Molding method for molded article

Abstract

Provided is a method for molding a molded article, the method being capable of suppressing cracks in corners of the molded article. In this method for molding a molded article, a preform is molded in a pre-molding step in which the length of the longitudinal ridge of a pre-angled tube section is longer than the length of the longitudinal ridge of the local-angled tube section, and the length of the side of the bottom of the pre-angled tube section is equal to the length of the side of the bottom of the local-angled tube section, and the length of the side of the bottom of the local-angled tube section is equal to the length of the longitudinal ridge of the local-angled tube section. The depth of the center of the side of the bottom of the pre-angle cylinder part is smaller than the depth of the end part of the side. In the present molding step, the pre-angle tube section of the preform is pressed into the present molding die, and the material at the bottom of the pre-angle tube section is caused to flow toward the corner section of the pre-angle tube section while the bottom of the present-angle tube section is molded.

Description

Technical Field

[0001] The present invention relates to a molding method for a molded article, for example to a molding method for molding an article having a corner section and a flange section having a polygonal bottom by deep drawing of a sheet metal corner section. Background Technology

[0002] For example, the molding method of the molded article in Patent Document 1 includes the following steps: a preforming step, in which a preform is formed from a sheet metal into a cylindrical shape that is shallower than the molding depth of the molded article; and a molding step, in which the preform is formed to form the molded article.

[0003] At this time, in the preforming process, the length of each side of the bottom of the preform is set to be more than 0.9 times and less than 1.1 times the length of each side of the bottom of the formed product, so that the depth of the center of each side of the bottom of the preform is shallower than the depth of the end of each side.

[0004] Furthermore, in the preforming process, the depth of the preform is set to be less than 80% of the depth of the main molded product, and the inclination angle of the longitudinal edge of the preform is larger than the inclination angle of the longitudinal edge of the main molded product. In this way, by making the inclination angle of the longitudinal edge of the preform larger than the inclination angle of the longitudinal edge of the main molded product, an attempt is made to achieve a deeper forming depth of the main molded product.

[0005] Patent Document 1: Japanese Patent No. 7070820 Summary of the Invention

[0006] The applicant has discovered the following problem. In the molding method of the molded article in Patent Document 1, the material flow into the corner of the preform is insufficient during this molding process, which may cause cracking at the corner of the molded article.

[0007] This invention provides a molding method for a molded article that can suppress the cracking of the corners of the molded article.

[0008] A molding method for a molded article according to one aspect of the present invention includes molding an article having a polygonal bottom corner section and a flange section by deep drawing a sheet metal corner section. The molding method for the molded article includes the following steps:

[0009] In the preforming process, a preforming punch and a preforming die are used to preform the sheet metal to form a preformed article with a pre-angled cylindrical portion; and

[0010] In this forming process, a forming punch and a forming die are used to form the preform, thereby forming the molded product having the corner section.

[0011] In the preforming process, a preform is formed as follows: the length of the longitudinal edge of the pre-angled cylinder portion is longer than the length of the longitudinal edge of the main cylinder portion; the lengths of each side of the bottom of the pre-angled cylinder portion are equal to the lengths of each side of the bottom of the main cylinder portion; and the depth of the center of each side of the bottom of the pre-angled cylinder portion is shallower than the depth of the end of each side.

[0012] In the forming process, the pre-angled cylindrical part of the pre-formed article is pressed into the forming die by the forming punch. The forming punch causes the ends of each side of the bottom of the pre-angled cylindrical part to contact the forming die. While forming the bottom of the pre-angled cylindrical part, the material at the bottom of the pre-angled cylindrical part flows towards the corner of the pre-angled cylindrical part.

[0013] In the above-described molding method for the molded article, it is preferable that, in the pre-forming process, the pre-formed article is formed such that the depth of the ends of each side of the bottom of the pre-angle cylinder portion increases relative to the depth of each side of the bottom of the main angle cylinder portion.

[0014] In the above-described molding method for the molded article, it is preferable that, in the pre-forming process, a pre-protrusion is formed on the flange side of the corner of the pre-angle cylinder portion at a larger inclination angle relative to the bottom side portion of the corner, such that it inclines radially outward toward the corner as it moves toward the flange side.

[0015] In the forming process, the pre-protrusion is drawn deep by the forming punch and the forming die, and the flange side portion of the corner of the corner of the corner is formed at a larger angle relative to the bottom side portion of the corner ...

[0016] In the above-described forming method for the molded article, it is preferable that when the pre-protrusion is drawn deep by the punch and the die for forming the pre-protrusion, the cross-sectional area of ​​the pre-protrusion gradually changes in the manner in which the material of the pre-protrusion flows toward the flange side as it moves toward the flange side.

[0017] In the above-described molding method for the molded article, it is preferable that the outer circumferential radius of the bottom side of the pre-protrusion is larger than the outer circumferential radius of the flange side of the pre-protrusion and also larger than the outer circumferential radius of the bottom side of the main protrusion.

[0018] The outer circumferential radius of the flange side in the pre-protrusion is larger than the outer circumferential radius of the flange side in the main protrusion.

[0019] Invention Effects

[0020] According to the present invention, a molding method for a molded article is available that can suppress the cracking of the corners of the molded article. Attached Figure Description

[0021] Figure 1 (a) is a perspective view showing the molded article formed by the molding method of the embodiment. Figure 1 (b) is a perspective view showing the corner periphery of the molded article formed by the molding method of the embodiment.

[0022] Figure 2 This is a radial cross-sectional view of the corner of the molded article formed by the molding method of the embodiment.

[0023] Figure 3 (a) is a cross-sectional view showing the preforming process in the molding method of the molded article according to the embodiment. Figure 3 (b) is a cross-sectional view showing the state of the molding process of the molded article according to the embodiment at an intermediate stage. Figure 3 (c) is a cross-sectional view showing the completed state of the molding process in the molding method of the molded article of the embodiment.

[0024] Figure 4 (a) is a perspective view showing a preform formed in the preforming step of the molding method of the embodiment. Figure 4 (b) is a perspective view of the corner periphery of a preform formed in the preforming process of the molding method of the embodiment.

[0025] Figure 5 This is a diagram illustrating the flow of material from the bottom in the molding process of the molding method for the molded article of the embodiment.

[0026] Figure 6 This is a diagram illustrating the flow of material in the corners during the molding process of the molding method for the molded article of the embodiment. Detailed Implementation

[0027] Hereinafter, specific embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, the present invention is not limited to these embodiments. Furthermore, for clarity, the following description and drawings have been appropriately simplified.

[0028] Figure 1 (a) is a perspective view showing the molded article formed by the molding method of this embodiment. Figure 1 (b) is a perspective view showing the corner periphery of the molded article formed by the molding method of this embodiment.

[0029] Figure 2This is a radial cross-sectional view of the corner of the molded article formed by the molding method of this embodiment. Furthermore, in the following description, a three-dimensional (XYZ) coordinate system will be used for clarity.

[0030] This molded article 1, for example, is as follows Figure 1 As shown in (a) and (b), the corner tube portion 2 and the flange portion 3 are provided, and are formed by deep drawing of the corner tube as described later. The corner tube portion 2 is rectangular in shape when viewed from the Z-axis direction, and is a concave shape on the Z-axis+ side. The corner tube portion 2 includes a bottom 2a, a side wall portion 2b, and a protrusion 2c.

[0031] like Figure 1 As shown in (a) and (b), the bottom 2a is roughly rectangular when viewed from the Z-axis direction and is arranged to be roughly parallel to the XY plane. The side wall portion 2b hangs down from each side 2d of the bottom 2a toward the Z-axis side and tilts toward the inside of the corner tube portion 2 as it moves toward the Z-axis side.

[0032] like Figure 1 As shown in (a) and (b), the Z-axis + side edge 2e (i.e., the bottom edge 2d) of the side wall portion 2b and the Z-axis - side edge 2f of the side wall portion 2b are generally arranged on the XY plane. Furthermore, a longitudinal ridge line 2g is arranged between adjacent side wall portions 2b.

[0033] like Figure 1 As shown in (a) and (b), the side wall portion 2b is formed by the Z-axis + side edge 2e, the Z-axis - side edge 2f, and the adjacent longitudinal edge line 2g, into an approximately isosceles trapezoidal shape in which the Z-axis + side edge 2e is shorter than the Z-axis - side edge 2f when viewed from a direction orthogonal to the Z-axis direction.

[0034] like Figure 1 (b) and Figure 2 As shown, the protrusion 2c is formed on the Z-axis side of the corner portion 2h of the corner tube portion 2. For example, the protrusion 2c can be disposed in a portion approximately 1 / 2 of the depth of the corner portion 2h in the Z-axis direction.

[0035] like Figure 1 (b) and Figure 2 As shown, the protrusion 2c is inclined at a large angle relative to the Z-axis+ side of the corner portion 2h of the corner tube portion 2, and tilts radially outward toward the Z-axis-side. For example, the protrusion 2c may be inclined at an angle of about 5° relative to the Z-axis+ side of the corner portion 2h of the corner tube portion 2.

[0036] The cross-sectional area of ​​the protrusion 2c gradually changes as it faces the Z-axis side. For example, in the XY plane, the outer radius of the protrusion 2c on the Z-axis+ side can be about 10 mm, and the outer radius of the protrusion 2c on the Z-axis-side can be about 8 mm.

[0037] like Figure 1 As shown in (a) and (b), the flange portion 3 is approximately rectangular in shape when viewed from the Z-axis direction, and protrudes outward from the Z-axis side edge 2f of each side wall portion 2b in a direction orthogonal to the Z-axis direction. The flange portion 3 is configured to be approximately parallel to the XY plane.

[0038] For example, this molded article 1 can be molded such that the depth of the corner section 2 in the Z-axis direction is 125mm, the length of the side edge 2f of the side wall section 2b in the Z-axis direction and the length in the X-axis direction and the Y-axis direction are 1200mm respectively, the width of the flange section 3 in the direction orthogonal to the Z-axis direction is 30mm, the corner radius R is 10mm, the flange radius R and the bottom radius R are 3mm, and the inclination angle of the side wall section 2b is 95°.

[0039] This molded article 1 can be formed by the following molding method. Figure 3 (a) is a cross-sectional view showing the preforming process in the molding method of the molded article according to this embodiment. Figure 3 (b) is a cross-sectional view showing the state of the molding process of the molded article according to this embodiment at an intermediate stage. Figure 3 (c) is a cross-sectional view showing the completed state of this molding step in the molding method of the molded article according to this embodiment. Additionally, in Figure 3 In (a) to (c), the protrusion 2c of the molded article 1 and the pre-protrusion 9c of the pre-molded article 8 are omitted.

[0040] First, the sheet material 4, which is roughly rectangular when viewed from the Z-axis direction, is arranged to be roughly parallel to the XY plane, such as... Figure 3 As shown in (a), the periphery of the sheet metal 4 is held by the preforming die 5 and the sheet metal holder 6, while the preforming punch 7 presses the sheet metal 4 into the cavity 5a of the preforming die 5 to preform the preformed product 8. Here, the sheet metal 4 can be, for example, an SCGA270D with a sheet thickness of 1 mm.

[0041] Figure 4 (a) is a perspective view showing a preform formed in the preforming process of the molding method of the molded article according to this embodiment. Figure 4 (b) is a perspective view of the corner periphery of a preform formed in the preforming process of the molding method of the molded article in this embodiment.

[0042] like Figure 4As shown in (a) and (b), the preform 8 includes a pre-angle cylinder portion 9 and a pre-flange portion 10. The pre-angle cylinder portion 9 includes a bottom 9a, a side wall portion 9b, and a pre-protrusion portion 9c. The bottom 9a is generally rectangular when viewed from the Z-axis direction, and the corners of the bottom 9a are generally arranged on the XY plane.

[0043] For example, such as Figure 4 As shown in (a) and (b), a recessed portion 9d is formed at approximately the center of the bottom 9a, which is recessed towards the Z-axis. The Z-axis portion 9e of the recessed portion 9d is approximately rectangular when viewed from the Z direction and is arranged to be approximately parallel to the XY plane.

[0044] The length of each side 9f of the bottom 9a (i.e., the Z-axis of the side wall portion 9b + the side edge 9g) is approximately equal to the length of the side 2d of the bottom 2a of this corner tube portion 2, and the depth of the side edge 9f at approximately the center of the bottom 9a in the Z-axis direction is shallower than the depth of the side edge 9f at both ends in the Z-axis direction.

[0045] That is, such as Figure 4 As shown in (a) and (b), the approximate central portion of the edge 9f of the bottom 9a is positioned on the Z-axis side compared to the two ends of the edge 9f. Therefore, the edge 9f of the bottom 9a is, for example, a curved shape with the approximate central portion of the edge 9f recessed on the Z-axis side.

[0046] At this time, the depth of the end of the edge 9f of the bottom 9a in the Z-axis direction is preferably deeper than the depth of the end of the edge 2d of the bottom 2a of this corner tube portion 2 in the Z-axis direction. For example, the depth of the end of the edge 9f of the bottom 9a in the Z-axis direction is preferably about 4mm to 10mm deeper than the depth of the end of the edge 2d of the bottom 2a of this corner tube portion 2 in the Z-axis direction.

[0047] like Figure 4 As shown in (a) and (b), the sidewall portion 9b descends from each side 9f of the bottom 9a toward the Z-axis side, and slopes inward toward the pre-angle cylinder portion 9 as it moves toward the Z-axis+ side. The Z-axis side edge 9h of the sidewall portion 9b is generally positioned on the XY plane. Furthermore, a longitudinal ridge line 9i is provided between adjacent sidewall portions 9b.

[0048] like Figure 4 As shown in (a) and (b), the sidewall portion 9b is formed by the Z-axis + side edge 9g, the Z-axis - side edge 9h, and the adjacent longitudinal edge 9i, into an approximately isosceles trapezoidal shape in which the Z-axis + side edge 9g is recessed when viewed from a direction orthogonal to the Z-axis direction, and the length between the ends of the Z-axis + side edge 9g of the sidewall portion 9b is shorter than the length between the ends of the Z-axis - side edge 9h of the sidewall portion 9b in the XY plane.

[0049] At this time, the corner R of the pre-angle cylinder 9 is preferably larger than the corner R of the main corner cylinder 2, and the flange R and bottom R of the pre-angle cylinder 9 are preferably larger than the flange R and bottom R of the main corner cylinder 2. In this way, by making the radius of each part of the pre-angle cylinder 9 larger than the radius of each part of the main corner cylinder 2, it is possible to suppress the generation of wrinkles or breakage of each part in the pre-flange 10.

[0050] like Figure 4 As shown in (b), the pre-protrusion 9c is formed on the Z-axis side of the corner 9j of the pre-angle cylinder 9. At this time, the pre-protrusion 9c can be disposed, for example, at approximately 1 / 2 of the depth of the corner 9j of the pre-angle cylinder 9 in the Z-axis direction.

[0051] like Figure 4 As shown in (b), the pre-protrusion 9c is inclined at a large angle relative to the Z-axis + side of the corner 9j of the pre-angle cylinder 9, and is inclined radially outward toward the Z-axis - side, so as to suppress wrinkles around the corner 9j of the pre-angle cylinder 9 in the pre-flange 10 when the sheet 4 is pre-formed.

[0052] For example, the pre-protrusion 9c is inclined at an angle of approximately 5° relative to the Z-axis+ side of the corner 9j of the pre-angle cylinder 9. Furthermore, it is preferable that during this forming process, the material of the pre-protrusion 9c can flow toward the Z-axis side, and that between the pre-forming step and this forming step, the cross-sectional area of ​​the pre-protrusion 9c gradually changes toward the Z-axis side to suppress the flow of material in the region near the pre-protrusion 9c in the sidewall portion 9b of the pre-angle cylinder 9.

[0053] For example, the outer circumferential radius of the pre-protrusion 9c on the XY plane is larger at the end of the pre-protrusion 9c on the Z-axis+ side than the outer circumferential radius of the end of the protrusion 2c of the corner tube 2 on the Z-axis+ side, and larger at the end of the pre-protrusion 9c on the Z-axis- side than the outer circumferential radius of the end of the protrusion 2c of the corner tube 2 on the Z-axis- side.

[0054] like Figure 4 As shown in (a) and (b), the pre-flange portion 10 is formed around the pre-angle cylinder portion 9 during the pre-forming of the sheet metal 4. The pre-flange portion 10 is configured to be substantially parallel to the XY plane.

[0055] As described above, since the pre-protrusion 9c is provided, which is inclined to the Z-axis side of the corner 9j of the pre-angle cylinder 9, the flow of material from the pre-flange 10 to the corner 9j of the pre-angle cylinder 9 during preforming can be suppressed compared with the case where the pre-protrusion 9c is not formed, and wrinkles can be suppressed in the pre-flange 10.

[0056] Next, as Figure 3As shown in (b), the pre-flange portion 10 of the preformed article 8 is placed on the sheet metal holder 6, and the forming punch 11 is moved toward the Z-axis + side so that the forming punch 11 contacts the Z-axis-side portion 9e of the recess 9d of the bottom 9a in the pre-angle cylinder portion 9. At the same time, the forming die 12 is moved toward the Z-axis-side, and the pre-angle cylinder portion 9 of the preformed article 8 is pressed into the cavity 12a of the forming die 12 by the forming punch 11.

[0057] Moreover, such as Figure 3 As shown in (c), the pre-flange portion 10 of the preform 8 is held by the sheet metal holder 6 and the forming die 12, while the forming punch 11 is moved toward the Z-axis + side. The forming punch 11 presses the pre-angle cylinder portion 9 of the preform 8 and causes it to move along the cavity 12a of the forming die 12, thereby forming the preform 1.

[0058] Here, Figure 5 This is a diagram illustrating the flow of material from the bottom during the molding process of the molding method for the molded article of this embodiment. Figure 6 This is a diagram illustrating the flow of material in the corner of the molding process in the molding method of the molded article of this embodiment.

[0059] In addition, Figure 5 and Figure 6 In the diagram, arrows indicate the direction of material flow during this forming process. Furthermore, in... Figure 5 and Figure 6 In the diagram, dashed lines represent the edges of the preform, while solid lines represent the edges of the finished product.

[0060] In this embodiment, the approximate center of the edge 9f of the bottom 9a of the pre-angle cylinder 9 is disposed on the Z-axis side compared to the end of the edge 9f, and the depth of the end of the edge 9f of the bottom 9a of the pre-angle cylinder 9 in the Z-axis direction is deeper than the depth of the edge 2d of the bottom 2a of the main angle cylinder 2 in the Z-axis direction.

[0061] Therefore, as Figure 3 As shown in (b), the end of the edge 9f of the bottom 9a of the pre-angle cylinder 9 contacts the Z-axis + side surface of the cavity 12a of the molding die 12, while the Z-axis - side portion 9e of the recess 9d of the bottom 9a in the pre-angle cylinder 9 is pressed into the Z-axis + side.

[0062] Therefore, as Figure 5 As shown, the material at the bottom 9a of the pre-angle cylinder 9 flows toward the corner 9j of the pre-angle cylinder 9. Therefore, insufficient material flow into the corner 9j can be suppressed, and cracking of the corner 2h of the pre-angle cylinder 2 of this molded article 1 can be suppressed.

[0063] Furthermore, the pre-protrusion 9c of the pre-angle cylinder 9 is drawn deep by the forming punch 11 and the forming die 12, but the cross-sectional area of ​​the pre-protrusion 9c gradually changes as it moves toward the Z-axis side, therefore... Figure 6 As shown, the material of the pre-protrusion 9c flows toward the Z-axis side.

[0064] Therefore, in this forming process, the flow of material from the pre-flange portion 10 of the pre-formed article 8 to the corner portion 9j of the pre-corner cylinder portion 9 can be suppressed, and the generation of wrinkles in the flange portion 3 can be suppressed. Moreover, even if wrinkles are generated in the flange portion 3, the outer circumferential radius of the end portion on the Z-axis side of the protrusion 2c is smaller than the outer circumferential radius of the end portion on the Z-axis+ side, thus reducing the number of wrinkles.

[0065] Furthermore, since the cross-sectional area of ​​the pre-protrusion 9c gradually changes towards the Z-axis side, therefore... Figure 6 As shown, between the preforming process and the main forming process, suppressing the flow of material in the vicinity of the pre-protrusion 9c in the side wall portion 9b of the pre-angle cylinder portion 9 can suppress the cracking of the side wall portion 2b of the main angle cylinder portion 2 of the molded article 1.

[0066] Thus, the molding method of the molded article (i.e., the molded article 1) of this embodiment pre-forms a pre-molded article 8 in which the length of the longitudinal edge 9i of the pre-angle cylinder 9 is longer than the length of the longitudinal edge 2g of the main cylinder 2, the length of each side 9f of the bottom 9a of the pre-angle cylinder 9 is equal to the length of each side 2d of the bottom 2a of the main cylinder 2, and the depth in the Z-axis direction of the center of each side 9f of the bottom 9a of the pre-angle cylinder 9 is shallower than the depth in the Z-axis direction of the end of each side 9f.

[0067] Therefore, in this molding process, the excess material at the bottom 9a of the pre-angle cylinder 9 when forming the bottom 2a of the pre-angle cylinder 2 can flow to the corner 9j of the pre-angle cylinder 9. As a result, compared with the molding method of a general molded article, it is possible to suppress insufficient flow of material to the corner 9j of the pre-angle cylinder 9, suppress the cracking of the corner 2h of the pre-angle cylinder 2 of the molded article 1, and at the same time, it is possible to achieve a deeper molding depth.

[0068] Furthermore, taking the shapes of the protrusion 2c of the molded article 1 and the pre-protrusion 9c of the pre-formed article 8 as examples, any shape that can suppress the generation of wrinkles in the flange portion 3 of the molded article 1 and suppress cracking in the area near the protrusion 2c in the sidewall portion 2b of the molded article 1 is acceptable. Moreover, the protrusion 2c of the molded article 1 and the pre-protrusion 9c of the pre-formed article 8 may be omitted.

[0069] The corner section 2 of the molded article 1 in this embodiment is roughly rectangular when viewed from the Z-axis direction, but it can be polygonal as long as it is not.

[0070] This invention is not limited to the above-described embodiments, and appropriate changes can be made without departing from the spirit of the invention.

[0071] Symbol Explanation

[0072] 1-This molded part; 2-This corner section; 2a-Bottom; 2b-Side wall section; 2c-This protrusion; 2d-Edge of the bottom; 2e-Z-axis + side edge of the side wall section; 2f-Z-axis - side edge of the side wall section; 2g-Longitudinal ridge line; 2h-Corner; 3-This flange section; 4-Sheet metal; 5-Pre-forming die; 5a-Cavity; 6-Sheet metal holder; 7-Pre-forming punch; 8-Pre-formed part 9-Pre-angle cylinder part, 9a-Bottom, 9b-Side wall part, 9c-Pre-protrusion part, 9d-Recessed part, 9e-Z-axis side part of the recessed part, 9f-Edge of the bottom, 9g-Z-axis+side edge of the side wall part, 9h-Z-axis side edge of the side wall part, 9i-Longitudinal ridge line, 9j-Corner part, 10-Pre-flange part, 11-Punch for this forming, 12-Die for this forming, 12a-Cavity.

Claims

1. A method for forming a molded article, comprising forming an article having a polygonal bottom corner section and a flange section by deep drawing a sheet metal corner section, the method being characterized by comprising the following steps: In the preforming process, a preforming punch and a preforming die are used to preform the sheet metal to form a preformed article with a pre-angled cylindrical portion; and In this forming process, a forming punch and a forming die are used to form the preform, thereby forming the molded product having the corner section. In the preforming process, a preform is formed as follows: the length of the longitudinal edge of the pre-angled cylinder portion is longer than the length of the longitudinal edge of the main cylinder portion; the lengths of each side of the bottom of the pre-angled cylinder portion are equal to the lengths of each side of the bottom of the main cylinder portion; and the depth of the center of each side of the bottom of the pre-angled cylinder portion is shallower than the depth of the end of each side. In the forming process, the pre-angled cylindrical part of the preform is pressed into the forming die by the forming punch. The forming punch causes the ends of each side of the bottom of the pre-angled cylindrical part to contact the forming die. While forming the bottom of the pre-angled cylindrical part, the material at the bottom of the pre-angled cylindrical part flows towards the corner of the pre-angled cylindrical part.

2. The molding method for the molded article according to claim 1, characterized in that, In the preforming process, the preform is formed such that the depth of the ends of each side of the bottom of the pre-angle cylinder portion increases relative to the depth of each side of the bottom of the main angle cylinder portion.

3. The molding method for the molded article according to claim 1 or 2, characterized in that, In the preforming process, a pre-protrusion is formed on the flange side of the corner of the pre-angle cylinder at a larger inclination angle relative to the bottom side portion of the corner. This pre-protrusion inclines radially outward toward the corner as it moves toward the flange side. In the forming process, the pre-protrusion is drawn deep by the forming punch and the forming die, and the protrusion is formed at a larger angle relative to the bottom side of the corner ...

4. The molding method for the molded article according to claim 3, characterized in that, When the pre-protrusion is drawn through the forming punch and the forming die, the cross-sectional area of ​​the pre-protrusion causes the material of the pre-protrusion to flow towards the flange side in a manner that gradually changes as it moves towards the flange side.

5. The molding method for the molded article according to claim 4, characterized in that, The outer circumferential radius of the bottom side of the pre-protrusion is larger than the outer circumferential radius of the flange side of the pre-protrusion and also larger than the outer circumferential radius of the bottom side of the main protrusion. The outer circumferential radius of the flange side in the pre-protrusion is larger than the outer circumferential radius of the flange side in the main protrusion.

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