Abstract
In order to estimate dynamic stiffness of a spindle on a machining center, a method based on the natural frequency of a single-degree-of-freedom vibration system attached to the spindle was developed. Concerning the radial direction, a straight bar was fixed at the spindle of the machine, and the bar was excited by an impulse hammer in radial direction, and the natural frequency of bending motion of the bar was measured. Then the stiffness of the fixed end of the bar was calculated by using the frequency. Concerning the axial direction, the spindle with an additional mass and without the mass were also excited by the impulse hammer in axial direction, and the natural frequencies of the axial vibration of the spindle were measured. Then the axial stiffness of the spindle was calculated by using the weight of the additional mass and the frequencies. The end milling tests were also carried out on the machines, and the surface roughness of the workpiece was compared to the stiffness of the machine.
