Patent ID: 8511949
Filing Date: 2013-08-20
Classification: B23C,Y10T

Abstract:
1. A method of cutting a tree-shaped groove for mounting a turbine blade on an outer circumference of a rotor, the tree-shaped groove being an upside-down Christmas tree shape machined such that the tree-shaped groove is bilaterally symmetrical with respect to a center of the groove and the tree-shaped groove gradually becomes narrower in a groove depth direction, the tree-shaped groove including, in order toward the groove depth direction, a first narrow portion having a first narrow groove width, a second narrow portion having a second narrow groove width that is narrower than the first narrow portion, a third narrow portion having a third narrow groove width that is narrower than the second narrow portion, a first wide portion that is between the first narrow portion and the second narrow portion and that has a first wide groove width, and a second wide portion that is between the second narrow portion and the third narrow portion and that has a second wide groove width that is narrower than the first wide portion, the cutting being performed by a first tool and a second tool, the first tool including as a cutting edge portion a column portion and a cone portion, which is provided on a tip end of the column portion and that has a tapered shape in which the diameter decreases toward a tip end of the cone portion, the cutting edge portion being provided on a tip end of a tool body that can be rotated around an axis, and the second tool being a tool whose diameter gradually changes toward a tool tip end such that the diameter increases and decreases corresponding to a change in the groove width of the tree-shaped groove, that includes, in order from a tool back end toward the tool tip end, a first reduced diameter portion, a first expanded diameter portion, a second reduced diameter portion, a second expanded diameter portion, and a third reduced diameter portion, and that is provided with nicks on the first reduced diameter portion, the first expanded diameter portion, and the second expanded diameter portion to reduce contact friction with a work material and to improve chip removal, and that is not provided with a nick on either the second reduced diameter portion or the third reduced diameter portion, the method comprising: a rough cutting step of cutting by the first tool of a tapered shape in which the groove width becomes narrower toward the groove depth direction, while first, second, and third specified cutting allowances are left for portions that will become the first, second, and third narrow portions; a semi-finishing step of performing cutting by the second tool such that fourth and fifth specified cutting allowances are left for portions that will become the first and second wide portions while avoiding the portions that will become the first, second, and third narrow portions; and a finishing step of cutting the first, second, third, fourth and fifth cutting allowances, the rough cutting step further comprising: the semi-finishing step further comprising: