Wire electrode for wirecut electrical discharge machining with carbonaceous surface layer and the preparation methods thereof

A method for preparing a wire electrode for wirecut electrical discharge machining (WEDM) having a carbonaceous surface layer, said method comprising:

• (1) preparing a brass wire blank, a copper wire blank or a carbon steel wire blank having a diameter of 0.3 to 1.5 mm by plating a layer of a mixture of zinc, CHO organic matter, aluminum salt and potassium salt on the surface of the wire by online continuous electroplating, wherein the content of CHO organic matter in the mixture is less than 0.5%, wherein the content of aluminum and potassium salts is less than 0.5%, relative to the total mixture, and wherein the remainder is zinc, wherein the layer of the surface-plated mixture has a thickness of 1 to 30 μm on the surface of the blank;
• (2) subjecting the plated blank to a carbon precipitation reaction, in a closed environment containing 90% or more of nitrogen, wherein the reaction temperature is 100 to 900° C., the reaction time is 0.5 s to 20 hrs, and the cooling temperature is controlled at below 100° C., wherein the temperature of the furnace is uniform within ±10° C.;
• (3) cleaning the wire blank after the carbon precipitation reaction using a volatile aviation kerosene and pre-stretching and stress-relieving the wire blank to a diameter of 0.1 to 1.0 mm, the tensile speed of the pre-stretching step being form 100 to 900 m/min and the voltage of the stress-relieving annealing step being 5 to 100 V at an annealing current of from 5 to 100 A;
• (4) placing the wire blank having a diameter of from 0.1 to 1.0 mm as obtained in step (3) in a furnace for an annealing treatment with the annealing conditions being as follows
• nitrogen,
• holding temperature 200 to 600° C.,
• holding time 30 to 600 min,
• cooling temperature controlled below 200° C., and
• temperature uniformity in the furnace±10° C.;
• (5) continuously drawing the annealed wire blank to a finished product diameter of 0.02 to 0.35 mm and subjecting it to stress relief annealing with the pass processing rate controlled at 5 to 25%, the total processing rate controlled at 50 to 89% and the tensile speed controlled at 500 to 1,800 m/min, wherein the stress relief annealing voltage is 20 to 40 V and the annealing current is 10 to 60 A.