JP2004276040A - Method for manufacturing uneven thickness pipe and uneven thickness pipe - Google Patents

Abstract

Provided is an uneven thickness pipe suitable as a lightweight material for a mechanical part such as a rack bar of an automobile.
Kind Code: A1 A method for increasing the thickness of an inner periphery of a metal tube material formed with a uniform thickness in a circumferential direction, wherein a cross-section of the metal tube material is circumferentially divided into a low-strength region and a high-strength region. And then performing a diameter reduction process, and a method for manufacturing an uneven thickness pipe manufactured by the method. In the method of manufacturing the uneven thickness pipe, when forming the low-strength region and the high-strength region, as a first method, a part of the work-hardened metal tube material in the circumferential direction is softened and heat-treated. As a third method, a temperature distribution is formed in the circumferential direction of the metal tube material, and as a third method, a low-strength metal plate and a high-strength metal plate having an arc-shaped cross section are combined, and then straight edges are joined. Can be configured.
[Selection diagram] Fig. 1

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for manufacturing an uneven thickness pipe having a thick portion and a thin portion in a circumferential direction of a cross section by increasing the thickness of the inner wall of the tube, and to an uneven thickness tube.
[0002]
[Prior art]
2. Description of the Related Art In mechanical parts for automobiles, there are many cases in which an outer peripheral surface of a solid metal material such as a metal round bar is partially cut and used. In order to respond to the need to reduce the weight of such mechanical parts, it is common to replace the material with a metal pipe.However, in the case of a metal pipe with a uniform thickness in the circumferential direction, the thickness should be reduced at the part where cutting is performed. In order to ensure this, the thickness of the metal tube material cannot be reduced, which limits the weight reduction of the material.
[0003]
On the other hand, by using an uneven thickness pipe as the metal pipe material and making the thick part in the circumferential direction a portion to be cut, the weight of the mechanical component can be effectively reduced. Hereinafter, this will be described with reference to a steering rack bar (hereinafter, simply referred to as "rack bar") for converting the rotational movement of the vehicle steering wheel into a linear movement.
[0004]
FIG. 6 is a diagram illustrating a configuration example of a rack bar made of round steel. (A) is a partial perspective view, and (b) is a cross-sectional view in the XX view showing the configuration of the rack tooth bottom. The rack bar 100 made of round steel shown in FIG. 5A has a material diameter D of 25 to 35 mm, a material length of 500 to 700 mm, and a rack 100b near the end of the round steel 100a. The air vent hole 100e is machined and used in a gun drilled shape.
[0005]
Then, as shown in FIG. 5B, at the position of the rack tooth bottom 100d, in order to secure the tooth width w, first, the flat surface that becomes the tooth tip portion 100c is machined, and then the gear cutting is performed. In order to improve the fuel economy of automobiles, rack bars are being replaced by metal pipes in response to the need for weight reduction of parts.
[0006]
FIG. 7 is a diagram illustrating a configuration example of a rack bar using a metal tube as a material. In response to the need for weight reduction of parts for improving the fuel efficiency of automobiles, the use of metal tubes for rack bars has been promoted. The rack portion of the hollow rack bar 110 shown in FIG. 7 is subjected to gear cutting after the flat surface serving as the tooth tip portion 110c is machined on the outer surface of the metal tube material, as in FIG. In this case, since the inner diameter portion of the metal tube material is used as an air vent hole, drilling by gun drilling is unnecessary, but in order to secure the wall thickness h between the tooth bottom 110d and the tube inner wall 111, A thick pipe having a thickness T of at least about 10 mm is required for the metal pipe material, and accordingly, the inner diameter d needs to be reduced.
[0007]
Therefore, in the hollow rack bar 110 shown in FIG. 7, the effect of weight reduction is small. In addition, such a small-diameter and thick-walled metal tube material usually needs to be manufactured by cold drawing after manufacturing a raw tube by hot extrusion or the like. is there.
[0008]
By the way, in the hollow rack bar 110 shown in FIG. 7, in order to secure the root thickness h after cutting and gear cutting of the flat portion and to increase the inner diameter d of the material steel pipe as much as possible, the portion to be gear-cut is required. The use of an uneven thickness tube having a large wall thickness and a small wall thickness at other portions is advantageous for weight reduction of parts.
[0009]
FIG. 8 is a view showing a configuration of an uneven thickness pipe according to the present invention, which can be used as a metal pipe material of a hollow rack bar. FIGS. It shows a front view and a longitudinal sectional view of a part to be processed. In FIG. 8, the upper part of the outer diameter central axis is the thick part 120a, the lower part is the thin part 120b, and the sectional shape of the inner diameter part is substantially D-shaped.
[0010]
If the maximum thickness of the thick portion 120a is ta and the minimum thickness of the thin portion 120b opposed thereto is tb, and the thickness deviation rate α is defined by the following equation (a), the deviation becomes larger as α increases. large.
[0011]
α = 2 (ta−tb) / (ta + tb) (a)
As a method for manufacturing the uneven thickness pipe shown in FIG. 8, for example, there are methods proposed in Patent Literature 1 and Patent Literature 2 which employ an extrusion method.
[0012]
However, when the pipe manufacturing method described in these patent documents is used, the production equipment becomes large-scale, and at the same time, in order to manufacture a pipe having a small outer diameter (φ25 to 30), the productivity is low. There is a problem that the manufacturing cost increases.
[0013]
[Patent Document 1]
JP-A-52-86960 [Patent Document 2]
Japanese Patent Application Laid-Open No. H5-154539
[Problems to be solved by the invention]
The present invention uses a metal tube mass-produced in a normal industrial process as a material, generates uneven wall thickness, efficiently manufactures an uneven thickness tube as shown in FIG. It is an object of the present invention to provide a method for manufacturing an uneven thickness pipe capable of realizing weight reduction of a mechanical part such as a bar and an uneven thickness pipe manufactured using the method.
[0015]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, the present inventors have studied various methods for manufacturing an uneven thickness tube while paying attention to the following two basic conditions.
(A) As a metal tube as a starting material for processing, a metal tube formed to have a uniform thickness in the circumferential direction (hereinafter, simply referred to as a “flat tube”) is used. The metal pipe material is not limited to a seamless pipe, a welded pipe, and a forged pipe.
(B) The uneven thickness pipe is manufactured by plastic working (hereinafter, simply referred to as “diameter reducing processing”) for reducing the outer diameter of the metal pipe material.
[0016]
The above (a) and (b) were taken into consideration in order to reduce the manufacturing cost of the uneven thickness pipe by diverting the uniform thickness pipe excellent in industrial mass productivity to the metal pipe material.
[0017]
Then, if the above uniform pipe was diverted to a metal pipe material and subjected to plastic working to generate an uneven thickness increase, it was noticed that the uneven pipe shown in FIG. 8 could be manufactured. is there.
[0018]
Specifically, of the uneven thickness increase, the metal portion is set such that a portion having a large increase in thickness becomes the thick portion 120a shown in FIG. 8 and a portion having a small increase in thickness becomes the thin portion 120b shown in FIG. Various methods for plastic working of pipe material were studied. As a result, if the above-described diameter reduction processing is performed by providing a strength difference in the circumferential direction of the cross section of the metal pipe material formed of the uniform pipe, the uneven pipe 120 shown in FIG. 8 can be efficiently manufactured at low cost. I learned that I can do it.
[0019]
The present invention has been completed on the basis of the above findings, and includes the following (1) and (2) methods for manufacturing an uneven thickness tube and (3) an uneven thickness tube.
(1) A method for producing an uneven thickness pipe by generating an uneven thickness increase in a circumferential direction with respect to a metal pipe material formed with a uniform thickness in a circumferential direction, wherein a cross section of the metal pipe material is provided. Is characterized by forming a low-strength region and a high-strength region in the circumferential direction, and then performing diameter reduction processing.
(2) In the method for manufacturing an uneven thickness pipe according to the above (1), as a first method, a part of the work-hardened metal pipe material in a circumferential direction is softened and heat-treated, so that a low-strength region in the circumferential direction of the cross section is obtained. And a high strength region.
[0020]
As a second method, a low-strength region and a high-strength region can be formed in the circumferential direction of the cross section by forming a temperature distribution in the circumferential direction of the metal tube material. Further, as a third method, a metal pipe material is formed by combining a low-strength metal plate and a high-strength metal plate having an arc cross-sectional shape having the same plate thickness and radius of curvature, and then joining the linear edges. It is also possible to form a low-strength region and a high-strength region in the circumferential direction of the cross section.
(3) An uneven thickness pipe having an uneven wall thickness generated on the inner circumference of the pipe and having a different thickness depending on a circumferential portion, wherein a portion having a small thickness is located opposite to a portion having a large thickness, A cross-sectional shape of the inner diameter portion of the non-uniform wall tube is substantially D-shaped.
[0021]
In the description of the present invention, the “uniform pipe” is a metal pipe formed in the circumferential direction with a uniform thickness, but includes an inevitable circumferential unevenness in the circumferential direction, and has a substantially uniform thickness. It means a thick metal tube. However, the "flat pipe" to which the present invention is applied is not limited to a metal pipe having a circular cross section, and includes a flat pipe having an oval cross section as long as the circumferential direction has a uniform thickness.
[0022]
BEST MODE FOR CARRYING OUT THE INVENTION
The manufacturing method of the uneven thickness pipe of the present invention can be realized by forming a cross section of a metal pipe material formed of a uniform thickness pipe into a low-strength region and a high-strength region in a circumferential direction, and then performing a diameter reduction process. Hereinafter, the details of the present invention will be described with reference to the drawings.
[0023]
FIG. 1 is a diagram illustrating the configuration of a uniform-walled tube and a reduced-diameter uneven-walled tube used as a metal tube material in the manufacturing method of the present invention. (A) shows a cross-sectional configuration of a uniform-wall tube, and (b) shows a cross-sectional configuration of an uneven-wall tube. In the present invention, the outer diameter D0 and the thickness t0 of the uniform pipe 1 are set to the outer diameter D, and the thickness of the uneven pipe 120 is set to the outer diameter D. And The degree of reduction in diameter reduction is defined by an outer diameter ratio D0 / D (hereinafter, referred to as “drawing ratio γ”).
[0024]
As shown in FIG. 1A, the cross section of the flattened tube 1 is composed of a region A and a region B. These are the regions A and B of the cross section of the uneven wall 120 shown in FIG. Respectively. The expansion of the area B of the uniform thickness pipe 1 is indicated by a circumferential length lb, and the expansion of the area B of the uneven wall 120 is indicated by a circumferential length lb ', but the behavior of the circumferential lengths lb, lb' Will be described later. Further, the circumferential lengths lb and lb 'indicate the circumferential lengths at the center of the thickness in the uniform thickness pipe 1 or the uneven thickness pipe 120.
[0025]
The increase in the wall thickness of the pipe circumference due to the diameter reduction processing is large in the region A of the uniform wall tube 1 and is small in the region B. More specifically, as shown in FIG. 1B, the wall thickness increase of the region B is gradually increased from the cross section CC (also the cross section DD) to the cross section AA to thereby increase the thickness of the uneven thickness pipe 120. Thickness distribution can be adjusted. Such uneven wall thickness increase of the pipe circumference can be realized by making the magnitude of the deformation due to the circumferential compression force in the diameter reduction processing uneven in the circumferential direction of the pipe.
[0026]
FIG. 2 schematically shows the relationship between the circumferential compressive force F and the wall thickness t deformed with the circumferential compressive force F in the diameter reduction process, using the cross section AA of the area B and the cross section BB of the area B as typical examples. FIG. Curves Fa and Fb in the figure show the product of the yield stress and the thickness of each of the cross sections AA and BB in the circumferential compression.
[0027]
Therefore, the increase in Fa and Fb due to the increase in wall thickness due to the diameter reduction processing includes the effect of work hardening of the material in the cross section AA and the cross section BB. However, Fa0 and Fb0 in the figure indicate the circumferential compressive force at which the wall thickness starts increasing in the cross section AA and the cross section BB, respectively.
[0028]
The product of the circumferential compressive stress (σ) acting on the thick section (for example, section AA, section BB, etc.) and the thickness (t) of the portion in the diameter reduction processing (hereinafter, “the circumferential compressive force”) F ”) is basically the same in any thick section. For example, when the circumferential compressive force in the diameter reduction processing is F1, as shown in FIG. 2, the wall thickness increases to ta1 due to the compressive deformation in the cross section AA.
[0029]
On the other hand, since F1 <Fb0, there is no deformation due to the circumferential compressive force in the cross section BB, and there is no increase in wall thickness. If these relationships are applied to the diameter reduction processing shown in FIG. 1, the thickness of the cross section AA (region a) in the same (b) is ta = ta1, and the thickness of the cross section BB (region b) is obtained. The thickness remains at tb = t0.
[0030]
Next, when the circumferential compressive force in the diameter reduction processing increases to F2, as shown in FIG. 2, the thickness of the cross section AA increases to ta2, and the thickness of the cross section BB slightly increases. tb2. Similarly, if these relationships are applied to the diameter reduction processing shown in FIG. 1, the thickness of the section AA (area A) in the same (b) is ta = ta2, and the section BB (area B) ) Is tb = tb2.
[0031]
In other words, the thickness of the cross-section AA and the cross-section BB after the diameter reduction processing can be adjusted by Fa, Fb and the circumferential compressive force F to be applied. For example, when the circumferential compressive force F is constant, the difference between the wall thickness increase between the section AA and the section BB can be increased by increasing the difference between Fa and Fb. On the other hand, when Fa and Fb are constant, by increasing the circumferential compressive force F, it is possible to increase the difference in wall thickness increase between the cross section AA and the cross section BB.
[0032]
When increasing the circumferential compression force F, two means can be adopted. The first is a means for increasing the drawing ratio γ, and the second is a means for increasing the circumferential length lb of the metal tube material in the region b of the uniform tube.
[0033]
As shown in FIG. 1, in the second means, the increase in the circumferential length lb at the center of the thickness promotes an increase in deformation due to the circumferential compressive force in the region A, and the thickness of the section AA is increased. It will promote the increase. That is, the increase in the circumferential length lb of the uniform thickness tube 1 increases the circumferential length lb ′ in the region B of the uneven thickness tube 120.
[0034]
FIG. 3 is a diagram showing an example of the inner surface shape of the uneven wall tube due to an increase in wall thickness accompanying the diameter reduction processing. As described above, the increase in the circumferential length lb increases the circumferential length lb ′ of the uneven thickness pipe 120. Therefore, when the circumferential length lb is excessively increased and diameter reduction processing is performed, FIG. As described above, the increase in the thickness of the cross section A-A becomes large, so that the cross section AA swells on the inner surface side.
[0035]
Therefore, it is necessary to select the circumferential length lb at the center of the wall thickness of the uniform wall tube 1 according to the target inner surface shape of the uneven wall tube 120. In addition, it goes without saying that the increase in the thickness of the metal tube material described with reference to FIG. 2 is also applied to cross sections other than the cross section AA and the cross section BB. By adjusting the yield stress with respect to the thickness, it is possible to form a predetermined thickness distribution in the obtained uneven wall.
[0036]
Next, in the manufacturing method of the present invention, a method of forming a yield stress distribution in a circumferential direction of a cross section of a metal tube material, that is, a method of forming a low strength region and a high strength region in a circumferential direction of the cross section will be described. . There are the following three methods.
[0037]
In the first method, after a pipe is subjected to cold working such as drawing processing to produce a flattened pipe 1 having a shape shown in FIG. 1A, a portion corresponding to the area A shown in FIG. This is a method of reducing the hardness of the region A by lowering the hardness than the region B by removing the stress by heating and further recrystallizing.
[0038]
Next, in the second method, after manufacturing the flattened tube 1 having the shape shown in FIG. 1A, only the portion corresponding to the region A shown in FIG. Is a method of performing partial heating so that is smaller than a region corresponding to the region b.
[0039]
Further, the third method is a method in which the regions A and B of the flattened tube 1 having the shape shown in FIG. 1A are made of low-strength and high-strength materials, respectively. To give a specific example, the regions A and B are each formed into a circular cross-section by a method such as roll forming of a low-strength and high-strength plate, and then the cross-section C-C and the cross-section D- shown in FIG. This is a method of manufacturing the flattened tube 1 by joining at a position D by a method such as laser welding.
[0040]
FIG. 4 is a diagram illustrating an example of a method for reducing the diameter of a metal tube material, which can be employed in the manufacturing method of the present invention. FIG. 4A shows a die drawing method, in which a chuck 11 attached to a pulling device (not shown) grips and pulls the tip of a flattened tube 1 made of a metal pipe material, and has an axisymmetric tapered inner shell. The outer diameter is reduced by a die 10 having a portion, and processed into an uneven thickness tube 120.
[0041]
Next, FIG. 4 (b) shows a die pushing method, in which a press-fitting 21 attached to a pressing device (not shown) is used to cut the axially symmetric tapered inner wall portion of the metal flat tube 1 into an axisymmetric tapered shape. It is pressed into a die 20 having the same and is processed into a flat tube 120.
[0042]
Further, FIG. 4C shows a rotary age method, in which a uniform tube 1 as a metal tube material is fed in an axial direction into a plurality of dies 30 moving up and down at a high speed by a driving device (not shown) while rotating the same. Process into a tube 120.
[0043]
In order to form the yield stress distribution in the circumferential direction of the metal tube material, when performing partial heating by the second method, the diameter is rapidly reduced immediately after heating so that the temperature distribution formed in the circumferential direction does not change. Processing is necessary. To this end, it is desirable to rapidly perform partial heating by a method such as high-frequency heating immediately before the die processing for performing the diameter reduction processing shown in FIGS.
[0044]
The diameter reducing method shown in FIG. 4 is a method in which the uniform diameter pipe 1 having a circular cross section is used as a metal pipe material and the diameter reducing processing is advanced in the axial direction while maintaining the circular cross section. However, the manufacturing method of the present invention is not limited to this. The flattened pipe as the metal pipe material is first formed into a flat pipe having an oval cross section (a flattened pipe), and then the diameter is reduced. A method of manufacturing an uneven thickness pipe by using the method can also be adopted.
[0045]
FIG. 5 is a diagram illustrating a method of reducing the diameter of a metal pipe blank formed into a flat tube having an oval cross section in the manufacturing method of the present invention. FIG. 5A shows a state in which the flat tube 2 as a metal tube material is set in a semicircular cross-sectional groove 41a of a lower die 41 attached to a bed of a press (not shown). Here, the cross section of the flat tube 2 is composed of a region a and a region b, similarly to the flat tube 1 shown in FIG. 1, and a yield stress distribution with respect to a predetermined circumferential compression is formed.
[0046]
In order to form the circumferential distribution of the yield stress in the flat tube 2, when performing the partial heating by the above-described second method, the flat heating is performed after the material is flattened so that the temperature distribution formed in the circumferential direction does not change. It is desirable to carry out.
[0047]
After the setting shown in FIG. 5 (a), the upper die 40 attached to the upper ram of the same press (not shown) is lowered from above, and the flattened flat tube 2 is moved in the long diameter direction by the semicircular cross-sectional groove 40a of the upper die 40. Press FIG. 5B shows a state in which the diameter reduction processing has been completed and the uneven thickness pipe 120 has been obtained. Next, effects of the manufacturing method of the present invention will be described based on examples.
[0048]
【Example】
(Example 1)
It was confirmed that the metal pipe material was made of a seamless steel pipe and the diameter reduction was performed by drawing using a die. Using a seamless steel pipe STKM12A (JIS G 3445, yield strength YS = 350 MPa, tensile strength TS = 410 MPa) having an outer diameter of 48.6 mm and a wall thickness of 8 mm as a raw pipe, outer diameter D0 = 35 mm by cold die drawing, It was finished to a steel pipe having a wall thickness t0 = 5 mm. In this state, YS = 610 MPa and TS = 620 MPa.
[0049]
Thereafter, while the area B having a circumferential length lb = 40 mm shown in FIG. 1A was water-cooled, the area B was heated and cooled at 680 ° C. for 10 minutes to obtain a flat tube 1. In the area A in this state, YS = 310 MPa and TS = 370 MPa.
[0050]
When the flat tube 1 was subjected to a diameter reducing process to an outer diameter of 30 mm by a die drawing method shown in FIG. 4A, the thickness ta of the section AA in a region A shown in FIG. Although the wall thickness increased up to that point, the increase was suppressed in the region B, and tb was kept at 5 mm, and the wall thickness deviation tube α of 0.67 was obtained.
(Example 2)
The case where the metal pipe material was made of a welded steel pipe and the diameter reduction processing was performed by the rotary age method was confirmed. An electric resistance welded steel pipe STKM13C (JIS G 3445, YS = 530 MPa, TS = 620 MPa) having an outer diameter of 42.7 mm and a wall thickness of 6 mm was used as a raw pipe, and had a circumferential length lb = 50 mm shown in FIG. The portion excluding the region B, that is, the section AA of the region B and its vicinity was heated to 700 ° C. by high-frequency heating. At this time, in the area A, YS = 100 MPa and TS = 120 MPa. The material strength of the region B was the same as that of the raw tube.
[0051]
Immediately after the high-frequency heating of the above-mentioned region (a), the outer diameter was reduced to 30 mm by the rotary age method shown in FIG. 4 (c). As a result, the thickness of the region (a) shown in FIG. On the other hand, the thickness of the region B was only tb = 7 mm, and the thickness deviation tube 120 having the thickness deviation ratio α = 0.67 was obtained.
(Example 3)
It was confirmed that the metal tube material was formed by laser welding using a hot-rolled steel sheet, and the diameter reduction was performed by a die indentation method. A flat tube having an outer diameter D0 = 35 mm and a wall thickness t0 = 5 mm as a metal tube material is subjected to press bending of a hot-rolled steel plate SPHC (JIS G 3131, YS = 310 MPa, TS = 350 MPa) having a thickness of 5 mm. 5mm hot-rolled steel plate SPFH60 (JIS G 3134, YS = 580MPa, TS = 650MPa) is press-bent to form a member having a region b with a circumferential length lb = 39mm, and a longitudinal edge of both. They were manufactured by laser welding each other.
[0052]
When the obtained uniform-walled tube was subjected to a diameter-reducing process by an indenting method shown in FIG. 4B so as to have an outer diameter of 30 mm, the region A shown in FIG. However, in region (b), the thickness was not increased to tb = 5 mm, and the thickness deviation tube 120 having the thickness deviation ratio α = 0.67 was obtained.
(Example 4)
The case where the metal tube material was flattened into an oval cross section by using a forged steel pipe and the diameter was reduced by cold press forming was confirmed. Forged steel pipe STKM13C (JIS G 3445, YS = 530MPa, TS = 620MPa) having an outer diameter of 42.7mm and a thickness of 8mm is flattened into an oval cross section with a major axis of 50mm and a minor axis of 30mm by cold press molding to obtain uniform wall thickness. A thick metal tube blank was manufactured.
[0053]
After the temperature of the entire metal tube material was raised to 700 ° C., a portion B having a circumferential length lb = 40 mm shown in FIG. 5A was water-cooled. At this time, YS = 100 MPa and TS = 120 MPa in the section AA of the area A. The material strength of the region B was the same as that of the metal tube material before heating.
[0054]
Next, as shown in FIG. 5B, the outer diameter φ30 was reduced in diameter. In the region (a) after the diameter reduction processing, the thickness is increased to ta = 16 mm, and the thickness of the region (b) is suppressed to increase to tb = 10 mm, and the uneven thickness tube 120 having the uneven thickness ratio α = 0.46 is obtained. Was done.
[0055]
【The invention's effect】
According to the method for manufacturing an uneven thickness pipe of the present invention, a uniform pipe such as a seamless pipe, a welded pipe, or a forged pipe, which is mass-produced in a normal industrial process, is used as a material, and is subjected to a diameter reducing process to reduce the diameter of the material. Since uneven wall thickness can be produced unevenly in the circumference and the uneven thickness pipe can be manufactured efficiently, the required processing equipment is simpler and less expensive than the conventional hot extrusion method.
[0056]
In addition, if it is used as a material for automobile rack bars, etc., it is possible to reduce the weight of rack bars manufactured by machining conventional round steel, and to use uneven pipes that can exert a remarkable effect on fuel efficiency. Can be manufactured.
[Brief description of the drawings]
BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is a view for explaining the configuration of a uniform-wall tube and a reduced-diameter uneven-wall tube used as a metal tube material in the production method of the present invention, and FIG. FIG. 2B shows a cross-sectional configuration of the uneven thickness pipe.
FIG. 2 is a diagram schematically showing a relationship between a circumferential compressive force F and a change in a thickness t associated with the circumferential compressing force F in a diameter reduction process, using a cross section AA of a region A and a cross section BB of a region B as typical examples. It is. .
FIG. 3 is a diagram showing an example of the inner surface shape of a wall-thickness tube due to an increase in wall thickness due to diameter reduction.
4A and 4B are diagrams illustrating an example of a method of reducing the diameter of a metal tube material that can be employed in the manufacturing method of the present invention. FIG. 4A illustrates a die drawing method, and FIG. 4B illustrates a die pressing method. , (C) shows the rotary age method.
FIG. 5 is a diagram illustrating a method of reducing the diameter of a metal pipe blank formed into a flat tube having an oval cross section in the manufacturing method of the present invention.
FIG. 6 is a diagram showing a configuration example of a rack bar made of round steel. (A) is a partial perspective view, and (b) is a cross-sectional view in the XX view showing the configuration of the rack tooth bottom.
FIG. 7 is a diagram showing a configuration example of a rack bar using a metal tube as a material.
FIGS. 8A and 8B are diagrams showing a configuration of an uneven thickness tube that can be used as a metal tube material of a rack bar. FIGS. 8A and 8B are a front view and a vertical cross-sectional view of a portion where a rack portion is processed. Is shown.
[Explanation of symbols]
1: Flat tube, 2: Flat tube 10, 20, 30: Die 11: Chuck, 21: Pusher 40: Upper die, 41: Lower die 100, 110: Rack bar 120: Deflected pipe

Claims (5)

A method for producing an uneven thickness tube by generating an uneven thickness increase in the circumferential direction with respect to a metal tube material formed with a uniform thickness in the circumferential direction, wherein a cross section of the metal tube material is formed in the circumferential direction. A method for manufacturing an uneven thickness tube, comprising: forming a low-strength region and a high-strength region, and then performing plastic working to reduce the outer diameter. 2. The uneven thickness according to claim 1, wherein a low-strength region and a high-strength region are formed in the circumferential direction of the cross section by softening and heat-treating a part of the work-hardened metal tube material in the circumferential direction. Pipe manufacturing method. 2. The method for manufacturing an uneven thickness tube according to claim 1, wherein a low-strength region and a high-strength region are formed in a circumferential direction of a cross section of the metal tube material by forming a temperature distribution in a circumferential direction of the metal tube material. . By combining the above-described metal tube material with a low-strength metal plate and a high-strength metal plate having an arc cross-sectional shape having the same plate thickness and the same radius of curvature, and then joining the linear edges, the cross-sectional circumferential direction is reduced. The method according to claim 1, wherein the method comprises forming a strength region and a high strength region. An uneven thickness pipe that has an uneven wall thickness generated at the inner circumference of the pipe and has a different thickness depending on a circumferential portion, and a thin wall section is located opposite to the thick wall section. Characterized in that the cross-sectional shape of the inner diameter portion is substantially D-shaped.

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