Integrated rear rail structure and method for a vehicle

Abstract

The present disclosure relates to an integrated rear rail structure for a vehicle framework. The integrated rear rail structure includes a first rear rail, a second rear rail, and one or more cross members connecting the first rear rail to the second rear rail. The integrated rear rail structure is formed by deforming a single bonded blank. The single bonded blank includes at least one first blank joined to a second blank such that the first blank partially overlaps the second blank to form one or more overlapping regions. The present disclosure also relates to a method for manufacturing such an integrated rear rail structure.

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit of European Patent Application No. 22 382 942.5, filed October 6, 2022. The present disclosure relates to an integrated rear rail structure for a vehicle, the integrated rear rail structure including a first rear rail, a second rear rail, and one or more cross members connecting the rear rails. The present disclosure also relates to a method for manufacturing such an integrated rear rail structure. [Background technology]

[0002] Vehicles such as automobiles incorporate structural frameworks designed to withstand loads that the vehicle may be subjected to during its lifetime, and the structural frameworks are further designed to withstand and absorb impacts, for example, in the event of a collision with another vehicle or road structure.

[0003] The demand for lightweighting in the automotive industry has led to the development and implementation of lightweight materials or components, as well as related manufacturing processes and tools. The demand for lightweighting is driven in particular by the goal of reducing CO2 emissions. Increasing concern for occupant safety has also led to the adoption of materials that improve the vehicle's integrity during a crash, also improving energy absorption.

[0004] A process known as hot formed die quenching (HFDQ) typically uses boron steel sheet to create stamped components with ultra-high strength steel (UHSS) properties, for example, tensile strengths of 1.500 MPa or 2.000 MPa or greater. The increased strength allows for the use of thinner gauge material, resulting in weight savings over conventional cold-stamped mild steel components. Throughout this disclosure, UHSS can be considered a steel that has an ultimate tensile strength of 1.000 MPa or greater after a compression hardening process.

[0005] In the HFDQ process, the blank to be hot-formed can be heated to a predetermined temperature, for example, above the austenitizing temperature (particularly between Ac3 and, for example, the evaporation temperature of the coating on the blank). A furnace system may be used for this purpose. Depending on specific needs, the furnace system may be supplemented with additional heaters, for example, induction heaters or infrared heaters. Heating the blank reduces its strength and increases its deformability, thus facilitating the hot stamping process.

[0006] Several ultra-high strength steels (UHSS) for hot stamping and hardening are known. The blanks can be made of coated or uncoated boron steels, such as Usibor® (22MnB5), available from ArcelorMittal.

[0007] Hot mold quenching is sometimes referred to as "press hardening" or "hot stamping," and these terms are used interchangeably throughout this disclosure.

[0008] Typical vehicle components that can be manufactured using the HFDQ process include door beams, bumper beams, cross / side members, A / B pillar reinforcements, front and rear rails, seat cross members, and roof rails.

[0009] Hot forming of boron steels is becoming increasingly popular in the automotive industry due to their excellent strength and formability. Thus, many structural components that were traditionally cold formed from mild steel are being replaced with hot-formed equivalents, which offer significant improvements in strength. This allows the thickness (and therefore weight) of the material to be reduced while maintaining the same strength. However, hot-formed components offer very low levels of ductility and energy absorption in the as-formed state.

[0010] To improve ductility and energy absorption in specific regions of a component, it is known to introduce softer regions within the same component. This results in locally improved ductility while maintaining the required high strength overall. By locally tailoring the microstructure and mechanical properties of specific structural components so that they contain very high strength (very hard) regions, i.e., high ultimate tensile strength and high yield strength, and regions of increased ductility (softer) regions, i.e., low ultimate tensile strength, low yield strength, and increased elongation before fracture, it may be possible to improve their overall energy absorption, maintain their structural integrity during crash situations, and reduce their overall weight. Such soft zones can also favorably alter the kinematic behavior of the component in the event of collapse upon impact.

[0011] A known method for creating a ductile region ("soft zone" or "soft zone") in a vehicle structural component involves providing a tool including a pair of complementary upper and lower die units, each unit having a separate die element (steel block). The blank to be hot-formed is preheated, for example by a furnace system, to a predetermined temperature, for example above the austenitizing temperature, to reduce its strength, i.e., to facilitate the hot stamping process.

[0012] Die elements may be designed to operate at different temperatures to achieve different cooling rates in different regions of the component being formed during the quenching process, resulting in different material properties in the final product, such as softer regions that generally have lower ultimate tensile strength and yield strength but allow for greater elongation before fracture. For example, one die element may be cooled to quench the corresponding region of the component being produced at a higher cooling rate, thereby rapidly reducing the component's temperature and achieving a hard martensitic microstructure. Another adjacent die element may be heated to ensure that the corresponding portion of the component being produced is cooled at a lower cooling rate, for example, to achieve a softer microstructure containing bainite, ferrite, and / or pearlite. Such regions of the component may remain at a higher temperature than the remainder of the component when it exits the die.

[0013] Other methods for obtaining hot stamped components with regions of different mechanical properties include, for example, controlled or differential heating before stamping and localized heat treatment after the stamping process to change the local microstructure and obtain different mechanical properties. Further possibilities include the use of patchwork blanks and tailor welded blanks (TWBs), which combine different thicknesses and / or materials of the blanks.

[0014] Several methods of differential heating before stamping are known. In one example, a nozzle or set of nozzles can emit a fluid flow, e.g., compressed cooling air, toward a portion of the blank to be cooled, e.g., while the bank is still in the furnace system. Other portions of the blank can be maintained at a higher temperature. This allows for a blank to have a tailored temperature profile along its length and / or width. In some examples, the blank can be further heated in an oven before being subjected to the stamping process.

[0015] In another example, an array of independently controllable infrared heaters can be used to control the temperature along the blank.

[0016] Some elements of an automobile's structural framework, such as the pillars (A-pillar, B-pillar, C-pillar), integral door rings, rockers, floors, and loom rockers, among others, can have one or more regions with a substantially U-shaped (also known as a "hat" shape) cross section. These structural components can be manufactured in a variety of ways and can be made from a variety of materials. Lightweight materials that improve energy absorption during a crash while maintaining the integrity of the vehicle are desired.

[0017] Throughout this disclosure, a U-shaped cross section can be understood to refer to a structural member having, in cross section (generally, a transverse plane substantially perpendicular to the longitudinal axis of the structural member), a bottom wall and two side walls. U-shaped cross sections are generally known for their favorable moment of inertia to weight ratio. The two side walls may form an obtuse angle with the bottom wall, e.g., between 90° and 135°. The two side walls may include outwardly extending lateral flanges. The bottom wall and side walls may be substantially straight, but may also include transitions, curved portions, recesses, or protrusions.

[0018] In addition to the ultra-high strength steels mentioned above, more ductile steels can be used in parts of the structural framework that require energy absorption. Examples of ductile steels include Ductibor® 500, Ductibor® 1000, and CRL-340LA.

[0019] UHSS can exhibit high tensile strengths of 1,500 MPa and even 2,000 MPa or more, especially after press hardening. Upon hardening, UHSS can have a martensitic microstructure. This microstructure allows for increased ultimate tensile and yield strength per unit of weight.

[0020] Some ductile steels may also be heated and pressed (i.e., used in hot stamping processes), but do not have a martensitic microstructure after the process. As a result, they have lower tensile and yield strengths than UHSS, but they have higher elongation to failure.

[0021] Although ductile steel allows for energy absorption by structural components, it may not be easy to control and predict how the structural components may behave during a vehicle crash. Furthermore, it is preferable that the overall weight of the vehicle framework be as small as possible to reduce fuel consumption. Also, it is not easy to increase energy absorption while maintaining a certain structural integrity of the structural components.

[0022] The present disclosure seeks to provide improvements in weight reduction and controlled deformation and energy absorption by a one-piece rear rail structure for a vehicle framework when subjected to a load. Summary of the Invention

[0023] In a first aspect, a one-piece rear rail structure for a vehicle framework is provided. The one-piece rear rail structure includes a first rear rail, a second rear rail, and one or more cross members connecting the first rear rail to the second rear rail. The one-piece rear rail structure is formed by deforming a single bonded blank. The single bonded blank includes at least one first blank joined to a second blank such that the first blank partially overlaps the second blank to form one or more overlapping regions.

[0024] This aspect provides a structure with a simplified manufacturing process. Because the one-piece rear rail structure is manufactured by deforming a single blank, manufacturing time and associated costs can be reduced. Furthermore, other post-manufacturing processes, such as welding, that may affect the mechanical properties of the components are avoided. At the same time, the provided structure can have sufficient strength, rigidity, and energy absorption to protect vehicle passengers in the event of an impact, such as a rear impact.

[0025] Because the combined blank formed into a one-piece rear rail structure is comprised of several blanks, they can be configured to absorb impact energy and transfer impact loads to appropriate areas of the vehicle framework, thereby preventing deformation of safety zones within the vehicle. The blanks that together form the combined blank are referred to herein as "blanks," but may also be considered "sub-blanks," meaning blanks that form part of a larger blank. One or more of the individual blanks combined into the combined blank may also include smaller blanks or sub-blanks.

[0026] Additionally, the overlapping areas locally increase the mechanical properties of these areas of the structure, allowing the structure to tailor its strength and stiffness as needed, thereby improving the overall strength of the structure per unit of weight. At the same time, the overlapping areas provide localized limits to deformation, preserving the interior space of the vehicle.

[0027] Throughout this disclosure, references to "mechanical properties of a part" may be understood as mechanical properties of the material forming said part. Thus, unless otherwise specified, comparisons of mechanical properties of parts, components, or other parts are to the material, and not to the geometry or other particularities of the material.

[0028] Higher mechanical properties may be understood herein as higher ultimate tensile strength and / or higher yield strength, while lower mechanical properties may be understood herein as lower ultimate tensile strength and / or lower yield strength. Ultimate tensile strength and yield strength are considered herein as material properties of the material after the manufacturing process. Ultimate tensile strength and yield strength can be determined in a standard tensile strength test, for example, using A30, A50, or A80 test specimens in a quasi-static load test.

[0029] Comparisons between lower and higher mechanical properties should be performed using the same test conditions and specimen size. To compare the yield strength of different sections, specimens made of the same material as the main soft zone section can be prepared and tested on a universal testing machine (UTM).

[0030] In an example, the one-piece rear rail structure may be fabricated by hot stamping, and the structure may be formed in a single forming step. Further, if desired, when applying hot stamping, different regions of the structure may be subjected to different temperature treatments, resulting in regions with different mechanical properties.

[0031] In an example, the overlap region substantially corresponds to one or more transitions between one of the rails and one of the cross members. This results in a connection between the rail and the cross member with improved mechanical properties, enhancing the overall kinematic behavior of the structure. Thus, the transition between the rail and the cross member may be designed to have higher mechanical properties than the remainder of the one-piece rear rail structure.

[0032] In some examples, the first rear rail and the second rear rail include a first region configured to attach the one-piece rear rail structure to the chassis, and the first region has an ultimate tensile strength after hot stamping of 1,500 MPa or greater, which provides a secure connection between the one-piece rear rail structure and the vehicle chassis and creates a robust load path for transferring loads from the impact point to specific components of the vehicle framework.

[0033] In some examples, the first rear rail and the second rear rail include a second region that is more ductile than the first region. The second region may have a hot stamped ultimate tensile strength of 700 to 1200 MPa and a hot stamped yield strength of 500 to 900 MPa. This second region is more ductile than the rest of the rear rail, allowing for increased energy absorption during impact. This can reduce vehicle acceleration after impact, control rail deformation, and avoid loads or deformations reaching other regions of the integral rear rail structure.

[0034] In some embodiments, the first and second regions have different microstructures, which may be achieved by applying different temperature treatments to the first and second regions. Thus, in some embodiments, a single blank having a substantially homogeneous material composition may be used to form a rear rail having distinct regions with different mechanical properties.

[0035] In some instances, a single bonded blank can include different thicknesses and / or materials. Regions of increased thickness can be located in areas where stress loads and concentrations may be higher in the event of an impact. Specifically, regions of increased thickness can be formed by overlapping two blanks. Furthermore, materials with higher mechanical properties can be located in areas intended to reduce structural deformation, while materials with lower mechanical properties can be located in areas intended to absorb impact energy and deform during impact.

[0036] In some examples, at least one of the rail and cross-member of the integrated rear rail structure has a substantially U-shaped cross-section. The U-shaped cross-section includes a bottom wall, a first side wall, a second side wall, a first lateral flange projecting outwardly at a terminal end of the first side wall, and a second lateral flange projecting outwardly at a terminal end of the second side wall. The U-shaped cross-section increases the moment of inertia of the region in which it is formed, improving the member's resistance to impacts, particularly impacts at an angle relative to the longitudinal direction of the member.

[0037] In an example, the integrated rear rail structure can further include a cover plate attached to the rear rail and substantially closing the cross section of the U. The cover plate can be made of the same or a different material as the rear rail and can increase energy absorption and stiffness of the integrated rear rail structure.

[0038] In some examples, the integrated rear rail structure can also include at least a portion of the floor panel. For example, the rear rails can be connected to one another by a portion of the floor panel. In examples, the floor panel can be formed by a blank that is joined to another blank to form a combined blank. The floor panel can include any of the features, such as materials, disclosed herein with respect to the rear rail and cross member. In examples, the floor panel can be integrated into the cross member, i.e., have a structural member connecting the first and second rear rails.

[0039] In a further aspect, a method for manufacturing a one-piece rear rail structure for a vehicle framework according to the present disclosure is provided, the one-piece rear rail structure including first and second rear rails and one or more cross members.

[0040] The method includes providing a combined blank. The method further includes providing a first blank and a second blank and positioning the first blank and the second blank such that the first blank partially overlaps the second blank in an overlap region. The method further includes joining the first blank to the second blank in the overlap region to form a combined blank. The method further includes at least partially heating the combined blank above an austenitizing temperature and press-hardening the heated combined blank to form a one-piece rear rail structure.

[0041] This method can reduce manufacturing costs associated with multi-component structures requiring several manufacturing and assembly steps. Thus, the disclosed method allows, among other things, to reduce manufacturing time and manufacturing facility floor space. Furthermore, the method provides a one-piece rear rail structure with enhanced mechanical properties, both in terms of impact resistance and deformation behavior. Furthermore, the disclosed method provides a one-piece rear rail structure with an improved impact protection-to-weight ratio compared to alternative approaches.

[0042] A combined blank is herein understood to mean a blank, e.g., a metal sheet or flat metal plate, forming a blank, e.g., a main component. The combined blank may be at least partially made of hardenable steel, in particular boron steel. The combined blank's thickness may typically be 1-2.5 mm. The combined blank may be produced by joining two or more blanks together. The blanks that make up the combined blank may themselves be made of further (sub-blanks); for example, one of the blanks that make up the combined blank, which is joined to another blank by overlapping, may itself be a tailor-welded blank (TWB).

[0043] In some examples of this method, at least one of the overlap areas between the first blank and the second blank can substantially correspond to the transition between the rail and the cross member. Traditionally, the rail and cross member are manufactured separately and then joined together. By joining several blanks to obtain a single, integrally formed rear rail structure, some material is lost at the transition between the rail and the cross member. To compensate for this material loss, strength can be increased locally by increasing thickness by creating overlap areas precisely where needed. Such overlaps are relatively small and therefore can be more effective than the use of tailor-welded blanks (TWBs), which require different materials or thicknesses over larger areas. It is also more efficient and effective than, for example, high-pressure die-casting of aluminum, which requires more aluminum to achieve the same strength as a hot-stamped UHSS component.

[0044] In some example methods, the first blank and the second blank may be attached together by spot welding.

[0045] In some further examples, the first region of the one-piece rear rail structure can have an ultimate tensile strength after press hardening of 1,500 MPa or greater, and the second region of the one-piece rear rail structure can have an ultimate tensile strength after press hardening of 700 to 1,200 MPa.

[0046] The first region can be configured to substantially withstand loads during an impact. The first region can be configured to connect the integrated rear rail structure to other structural components of the vehicle, such as the chassis. Furthermore, the second region can be configured to absorb energy and deform during an impact, cushioning acceleration experienced by vehicle occupants and limiting the transfer of loads to other vehicle components.

[0047] In some instances, a first region of the combined blank is subjected to a different heat treatment than a second region of the combined blank, which allows for the formation of regions with different mechanical properties, for example, due to differences in microstructure.

[0048] Non-limiting examples of the present disclosure are described below with reference to the accompanying drawings. [Brief explanation of the drawings]

[0049] [Figure 1] FIG. 2 is a schematic diagram illustrating a bottom view of an example integrated rear rail structure for a vehicle according to the present disclosure. [Figure 2] FIG. 10 is a schematic illustration of an exploded view of a portion of another example integrated rear rail structure according to the present disclosure. [Figure 3] 2 is a schematic cross-sectional view across the plane AA' of FIG. 1; FIG. [Figure 4] FIG. 10 is a schematic cross-sectional view of another example of an integrated rear rail structure according to the present disclosure. [Figure 5] 10A-10C are schematic diagrams illustrating another exemplary view of a portion of another example integrated rear rail structure. [Figure 6A] 1 is a schematic top view of another example of an integrated rear rail structure for a vehicle according to the present disclosure. FIG. [Figure 6B] FIG. 6B is a schematic diagram illustrating a bottom perspective view of the example integrated rear rail structure of FIG. 6A. [Figure 7A] FIG. 10 is a schematic diagram of a single blank prior to forming another example of a one-piece rear rail structure. [Figure 7B] FIG. 7B shows a schematic representation of a portion of a component obtained after hot stamping of the single blank of FIG. 7A. [Figure 7C] FIG. 7B shows a schematic representation of a portion of a component obtained after hot stamping of the single blank of FIG. 7A. [Figure 8] 10A-10C are schematic diagrams illustrating a single blank prior to forming of a further example of a one-piece rear rail structure. [Figure 9] 1 is a flowchart of a method for manufacturing a structural component at least partially configured to support bending loads. DETAILED DESCRIPTION OF THE INVENTION

[0050] The drawings depict exemplary embodiments and are used solely as an aid in understanding the claimed subject matter and are not intended to be limiting in any way.

[0051] FIG. 1 schematically illustrates a bottom view of an example of an integrated rear rail structure 100 for a vehicle framework. The integrated rear rail structure 100 includes a first rear rail 10, a second rear rail 20, and one or more cross members 30, 40 connecting the first rear rail 10 to the second rear rail 20. Furthermore, the integrated rear rail structure 100 is formed by deforming a single blank. The single blank includes at least one first blank joined to a second blank such that the first blank partially overlaps the second sub-blank to form one or more overlap regions 50.

[0052] 1, the integrated rear rail structure 100 includes two cross members 30, 40, although other numbers of cross members may be used in other examples. For example, the integrated rear rail 100 may include only one cross member, or three or more cross members. Furthermore, the cross members 30, 40 may be distributed in different ways; for example, the spacing between the cross members 30 and 40 may be increased or decreased depending on the specifications of the integrated rear rail structure 100.

[0053] Because the rear rail structure disclosed herein is made of a single (integrally formed) element, there are no separate components that qualify as rails or cross members, and the boundary between them is not very clear. Thus, the terms "rail portion" and "cross member portion" may be used to refer to portions of the same element that function as rails or cross members.

[0054] In the illustrated example, the one-piece rear rail structure 100 may be fabricated by hot stamping. For example, it may be manufactured by a direct hot stamping manufacturing process or an indirect hot stamping manufacturing process. In other examples, the one-piece rear rail structure 100 may be manufactured by cold stamping or other manufacturing processes. Further details of the component manufacturing processes are described in connection with FIGS. 6-8.

[0055] In some examples, the one-piece rear rail structure 100 can be made of a boron steel such as Usibor®, for example, Usibor® 1500 (or any 22MnB5 steel with or without a protective coating), Usibor® 2000 (or any 37MnB5 steel), or any martensitic or ultra-high strength steel (UHSS). Usibor® is commercially available from ArcelorMittal.

[0056] Usibor® 1500 is supplied in the ferrite-pearlite phase. This is a fine grain structure distributed in a homogeneous pattern. Its mechanical properties are related to this structure. After heating, a hot stamping process, and subsequent rapid cooling, a martensitic microstructure is created. This results in a significant increase in tensile strength and yield strength.

[0057] The composition of Usibor® 1500 is summarized below in weight percent (the remainder is iron (Fe) and impurities): Maximum carbon (C) (%): 0.25 Maximum silicon (Si) (%): 0.4 Maximum manganese (Mn) (%): 1.4 Maximum phosphorus (P) (%): 0.03 Maximum sulfur (S) (%): 0.01 Aluminum (Al) (%): 0.01-0.1 Maximum Titanium (Ti) (%): 0.05 Maximum Niobium (Nb) (%): 0.01 Maximum copper (Cu)(%):0.20 Maximum boron (B) (%): 0.005 Maximum Chromium (Cr) (%): 0.35

[0058] Usibor® 2000 is another boron steel with even higher strength. After the hot stamping die quenching process, Usibor® 2000's yield strength may be 1300 MPa or greater, and its ultimate tensile strength may be greater than 1800 MPa.

[0059] The composition of Usibor® 2000 is summarized below in weight percent (the remainder is iron (Fe) and impurities): Maximum carbon (C) (%): 0.36 Maximum silicon (Si) (%): 0.8 Maximum manganese (Mn) (%): 0.8 Maximum phosphorus (P) (%): 0.03 Maximum sulfur (S) (%): 0.01 Aluminum (Al) (%): 0.01-0.06 Maximum Titanium (Ti) (%): 0.07 Maximum Niobium (Nb) (%): 0.07 Maximum copper (Cu)(%):0.20 Maximum boron (B) (%): 0.005 Maximum Chromium (Cr) (%): 0.50 Maximum Molybdenum (Mb) (%): 0.50

[0060] The 22MnB5 may be provided with an aluminum-silicon coating to avoid decarburization and scale formation during the forming process.

[0061] Several 22MnB5 steels with similar chemical compositions are commercially available. However, the exact amounts of each component in 22MnB5 steel may vary slightly depending on the manufacturer. Other ultra-high strength steels include BTR165, available from Benteler.

[0062] In an example, the integrated rear rail structure 100 may include members made of different materials. For example, the first rear rail 10 and the second rear rail 20 may be made of UHSS, such as 22MnB5 or another boron steel, in some areas and a more ductile steel in other areas, and the cross members 30 may be made of UHSS.

[0063] Additionally, the type of UHSS can be varied depending on requirements. For example, 22MnB5 or Usibor® 1500 can be used in the stiffer regions of the rail, while the first cross member 30 and second cross member 40 can be made of, for example, 37MnB5 or Usibor® 2000. Other materials can be selected to form the integral rear rail structure 100 depending on the desired dynamic response and mechanical properties. Furthermore, a given member can have regions made of different materials. For example, the first rear rail 10 and the second rear rail 20 can have a first region 11 made of Usibor® 2000 and a second region 12 made of Usibor® 1500 or Ductibor® 1000.

[0064] Ductibor® is a steel with much higher ductility than Usibor® material, and components made from this material can be effective at absorbing energy during impact. Ductibor® 500 has a yield strength of 400 MPa or greater and an ultimate tensile strength of 550 MPa or greater.

[0065] The composition of Ductibor® 500 is summarized below in weight percent (the remainder is iron (Fe) and impurities): Maximum carbon (C) (%): 0.1 Maximum silicon (Si) (%): 0.5 Maximum manganese (Mn) (%): 1.7 Maximum phosphorus (P) (%): 0.03 Maximum sulfur (S) (%): 0.025 Aluminum (Al) (%): 0.015-0.2 Maximum Titanium (Ti) (%): 0.09 Maximum Niobium (Nb) (%): 0.10 Maximum copper (Cu)(%):0.20 Maximum boron (B) (%): 0.001 Maximum Chromium (Cr) (%): 0.20

[0066] Ductibor® 1000 may have a yield strength of 800 MPa or greater and an ultimate tensile strength of 1000 MPa or greater. The composition of Ductibor® 1000 is summarized below in weight percent (the remainder being iron (Fe) and impurities): Maximum carbon (C) (%): 0.10 Maximum silicon (Si) (%): 0.6 Maximum manganese (Mn) (%): 1.8 Maximum phosphorus (P) (%): 0.03 Maximum sulfur (S) (%): 0.01 Aluminum (Al) (%): 0.01-0.1 Maximum Titanium (Ti) (%): 0.05 Maximum Niobium (Nb) (%): 0.10 Maximum copper (Cu)(%):0.20 Maximum boron (B) (%): 0.005 Maximum Chromium (Cr) (%): 0.20

[0067] As shown in Figure 1, the overlap region 50 can substantially correspond to one or more transitions between one of the rails 10, 20 and one of the cross members 30, 40. This improves the mechanical properties of the connection between the members. The transition between the rail portion and the cross member is the region where the rail portion meets the cross member portion, in other words, where the rail portion changes from a substantially longitudinally disposed body to a substantially transversely disposed body.

[0068] In this illustrated example, the first rear rail 10 and the second rear rail 20 may include first regions 11, 21 configured to attach the integrated rear rail structure 100 to the chassis. The stiffness and strength required in the regions that interface with the chassis may be higher. The first regions 11, 21 may be made of a suitable UHSS, such as 22MnB5, and may have an ultimate tensile strength after hot stamping of 1.500 MPa or greater, more specifically 1.800 MPa or greater.

[0069] Additionally, the first and second rear rails 10 and 20 may also include second regions 12, 22 having a hot stamped ultimate tensile strength of 700 to 1200 MPa and a hot stamped yield strength of 500 to 900 MPa. These second regions 12, 22 may be configured to absorb energy and deform during an impact. These second regions 12, 22 may be formed of Ductibor® or other suitable steel that is more ductile than the steel for the first region. The transition between the second regions 12, 22 and the remainder of the rear rails may include an overlap region. Alternatively, the second regions 12, 22 and the remainder of the rear rails 10, 20 may be formed as tailor-welded blanks, i.e., individual blanks may be welded together in an edge-to-edge welding process ("butt joint").

[0070] Additionally, different regions of the one-piece rear rail structure 100 may be made using a blank of the same (base) material but with different local microstructures. For example, the first region 11, 21 and the second region 12, 22 may be made of materials having substantially the same composition but different local microstructures. This can be achieved by applying different heat treatments before, during, or after the stamping process. For example, local heat treatment using induction heating or a laser after the stamping process can result in the regions 11, 21, 12, 22 having different mechanical properties.

[0071] In the example shown in FIG. 1, a first region 11, 21 of the rear rail 10, 20 can have a martensitic microstructure, and a second region 12, 22 of the rail can have a microstructure including bainite, ferrite, and / or pearlite.

[0072] The overlap region 50 may have a width of 10 mm to 100 mm, specifically 20 mm to 60 mm, more specifically 20 mm to 50 mm, i.e., the overlap region extends across the entire width of the cross member 30 and may extend into the rail portion by, for example, 20 mm to 60 mm.

[0073] The area of ​​the overlapping area at the transition between one of the rear rails and the crosspiece may be, for example, 20 to 600 cm 2 , specifically 30 to 500 cm 2 , more specifically 40-450cm 2 may be.

[0074] 2 schematically illustrates an exploded view of a portion of another example of an integrated rear rail structure 100 according to the present disclosure. The exploded view shows the first rear rail 10 and cross member 30. While the rail and cross member are shown as separate components in this exploded view, it will be apparent that in reality they are formed as a single, integral structure.

[0075] 2 shows the overlap area 50 between these two members. As can be seen, the first rear rail 10 and the cross member have mating shapes in the overlap area 50 as a result of a single forming operation. Note that the overlap area 50 is marked by a rectangular box with dashed lines and is only partially shown here because the overlap area 50 can extend across the entire width of the cross member 30.

[0076] 2 further illustrates that the first rear rail 10 can have a substantially U-shaped cross-section. The U-shape has a bottom wall 15, a first side wall 16, a second side wall 17, and a first lateral flange 18 that projects outwardly at an end of the first side wall 16. Although not shown, the U-shaped cross-section may also have a second lateral flange that projects outwardly at an end of the second side wall 17 in this example (e.g., at another longitudinal position) or other examples.

[0077] In some examples, the side flanges 18 may have a different microstructure than the sidewalls to which they are attached. More specifically, the side flanges may have lower mechanical properties than the sidewalls to which they are located to facilitate connection with other components, such as other vehicle framework components. For example, localized heat treatment may be performed on the portions of the flanges that will be joined to adjacent structures, or differential cooling may be applied within a heat press apparatus.

[0078] 2 illustrates that the cross-member 30 may have a U-shaped cross-section. Additionally, any member of the integrated rear rail structure 100 may define other cross-sectional shapes. For example, any member of the integrated rear rail structure 100 may define an L-shaped cross-section along at least a portion of its length, a W-shaped cross-section along a portion of its length, or other cross-section.

[0079] Although not shown in the example of FIG. 2 , the bottom wall 15 may be curved along its bottom or may include a recess or protrusion. This also applies to the sidewalls 16, 17, which are not necessarily completely straight. The sidewalls 16, 17 may include straight sections with curved transition zones between the straight sections. In addition, the sidewalls 16, 17 may or may not be symmetrical. For example, the height of the first sidewall 16 may be different from the height of the second sidewall 17. In some examples, the height of the first sidewall 16 and / or the second sidewall 17 along its length may also vary. In examples, the width of the bottom wall 15 may also vary along its length. Furthermore, the width of the bottom wall 15 may be different from the height of the first sidewall 16 and / or the second sidewall 17. Other examples may include any combination of the above examples.

[0080] FIG. 2 also shows that the one-piece rear rail structure can include a cover plate 60. The cover plate 60 may be formed by one or more cover components 61, 62. Indeed, in this example, the cover plate 60 includes a first cover component 61 configured to close the U-shaped cross section of the first rear rail 10 and a second cover component 62 configured to close the U-shaped cross section of the cross member 30. As mentioned above, the cover plate 60 may also be manufactured in a single forming step. The cover plate 60 can be shaped to at least partially close the cross section of the member (U-shaped or other shape) to increase rigidity, particularly torsional rigidity.

[0081] In the example shown in FIG. 2 , the first cover component 61 includes a vertical flange 63 configured to be coupled to the vertical region of the second side wall 17 of the first rear rail 10. Additionally, the first cover component 61 includes a horizontal flange 64 configured to be coupled to the first flange 18 of the rear rail 10. Thus, the first cover component 61 may be coupled to the first rear rail 10 via the flanges 63, 64 by welding. Additionally, the second cover component 62 may be coupled to the cross member 30 via the flange in a similar manner, i.e., by welding. Both remote laser welding and spot welding may be used.

[0082] Additionally, the first cover component 61 and the second cover component 62 may have different mechanical properties. Indeed, the cover components 61, 62 may also have regions with different mechanical properties, for example, the flanges 63, 64 may be made of a material with lower mechanical properties than the remainder of the cover component 61. The cover plate 60 according to the present disclosure may include other numbers of cover components, i.e., three or more, as well as other relative sizes and geometric shapes.

[0083] Figure 3 shows a schematic cross-sectional view across plane A-A' of Figure 1. While Figure 3 illustrates the transition between a portion of first rear rail 10 and a portion of cross-member 30, the same applies to transitions between other members of integrated rear rail structure 100. In this example, first rear rail 10 includes a U-shaped cross-section having a bottom wall 15, a first side wall 16, a second side wall 17, and a first lateral flange 18 projecting outwardly at the end of first side wall 16. Flange 18 overlaps a portion of cross-member 30, forming an overlap region 50.

[0084] In this example, the rail section flange 18 and cross member 30 are attached together by spot welding. Note that spot welds 51 are shown schematically as circular dots. Multiple spot welds 51 can be used to connect the first rear rail 10 to the cross member 30. In other examples, other joining techniques can be used, particularly other welding techniques such as laser welding. Note also that while the spot welds are shown on the final product, in practice the spot welds (or other joints) are performed before the blank is deformed, i.e., before the hot stamping process. Therefore, the welds can be performed on a flat blank, which facilitates welding.

[0085] As previously mentioned, the width of the overlap region 50 can be tailored to the specifications of the structure 100. Thus, if the integrated rear rail structure 100 is designed to withstand higher impact loads, e.g., a vehicle with a higher mass, the width can be increased.

[0086] 3 also shows that the connection between the cross member 30 and the first rear rail 10 leaves an open space 55 where other vehicle components, such as electronic components, may be placed. In this example, the aspect of making the rear rail structure as a one-piece structure creates extra space for vehicle components.

[0087] Figure 4 is similar to Figure 3 but shows a cross-sectional view of another example of a one-piece rear rail structure 100. More precisely, the one-piece rear rail structure 100 of Figure 4 includes an overlap region 50 located on the rear rail bottom wall 15 having a U-shaped cross section. As described in connection with Figure 3, multiple spot welds 51 can be used to connect the structural members.

[0088] 4, the combined blank that is transformed to form the one-piece rear rail structure 100 is formed from multiple blanks. Thus, a first blank may be formed to have a substantially L-shaped cross-section, and a second blank may be formed to mate with the first blank to form the U-shaped rear rail 10. Additionally, the second blank may also form a U-shaped cross-section (not visible in the illustrated view).

[0089] FIG. 5 schematically illustrates another portion of a further example of an integrated rear rail structure 100, including a cover plate 60. In this example, the integrated rear rail structure 100 includes a first rear rail 10 and a cross member 30, both of which have a closed cross section. A second rear rail (not shown) may also have a closed cross section. Furthermore, FIG. 6 illustrates that the overlap region 50 substantially corresponds to the transition between the rail 10 and the cross member 30, and that the arrangement between these structural members can provide a clear space 55 in which other vehicle components, such as electronic components, can be located.

[0090] As described in connection with Figure 2, the closed cross section can be formed by attaching a cover plate 60 to the rear rail and cross member, for example, to the first rear rail 10 and cross member 30, both of which have a U-shaped cross section. The cover plate 60 may be attached to the rear rail and cross member by spot welding.

[0091] 6A and 6B schematically illustrate another example of an integrated rear rail structure 100 for a vehicle according to the present disclosure. Fig. 6A illustrates a top view of the integrated rear rail 100, and Fig. 6B illustrates a bottom perspective view of the integrated rear rail 100.

[0092] In the example of FIG. 6A, the overlap region 50 is shown with diagonal lines.

[0093] 6A shows that the one-piece rear rail structure 100 includes a first rear rail 10, a second rear rail 20, and a cross member 30. The one-piece rear rail structure 100 can be made by hot stamping a single (combined) blank. In this example, the combined blank is made from seven smaller blanks: two blanks for each of the rails and three blanks that make up the cross member.

[0094] The cross member 30 of the integrated rear rail structure 100 may be made from three blanks 31, 32, 33 configured to connect the first rear rail 10 to the second rear rail 20. Thus, the cross member 30 may be made from two blanks 31, 33 that substantially correspond to the transition between the rails 10, 20 and the cross member 30, and a central blank 32 that connects the two side components 31, 33 to one another.

[0095] As can be seen in Figure 6A, the overlap region 50 between different blanks may be designed to have different widths. For example, the overlap region 50, which substantially corresponds to the transition between the rail 10, 20 and the cross member 30, may have a width of, for example, 30 mm to 60 mm, in combination with substantially the full width of the cross member (i.e., across the U-shape, preferably including the flanges of the U-shape). Alternatively, the overlap region may extend across the full width of the rear rail 10, 20, e.g., across the full width of the cross member, at least in the transition region of the rail to the cross member.

[0096] Additionally, the width of the overlap region 50 between the blanks 31, 33 and the central blank 32 may be between 10 mm and 30 mm. In this case, the overlap extends across the width of the central blank 32 (i.e., the width of the cross member), and the overlap extends, for example, between 10 mm and 30 mm along the transverse direction of the vehicle (the longitudinal direction of the cross member). The width of the overlap region 50 can be varied to adapt the mechanical properties of the integrated rear rail structure 100 to different applications.

[0097] Furthermore, FIG. 6A illustrates that the rear rails 10, 20 can include two regions made of materials with different mechanical properties. For example, the first region 11 of the first rear rail 10 and the first region 21 of the second rear rail 20 can each be made of a steel with high mechanical properties, such as 22MnB5 or 37MnB5. Furthermore, the second region 12 of the first rear rail 10 and the second region 22 of the second rear rail 20 can each be made of a steel with lower mechanical properties, such as a more ductile steel. The blanks for the first region 11, 12 and the second region 21, 22 of each rear rail 10, 20 can also define an overlap region 50. The width of the overlap region within the rail can be at least 10 mm, specifically 10 to 50 mm (i.e., the overlap region extends substantially across the width of the rail section, with an overlap of 10 to 20 mm in the longitudinal direction of the vehicle).

[0098] In some examples, cross member 30 may be formed of materials having different mechanical properties. For example, the blanks that make up sides 31, 33 of cross member 30 may be made of the same steel or a different material as the blank that makes up central portion 32 of cross member 30. The material used to manufacture cross member 30 may be any of the Usibor® and Ductibor® materials disclosed above, or any other suitable steel.

[0099] 6B illustrates that the first and second rear rails 10 and 20 and the cross-member 30 may define a substantially U-shaped cross-section. Additionally, it also illustrates that the cross-sectional geometry of the one-piece rear rail 100 may vary along its length and width. Additionally, the cross-section may include one or more flanges, which may also vary in different regions of the first and second rear rails 10 and 20 and the cross-member 30.

[0100] In the example shown, it can be seen that the rear rail may have a (mounting) flange on the inside, but no flange on its outside, or only a flange from the transition to the front of the cross member.

[0101] 6, and in other examples, the blanks forming the overlap region can be joined using spot welding or laser welding. Laser welding can include the use of multiple "stitches," such as short, straight welds. Laser welding can additionally or alternatively include continuous welds along one or more of the overlap regions, particularly along all edges.

[0102] The use of longer welds rather than spot welds avoids stress concentrations that can occur around spot welds, which can prevent or delay rupture in the event of a vehicle impact or collision.

[0103] The use of continuous welds along the edges of overlapping areas may be preferable when fluid tightness is required. Avoiding fluid, e.g., liquid, leakage may be important in certain areas of a vehicle. The use of spot welds leaves some space between the sub-blanks or blanks assembled together to form the combined blank, allowing fluids to escape through these small spaces.

[0104] The use of longer welds, particularly laser welding, can also improve the stamping process and avoid potential separation between the blanks or sub-blanks during the stamping process.

[0105] 7A schematically illustrates a top view of an example of a combined blank 1000 for forming a one-piece rear rail structure 100 according to the present disclosure. The combined blank 1000 in this example includes four blanks 1100, 1200, 1300, 1400. The first blank 1100 and the second blank 1200 may be configured to form the rear rail structures 10, 20, and the third and fourth blanks 1300, 1400 may be configured to form the cross members 30, 40.

[0106] The blanks 1100, 1200, 1300, and 1400 may be made of different materials and / or thicknesses. For example, the first blank 1100 and the second blank 1200 may be made of UHSS of a given thickness, or may be formed as tailor-welded blanks including a more resistant material, such as UHSS, and a more ductile material, for example, near the load-bearing end. The third and fourth blanks may be formed of UHSS or other steel, each having a different thickness of the same.

[0107] All of the blanks can be joined together to form the combined blank 1000. The combined blank 1000 can then be subjected to a forming operation, such as a hot stamping operation, to form the unitary rear rail structure 100 as disclosed above.

[0108] In some examples, portions of the structure (or portions of the combined blank 1000) can be subjected to a different heat treatment than other portions of the structure. For example, the first portions 1110, 1210 originally associated with the first blank 1100 and the second blank 1200 can be cooled at a high cooling rate to rapidly reduce the temperature of the portions and obtain a hard martensitic microstructure, while the second portions 1120, 1220 originally associated with the first blank 1100 and the second blank 1200 may be cooled at a slower cooling rate to obtain a softer microstructure including, for example, bainite, ferrite, and / or pearlite.

[0109] In the example shown in FIG. 7A, all blanks 1100, 1200, 1300, 1400 have a thickness of 1 to 2.5 mm, although blanks of other thicknesses can also be used.

[0110] Additionally, some of the blanks 1100, 1200, 1300, 1400 in Figure 7A form overlap regions 1500. In particular, one or more transitions between a rail portion and a crosspiece portion may be reinforced through the use of overlap regions, which may be located substantially or primarily within the rail portion.

[0111] 7B and 7C show a schematic representation of a portion of an example of the resulting one-piece rear rail structure, where the overlap region 50 at the transition between the rail portion 20 and the crosspiece portion 30 may be a seed.

[0112] It can be seen that the overlap region has a substantial length and width to provide increased stiffness and strength at the transition between the rail and the cross member. As shown in Figure 7B, the length of the overlap region may be, for example, 15-30 cm, particularly 20-25 cm. As seen in the bottom view of Figure 7, the overlap region extends approximately 12-20 cm along the length of the cross member and substantially across the entire U-shaped bottom of the rail section.

[0113] In this example, the width of the overlap region corresponds to the width of the cross-member portion 30. Also, the width of the overlap region can optionally expand both forward and backward in the rail portion, as shown in Figure 7C. For example, the transition region can expand backward and forward by 2 to 10 cm, specifically 3 to 8 cm.

[0114] As described in connection with the one-piece rear rail structure 100, the combined blank 1000 can include a different number of blanks. For example, the combined blank 1000 can include two blanks, three blanks, or more than four blanks.

[0115] FIG. 8 schematically illustrates a top view of another example of a combined blank 1000 for forming a one-piece rear rail structure 100 according to the present disclosure. The combined blank of FIG. 8 also includes four blanks 1100, 1200, 1400, and 1600. The first blank 1100 and the second blank 1200 are configured to form the rear rail structure (10, 20 in FIG. 1), and the third blank 1400 is configured to form a cross member (30 or 40 in FIG. 1). Additionally, the combined blank 1000 includes a fourth blank 1600 configured to form at least a portion of a floor panel. In some examples, due to lower mechanical requirements, the fourth blank 1600 may be made of a thinner material, e.g., 0.7 to 1.5 mm, and may have lower mechanical properties than the remainder of the combined blank 1000 after forming.

[0116] FIG. 9 illustrates a block diagram of a method 200 for manufacturing a one-piece rear rail structure 100 including first and second rear rails and one or more cross members according to an example of the present disclosure.

[0117] The method 200 includes, at block 201, providing a first blank 1100 and a second blank 1300. The method further includes, at block 202, positioning the first blank 1100 and the second blank 1300 such that the first blank 1100 partially overlaps the second blank 1300 in an overlap region 1500. The method further includes, at block 203, joining the first blank 1100 to the second sub-blank 1300 at the overlap region 1500 to form a combined blank 1000. The method further includes, at block 204, at least partially heating the combined blank 1000 above an austenitizing temperature. The method further includes, at block 205, press-hardening the heated combined blank 1000 to form the one-piece rear rail structure 100.

[0118] Further, providing the combined blank 1000 includes providing a first blank 1100 and a second blank 1300 such that the first blank 1100 partially overlaps the second blank 1300 to form one or more overlapping regions 1500. Further, the formed integrated rear rail structure 100 includes a first rear rail 10 and a second rear rail 20 and one or more cross members 30, 40.

[0119] As previously discussed, the provided method 200 allows for the formation of the one-piece rear rail structure 100 in a single forming step. Additionally, the formed one-piece rear rail structure 100 has improved mechanical properties, particularly at the transitions between the sub-blanks 1100, 1200, 1300, 1400 due to the overlap regions 1500, 1500.

[0120] The combined blank can be made from any type of hardenable steel, particularly boron steel, as previously described for the one-piece rear rail structure 100.

[0121] In the example, at least one of the overlap regions 1500 , 50 between the first blank 1100 and the second blank 1300 substantially corresponds to the transition between the rail 10 and the cross-member 30 .

[0122] Additionally, the method 200 may include joining the first blank 1100 and the second blank 1300 together by spot welding.

[0123] Additionally, the heating step 202 of the method 200 may include heating the first region 1110 of the combined blank 1000 differently from the second region 1120 of the combined blank 1000. For example, the combined blank 1000 may be heated substantially uniformly above the austenitizing temperature, after which the second region 1120 of the combined blank 1000 may be cooled below the austenitizing temperature.

[0124] In an embodiment, bonded blank 1000 can be heated above Ac3 and portions 1120, 1220 of bonded blank 1000 can be cooled to a temperature below Ac3 or even below Ac1 before bonded blank 1000 is deformed. Other portions can be maintained above Ac3 until bonded blank 1000 is deformed, or can be temporarily cooled and then heated back above Ac3.

[0125] Thus, different temperatures may lead to different microstructures or strength properties being set in the respective portions of the one-piece rear rail structure 100, particularly during subsequent rapid cooling ("quenching"), for example, in the die of a press tool.

[0126] In an example, the combined blank is formed during a press hardening step 203 to form the one-piece rear rail structure and simultaneously quenched to below 400°C, specifically below 300°C.

[0127] Additionally, the method 200 may be adapted to form a one-piece rear rail structure 100 having any combination of the aforementioned technical features.

[0128] While only a few examples are disclosed herein, other alternatives, modifications, uses, and / or equivalents are possible. Moreover, all possible combinations of the examples described are also covered. Therefore, the scope of the present disclosure should not be limited by the specific examples, but should be determined solely by a fair reading of the appended claims.

Claims

1. An integrated rear rail structure for a vehicle, the integrated rear rail structure includes a first rear rail portion, a second rear rail portion, and one or more cross member portions connecting the first rear rail portion to the second rear rail portion, The aforementioned integrated rear rail structure is formed by deforming a single coupling blank, The single bonded blank includes at least one first blank joined to the second blank such that the first blank partially overlaps with the second blank to form one or more overlapping regions. The overlapping region substantially corresponds to the transition between the first rear rail portion and one of the cross member portions, and the transition between the second rear rail portion and one of the cross member portions, in an integrated rear rail structure.

2. The integrated rear rail structure according to claim 1, wherein the integrated rear rail structure is made by hot stamping.

3. The integrated rear rail structure according to claim 1, wherein the overlapping region extends at least 20 mm within the rail portion.

4. The integrated rear rail structure according to claim 3, wherein the overlapping region extends 20 mm to 60 mm within the rail portion.

5. The integrated rear rail structure according to claim 1, wherein the overlapping region extends across the entire width of the horizontal member portion.

6. The integrated rear rail structure according to claim 1, wherein the overlapping region extends over the entire width of the rear rail portion at least in the transition portion from the rail portion to the horizontal member portion.

7. The integrated rear rail structure according to claim 1, wherein the area of ​​one of the overlapping regions is 20 to 600 cm².

8. The integrated rear rail structure according to claim 7, wherein the area of ​​one of the overlapping regions is 30 to 500 cm².

9. The integrated rear rail structure according to claim 1, wherein the first rear rail portion and the second rear rail portion include a first region configured to attach the integrated rear rail structure to the chassis, and the first region has an ultimate tensile strength of 1500 MPa or more.

10. The integrated rear rail structure according to claim 9, wherein the first rear rail portion and the second rear rail portion include a second region having an ultimate tensile strength of 700 to 1200 MPa and a yield strength after hot stamping of 500 to 900 MPa.

11. The integrated rear rail structure according to claim 9, wherein the first region and the second region have different microstructures.

12. At least one of the first rear rail portion, the second rear rail portion, and the cross member portion has a substantially U-shaped cross-section. The integrated rear rail structure according to claim 1, wherein the U-shape comprises a bottom wall, a first side wall, a second side wall, a first lateral flange projecting outward at the end of the first side wall, and a second lateral flange projecting outward at the end of the second side wall.

13. The integrated rear rail structure according to claim 12, further comprising a cover plate attached to the first rear rail portion and the second rear rail portion, which substantially closes the U-shaped cross-section.

14. The integrated rear rail structure according to claim 1, wherein the single bonding blank comprises different thicknesses and / or materials.

15. The integrated rear rail structure according to claim 1, further comprising at least a portion of the floor panel.

16. A method for manufacturing an integrated rear rail structure for a vehicle according to claim 1, To provide a first blank and a second blank, The first blank and the second blank are arranged such that the first blank partially overlaps with the second blank within the overlapping area, The first blank is joined to the second blank in the overlapping region to form a combined blank, The bond blank is heated to at least partially above the austenitization temperature, This includes press-hardening the heated bonding blank to form the integrated rear rail structure, A method for forming the integrated rear rail structure, comprising a first rear rail portion and a second rear rail portion, and one or more horizontal member portions.

17. The method according to claim 16, wherein the first blank and the second blank are joined by spot welding.

18. The method according to claim 16, wherein the first region of the integrated rear rail structure has an ultimate tensile strength after press hardening of 1500 MPa or more, and the second region of the integrated rear rail structure has an ultimate tensile strength after press hardening of 700 to 1200 MPa.

19. The method according to claim 18, wherein the first region of the bonding blank is subjected to a different heat treatment than the second region of the bonding blank.

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