Examination of surface location error due to phasing of cutter vibrations

The purpose of this research is to investigate the relative importance of s pindle speed, system dynamics, and cutting conditions on the accuracy of su rface location in computer numerical-control (CNC) finish machining operati ons. The relationship between the spindle speed, the most flexible modes of the machine/cutting tool system and the final part dimensions is rather co mplex. The underlying theory, based on the situation of forced vibrations, is outlined. It is shown that the critical factor is the ratio of the tooth passing frequency to the system most flexible mode and corresponding natur al frequency. Simple analytical calculations are carried out to illustrate the overcut/undercut surface error phenomenon. A simple simulation for end milling operations is also described which calculates the force on the cutt er, the resulting cutter deflection, and the final error of surface. A comp arison between the simulated and experimental results is presented. From ex perimental data, it shown that a change in surface location land part dimen sion) of up to 50 mu m is seen for a set of given conditions (i.e., cutter, material, chip load) simply by changing spindle speeds. Furthermore, it is seen that certain spindle speeds produce surfaces with no error introduced by the machining process. (C) 1999 Elsevier Science Inc. All rights reserv ed.