Mold and method for molding flexible externally toothed gear

A mold used to mold a flexible externally toothed gear, which is one of constituent components of a strain wave gearing and which has a cylindrical part capable of flexing in a radial direction, the mold characterized by comprising:

• an outer die that defines an outer peripheral surface shape of the cylindrical part, and
• a center die that defines an inner peripheral surface shape of the cylindrical part, wherein
• the center die has
• a die divided part that is divided in a circumferential direction to have a plurality of divided dies and defines the inner peripheral surface shape of the cylindrical part, and
• a divided die movement mechanism that causes each of the divided dies of the die divided part to retract from a molding position to a retracted position radially inward of the molding position, and wherein
• the flexible externally toothed gear to be molded meshes with a rigid internally toothed gear, which is one of the constituent components of the strain wave gearing, at a plurality of positions equiangularly spaced in the circumferential direction;
• the die divided part is constituted of the plurality of the divided dies divided by a plurality of division lines extending in an axial direction and formed at positions equiangularly spaced along the circumferential direction;
• and
• where m and n are positive integers, and where m is the number of meshing positions of the flexible externally toothed gear, and n is the number of divisions of the divided dies,
• when m is an even number, n is an odd number relatively prime to m, and
• when m is an odd number n is an even number relatively prime to m.