A study of fiducial aided calibration and positioning for precision manufacture of freeform surfaces

Precision manufacturing of freeform surfaces requires accurate positioning of workpiece on the machine tool and measurement instrument with high repeatability during the manufacturing cycle. However, the geometric complexity of ultra-precision freeform surfaces brings considerable challenges in precisely localizing the workpiece for different processes including the machining process and the measurement process. This paper presents a study of a Fiducial Aided Calibration and Positioning (FACP) method to achieve better accuracy and efficiency in manufacturing of the ultra-precision freeform surfaces. The FACP method makes use of fiducials to purposely design high precision fiducial fixtures to form a Fiducialaided Computer Aided Design (FA-CAD) of the freeform workpiece which not only calibrates the geometric error of the volume of the machine tool where machining is undertaken but also establishes an intrinsic reference datum of the workpiece for precise location on the machine tool and the measuring instrument so as to link the machining and the measurement process for form characterization and compensation of the form errors of the workpiece. Some preliminary experiments are conducted to realize the capability of the method.