JP2001071038A - Hollow extruded shape material, bending method therefor and dent quantity estimating method in bending of hollow extruded shape material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a light weight hollow extruded shape material hardly causing a dent on an outside wall in bending and capable of surely joining with another member at the outside wall. SOLUTION: When a distance from a bending neutral axis in bending to a bending outside wall 2 is h/2, a bending radius is R, the proof stress of a hollow extruded shape material is σy, a shape parameter of the hollow extruded shape is F=(tf/b)2(h/b)(h/b+Tw3/tf3) (wherein a width of the bending outside wall is (b), a thickness of the bending outside wall 2 is tf, a thickness of side walls connecting to the bending outside wall is tw), σyh2/RF<=8000 is satisfied.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bent hollow extruded member such as a structural member or a building material made of, for example, an aluminum alloy, a method of bending the hollow extruded member, and a prediction of a dent amount in the bending of the hollow extruded member. About the method.

[0002]

2. Description of the Related Art For structural members of transportation equipment such as A-pillars and B-pillars of automobiles, reinforcing members (energy absorbing members) such as bumpers and door beams, and building materials, for example, aluminum (Al) alloy is used from the viewpoint of weight reduction. The use of hollow extruded profiles is being studied. When such a hollow extruded shape is used, for example, bending such as draw bending, press bending, and multi-bending is often indispensable.

[0003]

When a hollow extruded section is subjected to a bending process, especially when the bending radius is small and the cross section of the section is thin, the bending is performed before the predetermined bending amount is achieved. A dent may occur on the outer side wall (bending outer flange). When the bent outer wall of the hollow extruded shape member is dented as described above, when the bent outer wall is bonded to another member, it is difficult to reliably connect both members, and the bent outer wall is exposed to the public. In the case of the appearance portion, the appearance is impaired and it is not preferable in terms of the tactile sensation.

Therefore, a mandrel is often inserted into the inside of the profile at the time of bending in order to prevent the occurrence of dents. However, even with this technique, it is possible to avoid the occurrence of dents in areas not restrained by the mandrel. Can not do. Further, in the case of tension bending by a stretch bender, bending may be performed in a state in which liquid or air pressure is applied to the inside of the profile in order to prevent the occurrence of dents when tension is applied. However, there is a disadvantage that the processing cycle time is longer than that of press bending or draw bending.
In addition, bending work is performed while the hollow part is filled with beads, sand, ice, resin, low melting point metal, etc., and the filling is later removed, but the number of processing steps and the cycle time are increased. Therefore, it is not suitable for mass production because the cost increases.

Further, as a general method of suppressing dents from the cross-sectional shape, it is conceivable to increase the wall thickness or add a middle rib. However, according to this method, an increase in the weight of the profile due to excessive design is a problem. Becomes Therefore, in order to reduce the weight of the hollow extruded profile, it is necessary to optimize the cross-sectional shape such as the wall thickness. However, at present, the factors that affect the cross-sectional shape of the hollow extruded profile when it is bent are not clear, so experience and trial and error have to determine the specific shape. It is difficult to obtain a hollow extruded profile which is optimally lightened in a range having a dent capable of performing a perfect joining or a range having a dent which does not pose a problem in appearance and touch.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a lightweight hollow extruded mold which is hardly dented on the bent outer wall when subjected to bending and can be securely connected to other members on the bent outer wall. It is to provide a material and a bending method thereof.

A further object of the present invention is to prevent a bent outer wall from being easily dented when subjected to a bending process, and to prevent a problem in appearance and tactile sensation even if the bent outer wall becomes an external portion. Further, it is an object of the present invention to provide a hollow extruded member having a light weight and a bending method thereof.

It is a further object of the present invention to provide a method for predicting the amount of dent in the bending of a hollow extruded member which can reliably predict the amount of dent when the bending is performed.

[0009]

Here, the relationship between the amount of depression on the outer wall of the bent portion and the shape of the hollow extruded shape when a hollow extruded shape having a substantially rectangular cross-section is bent is analyzed. Will be considered. FIG. 1 is a schematic view of a hollow extruded profile having a substantially rectangular cross-sectional profile in a state where a bending process with a bending radius R is performed. Note that, in FIG. 1, illustration of a portion existing symmetrically with a right portion on the left side of the XY plane is omitted. The hollow extruded profile 1 shown in FIG. 1 has a bent outer wall (tensile flange) 2, a bent inner wall (compression flange) 3,
And webs (sidewalls) 4 and 5 connected to them.

A hollow extruded profile 1 shown in FIG. 1 is made of a material having a proof stress σ _y, and has a width b of a bending outer wall 2 and a bending inner wall 3, and webs 4, 5 connected to the bending outer wall 2.
H, the thickness t _{f of} the bending outer wall 2 and the bending inner wall 3,
Its shape by the wall thickness t _w of the web 4 and 5 is characterized. Since the hollow extruded profile 1 has a rectangular cross section, the bending neutral shaft 6 is located at the center of the webs 4 and 5 in the width direction. Therefore, the distance from the bending neutral axis 6 to the bending outer wall 2 is h / 2.

As shown in FIG. 1, a hollow extruded section 1 is deformed symmetrically by being subjected to a bending process, and a bent outer wall 2 is formed.
Is recessed in the direction of the bending center O, that is, inward of the hollow, so that the recess amount near the center in the width direction (hereinafter referred to as “bending center recess amount”) becomes “a”. (The original position of the bent outer wall 2 is indicated by reference numeral 2a). Also, the bending inner side wall 3 is curved so as to be depressed inward in the hollow by performing the same bending process. Conversely, the webs 4 and 5 are curved so as to expand in the hollow outer direction by performing similar bending. The bending strain energy generated in the width direction of each wall such as the bending outer wall 2 increases as the amount of depression or bulge of the bending outer wall 2 increases.

On the other hand, when the bending outer wall 2 is subjected to bending, a strain is generated in the circumferential direction (θ direction). The amount of strain in the circumferential direction and the resulting strain energy decrease as the amount of depression of the outer bending wall 2 increases and the outer bending wall 2 approaches the bending neutral axis. The same applies to the bending outer wall 3.

Therefore, the bending center dent amount a of the bending outer wall 2
Can be determined from the condition that the increase in strain energy in the displacement direction and the decrease in strain energy in the circumferential direction in the entire hollow extruded profile 1 are balanced to minimize the potential energy of the entire system of the hollow extruded profile 1.

The potential energy V of the entire hollow extruded profile 1 is expressed by the following equation (1), where U is the total strain energy of the hollow extruded profile 1 by bending and W is the work done by an external force. expressed. V = U-W (1)

Accordingly, the bending center concave amount a of the hollow extruded profile 1 can be obtained by using the principle of the minimum potential energy represented by the following equation (2). (∂V / ∂a) = 0 (2)

Hereinafter, the bending center depression amount a is calculated based on the equation (2). The depression amount (or swelling amount) generated in the bending outer side wall 2, the bending inner side wall 3, and the webs 4, 5 is restricted by a mold. It is assumed that the values are 0 at the bending start point and the bending end point, and the dent (or bulge) in the middle of the bending is approximated by a cosine curve.

The total strain energy U is approximately equal to the strain energy U due to the circumferential strain of the hollow extruded profile 1.
s and the strain energy Ub due to the strain in the displacement direction. The strain energy Us and the strain energy Ub are generated in the bending outer wall 2 and the bending inner wall 3 (hereinafter, these may be referred to as “flanges”) and the webs 4 and 5, respectively. Assuming that -flange and the strain energy of the web portion are expressed by subscripts -web, respectively, the total strain energy U can be expressed by the following equation (3). U = Us-flange + Us-web + Ub-flange + Ub-web (3) In equation (3), webs 4 and 5 due to circumferential strain
Is a constant that does not depend on the bending center dent amount a.

On the other hand, the work W exerted by an external force when bending the hollow extruded profile 1 can be expressed by the following equation (4) when the work W is divided into a flange portion and a web. W = W-flange + W-web (4) In equation (4), the work W-web made by the external force applied to the webs 4 and 5 is a constant that does not depend on the bending center dent amount a.

By solving equation (2) based on the above conditions,
The bending center depression amount a can be approximately expressed by the following equation (5). a∝σ _y h ² / RF (5) That is, it can be seen that the bending center dent amount “a” is approximately proportional to σ _y h ² / RF. Here, F is given by the following equation (6).
Is the shape parameter represented by F = (t _f / b) ² (h / b) (h / b + _tw ³ / t _f ³ ) (6)

The inventor of the present invention has confirmed that the predicted amount of the bending center dent amount “a” based on the analytical solution described above agrees well with the bending center dent amount “a” obtained by the FEM analysis.

Next, the case where the hollow extruded section 1 is joined to another member on the bent outer wall 2 will be considered. In order to join other members to the bending outer wall 2, the standard is that the gap between the two is generally 1 mm or less in the case of spot welding, and the gap between the two is 0.5 mm or less due to airtightness in the case of joining with the glass surface. Required. As can be seen from Equations (5) and (6), as one of means for reducing the bending center recess amount a, the thickness of the bending outer wall 2 may be increased. In this case, it is not always necessary to set the bending center dent amount a to 0.5 mm or less in cases other than bonding with a glass surface. Thus, the lightest cross-sectional shape can be obtained without the problem described above. However, in the case of bonding with a glass surface, it is preferable that the bending center dent amount a be 0.5 mm or less.

The bending center dent amount a, which will be described in detail in the following embodiments.
And the value of σ _y h ² / RF, the bending center dent amount a
Σ _y h ² / RF when is 1 mm and 0.5 mm
Are 8000 and 3000, respectively. Therefore, in a hollow extruded profile to be joined to another member on the bending outer wall, it is necessary that σ _y h ² / RF ≦ 8000 at least, and σ _y h ² depends on the mating member to be joined.
/ RF ≦ 3000 is preferred.

In other words, the hollow extruded profile of the first aspect has a substantially rectangular cross section, and is formed by joining a bent outer wall formed by bending and another member.
The distance from the bending neutral axis by the bending to the bending outer wall is h / 2, the bending radius is R, the proof stress of the hollow extruded profile is σ _y , and the shape parameter of the hollow extruded profile is F =
(T _f / b) ² (h / b) (h / b + _tw ³ / t _f ³ )
(The width of the bent outer wall is b, and the thickness of the bent outer wall is t.
_f, and t _w the thickness of the side wall continuous to the bending outer wall)
Satisfies σ _y h ² / RF ≦ 8000. The hollow extruded member according to claim 2 satisfies σ _y h ² / RF ≦ 3000.

In the hollow extruded profile according to the first and second aspects, when the bending process is performed, the bent outer wall is less likely to be dented, and the bent outer wall can be securely joined to other members, and has a large wall thickness. Has the advantage that it is not necessary to be thick and is relatively lightweight.

In another aspect, the present invention is a method for bending a hollow extruded shape. That is, the method for bending a hollow extruded profile according to claim 8 has a substantially rectangular cross section, and is a method for bending a hollow extruded profile in which a bent outer wall formed by bending and another member are joined. , The distance from the bending neutral axis by the bending to the bending outer wall is h
/ 2, the bending radius is R, the proof stress of the hollow extruded profile is σ _y ,
The shape parameter of the hollow extruded profile is represented by F = (t _f / b)
² (h / b) (h / b + _tw ³ / t _f ³ ) (the width of the bent outer wall is b, the thickness of the bent outer wall is t _f , and the thickness of the side wall connected to the bent outer wall is t _w ), σ _y
Bending is performed so as to satisfy h ² / RF ≦ 8000.

Next, the case where the bent outer wall 2 of the hollow extruded profile 1 becomes an external part will be considered. Generally, whether or not the dent of the bending outer wall 2 is defective in appearance is determined by visual observation or evaluation by a touch finger. That is, this means that the curvature of the concave portion is evaluated, and is simply evaluated as (bending center concave amount a / flange width b).

From the experimental results of the inventor, it was difficult to judge the presence of a dent at a / b = 0.005 by evaluation with a touch finger. Further, in the visual evaluation, it was difficult to determine the presence of the dent when a / b was about 0.015 or less.

The values of a / b and σ _y, which will be described in detail in the following embodiments,
From the relationship with the value of h ² / RFb, the values of σ _y h ² / RFb when a / b is 0.015 and 0.005 mm are 80 and 40, respectively. That is, when the bent outer wall 2 is an external part, it is necessary that σ _y h ² / RFb ≦ 80 is at least necessary so that no dent is visually observed. Needs to be σ _y h ² / RFb ≦ 40.

That is, the hollow extruded member according to claim 3 is substantially
It has a rectangular cross section and is formed by bending
In a hollow extruded profile whose outer wall is an external part, the bending
The distance from the bending neutral axis by machining to the bending outer wall is
h / 2, R is the bending center radius, and the proof stress of the hollow extruded profile is
σ_y, The shape parameter of the hollow extruded profile is F = (t _f
/ B)^Two(H / b) (h / b + t_w ^Three/ T_f ^Three) (Above
The width of the bent outer wall is b, and the thickness of the bent outer wall is t_f,Previous
The thickness of the side wall connected to the outer side wall is t_wAnd
And σ_yh^Two/ RFb ≦ 80
It is assumed that. Further, the hollow extruded profile of claim 4 is:
σ_yh^Two/ RFb ≦ 40
Things.

According to the third and fourth aspects of the present invention, the hollow extruded member is less likely to have dents in the bent outer wall when the bending process is performed, and causes a problem in appearance and tactile sensation even when the bent outer wall becomes an external portion. This has the advantage that there is no need to increase the wall thickness and the weight is relatively low.

In another aspect, the present invention is a method for bending a hollow extruded shape. That is, the method for bending a hollow extruded shape according to claim 9 is a method for bending a hollow extruded shape having a substantially rectangular cross-section and having a bent outer wall formed by bending as an external portion. The distance from the bending neutral axis by the bending process to the bending outer wall is h / 2, the bending center radius is R, the proof stress of the hollow extruded profile is σ _y , and the shape parameter of the hollow extruded profile is F = (t _f / B)
² (h / b) (h / b + _tw ³ / t _f ³ ) (the width of the bent outer wall is b, the thickness of the bent outer wall is t _f , and the thickness of the side wall connected to the bent outer wall is t _w ), σ _y
Bending is performed so as to satisfy h ² / RFb ≦ 80.

Further, the hollow extruded profile of the present invention may be used as a structural member for an automobile (Claim 5) or as a building material (Claim 6).

[0033] The hollow extruded profile of the present invention is 6000
Preferably, it is made of any one of a series aluminum alloy and a 7000 series aluminum alloy. For example, the use of a high-strength material of 7000 series aluminum alloy according to AA or JIS standards has the effect of making the hollow extruded profile thinner. 700 as an example of a 7000 series aluminum alloy
The 3 aluminum alloy is an Al—Zn—Mg—Cu-based alloy, and is basically composed of 5.0 to 6.5% by weight of Zn, Mg
0.5 to 1.0% by weight, 0.35% by weight of Fe, Mn
0.3% by weight, 0.3% by weight of Si, 0.2% by weight of Cu, 0.2% by weight of Cr, 0.2% by weight of Ti, the balance containing Al and inevitable impurities. . However, even if the components do not always meet the specifications, the composition of the components can be appropriately changed. That is, it is permissible to change the component range of the above-mentioned elements and appropriately include other elements according to more specific applications and required characteristics. Also, 1000 series,
An aluminum alloy such as 3000 series may be used as a material.

In another aspect, the present invention is a method for predicting a dent amount in bending of a hollow extruded profile. That is, the method for predicting the amount of dent in the bending of a hollow extruded profile according to claim 10 is the method for predicting the amount of dent in the bending of a hollow extruded profile having a substantially rectangular cross-section, wherein the bending outside of the bending neutral axis by the bending is performed. The distance to the wall is h /
2. The bending radius is R, the proof stress of the hollow extruded section is σ _y , and the shape parameter of the hollow extruded section is F = (t _f / b) ²
(H / b) (h / b + t w 3 / t f 3) ( the bending width of the outer wall b, the bending wall thickness of the outer wall t _f, the bending wall thickness of the side wall continuous to the outer wall t _w Σ _y h
By calculating ² / RF, the amount of dent of the outer bending wall in the bending process is predicted.

Here, the predetermined value may be set to one of the above-mentioned numerical values depending on whether the bent outer wall is joined to another member or becomes an external part.

According to the tenth aspect of the present invention, the method of predicting the amount of dent in the bending of a hollow extruded shape member can reliably predict the amount of dent when the bending is performed. Therefore, it is possible to easily and simply design a hollow extruded member capable of suppressing the dent during the bending process to a predetermined amount or less.

[0037]

EXAMPLES Two types of test materials (6N01-T1 material (σ _y :
12 kgf / mm ² ), 6N01-T5 material (σ _y : 2)
For 2.5 kgf / mm ² )), three kinds of hollow extruded profiles having a substantially rectangular cross-sectional shape were prepared, and the bending radius R of each hollow extruded profile was variously changed within a range of 100 to 2000 mm. The bending center dent amount “a” when the bending process was performed was measured. At this time, as the hollow extruded shape, one having a mouth-shaped cross-sectional shape as shown in FIG. 1 and one having a substantially mouth-shaped cross-sectional shape as shown in FIGS. Created. Also, the cross-sectional size (length × width) and wall thickness of these hollow extruded shapes were set to 20 mm × 20.
mm (wall thickness 1.5-3.0mm), 10mm x 20mm
(Wall thickness 1.5 to 3.0 mm), 40 mm × 40 mm (Wall thickness 1.5 to 3.0 mm), 40 mm × 20 mm (Wall thickness 1.5 to 3.0 mm), 20 mm × 40 mm (Wall thickness 1.
5 to 3.0 mm), 60 mm x 60 mm (wall thickness 1.5 to
4.0 mm), and the bending center dent amount was measured for each of them.

The hollow extruded profile whose cross-sectional shape is shown in FIG. 2A has a substantially mouth-shaped cross-sectional shape, but the left and right webs are inclined inward at the upper side and the upper wall portion (width b ) Is shorter than the bottom wall, so that the bending neutral axis is not at the center of the web but rather slightly below it. FIG.
For hollow extruded shape member (a), the average thickness of the upper web and lower web than the bending neutral axis and the thickness t _w of the web.

The hollow extruded profile whose cross-sectional shape is shown in FIG. 2 (b) has a substantially mouth-shaped cross-sectional shape, but the flange protrudes from the bottom wall (width b) in the same direction as this. I have. Therefore, the bending neutral axis is displaced below the center of the web. Therefore, in the examples of FIGS. 2A and 2B, the width of the web is not h but converted to be longer.

Based on the measurement result, the parameter σ _y h ²
Fig. 3 shows the result of rearranging the bending center dent amount a against / RF.
Shown in The plot points (indicated by circles) in FIG. 3 tend to increase with an increase in the parameter σ _y h ² / RF, although there are some variations. This variation is due to the influence of the work hardening characteristics of the material and the collapse of the entire cross section during the processing.

FIG. 3 shows that σ _y h ² / RF ≦ 8000 must be _satisfied in order to reduce the bending center depression amount a to 1 mm or less. Also, the bending center dent amount a is 0.5 m.
It is understood that σ _y h ² / RF ≦ 3000 needs to be _satisfied in order to make m or less.

Also, based on the measurement result, the parameter σ
FIG. 4 shows the result of arranging a / b with respect to _y h2 / RFb. The plot points (shown by circles) in FIG. 4 tend to increase with an increase in the parameter σ _y h ² / RFb, though there are some variations.

From FIG. 4, a / b is set to 0.015 or less.
For σ_yh^Two/ RFb ≦ 80
I understand. Also, in order to set a / b to 0.005 or less.
Is σ _yh^Two/ RFb ≦ 40
You.

Although the embodiment of the present invention has been described above, the present invention is not limited to this, and various design changes can be made within the scope described in the claims. For example, the cross-sectional shape of the hollow extruded shape member may be not a mouth shape but a day shape, an eye shape, a rice shape and the like.

[0045]

As described above, according to the first and second aspects, it is difficult for the bent outer wall to be dented when the bending process is performed, and the bent outer wall can be securely connected to other members. In addition, a hollow extruded profile that is lightweight can be obtained. According to claim 8, such a hollow extruded profile can be manufactured.

According to the third and fourth aspects of the present invention, the bent outer wall is less likely to be dented when the bending process is performed, and does not cause a problem in appearance and tactile sensation even if the bent outer wall becomes an external portion. In addition, a hollow extruded profile that is lightweight can be obtained. According to the ninth aspect, such a hollow extruded profile can be manufactured.

According to the tenth aspect, the amount of dents when bending is performed can be reliably predicted.
It becomes possible to easily and simply design a hollow extruded shape member capable of suppressing the dent during the bending process to a predetermined amount or less.

[Brief description of the drawings]

FIG. 1 is a schematic view showing a state in which a hollow extruded shape having a substantially rectangular cross-sectional shape is bent.

FIG. 2 is a sectional view of a hollow extruded profile according to an embodiment of the present invention.

FIG. 3 shows a parameter σ _y h ² in an embodiment of the present invention.
6 is a graph showing a relationship between / RF and a bending center dent amount a.

FIG. 4 shows a parameter σ _y h ² in an embodiment of the present invention.
6 is a graph showing the relationship between / RFb and a / b.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Hollow extruded profile 2 Bending outer wall 3 Bending inner wall 4, 5 Web 6 Bending neutral axis

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) B62D 25/04 B62D 25/04 A B E04C 3/04 E04C 3/04 F16S 3/00 F16S 3/00

Claims (10)

[Claims] 1. A hollow extruded member having a substantially rectangular cross-section, in which a bent outer wall formed by a bending process and another member are joined, wherein: from a bending neutral axis by the bending process to the bent outer wall. , The bending radius is R, the proof stress of the hollow extruded profile is σ _y , and the shape parameter of the hollow extruded profile is F =
(T _f / b) ² (h / b) (h / b + _tw ³ / t _f ³ )
(The width of the bent outer wall is b, and the thickness of the bent outer wall is t.
_f, and t _w the thickness of the side wall continuous to the bending outer wall)
A hollow extruded shape material satisfying σ _y h ² / RF ≦ 8000. 2. The hollow extruded profile according to claim 1, wherein σ _y h ² / RF ≦ 3000 is satisfied. 3. A hollow extruded material having a substantially rectangular cross section and having a bent outer wall formed by bending as an external part, wherein a distance from the bending neutral axis formed by the bending to the bent outer wall is determined. h / 2, the bending center radius is R, the proof stress of the hollow extruded profile is σ _y , and the shape parameter of the hollow extruded profile is F
= (T _f / b) ² (h / b) (h / b + _tw ³ /
t _f ³⁾ (the bending width of the outer wall b, the bending wall thickness of the outer wall t _f, the bending wall thickness of the side wall continuous to the outer wall t _w
), Characterized by satisfying σ _y h ² / RFb ≦ 80. 4. The hollow extruded profile according to claim 3, wherein satisfies σ _y h ² / RFb ≦ 40. 5. The hollow extruded profile according to claim 1, which is used as a structural member for an automobile. 6. The hollow extruded profile according to claim 1, which is used as a building material. 7. A 6000 series aluminum alloy and 70
The hollow extruded shape according to any one of claims 1 to 6, wherein the hollow extruded shape is made of any one of a 00 series aluminum alloy. 8. A method for bending a hollow extruded member having a substantially rectangular cross-section, in which a bending outer wall formed by bending and another member are joined, wherein: The distance to the bending outer wall is h / 2, the bending radius is R, the proof stress of the hollow extruded profile is σ _y , and the shape parameter of the hollow extruded profile is F =
(T _f / b) ² (h / b) (h / b + _tw ³ / t _f ³ )
(The width of the bent outer wall is b, and the thickness of the bent outer wall is t.
_f, and t _w the thickness of the side wall continuous to the bending outer wall)
A method of bending a hollow extruded shape material, wherein bending is performed so as to satisfy σ _y h ² / RF ≦ 8000. 9. A method for bending a hollow extruded shape member having a substantially rectangular cross section and having a bent outer wall formed by bending as an external portion, wherein the bending outer wall is bent from a bending neutral axis by the bending. Is h / 2, the bending center radius is R, the proof stress of the hollow extruded profile is σ _y , and the shape parameter of the hollow extruded profile is F
= (T _f / b) ² (h / b) (h / b + _tw ³ /
t _f ³⁾ (the bending width of the outer wall b, the bending wall thickness of the outer wall t _f, the bending wall thickness of the side wall continuous to the outer wall t _w
Bending method of hollow extruded shape material, characterized in that bending is performed so as to satisfy σ _y h ² / RFb ≦ 80. 10. A method for predicting a dent amount in bending of a hollow extruded profile having a substantially rectangular cross section, wherein a distance from a bending neutral axis by the bending to the bending outer wall is h / 2, a bending radius is R, The proof stress of the hollow extruded profile is σ _y , and the shape parameter of the hollow extruded profile is F =
(T _f / b) ² (h / b) (h / b + _tw ³ / t _f ³ )
(The width of the bent outer wall is b, and the thickness of the bent outer wall is t.
_f, and t _w the thickness of the side wall continuous to the bending outer wall)
Calculating a σ _y h ² / RF to predict a dent amount of the bending outer wall in the bending process.