Manufacturing method for press-formed products

Abstract

When press-forming tailored blanks, notches are made in the outer edge of the low-strength steel plate to distribute stress not only along the weld line but also in the notched area. [Solution] The method for manufacturing a press-formed product includes, in a tailored blank before press working, forming a notch near the weld line on the outer edge of the first steel plate, which has lower strength than the second steel plate, and recessing inward from the tip of the weld line, and providing multiple curved portions in the notch, where multiple locations on the outer circumference of the first steel plate are curved with a predetermined curvature.

Description

Technical Field

[0001] The present disclosure relates to a method for manufacturing a press-formed product by press-forming a tailored blank.

Background Art

[0002] Patent Document 1 describes a method of press-forming an assembled blank in which steel plates having different thicknesses are butt-welded, wherein a portion close to the weld line end of the thin steel plate having a lower strength is recessed inward from the weld line end.

[0003] According to this manufacturing method, by providing a recess in the low-strength steel plate, the stress applied to the weld line end of the assembled blank during press-forming is dispersed to the recess side, preventing stress concentration at the weld line end and suppressing the occurrence of cracks in the weld line.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, in the manufacturing method described in Patent Document 1, only an arc-shaped notch is provided as a recess at the outer peripheral edge of the low-strength steel plate. Therefore, during press-forming, stress may concentrate on the arc-shaped notch, causing the notch to break. That is, in the manufacturing method described in Patent Document 1, although the occurrence of cracks in the weld line can be suppressed by providing an arc-shaped notch as a recess, the breakage of the notch may not be suppressed.

[0006] One aspect of this disclosure is to enable the distribution of stress applied not only to the weld line but also to the notched portion by providing a notch at the outer edge of a low-strength steel plate when press-forming a tailored blank. [Means for solving the problem]

[0007] A method for manufacturing a press-formed product according to one aspect of the present disclosure is a method for manufacturing a press-formed product by press-forming a tailored blank obtained by welding steel plates having different strengths and thicknesses.

[0008] This manufacturing method includes, in the tailored blank before press working, forming a notch near the weld line at the outer edge of the first steel plate, which has lower strength than the second steel plate, among two steel plates adjacent to each other across the weld line, and recessing inward from the tip of the weld line, and providing multiple curved portions in the notch, where multiple locations on the outer circumference of the first steel plate are curved with a predetermined curvature.

[0009] In tailored blanks, the first steel plate, which has lower strength, is the one of the two steel plates welded together that has lower strength. For example, if the strengths are the same, it will be the steel plate with the thinner thickness. If the strengths and thicknesses are different, the first steel plate is the one that has lower overall strength, including the thickness.

[0010] As described above, according to the manufacturing method of this disclosure, a notch is provided at the outer edge of the first steel plate, which has low strength in the tailored blank. Therefore, similar to the recess described in Patent Document 1, it is possible to suppress the concentration of stress at the end of the weld line during press working. Furthermore, since the notch has multiple curved sections, the stress applied to the notch can be distributed to the multiple curved sections.

[0011] In other words, when stress is applied in a direction that tears the weld line during press working of a tailored blank, the starting point of deformation becomes the notch, and furthermore, at the notch, there are multiple starting points of deformation corresponding to multiple curved sections. When there are multiple starting points of deformation, the amount of deformation per starting point becomes smaller, so the stress applied to the end of the weld line during press working is distributed to multiple curved sections, thereby suppressing crack formation and fracture in the weld line and notch.

[0012] In this case, while a stress distribution effect was obtained when the number of curved sections in the notch was four or less, no effective effect was obtained even when the number of curved sections was five or more. Therefore, it is best to keep the number of curved sections in the notch between two and four.

[0013] Furthermore, in the notched portion, the multiple curved portions may be shaped such that the outer circumference of the first steel plate is a polygonal shape having multiple corners, and each corner is curved with a predetermined curvature. In this case, it is desirable that the angle of each corner corresponding to the multiple curved sections is greater at the corners further from the weld line (θ) than at the corner closest to the weld line (γ) (θ>γ). This is because if θ<γ, the starting point of material flow in the low-strength first steel plate generated during press working will be at the curved section corresponding to the corner further from the weld line, and fracture is more likely to occur at the corner of that curved section.

[0014] In other words, by setting the angle of the corners as described above, the stress applied to the curved section corresponding to the corners far from the weld line is distributed to the curved section corresponding to the corner closest to the weld line, thereby better suppressing the formation of cracks in the curved section of the notch during press working.

[0015] Furthermore, if stress is distributed to the curved portion closest to the weld line in the notch, cracks may form in that curved portion in some cases. Therefore, in the notch, the curvature of the multiple curved portions may be set such that the curvature of the curved portion further from the weld line is smaller than the curvature of the curved portion closest to the weld line. In this way, stress can be distributed more effectively across the multiple curved portions in the notch, and crack formation in any of the curved portions of the notch during press working can be suppressed. [Brief explanation of the drawing]

[0016] [Figure 1] This is a schematic perspective view of a press-formed product according to the embodiment. [Figure 2] These are plan views showing the state of a tailored blank before and after press working. Figure 2A shows the tailored blank before press working, and Figure 2B shows the press-formed product after press working. [Figure 3] This is an explanatory diagram of a die used in press forming of tailored blanks. [Figure 4] This is an explanatory diagram illustrating the shape of the notch located near the weld line of a tailored blank. [Figure 5] This is an explanatory diagram showing the shape of the notch in the first modified example. [Figure 6] This is an explanatory diagram showing the shape of the notch in the second modified example. [Modes for carrying out the invention]

[0017] Hereinafter, exemplary embodiments of the present disclosure will be described with reference to the drawings. [Embodiment] [Composition of press-formed product] The press-formed product 1 shown in Figure 1 is manufactured as shown in Figure 2B by press-forming the tailored blank 10 shown in Figure 2A. Hereinafter, the thickness direction of the press-formed product 1 and the tailored blank 10 will be referred to as the vertical direction. The direction in which the second steel plate 12, described later, is positioned relative to the first steel plate 11, described later, will be referred to as the left-right direction. The longitudinal direction of the second steel plate 12 will be referred to as the front-back direction.

[0018] Note that these directions are defined for convenience of explanation and do not limit the usage mode of the press-formed product 1. Also, in the perspective view shown in FIG. 1, it represents the state of viewing the right half of the press-formed product 1 shown in FIG. 2B.

[0019] The press-formed product 1 is, as an example, used as a rear floor panel mounted on a vehicle. The press-formed product 1 includes a top plate portion 2, a side wall portion 3, and a flange portion 4. The top plate portion 2 is a plate-like portion that spreads in the same plane, and has a substantially rectangular shape in a top view seen from a direction orthogonal to the plate surface (see FIG. 2B). Note that arbitrary concavities and convexities may be provided on the top plate portion 2.

[0020] The side wall portion 3 is a plate-like portion that stands upright from the edge portion of the top plate portion 2 so as to surround the top plate portion 2. Specifically, the side wall portion 3 is a wall that extends downward from the front edge of the top plate portion 2, the left edge of the top plate portion 2, and the right edge of the top plate portion 2. In other words, the side wall portion 3 is a wall that surrounds the top plate portion 2 from three directions. Therefore, among the press-formed product 1, the portions of the top plate portion 2 and the side wall portion 3 have a bag-shaped outer shape.

[0021] Note that the bag shape is a shape that can accommodate an object in a space and has an opening for taking in and out the object. For this reason, in the press-formed product 1, it is possible to accommodate an object in the space surrounded by the top plate portion 2 and the side wall portion 3. Also, it is possible to take in and out an object from the opening formed on the opposite side of the top plate portion 2 across the side wall portion 3.

[0022] In the present embodiment, the side wall portion 3 extends so as to be slightly inclined toward the top plate portion 2 from the lower side to the upper side. That is, the cross section orthogonal to the front-rear direction in the top plate portion 2 and the side wall portion 3 is trapezoidal. Also, the cross section orthogonal to the vertical direction in the side wall portion 3 is substantially U-shaped.

[0023] The flange portion 4 is a plate-like portion that extends from the side wall portion 3 in a direction intersecting the side wall portion 3, and is positioned to surround the top plate portion 2 when viewed from a direction perpendicular to the plate surface. More specifically, the flange portion 4 is a plate that extends from the edge of the side wall portion 3 opposite to the top plate portion 2, away from the top plate portion 2, and approximately parallel to the top plate portion 2. In other words, the flange portion 4 is a plate that surrounds the top plate portion 2 from three directions when viewed from above.

[0024] As shown in Figure 2B, the press-formed product 1 comprises a first steel plate 11 from which a top plate portion 2 and side wall portions 3 are formed by press processing, and a second steel plate 12 and a third steel plate 13 arranged to the left and right of the first steel plate 11.

[0025] [Tailored Blank Construction] As shown in Figure 2A, in the tailored blank 10 before press working, the first steel plate 11 is a substantially rectangular plate-shaped member, for example, with a plate thickness of 0.6 mm and a tensile strength of 270 MPa.

[0026] Furthermore, the second steel plate 12 is positioned on both the left and right sides of the first steel plate 11, is long in the front-to-back direction, and is a rectangular plate-shaped member with the same length as the first steel plate 11. Its thickness is greater than that of the first steel plate 11, and its tensile strength is higher than that of the first steel plate 11. For example, the thickness of the second steel plate 12 is 1.0 mm, and its tensile strength is 780 MPa. The difference in tensile strength between the first steel plate 11 and the second steel plate 12 is due, for example, to differences in material.

[0027] Therefore, the first steel plate 11 has lower strength than the second steel plate 12. Note that the difference in strength between the first steel plate 11 and the second steel plate 12 can be determined, for example, by comparing the values ​​obtained by multiplying the tensile strength of each steel plate 11 and 12 by their thickness, even if the steel plates have the same tensile strength or thickness.

[0028] The second steel plate 12 is joined to the left and right sides of the first steel plate 11 by welding, and in the tailored blank 10 before press working, the weld line 14 between it and the first steel plate 11 is a straight line extending in the front-to-back direction.

[0029] Next, the third steel plate 13 is positioned on the opposite side of the second steel plates 12 from the first steel plates 11, in other words, on the outside. It is a plate-shaped member with a shorter length in the front-to-back direction than the second steel plates 12, a thinner plate thickness than the second steel plates 12, and a lower tensile strength. Therefore, the third steel plate 13 has lower strength than the second steel plates 12.

[0030] The third steel plate 13 is joined to the second steel plate 12 by welding on both the left and right sides, and in the tailored blank 10 before press working, the weld line 15 between it and the second steel plate 12 is a straight line extending in the front-to-back direction.

[0031] [Pressing] The press-formed product 1 of this embodiment is created by press-forming (more specifically, deep drawing) the processing area 8 of the first steel plate 11, shown by the dotted line in Figure 2A, using the die shown in Figure 3, in a tailored blank 10 configured as described above.

[0032] In other words, the press-formed product 1 is created by forming a top plate portion 2 and a side wall portion 3 in the processing area 8 of the first steel plate 11 in the tailored blank 10 by press working, and forming a flange portion 4 around the side wall portion 3.

[0033] In this press working process, a press forming apparatus equipped with a die 31, a punch 32, and a blank holder 33 is used, as shown in Figure 3. Figure 3 shows the molds arranged for the III-III cross section passing through the weld line 14 on the right side of the tailored blank 10 shown in Figure 2A, and each of these molds is configured symmetrically with respect to the center line of the tailored blank 10.

[0034] The die 31 corresponds to the first mold of this disclosure and is positioned above the plate surface of the tailored blank 10. The blank holder 33 is for fixing the tailored blank 10 by clamping it from above and below between itself and the die 31, and is positioned below the plate surface of the tailored blank 10.

[0035] The punch 32 corresponds to the second die of this disclosure and is positioned below the clamping surface of the tailored blank 10 by the die 31 and blank holder 33 before press working. During press working, the punch 32 is moved upward relative to the die 31 and blank holder 33 that clamp the tailored blank 10 via a drive mechanism (not shown).

[0036] Thus, the tailored blank 10 is press-formed (more specifically, drawn) using the die shown in Figure 3. During this press-forming process, the processing area 8 shown in Figure 2A is deformed in the tailored blank 10, causing the weld line 14 to move toward the first steel plate 11 (in the X2 direction shown in Figure 2B) behind where the top plate portion 2 and side wall portion 3 are formed.

[0037] In contrast, at the front of the tailored blank 10, the weld line 14 moves to the opposite side from the first steel plate 11 (in the X1 direction shown in Figure 2B). When the weld line 14 moves in this way, the stress applied to the tip of the weld line 14 away from the processing area 8 can cause cracks to form in the weld line 14, and it may break.

[0038] [Structure and effect of the notch] Therefore, in this embodiment, as shown in Figure 2, a notch 20 is formed on the front outer peripheral edge of the first steel plate 12, which has lower strength than the second steel plate 12, at a position near the weld line 14 and away from the weld line 14, and recessed inward from the tip of the weld line 14.

[0039] In other words, by providing a notch 20 in the first steel plate 12, which is more easily deformed than the second steel plate 12, the stress applied to the tip of the weld line 14 during the aforementioned press working is distributed to the notch 20 side.

[0040] As a result, according to this embodiment, it is possible to suppress the fracture of the tailored blank 10 due to cracks forming from the tip of the weld line 14 during the press working process described above. Furthermore, the notch 20 is not made into an arc shape as described in Patent Document 1, but is instead composed of two curved portions 22 and 24 as shown in Figure 4.

[0041] These two curved sections 22 and 24 are formed by creating a polygonal shape with two corners A and B on the outer circumference of the first steel plate 11 (in other words, the inner circumference of the notch 20), with each corner A and B curved with a predetermined curvature. The two corners A and B are formed by combining three straight lines L1, L2, and L3.

[0042] Furthermore, the angle θ of corner A corresponding to the curved portion 22 is set to be larger than the angle γ of corner B corresponding to the curved portion 24 that is closer to the weld line 14 (in other words, θ > γ). Also, the curvature of the curved portion 22 is set to be smaller than the curvature of the curved portion 24 that is closer to the weld line 14.

[0043] Thus, when the notch 20 is composed of two curved sections 22 and 24, the starting points of deformation in the notch 20 due to the stress applied to the tip of the weld line 14 are the two curved sections 22 and 24, or in other words, the two corners A and B, and the amount of deformation at each starting point that occurs during press working becomes smaller.

[0044] Therefore, according to this embodiment, during press working, the stress applied to the tip of the weld line 14 is not only distributed to the notch 20 side, but the stress applied to the notch 20 due to this distribution can be further distributed by the two curved portions 22 and 24.

[0045] Therefore, according to this embodiment, it is possible not only to suppress the formation of cracks in the tip portion of the weld line 14 during press working, but also to suppress the formation of cracks in any of the curved portions 22 and 24 in the notch portion 20.

[0046] Therefore, it is possible to suppress the fracture of the tailored blank 10 near the weld line 14 during the press working described above. Furthermore, in this embodiment, since the angle θ of corner A and the angle γ of corner B are set such that θ > γ, cracks that occur in the notch 20 during press working can be suppressed more effectively.

[0047] In other words, if the angle θ of corner A and the angle γ of corner B are set such that θ < γ, the starting point of material flow in the notch 20 during press working becomes corner A, making fracture more likely to occur at corner A. Therefore, in this embodiment, by setting θ > γ, the stress applied to the curved portion 22 away from the weld line 14 in the notch 20 during press working is distributed to the curved portion 24 closer to the weld line 14, thereby better suppressing crack formation in the notch 20.

[0048] Furthermore, in this embodiment, since the curvature of the curved portion 22 is set to be smaller than the curvature of the curved portion 24 that is closer to the weld line 14, the stress applied to the notch portion 20 during press working can be distributed more effectively by the curved portions 22 and 24.

[0049] Therefore, according to this embodiment, it is possible to prevent cracks from forming at either the tip of the weld line 14 or the curved portions 22 and 24 of the notch 20 during the press working process described above, thereby preventing the tailored blank 10 from breaking.

[0050] [First variation] In the above embodiment, the side of the notch 20 having curved portions 22 and 24 that is opposite to the weld line 14 is configured such that the outer edge of the tailored blank 10 extends straight in the left-right direction.

[0051] In contrast, in this first modified example, as shown in Figure 5, the outer edge of the notch 20 opposite to the weld line 14 is bent outward (in other words downward) at the corner C, so that it becomes a straight line extending straight from the tip of the weld line 14.

[0052] In other words, in this first modified example, the notch 20 includes, in addition to the two curved portions 22 and 24 that distribute stress as described above, a curved portion in which the corner C is curved with a predetermined curvature, and the notch 20 as a whole is a recess in which the outer circumference of the tailored blank 10 is recessed inward.

[0053] Even in this way, the stress applied to the tip of the weld line 14 during the press working described above can be distributed to the multiple curved portions of the notch 20, thereby suppressing the formation of cracks in the tip of the weld line 14 and the notch 20.

[0054] In the above embodiment and the first modified example, there are two or three curved sections within the notch 20, but the number of these curved sections may be further increased. However, simulation results showed that the number of curved sections capable of distributing stress in the notch 20 should be four or less, and increasing the number beyond that does not yield significant benefits.

[0055] [Second variation] Next, in the above embodiment, as shown in Figure 4, in the notch 20, of the three straight lines L1 to L3 that form corners A and B corresponding to the two curved portions 22 and 24, the two outer straight lines L1 and L3 are perpendicular to each other.

[0056] In contrast, in this second modified example, as shown in Figure 6, in the notch 20, of the three straight lines L1 to L3 that form corners A and B, the two outer straight lines L1 and L3 intersect at an angle δ greater than 90 degrees (for example, 105 degrees).

[0057] Even in this way, the stress applied to the tip of the weld line 14 during the press working described above can be distributed by the curved portions 22 and 24 of the notch 20, thereby suppressing the formation of cracks in the tip of the weld line 14 and the notch 20.

[0058] [Other embodiments] Although embodiments of the present disclosure have been described above, the present disclosure is not limited to the embodiments described above and can be implemented in various modified forms.

[0059] For example, in the above embodiment, the case of manufacturing a rear floor panel of a vehicle as press-formed product 1 was described, but the manufacturing method of this disclosure can also be used to manufacture press-formed products other than the rear floor panel, such as the front pillar and center pillar of a vehicle. In other words, the manufacturing method of this disclosure can be applied in the same manner as in the above embodiment to any press-formed product manufactured by press-working a tailored blank, and the same effects can be obtained.

[0060] Furthermore, in the above embodiment, the tailored blank 10 was described as being manufactured by drawing a first steel plate 11 which has lower strength than the second steel plate 12 that is welded. However, the manufacturing method of the present disclosure is not limited to drawing, and can be applied in the same manner as in the above embodiment even when other press working, such as bending, is performed.

[0061] Furthermore, the manufacturing method of this disclosure is not limited to cases where the first steel sheet 11, which has lower strength than the second steel sheet 12, is press-formed. In other words, the manufacturing method of this disclosure can be applied in the same manner as in the above embodiments even when only the second steel sheet 12 is press-formed and not the first steel sheet 11, or when a region including both the first steel sheet 11 and the second steel sheet 12 is press-formed.

[0062] Furthermore, the number of curved sections within the notch 20 and the angles of the corners corresponding to the curved sections are not limited to those described in the above embodiment or the first and second modified examples, and can be set appropriately so as not to cause cracks in the tip of the weld line 14 or the notch 20 during press working.

[0063] Furthermore, in the above embodiment, the position of the notch 20 was described as being outside the processing area 8, which is drawn using the die 31 as the first mold and the punch 32 as the second mold in the first steel plate 11.

[0064] However, the position of the notch 20 only needs to be such that it can distribute the stress applied to the tip of the weld line 14 during press working, and depending on the type of press working, the notch 20 may be located within the processing area 8. However, it is preferable to place the notch 20 outside the processing area 8, as this makes it easier to distribute the stress.

[0065] Furthermore, in the above embodiment, the notch 20 was described as being provided in the first steel plate 11, which has lower strength than the second steel plate 12. However, it may also be provided in the second steel plate 12, which has higher strength, in addition to the first steel plate 11, which has lower strength.

[0066] Furthermore, the functions of one component in the above embodiment may be distributed among multiple components, or the functions of multiple components may be integrated into one component. Also, some parts of the configuration of the above embodiment may be omitted. In addition, at least some parts of the configuration of the above embodiment may be added to, replaced, etc., in the configuration of other above embodiments.

[0067] [Technical Concept Disclosed in This Specified Specification] [Item 1] A manufacturing method for producing a press-formed product by press-forming a tailored blank obtained by welding steel plates having different strengths and thicknesses, In the tailored blank before the press working, Of the two steel plates adjacent to each other across the weld line, the first steel plate, which has lower strength than the second steel plate, has a notch formed on its outer edge near the weld line, which is recessed inward from the tip of the weld line. The notch portion is provided with multiple curved portions formed by curving multiple locations on the outer circumference of the first steel plate with a predetermined curvature. A method for manufacturing press-formed products, including the method described above.

[0068] [Item 2] The method for manufacturing a press-formed product according to item 1, wherein the number of curved portions in the notch is four or less.

[0069] [Item 3] In the aforementioned notch, the plurality of curved portions are shaped such that the outer circumference of the first steel plate is a polygonal shape having a plurality of corners, and each corner is curved with a predetermined curvature. A method for manufacturing a press-formed product according to item 1 or item 2, wherein the angles of each corner corresponding to the plurality of curved portions are set such that the angle of the corner further from the weld line is larger than the angle of the corner closest to the weld line.

[0070] [Item 4] A method for manufacturing a press-formed product according to any one of items 1 to 3, wherein the curvature of the plurality of curved portions is set such that the curvature of the curved portion further away from the weld line is smaller than the curvature of the curved portion closest to the weld line. [Explanation of Symbols]

[0071] 1... Press-formed product, 10... Tailored blank, 11... First steel plate, 12... Second steel plate, 14... Welding line, 20... Notch, 22... Curved section, 24... Curved section, 31... Die, 32... Punch.

Claims

1. A manufacturing method for producing a press-formed product by press-forming a tailored blank obtained by welding steel plates having different strengths and thicknesses, In the tailored blank before the press working, Of the two steel plates adjacent to each other across the weld line, the first steel plate, which has lower strength than the second steel plate, has a notch formed on its outer edge near the weld line, which is recessed inward from the tip of the weld line. The notch portion is provided with multiple curved portions formed by curving multiple locations on the outer circumference of the first steel plate with a predetermined curvature. A method for manufacturing press-formed products, including the method described above.

2. The method for manufacturing a press-formed product according to claim 1, wherein the number of curved portions in the notch is four or less.

3. In the aforementioned notch, the plurality of curved portions are shaped such that the outer circumference of the first steel plate is a polygonal shape having a plurality of corners, and each corner is curved with a predetermined curvature. A method for manufacturing a press-formed product according to claim 1 or claim 2, wherein the angles of each corner corresponding to the plurality of curved portions are set such that the angle of the corner further from the weld line is larger than the angle of the corner closest to the weld line.

4. The method for manufacturing a press-formed product according to claim 1 or 2, wherein the curvature of the plurality of curved portions is set such that the curvature of the curved portion further from the weld line is smaller than the curvature of the curved portion closest to the weld line.

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