On microwave drilling of metal-based materials at 2.45 GHz

This work investigates microwave drilling of steel sheets with plasma channel triggered by microwave-metal discharge at the pointed end of a thoriated tungsten tool. The plasma channel was induced inside a multimode domestic microwave applicator operating in atmospheric condition at the frequency of 2.45 GHz. The thermal energy of the microwave-metal discharge-induced plasma channel caused the thermal ablation of the steel sheets by melting and vaporization. Sheets of galvanized steel and stainless steel (thickness - 0.5 mm) were drilled to generate through holes. Undersized holes in galvanized steel were observed for the microwave exposure time of 40 s, while an increase in microwave exposure time to 65 s resulted in hole overcut and wider thermal damage. Wider thermal damage zone observed in stainless steel sheets is attributed to lower melting temperature and lower thermal conductivity of stainless steel. Characterization of drilled holes indicated that the quality of holes obtained in both the sheet material is yet to be comparable with other non-traditional drilling methods such as electrical discharge machining and electrochemical machining. A hypothesis of microwave drilling of metals has been proposed based on the experiment results.