JP2013013911A - Method for producing forming member - Google Patents

Abstract

A method for producing a molded member having excellent burring formability and flange formability is provided.
A step of forming a pilot hole 2 in a blank material 1 made of a metal plate by punching, and a sleeve portion by punching out the periphery of the pilot hole 2 of the blank material 1 in a cylindrical shape while expanding by burring. 3 and a step of forming the flange portion 4 by bending the distal end side of the sleeve portion 3 in the diameter-enlarging direction by flange molding, wherein the edge portion of the flange portion 4 is formed. Among the flange deformed end shapes formed with the straight line portion 4a having a straight line shape and the curved line portion 4b having a curved line shape, the minimum width of the flange portion 4 forming the curved line portion 4a is defined as d ₁ , Burring molding and flange molding are performed in a range where d ₂ / d ₁ ≧ 0.42, where d ₂ is the minimum width of the flange portion 4 forming the straight line portion 4b.
[Selection] Figure 1

Description

  According to the present invention, a sleeve is formed by punching a blank made of a metal plate material such as a steel material or a light alloy material by punching and then punching it into a cylindrical shape while expanding the periphery of the hole by burring. The present invention relates to a method for manufacturing a molded member in which a flange portion is formed by forming a portion and bending the distal end side of the sleeve portion in a diameter-enlarging direction by flange molding.

  A blank material (molded member) made of a metal plate material, particularly a steel plate material, can be formed into members having various shapes by press working. Further, the press work is roughly divided into a shearing process (separation process) and a forming process. Of these, burring molding and flange molding that undergo plastic deformation at the end of the blank are particularly important in the molding process.

  In such a part that undergoes plastic deformation by burring or flange molding, there is a strain gradient toward its end, and cracks may occur during molding, so improving the formability at this part is a problem. (For example, refer to Patent Document 1).

  In the field of steel materials in response to this problem, for example, steel materials excellent in burring and flange formability are being developed with the aim of improving the formability of the material itself. On the other hand, Patent Document 1 below discloses a technique for improving the formability by locally modifying the base plate shape so as to alleviate the deformation gradient of the fracture risk part.

JP 2009-214118 A

  By the way, in the blank material which receives the above-mentioned burring molding or flange molding, the end shape may be determined in advance depending on the design of the product. In particular, since the end shape of the blank material may be composed of a curved portion having a certain curvature and a straight portion that forms a straight line, it is required to improve the formability in such an end shape. Yes.

  The present invention has been proposed in view of such a conventional situation, and a blank material subjected to burring molding and flange molding, in particular, by performing flange molding after burring molding, its end shape is curved. A method for producing a molded member excellent in burring formability and flange formability, which can reduce end strain (deformation amount) and greatly improve formability in a blank material including a straight portion and a straight portion The purpose is to provide.

  In order to achieve the above object, the present inventors examined the breaking condition at the flange deformation end portion of the blank material whose end portion shape includes a curved portion and a straight portion by performing flange forming after burring forming. As a result, it was found that the deformation was concentrated near the boundary between the curved portion and the straight portion at the flange deformation end portion, and the fracture occurred.

  Therefore, as a result of various studies, the present inventors, when forming the vicinity of the boundary between the curved portion and the straight portion at the flange deformed end portion of the blank material subjected to burring molding and flange molding, The inventors have found that by optimizing the curvature difference of the trim shape, the concentration of plastic deformation near the boundary can be alleviated and the formability of the blank material can be improved, and the present invention has been completed.

That is, the gist of the present invention aimed at solving the above problems is as follows.
(1) a step of forming a pilot hole in a blank material made of a metal plate by punching;
Forming a sleeve portion by punching out into a cylindrical shape while expanding the periphery of the blank hole of the blank material by burring;
Forming the flange portion by bending the distal end side of the sleeve portion in the diameter-enlarging direction by flange molding,
When the minimum radius of the pilot hole is R ₁ [mm] and the hole expansion limit value in the clearance when the pilot hole is punched with a predetermined clearance is λ, the maximum diameter of the sleeve portion is 2R _1. The method for producing a molded member, wherein the burring molding is performed within a range of (λ + 1) [mm] or less and a maximum height of the sleeve portion being R ₁ · λ [mm] or less.
(2) Further, the curved portion is formed in a flange deformed end shape formed by having a curved portion having a curved shape and a straight portion having a linear shape at an edge of the flange portion. When the minimum width of the flange portion is d ₁ and the minimum width of the flange portion forming the linear portion is d ₂ ,
d ₂ / d ₁ ≧ 0.42
The method for producing a molded member according to (1), wherein the burring molding and the flange molding are performed within a range.
(3) Furthermore, when the Rankford value is r, and the plate thickness reduction value corresponding to the true strain of the hole expansion limit value λ is εw ^CL ,
d ₂ / d ₁ ≧ (d ₂ / d ₁ ) ^{CL
_{(D 2 / d 1) CL}} = {(B 2 -4A (C-εw CL)) 0.5 -B} / 2A,
εw ^CL = (r / (1 + r)) · ln (1 + λ),
−0.18 ≦ A ≦ 0.17,
0.055 ≦ B ≦ 0.06,
0.299 ≦ C ≦ 0.305
The method for producing a formed member according to (2), wherein a cold-rolled steel sheet having an r value and a λ value satisfying the above relationship is used.
(4) In addition, the maximum diameter of the flange portion forming the curved portion when the phi _1,
λ ≧ (φ ₁ −2R ₁ ) / 2R ₁
The method for producing a molded member according to (2) or (3), wherein the burring molding and the flange molding are performed within a range.
(5) The method for manufacturing a molded member according to any one of (1) to (4), wherein a steel plate having a thickness of 0.5 to 1.8 mm is used as the blank material.
(6) A cold rolled steel sheet having a tensile strength of 440 MPa or less is used as the blank material, The method for producing a molded member according to any one of (1) to (5).

  As described above, according to the present invention, in a blank material subjected to burring and flange molding, in particular, a blank material including a curved portion and a straight portion by applying flange molding after burring molding. The end strain (deformation amount) can be reduced and the moldability can be greatly improved.

FIG. 1 is a plan view, an X direction sectional view, and a Y direction sectional view showing an example of a molded member manufactured by applying the present invention. FIG. 2 is a plan view showing a state in which a pilot hole is formed in the blank material by punching. FIG. 3 is a plan view, a cross-sectional view in the X direction, and a cross-sectional view in the Y direction, showing a state in which the sleeve portion is formed on the blank material by burring. FIG. 4A is a perspective view showing an initial stage of burring molding and a perspective view showing an end stage of burring molding. Fig.5 (a) is a top view which shows the fracture | rupture danger part after flange shaping | molding, and a top view which shows the fracture | rupture danger part after burring shaping | molding. FIG. 6 is a characteristic diagram showing the relationship between the value of d ₂ / d ₁ and the thickness reduction value. FIG. 7 is a characteristic diagram showing the relationship between the d ₂ / d ₁ value and the plate thickness reduction value in steel types A to F. FIG. 8 is a characteristic diagram showing the relationship between the value of R ₂ / R ₃ and the thickness reduction value. FIG. 9 is a characteristic diagram showing the relationship between the position of the trim curve and the thickness reduction value.

Hereinafter, a method for producing a molded member to which the present invention is applied will be described in detail with reference to the drawings.
For example, as shown in FIG. 1, a molded member manufactured by applying the present invention has a blank 1 made of a metal plate such as a steel material or a light alloy material, and after forming a pilot hole 2 by punching, A sleeve portion 3 formed by punching out the periphery of the pilot hole 2 into a cylindrical shape while expanding by burring molding, and a flange portion formed by bending the distal end side of the sleeve portion 3 in the diameter expansion direction by flange molding 4 and is schematically configured.

  In addition, this molded member has a flange deformed end shape including a curved portion 4a having a curved shape and a straight portion 4b having a linear shape at the end edge of the flange portion 4. Specifically, the flange deformed end shape is obtained by providing a straight portion 4b formed linearly with a predetermined length L on a part of the flange portion 4 formed in an arc shape with a constant curvature R by the curved portion 4a. It is the shape that was provided. In other words, this flange deformed end shape is such that a pair of straight line portions 4b are arranged in parallel with a predetermined length L on both sides of the dividing line X passing through the center O of the pilot hole 2, and these straight line portions 4b. The curved portion 4a forms an arc with a constant curvature R, and the flange portion 4 protruding in the diameter increasing direction from the tip of the sleeve portion 3 is formed.

Here, in the molded member shown in FIG. 1, the thickness of the blank 1 is t, the maximum diameter of the sleeve 3 is φ ₀ , and the height of the sleeve 3 (from the thickness center of the blank 1 to the flange 4 the Z-direction distance) to the thickness center and H _1, the maximum diameter of the flange portion 4 φ _{1 (=} 2R), the minimum width of the flange portion 4 to form a curved portion 4a d _1, the linear portion 4a formed of the minimum width of the flange portion 4 which is intended to represent a d _2.

  The manufacturing method of the molded member to which the present invention is applied includes a step of forming a pilot hole 2 in the blank material 1 by punching, and a cylindrical shape while expanding the periphery of the pilot hole 2 of the blank material 1 by burring. 1 to form the molding member shown in FIG. 1 through a step of forming the sleeve portion 3 and a step of forming the flange portion 4 by bending the distal end side of the sleeve portion 3 in the diameter increasing direction by flange molding. To do.

Among these, the blank 1 is formed with a pilot hole 2 having a trim shape as shown in FIG. 2 by punching. Specifically, the trim shape of the pilot hole 2 includes a first trim curve 2 a that draws an arc having a radius R ₁ from the center O of the pilot hole 2 on the XY plane shown in FIG. A second trim curve 2b that draws an arc with a radius R ₂ (<R ₁ ) from a position O ′ that is offset in the −X direction from the center O, and a radius R that is in contact with the first and second trim curves 2a and 2b ₃ (<R ₂ ) is a shape drawn by continuously connecting a third trim curve 2 c that draws an arc.

  And the sleeve part 3 becomes a sleeve deformation | transformation edge part shape as shown in FIG. 3 after burring shaping | molding. Specifically, the sleeve deformed end shape is such that the first curved portion 3a of the pilot hole 2 is convex toward the distal end side by the portion that draws the first trim curve 2a of the pilot hole 2, and A portion that draws the second trim curve 2b forms a second curved portion 3b that is concave toward the base end side. Moreover, the part which draws the 3rd trim curve 2c of the said pilot hole 2 becomes a part which connects between these 1st curve parts 3a and 2nd curve parts 3b continuously.

Here, in the present invention, when the hole expansion limit value in the clearance when the pilot hole 2 is punched with a predetermined clearance is λ, the maximum diameter φ ₀ of the sleeve portion 3 is 2R ₁ · (λ + 1) [ mm] or less, and burring is performed in a range where the maximum height H ₀ of the sleeve portion 3 is R ₁ · λ [mm] or less.

The radius R ₁ of the first trim curve 2 a represents the minimum radius of the pilot hole 2, and the maximum height H ₀ of the sleeve portion 3 is the sleeve portion from the thickness center of the blank material 1 after burring. 3 represents the distance in the Z direction to the tip of 3 (the tip of the first curved portion 3a).

When the hole expansion limit value is λ, the radius that can be expanded by burring is R ₁ · (1 + λ) [mm], so the maximum diameter φ ₀ of the sleeve portion 3 is 2R ₁ · (λ + 1) [mm. It becomes the following. Further, since the length of the expanded diameter by burring is the difference between the diameter after the expansion and the diameter before the expansion, this difference becomes R ₁ · (1 + λ) −R ₁ , and as a result, the maximum of the sleeve portion 3 is obtained. The height H ₀ is R ₁ · λ [mm] or less.

  And the flange part 4 becomes a flange deformation | transformation edge part shape as shown in the said FIG. 1 after flange molding. That is, this flange deformed end shape forms the curved portion 4a of the flange portion 4 by the portion that becomes the first curved portion 3a of the sleeve portion 3, and becomes the second curved portion 3b of the sleeve portion 3. The straight part 4b of the flange part 4 is formed by the part. The boundary portion between the curved portion 4 a and the straight portion 4 b of the flange portion 4 corresponds to the central portion of the third trim curve 2 c of the pilot hole 2.

  By the way, the present inventors conducted flange forming after burring forming, and as a result of investigating the breaking state at the flange deformed end portion of the blank whose end portion shape includes the curved portion 4a and the straight portion 4b, the flange deformed end It was found that the deformation concentrated in the vicinity of the boundary between the curved portion 4a and the straight portion 4b in the portion, and the fracture occurred.

  That is, in the molded member shown in FIG. 1, the end portion deformation amount of the flange portion 4 is not uniform depending on the positions of the first curved portion 3 a and the second curved portion 3 b of the sleeve portion 3 described above. Specifically, in the initial stage of burring shown in FIG. 4A, a sleeve that is punched into a cylindrical shape using the conical or cylindrical burring punch 100 while expanding the periphery of the pilot hole 2 of the blank 1. Both the first curved portion 3a and the second curved portion 3b of the portion 3 are subjected to burring deformation. On the other hand, in the end stage of burring shown in FIG. 4B, the first curved portion 3a is subjected to burring deformation, but the second curved portion 3b having a lower height than the first curved portion 3a is used. The area responsible for burring deformation is small, and strain concentration occurs at the end due to tensile deformation in the hole edge direction. Further, the plate thickness reduction accompanying the burring molding is also remarkably generated at this portion.

  Then, the second curved portion 3 b of the sleeve portion 3 becomes the straight portion 4 b of the flange portion 4 by receiving the flange forming after the burring. Therefore, in this portion, the plate thickness reduction due to the strain concentration has already occurred during the burring forming, and the plate thickness reduction further proceeds due to the further strain concentration during the flange forming.

  For this reason, as shown to Fig.5 (a), the fracture | rupture danger site | part S of a shaping | molding member becomes the edge part vicinity of the linear part 4b of the flange part 4. FIG. Further, as shown in FIG. 5B, the breakable risk portion S is located at the same position as the second curved portion 3b of the sleeve portion 3 which is a strain concentration portion during burring molding.

  Therefore, as a result of various studies based on the above findings, the present inventors have found that the vicinity of the boundary between the curved portion 4a and the straight portion 4b at the flange deformation end portion of the blank material subjected to burring and flange forming. It was found that by optimizing the difference in curvature in the trim shape of the pilot hole 2 when forming the sheet, the concentration of plastic deformation near the boundary can be alleviated and the formability of the blank can be improved.

  That is, by performing flange molding after burring molding, in order to suppress breakage at the flange deformation end portion of the blank material whose end shape includes the curved portion 4a and the straight portion 4b, the end portion of the flange portion 4 described above is used. It is effective to reduce the amount of deformation (plate thickness reduction amount and plastic strain).

  For example, when the trim shape of the pilot hole 2 that undergoes burring is a closed curve with a constant curvature, that is, a circle, the end deformation amount is the difference between the diameter of the pilot hole 2 and the diameter of the sleeve part 3 after burring, It is generally known that the gradient increases in a positive relationship.

  Therefore, in order to reduce the deformation amount of the end portion, the fracture risk portion S shown in FIG. 5B, that is, the second curved portion 3b of the sleeve portion 3 shown in FIG. It is considered effective to move in the −Z direction as viewed from the surface to reduce the deformation amount itself during the burring deformation.

  As a result, the linear portion 4b of the flange portion 4 shown in FIG. 5A moves in the + X direction when viewed from the XY plane shown in FIG. This is equivalent to moving the vertex P of the second trim curve 2b shown in FIGS. 2 and 5B in the −X direction when viewed from the XY plane.

Note that this movement amount, X-coordinate at the vertex P of the second trimming curves 2b shown in FIG. 2, the radius R ₁ of the first trimming curves 2a diameter phi ₀ of the sleeve portion 3 (burring punch 100) It is within a value (φ ₀ -2R ₁ ) obtained by subtracting 2 times.

Further, the present inventors set the value of d ₂ / d ₁ when the minimum width d ₁ of the flange portion 4 forming the curved portion 4a and the minimum width d ₂ of the flange portion 4 forming the straight portion 4b are set. Formed member between 0.56 and 0.28 when the linear portion 4b is moved in the + X direction, and when the value of d ₂ / d ₁ is 0.14 and the linear portion 4b is moved in the + X direction The thickness reduction values were compared in Example 1 below. In addition, the blank material uses the steel plate whose tensile strength is 440 Mpa or less.

As a result, contrary to expectation, by moving d ₂ / d ₁ in the + X direction from 0.56 to 0.28, the thickness reduction value is slightly decreased although it does not change substantially. When the plate was moved from .28 to 0.14 and + X, the thickness reduction value increased.

Next, in order to investigate this phenomenon in detail, in the following Example 2, the inventors of the second trim curve 2b at the position of the straight line portion 4b where d ₂ / d ₁ is 0.28. the thickness reduction value when increasing the radius R ₂ were measured.

As a result, the thickness reduction value decreased in a parabolic manner as the radius R2 of the _second trim curve 2b increased. This is considered to be because the area responsible for deformation was increased and the tensile deformation was reduced by increasing the radius R2 of the _second trim curve 2b.

Next, the inventors set the center O ′ of the second trim curve 2b in FIG. 2 at the position of the straight line portion 4b where d ₂ / d ₁ is 0.28 in Example 3 below. The plate thickness reduction value when moved to the center O side (+ X direction) of the prepared pilot hole 2 was measured.

As a result, the thickness reduction value increased as the center O ′ of the second trim curve 2b moved to the center O side of the pilot hole 2. This is the distance between the diameter phi ₀ and second trim curve 2b of the sleeve portion 3 (burring punch 100), i.e., presumably because the deformation amount itself during burring deformation increases.

Here, in Example 1 below, the linear portion 4b was moved in the −X direction (decreasing the value of d ₂ / d ₁ ), but in order to maintain the linearity of the linear portion 4b of the molded member. As a result of increasing the radius R ₂ of the second trim curve ₂ b, the position of the straight line portion 4 b is moved toward the center of the pilot hole 2, and the phenomenon verified in the following Example 2 and Example 3 competes. It is thought that.

Therefore, by performing flange forming after burring forming, in the blank material 1 whose end shape includes the curved portion 4a and the straight portion 4b, if the value of d ₂ / d ₁ is 0.42 or more, the plate thickness decreases. Since the values are almost saturated, in the present invention, burring molding and flange molding are performed within a range where d ₂ / d ₁ ≧ 0.42. As a result, the end portion deformation amount (plate thickness reduction amount and plastic strain) of the flange portion 4 can be reduced, the breakage at the flange deformation end portion can be suppressed, and the formability can be greatly improved.

A plate thickness reduction value εw ^CL corresponding to the true strain of the hole expansion limit value λ is expressed by the following formula (1). In addition, r in following formula (1) represents the Rankford value of a molded member.
εw ^CL = (r / (1 + r)) · ln (1 + λ) (1)

  According to the above formula (1), if the thickness reduction value of the end portion of the molded member is a value equal to or less than the above formula (1), the fracture due to molding does not occur.

Further, from the result of Example 1 below, the relationship between the thickness reduction value εw ^CL and d ₂ / d ₁ in the range where d ₂ / d ₁ ≧ 0.42 is expressed by the following formula (2). It is approximated by a quadratic equation.
^{_{(D 2 / d 1) CL}} = {(B 2 -4A (C-εw CL)) 0.5 -B} / 2A ... (2)
However,
−0.18 ≦ A ≦ 0.17,
0.055 ≦ B ≦ 0.06,
0.299 ≦ C ≦ 0.305
The values of A, B, and C are calculated as a regression curve based on a quadratic equation based on the average value at each d ₂ / d _1. Is calculated.

Therefore, by satisfying the relationship of the following formula (3), it is determined that the fracture due to molding does not occur.
d ₂ / d ₁ ≧ (d ₂ / d ₁ ) ^CL (3)

From the above, it is preferable to use a cold-rolled steel sheet having a Rankford value r and a hole expansion limit value λ that satisfy the relationship of the above formula (3). Conversely, from the above formula (3), when the value of d ₂ / d ₁ is determined due to design constraints, the Rankford value r and the hole expansion limit, which are necessary characteristics required for the blank 1 of the molded member Since the value λ is obtained, the steel plate can be easily selected.

The maximum in the molding member, the minimum radius of the prepared hole 2 from the first trim curve 2a is R _1, through the sleeve portion 3 of the diameter phi ₀ during burring, the flange portion 4 during flanging of the present invention until a diameter of phi ₁ curve portion 4a, so that the molding ends undergo deformation. Further, the strain amount ε corresponding to the diameter expansion at the end is expressed by the following formula (4).
ε = (φ ₁ −2R ₁ ) / 2R ₁ (4)

Therefore, when the hole expansion limit value λ is equal to or less than ε, a fracture due to molding occurs on the entire end surface. Therefore, in the present invention, burring molding and It is preferable to perform flange molding.
λ ≧ (φ ₁ −2R ₁ ) / 2R ₁ (5)

  Hereinafter, the effects of the present invention will be made clearer by examples. In addition, this invention is not limited to a following example, In the range which does not change the summary, it can change suitably and can implement.

Example 1
First, in Example 1, in the flange deformed end shape in which d ₁ / φ ₀ of the molded member shown in FIG. 1 is 0.1 and 2R ₁ / φ ₀ is 0.25, the value of d ₂ / d ₁ Was changed in the range of 0.14 to 0.7, the blank material 1 was molded, and its thickness reduction value (sheet thickness direction strain) was measured.

  A cold-rolled steel sheet (steel type A) shown in Table 1 was used as the blank material. In addition, the friction coefficient in Table 1 was identified by measuring sliding resistance by a flat bead pull-out test having a width of 20 mm. Moreover, the tensile test using a JIS13 test piece was done, and the yield stress in Table 1, tensile strength, uniform elongation, total elongation, and r value were calculated | required. The hole expansion limit value λ is identified by subjecting a φ10mm round hole to a conical punch with an apex angle of 90 degrees, and the diameter expansion rate at the point when a crack occurs at the end of the punched hole. As measured. As a result, when the one-side clearance at the time of punching was 20%, the λ value was 114%, and when the one-side clearance was 10%, the λ value was 134%. Therefore, punching was performed with a one-side clearance of 10% having a high λ value. Further, the shoulder R of the burring punch 100 used at the time of burring molding is set to be equal to or smaller than the width of the first trim curve 2a of the prepared hole 2 and the protruding second trim curve 2b.

Then, before forming, the circle centered on the pilot hole 2 of the blank material 1 is divided into 260 equal parts, a grid is drawn in the projection direction, and the grid interval is set as the gauge length, and the grid interval after burring and flange forming is set as the grid length. By measuring each, the amount of end strain of the molded member was measured, and the thickness reduction value (maximum value) of the molded end portion was obtained from the measured strain value and Rankford value. The result is shown in FIG. Note that the plate thickness reduction value showed a maximum value on the straight portion 4a side near the boundary between the curved portion 4b and the straight portion 4a of the flange portion 4 regardless of the value of d ₂ / d ₁ . Moreover, the crack by shaping | molding was not recognized by the shaping | molding edge part of the blank 1 after shaping | molding.

As shown in FIG. 6, when the value of d ₂ / d ₁ is 0.42 or more, the thickness reduction value of the forming end portion tends to be saturated, whereas the value of d ₂ / d ₁ is 0.42 If it is less than this, the thickness reduction value of the molding end tends to increase. Further, the increasing tendency of the thickness reduction value is a parabolic shape.

Moreover, the same measurement as Example 1 was performed using the various cold-rolled steel plates (steel types A to F) shown in Table 1. As a result, as shown in FIG. 7, it was found that the decrease in the thickness reduction value tends to be saturated when the value of d ₂ / d ₁ is about 0.4 or more regardless of the steel type. Moreover, in the cold-rolled steel sheet having a tensile strength of 440 MPa or less, transition to saturation was recognized with 0.42 being the lower limit. Accordingly, it can be seen that the value of d ₂ / d ₁ is preferably set to 0.42 or more in order to aim at a reduction in the thickness reduction value.

(Example 2)
Next, in Example 2, in order to investigate the phenomenon of Example 1 in detail, the radius of the second trim curve 2b at the position of the straight line portion 4a where the value of d ₂ / d ₁ is 0.28. As R ₂ , the thickness reduction value was measured when R ₂ / R ₃ was increased in the range of 0.33 to 0.465. The result is shown in FIG. In Example 2, the same cold rolled steel sheet (steel type A) as in Example 1 was used.

As a result, as shown in FIG. 8, the thickness reduction value decreased in a parabolic shape. This is probably because the area responsible for deformation was increased and the tensile deformation was reduced by increasing the radius R2 of the _second trim curve 2b as described above.

(Example 3)
Next, in Example 3, the center O of the second trim curve 2b is set as the radius R2 of the _second trim curve 2b at the position of the straight line portion 4a where the value of d ₂ / d ₁ is 0.28. The plate thickness reduction value when 'was moved to the center O side of the pilot hole 2 was measured. The result is shown in FIG.

As a result, as shown in FIG. 9, the thickness reduction value increased as the center O ′ of the second trim curve 2 b moved to the center O side of the pilot hole 2. This is the distance between the diameter phi ₀ and second trim curve 2b of the sleeve portion 3 (burring punch 100), i.e., presumably because the deformation amount itself during burring deformation increases. Note that the increasing tendency is not as significant as the influence of the radius R ₂ of the second trim curve 2b shown in the second embodiment.

Example 4
Next, in Example 4, as shown in FIG. 6, when εw ^CL becomes 0.45 under the condition of a clearance of 10% and the thickness reduction value after forming becomes 0.45 or more, the formed member breaks. It turns out that the risk is high.

The plate thickness reduction value at the forming end was 0.302 at the maximum and εw ^CL was 0.45, which indicates that the steel type can withstand deformation of the forming end.

  Next, the hole expansion limit value λ in the clearance was intentionally lowered under the condition of the clearance of 40%, and the same forming was performed with the steel type A. The hole expansion limit value in the hole expansion test is 0.66, and εwCL is 0.30.

As shown by x in FIG. 6, when the clearance value is formed at 40%, if the value of d ₂ / d ₁ is 0.28 or less, the vicinity of the boundary between the curved portion 4b and the straight portion 4a of the flange portion 4 Cracks occurred on the straight part 4a side. Therefore, in a steel type in which εw ^CL is 0.30, it can be determined that d ₂ / d _{1 has} a value of 0.28 or less and cannot be formed.

Further, when d ₂ / d ₁ is fixed according to the design requirements, for example, when each steel type in Table 1 in this example is a candidate material, the plate thickness reduction value εw ^CL from the hole expansion limit value λ of each steel type ₁ is investigated in advance, and the thickness reduction value of d ₂ / d _{1 that} is equal to or greater than the intersection with the upper limit curve of the approximate curve is compared with the thickness reduction value εw ^CL ₂ estimated from the above equation (2). If εw ^CL ₁ is equal to or greater than εw ^CL _2, it can be determined that any steel type can be formed, so that it is possible to select a formable steel type.

  DESCRIPTION OF SYMBOLS 1 ... Blank material 2 ... Pilot hole 2a ... 1st trim curve 2b ... 2nd trim curve 2c ... 3rd trim curve 3 ... Sleeve part 3a ... 1st curve part 3b ... 2nd curve part 4 ... Flange Part 4a ... Curve part 4b ... Straight line part

Claims (6)

Forming a pilot hole in a blank made of a metal plate by punching; and
Forming a sleeve portion by punching out into a cylindrical shape while expanding the periphery of the blank hole of the blank material by burring;
Forming the flange portion by bending the distal end side of the sleeve portion in the diameter-enlarging direction by flange molding,
When the minimum radius of the pilot hole is R ₁ [mm] and the hole expansion limit value in the clearance when the pilot hole is punched with a predetermined clearance is λ, the maximum diameter of the sleeve portion is 2R _1. The method for producing a molded member, wherein the burring molding is performed within a range of (λ + 1) [mm] or less and a maximum height of the sleeve portion being R ₁ · λ [mm] or less. Furthermore, the flange part which forms the said curve part among the flange deformation | transformation end part shapes which have the curve part which makes a curvilinear shape, and the linear part which makes a linear shape in the edge part of the said flange part is shown. When the minimum width is d ₁ and the minimum width of the flange portion forming the straight line portion is d ₂ ,
d ₂ / d ₁ ≧ 0.42
The method for producing a molded member according to claim 1, wherein the burring molding and the flange molding are performed within a range. Furthermore, when the Rankford value is r and the thickness reduction value corresponding to the true strain of the hole expansion limit value λ is εw ^CL ,
d ₂ / d ₁ ≧ (d ₂ / d ₁ ) ^{CL
_{(D 2 / d 1) CL}} = {(B 2 -4A (C-εw CL)) 0.5 -B} / 2A,
εw ^CL = (r / (1 + r)) · ln (1 + λ),
−0.18 ≦ A ≦ 0.17,
0.055 ≦ B ≦ 0.06,
0.299 ≦ C ≦ 0.305
The method for producing a formed member according to claim 2, wherein a cold-rolled steel sheet having r value and λ value satisfying the relationship is used. Further, the maximum diameter of the flange portion forming the curved portion when the phi _1,
λ ≧ (φ ₁ −2R ₁ ) / 2R ₁
The method for producing a molded member according to claim 2 or 3, wherein the burring molding and the flange molding are performed within a range.   The method for producing a molded member according to any one of claims 1 to 4, wherein a steel plate having a thickness of 0.5 to 1.8 mm is used as the blank material.   A cold-rolled steel sheet having a tensile strength of 440 MPa or less is used as the blank material. The method for producing a molded member according to any one of claims 1 to 5, wherein