Processing method of tube body, manufacturing method of cylinder device and cylinder device manufactured by the same

Abstract

There is provided a processing method of a tube body comprising the steps of a tube-expanding step wherein a base tube is partially retained with a chuck unit having a rotational function, and a mandrel is pressed in to an end portion of the base tube so as to expand the end portion of the base tube; and a rotation ironing step wherein the chuck unit rotates the base tube together with the mandrel a roller die is pressed against an outer-periphery surface of the end portion of the base tube and the roller die is moved with respect to the base tube and in an axial direction thereof so as to deform an inner periphery surface of the end portion of the base tube into a shape corresponding to an external shape of the mandrel.

Description

BACKGROUND OF THE INVENTION[0001]1. Field of the Invention[0002]The present invention relates to a processing method of a tube body wherein thickness of an end portion of the tube body is reduced by plastic working so as to finish in a predetermined dimension, a manufacturing method of a cylinder device using the processing method, and the cylinder device manufactured by the same.[0003]2. Description of the Related Art[0004]For example, as regards a hydraulic damper (shock absorber) of a twin tube type, as shown in FIGS. 11 and 12, an inner cylinder 1 slidably housing a piston 8 is introduced into an outer cylinder 2 with a base. One end of a piston rod 3, opposite to the other end connected to the piston 8, is inserted into a rod guide 4 and an oil seal 5 both installed in an open end of the inner cylinder 1 and the outer cylinder 2 so as to extend outside. According to extension and compression movement of the piston rod 3, damping force will be generated by flow resistance of hyd...

AI Technical Summary

Benefits of technology

The present invention provides a processing method for the end portion of a tube body that allows for high accuracy without generating chips or burrs. This is achieved through a tube-expanding step and a rotation ironing step where a roller die is pressed against the outer-periphery surface of the end portion of the base tube and moved in an axial direction to deform its inner-periphery surface into a shape corresponding to the external shape of the mandrel. The invention also provides a manufacturing method of a cylinder device comprising the steps of manufacturing a cylinder by the processing method of the tube body, assembling interior parts, and curling the tip end portion of the cylinder to prevent the interior parts from falling off. Additionally, the invention provides a cylinder device comprising a curled portion formed by curling the tip end portion of the cylinder so as to prevent the rod guide from falling off from the cylinder. Overall, the invention allows for precise processing of the end portion of the tube body without relying on cutting work.

Problems solved by technology

However, highly precise work will be needed to perform conventional methods in which the end portion of the outer cylinder 2 is processed by cutting work, so that it inevitably requires considerable time and man-hour, resulting in increase of work cost.

Further, there is a risk that chips or burrs produced by the cutting work adhere to the inner surface of the outer cylinder 2, and then enter as foreign materials (contamination) into the hydraulic damper.

Thus, in case of obtaining the predetermined area reduction rate with respect to the hydraulic damper for the strut suspension in which to have a relatively thick outer cylinder (tube body), molding force necessary for the parallel swaging work needs to go over a buckling load of the base tube, being virtually incapable of molding such a hydraulic damper.

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