Method of formation of impeller with shape defined by plurality of lines and such impeller

A method of formation of an impeller comprised of a hub on a hub surface of which a plurality of blades are provided,

• the method of formation of an impeller comprising
• a step of preparing the hub,
• a first curve defining step which defines a first hub surface curve which extends along a hub surface of said hub and a first shroud surface curve which extends along a shroud surface of a blade to be formed, at a base end side of said hub, wherein a straight line segment which connects a top end of the first hub surface curve and a top end of the first shroud surface curve is in a plane that is perpendicular to an axis of rotation of the hub;
• a first dividing step in which each of the first hub surface curve and the first shroud surface curve is divided into a predetermined number of equal intervals at divided locations of equal intervals,
• a first part forming step which connects each of the divided locations of equal intervals of the first hub surface curve and first shroud surface curve by a first group of the straight line segments to form a first part of the blade, whereby each divided location is coextensive with adjacent straight line segments of the first group of the straight line segments,
• a second curve defining step which defines a second hub surface curve which extends along a hub surface of said hub and connects with said first hub surface curve and a second shroud surface curve which extends along said shroud surface and connects with said first shroud surface curve, at a distal end side of said hub, wherein a straight line segment of the second curve which connects a bottom end of the second hub surface curve and a bottom end of the second shroud surface curve is parallel to the plane that passes through the axis of rotation of the hub;
• a second dividing step in which each of the second hub surface curve and the second shroud surface curve is divided into a predetermined number of equal intervals at divided locations of equal intervals,
• a second part forming step which connects each of the divided locations of equal intervals of the second hub surface curve and second shroud surface curve by a second group of the straight line segments of the second curve to form a second part of said blade, whereby each divided location of the second curve is coextensive with adjacent straight line segments of the second group of the straight line segments,
• a single blade forming step which couples said first part and said second part to form a single blade,
• a multiple blade forming step which repeats said first curve defining step to said blade forming step to arrange a plurality of blades to a hub surface of said hub, and
• a short blade forming step which provides a plurality of short blades which are shorter in height than said blade at a hub surface of said hub, and wherein said first part of said blade has a height that is substantially equal to a height of said short blades.