Abstract

Use of microwave energy at 2.45 GHz for micromachining offers promising nontraditional machining technique for brittle materials like glass. However, process is yet to be analyzed for better understanding of the process mechanism to minimize the defects associated with the thermal damages in the machined materials. In the present paper, the process was studied using the finite element method, and a 3D model of the microwave drilling setup was developed using COMSOL Multiphysics v5.2 software. Simulation was carried out to study the thermal characteristics of the materials with time while irradiated during the process. The main affecting parameters were analyzed to find out the possible reasons for the defect associated with this process. Simulation of the microwave drilling process was carried out for a combination of graphite concentrator (diameter = 500 µm) and borosilicate glass (thickness = 1.2 mm) at 700 W. Simulation results revealed that the electric field intensity near the concentrator tip was higher (approximately \(8.99 \times 10^{6} \,{\text{V}}/{\text{m}}\)) enough to ionize the air dielectric media which causes the generation of plasma around the tip of concentrator. The maximum temperature in the machining zone was observed approximately 1100 °C in 6 s. The rapid rise in temperature in the specimen induces a very high thermal stress (approximately 85 MPa) which reaches beyond the fracture strength of the borosilicate glass. The experimental investigation of the same concentrator-specimen combination demonstrated the similar pattern of fracture while drilling in the air using the same processing parameters.

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