JP2003094115A - Method for bending metal plate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for bending a metal plate which can lessen a defective angle change of a bent portion of a material to be formed, without changing the shape of a product and without the necessity for using any special mold and facility. SOLUTION: The newly invented method for bending a metal plate comprises a first forming process (A) in which a metal plate is bent to obtain a first formed material 21 having a bent portion 21B and a second forming process (B) in which the first formed material 21 is bent in the same direction as its bent portion 21B so that the bent portion 21B of the first formed material 21 is subjected to re-bending.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an automobile part, etc.
The present invention relates to a method for forming a molded member using a metal plate as a material, and relates to improving a defective shape of an angle change of a bent portion of the molded member caused by elastic recovery, which occurs after the mold is released from the mold.

[0002]

2. Description of the Related Art In recent years, in order to improve fuel efficiency, consider the environment, and improve safety, the body and parts of automobiles have been strengthened and reduced in weight. With respect to press-formed members made of metal plates, which occupy most of the parts, steel plates are being strengthened (high tensile strength) and conversion to lightweight materials such as aluminum alloy plates is being promoted.

A typical example of the press-formed member is shown in FIG. FIG. 1A shows an L-shaped member in which a vertical flat portion 53 is formed at a right angle on one end of an upper flat portion 51 via a bent portion 52.
(B) shows a U-shaped member in which the L-shaped members are symmetrically arranged, and (C) shows a vertical flat portion 63 formed at a right angle on one end of an upper flat portion 61 via a bent portion 62 and the other end. Shows a Z-shaped member in which a flange portion 65 is formed in parallel with the upper flat portion 61 via a bent portion 64, and (D) shows a hat channel-shaped member in which the Z-shaped member is symmetrically arranged. .
These forming members are integrally formed from a raw metal sheet by moving a forming die having a forming surface corresponding to the shape of the forming member and a forming punch (sometimes called a "bending blade") relative to each other. It

However, when press forming is performed using a metal plate such as a high-strength steel plate or an aluminum alloy plate, the elastic recovery (spring back) after release from the mold is large, and thus the dimensional accuracy of the formed member deteriorates. For example, FIG. 2A shows the U-shaped member shape before release (target molding shape) with a two-dot chain line, and shows the member shape after release with a solid line, and FIG. 2B shows the release of the hat channel shape member. The shape of the member before the mold (target shape) is shown by a chain double-dashed line, and the shape of the member after release is shown by a solid line. In both cases, the angle change defect Δθ ( An angle between the tangent line at the bending stop on the side of the vertical flat portion of the bent portion and the vertical flat portion of the target molded shape is generated. In addition, in the case of the hat channel-shaped member (Z-shaped member), in addition to the poor angle change of the bent portion 62, a warp curved outward (a bending stop at both ends of the vertical flat portion is generated in the vertical flat portion 63 that receives bending and bending back). The maximum separation distance between the connecting line segment and the warp is indicated by δ). Bending and bending back means that after the plate material is once bent and formed, the bent part undergoes bending and forming (bending back) in the opposite direction to the original direction, and the bent back part elastically recovers in the original bending direction. And transform.

Various methods have been proposed for preventing defective angular change of the bent portion of the molded member. For example, a method of designing the shape of a molding die so as to have a uniform size in a spring-back state, as described in JP-A-7-204743 and JP-A-7-204743, the ridgeline of the bent portion. A method of forming a reverse bending rounded portion in the direction opposite to the forming bending direction, as described in JP-A-8-174074, compressive stress is applied in the plate thickness direction of the bending portion to reduce residual stress. Methods to reduce it have been proposed.

[0006]

However, in the above method, it is difficult to design the optimum shape of the molding die (tool), some trial and error cannot be avoided, the cost of the die is increased, and the manufacturing start time is increased. Cause delays. According to this method, an unnecessary reverse bending radius portion is recessed in the bending portion of the product, so that the appearance of the product must be changed and the appearance is not bad. The other method requires equipment other than a press such as a compressive force applying device. The present invention has been made in view of the above problems, and a metal capable of reducing an angular change defect of a bending portion of a molding member without changing a product shape, and without requiring a special mold or equipment. An object is to provide a method for bending a plate.

[0007]

According to the present invention, a first forming member having a bent portion is formed by bending a metal plate.
Bending forming method for a metal plate, comprising: a forming step; and a second forming step of forming the first forming member by bending in the same direction as the bending direction of the bending portion so that the bending portion of the first forming member receives bending back. Will be provided.

As another aspect of the present invention, the first forming punch is relatively moved from the first flat forming portion to the first forming die having the second flat forming portion formed through the bending forming portion having the radius R1. A first forming step in which a metal plate is bend-formed by the bend forming part, and a first forming member is obtained in which a first flat part and a second flat part are coupled via the bend part formed by the bend forming part. And the second forming punch is moved relative to the second forming die in which the second flat forming portion is formed from the first flat forming portion via the bending forming portion having the radius R2, thereby moving the first forming member to the second forming die. A second forming step of forming a bend by a bend forming part of a forming die, wherein in the second forming step, the second flat part of the first forming member is arranged on the second flat part side of the second forming die. The bent portion of the first molded member is the second component. Method for bending a molded metal plate is provided to receive a bent back in contact with the bending portion and / or the second flat forming portion of the die.

According to this aspect, in the second forming step, a part of the bent portion of the first forming member is brought into contact with a bend stop portion of the bend forming portion of the second forming die on the second flat forming portion side. Preferably. In addition, the first molding member includes a first flat molding portion, a bending molding portion, and a second molding portion of the first molding die.
When it is assumed that the second flat part of the first molding member and the second mold of the second molding die are assumed to be molded along the flat molding part.
The distance from the flat forming portion is ΔW, and the ratio of the region where the bent portion of the first forming member abuts the second flat forming portion of the second forming die to the entire length of the same in the second forming step is k.
Then, k is obtained by the following equation (A), ΔW is obtained by the following equation (B) using the obtained k, and the assumed second flat portion of the first forming member and second die of the second forming die are obtained. It is preferable to perform the second molding step with the distance between the two flat molding portions being ΔW. k = −0.4836 · ln (R2 / R1) +0.1817 (A) ΔW = (π / 2-1) R2 + (1- (1-k) · π / 2) R1 (B) When R2 is 5 mm or more, R1 ≦
1.5R2, and when R2 is less than 5 mm, R1> 1.
It is preferably 5R1.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION As shown in FIG. 1, the object to be molded according to the present invention is a U-shaped member, a hat channel-shaped member, or an L-shaped member, a Z-shaped member or the like obtained by bisecting these members with an axis of symmetry. A molded member having a bent portion that is bent is included,
Here, the present invention will be described in detail with reference to the most basic L-shaped member (FIG. 1A).

In the forming method of the present invention (sometimes referred to as a double bending forming method), the metal plate is bent and formed in the first forming step to obtain a first formed member having a bent portion, and then the second forming is performed. In the step, the first forming member is bent and formed in the same direction as the first forming step, and in the second forming step, the bent portion of the first forming member is bent back. By bending back the bent portion of the first molding member, a moment in a direction opposite to the bending moment that causes the angle change of the bending portion of the second molding member obtained in the second molding step is generated, and the bending portion of the second member is generated. It is possible to suppress the change in angle.

FIG. 3 shows a molding die for carrying out the molding method of the present invention. (A) is a first molding die used in the first molding step, and (B) is a second molding step. Second to use
The figure shows the molding start state of the molding die. The first and second molding dies include first and second molding dies 1 and 11, first and second molding punches 2 and 12, and first and second molding dies 1 and 1, respectively.
It is provided with first and second pads 3 and 13 for pressingly holding the metal plate W between the upper flat forming portions 4 and 14 forming the upper surface of 11. The first and second forming dies 1 and 11 are formed from the upper flat forming portions 4 and 14 to the bending forming portions 5 having radii R1 and R2.
Vertical flat forming portions 6, 16 are formed at right angles to the upper flat forming portions 4, 14 via 15. The first molding die and the second molding die are the first and second molding dies 1 and 11.
The common ones can be used except for. The upper flat forming portions 4 and 14 of the forming dies 1 and 11 correspond to the first flat forming portion of the present invention, and the vertical flat forming portions 6 and 16 correspond to the second flat forming portion.

According to the molding method of the present invention, first, in the first molding step, the metal plate W has the one end portion thereof shown in (A) and the upper flat molding portion 4 of the first molding die 1 and the first pad. 3 is pressed and sandwiched between them and the forming punch 2 is lowered to the forming die 1 side, whereby the other end of the metal plate W is bent and formed by the bending and forming portion 5 of the first forming die 1. As a result, the upper flat portion 21A placed and held on the upper flat forming portion 4 of the first forming die 1, the bent portion 21B formed by the bending forming portion 5, and the vertical flat portion formed by the vertical flat forming portion 6 are formed. A substantially L-shaped first molding member 21 in which the portion 21C is coupled is obtained.

Next, in the second molding step, the first molding member 21 becomes the upper flat molding portion 4, the bending molding portion 5, and the vertical flat molding portion 6 of the first molding die 1 as shown in (B). ΔW ≧ 0, where ΔW is the distance between the inner surface of the vertical flat portion 21C and the vertical flat forming portion 16 of the second forming die 11 when it is assumed that the vertical flat forming portion 16 is formed along the vertical flat portion 21C. The end portion of the upper flat portion 21A of the first forming member 21 that is actually bent and formed in the first forming step is placed on the upper flat forming portion 14 of the second forming die 11 by the second pad 13. It is pressed and held, and the second forming punch 12 is lowered to perform bending forming. As a result, the second molding die 11
Upper flat portion 22A placed and held on the upper flat forming portion 14
And the bent portion 22B formed by the bend forming portion 15.
And the vertical flat portion 22 formed by the vertical flat forming portion 16.
The second molded member 22 coupled with C is obtained. In the second forming step, since ΔW ≧ 0, the bent portion 21B of the first forming member 21 abuts the forming surface of the bending forming portion 15 of the second forming die 11, the vertical flat forming portion 16, or both. Is bent and formed, and at this time, the first forming member 2
The bent portion 21B of No. 1 is bent back. In (B), ΔX is the bending stop point on the upper flat portion side of the bent portion 21B of the first forming member 21 before and after the start of the second forming step and the bent portion 22B of the second forming member 22. The distance from the bending stop point on the upper flat part side is shown.

According to the double bending method as described above, since the bent portion 21B of the first forming member 21 is bent back in the second forming step, as shown in FIG.
Although an elastic recovery moment (+ M) that causes an angle change defect Δθ is generated in the bent portion 22B of the second molded member 22, the vertical flat portion of the second molded member 22 corresponding to the bent portion 21B of the first molded member 21 in the illustrated example. A moment (-M) in a direction canceling the Δθ is generated in a part 21B ′ of 22C. Therefore, Δθ is reduced after the mold release.

In order to confirm the effect of the above-described double bending method, a steel plate having a plate thickness of 1.0 mm and a tensile strength of 460 MPa was actually used, and the conditions of R1, R2 and ΔW (≧ 0) shown in Table 1 were used. The L-shaped member was molded below, and the angle change defect Δθ2 of the bent portion of the second molded member after molding was measured. For comparison, bending was performed once using only the forming die (radius R2 of the bending portion) used in the second forming step, and the angular change defect Δθ1 of the bending portion that occurred after release was measured. The angle change defect reduction rate A was calculated by the following formula. Table 1 also shows these measurement results and calculation results. A (%) = (Δθ1−Δθ2) / Δθ1 × 100

[0017]

[Table 1]

From Table 1, the angle change defect reduction rate A is A> under all the molding conditions by performing the bending molding twice.
It was 0%, and it was confirmed that double bending could suppress defective angular change. Furthermore, A
It was found that there is a condition of ≧ 100%, that is, Δθ2 <0 °.

Next, R where Δθ2 is 0 ° as much as possible
The optimum condition setting will be described based on the result of examining the conditions of 1, R2, and ΔW. First, Δ1 of Sample Nos. 24 to 28 in Table 1 in which R1 = R2 = 5 mm and ΔW was changed.
FIG. 5 shows the result of arranging the relationship between 1, Δθ2 and ΔW. From this graph, it was found that Δθ2 is a certain optimum ΔW and Δθ2 has the minimum value. This optimum ΔW was examined. FIG. 6 shows a molding state in the second molding step. As shown in FIG. 6, the bending of the first molding member 21 is performed at the bending stop portion P on the vertical flat portion side of the bending portion 22B of the second molding member 22. It was found that Δθ2 tends to be the minimum when part of the portion 21B is present.

This point will be described in more detail. As shown in FIG. 6, the total length of the corresponding portion 21B ′ of the bent portion 21B of the first forming member 21 of the second forming member 22 is 1, and the corresponding portion 21B ′ is the vertical flat forming portion 16 of the second forming die 11. ΔX (FIG. 3), where k is the ratio of the region related to the above, that is, P is the ratio of the bent portion 21B of the first molding portion 21 corresponding to the vertical flat portion 22C of the second molding member 22.
(See (B)) is expressed by the following equation (1). On the other hand, FIG.
From (B), ΔW is expressed by the following equation (2), and ΔX in equation (1) is
By substituting into Eq. (2), Eq. (3) is obtained. ΔX = π / 2 · R2- (1-k) · π / 2 · R1 (1) ΔW = ΔX−R2 + R1 (2) ΔW = (π / 2−1) R2 + (1- (1- k) · π / 2) R1 (3) In the case of FIG. 5, ΔW2 is 2 mm, and Δθ2 is the minimum, so ΔW = 2 is substituted from the equation (3) and k is calculated as k =
0.255 is obtained. This means that the bending portion of the first forming member is formed so that the bending portion of the second forming die takes about ¾.

Here, the reason why Δθ2 increases when ΔW increases after Δθ2 takes the minimum value in FIG. 5 will be described. When ΔW is increased, a region including the bent portion 21B of the first forming member 21 bulges outside the bend forming portion 15 of the second forming die 11 when the second forming is intended, and the bulge portion is formed in the second forming punch 12. 7A is crushed by the corner portions of the. As shown in FIG. 7 (B), the moment generated in the bulge portion causes a moment (+ M) that increases the angle change defect to occur in various portions, and reduces a moment (−M) that cancels the angle change defect. Therefore, when ΔW increases, Δθ2 also increases.

Next, when the radius R2 of the bending portion 15 of the second forming die 11 which determines the radius of the bending portion of the product is given, the optimum R1, ΔW (k) which can suppress Δθ2 as small as possible. ) Will be described.

In order to solve this problem, the inventor first investigated the value of R2 / R1, k that minimizes Δθ2 when molding with various combinations of R1 and R2 based on the data in Table 1. The results are also shown in Table 1. Note that Δθ
The bent portion of the sample that was bent twice to minimize 2 was bent along R2 of the second molding die. FIG. 8 shows a graph in which the relationship between R2 / R1 and the minimum Δθ2 is obtained based on these data, that is, the value of the constant k that can bring Δθ2 closest to 0 °. From FIG. 8, constants k and R that bring Δθ2 closest to 0 ° are obtained.
There is a very strong correlation between 2 / R1 and R2 / R1.
It can be seen that the value of k should be large when R is small and the value of k should be small when R2 / R1 was large. The following approximate expression (4) is obtained from the data in FIG.
The optimum k value can be obtained for 2 / R1. k = -0.4836 · ln (R2 / R1) +0.1817 (4)

Further, when the radii (target radius = R2) of the bent portions of the product (second molding member) are the same, Δθ2 is most 0 °.
R1 which can be brought close to will be described. FIG. 9 shows a graph in which the relationship between R2 / R1 and Δθ2 is arranged for each R2 based on the sample data of R2 / R1 and k that takes the minimum Δθ2 in Table 1 above. However, in FIG. 9, the value of Δθ1 for only one-time bending is shown as Δθ2 of R2 / R1 = 0 (R1 = ∞) in the figure. From Figure 9, R2 is large,
If the angle change defect Δθ1 at the time of one-time bending is large, R2
/ R1 needs to be increased, and if R2 is small and the angle change defect Δθ1 at one bending is also small, R2 / R1
It turns out that can be made smaller. For example, R2 ≧ 5mm
In this case, by setting R2 / R1 to 1.5 or more, Δθ2
Can be approximately 1 ° or less. Also, R2 <5mm
In the case of, R2 / R1 is less than 1.5, preferably 0.2
By setting 5 <R2 / R1 <1.5, Δθ2 is almost 1 °.
It can be:

The above description is an example of double bending for a 440 MPa class 1.0 mm steel plate, and the combination of R1 (mm), R2 (mm) and ΔW (mm) that can achieve Δθ2 ≈ 0 ° is as follows. It was the street. (R2, R1, ΔW) = (3, 3, 1), (5, 3,
1), (10, 5, 2) Under such a combination of conditions, a higher strength steel plate (tensile strength 1008 MPa, plate thickness 1.2 mm) and 5000
Series aluminum alloy plate (tensile strength 281 MPa, plate thickness 1.
(0 mm) was bent twice and Δθ2 was measured. For comparison, the second molding die having the bending portion having the radius R2 was used to perform bending once, and the angle change defect Δθ1 of the bending portion after releasing was measured. These measurement results are shown in comparison with each other in FIG. 10 (in the case of high strength steel plate) and FIG. 11 (in the case of aluminum alloy plate). From the figure, it was confirmed that the double-bend forming of the present invention is excellent in the effect of reducing the angular change defect of the bent portion regardless of the material strength and the material.

The present invention is not limited to the above L-shaped member and Z-shaped member, but can be similarly applied to a U-shaped member and a hat channel member in which these are symmetrically arranged. In the case of the symmetrical U-shaped member and hat channel type member, the left and right vertical flat portions are simultaneously press-molded, and the deformation of the upper flat portion is originally small, so a pad for pressing and holding the metal plate is not necessarily required. Further, the press device for carrying out the present invention is not particularly limited, and any type of press such as a hydraulic press, a mechanical press, and a counter hydraulic press can be used.

Furthermore, the double bending method of the present invention is the first
Instead of separately performing the forming step and the second forming step, one action forming may be performed in which two steps are performed by one operation of the forming punch. Hereinafter, the molding die (where R is
1 = R2 = R) and its operation will be described with an example.

As shown in FIG. 12, a molding die for carrying out the present invention by one-action molding has a molding die 3 in which a vertical flat molding portion is formed from an upper flat molding surface through a bending molding portion.
1, a pad 33 for pressing and sandwiching the metal plate W between the upper flat forming part of the forming die 31, and a forming punch 32 for forming the metal plate W from the bending forming part along the vertical flat forming part. And a positioning member 35 for horizontally positioning the molding die 31 in the mold case 34. The forming punch 32 has a first flat forming portion 32A and a second flat forming portion 32 which are parallel to the forming die 31 from the bottom flat portion.
B is provided stepwise through the step portion 32C. on the other hand,
The molding die 31 is urged to the rear side of the mold case 34 by an elastic member so as to be movable back and forth, and a first positioning surface portion 31A and a second positioning surface portion 31B are provided stepwise on the rear side surface of the molding die 31. ing. The positioning member 35 is urged upward by an elastic member and is housed in the mold case 34 so as to be able to move up and down. The positioning member 35 has a first positioning surface portion 31A or a second positioning surface portion 31B of the molding die 31. An abutting surface portion 36 is formed which abuts and positions the horizontal position.

FIG. 13A shows a state where the forming is started. As the forming punch 32 descends, the metal plate W is bent and formed by the flat bottom portion and the first flat forming portion 32A, and (B).
After the flat bottom portion comes into contact with the positioning member 35, as shown in FIG. Then, as shown in (C), when the contact surface portion 36 of the positioning member 35 is disengaged from the first positioning surface portion 31A of the molding die 31 by pushing down the molding punch 32, the molding die 31 moves backward by ΔW, The second positioning surface portion 31B comes into contact with the contact surface portion 36 and is positioned in the horizontal direction. Further, the forming punch 32 continues to descend as shown in (D), and at the second flat forming portion 32B thereof, the first punch formed once by bending is formed.
The L-shaped member is bent and formed by the step portion 32C and the second flat forming portion 32B so that the bent portion of the first L-shaped forming member is bent back.

[0030]

According to the double bending method of the present invention, since the bent portion of the metal plate formed in the first forming step is bent back in the second forming step, the second portion is formed in this portion.
A bending moment in a direction opposite to the bending moment generated in the bending portion formed in the forming step is generated, and the angular deformation defect of the bending portion formed in the second forming step can be reduced. Further, according to the molding method of the present invention, a normal press,
Since it can be easily carried out using a molding die, it has excellent productivity.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of various molded members having a bent portion.

FIG. 2 is an explanatory diagram showing an angle change defect Δθ in a bent portion of a U-shaped member and a hat channel-shaped member.

FIG. 3 is a cross-sectional explanatory view showing a positional relationship between a molding die and a metal plate in a molding start state of (A) first molding step and (B) second molding step of the double bending method of the present invention. .

FIG. 4 is an explanatory cross-sectional view showing a bending moment generation state of the forming member after the second forming step.

FIG. 5 is a graph showing the relationship between the shift distance ΔW of the first molding member with respect to the second molding die and the angular change defect Δθ2 of the bent portion of the second molding member.

FIG. 6 is a cross-sectional explanatory view showing a correspondence relationship between bent portions of the first molding member in the second molding member.

7A is a cross-sectional explanatory view showing the deformation behavior of the metal plate during double bending when (A) ΔW is large, and (B) a cross-sectional explanatory view showing a bending moment generation state around the bent portion of the metal plate. is there.

FIG. 8 is a graph showing the relationship between R2 / R1 and a constant k that brings the angle change defect Δθ2 of the bent portion of the second molded member closer to zero.

FIG. 9 shows that the radius R2 of the bending portion of the second forming die is 3,
It is a graph which shows the relationship between (DELTA) (theta) 2 and R2 / R1 in each case of 5 and 10 mm.

FIG. 10: Double bending forming of high strength steel plate and conventional 1
The angle change defect Δθ due to the bending process is set to R2 = 3, 5, 1
It is a graph comparing every 0 mm.

FIG. 11 is a graph showing an angle change defect Δθ between the double bending and the conventional single bending of an aluminum alloy plate, which is R2 =
It is the graph which compared every 3, 5, 10 mm.

FIG. 12 is a cross-sectional explanatory view showing a molding die for performing bending molding twice with one action of a molding punch and its operation.

[Explanation of symbols]

1,11 First and second molding dies 2,12 First and second forming punch 3,13 First and second pads 4,14 Top flat forming part 5,15 Bending forming part 6,16 Vertical flat forming part 21 First Forming Member 21A Upper flat part 21B Bend 21C Vertical flat part 22 Second molding member

Claims (5)

[Claims] 1. A first forming step of bending a metal plate to obtain a first formed member having a bent portion, and bending the first formed member so that the bent portion of the first formed member is bent back. A bending forming method for a metal plate, comprising a second forming step of forming the portion in the same direction as the bending direction. 2. The bending forming of a metal plate by relatively moving a first forming punch from a first flat forming portion to a first forming die having a second flat forming portion through a bend forming portion having a radius R1. The first flat part and the second flat part
A first forming step of obtaining a first forming member in which a flat portion is coupled via a bent portion formed by the bend forming portion, and a second forming step from the first flat forming portion through a bend forming portion having a radius R2.
A second forming step of bending and forming the first forming member by a bend forming portion of the second forming die by relatively moving a second forming punch to a second forming die in which a flat forming portion is formed, In the second forming step, the second flat portion of the first forming member is arranged on the second flat portion side of the second forming die, and the bent portion of the first forming member is the bend forming portion of the second forming die. And / or a method of bending a metal plate that abuts against the second flat forming portion and is subjected to bending back. 3. The method according to claim 2, wherein in the second forming step, a part of the bent portion of the first forming member abuts on a bend stop portion of the bend forming portion of the second forming die on the second flat forming portion side. The described method for forming and bending a metal plate. 4. The first molding member is the first molding die of the first molding die.
When it is assumed that the molding is performed along the flat forming portion, the bending forming portion, and the second flat forming portion, the distance between the assumed second flat portion of the first forming member and the second flat forming portion of the second forming die is When ΔW is set and k is a ratio of a region in which the bent portion of the first forming member abuts the second flat forming portion of the second forming die to the entire length of the bent portion in the second forming step, k is as follows. A) was obtained by the equation A), and ΔW was obtained by the following equation (B) using the obtained k, and the distance between the assumed second flat portion of the first forming member and the second flat forming portion of the second forming die was ΔW. The method for bending and forming a metal plate according to claim 2 or 3, wherein the second forming step is performed. k = −0.4836 · ln (R2 / R1) +0.1817 (A) ΔW = (π / 2-1) R2 + (1- (1-k) · π / 2) R1 (B) 5. R1 ≦ 1.5R2 when R2 is 5 mm or more, and R1 when R2 is less than 5 mm.
1> 1.5R1 is set, The bending forming method of the metal plate as described in any one of Claims 2-4.