Conventional machining of complex parts having three-dimensional curved surfaces is done by two processes using a five-axis machining center and a grinding machine. Although these tools make it possible to machine a product with complicated profiles, the tool path is complex and the process is time consuming. Also, because the amount of movement accompanying the control of the tool position increases, the productivity decreases. Therefore, we developed a CNC lathe for high-speed and high-efficiency machining in a previous study. The NC positioning table on which the tool is mounted is synchronized with the rotation angle of the main spindle; thus, the developed CNC lathe can form a three-dimensional curved surface on a workpiece. However, the previous study did not evaluate the surface profile of a product created with the developed CNC lathe.

In this study, for the purpose of improving the contour accuracy of the machined workpiece, we propose a method for on-machine measurement and compensated machine tool position using the measurement result. The proposed on-machine measurement method is a non-contact method that employs a line laser displacement sensor. In the proposed method, the workpiece attached to the spindle of the CNC lathe is moved to a sensor reference position and measured. The measurement position is recorded in the NC machining program; thus, it is possible to adjust the tool position during machining to reduce the machining error by feeding the measurement results back to the machining program. Because machining is started in a state offset from the machining origin, the compensated machining can deal with both overcutting and undercutting of the workpiece. Testing of the proposed compensated method confirmed improvement in the desired profile accuracy.

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