Microstructuring of non-conductive silicon carbide by electrical discharge machining

The electrical discharge machining process is an established process for machining materials regardless of their mechanical properties. Thus this process is especially attractive for materials which are hard to machine with conventional machining methods. The only requirement a material has to fulfil is having a certain electrical conductivity. Ceramic materials, (e.g. zirconia, silicon nitride or silicon carbide) exhibit excellent mechanical properties but are mostly electrically non-conductive. This can be compensated by an applied, electrically conductive assisting electrode. With this modification, the electrical discharge machining of non-conductive ceramic material is enabled. In this study the micro electrical discharge machining of non-conductive sintered silicon carbide is investigated. The drilling process shows instabilities due to the excessive generation of carbon products. A stabilisation of the process up to the maximum depth of 420 μm is realized by two approaches: adapting process parameters and adapting the tool electrode geometry. An analysis of the amount of infeed used in a milling process shows that an infeed of 15 μm has the best material removal rate to tool wear rate ratio. A maximum material removal rate of 3.58 × 10⁻³ mm³/min is achieved. Detached microstructures with an aspect ratio of 30 are machined. A conducted surface analysis indicates that the present removal mechanism is thermally induced spalling. Furthermore no heat affected zone is present in the machined near-surface area.