Abstract: A groove processing device, which processes a cylinder groove to an inner circumference of a cylinder to protrude from an inner circumferential surface toward an outer circumferential surface side and extend in a center line direction of the cylinder, includes: a first groove processing unit that process both end portions of the cylinder groove in a circumferential direction thereof, and a second groove processing unit that processes a center portion of the cylinder groove in the circumferential direction thereof, wherein an outermost circumferential portion of each of the first groove processing unit and the second groove processing unit being formed to be a chevron shape so that a center portion thereof in the circumferential direction of the cylinder protrudes, and an inclination angle from a vertex portion in the outermost circumferential portion of the first groove processing unit is larger than that of the second groove processing unit.

Abstract: A groove processing device, which processes a cylinder groove to an inner circumference of a cylinder to protrude from an inner circumferential surface toward an outer circumferential surface side and extend in a center line direction of the cylinder, includes: a first groove processing unit that process both end portions of the cylinder groove in a circumferential direction thereof, and a second groove processing unit that processes a center portion of the cylinder groove in the circumferential direction thereof, wherein an outermost circumferential portion of each of the first groove processing unit and the second groove processing unit being formed to be a chevron shape so that a center portion thereof in the circumferential direction of the cylinder protrudes, and an inclination angle from a vertex portion in the outermost circumferential portion of the first groove processing unit is larger than that of the second groove processing unit.

Abstract: In a tube expanding apparatus of a damper tube supporting a thrust force of a punch applied to the damper tube by a stopper at a time of retaining one end of the damper tube by the stopper, inserting the other end of the damper tube to a die, inserting the punch to the other end of the damper tube so as to propel, and expand the other end of the damper tube while carrying out an ironing operation, the apparatus is provided with a stopper releasing means for releasing the stopper at a time when a load in an axial direction applied to the damper tube due to an elongation by the ironing work of the damper tube increases over a critical load which is previously determined to be a smaller load than an expected buckling load in the damper tube.

Abstract: In a tube expanding apparatus of a damper tube supporting a thrust force of a punch applied to the damper tube by a stopper at a time of retaining one end of the damper tube by the stopper, inserting the other end of the damper tube to a die, inserting the punch to the other end of the damper tube so as to propel, and expand the other end of the damper tube while carrying out an ironing operation, the apparatus is provided with a stopper releasing means for releasing the stopper at a time when a load in an axial direction applied to the damper tube due to an elongation by the ironing work of the damper tube increases over a critical load which is previously determined to be a smaller load than an expected buckling load in the damper tube.