Experimental Study On Machinability And Grinding Of Aspheric Lens

With the development of technology, optical aspheric parts are widely used ingovernmental military equipments and commercial optoelectronics for theirunparalleled excellent optical properties. As infrared detection and manufacturing turninto important techniques of modern warfare day by day, the manufacturing andmachining of infrared aspheric parts with high optical properties has become researchhotspots. Monocrystalline silicon and ZnS are commonly used in infrared window andcowling, besides they are brittle materials with largely different hardness. In order toobtain high-precision optical aspheric lens, the machinability of silicon and ZnS are firststudied by indentation and scratch test in this paper. And then high efficiency andaccuracy machining of silicon and ZnS are achieved by ultra-precision grindingtechnology.First micro/nano indentation on silicon and ZnS are performed and the values ofhardness, fracture toughness and critical cutting depth etc are determined, providingdata reference for grinding. Then the stress-strain model is established according toload-displacement obtained in nano-indentation. The simulation of indentation revealsthe internal residual stress changes of loading/unloading duration and studies the effectsof load and indenter shape on internal residual stress, further explaining the micro-indentation morphology. Next in order to investigate the scratch topography andsubsurface integrity, single-point scratch test and simulation are accomplished and thesubsurface damage is studied by taper polishing-etching method. The results obtainedby SEM demonstrate the possibility of ZnS to achieve stable grinding and the non-uniform dislocations are the main subsurface damage.Based on the results of machinability analysis, the effecting trends of grindingdepth, spindle speed and feeding rate on the grinding force, surface roughness andaccuracy are investigated by orthogonal experiment of ZnS. What’s more, theoptimization of these three factors is done to determine the best combination of facegrinding process parameters. The above results provide the parameters evidence forcross axis aspheric grinding.Finally the convex aspheric grinding of silicon and concave aspheric grinding ofZnS are performed on an ultra-precision aspheric grinding machine using the bestcombination of grinding parameters. By analyzing the surface formation mechanism ofgrinding workpieces, it can be concluded that the cross axis grinding precision of ZnS ispoor and the forms of surface damage are diverse. While the grinding precision ofsilicon is better and the surface damage is micro-chipping.