Theoretical And Experimental Research On The Measurement Of Grinding Subsurface Damages For Optical Materials

Subsurface damages produced in grinding process will influence operational life, secular stability, imaging quality, coating quality, and laser-induced damage threshold of optical elements. Thus accurate measurement of the subsurface damage depth is the precondition in determining the removal amount of material in subsequent processes and optimizing grinding parameters in order to improve the machining quality. In this paper, production mechanism of subsurface damage of optical materials in grinding process was summarized. On the basis of the production mechanism, subsurface damage depth of ground K9 glass was measured by HF differential etch rate method, taper polishing method and magnetorhelolgical polishing spot method. Furthermore, a nondestructive and rapid survey of subsurface damage depth was achieved by researching on the proportional relationship between the subsurface damage depth and surface roughness. The main work and achievements are as follows:1. The mechanical properties of optical materials and the production mechanism of subsurface damage in grinding process are summarized, which provide theoretical basis for the subsurface damage measurement.2. Based on the traditional Constancy of HF chemical etch rate method, a HF differential etch rate method is presented using relative etch rate and differential principle. With the improved method subsurface damage depth can be measured in a more accurate way.3. A preliminary real-time measurement is developed on the basis of the HF differential etch rate method. The new method has tremendous potential in improving measurement efficiency.4. The taper polishing method is improved to measure the subsurface damage depth of ground K9 glass. Besides, the magnetorhelolgical polishing spot method is applied to increase measurement accuracy.5. A model for median cracks depth is improved, on the basis of which a model for the correlation between subsurface damage and surface roughness is also amended. Then, a prediction method of subsurface damage depth is constructed by process parameters and surface quality, consequently, a nondestructive and rapid survey of subsurface damage depth can be achieved.