Patent ID: 7102096

Claim:
A method for electric-discharge machining a turbine having a plurality of blades formed along a circumference thereof, the method comprising: a) preparing a disc material divided into a first portion and a second portion on a basis of a symmetrical line; b) fixing the disc material, with the first portion facing upward; c) forming an initial profile of at least one of the plurality of blades at the first portion of the disc material using at least two roughing tool electrodes to concurrently form a roughing space at the first portion, the at least two roughing tool electrodes moving generally downward and circumferentially along a desired roughing lead angle with respect to a surface of the first portion; d) leading at least two finishing tool electrodes into the roughing space to concurrently machine the at least one of the plurality of blades, the at least two finishing tool electrodes moving generally downward and circumferentially along a desired finishing lead angle with respect to a surface of the first portion and each of the at least two finishing tool electrodes pivotally reciprocate about a reciprocation axis generally parallel with the surface of the first portion; e) rotating the disc material and fixing the disc material, with the second portion facing upward; f) forming an initial profile of the at least one of the plurality of blades at the second portion of the disc material using at least two roughing tool electrodes to concurrently form a roughing space at the second portion, the at least two roughing tool electrodes moving generally downward and circumferentially along the desired roughing lead angle with respect to a surface of the second portion; and g) leading at least two finishing tool electrodes into the roughing space formed at the second portion to concurrently machine the at least one of the plurality of blades, the at least two finishing tool electrodes moving generally downward and circumferentially along the desired finishing lead angle with respect to a surface of the second portion and each of the at least two finishing tool electrodes pivotally reciprocate about a reciprocation axis generally parallel with the surface of the second portion, and wherein the at least two finishing tool electrodes cut through the symmetrical line by about 0.1 mm to about 0.3 mm.