Search

(1) 切込みや逃げ面接触長さを変化させることにより, 切屑, 被削材, 工具への切削熱の流入割合を求めることができた.(2) 切削熱の切屑への流入割合は, 切削速度の上昇とともに増加し, 被削材, 工具へは減少していく.(3) 高速切削になるにつれて, 逃げ面での摩擦による発熱は無視できなくなる.

A method to identify a mathematical model which represents the relationship between thermal displacement and temperature on a machine for compensation of the displacement has been proposed. The model uses moving averaged time series data of temperatures to reduce the measuring points and to keep the good agreement between actual and estimated displacement even for a wide range conditions. The parameters in this model are determined by data of the displacement and the temperatures obtained from six operating conditions of a machine. The new mathematical model can estimate that thermal displacement over 50μm within 2μm accuracy by 14 points of temperature measured. more...

Based on the fact that conventional cutting can not avoid the circularity error which is caused by cutting a deformed workpiece held by three-jaw power chuck, this paper describes three methods to compensate the circularity error using an NC lathe with the tool post driven by PZT to trace the surface of the deformed workpiece so that the resultant cut geometry becomes an ideal one after unclamping. The developed methods can realize a constant depth of cut for the deformed workpiece, during cutting by using the prediction by FEM and/or the measured data of circularity. The predicted data are accurate enough to use as the control input to drive the tool post and the results obtained by using developed apparatus showed the improvement of roundness up to 80% with respect to the component of the three undulations per revolution. more...

A hybrid bearing is proposed for high speed machine tool spindle. The bearing composed of two angular contact ball bearings in a series arrangement and has a middle race between double column rolling elements besides the inner and outer race. The third race rotates with keeping a balance of the inner and outer bearing's friction. The spindle rotates at the speed of the sum of the inner and outer bearing's speed. The friction torque of the proposed bearing is less than a conventional bearing's one. But the simulation showed that the bearing has an effective speed range due to the retainer speed and the centrifugal force of the balls. At the critical speed, the friction torque of the bearing coincides with a conventional bearing's one. The critical speed can be rised by use of ceramics balls or small steel balls and an optimum lubricant system. A preliminary experiment of the proposed bearing showed that the final temperature rise of outer race is three degrees C only at 10000 rpm. The experimental critical spindle speed was about 8000 rpm against theoretical 17500 rpm. more...

An effective method has been proposed to evaluate the thermal deformation of an NC machine tool. This method uses a touch probe and a master block, as well as a mathematical model of thermal deformation derived based on the finite element method. Thermal displacement between the spindle and the table is measured for three directional components in Y-Z plane of the machine along the Z axis movement. Then, by determining the parameters in the mathematical model so that the measured thermal deformation fits the corresponding value of the model, each deformation of the head and the column as well as its change due to relative position is clarified. Experiments have been carried out by rotating the main spindle of a machining center without cutting to verify the effectiveness of the method. more...

Based on the idea that the dynamic performance of a machine-tool should be evaluated in terms of its machining accuracy, a new test method is proposed which uses the machined surface as a measure of performance evaluation. The cross sectional profile of the machined test piece surface is measured in the direction orthogonal to feed direction, and nine different indexes which characterize the profile are extracted. These indexes are then checked based on the concept of SN ratio to select "straightness error of the profile" as the best one. Finally eight different machining centers are tested by using the performance index thus determined to confirm the validity of the method. more...

Based on the fact that the major sources of the machining error in end milling operation are the deflection of the machine-tool structure including tool holder, end mill, and their connecting parts, the relation between these deflections and the machining error is formulated. According to this formulation, the instantaneous cutting force can be calculated by using an oblique cutting model and then the machining error and its individual error components can be analyzed. The results obtained are as follows: Cutting force calculated by using an oblique cutting model is close to the measured value. Machining error and its components can be predicted qualitatively and quantitatively for various cutting conditions. Error component due to the end mill deflection decreases when the cutting point approaches to the holder-end side. Deformation of the jointed part at the end mill-holder connection can not be neglected, and varies depending on the tool holder used. more...