Ultra-precision machining of Fresnel lens mould by single-point diamond turning based on axis B rotation

To promote the machining precision of Fresnel lens mould, a true circle processing method with a single-point diamond turning (SPDT) was proposed. In this method, the arc-curved surface of Fresnel lens mould grooves was processed with axis B rotation, and the frequent servo feed of each axis in the processing with traditional interpolation method was avoided. Moreover, the distribution of the arc-curved surface of the Fresnel lens mould was analyzed. All the centers of the arc-curved surfaces were distributed on the lens axle. The method was realized to process the Fresnel lens mould by combing the processing performance of a four-axis ultra-precision machine tool using axis Z to aid movement and axis B rotation. The straight blade of the tool was replaced by a circular curve by optimizing a single-point diamond tool shape according to the Fresnel lens mould characteristic to reduce the cutting force of the tip of the main cutting edge. Machining experiment on the Fresnel lens mould was studied. A mould with the diameter of 46 mm and curvature radius of 90 mm was processed. Surface of the Fresnel lens was measured using a scanning white-light interferometer. The mould surface roughness was Ra 7.3 nm. The grooves of the lens mould were sharp, and the mould teeth were accordant. Experimental results showed that the machining precision by the proposed Fresnel lens mould with the true circle turning method was high.