Prediction of Subsurface Damage of Glass-ceramics by Fixed Abrasive Lapping

Glass-ceramics with its superior chemical, physical and mechanical properties is widely used as a key material in the manufacturing of optical components in the fields of aviation, aerospace, and defense and military industries, etc. However, subsurface damage caused by the manufacturing process can seriously affect the strength of the parts, stability of performance and other service characteristics. The common method for detecting subsurface damage is mainly experimental measurement after processing, which can cause damage to the workpiece. Although the simulation analysis method can perform subsurface damage prediction, it fails to complete the detection of residual stress. Therefore, the evaluation of glass-ceramics surface and subsurface damage is to remain a challenge. In order to quickly, accurately and comprehensively predict the subsurface damage of glass-ceramics during the lapping process, the work aims to establish a discrete element model (DEM) of glass-ceramics with Corning 7972 as the model standard, and simulate and analyze the effect of lapping process parameters on the subsurface damage of the workpiece under the lapping pressure of 3.5, 5, 7, 10 and 15 kPa, respectively. At the same time, lapping tests were designed on the precision polishing machine. The glass-ceramics wafer with 7.5 cm diameter and 5 mm thickness was selected as workpiece under the same lapping pressure as simulation conditions. The lapping parameters were set to the workpiece speed of 80 r/min, the lapping disc speed of 85 r/min, the lapping fluid flow rate of 80 mL/min, and the lapping time of 30 min. The subsurface damage layer of the lapped glass-ceramics was detected and calculated by the angle polishing method (APM). The reliability of the discrete element simulation was verified by comparing and analyzing the experimental results with the simulation results. The results show that the depth of subsurface crack layer of glass-ceramics is 1.86, 1.75, 1.73, 1.63 and 1.38 μm at 15, 10, 7, 5 and 3.5 kPa respectively. The depth of subsurface crack layers by simulation tests at the same pressures is 2.07, 1.87, 1.75, 1.56 and 1.23 μm. The number of subsurface micro-crack drops with the decrease of lapping pressure. The distribution depth of lapping residual stress layer is greater than that of micro-crack layer, the residual stress in the x direction is mainly compressive stress, and that in the y direction is mainly tensile stress. As the lapping pressure decreases, the stresses in both the x and y directions have a tendency to gradually decrease, and there is a larger residual tensile stress at the tip of the micro-crack. The surface and subsurface damage such as longitudinal and transverse micro-crack, and residual stresses exists in glass-ceramics after fixed abrasive lapping process. The regulations of the depth of the subsurface crack layer obtained by the angle polishing method are consistent with the pattern of the simulation results and its deviation is in the range of −10.87%-11.29%. The deviation between the residual stress simulation results and the experimental results is 7.89%. Therefore, discrete element simulation analysis method can accurately predict the subsurface damage of glass-ceramics lapped by fixed abrasive lapping, and it provides a theoretical reference for the formulation of lapping and polishing process parameters. © 2024 Chongqing Wujiu Periodicals Press. All rights reserved.