JPH10296373A - Production of rack shaft and device therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To precisely deform a flat art without generating of recessing by plastically deforming a steel tube into a flat while, in, the state of a flat part forming roler being pressed to the intermediate part of the steel tube, the roller is brought into rolling contact with the intermediate part. SOLUTION: A steel tube P is inserted and set in an inserting hole 11 of a holding tool. A cylinder 32 of a moving means 3 is driven and the steel tube P is moved together with a slider 5. A 1st roller 2 is rotationally driven in synchronization with the movement of the steel tube P with a driving part. A forming part 22 of the 1st roller 2 is bitten in the steel tube P by a prescribed amount. In this state, the steel tube P is moved and a flat part P1 is formed. The cross section of the steel tube is thereby formed into a nearly D-like hollow shape. After the flat part P1 is formed on the steel tube P, a 2nd roller for a rack forming having teeth on the outer circumference is pressed to the flat part of the steel tube, the 2nd roller and the steel tube are moved relatively and a rack tooth is formed on the flat part. In this way, the seizure of the steel tube and the 1st roller 2 can be surely prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for manufacturing a rack shaft used for a vehicle steering system or the like.

[0002]

2. Description of the Related Art Conventionally, as a steering device for a vehicle, a pinion is meshed with a rack tooth formed on a rack shaft, and the rack shaft is moved in an axial direction with rotation of the pinion by steering. 2. Description of the Related Art A rack and pinion type steering device for steering a vehicle has been provided. As shown in FIGS. 12 and 13, the rack shaft used in the rack-and-pinion type steering device is formed of a steel pipe P to reduce the weight, and a rack that meshes with the pinion is provided at an intermediate portion in the axial direction. Teeth 90 are formed. This rack tooth 90
Is formed by forming a flat portion 92 by plastic deformation with the arc portion 91 of the steel pipe P left and performing gear cutting on the outer surface thereof.
The portion is hardened to a predetermined hardness by induction hardening.

As a method of forming the flat portion 92 of the rack shaft, as shown in FIGS. 14 and 15, the steel pipe P is held by a mold 93 comprising an upper die 93a and a lower die 93b, and the lower surface is formed. A method of press-forming a steel pipe P with a flat forming punch 94 is generally employed. However, in this method, since the steel pipe P is rapidly plastically deformed, as shown by the two-dot chain line in FIG. There is a problem that a crack is easily generated in a portion having a large amount of deformation, such as an inner corner portion Pa where the inside of the circle crosses the inside of the arc portion 91.

Therefore, as shown in FIG. 16, a rod-shaped jig 95 arranged obliquely with respect to the axis of the steel pipe P is moved in the axial direction of the steel pipe P while being pressed against the steel pipe P, so that the flat part is formed. 92 has been proposed (see Japanese Patent Publication No. 5-88662).

[0005]

However, in the method using the rod-shaped jig 95, the jig 95 and the steel pipe P come into frictional contact under high pressure. Both may seize due to resistance. For this reason, it is necessary to apply a lubricating treatment such as a Bondeleube treatment to the steel pipe P in advance to prevent the occurrence of the above-mentioned seizure. The present invention has been made in view of the above problems, and provides a method and apparatus for manufacturing a rack shaft that does not require lubrication treatment of a steel pipe and that can form a flat portion with high accuracy without generating cracks. The purpose is to:

[0006]

In order to achieve the above object, a method of manufacturing a rack shaft according to the present invention is characterized in that an axially middle portion of a steel pipe having a substantially circular cross section is plastically deformed flatly into a substantially D-shaped hollow shape. Then, in a method of manufacturing a rack shaft that forms rack teeth meshing with a pinion on the outer surface of the flat portion,
While pressing the first roller for forming a flat portion against the middle of the steel pipe, the steel pipe and the first roller are relatively moved in the axial direction of the steel pipe, and the steel pipe is rolled while being in rolling contact with the steel pipe. The method includes a step of flat plastic deformation (claim 1).

According to the method of manufacturing the rack shaft having the above configuration, the steel pipe is flatly plastically deformed while the first roller is in rolling contact with the steel pipe, so that frictional sliding resistance between the two can be extremely reduced. . For this reason, the lubrication treatment of the steel pipe, which is conventionally required to prevent the seizure between the first roller and the steel pipe, is not required. Further, since the steel pipe can be gradually plastically deformed along the axial direction, it is possible to prevent a flat portion from being dented and deformed or a crack from being generated in a portion having a large amount of deformation as in the case of press forming. be able to.

Preferably, the first roller is driven to rotate in synchronization with the relative movement with the steel pipe (claim 2). In this case, when the relative movement between the steel pipe and the first roller occurs, the first roller slips between the two. Can be effectively prevented.

The method of manufacturing a rack shaft according to the present invention is characterized in that, after forming a flat portion on the steel pipe, a rack roller forming second roller having teeth on the outer periphery is pressed against the flat portion of the steel pipe.
The method may include a step of relatively moving the steel pipe and the second roller in the axial direction of the steel pipe, and plastically deforming the flat part of the steel pipe while rotating the second roller to form rack teeth on the flat part ( Claim 3). According to the rack shaft manufacturing method, since the flat portion is plastically deformed by the second roller to form the rack teeth on the flat portion, the residual stress generated in the flat portion when the flat portion is formed by the plastic deformation. Rack teeth can be formed without being affected.

The method of manufacturing a rack shaft according to the present invention includes a step of forming a flat portion on the steel pipe and then press-forming the flat portion of the steel pipe with a rack tooth forming die to form rack teeth. (Claim 4). Also in this method of manufacturing the rack shaft, since the flat portion is plastically deformed to form the rack teeth on the flat portion, the rack teeth can be formed without being affected by the residual stress of the flat portion.

[0011] The rack shaft manufacturing apparatus of the present invention includes:
In a rack shaft manufacturing apparatus in which an axial middle part of a steel pipe having a substantially circular cross section is plastically deformed flat into a hollow shape having a substantially D-shaped cross section, a holder for holding the steel pipe and a middle part of the steel pipe are pressed. A first roller for forming a rotatable flat part,
With the first roller pressed against the steel pipe, the steel pipe and the first roller
A moving means for relatively moving the roller in the axial direction of the steel pipe and flatly plastically deforming the steel pipe while the first roller is in rolling contact with the steel pipe (claim 5).

According to the rack shaft manufacturing apparatus, the steel pipe is held by the holder and the first roller is pressed against the steel pipe, and the moving means moves the steel pipe and the first roller in the axial direction of the steel pipe. Relative movement to the first
The steel pipe can be plastically deformed flat while the roller is in rolling contact with the steel pipe. For this reason, the frictional sliding resistance between the steel pipe and the first roller can be extremely reduced,
The need for lubricating the steel pipe to prevent seizure of both is eliminated. Further, since the steel pipe can be gradually plastically deformed along the axial direction, it is possible to prevent a flat portion from being dented and deformed or a crack from being generated in a portion having a large amount of deformation as in the case of press forming. be able to.

[0013] The rack shaft manufacturing apparatus preferably includes a roller drive section for rotating and driving the first roller in synchronization with the relative movement between the steel pipe and the first roller.
In this case, it is possible to effectively prevent a slip from occurring between the steel pipe and the first roller during the relative movement.

The roller drive unit includes a rack integrated with the holder and extending parallel to the axis of the steel pipe, and a pinion connected to the support shaft of the first roller so as to be integrally rotatable and meshing with the rack. Preferred (claim 7). In this case, the movement of the steel pipe and the rotation drive of the first roller can be linked with each other by the rack and the pinion.
Therefore, one drive source can be used as both the drive source of the moving unit and the drive source of the roller drive unit.

The first roller preferably includes a base fitted to the support shaft, and a fan-shaped formed portion projecting from the outer periphery of the base and having a circumferential length substantially equal to the entire length of the flat portion. In this case, in this case, the steel pipe can be flatly plastically deformed as it is by making the formed portion bite into the steel pipe with the rotation of the first roller. For this reason, a mechanism for changing the relative distance between the first roller and the steel pipe to make the first roller bite into the steel pipe becomes unnecessary.

[0016]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a longitudinal sectional view showing a rack shaft manufacturing apparatus used for carrying out the rack shaft manufacturing method of the present invention, and FIG. 2 is a transverse sectional view thereof. This rack shaft manufacturing device is configured to flatly plastically deform an intermediate portion of a steel pipe P having a substantially circular cross section into a hollow shape with a substantially D-shaped cross section (see FIG. 4). A holder 1 for holding the steel pipe P, a first roller 2 for forming a flat portion pressed against an intermediate part of the steel pipe P, and the steel pipe P in a state where the first roller 2 is pressed against the steel pipe P.
Moving means 3 for moving along the axial direction of steel pipe P
And a roller driving unit 4 for rotatingly driving the first roller 2 in synchronization with the movement of the steel pipe P, a slider 5 for supporting the holder 1, and a frame 6 for integrally holding these components. It is configured.

The holder 1 has a cylindrical shape having an insertion hole 11 for inserting a steel pipe P, and an upper portion thereof has
A through hole 12 for introducing the first roller 2 is formed. The axial length of the through hole 12 is the flat portion P1 of the steel pipe P.
Is set to be slightly longer than the overall length of the first roller 2, and the circumferential width is set to be substantially equal to the width of a later-described forming portion 22 of the first roller 2. The insertion hole 11
Is set to be substantially equal to the outer diameter of the steel pipe P. The holder 1 is integrated with the slider 5 in a state where movement in the axial direction is restricted.
Is slidably held in the axial direction of the steel pipe P by a bottom plate 61 of the frame 6 and a pair of side plates 62.
An opening 51 for introducing the first roller 2 is formed in the upper part of the slider 5. The pair of side plates 62 are interconnected by a bottom plate 61 and a top plate 63.

The first roller 2 for forming a flat portion includes a support shaft 23.
And a fan-shaped molded portion 22 protruding from the outer periphery of the base 21. The base 21 is bolted to the enlarged diameter portion 23a of the support shaft 23,
The movement in the axial direction is restricted, and the key 24 fitted between the support shaft 23 and the support shaft 23 make it possible to rotate integrally with the support shaft 23. The molding part 22 includes:
The circumferential length is set substantially equal to the entire length of the flat portion P1 of the steel pipe P, and the width is set to be approximately the same as the flat portion P1 of the steel pipe P. The molded portion 22 is formed in the through hole 12 of the holder 1.
The outer periphery thereof can advance a predetermined amount into the insertion hole 11 of the holder 1 so that the flat portion P1 can be formed in the steel pipe P. The support shaft 23 is rotatably mounted between a pair of side plates 62 of the frame 6 via a slide bearing 25.

The moving means 3 includes a contact portion 31 which comes into contact with one end surface of the slider 5, the holder 1, and the steel pipe P held by the holder 1, and the slider 5, A hydraulic cylinder 32 as a drive source for simultaneously pressing the holder 1 and the steel pipe P is provided. This moving means 3
Moves the holder 1 and the like by a distance corresponding to the entire length of the flat portion P1 of the steel pipe P.

The roller drive section 4 is composed of a rack 41 bolted to the slider 5 and integrated with the holder 1, and a pinion 42 meshed with the rack 41. The rack 41 extends parallel to the axis of the steel pipe P with the rack teeth 41a facing upward (see FIG. 3), and has a total length longer than the total length of the flat portion P1 of the steel pipe P. Is set to The above pinion 42
Is bolted to the enlarged diameter portion 23a of the support shaft 23 to restrict its movement in the axial direction.
3 and is rotatable integrally with the support shaft 23 by a key (not shown) fitted to the support shaft 23. Therefore, when the slider 5 is moved by the moving means 3, the first roller 2 can be rotationally driven via the pinion 42 and the support shaft 23 in conjunction with the movement. Further, the pitch circle radius of the pinion 42 matches the radius of the forming portion 22 of the first roller 2, whereby the movement of the slider 5 and the rotation drive of the first roller 2 can be synchronized.
As described above, since the roller driving unit 4 can rotationally drive the first roller 2 in conjunction with the movement of the slider 5, a dedicated driving source for driving the first roller 2 is unnecessary. Therefore, the structure can be simplified and the cost can be reduced. The forming portion 2 of the first roller 2
Reference numeral 2 denotes a state where the steel pipe P is retracted from the insertion hole 11 of the holder 1 so that the steel pipe P can be inserted into the holder 1 without hindrance while the holder 1 is moved to the home position (the right end in FIG. 1). .

A method of forming the flat portion P1 on the steel pipe P using the rack shaft manufacturing apparatus having the above configuration will be described below. First, as shown in FIG. 1, in a state where the holder 1 is moved to the home position, the insertion hole 11 of the holder 1 is moved.
The steel pipe P is set through the steel pipe P. Then
The hydraulic cylinder 32 of the moving means 3 is driven to move the steel pipe P together with the holder 1 and the slider 5 to the left in FIG. Then, the first roller 2 can be rotationally driven clockwise in FIG. 3 in synchronization with the movement of the steel pipe P by the roller driving unit 4, whereby the outer peripheral end of the forming unit 22 of the first roller 2 is formed. The portion can be cut into the steel pipe P by a predetermined amount (see FIG. 5). When the steel pipe P is continuously moved in the same direction as above in this state,
While the rolling portion 22 is in rolling contact with the steel pipe P, the steel pipe P is gradually plastically deformed (see FIG. 6), and finally a flat portion P1 having a length corresponding to the circumferential length of the forming portion 22 is formed. (See FIG. 7).

As described above, since the steel pipe P is flatly and plastically deformed while the forming portion 22 of the first roller 2 is in rolling contact with the steel pipe P, the frictional sliding resistance between the steel pipe P and the first roller 2 is substantially reduced. It can be negligibly small. Therefore, it is not necessary to perform a lubrication process on the steel pipe P in advance in order to prevent seizure between the steel pipe P and the first roller 2.
Moreover, since the first roller 2 is forcibly driven to rotate in synchronization with the movement of the steel pipe P by the roller driving unit 4, it is possible to effectively prevent the slippage between the steel pipe P and the first roller 2 during the movement. Can be prevented. Therefore, seizure between the steel pipe P and the first roller 2 can be more reliably prevented, and the surface of the flat portion P1 can be finished smoothly. Further, since the steel pipe P can be gradually plastically deformed along its axial direction, the flat portion P is concavely deformed or the flat portion P1 on the inner periphery of the steel pipe P and the arc portion are formed as in the case of press forming. Cracks can be prevented from occurring at intersections with P2 and the like. Further, since the rack shaft manufacturing apparatus can cause the formed portion 22 to bite into the steel pipe P by rotating the first roller 2, the rack roller manufacturing apparatus includes: A mechanism for raising and lowering the one roller 2 or the steel pipe P is not required, so that the structure can be simplified and the cost can be reduced.

Next, the steel pipe P having the flat portion P1 is formed.
Next, the step of forming the rack teeth P3 shown in FIG. 8 will be described. The rack teeth P3 can be formed by replacing the first roller 2 for forming a flat portion with the second roller 7 for forming rack teeth in the above-described rack shaft manufacturing apparatus. As shown in FIG. 9, the second roller 7 has an annular base 71 fitted to the support shaft 23 and a fan-shaped molding 72 protruding from the outer periphery of the base 71. A tooth 73 having a shape corresponding to the rack tooth P3 is formed on the outer periphery of the molded portion 72. When the rack teeth P3 are formed, the steel pipe P having the flat portion P1 is inserted into the insertion hole 11 of the holder 1 while the holder 1 is moved to the home position, and the steel pipe P is set. At this time, the flat portion P1 is directed upward, and a mandrel 74 for receiving the load applied to the flat portion P1 is inserted into at least a portion corresponding to the flat portion P1 inside the steel pipe P. Next, the hydraulic cylinder 32 of the moving means 3 is driven to move the steel pipe P together with the holder 1 and the slider 5 to the left in FIG. Thereby, the second
While rotating the roller 7, the flat portion P1 of the steel pipe P is sequentially plastically deformed by the teeth 73 of the second roller 7 (see FIG. 10), so that the rack teeth P3 can be formed in the flat portion P1.

As described above, by forming the rack teeth P3 by plastically deforming the flat portion P1 of the steel pipe P, the rack teeth P3 are not affected by the residual stress of the flat portion P1.
Can be formed with high precision. That is, when the flat portion P1 of the steel pipe P is plastically deformed by the first roller 2 for forming the flat portion, residual stress is generated in the flat portion P1, and the flat portion P1 is formed by gear cutting using a broach blade.
1, when the rack teeth P3 are formed using the second roller 7, the accuracy of the rack teeth P3 is reduced due to the influence of the residual stress. The rack teeth P3 can be formed with high accuracy without receiving. In addition, if the rack teeth P3 are to be finished with high precision by the above-described gear cutting, it is necessary to change the profile of the broach blade or to change the design of the jig, so that the processing cost of the rack teeth P3 is high. Although the problem of sticking occurs, by forming the rack teeth P3 with the second roller 7, such a problem can be avoided. The processing of the rack teeth P3 may be performed by warm working in addition to cold working.

FIG. 11 shows rack teeth P3 formed by press molding.
FIG. 9 is a cross-sectional view of a main part showing a method of forming a semiconductor device. In this embodiment, a forming punch 8 having teeth 81 corresponding to rack teeth P3 provided in series is used as a forming die for forming rack teeth, and a steel pipe P is held by a holding die 82,
While the mandrel 83 for receiving the load applied to the flat portion P1 is inserted into at least a portion corresponding to the flat portion P1 inside the steel pipe P, the forming punch 8 is pressed against the flat portion P1 by pressing and plastically deformed. Thus, the rack teeth P3 are formed on the flat portion P1. Also in this embodiment, since the rack teeth P3 are formed by plastically deforming the flat portion P1 of the steel pipe P, the rack teeth P3 can be formed with high accuracy without being affected by the residual stress of the flat portion P1. As well as rack teeth P
The processing cost can be reduced as compared with the case of forming No. 3. In addition, about the said press molding, you may perform by warm working other than cold working.

The present invention is not limited to the above embodiment. For example, in the rack shaft manufacturing apparatus, the first roller 2 is configured to be movable with respect to the steel pipe P,
The first roller 2 may be moved along the steel pipe P by moving means. In this case, the first roller 2 is pressed and moved by using a hydraulic cylinder as a drive source,
Using a hydraulic motor or geared motor as a drive source,
Alternatively, the pinion 42 may be driven to rotate.

[0027]

As described above, according to the method of manufacturing a rack shaft according to the first aspect, the steel pipe is flatly plastically deformed while the first roller for forming the flat portion is in rolling contact with the steel pipe. Can be extremely reduced. For this reason, lubrication treatment of the steel pipe for preventing seizure between the first roller and the steel pipe is not required, and the manufacturing cost of the rack shaft can be reduced accordingly. Also, since the steel pipe can be gradually plastically deformed along the axial direction,
The flat portion can be formed with high precision without causing dent deformation, and a crack can be prevented from being generated in a portion having a large amount of deformation.

According to the rack shaft manufacturing method of the present invention, the first roller is driven to rotate in synchronization with the relative movement between the steel pipe and the first roller, so that the relative movement between the steel pipe and the first roller is achieved. Occasionally, it is possible to effectively prevent a slip from occurring between the two. For this reason, seizure between the steel pipe and the first roller can be more reliably prevented.

According to the method of manufacturing the rack shaft according to the third aspect, the flat portion is plastically deformed by the second roller for forming the rack teeth, and the rack teeth are formed on the flat portion. By forming the portion, the rack teeth can be formed without being affected by the residual stress generated in the flat portion. For this reason, rack teeth can be formed with high precision.

According to the method of manufacturing a rack shaft according to the fourth aspect, the flat teeth are plastically deformed to form the rack teeth by press molding using a molding die for rack teeth molding. By forming the flat portion, the rack teeth can be formed without being affected by the residual stress generated in the flat portion. For this reason, rack teeth can be formed with high precision.

In the rack shaft manufacturing apparatus according to the fifth aspect, the steel pipe and the first roller are moved in the axial direction of the steel pipe by moving means while the first roller is pressed against the steel pipe held by the holder. By relatively moving the first roller, the steel pipe can be plastically deformed flat while the first roller is in rolling contact with the steel pipe. For this reason, the frictional sliding resistance between the steel pipe and the first roller can be extremely reduced, and the lubrication treatment of the steel pipe to prevent seizure of both becomes unnecessary, and the manufacturing cost of the rack shaft is accordingly reduced. Can be cheaper. In addition, since the steel pipe can be gradually plastically deformed along the axial direction, the flat part can be formed with high precision without dent deformation, and cracks are prevented from occurring in the parts with large deformation. can do.

According to the rack shaft manufacturing apparatus of the sixth aspect, the first roller can be rotationally driven by the roller driving section in synchronization with the relative movement between the steel pipe and the first roller. Occasionally, it is possible to effectively prevent a slip from occurring between the two. For this reason, seizure between the steel pipe and the first roller can be more reliably prevented.

According to the rack shaft manufacturing apparatus of the present invention, the movement of the steel pipe and the rotational drive of the first roller can be linked by the rack and the pinion. One drive source can also be used as the drive source for the unit. Therefore, simplification of the structure of the device and reduction in cost can be achieved. According to the apparatus for manufacturing a rack shaft according to claim 8, since the formed portion can be cut into the steel pipe only by rotating the first roller, the first roller is cut into the steel pipe. A mechanism for changing the relative distance between the steel pipe and the steel pipe becomes unnecessary. Therefore, simplification of the structure of the device can be achieved.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view showing one embodiment of a rack shaft manufacturing apparatus of the present invention.

FIG. 2 is a transverse sectional view of the same.

FIG. 3 is a sectional view of a main part of a rack shaft manufacturing apparatus.

FIG. 4 is a perspective view showing a steel pipe having a flat portion formed.

FIG. 5 is a vertical cross-sectional view showing a flat portion in the middle of molding.

FIG. 6 is a vertical cross-sectional view showing a flat portion in the process of being formed.

FIG. 7 is a longitudinal sectional view showing a completed state of the flat portion.

FIG. 8 is a perspective view showing a rack shaft.

FIG. 9 is a vertical cross-sectional view showing a process of forming the rack teeth.

FIG. 10 is a vertical cross-sectional view showing the process of forming the rack teeth.

FIG. 11 is a longitudinal sectional view showing another method of forming the rack teeth.

FIG. 12 is a front view showing a rack shaft.

FIG. 13 is a sectional view taken along line XIII-XIII of FIG.

FIG. 14 is a longitudinal sectional view showing a conventional example.

15 is a sectional view taken along line XV-XV in FIG.

FIG. 16 is a longitudinal sectional view showing another conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Holder 2 1st roller 21 base 22 forming part 3 moving means 4 roller drive part 41 rack 42 pinion 7 2nd roller 71 tooth 8 forming punch (forming die) P steel pipe P1 flat part P3 rack tooth

[Procedure amendment]

[Submission date] February 24, 1998

[Procedure amendment 1]

[Document name to be amended] Drawing

[Correction target item name] Fig. 1

[Correction method] Change

[Correction contents]

FIG.

[Procedure amendment 2]

[Document name to be amended] Drawing

[Correction target item name] Figure 2

[Correction method] Change

[Correction contents]

FIG. 2

Claims (8)

[Claims] 1. A rack in which an axially middle portion of a steel pipe having a substantially circular cross section is plastically deformed flat into a substantially D-shaped hollow cross section, and a rack tooth is formed on an outer surface of the flat portion so as to mesh with a pinion. In the method of manufacturing a shaft, the steel pipe and the first roller are relatively moved in the axial direction of the steel pipe while the first roller for forming a flat portion is pressed against the middle of the steel pipe, and the first roller is moved to the steel pipe. A method of manufacturing a rack shaft, comprising a step of flatly plastically deforming a steel pipe while making rolling contact. 2. The method according to claim 1, wherein the first roller is driven to rotate in synchronization with the relative movement between the steel pipe and the first roller. 3. After forming a flat portion on the steel pipe, the steel pipe and the second roller are connected to each other with a second roller for forming a rack tooth having teeth on the outer periphery pressed against the flat portion of the steel pipe. 2. The method of manufacturing a rack shaft according to claim 1, further comprising the step of plastically deforming a flat portion of the steel pipe while rotating the second roller relative to the flat portion to form rack teeth on the flat portion. 4. The rack shaft manufacturing method according to claim 1, further comprising the step of forming the rack teeth by press-forming the flat portion of the steel pipe by using a rack tooth forming mold after forming the flat portion on the steel pipe. . 5. An apparatus for manufacturing a rack shaft in which an axial middle portion of a steel pipe having a substantially circular cross section is flatly plastically deformed to have a substantially D-shaped hollow cross section, a holder for holding the steel pipe, and a holder for the steel pipe. A first roller for forming a rotatable flat portion that is pressed against an intermediate portion; and a first roller that is pressed against the steel pipe while the first roller is pressed against the steel pipe.
Moving means for relatively moving the roller in the axial direction of the steel pipe and flatly plastically deforming the steel pipe while the first roller is in rolling contact with the steel pipe. 6. The rack shaft manufacturing apparatus according to claim 5, further comprising a roller driving unit that drives the first roller to rotate in synchronization with the relative movement between the steel pipe and the first roller. 7. The roller drive unit includes a rack integrated with the holder and extending parallel to the axis of the steel pipe, and a pinion that is integrally rotatably connected to a support shaft of the first roller and meshes with the rack. The rack shaft manufacturing apparatus according to claim 6. 8. The first roller comprises a base fitted to a support shaft, and a fan-shaped formed portion projecting from the outer periphery of the base and having a circumferential length substantially equal to the entire length of the flat portion. 5. The apparatus for manufacturing a rack shaft according to 5.