WO2022118622A1

WO2022118622A1 - Production method for steel component

Info

Publication number: WO2022118622A1
Application number: PCT/JP2021/041318
Authority: WO
Inventors: 寛之田中
Original assignee: 株式会社神戸製鋼所
Priority date: 2020-12-01
Filing date: 2021-11-10
Publication date: 2022-06-09
Also published as: JP7448464B2; JP2022087659A

Abstract

A production method for a steel component which has a curved shape in the longitudinal direction, has a U-shape or hat-shape cross-section in a direction perpendicular to the longitudinal direction, and has formed in a curved-recess-side vertical wall portion thereof a stepped portion that broadens toward an opening, the production method comprising: a first step for producing an intermediate component which is formed with a molding material, and which has a stepped portion in a cross section perpendicular to the longitudinal direction, the stepped portion, when compared with the steel component, having the same length as the steel component as seen in a top view but having a longer shape than the steel component as seen in a cross-sectional view; and a second step for shaping the intermediate component using a metal die, which has a curved-recess-side vertical wall portion having the same shape as that of the steel component, and transforming the shape of the curved-recess-side vertical wall portion of the intermediate component into the same shape as the curved-recess-side vertical wall portion of the steel component.

Description

Manufacturing method of steel parts

This disclosure relates to a method for manufacturing steel parts.

In recent years, high-strength steel materials are being applied to vehicle body structural parts in order to achieve both improved collision safety and weight reduction of automobile bodies. However, when high-strength steel materials are press-molded to manufacture vehicle body structural parts, molding defects such as springback are likely to occur. In particular, in the case of a vehicle body structural part having a U-shaped or hat-shaped cross section such as an A-pillar and curved in the longitudinal direction, molding defects such as springback occur, resulting in poor shape and dimensional accuracy. Cheap.

For the purpose of eliminating the above-mentioned inaccuracy, Patent Document 1 describes in a press forming method of forming a metal plate by a relative linear movement of a die and a punch, which shrinks and flanges before the bottom dead point of the press in the final press process. By forming multiple surplus beads in the part to be the part and applying tensile stress to the shrinking flange molding part to level the residual stress of the shrinking flange molding part, the residual stress of the press-molded product is leveled. It is shown.

Patent Document 2 is a method for molding a metal member having a U-shaped or hat-shaped cross section and having a shape curved in the longitudinal direction, and includes a curved portion in a region of the metal member in the longitudinal direction. For some, in the first molding step, an intermediate product is molded with the same radius of curvature as the product shape and wider than the product shape, and in the second molding step, the width is smaller than the width in the first molding step. , The remaining part other than a part including the curved portion is molded without changing the width of the mold and the radius of curvature in the first molding step and the second molding step. It is shown that the entire molded product has a product shape or a substantially product shape.

Further, Patent Document 3 describes a method of molding a metal member having a U-shaped or hat-shaped cross section and having a shape curved in the longitudinal direction, among a plurality of curved portions formed on the metal member. For at least one curved portion, in the first molding step, an intermediate product is molded with a radius of curvature larger than the product shape, and in the second molding step, the intermediate product is molded to be smaller than the radius of curvature in the first molding step. The remaining part other than the curved part may be molded without changing the radius of curvature of the mold in the first molding step and the second molding step, and the entire molded product may have a product shape or a substantially product shape. It is shown.

Japanese Unexamined Patent Publication No. 2009-255117 Japanese Unexamined Patent Publication No. 2010-64137 Japanese Unexamined Patent Publication No. 2010-64138

In Patent Document 1, for the purpose of leveling the residual stress of the flange forming portion, an intermediate forming of forming a bead on the stretched flange portion and a forming process of crushing the bead are carried out. However, this method is a method of controlling the shape of the flange portion, and does not reduce the residual stress generated in the vertical wall portion of the U-shaped or hat-shaped component.

In

Patent Documents

2 and 3, in the first molding step, an intermediate product having a longer line length in the longitudinal direction is formed when viewed from the top view, and then in the second molding step, it is molded into the shape of the final product. By doing so, the residual stress in the longitudinal direction is reduced. However, when the line length in the longitudinal direction is long, the mold may not be set properly in the molding process for obtaining the final shape. Further,

Patent Documents

2 and 3 do not manufacture parts having a complicated vertical wall surface, and there is a demand for a means for reducing partial residual stress according to the complicated shape.

The present disclosure has been made in view of the above circumstances, and an object thereof is to provide a manufacturing method capable of easily forming steel parts having a complicated shape and high strength with good shape and dimensional accuracy. It is in.

Aspect 1 of the present invention is
It has a shape curved in the longitudinal direction, and the shape of the cross section perpendicular to the longitudinal direction is U-shaped or hat-shaped, and a stepped portion having a divergent shape toward the opening is formed on the vertical wall portion on the curved concave portion side. It is a method of manufacturing steel parts that has
Using a forming material, the line length of the stepped portion in the cross section perpendicular to the longitudinal direction is the same as the steel part in the top view and longer than the steel part in the cross section when compared with the steel part. The first step of manufacturing intermediate parts with a shape,
Using the intermediate part, the vertical wall portion on the curved concave portion side is molded with a mold having the same shape as the steel part, and the shape of the vertical wall portion on the curved concave portion side of the intermediate part is changed to the vertical wall portion on the curved concave portion side of the steel part. It is a method for manufacturing a steel part, which includes a second step of transforming the shape of a wall portion.

Aspect 2 of the present invention is
The line length of the stepped portion in the cross section perpendicular to the longitudinal direction of the intermediate part is more than 1.00 times and 1.10 times or less of the line length of the stepped portion in the cross section perpendicular to the longitudinal direction of the steel part. The method for manufacturing a steel part according to the first aspect, which is the length of the above.

Aspect 3 of the present invention is
The method for manufacturing a steel part according to

aspect

1 or 2, wherein the steel plate constituting the steel part has a tensile strength of 980 MPa or more.

According to the present disclosure, it is possible to provide a method for manufacturing a steel part, which can easily form a steel part having a complicated shape and high strength with good shape and dimensional accuracy.

It is a schematic perspective view of the steel part which concerns on one Embodiment of this invention. It is a schematic top view of the steel part which concerns on one Embodiment of this invention. In one embodiment of the present invention, it is a schematic diagram explaining both ends of the line length when the line length of the step portion in the cross section perpendicular to the longitudinal direction is viewed in cross section. It is a schematic perspective view of the intermediate part which concerns on one Embodiment of this invention. A is a schematic cross-sectional view in a direction perpendicular to the longitudinal direction, and B is a schematic top view of the intermediate component according to the embodiment of the present invention. FIG. 5 is an enlarged view of a schematic cross-sectional view of FIG. It is an enlarged view of the step portion in the schematic cross-sectional view of FIG. It is a figure which illustrates the position to which the step portion of the intermediate component which concerns on other embodiment of this invention is applied. It is a schematic top view of the steel part targeted in an Example. 9 is a cross-sectional view taken along the line AA of FIG. It is a process diagram in an Example. It is a schematic cross-sectional view which shows the molding procedure of the 1st step (draw molding) in an Example, A is before molding, B is molding, C is after molding. It is a schematic cross-sectional view which shows the molding procedure of the 2nd step (form molding) in an Example, A is before molding, B is molding, C is after molding. It is a figure which shows the characteristic of the steel plate used in an Example. It is a stress distribution map obtained in the example, A is the result of the comparative example, and B is the result of the example. It is a figure which shows the line length of the step portion of the intermediate part molded in an Example.

Hereinafter, one embodiment of the present invention will be described with reference to the drawings, but the embodiments are exemplified in order to embody the technical idea of the present invention, and the technical idea of the present disclosure is described. The shape is not limited to the shape shown in such an embodiment.

FIG. 1 is a perspective view schematically showing the steel part 1 targeted in the present embodiment. Further, FIG. 2 is a top view schematically showing the steel part 1. As shown in FIGS. 1 and 2, the steel part 1 targeted in the present embodiment has a shape curved in the longitudinal direction L1, and the cross section perpendicular to the longitudinal direction is U-shaped or hat-shaped. It has a stepped portion 3 having a divergent shape toward the opening 2. Further, the steel component 1 shown in FIGS. 1 and 2 has a top plate portion 4 and vertical wall portions 5A and 5B, and of the two vertical wall portions, the vertical wall portion 5A on the curved recess side is a stepped portion. It has 3 and a flange portion 6. In FIG. 1, W indicates the width direction of the steel component 1.

When the steel part 1 was molded with a mold to obtain the steel part 1, the position of the end portion of the obtained steel part 1 was lowered as shown by the downward arrow in FIG. 2, and the steel part 1 was moved to the curved concave portion side. Poor shape accuracy such as deformation, specifically, "swinging" occurs. This poor shape accuracy is more likely to occur as the strength of the steel sheet used for the steel part increases. The present inventor investigated the cause of the above-mentioned swing. In particular, the stress distribution of the part after molding was obtained by simulation analysis with the molding conditions set. As a result, as shown in FIG. 15A in the examples described later, it was found that high tensile stress was generated in the vicinity of the step portion formed on the vertical wall portion on the curved recess side in the longitudinal direction. Therefore, focusing on the tensile stress of this stepped portion, we conducted diligent research to suppress the above-mentioned swing. If the molding process is designed using the shape of the stepped portion, compressive stress will be applied to the portion where the tensile stress is generated. It was found that the residual stress after molding can be reduced as a result, and that the mold can be easily set when molding using the mold.

Specifically, as a method for manufacturing a steel part, a molding material is used, and first, when the line length of the step portion in the cross section perpendicular to the longitudinal direction is compared with the steel part, the steel part and the steel part are viewed from above. The first step of temporarily manufacturing an intermediate part, which is the same and has a shape longer than the steel part in terms of cross section, and the gold having the same shape as the steel part in the vertical wall portion on the curved recess side using the intermediate part. It has been found that the intermediate part may be molded with a mold to have a second step of transforming the shape of the vertical wall portion on the curved concave portion side of the intermediate part into the shape of the vertical wall portion on the curved concave portion side of the steel part. rice field. As described above, in the present disclosure, the vertical wall portion of the steel part has a stepped portion, and the line length of the stepped portion in the cross section perpendicular to the longitudinal direction is the same in the top view when the intermediate part and the steel part are compared. Therefore, in the cross-sectional view, the intermediate parts are longer than the steel parts. The same line length means that the line has the same length and position. In these respects, the steel parts according to this embodiment are different from the members of Patent Document 2 and Patent Document 3.

In the present embodiment, in the shape of the step portion in the cross section perpendicular to the longitudinal direction, both ends of the line length of the step portion are the same for the steel part and the intermediate part when viewed in cross section, and the line length of the step portion is steel. Intermediate parts are longer than parts. The line length of the step portion means from one end to the other end of the line length constituting the step portion. For example, in the case of the step portion as schematically shown in FIG. 6 described later, one concave angle. Refers to the portion P1 to the other concave corner portion P2. Alternatively, for example, when the concave corner portion has a curvature R as illustrated in FIG. 3, the contact point between the straight line Q1 forming the vertical wall and the cross-sectional line R1 is set as one end P11, and the straight line Q2 forming the vertical wall (flange portion). And the contact point of the cross-sectional line R2 is the other end P21, and means from one end P11 to the other end P21. In this embodiment, the length of the line length may be changed between these two ends.

Hereinafter, the method for manufacturing steel parts according to this embodiment will be described in detail.

(First step)
In the first step, a molding material is used, and the line length of the step portion in the cross section perpendicular to the longitudinal direction is the same as that of the steel part in the top view when compared with the steel part, and the cross section is the same. Manufacture intermediate parts that have a longer shape than steel parts.

FIG. 4 shows a schematic perspective view of the intermediate parts manufactured in this step, FIG. 5A shows a schematic cross-sectional view perpendicular to the longitudinal direction of the intermediate parts, and FIG. 5B shows a schematic top view of the intermediate parts in the longitudinal direction. The dotted lines shown in FIGS. 4 and 5 indicate the shape of the steel part to be formed in the second step. As shown by double-headed arrows in FIG. 5B, the line length of the stepped portion in the cross section perpendicular to the longitudinal direction is the same for the intermediate part and the steel part when viewed from above. FIG. 6 is an enlarged schematic view of a cross-sectional view of FIG. 5A. FIG. 6 is also a cross-sectional view of the line length of the stepped portion in the cross section perpendicular to the longitudinal direction. As shown in FIG. 6, the line length L22 of the stepped portion of the intermediate part is made longer than the line length L21 of the stepped portion of the steel part. Further, as shown in FIG. 6, the positions of both ends P1 and P2 of the line length constituting the step portion are the same as the positions of both ends P1 and P2 of the line length of the step portion of the steel component.

By making the line length L22 of the stepped portion of the intermediate part into the above-mentioned form, in the second step, when molding with a mold having the shape of a steel part, (the line length L22 of the stepped portion of the intermediate part-the step of the steel part) in the above cross section. The excess line length portion represented by the line length L21) of the portion is crushed and the material tries to spread in the longitudinal direction, but is blocked by the surrounding material and is compressed, and compressive stress is generated. As a result, the tensile stress generated in the intermediate part of the first step is canceled by the compressive stress generated in the molding of the second step of the next step, the residual stress is reduced, and the swing caused by the high tensile stress is generated. It is thought to be suppressed.

Further, by matching both ends P1 and P2 of the line length constituting the step portion of the intermediate part with both ends P1 and P2 of the line length of the step portion of the steel part, the intermediate part can be formed into the intermediate part in the second step. At the time of application, it is easy to fit the mold in the shape of the stepped portion of the steel part into the stepped portion of the intermediate part, and as a result, it can be reliably formed and compressive stress can be applied.

The wire length constituting the stepped portion of the intermediate component may be a length having a ratio of more than 1.00 to the wire length of the stepped portion of the steel component. On the other hand, from the viewpoint of easily mating the molds of the steel parts with the intermediate parts and surely applying the compressive stress to the intermediate parts, the above ratio is preferably 1.10 or less, and more preferably 1. It is 06 or less.

The shape of the stepped portion in the cross section of the intermediate part is not particularly limited as long as it preferably satisfies the ratio of the above line lengths and can easily fit the mold of the steel part in the second step. FIG. 7 is an enlargement of a part of FIG. When the shape of the stepped portion in the cross section of the steel part is as shown by the broken line in FIG. 7, for example, the surplus line length can be determined as the line length L22 of the stepped portion of the intermediate part as follows. That is, when the angle formed by the ceiling surface A1 of the stepped portion of the steel part and the ceiling surface B1 of the stepped portion of the intermediate part is θ1 with the end portion P1 as the axis, the angle θ1 is, for example, 1 degree or more and 10 degrees or less. It can be changed within the range. Further, when the angle formed by the vertical wall surface A2 of the stepped portion of the steel part and the vertical wall surface B2 of the stepped portion of the intermediate part is θ2 with the end portion P2 as the axis, the angle θ2 is, for example, 1 degree or more and 10 degrees or less. It can be changed within the range. The angle θ2 is set within a range in which the angle θ3 formed by the bottom surface and the vertical wall surface B2 does not exceed 90 degrees from the viewpoint of easily fitting the molds of the steel parts and forming them well.

In FIGS. 4 and 5 used for explaining the manufacturing method of the present embodiment, an example in which the cross section is the above-described embodiment is given over the entire area in the longitudinal direction, but the present invention is not limited to this, and the cross section is not limited to this, and is one place or intermittent in the longitudinal direction. The cross section can be in the above-mentioned form at a plurality of locations. According to the present disclosure, by making the cross section of the portion to which the compressive stress is desired to be applied in the longitudinal direction into the above-mentioned form, the compressive stress can be partially applied to the portion. Therefore, the shape of the cross section can be changed at any plurality of places where compressive stress is desired to be applied. In that respect, the degree of freedom in applying compressive stress is higher than that in Patent Document 2 and Patent Document 3, and compressive stress can be applied as needed. For example, as shown in FIG. 8 as a shaded portion, the cross-sectional shape can be changed in a desired plurality of regions to apply compressive stress.

The molding material used in the first step may be an intermediate product obtained by molding other than the target portion, in addition to the unprocessed steel plate.

In the first step, it suffices if the above intermediate parts can be molded, and the molding method does not matter. For example, as press molding, draw (drawing) molding or foam (bending) molding can be performed. The intermediate part has the same line length as the steel part in the top view and is longer than the steel part in the cross section when the shape of the step portion in the cross section perpendicular to the longitudinal direction is compared with the steel part. It can be molded using a mold having a wire length.

As the first step, for example, in order to obtain an A-pillar, for example, when drawing (drawing) molding is performed, it is cold working (normal temperature), and the pressing speed: about 40 to 60 SPM in the actual machine (in the case of analysis, the molding speed). Since there is no effect, the conditions can be 1000 SPM), holder pressurization: 60 to 100 ton. In draw molding, for example, as shown in Examples described later, in a molding apparatus provided with a die, a punch, and a holder (wrinkle retainer), the steel plate edge is sandwiched between the die and the holder, and the vertical wall is tensioned. Is mentioned.

The decrease in dimensional accuracy such as swinging is more likely to occur as the tensile strength of the steel plate constituting the steel part is higher. Therefore, the manufacturing method of the present embodiment can be more effective when the steel sheet having a tensile strength of 980 MPa or more is used as the original plate for molding. The tensile strength may be 1180 MPa or more. Even if the tensile strength increases, the configuration and working effect according to the present embodiment do not change, so that the upper limit of the tensile strength of the steel sheet used for manufacturing the steel parts of the present embodiment is not particularly limited. For example, from the viewpoint of the life of the mold used at the time of manufacturing, the upper limit of the tensile strength can be set to about 1800 MPa. As the steel sheet, for example, a steel sheet having a thickness of 0.8 mm or more and 2.0 mm or less can be targeted.

After the first step and before the second step, a step of performing piercing (punching hole machining), outer peripheral trimming (shearing), or the like may be provided. After performing these processes, or instead of these processes, a portion other than the step portion to be molded in the present embodiment, for example, the vertical wall portion 5B in FIG. 1 is processed into the shape of the final product. , The second processing may be performed.

(Second step)
After the first step, the intermediate parts are molded with a mold having the same stepped portion as the final product, and a steel part having the same stepped portion as the final product is manufactured.

In the second step, by molding the stepped portion of the intermediate part with a mold having the same shape as the final product, compressive stress can be generated in the stepped portion of the molded part as described above. As a result, the residual stress is reduced and the swing can be suppressed.

The steel part according to the present embodiment may be a final molded product or an intermediate molded product for further molding a portion other than the step portion. Alternatively, as described later, the final molded product or the intermediate molded product may be further subjected to processing other than molding. When the steel part is a final molded product, a mold having the same shape as the final molded product may be used for a portion other than the step portion as the mold. When the steel part is the intermediate molded product, a mold having at least a step portion having the same shape as the final molded product may be used.

In the second step, it is sufficient if the above steel parts can be formed, and the forming method does not matter. For example, as press molding, draw (drawing) molding and foam (bending) molding can be performed.

As a second step, for example, in obtaining an A-pillar, for example, in the case of foam (bending) molding, cold working (normal temperature), press speed: about 40 to 60 SPM in an actual machine (in the case of analysis, the molding speed). Since there is no effect, the condition can be 1000 SPM).

In the manufacturing method in the present embodiment, after the second step, the intermediate molded product may be further provided with a step of molding a portion other than the step portion. Further, if necessary, the final molded product or the intermediate molded product may be provided with a step other than molding, such as piercing (punching hole processing) and outer peripheral trimming (shearing).

In the above-exemplified drawing, the component having one step portion on the vertical wall portion 5A has been described, but the step portion may be one step or a multi-step portion having two or more steps. Further, it is a component having a stepped portion in both the vertical wall portion 5A and the vertical wall portion 5B, and the stepped portion provided in the vertical wall portion 5A may be formed as in the present embodiment.

(Applicable parts)
As the steel parts according to the present embodiment, for example, a shaped part having a top plate portion and a vertical wall, curved in the longitudinal direction, and having a stepped portion at least on the vertical wall portion on the curved concave portion side, specifically, Press-molded products used for vehicle body structural parts, such as A-pillars and front pillars, can be mentioned.

Hereinafter, embodiments of the present invention will be described in more detail with reference to examples. The embodiments of the present invention are not limited by the following examples, and may be modified as appropriate to the extent that they can meet the above-mentioned and later gist, and both of them are disclosed in the present disclosure. Included in the technical scope.

[Example 1]
In Example 1, a simulation analysis by CAE was performed for the production of the A pillar schematically shown in FIG. 9 as a steel part. FIG. 10 is a cross-sectional view taken along the line AA in FIG. FIG. 10 is also a cross-sectional view of the line length of the stepped portion in the cross section perpendicular to the longitudinal direction. As shown in FIGS. 9 and 10, the target steel part is curved in the width direction along the longitudinal direction, has a top plate portion 4 and a flange portion 6, and has a stepped portion on the vertical wall portion 5A on the curved concave portion side. Has 3.

In the simulation analysis in this example, the process shown in FIG. 11 was followed. In this embodiment, as the first step, draw molding of step 11 (S11) is performed, and as the second step, foam molding with PAD of step 21 (S21) is performed. In FIG. 11, “trim1” in step 12 (S12) means that the outer peripheral trimming process (shearing process) is performed. Further, "SB1" in step 13 (S13) and "SB2" in step 23 (S23) mean the calculation process of the springback after molding in this simulation analysis.

As the first embodiment, in the first step, as shown in the schematic cross-sectional view shown in FIG. 12, an unprocessed steel sheet was drawn-formed as A → B → C to obtain an intermediate part. Specifically, A: before molding, the steel plate 13 is set between the die 11 and the holder 12, and B: during molding and C: as shown after molding, the end portion of the steel plate 13 is sandwiched between the die 11 and the holder 12. In this state, molding was performed with a punch 14 from the lower part to obtain an intermediate part 15. The shape of the stepped portion in the die 11 and the shape of the stepped portion of the punch 14, that is, the shape of the elliptical dotted line portion in FIG. The shape is longer than the line length of, that is, the shape is provided with an extra line length. In the first embodiment, the ratio of the stepped portion of the steel component to the line length is set to 1.05. Further, as a comparative example, a die 11 having a stepped portion and a punch 14 having a stepped portion formed with the same mold as the final product was also prepared.

After the first step, in the second step, as shown in the schematic cross-sectional view shown in FIG. 13, the intermediate parts obtained by the molding of FIG. 12 are used, and the steel parts are formed by foam forming as A → B → C. Obtained. In FIG. 13, one of the dies that press the intermediate parts from above during molding is the die 16 of FIG. 13A, and the other die is located at a position away from the stepped portion of the intermediate parts and is not shown. In detail, A: before molding, the pad 17 is pressed from above the intermediate part 15, B: during molding and C: as shown after molding, the die 16 above the intermediate part 15 and the punch below the intermediate part. Forming at 18, a steel part 19 was obtained.

In the simulation analysis, a steel sheet having a tensile strength of 1552 MPa, which shows the relationship between the true strain and the true stress shown in FIG. 14, is used as the material to be used, and the steps shown in FIG. 11 described above are used under the following analysis conditions and molding conditions. A simulation analysis was performed in which machining was performed in order. The analysis conditions in the simulation analysis and the molding conditions other than the above are as follows.

(1) Analysis condition element type: complete integral (elfform = 16) torsional rigidity addition (IHQ = 8)
Number of integration points: 5 points Friction coefficient: 0.12
Element size: 2mm x 2mm
Plate thickness: 1.4 mm
Material used: CR1470MS (yield point YP: 1311MPa, tensile strength TS: 1552MPa, elongation EL: 8.4%)
Software used: JSTAMP (registered trademark) / NV 2.15 manufactured by JSOL Co., Ltd.
Solver: LS-DYNA (registered trademark) R9.2.0 double precision mpp manufactured by JSOL Co., Ltd.

(2) Molding conditions 1st step (DRAW)
Maximum speed: 1000mm / sec
Molding pressure: 1000 ton
BHF: 70 ton (with a fixed push)
2nd process (FORM with PAD)
Maximum speed: 1000mm / sec
Molding pressure: 600 ton
BHF: 30 ton (with a fixed push)
Steel plate temperature: normal temperature

As a result of performing simulation analysis under the above conditions, the result of measuring the stress of the dotted elliptical portion in FIG. 9 is shown in FIG. FIG. 15A is the result of Comparative Example, and FIG. 15B is the result of Example 1 of the present invention. From the results of FIG. 15, according to the embodiment of the present invention, the color tone indicating the tensile stress of the stepped portion is lightened, and the tensile stress generated in the molding in the first step is generated by the molding in the second step. It can be seen that the tensile stress was reduced by being canceled by the compressive stress. Further, as the degree of swing of the steel parts of the first and comparative examples of the present invention, the position of the mold used in the second step, that is, from the end of the mold of the steel parts, in the portion indicated by the arrow in FIG. The displacement of was calculated. From the position of the arrow in FIG. 9, the upward direction is indicated by a plus and the downward direction is indicated by a minus. The results are shown in Table 1.

It can be seen that by manufacturing the steel parts through the process according to the present embodiment, even if the strength is high, the swinging is reduced and the steel parts with improved shape accuracy can be obtained.

[Example 2]
The line length of the stepped part of the intermediate part was changed, and the degree of swing was confirmed. Simulation analysis was performed in the same manner as in Example 1 of the present invention, except that the line length of the stepped portion of the intermediate component was set as shown in FIG. 16 and Table 2 below. In FIG. 16, L31 indicates the line length of Example 1 of the present invention, L32 indicates the line length of Example 2 of the present invention, and L33 indicates the line length of Example 3 of the present invention. Further, in FIG. 16, an enlarged view of the dotted elliptical portion is shown in the lower part of FIG. As shown in the enlarged view, when the angle of the line length L31 of the first invention example is θ1 exemplified in FIG. 7, in the second invention example 2, a straight line is drawn so as to be an angle (θ1-3 degrees). After drawing, the line length L32 was formed, and in Example 3 of the present invention, the line length L33 was formed after drawing a straight line so as to have an angle (θ1 + 3 degrees). The results of the above simulation analysis are shown in Table 2 below.

From Table 2, it was found that in any of the present invention examples of the present invention example 2 and the present invention example 3, the swinging was sufficiently suppressed as compared with the comparative example, as in the case of the present invention example 1.

This application is accompanied by a priority claim based on Japanese Patent Application No. 2020-199719 as a basic application. Japanese Patent Application No. 2020-199719 is incorporated herein by reference.

1 Steel parts 2 Opening 3 Steps 4 Top plate 5A Vertical wall on the curved convex side 5B Vertical wall on the curved concave side 6 Flange L21 Line length of the step on the steel parts L22, L31, L32, L33 Intermediate Line length of stepped part P1, P2, P11, P21 End of line length forming stepped part Q1, Q2 Straight line R1, R2 cross-section line forming vertical wall 11 Draw forming die 12 Draw forming holder 13 Steel plate 14 Draw forming punch 15 Intermediate parts 16 Foam forming die 17 Foam forming pad 18 Foam forming punch

Claims

It has a shape curved in the longitudinal direction, and the shape of the cross section perpendicular to the longitudinal direction is U-shaped or hat-shaped, and a stepped portion having a divergent shape toward the opening is formed on the vertical wall portion on the curved concave portion side. It is a method of manufacturing steel parts that has
Using a forming material, the line length of the stepped portion in the cross section perpendicular to the longitudinal direction is the same as the steel part in the top view and longer than the steel part in the cross section when compared with the steel part. The first step of manufacturing intermediate parts with a shape,
Using the intermediate part, the vertical wall portion on the curved concave portion side is molded with a mold having the same shape as the steel part, and the shape of the vertical wall portion on the curved concave portion side of the intermediate part is changed to the vertical wall portion on the curved concave portion side of the steel part. A method for manufacturing a steel part, which comprises a second step of transforming the shape of a wall portion.
The line length of the stepped portion in the cross section perpendicular to the longitudinal direction of the intermediate part is more than 1.00 times and 1.10 times or less of the line length of the stepped portion in the cross section perpendicular to the longitudinal direction of the steel part. The method for manufacturing a steel part according to claim 1, which is the length of the above.
The method for manufacturing a steel part according to claim 1 or 2, wherein the tensile strength of the steel plate constituting the steel part is 980 MPa or more.