Abstract: Off-axis aspheric mirrors are the key components in a high-resolution, large field-of-view space camera, and are very hard to machine due to extremely strict requirements on shape accuracy and surface quality. Therefore it is a bottleneck of the advanced optical manufacturing technology. Computer-aided NC programming techniques for mirror blanks with large-diameter, high-steepness, large-deviation, and large off-axis-amount are developed. An oblique five-axis processing method with a decenter spiral tool path is proposed to avoid the residual shape error in the geometric center of mirror blank. Based on a five-axis ultrasonic vibration-assisted machining center, a 900 mm×660 mm diameter off-axis aspheric SiC mirror blank is successfully machined, obtaining a surface accuracy of 18.8 μm peak to valley (PV), and 3.5 μm root mean square (RMS). Effective and precision machining technologies in accordance with the equation of the off-axis aspherical mirrors with huge scale-precision ratio are provided.

Key words: CAD/CAM, Off-axis asphere, Precision grinding, SiC mirror, Tool path optimization, Ultrasonic-vibration assisted machining