Spin forming a tubular workpiece to form a radial flange on a tubular flange and a bead or thick rim on the radial flange

In a method of spin forming a cylindrical sheet metal workpiece, to form a sheet metal connector ring for sheet metal ducting, by using a mandrel that has an open center, a generally radial forming surface surrounding the open center, and an outer diameter, wherein a first end portion of the workpiece is positioned in the open center of the mandrel, and is secured to the mandrel, and a second end portion of the workpiece projects axially outwardly from the center opening in the mandrel and has an outer end part, and wherein the mandrel and the workpiece are spun together about a common spin axis and the second end portion of the workpiece is progressively stretched in diameter and moved radially outwardly along the generally radial forming surface of the mandrel by a forming roller, the improvement comprising:

• mounting the mandrel for rotation about a substantially vertical spin axis with its generally radial forming surface in a substantially horizontal plane;
• mounting the forming roller for rotation about an axis that is in a common radial plane with the spin axis of the mandrel;
• providing the roller with a convex face and a periphery;
• placing the roller inside the second end portion of the workpiece, with its convex face directed radially outwardly towards the second end portion of the workpiece and its periphery directed downwardly;
• spring biasing the roller downwardly when it is inside the second end portion of the workpiece, to place its periphery initially below the level of the radial forming surface;
• spinning the mandrel and the workpiece around the spin axis of the mandrel;
• moving the roller radially outwardly of the mandrel and its convex face against the second end portion of the workpiece, so as to radially stretch the second end portion of the workpiece as the roller moves radially outwardly;
• positioning the periphery of the roller where it will press the second end portion of the workpiece against the generally radial forming surface as it moves radially outwardly,
• whereby as the roller moves radially outwardly its contact with the second end portion of the workpiece will move the roller upwardly against the spring bias, allowing the second end portion of the workpiece to move radially outwardly along the radial forming surface, between the periphery of the roller and the radial forming surface;
• and
• continuing the radial outward movement of the roller against the second end portion of the workpiece at least until a predetermined amount of the second end portion of the workpiece is against the radial forming surface below and behind the roller and a remainder of the second end portion of the workpiece is forwardly of the roller against its convex face.