Ultra-precision raster grinding of monocrystalline silicon biconical free-form optics using arc-shaped diamond grinding wheels

Free-form optics are becoming increasingly indispensible in a series of industries, such as aviation, aerospace, medical, digital video and audio optoelectronics, owing to its enhanced optical performance, fewer surfaces, lower mass, lower cost, smaller package-size and reduced stray-light, etc. However, the ultra-precision machining of free-form surface optics, especially the non-rotational asymmetric free-form optics is still faces a great challenge. In this study, ultra-precision grinding of the non-rotational asymmetric biconical free-form optics with raster grinding path was studied. Firstly, a novel feeding compensation truing strategy for truing the arc-shape grinding wheels with high-precision was proposed. A D46 μm metal-bonded grinding wheel and a D7μm resin-bonded diamond wheel, were successfully trued with high profile accuracy and desired surface topography. Subsequently, the influence of the significant grinding factors like grinding path, scallop height, contact arc length and the grinding wheel wear on the ground profile accuracy and surface quality of the biconical free-form optics was theoretically and and experimentally analyzed. Eventually, a larger size monocrystalline silicon biconical free-form optics with profile accuracy 6.0 μm and nanometer surface roughness was successfully manufactured by raster grinding combined the technology introduced in this paper.