METHOD AND APPARATUS FOR PLASTIC WORKING OF HOLLOW RACK BAR AND HOLLOW RACK BAR

Abstract

A preparatory working device by which a work piece to be fed to a rack bar forging device is obtained. The device is provided with a die sets for obtaining a diameter reduction at a location of a blank pipe, which becomes a toothed part of a rack bar, while the wall thickness being substantially unchanged or slightly increased. The device is further provided with a die set for reducing a wall thickness at a location of the blank pipe, which becomes a connection part of the rack bar. The wall thickness reduction is one half of the initial thickness, which causes the length of the work piece to be elongated. Then a rack bar forging by a die set is done.

Description

BRIEF EXPLANATION OF ATTACHED DRAWINGS

FIGS. 1 a to 1e are schematic views of a series of stages for producing a rack bar according to the present invention.

FIG. 2 is a schematic view of a process for forging a rack bar from a pipe shaped blank by using a shuttle type rack bar forging system.

FIGS. 3 a to 3c are schematic views of a series of stages for carrying out a diameter reduction of a blank pipe.

FIGS. 4 a to 4g are schematic views of a series of stages for carrying out a wall thickness reduction of a blank after subjected to the diameter reduction process.

FIGS. 5 a to 5d are schematic views of a series of stages for obtaining, from an initial blank, under one shot principle, a worked blank suitably for a supply to a subsequent rack bar forging process.

Claims

1. Method for producing a rack bar comprising the steps of: providing a work piece of pipe shape;subjecting the pipe shaped work piece to plastic workings for adjusting wall thickness of the work piece to desired values at the respective positions along the length of the work piece corresponding to functions as required, and;forging linearly spaced toothed portions on the work piece after subjected to said wall thickness adjustment, thereby obtaining a rack bar.

2. Method according to claim 1, wherein the adjustment of the wall thickness values is done by a single integrated step.

3. Method according to claim 1, wherein the adjustment of the wall thickness values is done by a plurality of divided steps.

4. Method for producing a rack bar comprising the steps of: providing a work piece of pipe shape;subjecting the pipe shaped work piece to plastic workings for reducing the wall thickness of the work piece except at a location where the rack is to be formed, while freeing the corresponding plastic extension of the work piece along the length of the work piece, and;forging linearly spaced toothed portions on the portion of the work piece of unchanged wall thickness or slightly increased wall thickness after subjected to said local wall thickness adjustment, thereby obtaining a rack bar.

5. Method according to claim 4, wherein the adjustment of the wall thickness values is done by a single integrated step.

6. Method according to claim 4, wherein the adjustment of the wall thickness values is done by a plurality of divided steps.

7. In an apparatus for producing a rack bar from a pipe shaped work piece, wherein the work piece is held by a die set having linearly spaced toothed portions, and a mandrel is inserted to the work piece so that toothed portion corresponding to the toothed portions on the die set are forged to the pipe shaped work piece, the improvement comprising a device for effecting an adjustment of the wall thickness of the work piece to desired values at the respective positions along the length of the work piece corresponding to functions as required, prior to the execution of the forging of the rack bar.

8. An apparatus according to claim 7, wherein said device comprising: a die set including an elongated mandrel and a plurality of dies, and;a driving means for moving the work piece to the first die set for effecting the desired adjusting wall thickness of the work piece.

9. A hollow rack bar used as a steering part of a vehicle, which is forged from a pipe shaped blank, including a first portion of a wall thickness, which substantially the same as or slightly increased from the wall thickness of the blank pipe and a second portion of a wall thickness, which is highly reduced from the wall thickness of the blank pipe and which is elongated for a length corresponding to the reduction of the wall thickness, the rack portion being formed on the first portion of the blank pipe.