Method for manufacturing a press-formed component, press-formed component, method for manufacturing a blank for press forming, and blank for press forming

Abstract

The present invention provides a blank (integrated blank) for suppressing cracking and the like when a plurality of partial blanks are partially overlapped to form an integrated blank and the integrated blank is subjected to press forming. A press-formed blank formed by joining a plurality of partial blanks formed of a steel sheet has an overlapping portion in which at least two partial blanks are partially overlapped, and in a method of manufacturing the press-formed blank, the material flow amount (movement vector of a point on each partial blank) of the partial blanks of the overlapping portion caused by press forming is calculated in advance, only the partial blanks whose difference in material flow amount (movement vector) is smaller than a predetermined limit value are joined, thereby manufacturing the press-formed blank, and after the blank is subjected to hot press forming, the other partial blanks of the overlapping portion are joined to obtain a desired press-formed component.

Description

[0001] This application is a divisional application of application No. 202480049541.5, filed on April 24, 2024, entitled "Method for manufacturing stamped parts, stamped parts, method for manufacturing stamped blanks and stamped blanks". Technical Field

[0002] This invention relates to a method for manufacturing stamped parts using welded blanks, stamped parts, a method for manufacturing stamped blanks, and stamped blanks. Background Technology

[0003] With the automotive industry as a central focus, there is a growing demand for reducing life-cycle GHG (total greenhouse gas emissions) and increasing the efficiency of manufacturing production lines based on reducing the number of components and eliminating processes, leading to the integration of components and modules. Therefore, with the introduction of optimized design, there is a growing demand for stamping-based component manufacturing using tailored welded blanks (TWBs), which combine different types of steel sheets into a single unit. Various stamping technologies for TWBs have been proposed previously (e.g., Patent Document 1).

[0004] Integrated blanks (TWB) are typically manufactured by butt-welding individual blanks (partial blanks) formed from steel plates of different thicknesses and grades. With the increasing size of integrated blanks, a method has been proposed to manufacture integrated blanks by partially overlapping two partial blanks and spot-welding the overlapping portion (Patent Document 2). In the trend towards larger components and modules, and the accompanying trend towards more efficient and lower-cost component manufacturing, component manufacturing based on one-time stamping forming of integrated blanks is attracting increasing attention.

[0005] For example, Patent Document 3 describes the following: In the manufacturing of automotive structural components, when the inner front pillar, inner middle pillar, and inner side rail are manufactured separately by hot stamping, reinforcing blanks are locally installed on the inner front pillar and inner middle pillar during hot stamping. However, the automotive structural components disclosed in Patent Document 3 are, in a broad sense, integrally formed from each part, not integrally formed from the entire automotive structural component (the upper door frame component in Patent Document 3).

[0006] Existing technical documents Patent documents Patent Document 1: International Publication No. 2020 / 059804 Patent Document 2: Japanese Patent Publication No. 2021-528248 Patent Document 3: International Publication No. 2017 / 098427 Summary of the Invention

[0007] The problem that the invention aims to solve When stamping a monolithic blank obtained by overlapping and joining two blanks (e.g., spot welding, overlap welding), cracks or other fractures are sometimes observed at the overlapping portion of the blanks. If cracks or other fractures occur in the part, the part's quality deteriorates significantly and it is discarded. In other words, fractures in stamped parts not only lead to quality problems but also to productivity issues.

[0008] Such problems were not identified in hot stamping (hot pressing), which allows for greater processing strain compared to cold working. In particular, with the increasing demand for complex shapes of parts and the need for unibody molding of large parts (such as automotive structural components like door frames), the problem becomes significant in unibody molding based on hot stamping, which requires integral blanks based on welded blanks, sometimes resulting in cracks or other fractures observed at the overlapping portions of the blanks.

[0009] The objective of this invention is to suppress cracks and other fractures when stamping an integral blank formed by partially overlapping multiple partial blanks.

[0010] Methods for solving problems In order to achieve the above-mentioned problems, the inventors conducted in-depth research and obtained the following insights.

[0011] (a) First, when joining multiple partial blanks formed from steel plates into one piece, a stamping blank having an overlapping portion where at least two partial blanks partially overlap was manufactured, and the fracture occurrence state was investigated and verified. As an example, a stamping blank in which the overlapping portion was joined by spot welding was manufactured and investigated and verified.

[0012] Observation of stamped parts reveals that partial breakage occurred at the overlapping portion, where some blanks overlapped. Taking a car door frame as an example, analysis through experiments and simulations shows that at the overlapping portion of the lower A-pillar component (the lower part of the A-pillar, L-shaped) and the lower B-pillar component (the lower part of the B-pillar, T-shaped), breakage occurred in and around the area where the tensile flange deformed. Conversely, no breakage occurred in the portion where tensile flange deformation did not occur.

[0013] (b) Further analysis revealed that the fracture occurred at (i) the parts where the material flow behavior of the blanks was significantly different during the deformation of the overlapping part, and (ii) the parts where the material flow was restricted by the joint (spot welding in the case of the investigated example).

[0014] That is, it can be considered that when the difference in material flow between some blanks increases due to stamping, shear deformation occurs at the joint (spot weld), resulting in a large deformation concentration near the spot weld (reason (i)). Therefore, it can be considered that since the material flow is restricted by the joint (spot weld), deformations that accompany the material flow, such as tensile flange deformation, do not occur, leading to deformation concentration and fracture (reason (ii)).

[0015] Even in hot stamping (hot pressing), which allows for greater processing strain compared to cold working, this becomes apparent during processing accompanied by significant deformation. With the increasing demand for complex part shapes, there is a need for integrated blanks and hot stamping methods that facilitate the hot stamping of integral blanks based on welded blanks.

[0016] (c) In order to suppress fracture, the inventors analyzed the material flow behavior of a portion of the blank in hot stamping by simulation and conceived of suppressing fracture during hot stamping by dividing the blank into a portion with a small difference in material flow and a portion with a large difference in material flow, and only joining the blanks in the portion with a small difference in material flow (spot welding, overlapping welding, etc.).

[0017] The results confirmed that even in areas where the material flow difference between blanks is large, such as the portion where the tension flange is deformed, fracture will not occur as long as the blanks are not joined.

[0018] It was also confirmed that the unjoined parts of the overlapping section are joined by spot welding or other means after hot stamping, thereby obtaining a stamped part that is partially integrated from the blank.

[0019] The above describes a stamping blank formed by joining overlapping portions of a blank through spot welding. However, this is not limited to spot welding; the same applies when overlapping portions are joined by other joining methods, such as overlapping welding (arc welding, laser welding), lap fillet welding (arc welding, laser welding), brazing, friction stir joining (FSW), friction pressing, etc.

[0020] It has been confirmed that, through these methods, even a one-piece blank (TWB) with multiple overlapping parts (overlapping portions) can be hot-stamped without fracture, resulting in stamped parts with strength and rigidity.

[0021] This invention is based on the above insights, and its main points are as follows.

[0022] [1-1] A method for manufacturing a stamped part, characterized in that it comprises: A blank processing step for stamping and forming yields a blank for stamping and forming that integrates multiple partial blanks formed from steel plates, wherein the blank for stamping and forming has an overlapping portion formed by at least two of the partial blanks partially overlapping. A hot stamping process, wherein a stamped product is obtained by hot stamping the blank for stamping; and The post-stamping component joining process joins a portion of the stamped part together. The blank processing step for stamping includes the following steps: pre-determining the material inflow amount of each of the blanks constituting the overlapping portion caused by stamping, and joining the blanks constituting the overlapping portion only in the portion where the difference in the material inflow amount of the blanks is less than a predetermined limit value. The post-stamping component joining process includes the following steps: joining the parts of the overlapping portion that were not joined in the stamping blank processing process.

[0023] The predetermined limit value, for example, is the difference in material flow generated by hot stamping (e.g., the deviation between materials (partial blanks) generated when not welded at the location corresponding to the welded part), can be set as the deviation when it is below the tensile shear stress (TSS) allowed when it becomes a component.

[0024] [1-2] A method for manufacturing a stamped part, wherein the joining is spot welded, as described in [1-1], the method for manufacturing a stamped part, characterized in that it comprises: A blank processing step for stamping and forming yields a blank for stamping and forming that integrates multiple partial blanks formed from steel plates, wherein the blank for stamping and forming has an overlapping portion formed by the partial blanks partially overlapping. A hot stamping process, wherein a stamped product is obtained by hot stamping the blank for stamping; and In the post-stamping component joining process, a portion of the stamped part is spot-welded. The blank processing step for stamping includes the following steps: pre-determining the material inflow amount of each portion of the blank in the overlapping part caused by stamping, and spot welding the portion of the blank constituting the overlapping part only where the difference in the material inflow amount of the portion of the blank is less than a predetermined limit value. The post-stamping component joining process includes the following steps: spot welding the parts of the overlapping portion that were not spot welded in the stamping blank processing process.

[0025] [1-3] In the method for manufacturing stamped parts according to [1] or [1-2] above, the predetermined limit value is 1 mm, preferably 0.5 mm, based on the absolute value of the difference in material inflow of the partial blank caused by stamping.

[0026] [1-4] The method for manufacturing a stamped part according to any one of [1-1] to [1-3] above, wherein the overlapping portion of the stamped part includes an L-shaped or T-shaped portion.

[0027] [2-1] A stamped part, characterized in that, Joining together multiple blanks formed from steel plates. The blanks are joined by multiple joining portions at the overlapping portion formed by the partial overlap of at least two of the aforementioned blanks. In a cross-section perpendicular to the surface of the outermost portion of the blank and the surface of the portion containing the center of the joining portion, at a position one-quarter of the plate thickness from the surface of the portion of the blank that joins with the other portions of the blank. When the Vickers hardness at a location where the joint is separated from the center of the joint by more than 15 mm and where the joint is not performed is set to Hvm. One of the plurality of joint portions is such that, within a range of 5 mm from the end of the joint portion toward the base material (or 12 mm from the center of the joint portion), the difference between the maximum and minimum Vickers hardness, ΔHv, is less than 0.2Hvm, preferably less than 0.1Hvm. The other joints of the plurality of joints (joints other than the aforementioned one) are such that ΔHv is 0.2Hvm or more, preferably 0.3Hvm, 0.4Hvm or 0.5Hvm or more.

[0028] Additionally, the outermost portion of the blank here refers to the portion of the blank on the surface side of the upper surface when the stamped part is placed with its convex shape facing upwards.

[0029] [2-2] A stamped forming component, wherein the stamped forming component described in [2-1] is joined by spot welding, characterized in that, Joining together multiple blanks formed from steel plates. At least two of the aforementioned partial blanks are joined together at their partially overlapping portions by multiple spot welds. In the cross-section of the outermost portion of the blank containing the center of the spot weld, at a position 1 / 4 of the plate thickness from the surface of the portion of the blank... When the hardness of the location separated from the center of the spot weld by more than 15 mm and where no spot weld was performed is set to Hvm, A portion of the multiple spot welds is characterized by the difference between the maximum and minimum hardness (ΔHv) within a radius of 12mm from the center being less than 0.2Hvm, preferably less than 0.1Hvm. Other spot welds (spot welds other than the aforementioned portion) at the multiple spot welds shall have a ΔHv of 0.2Hvm or more, preferably 0.3Hvm, 0.4Hvm or 0.5Hvm or more.

[0030] Additionally, the outermost portion of the blank here refers to the portion of the blank on the surface side of the upper surface when the stamped part is placed with its convex shape facing upwards.

[0031] [2-3] According to the stamping part described in [2-1] or [2-2] above, a portion of the overlapping portion is the portion in which the absolute value of the difference between the material inflow amounts of the partial blanks in the overlapping portion caused by stamping is less than a predetermined limit value when the material inflow amount of the partial blanks in the overlapping portion is calculated in advance.

[0032] The specific analysis method is as follows. First, the three-dimensional shape of the stamped part is measured to create shape data for the part. Based on the created shape data, for example, using an AUTOFORM R.10 from AUTOFORM Corporation, the part is unfolded to create data for the blank used in stamping. Using the obtained blank data, the difference in material flow rate of each part can be analyzed using the same method as the analysis method for the difference in material flow rate of a portion of the blank in the forming method of the stamped part described above.

[0033] [2-4] According to the stamping part described in [2-3] above, the predetermined limit value is 1 mm, preferably 0.5 mm, based on the absolute value of the difference in material inflow of the partial blank caused by stamping.

[0034] [2-5] A stamped part according to any one of [2] to [2-4], wherein the other part of the overlapping portion (the part other than the part of the overlapping portion) is a part that is stretched and deformed by stamping.

[0035] That is, the stamped part according to any one of [2] to [2-4], wherein the joint portion other than the one of the plurality of joint portions is configured as a portion that is stretched and deformed by stamping.

[0036] Furthermore, the portion subjected to tensile deformation through stamping refers to a portion of the overlapping part where, when the material inflow of the portion of the blank in the overlapping part caused by stamping is calculated in advance, the absolute value of the difference in the material inflow of the portion of the blank is greater than a predetermined limit value. Moreover, this analysis method, by performing three-dimensional shape measurement on the stamped part as described above, generates shape data for the part, and analyzes the shape data using, for example, AUTOFORM R.10 from AUTOFORM Corporation, thereby identifying the portion subjected to tensile deformation.

[0037] [2-6] The stamping part according to any one of [2-1] to [2-5] above, wherein the overlapping portion of the stamping part includes an L-shaped or T-shaped portion.

[0038] [3-1] A method for manufacturing a stamping blank, wherein a stamping blank formed by joining multiple partial blanks formed from steel plates is provided, having at least two of the partial blanks partially overlapping to form an overlapping portion, characterized by comprising the following steps: The material inflow amount of each of the blanks in the overlapping section caused by stamping is calculated in advance, and the blanks constituting the overlapping section are joined only in the part where the difference in the material inflow amount of the blanks is less than a predetermined limit value.

[0039] [3-2] A method for manufacturing a blank for stamping, wherein the blank for stamping described in [3-1] is joined by spot welding, characterized in that, In a stamping blank that integrates multiple partial blanks formed from steel plates, there is an overlapping portion formed by at least two of the partial blanks partially overlapping. The method for manufacturing the blank for stamping includes the following steps: pre-determining the material inflow amount of each of the blanks in the overlapping part caused by stamping, and spot welding the blanks constituting the overlapping part only in the part where the difference in the material inflow amount of the blanks is less than a predetermined limit value.

[0040] [3-3] In the method for manufacturing blanks for stamping as described in [3-1] or [3-2] above, the predetermined limit value is 1 mm, preferably 0.5 mm, based on the absolute value of the difference in material inflow of the portion of the blank caused by stamping.

[0041] [3-4] The method for manufacturing a blank for stamping according to any one of [3-1] to [3-3] above, wherein the overlapping portion of the blank for stamping includes an L-shaped or T-shaped portion.

[0042] [4-1] A stamping blank is a stamping blank formed by joining multiple partial blanks formed from steel plates, having an overlapping portion formed by at least two of the partial blanks partially overlapping, characterized in that... The portion of blanks constituting the overlapping portion is joined in a part of the overlapping portion and not joined in other parts.

[0043] [4-2] A stamping blank, wherein the stamping blank described above [4-1] is joined by spot welding, characterized in that... In a stamping blank that integrates multiple partial blanks formed from steel plates, there is an overlapping portion formed by at least two of the partial blanks partially overlapping. The blanks constituting the overlapping portion are joined by spot welding in a part of the overlapping portion, but not in other parts.

[0044] [4-3] According to the stamping blank described in [4-1] or [4-2] above, a portion of the overlapping portion is the portion in which the absolute value of the difference in the material inflow of the partial blanks in the overlapping portion caused by stamping is less than a predetermined limit value when the material inflow of each partial blank in the overlapping portion is calculated in advance.

[0045] [4-4] According to the blank for stamping described in [4-3] above, the predetermined limit value is 1 mm, preferably 0.5 mm, based on the absolute value of the difference in material inflow caused by stamping of the portion of the blank.

[0046] [4-5] The blank for stamping according to any one of [4-1] to [4-4] above, wherein the other part of the overlapping portion (the part other than the part of the overlapping portion) is the part that is stretched and deformed by stamping.

[0047] [4-6] The blank for stamping according to any one of [4-1] to [4-5] above, wherein the overlapping portion of the blank for stamping includes an L-shaped or T-shaped portion.

[0048] Invention Effects According to the present invention, a stamped product in which cracks and other fractures are suppressed during stamping (hot stamping) of a one-piece blank (TWB), wherein the one-piece blank is a stamping blank formed by joining multiple partial blanks together, and has an overlapping portion formed by the partial blanks being partially overlapped. Therefore, even large parts with complex shapes can be manufactured efficiently and with good productivity. Furthermore, parts with excellent impact resistance can be obtained. Attached Figure Description

[0049] Figure 1 It is a schematic diagram showing the appearance of a car's single mast.

[0050] Figure 2 This diagram illustrates the existing general TWB-based part manufacturing process using stamping.

[0051] Figure 3 It is a schematic diagram illustrating the composition of the blank used for stamping the door frame.

[0052] Figure 4 This is a conceptual diagram representing the stress analysis results of the overlapping part of the lower A-pillar component. Figure 4 (a) is a conceptual diagram using contour lines to represent the stress state of the lower part of the A-pillar when viewed from the outside. Figure 4 (b) is a conceptual diagram using contour lines to represent the stress state of the door sill when viewed from the inside.

[0053] Figure 5 This is a conceptual diagram illustrating an example of spot welding on the overlapping portion of the lower A-pillar component. Figure 5 (a) represents an example of the spot weld location for the overlapping portion of the lower A-pillar component. Figure 5 (b) is a conceptual diagram used to illustrate the parts of these spot welds that are at risk of breakage, enclosed by solid lines and enclosed by dashed lines, indicating the parts that are not at risk of breakage.

[0054] Figure 6 This is a conceptual diagram representing the spot weld positions of the overlapping sections, determined through simulation-based analysis. Figure 6 (a) shows an example of spot welding on the overlapping portion (L-shaped) of the lower A-pillar component and the overlapping portion (T-shaped) of the lower B-pillar component when viewed from the outside. Figure 6 (b) is a conceptual diagram representing the same part when viewed from the inside.

[0055] Figure 7 The result is obtained through FEM-based simulation. Figure 6 A conceptual diagram of the stress state of an integral blank after hot stamping. Figure 7 (a) is a conceptual diagram showing the stress state of the overlapping portion (L-shaped) of the lower A-pillar and the overlapping portion (T-shaped) of the lower B-pillar when viewed from the outside. Figure 7 (b) is a conceptual diagram representing the same part when viewed from the inside.

[0056] Figure 8 This is a diagram illustrating the component manufacturing process of the TWB based on stamping forming according to the present invention.

[0057] Figure 9 This is an explanatory diagram used to illustrate the HAZ softening section based on spot welding.

[0058] Figure 10 This is a conceptual diagram illustrating an application example of the present invention in a floor module for automobiles.

[0059] Figure 11 This indicates the overlapping welding position of the overlapping portion, determined through simulation-based analysis, and represents the replacement... Figure 6 A conceptual diagram illustrating an example of spot welding followed by overlapping welding. Figure 11 (a) shows an example of overlapping welding of the overlapping portions (L-shaped) of the lower A-pillar component and the overlapping portions (T-shaped) of the lower B-pillar component when viewed from the outside. Figure 11 (b) is a conceptual diagram representing the same part when viewed from the inside. Detailed Implementation

[0060] Regarding this invention, one embodiment of the invention (hereinafter referred to as the invention) namely, the door frame of an automobile will be described as an example. Figure 1 This diagram shows the external appearance of a single car door frame 1, an example of a car door frame. Even this single door frame 1 is typically constructed from a combination of various steel sheets. For example, from the viewpoint of ensuring interior space during a collision, the upper 2.0 GPa high-strength steel sheet and the lower 1.3 GPa high-strength steel sheet (which connects to the door sill 4) used in the A-pillar 2 (also called the front pillar) and B-pillar 3 (also called the center pillar) of the door frame 1 are sometimes combined to ensure workability and toughness. When such a component is manufactured by stamping, a monolithic blank (TWB: welded blank) is created by joining the partial blanks of various parts as a stamping blank. This monolithic blank is then stamped to manufacture the components constituting the door frame. These components are then further welded to manufacture the door frame.

[0061] Figure 2 This section outlines the manufacturing process of a typical TWB-based stamping component (stamping part).

[0062] Partial blank processing: This refers to the process of manufacturing a part from a single, integral blank. Partial blanks are cut (punched) from a specified steel plate and then refined through processes such as laser finishing.

[0063] The blank processing step for stamping is the process of joining the obtained partial blanks to manufacture a stamping blank (integrated blank). There are no particular limitations on the joining method for the partial blanks. For example, when welding the partial blanks together, laser welding or arc welding can be used. Alternatively, partial blanks can be overlapped, and the overlapping parts can be joined using methods such as spot welding (resistance spot welding, laser spot welding, etc.), overlap welding (arc welding, laser welding), lap fillet welding (arc welding, laser welding), brazing, friction stir welding (FSW), and friction press welding. By combining and joining specified partial blanks into one piece, a stamping blank can be obtained.

[0064] Hot stamping is a process of hot stamping a blank (integral blank) for forming. By stamping the blank, a part or a part close to the shape of the part (near-net-shape) can be obtained (the part obtained after the hot stamping process is called a stamped part). There are no particular limitations on the stamping method, but hot stamping is generally preferred when stamping blanks made of high-strength steel sheets (e.g., steel sheets with strength exceeding 590 MPa). Hot stamping, also known as hot pressing (hot pressing construction method), is a stamping method in which the blank (steel sheet) is heated to an austenitic temperature range of approximately 900°C, and then rapidly cooled during stamping to achieve martensitic phase transformation quenching. Hot stamping has the following characteristics: because forming is performed at high temperatures, the stamping load can be reduced; and due to the martensitic phase transformation, the formed part has high strength and excellent shape retention. Therefore, it is often used for stamping high-strength steel sheets.

[0065] Finishing process: This is the process of refining the stamped part (including parts that have reached the final part shape and near-net-shape parts) after hot stamping. There are no particular limitations on the method for refining the stamped part. For example, it includes processing such as laser removal of burrs generated at the ends of the stamped part to adjust it to a specified shape (laser finishing). Furthermore, in the case of near-net-shape stamped parts, this includes processing to achieve the final part shape. If the stamped part has reached its final shape through hot stamping, this finishing process can be omitted.

[0066] Post-stamping component joining process: This process involves joining other components to the stamped part when further joining is required. The joining method for these other components is not particularly limited. For example, sometimes they are joined using spot welding, arc welding, laser welding, brazing, etc. Additionally, stamped parts may be fitted with localized reinforcements or joined with components that cannot be formed simultaneously through stamping. Of course, this post-stamping component joining process can be omitted if joining other components is not required.

[0067] Through these processes, the final product (stamped part) can be obtained. Furthermore, the manufacturing process of TWB's stamped parts is not limited to the processes described above. Additional processes can be added as needed.

[0068] Recently, there has been a demand for more efficient and lower-cost component manufacturing, and a pursuit of larger components and modules (components formed by further combining smaller components). For example, in the case of automobile door frames, there is a requirement to manufacture the door frame through a one-time stamping process, rather than manufacturing and assembling the A-pillars, B-pillars, etc., separately. Therefore, there is a need for stamping blanks for one-time stamping of door frames.

[0069] Figure 3 Indicates door frame 1 ( Figure 3 Example of a blank 30 for stamping (e.g., a single-vehicle mast). Figure 3 The stamping blank 31 is formed by joining together portions of the blanks corresponding to the upper A-pillar 31 (also called the upper A-pillar part), the lower A-pillar 32 (also called the lower A-pillar part), the upper B-pillar 33 (also called the upper B-pillar part), the lower B-pillar 34 (also called the lower B-pillar part), and the door sill 35. The steel grade and plate thickness of the blanks for each part can be the same or different. Figure 3 In the example, the lower A-pillar member 32 is made of 1.5 GPa grade steel plate with a thickness of 1.4 mm; the upper B-pillar member 33 is made of 2.0 GPa grade steel plate with a thickness of 1.4 mm; the lower B-pillar member 34 is made of 1.0 GPa grade steel plate with a thickness of 1.2 mm; the door sill 35 is made of 1.5 GPa grade steel plate with a thickness of 1.2 mm; and the upper A-pillar member 31 is made of 2.0 GPa grade steel plate with a thickness of 1.4 mm. These partial blanks are joined together to manufacture an integral stamping blank 30 (hereinafter sometimes referred to as an integral blank).

[0070] exist Figure 3 In the example, in the case of door frame 1, the lower A-pillar (lower A-pillar side piece) 32 is overlapped and joined with the door sill 35, the lower B-pillar (lower B-pillar side piece) 34 is overlapped with the door sill 35, and the upper B-pillar (upper B-pillar side piece) 33 is overlapped with the upper A-pillar (upper A-pillar side piece) 31 to manufacture door frame 1. Therefore, in order to manufacture such door frame by one-time stamping, the blank corresponding to the lower A-pillar side piece 32 and the blank corresponding to the door sill 35 are overlapped to manufacture an integral blank 30. Similarly, the blanks constituting the lower B-pillar side piece 34 and the door sill 35, and the upper B-pillar side piece 33 and the upper A-pillar side piece 31 are overlapped to manufacture an integral blank 30. Figure 3 This section outlines the composition of a portion of the blank used for stamping the car door frame. Figure 3The overlapping parts are indicated by shading. The overlapping part 36 of the lower A-pillar piece 32 and the door sill 35 is L-shaped, the overlapping part 37 of the lower B-pillar piece 34 and the door sill 35 is T-shaped, and the overlapping part 38 of the upper B-pillar piece 33 and the upper A-pillar piece 31 is also T-shaped.

[0071] In addition, Figure 3 In the example, the overlapping section consists of two blank parts, but the number of overlapping blank parts is not limited. For example, more than three blank parts can overlap. The decision depends on the required characteristics and shape of the final manufactured part.

[0072] Thus, a shape roughly L-shaped when viewed vertically above the surface of a component is called an L-shape, and a shape roughly T-shaped is called a T-shape. In three-dimensional structures with a cap-shaped cross-section, such as the overlapping portion 36 of the A-pillar lower side piece 32 and the door sill 35, when viewed from above, the material flow at the corners becomes complex due to the complex shape, such as an L-shape or a T-shape. Therefore, cracking is prone to occur due to the stamping process of the integral blank.

[0073] [Overlapping Department] When manufacturing a monolithic blank by joining overlapping parts as a whole, fracture (cracks, breaks, etc.) sometimes occurs at the overlapping part after stamping. Observing the fractured parts, it can be seen that fractures occur more frequently in areas where the sheet thickness is significantly reduced due to stamping. Therefore, the present invention was completed by analyzing the causes of fracture.

[0074] Furthermore, there are no particular limitations on the joining methods for overlapping portions of blanks and for joining stamped parts. Examples of joining methods include resistance welding (resistance spot welding, projection welding, seam welding, etc.), arc welding (overlapping arc welding, lap corner arc welding), laser welding (overlapping laser welding, lap corner laser welding, laser spot welding), friction stir welding (FSW), friction pressing, and brazing. Additionally, mechanical fastening methods can be used for joining stamped parts.

[0075] In the following description of the present invention, spot welding (resistance spot welding) will be used as an example for the application of the joining method. The present invention is not limited to the manner described below. In particular, the joining method is not limited to spot welding, and various joining methods described above and similar joining methods can be applied. By replacing spot welding in the description with other joining methods, the application of other joining methods can be understood.

[0076] The causes of fracture can be analyzed using simulation methods such as the finite element method (FEM). The inventors conducted an analysis based on FEM. Figure 4This indicates the analysis results at the L-shaped overlap 36 between the lower A-pillar component 32 and the door sill 35. Figure 4 (a) The stress state of the lower component 32 of column A when viewed from the outside is shown by contour lines. Figure 4 (b) shows the stress state of the door sill 35 as viewed from the inside using a contour plot. Furthermore, the actual fracture occurs in the portion enclosed by the ellipse, corresponding to the denser area in the contour plot. Comparing these confirms that fracture actually occurred in the portion shown in the simulation as having high shear stress and being in a fracture state.

[0077] Based on the analysis results, the following factors are identified as the main causes of fracture: (i) significant differences in the material flow behavior of the blanks during deformation at the overlapping part; and (ii) material flow behavior is restricted by spot welding. Here, material flow refers to the deformation (movement) of material due to stamping, and material flow behavior refers to the deformation behavior of material at a specific location before and after stamping, including the direction and distance of deformation (movement).

[0078] When the difference in material inflow between parts of the billet increases (reason (i)), it can be assumed that shear deformation occurs at the spot weld, resulting in a large deformation concentration near the spot weld. Therefore, since the material flow is restricted (reason (ii)), deformations that accompany the material inflow, such as tensile flange deformation, do not occur. As a result, it can be assumed that deformation becomes more likely to concentrate and lead to fracture.

[0079] Therefore, in order to suppress the breakage of the integral blank caused by stamping, the inventors focused on the material flow behavior of some blanks in hot stamping. That is, the following situation was conceived and developed: the material flow behavior of each blank constituting the overlapping part is mastered in advance by simulation, and the part with a small difference in the amount of material flow between the blanks is divided into a part with a large difference in the amount of material flow between the blanks. Only in the part with a small difference in the amount of material flow is some blank spot welded to each other, and no spot welding is performed in other parts, thereby suppressing breakage during stamping.

[0080] As a result, it was confirmed that even in areas where the material flow rate of the blanks differs significantly, such as the portion undergoing tensile flange deformation, hot stamping can be performed without fracture as long as spot welding is not performed. That is, it was confirmed that even if the aforementioned reasons (i) remain, resulting in a significant difference in material flow rate of the blanks during overlapping deformation, fracture can be suppressed by eliminating the reasons (ii) and restricting the material flow rate through spot welding.

[0081] The difference in material inflow between different parts of the blank refers to the absolute value of the difference in the movement vectors of each point (position) in the blank that constitutes the overlapping part, corresponding to any point (position) of the overlapping part before forming, as a result of the movement during stamping. That is, based on the point (position) of each part of the blank corresponding to any point (position) of the overlapping part after stamping, the movement vector of that point is calculated, and the absolute value of the difference in the movement vectors of each part of the blank (the distance between each moved point (position)) is taken as the difference in material inflow (deviation) at that point (any point in the overlapping part).

[0082] A specific example of simulation is shown. As described above, spot welding is used as an example, but this example can be applied to other joining methods. For example, at least one point (e.g., the center of gravity of the overlapping part, the center of gravity of the top part, etc.) of the part that becomes the top surface (the part pressed by the liner or die) during stamping in the overlapping part is fixed (meaning it is joined by spot welding, etc.), and a stamping (hot stamping) analysis of the integral blank is performed (simulation analysis based on FEM, etc.). At this time, the movement vector of each point is calculated based on the position of each point of the partial blank corresponding to any point of the overlapping part before and after movement. The absolute value of the difference between the movement vectors of the corresponding points of each partial blank is calculated as the material flow difference (deviation) of that point. If the calculated material flow difference (deviation) is less than a preset limit value (described later, for example, 1 mm, preferably 0.5 mm), the material flow difference is small, so it can be set as the point (position) where spot welding is performed before stamping. On the other hand, if the calculated material inflow difference (deviation) is larger than the preset limit value, the material inflow difference is large. Therefore, spot welding can be performed after stamping without performing spot welding before stamping.

[0083] The inventors investigated the relationship between the material inflow difference (deviation) in hot-stamped joints and the tensile shear strength (TSS) at room temperature. The results showed that if the material inflow difference (deviation) during hot stamping is 0-1 mm (greater than 0 mm but less than 1 mm), the tensile shear strength (TSS) at room temperature becomes equal to or greater than the original TSS (TSS with a deviation of 0 mm). The technical reason for this phenomenon is not yet clear, but it is speculated that when the deviation is small (less than 1 mm), the superposition effect of processing strain introduced by hot stamping and hardening based on quenching may be obtained.

[0084] Let's illustrate this with a specific test example. Prepare the following test piece: A joint (test piece) formed by overlapping and spot-welding 1.5 GPa grade steel plates (1.2 mm thick) is heated to 900°C and held for 1 minute. Then, the steel plates are stretched at 740°C with a specified deviation (offset), followed by quenching. Next, the test piece is stretched at 1 mm / s at room temperature, and the offset between the two steel plates and the tensile shear strength (TSS) of the joint (spot-welded part) at room temperature are observed. The results show that if the offset of the steel plates at heat is 0~1.0 mm, the TSS of the joint at room temperature is equal to or greater than that when the offset is 0 mm (i.e., no heat deformation). On the other hand, if the offset exceeds 1.0 mm, the TSS tends to decrease. Specifically, under the conditions of this experiment, it was confirmed that, compared with the TSS when the deviation was 0 mm, the TSS was 102% when the deviation was 0.1 mm, 105% when it was 0.3 mm, 107% when it was 0.5 mm, 102% when it was 0.7 mm, 100% when it was 1.0 mm, 90% when it was 1.2 mm, 86% when it was 1.5 mm, and 71% when it was 2.0 mm. That is, it was discovered for the first time that even in hot stamping (hot pressing), even if there is a material inflow difference (deviation) of less than 0.0 mm to 1.0 mm at the spot welding point, the same or higher tensile shear strength can be ensured compared with the case where no deformation occurs.

[0085] According to this new insight, when hot stamping is performed on an integral blank formed from overlapping blanks, the limit value of the material flow difference (deviation) can be set to 1.0 mm, preferably preset to 0.9 mm, 0.8 mm, 0.7 mm, 0.6 mm or 0.5 mm.

[0086] The point (location) for determining the material inflow difference does not need to be specifically limited. For example, the material inflow difference can be analyzed at a point (location) set as the final spot welding location. Alternatively, the analysis mesh can be refined to identify regions where the material inflow difference is below a limit value. In this case, the spot welding point (location) before stamping can be set within the region where the material inflow difference is small.

[0087] Figure 5 (a) shows an example of the spot weld locations (black circles (●) in the figure) at the overlapping portion 36 of the lower A-pillar component 32 and the door sill 35. In cases where spot welding was performed at all locations before stamping, such as... Figure 4 As shown in (a) and (b), at the actual fracture site ( Figure 4 The portion enclosed by the ellipse in (a) and (b) is identified as stress concentration.

[0088] Next, assuming only in Figure 5Spot welding is performed on the point of the double circle (a point with a black circle inside a white circle) approximately in the center of the overlapping part 36 shown in (a). Spot welding is not performed on all other marked locations (only the points indicated by the black circle mark (●)). The stamping process is simulated using FEM to determine the material inflow (movement vector) of the lower A-pillar 32 and the door sill 35. In addition, the material inflow (movement vector) of the corresponding point of the blank constituting the overlapping part 36 is also determined at each node of the FEM, and the difference in the material inflow (movement vector) of each blank part is determined (material inflow difference). The limit value of the absolute value of the difference in material inflow at the corresponding node (sometimes simply referred to as the limit value of the material inflow difference) is set to 1.0 mm as described above, and the part with a material inflow difference greater than this is defined as the part with a risk of breakage. As a result, in Figure 5 In (b), the portion 40 enclosed by the solid line is the portion 40 that is determined to be at risk of breakage if it is spot welded and then stamped.

[0089] If the difference in material inflow is small, there are no particular limitations on the method for determining the region. As mentioned above, it can be set based on analysis based on simulations such as FEM, prior offline tests, and actual values ​​in actual stamping.

[0090] In addition to evaluating the difference in material inflow, the reduction rate of sheet thickness can also be evaluated. For example, in the case of FEM simulation, the reduction rate of sheet thickness for each element can be calculated and taken into account in the aforementioned difference in material inflow. This is because, in the portion with a larger reduction rate of sheet thickness, deformation is more likely to concentrate at the spot welds, thus increasing the risk of fracture. In this case, a limit value can be determined based on the reduction rate of sheet thickness. The reason for setting the limit value as an absolute value is that there are cases where the sheet thickness increases (e.g., wrinkles occur), in which case the reduction rate of sheet thickness is represented as a negative value. 10% of the absolute value of the reduction rate of sheet thickness can be set as the limit value, and the portion of the reduction rate of sheet thickness above this value is considered the portion with a higher risk of fracture. The limit values ​​of the reduction rate of sheet thickness are preferably set to 9%, 8%, 7%, 6%, or 5%. Since it can be directly calculated through FEM analysis, the reduction rate of sheet thickness is also a relatively easy indicator to grasp.

[0091] exist Figure 5 In (b), the portion enclosed by a solid line represents the portion 40 where there is a risk of breakage. Conversely, the portion enclosed by a thick dashed line represents the portion 41 where there is a lower risk of breakage. Spot welding is performed only at the spot weld points entering this portion (the portion where the sheet thickness reduction rate is below the limit value) 41, where the risk of breakage is lower due to stamping, thus creating a monolithic blank. Of course, when entering other portions (the portions where there is a risk of breakage), Figure 5In the case of the part 40) which is at risk of breakage enclosed by the solid line of (b), an integral blank is manufactured without spot welding.

[0092] The overlapping portion 37 of the lower B-pillar member 34 and the door sill 35, and the overlapping portion 38 of the upper B-pillar member 33 and the upper A-pillar member 31, are similarly determined to determine the parts to be spot welded and other parts (parts not to be spot welded), and a blank 30 for stamping is manufactured. Figure 6 This is a conceptual diagram showing the spot welding positions of the overlapping portions 36 and 37 of the lower A-pillar component 34 and the lower B-pillar component 34 with the door sill 35, determined through simulation-based analysis. Figure 6 (a) shows the spot weld positions of the overlap 36 (L-shaped) between the lower A-pillar member 32 and the sill 35 and the lower B-pillar member 34 and the sill 35, as viewed from the outside. Figure 6 (b) shows the spot welding positions of the overlapping portions 36 and 37 of the door sill 35 when viewed from the inside. The integral blank, which is formed by joining the various blanks in this way, is hot-stamped to manufacture a stamped part that becomes a door frame.

[0093] Figure 7 The results were obtained through FEM simulation. Figure 6 The diagram shows the stress state of the integrated blank 30 after hot stamping. Figure 7 (a) shows the stress state of the overlapping portion 36 (L-shaped) of the lower A-pillar member 32 and the overlapping portion 37 (T-shaped) of the lower B-pillar member 34 when viewed from the outside. Figure 7 In (a), the thick dashed line represents the part 41 with a lower risk of breakage, where spot welding is performed only. Figure 7 (b) shows the stress state of the overlapping portions 36 and 37 of the door sill 35 when viewed from the inside. After the actual hot stamping of the integral blank, that is, in the stamped part that becomes the door frame, no fracture was observed at any of the overlapping portions.

[0094] As an example of a joint other than spot welding, in Figure 11 An example of overlapping laser welding is shown in the figure. Figure 11 An example is in manufacturing and Figure 6 When using the same integral blank, replace Figure 6 Overlapping laser welding was performed using spot welding. Figure 11 and Figure 6 same, Figure 11 (a) shows the welding positions (position of the overlapping weld line 42) of the lower A-pillar member 32 and the sill 35 (L-shaped) and the lower B-pillar member 34 and the sill 35 (T-shaped) when viewed from the outside. Figure 11In (a), the thick dashed line represents the part 41 with a lower risk of breakage, where overlapping welding is only performed. Figure 11 (b) shows the welding positions (position of welding line 42) of the overlapping parts 36 and 37 of the door sill 35 when viewed from the inside. The integral blank formed by joining the various blanks in this way is hot-stamped to manufacture a stamped part that becomes a door frame.

[0095] In this case, overlapping laser welding is performed only on the portion 41 where the risk of fracture is lower to create an integral blank, but the routing method of the weld line 42 of the overlapping weld is not particularly limited. Similar to the weld point determined by spot welding, the joint can be performed at the end or center of the overlapping portion of the blank, or both. Figure 11 The stress state of the integral blank 30 manufactured in this way after hot stamping is also shown using contour plots. This allows for comparison with the case where an integral blank is manufactured by spot welding. Figure 7 The stress states were roughly equal, and no fractures were observed in the overlapping portions of some billets.

[0096] In summary, the material inflow amount (movement vector) of each part of the blank in the overlapping section caused by stamping can be calculated in advance. Only the parts of the blank that form the overlapping section are joined together when the absolute value of the difference in material inflow amount at corresponding positions of each part of the blank (the absolute value of the difference in movement vectors) is less than a predetermined limit. There are no particular limitations on the method for calculating the difference in material inflow amount of the parts of the blank in advance through simulation. For example, the deformation behavior of the material can be calculated by FEM, or it can be calculated by conducting stamping tests on test pieces simulating the actual overlapping section. In addition, the thickness reduction rate of the blank before and after stamping at specific positions of the part of the blank can be further considered for evaluation.

[0097] Whether the difference in material inflow is significant can be assessed using a predetermined limit value. There are no particular limitations on how this limit value is set. It can be based on prior analysis using simulations such as FEM, or actual values. When evaluating based on the thickness reduction rate, the limit value can be determined by the absolute value of the thickness reduction rate of the overlapping portion of the billet. The reason for setting the limit value as an absolute value is to account for situations where the thickness increases (e.g., wrinkles occur).

[0098] In particular, as explained above, the L-shaped portion, such as the overlap 36 between the lower A-pillar member 32 and the door sill 35, and the T-shaped portion, such as the overlap 37 between the lower B-pillar member 34 and the door sill 35, are portions that undergo complex deformation (complex material inflow behavior), and therefore the effect becomes significant when the present invention is applied.

[0099] [Jointing in the process of joining parts after stamping] In integral blanks, the unjoined portions in the overlapping parts are not joined (e.g., spot welding) after stamping, which sometimes results in insufficient strength and rigidity, failing to achieve the designed performance. Therefore, after stamping (after the stamping process), the unjoined portions in the overlapping parts that were not joined during the blank processing steps for stamping can be joined (e.g., spot welding).

[0100] Typically, after stamping a single-piece blank to obtain a stamped part, it is common to further join additional parts to the stamped part (post-stamping part joining process). Therefore, the post-stamping part joining process can include a step of joining (spot welding, etc.) the unjoined portions of overlapping parts. This is because by joining the unjoined portions of overlapping parts in the extension of the conventional post-stamping part joining process, it can be effectively achieved without adding new steps. Through these processes, a stamped part can be obtained.

[0101] Based on the above description, a summary of the manufacturing process of the TWB-based stamped part of the present invention is shown below. Figure 8 Compared to previous manufacturing processes ( Figure 2 In comparison, the differences are as follows. The blank processing step for stamping includes the following steps: pre-analyzing the material flow of the overlapping portion of the blank, identifying portions exceeding predetermined limits as fracture risk areas, and joining only the portion outside the fracture risk area of ​​the overlapping portion, i.e., a part of the overlapping portion. It further includes a step of joining the remaining portion (the part that was not joined during the post-stamping part joining process).

[0102] [Stamped parts] The component (stamped part) obtained by the method described above is a stamped part in which an integral blank formed by joining multiple partial blanks formed from steel sheets is formed. At least two partial blanks partially overlap, and the blanks constituting the overlapping portion are joined at multiple joints. One of the joints of the overlapping portion is formed before hot stamping, and the remaining portion (the joints other than one part) is formed after hot stamping. Therefore, in cases where joining is performed based on spot welding, overlap welding, friction stir joining, friction press joining, etc., the HAZ softening portion generated before hot stamping disappears through heat treatment during hot stamping. On the other hand, joints formed by welding, friction stir joining, etc., performed after hot stamping, do not undergo heat treatment through hot stamping, and therefore retain HAZ softening portions. That is, in the obtained component (stamped part), the joints of the overlapping portion do not have HAZ softening portions in one part of the overlapping portion, but have HAZ softening portions in other parts. Hereinafter, spot welding will be used as an example. As mentioned above, the joining method is not particularly limited to spot welding.

[0103] The HAZ softening zone refers to the phenomenon where the heat-affected zone (HAZ) of the base metal, located just outside the outer edge of the weld metal in spot welding, arc welding, and similar processes, softens compared to the base metal due to tempering. The same applies to friction stir welding, friction press welding, and brazing; the softened zone formed in the HAZ of the base metal just outside the outer edge of the joint is called the HAZ softening zone. The following explanation uses spot welding as an example.

[0104] Figure 9 This example illustrates the correspondence between the cross-sectional survey results of the spot weld test piece 90 and the hardness distribution of the spot weld portion 91 (near the spot weld point) and the base material 92 (corresponding to a portion of the blank). Furthermore, unless otherwise specified, hardness (hardness) refers to Vickers hardness. As per... Figure 9 As is known, the spot weld portion, including the joint (weld nugget), has a hardness of approximately Hv500 due to quenching (the spot weld shows approximately the same hardness, so the hardness of the center of the spot weld can be taken as a representative value). On the other hand, it is known that at a point approximately 1 mm away from the end (outer edge) of the spot weld nugget 93 (near the outer edge of the spot weld portion), the hardness becomes approximately Hv300 and softens. This softened portion is the HAZ softened portion. Typically, the HAZ softened portion occurs within a region of 5 mm or less, even when it is far away from the end (outer edge) of the joint portion (weld nugget, weld metal).

[0105] As the distance from the joint (melt nucleus 93) increases further, the hardness converges to the hardness of the base material 92 (at... Figure 9 In this context, Hv represents a hardness that converges to less than Hv500. The hardness of the HAZ-softened portion relative to the center of the spot weld 91 is, for example, reduced by more than Hv50 when the base material 92 is a 1.0 GPa grade steel plate, reduced by more than Hv100 when it is a 1.5 GPa grade steel plate, and reduced by more than Hv150 when it is a 2.0 GPa grade steel plate. In summary, if the hardness of the base material 92, i.e., the hardness of the portion of the base material 92 unaffected by the spot weld, is defined as Hvm, and the maximum value of the hardness measured within a radius of 12 mm from the center of the spot weld portion 91 (or within 5 mm from the end of the joint portion outwards (towards the base material side)) is defined as the maximum hardness, the minimum value as the minimum hardness, and the difference between the maximum and minimum hardness as ΔHv, then without HAZ softening, ΔHv can be less than 0.2Hvm, preferably less than 0.1Hvm. Conversely, when HAZ softening occurs, ΔHv can be 0.2Hvm or more, preferably 0.3Hvm, 0.4Hvm or 0.5Hvm or more.

[0106] Regarding the hardness distribution of the HAZ softened portion, it can be determined by measuring the hardness (Vickers hardness) in a cross-section along the thickness direction at the center of the joint portion of the outermost portion of the blank (the center of the spot weld), at a position one-quarter of the thickness from the surface of this portion of the blank that connects with other portions of the blank, along a straight line (hardness measurement line) parallel to the surface of the portion of the blank, from the center of the spot weld outwards. For example, the hardness distribution can be measured in a cross-section along the thickness direction of the outermost portion of the blank constituting the overlapping portion. First, as the hardness of the base material (the hardness of the portion of the base material not affected by the spot weld), the hardness at a position separated from the center of the spot weld by 15 mm or more and where the spot weld was not performed is measured, and this hardness is set as Hvm. In addition, the outermost portion of the blank here refers to the portion of the blank on the surface side of the upper surface when the stamped part is placed with its convex shape facing upwards.

[0107] Next, hardness measurements are performed in a straight line from the center of the spot weld to 12 mm, moving outward from the outer edge of the spot weld dot and along the centerline of a portion of the blank's thickness. This allows us to determine ΔHv. Specifically, for the range from 0.5–1 mm inside the outer edge of the spot weld dot to 2–3 mm outside the outer edge, measurements can be performed at intervals of 0.1–0.2 mm. This is because within this range, there are often cases where the minimum hardness of the HAZ softened area caused by spot welding is present.

[0108] Spot welding without a HAZ softening portion is performed before hot stamping. That is, spot welding is performed on portions of the overlapping blanks where the difference in material flow is small. On the other hand, spot welding with a HAZ softening portion is performed after hot stamping, and therefore is performed on portions of the blanks where the difference in material flow is large, for example, portions that are deformed by stretching flanges during stamping. In other words, the stamped part of the present invention has a ΔHv of less than 0.2Hvm for a portion of the multiple spot welds (at least one spot weld that is joined before hot stamping). On the other hand, other spot welds (spot welds other than the aforementioned portion, at least one other spot weld that is joined after hot stamping) have a ΔHv of 0.2Hvm or more because they have a HAZ softening portion.

[0109] Furthermore, as described in the above-described stamping method, the stamping component of the present invention is a stamping component in which the material inflow amount of each part of the blank in the overlapping portion caused by stamping is predetermined, and the portion where the absolute value of the difference in material inflow amount between each part of the blank is less than a predetermined limit value is joined by spot welding or the like before stamping. That is, a portion of the above-mentioned multiple spot welds (spot welds where ΔHv is less than 0.2Hvm) is the portion that meets this condition, that is, the portion where the absolute value of the difference in material inflow amount is less than a predetermined limit value.

[0110] Based on the shape of the stamped part, it can be determined whether spot welding was performed only in the portion where the absolute value of the difference in material flow between the blanks is less than a limit value before stamping. For example, the shape data of the part can be obtained by measuring the three-dimensional shape centered on the overlapping portion of the blanks in the stamped part, and then analyzed. Data on the blanks of the overlapping portion before stamping can be generated based on the obtained three-dimensional shape data. For example, by using an apparatus such as the AUTOFORM R.10 manufactured by AUTOFORM Corporation, data on the blanks for stamping can be obtained based on the shape data of the stamped part. Using the obtained blank data, as described in the above-described method for manufacturing stamped parts, the difference in material flow between the blanks caused by stamping can be analyzed by FEM or the like. Thus, it can be determined whether spot welding without HAZ softening (spot welding performed before stamping) belongs to the portion where the difference in material flow is less than a limit value due to stamping. Similarly, it is possible to determine whether spot welds with HAZ softening (spot welds performed after stamping) belong to the part where the difference in material inflow due to stamping is greater than the limit value.

[0111] The above explanation uses spot welding as an example. In joining methods other than spot welding, such as arc welding and laser welding where the base material steel plate is heated and melted for joining, and in friction stir welding, friction pressing, and brazing where the base material steel plate is heated for joining without melting, a HAZ softened portion is also generated in the joined portion after hot stamping. For example, in arc welding, a HAZ softened portion is generated in the base material outside the outer edge of the weld metal. Similarly, in friction stir welding, a HAZ softened portion is generated in the base material outside the outer edge of the joined portion. In joining methods other than spot welding, similarly to spot welding, Vickers hardness can be measured along a hardness measurement line located at a position 1 / 4 of the plate thickness from the surface of the part ...

[0112] For example, in the case of lap welds and overlapping welds based on arc welding and laser welding, the hardness distribution can be measured by determining a hardness measurement line in a section perpendicular to the weld line. In this case, the center of the joint can be set as the center of the hardness measurement line in the weld metal. In the case of friction stir welding, friction press welding, and brazing, the hardness distribution can also be measured in the same way as in spot welding.

[0113] The method for measuring hardness distribution is the same as that for spot welding described above, so it is sufficient to follow the method. Specifically, in a portion of the blank to be measured, when the Vickers hardness at a location 15 mm or more away from the center of the joint (weld metal, etc.) and not yet joined is defined as Hvm, the difference between the maximum and minimum Vickers hardness within a range of 5 mm outward from the end of the joint can be defined as ΔHv. Furthermore, a portion of the joint (the part that was hot-stamped after joining) experiences HAZ softening, so ΔHv is less than 0.2Hvm, preferably less than 0.1Hvm. Other joint portions (joint portions other than the aforementioned portion, such as those joined after hot stamping) experience HAZ softening, so ΔHv is 0.2Hvm or more, preferably 0.3Hvm, 0.4Hvm, or 0.5Hvm or more.

[0114] [Other Embodiments] Figure 10 This diagram illustrates an embodiment of application to a floor module 100 in a vehicle. Conventionally, floor modules are manufactured by separately manufacturing components and then joining them together (spot welding, etc.). However, the floor module 100 can be manufactured by applying the blank manufacturing method of the present invention to manufacture an integral blank (stamping blank) for the front module 100 and performing a one-time hot stamping. In this case, the blank and blank manufacturing method of the present invention are applied to the joining (spot welding, etc.) of the six overlapping portions 101. As a result, even with a one-time hot stamping, the floor module 100 can be obtained without any breakage of the overlapping portions 101.

[0115] As described above, the parts (stamped parts) obtained by the present invention have excellent impact resistance without cracks or the like. Compared with conventional spot-welded assemblies, where all parts are spot-welded before or after hot stamping, the stamped parts of the present invention have the following advantages.

[0116] Compared to conventional parts where all parts are spot-welded before hot stamping, the formability of the stamped parts of the present invention is improved. Therefore, the depth of the parts can be increased, the angle of the upright sections can be steeper, and the full plastic bending moment of each section can be improved. Furthermore, excessive reduction in sheet thickness introduced into joints (such as spot welds) where material flow is greater can be eliminated, thus improving the impact resistance of the module.

[0117] Furthermore, the stamped parts of the present invention mainly eliminate the HAZ softening portion of the top surface (e.g., the top surface of a part that has become a hat-shaped cross section), which can improve the bonding force between the parts and improve the impact resistance of the module.

[0118] The above description, using automotive door frames and floor modules as examples, illustrates the stamping blanks, the method for manufacturing the stamping blanks, the stamping parts, and the method for manufacturing the stamping parts of the present invention. These blanks, parts, and their manufacturing methods are not limited to the embodiments described above. The present invention can be applied in various ways, regardless of type or structure, as long as it is a TWB with overlapping portions.

[0119] Industrial availability This invention can be widely used in industries such as automobiles and other transportation machinery, general machinery, and electrical equipment.

[0120] Explanation of symbols 1. Car door frame 2. A-pillar (front pillar) 3. B-pillar (middle pillar) 4. Car door sills 30. Blanks for stamping 31. Upper A-pillar component (upper A-pillar) 32. Lower A-pillar component (lower A-pillar) 33. Upper B-pillar component (upper B-pillar) 34. Lower B-pillar component (lower B-pillar) 35 car door sill 36. The overlapping part of the lower A-pillar component and the door sill 37. The overlapping part of the lower B-pillar component and the door sill. 38. The overlapping part of the upper part of the B-pillar and the upper part of the A-pillar 40. Sections at risk of fracture 41. Sections with lower risk of fracture 42 Overlapping welding lines 90 spot welding test piece 91. Spot welding section (spot welding points) 92 Base Material 93 Melting Core

Claims

1. A blank for stamping, comprising joining multiple partial blanks formed from steel plates into one piece, and having at least two overlapping portions formed by partial overlap of said partial blanks, characterized in that, The portions of the blanks constituting the overlapping portion are joined in one part of the overlapping portion, but not in other parts. A portion of the overlapping portion is such that, when the material inflow amount of each portion of the blanks in the overlapping portion caused by stamping is determined in advance, the absolute value of the difference in the material inflow amount of the portion of the blanks is smaller than a predetermined limit value.

2. The blank for stamping according to claim 1, wherein, The joint is a spot weld.

3. The blank for stamping according to claim 1, wherein, The predetermined limit value is based on the absolute value of the difference in material inflow caused by stamping of the portion of the blank, which is 1 mm.

4. The blank for stamping according to any one of claims 1 to 3, wherein, The other parts of the overlapping portion are those that are stretched and deformed by stamping.

5. The blank for stamping according to any one of claims 1 to 3, wherein, The overlapping portion of the blank for stamping includes an L-shaped or T-shaped portion.

6. The blank for stamping according to claim 4, wherein, The overlapping portion of the blank for stamping includes an L-shaped or T-shaped portion.

7. The blank for stamping according to claim 2, wherein, The predetermined limit value is based on the absolute value of the difference in material inflow caused by stamping of the portion of the blank, which is 1 mm.

8. The blank for stamping according to claim 7, wherein, The other parts of the overlapping portion are those that are stretched and deformed by stamping.

9. The blank for stamping according to claim 7, wherein, The overlapping portion of the blank for stamping includes an L-shaped or T-shaped portion.

10. The blank for stamping according to claim 8, wherein, The overlapping portion of the blank for stamping includes an L-shaped or T-shaped portion.

Images