A photoelasticity approach for characterization of defects in microwave drilling of soda lime glass

Need for drilling micro holes has been on rise in many miniature applications including biotechnology. Micro machining of such features is difficult to realize, particularly on difficult-to-machine hard and brittle materials like soda lime glass. Defect characterization with precision in micro-nano scale is even more challenging. Conventional approaches appear inadequate in such cases while fabrication as well as in characterization. In the present work, holes of 900 mu m diameter were drilled on soda lime glass using a novel thermal-based approach called 'microwave drilling'. It uses the phenomenon of thermal ablation with plasma heat created by the applied microwave energy through a tool. The energy was applied in the range of 90-900 W at 2.45 GHz in a multi-mode applicator. The glass specimens were subjected to high localized heat, which also caused some defects like cracking and deformation due to melting in the drilling zone. A photoelasticity approach was employed to characterize these defects. A setup was developed using a polarizer and a CCD camera to obtain the birefringence patterns. The patterns were analyzed to assess the defects. The microwave drilling process was also simulated and the stress-temperature relationships were studied. Simulation results substantiated the experimental observations. Details are discussed with evidences. (C) 2015 Elsevier B.V. All rights reserved.