Electrical Discharge Machining of Alumina Using Ni-Cr Coating and SnO Powder-Mixed Dielectric Medium
Anna A. Okunkova, М. A. Volosova, E.Yu. Kropotkina, Khaled Hamdy, Sergey N. Grigoriev
Abstract
Aluminum-based ceramics exhibit excellent wear resistance and hot hardness that are suitable for various responsible applications allowing products to work under extreme mechanical and thermal loads (up to 1000 °C). The problem of high-precision forming complex-shaped parts is a known engineering challenge due to the insulating properties of aluminum-containing ceramics and the formation of chemically active carbides in a hydrocarbon medium. The alternative approach for electrical discharge machining non-conductive sintered Al2O3 in the water-based medium using nickel-chrome plasma-vapor-deposed coating of 12 mm, SnO powder suspension (particle diameter of ⌀10 µm, concentration of 150 g/L), and brass wire-tool is proposed. The productivity was evaluated by calculating the material removal rate and discharge gap for various combinations of pulse frequency and duration. The maximal material removal rate of 0.0014 mm3/s was achieved for a pulse frequency of 30 kHz and pulse duration of 1.7–2.5 μs. The recommended value of the interelectrode gap is 48.0 ± 4.9 µm. The possibility of electrical discharge machining aluminum-containing insulating ceramics without using hydrocarbons, carbon and copper-group assisting measures was proposed and shown for the first time. The chemical content of the debris in the interelectrode gap between components of the materials was thermochemically analyzed.