| 摘要 |
<p>PROBLEM TO BE SOLVED: To secure the clearance between a die for forming and a bottomed cylindrical blank, to improve the service life of the die by improving the lubricity and to prevent defect formation such as flaws wrinkles and barrel part buckling on a bottomed cylindrical body. SOLUTION: When a tapered surface and a diameter-shrinkage surface continuing to the tapered surface are extruded with the die and a punch while shrinking the diameter of the opening part at the other end part of the bottomed cylindrical blank provided with the bottom part in the vicinity of the one end part, before forming the diameter-shrinkage surface of the bottomed cylindrical blank, the thickness in a prescribed length of the side surface at the opening part of this blank is thinned beforehand and/or circular tapered surface on the tapered surface continuing to the diameter shrinkage surface is formed. Therefore, little clearance is formed along the formed inner peripheral surface of the die for forming when the extrusion forming is executed at the interval with the bottomed cylindrical blank and the lubricity when the extrusion-forming is executed is increased and also the area of the formed contacting surface is reduced and the flow of a material of the bottomed cylindrical blank is promoted. In this way, the resistance to the formed surface for forming is reduced.</p> |
