Dynamic analysis of disc spring effects on the contact pressure of the collet—spindle interface in a high-speed spindle system

Abstract

In a high-speed gas spindle, the drawbar force required to hold the drill bit is produced by the deformation of disc spring stacks. This drawbar force, applied to the collet—spindle interface, generates a contact pressure on the collet to hold the drill bit in position. Thus, the behaviour of the collet—spindle interface is critical to machining quality. Accordingly, this study investigated how disc spring characteristics affect the collet—spindle interface in a high-speed spindle. Typi-cally, the drawbar force will decrease following the deformation of disc springs resulting from the effects of centrifugal force at high rotational speeds. This effect must be considered, especially in high-speed spindle applications. This study first measured the drawbar force experimentally and compared these results with theoretical and finite-element analysis (FEA) data under static conditions (i.e. no rotation). Having obtained satisfactory agreement among these data, the FEA was extended to a further investigation. Properties of the collet—spindle contact interface were analysed, given changes in rotational speed from 0 to 300 000 r/min under various disc spring deflections, various friction coefficients between the disc springs and their support, and distinct taper angles at the collet—spindle interface. All of these conditions are discussed here. These essential parameters are believed to cover much of the design of high-speed gas spindle systems.