Reinforcement insert for a vehicle side structure

Abstract

Side structure (1 ) for an automotive vehicle comprising a B-pillar (2), located between a front and a rear door opening, and a roof rail (3), extending along a roof panel, said roof rail (3) being attached to an upper portion (23) of said B-pillar (2) in an intermediate portion (33) of said roof rail (3), said B-pillar (2) comprising an inner and an outer B-pillar (21, 22) and said roof rail (3) comprising an inner and an outer roof rail (31, 32), said inner and outer parts (21, 22, 31, 32) enclosing a hollow volume (5), said side structure (1 ) comprising a reinforced portion (11 ) extending along said upper portion (23) of said B-pillar (2) and along said intermediate portion (33) of said roof rail (3), wherein an insert (6) occupies part of said hollow volume (5) in said reinforced portion (11 ) and wherein said insert (6) is made of metallic material.

Description

[0001] Reinforcement insert for a vehicle side structure

[0002]

[0001] The present invention relates to an automotive vehicle side structure and more precisely to the B-pillar (also known as center pillar) and roof rails, which are located respectively in between the front and rear door opening and alongside the roof panel. The top of the B-pillar and the center of the roof rail, in the area where it is joined to said B-pillar, plays an important structural role in the case of a crash. For example, in the case of a side impact or in the case of a rollover scenario, in which the vehicle rolls over onto itself. In this latter situation, when the vehicle is turned upside down, there is a risk that the weight of the vehicle crushes the top frame of the vehicle, seriously jeopardizing the safety of the occupants.

[0003]

[0002] This rollover scenario is the object of several regulatory tests. The American Insurance Institute for Highway Safety (I IHS), the European New Car Assessment Program (Euro-NCAP) and the Chinese New Car Assessment Program (C-NCAP) all provide for rollover roof crush tests to simulate the crushing force that the weight of a vehicle exerts onto its own top frame when rolling over onto itself. In these tests, an angled metal plate is pushed down on to one side of the roof at a slow but constant speed and forced to advance by 127mm inside the vehicle structure. The necessary force to reach this displacement is recorded and compared to the curb weight of the vehicle to compute a strength to weight ratio. More precisely, the peak force F to reach the desired 127mm of crush, expressed in Newtons, is divided by the equivalent force M of the vehicle weight, also expressed in Newtons and obtained by multiplying the curb weight by 9.8m / s2. The result is called the strength to weight ratio - because it is the result of the division of two values both expressed in Newtons, the strength to weight ratio itself is a dimensionless value. The minimum strength to weight ratio to pass the test is 1.5 in China, 2.75 in Europe and 4 in North America. Examples of how to compute this strength to weight ratio can be found in table 3 below.

[0004]

[0003] With the advent of electric power trains, automotive vehicles are getting heavier due to the added weight of the underfloor batteries. According to the size and range of the vehicle, the battery pack can reach more than one ton. This additional weight increases the pressure on the B-pillar and roof rails. This concerns all types of models and is all the more critical in the case of heavy and top-heavy vehicles such as electrical sport utility vehicles (SLIVs) and particularly high-end SLIVs advertising long driving ranges and thus heavy battery packs.

[0005]

[0004] In order to pass the roof crush tests in these increasingly severe conditions, car manufacturers can redesign the architecture of the vehicles in order to use more resistant and thicker materials for the top of the B-pillar and the side rail. Such redesigns however result in overall heavier vehicles and are costly. Another solution is to use custom composite inserts, fitted into the hollow volumes of the B-pillar and side rails. However, producing these composite inserts requires producing specific tooling and their assembly into the vehicle structure is a complex and potentially costly additional manufacturing step.

[0006]

[0005] The current invention provides for a vehicle side structure which can withstand severe crash conditions, in particular roof crush conditions, while minimizing the complexity of vehicle redesign and additional assembly steps. Furthermore, the current invention allows for a flexible solution that is suitable to reinforce the side structure without having to redesign it, allowing on the same platform to produce reinforced and non-reinforced side structures. For example, this allows to produce lower and higher weight vehicles on the same platform, for example to accommodate for a range of models on the same platform, from basic models having small lightweight battery packs to higher end vehicles having large and heavy battery packs.

[0007]

[0006] The current invention further provides for an assembly process to produce such a reinforced vehicle side structure.

[0008]

[0007] The object of the present invention is achieved by providing a side structure according to claim 1 , optionally comprising the features of claims 2 to 10 taken individually or according to any possible combination.

[0009]

[0008] Other aspects and advantages of the invention will appear upon reading the following description, given by way of example, and made in reference to the appended drawings, which are in no way limitative, wherein:

[0009] -Figure 1 is an overall perspective view of a vehicle highlighting the position of a side structure according to the invention.

[0010]

[0010] -Figure 2 is a perspective view of a first embodiment of a side structure according to the invention.

[0011]

[0011] -Figure 3 is a perspective view of a specific embodiment of an insert according to the invention.

[0012]

[0012] -Figures 4a, 4b, 4c are perspective views of an assembly sequence of an embodiment of the manufacturing process of a side structure according to the invention.

[0013]

[0013] In the following descriptions and claims, the directional terms are defined according to the usual directions of a mounted vehicle.

[0014]

[0014] In particular, the terms “top”, “up”, “upper”, “above”, “bottom”, “low”, “lower”, “below” etc. are defined according to the elevation direction of a vehicle. The terms “front”, “back”, “rear”, “front”, “forward”, backward” etc. are defined according to the longitudinal direction of a vehicle, i.e. the direction in which the vehicle moves forward when following a straight line. The terms “left”, “right”, “transverse”, etc. are defined according to the orientation parallel to the width of the vehicle. The terms “steering side” and “passenger side” referred to the general transversal direction respectively of where the driver and the passenger sit in a vehicle. Such directions will naturally be different according to whether the vehicle is a left-hand or right-hand drive vehicle. The terms “inner”, “outer” are to be understood according to the width direction of the vehicle: the “inner” is closest to the central axis of the vehicle, i.e. closest to the inside of the vehicle, whereas the “outer” is located further away from said central axis of the vehicle, in effect closer to the outside of the vehicle. The same applies to the terms “distal” and “central”: the “distal” part is located closest to the outside of the vehicle and the “central” part closest to the center of the vehicle. The term “horizontal” refers to the orientation of the plane comprising the longitudinal and the transverse directions. The term “vertical” refers to any orientation comprising the elevation direction.

[0015]

[0015] In the following figures, the orientations and spatial references are all made using an X, Y, Z coordinates referential, wherein Z is the elevation direction of the vehicle, X is the longitudinal direction of the vehicle and Y is the transverse direction of the vehicle. The X axis is oriented such that the X coordinates increase in the front to rear direction, i.e. a position located further back in the vehicle will have a higher X coordinate than a position located further in the front of the vehicle. The referential is represented in each figure. When the figure is a 2D flat representation, the axis which is outside of the figure is represented by a dot in a circle when it is pointing towards the reader and by a cross in a circle when it is pointing away from the reader, following established conventions.

[0016]

[0016] By “substantially parallel” or “substantially perpendicular” it is meant a direction

[0017]

[0017] which can deviate from the parallel or perpendicular direction by no more than 15°.

[0018]

[0018] A steel sheet refers to a flat sheet of steel. It has a top and bottom face, which are also referred to as a top and bottom side or as a top and bottom surface. The distance between said faces is designated as the thickness of the sheet. The thickness can be measured for example using a micrometer, the spindle and anvil of which are placed on the top and bottom faces. In a similar way, the thickness can also be measured on a formed part.

[0019]

[0019] By average thickness of a part, or of a portion of a part, it is meant the overall average thickness of the material making up the part after it has been formed into a 3-dimensional part from an initially flat sheet.

[0020]

[0020] Tailor welded blanks are made by assembling together, for example by laser welding, several sheets or cut-out blanks of steel, known as subblanks, in order to optimize the performance of the part in its different areas, to reduce overall part weight, to reduce overall part cost and to reduce material scrap. The sub-blanks forming the tailor welded blanks can be assembled with or without overlap, for example they can be laser butt-welded (no overlap), or they can be spot-welded to one another (with overlap).

[0021]

[0021] A flexible blank is a type of tailor welded blank including regions wherein at least part of the connection between the different sub-blanks is not rigid, allowing the sub-blanks to move in different directions during the forming operation in the corresponding regions.

[0022] By opposition to a tailor welded blank, a monolithic blank refers to a blank which consists of one single sub-blank, without several sub-blanks being combined together.

[0022]

[0023] A tailor rolled blank is a blank having multiple sheet thicknesses obtained by differential rolling during the steel sheet production process.

[0023]

[0024] A patched blank is a blank comprising a main blank to which is attached at least one further reinforcing blank, known as a patch, designed to locally increase the thickness and mechanical resistance of said blank. Said patch can be fixed to the main blank by spot welding, laser stitch welding, adhesive bonding, clinching or any other known assembly technique. The main blank can be a tailor welded blank, a tailor rolled blank or a combination of both. In the case of tailor welded blanks in which the subblanks are assembled together by butt to butt welding, a patch can be advantageously applied to the welded area in order to increase the mechanical resistance of the welded area.

[0024]

[0025] The ultimate tensile strength, the yield strength and the elongation are measured according to ISO standard ISO 6892-1 , published in October 2009. The tensile test specimens are cut-out from flat areas. If necessary, small size tensile test samples are taken to accommodate for the total available flat area on the part.

[0025]

[0026] The bending angle is measured according to the VDA-238 bending standard. For the same material, the bending angle depends on the thickness. For the sake of simplicity, the bending angle values of the current invention refer to a thickness of 1.5mm. If the thickness is different than 1.5mm, the bending angle value needs to be normalized to 1.5mm by the following calculation where a1.5 is the bending angle normalized at 1.5mm, t is the thickness, and at is the bending angle for thickness t:

[0026]

[0027] a1.5 = (at x t) / 1.5

[0027]

[0028] Cold stamping is a forming technology for metals which involves shaping a metallic sheet into a formed part by pressing it between an upper and lower die, called the cold stamping tool. For example, the cold stamping tool has a blank holder which allows to hold the metallic sheet on its sides. For example, the cold stamping tool consists of several steps, each involving an upper and lower die to produce complex shapes and I or to perform further operations such as punching holes in the part or trimming its sides. Other cold forming technologies exist such as for example roll forming, which involves bending a continuous sheet between a successive set of rolls, simple bending which involves simply bending a sheet of steel using a press and an upper and lower bending tool etc.

[0028]

[0029] Roll forming is a continuous metal forming process taking a sheet, a strip, or a coil and bending or forming it to a continuous cross section. The process is performed between successive pairs of rolls that change the shape until the desired section is completed. Said section is called the roll forming section and the direction in which the material is being roll formed, i.e. the direction separating two successive pairs of rolls, is called the roll forming direction.

[0029]

[0030] Hot stamping is a forming technology for steel which involves heating a blank of steel, or a preformed part made from a blank of steel, up to a temperature at which the microstructure of the steel has at least partially transformed to austenite, forming the blank or preformed part at high temperature by stamping it and simultaneously quenching the formed part to obtain a microstructure having a very high strength, possibly with an additional partitioning or tempering step in the heat treatment.

[0030]

[0031] A complex hot stamping process is a particular type of hot stamping process including at least one stamping step and consisting of at least two process steps performed at high temperature, above 300°C. For example, a complex process can involve a first stamping operation and a subsequent hot trimming operation, so that the finished part, at the exit of the hot stamping process, does not need to be further trimmed. For example, a complex process can involve several successive stamping steps in order to manufacture parts having more complex shapes than what can be realized using a single stamping operation. For example, the parts are automatically transferred from one operation to another by using for example a transfer press. For example, the parts stay in the same tool, which is a multipurpose tool that can perform the different operations, such as a first stamping and a subsequent in-tool trimming operation.

[0032] A partial hardening hot stamping process is a hot stamping process in which the heat profile to which the blank is submitted is purposely tailored to be different in different areas of the blank, in order to obtain different material properties in these different areas at the end of the hot stamping process. For example, this allows to produce hot stamped parts using a single metallic blank made of a single material which will have different levels of hardness and elongation in different areas of the final part. For example, this allows to produce parts having soft zones and hard zones, said soft zones being able to deform under an impact load in order to absorb energy, whereas said hard zones will resist intrusion by resisting deformation. There are several different technologies to implement partial hardening. For example, the material can be heated at different temperatures in different areas of the blank, the higher temperature areas will be fully austenitic at the exit of the austenitizing furnace resulting in a very hard microstructure after hot stamping, whereas the lower temperature areas will have an intercritical ferrite I austenite microstructure at the exit of the austenitizing furnace resulting in a lower hardness microstructure after hot stamping. For example, the material can be quenched at different quenching speeds in different areas of the blank during the hot stamping step itself, the areas quenched at a higher quenching speed will have a higher hardness than those quenched at a lower speed.

[0031]

[0033] Referring to figure 1 , an automotive vehicle having a side structure 1 is described. Said side structure 1 is designed to guarantee the overall stiffness of the vehicle and to guarantee the safety of its occupants in the event of a crash.

[0032]

[0034] The side structure 1 comprises a B-pillar 2, which extends substantially horizontally between the front and rear door openings. It also comprises a roof rail 3, which extends along a roof panel - said roof panel is not shown in the attached figures for clarity’s sake. The roof rail 3 and B-pillar 2 are attached to one another at the top of said B-pillar 2, in an upper portion 23 of said B-pillar and in between the two longitudinal extremities of said roof rail 3, in an intermediate portion 33 of said roof rail. Said roof rail intermediate portion 33 extends over the attachment area between the roof rail 3 and the B-pillar 2 and extends longitudinally towards the front and the back of the vehicle around said attachment area, but does not extend over the full length of said roof rail. In practice, it only occupies a small portion of the longitudinal length of said roof rail, for example less than 30% of said longitudinal length, for example less than 20% of said longitudinal length, for example less than 15% of said longitudinal length.

[0033]

[0035] In a specific embodiment, the B-pillar 2 and roof rail 3 are made of steel. For example, the roof rail and I or the B-pillar are made by hot stamping press hardening steel. For example, the roof rail and I or the B-pillar are made by hot stamping tailor welded blanks made from different grades and I or thicknesses of press hardening steel.

[0034]

[0036] In a specific embodiment, the B-pillar 2 and I or the roof rail 3 are made of aluminum.

[0035]

[0037] Referring to figure 2, in order to ensure a good rigidity and crash resistance of said side structure 1 , both the B-pillar and roof rail are made of inner and outer shells that enclose a hollow volume 5. Thus, the B-pillar 2 comprises an inner and an outer B-pillar 21 , 22 and the roof rail 3 comprises an inner and an outer roof rail 31 , 32, said inner and outer parts 21 , 22, 31 , 32 enclosing said hollow volume 5.

[0036]

[0038] In order to ensure maximum stiffness and crash resistance, in particular in the event of a rollover scenario, said side structure 1 further comprises a reinforced portion 11 extending along said upper portion 23 of said B-pillar 2 and along said intermediate portion 33 of said roof rail 3. Said reinforced portion 11 is strengthened by the presence of an insert 6 which is located within said hollow volume 5 and occupies at least part of said hollow volume 5. Said insert 6 is made out of metallic material, for example out of steel, or out of aluminum or out of titanium. By using a metallic insert, it is possible to obtain a very good compromise between part weight, strength and production cost.

[0037]

[0039] The use of a dedicated insert 6 to reinforce the side structure allows to improve the mechanical resistance of an existing side structure without changing its overall design. For example, in the case of an automotive vehicle offering different versions of the same model, it is possible to keep a single overall side structure design with tailored properties in the reinforced portion 11 according to the needs of the specific model. For example, in the case of a light version, having for example no or little battery capacity, the side structure 1 will be free of a reinforced portion and no insert is used. On the other hand, for heavier versions, having for example a large underfloor battery, the vehicle will comprise a side structure 1 according to the invention with a reinforced portion 11 having a metallic insert 6. It is even possible to consider several different versions with increasing vehicle weight each having a specific insert 6 in order to optimize the weight and resistance of the side structure.

[0038]

[0040] The insert 6 is attached to the side structure 1 either by attaching it to the inner elements (B-pillar inner, roof rail inner 21 , 31 ) or the outer elements (B-pillar outer, roof rail outer 22, 32) or to both. It is possible to attach said insert 6 only to the B-pillar or only to the roof rail or to both. The choice of attachment areas will depend on the overall assembly sequence and on other considerations such as for example Noise Vibration Harshness (NVH) performance. Indeed, if the insert is not properly attached to the side structure it could vibrate within the hollow space 5 when the vehicle is in use, causing discomfort to the occupants.

[0039]

[0041] In a specific embodiment, the insert 6 is attached to the side structure 1 in said reinforced portion 11 by welding it to said side structure 1 . This is particularly advantageous when using steel both for the B-pillar and I or roof rail to which the insert is attached and when the insert itself is made of steel. Indeed, welding is a robust, widely applied way of assembling elements made of steel.

[0040]

[0042] For example, the insert 6 is attached to the side structure by spot welding. For example, the insert 6 is attached to the side structure by resistance spot welding or by laser spot welding. In the case of laser welding, it is possible to use laser welding stitches, which are small discontinuous welds following one another along the attachment area. Laser stitches allow to efficiently attach parts by laser welding while reducing the welding time compared to an assembly in which the parts are attached using a continuous laser weld. In the case of laser welding, it is also possible to attach the parts using remote laser welding, which allows for maximum industrial flexibility.

[0043] In a specific embodiment, the insert 6 is equipped with flanges 61 to facilitate assembly, for example by welding. Said flanges 61 are flat surfaces running along at least part of the periphery of said insert 6. The use of flanges 61 allows to have a relatively large flat surface over which the insert 6 can be assembled to the side structure 1 for example by welding.

[0041]

[0044] In a specific embodiment, the B-pillar inner 21 and the roof rail inner

[0042] 31 are made of steel and said insert 6 is attached by welding it to said roof rail inner 31 in an attachment area 34. Furthermore, the carbon content of the material in said attachment area 34 is lower than the carbon content of the material of the inner B-pillar 21 in the upper portion 23 of said B-pillar 2. Advantageously this allows to weld the insert 6 easily to the side structure 1 - indeed the welding process is dependent on the carbon content of the materials to be welded and generally speaking it is easier to find a good welding range with good welding parameters when welding to steel parts having a lower carbon content.

[0043]

[0045] In a specific embodiment the B-pillar outer 22 and roof rail outer 32 are made of steel and said insert 6 is attached by welding it to said roof rail outer

[0044] 32 in an attachment area 34. Furthermore, the carbon content of the material in said attachment area 34 is lower than the carbon content of the material of the B-pillar outer 22 in the upper portion 23 of said B-pillar 2. This yields the same advantages as described above in the case of welding to the inner elements of the side structure.

[0045]

[0046] In a specific embodiment, the insert 6 is manufactured using additive manufacturing, also known as 3D printing. For example, the insert 6 is manufactured by Wire Laser Additive Manufacturing (WLAM), or by Wire Arc Additive Manufacturing (WAAM) or by Direct Energy Deposition (DED) or any other suitable additive manufacturing process. Advantageously, using additive manufacturing allows to produce complex shapes which can optimize the material usage for the required performance. The shape and thickness of the walls of said insert can vary continuously to optimize its performance. In a specific embodiment, the insert is hollow, having outer walls that encircle a hollow volume - advantageously this confers rigidity to the insert. For example, said insert 6 is produced by additively manufacturing a part that has been designed using topology optimization to reach an optimal shape for the desired performance. Furthermore, the hollow space 5 in between the inner and outer elements of the side structure 1 can be narrow - using additive manufacturing can allow to produce an insert having a shape which precisely fits into the hollow space in said reinforced portion 11 . Using additive manufacturing further presents the advantage that no specific tooling is required to produce the insert (no stamping die for example). This is interesting for example in the above-described case where the insert 6 is used on only part of the versions of a given vehicle, in which case the production volume for the insert 6 could be quite small and it would be overly costly in time and investment to produce specific tools for such small volumes.

[0046]

[0047] In a specific embodiment, said insert 6 is produced by forming one or several tubes, for example by stamping or bending or hydroforming said tube or tubes. Advantageously, this allows to produce robust and rigid inserts 6 using efficient and productive tube forming processes and relatively low cost tubes as raw material.

[0047]

[0048] In a specific embodiment, said insert 6 is produced by forming one or several blanks of metal, for example by stamping or roll forming said blank or blanks. Advantageously, this allows to produce robust and rigid inserts 6 using efficient and productive blank forming processes and relatively low cost blanks as raw material.

[0048]

[0049] In a specific embodiment, said insert 6 is formed as one single part, for example by additive manufacturing. Advantageously, this allows for a simple one step production process of said insert 6. This also allows for a one step assembly of the insert 6 to the side structure 1 . For example, in this specific case, the insert 6 is produced by additive manufacturing and has a generally Y-shaped structure, such as depicted on figure 2. The insert 6 has a base 6B generally extending over the B-pillar upper 23 which then branches out into a left and right upper insert 6L, 6R, which extends over the top part of the B-pillar upper 23 and over the roof rail intermediate portion 33. This type of Y-shaped design allows to produce the part industrially in a single part using additive manufacturing.

[0050] In a specific embodiment, such as depicted on figure 3 and on the assembly sequence of figures 4a, 4b and 4c, said insert 6 is produced by manufacturing 2 different sub-parts. The resulting insert 6 is generally T- shaped. A first sub-part 6V extends generally vertically along the B-pillar upper 23, a second sub-part 6H extends generally horizontally along the roof rail intermediate portion 33. Said sub-parts 6V, 6H are for example made by additive manufacturing, or tube forming, or sheet metal forming - it is also possible to use a combination of processes, applying two different forming process for each sub-part. By lifting the design constraints associated to manufacturing the part as one single item, this embodiment allows to tune the shape, material and thickness of each sub-part in order to reach overall optimal performance, material usage and weight.

[0049]

[0051] In a specific embodiment, said insert 6 is made using additive manufacturing and the material used to produce said insert is steel comprising in weight % the following range of elements, the remainder of the composition being Fe and inevitable impurities resulting from the elaboration process:

[0050] Table : wire composition embodiment

[0051]

[0052] For example, the above composition is used when applying a wire based additive manufacturing process such as WLAM or WAAM.

[0052]

[0053] In a specific embodiment, said insert 6 is made by additive manufacturing using a wire or a powder which in itself has a low resistance to corrosion - said insert 6 is then post coated with a corrosion resistance coating.

[0053]

[0054] In a specific embodiment, the hollow volume 5 is further occupied by a noise and I or vibration damping material in order to improve the NVH performance of the vehicle. For example, said damping material is a foam or a polymer material. For example, said damping material occupies the entire hollow volume 5 of the reinforced portion 11 - in this embodiment, the insert 6 is fully encased in between the inner and outer elements of the side structure and within the damping material. For example, said damping material is only applied in the hollow volume 5 of the reinforced portion 11 extending along the B-pillar.

[0054]

[0055] In a specific embodiment, the B-pillar inner 21 and the roof rail inner

[0055] 31 are part of a single standalone part, manufactured for example by cold stamping or hot stamping a single tailor welded blank or a single tailor rolled blank. For example, the B-pillar inner 21 and the roof rail inner 31 are part of a bigger standalone assembly known as a door ring inner, which forms a full circle around the front door or rear door opening or both openings (in this case the assembly is known as a double door ring inner). Said door ring inner or double door ring inner is for example hot stamped in one single stamping operation using a large tailor welded blank.

[0056]

[0056] In a specific embodiment, the B-pillar outer 22 and the roof rail outer

[0057] 32 are part of a single standalone part, manufactured for example by cold stamping or hot stamping a single tailor welded blank or a single tailor rolled blank. For example, the B-pillar outer 22 and the roof rail outer 32 are part of a bigger standalone assembly known as a door ring outer, which forms a full circle around the front door or rear door opening or both openings (in this case the assembly is known as a double door ring outer). Said door ring outer or double door ring outer is for example hot stamped in one single stamping operation using a large tailor welded blank.

[0058]

[0057] In a specific embodiment the side structure 1 , i.e. the inner and outer B-pillar 21 , 22 and the inner and outer roof rail 31 , 32, is made by cold stamping steel blanks comprising one of the following materials, either in the form of monolithic blanks or tailor rolled blanks or combined in the form of tailor welded blanks:

[0059]

[0058] Steel having a chemical composition comprising in weight %: 0.13% < C < 0.25%, 2.0 % < Mn < 3.0%, 1 .2% < Si < 2.5%, 0.02% < Al < 1 .0%, with 1 .22% < Si+AI < 2.5%, Nb < 0.05%, Cr < 0.5%, Mo < 0.5%, Ti < 0.05 %, the remainder being Fe and unavoidable impurities and having a microstructure comprising from 8% to 15% of retained austenite, the remainder being ferrite, martensite and bainite, wherein the sum of martensite and bainite fractions is comprised from 70% to 92%. With this composition, the steel sheet has, as measured in the rolling direction, a yield strength comprised from 600MPa to 750MPa and an ultimate tensile strength comprised from 980MPa to 1300MPa while keeping a total elongation above 19%.

[0060]

[0059] Steel having a chemical composition comprising in weight %: %: 0.15% < C < 0.25%, 1.4 % < Mn < 2.6%, 0.6% < Si < 1 .5%, 0.02% < Al < 1.0%, with 1.0% < Si+AI < 2.4%, Nb < 0.05%, Cr < 0.5%, Mo < 0.5%, the remainder being Fe and unavoidable impurities and having a microstructure comprising from 10% to 20% of retained austenite, the remainder being ferrite, martensite and bainite. With this composition, the steel sheet has, as measured in the rolling direction, a yield strength comprised from 850MPa to 1060MPa and an ultimate tensile strength comprised from 1180MPa to 1330MPa while keeping a total elongation above 13%.

[0061]

[0060] Fully martensitic steel wherein the composition of the fully martensitic steel comprises in % weight: 0.15% < C < 0.5%.

[0062]

[0061] Dual phase steel having a microstructure comprising at least martensite and ferrite and having a UTS of at least 590MPa.

[0063]

[0062] Dual phase steel having a microstructure comprising at least martensite and ferrite and having a UTS of at least 780MPa.

[0064]

[0063] Dual phase steel having a microstructure comprising at least martensite and ferrite and having a UTS of at least 980MPa.

[0065]

[0064] In a specific embodiment the the side structure 1 , i.e. the inner and outer B-pillar 21 , 22 and the inner and outer roof rail 31 , 32, is made by hot stamping steel blanks comprising one of the following materials, either in the form of monolithic blanks or tailor rolled blanks or combined in the form of tailor welded blanks:

[0066]

[0065] Steel having a composition comprising in % weight: 0.06% < C < 0.1 %, 1 % < Mn < 2%, Si < 0.5%, Al <0.1 %, 0.02% < Cr < 0.1 %, 0.02% < Nb < 0.1 %, 0.0003% < B < 0.01 %, N < 0.01 %, S < 0.003%, P < 0.020% less than 0,1 % of Cu, Ni and Mo, the remainder being iron and unavoidable impurities resulting from the elaboration. With this composition range, the yield strength of the corresponding area after hot stamping is comprised from 700 to 950MPa, the tensile strength from 950MPa to 1200MPa and the bending angle is above 75°.

[0067]

[0066] Steel having an ultimate tensile strength after hot stamping which is comprised from 1300MPa to 1650MPa and a yield strength which is comprised from 950MPa to 1250MPa.

[0068]

[0067] Steel having an ultimate tensile strength after hot stamping which is comprised from 1300MPa to 1650MPa, a yield strength which is comprised from 950MPa to 1250MPa and a bending angle which is above 75°.

[0069]

[0068] Steel having a composition comprising in % weight: 0.20% < C < 0.25%, 1.1 % < Mn < 1.4%, 0.15% < Si < 0.35%, Cr < 0.30%, 0.020% < Ti < 0.060%, 0.020% < Al < 0.060%, S < 0.005%, P < 0.025%, 0.002% < B < 0.004%, the remainder being iron and unavoidable impurities resulting from the elaboration. With this composition range, the ultimate tensile strength of the corresponding area of the part after hot stamping is comprised from 1300MPa to 1650MPa and the yield strength is comprised from 950MPa to 1250MPa.

[0070]

[0069] Steel having a tensile strength after press-hardening higher than 1800 MPa.

[0071]

[0070] Steel having a composition which comprises in % weight: 0.24% < C

[0072] < 0.38%, 0.40% < Mn < 3%, 0.10% < Si < 0.70%, 0.015% < Al < 0.070%, Cr

[0073] < 2%, 0.25% < Ni < 2%, 0.015% < Ti < 0.10%, Nb < 0.060%, 0.0005% < B

[0074] < 0.0040%, 0.003% < N < 0.010%, S < 0,005%, P < 0,025%, %, the remainder being iron and unavoidable impurities resulting from the elaboration. With this composition range, the tensile strength of the corresponding area after hot stamping is higher than 1800 MPa.

[0075]

[0071] Steel having a composition which comprises in %weight : C : 0.15 - 0.25 %, Mn: 0.5 - 1.8 %, Si : 0.1 - 1.25 %, Al : 0.01 - 0.1 %, Cr : 0.1 - 1.0 %, Ti: 0.01 -0.1 %, B: 0.001 - 0.004 %, P < 0.020 %, S < 0.010 %, N < 0.010 % and comprising optionally one or more of the following elements, by weight percent: Mo < 0.40 %, Nb < 0.08 %, Ca < 0.1 %, the remainder of the composition being iron and unavoidable impurities resulting from the smelting.

[0072] Steel having a composition which comprises in %weight : C : 0.26 - 0.40 %, Mn: 0.5 - 1.8 %, Si : 0.1 - 1.25 %, Al : 0.01 - 0.1 %, Cr : 0.1 - 1.0 %, Ti: 0.01 -0.1 %, B: 0.001 - 0.004 %, P < 0.020 %, S < 0.010 %, N < 0.010 % and comprising optionally one or more of the following elements, by weight percent: Ni < 0.5 %, Mo < 0.40 %, Nb < 0.08 %, Ca < 0.1 % the remainder of the composition being iron and unavoidable impurities resulting from the smelting. With this composition range, the tensile strength of the corresponding area after hot stamping is higher than 1350 MPa and the bending angle is higher than 70°.

[0076]

[0073] Steel having a composition which comprises in %weight : C : 0.2 - 0.34 %, Mn: 0.50 - 1.24 %, Si: 0.5 - 2 %, P < 0.020 %, S < 0.010 %, N < 0.010 %, and comprising optionally one or more of the following elements, by weight percent: Al: <0.2 %, Cr < 0.8 %, Nb < 0.06 %, Ti < 0.06 %, B < 0.005%, Mo < 0.35%, the remainder of the composition being iron and unavoidable impurities resulting from the smelting. With this composition range, the tensile strength of the corresponding area after hot stamping is equal to or higher than 1000 MPa and the bending angle is higher than 55°.

[0077]

[0074] Steel having a composition which comprises in %weight : C : 0.13 - 0.4 %, Mn: 0.4 - 4.2 %, Si : 0.1 - 2.5%, Cr < 2 %, Mo < 0.65 %, Nb < 0.1 %, Al < 3.0 %, Ti < 0.1 %, B < 0.005 %, P < 0.025 %, S < 0.01 %, N < 0.01 %, Ni < 2.0%, Ca < 0.1 %, W < 0.30%, V < 0.1 %, Cu < 0.2%, and verifying the following combination: 114 - 68*C - 18*Mn + 20*Si - 56*Cr - 60*Ni - 36*AI + 38*Mo + 79*Nb - 17691 *B < 20, the remainder of the composition being iron and unavoidable impurities resulting from the smelting. For example, this composition is used when hot stamping the part using a multistep process.

[0078]

[0075] Steel which is coated with an aluminum-based metallic coating. By aluminum based it is meant a coating that comprises at least 50% of aluminum in weight. For example, the metallic coating is an aluminum-based coating comprising 8 - 12% in weight of Si. For example, the metallic coating is applied by dipping the base material in a molten metallic bath. Advantageously, applying an aluminum-based metallic coating avoids the formation of surface scale during the heating step of the hot stamping process, which in turns allows to produce the parts by hot stamping without a subsequent sand blasting operation. Furthermore, the aluminum-based coating also provides corrosion protection to the metallic part while in service, for example on an automotive vehicle.

[0079]

[0076] Steel which is coated with an aluminum-based metallic coating comprising from 2.0 to 24.0% by weight of zinc, from 1 .1 to 12.0% by weight of silicon, optionally from 0 to 8.0% by weight of magnesium, and optionally additional elements chosen from Pb, Ni, Zr, or Hf, the content by weight of each additional element being inferior to 0.3% by weight, the balance being aluminum and optionally unavoidable impurities. Advantageously, this type of metallic coating affords very good corrosion protection on the part, as well as a good surface aspect after hot stamping.

[0080]

[0077] In a specific embodiment, one or several elements of the side structure 1 is made by hot stamping a laser welded blank comprising at least one sub blank having an aluminum based metallic coating and said at least one aluminum coated sub blank is prepared before-hand by ablating at least part of the metallic coating on the edges to be welded. Advantageously, this removes part of the aluminum present in the coating, which would pollute the weld seam and deteriorate its mechanical properties.

[0081]

[0078] In a particular embodiment, at least one sub-blank of the steel sheet comprises at least one area having at least one side topped with an emissivity increasing top layer. Said emissivity increasing top layer is applied on the outermost surface of said sub-blank. Said emissivity increasing top layer allows the surface of said sub blank to have a higher emissivity compared to the same sub-blank which is not coated with said emissivity increasing top layer. Said emissivity increasing top layer can be applied either on the top or the bottom side of a sub-blank. Said emissivity increasing top layer can also be applied on both sides of said sub-blank. If said sub-blank comprises a metallic coating, such as described previously, the emissivity increasing top layer is applied on top of said metallic coating. Indeed, for the emissivity increasing top layer to increase the em issivity of the surface, it needs to cover the outermost surface of the sub-blank. Advantageously, said emissivity increasing top layer will allow to increase the heating rate of said sub-blank and therefore increase the productivity of the heating step of the hot stamping process. When using several sub blanks of differing thicknesses, said emissivity increasing top layer is advantageously applied to the sub-blanks having the highest thickness, or to a patched area which will have a higher thickness compared to the main sub-blank, in order to decrease the difference in heating time between the different sub-blanks or areas and therefore increase productivity, increase the hot stamping process window and overall allow to obtain a final part having homogeneous surface properties.

[0082]

[0079] An example of a process to manufacture a side structure 1 according to the invention will now be described.

[0083]

[0080] -A B-pillar inner 21 , assembled to a roof rail inner 31 are provided,

[0084]

[0081] -A B-pillar outer 22, assembled to a roof rail outer 32 are provided,

[0085]

[0082] -An insert 6 according to the invention is provided,

[0086]

[0083] -Said insert 6 is assembled either to the sub-assembly comprising the B-pillar inner 21 and roof rail inner 31 or to the sub-assembly comprising the B-pillar outer 22 and roof rail outer 32,

[0087]

[0084] -Said sub-assembly comprising the B-pillar inner 21 and roof rail inner 31 and sub-assembly comprising the B-pillar outer 22 and roof rail outer 32, are then assembled together to form the side structure 1 .

[0088]

[0085] In a specific embodiment, such as depicted on figures 4a, 4b and 4c, the insert s is made of two sub-parts horizontal portion 6H and vertical portion 6V. The horizontal portion 6H of the insert 6 is first assembled to the roof rail inner 31 (figure 4a). The vertical portion 6V is then assembled to the B-pillar inner 21 (figure 4b, in this figure the vertical portion depicted before being assembled). In a particular embodiment, the horizontal and vertical potions 6H, 6V are welded to one another. The thus reinforced sub-assembly comprising the B-pillar inner 21 , roof rail inner 31 and insert 6 is then assembled to sub-assembly comprising the B-pillar outer 22 and roof rail outer 32 to form the side structure 1 (figure 4c).

[0089]

[0086] In a specific embodiment, distinct from the above-described assembly processes, the insert 6 is kept in place in the hollow space 5 in between the inner and outer elements of the side structure 1 thanks to the pressure applied on it by the inner and outer elements once they are assembled together. For example, said insert 6 is first positioned on the B-pillar inner 21 and roof rail inner 31 assembly. The B-pillar outer 22 and roof rail inner 32 are then assembled to said inner elements, for example by welding. The design of said insert 6 is such that once the inner and outer elements are assembled together, said insert 6 is in contact with both the inner and outer elements with a sufficient contact pressure to keep it stable and in place within the hollow volume 5. Advantageously, this type of assembly method dispenses from welding or gluing or any other type of physical attachment step of the insert to the side structure, which saves a manufacturing operation, simplifies production, increases productivity and lowers costs. Optionally, the above-described assembly process can include a step of physically attaching the insert 6 to the side structure inner or outer elements before the inner and outer elements of said side structure 1 are assembled together. Advantageously, this allows to keep in place the insert 6 during the assembly process, before it is squeezed tight between the inner and outer elements. Only a very light attachment needs to be used, such as for example light gluing or only a minimal amount of spot welds.

[0090]

[0087] In the above described embodiment in which a damping material is used in the hollow volume 5 of the reinforced portion 11 , said damping material is for example applied once said insert 6 has been put in place against the inner or outer elements of the side structure 1 and before said inner or outer elements are assembled to their inner or outer counterpart.

[0091]

[0088] The invention will now be illustrated by way of an example based on numerical simulations of different configurations of side structures 1 .

[0092]

[0089] Table 1 summarizes the characteristics in terms of thickness, mass and performance of the different elements making up a side structure 1 .

[0093]

[0090] In all the configurations of the examples the B-pillar inner and outer 21 , 22 as well as the roof rail inner and outer 31 , 32 are made by hot stamping a steel to form hot-stamped parts which have after hot stamping an ultimate tensile strength of 1500MPa and a yield strength of 1000MPa.

[0094]

[0091] The baseline corresponds to a design which is not according to the invention. Contrary to the design of the invention, in which the insert 6 is located within the hollow volume 5 in between the inner and outer elements of the side structure, the baseline design comprises an outer reinforcement which is attached to the outside of the side structure 1. The outer reinforcement is an elongated part having a top hat cross section and which is attached to the B-pillar outer 22 and roof rail outer 32 by spot welding it on its flanges. Said outer reinforcement is made by hot stamping a steel to form a hot-stamped part which have after hot stamping an ultimate tensile strength of 1500MPa and a yield strength of 1000MPa.

[0095]

[0092] The insert 6 of the current invention V1 is T-shaped, while it is Y- shaped in the case of the current invention V2. Said inserts 6 are made by WLAM using a wire having the following composition:

[0096] Tab e 2: insert wire composition of the examples

[0097]

[0093] Thanks to this composition, the mechanical properties of the insert 6 after WLAM are the following: tensile strength of 1200MPa and yield strength of 940MPa.

[0098]

[0094] The overall performance of the side structure 1 according to the different designs is expressed in terms of strength to weight ratio as defined in the above-described rollover roof crush test.

[0099]

[0100] Table 3: Side structure characteristics of the examples

[0101]

[0095] Thanks to the implementation of the current invention, it was possible to reach a higher roof crush strength to weight ratio while lowering the overall mass of the side structure from 9kg to 8kg, saving a very significant 2 kg (2 sides) per vehicle. This excellent result is achieved by using an insert 6 according to the invention located in the hollow volume 5 in between the inner and outer elements of the side structure. The use of said insert 6 allows to reduce the thickness of the inner and outer B-pillar 21 , 22

Claims

CLAIMS1 ) Side structure (1 ) for an automotive vehicle comprising a B-pillar (2), located between a front and a rear door opening, and a roof rail (3), extending along a roof panel, said roof rail (3) being attached to an upper portion (23) of said B-pillar (2) in an intermediate portion (33) of said roof rail (3), said B-pillar (2) comprising an inner and an outer B-pillar (21 , 22) and said roof rail (3) comprising an inner and an outer roof rail (31 , 32), said inner and outer parts (21 , 22, 31 , 32) enclosing a hollow volume (5), said side structure (1 ) comprising a reinforced portion (11 ) extending along said upper portion (23) of said B-pillar (2) and along said intermediate portion (33) of said roof rail (3), wherein an insert (6) occupies part of said hollow volume (5) in said reinforced portion (11 ) and wherein said insert (6) is made of metallic material.2) Side structure (1 ) according to any one of claims 1 to 3, wherein said insert (6) is attached to said side structure (1 ) by welding.3) Side structure (1 ) according to claim 2, wherein said insert (6) comprises flanges (61 ) and wherein said insert (6) is attached to said side structure (1 ) by welding along said flanges (61 ).4) Side structure (1 ) according to claim 2 or 3, wherein said insert (6) is attached to said side structure (1 ) by spot welding.5) Side structure (1 ) according to claim 2 or 3, wherein said insert (6) is attached to said side structure (1 ) by laser welding.6) Side structure (1 ) according to any one of claims 1 to 5, wherein in said reinforced portion (11 ), said B-pillar inner (21 ) and said roof rail inner (31 ) are made of steel and said insert (6) is attached by welding it to said roof rail inner (31 ) in an attachment area (34) and wherein the carbon content of thematerial in said attachment area (34) is lower than the carbon content of the material of the inner B-pillar (21 ) in the upper portion (23) of said B-pillar (2).7) Side structure (1 ) according to any one of claims 1 to 5, wherein in said reinforced portion (11 ), said B-pillar outer (22) and said roof rail outer (32) are made of steel and said insert (6) is attached by welding it to said roof rail outer (32) in an attachment area (34) and wherein the carbon content of the material in said attachment area (34) is lower than the carbon content of the material of the B-pillar outer (22) in the upper portion (23) of said B-pillar (2).8) Side structure (1 ) according to any one of claims 1 to 7, wherein said insert (6) is produced by an additive manufacturing process.9) Side structure (1 ) according to any one of claims 1 to 8, wherein said insert (6) is produced in one single part.10)Side structure (1 ) according to any one of claims 1 to 8, wherein said insert (6) is produced in two separate parts, a first sub-part (6V) extending generally vertically along the B-pillar upper (23) and a second sub-part (6H) extending generally horizontally along the roof rail intermediate portion (33).