Wire electrode for electro-discharge machining and method of manufacturing same

Claim 1

A process of manufacturing a spark erosion electrode, said process comprising (a) plating with zinc, by galvanising, a core wire made of brass, and of a diameter more than the desired diameter of the final wire; (b) putting coil(s) of the zinc plated wire in a bath pot; and heating the pot in a furnace with double vacuum atmosphere being maintained by creating a vacuum in the bath pot and also in the furnace, to avoid oxidation on the surface of the wire, said heating being commenced at a starting temperature of 60° to 70° C. and raising the temperature gradually to a final temperature between 350° C. to 370° C. through a prolonged period of more than 24 hours, the temperature of the furnace being increased gradually from said starting temperature to said final temperature of the bath depending on (i) the required thickness of zinc to be absorbed within the brass of the core wire, and (ii) the diameter of the core wire, said final temperature being maintained for 18 to 20 hours, (c) gradually cooling the bath pot up to the ambient temperature through a prolonged period of about 24 hours; (d) pickling the coil(s) of wire, so heated and cooled, to remove slight coating of nitride, formed out of non-oxidizing atmosphere during said heating/cooling; (e) drawing the wire to reduce its diameter to an intermediate stage almost up to the desired final diameter thereof; (f) gradually heating the so cooled coil(s) of the wire in double vacuum atmosphere through a prolonged period of over 24 hours, as in step (b), and (g) finally drawing the wire up to its desired diameter, followed by resistance annealing of said wire, by a resistance heating arrangement, where high current of electromotive force is caused to be passed through the wire at low voltage so as to heat the wire substantially immediately due to the resistance of the wire.