Manufacturing method for molded parts

Abstract

The present invention provides a method for manufacturing a molded part, comprising: a first molding step of molding a base material to mold a first molded product including a first upper flange and a pair of first web members formed extending in a direction intersecting at both left-right ends of the first upper flange; and a second forming step of compressing the first molded product to mold a second molded product including a second upper flange and a pair of second web members formed extending in a direction intersecting at both left-right ends of the second upper flange; wherein the length of the first upper flange is longer than the length of the second upper flange and the length of the first web members is longer than the length of the second web members on a width cross section.

Description

[Technical field]

[0001] The present invention relates to a method for producing a molded part. [Background technology]

[0002] It is to be understood that the content of this section is merely provided as background information for the present invention and may not constitute prior art.

[0003] Automotive structural parts are developed for various purposes, such as high-strength shaped parts, high-rigidity parts, compression collision parts, bending collision parts, etc. In particular, parts that are made up of multiple parts and support complex collision loads must simultaneously maintain different collision characteristics within a single part. Taking a side member as an example, in the event of a collision, the area adjacent to the load must collapse to absorb the collision energy, while the area away from the load must support the collision energy.

[0004] In order to impart different crash characteristics to a single part, it is possible to design each region constituting the part to have a different cross section so that the cross sectional moment resisting an external load is different, and to impart a local step to the surface of the region that absorbs energy during a crash to induce sequential collapse.

[0005] Hot press forming is a representative method for manufacturing parts that simultaneously have different crash properties. Although hot press forming has the disadvantages of heating equipment taking up a large space and high initial capital investment costs, it has excellent cold formability and shape fixability because it forms the parts under high temperature conditions with relatively high ductility and low flow stress, and is applied to many new vehicle platforms.

[0006] Recently, efforts have been made to reduce costs by applying technology that allows two to four parts to be molded simultaneously in one press operation, but the high price of raw materials continues to drive up the cost of the vehicle. For this reason, global automobile and parts companies are trying to replace some of the body parts that use hot press molding technology with cold press molding methods in order to reduce costs.

[0007] In response to these demands, Global Steel is developing a steel material that has high strength (gigasteel) with a tensile strength of 1000MPa and excellent ductility, as well as a new forming technology suitable for this type of steel.However, since parts with different collision characteristics have very complex shapes, such as deep depths, varying cross sections, and bending up and down and left and right, when forming gigasteel, which has relatively poor ductility, by cold stamping, serious problems such as necking, cracks, wrinkles, and shape freeze are occurring.

[0008] Of the above problems, shape fixability is a springback issue where the shape changes due to elastic recovery when the formed part is released from the die. Types of springback include punch R spread, wall bending, and cross-sectional distortion. The magnitude of this springback increases with increasing strength, and is an important issue that must be resolved in order to expand the application of parts made by cold stamping of Gigasteel. Springback is known to be mainly caused by non-uniform stress in the thickness direction and compressive residual stress, and various solutions to resolve this issue need to be considered. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Korean Patent No. 10-1995-0003541 Summary of the Invention [Problem to be solved by the invention]

[0010] One aspect of the present invention is to provide a method for producing a molded part having excellent shape freezing ability by eliminating springback to a level that allows shape correction. [Means for solving the problem]

[0011] As one aspect of achieving the above-mentioned object, the present invention provides a method for manufacturing a molded part, comprising: a first molding step of molding a base material to mold a first molded product including a first upper flange and a pair of first web members formed extending in a direction intersecting at both left and right ends of the first upper flange; and a second molding step of compressing the first molded product to mold a second molded product including a second upper flange and a pair of second web members formed extending in a direction intersecting at both left and right ends of the second upper flange; wherein, in a width cross section, the length of the first upper flange is longer than the length of the second upper flange and the length of the first web members is longer than the length of the second web members.

[0012] The length of the first upper flange in a widthwise cross section may be 105% or more and 120% or less of the length of the second upper flange, and the length of the first web member in a widthwise cross section may be 105% or more and 120% or less of the length of the second web member.

[0013] The second forming step may begin when a first boundary point between the first upper flange and the first web member and a second boundary point between the second upper flange and the second web member overlap.

[0014] The second molding step may be performed in a state where both sides of an overlapping portion where the first boundary point and the second boundary point are overlapped are pressed by a mold.

[0015] The first molded article may have a curved section around a first boundary point between the first upper flange and the first web member.

[0016] The first molded article may have a straight section around a first boundary point between the first upper flange and the first web member.

[0017] The second molding step can form a vertical bead portion in which protruding surfaces and indented surfaces are alternately formed along the front-to-rear direction of the second web member, and the protruding surfaces and the indented surfaces are connected by inclined surfaces.

[0018] The vertical bead portion may be formed on the second web member at an outer protruding portion that protrudes convexly from the second web member in a direction away from the second upper flange.

[0019] The vertical bead portions may be spaced apart from one another in a number of 2 to 8 in the front-rear direction of the second web member.

[0020] The length of the embedded surface of the vertical bead portion in the front-rear direction may be in the range of 5 times or more and 30 times or less the thickness of the base material.

[0021] The vertical bead portion may have a distance between an extension line of the protruding surface and an extension line of the recessed surface that is in a range of not less than two times the thickness of the base material and not more than ten times the thickness of the base material.

[0022] The length of the protruding surface of the vertical bead portion in the front-rear direction may be in the range of 5 times or more and 30 times or less the thickness of the base material.

[0023] The vertical bead portion has an arc-shaped shoulder portion at the boundary between the protruding surface and the recessed surface, and the radius of curvature of the shoulder portion can be in the range of 4 to 10 times the thickness of the base material.

[0024] The second molded product is formed to extend in the front-rear direction, and the positions of the cross sections of the second molded product in the up-down and left-right directions can be varied depending on the position in the front-rear direction.

[0025] The second molded product may have a first position variable section in the range of 80 to 200 mm in the vertical direction of the second upper flange, and the second molded product may have a second position variable section in the range of 40 to 120 mm in the horizontal direction of the second upper flange.

[0026] The base material may be a steel plate having a thickness in the range of 1.2 to 1.8 mm, and the base material may be a steel material having a tensile strength of 980 MPa or more.

[0027] A cold forming method may be applied in the first forming step and the second forming step. Effect of the Invention

[0028] According to one embodiment of the present invention, springback is eliminated to a level that allows shape correction, and an excellent effect of shape freezing is achieved. [Brief description of the drawings]

[0029] [Figure 1a] In this drawing, a first molded product in a first molding stage is shown by a solid line, and a second molded product in a second molding stage is shown by a dotted line. [Figure 1b] In this drawing, the second molded product in the second molding stage is shown by a solid line, and the first molded product in the first molding stage is shown by a dashed line. [Figure 2a] 1 is a view showing a first molded product of a comparative example to be compared with the first molded product of the present invention. [Figure 2b] 2b is a view showing a first molded product according to an embodiment of the present invention compared with the comparative example of FIG. 2a. [Figure 2c] 2b is a view showing a first molded product according to another embodiment of the present invention, which is compared with the comparative example of FIG. 2a. [Figure 3a] 2 is a perspective view of a second molded product produced by a molded part manufacturing method according to one embodiment of the present invention. FIG. [Figure 3b] 3b are cross-sectional views taken along the lines AA' and BB' of FIG. 3a. [Figure 4a] FIG. 3b is an example of a cross-sectional view taken along the line CC' of FIG. 3a. [Figure 4b]3b is another example of a cross-sectional view taken along the line CC' of FIG. 3a. [Figure 5a] 1 is a view showing a springback state when the first forming step is not performed. [Figure 5b] 1 is a view showing a springback state after a first forming step. [Figure 6a] 13 is a view showing a springback state when a vertical bead portion is not formed in the second forming step. [Figure 6b] 13 is a view showing a springback state when a vertical bead portion is formed in a second forming step. [Figure 7a] 13 is a view showing a springback state when the interval between vertical beads formed in the second forming step is excessive. [Figure 7b] 13 is a view showing a springback state when the interval between vertical beads formed in the second forming step is good. [Figure 8] 1 is a diagram comparing various performance improvements between a comparative example in which the method for manufacturing a molded part of the present invention is not applied and an embodiment in which the method for manufacturing a molded part of the present invention is applied. [Figure 9a] 9 is a diagram comparing the spread angle of the punch R portion of the comparative example of FIG. 8 with that of the embodiment. [Figure 9b] 9 is a diagram comparing the spread angle of the punch R portion of the comparative example of FIG. 8 with that of the embodiment. [Figure 10a] 9 is a diagram comparing the radius of curvature of the wall bending between the comparative example of FIG. 8 and the embodiment. [Figure 10b] 9 is a diagram comparing the radius of curvature of the wall bending between the comparative example of FIG. 8 and the embodiment. [Figure 11a] 9 is a diagram comparing the angle of cross-sectional distortion between the comparative example of FIG. 8 and the embodiment. [Figure 11b] 9 is a diagram comparing the angle of cross-sectional distortion between the comparative example of FIG. 8 and the embodiment. [Figure 12a] 2 is a side view of a second molded product produced by a molded part manufacturing method according to one embodiment of the present invention. FIG. [Figure 12b] 2 is a plan view of a second molded product produced by a molded part manufacturing method according to one embodiment of the present invention. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0030] Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. However, the embodiments of the present invention can be modified into several other forms, and the scope of the present invention is not limited to the embodiments described below. Furthermore, the embodiments of the present invention are provided to more completely explain the present invention to those having average knowledge in the art. The shapes and sizes of elements in the drawings may be scaled (or highlighted or simplified) for clearer explanation.

[0031] With reference to the drawings, the manufacturing method of the present invention shows the first and second molded products in the left-right, up-down, and front-to-back directions, and the detailed description of the invention also uses the terms left-right, up-down, and front-to-back, but this is for convenience of explanation, and the technical features of the manufacturing method of the present invention are not limited to these directions.

[0032] In the following, the X-axis shown in the attached drawings is the front-rear direction of the first and second molded products, etc., the Y-axis is the left-right direction of the first and second molded products, etc., and the Z-axis is the up-down direction of the first and second molded products, etc. A cross section in the length direction is a cross section on the XZ-axis, and a cross section in the width direction is a cross section on the YZ-axis.

[0033] Hereinafter, components included in a method for manufacturing a molded part according to an embodiment of the present invention will be described in detail with reference to FIGS. 1a and 1b.

[0034] FIG. 1a is a drawing in which the first molded product 100 in the first molding stage is shown in a solid line and the second molded product 200 in the second molding stage is shown in a dotted line, and FIG. 1b is a drawing in which the second molded product 200 in the second molding stage is shown in a solid line and the first molded product 100 in the first molding stage is shown in a dotted line.

[0035] A method for producing a molded part according to an embodiment of the present invention may include a first molding step and a second molding step.

[0036] The first molding step can mold a base material to form a first molded product 100 including a first upper flange 110 and a pair of first web members 130 formed extending in intersecting directions at both left and right ends of the first upper flange 110.

[0037] Of course, the first molded product 100 may be formed with a first lower flange 150 extending in a direction intersecting with the first web member 130. As an example, the first web member 130 may include a lower curved portion in the up-down direction, and the first lower flange 150 may include only a straight section.

[0038] The second molding step may compress the first molded product 100 to mold a second molded product 200 including a second upper flange 210 and a pair of second web members 230 formed extending in intersecting directions at both left and right ends of the second upper flange 210.

[0039] Of course, the second molded product 200 may be formed with a second lower flange 250 extending in a direction intersecting with the second web member 230. As an example, the second web member 230 may include a lower curved portion in the up-down direction, and the second lower flange 250 may include only a straight section.

[0040] In a cross section in the width direction, the length of the first upper flange 110 can be longer than the length of the second upper flange 210 , and the length of the first web member 130 can be longer than the length of the second web member 230 .

[0041] The second molding step may be a step of compressing the first molded product 100 to conform to the final cross section of the second molded product 200. When the second molding step is completed, the first molded product 100 may be molded into the second molded product 200 that conforms to the final cross section of the final product. That is, the second molded product 200 may be the final product.

[0042] The method for producing the molded part of the present invention can employ a cold press molding method.

[0043] On a widthwise cross section, the length of the first upper flange 110 can be greater than or equal to 105% and less than or equal to 120% of the length of the second upper flange 210, and on a widthwise cross section, the length of the first web member 130 can be greater than or equal to 105% and less than or equal to 120% of the length of the second web member 230.

[0044] As the first molded part 100 is compressed and molded with the second molded part 200 , the first upper flange 110 can be compressed with the second upper flange 210 and the first web member 130 can be compressed with the second web member 230 .

[0045] If the length of the first upper flange 110 is less than 105% of the length of the second upper flange 210, it becomes difficult to induce tensile residual stress, and if the length of the first upper flange 110 exceeds 120% of the length of the second upper flange 210, there is a problem that wrinkles will occur in the second upper flange 210, increasing the likelihood of defects occurring in the second molded product 200.

[0046] If the length of the first web member 130 is less than 105% of the length of the second web member 230, it becomes difficult to induce tensile residual stress, and if the length of the first web member 130 exceeds 120% of the length of the second web member 230, there is a problem that wrinkles will occur in the second web member 230, increasing the likelihood of defects occurring in the second molded product 200.

[0047] Figure 2a is a drawing showing a first molded product 100 of a comparative example compared to the first molded product 100 of the present invention, Figure 2b is a drawing showing a first molded product 100 according to an embodiment of the present invention compared to the comparative example of Figure 2a, and Figure 2c is a drawing showing a first molded product 100 according to another embodiment of the present invention compared to the comparative example of Figure 2a.

[0048] Referring to Figure 2a, in the case of the first molded product 100 of the comparative example compared to the first molded product 100 of the present invention, it can be seen that the first boundary point between the first upper flange 110 and the first web member 130 and the second boundary point between the second upper flange 210 and the second web member 230 do not overlap.

[0049] Since the first compression section, in which the first upper flange 110 is compressed and molded by the second upper flange 210, and the second compression section, in which the first web member 130 is compressed and molded by the second web member 230, are no longer distinct, there is a problem in that wrinkles frequently occur in the second molded product 200 due to phenomena such as the first compression section and the second compression section being pressed against each other.

[0050] Referring to Figures 2b and 2c, the second forming stage may begin when a first boundary point between the first upper flange 110 and the first web member 130 and a second boundary point between the second upper flange 210 and the second web member 230 overlap.

[0051] The first molded product 100 may have a first boundary point between a first upper flange 110 and a first web member 130, and the second molded product 200 may have a second boundary point between a second upper flange 210 and a second web member 230.

[0052] Molding is performed with the first and second boundary points overlapping, and compression molding can proceed in a state in which a first compression section in which the first upper flange 110 is compression molded with the second upper flange 210 and a second compression section in which the first web member 130 is compression molded with the second web member 230 are separated.

[0053] In the second molding step, molding may proceed in a state where both sides of an overlapping portion where the first boundary point and the second boundary point overlap are pressed by a mold.

[0054] In the second molding step, molding proceeds with both sides of the overlapping portion where the first boundary point and the second boundary point overlap being pressed by a mold, so that the overlapping portion can be firmly fixed by the mold in a state in which a section where the first upper flange 110 is compression molded by the second upper flange 210 and a section where the first web member 130 is compression molded by the second web member 230 are separated.

[0055] Therefore, since compression molding proceeds with the first compression section and the second compression section firmly fixed, it is possible to prevent wrinkles from frequently occurring in the second molded product 200 due to phenomena such as the first compression section being pressed by the second compression section.

[0056] Referring to FIG. 2 b , the first molded article 100 may have a curved section around a first interface point between the first top flange 110 and the first web member 130 .

[0057] Referring to FIG. 2 c , the first molded article 100 may be a straight section around a first boundary point between the first top flange 110 and the first web member 130 .

[0058] FIG. 3a is a perspective view of a second molded part 200 produced by a molded part manufacturing method according to an embodiment of the present invention, and FIG. 3b is a cross-sectional view taken along the lines AA' and BB' of FIG. 3a.

[0059] FIG. 4a is an example of a cross-sectional view taken along the line CC' in FIG. 3a, and FIG. 4b is another example of a cross-sectional view taken along the line CC' in FIG. 3a.

[0060] The size of the cross section of the second molded product 200 may be variable in the front-rear direction. The cross section of the second molded product 200 may be designed to be different for each region constituting the molded part, to vary the cross-sectional moment resisting an external load, and to provide a local step on the surface of the region that absorbs energy during a collision, thereby inducing sequential collapse.

[0061] The second molding step forms a vertical bead portion 270 in which protruding surfaces 271 and indented surfaces 273 are alternately formed along the front-to-rear direction of the second web member 230, and the protruding surfaces 271 and the indented surfaces 273 are connected by inclined surfaces 275.

[0062] The vertical bead portion 270 may be formed in a plurality of portions spaced apart in the front-rear direction of the second web member 230, and the vertical bead portion 270 may be formed with an inwardly extending surface 273 extending in the vertical direction and a protruding surface 271 extending in the vertical direction.

[0063] The vertical bead portion 270 is formed in a plurality of portions spaced apart in the front-rear direction of the second web member 230, thereby increasing the rigidity of the second web member 230 and reducing cross-sectional distortion. As a result, springback is eliminated to a level where shape correction is possible, and a final product with excellent shape holdability can be produced.

[0064] Here, springback is a phenomenon in which the shape of a molded part changes due to elastic recovery when the molded part is released from a die after molding, and the reduced springback leads to excellent shape freezing properties.

[0065] As an example, it may be preferable to reduce the angle of cross-sectional distortion due to springback or the like to 3 degrees or less.

[0066] The vertical bead portion 270 may be formed on the second web member 230, and may be formed on an outer protruding portion 290 that protrudes convexly from the second web member 230 in a direction away from the second upper flange 210. The outer protruding portion 290 is a portion of the second web member 230 that protrudes convexly outward in the left-right direction.

[0067] By forming the outer protruding portion 290 that protrudes outward in a convex shape in the left-right direction from the second web member 230, the vertical bead portion 270 plays a role in converting compressive residual stress into tensile residual stress in the outer protruding portion 290, thereby achieving the effect of stably reducing springback in the outer protruding portion 290.

[0068] Two to eight vertical bead portions 270 may be spaced apart in the front-rear direction of the second web member 230. Only when at least two vertical bead portions 270 are continuously arranged can tensile residual stress be induced, and if the number of vertical bead portions 270 exceeds eight, the risk of shear cracking may increase.

[0069] The length L1 of the inset surface in the front-rear direction of the vertical bead portion 270 can be in the range of 5 times or more and 30 times or less the thickness of the base material.

[0070] If the length L1 of the inset surface in the front-to-back direction is less than 5 times the thickness of the base material, the risk of necking and cracking may increase, and if the length L1 of the inset surface in the front-to-back direction is more than 30 times the thickness of the base material, it may become difficult to induce tensile residual stress.

[0071] In the vertical bead portion 270, a distance L2 between an extension line of the protruding surface 271 and an extension line of the recessed surface 273 may be in a range of not less than two times the thickness of the base material and not more than ten times the thickness of the base material.

[0072] If the distance L2 between the extension line of the protruding surface 271 and the extension line of the inset surface 273 is less than twice the thickness of the base material, the increase in cross-sectional rigidity is small and rigidity reinforcement is not efficient, and if the distance L2 between the extension line of the protruding surface 271 and the extension line of the inset surface 273 exceeds 10 times the thickness of the base material, the risk of necking and cracking may increase.

[0073] The length L3 of the protruding surface of the vertical bead portion 270 in the front-rear direction may be in the range of 5 times or more and 30 times or less the thickness of the base material.

[0074] If the length L3 of the protruding surface in the front-to-back direction is less than 5 times the thickness of the base material, the risk of necking and cracking may increase, and if the length L3 of the protruding surface in the front-to-back direction is more than 30 times the thickness of the base material, the material yield may decrease.

[0075] Fig. 4a is an example of a cross-sectional view taken along the CC' direction in Fig. 3a, and Fig. 4b is another example of a cross-sectional view taken along the CC' direction in Fig. 3a. In Fig. 4a and Fig. 4b, the length L3 of the protruding surface in the front-rear direction is the same, and the distance L2 between the extension line of the protruding surface 271 and the extension line of the introjected surface 273 is the same. In Fig. 4b, the length L1 of the introjected surface in the front-rear direction is about twice as long as that in Fig. 4a.

[0076] The vertical bead portion 270 has an arc-shaped shoulder portion 277 formed at the boundary between the protruding surface 271 and the inset surface 273, and the radius of curvature of the shoulder portion 277 can be in the range of 4 to 10 times the thickness of the base material.

[0077] If the radius of curvature of the shoulder portion 277 is less than four times the thickness of the base material, the risk of bending cracks increases, and if the radius of curvature of the shoulder portion 277 exceeds ten times the thickness of the base material, the induction of tensile residual stress may be small, resulting in a small increase in cross-sectional rigidity.

[0078] The degree of occurrence of springback will be compared and described below with reference to Figures 5a to 7b. In Figures 5a to 7b, the state where springback does not occur is shown by dotted lines, and the state where springback occurs is shown by solid lines.

[0079] FIG. 5a is a diagram showing the springback state in the case of Comparative Example E1, which did not undergo the first forming step, and FIG. 5b is a diagram showing the springback state in the case of Example E2, which did undergo the first forming step.

[0080] Referring to Figures 5a and 5b, it can be seen that in the case of Comparative Example E1, which did not undergo the first forming step, springback occurred to a greater extent than in the case of Example E2, which did undergo the first forming step, resulting in significant shape and dimensional errors in the final product.

[0081] FIG. 6a is a diagram showing the springback state for comparison example E1 in which the vertical bead portion 270 is not formed in the second forming step, and FIG. 6b is a diagram showing the springback state for example E2 in which the vertical bead portion 270 is formed in the second forming step.

[0082] 6a and 6b, it can be seen that in the case of Comparative Example E1, in which the vertical bead portion 270 is not formed in the second forming step, springback occurs to a greater extent than in the case of Example E2, in which the vertical bead portion 270 is formed in the second forming step, resulting in significant shape and dimensional errors in the final product.

[0083] FIG. 7a is a diagram showing the springback state in the case of Comparative Example E1 in which the spacing between the vertical bead portions 270 formed in the second forming step is excessive, and FIG. 7b is a diagram showing the springback state in the case of Example E2 in which the spacing between the vertical bead portions 270 formed in the second forming step is good.

[0084] 7a and 7b, it can be seen that in the case of Comparative Example E1, in which the spacing of the vertical bead portions 270 formed in the second forming step is excessive, springback occurs to a greater extent than in the case of Example E2, in which the spacing of the vertical bead portions 270 formed in the second forming step is good, resulting in significant errors in the shape and dimensions of the final product.

[0085] Below, with reference to Figures 8 to 11b, various performance improvements of Comparative Example E1, to which the manufacturing method for molded parts is not applied, and Example E2, to which the manufacturing method for molded parts of the present invention is applied, will be compared and explained.

[0086] FIG. 8 is a diagram comparing various performance improvements between Comparative Example E1, to which the method for producing a molded part of the present invention is not applied, and Example E2, to which the method for producing a molded part of the present invention is applied.

[0087] Figures 9a and 9b are diagrams comparing the spread angle S of the punch R portion of Comparative Example E1 and Example E2 of Figure 8. In Figures 9a to 9b, the dotted lines indicate the state in which the punch R portion does not spread, and the solid lines indicate the state in which the punch R portion spreads.

[0088] 9a and 9b, in the case of Comparative Example E1, the spread angle S of the punch R portion is 12 degrees, and in the case of Example E2, the spread angle S of the punch R portion is 2 degrees. It can be seen that in Comparative Example E1, a large springback occurs, the spread angle S of the punch R portion becomes large, and the shape and dimensional errors of the final product occur significantly.

[0089] Figures 10a and 10b are diagrams comparing the radius of curvature T of the wall bending between Comparative Example E1 and Example E2 in Figure 8. In Figures 10a to 10b, the dotted line indicates a state in which no wall bending has occurred, and the solid line indicates a state in which wall bending has occurred.

[0090] 10a and 10b, in the case of Comparative Example E1, the curvature radius T of the wall bending is 150 mm, and in the case of Example E2, the curvature radius T of the wall bending is 300 mm. It can be seen that in Comparative Example E1, the springback is large, the curvature radius T of the wall bending is small, and the wall bending is large, resulting in significant shape and dimensional errors in the final product.

[0091] Figures 11a and 11b are diagrams comparing the cross-sectional distortion angle U between Comparative Example E1 and Example E2 in Figure 8. In Figures 11a to 11b, the dotted line indicates a state in which no cross-sectional distortion has occurred, and the solid line indicates a state in which cross-sectional distortion has occurred.

[0092] 11a and 11b, the cross-sectional distortion angle U of Comparative Example E1 is 9 degrees, and the cross-sectional distortion angle U of Example E2 is 2 degrees. It can be seen that in Comparative Example E1, a large springback occurs, the cross-sectional distortion angle becomes large, and the shape and dimensional errors of the final product occur significantly.

[0093] FIG. 12a is a side view of a second molded part 200 produced by a method for manufacturing a molded part according to an embodiment of the present invention.

[0094] FIG. 12b is a plan view of a second molded part 200 produced by a method for manufacturing a molded part according to an embodiment of the present invention.

[0095] The second molded product 200 is formed to extend in the front-rear direction, and the positions of the cross sections of the second molded product 200 in the up-down and left-right directions can be changed according to the position in the front-rear direction.

[0096] The second molded product 200 has a second upper flange 210 having a first position variable section in the range of 80 to 200 mm in the vertical direction, and the second upper flange 210 of the second molded product 200 has a second position variable section in the range of 40 to 120 mm in the horizontal direction.

[0097] As an example, the second molded product 200 may have a difference in the vertical direction from the uppermost part to the lowermost part in a range of 80 to 200 mm based on the left-right central part of the second upper flange 210, and the second molded product 200 may have a difference in the vertical direction from the leftmost part to the rightmost part in a range of 40 to 120 mm based on the left-right central part of the second upper flange 210.

[0098] The base material is a steel plate having a thickness in the range of 1.2 to 1.8 mm, and the base material can be a steel material having a tensile strength of 980 MPa or more.

[0099] In the first and second forming steps, a cold forming method may be applied. The cold forming method applied in the first and second forming steps may be a cold stamping forming method or a cold press forming method.

[0100] The manufacturing method of the molded part of the present invention applies a cold forming method in the first and second forming stages, thereby reducing capital investment costs unlike hot forming methods, which require excessive capital investment costs, and at the same time, eliminating springback of the manufactured molded part to a level that allows shape correction, thereby achieving excellent shape fixability.

[0101] Although the embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and it will be apparent to those having ordinary skill in the art that various modifications and variations are possible without departing from the technical idea of ​​the present invention described in the claims. [Explanation of symbols]

[0102] 100 first molded product 110 first upper flange 130 first web member 150 first lower flange 200 Second molded part 210 Second upper flange 230 second web member 250 second lower flange 270 Vertical bead portion 271 Protruding surface 273 Inner surface 275 Inclined surface 277 Shoulder part 290 External protruding part E1 Comparative Example E2 Example L1 Length of the inset surface in the front-rear direction L2 Distance between the extension line of the protruding surface and the extension line of the inward surface L3: Length of protruding surface in anterior-posterior direction P1 1st boundary point P2 2nd boundary point S: Expansion angle of punch R T: Radius of curvature of wall bend U section distortion angle

Claims

1. a first molding step of molding a base material to form a first molded product including a first upper flange and a pair of first web members extending in a direction intersecting both ends of the first upper flange in a left-right direction; a second molding step of compressing the first molded product to mold a second molded product including a second upper flange and a pair of second web members formed to extend in a direction intersecting both left and right ends of the second upper flange; Including, A method for producing a molded part, wherein, in a cross-section in the width direction, a length of the first upper flange is longer than a length of the second upper flange, and a length of the first web member is longer than a length of the second web member.

2. A length of the first upper flange in a cross section in the width direction is 105% or more and 120% or less of a length of the second upper flange, The method for producing a molded part according to claim 1 , wherein a length of the first web member in a cross section in the width direction is 105% or more and 120% or less of a length of the second web member.

3. The second forming step includes:

2. The method of claim 1, wherein molding begins with a first boundary point between the first top flange and the first web member overlapping a second boundary point between the second top flange and the second web member.

4. The second forming step includes: The method for manufacturing a molded part according to claim 3 , wherein molding proceeds in a state in which both sides of an overlapping portion where the first boundary point and the second boundary point overlap are pressed by a mold.

5. The first molded product is The method of claim 1 , wherein a perimeter of a first interface point between the first upper flange and the first web member is a curved section.

6. The first molded product is The method of claim 1 , wherein a perimeter of a first interface point between the first top flange and the first web member is a straight section.

7. The second forming step includes: The method for manufacturing a molded part according to claim 1, wherein protruding surfaces and indented surfaces are alternately formed along the front-to-rear direction on the second web member, and a vertical bead portion is formed between the protruding surfaces and the indented surfaces and connected by an inclined surface.

8. The method for producing a molded part according to claim 7 , wherein the vertical bead portion is formed on the second web member and is formed on an outwardly projecting portion of the second web member that projects convexly in a direction away from the second upper flange.

9. The vertical bead portion is The method for producing a molded part according to claim 7, wherein 2 to 8 of the second web members are spaced apart in the front-to-rear direction of the second web member.

10. The vertical bead portion is The method for producing a molded part according to claim 7 , wherein the length of the recessed surface in the front-rear direction is in the range of 5 times or more and 30 times or less than the thickness of the base material.

11. The vertical bead portion is The method for producing a molded part according to claim 7 , wherein a distance between an extension of the protruding surface and an extension of the recessed surface is in a range of from two times the thickness of the base material to ten times the thickness of the base material.

12. The vertical bead portion is The method for producing a molded part according to claim 7 , wherein the length of the protruding surface in the front-rear direction is in the range of 5 times or more and 30 times or less than the thickness of the base material.

13. The vertical bead portion is An arc-shaped shoulder portion is formed at the boundary between the protruding surface and the inwardly recessed surface, The method of claim 7, wherein the radius of curvature of the shoulder portion is in the range of 4 to 10 times the thickness of the base material.

14. The method for manufacturing a molded part according to claim 1 , wherein the second molded product is formed to extend in a front-rear direction, and the positions of the cross sections of the second molded product in the up-down and left-right directions vary depending on the position in the front-rear direction.

15. The second molded product has a first position variable section in which the second upper flange has a range of 80 to 200 mm in the up-down direction, The method for manufacturing a molded part according to claim 1, wherein the second molded product has a second position variable section of the second upper flange in the left-right direction in a range of 40 to 120 mm.

16. The method for producing a molded part according to claim 1, wherein the base material is a steel plate having a thickness in the range of 1.2 to 1.8 mm, and the base material is a steel material having a tensile strength of 980 MPa or more.

17. The method for producing a moulded part according to any one of claims 1 to 16, wherein in the first and second moulding steps a cold forming method is applied.

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