Characterization of glass surface damaged by alumina abrasive grains

The quality of an optical glass component is influenced by the presence of surface and subsurface defects generated by machining processes, especially lapping. However, the damaged area is characterized by roughness and crack layers that contribute to reduce the componentʹs mechanical and optical performances. Evaluation of these defects leads to the obtainment of the best finishing technique for optical glass components. s work, the effect of the lapping technological parameters (lapping time and alumina abrasive grain size) on the glass surface roughness as well as the depth of the damaged layer were determined. Furthermore, a proportionality constant between the total height of the roughness profile (Rt) and the subsurface damage layer was calculated. The damaged depth was characterized using mechanical techniques and microscopic analysis. The obtained results show an important damage of the glass surface, since the first few seconds of contact time between the surface and the grains. The increase of the lapping time gives rise to the propagation of this damage to reach its maximum and then a material removal rate is observed. At the end of the operation, a defined final surface roughness and a subsurface damaged layer are obtained. The proportionality constant between the subsurface damage layer and the total height of the roughness profile (Rt) was found to be 6.7 ± 0.8.