at 25,000r/min can be obtained by using the macro-micro hybrid method. The contact ratio of taper surface and maximum nodal pressure of contact surfaces is used as constraint conditions to ensure the connection reliability and the working life of the toolholder-spindle system. The particle swarm optimization algorithm with suitable parameters for this problem is used to search the optimal stiffness of joint automatically. The optimal stiffness of joint and pressure distribution of taper surface are compared with the initial values for validating the effectiveness of the optimization results. This research is valuable for guiding the application of BTF-type toolholder-spindle system at the high speed 25,000r/min.