Design and Comparison of Dual-Purpose Stator Windings for Active Chatter Suppression in Milling Spindles

The effect of chatter is one of the main obstacles to increasing metal removal rates in modern high-speed cutting (HSC). Active damping approaches using electromagnetic actuators have gained popularity in recent years but none of them found significant industrial usage. One of the major drawbacks of the existing solutions is the missing geometrical and electrical integration which inevitably leads to a lengthening of the milling spindle inherently with lower rigidity values or a loss of power. In this paper, we aim for an approach without additional actuators. By using the concept of a bearingless motor to apply the damping forces onto the rotor, we achieve a fully geometrical and electrical integrated design. In addition, the implementation of a so-called dual-purpose or combined winding allows us to freely shift the total spindle power between torque and force generation which can lead to better-dimensioned spindle motors. The main premise is to keep high industrial proximity so that no geometrical changes are to be made to the motor, but the force generation is achieved solely by rewinding the stator. The chatter damping function shall always just be an extension of the drive function so that the new machine is never worse than the original one. After a pre-study, the two most promising dual-purpose windings—dual-purpose no-voltage and multiphase—are compared against the conventional separated windings design. The main evaluation criteria are a torque characteristic equivalent to the original motor and high radial forces with a low ripple for all rotor positions. The simulations are carried out as 2D finite element simulations at an uncontrolled machine. Many references between the separated and dual-purpose winding designs can be drawn. A multiphase approach with twelve phases in total works best with minimal changes to the original winding, an identical torque, and excellent force characteristics and leads to the commission of a prototype.