Research On Fixed Abrasive Polishing Of ZnS Crystal

With the rapid development of infrared technology, zinc sulfide crystals are widely used in infrared imaging, infrared guidance, infrared countermeasure and other technical fields. Due to the soft and brittle properties of zinc sulfide, surface defects such as scratches, micro cracks are easily generated in machining process, which affect performance and service life of device. In this paper,fixed abrasive polishing technology was adopted to polish zinc sulfide crystals, material removal mechanism and process parameters was studied. results are as follows.(1) Material removal mechanism of zinc sulfide crystal was studied, and cutting depth model of single abrasive was established. The hardness of zinc sulfide crystal was 1.83 GPa by micro indentation method, and theory critical cutting depth is 1.17 μm by classical critical depth formula.Single abrasive scratch test found that actual critical depth is 211.5 nm and critical load is 5.69 mN.The cutting depth model of single abrasive shows that cutting depth is proportional to radius of abrasive, and 2/3 time of pressure.(2) The optimization experiment of fixed abrasive pad was carried out. Effect of abrasive type,abrasive size, matrix type on fixed abrasive polishing of zinc sulfide crystal was studied. The experimental results show that material removal rate and surface quality by diamond polishing pad are superior to that of cerium oxide polishing pad. The optimal surface quality is obtained by diamond polishing pad with size 2-4 μm, and material removal rate is high. There is no obvious scratch and pit defects on crystal surface by A type matrix, and surface quality is excellent. The optimal parameters is diamond abrasive, size 2-4 μm, A type matrix.(3) The effect of acid and alkaline slurry on fixed abrasive polishing of zinc sulfide crystal was studied. Material removal rate is very low by alkaline slurry polishing, which is far less than that of acidic slurry. Citric acid slurry is the most suitable for the fixed abrasive polishing of zinc sulfide crystal with material removal rate 437 nm/min, surface roughness Sa 4.22 nm.(4) The process parameters of fixed abrasive polishing of zinc sulfide crystal were optimized by orthogonal experiment. Effects of rotational speed, pressure, pH value and concentration of hydrogen peroxide on fixed abrasive polishing of zinc sulfide crystals were studied. Comprehensive consideration of surface roughness and material removal rate, the optimum polishing parameters is rotate speed 80 r/min, polishing pressure 20 kPa, pH 4, and hydrogen peroxide 0.5%. Material removal rate is 391 nm/min, and surface roughness Sa is 2.7 nm. There is no obvious pit and scratchdamage under the optimal polishing parameters.