A Study on The Effect of Rotational Dynamic Characteristics of a Machine Tool Spindle Drive on Milling Processes

Abstract

A milling operation is inherently an intermittent material removal process where cutter engagement and disengagement is repeated until the end of the material removal process. During the process, the cutter receives multiple impacts and mechanical and thermal vibrations which eventually damage the cutting edge. The optimum rigidity and damping of the spindle motor for the least tool damage highly depends on the cutter and workpiece material properties and the cutting application. This paper introduces the concept of flexible rotational rigidity control using a high performance Permanent Magnet Synchronous Motor (PMSM) which is used as a direct spindle drive. With the PMSM spindle, the spindle rotational characteristics can be adjusted for optimizing the cutting process in order to prevent tools from unwanted premature damage. Simulation models of the spindle motor drive system are presented, which show that a very stiff spindle can be realized by fully utilizing the potential capability of the PMSM and a spindle with the same dynamic properties of a conventionally used induction motor can be realized with a single PMSM spindle. The system prototype and feasibility studies are also presented in this paper. The experimental results show that the PMSM spindle characteristics behave differently depending on the controller setting, and the spindle motor drive system rotational characteristics greatly affect the cutting process, which confirms the importance of the flexible motor control concept.