Application of tool electrodes oxidised with humid and dry air during the electro-discharge drilling of MAR-M247 alloy

The requirements and challenges of machining advanced materials in the field of aerospace, automotive and tool industry are increasing constantly. Due to their mechanical properties, cutting of high-strength materials such as superalloys is severely limited. Electro-discharge drilling can be used for the manufacturing of holes in hard to machine materials. Although electrical discharge machining (EDM) is successfully applied to the machining of holes in turbine blades, a lack of performance and challenges concerning the geometrical accuracy still remain. By applying inner flushing, the resulting electrically conductive debris is flushed through the lateral working gap, increasing the probability of arcs and short circuits. The resulting increased tool wear, conicity of the hole, limited hole depth and process instabilities are still challenging in electro-discharge drilling. In order to decrease the effects of the arcs and short circuits, a surface modification is appli ed to increase the electrical resistance of the lateral surface of the tool electrode. As a result, the mentioned impairments occur less frequently due to decreased occurrence of arcs and short circuits in the lateral working gap. For the present investigation copper tool electrodes were thermally oxidised in dry and humid air with different durations and used afterwards for electro-discharge drilling of MAR-M247. The tests were carried out on the machine tool AGIETRON Compact 1 from the company GF AgieCharmilles, Losone, Switzerland. Holes with a depth of t = 11 mm were drilled using various surface-modified tool electrodes with a diameter of d = 2 mm. Oxidation with dry air and a extended oxidation time resulted in a 18 % lower erosion duration, accompanied by an increase of the linear wear of the tool electrode Île below 10 %.