Method for laser welding

Abstract

The present disclosure relates to methods for joining a first component to a second component with a laser welded lap joint. The laser seam of individual welds is substantially G-shaped. The weld seam comprises a substantially circular portion and a substantially straight portion at an end of the substantially circular portion, the substantially circular portion having a radius and corresponding to a circular arc around a circle centre with a central angle of 270º - 350º, and the substantially straight portion extending radially to the circle centre. The methods may be practiced on blanks prior to forming or on already formed components. The present disclosure further relates to weld assemblies obtained with such methods.

Description

METHOD FOR LASER WELDING

[0001] The present application claims the benefit of European patent application n° 24 382 220.2 filed on 29thof February, 2024.

[0002] The present disclosure relates to methods for welding, and more particularly relates to remote laser welding and lap joint welding. The present disclosure further relates to methods for joining blanks or components in a lap joint.BACKGROUND

[0003] In the automotive industry, the development and implementation of lightweight materials or components is becoming more important in order to satisfy criteria for manufacturing lighter vehicles. The demand for weight reduction is especially driven by the goal of reduction of CO2 emissions. Additionally, the growing concern regarding occupant safety also leads to the adoption of materials which improve the integrity and the energy absorption of the vehicle during a crash.

[0004] Press hardening, also known as Hot Forming Die Quenching (HFDQ) or “hot stamping” 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. 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 others.

[0008] UHSS 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 UHSS may have a martensitic microstructure. This microstructure enables an increased maximum tensile strength and yield strength per weight unit.

[0009] 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.

[0010] Other forming processes that are used in the automotive industry for the manufacture of the vehicle framework include cold stamping, hydroforming and roll forming. In most of these processes, steel blanks are used.

[0011] Other materials that are used in the automotive industry to reduce the weight of the structural framework include composite materials (e.g., fibre reinforced polymers) and aluminium. Aluminium finds use both in traditional metal forming processes, and in processes such as high pressure die casting.

[0012] Prior to a metal forming process, such as hot stamping or cold stamping, several blanks may be joined to each other to form a Tailor Welded Blank (TWB) comprising different thicknesses or different materials. The idea of the use of TWB is that a resulting component can be optimized in terms of weight and provide tailored strength and stiffness where needed. A TWB is generally formed by edge-to-edge butt welding of the different blanks. TWB may be made of several aluminium blanks, or several steel blanks, but it is also known to combine e.g., aluminium blanks with steel blanks in the same TWB.

[0013] In other cases, blanks may be joined to each other in a lap weld joint: one blank partially or completely overlaps another blank. A combined blank may have a thickness tailored to provide increased strength and stiffness in specific portions of the blank and thecomponent obtained after forming. The combined blank may be subjected e.g., to a hot stamping or cold stamping process.

[0014] A patchwork blank is an example hereof. Another example is a combined blank to form e.g., a unitary door ring such as disclosed in W02020 / 002335. Such a combined blank may also be called an Overlap Patch Blank.

[0015] In these cases, resistance spot welding (or simply “spot welding”) is generally used to join the individual blanks to each other. Resistance spot welding has a number of disadvantages: the process can only be carried out to join flat blanks or components, or to join blanks or components to each other at flat portions thereof. Spot welding cannot be carried out on e.g., parts having a closed cross-section. Another disadvantage of spot welding is that the process is relatively slow compared to e.g., laser welding. It has further been found that in hot stamping or cold stamping processes that are carried out after joining the blanks to each other, some of the spot welds do not have sufficient shear strength (depending on how much deformation takes place during stamping).

[0016] The present disclosure provides examples of methods and assemblies which can overcome at least some of the aforementioned drawbacks.SUMMARY

[0017] In a first aspect, a method for joining a first component to a second component is provided. The method comprises positioning the first and second components such that the first component at least partially overlaps the second component in an overlap region, and laser welding the first component to the second component with a weld seam in the overlap region. The weld seam comprises a substantially circular portion and a substantially straight portion at an end of the substantially circular portion, the substantially circular portion having a radius and corresponding to a circular arc around a circle centre with a central angle of 270° - 350°, and the substantially straight portion extending radially to the circle centre.

[0018] In accordance with this aspect, a method for joining components is provided which is an alternative to the use of spot welding in (over)lap joints. The method can be carried out more quickly since (remote) laser welding can be used. The use of laser welding also allows welding to be carried out in occasions where spot welds are impossible, e.g., curved surfaces, hydroformed components and other.

[0019] The welds in accordance with this aspect have a weld seam which may be regarded as substantially G-shaped i.e., a shape corresponding substantially to the letter G. Thewelds with this specific weld seam exhibit good shear strength, and in particular independently of the direction of shear load. In known prior art laser welds, the shear strength depends significantly on the direction of a shear load. This means that the prior art assemblies behave differently depending on the loads applied. In automotive applications, such as in a vehicle structural framework, all load directions throughout the lifetime of a component can however generally not be predicted, and it is thus important that a component behaves well under loads from different load directions.

[0020] Remote laser welding is a welding process that utilizes laser technology to join materials together from a distance. In traditional welding processes, the welder is in close proximity to the workpiece, manipulating the welding equipment directly. Remote laser welding, on the other hand, involves using a laser beam to perform the welding operation from a remote location, often with the help of advanced robotic systems.

[0021] In a further aspect, a welded assembly that is obtainable by an example of the aforementioned method is provided. In accordance with this aspect, a welded assembly comprising a first component and a second component is provided. The first component is arranged at least partially on top of the second component in an overlap region, and the first component is laser welded in the overlap region with one or more weld seams comprising a substantially circular portion and a substantially straight portion at an end of the substantially circular portion. The substantially circular portion corresponds to a circular arc around a circle centre with a central angle of 270° - 350°, and the substantially straight portion extending radially to the circle centre.

[0022] In yet a further aspect, a welded assembly comprising a first component and a second component is provided, wherein the first component is arranged at least partially on top of the second component in an overlap region, and wherein the first component is laser welded in the overlap region with one or more substantially G-shaped weld seams to the second component.

[0023] In some examples, the central angle of the circular arc is 300 - 350°, specifically 320 - 345°. In these examples, the circular portion of the G-shape is almost closed. These examples are specifically suitable for substituting spot welds, i.e. , for applications in which typically multiple spot welds would be used.

[0024] In some examples, the central angle of the circular arc may be 270 - 300° and the weld further comprising an additional linear portion extending away from the circle centre. In these examples, substantially linear welds may be used, e.g., along edges of a component to provide a fluid tight joint. At one end (or both ends) of the linear weld, a G-shape may be provided. The G-shape can reduce stress concentrations at the end of linear welds, and thereby the initiation of cracks.

[0025] In some examples, a radius of the substantially circular portion may be 1 - 25 mm, specifically 2 - 10 mm, more specifically 3 - 7 mm.

[0026] In some examples, the weld seam may extend through the thickness of the first component and second component. In other examples, the weld seam extends only partially though the thickness of the second component. When the weld only extends partially through the thickness of the second component, one external surface of the assembly is substantially free of any markings, and this weld may be preferred for surfaces that are visible in the end product. It may further reduce cycle time and power consumption and tool wear. In some examples, to compensate the loss of strength of the bond due to the partial penetration, the size of the G-shape or e.g., the laser spot size may be increased.

[0027] Different laser settings may be used depending on the implementation. A laser power may be chosen to be sufficient for melting the blanks / components to be joined and may be e.g., 2 - 10 kW. Different types of lasers may be used, e.g. disk laser, CO2 laser, fibre laser or ND: YaG solid state laser.

[0028] In examples, the laser welding includes laser welding with more than one laser spot. The laser welding may additionally or alternatively include laser welding with a wobbling laser spot and or with laser beam defocus. If the laser beam is defocused, it spreads out over a larger area, resulting in a shallower and wider weld pool. In some cases, a wobbling laser spot, the use of various spots and / or defocused laser beams may be used to e.g., mix a coating (of e.g. a metal blank) through the weld pool.

[0029] In some examples, the first component is a substantially flat first metal blank, and the second component is a substantially flat second metal blank and a combined blank includes the first metal blank joined to the second metal blank. After joining the combined blank may be subjected to a (metal) forming method such as e.g., hot stamping.

[0030] The first and second metal blanks may be aluminium alloy blanks. Optionally, the aluminium alloy is selected from a group comprising 5000, 6000 and 7000 series aluminium alloys. In other examples, the first and second metal blanks may be steel blanks, specifically boron steel blanks. In yet other examples, a steel blank may be joined to an aluminium blank.

[0031] In the case of steel blanks, and particularly boron steel blanks, the blanks may comprise a corrosion protective coating, specifically an AlSi coating or Zinc based coating.In examples, the corrosion protective coating may be at least partially removed in the overlapping region prior to joining the first blank to the second blank. Particularly the aluminium of an aluminium-silicon coating if mixed in the weld pool may be problematic. The presence of aluminium may promote the creation of ferrite and perlite in a hot stamping process and thereby can affect the creation of a martensitic microstructure which is to provide high strength and stiffness. Prior to positioning the blanks on top of each other, part of the coating or the whole coating may be removed through ablation prior to welding. In other examples, other techniques including e.g., multi-spot welding, defocused welding and / or a wobbling laser spot may be used to avoid such problems.

[0032] In other examples, the first and second components that are joined to each other may be components after metal forming, e.g., hot stamping, roll forming or hydro forming. As mentioned before, the use of remote laser welding allows also surfaces with some curvature to be joined.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:Figures 1A - 1C schematically illustrate a lap joint welding;Figures 2A - 2C schematically illustrate a weld seam according to examples of the present disclosure;Figures 3A - 3G schematically illustrate different examples of weld seams and test results of shear strength obtained for the welds in different directions;Figure 4A schematically illustrates an example of manufacturing an automotive component;Figures 4B - 4D schematically illustrate examples of blanks and components which may be manufactured with the method of figure 4A;Figure 5 schematically illustrates another implementation of the welds according to the present disclosure; andFigure 6A - 6C schematically illustrate a test set-up and test results of a B-pillar made of overlapped blanks using different kinds of welds-

[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] Figures 1A - 10 schematically illustrate examples of lap joint welding. Figure 1A illustrates a cross-sectional view, whereas figure 1 B illustrates a top view. A first component 10 is positioned on top of second component 12 such that an overlapping region 14 is formed. In some cases, the overlap may be partial (as illustrated in figure 1), and in other cases, the overlap may be complete. In the case of a complete overlap the first component is entirely positioned on top of the second component.

[0037] As illustrated in figure 1 B, the first and second components may traditionally be joined to each other through a plurality of spot welds in the overlapping region.

[0038] In accordance with the present disclosure, as illustrated in figure 1 C, the first and second components may be joined to each other through a plurality of substantially G- shaped welds instead.

[0039] In some examples, the first and second components may be components that have been formed and shaped in a forming process. E.g., a roll formed component may be joined to a stamped component, or two cold or hot stamped components may be joined to each other. With the G-shaped weld according to examples disclosed herein, which may be provided through remote laser welding, joining can be carried out more quickly than with spot welds. At the same time, the heat affected zone (HAZ) is relatively small.

[0040] In other examples, the first and second components may be blanks or flat metal sheets which are joined to each other prior to a metal forming process such as e.g., cold or hot stamping. The blanks may be aluminium alloy blanks in some examples or steel blanks in other examples. The steel blanks may be of press hardenable steel such as boron steel e.g., 22MnB5, 37MB5 or 38MnB5. In some cases, the steel blanks may include a protective coating such as an aluminium-silicon coating or zinc coating, which may be removed prior to welding.

[0041] In examples, the blanks may have a thickness of e.g., 0,8 - 3 mm, specifically 0,8 - 2 mm. The blanks may have the same thickness or different ones. It will be clear that more than two blanks may be joined to each other in the same fashion.

[0042] Figure 2A shows a substantially G-shaped weld seam in accordance with an example of the present disclosure. The weld seam 20 comprises a substantially circularportion 22 and a substantially straight portion 26 at an end of the substantially circular portion. The substantially circular portion 26 has a radius and corresponding to a circular arc around a circle centre 24 with a central angle of 270° - 350°. The substantially straight portion 26 extends radially to the circle centre 24.

[0043] The central angle of a circular arc is defined as the angle formed at the centre of a circle by two radii that define the arc. That is, with the central angle of 270 - 350°, the angle a indicated in figure 2A may be between 10 and 90°.

[0044] In some examples, like in the example of figure 2A, the substantially straight portion 26 includes a portion 26B that extends beyond the circle centre. The substantially straight portion 26 may extend beyond the circle centre by e.g., 10 - 50% of the radius of the substantially circular portion 22.

[0045] In preferred examples, the central angle of the circular arc may be 300 - 350°, specifically 320 - 345°.

[0046] In some examples, the weld seam 20 incudes a rounded transition 28 between the substantially circular portion 22 and the substantially straight portion 26. The rounded transition 28 may have a transition radius of 10 - 50%, specifically 15 - 30% of the radius of the substantially circular portion 22.

[0047] It will be clear that G-shaped welds of different dimensions may be provided. With reference to figure 2B, some dimensions may be illustrated. A diameter E of the substantially circular portion may be e.g., 2 - 50 mm, specifically 4 - 20 mm, and more specifically 6 - 14 mm. The radius B of the substantially circular portion may be e.g., 1 - 25 mm, specifically 2 - 10 mm, and more specifically 3 - 7 mm.

[0048] The rounded transition 28 may have a transition radius RF of 10 - 50%, specifically 15 - 30% of the radius of the substantially circular portion 22, i.e. , the transition radius may be e.g. 0.1 - 12.5 mm, specifically 0.5 - 1.5 mm.

[0049] A distance C between an end of the substantially circular portion and the straight portion 26 may be 0.5 - 15 mm, specifically 1 - 10 mm, more specifically about 1.25 mm. A distance D between the start of the transition portion 28 and the substantially straight portion 26 may be 0.5 - 15 mm, more specifically about 1.25 mm.

[0050] Figure 20 schematically illustrates another example of a weld seam according to the present disclosure. The central angle of the circular arc in this example may be 270 - 300°, specifically about 270°, and the weld seam 20 further comprising an additional linear portion 29 extending away from the circle centre.

[0051] The G-shaped weld seam is arranged at one end of the rectilinear weld 29. In some examples, a G-shaped weld seam may be provided at both ends of a substantially rectilinear weld. Rectilinear welds may be used to provide a fluid tight joint between the two components. The G-shape can reduce stress concentrations at the end of linear welds, and thereby the initiation of cracks.

[0052] Figures 3A - 3F schematically illustrate different examples of weld seams and shear strength of the welds in different directions. In order to text the performance of the weld, and compare its performance to other known welds, experiments were carried out.

[0053] The test chosen for the trials was lap-shear test and for this purpose, the metal sheets joined to each other were lap shear rectangular specimens with 105x45mm dimensions and an overlap of 45 mm * 45 mm. The material used for both blanks was 22MnB5 LIHSS in as-delivered conditions with a standard AlSi coating. The thickness of the top sheets was 1 ,6mm and 1 ,2mm for the bottom ones.

[0054] The welding equipment that was used for that study consisted of a TruDisk 4001 laser source with up to 4kW laser power, a PFO 3D-2 remote welding head with scanning and a beam delivery cable with 200pm diameter.

[0055] The laser welding parameters used for all the trials were the same, specifically a laser power of 4kW at a constant feed rate of 65 mm / s and beam defocus of +7, 5mm. After preparing the welded assemblies, they were submitted to shear loads from three different directions as illustrated in figure 3G.

[0056] Figure 3A illustrates a first known weld seam with a zigzag configuration. Figure 3B illustrates the obtained test results. It may be seen that there is a large difference between the shear load strength depending on the direction of the load.

[0057] Figure 30 illustrates another known weld seam, a so-called staple seam. As the test results of figure 3D illustrate, the staple seam exhibits good strength in one direction (45°), but significantly lower strength in the other two directions.

[0058] Figure 3E schematically illustrates an example of a substantially G-shaped weld, and Figure 3F illustrates the test results. Contrary to the other welds, the shear strength is substantially the same in the three different directions.

[0059] The substantially G-shaped weld seam geometry thus is suitable to use as a substitution for spotwelds. It was moreover found that the peak force before fracture was greater than that of spot-welds due to the larger surface area covered by the weld. In the case of blanks being joined to each other prior to a forming operation, this means that thecombined blank obtained by using G-shaped welds can sustain more deformation in the forming process without the blanks separating from each other.

[0060] Figure 4A illustrates a flowchart of an example of a method 30 for manufacturing a component e.g., for a structural framework of a vehicle. Method 30 comprises, at block 32, the manufacture of multiple blanks. The blanks may be cut from a steel coil in one example.

[0061] Method 30 then further comprises a method for joining a first component to a second component comprising, at block 34, positioning the first and second components such that the first component at least partially overlaps the second component in an overlap region. The method further comprises, at block 36, laser welding the first component to the second component with a weld seam in the overlap region, wherein the weld seam is substantially G-shaped.

[0062] The G-shaped weld seam may correspond substantially to the examples illustrated and commented with respect to figure 2. The G-shaped weld comprises a substantially circular portion and a substantially straight portion at an end of the substantially circular portion, the substantially circular portion having a radius and corresponding to a circular arc around a circle centre with a central angle of 270° - 350°, the substantially straight portion extending radially to the circle centre.

[0063] Method 30 in this example further comprises subjecting the resulting assembly to a hot stamping operation at block 38.

[0064] Figures 4B - 4D show examples of combined blanks comprising areas with different thickness. In the examples shown in these figures, the combined blanks are formed by a plurality of blanks. In examples, individual blanks may have a thickness of 0,8 - 2mm, for example 1 ,2 mm. If both blanks have a thickness of 1 ,2 mm, the thickness may be 2,4 mm in the area of overlap.

[0065] Specifically, larger blanks comprising length and width of e.g., 1 - 2 meters or more, may be manufactured by joining individual blanks to each other prior to a forming operation. In some examples, the blanks with overlapping regions may comprise blanks which after forming may be at least one of a unitary roof ring of a vehicle, a unitary rear ring of a vehicle, unitary door ring of a vehicle, a unitary firewall panel of a vehicle, a frame for the protection of a battery box of a vehicle and a unitary bumper beam assembly of a vehicle. Overall heating process may be improved and a high throughput in a hot stamping production line may be achieved.

[0066] Figure 4B shows an example of a blank before being deformed to form a unitary roof ring of a vehicle. As shown in figure 4B, the unitary roof ring may be made from four blanks, a first blank 310, a second blank 320, a third blank 330 and a fourth blank 340, wherein the first and second blanks 310, 320 may be longitudinal beam blanks, and the third and fourth blanks 330, 340 may be crossbeam blanks. The longitudinal beam blanks may be joined to the front cross beam blank and to the rear cross beam blank, forming a substantially closed ring shape. The blanks may be joined to each other e.g., through laser welding or spot welding.

[0067] The blanks may be joined with each other by forming one or more overlapping regions 350 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.

[0068] Also shown in figure 4B, a patch blank 370 may be joined to at least one of the plurality of the blanks that form combined blank 300. 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”.

[0069] A patch blank 370 may be added as a reinforcement in order to increase strength of a specific area of the blank 300. The overlapping region formed by overlapping a patch blank 370 with another blank comprises increased thickness as compared to the remainder areas of the blank. In some examples, preheating one or more preselected areas of the blank may comprise preheating an area of the blank comprising a patch blank.

[0070] The plurality of blanks 310 - 340 may comprise different thicknesses and / or different materials.

[0071] In any of the overlapping regions 350, 370 disclosed in the example of figure 4B, the substantially G-shaped weld seams as disclosed in e.g., figures 2A and 2B may be used to join the blanks to each other.

[0072] In some examples the blank or the hereinbefore described blanks may be made from ultra-high strength steels (LIHSS). Boron steel, e.g., 22MnB5, or other steelcompositions mentioned or referred to before may be suitable LIHSS. These blanks, e.g., boron steel blanks, may comprise an aluminium silicon coating or zinc coating.

[0073] 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

[0074] llsibor® 1500P may have a yield strength of e.g., 1.100 MPa, and an ultimate tensile strength of 1 .500 MPa.

[0075] Usibor® 2000 is an example of a 37MnB5 steel, which 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

[0076] MBW-K® 1900 is a manganese-boron steel 34MnB4 from ThyssenKrupp™ which may have an ultimate tensile strength of 1900 MPa. The chemical composition of MBW-K® 1900 is summarised below in weight in percentages (rest is iron (Fe) and impurities):Maximum carbon (C) (%): 0.38Maximum silicon (Si) (%): 0.40Maximum manganese (Mn) (%): 1.40Maximum phosphorus (P) (%): 0.025Maximum sulphur (S) (%): 0.010Minimum aluminium (Al) (%): 0.015Maximum chromium and molybdenum (Cr + Mo) (%): 0.50Maximum titanium (Ti) (%): 0.13Maximum boron (B) (%): 0.005

[0077] The plurality of blanks that form the combined blank may comprise different material and / or thicknesses. For example, blanks of press hardenable manganese boron steels like llsibor® or MBW-K® 1900 (e.g., llsibor® 1500 and / or llsibor® 2000) may be used in the blanks forming the combined blank. Using these types of materials in hot forming and subsequent quenching processes leads to a predominantly martensitic structure. One or more of the blanks may be made from a different material, e.g., Ductibor® 1000.

[0078] Ductibor® 1000 is another material used in hot stamping for increasing the elongation when compared to Usibor® 1500 and Usibor® 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

[0079] 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 behaviour in case of a collapse of a component under an impact.

[0080] 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).

[0081] 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 die element 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 neighbouring die element may be heated in order toensure 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.

[0082] Alternative methods for creating regions with increased ductility include differential heating prior to stamping, and / or local heat treatments (using e.g., laser, IR heating or induction heating) after a stamping operation.

[0083] In yet further examples, the combined blank may comprise one or more blanks of aluminium alloys. The aluminium of the blank may be an aluminium alloy selected from the groups 5000, 6000 and 7000 series aluminium alloys. These series are characterized by their strength, corrosion resistance and weldability.

[0084] Specifically, the aluminium material of at least one of the first and second blanks can be selected from the following group: AA5082, AA5083, AA5182, AA5183, AA5754, AA5454, AA6005, AA6022, AA6016, AA6451, AA6111 , AA6014, AA6501, AA6181, AA6061, AA6021, AA7204, and their variants.

[0085] Other examples of implementations of the G-shaped welds are illustrated in figures 4C and 4D. Figure 4C illustrates a reinforcement of a B-pillar. The reinforcement of a B- pillar may be made by hot stamping a combined blank comprising a main blank 40 and a patch 42 positioned on top of the main blank. As schematically illustrated in figure 4C, a plurality of G-shaped welds may be used to join the main blank 40 to the patch 42. The resulting combined blank may be heated to above an austenization temperature and subsequently deformed and quenched. The same materials or similar materials as those mentioned with respect to figure 4B may be used in the example of figure 4G.

[0086] Figure 4D illustrates a combined blank 50 for the manufacture of a unitary door ring. The unitary door ring comprises a rocker portion, a hinge pillar portion, an A-pillar portion and a B-pillar portion. The term “portion” is herein used, because in the resulting unitary door ring, there are no separate B-pillar, A-pillar, hinge pillar and rocker, since there is only a single structure.

[0087] The combined blank 50 in this example comprises a blank 51 corresponding to a rocker portion, a blank 52 corresponding substantially to a hinge pillar, a blank 53 corresponding substantially to the A-pillar, a blank 54 corresponding to an upper region of the B-pillar and a blank 55 corresponding to a lower region of the B-pillar.

[0088] In this example, each of the blanks 51 , 52, 53, 54, and 55 are arranged to be partially overlapping, i.e. an overlapping region 56 is formed between the blank 55 of the lower B- pillar and blank 51 corresponding to the rocker; an overlapping region 57 is formed between the blank 51 corresponding to the rocker, and the blank 52 corresponding to the hinge pillar; an overlapping region 58 is formed between the blank 52 corresponding to the hinge pillar and the blank 53 corresponding to the A-pillar; an overlapping region 59 between blank 53 corresponding to the A-pillar and blank 54 corresponding to the B-pillar; and an overlapping region 60 formed between the blank 54 of the upper B-pillar and the blank 55 of the lower B-pillar.

[0089] G-shaped welds may be used in one or more, or all overlapping regions to join the blanks to each other. The combined blank may be subjected to a hot stamping process, and again, the same or similar materials may be used as mentioned before for this process. And similarly, as before, the individual blanks may have different thicknesses and / or may be made of different materials.

[0090] Figure 5 illustrates yet another example of an implementation of the use of the G- shaped welds. In the example of figure 5, previously formed components are joined to each other. Figure 5 schematically illustrates a cross-sectional view of the joint between a tubular reinforcement 70 and a panel 72. The tubular reinforcement may be made e.g., by hydroforming and in this example may be made of an aluminium alloy. The panel 72 may have been made in a forming process such as e.g., cold stamping. The panel 72 may be made of a suitable steel.

[0091] Also in this example, a plurality of G-shaped welds 44 (e.g., a row of welds) may be used to join the reinforcement 70 to the panel 72. The use of G-shaped welds may thus, similar to spot welding, provide welds which have a substantially constant shear strength independent of the direction of the shear load. Contrary to spot welds, the G-shaped welds may also be used to join a tubular component, i.e., a component with a closed cross-section, to another component since the laser only needs to access from one side.

[0092] Tests have been carried out to indeed compare the strength of spot welds with the strength of G-shaped welds, and in particular under bending loads in a B-pillar. Figure 6A schematically illustrates the configuration of the tested B-pillar. The B-pillar is made by hot stamping of a llsibor ® 1500 boron steel blank. The main blank 80 of the B-pillar has thickness of 1.6 mm. A patch 82 is arranged in a central portion of the B-pillar. The patch is made from the same material and has thickness of 1.2 mm. The central portion of the B-pillar thus has a thickness of 2.8 mm, whereas the rest of the B-pillar has thickness of 1.6 mm.

[0093] In order to test the behaviour of the welds, different versions of B-pillars were prepared. In one series of specimens, the patch was joint to the main blank using 32 spot welds having an area of about 45 mm2. In another series of specimens, the patch was joint to the main blank using 32 G-shaped welds, with an area of similar size.

[0094] The set-up for the test is schematically illustrated in fig. 6B. Both a top end and a lower end of the B-pillar are supported. A substantially cylindrical roller is pushed down on the B-pillar at about half the height of the B-pillar. The force is gradually increased, whereas the downwards deformation of the B-pillar (the “intrusion”) is measured.

[0095] The results for three test specimens of each type are shown in figure 60. It can be derived from figure 60 that the bending behaviour and force-intrusion behaviour of both types of welds are very similar. The results of the specimens of B pillars with spot welds are identified as RSW-1 , 2 and 3 respectively, whereas the other specimens are identified as G1-1 , 2 and 3. However, the G-shaped welds provide the aforementioned advantages related to the use of remote laser welding instead of spot welding.

[0096] For completeness, various aspects of the present disclosure are set out in the following numbered clauses:Clause 1 . A method for joining a first component to a second component, comprising: positioning the first and second components such that the first component at least partially overlaps the second component in an overlap region, laser welding the first component to the second component with a weld seam in the overlap region, wherein the weld seam comprises a substantially circular portion and a substantially straight portion at an end of the substantially circular portion, the substantially circular portion having a radius and corresponding to a circular arc around a circle centre with a central angle of 270° - 350°, the substantially straight portion extending radially to the circle centre.Clause 2. The method of clause 1 , wherein the substantially straight portion extends radially beyond the circle centre.Clause 3. The method of clause 2, wherein the substantially straight portion extends beyond the circle centre by 10 - 50% of the radius.Clause 4. The method of any of clauses 1 - 3, wherein the central angle of the circular arc is 300 - 350°, specifically 320 - 345°.Clause 5. The method of any of clauses 1 - 3, wherein the central angle of the circular arc is 270 - 300° and the weld further comprising an additional linear portion extending away from the circle centre.Clause 6. The method of any of clauses 1 - 4, wherein a radius of the substantially circular portion is 1 - 25 mm, specifically 2 - 10 mm, more specifically 3 - 7 mm.Clause 7. The method of any of clauses 1 - 5, wherein the weld seam includes a rounded transition between the substantially circular portion and the substantially straight portion.Clause 8. The method of clause 6, wherein the rounded transition has a transition radius of 10 - 50%, specifically 15 - 30% of the radius of the substantially circular portion.Clause 9. The method of any of clauses 1 - 8, wherein the weld seam extends through the thickness of the first component and second component.Clause 10. The method of any of clauses 1 - 8, wherein the weld seam extends only partially though the thickness of the second component.Clause 11. The method of any of clauses 1 - 10, wherein the laser welding includes laser welding with more than one laser spot.Clause 12. The method of any of clauses 1 - 11 , wherein the laser welding includes laser welding with a wobbling laser spot.Clause 13. The method of any of clauses 1 - 12, wherein the laser welding comprises welding with a laser power of 2 - 10kW, specifically 3 - 8kW.Clause 14. The method of any of clauses 1 - 13, wherein a linear welding speed is 40 - 80 mm / s.Clause 15. The method of any of clauses 1 - 14, wherein a laser beam defocus is + / - 3 - 10 mm, specifically + / - 5 - 8 mm.Clause 16. The method of any of clauses 1 - 15, wherein the laser welding is performed with an Nd: YAG laser.Clause 17. The method of any of clauses 1 - 16, wherein the laser welding is performed with a CO2 laser or fibre laser.Clause 18. The method of any of clauses 1 - 17, wherein the first component is a substantially flat first metal blank, and the second component is a substantially flat second metal blank and a combined blank includes the first metal blank joined to the second metal blank.Clause 19. The method of clause 18, further comprising forming the combined blank, specifically cold or hot stamping the combined blank.Clause 20. The method of clause 18 or 19, wherein the first and second metal blanks are aluminium alloy blanks.Clause 21. The method of clause 20, wherein the aluminium alloy is selected from a group comprising 5000, 6000 and 7000 series aluminium alloys.Clause 22. The method of clause 18 or 19, wherein the first and second metal blanks are steel blanks, specifically boron steel blanks.Clause 23. The method of clause 22, wherein the steel blanks comprise a corrosion protective coating, specifically an AlSi coating or Zinc based coating.Clause 24. The method of clause 23, wherein the corrosion protective coating is at least partially removed in the overlapping region prior to joining the first blank to the second blank.Clause 25. The method of any of clauses 1 - 17, wherein the first and second components are components after metal forming.Clause 26. The method of clause 25, wherein at least one of the first and second components is obtained after stamping, specifically hot stamping.Clause 27. The method of clauses 25 or 26, wherein at least one of the first and second components is obtained after roll forming or hydro forming.Clause 28. A welded assembly that is obtainable by any of the methods of clauses 1 - 27.Clause 29. A welded assembly comprising a first component and a second component, the first component being arranged at least partially on top of the second component in an overlap region, the first component being laser welded in the overlap region with one or more weld seams comprising a substantially circular portion and a substantially straight portion at an end of the substantially circular portion,the substantially circular portion corresponding to a circular arc around a circle centre with a central angle of 270° - 350°, the substantially straight portion extending radially to the circle centre.Clause 30. The assembly of clause 29, wherein the substantially straight portion extends radially beyond the circle centre.Clause 31. The assembly of clause 29, wherein the substantially straight portion extends beyond the circle centre by 10 - 50% of the radius.Clause 32. The assembly of any of clauses 29 - 31, wherein the central angle of the circular arc is 300 - 350°, specifically 320 - 345°.Clause 33. The assembly of any of clauses 29 - 31, wherein the central angle of the circular arc is 270 - 300° and the weld further comprising an additional linear portion extending away from the circle centre.Clause 34. The assembly of any of clauses 29 - 33, wherein a radius of the substantially circular portion is 1 - 25 mm, specifically 2 - 10 mm, more specifically 3 - 7 mm.Clause 35. The assembly of any of clauses 29 - 34, wherein the weld seam incudes a rounded transition between the substantially circular portion and the substantially straight portion.Clause 36. The assembly of clause 35, wherein the rounded transition has a transition radius of 10 - 50%, specifically 15 - 30% of the radius of the substantially circular portion.Clause 37. The assembly of any of clauses 29 - 36, wherein the weld seam extends through the thickness of the first component and second component.Clause 38. The assembly of any of clauses 29 - 36, wherein the weld seam extends only partially though the thickness of the second component.Clause 39. The assembly of any of clauses 29 - 38, wherein the first component is a substantially flat first metal blank, and the second component is a substantially flat second metal blank and a combined blank includes the first metal blank joined to the second metal blank.Clause 40. The assembly of clause 39, wherein the first and second metal blanks are aluminium alloy blanks, specifically wherein the aluminium alloy is selected from a group comprising 5000, 6000 and 7000 series aluminium alloys.Clause 41 . The assembly of any of clauses 29 - 38, wherein the first and second metal blanks are steel blanks, specifically boron steel blanks.Clause 42. The assembly of clause 41 , wherein the steel blanks comprise a corrosion protective coating, specifically an AlSi coating or Zinc based coating.Clause 43. The assembly of any of clauses 29 - 38, wherein the first and second components are components after metal forming.Clause 44. The assembly of clause 43, wherein at least one of the first and second components is a stamped component, specifically a hot stamped component.Clause 45. The assembly of clause 43 or 44, wherein at least one of the first and second components is a roll formed or hydro formed component.Clause 46. A welded assembly comprising a first component and a second component, the first component being arranged at least partially on top of the second component in an overlap region,the first component being laser welded in the overlap region with one or more substantially G-shaped weld seams to the second component.

[0097] 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 joining a first component to a second component, comprising: positioning the first and second components such that the first component at least partially overlaps the second component in an overlap region, laser welding the first component to the second component with a weld seam in the overlap region, wherein the weld seam comprises a substantially circular portion and a substantially straight portion at an end of the substantially circular portion, the substantially circular portion having a radius and corresponding to a circular arc around a circle centre with a central angle of 270° - 350°, the substantially straight portion extending radially to the circle centre.

2. The method of claim 1 , wherein the substantially straight portion extends radially beyond the circle centre.

3. The method of claim 2, wherein the substantially straight portion extends beyond the circle centre by 10 - 50% of the radius.

4. The method of any of claims 1 - 3, wherein the central angle of the circular arc is 300 - 350°, specifically 320 - 345°5. The method of any of claims 1 - 3, wherein the central angle of the circular arc is 270 - 300° and the weld further comprising an additional linear portion extending away from the circle centre.

6. The method of any of claims 1 - 5, wherein a radius of the substantially circular portion is 1 - 25 mm, specifically 2 - 10 mm, more specifically 3 - 7 mm.

7. The method of any of claims 1 - 6, wherein the weld seam includes a rounded transition between the substantially circular portion and the substantially straight portion.

8. The method of claim 7, wherein the rounded transition has a transition radius of 10 - 50%, specifically 15 - 30% of the radius of the substantially circular portion.

9. The method of any of claims 1 - 8, wherein the laser welding includes laser welding with more than one laser spot and / or with a wobbling laser spot.

10. The method of any of claims 1 - 9, wherein the first component is a substantially flat first metal blank, and the second component is a substantially flat second metal blank and a combined blank includes the first metal blank joined to the second metal blank.11 . The method of claim 10, further comprising forming the combined blank, specifically cold or hot stamping the combined blank.

12. The method of claim 10 or 11 , wherein the first and second metal blanks are aluminium alloy blanks, specifically wherein the aluminium alloy is selected from a group comprising 5000, 6000 and 7000 series aluminium alloys.

13. The method of claim 10 or 11 , wherein the first and second metal blanks are steel blanks, specifically boron steel blanks.

14. The method of any of claims 1 - 9, wherein the first and second components are components after metal forming, specifically wherein at least one of the first and second components is obtained after stamping, after roll forming or hydro forming.

15. A welded assembly comprising a first component and a second component, the first component being arranged at least partially on top of the second component in an overlap region, the first component being laser welded in the overlap region with one or more weld seams comprising a substantially circular portion and a substantially straight portion at an end of the substantially circular portion, the substantially circular portion corresponding to a circular arc around a circle centre with a central angle of 270° - 350°, the substantially straight portion extending radially to the circle centre.