Method for manufacturing press-formed products, and press apparatus

Abstract

This method suppresses the concentration of compressive strain in a workpiece formed by press forming involving shrink flange forming. [Solution] A method for manufacturing a press-formed product comprises the steps of preparing a mold set including a first mold, a pad, and a second mold, and press-forming a workpiece. The protrusion of the first mold includes a first shoulder. The first shoulder includes a curved portion that curves outward in a convex shape when viewed from the pressing direction, and the curved portion includes a corner portion with a small radius of curvature. The pad includes a pad surface and a projection provided at a position that overlaps with at least a part of the corner portion of the first shoulder when viewed from the pressing direction. The press-forming step includes a preliminary bending step in which, with the top surface of the protrusion supporting the workpiece, the projection of the pad presses and bends the portion of the workpiece that overlaps with the corner portion of the first shoulder in the pressing direction, and a forming step in which, after the preliminary bending step, the portion of the workpiece that overlaps with the portion of the first shoulder other than the corner portion in the pressing direction is bent.

Description

Technical Field

[0001] The present invention relates to a press forming technique using a mold.

Background Art

[0002] Press formed products are manufactured by press forming a metal plate. By using a mold and performing drawing or bending on the metal plate as a material, press formed products are manufactured. In press forming, various techniques for improving the quality of press formed products have been proposed.

[0003] For example, International Publication No. 2015 / 155943 (Patent Document 1) describes a press formed product having a corner flange portion and a manufacturing method thereof. The press formed product has a top plate portion, flange portions extending from the sides of the top plate portion, and a corner flange portion extending from a corner portion connecting adjacent sides. In the manufacturing method, using a punch, a die, and a convex tool corresponding to the corner flange portion, the blank is bent to form the flange portion. By the relative movement of the convex tool with respect to the punch, the corner flange portion is formed prior to the bending of the blank by the die. Thereby, wrinkles are suppressed in the corner flange portion.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In press forming, the workpiece is formed using a die with a convex portion and a die with a corresponding concave portion. When the shoulder of the convex portion of the die has a curved portion that curves outward when viewed from the pressing direction, a portion of the workpiece is formed with a shrink flange. It has been found that if there is a corner with a small radius of curvature in the curved portion of the shoulder of this die, compressive strain may concentrate in the part of the workpiece corresponding to the corner. This concentration of strain in the workpiece remains in the press-formed product after demolding.

[0006] Therefore, this disclosure provides a method for manufacturing a press-formed product and a press apparatus that can suppress the concentration of compressive strain in a workpiece during press forming involving shrink flange forming. [Means for solving the problem]

[0007] The method for manufacturing a press-formed product in an embodiment of the present invention is as follows: A step of preparing a mold set including a first mold having a protrusion that protrudes in the pressing direction, a pad provided at a position opposite to the protrusion of the first mold in the pressing direction, and a second mold having a recess corresponding to the protrusion of the first mold, A step of placing the material to be molded between the first mold and the second mold, The process includes the step of moving at least one of the first mold and the second mold from the molding start position to the bottom dead center in the pressing direction, and press-molding the workpiece, The protrusion of the first mold includes a top surface, a side surface, and a first shoulder portion between the top surface and the side surface, the first shoulder portion includes a curved portion that curves outward in a convex manner when viewed from the pressing direction, and the curved portion includes a corner portion whose radius of curvature is smaller than that of the adjacent portion when viewed from the pressing direction. The pad includes a pad surface that overlaps with at least a portion of the top surface of the convex portion of the first mold when viewed from the pressing direction, and a projection that is provided at a position that overlaps with at least a portion of the corner portion of the first shoulder of the convex portion of the first mold when viewed from the pressing direction, and that protrudes toward the corner portion in the pressing direction. The process of press-forming the aforementioned material to be molded is as follows: With the top surface of the convex portion of the first mold supporting the workpiece, a preliminary bending step is performed in which the projection of the pad presses and bends the portion of the workpiece that overlaps with the corner portion of the first shoulder in the pressing direction, The molding process includes, after the preceding bending step, a step in which, with the pad surface of the pad and the top surface of the convex portion of the first die holding the workpiece between them, the first die and the second die move closer to each other and reach the bottom dead center, thereby bending the portion of the workpiece that overlaps with the portion of the first shoulder portion other than the corner portion in the pressing direction along the first shoulder portion, and press-molding the workpiece. [Brief explanation of the drawing]

[0008] [Figure 1] Figure 1 shows an example of a press-formed product. [Figure 2] Figure 2 shows the molding process in CAE analysis of press forming. [Figure 3] Figure 3 is a perspective view showing an example of the configuration of the press apparatus according to this embodiment. [Figure 4] Figure 4 shows the positional relationship of the first die 1, the second die 2, and the pad 3 of the press apparatus shown in Figure 1, as viewed from the pressing direction. [Figure 5] Figure 5 is a cross-sectional view of the VV line in Figure 4. [Figure 6] Figure 6 is a magnified view of a portion of Figure 5. [Figure 7] Figure 7 is a cross-sectional view along line BB in Figure 4. [Figure 8] Figures 3 to 7 show examples of press forming processes using the press equipment shown. [Figure 9] Figure 9 shows a modified example of the projection 3a of the pad 3. [Figure 10] Figure 10 is a perspective view showing a modified example of a press-formed product. [Figure 11] Figure 11 shows an example of a die used for forming the press-formed product shown in Figure 10. [Figure 12] Figure 12 shows the model used in the analysis. [Figure 13]Figure 13 shows the analysis results of press forming. [Figure 14] Figure 14 shows the analysis results of press forming. [Modes for carrying out the invention]

[0009] Figure 1 shows an example of a press-formed product. The press-formed product 100 includes a top surface 101 and a side wall 102 extending from the top surface 101. The ridge 103 between the top surface 101 and the side wall 102 includes a corner 103a that curves outward. The inventors have found that distortion caused by press forming may concentrate at this corner 103a and the portion of the side wall 102 extending from the corner 103a, i.e., the side wall corner 102a. Hereinafter, the corner 103a and the side wall corner 102a of the press-formed product 100 will be referred to as the corner portion.

[0010] The inventors investigated the cause of strain concentration at the corners of press-formed products and concluded that the following mechanism exists. Figure 2 shows the forming process in a CAE analysis of press forming. As shown in Figure 2, press forming is performed using a press device equipped with a first die 11 having a convex portion, a second die 12 having a concave portion corresponding to the convex portion, and a pad 13 positioned opposite the convex portion. With the workpiece W1 held between the convex portion of the first die 11 and the pad 13, the convex portion and the concave portion are brought relatively closer in the pressing direction and moved to the bottom dead center, thereby forming the workpiece W1 into a shape corresponding to the convex portion and the concave portion. During the forming process, the workpiece W1 is bent along the shoulder portion of the convex portion. The shoulder portion of the convex portion includes a curved portion that curves outward in a convex shape when viewed from the pressing direction. The portion of the workpiece W1 that is bent at this curved portion of the shoulder portion and becomes a side wall is shrink flange formed.

[0011] The shrink flange forming also occurs, for example, at the corner portions (e.g., 103a, 102a in FIG. 1) of the workpiece W1. In shrink flange forming, the workpiece is formed while undergoing compressive deformation. The direction of this compressive deformation is the circumferential direction. The circumferential direction usually follows the ridge line of the curved portion of the shoulder of the convex part as viewed from the press direction. As shown in FIG. 2, if there is a notch at the end of the portion where shrink flange forming is performed, the end, that is, the direction along the notch (arrow F1 in FIG. 2) may be the circumferential direction. Circumferential compressive strain due to shrink flange forming occurs in the portion that becomes the corner part during forming. At this time, since the deformation by shrink flange forming is the largest near the circumferential center of the corner part, the compressive strain near the center becomes large.

[0012] As shown by arrow F2 in FIG. 2, when the workpiece is bent along the shoulder of the convex part of the first mold, a side wall is formed. In the portion that becomes the corner part of the workpiece, by being compressed in the circumferential direction by shrink flange forming, a bulging deformation occurs outward, that is, in the direction opposite to the bending direction. Due to this deformation, a ridge occurs near the circumferential center of the portion that becomes the corner part of the workpiece. The ridge extends along a virtual line that is substantially perpendicular to the ridge line of the shoulder of the convex part of the first mold as viewed from the press direction, for example, as shown by the dotted line F3 in FIG. 2. Thus, the portion that becomes the corner part of the workpiece is not in direct contact with the shoulder of the convex part of the first mold during forming, and the circumferential line length becomes excessive due to shrink flange forming. Therefore, the portion that becomes the corner part of the workpiece is formed without being held by the mold. As a result, when the workpiece is bent to form a corner part, a particularly bulging deformation occurs near the center of the portion that becomes the corner part of the workpiece. As a result, concentration of compressive strain occurs on the surface that becomes the inner side of the bending of the bulging deformation of the corner part of the workpiece.

[0013] Thus, compressive strain is concentrated near the center of the portion that becomes the corner part of the workpiece due to the deformation by shrink flange forming and the outward bulging deformation.

[0014] < The inventors investigated a manufacturing method that would suppress deformation concentration at the corner portion of the workpiece during molding. After diligent investigation, they conceived of providing a projection on the pad that holds the workpiece, which protrudes in the pressing direction, at a position that overlaps with the corner portion of the shoulder of the mold's protrusion when viewed from the pressing direction. Then, in press molding, they conceived of pressing and bending the portion of the workpiece that overlaps with the corner portion when viewed from the pressing direction using the projection on the pad, and then pressing the workpiece with the pad to move at least one of the first and second molds to the bottom dead center. In this way, the portion of the workpiece that overlaps with the corner portion when viewed from the pressing direction is first deformed primarily by bending using the projection on the pad, and then, while pressing this portion with the projection on the pad, the portions on both sides of this portion can be bent. This makes it possible to alleviate the concentration of compressive strain near the center of the portion of the workpiece that is bent at the corner of the mold's shoulder and becomes the corner portion of the press-molded product. As a result, the strain that occurs near the center of the corner portion after demolding can be reduced. The following embodiments are based on this finding.

[0015] (Manufacturing method 1) The method for manufacturing a press-formed product in an embodiment of the present invention is as follows: A step of preparing a mold set including a first mold having a protrusion that protrudes in the pressing direction, a pad provided at a position opposite to the protrusion of the first mold in the pressing direction, and a second mold having a recess corresponding to the protrusion of the first mold, A step of placing the material to be molded between the first mold and the second mold, The process includes the step of moving at least one of the first mold and the second mold from the molding start position to the bottom dead center in the pressing direction, and press-molding the workpiece, The protrusion of the first mold includes a top surface, a side surface, and a first shoulder portion between the top surface and the side surface, the first shoulder portion includes a curved portion that curves outward in a convex manner when viewed from the pressing direction, and the curved portion includes a corner portion whose radius of curvature is smaller than that of the adjacent portion when viewed from the pressing direction. The pad includes a pad surface that overlaps with at least a portion of the top surface of the convex portion of the first mold when viewed from the pressing direction, and a projection that is provided at a position that overlaps with at least a portion of the corner portion of the first shoulder of the convex portion of the first mold when viewed from the pressing direction, and that protrudes toward the corner portion in the pressing direction. The process of press-forming the aforementioned material to be molded is as follows: With the top surface of the convex portion of the first mold supporting the workpiece, a preliminary bending step is performed in which the projection of the pad presses and bends the portion of the workpiece that overlaps with the corner portion of the first shoulder in the pressing direction, The molding process includes, after the preceding bending step, a step in which, with the pad surface of the pad and the top surface of the convex portion of the first die holding the workpiece between them, the first die and the second die move closer to each other and reach the bottom dead center, thereby bending the portion of the workpiece that overlaps with the portion of the first shoulder portion other than the corner portion in the pressing direction along the first shoulder portion, and press-molding the workpiece.

[0016] The first shoulder of the convex portion of the first die has a curved portion that curves outward when viewed from the pressing direction, and the curved portion includes a corner portion with a locally small radius of curvature. The workpiece is press-formed using the first die having a convex portion including such a corner portion and a second die having a recess corresponding to the convex portion. In press forming, the workpiece is bent in contact with the first shoulder of the convex portion. The portion of the workpiece bent at the curved portion of the first shoulder is subjected not only to bending but also to shrink flange forming. In the pre-bending process, the protrusion of the pad presses the portion of the workpiece that overlaps with the corner portion when viewed from the pressing direction ahead of the portion that overlaps with the first shoulder portion other than the corner portion. As a result, a bending-dominant deformation is applied to the portion of the workpiece that overlaps with the corner portion when viewed from the pressing direction. Subsequently, during the molding process, bending is applied to the portion of the workpiece that overlaps with the first shoulder portion (excluding the corner portion) when viewed from the pressing direction. This applies shrink flange forming to the portion of the workpiece that overlaps with the corner portion and the portion outside of it (hereinafter referred to as the corner portion). Since the portion of the workpiece that overlaps with the corner portion is held down by the protrusions of the pad, the deformation of the corner portion of the workpiece can be distributed in the circumferential direction. Therefore, the concentration of strain on the corner portion of the workpiece is mitigated. In other words, in a workpiece subjected to press molding with shrink flange forming, the concentration of compressive strain can be suppressed.

[0017] The radius of curvature of the corner section as viewed from the pressing direction is preferably 5 to 100 mm, and more preferably 5 to 20 mm. When the radius of curvature of the corner section is 5 to 20 mm, the degree of strain concentration increases. Therefore, in this case, the effect of suppressing strain concentration is increased. The radius of curvature of the first shoulder section as viewed from the pressing direction is the radius of curvature of the ridge line formed by the first shoulder section (the ridge line is defined as the end of the radius on the outside of the first shoulder section as viewed from the pressing direction). The radius of curvature is defined at any point on the ridge line of the first shoulder section as viewed from the pressing direction. That is, the radius of curvature is defined with any point on the ridge line as the reference point. The radius of curvature at one point on the ridge line (reference point) is defined by using the normal to the reference point (a line perpendicular to the ridge line) as the reference line, and the radius of the circle passing through two points on the ridge line at a distance of 3 mm from the reference line and the reference point as the radius of curvature.

[0018] (Manufacturing method 2) In the above manufacturing method 1, in the preliminary bending step, at least one of the pad and the first mold moves in the pressing direction, so that the projection of the pad presses and bends the portion of the workpiece that overlaps with the corner portion of the first shoulder in the pressing direction. After that, the pad surface of the pad and the top surface of the convex portion of the first mold hold the workpiece between them, and there may be a gap between the corner portion and the workpiece. This allows the portion of the workpiece that overlaps with the corner portion to be appropriately pressed by the projection in the preliminary bending step, thereby distributing the deformation.

[0019] (Manufacturing method 3) In the above manufacturing method 1 or 2, the protrusion of the pad may include a portion located outside the corner portion of the first shoulder of the protrusion of the first mold, when viewed from the pressing direction. This allows the pad's protrusion to press down on the portion of the workpiece from the portion overlapping with the corner of the workpiece in the pressing direction to a position outside of that portion during the preliminary bending process. As a result, the deformation of the portion of the workpiece corresponding to the corner is more easily dispersed in the circumferential direction during the preliminary bending process using the protrusion. For example, if there is a notch in the workpiece outside the portion overlapping with the corner when viewed from the pressing direction, the pad's protrusion can press down on the workpiece from the portion overlapping with the corner to a position closer to the end of the notch. Note that the position outside the corner when viewed from the pressing direction is the position outside the corner in a direction perpendicular to the tangent to the ridge of the corner (end of the outer radius) when viewed from the pressing direction.

[0020] The entire projection of the pad may be located inside the side surface of the recess of the second die when viewed from the pressing direction. The entire side surface of the recess of the second die may be located outside the side surface of the convex portion when viewed from the pressing direction, and at least a portion of the side surface of the recess of the second die may overlap with at least a portion of the side surface of the convex portion when viewed from the pressing direction.

[0021] In the preceding bending process, the portion of the pad's projection located outside the corner portion when viewed from the pressing direction may press against the workpiece. This allows the pad's projection to press against the portion of the workpiece from the point where it overlaps with the corner portion to the point outside of it when viewed from the pressing direction. As a result, the deformation of the corner portion of the workpiece during the preceding bending process by the projection is more easily dispersed in the circumferential direction.

[0022] (Manufacturing method 4) In any of the above manufacturing methods 1 to 3, the first shoulder of the protrusion of the first mold may include, when viewed from the pressing direction, two straight sections and a curved section that curves outward between the two straight sections. The inner angle between the imaginary lines in the extending direction of the two straight sections may be 120 degrees or less. The straight sections include not only cases where the ridge line forming the first shoulder (the line ending in R on the outside of the first shoulder) when viewed from the pressing direction is strictly straight, but also cases where it is slightly curved to the extent that it can be considered straight. The portion of the ridge line with a radius of curvature of 300 mm or more when viewed from the pressing direction is considered a straight section.

[0023] In any of the above manufacturing methods 1 to 3, the curved portion of the first shoulder may include the corner portion and adjacent curved portions that have a larger radius of curvature than the adjacent corner portions when viewed from the pressing direction. In this case, when viewed from the pressing direction, the angle between the two tangents at the boundary between the two adjacent curved portions and the corner portion may be 120 degrees or less.

[0024] (Manufacturing method 5) In any of the above manufacturing methods 1 to 4, during the molding process, while the pad surface of the pad and the top surface of the convex portion of the first mold hold the workpiece between them, as the first mold and the second mold approach each other and reach the bottom dead center, the surface of the workpiece opposite to the surface being pressed by the second mold on the outside of the recess, as viewed from the pressing direction, can be left unrestrained. This enables pad bending molding. In other words, instead of pressing and restraining the end of the workpiece between the second mold and the holder, pad bending molding can be performed, bending the workpiece without restraining the surface of the workpiece opposite to the second mold. For example, in pad bending molding, during the molding process, the workpiece is not held between the outer surface extending outside the recess of the second mold and the holder from the time the second mold starts pressing the workpiece until the bottom dead center.

[0025] (Composition 1) The press apparatus in the embodiment of the present invention is A first mold having a protrusion that protrudes in the pressing direction, A pad provided at a position opposite to the protrusion of the first mold in the pressing direction, and movable in the pressing direction relative to the first mold, The system includes a second mold having a recess corresponding to a protrusion of the first mold and being movable in the pressing direction relative to the first mold. The protrusion of the first mold includes a top surface, a side surface, and a first shoulder portion between the top surface and the side surface, the first shoulder portion includes a curved portion that curves outward in a convex manner when viewed from the pressing direction, and the curved portion includes a corner portion whose radius of curvature is smaller than that of the adjacent portion when viewed from the pressing direction. The pad includes a pad surface that faces the top surface of the convex portion of the first mold and overlaps with at least a portion of the top surface when viewed from the pressing direction, and a projection that is provided at a position that overlaps with at least a portion of the corner portion of the first shoulder of the convex portion of the first mold when viewed from the pressing direction, and that protrudes toward the corner portion in the pressing direction. The second mold includes a side surface of the recess corresponding to the side surface of the convex portion of the first mold, an outward surface extending outward from the recess when viewed from the pressing direction, and a second shoulder portion between the side surface and the outward surface. The amount of the projection protruding from the pad surface in the pressing direction is greater than the amount of the portion of the pad that overlaps with the portion of the first shoulder other than the corner portion and the region outside thereof, when viewed from the pressing direction, protruding from the pad surface in the pressing direction.

[0026] According to the above configuration 1, when the workpiece is supported by the top surface of the convex portion of the first die, and the pad is brought closer to the first die, the protrusion of the pad first presses against the portion of the workpiece that overlaps with the corner portion of the first shoulder in the pressing direction. This applies a bending-dominant deformation to the portion of the workpiece that overlaps with the corner portion when viewed from the pressing direction. Subsequently, the pad surface presses down on the workpiece. As the first die and the second die move closer in the pressing direction while the pad surface of the pad and the top surface of the convex portion of the first die hold the workpiece between them, bending is applied to the portion of the workpiece that overlaps with the first shoulder portion other than the corner portion. This applies shrink flange forming to the portion of the workpiece corresponding to the corner portion. At this time, since the portion of the workpiece that overlaps with the corner portion is pressed down by the protrusion of the pad, the deformation of the portion of the workpiece corresponding to the corner portion can be distributed in the circumferential direction. Therefore, it is possible to suppress the concentration of compressive strain in the workpiece during press forming accompanied by shrink flange forming.

[0027] The entire pad surface may be a surface perpendicular to the pressing direction. Alternatively, the pad surface may include steps or inclined surfaces that are tilted relative to the surface perpendicular to the pressing direction. In cases where the position of the pad surface in the pressing direction varies depending on the location, "the amount of projection of the protrusion from the pad surface in the pressing direction" is defined as the amount of projection at the cross section where the projection is maximized, relative to a virtual line perpendicular to the pressing direction that passes through a point on the pad that coincides with the boundary between the corner and the top surface when viewed from the pressing direction, and includes lines perpendicular to the tangents of each point on the edge of the corner (i.e., the end of the radius outside the corner when viewed from the pressing direction) as viewed from the pressing direction. Note that the amount of projection in each cross section is the distance in the pressing direction from the virtual line to the point of the projection that protrudes the most in the pressing direction. Furthermore, the "amount of protrusion in the pressing direction from the pad surface of the portion of the pad that overlaps with the portion of the first shoulder other than the corner portion and the area outside thereto when viewed from the pressing direction (the portion corresponding to the non-corner portion)" is defined as the largest amount of protrusion of the portion corresponding to the non-corner portion relative to a virtual line perpendicular to the pressing direction that passes through a point of the pad that overlaps with the boundary between the first shoulder and the top surface when viewed from the pressing direction, in a cross-section of a plane parallel to the pressing direction that includes a line perpendicular to the tangent to each point of the ridge of the portion of the first shoulder other than the corner portion (i.e., the end of the R outside the portion of the first shoulder other than the corner portion) when viewed from the pressing direction, and is perpendicular to the pressing direction. Note that the amount of protrusion of the portion corresponding to the non-corner portion in each cross-section is the distance in the pressing direction from the virtual line to the point that protrudes the most in that portion. Note that if the portion corresponding to the non-corner portion does not protrude from the pad surface, the amount of protrusion is 0. In addition, the portion corresponding to the non-corner portion may not include the portion that overlaps with the area outside the first shoulder when viewed from the pressing direction.

[0028] Furthermore, the first shoulder portion may have multiple corners, and a protrusion corresponding to at least one of these corners may be provided on the pad. If a protrusion corresponding to each of the multiple corners is provided on the pad, the amount of protrusion for each of the protrusions corresponding to the multiple corners is determined as described above.

[0029] (Configuration 2) In the above configuration 1, the protrusion of the pad may be formed such that, with the pad surface of the pad and the top surface of the convex portion of the first mold sandwiching and holding the workpiece, the portion of the workpiece that overlaps with the corner portion in the pressing direction is pushed toward the first mold and bent, and a gap is created between the workpiece and the corner portion. This allows the portion of the workpiece that overlaps with the corner portion to be appropriately pressed by the protrusion and the deformation to be distributed.

[0030] As an example of the above configuration 2, the protrusion of the pad may be formed such that, with the pad surface of the pad and the top surface of the convex portion of the first mold holding the workpiece between them, there is a portion where the minimum value of the distance between the protrusion of the pad and the corner portion in a direction perpendicular to the surface of the corner portion is equal to or greater than the maximum value of the distance between the pad surface and the top surface of the convex portion in a direction perpendicular to the top surface.

[0031] (Composition 3) In the above configuration 1 or 2, the protrusion of the pad may include a portion located outside the corner portion of the first shoulder of the protrusion of the first mold when viewed from the pressing direction. This makes it easier for deformation in the part of the workpiece to bend by pressing and bending the part that overlaps with the corner portion when viewed from the pressing direction, and then bending other parts. The protrusion of the pad may be formed in a range that does not extend beyond the area that overlaps with the corner portion when viewed from the pressing direction. In this case as well, the effect of mitigating the concentration of strain on the part of the workpiece corresponding to the corner portion can be obtained.

[0032] The protrusion may be formed such that the distance in the pressing direction of the point of the pad protrusion that coincides with the point of the corner portion when viewed from the pressing direction relative to the pad surface (projection distance) is not greater than the distance in the pressing direction of the point of the corner portion relative to the top surface (i.e., setback distance). This allows the distance between the protrusion and the corner portion to be appropriately controlled while the workpiece is held between the pad surface and the top surface of the protrusion of the first mold. If the position of the pad surface in the pressing direction varies depending on the location, the "distance in the pressing direction of the point of the pad protrusion relative to the pad surface" is the distance in the pressing direction between the point of the protrusion and an imaginary line perpendicular to the pressing direction that passes through the point of the pad that coincides with the boundary between the corner portion and the top surface when viewed from the pressing direction, in a cross-section of a plane that is perpendicular to the pressing direction, includes a line passing through the point of the protrusion, and is parallel to the pressing direction when viewed from the pressing direction. The distance in the pressing direction of the point of the corner portion relative to the top surface is the distance in the pressing direction between the point of the corner portion and an imaginary line perpendicular to the pressing direction that passes through the boundary between the corner portion and the top surface in the cross-section.

[0033] The protrusions on the pad may be formed so as not to be present in the region that overlaps with the top surface of the convex portion of the first mold when viewed from the pressing direction. In this case, the protrusions do not hinder the holding of the workpiece when it is sandwiched and held between the pad surface and the top surface of the convex portion of the first mold. Alternatively, the protrusions may be formed so as not to be present in the region that overlaps with the top surface of the convex portion of the first mold and the first shoulder portion other than the corner portion when viewed from the pressing direction. Or, the protrusions may be formed to extend from the region that overlaps with the corner portion to the region that overlaps with the portion of the first shoulder other than the corner portion when viewed from the pressing direction. In this case, the protrusions may be formed such that the amount of protrusion decreases as it moves away from the corner portion in the region that overlaps with the portion of the first shoulder other than the corner portion when viewed from the pressing direction.

[0034] (Composition 4) In any of the above configurations 1 to 3, the first shoulder of the protrusion of the first mold may include, when viewed from the pressing direction, two straight sections and a curved section that curves outward between the two straight sections. The inner angle between the imaginary lines in the extending direction of the two straight sections may be 120 degrees or less.

[0035] The embodiments of the present invention will be described in detail below with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals, and their descriptions will not be repeated. The dimensional ratios between the constituent members shown in each drawing do not necessarily represent the actual dimensional ratios.

[0036] Figure 3 is a perspective view showing an example of the configuration of the press apparatus of this embodiment. Figure 4 is a diagram showing the positional relationship of the first die 1, the second die 2, and the pad 3 of the press apparatus shown in Figure 1, as viewed from the pressing direction. Figure 5 is a cross-sectional view taken along line VV of Figure 4. Figure 6 is a partially enlarged view of Figure 5. Figure 7 is a cross-sectional view taken along line BB of Figure 4.

[0037] In the example shown in Figure 3, the press apparatus comprises a die set consisting of a first die 1 having a protrusion 1A, a second die 2 having a recess 2A with a shape corresponding to the protrusion 1A, and a pad 3. At least one of the first die 1 and the second die 2 is configured to be movable in the press direction FP from the molding start position to the bottom dead center. The protrusion 1A of the first die 1 protrudes toward the pad 3 in the press direction FP. In the example shown in Figure 3, the recess 2A is formed as a hole into which the protrusion 1A can be inserted in the press direction. The pad 3 is positioned opposite the protrusion 1A in the press direction. The pad 3 is movable in the press direction relative to both the first die 1 and the second die 2. The pad 3 includes a pad surface 3b and a projection 3a. The projection 3a protrudes beyond the pad surface 3b in the press direction. The projection 3a protrudes toward the first die 1, i.e., the corner portion 1bc. The pad surface 3b faces the top surface 1a in the press direction. The shape of the pad surface 3b corresponds to the shape of the top surface 1a.

[0038] As shown in Figure 4, when viewed from the pressing direction, the entire pad 3 and the entire protrusion 1A are positioned inside the recess 2A. In Figure 4, the protrusion 3a of the pad 3 is shown in gray, and the portion of the pad 3 other than the protrusion 3a is the pad surface 3b. At least a portion of the pad surface 3b overlaps with at least a portion of the top surface 1a of the protrusion 1A when viewed from the pressing direction. In Figure 4, the shoulder portion 1b of the protrusion 1A is shown with dot hatching. The shoulder portion 1b of the protrusion 1A includes a curved portion 1bt that curves outward convexly when viewed from the pressing direction. The curved portion 1bt includes a corner portion 1bc with a smaller radius of curvature than the adjacent portion when viewed from the pressing direction. In Figure 4, the corner portion 1bc is shown with diagonal hatching. The protrusion 3a of the pad 3 is provided at a position that overlaps with at least a portion of the corner portion 1bc of the protrusion 1A when viewed from the pressing direction. In the example shown in Figure 4, the projection 3a includes a portion located outside the corner portion 1bc when viewed from the pressing direction. In Figure 4, the gray and dot hatching of the corner portion 1bc are omitted for clarity, but the projection 3a overlaps with the entire corner portion 1bc when viewed from the pressing direction. Thus, the projection 3a is provided at a position on the shoulder portion 1b opposite the corner portion 1bc in the pressing direction.

[0039] In the example shown in Figure 4, the radius of curvature of the corner portion 1bc is approximately constant. The projection 3a is positioned at least at the center of the ridge formed by the corner portion 1bc, i.e., the circumferential center, when viewed from the pressing direction. The shape of the projection 3a is not particularly limited, but for example, the region that overlaps with the center of the ridge formed by the corner portion 1bc when viewed from the pressing direction may be formed such that the projection height in the pressing direction is highest, and the projection height monotonically decreases as it moves away from that region in the circumferential direction.

[0040] The ridge forming the shoulder portion 1b of the convex portion 1A is the ridge formed by the outer R-end of the shoulder portion 1b (see 1b1 in Figure 6) when viewed from the pressing direction. The radius of curvature of the curved portion 1bt is the radius of curvature of the ridge of the shoulder portion 1b when viewed from the pressing direction. As shown in Figure 6, the surface of the shoulder portion 1b (first shoulder portion) is a curved surface that forms an R. When viewed from the pressing direction, the area between the inner R-end 1b2 and the outer R-end 1b1 is the shoulder portion 1b. In other words, the R-shaped portion between the top surface 1a and the side surface 1c is the shoulder portion 1b.

[0041] As shown in Figure 5, the protrusion 1A includes a top surface 1a, a shoulder 1b, and a side surface 1c. These are formed in a continuous manner. The shoulder 1b is the portion between the top surface 1a and the side surface 1c. The shoulder 1b of the protrusion 1A is an example of a first shoulder. The second mold 2 includes a side surface 2c of the recess 2A, an outward surface 2e extending outward from the recess 2A when viewed from the pressing direction, and a shoulder 2d between the side surface 2c and the outward surface 2e. The outward surface 2e extends along a direction perpendicular to the pressing direction. The shoulder 2d is an example of a second shoulder. In the example in Figure 5, the recess 2A of the second mold 2 is formed by a through hole and does not have a bottom surface that overlaps with the top surface 1a of the protrusion 1A when viewed from the pressing direction. As a modification, the recess 2A may have a bottom surface that overlaps with at least a portion of the top surface 1a of the protrusion 1A when viewed from the pressing direction. In the example shown in Figure 5, the pad 3 is supported by a pad support 31 that is movable in the pressing direction relative to the second die 2. Although not shown, the press device may also include a first support for supporting the first die 1 and a second support for supporting the second die 2. For example, one of the first and second support parts may be a bolster and the other a slider. The pad support 31 is, for example, movably mounted relative to the second support part.

[0042] Figure 6 shows a cross-section in a plane parallel to the press direction, which includes a line (normal) perpendicular to the tangent to the edge of the corner portion 1bc (end of outer radius 1b1) as viewed from the press direction. As shown in Figure 6, the projection 3a includes a portion that overlaps with the corner portion 1bc of the shoulder portion 1b of the convex portion 1A as viewed from the press direction (hereinafter sometimes simply referred to as the "corner portion corresponding portion"). In the example of Figure 6, the projection 3a is formed such that, in the corner portion corresponding portion, the distance it protrudes toward the convex portion 1A in the press direction (i.e., the protrusion distance) increases as it moves toward the outside of the pad 3 as viewed from the press direction. That is, the surface of the corner portion corresponding portion of the projection 3a includes an inclined surface in which the protrusion distance toward the convex portion 1A in the press direction increases as it moves toward the outside in the direction perpendicular to the press direction.

[0043] This inclined surface may be, for example, a curved surface. Furthermore, the shape of the inclined surface may be approximately the same as the shape of the curved surface of the corner portion 1bc. That is, the distance in the pressing direction between the inclined surface of the projection 3a and the curved surface of the corner portion 1bc may be approximately constant across the entire inclined surface. In the cross-section of Figure 6, the curve of the corner portion 1bc and at least a portion of the curve of the corner-corresponding portion of the projection 3a may have the same shape. That is, in this cross-section, the distance in the pressing direction between the corner-corresponding portion of the projection 3a and at least a portion of the curve of the corner portion 1bc may be constant. Note that the ridge line of the corner portion 1bc is the line of the R-end 1b1 outside the corner portion 1bc, i.e., the boundary line between the corner portion 1bc and the side surface 1c.

[0044] As shown in Figure 6, the projection 3a may be formed such that the distance h3 in the pressing direction of point 3ap of the projection 3a of the pad 3 that coincides with any point 1bcp of the corner portion 1bc when viewed from the pressing direction, relative to the pad surface 3b, is not greater than the distance h1 in the pressing direction of point 1bcp relative to the top surface 1a of the corner portion 1bc (i.e., the setback distance) (h3 ≤ h1).

[0045] In the example shown in Figure 6, the projection 3a is not provided in the region that overlaps with the top surface 1a of the convex portion 1A of the first mold 1 when viewed from the pressing direction. That is, the pad surface 3b is provided over the entire region that overlaps with the top surface 1a when viewed from the pressing direction.

[0046] In the example shown in Figure 6, the projection 3a is formed extending from the corner portion to the outside of the corner portion 1bc. That is, when viewed from the pressing direction, the projection 3a includes a portion located outside the corner portion 1bc in a direction perpendicular to the tangent to the edge of the corner portion 1bc (outside the dashed line J1). Also, when viewed from the pressing direction, the entire projection 3a is located inside the side surface 2c of the recess 2A of the second mold 2. In the example shown in Figure 6, the most protruding portion of the projection 3a in the pressing direction is located outside the portion that overlaps with the corner portion 1bc and inside the side surface 2c when viewed from the pressing direction. Note that the most protruding portion of the projection 3a in the pressing direction may be located in the portion that overlaps with the corner portion 1bc when viewed from the pressing direction. Furthermore, the projection 3a may be formed so as not to be provided in the region outside the corner portion 1bc (outside the dashed line J1 in the example shown in Figure 6) when viewed from the pressing direction.

[0047] Figure 6 shows the state in which the pad surface 3b of the pad 3 is in contact with the material to be molded W1 and is pressing down on the material to be molded W1. In this state, one surface of the material to be molded W1 is in contact with the pad surface 3b and the other surface is in contact with the top surface 1a of the protrusion 1A. That is, Figure 6 shows the state in which the top surface 1a of the protrusion 1A supports the material to be molded W1 and the pad surface 3b of the pad 3 is pressing down on the material to be molded W1. In this state in which the material to be molded W1 is held between the pad surface 3b and the top surface 1a, the protrusion 3a is formed such that the minimum distance C2 between the protrusion 3a and the corner portion 1bc is the same as or greater than the distance C1 between the pad surface 3b and the top surface 1a (C2 ≥ C1).

[0048] Figure 7 shows a cross-section in a plane parallel to the press direction, which includes a line (normal) perpendicular to the tangent to the edge of the shoulder portion 1b (outer R end 1b1) other than the corner portion 1bc when viewed from the press direction. In the example shown in Figure 7, the portion of the pad 3 3c (hereinafter simply referred to as "part 3c corresponding to the non-corner portion") that overlaps with the portion of the shoulder portion 1b other than the corner portion 1bc and the area outside that portion (the area outside the dashed line J1 in Figure 7) when viewed from the press direction, does not have any protrusions that project from the pad surface 3b in the press direction. That is, the part 3c corresponding to the non-corner portion of the pad 3 is part of the pad surface 3b. However, protrusions may be provided in the part 3c corresponding to the non-corner portion of the pad 3. In this case, the amount of projection of the projection 3a corresponding to the corner portion 1bc relative to the pad surface 3b in the press direction is made greater than the amount of projection of the part 3c corresponding to the non-corner portion relative to the pad surface 3b in the press direction. As a result, when the pad 3 approaches the protrusion 1A, the projection 3a will press against the workpiece W1 before the corresponding portion 3c other than the corner portion.

[0049] Figures 6 and 7 show that the entire pad surface 3b is in a plane perpendicular to the pressing direction, and the overall position of the pad surface 3b in the pressing direction is the same. In contrast, the pad surface 3b may include steps or surfaces inclined with respect to the plane perpendicular to the pressing direction. In this case, the amount of projection 3a protruding from the pad surface 3b in the pressing direction is determined, for example, at the cross section of a plane parallel to the pressing direction that includes lines perpendicular to the tangents of each point on the edge of the corner portion 1bc (outer R end 1b1) as viewed from the pressing direction, where the projection of the projection 3a in the pressing direction is maximized (as shown in Figure 6 as an example). In this cross section, the amount of projection 3a protruding from the pad surface in the pressing direction with respect to a virtual line perpendicular to the pressing direction that passes through point 3bt on the pad that coincides with the boundary 1b2 between the corner portion 1bc and the top surface 1a as viewed from the pressing direction is defined as the amount of projection 3a protruding from the pad surface in the pressing direction. In the example in Figure 6, the amount of protrusion = H3. The amount of protrusion in the pressing direction at each position of the non-corner portion is, for example, the amount of protrusion in the pressing direction of the non-corner portion 3c relative to a virtual line perpendicular to the pressing direction that passes through point 3bt of the pad, which coincides with the boundary between the first shoulder portion 1b and the top surface 1a (inner R end 1b2) when viewed from the pressing direction, in the cross-section shown in Figure 7. In the example in Figure 7, the amount of protrusion of the non-corner portion is 0. The amount of protrusion of the projection 3a corresponding to the corner portion 1bc is greater than the maximum amount of protrusion at each position of the non-corner portion.

[0050] Figure 6 shows a cross-section of the corner portion 1bc as viewed from the pressing direction, passing through a line perpendicular to the tangent to the edge of the corner portion 1bc at the center of the corner portion 1bc (see Figure 4). The projection 3a has the largest protrusion at a position that coincides with the center in the direction in which the edge of the corner portion 1bc (outer R termination 1b1) extends as viewed from the pressing direction, and the amount of protrusion decreases as it moves away from this center in the direction in which the edge extends. In the example in Figure 4, the projection 3a is formed extending from the region that coincides with the corner portion 1bc as viewed from the pressing direction to the region adjacent to the corner portion 1bc in the direction in which the edge of the corner portion 1bc extends.

[0051] Figure 8 shows an example of a press molding process using the press apparatus shown in Figures 3 to 7. Figure 8(a) shows the convex portion 1A and the workpiece W1 at the start of molding. At the start of molding, the workpiece W1 is supported by the top surface 1a of the convex portion 1A, and the pad 3 and the second mold 2 are separated from the workpiece W1. After molding starts, the pad 3 moves toward the convex portion 1A in the pressing direction. First, the projection 3a of the pad 3 contacts the portion of the workpiece W1 that overlaps with the corner portion 1bc when viewed from the pressing direction. Then, the pad surface 3b contacts the portion of the workpiece W1 that overlaps with the top surface 1a when viewed from the pressing direction. In this way, when the workpiece W1 is pressed by the pad 3, the projection 3a first presses the portion of the workpiece W1 that overlaps with the corner portion 1bc when viewed from the pressing direction, so that the portion of the workpiece W1 that overlaps with the corner portion 1bc when viewed from the pressing direction is bent first and molded into a shape along the shoulder portion 1b. Figure 8(b) shows the state in which only the projection 3a of the pad 3 is pressing and bending the workpiece. The dashed area A3a in Figure 8(b) is the area in contact with the workpiece W1. At this time, the workpiece W1 undergoes deformation mainly due to bending, but is secondarily accompanied by deformation due to shrinkage flange forming. Note that the part of the workpiece W1 that deforms at this time, i.e., the part corresponding to the corner, is not necessarily the same as the part that overlaps with the corner 1bc in the pressing direction. The part corresponding to the corner is at least a part of the area that combines the part of the workpiece W1 that overlaps with the corner 1bc when viewed from the pressing direction, and the part between that overlapping part and the end of the workpiece W1. The pad 3 moves toward the projection 1A in the pressing direction until the pad surface 3b and the top surface 1a of the projection 1A hold the workpiece W1 between them. In this state, the workpiece W1 is between the pad surface 3b and the projection 1A, and the pad surface 3b is closest to the projection 1A. In this state, the pad surface 3b is in contact with one surface of the material to be molded W1, and the top surface 1a is in contact with the other surface. In this state, it is preferable that the shape of the pad surface 3b corresponds to the shape of the top surface 1a, such that there is substantially no gap between the pad surface 3b and the material to be molded W1, and between the top surface 1a and the material to be molded W1.

[0052] With the workpiece W1 held between the pad surface 3b of pad 3 and the top surface 1a of the protrusion 1A, the second die 2 moves towards the first die 1. The shoulder portion 2d of the second die 2 pushes the workpiece W1. The workpiece W1 is bent into a shape that follows the shoulder portion 1b of the protrusion 1A. Figure 8(c) shows the state in which the workpiece W1 is pushed by the second die and bent into a shape that follows the shoulder portion 1b of the protrusion 1A. At this time, the portion of the workpiece W1 that overlaps with the shoulder portion 1b, excluding the corner portion 1bc, when viewed from the pressing direction, is mainly bent. Also, since the portion of the workpiece W1 that overlaps with the corner portion 1bc in the pressing direction is held down by the projection 3a, the portion of the workpiece W1 corresponding to the corner portion mainly undergoes deformation by shrink flange forming. Press forming ends when the second die 2 reaches the bottom dead center. Figure 8(d) shows the protrusion 1A and the workpiece W1 at the bottom dead center.

[0053] As described above, by first deforming the portion of the material to be molded W1 corresponding to the corner, the deformation caused by shrink flange forming and bending deformation can be distributed at least circumferentially from the center of the portion corresponding to the corner. In other words, the concentration of shrink flange deformation and bending deformation near the center of the portion corresponding to the corner can be mitigated. Therefore, the distortion that occurs in the center of the corner after demolding can be reduced.

[0054] In the example shown in Figure 8, when the shoulder portion 2d of the second die 2 presses and bends the workpiece W1, the surface of the workpiece W1 opposite to the pressed surface is not restrained by a holder or the like. In other words, the example in Figure 8 is an example of pad bending molding in which the portion of the workpiece W1 that overlaps with the outer surface 1a of the convex portion 1A, as viewed from the pressing direction, is bent without restraint. Note that this embodiment is not limited to pad bending molding and can be applied to deep drawing molding. In the case of deep drawing molding, for example, the end of the workpiece W1 may be held between the outer surface 2e of the second die 2 and a holder, and the preliminary bending process and the molding process, or only the molding process, may be performed.

[0055] (Example of protrusion configuration) FIG. 9 is a view showing a modified example of the protrusion 3a. FIG. 9 shows a cross section in a plane parallel to the pressing direction, including a line (normal line) perpendicular to the tangent line of the ridge line (outer R stop 1b1) of the corner portion 1bc as viewed from the pressing direction. FIG. 9 shows a state where the pad surface 3b is in contact with the workpiece W1. In this state, the protrusion 3a can be formed so that a gap is generated between the corner portion 1bc and the workpiece W1. In the example of FIG. 9, in a state where the workpiece W1 is held between the pad surface 3b and the top surface 1a, the protrusion 3a is formed such that the minimum distance C2 between the protrusion 3a and the corner portion 1bc is equal to or greater than the distance C1 between the pad surface 3b and the top surface 1a (C2≧C1). When the thickness of the workpiece W1 is constant, the distance C1 is also constant. When the thickness is not constant and the distance C1 between the pad surface 3b and the top surface 1a is not constant, the maximum value of the distance between the pad surface 3b and the top surface 1a is taken as the distance C1. The distances C1 and C2 are both distances in a direction perpendicular to the surface of the first mold 1.

[0056] In order to sufficiently press the workpiece W1 with the protrusion 3a and further enhance the effect of reducing the concentration of strain, it is preferable that a certain amount of the height H3 (projection amount) of the pad protrusion 3a with respect to the height H1 of the corner portion 1bc is ensured. If the workpiece is pressed too much with the protrusion 3a, wrinkles may occur near the corner portion or concentration of deformation may occur. Therefore, the height H3 of the pad protrusion 3a with respect to the height H1 should not be too large. From these viewpoints, for example, 0.2 < H3 / H1 < 0.8 is preferable, and 0.2 < H3 / H1 < 0.6 is more preferable. In this range, the effect of reducing strain concentration becomes higher.

[0057] In the example of FIG. 4, the curved portion 1bt of the shoulder 1b of the convex portion 1A of the first mold 1 is between the two straight portions 1bL as viewed from the pressing direction. In the example of FIG. 4, the inner angles θ1 to θ4 between the virtual lines in the extending direction of the straight portions 1bL adjacent to both sides of each curved portion 1bt are all 120 degrees or less.

[0058] As a variation of this, at least a portion of the straight sections 1bL adjacent to the curved section 1bt, which includes the corner section 1bc, may be replaced by a portion of the curved section. For example, the entire straight sections 1bL adjacent to the curved section 1bt, which includes the corner section 1bc, may be replaced by a portion of the curved section. In this case, the radii of curvature of the curves on either side of the corner section 1bc will be greater than the radii of curvature of the corner section 1bc. That is, the curved section includes the corner section 1bc and the curved sections adjacent to the corner section 1bc when viewed from the pressing direction. The radii of curvature of the adjacent curved sections are greater than the radii of curvature of the corner section. For example, as shown in Figure 10, a press-formed product 100 having a shape in which the ridge section 103 between the top surface 101 and the side wall 102 is curved outward in a convex shape can also be manufactured by press forming in this embodiment. Figure 11 shows the shape of the ridge line (outer R-end 1b1 of the shoulder portion 1b) of the shoulder portion 1b of the convex portion 1A of the first die 1 used for press forming of the press-formed product shown in Figure 10, as viewed from the pressing direction. In the example shown in Figure 11, as viewed from the pressing direction, the radius of curvature r1 of the corner portion 1bc is smaller than the radius of curvature r2 of the shoulder portions 1b on either side of it. Also, in the example in Figure 11, as viewed from the pressing direction, the inner angle θ5 of the two tangents LS1 and LS2 at the boundary between the two adjacent curved portions and the corner portion can be 120 degrees or less.

[0059] The press apparatus and method for manufacturing press-formed products of this embodiment can be suitably applied, for example, to the press forming of ultra-high-tensile steel. In press-formed products made from ultra-high-tensile steel, suppressing strain concentration enhances the quality improvement effect. For example, suppressing strain concentration can further suppress hydrogen embrittlement. Ultra-high-tensile steel is a material with a tensile strength of 1180 MPa or higher. The effect of suppressing strain concentration in this embodiment is even greater when the material to be formed has a tensile strength of 1470 MPa or higher. The upper limit of the tensile strength of the material to be formed is not particularly limited, but for example, the material to be formed may be 3000 MPa or less.

[0060] The thickness of the material to be molded in this embodiment is not particularly limited, but for example, 0.8 to 2.3 mm is preferred, and 1.0 to 1.8 mm is more preferred.

[0061] The press apparatus and manufacturing method for press-formed products of this embodiment can be suitably applied, for example, to the manufacture of automotive parts. For example, the press apparatus and manufacturing method of this embodiment can be applied to automotive parts having corner sections involving shrink flange forming, such as shoulder brackets, side frame inners, or other such parts. This makes it possible to provide high-quality automotive parts.

[0062] The above example shows a case where there is a notch at the outer edge of the corner portion of the workpiece. However, this embodiment can also be applied to workpieces with a shape that does not have a notch at the outer edge of the corner portion. In this case as well, strain concentration in the corner portion can be suppressed.

[0063] In the example above, the shoulder portion 1b (first shoulder portion) has multiple corner portions 1bc, and a projection corresponding to each of the multiple corner portions 1bc is provided on the pad 3. As a variation of this, a projection corresponding to some of the multiple corner portions of the first shoulder portion may be provided on the pad. That is, a projection corresponding to at least one of the multiple corner portions of the first shoulder portion may be provided on the pad.

[0064] (Analysis results) CAE analysis of the press forming process in the above embodiment was performed. Figure 12 shows the model used for the analysis. As shown in Figure 12(a), a simulation of press forming was performed using models of a first mold 1 with a convex portion, a second mold 2 with a concave portion, a pad 3, and a workpiece W1. The model was constructed using complete integration of shell elements. The mesh size of the elements in the plane was set to 1.0 mm, and the number of integration points in the thickness direction was set to 7. Cold-rolled steel sheet with a tensile strength of 1480 MPa and a thickness of 1.2 mm was used as the workpiece W1. Figure 12(b) shows the shape of the convex portion 1A of the first mold 1 and the model of the workpiece W1 as viewed from the pressing direction.

[0065] As shown in Figure 12(b), the angles of the corners of the protrusion 1A of the first mold 1, that is, the angles of adjacent sides of the protrusion 1A as viewed from the pressing direction, were set to 60°, 90°, and 120°. The radii of curvature, i.e., R, of the corners of the protrusion 1A as viewed from the pressing direction were set to 5 mm and 10 mm. The radius of curvature, i.e., shoulder R, of the first shoulder portion 1b of the protrusion 1A in a cross section parallel to the pressing direction was set to 6 mm. The bottom W1a (center) of the corner notch of the workpiece W1 was positioned so as to coincide with the center of the corner portion 1bc of the protrusion 1A of the first mold as viewed from the pressing direction (see enlarged view of Figure 12(b)). The radius of curvature, i.e., R, of the corner of the notch of the workpiece W1 as viewed from the pressing direction was set to 5 mm, and a length of 10 mm from the end of the corner R was extended as the part that becomes the side wall after molding.

[0066] Figure 12(c) is an enlarged view of the area around the protrusion 3a of the pad 3 model. The height of the protrusion 3a in the pressing direction was set to 3 mm, and was set to 0.5 (i.e., H3 / H1 = 0.5) relative to the shoulder R = 6 mm of the convex part 1A. The area on the pad 3 to which the protrusion 3a is attached was defined as the distance from the end of the corner R to 20 mm when viewed from the pressing direction. Figure 12(d) is a cross-section of line AA in Figure 12(c). The surface of the protrusion that presses against the workpiece was the outer surface of the first mold 1 offset outward by 1.4 mm (plate thickness + 0.2 mm). The distance between the side surface of the convex part 1A of the first mold 1 and the side surface of the recess of the second mold 2 was set to 1.4 mm. The distance between the side surface of the pad 3 and the side surface of the recess of the second mold 2 was set to 0.2 mm.

[0067] Figure 13 shows the analysis results of press forming using a pad without protrusions and press forming using a pad with protrusions 3a. Figure 13 shows the shape of the corner area of ​​the press-formed product after demolding. By using a pad with protrusions 3a, the corner portion of the workpiece W1 is deformed first, and then, while holding the workpiece W1 with the pad and the protrusions, the portion of the workpiece that overlaps with the first shoulder portion other than the corner portion when viewed from the pressing direction can be bent. As a result, the deformation due to shrink flange forming and bending forming, which was concentrated near the center of the corner in bending forming with a pad without protrusions, can be distributed to the entire corner. In the example in Figure 13, in press forming using a pad without protrusions, the deformation is concentrated near the center P1 of the corner of the press-formed product, and the area near the center P1 is pointed. In press forming using a pad with protrusions, the deformation near the center P1 of the corner of the press-formed product is distributed around it, and the area near the center P1 is deformed smoothly.

[0068] Figure 14 shows the analysis results for press forming using a pad without protrusions and press forming using a pad with protrusions 3a. Figure 14 shows the strain distribution near the corner of the press-formed product after demolding, i.e., after springback. Darker areas indicate areas with higher compressive strain. Figure 14(a) shows the strain distribution when using a pad without protrusions. Figure 14(b) shows the strain distribution when using a pad with protrusions. In Figure 14(a), there is a maximum strain point near P1 in the center of the corner. In Figure 14(b), the strain is dispersed, and there is no maximum strain point near P1. Furthermore, Figure 14(b) shows that the strain near P1 in the center of the corner is reduced by press forming using a pad with protrusions.

[0069] Table 1 below shows the analysis results. The equivalent plastic strain in Table 1 below is the strain value at the center of the corner of the press-formed product, i.e., at the bottom of the notch (P1 in Figure 14(b)). [Table 1]

[0070] As shown in Table 1, in Examples 1 to 8, which are press-formed using pads with protrusions, the distortion is reduced compared to Comparative Examples 1 to 4, which are press-formed using pads without protrusions.

[0071] Although one embodiment of the present invention has been described above, the above-described embodiments are merely illustrative examples for carrying out the present invention. Therefore, the present invention is not limited to the above-described embodiments, and it is possible to carry out the above-described embodiments by appropriately modifying them without departing from the spirit of the present invention. [Explanation of Symbols]

[0072] 1: First mold, 2: Second mold, 3: Pad, 3a: Protrusion

Claims

1. A step of preparing a mold set including a first mold having a protrusion that protrudes in the pressing direction, a pad provided at a position opposite to the protrusion of the first mold in the pressing direction, and a second mold having a recess corresponding to the protrusion of the first mold, A step of placing the material to be molded between the first mold and the second mold, The process includes the step of moving at least one of the first mold and the second mold from the molding start position to the bottom dead center in the pressing direction, and press-molding the workpiece, The protrusion of the first mold includes a top surface, a side surface, and a first shoulder portion between the top surface and the side surface, the first shoulder portion includes a curved portion that curves outward in a convex manner when viewed from the pressing direction, and the curved portion includes a corner portion whose radius of curvature is smaller than that of the adjacent portion when viewed from the pressing direction. The pad includes a pad surface that overlaps with at least a portion of the top surface of the convex portion of the first mold when viewed from the pressing direction, and a projection that is provided at a position that overlaps with at least a portion of the corner portion of the first shoulder of the convex portion of the first mold when viewed from the pressing direction, and that protrudes toward the corner portion in the pressing direction. The process of press-forming the aforementioned material to be molded is as follows: With the top surface of the convex portion of the first mold supporting the workpiece, the projection of the pad presses and bends the portion of the workpiece that overlaps with the corner portion of the first shoulder in the pressing direction; A method for manufacturing a press-formed product, comprising the following steps: after the preceding bending step, the pad surface of the pad and the top surface of the convex portion of the first mold hold the workpiece between them, and the first mold and the second mold move closer to each other and reach their bottom dead center, thereby bending the portion of the workpiece that overlaps with the portion of the first shoulder portion other than the corner portion in the pressing direction along the first shoulder portion, and press-forming the workpiece.

2. A method for manufacturing a press-formed article according to claim 1, A method for manufacturing a press-formed product, wherein in the preceding bending step, at least one of the pad and the first mold moves in the pressing direction, so that the projection of the pad presses and bends the portion of the workpiece that overlaps with the corner portion of the first shoulder in the pressing direction, and thereafter the pad surface of the pad and the top surface of the convex portion of the first mold hold the workpiece between them, and there is a gap between the corner portion and the workpiece.

3. A method for manufacturing a press-formed article according to claim 1 or 2, A method for manufacturing a press-formed product, wherein the protrusion of the pad includes a portion located outside the corner portion of the first shoulder of the convex portion of the first mold when viewed from the pressing direction.

4. A method for manufacturing a press-formed article according to claim 1 or 2, A method for manufacturing a press-formed product, wherein the first shoulder of the convex portion of the first mold includes, when viewed from the pressing direction, two straight portions and a curved portion that curves outwardly convexly between the two straight portions, and the inner angle between the imaginary lines in the extending direction of the two straight portions is 120 degrees or less.

5. A method for manufacturing a press-formed article according to claim 1 or 2, A method for manufacturing a press-formed product, wherein, in the molding process, the pad surface of the pad and the top surface of the convex portion of the first mold hold the workpiece between them, and as the first mold and the second mold approach each other and reach the bottom dead center, the surface of the workpiece opposite to the surface pressed by the second mold on the outside of the recess, as viewed from the pressing direction, is not restrained.

6. A first mold having a protrusion that protrudes in the pressing direction, A pad is provided at a position opposite to the protrusion of the first mold in the pressing direction and is movable in the pressing direction relative to the first mold, The present invention comprises a second mold having a recess corresponding to a protrusion of the first mold and being movable in the pressing direction relative to the first mold, The protrusion of the first mold includes a top surface, a side surface, and a first shoulder portion between the top surface and the side surface, the first shoulder portion includes a curved portion that curves outward in a convex manner when viewed from the pressing direction, and the curved portion includes a corner portion whose radius of curvature is smaller than that of the adjacent portion when viewed from the pressing direction. The pad includes a pad surface that faces the top surface of the convex portion of the first mold and overlaps with at least a portion of the top surface when viewed from the pressing direction, and a projection that is positioned to overlap with at least a portion of the corner portion of the first shoulder of the convex portion of the first mold when viewed from the pressing direction, and that protrudes toward the corner portion in the pressing direction. The second mold includes a side surface of the recess corresponding to the side surface of the convex portion of the first mold, an outward surface extending outward from the recess when viewed from the pressing direction, and a second shoulder portion between the side surface and the outward surface. A press device wherein the amount of the projection protruding from the pad surface in the pressing direction is greater than the amount of the portion of the pad that overlaps with the portion of the first shoulder other than the corner portion and the region outside thereof, as viewed from the pressing direction, protruding from the pad surface in the pressing direction.

7. A press apparatus according to claim 6, A press device in which the projection of the pad is formed such that, with the pad surface of the pad and the top surface of the convex portion of the first mold sandwiching and holding the workpiece, the portion of the workpiece that overlaps with the corner portion in the pressing direction is pushed toward the first mold and bent, and a gap is created between the workpiece and the corner portion.

8. A press apparatus according to claim 6 or 7, A press apparatus in which, when viewed from the pressing direction, the protrusion of the pad includes a portion located outside the corner portion of the first shoulder of the convex portion of the first mold.

9. A press apparatus according to claim 6 or 7, A press apparatus in which the first shoulder of the protrusion of the first die includes, when viewed from the pressing direction, two straight sections and a curved section that curves outwardly convexly between the two straight sections, and the inner angle between the imaginary lines in the extending direction of the two straight sections is 120 degrees or less.

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