Spinning apparatus and spinning method

A method of manufacturing a vehicle wheel rim from a tube material having a uniform thickness conducted by using a spinning apparatus which includes (a) a spindle-side chuck having a conical concavity, (b) a mandrel including (i) a mandrel-side chuck formed in a form of a conical convexity corresponding in configuration to the conical concavity of the spindle-side chuck and (ii) a cylindrical portion for supporting the tube material, the mandrel-side chuck including a cylindrical portion-side end of the mandrel-side chuck encompassed within the conical convexity configuration, a diameter at the cylindrical portion-side end of the mandrel-side chuck configured to be larger than an inner diameter of the tube material and (c) a spinning roll for decreasing the thickness of the tube material by pressing the spinning roll against the tube material when the tube material is supported by the cylindrical portion of the mandrel, the method comprising:

• clamping the tube material at a first axial end portion of the tube material between the conical concavity of the spindle-side chuck and the conical convexity of the mandrel-side chuck;
• decreasing by spinning the thickness of the tube material by pressing the spinning roll against the tube material supported by the cylindrical portion of the mandrel to form a formed tube having a non-uniform thickness;
• flaring axially opposite ends of the formed tube to conical configurations;
• and
• roll-forming the formed tube to a configuration of the vehicle wheel rim, wherein
• at the clamping step, the first axial end portion of the tube material is enlarged in diameter and radially inwardly formed to a conical configuration and a portion of the tube material other than the first axial end portion of the tube material is enlarged in diameter and supported by the cylindrical portion of the mandrel, by inserting the mandrel-side chuck and the cylindrical portion of the mandrel into the tube material, and
• at the flaring step, the first axial end portion which has been radially inwardly formed to a conical configuration at the clamping step is reversely bent to a radially outwardly flared configuration.