JP2016144824A - Press workability evaluation device and press workability evaluation method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an evaluation device and an evaluation method for correctly grasping a strain state of various processing elements during composite molding without obtaining a desired composite molding.SOLUTION: A press workability evaluation device 1 comprises: a punch 13 having a salient 132 of a multi-branched shape including three or more branches 132A, 132B, 132C, etc.; a die 23 having a recess 231 which can be fitted to the salient 132, and a die side plane part 232 which surrounds the recess 231; and a plate presser 32 which has a plate presser side plane part 321 which is substantially parallel to the die side plane part 232, and can sandwich an object material of press molding between the die side plane part 232 and the plate presser side plane part 321.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a press workability evaluation apparatus and a press workability evaluation method.

  A press-formed product using a steel material or a non-ferrous material has a desired shape by causing a predetermined plastic deformation in each part.

Processing elements for plastic deformation in press molding are roughly classified into four types according to combinations of deformation in the tensile direction, deformation in the compression direction, and no deformation using the maximum principal strain and the minimum principal strain. The three orthogonal axes that maintain orthogonality after deformation are called the main axes of distortion. The vertical distortion in the main axis direction is the main distortion, and the maximum and minimum values are called the maximum main distortion and the minimum main distortion. ing. FIG. 8 illustrates these processing elements. The maximum principal strain is represented by ε ₁ , the minimum principal strain is represented by ε ₂ , and the plate thickness direction strain orthogonal to both the maximum principal strain ε ₁ and the minimum principal strain ε ₂ is represented by ε _t .
A machining element in which the maximum principal strain ε ₁ is tensile deformation and the minimum principal strain ε ₂ is not deformed is referred to as “planar strain tensile deformation” (A in FIG. 8), and the maximum principal strain ε ₁ and the minimum principal strain ε. _A working element in which 2 is a tensile deformation is called a “biaxial tensile deformation” (C in FIG. 8), a working element in which the maximum principal strain ε ₁ is a tensile deformation and the minimum principal strain ε ₂ is a compressive deformation. Is referred to as “shrink flange deformation” (D in FIG. 8), the maximum principal strain ε ₁ is tensile deformation, the minimum principal strain ε ₂ is compression deformation, and the compression is a strain equivalent to half the tension. Is referred to as “uniaxial tensile deformation” or “stretch flange deformation” (FIG. 8B).

  By the way, there are many methods for evaluating the workability of a steel material or a non-ferrous material, but most are evaluations of a single molding with one processing element. For example, a method for evaluating workability by single molding such as a hole expansion test and a saddle type test is performed. In addition, as a method for evaluating stretch flange formability of a metal plate, a metal blank having a corner cut into a V shape is press-molded by using a punch, a die and a pad to increase the stretch flange formability of the metal plate. A test method for evaluation is known (Patent Document 1).

JP 2008-264829 A

  However, in actual pressing, composite molding in which a plurality of processing elements are included in one molded product is mainly used. For example, as shown in FIG. 16, a press-formed part having a structure in which a tube branches from one to a plurality of pipes has four typical processing elements (plane strain tensile deformation, It is a composite molded article including all of biaxial tensile deformation, shrinking flange deformation, and uniaxial tensile deformation. In order to evaluate the processing stability of a composite molded product, it is necessary to accurately grasp the strain state of various processing elements. By accurately grasping the strain state of various processing elements during composite molding, the primary It becomes possible to accurately specify the cracking risk part in processing and the degree of processing of each part before performing secondary processing.

  However, the workability evaluation methods so far have evaluated the strain state for each single work element, and compared this with the actual composite molded product, which has been the final evaluation. However, since composite molding is largely influenced by other processing elements adjacent to each other in one molded product, there is a flaw between the evaluation result in single molding and the evaluation result in composite molding. There was a case.

  The present invention has been made to solve the above-described problems, and provides an evaluation apparatus and an evaluation method for accurately grasping the strain state of various processing elements at the time of composite molding with a single molded product. It is.

  The inventors of the present invention have made extensive studies to solve the above problems. As a result, it has been found that the above-described problems can be solved by using an apparatus including a punch and a die having a specific shape, and the present invention has been completed. Specifically, the present invention provides the following.

  (1) The present invention provides a punch having a multi-branch-shaped convex portion comprising three or more branches, a multi-branch-shaped concave portion comprising three or more branches that can be fitted to the convex portion, and a die surrounding the concave portion. A die having a side plane part and a plate presser side plane part substantially parallel to the die side plane part, and the target material to be pressed can be sandwiched between the die side plane part and the plate presser side plane part. A press workability evaluation apparatus for evaluating press workability of the target material.

  (2) In the present invention, when there are three multi-branched branches, the angles between adjacent branches are obtuse, and when there are four multi-branched branches, adjacent branches are The press workability evaluation apparatus according to (1), wherein an angle formed by the two branches is substantially a right angle, and when there are five or more multi-branched branches, the angles formed by adjacent branches are acute angles with each other. .

  (3) The present invention is the press workability evaluation apparatus according to the above (1) or (2), wherein the multi-branched branch has four branches, and the convex part and the concave part have a substantially cross shape. .

  (4) In the present invention, when the die is viewed in plan, the corner portion of the recess is curved, the width of the branch of the die is Wd, and the radius of curvature at the corner portion of the branch of the die is When Rc is set, the ratio Wd / Rc of the Wd to the Rc is 2 or more and less than 15, and when the punch is viewed from the front, the shoulder at the top of the convex portion is curved, and the shoulder When the radius of curvature at the portion is Rp, the thickness of the convex portion is Hp, and when the die is viewed in cross section, the bottom portion of the concave portion is curved, and the curvature radius of the bottom portion is Rd. The press workability evaluation apparatus according to any one of (1) to (3), wherein Hp ≧ (Rp + Rd) / 2.

  (5) The present invention provides a punch having a multi-branch-shaped concave portion composed of three or more branches, a multi-branch-shaped convex portion including three or more branches that can be fitted to the concave portion, and a die surrounding the convex portion. A die having a side plane part and a plate presser side plane part substantially parallel to the die side plane part, and the target material to be pressed can be sandwiched between the die side plane part and the plate presser side plane part. A press workability evaluation apparatus for evaluating press workability of the target material.

  (6) This invention press-forms the target material used as the object of press molding using the press workability evaluation apparatus in any one of said (1) to (5), and obtains a press-molded body. Press workability, including a process, and a deformation amount measuring step of measuring at least two kinds of deformation amounts among plane strain tensile deformation, uniaxial tensile deformation, biaxial tensile deformation and shrinkage flange deformation of the press-formed body. This is an evaluation method.

  (7) In the present invention, in the deformation amount measuring step, a plurality of marks are transferred in advance to the target material, the maximum principal strain and the minimum principal strain of the marks before and after press molding are measured, and the press molded body The plane strain tensile deformation is a portion corresponding to a region including the bottom adjacent to the corner of the convex portion, where the maximum principal strain is the largest and the minimum principal strain is substantially undeformed. The amount of deformation involved in the main body, the portion corresponding to the region of the side surface in the length direction in the branch of the press-formed body, the deformation amount of the portion where the maximum principal strain is the largest and the minimum principal strain is the compression deformation , The amount of deformation mainly involving the uniaxial tensile deformation, the corner portion of the convex portion of the press-molded body, and the portion corresponding to the region that is the shoulder portion, the largest principal strain is the largest , The amount of deformation at the location where the minimum principal strain is tensile deformation, And the deformation amount of the portion corresponding to the region of the flat portion surrounding the convex portion of the press-formed body, where the maximum principal strain is the largest and the smallest principal strain is the smallest. The press workability evaluation method according to the above (6), which is a step of setting a deformation amount mainly involving deformation.

  (8) The present invention further includes a crack prediction step of plotting a relationship between the maximum principal strain and the minimum principal strain of the plurality of marks and predicting a crack of the press-formed body from the result of the plot. The press workability evaluation method described in 1.

  (9) The present invention uses a blank having a quadrangular shape, an octagonal shape, an elliptical shape, or a circular shape as the target material, and the press workability evaluation method according to any one of the above (5) to (8) It is.

  When the target material to be press-molded is press-molded using the press workability evaluation apparatus according to the present invention, a press-molded body is obtained. This press-molded body has a multi-branch-shaped convex portion composed of three or more branches and a substantially flat plane portion surrounding the convex portion.

  In this press molding, the portion corresponding to the region including the bottom adjacent to the corner of the convex portion of the flat portion surrounding the convex portion of the press-molded body, the largest principal strain being the largest, the smallest principal strain being By measuring the amount of deformation before and after pressing at a location where there is no substantial deformation, it is possible to measure the amount of deformation mainly involving the plane strain tensile deformation of the press-formed body.

  In addition, by measuring the amount of deformation before and after pressing at a portion corresponding to the region of the side surface in the length direction in the branch of the press-formed body, where the largest principal strain is the largest and the smallest principal strain is compression deformation. The amount of deformation mainly involving uniaxial tensile deformation of the press-molded product can be measured.

  And the deformation before and after the press at the corner of the convex part of the press-molded body and corresponding to the region which is the shoulder, where the largest principal strain is the largest and the smallest principal strain is the tensile deformation By measuring the amount, it is possible to measure the amount of deformation mainly involving the biaxial tensile deformation of the press-formed body.

  Furthermore, by measuring the amount of deformation before and after pressing at a location corresponding to the region of the flat portion surrounding the convex portion of the press-formed body, where the maximum principal strain is the largest and the smallest principal strain is the smallest, It is possible to measure the amount of deformation in which the body shrinkage flange deformation is mainly involved.

  According to the present invention, various processing elements (planar strain tensile deformation, biaxial tensile deformation, shrinkage flange deformation, and uniaxial) when the target material to be press-molded is subjected to composite press molding without obtaining a desired composite molded product. The strain state (tensile deformation) can be accurately grasped.

It is a schematic sectional drawing for demonstrating the press workability evaluation apparatus 1 which concerns on this invention. It is a figure for demonstrating the punch 13 which concerns on one Embodiment. It is a figure for demonstrating the punch 13 which concerns on other embodiment. It is a figure for demonstrating the dice | dies 23. FIG. It is a figure for demonstrating the board presser. It is a schematic explanatory drawing which shows an example of the press molded object 40 obtained using the press molding method which concerns on this invention. It is a figure for demonstrating the state of a press molding regarding ratio Wd / Rc of the width Wd of the branch in the die | dye 23, and the curvature radius Rc of a corner | angular part. It is a figure for demonstrating the processing element of the plastic deformation of press molding. It is a figure which shows the relationship between the minimum principal strain in each said process element, and the largest principal strain. It is a figure which shows the dimension of the die | dye and punch which were used in Test Example 1 and 2. FIG. It is a figure which shows the distortion distribution before and behind the process of the press molding which concerns on a test example. It is a figure which shows the distortion state of the press-molded body which concerns on a test example. FIG. 12 is a diagram obtained by superimposing ad in FIG. 11 on FIG. It is a figure which shows the plate | board thickness change rate in the position ad in FIG. It is a figure which shows the tensile strain state of the largest principal strain direction in the position ac of FIG. It is a figure which shows an example of the press molding component which has a structure where a pipe | tube branches from one to several.

  Hereinafter, specific embodiments of the present invention will be described in detail. However, the present invention is not limited to the following embodiments, and may be implemented with appropriate modifications within the scope of the object of the present invention. can do.

<Press workability evaluation apparatus 1>
FIG. 1 is a schematic diagram for explaining a press workability evaluation apparatus 1 according to the present invention. The press workability evaluation apparatus 1 includes a punch portion 10, a die portion 20 that can be fitted to the punch portion 10, and guide portions 30 </ b> A and 30 </ b> B provided on both sides of the punch portion 10 and the die portion 20.

  The punch unit 10 includes a bottom plate 11, a punch holder 12 provided on the surface of the bottom plate 11, and a punch 13 supported on the surface of the punch holder. The die portion 20 includes an upper plate 21, a die holder 22 provided on the bottom surface of the upper plate, and a die 23 supported on the bottom surface of the die holder 22. The guide portions 30A and 30B are provided on both sides of the die portion 20 and are provided on both sides of the punch pins 10 and guide pins 31A and 31B that define the moving direction of the die portion 20, and target materials (hereinafter referred to as press forming objects). , Abbreviated as “material to be press-molded”) and the plate retainers 32A and 32B that can be sandwiched together with the die part 20, and cushion pins 33A and 33B that are provided at the bottom of the plate retainers 32A and 32B and support the plate retainers 32A and 32B. And have. FIG. 1 shows a mode in which a plate material 50 as a material to be press-molded is arranged between the punch 10 and the die 23. The plate member 50 is drawn between the punch 13 and the die 23 during the press work, and the outer periphery thereof contracts. Therefore, the plate member 50 having a sufficiently larger width than the punch 13 is used.

[Punch 13]
FIG. 2A is a schematic perspective view showing an example of the punch 13 and is an example in the case where there are four multi-branched branches. The punch 13 has a convex portion 132. The convex part 132 has a multi-branch shape composed of four convex parts 132A, 132B, 132C, 132D.

  FIG. 2B is a plan view of the punch 13, and FIG. 2C is a front view of the punch 13.

  The convex portion 132 has a multi-branch shape including three or more branches 132A, 132B, 132C, and 132D. If the convex portion 132 of the punch 13 is not formed in a multi-branch shape, when the press molding is performed, it is not possible to form an intersecting portion where adjacent branches of the press molded body intersect with each other. Since strain tensile deformation cannot be measured suitably, it is not preferable.

  The number of branches is not particularly limited, but the shape of the press-molded body is relatively simple. From among the plane strain tensile deformation, uniaxial tensile deformation, biaxial tensile deformation, and shrinkage flange deformation of the press molded body. The number of branches is preferably 3 or more and 8 or less, more preferably 3 or more and 5 or less, in that at least two or more deformation amounts can be measured relatively easily. Further, when examining the effect of the rolling direction of the material at the branch tip or branch intersection, it is 0 °, 45 °, 90 ° with respect to the rolling direction of the material to be press-formed, which is performed in a general tensile test. In order to collect accurate distortion amount data in each direction, the number of branches is particularly preferably four.

  The preferred angle between adjacent branches varies depending on the number of multi-branched branches. When there are three multi-branched branches, it is preferable that the angles formed by adjacent branches are obtuse. When there are four multi-branched branches, it is preferable that the angle formed between adjacent branches is substantially a right angle. When there are five or more multi-branched branches, it is preferable that the angles formed by adjacent branches are acute angles. It should be noted that the angle formed between adjacent branches may include both an obtuse angle and an acute angle.

  3A is a plan view showing an example of a punch 13 ′ having three multi-branched branches, and FIG. 3B is a punch 13 having five multi-branched branches. It is a top view which shows an example of ''. Adjacent branches as shown in FIGS. 2 and 3 in order to more accurately grasp the deformation state of various processing elements (plane strain tensile deformation, biaxial tensile deformation, contraction flange deformation and uniaxial tensile deformation). More preferably, the angles formed by are substantially equal to each other. That is, the angle formed by adjacent branches is more preferably about (number of branches) / 360 °. Specifically, when there are three multi-branched branches, it is preferable that the angles formed by adjacent branches are approximately 120 ° with each other, and the convex portion 12 is formed in a substantially three-pointed shape. When there are three multi-branched branches, it is preferable that the angles formed by adjacent branches are substantially perpendicular to each other, and the convex portion 12 is formed in a substantially cross shape. Further, when there are five multi-branched branches, the angle between adjacent branches is approximately 72 °, and it is preferable that they are substantially star-shaped.

As shown in FIG. 2B, when the punch 13 has a plan view of the convex portion 132 of the punch, the punch corner portion e ₁ of the convex portion 132 is curved inward in the radial direction of the punch 13. A punch corner f ₁ of 132 is curved outward in the radial direction of the punch 13. In this specification, the punch corners e ₁ of the protrusion 132, of the periphery of the convex portion 132 (edge), refers to a branch is formed in a convex direction protrudes peripheral portion, the punch corner of the protrusion 132 The part f ₁ refers to a part formed in the concave direction formed by adjacent branches in the peripheral edge (edge) of the convex part 132.

In addition, as shown in FIG. 2C, when the punch protrusion 132 is viewed from the front, the punch shoulder g at the top of the branches 132A, 132B, 132C, 132D among the peripheral edges (edges) of the protrusion 132. ₁ has an R (curve) that is curved with a radius of curvature Rp on the radially inner side of the punch 13, and the outer shape from the punch shoulder g ₁ toward the base of the convex portion 132 has a shape extending substantially in the vertical direction. Yes. In this specification, the top part of the convex part 132 refers to the side of the convex part 132 that comes into contact with the material to be pressed, and the base part of the convex part 132 is disposed on the punch holder 12 in the convex part 132. Say the side.

  In addition, when the thickness from the top to the base of the convex portion 132 of the punch is Hp, it is preferable that Hp ≧ (Rp + Rd) / 2. When Hp is (Rp + Rd) / 2 or more, the plane strain tensile deformation and uniaxial tensile deformation of a press-molded product obtained by press-molding the target material can be suitably measured.

[Dice 23]
FIG. 4A is a schematic perspective view showing an example of the die 23, which is an example of the die used in combination with the punch 13 having four branches. 4B is a plan view of the die 23, and FIG. 4C is a cross-sectional view taken along line XX of FIG. 4A.

  As shown to (a) of FIG. 4, the die | dye 23 is formed so that fitting with the punch 13 is possible. The die 23 has four concave portions 231 that can be fitted to the convex portion 132 of the punch 13, and a die-side flat portion 232 that surrounds the concave portion 231.

As shown in FIG. 4B, when the dice 23 has a plan view of the recess 231, the dice corners e ₂ of the branches 231 A, 231 B, 231 C, and 231 D of the recess 231 are curved radially inward of the dice 23. and none of R (curve) for curving radius Rc, branches of the recess 132 231A, 231B, 231C, die corners _{f 2} of 231D causes the bending radius of curvature Rc in the radially outer side of the die 23 R (curve) I am doing. In this specification, the dice corners e ₂ of the branches 231A, 231B, 231C, and 231D of the recess 231 refer to portions formed in the convex direction on the periphery (edge) of the recess 231, and the branch 231A of the recess 231. The die corners f _{2 of} 231B, 231C, and 231D are portions formed in the concave direction among the peripheral edges (edges) of the concave portion 231.

Further, as shown in FIG. 4 (c), when the concave portion 231 of the die is viewed in a cross section of the concave portion (XX plane in FIG. 4 (a)), the side of the concave portion 231 on the side in contact with the material to be pressed. The bottom h ₂ forms an R (curve) that is curved with a radius of curvature Rd on the outside in the radial direction of the die 23. Contour extending from the die bottom part h ₂ at the base of the recess 231 has a shape extending substantially longitudinally. In this specification, the base of the recess 231 refers to the side of the recess 231 that is disposed on the die holder 22.

In order to be able to suitably measure the biaxial tension and shrinkage flange of the press-molded body obtained by press-molding the target material, the width of the branches 231A, 231B, 231C, 231D of the die recess 231 is Wd, and the branches 231A, When the radius of curvature at the die corner portion e ₂ of 231B, 231C, 231D is Rc, the ratio Wd / Rc of Wd to Rc is preferably 2 or more and less than 15, and more preferably 3 or more and less than 12. .

As shown in FIG. 7A, if Wd / Rc is too small (Rc is too large), in the press-molded body, stress is locally concentrated at the boundary of the branch corner e ₃ , and the press-molded body Can cause cracking. As shown in (b) of FIG. 7, Wd / Rc is too large (when Rc is too small), the pressed bodies, plastic strain region is reduced in the circumferential direction of the corner portion e ₃ of the branch, corner e ₃ is not preferable because cracks may occur. In addition, in this specification, a curvature radius shall mean the value calculated | required with the contour shape measuring device (model: Contracer CV-2000, product made by Mitutoyo Corporation).

[Plate presser 32]
FIG. 5 is a view for explaining the plate presser 32. The plate retainer 32 has a plate retainer side planar portion 321 substantially parallel to the die side planar portion 232, and is configured to be able to sandwich a press molding target material between the die side planar portion 232 and the plate retainer side planar portion 321. When the press workability evaluation apparatus 1 does not include the plate presser 32, when the material to be press-molded is press-molded, the substantially planar region surrounding the multi-branched region of the press-molded body cannot be formed, and the press-molded body shrinks. This is not preferable because the flange deformation cannot be measured appropriately.

[Modification]
1 to 5, the punch 13 has a convex multi-branch shape and the die 23 has a concave multi-branch shape. However, the present invention is not limited to this. Even when the punch 13 has a concave multi-branch shape and the die 23 has a convex multi-branch shape, the same effect can be obtained.

  Specifically, the press workability evaluation apparatus includes a punch having a multi-branch-shaped concave portion including three or more branches at the tip, and a multi-branched convex portion including three or more branches that can be fitted to the concave portion, And a die having a die side plane part surrounding the convex part, and a plate presser side plane part substantially parallel to the die side plane part, and the material to be press-molded is the die side plane part and the plate presser side plane part. It may be provided with a plate presser that can be sandwiched between.

  Even in the press workability evaluation apparatus according to this modified example, if the unevenness of the punch and the die is exchanged, the angle between adjacent branches and the parameters such as Wd, Rc, Hp, Rp, and Rd are suitable. This range is the same as described above.

<Method for evaluating press workability>
Hereinafter, the press workability evaluation method according to the present invention will be described. In this method, a material to be press-molded is press-molded by using the above-described press workability evaluation apparatus 1 to obtain a press-molded body, plane strain tensile deformation, uniaxial tensile deformation, biaxial of the press-molded body A deformation amount measuring step of measuring at least two kinds of deformation amounts among the tensile deformation and the contraction flange deformation. The method of the present invention plots the relationship between the maximum principal strain and the minimum principal strain for each of the two or more types of deformation measured in the deformation amount measurement step, and predicts cracks in the press-formed product from the results of the plot. It is preferable to further include a crack prediction step.

[Press forming process]
The press molding step is a step of press molding a press molding target material using the press workability evaluation apparatus 1 described above. Using a die composed of a punch 13 and a die 23 having a predetermined shape, the plate material to be press-molded is subjected to press work, and a press-worked body having a shape corresponding to the punch shape and the die shape is formed. Since the plate material is drawn between the punch 13 and the die 23, a plate material having a width sufficiently larger than the width of the punch 13 is used.

  FIG. 6 is a schematic view showing an example of a press-formed body 40 obtained in the press-forming step. 6 (a) is an image, FIG. 6 (b) is a perspective view schematically showing it, and FIG. 6 (c) is a plan view thereof, and FIG. 6 (d). ) Shows a front view from the direction marked Z in FIG. The press-molded body 40 has a convex portion 41 and a substantially flat plane portion 42 surrounding the convex portion 41. Moreover, the convex part 41 is exhibiting the multi-branch shape which consists of the branches 43A, 43B, 43C, and 43D.

Since the material to be press-molded is deformed by being processed between the branch 132 of the punch 13 and the concave portion 231 of the die 23, the convex portion 41 (branches 43A, 43B, etc.) of the press-formed body 40 is formed by the punch 132A, 132B, etc. The flat portion 42 is shaped so as to correspond to the top surface of the die 23 and the flat surface of the plate presser 32. Molded. That is, the convex part 41 of the press-molded body has a shape corresponding to the punch corner part e ₁ , the punch corner part f ₁ , and the punch shoulder part g ₁ of the punch 13 as shown in FIGS. As the shapes corresponding to the die corner part e ₂ , the die corner part f ₂ , and the die bottom part h ₂ of the die 23 as shown in FIGS. 4A to 4C, the corner part e ₃ , the corner part f ₃ , and the shoulder part. Sites such as g ₃ and bottom h ₃ are provided.

[Deformation measurement process]
The deformation amount measuring step is a step of measuring at least two or more types of deformation amounts among the plane strain tensile deformation, uniaxial tensile deformation, biaxial tensile deformation, and shrinkage flange deformation of the press-formed body.

As a method for measuring the amount of deformation, the following steps (1) to (4) may be performed using a non-contact strain measuring device ARGUS (manufactured by GOM / Kobelco Research Institute).
(1) Formed by electrolytic transfer of φ0.8 mm dot marks (1.5 mm intervals) as a plurality of marks on the surface of a press molding target material (test material).
(2) Photograph the formed dot marks from multiple directions using a CCD camera before and after processing.
(3) The distance between dots before and after processing is measured based on the photographed dot mark, and the maximum principal strain and the minimum principal strain are calculated from the amount of change.
(4) Based on the maximum principal strain and the minimum principal strain, at least two types of deformation amounts are measured from the plane strain tensile deformation, uniaxial tensile deformation, biaxial tensile deformation, and shrinkage flange deformation of the press-formed body.

  In order to describe the procedure (4) in detail, first, the processing elements for plastic deformation of press molding will be described with reference to FIG.

The plastic deformation processing elements are roughly classified into four types according to combinations of deformation in the tensile direction, deformation in the compression direction, and no deformation using the maximum principal strain and the minimum principal strain. FIG. 8 shows the machining elements. The maximum principal strain is ε ₁ , the minimum principal strain is ε ₂ , and the plate thickness direction strain orthogonal to both the maximum principal strain ε ₁ and the minimum principal strain ε ₂ is shown. It has been described as ε _t.
A machining element in which the maximum principal strain ε ₁ is tensile deformation and the minimum principal strain ε ₂ is not deformed is referred to as “planar strain tensile deformation” (A in FIG. 8). A machining element in which the maximum principal strain ε ₁ and the minimum principal strain ε ₂ are both tensile deformations is referred to as “biaxial tensile deformation” (C in FIG. 8). A machining element in which the maximum principal strain ε ₁ is tensile deformation and the minimum principal strain ε ₂ is compression deformation is referred to as “shrink flange deformation” (D in FIG. 8). The machining element in which the maximum principal strain ε ₁ is tensile deformation, the minimum principal strain ε ₂ is compression deformation, and the compression is a strain equivalent to ½ of tension is “uniaxial tensile deformation” or “stretch flange deformation” ( This is referred to as B) in FIG.

Next, procedure (4) will be described. First, in the plane strain tensile deformation, since the maximum principal strain ε ₁ is a tensile deformation and the minimum principal strain ε ₂ is a working element without deformation, a region having a strain state close to the working element in a press-formed product. Can be determined to be a region processed by being strongly subjected to plane strain tensile deformation. In the present embodiment, a press-molded body 40 as shown in FIG. 6 is formed by processing with the punch 13 shown in FIG. 2 and the die 23 shown in FIG. On the periphery of the convex portion 41 of the press-formed body 40, the region C is adjacent to the corner portion f ₃ having a shape corresponding to the punch corner portion f ₁ of the punch 13 and corresponding to the die even portion f ₂ of the die 23. Is formed. The region C includes a bottom portion h ₃ having a curved shape formed corresponding to the radius of curvature Rd of the die bottom portion h ₂ of the die 23. The region C is a region that is strongly subjected to plane strain tensile deformation because the maximum principal strain ε ₁ is large and the minimum principal strain ε ₂ is measured with a strain amount close to zero. In the region C, the amount of deformation before and after pressing at a location where the maximum principal strain ε ₁ is the largest and the minimum principal strain ε ₂ is substantially undeformed is an amount mainly involving plane strain tensile deformation.

In the uniaxial tensile deformation, the maximum principal strain ε ₁ is tensile deformation, the minimum principal strain ε ₂ is compression deformation, and the strain amount due to compression is a processing element corresponding to ½ of the strain amount due to tension. In the present embodiment, a region S is formed on the side surfaces in the length direction of the branches 43A, 43B, 43C, and 43D of the press-formed body 40 shown in FIG. The area S corresponds to the shape extending in the substantially vertical direction from the punch base to punch shoulder c _1, which is formed corresponding to the shape extending in the substantially vertical direction from the die base to the die shoulder c ₂ It includes areas. The region S is a region where the maximum principal strain ε ₁ is large and the minimum principal strain ε ₂ is measured as compressive deformation, and thus is strongly subjected to uniaxial tensile deformation. In the region S, the amount of deformation before and after pressing at the place where the maximum principal strain ε ₁ is the largest and the minimum principal strain ε ₂ is the compressive deformation is the amount mainly involving uniaxial tensile deformation.

Biaxial tensile deformation is a processing element in which the maximum principal strain ε ₁ and the minimum principal strain ε ₂ are both tensile deformations. In the present embodiment, a region T which is a corner portion of the convex portion 41 of the press-formed body 40 shown in FIG. 6 and is a shoulder portion is formed. The region T includes regions formed corresponding to the shapes of the punch corner part e ₁ and the punch shoulder part g ₁ of the punch 13 and the die corner part e ₂ and the die bottom part h ₂ of the die 23. The region T is a region that is strongly subjected to biaxial tensile deformation because the maximum principal strain ε ₁ and the minimum principal strain ε ₂ are measured as large tensile strains. In the region T, the amount of deformation before and after pressing at the location where the maximum principal strain ε ₁ is the largest and the minimum principal strain ε ₂ is the tensile deformation is an amount mainly involving the biaxial tensile deformation.

Shrink flange deformation is a working element in which the maximum principal strain ε ₁ is tensile deformation and the minimum principal strain ε ₂ is compression deformation. In the present embodiment, in the flat portion 42 of the press-formed body 40 shown in FIG. 6, for example, the region F around the corner of the convex portion corresponds to the upper surface on the top side of the die 23 and the flat surface of the plate presser 32. It includes the formed region. The region F is a region that is strongly subjected to shrinkage flange deformation because the maximum principal strain ε ₁ is measured as a large tensile strain and the minimum principal strain ε ₂ is measured as a large compressive strain. In the region F, the maximum principal strain epsilon ₁ is the largest, the minimum principal strain epsilon ₂ amount of deformation before and after the press of the smallest portion, shrinkage flange deformation is the amount involved in principal.

[Crack prediction process]
The crack prediction process will be described with reference to FIG. The crack prediction step is a step of plotting the relationship between the maximum principal strain and the minimum principal strain for each of two or more types of deformation measured in the deformation amount measurement step, and predicting the crack of the press-formed body from the result of this plot. is there. This plot can be created as a shaping diagram, for example. In this specification, crack prediction is performed using the non-contact strain measuring device ARGUS.

9, the ordinate indicates the magnitude of the maximum principal strain epsilon _1, the horizontal axis indicates the magnitude of the minimum principal strain epsilon _2. In the case of plane strain tensile deformation, since the maximum principal strain ε ₁ is tensile deformation and the minimum principal strain ε ₂ is not deformed, the deformation form in the direction of the straight line L ₁ (ε ₂ = 0) corresponding to the vertical axis in FIG. Corresponds to plane strain tensile deformation.

In the case of biaxial tensile deformation, since the maximum principal strain ε ₁ and the minimum principal strain ε ₂ are both tensile deformations, the deformation form in the direction of the straight line L ₃ (ε ₁ = ε ₂ ) in FIG. Corresponds to deformation.

In the case of shrinkage flange deformation, since the maximum principal strain ε ₁ is tensile deformation and the minimum principal strain ε ₂ is compression deformation, the deformation form in the direction of the straight line L ₄ (ε ₁ = −ε ₂ ) in FIG. Corresponds to shrinkage flange deformation.

In the case of uniaxial tensile deformation (elongation flange deformation), since the strain amount due to compression is equivalent to ½ of the strain amount due to tension, the deformation form in the direction of the straight line L ₂ (ε ₁ = −2ε ₂ ) in FIG. Corresponds to uniaxial tensile deformation.

If the amount of strain at the time of press working becomes excessive, processing cracks are likely to occur. As shown in FIG. 9, as the maximum principal strain ε ₁ and the minimum principal strain ε ₂ increase, tensile cracks are more likely to occur. On the other hand, when the maximum principal strain ε ₁ is reduced and the minimum principal strain ε ₂ is shifted in the compressing direction (minus side), the occurrence of tensile cracks is suppressed.

Further, the processing elements indicated by L _{1 to} L ₄ have a decrease or increase in the plate thickness depending on the respective strain states. When this plate thickness change amount becomes excessive, the processing cracks occur, Depending on the thickness change, tensile cracks or compression cracks are likely to occur. Among these, in the deformation mode close to L _{1 to} L ₃ , the ratio of tensile deformation is large and the thickness is in the direction of decreasing, so the occurrence of tensile cracks is predicted. Variations in close proximity to L ₄ represents the proportion of compressive deformation is large, because the direction in which the plate thickness is increased, the occurrence of compression cracking is predicted.

The present invention measures the strain state (strain distribution) after being pressed under such a prediction, and based on the strain state of the portion that is strongly receiving the processing elements L _{1 to} L ₄ , It predicts the possibility of processing cracks and evaluates the press workability of the original sheet.
Specifically, the strain state (strain distribution) is measured in the deformed region subjected to press processing, plotted as a forming diagram, and from the plotted results, a location where the maximum main strain and the minimum main strain are large is specified, The plate thickness reduction rate can be calculated based on the strain state at this specific location, and the success or failure of the work crack can be predicted.

  According to the present invention, various processing elements (planar strain tensile deformation, biaxial tensile deformation, contraction flange deformation, and uniaxial tensile deformation) when the material to be pressed is subjected to composite press molding without obtaining a desired composite molded product. The strain state can be accurately grasped. If there is a plot at a location where the maximum principal strain is large or a location where the minimum principal strain is large, it can be predicted that the plate thickness of the measurement target can be greatly reduced when the measurement target is press-molded. As a result, it can be predicted that when the material to be press-molded is subjected to composite press molding, the composite press-molded product produced is likely to crack.

Furthermore, results of plotting of the _above, as compared to the strain on the L 1 ~L _4, it is possible to determine the degree (proximity) coming close to the L 1 ~L _4. When the molding material and processing conditions are changed, the strain amount and proximity of the measurement area also change. By comparing changes in the strain amount and proximity, the processability and processing stability of the molding material can be evaluated and suitable. Machining conditions can be evaluated.

EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited thereto.

<Manufacture of press-molded bodies>
[Test Example 1]
SUS430 (ferritic stainless steel) with a plate thickness of 0.8 mm is used as a test material, and a press molding target material cut into a substantially square shape with a side of 300 mm is shown below in the press workability evaluation apparatus. Press molding was performed under the pressing conditions to obtain a press-molded body.

  FIG. 10A shows a plan view of the die 23 used, and FIG. 10B shows a cross-sectional view of the die 23 taken along line YY. FIG. 10 (c) shows a front view of the used punch 13.

(Press conditions)
Equipment: 2000kN Servo press Dies and punches: As shown in Fig. 10 Plate pressing force: 9.5 tons Speed: 5spm
Lubrication condition: Surface protective film for processing SPV3633 (manufactured by Nitto Denko Corporation)
Target material direction: The rolling direction is parallel to the longitudinal direction of the mold. Processing height: 32 mm

[Test Example 2]
A press-formed body is obtained by the same method as in Test Example 1 except that the material to be press-molded is SUS430 improved steel (ferritic stainless steel for high workability) having a length of 300 mm square and a plate thickness of 0.8 mm. It was.

<Analysis>
(Measurement of deformation)
As described above, the amount of deformation was measured by the following method using a non-contact strain measuring device ARGUS (manufactured by GOM / Kobelco Research Institute).
(1) φ0.8 mm dot marks (1.5 mm intervals) were formed by electrolytic transfer on the surface of the target material (test material) before processing.
(2) The dot mark before press processing and the dot mark after press processing were photographed from multiple directions using a CCD camera.
(3) The distance between dots before and after processing was measured based on the photographed dot marks, and the maximum principal strain and the minimum principal strain were calculated from the amount of change.

[Creation of forming line]
From the above calculation results, for each dot mark, a plurality of coordinates can be obtained with the maximum principal strain as the vertical axis coordinate and the minimum main strain as the horizontal axis coordinate. FIG. 11 shows a strain distribution obtained by plotting the plurality of coordinates. In this strain distribution, the deformation in the direction of the straight line L ₁ (ε ₂ = 0) corresponds to plane strain tensile deformation, and the deformation in the direction of the straight line L ₂ (ε ₁ = −2ε ₂ ) corresponds to uniaxial tensile deformation. . The deformation in the direction of the straight line L ₃ (ε ₁ = ε ₂ ) corresponds to biaxial tensile deformation, and the deformation in the direction of the straight line L ₄ (ε ₁ = −ε ₂ ) corresponds to shrinkage flange deformation. The shaded area corresponds to the size of the maximum principal distortion, and indicates that the maximum principal distortion amount is larger as the color is lighter, and the maximum principal distortion amount is smaller as the color is closer to dark color.

Further, a forming line can be obtained by connecting the outermost lines of the strain distribution. For example, in the forming line shown in FIG. 11, a curved line having a shape protruding from a to d is drawn. These a to d are located at locations where the maximum principal strain ε ₁ and the minimum principal strain ε ₂ are large in the region measured by the press-molded body, and the deformation forms of the four processing elements A to D are strongly strengthened. This is the area you are receiving. These measurement points, of which, is a point closest to the straight line L _1, corresponds to a suitable location for placement of the plane strain tensile deformation, b that is closest to the straight line L ₂ is a uniaxial tensile deformation corresponds to a suitable location for placement, the c point closest to the straight line L _3, the biaxial tensile corresponds to a suitable location for placement of the deformation, d that is closest to the straight line L ₄ are, shrinkage measurements flange deformation It corresponds to a suitable location.

As shown in FIG. 11, the press-molded body according to Test Example 2 is compared with the press-molded body according to Test Example 1 at point a (measurement location mainly involving plane strain tensile deformation), point c (biaxial). The maximum principal strain ε ₁ at the measurement location where the tensile deformation is mainly involved) and the point d (measurement location where the shrinkage flange deformation is mainly involved) was small. From this, the stainless steel used in Test Example 2 has a smaller reduction in plate thickness than the stainless steel used in Test Example 1, and when the composite press-molded into an arbitrary shape, cracks in the press-formed product are not observed. It is thought that it was suppressed.

Table 1 summarizes the conditions under which machining cracks are likely to occur in the machining region. In addition to large maximum principal strain and minimum principal strain, work cracks are likely to occur depending on the degree to which a to d are close to or separated from L _{1 to} L ₄ . The reason will be described based on the fact that the plate material during press molding has a constant volume relationship.

For example, if a is close to L _1, by the tensile strain is biased in one axial direction (maximum principal strain direction), becomes narrow strain range in the plane of the plate, it tends to occur a local thickness reduction . b is if leaving the maximum principal strain direction from L _2, the effect of the plate thickness increase due to compressive strain is reduced, leading to local thickness reduction. Further, when c is close to L ₃ , the strain is equalized in the biaxial direction, so that the in-plane strain is easily spread uniformly, whereas when c is away from L _{3 in the} maximum principal strain direction, The uniform strain area becomes narrow and local thickness reduction is likely to occur. If d is separated from L ₄ to the minimum principal strain direction, pulling elements of one axial (maximum principal strain direction) is reduced, since the compressive strain in the plane of the plate becomes excessive, the follow-up of the plate thickness increases It becomes difficult and cracking is likely to occur.

  FIG. 12 schematically shows the strain distribution visualized by superimposing the strain distribution shown in FIG. 11 on the press-formed body. A broken line shows the outline of the convex part of a press-molded body. The position of the solid line corresponds to the position of each dot mark, the direction of the solid line corresponds to the direction of the maximum principal strain for each dot mark, and the length of the solid line is the size of the maximum principal strain for each dot mark. Correspond. In addition, the shaded area corresponds to the size of the maximum principal distortion, indicating that the maximum principal distortion amount is larger as the color is closer to light color, and that the maximum principal distortion amount is smaller as the color is closer to dark color. Show.

FIG. 13 is a detailed description of the maximum principal strain and the minimum principal strain at locations corresponding to the points a to d shown in FIG. Portions surrounded by circles a to d indicate portions corresponding to the points a to d. An arrow ε ₁ described in a circle indicates a direction in which the maximum principal strain is generated at the points a to d, and an arrow ε ₂ indicates a direction in which the minimum principal strain is generated at the points a to d. The direction of the arrow indicates the direction of deformation, the outward arrow indicates that the deformation is tensile deformation, and the inward arrow indicates that the deformation is compression deformation. Incidentally, the measurement of plane strain tensile deformation is suitable at the position of point a, the measurement of uniaxial tensile deformation is suitable at the position of point b, and the measurement of biaxial tensile deformation is suitable at the position of point c, At the position of the point d, it is preferable to measure the shrinkage flange deformation. Hereinafter, the points a to d may be referred to as positions a to d.

As shown in FIG. 13, (a) at a location corresponding to a region including the bottom h ₃ adjacent to the corner f ₃ of the convex portion of the press-molded body (a region including the position a and corresponding to C in FIG. 6). It can be seen that plane strain tensile deformation occurs. In addition, it is understood that (a) uniaxial tensile deformation occurs in a portion corresponding to the region of the side surface in the length direction in the branch of the press-formed body (the region including the position b and corresponding to S in FIG. 6). . In addition, (c) a portion corresponding to a region that is the corner portion e ₃ of the convex portion of the press-formed body and that is the shoulder portion g ₃ (a region that includes the position c and corresponds to T in FIG. 6) It can be seen that axial tensile deformation has occurred. In addition, it can be seen that (f) shrinkage flange deformation occurs in a portion corresponding to the area of the flat portion of the press-molded body (an area including the position d and corresponding to F in FIG. 6). That is, the press-formed body according to the test example includes all of four processing elements (plane strain tensile deformation, biaxial tensile deformation, shrinkage flange deformation, and uniaxial tensile deformation), and the position a is plane strain tensile deformation. For measurement, position b is suitable for measurement of uniaxial tensile deformation, position c is suitable for measurement of biaxial tensile deformation, and position d is suitable for measurement of uniaxial tensile deformation.

[Relationship between various deformations and plate thickness change rate]
The plate thickness change rate before and after press molding was measured at positions a to d in FIG. The change in the plate thickness was measured with an ultrasonic thickness meter (model: 38DL-PLUS, manufactured by Olympus Corporation). FIG. 14 shows the result. As shown in FIG. 14, the press-formed body according to Test Example 2 has a reduced plate thickness change rate at positions a to c and a reduction in plate thickness compared to the press-formed body according to Test Example 1. . Therefore, it can be seen that when the steel material of Test Example 1 is subjected to composite press molding into an arbitrary shape, cracking of the press-formed product can be suppressed.

[Degree of tension in the maximum principal strain direction]
FIG. 15 shows the tensile strain state in the maximum principal strain direction at positions a to c in FIG. In FIG. 15, the direction of the arrow indicates the direction of the maximum principal strain, and the size of the arrow indicates the size of the maximum principal strain. Further, the shade corresponds to the size of the maximum principal strain, and indicates that the maximum principal strain amount is larger as the color is lighter, and the maximum principal strain amount is smaller as the color is closer to dark color.

  In FIG. 15, a position “a” is a portion suitable for measurement of plane strain tensile deformation, and is a portion where the plate thickness of the press-formed body decreases as shown in FIG. As shown in FIG. 15, the press-formed body according to Test Example 2 had a smaller plane strain tensile deformation amount than the press-formed body according to Test Example 1, and the plate thickness change rate was suppressed.

  Further, in FIG. 15, position b is a location suitable for measurement of uniaxial tensile deformation, and the press-formed body according to Test Example 2 is more uniaxial tensile deformation amount than the press-formed body according to Test Example 1. Was big.

  From these facts, the press-formed body according to Test Example 2 undergoes uniaxial tensile deformation at the position b as compared with the press-formed body according to Test Example 1, and as a result, the plane strain at the position a adjacent to the position b. It is thought that the tensile deformation was suppressed to a low level and the plate thickness change rate was suppressed to a low level.

The r value (plastic strain ratio) is an index indicating the ratio ε _w / ε _t of the logarithmic strain ε _w in the width direction and the logarithmic strain ε _{t in the} plate thickness. When a plate material having a high r value is pulled and deformed, the reduction rate of the plate thickness is low and it is difficult for the plate material to be thinned. Therefore, the material is less likely to break during deep drawing than a plate material having a low r value. From this, it can be said that the processing by simple tensile deformation is a processing element that is strongly influenced by the r value.

  Therefore, the r value was measured for each of the press-formed bodies according to Test Examples 1 and 2. The r value of the press-formed body according to Test Example 1 was 0.90 on average, and the r value of the press-formed body according to Test Example 2 was 1.74 on average. This result is consistent with the tendency shown in FIG. 14 in which the press-formed body according to Test Example 2 in which simple tensile deformation was large compared with the press-formed body according to Test Example 1 in which the plate thickness reduction rate was suppressed. Met.

  From the above, by using the press workability evaluation apparatus according to the present invention, various processing elements (plane strain tensile deformation, biaxial tensile deformation, contraction flange deformation, and uniaxial tension at the time of composite molding by one molded product. Deformation) can be accurately grasped. Since it is not necessary to compare with the evaluation result by a single processing element as in the prior art, there is no problem caused by the conflict between single molding evaluation and composite molding evaluation. Therefore, it is possible to accurately evaluate processability and process stability of an actual composite molded product.

  In addition, by plotting the measurement results and obtaining the strain distribution, it is possible to unify and grasp the strain state, so that the difference in formability and workability between the molding target materials can be compared.

  Moreover, the workability for each material to be molded can be evaluated by comparing the forming diagram and the plate thickness reduction rate.

<Optimization of die and punch shape>
[Test Example 3]
Using the same high-working ferritic stainless steel as in Test Example 2 as a test material and using a press-molding target material cut into a substantially square shape with a side of 300 mm, the press workability evaluation apparatus uses the following press conditions. A plurality of types of press-molded bodies were obtained by press molding.

(Press conditions)
The shapes of the die and punch are as shown in FIGS. The ratio Wd / Rc between the branch width Wd and the radius of curvature Rc of the corner of the branch is eight types of 1, 1.5, 2, 2.5, 5, 10, 15, and 15.5. Other conditions are the same as in Test Example 2.

With respect to various press-formed bodies obtained in Test Example 3, the state of branch cracks was observed. The case where there is no branch crack is indicated by “◯”, and as shown in FIG. 7A, the case where a crack occurs at the boundary of the corner e ₃ is indicated by “× ₁ ”. As shown, the case where a crack occurred at the corner e ₃ was defined as “× ₂ ”. The results are shown in Table 2.

As shown in Table 2, when Wd / Rc was 2 or more and 15 or less, cracks did not occur in the branches of the press-formed body. On the other hand, when Wd / Rc is less than 2, as shown in (a) of FIG. 7, the stress at the boundary of the corner e ₃ in pressed bodies is concentrated locally, cracking of the pressed bodies occurs . Further, when Wd / Rc exceeds 15, as shown in FIG. 7 (b), plastic strain region is reduced in the circumferential direction of the branch corners e ₃ in pressed bodies, cracks at the corners e ₃ Occurred.

[Test Example 4]
Using the same high-working ferritic stainless steel as in Test Example 2 as a test material and using a press-molding target material cut into a substantially square shape with a side of 300 mm, the press workability evaluation apparatus uses the following press conditions. A plurality of types of press-molded bodies were obtained by press molding.

(Press conditions)
The shapes of the die and punch are as shown in FIGS. When the convex portion of the punch 13 is viewed from the front, the thickness of the convex portion is Hp, the radius of curvature of the punch shoulder g ₁ is Rp, and the radius of curvature of the die bottom h ₃ is Rd, and Hp and (Rp + Rd) The ratio Hp / (Rp + Rd) is 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2 There are 10 types. Other conditions are the same as in Test Example 2.

  For various press-formed bodies obtained in Test Example 4, [Measurement of Deformation] and [Creation of Forming Line] of <Analysis> in Test Example 2 were performed, and four processing elements (plane strain tensile deformation) , Biaxial tensile deformation, shrinking flange deformation, and uniaxial tensile deformation) were confirmed. The case where the deformation appeared was “◯”, and the case where the deformation was not shown was “x”. The results are shown in Table 3.

As shown in Table 3, in the press-molded product obtained by press-molding the target material, Hp / (Rp + Rd) is 0.5 or more, that is, when Hp is 0.5 times or more of (Rp + Rd), It was confirmed that all of the four processing elements (plane strain tensile deformation, biaxial tensile deformation, shrinkage flange deformation, and uniaxial tensile deformation) can be suitably measured. On the other hand, in a press-molded body having Hp / (Rp + Rd) of less than 0.5, that is, Hp of less than 0.5 times (Rp + Rd), only biaxial tensile deformation can be measured among the four working elements. Other processing elements (plane strain tensile deformation, shrinkage flange deformation, and uniaxial tensile deformation) could not be suitably measured.
When Hp ≧ (Rp + Rd) / 2, a plurality of processing elements appear in one press-formed body, which is preferable in that it can be used for evaluation of workability.

DESCRIPTION OF SYMBOLS 1 Press workability evaluation apparatus 10 Punch part 11 Bottom plate 12 Punch holder 13 Punch 132 Convex part 20 Die part 21 Upper plate 22 Die holder 23 Dice 231 Recess 232 Dice side plane part 30, 30A, 30B Guide part 31, 31A, 31B Guide Pin 32, 32A, 32B Plate presser 321 Plate presser side plane portion 33 Cushion pin 40 Press molded body 41 Press molded body convex portion 42 Planar portion 43 Branch 50 Plate material

Claims (9)

A punch having a multi-branch-shaped convex part composed of three or more branches;
A dice having a multi-branch-shaped concave portion composed of three or more branches that can be fitted to the convex portion, and a die-side flat portion surrounding the concave portion;
A plate presser side plane portion substantially parallel to the die side plane portion, and a plate presser capable of sandwiching a target material to be pressed by the die side plane portion and the plate press side plane portion, Press workability evaluation device that evaluates press workability of target materials. When there are three multi-branched branches, the angles formed by adjacent branches are obtuse angles,
When there are four multi-branched branches, the angle between adjacent branches is substantially a right angle;
The press workability evaluation apparatus according to claim 1, wherein when there are five or more multi-branched branches, angles formed by adjacent branches are acute to each other.   The press workability evaluation apparatus according to claim 1 or 2, wherein the number of the multi-branched branches is four, and the convex part and the concave part have a substantially cross shape. When the die is viewed in plan, the corners of the recesses are curved, the width of the branch of the die is Wd, and the radius of curvature at the corner of the branch of the die is Rc. The ratio Wd / Rc to Rc is 2 or more and less than 15,
When the punch is viewed from the front, the shoulder at the top of the convex portion is curved, the radius of curvature at the shoulder is Rp, the thickness of the convex is Hp, and the die is cross-sectioned. 4. The press workability according to claim 1, wherein when viewed, the bottom of the recess is curved, and Hp ≧ (Rp + Rd) / 2, where Rd is the radius of curvature of the bottom. 5. Evaluation device. A punch having a multi-branch-shaped recess composed of three or more branches;
A die having a multi-branch-shaped convex portion comprising three or more branches that can be fitted to the concave portion, and a die-side flat portion surrounding the convex portion;
A plate presser side plane portion substantially parallel to the die side plane portion, and a plate presser capable of sandwiching a target material to be pressed by the die side plane portion and the plate press side plane portion, Press workability evaluation device that evaluates press workability of target materials. A press molding step of subjecting a target material to be subjected to press molding to press molding using the press workability evaluation apparatus according to any one of claims 1 to 5 to obtain a press molded body,
A deformation amount measuring step of measuring at least two kinds of deformation amounts among plane strain tensile deformation, uniaxial tensile deformation, biaxial tensile deformation, and shrinkage flange deformation of the press-molded product. . The deformation amount measuring step includes
A plurality of marks are previously transferred to the target material,
Measure the maximum principal strain and the minimum principal strain of the mark before and after press molding,
The amount of deformation of a portion corresponding to the region including the bottom adjacent to the corner of the convex portion of the press-molded body, wherein the maximum principal strain is the largest and the minimum principal strain is substantially undeformed. The amount of deformation in which strain tensile deformation is mainly involved,
The portion corresponding to the region of the side surface in the length direction in the branch of the press-formed body, where the maximum principal strain is the largest and the minimum principal strain is the compressive deformation, the deformation amount is mainly the uniaxial tensile deformation The amount of deformation involved in
It is a corner corresponding to the region of the convex portion of the press-formed body and the shoulder portion, the maximum principal strain is the largest, the deformation amount of the portion where the minimum principal strain is tensile deformation, The amount of deformation mainly involving the biaxial tensile deformation,
The deformation corresponding to the region of the flat portion surrounding the convex portion of the press-formed body, where the maximum principal strain is the largest and the smallest principal strain is the smallest, the deformation mainly involving the shrinkage flange deformation The method for evaluating press workability according to claim 6, wherein the method is a step of making a quantity.   The evaluation of press workability according to claim 7, further comprising a crack prediction step of plotting a relationship between the maximum principal strain and the minimum principal strain of the plurality of marks and predicting a crack of the press-formed body from the result of the plot. Method.   The press workability evaluation method according to any one of claims 6 to 8, wherein a blank having a quadrangular shape, an octagonal shape, an elliptical shape, or a circular shape is used as the target material.