JPH0683861B

PURPOSE:To reduce working stages in the case of forming a step differential part on the inner peripheral face of a work by executing the ironing of a cup like body at the times when the work is pushed down and ascended and reaching the metal flowed downwards to the lower part of the step differential part for forming of a mandrel. CONSTITUTION:The mandrel 5 providing the step part 7 for forming a step differential part expanding to the external part is inserted by energizing with a spring 8 into the die 4 having the projection 6 for ironing the trapezoidal cross section projecting in the inner diameter direction on the inner peripheral face. The opening end part of a cup like work 2 is engaged with the apex of this mandrel 5 up to the upper position of the step 7 and this cup 2 and mandrel 5 are pushed down by a punch 15. The outer peripheral face of the side wall of the cup 2 is subjected to ironing by the upper face of the projection 6, the metal at the side wall is flowed downwards and the metal having passed through the projection is expanded to the external part. The mandrel is then ascended, the metal expanded to the external part is subjected to ironing with the lower face of the projection 6, the metal flowed downwards is moved and a step differential part is formed on the inner peripheral face of the work 2. The number of dies is thus reduced.