Conventional machining of complex parts having three-dimensional curved surfaces is performed in two steps using a five-axis machining center and a grinding machine. There is a problem with productivity. Therefore, we developed a CNC lathe to cope with high-speed machining. The newly developed CNC lathe has four axes (X1, X2, Z, C). In this machining, the tool on the X axis follows the curved surface synchronously with the rotation angle of the spindle. This cutting method enables machining of the three-dimensional curved surface. By adopting a linear motor for the X axis, high-speed reciprocal motion of the tool is realized, and the machining time has been reduced to approximately 1/30, as compared with the conventional milling process. In this operation, since high-response motion is required for the tool positioning, a certain profile error remains even if repeated control is applied using the linear scale.
In the present study, for the purpose of improving the contour accuracy of a three-dimensional curved surface, we report the result of compensation between the profile measurement method of workpiece and the desired profile accuracy. After machining a three-dimensional curved surface by the developed CNC lathe, a line laser displacement sensor is used to measure the workpiece profile on the machine without removing the workpiece. The position of the machining program is measured by synchronizing the controller of the CNC lathe and the line laser displacement gauge. In addition, the desired profile accuracy is improved by compensating for the error between the desired profile accuracy and the measurement result.