Method and apparatus for produced stepped tubes

Abstract

A method of producing a stepped tube, the method including the steps of preparing a straight mother tube with a stepped wall portion of a smaller inside diameter on the inner periphery thereof at a predetermined position in the longitudinal direction of the tube between opposite straight portions of a larger inside diameter; inserting the mother tube in a clearance a split die having a die cavity between bearing portions provided at opposite ends thereof and separable into first and second halves in the longitudinal direction at a median point of the die cavity and a plug member extensible through the die cavity; gripping a mouth portion of the mother tube by a carriage while positioning the plug member at one of the die bearing portions on the side of the carriage; moving the carriage in the longitudinal direction of the tube until the stepped wall portion on the inner periphery of the mother tube aligns with the die cavity, thereby expanding and stretching one of the straight portions; next moving the plug member up to the other die bearing portion to expand the inner stepped wall portion into and along the die cavity, forming a reversed stepped wall portion on the outer periphery of the mother tube; releasing the joined first and second halves of the split die to permit the first die half on the side of the carriage to move in the longitudinal direction of the tube; and moving the carriage again in the longitudinal direction of the tube to expand and stretch the other straight portion, thereby forming a tube with a circumferential stepped wall portion from a mother tube with an inner stepped wall portion.