A unitary rear ring of a vehicle framework

Abstract

The present disclosure relates to methods for manufacturing a unitary rear ring of a vehicle framework, the rear ring substantially completely surrounding a back door opening of the vehicle. The method comprises providing a plurality of blanks, joining the blanks to each other to form a combined blank, and deforming the combined blank to form the unitary rear ring. The unitary rear ring includes first and second rear pillar portions each connected to a front cross member and to a rear cross member to form a substantially closed ring shape. The present disclosure further relates to unitary rear rings obtainable by such methods.

Description

A UNITARY REAR RING OF A VEHICLE FRAMEWORK

[0001] The present application claims the benefit of European patent application n° EP23383277.3 filed on December 12th, 2023. The present disclosure relates to unitary rear rings for vehicles and methods of manufacturing unitary rear rings for vehicles.BACKGROUND

[0002] Vehicles such as cars incorporate a structural skeleton designed to withstand all loads that the vehicle may be subjected to during its lifetime. The structural skeleton is further designed to withstand and absorb impacts, in case of e.g. collisions with other cars, obstacles or pedestrians.

[0003] The structural skeleton of a vehicle, e.g. a car, in this sense may include e.g. bumpers, pillars (A-pillar, B-pillar, C-pillar, D-pillar), side impact beams, rockers or sills, hinge pillars and shock absorbers.

[0004] Press hardening, also known as Hot Forming Die Quenching (HFDQ) typically uses boron steel sheets to create stamped components with Ultra-high Strength Steel (UHSS) properties, with tensile strengths of e.g. 1.500 MPa or 2.000 MPa or even more. The increase in strength allows for a thinner gauge material to be used, which results in weight savings over conventionally cold stamped mild steel components. Throughout the present disclosure UHSS may be regarded as a steel having an ultimate tensile strength of 1.000 MPa or more, particularly after a press hardening process.

[0005] In a HFDQ process, a blank to be hot formed may be heated to a predetermined temperature e.g. austenization temperature or higher (and particularly between Ac3 and an evaporation temperature of e.g. a coating of the blank). A furnace system may be used for this purpose. Depending on the specific needs, a furnace system may be complemented with additional heaters, e.g. induction or infrared heaters. By heating the blank, the strength of the blank is decreased and deformability increases i.e. to facilitate the hot stamping process.

[0006] There are several known Ultra-high Strength steels (UHSS) for hot stamping and hardening. The blank to be hot formed may be made e.g. of a boron steel, coated or uncoated, such as Usibor® (22MnB5) commercially available from ArcelorMittal.

[0007] Typical vehicle components that may be manufactured using the HFDQ process include: door beams, bumper beams, cross / side members, A / B pillar reinforcements, front and rear rails, seat crossmembers and rear rails.

[0008] Hot forming of boron steels is becoming increasingly popular in the automotive industry due to their excellent strength and formability. Many structural components that were traditionally cold formed from mild steel are thus being replaced with hot formed equivalents that offer a significant increase in strength. This allows for reductions in material thickness (and thus weight) while maintaining the same strength.

[0009] In order to improve the ductility and energy absorption in specific areas of a component, it is known to introduce softer regions within the same component. This improves ductility locally while maintaining the required high strength overall. By locally tailoring the microstructure and mechanical properties of certain structural components such that they comprise regions with very high strength (very hard regions), i.e. regions with high ultimate tensile strength and high yield strength and regions with increased ductility (softer regions), i.e. regions with lower ultimate tensile strength and lower yield strength and increased elongation before break, it may be possible to improve their overall energy absorption and maintain their structural integrity during a crash situation and also reduce their overall weight. Such soft zones may also advantageously change the kinematic behavior in case of a collapse of a component under an impact.

[0010] Known methods of creating regions with increased ductility ("softzones" or "soft zones") in structural components of vehicles include the provision of tools comprising a pair of complementary upper and lower die units, each of the units having separate die elements (steel blocks). A blank to be hot formed is previously heated to a predetermined temperature e.g. austenization temperature or higher by, for example, a furnace system so as to decrease the strength i.e. to facilitate the hot stamping process.

[0011] The die elements may be designed to work at different temperatures, in order to have different cooling rates in different zones of the part being formed during the quenching process, and thereby resulting in different material properties in the final product e.g. soft areas which will generally have a lower ultimate tensile strength and a lower yield strength, but allow for more elongation before breaking. E.g. one dieelement may be cooled in order to quench the corresponding area of the component being manufactured at high cooling rates and to thereby reduce the temperature of the component rapidly and obtain a hard martensitic microstructure. Another neighboring die element may be heated in order to ensure that the corresponding portion of the component being manufactured cools down at a lower cooling rate, in order to obtain a softer microstructure, including e.g. bainite, ferrite and / or perlite. Such an area of the component may remain at higher temperatures than the rest of the component when it leaves the die.

[0012] Other methods for obtaining hot stamped components with areas of different mechanical properties include e.g. tailored or differentiated heating prior to stamping, and local heat treatments after a stamping process to change the local microstructure and obtain different mechanical properties. Yet further possibilities include the use of patchwork blanks, and Tailor Welded Blanks (TWB) combining different thicknesses and / or materials in blanks.

[0013] LIHSS may exhibit tensile strengths as high as 1.500 MPa, or even 2.000 MPa or more, particularly after a press hardening operation. Once hardened, a LIHSS may have a martensitic microstructure. This microstructure enables an increased maximum tensile strength and yield strength per weight unit.

[0014] In addition to the Ultra-high Strength Steels mentioned before, more ductile steels may also be used in parts of the structural skeleton requiring energy absorption. These steels may be used in hot stamping processes but will not obtain a martensitic microstructure in the process. Ductibor® 1000 is an example of a suitable, more ductile steel.

[0015] The rear frame of the structural skeleton of a vehicle may be formed by connecting multiple structural parts. These structural parts can form a rear ring which completely surrounds the back door of the vehicle and which in crash events plays an important role in the protection of the vehicle integrity. The back door of the vehicle may also be called “tailgate”. In general, the rear ring of a vehicle comprises four beams, i.e. left and right rear pillar portions and upper and lower cross members.

[0016] The four beams comprising the rear ring may have different thicknesses and may be manufactured differently. After manufacturing these four beams, they are generally welded together when being assembled with the rest of the vehicle framework or “Body-in-White”.

[0017] One problem that has been encountered is that the several welding spots and seams can lead to vulnerable parts in collision. Other issues to be considered are weight, manufacturability, time necessary to build the vehicle and cost.

[0018] The present disclosure provides examples of systems and methods that provide improvements over prior art rear vehicle structures.SUMMARY

[0019] In a first aspect, a method for manufacturing a unitary rear ring of a vehicle structural framework is provided. The rear ring substantially completely surrounding a back door opening of the vehicle. The method comprises providing a plurality of blanks, joining the blanks to form a combined blank and deforming the combined blank to form a unitary rear ring, wherein the unitary rear ring includes first and second rear pillar portions each connected to an upper cross member and to a lower cross member to form a substantially closed ring shape.

[0020] By first joining the blanks to each other to form a combined blank and then deforming the combined blank, a relatively lightweight and structurally resistant rear ring can be built in fewer manufacturing steps. Joining the blanks together prior to deforming enables manufacturing a rear ring with no or less heat affected zones, because welding operations after forming are reduced. Less heat affected zones reduce the risk of cracks in the rear frame of the structural skeleton in case of a collision. All this may allow having an increase in strength of the rear ring while reducing thickness of the blanks and reducing the weaknesses of the final rear ring. The crash performance may therefore be improved while achieving a mass reduction of the rear frame of the vehicle.

[0021] In some examples, joining the blanks comprises forming one or more overlapping regions formed by partially overlapping the blanks with each other. In this disclosure, partially overlapping two blanks means that only a portion of the two blanks overlaps. I.e. this is to be understood as that one blank is not entirely encompassed by another blank either before or after joining.

[0022] The one or more overlapping regions may be arranged to counteract the reduction of material and therefore of strength that may occur in some sections of the unitary rear ring when compared to solutions wherein the structural components are first formed and then joined to form the rear structural frame.

[0023] Alternatively, or additionally, the overlap may be arranged in locations wherein high loads are expected e.g. by arranging patch blanks within the blanks.

[0024] In some examples, the plurality of blanks may comprise first and second rear pillar blanks and upper and lower cross member blanks.

[0025] In some examples, one of the overlapping regions may be formed in a junction of the lower cross member with one of the rear pillar portions. In other examples, overlapping regions may be formed in each of the junctions of the rear pillar portion with the upper and lower cross members.

[0026] Throughout the present disclosure, upper and lower cross member blanks may be regarded as blanks that are subsequently deformed to form the upper and lower cross members of the rear ring of the vehicle. Similarly, the rear pillar blanks may be regarded as blanks that are subsequently deformed to form rear pillar portions of the rear ring of the vehicle.

[0027] Throughout the present disclosure, a back door opening of a vehicle may be regarded as the empty space or hole present in the rear part of the vehicle, generally covered by a tailgate.

[0028] In some examples, the plurality of blanks may be made from an ultra-high strength steel (LIHSS), one or more of the blanks may be made specifically from boron steel. In other examples, the plurality of blanks may be made of aluminium.

[0029] In some examples, the unitary rear ring may comprise regions of increased ductility. Specific strength, anti-intrusion and energy absorption requirements may be achieved and weight may be optimized.

[0030] In some examples, deforming the combined blank to form a unitary rear ring of a vehicle framework comprises hot stamping the combined blank. Hot stamping is a process which allows suitable deformation of ultra-high strength steel to form the complicated resulting structure of the unitary rear ring.

[0031] In some examples, deforming the combined blank may be done in a single operation. Deforming the combined blank in a single operation may result in the improvement of the efficiency of the manufacturing process of a rear ring of a vehicle framework.

[0032] In a further aspect, a unitary rear ring as obtained by a method according to any of the examples herein described is provided.BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Non-limiting examples of the present disclosure will be described in the following, with reference to the appended figures, in which:Figure 1 shows an example of a unitary rear ring of a vehicle framework;Figure 2 shows an example of a plurality of blanks prior to being joined to form a combined blank;Figure 3 shows an example of a schematic view of a combined blank formed by the four joined blanks of figure 2;Figure 4 shows another example of a plurality of blanks prior to being joined to form a combined blank;Figure 5 shows a combined blank formed by the blanks of figure 4 with additional patch blanks;Figure 6 shows an example of six blanks prior to being joined to form a combined blank;Figure 7 shows the plurality of blanks of figure 6 joined together and forming a combined blank;Figure 8 shows a further example of a plurality of blanks prior to being joined to form a combined blank;Figure 9 shows a combined blank formed by joining the blanks of figure 8; shows an example of a combined blank comprising patch blanks; andFigure 10 is a flow chart of a method for manufacturing a unitary rear ring of a vehicle framework.

[0034] The figures refer to example implementations and may only be used as an aid for understanding the claimed subject matter, not for limiting it in any sense.DETAILED DESCRIPTION OF EXAMPLES

[0035] In these figures, the same reference signs have been used to designate matching elements.

[0036] Figure 1 schematically represents a unitary rear ring 100 of a vehicle framework according to an example of the present disclosure. The unitary rear ring 100 includesfirst and second rear pillar portions 10, 20 each connected to an upper cross member 30 and to a lower cross member 40 to form a substantially closed ring shape.

[0037] In some examples, the unitary rear ring 100 may be installed in the rear frame of the vehicle framework and may define a rear structural frame of a vehicle. The rear ring substantially completely surrounds a back door opening of the vehicle. The rear ring may connect both lateral sides of the vehicle. The unitary rear ring may be joined to other parts of the vehicle framework, like the A-pillars, C-pillars and rear panels.

[0038] Hinges for rotating the back door open may be arranged along the upper cross member 30.

[0039] The unitary rear ring 100 may be made from a plurality of blanks in a single deformation process. As schematically illustrated in Figure 2, the unitary rear ring 100 may be made from four blanks, a first blank 1 , a second blank 2, a third blank 3 and a fourth blank 4, wherein the first and second blanks 1 , 2 may be rear pillar blanks 1 , 2, and the third and fourth blanks 3, 4 may be upper and lower cross member blanks 3, 4. The blanks may be joined to form a combined blank. The rear pillar blanks 1 , 2 may be joined to the upper cross member blank 3 and to the lower cross member blank 4.

[0040] A combined blank 5 including the four blanks 1 , 2, 3, 4 may thus be formed as shown in Figure 3. In a subsequent step, the combined blank 5 may be deformed. Particularly, the combined blank may be heated to above an austenization temperature, e.g. around 900 - 920°C in a furnace or an alternative heating system. And subsequently, the combined blank may be deformed and hardened in a press apparatus. Particularly, rapid cooling above a critical cooling rate of the combined blank may achieve a martensitic microstructure and high ultimate tensile strength and high yield strength.

[0041] In some examples, joining the blanks to form a combined blank 5 comprises providing the combined blank 5 with a substantially squared (annular) shape. The combined blank 5 may substantially comprise two portions corresponding to the rear pillar portion blanks 1 , 2. These are shown as vertical portions in figure 3. The combined blank may further comprise two portions, substantially perpendicular to the previous portions (shown horizontally in figure 3), and corresponding to the upper and lower cross member blanks 3, 4. Even though the portions are shown as vertical and horizontal, it will be clear that the combined blank may be positioned in a substantially flat position in a press. The combined blank 5 may delimit or delineate a back dooropening of the vehicle, substantially surrounding a back door opening of the vehicle. The opening typically comprises two upper corners and two lower corners.

[0042] In some examples, the blanks may be joined with each other forming one or more overlapping regions 6 formed by partially overlapping the blanks with each other. That is, one blank is only partially positioned over another blank and the blanks are then joined to each other. An overlapping region thus acquires an increased thickness as compared to the remainder of the blanks. Such an increase in thickness can be used to tailor mechanical properties as needed and provide local reinforcements, e.g. in areas where increased strength and / or stiffness are required.

[0043] In some examples, overlapping regions 6 may be formed at or near a junction or transition of the lower cross member 30 with one of the rear pillar portions 10, 20. When combining the different components into a unitary rear ring 100 by deforming a single blank, these junctions have less material than they would have when separately manufacturing component and subsequently welding them together. By providing overlapping regions 6 at or near those junctions, extra material can be added and thus maintain mechanical behaviour and kinematic properties of the rear ring 100.

[0044] The overlapping region of this example may have a surface area of e.g. 5 - 30 cm2, specifically of about 8 -20 cm2. In examples, the overlapping region at the junction of pillar and cross member may occupy substantially the width of the pillar, and substantially the height of the cross member.

[0045] In other examples, the combined blank might be formed by edge-to-edge welding of blanks (like a Tailor Welded Blank), or the combined blank might be formed both by using overlapping blanks in specific regions, and using edge-to-edge welding in other regions.

[0046] Welding, and specifically edge-to-edge welding may involve the ablation or other removal of a part of a coating of the blanks if the blanks are coated. AlSi coatings and Zn coatings are well known in the art. In further examples, a filler material may be used to dilute the coating in the weld zone. The filler material may be a filler wire, and in specific examples, multiple laser beams may be used to melt the blanks and the filler wire.

[0047] In other examples, overlapping regions 6 may be formed at one or more of the junction of the pillars with the cross-members. In particular, an overlapping region may be formed at each of the junctions of the upper and lower cross members 30, 40 withthe two rear pillar portions 10, 20. Suitable dimensions for the overlapping region 6 may be chosen taking into account weldability, strength and stiffness requirements. A larger overlapping region 6 means an increase in thickness over a larger area, and thus an increase in strength and stiffness locally in the rear ring 100. In some examples, the overlapping region 6 may have a length Li corresponding to a width of the rear pillar portion 10, 20.

[0048] At least an overlapping region 6 may be formed within the upper cross member 30 of the rear ring. The blanks constituting the rear pillars 10, 20 overlap with the blank(s) constituting the upper cross member 30. In the resulting product, the overlap may be positioned completely or almost completely within the upper cross member 30 of the resulting unitary rear ring 100. The overlapping may be done by any of laser welding, arc welding or spot welding. In some examples, the areas where the hinges of the back door are arranged may be reinforced using a partial overlap.

[0049] In some examples, as shown in Figure 3, joining the blanks comprises joining a first end of a first rear pillar blank 1 to a first end of an upper cross member blank 3 and a second end of the first rear pillar blank 1 to a lower cross member blank 4. Further, joining the blanks comprises joining a first end of a second rear pillar blank 2 to a second end of an upper cross member blank 3 and a second end of a second rear pillar blank 2 to a lower cross member blank 4. The blanks may be welded to each other, e.g. through laser welding or spot welding. The region 6 where the blanks are joined may be seen in Figure 3.

[0050] In some examples, the overlapping portion at the junction of the rear pillar portion and the upper cross member may be located in a substantially horizontal portion of the rear ring. In particular, the overlapping region 6 located in the upper cross member blank 3 may be positioned entirely within the upper cross member i.e. rather than extending vertically within the rear pillar. In these examples, the overlapping regions 6 in the combined blank 5 formed by joining the first rear pillar blank 1 to the upper and / or lower cross member blanks 3, 4 may be longitudinally displaced from one another.

[0051] In addition, in the example shown in figure 3, the overlapping region 6 formed by joining the rear pillar blank 2 with the lower cross member 4 may not be entirely positioned within the rear pillar portion of the rear ring, but rather may also extend horizontally into the lower cross member. In some examples, the overlapping regions 6 may substantially delimit an upper portion and a lower portion of the back dooropening. In some examples, the overlapping regions 6 may substantially delimit the upper and / or the lower corners of the rear door opening.

[0052] In some examples, the rear pillar blanks 1 , 2 may be joined to the upper and lower cross member blanks 3, 4 on the outer / upper side of the rear ring. In other examples, the rear pillar blanks 1 , 2 may be joined to the upper and lower cross member blanks 3, 4 on the inner / lower side of the rear ring.

[0053] Figure 4 shows another example of four blanks 1 , 2, 3, 4 which may be joined together to form a unitary rear ring 100 of a vehicle framework. As may be appreciated, the blanks shown in the example of figure 4 have a different shape than the ones shown in the example of figures 2 and 3. In this particular example, the blanks 3 and 4 which will constitute the cross-members include “vertical portions”, i.e. portions which will be arranged in the rear pillars. The blanks 1 and 2 of this example will constitute the rear pillars, but also include small “Horizontal extensions”, i.e. portions which will be arranged in the lower cross member. The combined blank 5 resulting from joining the four blanks of figure 4 together by overlapping the blanks with each other is schematically illustrated in figure 5.

[0054] Figure 5 shows overlapping regions 6 in each of the junctions or transitions of the upper and lower cross members blanks 3, 4 with the two rear pillar blanks 1 , 2. The overlapping regions located in the lower cross member blank of figure 5 is the same as the one disclosed in figure 3. However, in the example of figure 5, the two overlapping regions 6 formed in each of the rear pillar blanks 1 , 2 are substantially aligned longitudinally, the overlapping portions of the rear pillar blank 1 and the upper and lower member blanks 3, 4 being located in a substantially vertical portion of the rear ring. That is, the overlapping regions of this example are substantially located within the rear pillars.

[0055] As schematically illustrated in Figure 5, in some examples a patch blank 7 may be joined to at least one of the plurality of the blanks that may form the combined blank 5. A patch blank may be regarded herein as a blank that entirely overlaps another blank, i.e. a patch blank may be positioned entirely within a perimeter of another blank. The patch blank may be joined to the other blank by welding, e.g. spot welding or remote laser welding. The resulting combination of “basic” blank and patch blank may sometimes be referred to as “patchwork blank”.

[0056] A patch blank 7 may be added as a reinforcement in order to increase strength of a specific area of the combined blank 5. A patch blank 7 may be added in areas ofthe rear ring where additional strength may be needed, that is, where high loads may be expected.

[0057] In some examples, the patch blank 7 may be located in an area where the hinges of the back door may be arranged later. In some examples a patch blank 7 may be arranged within the upper cross member blank 3. In some examples, the patch blank 7 may have the same width as the upper cross member blank 3. In other examples, the width of the upper cross member blank 3 may be higher than the width of the patch blank 7.

[0058] In the example of figure 5, two patch blanks 7 are arranged in the upper cross member blank 3, such that the patch may only be located in a substantially horizontal portion of the rear ring. In other examples, a patch blank 7 may also be arranged in the rear pillar blanks 1 , 2 and / or in the lower cross member blank 4.

[0059] The patch blanks 7 may be joined to the upper cross member blank 3 by overlapping one of the blanks with the other blank and using spot welding. In other examples, alternative welding techniques may be used e.g. laser welding or arc welding. Laser welding using stitches along a perimeter of an overlapping region has been found to be effective in terms of manufacturing and to improve the behaviour in case of a crash.

[0060] In further examples, as shown in figures 6 and 7, the plurality of blanks may be formed by a plurality of blanks or sub-blanks, e.g. of different thicknesses and / or different materials. In these examples, the plurality of blanks forming the rear pillar blanks and / or the upper and lower cross member blanks may be Tailor Welded Blanks (TWB). The TWB may be formed by joining the sub-blanks by edge-to-edge welding, wherein welding may comprise laser welding. In other examples, the plurality of blanks forming the rear pillar blanks 1 , 2 and / or the upper and lower cross member blanks 3, 4 may be joined by forming one or more overlapping regions 6 formed by partially overlapping the blanks to each other. In these cases, any of laser welding, arc welding or spot welding may be used.

[0061] In the particular example of figures 6 and 7, the first rear pillar blank 1 is formed by two sub-blanks 1 a, 1 b and the second rear pillar blank 2 is formed by two sub-blanks 2a, 2b.

[0062] Figure 7 shows the combined blank 5 obtained after joining the blanks illustrated in figure 6. The combined blank 5 of figure 7 comprises in addition to theoverlapping regions 6 of the combined blank 5 of figure 5, an additional overlapping region 6 located in the rear pillar portion of the combined blank 5. Accordingly, the rear pillars may comprise three overlapping regions. Increased stiffness in a wider area of the unitary rear ring may be provided and higher loads may be withstood by increasing the number of the overlapping regions 6.

[0063] Figure 8 shows a further example of a plurality of blanks which may be joined together to be deformed and form a unitary rear ring 100. The shape of the plurality of blanks 1 , 2, 3, and 4 is different from the shape of the other blanks disclosed in the previous examples. Accordingly, the combined blank 5 formed by joining the blanks to each other may comprise overlapping regions 6 positioned in different locations of the combined blanks 5 of figures 3, 5 and 7.

[0064] In particular the overlapping regions 6 of the combined blank 5 of figure 9 delineate part of the lateral side of the back door opening of the vehicle. As shown in figure 9, the rear ring obtained after deforming the combined blank 5 may comprise two overlapping regions 6 located within the rear pillars, rather than within the rear pillars and the upper and lower cross members.

[0065] In some examples, the plurality of blanks that form the combined blank 5 may be made from different materials. In some examples, the blanks 1 , 2, 3, 4 may be made from ultra-high strength steels (LIHSS). Boron steel, e.g. 22MnB5, or other steel compositions mentioned or referred to before may be suitable LIHSS. These blanks, e.g. boron steel blanks, may comprise an aluminum silicon coating or zinc coating.

[0066] llsibor® 1500P is an example of a 22MnB5 steel. The composition of llsibor® is summarized below in weight percentages (rest is iron (Fe) and impurities):Maximum carbon (C) (%): 0.25Maximum silicon (Si) (%): 0.4Maximum manganese (Mn) (%): 1.4Maximum phosphorus (P) (%): 0.03Maximum sulphur (S) (%): 0.01Aluminium (Al) (%): 0.01 - 0.1Maximum titanium (Ti) (%): 0.05Maximum niobium (Nb) (%): 0.01Maximum copper (Cu) (%): 0.20Maximum boron (B) (%): 0.005Maximum chromium (Cr) (%): 0.35

[0067] llsibor® 1500P may have a yield strength of e.g. 1.100 MPa, and an ultimate tensile strength of 1.500 MPa.

[0068] llsibor® 2000 is another boron steel with even higher strength. The yield strength of Usibor® 2000 may be 1.400 MPa or more, and the ultimate tensile strength may be above 1.800 MPa. The composition of Usibor® 2000 is summarized below in weight percentages (rest is iron (Fe) and impurities):Maximum carbon (C) (%): 0.36Maximum silicon (Si) (%): 0.8Maximum manganese (Mn) (%): 0.8Maximum phosphorus (P) (%): 0.03Maximum sulphur (S) (%): 0.01Aluminium (Al) (%): 0.01 - 0.06Maximum titanium (Ti) (%): 0.07Maximum niobium (Nb) (%): 0.07Maximum copper (Cu) (%): 0.20Maximum boron (B) (%): 0.005Maximum chromium (Cr) (%): 0.50Maximum molybdenum (Mb) (%): 0.50

[0069] The plurality of blanks that form the combined blank 5 may comprise different material and / or thicknesses. For example, blanks of Usibor® (e.g. Usibor® 1500 and / or Usibor® 2000) may be used in the blanks forming the combined blank 5. Using these types of materials in hot forming and subsequent quenching processes leads to a predominantly martensitic structure due to the Usibor®. One or more of the blanks may be made from a different material, e.g. Ductibor® 1000. In further examples, blanks may be made of the same material, e.g. boron steel or aluminium, but their thickness may be varied.

[0070] Ductibor® 1000 is another material used in hot stamping for increasing the elongation when compared to llsibor® 1500 and llsibor® 2000. The yield strength of Ductibor® 1000 may be 800 MPa or more, and the ultimate tensile strength of 1000 MPa or more. The composition of Ductibor® 1000 is summarized below in weight percentages (rest is iron (Fe) and impurities):Maximum carbon (C) (%): 0.10Maximum silicon (Si) (%): 0.6Maximum manganese (Mn) (%): 1.8Maximum phosphorus (P) (%): 0.03Maximum sulphur (S) (%): 0.01Aluminium (Al) (%): 0.01 - 0.1Maximum titanium (Ti) (%): 0.05Maximum niobium (Nb) (%): 0.10Maximum copper (Cu) (%): 0.20Maximum boron (B) (%): 0.005Maximum chromium (Cr) (%): 0.20

[0071] In some examples, the blank may comprise aluminium. The aluminium of the blank may be an aluminium alloy selected from the groups 6000 and 7000 series aluminium alloys. These series are characterized by their strength, corrosion resistance and weldability.

[0072] In some examples, the unitary rear ring 100 may comprise areas with different ultimate tensile strength according to any of the examples herein described. In some of these examples, different materials may be used in the combined blank.

[0073] In some of these examples, the areas with different ultimate tensile strength may have a different microstructure.

[0074] Different microstructures may be created in a hot formed rear ring. These different microstructures may be created by heating a combined blank 5 above the austenitization temperature and then controlling the cooling of the combined blank 5 during shaping the combined blank 5 to form a rear ring 100 of a vehicle framework. The cooling of different areas of the combined blank 5 may be controlled by providing zones of the forming tool with heaters. Accordingly, the unitary rear ring 100 compriseszones with a predominantly martensitic structure and zones comprising ferrite, perlite or bainite or a mixed of thereof. Alternatively, a different microstructure, may be created by partially heating, e.g. using a laser beam, a portion of the unitary rear ring which has been press-hardened to change the predominantly martensitic structure to a structure containing ferrite and / or perlite and / or bainite and / or tempered martensite and a mixed of thereof. The tensile strength of the predominantly martensitic structure may be above 1400 MPa, and specifically above 1500 MPa.

[0075] The unitary rear ring 100 may thus be made from a material which may be effective for absorbing energy during an impact. In some examples, the rear pillar blanks 1 , 2 may be made at least from an ultra-high strength steel.

[0076] The thickness of the rear pillar portions 10, 20 may be of 0.5 - 2.5 mm, specifically of 0.8 - 2 mm. The rear pillar portions 10 may have an ultimate tensile strength of 1000 - 2000 MPa, specifically of 1500 - 2000 MPa.

[0077] In some examples, the cross member blanks 3, 4 may be made at least from an ultra-high strength steel.

[0078] The thickness of the upper and lower cross members 30, 40 may be of 0.5 - 2.5 mm, specifically of 0.8 - 2 mm. An overlapping region may have a thickness of 2 - 5mm, specifically 2 - 3.8 mm.

[0079] The upper and lower cross members 30, 40 may have an ultimate tensile strength of 1000 - 2000 MPa, specifically of 1500 - 2000 MPa. In some examples, the thickness of the upper and lower cross members 30, 40 may be less than the thickness of the rear pillars 10, 20. In other examples, the thickness of the upper and lower cross members 30, 40 may be equal to the thickness of the rear pillars 10, 20.

[0080] In some examples, joining the blanks to each other comprises welding the blanks to each other. In some examples, the blanks may be welded by spot welding and / or laser welding. In some examples, the combined blank formed by joining the blanks may be a Tailor Welded Blank. Joining the blanks before the deformation may make the joining easier due to the blanks being substantially flat at the moment of joining. Welding blanks prior to the deformation process by laser and / or spot welding may be efficient and precise.

[0081] Figure 10 schematically illustrates an example of the composite blank 5 of figure 3 after deforming.

[0082] Joining the blanks may result in weld seams or spots, critical areas which in case of a car crash may be easily broken. Deforming after joining may ensure that weld seams or spots are not present between blanks, providing a unitary rear ring 100 more resistant to crash events than other upper structural frames wherein the structural components are formed first and then joined. The hazards caused by these weld seams or spots disappear in the unitary rear ring 100, thereby reducing the risk of cracks in the unitary rear ring 100 in crash events. In addition, a unitary rear ring 100 may reduce time required to build a vehicle and may enable reducing thickness of neighbouring components of the rear ring 100 without compromising the thickness of its structural elements.

[0083] In some examples, deforming the combined blank 5 to form the unitary rear ring 100 may comprise hot forming or hot stamping the combined blank 5.

[0084] In some examples, hot forming may comprise heating the combined blank 5 above the austenitization temperature, and then forming the combined blank 5 to create the unitary rear ring 100. In some examples, forming may comprise two or more forming steps. These forming steps may comprise for example shaping, trimming or cutting and may be made in a single multi-stage press. Examples of multi-stage presses are known from e.g. US 9,492,859 B2 and WO 2016142367 A1.

[0085] Deforming may include hot forming, i.e. heating the combined blank 5 in an oven, possibly above an austenization temperature, specifically above Ac3. After heating in the oven, the combined blank 5 may be transferred to a press in which the combined blank 5 is deformed to obtain the final shape of the unitary rear ring 100. During and immediately after forming, quenching may be carried out. In particular, the quenching may include cooling above a critical cooling rate so that a martensitic microstructure is obtained.

[0086] In some examples, quenching may be avoided in selected portions of the rear ring. The unitary rear ring may comprise regions of increased ductility.

[0087] In some examples, deforming is done in one single operation. Deforming the combined blank 5 may provide a unitary rear ring 100 including two rear pillars 10, 20 each connected to an upper cross member 30 and to a lower cross member 40 to form a substantially closed ring shape.

[0088] In further examples, a rear ring 100 having substantially a ring shape comprising an upper cross member 30, a lower cross member 40, a first rear pillarportion 10 and a second rear pillar portion 20 may be made by deforming a single blank.

[0089] The unitary rear ring 100 of the present disclosure may have improved crash resistance and may be produced with less processes. Therefore, the crash performance may be improved while reducing mass of the structural skeleton of the vehicle and building complexity.

[0090] Figure 11 represents a flow chart of a method 200 for manufacturing a unitary rear ring of a vehicle framework. The method comprises providing a plurality of blanks 201 ; joining the blanks to each other to form a combined blank 202; deforming the combined blank to form a unitary rear ring 203.

[0091] In some examples, providing a plurality of blanks 201 may comprise providing a first and a second rear pillar blank 1 , 2, an upper cross member blank 3 and a lower cross member blank 4. In some examples, the plurality of blanks that form the combined blank 5 may be made from different materials. In some examples, the rear pillar blanks 1 , 2 and the upper and lower cross member blanks 3, 4 may be made from an ultra-high strength steel. In other examples the plurality of blanks may be made from aluminium.

[0092] In some examples, joining the blanks to each other to form a combined blank 202 may comprise forming one or more overlapping regions 6 formed by partially overlapping the blanks to each other. The overlapping region 6 may be formed in or near a junction or transition of the upper cross member 30 with one of the rear pillar portions 10, 20. The overlapping regions 6 may be formed in each of the junctions of the upper and lower cross members 30, 40 with the two rear pillar portions 10, 20.

[0093] Deforming the combined blank to form a unitary rear ring 203 may comprise hot forming or hot stamping the combined blank 5. Different microstructures may be created in a hot formed rear ring. These different microstructures may be created by heating a combined blank 5 above the austenization temperature. In some examples, during and after forming, quenching may be carried out. Quenching may include cooling above a critical cooling rate so that a martensitic microstructure is obtained.

[0094] In some examples, different microstructures may be obtained by heating a combined blank 5 above the austenization temperature and then controlling the cooling of the combined blank 5 during shaping the combined blank 5 to form a unitary rearring 100. In some examples, quenching may be avoided in selected portions of the unitary rear ring 100.

[0095] In some examples, deforming the combined blank to form a unitary rear ring 203 may be done in a single operation. The unitary rear ring 100 formed by deforming the combined blank 203 includes two rear pillar portions each connected to an upper cross member and to a lower cross member to form a substantially closed ring shape.

[0096] Although only a number of examples have been disclosed herein, other alternatives, modifications, uses and / or equivalents thereof are possible. Furthermore, all possible combinations of the described examples are also covered. Thus, the scope of the present disclosure should not be limited by particular examples, but should be determined only by a fair reading of the claims that follow.

Claims

CLAIMS1. A method for manufacturing a unitary rear ring (100) of a vehicle framework, the rear ring substantially completely surrounding a back door opening of the vehicle, the method comprising: providing a plurality of blanks (1 , 2, 3, 4); joining the blanks to form a combined blank (5); deforming the combined blank (5) to form the unitary rear ring (100); wherein the unitary rear ring (100) includes first and second rear pillar portions (10, 20) each connected to an upper cross member (30) and to a lower cross member (40) to form a substantially closed ring shape.

2. The method for manufacturing a unitary rear ring according to claim 1 , wherein joining the blanks comprises forming one or more overlapping regions formed by partially overlapping the blanks with each other.

3. The method for manufacturing a unitary rear ring according to claim 2, wherein an overlapping region is located in a substantially horizontal portion of the rear ring.

4. The method for manufacturing a unitary rear ring according to claim 2 or 3, wherein an overlapping region is located in a substantially vertical portion of the rear ring.

5. The method for manufacturing a unitary rear ring according to claim 2 - 4, wherein an overlapping region is formed in a junction of the lower cross member with one or more of the rear pillar portions.

6. The method for manufacturing a unitary rear ring according to claim 2 - 5, wherein overlapping regions are formed in each of the junctions of the rear pillar portions with the upper and lower cross members.

7. The method for manufacturing a unitary rear ring according to any of claims 1 - 6, wherein joining the blanks comprises welding the blanks to each other, and optionally comprises resistance spot welding and / or laser welding.

8. The method for manufacturing a unitary rear ring according to any of claims 1 - 7, wherein deforming the combined blank to form the unitary rear ring comprises hot stamping the combined blank.

9. The method for manufacturing a unitary rear ring according to any of claims 1- 8, wherein the plurality of blanks comprises first and second rear pillar blanks, an upper cross member blank and a lower cross member blank.

10. The method for manufacturing a unitary rear ring according to any of claims 1- 9, wherein a patch blank is joined to at least one of the plurality of blanks to form the combined blank.

11. The method for manufacturing a unitary rear ring according to claim 10, wherein the patch blank is arranged substantially in the upper cross member, and optionally wherein the patch blank is arranged near a junction of the upper cross member with one of the rear pillars.

12. The method for manufacturing a unitary rear ring according to any of claims 1 - 11 , wherein the plurality of blanks is made from an ultra high strength steel.

13. The method for manufacturing a unitary rear ring according to any of claims 1 - 11 , wherein the plurality of blanks is made of aluminium.

14. The method for manufacturing a unitary rear ring according to any of claims 1 - 13, wherein the unitary rear ring comprises regions of increased ductility.

15. A unitary rear ring (100) obtainable by a method according to any of claims 1 -

Images