Method for laser welding

Abstract

The present disclosure relates to methods for joining a first component to a second component. The methods comprise 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 one or more weld seams in the overlap region. The weld seams comprise a first weld seam including a substantially straight portion and having a first end, and one or more rounded seam portions. The straight portion intersects with at least one of the rounded seam portions. The one or more rounded seam portions enclose the first end of the first weld seam. The present disclosure further relates to cooling systems incorporating such welds, and battery units for vehicles incorporating such cooling systems.

Description

AUTOTECH ENGINEERING S.L. SEPTEMBER 23, 2025P2404 P5477PC00METHOD FOR LASER WELDING

[0001] The present application claims the benefit of European patent application n° EP24383032.0, filed on September 26th, 2025.

[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 aluminium or steel blanks or components in a lap joint.BACKGROUND

[0003] The rapid development of electric vehicles (EVs) and hybrid vehicles has forced the industry to design new car components, e.g. for weight reduction to achieve improved vehicle range, and for accommodating and protecting new car components among others. Structural components with new geometries and alternative materials are being manufactured and integrated into EVs to accomplish safety and weight reduction goals. Although reference will herein be made generically to electric vehicles or EVs, this is expressly intended to cover hybrid vehicles as well.

[0004] Traction batteries are an essential part of the EVs and are configured to provide power to an electric motor of the vehicle. The electronic and chemical nature of these batteries makes them particularly sensitive to high mechanical loads, e.g. crash impacts, and to high working temperatures. To extend battery lifespan, the automotive industry has put considerable effort into providing battery enclosures and load bearing structures suitable for EVs that combine battery protection and battery cooling. Thus, a wide range of battery components have been designed and developed during the last years to accommodate and to (mechanically and thermally) protect traction batteries.

[0005] The battery of an electric or hybrid vehicle can function as an energy storage element for powering an electrical motor and thus enabling the vehicle to move. A battery may include several cells, e.g. lithium-ion cells grouped into modules. The term “battery” within the present disclosure may be understood to refer to the battery or battery pack used for propulsion.

[0006] In order to drive the vehicle, the battery may be connected to one or more electrical motors. The electrical motor or “traction motor” may drive a wheel axle. For example, a front wheel axle may be driven by a front traction motor, and a rear wheel axle may be driven by a rear traction motor. It is also possible for a single traction motor to drive a single axle.

[0007] Steel battery boxes or battery trays have been developed for housing the battery. Also, battery boxes comprising aluminium, polymeric (plastic) or composite components are known. Further, appropriate cooling systems have to be provided to keep battery temperature within acceptable ranges, while reducing weight of the overall battery system.

[0008] Known cooling systems may include an aluminium or stainless steel cooling plate, which may form a top cover or bottom cover of the battery box. The cooling plate may incorporate one or more serpentine cooling channels. Water or other liquid is passed through the cooling channels, and thereby absorbs heat from the battery unit. The water / liquid that is heated up by absorbing the heat from the battery may be cooled in a heat exchanger and resupplied to the cooling plate.

[0009] The cooling plate is ordinarily made by brazing two aluminium or stainless steel sheets on top of each other. One or both of the sheets may comprise recesses, and when the sheets are joined to each other, the cooling channels are formed by the recesses and are established between the plates. Brazing the sheets requires a significant investment since large furnaces or heating systems are required. The high temperatures used in brazing may also lead to some deformation of the sheets, which leads to the problem of the sheets and the resulting plate not being flat (enough). If the sheets are not flat, the formation of the cooling channels and the ability to cool the battery unit are affected. Furthermore, brazing is generally regarded to be incompatible with the use of magnesium, which means that specific aluminium alloys cannot be used.

[0010] Alternatively, laser welding may be used to join the aluminium or stainless steel sheets. However, the use of laser welding can lead to fatigue problems due to stress concentrations around the ends of the weld seams. Moreover, it has been found that the end of weld seams can lead to leakage: when cooling liquid under pressure is supplied through the cooling channel(s), the liquid can escape at the end of the weld seam which may be weakened or cracked. Leakage of the cooling system is unacceptable since it could damage the battery.

[0011] The present disclosure provides examples of methods and cooling systems which can overcome at least some of the aforementioned drawbacks.SUMMARY

[0012] 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. The method further comprises laser welding the first component to the second component with one or more weld seams in the overlap region. The weld seams comprise a first weld seam having a first end and including at least a substantially straight portion. The one or more weld seams also comprise one or more rounded seam portions. The straight portion intersects with at least one of the rounded seam portions and the one or more rounded seam portions enclose the first end of the first weld seam.

[0013] In accordance with this aspect, laser welding of components is provided which is beneficial for applications in which the joint between components needs to be fluid tight. The use of laser welding can be faster and cheaper than brazing, and allows for a larger variety of materials to be used, including aluminium alloys containing magnesium such as 5000 series or 6000 series. Also, the problem of flatness of the components related to brazing may be avoided.

[0014] The one or more rounded seam portions encompassing the first end of the first weld seam avoid some of the stress concentrations that may occur around the end of laser weld seams. It has further been found to be effective to improve the fluid-tightness, since fluid cannot reach the weak point of the end of the first weld seam.

[0015] Herein, laser welding may particularly refer to remote laser welding. 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.

[0016] In a further aspect, an assembly is provided that is obtained or obtainable by an example of a method according to the first aspect.

[0017] In a further aspect, a cooling system is provided, which comprises a first sheet, and a second sheet, wherein at least one serpentine cooling channel is formed between the first and the second sheet. The cooling system further comprises one or more joints betweenthe first sheet and the second sheet in areas between portions of the serpentine cooling channel, and wherein a joint includes one or more weld seams comprising a first weld seam including a first end and including a substantially straight portion, and one or more rounded portions. The substantially straight portion intersects with at least one of the round seam portions, and the one or more round seam portions enclose the first end of the first weld seam.

[0018] In accordance with this aspect, a cooling system is provided which is fluid-tight or at least liquid-tight, and which can be relatively quickly and efficiently manufactured. At the same time, fatigue life of such a component and performance under high pressure (e.g. established with a burst pressure test) may be improved.

[0019] The sheets may be metallic sheets, and particularly aluminium or stainless steel sheets.

[0020] Rounded seam portions may herein be understood as seam portions that do not have sharp angles or vertices, which would promote stress concentration. The rounded seam portions may include any kind of smooth curve, and be or include oval or elliptic or circular portions.

[0021] A cooling system in accordance with this aspect may be used e.g. in combination with a vehicle battery. The cooling system may be a cooling plate arranged between battery cells, or a cover plate closing a battery box either at the top or at the bottom.

[0022] In yet a further aspect, therefore a battery unit for a vehicle is provided comprising such a cooling system.

[0023] In some examples, the first weld seam may include the one or more rounded seam portions enclosing the first end. I.e. the same weld seam includes the straight portion and the rounded portions and thus intersects with itself. A continuous weld seam which reduces stress concentrations around the end of the laser weld seam may therefore be provided. A characteristic of the use of a single weld seam for the joint or each joint is that the joining process can be quicker.

[0024] In some examples, the rounded seam portions of the first weld seam may comprise at least one loop. In specific examples, the first weld seam includes a loop formed by an initial straight portion including the first end, and two rounded portions forming the loop enclosing the first end.

[0025] In other examples, the weld seams may comprise a second weld seam including the one or more round seam portion enclosing the first end. In some examples, the second weldseam may be substantially circular. A substantially circular weld seam reduces stress concentrations around the end of the first weld seam.

[0026] In some examples, a diameter of the second weld seam may be 5 - 35 mm, specifically 15 - 25 mm.

[0027] In some examples, the second weld seam may comprise two circle portions. Welding in accordance with examples of the present disclosure particularly includes encompassing the end of the first weld seam such that liquid cannot reach the potentially weak point at the end of a weld seam. A second weld seam including two circle portions may be used for this purpose, wherein the ends of the circle portions are encompassed by the combination of circle portions.BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Non-limiting examples of the present disclosure will be described in the following, with reference to the appended figures, in which:Figures 1A - 10 schematically illustrate examples of cooling systems;Figures 2A - 20 schematically illustrate weld seams according to examples of the present disclosure;Figure 3 shows a battery unit 400 of a vehicle comprising a cooling system 300 according to an example of the present disclosure; andFigure 4 shows a flowchart of a method for joining a first component made of a first aluminium alloy to a second component made of a second aluminium alloy.

[0029] 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

[0030] In these figures, the same reference signs have been used to designate matching elements.

[0031] Figures 1A - 1C schematically illustrate examples of cooling systems 300. Figure 1A illustrates a top view of an overlap region of a cooling system 300 according to an example of the present disclosure. The overlap region may belong to a cooling plate.

[0032] The cooling system 300 comprises a first sheet 101 , and a second sheet 102. The sheets are positioned such that one of the sheets at least partially overlaps the other in an overlap region.

[0033] In some examples, the first and / or second sheets 101 , 102 may be made from aluminium alloys. In some examples, the aluminium alloys may be selected from a group comprising 5000 and 6000 series aluminium alloys. These series are characterized by their strength, corrosion resistance and weldability.

[0034] Specifically, the aluminium material of at least one of the first and second sheets can be selected from the following group: AA5082, AA5083, AA5182, AA5183, AA5754, AA5454, AA6005, AA6022, AA6016, AA6451 , AA6111 , AA6014, AA6501 , AA6181 , AA6061 , AA6021 , and their variants.

[0035] In other examples, the aluminium alloys may be selected from a group comprising 1000 and 3000 series aluminium alloys.

[0036] In further examples, the first and / or second sheets may be made from stainless steel. In some examples, the stainless steels may be selected from a group comprising 300, 400 and duplex series stainless steel.

[0037] Specifically, the stainless steel material of at least one of the first and second sheets can be selected from the following group: SS301 - 301 L, SS302, SS304 - 304L, SS310, SS316 - 316L, SS317 - 317L, SS321 , SS329, SS347, SS348, SS409, SS410 - 410L, SS416, SS430, SS434, SS436, SS439, SS441 , SS444, SS445, SS446, SS447, SS2205, S32550, SSZ100, S32750

[0038] In some examples, the first sheet 101 and the second sheet 102 may have a thickness of 0.2 - 15 mm, more preferably of 0.4 - 3 mm. For example, a bottom sheet may be 2 mm thick, and a top sheet 1 mm thick. In other examples, both sheets may have the same thickness.

[0039] In the cooling system 300 of the present disclosure, at least one serpentine cooling channel 150 is formed between the first and the second sheets 101 , 102. The serpentine cooling channel 150 may include a first substantially straight section, a second substantially straight section and a semicircular section connecting the first and second substantially straight sections. The cooling channel may thus comprise successive oblong partially oval portions.

[0040] In other examples, the sections forming the serpentine cooling channel may comprise other shapes. And in further examples, more than one serpentine cooling channel may be provided.

[0041] The cooling system 300 shown in the example of figure 1A comprises six parallel straight channel sections. The sections are connected between them forming a single path for a cooling fluid, which may flow through the cooling channels e.g. from a first side of the cooling system F1 to a second side of the cooling system F2.

[0042] Further, the cooling system 300 comprises a plurality of joints 200, which join the sheets 101 , 102 to each other. In particular, the cooling system 300 comprises one or more joints 200 between the first sheet 101 and the second sheet 102 in areas between portions of the serpentine cooling channel 150, specifically between the straight channel sections of the serpentine cooling channel(s).

[0043] The first and second sheets 101 , 102 may be joined such that the cooling fluid may only flow through recesses or undulations in the sheets and does not exit the cooling channels 150 formed between the sheets. It is possible however for the liquid that passes through the cooling channels to leak outside the cooling channel to a certain extent. The liquid however cannot flow to another portion of the serpentine cooling channel because the joints impede this.

[0044] Further, the first and second sheets are joined to each other along the edges of the sheets, which has been schematically illustrated in the same figure.

[0045] Figures 1 B and 1C show cross sections of examples of cooling systems 300 according to the present disclosure. The cross sections of these figures in this case coincide with the central axis indicated in figure 1A.

[0046] The cooling systems 300 comprise first and second sheets 101 , 102 and a serpentine cooling channel 150. The figures also show the position of joints 200 in areas of the first and second sheets 101 , 102 between portions of the serpentine cooling channels 150.

[0047] As shown in the figures, at least one of the first and second sheets 101 , 102 may comprise recesses or undulations 151 , such that cooling channels 150 may be formed by the space created by the recesses or undulations 151 and cooling fluid may flow through the cooling channel.

[0048] In the example shown in figure 1 B, the first sheet 101 may be substantially flat and the second sheet 102 may comprise one or more recesses or undulations 151.

[0049] In other examples, as schematically shown in figure 1 C, cooling channels 150 may be defined between undulations 151 in the first sheet 101 and in the second sheet 102.

[0050] Figure 2A shows a joint 200 according to an example of the present disclosure, specifically a joint 200 located between the straight sections of the serpentine cooling channel(s), and more specifically figure 2A illustrates one end of such a joint. The joint 200 includes one or more weld seams. The one or more weld seams comprise a first weld seam 201 including a substantially straight portion 210 and having a first end 201a.

[0051] The first end 201a of the first weld seam 210 may be arranged in or near the semicircular portion of the cooling channel 150. The substantially straight portion 210 of the first weld seam of the example extends between the first end 201a and a second end 201 b (although only a short portion of the weld seam is depicted in this figure. In reality, the straight portion would be significantly longer, particularly as long as or longer than the length of the straight section of the cooling channel).

[0052] The one or more weld seams forming the joint 200 further include one or more rounded seam portions 220. The straight portion 210 intersects with at least one of the rounded seam portions 220, and the one or more round seam portions 220 enclose the first end 210a of the first weld seam 201 .

[0053] The first end 201 a of the first weld seam 201 may be a weak point of the weld seam, comprising residual stresses which could lead to fatigue breaks. The one or more round seam portions 220 may relieve the residual stresses present in the first end 201a of the first weld seam while improving the sealing between the two sheets, providing a stronger joint and ensuring that the cooling fluid remains solely within the cooling channels.

[0054] In some examples, as shown in figure 2A, the joint 200 may include a second weld seam 202 (separate from the first weld seam) including the one or more rounded seam portion 220 enclosing the first end 101a. Accordingly, the joint 200 may be obtained in two welding steps. The second weld seam may preferably be carried out substantially immediately after the first weld seam.

[0055] In the example shown in figure 2A, the second weld seam 220 comprises a single rounded portion, and particularly the single round portion of the second weld seam 220 may be substantially circular. A joint comprising a closed round portion may be provided, ensuring an adequate fluid tightness with the presence of material at the weld seam i.e. the weld seam 220 inhibits fluid reaching the first end 201a where leaking to the outside could occur. A circular portion may lead to a second weld seam which avoids stressconcentrations. In further examples, the second weld seam may have a more oval or ovaloid shape.

[0056] As schematically shown in figure 2A, the second weld seam 220 may enclose the first end 201a of the first weld seam and may intersect with the substantially straight portion in an intersection point 250.

[0057] In some examples, the second weld seam 220 may be a circle with a diameter of 5 - 35 mm, specifically 15 - 25 mm. In a specific example, the diameter of the second weld seam may be about 28 mm.

[0058] Suitable laser types include solid state lasers e.g. Nd:YAG laser, fiber lasers, diode lasers and gas lasers e.g. CO2 lasers. Laser power may be varied in accordance with circumstances, e.g. depending on the thickness of the sheets.

[0059] In some examples, the first end 201a of the first weld seam may be located substantially in a central region of the rounded portion 220. In the example of figure 2A, the first end 201a corresponds substantially to the circle centre of the circular portion 220.

[0060] Figure 2B shows a joint 200 according to another example of the present disclosure. As shown in this particular example, the second weld seam 202 may comprise more than one rounded seam portion 202 enclosing the first end 201a of the first weld seam 210. In this particular example, the second weld seam 202 includes two circular portions i.e. two portions of a circle.

[0061] The two circle portions may intersect with each other (i.e. the second weld seam crosses over itself). The two circle portions together define a rounded shape which encloses the first end 201a of the first weld seam 201. Further, as already discussed with reference to figure 2A, the second weld seam 202 intersects with the first weld seam 201 in an intersection point 250.

[0062] Figure 2C shows a joint 200 according to yet another example of the present disclosure. The joint 200 includes a first continuous weld seam 201 having a first end 201a and including a straight portion 210. As in the previous example, the straight portion 210 may generally extend parallel to the straight portions of the serpentine cooling channel.

[0063] In the example of figure 2C, the first weld seam 201 includes a loop which encloses the first end 201a. I.e. the joint 200 of figure 2C is a continuous weld seam including both the straight portion and the rounded portions.

[0064] The loop includes more than one turn. In the specific example, the loop includes about 1 ,25 turns (i.e. about 450°). The loop may include one or more rounded portions andone or more rectilinear segments. As shown in the example of figure 2C, the loop 220 of the first weld seam 201 may comprise two separate rounded portions, a first rounded portion 221 and a second rounded portion 222. They are connected to each other through a rectilinear segment of the weld seam, and include a further rectilinear segment having first end 201a.

[0065] The first rounded portion 221 in this example forms an extension of the substantially straight portion. A rectilinear segment intersects with the straight portion in an intersection point 250. In the example of figure 2C, the first rounded portion 221 is substantially circular.

[0066] The second rounded portion 222 connects with the rectilinear segment and is curved in a direction of the first rounded portion to end in another rectilinear segment substantially at a centre point of the first rounded portion. This rectilinear segment intersects with the first rounded portion 221.

[0067] Figure 3 shows an example of a battery unit 400 of a vehicle comprising a cooling system 300 according to the present disclosure. In particular, the battery unit 400 comprises the cooling system 300 illustrated in figure 1C. In the illustrated example, the cooling system 300 may be a separate example from the battery tray and may e.g. be attached using mechanical fasteners.

[0068] The battery unit in this example further comprises a battery tray 410 configured to receive a plurality of battery cells 420. The cooling system 300 may be used to cool the battery cells. In this example, the cooling system 300 may form a cover plate for the battery unit 400. The cover plate closes the battery box and may seal the battery box from the outside. The temperature of the battery cells may be efficiently regulated using a cover plate as disclosed. In other examples, the cover plate may close the battery box from the bottom.

[0069] In further examples (not illustrated), the cooling system 300 may be joined by welding or with adhesives. In yet further examples, the cooling system may form part of the battery tray, and there is no separate cooling cover plate. In these examples, the battery cells may be received directly on the cooling system.

[0070] Figure 4 represents a flow chart of a method 500 for joining a first component 101 to a second component 102.

[0071] The method 500 comprises, at step 502, positioning the first and second components 101 , 102 such that the first component at least partially overlaps the second component in an overlap region. In examples, such as for the cooling system, the first and second components may completely overlap with each other.

[0072] The method further comprises, at step 504, laser welding the first component to the second component with one or more weld seams in the overlap region. The weld seams comprise a first weld seam 201 including a straight portion 210 and having a first end 201a. The weld seams further comprise one or more round seam portions 220. The straight portion 210 intersects with at least one of the round seam portions 220, and the one or more round seam portions 220 enclose the first end 201a of the first weld seam.

[0073] In some examples, the first weld seam 201 may include the one or more round seam portions 220 enclosing the first end 201a. In these examples, the method may comprise laser welding the first component to the second component with a continuous weld seam.

[0074] In other examples, the weld seam may comprise a second weld seam 202 including the one or more round seam portion 220 enclosing the first end 201a. The method may therefore comprise a first step of laser welding the first weld seam 201 and a second step of laser welding the second weld seam 202.

[0075] In some examples, as previously disclosed, the second weld seam 220 may be substantially circular.

[0076] As previously disclosed, in some examples, one or more cooling channels 150 may be formed between the first component 101 and the second component 102. The one or more weld seams may be arranged between portions of the cooling channels.

[0077] In some examples, the first and second components 101 , 102 may be made of a first aluminium alloy and a second aluminium alloy. In other examples, the first and second components 101 , 102 may be made of a first stainless steel and a second stainless steel.

[0078] In some examples, the first component 101 may be a sheet with one or more recesses and / or the second component may be a sheet with one or more recesses.

[0079] In further examples, the first and the second component 101 , 102 may be substantially flat sheets. In these examples, the recesses in one or more of the sheets may be formed after laser welding the sheets together. In some examples, the serpentine cooling channels may be formed by hydroforming or air blowing after performing the method 500 of the present disclosure.

[0080] It should be clear that features and characteristics only illustrated with respect to an example of a welding method may be used in the various embodiments of the cooling system and vice versa.

[0081] Although only a number of examples have been disclosed herein, other alternatives, modifications, uses and / or equivalents thereof are possible. Furthermore, all possiblecombinations 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 one or more weld seams in the overlap region, the weld seams comprising: a first weld seam including a first end and having a substantially straight portion, one or more rounded seam portions, wherein the substantially straight portion intersects with at least one of the rounded seam portions, and wherein the one or more rounded seam portions enclose the first end of the first weld seam.

2. The method of claim 1 , wherein the weld seams comprise a second weld seam including the one or more rounded seam portion enclosing the first end.

3. The method of claim 2, wherein the second weld seam is substantially circular.

4. The method of claim 3, wherein a diameter of the second weld seam is 5 - 35 mm, specifically 15 - 25 mm.

5. The method of any of claims 2 - 4, wherein the second weld seam comprises two circle portions.

6. The method of claim 1 , wherein the first weld seam includes the one or more rounded seam portions enclosing the first end.

7. The method of claim 6, wherein the rounded seam portions comprise a loop enclosing the first end, optionally wherein the loop is formed by two separate rounded portions.

8. The method of any of claims 1 - 7, wherein one or more cooling channels are formed between the first component and the second component, and wherein the one or more weld seams are arranged between portions of the cooling channels.

9. The method of claim 8, wherein the first component is a first aluminium or stainless steel sheet with one or more recesses and / or wherein the second component is a second aluminium or stainless steel sheet with one or more recesses.

10. The method of claim 8, wherein the cooling channels are formed after joining the first component to the second component, particularly wherein the cooling channels are formed by hydroforming.

11. The method of any of claims 1 - 10, wherein the first component and the second component have a thickness of 0.2 - 15 mm.

12. A cooling system comprising: a first sheet, and a second sheet, wherein at least one serpentine cooling channel is formed between the first and the second sheet, and comprising one or more joints between the first sheet and the second sheet in areas between portions of the serpentine cooling channel, and wherein a joint includes one or more weld seams comprising a first weld seam having a first end and including a substantially straight portion, and one or more round portions, wherein the substantially straight portion intersects with at least one of the rounded seam portions, and wherein the one or more rounded seam portions enclose the first end of the first weld seam.

13. The cooling system of claim 12, wherein the serpentine cooling channel includes a first substantially straight section, and a second substantially straight section, and a semicircular section connecting the first and second substantially straight sections, and wherein the first end of the first weld seam is arranged in or near the semicircular section.

14. A battery unit for a vehicle comprising the cooling system of claim 12 or 13.

15. The battery unit of claim 14, wherein the cooling system forms a cover plate for the battery unit.

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