| 主权项 |
1. A method of machining an impeller having a blade having a blade surface made up of line elements, using a 4-axis machining machine having three linear axes and one rotation axis,
the line elements that form the blade surface of the impeller being not parallel to each other but being skew to each other, an origin being defined at an optional position on a Z-axis which is a central axis of the impeller, and a plane that passes through the origin and is orthogonal to the Z-axis being defined as an XY plane, an X-axis being defined on the XY plane, and projection lines obtained by projecting the line elements onto the XY plane being defined as XY-projection lines of the line elements, an angle between the XY-projection line of each of the line elements and the X-axis being defined as a twist angle of the line element, a plane that includes the Z-axis and is not perpendicular to any one of the XY-projection lines of the line elements being defined as a Z-axis projection plane, projection lines obtained by projecting the line elements onto the Z-axis projection plane being defined as Z-axis projection lines of the line elements, a distance between the origin and an intersection of the Z-axis and an extension line of the Z-axis projection line of each of the line elements being defined as a Z-axis distance of the line element, and the blade of the impeller being formed of a surface made up of such line elements that a relationship between the Z-axis distance of the line element and the twist angle of the line elements is represented by a curve, and that an angle between the Z-axis and the Z-axis projection line of the line element is not a right angle but the Z-axis projection lines of the line elements are parallel to each other, the method comprising, when cutting the blade surface of the impeller by a lateral surface of a cylindrical rotating tool having a central rotational axis: fixing a central axis of rotation of a workpiece to such a position that is tilted from a horizontal surface by an angle between a perpendicular of the central axis of the impeller and the Z-axis projection line of the line element; rotating the workpiece in this state; moving the rotating tool so that the lateral line thereof is aligned with the line element; and machining the workpiece by the lateral surface of the rotating tool, wherein the central rotational axis of the cylindrical rotating tool is held at a predetermined angle relative to the Z-axis across an entirety of the blade surface between two of the line elements that form the blade surface, and said predetermined angle being equal to an angle between one of the line elements that form the blade surface and the Z-axis, and the predetermined angle is not a right angle. |
