Vehicle floor panel and method

Abstract

The present disclosure relates to a method for forming a floor panel for a vehicle framework, the method including the steps of providing a main blank made of press hardened steel, providing one or more first patch blanks, and welding the first patch blanks to the main blank to form a patchwork blank. The method further includes pressing the patchwork blanks to form a floor panel, the first patch blank being positioned along a portion of the main blank to form a first sheet cross member, and left and right portions of the first patch blank in an area of ​​the main blank to form an area of ​​the floor panel that is attached to a rocker are made of a steel that is more ductile than the steel of the main blank. The present disclosure further relates to a floor panel for a vehicle framework made from a single integral piece.

Description

[Technical field]

[0001] This application claims the benefit of European Patent Application No. 21 382 730.6, filed August 2, 2021.

[0002] The present disclosure relates to a floor panel for a vehicle frame. The present disclosure further relates to a method for manufacturing such a floor panel. [Background technology]

[0003] Vehicles such as automobiles incorporate a structural framework designed to withstand all loads that the vehicle may be subjected to during its life. The structural framework is further designed to withstand and absorb impacts, for example in the event of a collision with another vehicle. The structural framework is also designed to be as lightweight as possible in order to reduce the emission of pollutants such as CO2 into the environment.

[0004] The structural framework of an automobile may include, for example, bumper beams, pillars (e.g., A-pillars, B-pillars, C-pillars), side impact beams, and rocker panels. These and other structural members may have one or more regions with a substantially U-shaped (also called "hat" shaped) cross section. These structural members may be manufactured in a variety of ways and may be made from a variety of materials. As indicated above, lightweight materials that improve the integrity of the vehicle during a crash while at the same time improving energy absorption are desired.

[0005] In the automotive industry, it is commonly known that at least many vehicle frame structural members are made from ultra-high strength steels (UHSS), which exhibit optimized maximum strength per unit of weight and advantageous formability properties.

[0006] Ultra-high strength steels (UHSS) in the present disclosure may be considered as steels having an ultimate tensile strength of at least 1000 MPa. UHSS can achieve such high tensile strength after heat treatment, particularly hot forming. Some UHSS require rapid cooling to achieve a martensitic structure and corresponding high ultimate tensile strength. Other UHSS can achieve high ultimate tensile strength with relatively slow cooling, or even air cooling ("air hardening"). Some UHSS do not require hot forming and corresponding austenitization to achieve high ultimate tensile strength, but instead have and retain high strength after cold forming.

[0007] UHSS can exhibit high ultimate tensile strengths, especially after press hardening operations, of 1500 MPa and even 2000 MPa or more. In such a process, the steel blank is heated above the austenitizing temperature, especially above the Ac3 point (the temperature at which the transformation from ferrite to austenite is completed during heating), to substantially fully austenitize the blank. After a period of heating above this temperature, the blank is pressed, which causes the blank to deform. At the same time, the blank is quenched, which substantially "fully hardens" it and gives it a martensitic structure. Press hardening is also called "hot stamping" or, if quenched, "hot forming die quenching" (HFDQ).

[0008] The resulting materials and parts are very strong and stiff, but at the same time brittle: they can barely deform and can crack or break with small deformations. It is therefore known to tune the strength, stiffness and deformation properties by combining different materials in the deformation process, for example tailor welded blanks (TWBs) or by subjecting different areas or parts to different heat treatments.

[0009] Besides using suitable materials, suitable properties in terms of crash behavior and weight saving can be given to the structural members of a vehicle, for example by using patch welding. For example, a first patch can be welded to a main member to reinforce the main member where necessary, without adding undesirable weight. A blank with patches added is sometimes called a "patchwork blank" to distinguish it from a "tailor welded blank", where the blanks are welded end to end to join them together.

[0010] Typically, the patch is welded to the main piece by spot welding, a welding technique that is well known and widely used in the automotive sector.

[0011] A vehicle floor for a vehicle structural framework may be composed of several different pressed or otherwise formed sheet metal parts and reinforcements that need to be joined together to obtain the final vehicle floor. The different floor components may be manufactured by different hot or cold forming methods such as cold stamping, hot stamping (also known as press hardening or hot forming die quenching), roll forming or indirect hot stamping (also known as indirect press hardening).

[0012] Assembly can be a labor-intensive process when numerous welding operations are involved that result in deformation of the floor, and maintaining the desired floor shape can be difficult.

[0013] Furthermore, after the floor is fully assembled, it must be fed to a frame installation line for assembly to the vehicle frame. The assembled floor is a heavy and bulky part that is difficult to handle from a logistical standpoint.

[0014] Furthermore, with the proliferation of hybrid and electric vehicles, vehicle frames, such as automobile frames, are increasingly required to provide as much space as possible in the floor area to accommodate the vehicle's battery.

[0015] The battery is a relatively heavy and bulky component, and due to its weight it is preferably accommodated as low as possible in the vehicle frame in order to hinder the vehicle's dynamics as little as possible. Typically, the battery has the shape of a parallelepiped box with a very long and wide base, which extends mainly in the longitudinal direction of the vehicle and has a low height in order to preserve free space in the vehicle's interior compartment. The location of the battery leads to a complete redesign of the conventional vehicle floor shape in order to fulfill both the security function and the battery accommodation function.

[0016] DE202010017552U1 discloses a body structure, in particular a floor structure, for a motor vehicle with structural parts which define a load path in the event of a crash. In the region of the structural parts which are arranged in at least one defined load path, in particular in a front crash load path and / or a side crash load path and / or a rear crash load path, the components are formed at least in part by high-strength structural parts, preferably fully hardened or at least partially hardened high-strength structural parts made of hot-stamped or cold-stamped steel sheets, which structural parts are connected to one another directly or indirectly, preferably directly, in particular via a force and / or geometric and / or material connection.

[0017] Document WO2021 / 094405A1 discloses a hot stamping vehicle floor for a vehicle frame. DISCLOSURE OF THEINVENTION

[0018] In a first aspect of the disclosure, a method for forming a floor panel for a vehicle frame is provided. The method includes providing a main blank made of press hardened steel, providing one or more first patch blanks, and welding the first patch blanks to the main blank to form a patchwork blank. The method further includes pressing the patchwork blanks to form a floor panel, where the first patch blank is positioned along a portion of the main blank that forms a first sheet cross member, and left and right portions of the first patch blank in an area of ​​the main blank that forms an area of ​​the floor panel that is attached to a rocker are made of a steel material that is more ductile than the steel material of the main blank.

[0019] According to this aspect, a method of forming a floor panel is provided that can simplify the manufacturing process and provide a floor panel that has sufficient strength and rigidity, as well as energy absorption during impact, while reducing the weight of the floor panel.

[0020] Throughout this disclosure, a main blank can be considered to be a blank (e.g., a metal sheet or thin metal plate) that forms the main structure of the floor panel. A patchwork blank can be considered to be a blank that forms a localized patch on the main structure of the floor panel.

[0021] In an embodiment, the patchwork blank may have overlapping soft (or "ductile") and hard materials in areas designed to withstand compressive crash forces in the event of a crash situation. In these areas, the floor panel may be able to withstand more deformation (e.g., higher bending angles) without risk of rupture, making the vehicle safer.

[0022] The first seat cross member may be a front seat cross member or a rear seat cross member. The seat cross member may be considered herein as a laterally extending portion of the floor panel that provides stiffness and strength. The seat cross member may be configured to provide an anchor point and mount a seat of the vehicle.

[0023] The first patch blank may be positioned along a portion of the main blank that will form the first sheet cross member, but does not necessarily have to cover the entire cross member, i.e., it may cover only a certain portion of the cross member.

[0024] The welding of the first patch blank can be performed by one or more of the group consisting of resistance spot welding, standard laser welding, remote laser welding, resistance seam welding (RSEVV), gas metal arc welding, and hybrid laser and arc welding.

[0025] In examples, the first patch blank can include a center portion, and the center portion of the first patch blank between the left and right portions can be made of press hardened steel. In these examples, the patchwork blank in the center portion between the portions that are attached to the rocker can provide a localized increase in strength and stiffness. The thickness of the floor panel can be locally increased in this center region.

[0026] Further, the step of providing one or more first patch blanks may include forming a first tailor welded blank disposed along a portion of the main blank for forming the first sheet cross member, the first tailor welded blank including a left portion, a center portion, and a right portion of the first patch blank. In these examples, the manufacturing process may be further optimized, including tailoring mechanical properties across the width of the sheet cross member.

[0027] In some examples, the method may further include providing one or more second patch blanks and welding the second patch blanks to the main blank, where the second patch blanks may be positioned along a portion of the main blank to form a second sheet cross member, and left and right portions of the second patch blank in an area of ​​the main blank to form an area of ​​the floor panel to be attached to the rocker are made of a steel that is more ductile than the steel of the main blank. In these examples, both the front sheet cross member and the rear sheet cross member may include a patchwork blank.

[0028] In some embodiments, providing a main blank includes forming left and right openings in the main blank by cutting out left and right portions of the main blank, and the left and right portions of the first patch blank are welded to the main blank to cover the left and right openings. Thus, a method of forming a floor panel for a vehicle frame is provided. The method includes providing a main blank made from press hardened steel and forming openings in the main blank by cutting out left and right portions of the main blank. The method further includes providing one or more first patch blanks and welding the first patch blanks to the main blank to cover the left and right openings to form a patchwork blank. The method further includes pressing the patchwork blanks to form a floor panel, where the first patch blank is positioned along a portion of the main blank to form a first sheet cross member, and the left and right portions of the first patch blank in the area of ​​the main blank that forms the area of ​​the floor panel that is attached to the rocker are formed of a steel material that is more ductile than the steel material of the main blank. The first patch blank may, but need not, include further portions beyond the left and right portions.

[0029] In these instances, tailoring the mechanical properties of locally more ductile regions for energy absorption and to control the kinematics during deformation can be combined with further weight reduction.

[0030] In some examples, pressing the patchwork blank includes heating the patchwork blank above an austenitizing temperature and hot stamping the patchwork blank, hi other examples, pressing the patchwork blank includes cold pressing the patchwork blank, then heating the pressed patchwork blank above an austenitizing temperature, and then cooling the heated pressed patchwork blank.

[0031] Within the scope of the present disclosure, both indirect and direct hot stamping can be used. In direct hot stamping, the blank (particularly in the present disclosure, the patchwork blank) can be heated above the austenitizing temperature to achieve a partial or complete austenitic structure. In particular, the blank can be heated above the corresponding Ac3 temperature. After heating above the austenitizing temperature for a certain time, the blank is subjected to a deformation or drawing process in a press. The deformed blank is then cooled. Depending on the type of steel used and the cooling rate of the material, a martensitic structure may be obtained in at least a part of the deformed blank. In some cases, in order to obtain a martensitic structure, it is necessary to rapidly cool the blank. The critical cooling rate is, for example, about 25-30 °C / s. Rapid cooling can be performed in a press. In some instances, "passive cooling" (i.e., leaving the deformed blank to cool with air) may be sufficient to obtain a martensitic structure.

[0032] In indirect hot stamping, a blank (in this disclosure a patchwork blank) is deformed in the "cold state", e.g. at room temperature. Only after the blank has been deformed can it be subjected to a heat treatment to obtain the aforementioned martensitic structure. After deformation, the blank is heated above the austenitizing temperature and then cooled.

[0033] In further examples, multi-step processes and multi-step presses can be used. In a multi-step process, different blanks undergo different manufacturing steps simultaneously in a single press. For example, in a first station of such a press, a first pressing step is performed, in a second station a cooling step, and in a third station a trimming step is performed. In further stations further post-processing steps (e.g. proofing, cutting, drilling, etc.) may be performed. In a multi-step process, several forming stations can also be combined. In an example, a cooling station is not required. Multi-step processes can be used both with air-hardenable steels and with other UHSS that require quenching to obtain a martensitic structure.

[0034] In some instances, the central portion of the main blank and the first patch blank can be manufactured from boron steel, in particular the same boron steel, which is suitable for hot stamping and provides very high strength. For example, 22MnB5 steel or 22MnB8 steel can be used.

[0035] Examples of hardenable boron steels include 22MnB5 steel or Usibor® 1500 or 2000. Usibor® is commercially available from Arcelor Mittal.

[0036] To avoid decarburization and scale formation during the forming process, 22MnB5 steel can be coated with an aluminum-silicon coating. The composition of 22MnB5 steel is summarized below in weight percent (the remainder being iron (Fe) and impurities): C 0.20 - 0.25 Si 0.15 - 1.35 Mn 1.10 - 1.25 P < 0.025 S < 0.008 Cr 0.15 - 0.30 Ti 0.02 - 0.05 B 0.002 - 0.004 N < 0.009

[0037] 22MnB5 steel is available in several varieties with similar chemical compositions, but 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.

[0038] Usibor® 1500 is supplied in the ferrite-pearlite phase. This is a fine grain structure distributed in a homogeneous pattern. The mechanical properties are related to this structure. After heating, hot stamping and quenching, a martensitic structure forms. The result is a significant increase in ultimate strength and yield strength.

[0039] The composition of Usibor® 1500, summarized by weight %, is as follows (the remainder is iron (Fe) and inevitable impurities): C Si Mn PS Cr Ti 0.24 0.27 1.14 0.015 0.001 0.17 0.036 BN 0.003 0.004

[0040] Usibor® 2000 is another boron steel with even higher strength. The yield strength of Usibor® 2000 can be greater than 1400 MPa and the ultimate tensile strength can be greater than 1800 MPa after hot pressing die quench. The composition of Usibor® 2000 includes max 0.37 wt% carbon, max 1.4 wt% manganese, max 0.7 wt% silicon and max 0.005 wt% boron.

[0041] The left and right portions of the first patch blank intended to form the area of ​​the floor panel that will be attached to the rocker may be made of a more ductile steel (after hot forming) than the main blank. These portions may be made, for example, of Ductibor® 500 or Ductibor® 1000, or CRL340LA, also available from ArcelorMittal.

[0042] On the other hand, Ductibor® and other mild steels can also be used in hot forming and die quenching of hot forming. However, these steels do not form martensitic structures. The resulting steels have lower ultimate tensile strength and yield strength, but higher elongation to break.

[0043] Ductibor® 400 can have an ultimate tensile strength of 450 MPa or greater, Ductibor® 500 can have an ultimate tensile strength of 550 MPa or greater, and Ductibor® 1000 can have an ultimate tensile strength of 1000 MPa or greater.

[0044] CRL-340LA is a commercially available steel from SSAB. It is a high strength, low alloy steel intended for general pressing, bending and forming. Its composition is outlined below (weight %): C 0.1% or less Si 0.040% or less Mn 1% or less P 0.030% or less S max 0.025 Aluminum min 0.015%) Nb + Ti up to 0.1%

[0045] In an embodiment, the patch is designed to have more ductile properties than the main piece. The patch can be made from any steel that is suitable for forming, including hot and cold forming, and that provides suitable mechanical properties after such processing. Ductibor®, CRL-340LA and similar steels, e.g., low alloy steels, are suitable for the "softer" patch.

[0046] The combination of a softer patch with a "harder" main piece allows the floor panel to absorb more energy in the event of a collision, for example. Another aspect is that fracture of the main blank of the floor panel when subjected to bending loads is avoided or occurs only after significant deformation.

[0047] The patchwork blank may generally be made of a steel having greater ductility than the material of the main blank, for example the patches may be made of very high strength steel (VHSS) or extra high strength steel (EHSS).

[0048] Here, EHSS can be considered as steels having a yield strength (after forming or in the final product) between 550 MPa and 800 MPa, and VHSS can be considered as steels having a yield strength (after forming or in the final product) between 390 MPa and 550 MPa.

[0049] In some examples, the main blank can have a thickness between 0.5 and 3 mm, particularly between 0.8 and 1.5 mm. The main blank and the patchwork blank can have the same or similar thickness. In general, the thickness for most vehicle applications can be between 0.5 and 6 mm, particularly between 0.5 and 3 mm, more particularly between 0.8 and 1.5 mm.

[0050] In a further aspect, a floor panel for a vehicle frame is provided that is made from a single integral member. The floor panel extends longitudinally from front to rear and laterally between a left attachment region for attachment to a left rocker and a right attachment region for attachment to a right rocker. The floor panel includes a front seat cross member and a rear seat cross member, the front seat cross member and the rear seat cross member including left and right attachment portions for attachment to the left and right rockers, respectively. The floor panel includes a main rigid region and a secondary ductile region, the main rigid region including a central portion of the front seat cross member and the rear seat cross member, and the secondary ductile region including the left and right attachment portions. The secondary ductile region has a tensile strength lower than that of the main rigid region and a breaking elongation higher than that of the main rigid region.

[0051] This aspect provides a floor panel that is relatively lightweight yet provides a good balance between stiffness and strength, and energy absorption and safety during impact.

[0052] Exemplary embodiments of a vehicle floor according to the present disclosure can significantly reduce the number of parts required to obtain a final vehicle floor, which simplifies the manufacturing process and reduces costs since fewer parts are formed separately and joined together by welding. Furthermore, the thickness of the parts can also be reduced due to the possibility of using more hot stamped sheet metal blanks, which, together with the reduction in the number of single parts, can achieve an associated weight reduction.

[0053] In some embodiments, the sub-ductile region can extend substantially from front to rear along the left and right attachments. In these examples, a more ductile region is provided substantially along the entire length of the rocker. Cracking along the entire weld joint of the rocker and floor panel (which may both be formed from less ductile but higher strength UHSS) can be reduced or avoided.

[0054] In some embodiments, the minor ductile regions may substantially correspond to the left and right attachment portions of the front and rear sheet cross members.

[0055] In some embodiments, the sub-ductile region has a length along the longitudinal direction between 10 cm and 50 cm and a width along the transverse direction between 15 cm and 60 cm.

[0056] In some embodiments, the primary hard region may have a tensile strength greater than 1.200 MPa, particularly greater than 1.400 MPa, and the secondary ductile region may have a tensile strength between 500 and 1.000 MPa.

[0057] In an embodiment, the ductility of the patchwork blank (after hot forming) may be on the order of 10% to 80% higher than the ductility of the main blank. The ultimate tensile strength of the patchwork blank (after hot forming) may be on the order of 25% to 70% lower than the ultimate tensile strength of the main blank.

[0058] Ultimate tensile strength (UTS) (also referred to as "tensile strength"), as used herein, may be considered as the maximum stress that a material can withstand while being stretched or pulled before breaking.

[0059] The ultimate tensile strength can be determined by performing a tensile test and recording the engineering stress versus strain. The highest point on the stress-strain curve is the ultimate tensile strength and has units of stress.

[0060] In an embodiment, the floor panel may be obtained by a method according to any of the embodiments described herein.

[0061] The term "ductility" as used in this disclosure refers to a measure of a material's ability to undergo plastic deformation before fracture. Ductility can more commonly be expressed as the percent elongation at break or percent reduction in area at break from a standard tensile test according to the following ISO standard: ISO 6892-1:2016 Metallic materials - Tensile testing, test method at room temperature.

[0062] One method of calculating ductility is based on the percent elongation of the metal probe during such a tensile test, as follows: Percentage elongation = (Lf-Lo) / Lo where Lo is the initial probe length and Lf is the probe length at break.

[0063] Another way to measure ductility is reduction in area. Area reduction rate=(Ao-Af) / Ao where Ao is the initial cross-sectional area of ​​the probe cross-section and Af is the cross-sectional area of ​​the probe cross-section at break. [Brief description of the drawings]

[0064] [Figure 1A] 1 shows a schematic perspective view of a vehicle floor according to the prior art; [Figure 1B] 1 illustrates a schematic perspective view of an example vehicle floor panel according to the present disclosure. [Figure 2A] 2 illustrates a further example of a vehicle floor panel in a schematic manner; [Figure 2B] 2 illustrates a further example of a vehicle floor panel in a schematic manner; [Figure 2C] 2 illustrates a further example of a vehicle floor panel in a schematic manner; [Figure 3A] 1 illustrates a schematic of the behavior of an example vehicle floor panel according to the present disclosure compared to alternative designs. [Figure 3B] 1 illustrates a schematic of the behavior of an example vehicle floor panel according to the present disclosure compared to alternative designs. [Figure 3C] 1 illustrates a schematic of the behavior of an example vehicle floor panel according to the present disclosure compared to alternative designs. [Figure 4] 2 illustrates, in schematic form, yet another example of a vehicle floor panel according to the present disclosure; [Figure 5A] 1 shows two schematic examples of a method for manufacturing a vehicle floor panel. [Figure 5B] 1 shows two schematic examples of a method for manufacturing a vehicle floor panel. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0065] Non-limiting examples of the present disclosure are described below with reference to the accompanying drawings: Figure 1A shows a prior art vehicle floor 200. This prior art state of the art vehicle floor includes multiple sheet metal components including a front panel 202, a cross beam 204, a longitudinal beam 206, a beam stiffener 208, a rear panel 210, a middle panel 212, etc.

[0066] The vehicle floor 200 may be constructed from a total of 16 separate sheet metal pieces that are formed independently (in separate molding processes) and then joined together by any suitable welding process, such as spot welding, laser welding, etc. Once completed, the vehicle floor 200 will weigh in excess of 30 kg.

[0067] 1B shows a schematic diagram of a floor panel and method of manufacture according to an embodiment of the present disclosure. It can be seen that a single integral piece 10 incorporates, for example, a front seat cross member, a rear seat cross member, longitudinal beam sections, and panels which, in the embodiment of FIG. 1, are manufactured separately and then joined together.

[0068] Figure IB shows how two patchwork blanks can be added to a main piece, as indicated by the dashed arrows. Note that in this Figure IB, the patches and main piece are shown in a "ready" state, i.e., after hot forming, but in this example, the flat patchwork blank and the flat main piece blank are joined together prior to the hot stamping step.

[0069] The floor panel 10 for the vehicle frame is integrally formed and extends longitudinally from the front 14 to the rear 12 and laterally between a left mounting area 18 for mounting to a left rocker (driver's side) and a right mounting area 16 for mounting to a right rocker.

[0070] The floor panel includes a front seat cross member 20 and a rear seat cross member 30, the front and rear seat cross members 20, 30 including left and right mounting portions for mounting to left and right rockers, respectively (see also FIG. 2A).

[0071] The floor panel includes a main rigid region 19 (lightly hatched area) and secondary ductile regions 21, 31 (darkly hatched areas). The main rigid region includes the central portions of the front and rear seat cross members 20, 30, and the secondary ductile regions 21, 31 include the left and right mounting portions. The secondary ductile regions have a tensile strength lower than that of the main ductile region and a fracture elongation higher than that of the main ductile region.

[0072] The floor panel 10 can be manufactured using a method that includes the steps of providing a main blank 19 made from press hardened steel, providing one or more first patch blanks 22, and welding the first patch blanks 22 to the main blank 19 to form a patchwork blank.

[0073] The method may further include pressing the patchwork blanks to form the floor panel 10, where a first patch blank 22 is positioned along a portion of the main blank 19 to form a first sheet cross member 20. The first patch blank 22 may cover substantially the complete width of the floor panel from one rocker attachment area to another rocker attachment area.

[0074] The left and right portions 21 of the first patch blank 22 in the area of ​​the main blank 19 intended to form the area of ​​the floor panel 10 which is to be attached to the rocker are made of a steel which is more ductile than the steel of the main blank.

[0075] In some embodiments, the ductile region can have a longitudinal length between 10 cm and 50 cm and a lateral width between 15 cm and 60 cm.

[0076] In the embodiment of FIG. 1B, a central portion 23 of the first patch blank 22 between the left and right portions may be made of press hardened steel, specifically the same steel as the main blank.

[0077] In the embodiment of Fig. 1B, local ductility is provided at the attachment of the seat cross member (integrated in the floor panel).The advantage of such a floor panel in case of impact is explained with reference to Fig. 3.

[0078] 1B, the step of providing one or more first patch blanks includes forming a first tailor welded blank (TWB) 22 that is positioned along a portion of the main blank to form the first sheet cross member 20, the first tailor welded blank 22 including left 21, center 23 and right 21 portions of the first patch blank. In other embodiments, multiple separate patchwork blanks may be used in place of a single TWB.

[0079] In the embodiment of Figure 1B, the method further includes providing one or more second patch blanks 24 and welding the second patch blanks 24 to the main blank 19. The second patchwork blanks are positioned along a portion of the main blank to form a second seat cross member 30 (in this case the rear seat cross member). The second patchwork blank 24 may extend across substantially the entire width of the floor panel, i.e. from the attachment to one rocker to the attachment to the other rocker.

[0080] The left and right portions 31 of the second patch blank in the area of ​​the main blank intended to form the area of ​​the floor panel that will be attached to the rocker are made of a more ductile steel than the steel of the main blank. In this embodiment, both the rear seat cross member and the front seat cross member may have a similar construction and both may be made by providing TWBs 22, 24 that extend substantially from one side 18 to the other side 16 of the floor panel and are welded onto the main blank, i.e. the blanks are overlapping.

[0081] Any suitable welding technique may be used, such as resistance spot welding, standard laser welding, remote laser welding (laser welding where the laser head is more than 50 cm away from the weld), resistance seam welding (RSEVV), gas metal arc welding, hybrid laser and arc welding, etc.

[0082] The main blank 19 and the central parts 23, 33 can be made from boron steel, in particular from the same boron steel. For example, 22MnB5 steel or 22MnB8 steel can be used. The steel can have a coating, for example an AlSi coating or a Zn coating.

[0083] 2A and 2B are schematic top and bottom views, respectively, of a floor panel 10 according to different embodiments. In general, the same reference numbers are used to indicate the same or similar elements, including the rear 12 and front 14 portions of the floor panel, and the regions 18, 16 that are attached to the right or left rockers of the vehicle frame.

[0084] Similar to the embodiment of FIG. 1, the patchwork blank can be welded to the main blank 19 before the stamping step. However, in this embodiment, the step of providing the main blank includes forming left and right openings 27 in the main blank 19 by cutting out left and right portions 27, and the front and rear portions 29 (left and right in the figure) of the first patch blank are welded to the main blank to cover the left and right openings 27. Thus, there is little overlap between the patchwork blank and the main blank. The weight of the floor panel can be optimized. In the embodiment, the front and rear openings 27, 37 and the corresponding front and rear portions 29, 39 are provided in both the front seat cross member 20 and the rear seat cross member 30.

[0085] 2C shows a detailed view of the patchwork blanks 29, 39 added to the sheet cross members 20, 30. As seen in FIG. 2C, the sheet cross members can have a U-shaped cross section including a bottom 52, a first side wall 54, and a second side wall 56.

[0086] 2C, the patchwork blank may cover a bottom wall of the U-shaped cross section of the cross member. In particular, the patchwork blank may cover the bottom wall and extend to the first and second side walls 54, 56. The patchwork blank may extend from the bottom of the groove between the first side wall 54 and the bottom 52 to the bottom of the groove between the second side wall 56 and the bottom 52.

[0087] The floor panel rocker attachment area 16 in this embodiment may include first and second substantially planar portions 16A, 16B that may be attached to different planar support areas of the rocker.

[0088] In the example of FIG. 1B, the first and second portions of the patchwork blank are wider and may extend to the edges of the floor panel.

[0089] 3A-3C show schematic comparison of deformation in side pole impact of different configurations. In Fig. 3A-3C, cross-sectional views of floor panel at longitudinal position of seat cross member are provided. In the test, pole 60 impacts left rocker panel 42. Seat cross member of panel 10 extends from right rocker 44 to left rocker 42.

[0090] In Figure 3A, the sheet cross member in this example is formed by the overlap of a more ductile patch on a main blank. The ductile portion extends across substantially the full width of the floor panel, i.e. from the left rocker 42 to the right rocker 44.

[0091] In the event of a collision, there is a risk of the deformation being too great, as indicated by reference number 19. If the floor panel is locally too deformed, there is a risk that the battery area 50 may be damaged.

[0092] In Fig. 3B, to avoid this problem, the patchwork blank, which extends over the entire width of the sheet cross member, is made from the same material as the main blank, for example boron steel. As a result, the structure is stronger and stiffer and therefore less prone to deformation than in the example of Fig. 3A. However, there is a greater risk of fracture in the area close to reference 16. Local bending may be close to the fracture limit.

[0093] In Fig. 3C, a floor panel according to the present disclosure (in this particular case according to Fig. 1B) is shown in the case of a pole collision, i.e. a localized ductile patch is provided in the area of ​​attachment of the seat cross member to the rocker. As can be seen in Fig. 3C, the deformation is less than in the case of Fig. 3A, so there is no risk to the integrity of the battery box 50. The local deformation and bending in the area 16 can be reduced to some extent compared to the example of Fig. 3B. Even if there is the same local deformation and bending, the risk of fracture is much less, since the ductile patch allows a higher bending angle before fracture.

[0094] 4 shows yet another example of a vehicle floor panel according to the present disclosure, in which the floor panel 10 can be formed from a single piece in a single stamping step, similar to the embodiments of FIGS.

[0095] In the example of Figure 4, the secondary ductile regions extend substantially from front to rear along the left and right attachment regions 15A, 15B. That is, there is increased ductility along the entire length of the floor panel, in the attachment regions to the rocker. This can be achieved by providing a relatively large patchwork blank, welding it to the main blank along the attachment zones, and then hot stamping the floor panel.

[0096] In a further embodiment, the floor panel may be made from a single main blank, with the areas to be attached to the rockers receiving different heat treatments. In an example, the sides of the main blank may not be heated to the austenitizing temperature. In a further embodiment, partial tempering may be performed in a furnace to produce different areas in the main blank at different temperatures prior to deformation.

[0097] Figures 5A and 5B show two schematic examples of methods for manufacturing a vehicle floor panel. The method shown in Figure 5A is believed to be particularly suitable for the floor panel of Figure 1B. The method shown in Figure 5B is believed to be particularly suitable for the floor panel of Figure 2.

[0098] In block 110, a main blank is provided. The main blank may be made from UHSS, in particular boron steel. The main blank may have a thickness of, for example, between 0.5 and 3 mm.

[0099] At block 120, first and second TWBs (tailor welded blanks) are provided. The first TWB may be located in an area of ​​the main blank that will be deformed to form a first sheet cross member, e.g., a front sheet cross member. The second TWB may be located in an area of ​​the main blank that will be deformed to form a second sheet cross member, e.g., a rear sheet cross member.

[0100] The first and second TWBs may include sections of steel that are more ductile than the steel of the main blank. The section of the TWB located in the attachment area to the rocker may be more ductile. The central section of the TWB may be a harder steel.

[0101] At block 130, two TWBs may be welded to a main blank to form a patchwork blank.

[0102] Next, in block 140, the patchwork blank is heated to above the austenitizing temperature, in particular above the Ac3 point. The heating temperature can be above the Ac3 point and below the evaporation temperature of the coating on the blank. In an example, the heating temperature is between 870 and 950° C.

[0103] After a suitable heating time, e.g., several minutes, to ensure that the entire patchwork blank has an austenitic structure, the patchwork blank may be quenched in block 150. In particular, the die or press used to deform the patchwork blank may have integrated cooling channels. A cold liquid (e.g., water) may be supplied through the cooling channels to rapidly cool the patchwork blank to below 400°C, in particular below 300°C or below about 200°C.

[0104] The steel of the main blank and the central part of the sheet cross member can result in a martensitic structure and have an ultimate tensile strength between 1.400 MPa and about 2.000 MPa. The yield strength of these parts can be greater than 800 MPa.

[0105] The steel of the ductile part of the blank may have an ultimate tensile strength of between 400 MPa and 1.000 MPa, in particular between 500 MPa and 1.000 MPa.

[0106] In block 160, the resulting floor panel can be joined to the rest of the vehicle skeleton. The floor panel can be joined, for example, to a rocker. Such operations can include spot welding or other joining operations. Before joining to the rest of the skeleton, post-processing operations can be performed, including, for example, trimming, notching, calibration. In an embodiment, such post-processing operations can be performed in the same (multi-stage) press.

[0107] In the example of Figure 5B, an alternative method 190 for manufacturing a floor panel is provided. In block 110, a main blank 110 is provided. Prior to deforming the main blank, i.e. while the main blank is substantially flat, holes may be drilled (e.g. by laser cutting) in the main blank in block 122.

[0108] The patchwork blank may be welded to the main blank to cover the hole at block 132. The remaining steps of the method 190 may be substantially the same as the method 100 of FIG.

[0109] In embodiments of the present disclosure, a floor panel having sufficient strength, stiffness, and absorption capacity to comply with relevant tests, including crash tests, can be provided at a weight reduction of at least 10%, and even 20%, compared to the floor panel in the state of FIG. 1 .

[0110] While only a number of embodiments are disclosed herein, other alternatives, modifications, uses, and / or equivalents are possible. Moreover, all possible combinations of the described embodiments are covered. Thus, the scope of the disclosure should not be limited by the specific embodiments, but should be determined solely by a fair reading of the following claims.

Claims

1. A method of forming a floor panel for a vehicle skeleton, comprising: providing a main blank made of press-hardened steel; providing one or more first patch blanks; welding the first patch blank to the main blank to form a patchwork blank; pressing the patchwork blank to form a floor panel; wherein the first patch blank is arranged along a part of the main blank to form a first sheet cross member, the left and right portions of the first patch blank in the region of the main blank for forming the region of the floor panel attached to the rocker are made of steel with higher ductility than the steel of the main blank, and the central portion between the left and right portions of the first patch blank is made of press-hardened steel. A method.

2. The step of providing one or more first patch blanks includes forming a first tailor-welded blank arranged along a part of the main blank to form a first sheet cross member, wherein the first tailor-welded blank includes a left portion, a central portion, and a right portion of the first patch blank. The method according to claim 1.

3. including the step of providing one or more second patch blanks, wherein the second patch blank is arranged along a part of the main blank to form a second sheet cross member, and the left and right portions of the second patch blank in the region of the main blank for forming the region of the floor panel attached to the rocker are made of steel with higher ductility than the steel of the main blank. The method according to claim 1.

4. The step of providing the main blank includes forming a left opening and a right opening in the main blank by cutting off the left and right portions of the main blank, wherein the left and right portions of the first patch blank are welded to the main blank to cover the left opening and the right opening. The method according to claim 1.

5. The pressing of the patchwork blank includes heating the patchwork blank to a temperature above the austenitizing temperature and hot stamping the patchwork blank. The method according to claim 1.

6. The method according to claim 1, wherein the press of the patchwork blank cold presses the patchwork blank, then heats the pressed patchwork blank to a temperature above the austenitizing temperature, and then cools the heated and pressed patchwork blank.

7. The method according to claim 1, wherein the central portions of the main blank and the first patch blank are made of boron steel.

8. The method according to claim 7, wherein the central portions of the main blank and the first patch blank are made of the same boron steel.

9. The method according to claim 1, wherein the main blank has a thickness between 0.5 and 3 mm, particularly between 0.8 and 1.5 mm.

10. A floor panel for a vehicle skeleton made of a single integral member, the floor panel extends longitudinally from the front to the rear and extends laterally between a left mounting region for attachment to the left rocker and a right mounting region for attachment to the right rocker, the floor panel includes a front seat cross member and a rear seat cross member, and the front seat cross member and the rear seat cross member each include a left attachment portion and a right attachment portion for attachment to the left rocker and the right rocker, the floor panel includes a main hard region and a secondary ductile region, the main hard region includes the central portions of the front and rear seat cross members, and the secondary ductile region includes the left and right attachment portions, A floor panel, wherein the secondary ductile region has a tensile strength lower than that of the main hard region and an elongation at break higher than that of the main hard region.

11. The floor panel according to claim 10, wherein the secondary ductile region extends substantially from the front to the rear along the left and right mounting regions.

12. The floor panel according to claim 10, wherein the secondary ductile region substantially corresponds to the left and right attachment portions of the front seat cross member and the rear seat cross member.

13. The floor panel according to claim 10, wherein the secondary ductile region has a length between 10 cm and 50 cm along the longitudinal direction and a width between 15 cm and 60 cm along the transverse direction.

14. The tensile strength of the main hard region is greater than 1,200 MPa, particularly greater than 1,400 MPa, The floor panel according to claim 10, wherein the tensile strength of the secondary ductile region is between 500 MPa and 1,000 MPa.

15. The floor panel according to claim 10, wherein the floor panel is obtained by the method according to claim 1, the floor panel.

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