The stiffness of the spindle assembly of machine tools in general and also CNC machines in particular is an important criteria to evaluate the quality of machining. The initial stiffness of the spindle assembly is due to pre-load. During operating, the spindle assembly is wear under the influence of external loads including cutting force and speed. It reduces the stiffness of the spindle assembly, as well as decreasing machining accuracy. This study presents the results of various stiffness of the spindle assembly under external loads in laboratory conditions. Based on the relationship between the stiffness and the amount of axial wear of the spindle assembly according to the working time, as well as the permissible stiffness limit to predict remaining time, reliability and time of adjusting the pre-load to maintain stability and machining accuracy.
Keyword
Spindle unit of CNC machine, Stiffness of CNC machine tool spindle, wear of bearing, longevity, reliability
