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 manufacturing molded parts.

Background Art

[0002] It should be clarified that the content described in this part merely provides background information for the present invention and does not constitute the prior art.

[0003] Parts for automobile structures are developed according to various purposes such as high-strength shaped members, high-rigidity members, compression collision members, and bending collision members. In particular, parts to which a large number of components are attached and which support complex collision loads must simultaneously maintain different collision characteristics within a single part. Taking a side member as an example, during a collision, the load adjacent area must absorb collision energy while collapsing, and the area away from the load must support the collision energy.

[0004] In order to impart different collision characteristics to a single part, it can be considered to design the cross-section to be different for each region constituting the part, so that the cross-sectional moment resisting external loads is different, and to impart local steps to the surface of the region that absorbs energy during a collision to induce sequential collapse.

[0005] As a method for manufacturing parts having different collision characteristics simultaneously, hot press forming technology is representative. Although hot press forming technology has the disadvantages that the heating equipment occupies a large space and the initial equipment investment cost is high, because it is formed under high-temperature conditions with relatively high ductility and low flow stress, it has excellent formability and shape freezing property compared to cold forming, and is applied to many new vehicle platforms.

[0006] Recently, cost reductions have been attempted by applying technology that allows for the simultaneous molding of 2 to 4 parts in a single press operation. However, the high cost of raw materials remains a major factor driving up the overall cost of the vehicle. For these reasons, Global Auto and its parts companies continue to try to replace some of the body parts that are currently formed using hot press forming with cold press forming methods in order to reduce costs.

[0007] Global Steel Corporation has responded to these demands by developing steel materials that possess high strength (Gigasteel) of 1000 MPa class tensile strength while also having excellent ductility, as well as new forming technologies suitable for such steel types. However, because parts with different collision characteristics are deep, have changing cross-sections, and bend in all directions, resulting in extremely complex shapes, when forming Gigasteel, which has relatively insufficient ductility, by cold stamping, serious problems such as necking, cracking, wrinkling, and shape freezing occur.

[0008] Of the above problems, shape freezing is a problem of springback, where the shape of a molded part changes due to elastic recovery when it is released from the mold. Types of springback include widening of the punch radius, bending of the wall, and cross-sectional distortion. The magnitude of such springback increases with increasing strength, but it is an important problem that must be solved 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 it is necessary to consider various solutions to eliminate these. [Prior art documents] [Patent Documents]

[0009] [Patent Document 1] Korean Patent Publication No. 10-1995-0003541 [Overview of the project] [Problems that the invention aims to solve]

[0010] One aspect of the present invention is to provide a method for manufacturing molded parts in which springback is eliminated to a level that allows for shape correction, and which exhibits excellent shape retention properties. [Means for solving the problem]

[0011] As one aspect of achieving the above-mentioned objectives, the present invention provides a method for manufacturing a molded part, comprising: 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 formed in directions intersecting the left and right ends of the first upper flange; and a second molding step of compressing the first molded product to form a second molded product including a second upper flange and a pair of second web members formed in directions intersecting the left and 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 in the widthwise cross-section, and the length of the first web members is longer than the length of the second web members.

[0012] In the cross-section in the width direction, the length of the first upper flange is 105% to 120% of the length of the second upper flange, and the length of the first web member may be 105% to 120% of the length of the second web member.

[0013] The second molding step described above may begin with the first boundary point between the first upper flange and the first web member overlapping with the second boundary point between the second upper flange and the second web member.

[0014] In the second molding step described above, molding can proceed with both sides of the overlapping portion of the first boundary point and the second boundary point being pressed by the mold.

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

[0016] The periphery of the first boundary point between the first upper flange and the first web member of the first molded product can be a straight line section.

[0017] In the second molding step, a longitudinal bead portion can be formed in which protruding surfaces and recessed surfaces are alternately formed along the front-rear direction on the second web member, and the protruding surfaces and the recessed surfaces are connected by inclined surfaces.

[0018] The longitudinal bead portion can be formed on the second web member and can be formed on an outer protruding portion where the second web member protrudes convexly in a direction away from the second upper flange.

[0019] Two to eight longitudinal bead portions can be arranged at intervals in the front-rear direction of the second web member.

[0020] The longitudinal bead portion can have a range in which the length of the recessed surface in the front-rear direction is 5 times or more and 30 times or less the thickness of the base material.

[0021] The longitudinal bead portion can have a range in which the separation distance between the extension line of the protruding surface and the extension line of the recessed surface is 2 times or more and 10 times or less the thickness of the base material.

[0022] The longitudinal bead portion can have a range in which the length of the protruding surface in the front-rear direction is 5 times or more and 30 times or less the thickness of the base material.

[0023] An arcuate shoulder portion is formed at the boundary portion between the protruding surface and the recessed surface of the longitudinal bead portion, and the radius of curvature of the shoulder portion can be in the range of 4 times or more and 10 times or less 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 in the vertical and horizontal directions of the second molded product can be changed according to the position in the front-rear direction.

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

[0026] The thickness of the base material is a steel plate having a 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.

[0027] A cold forming method can be applied in the first forming stage and the second forming stage.

Effects of the Invention

[0028] According to an embodiment of the present invention, springback is eliminated at a level where shape correction is possible, and there is an excellent effect in shape freezing property.

Brief Description of the Drawings

[0029] [Figure 1a] The drawing shows the first molded product in the first forming stage in solid lines and the second molded product in the second forming stage in dotted lines. [Figure 1b] The drawing shows the second molded product in the second forming stage in solid lines and the first molded product in the first forming stage in dashed lines. [Figure 2a] The drawing shows the first molded product of the comparative example compared with the first molded product of the present invention. [Figure 2b] The drawing shows the first molded product according to an embodiment of the present invention compared with the comparative example of Fig. 2a. [Figure 2c] The drawing shows the first molded product according to another embodiment of the present invention compared with the comparative example of Fig. 2a. [Figure 3a] The perspective view of the second molded product manufactured by the manufacturing method of the molded part according to an embodiment of the present invention. [Figure 3b] The cross-sectional views in the A-A' direction and B-B' direction of Fig. 3a. [Figure 4a] An example of the cross-sectional view in the C-C' direction of Fig. 3a. [Figure 4b]This is another example of a cross-sectional view in the C-C' direction in Figure 3a. [Figure 5a] This drawing shows the springback state when the first molding stage has not been completed. [Figure 5b] This drawing shows the springback state after the first molding stage. [Figure 6a] This diagram shows the springback state when the vertical bead portion is not formed during the second molding stage. [Figure 6b] This diagram shows the springback state when a vertical bead is formed during the second molding stage. [Figure 7a] This diagram shows the springback state that occurs when the spacing between the vertical beads formed in the second molding stage is excessive. [Figure 7b] This diagram shows the springback state when the spacing of the vertical beads formed in the second molding stage is good. [Figure 8] This drawing compares various performance improvements between a comparative example in which the manufacturing method for molded parts of the present invention is not applied and an example in which the manufacturing method for molded parts of the present invention is applied. [Figure 9a] This diagram compares the expansion angle of the punch radius (R) portion in the comparative example and the embodiment shown in Figure 8. [Figure 9b] This diagram compares the expansion angle of the punch radius (R) portion in the comparative example and the embodiment shown in Figure 8. [Figure 10a] This diagram compares the radius of curvature of the wall bending in the comparative example and the embodiment shown in Figure 8. [Figure 10b] This diagram compares the radius of curvature of the wall bending in the comparative example and the embodiment shown in Figure 8. [Figure 11a] This diagram compares the angle of cross-sectional distortion in the comparative example and the embodiment shown in Figure 8. [Figure 11b] This diagram compares the angle of cross-sectional distortion in the comparative example and the embodiment shown in Figure 8. [Figure 12a] This is a side view of a second molded product manufactured by a method for manufacturing molded parts according to one embodiment of the present invention. [Figure 12b] This is a plan view of a second molded product manufactured by a method for manufacturing molded parts according to one embodiment of the present invention. [Modes for carrying out the invention]

[0030] Preferred embodiments of the present invention will be described below with reference to the attached drawings. However, 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, embodiments of the present invention are provided to give a more complete explanation of the present invention to a person with average skill in the art. The shapes and sizes of elements in the drawings may be enlarged or reduced (or highlighted or simplified) for a clearer explanation.

[0031] Referring to the drawings, the manufacturing method of the present invention shows the first and second molded products, etc., in the left-right, up-down, and front-back directions, and the detailed description of the invention also uses terms such as left-right, up-down, and front-back directions. However, this is for the 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 represents the front-to-back direction of the first and second molded products, the Y-axis represents the left-to-right direction of the first and second molded products, and the Z-axis represents the up-to-down direction of the first and second molded products. The cross-section in the length direction is the cross-section on the XZ axis, and the cross-section in the width direction is the cross-section on the YZ axis.

[0033] The components included in the manufacturing method of molded parts according to the embodiment of the present invention will be specifically described below with reference to Figures 1a and 1b.

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

[0035] The method for manufacturing 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 allows for the molding of a base material to form a first molded product 100 which includes a first upper flange 110 and a pair of first web members 130 that extend in directions intersecting the left and right ends of the first upper flange 110.

[0037] Of course, the first molded product 100 may have a first lower flange 150 formed extending in a direction intersecting the first web member 130. For example, the first web member 130 may include a lower curved portion in the vertical direction, and the first lower flange 150 may include only a straight section.

[0038] The second molding step allows for the molding of a second molded product 200, which includes a second upper flange 210 and a pair of second web members 230 that extend in directions intersecting the left and right ends of the second upper flange 210, by compressing the first molded product 100.

[0039] Of course, the second molded product 200 may have a second lower flange 250 formed extending in a direction intersecting the second web member 230. For example, the second web member 230 may include a lower curved portion in the vertical direction, while the second lower flange 250 may consist only of a straight section.

[0040] In the 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 in which the first molded product 100 is compressed to match the final cross-section of the second molded product 200. Once the second molding step is completed, the first molded product 100 can be molded with the second molded product 200, which has a final cross-section that matches the final product. In other words, the second molded product 200 can be the final product.

[0042] The method for manufacturing molded parts according to the present invention can be applied to a cold press forming process.

[0043] In the cross-section in the width direction, the length of the first upper flange 110 may be 105% or more and 120% or less of the length of the second upper flange 210, and in the cross-section in the width direction, the length of the first web member 130 may be 105% or more and 120% or less of the length of the second web member 230.

[0044] While the first molded product 100 is compressed and formed into the second molded product 200, the first upper flange 110 can be compressed by the second upper flange 210, and the first web member 130 can be compressed by 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. If the length of the first upper flange 110 exceeds 120% of the length of the second upper flange 210, there is a higher probability that wrinkles will form in the second upper flange 210 and defects will occur 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. If the length of the first web member 130 exceeds 120% of the length of the second web member 230, there is a high probability that wrinkles will form in the second web member 230 and defects will occur in the second molded product 200.

[0047] Figure 2a is a drawing showing a comparative example of 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 in 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 in Figure 2a.

[0048] Referring to Figure 2a, it can be seen that in the case of the first molded product 100 of the comparative example, which is compared to the first molded product 100 of the present invention, 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] A problem arises when the first compression section, in which the first upper flange 110 is compressed by the second upper flange 210, and the second compression section, in which the first web member 130 is compressed by the second web member 230, become indistinguishable, causing wrinkles to frequently occur in the second molded product 200 due to phenomena such as the first and second compression sections being pushed against each other.

[0050] Referring to Figures 2b and 2c, the second molding step can begin with the first boundary point between the first upper flange 110 and the first web member 130 overlapping with the second boundary point between the second upper flange 210 and the second web member 230.

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

[0052] The molding process can proceed with the first boundary point and the second boundary point overlapping, and the process is divided into a first compression section in which the first upper flange 110 is compressed by the second upper flange 210, and a second compression section in which the first web member 130 is compressed by the second web member 230.

[0053] In the second molding stage, molding can proceed with both sides of the overlapping portion between the first and second boundary points being pressurized by the mold.

[0054] In the second molding stage, molding proceeds with both sides of the overlapping portion where the first boundary point and the second boundary point overlap being pressed by the mold. This divides the overlapping portion into sections where the first upper flange 110 is compression molded by the second upper flange 210 and sections where the first web member 130 is compression molded by the second web member 230, allowing the overlapping portion to be firmly fixed by the mold.

[0055] Therefore, by proceeding with compression molding while the first and second compression sections are firmly fixed, it is possible to prevent frequent wrinkles from 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 Figure 2b, the first molded product 100 may have a curved section around the first boundary point between the first upper flange 110 and the first web member 130.

[0057] Referring to Figure 2c, the first molded product 100 may have a straight section around the first boundary point between the first upper flange 110 and the first web member 130.

[0058] Figure 3a is a perspective view of a second molded product 200 manufactured by the method for manufacturing molded parts according to an embodiment of the present invention, and Figure 3b is a cross-sectional view of Figure 3a in the A-A' and B-B' directions.

[0059] Figure 4a is an example of a cross-sectional view in the C-C' direction of Figure 3a, and Figure 4b is another example of a cross-sectional view in the C-C' direction of Figure 3a.

[0060] The second molded product 200 can have a variable cross-sectional size along the front-to-back direction. The second molded product 200 is designed so that the cross-section differs for each region constituting the molded part, thereby creating different cross-sectional moments that resist external loads, and providing local steps on the surface of the regions that absorb energy during a collision, thereby inducing sequential collapse.

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

[0062] Multiple vertical bead portions 270 are formed spaced apart in the front-rear direction of the second web member 230, and the vertical bead portions 270 can be formed with an inward surface 273 extending in the vertical direction and a protruding surface 271 extending in the vertical direction.

[0063] Multiple vertical bead portions 270 are formed 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. This eliminates springback to a level where shape correction is possible, resulting in the production of a final product with excellent shape holdability.

[0064] Here, springback is the phenomenon in which the shape of a molded part changes due to elastic recovery when it separates from the mold after molding. A reduction in springback results in superior shape retention.

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

[0066] The vertical bead portion 270 is formed on the second web member 230, and can be formed as an outer protruding portion 290 that protrudes convexly in the direction away from the second upper flange 210. The outer protruding portion 290 is the 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 from the second web member 230 in the left-right direction, the vertical bead portion 270 plays a role in converting compressive residual stress into tensile residual stress in the outer protruding portion 290, thereby having the effect of stably reducing springback in the outer protruding portion 290.

[0068] The longitudinal bead portions 270 can be spaced apart in the front-rear direction of the second web member 230, with 2 to 8 portions spaced apart. Tensile residual stress can only be induced when at least two or more longitudinal bead portions 270 are arranged in a continuous manner, and if the number of longitudinal bead portions 270 exceeds eight, the risk of shear cracking may increase.

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

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

[0071] The vertical bead portion 270 can have a separation distance L2 between the extension line of the protruding surface 271 and the extension line of the inward surface 273 that is in the range of more than twice the thickness of the base material and less than or equal to 10 times the thickness of the base material.

[0072] If the separation distance L2 between the extension line of the protruding surface 271 and the extension line of the inward surface 273 is less than twice the thickness of the base material, the increase in cross-sectional stiffness is small and the stiffness reinforcement is not efficient. If the separation distance L2 between the extension line of the protruding surface 271 and the extension line of the inward 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 can 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. If the length L3 of the protruding surface in the front-to-back direction exceeds 30 times the thickness of the base material, the material yield may decrease.

[0075] Figure 4a is an example of a cross-sectional view in the C-C' direction of Figure 3a, and Figure 4b is another example of a cross-sectional view in the C-C' direction of Figure 3a. In both Figure 4a and Figure 4b, the length L3 in the front-rear direction of the protruding surface is the same, and the separation distance L2 between the extension line of the protruding surface 271 and the extension line of the inward surface 273 is the same. In Figure 4b, the length L1 in the front-rear direction of the inward surface is formed to be about twice as long as in Figure 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 inward surface 273, and the radius of curvature of the shoulder portion 277 can be in the range of 4 times 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 cracking 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 slight, resulting in only a slight increase in cross-sectional stiffness.

[0078] Below, we will compare and explain the degree of springback occurrence with reference to Figures 5a to 7b. In Figures 5a to 7b, the state without springback is shown with a dotted line, and the state with springback is shown with a solid line.

[0079] Figure 5a shows the springback state in Comparative Example E1, which has not undergone the first molding stage, and Figure 5b shows the springback state in Example E2, which has undergone the first molding stage.

[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 molding stage, springback occurred significantly more than in the case of Example E2, which did undergo the first molding stage, and the shape and dimensional errors of the final product were also significantly larger.

[0081] Figure 6a shows the springback state in Comparative Example E1, where the vertical bead portion 270 is not formed in the second molding stage, and Figure 6b shows the springback state in Example E2, where the vertical bead portion 270 is formed in the second molding stage.

[0082] Referring to Figures 6a and 6b, it can be seen that in Comparative Example E1, where the vertical bead portion 270 is not formed in the second molding stage, springback occurs more significantly, and the shape and dimensional errors of the final product occur more substantially compared to Example E2, where the vertical bead portion 270 is formed in the second molding stage.

[0083] Figure 7a shows the springback state in Comparative Example E1, where the spacing of the vertical bead portions 270 formed in the second molding stage is excessive, and Figure 7b shows the springback state in Example E2, where the spacing of the vertical bead portions 270 formed in the second molding stage is good.

[0084] Referring to Figures 7a and 7b, it can be seen that in Comparative Example E1, where the spacing of the vertical bead portions 270 formed in the second molding stage is excessive, springback occurs significantly more, and the shape and dimensional errors of the final product occur significantly more compared to Example E2, where the spacing of the vertical bead portions 270 formed in the second molding stage is good.

[0085] In the following, with reference to Figures 8 to 11b, we will compare and explain various performance improvements between Comparative Example E1, in which the molded part manufacturing method of the present invention is not applied, and Example E2, in which the molded part manufacturing method of the present invention is applied.

[0086] Figure 8 is a diagram comparing various performance improvements between Comparative Example E1, to which the manufacturing method of molded parts according to the present invention is not applied, and Example E2, to which the manufacturing method of molded parts according to the present invention is applied.

[0087] Figures 9a and 9b are diagrams comparing the punch R-shaped expansion angle S of Comparative Example E1 and Example E2 in Figure 8. In Figures 9a and 9b, the state in which no expansion of the punch R-shaped portion occurs is shown with a dotted line, and the state in which expansion of the punch R-shaped portion occurs is shown with a solid line.

[0088] Referring to Figures 9a and 9b, in Comparative Example E1, the expansion angle S of the punch R portion is 12 degrees, while in Example E2, the expansion angle S of the punch R portion is 2 degrees. It can be seen that in Comparative Example E1, a large amount of springback occurs, the expansion angle S of the punch R portion becomes large, and a large error occurs in the shape and dimensions of the final product.

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

[0090] Referring to Figures 10a and 10b, in Comparative Example E1, the radius of curvature T of the wall bend is 150 mm, while in Example E2, the radius of curvature T of the wall bend is 300 mm. In Comparative Example E1, significant springback occurs, reducing the radius of curvature T of the wall bend, resulting in greater wall bending and significant dimensional errors in the final product's shape.

[0091] Figures 11a and 11b are diagrams comparing the angle U of cross-sectional strain between Comparative Example E1 and Example E2 in Figure 8. In Figures 11a and 11b, the state without cross-sectional strain is shown by a dotted line, and the state with cross-sectional strain is shown by a solid line.

[0092] Referring to Figures 11a and 11b, the angle U of cross-sectional distortion in Comparative Example E1 is 9 degrees, while in Example E2, the angle U of cross-sectional distortion is 2 degrees. It can be seen that in Comparative Example E1, a large amount of springback occurs, resulting in a large angle of cross-sectional distortion and significant errors in the shape and dimensions of the final product.

[0093] Figure 12a is a side view of a second molded product 200 manufactured by the method for manufacturing molded parts according to an embodiment of the present invention.

[0094] Figure 12b is a plan view of the second molded product 200 manufactured by the method for manufacturing molded parts according to an embodiment of the present invention.

[0095] The second molded product 200 is formed to extend in the front-to-back direction, and the position of the cross-section of the second molded product 200 in the vertical and horizontal directions can be varied according to its position in the front-to-back direction.

[0096] The second molded product 200 may have a second upper flange 210 that has a first position variable section ranging from 80 to 200 mm in the vertical direction, and a second position variable section ranging from 40 to 120 mm in the horizontal direction.

[0097] For example, the second molded product 200 may have a difference of 80 to 200 mm between its uppermost and lowermost parts in the vertical direction, relative to the central part of the second upper flange 210 in the horizontal direction, and the second molded product 200 may have a difference of 40 to 120 mm between its leftmost and rightmost parts in the horizontal direction, relative to the central part of the second upper flange 210 in the horizontal direction.

[0098] The base material is a steel plate with 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] Cold forming methods can be applied in the first and second forming stages. These cold forming methods may include cold stamping or cold press forming.

[0100] The present invention provides a method for manufacturing molded parts that, by applying a cold forming method in the first and second forming stages, reduces capital investment costs, unlike hot forming methods which require excessive capital investment. At the same time, it eliminates the springback of the manufactured molded parts to a level where shape correction is possible, thereby achieving excellent shape retention.

[0101] Although 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 obvious to those with ordinary skill in the art that various modifications and variations are possible without departing from the technical idea of ​​the present invention as described in the claims. [Explanation of symbols]

[0102] 100 First molded part 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 section 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 inner surface in the front-to-back direction L2 Distance between the extension line of the protruding surface and the extension line of the inward-facing surface L3 Length of the protruding surface in the front-to-back direction P1 1st boundary point P2 2nd boundary point S: Spread angle of the punched R section; T: Radius of curvature of the wall section. U-section distortion angle

Claims

1. A first molding step involves molding a base material to form a first molded product which includes a first upper flange and a pair of first web members that are formed extending in directions intersecting the left and right ends of the first upper flange, A second molding step in which the first molded product is compressed to form a second molded product including a second upper flange and a pair of second web members that extend in directions intersecting the left and right ends of the second upper flange. Includes, In the cross-section in the width direction, the length of the first upper flange is longer than the length of the second upper flange, and the length of the first web member is longer than the length of the second web member. The second molding step is, A method for manufacturing a molded part, wherein molding is started when the first boundary point between the first upper flange and the first web member and the second boundary point between the second upper flange and the second web member overlap.

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

3. The second molding step is, A method for manufacturing a molded part according to claim 1, wherein molding proceeds with both sides of the overlapping portion of the first boundary point and the second boundary point being pressed by a mold.

4. The first molded product is, The method for manufacturing a molded part according to claim 1, wherein the area around the first boundary point between the first upper flange and the first web member is a curved section.

5. The first molded product is, The method for manufacturing a molded part according to claim 1, wherein the area around the first boundary point between the first upper flange and the first web member is a straight section.

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

7. The method for manufacturing a molded part according to claim 6, wherein the vertical bead portion is formed on the second web member and is formed on an outer protruding portion that protrudes convexly in a direction away from the second upper flange of the second web member.

8. The aforementioned vertical bead portion is, The method for manufacturing a molded part according to claim 6, wherein 2 to 8 of the second web members are spaced apart in the front-rear direction of the second web member.

9. The aforementioned vertical bead portion is, The method for manufacturing a molded part according to claim 6, wherein the length of the inset surface in the front-rear direction is in the range of 5 times or more and 30 times or less the thickness of the base material.

10. The aforementioned vertical bead portion is, The method for manufacturing a molded part according to claim 6, wherein the separation distance between the extension line of the protruding surface and the extension line of the indented surface is in the range of more than twice the thickness of the base material and less than or equal to 10 times the thickness of the base material.

11. The aforementioned vertical bead portion is, The method for manufacturing a molded part according to claim 6, 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 the thickness of the base material.

12. The aforementioned vertical bead portion is, An arc-shaped shoulder portion is formed at the boundary between the protruding surface and the inward surface. The method for manufacturing a molded part according to claim 6, wherein the radius of curvature of the shoulder portion is in the range of 4 times or more and 10 times or less the thickness of the base material.

13. The method for manufacturing a molded part according to claim 1, wherein the second molded product is formed to extend in the front-rear direction, and the position of the cross-section of the second molded product in the vertical and horizontal directions is variable according to the position in the front-rear direction.

14. The second molded product has a first position variable section in which the second upper flange is in the vertical direction and ranges from 80 to 200 mm. The method for manufacturing a molded part according to claim 1, wherein the second molded product has a second position variable section in the left-right direction of 40 to 120 mm, wherein the second upper flange has a second position variable section in the left-right direction.

15. The method for manufacturing 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.

16. A method for manufacturing a molded part according to any one of claims 1 to 15, wherein a cold forming method is applied in the first molding step and the second molding step.

Images