DYNAMICS OF SPINDLE-BEARING SYSTEMS AT HIGH SPEEDS INCLUDING CUTTING LOAD EFFECTS

Increased use of high speed machining creates the need to predict spin dle-bearing performance at high speeds. Previous spindle-bearing model s simplify either spindle or bearing dynamics to the extent of prohibi ting a detailed analysis of a spindle with high speed motion. At high speeds, centrifugal loading in the bearing causes stiffness softening, creating a change in natural frequency. Therefore, spindle modeling r equires a comprehensive representation of the dynamics of shafts with complex geometry rotating at high speeds and supported by non-linear b earings. This paper presents a coupled system of spindle and bearing d ynamic models with numerical solution. Spindle dynamics are modeled us ing the influence coefficient method of discrete lumped masses, based on Timoshenko beam theory. Both linens and rotational bearing stiffnes s are included in the spindle model through solution of the angular-co ntact bearing model. The parameters of cutting loads, tool mass, and r otational speed are analyzed, and all are shown to affect the natural frequency. The computer model is both rapid and robust, and shows exce llent agreement with experimental analysis.