Patent ID: 7716809

Claim:
A method for making a double-walled yoke including a cup-shaped outer yoke and a tubular inner yoke nested in and secured to the outer yoke in a coaxial relationship, comprising: providing a cup-shaped member destined to form the outer yoke and having a diameter greater than that of the outer yoke; providing a tubular member destined to form the inner yoke; providing a cylindrical punch having an outer profile for defining an inner profile of the double-walled yoke; fitting the tubular member on the punch; fitting the cup-shaped member on the punch over the tubular member with a radial gap defined between the cup-shaped member and tubular member; providing a drawing die having an inner profile for defining an outer profile of the double-walled yoke; and fitting the drawing die on the cup-shaped member and drawing the cup-shaped member onto the tubular member so that the cup-shaped member is wrapped tightly around the tubular member, and the tubular member is thereby fixedly secured to the inner surface of the cup-shaped member, and the double-walled yoke including a cup-shaped outer yoke and a tubular inner yoke nested in and secured to the outer yoke in a coaxial relationship is formed by the two members.