Influence of Thermal Behavior of Spindle on Machining Accuracy in Micro-endmilling

This paper describes on the influence of thermal behavior of spindle on machining accuracy in micro-endmilling. In order to make clear the reasons why the depth of slot varies during slotting repeated, temperatures around the spindle head and the thermal expansion of spindle axis were investigated. The machine tool used for experiment was a small type of vertical machining center. The spindle used for experiment was a ball bearing spindle which rotated at 10000-40000 min(-1) The spindle head made of aluminum alloy had various cooling systems for spindle motor and ball bearings, and the temperature of spindle head changed only a few degrees C. Therefore it seems difficult to assume that the primary cause was thermal deformation of spindle head structure, even though the coefficient of thermal expansion of aluminum alloy is approximately twice of that of steel. Finally the thermal expansion of spindle axis was partly measured and relation between the thermal expansion and the variation of depth of slots was investigated. The main results obtained are as follows, (1) Slotting after a long period warming-up of spindle resulted in a small change of depth of slot, but slotting without any warming-up caused an initial rapid increase and then saturation of depth of slot, (2) Temperature rise of spindle head and adjacent structure seemed out of relation to the variation of depth of slot, (3) The partially measured thermal expansion of spindle as well as temperature of lower flange of spindle showed qualitatively similar change corresponding to depth of slot.