The effects of structural and servo modes in titanium machining

This paper shows that in titanium machining the metal removal rate may be limited by factors including the dynamic characteristics of the frame of the machine and the servo. Self-excited vibrations related to these components led to poor cutting performance and tool breakage. Measurements of the acceleration were made during a number of cuts. In combination with impact tests, these measurements were used to identify the natural frequencies and mode shapes associated with the structural modes. These measurements ultimately led to adjustment of parameters in the control loop (to modify the servo dynamics), to special tool selection (to disturb the regeneration), and to the choice of stable cutting speeds (to take advantage of the stability lobes). The resulting cutting conditions significantly improved the metal removal rate. The nature of current titanium machining makes the structural modes particularly problematic, and it is important to measure and consider them during process planning.