Method of producing injection-molding die for worm wheel, and method of producing worm wheel

A method of producing an injection-molding die for a worm wheel in which a master electrode having a shape similar to the worm wheel is formed and a cavity for injection-molding the worm wheel is formed using the master electrode, wherein:

• the worm wheel
• (1) has a circular arc-shaped tooth section that is a portion meshing with a worm and configuring a circular tube worm gear and a helical tooth section that is connected to one end side of the circular arc-shaped tooth section, and
• (2) has an angle of torsion at an arbitrary first reference point in a tooth depth direction of a tooth in a connecting section between the circular arc-shaped tooth section and the helical tooth section equal to an angle of torsion at a second reference point corresponding to the first reference point in the tooth depth direction of the tooth in a diameter portion of a throat of the circular arc-shaped tooth section;
• and
• the master electrode
• (1) has a first tooth section corresponding to the circular arc-shaped tooth section of the worm wheel and a second tooth section corresponding to the helical tooth section of the worm wheel,
• (2) has an angle of torsion at a position corresponding to the first reference point in the tooth depth direction of the tooth in a connecting section between the first tooth section and the second tooth section equal to an angle of torsion at a position corresponding to the first reference point in the tooth depth direction of the tooth at a position corresponding to the diameter portion of the throat of the first tooth section,
• (3) is divided at a position corresponding to the diameter portion of the throat of the first tooth section into a first divided master including a portion of the first tooth section and the second tooth section, and a second divided master including the other portion of the first tooth section, in which
• (4) the first divided master moves led by the first tooth section, while rotating with a lead of the first tooth section, and electrical-discharge-machines a die material from one side of the die material and
• (5) the second divided master moves led by the first tooth section, while rotating with a lead of the first tooth section, and electrical-discharge-machines a die material from the other side of the die material, and
• (6) forms the cavity in the die material.