Device comprising two conductive bars connected by laser welding

Abstract

The invention relates to a device comprising a first conductor bar (1) and a second conductor bar (2), the first conductor bar (1) and the second conductor bar (2) being superimposed in a connection area, said connection area comprising a laser weld which connects the two conductor bars (1, 2), the weld comprising a weld bead (8), characterized in that the weld bead (8) forms a crossing or an overlap with itself or another weld bead. This makes it possible to produce the desired weld pattern, optimizing the welded surface with respect to the available connection area. Figure for abstract: Figure 5

Description

Title of the invention: Device comprising two conductive bars connected by laser welding TECHNICAL FIELD OF THE INVENTION

[0001] The present invention relates to the field of mechanical and electrical connection between two conductive bars.

[0002] The present invention relates in particular to the connection between an inverter and the phases of an electrical machine whose operation is controlled by this inverter.

[0003] The invention is described and exemplified below in the context of such a connection between an inverter and an electric traction motor in a motor vehicle, which is the preferred application of the invention. The present invention is nevertheless applicable to any connection between two conductive bars. STATE OF THE ART

[0004] Many electrical devices use conductive bars to carry a large electric current.

[0005] These conductive bars are generally designated by the English term "busbars" or by the expression "bus bar". The conductive bars correspond to conductors, generally made of copper, which are used to transmit electrical power with low resistance and minimal losses. In the applications particularly targeted by the present invention, the conductive bars may for example have a thickness of between 0.5 mm and 5 mm, in particular between 0.8 mm and 3 mm.

[0006] An inverter comprises power modules, forming a “power stage”, and comprising electronic switches whose openings and closings are controlled appropriately by a control module, in order to supply the phases (for example the three phases) of an electrical machine.

[0007] In the context of an inverter, the support structures of the power modules (these supports are also called "leadframe") comprise such conductive bars which make it possible to connect the power modules.

[0008] The power modules are connected outside the inverter to the phases of the motor controlled by the inverter. The phases of the motor themselves, at the input of the motor, have the form of conductive bars, which must be connected to the conductive bars which are at the output of the inverter.

[0009] The power modules are also connected to a conductive bar linked to the capacitors of the inverter.

[0010] Thus, for the implementation of an inverter, and also for many other applications, it is often necessary to connect, mechanically and electrically, two conductive bars together.

[0011] The connection between two conductive bars must ensure the passage of current without creating significant resistance (which would result in energy losses, or even unacceptable heating at the connection). The connection must also be mechanically solid, to ensure good support between the components thus connected.

[0012] The most commonly used solution is to make an assembly by screws. In such an assembly, each conductive bar has a hole, the holes are aligned and crossed by a screw, and the bars are clamped between the head of the screw and a threaded insert in which the screw is engaged.

[0013] This solution has the advantage of simplicity, but has several disadvantages. First of all, screwing requires several parts to be added to make the connection: a screw, a threaded insert, and possibly one or more washers. This represents a weight that is not negligible. This has a cost, linked to the cost of the added parts but also to the logistics necessary to manage these different parts.

[0014] A screw connection also requires having a certain volume available around the connection to accommodate the screw head and the insert, as well as to allow the passage of a tool for installing the insert and screwing the screw. A screw connection also increases the volume required to ensure electrical insulation around the connection. In addition, it is not possible to easily provide effective cooling for this connection when it is made with a screw.

[0015] Also, making a screwed connection takes a certain amount of time, for the installation of the elements and for the screwing itself.

[0016] There is also always a risk of loosening, inherent in a screwed connection. Loosening can increase the electrical resistance in the connection.

[0017] Finally, in applications where the connection environment is and must remain particularly clean, a screwing operation should be avoided or carried out with great caution. Indeed, screwing is likely to produce and release small metal particles. The generation of such particles must be avoided in electronic circuits or near electronic circuits.

[0018] In order to avoid these drawbacks, it has been considered to make connections by welding, in particular by laser welding, between two conductive bars. Laser welding is a welding method in which two flat elements to be welded are superimposed and a laser beam is applied to the superimposed part of the elements to be welded. In particular, laser welding (or "laser welding") uses a highly concentrated laser beam as a heat source to melt and fuse the targeted materials, allowing a precise, rapid and automatable junction with a minimal heat-affected zone and limited deformations.

[0019] Document US20210408698 discloses power components whose electrical connections between two connection pins are made by laser welding. The welds envisaged are straight, or in the form of waves. However, the area thus welded has a fairly small effective welded width.

[0020] Document US20220355406 discloses a laser-welded power module busbar. The weld is a spiral shape. This weld is performed in two steps: a first C-shaped weld line (or bead) is made, up to a first intermediate point, then a second weld line (or bead) is formed starting from this intermediate point in order to form a spiral. This welding path is supposed to limit stress concentrations in the weld.

[0021] These welds can nevertheless be further improved in certain aspects. Statement of the invention

[0022] The present invention aims to improve the connection by laser welding between two conductive bars.

[0023] For this purpose, the invention relates to a device comprising a first conductive bar and a second conductive bar, the first conductive bar and the second conductive bar being superimposed in a connection zone. The connection zone comprises a laser weld which connects the two conductive bars, the weld comprising a weld bead. The weld bead forms a crossing or an overlap with itself or another weld bead.

[0024] Contrary to accepted practice in the field of laser welding, the Applicant has in fact found that under certain conditions it is advantageous to have weld beads cross or overlap. This makes it possible to produce the desired weld pattern, optimizing the welded surface in relation to the available bonding surface, for example by producing nested patterns. This is achieved while avoiding producing welds that are too close together in a short period of time. Indeed, since welding causes the release of smoke, this smoke could disrupt the laser diffraction welding if the laser beam is not moved out of the smoke. Furthermore, since welding causes significant localized heating, it is preferable not to carry out too much welding in the same area in a given time. This could generate local stresses in the conductive bars.

[0025] The weld bead may consist of a starting portion, a central portion, and a stopping portion, the depth of the weld being increasing in the starting portion, between a starting point of the starting portion and a starting point of the central portion, the depth of the weld being substantially constant in the central portion, and the depth of the weld being decreasing between a central portion end point and an end point of the stopping portion. The weld bead weld having a width L, a central portion start zone is defined as the zone of the central portion following the central portion start point over a length equal to the width L of the weld bead, and a central portion end zone is defined as the zone of the central portion preceding the central portion end point over a length equal to the width L of the weld bead. The central portion start zone or the central portion end zone can then be an overlap zone with another point of the weld bead or with another weld bead.

[0026] Thus, the applicant has found that the formation of a weld bead by laser welding causes portions at the beginning and end of the bead where the weld is imperfect, and of variable depth. The invention proposes to produce weld patterns taking this phenomenon into account. The existence of these start and stop portions is linked to the rapid but nevertheless not instantaneous establishment of the laser power, and to the thermal inertia of the conductive bars (the laser penetrating a hot surface better). By making the weld bead or weld beads meet at the start or end zones of the central portion (in which the weld is of the correct depth), it is ensured that the pattern formed, whether after or before this meeting (depending on whether the start or stop portion is considered) forms a correct weld, the depth of which reaches the second conductive bar.

[0027] Advantageously, one of the start zone of the central portion and the end zone of the central portion overlaps in whole or in part with the other of the start zone of the central portion and the end zone of the central portion or overlaps in whole or in part with the end zone or the start zone of the central portion of another weld bead.

[0028] The weld may comprise a weld bead tracing a closed shape.

[0029] The weld bead can form a rectangle.

[0030] The weld bead can form a circle or an ellipse.

[0031] The weld may comprise several weld beads each forming a closed shape, the weld beads being concentric.

[0032] The weld may comprise two weld beads, each weld bead forming an “L”, the two weld beads crossing each other twice to form a rectangle.

[0033] The weld may comprise two weld beads, each weld bead forming a “U” of the same dimension as the U of the other weld bead, the U’s being nested within each other so that a lateral branch of each U crosses a central branch of the other U.

[0034] The weld may comprise three weld beads, namely two “L” shaped beads placed symmetrically, in the plane of the weld, facing each other, and one third weld bead which is straight and which crosses the two L-shaped weld beads.

[0035] The invention also relates to an inverter comprising at least one power module and a set of capacitors, the inverter comprising a device as described above in which the first conductive bar is a direct current supply conductive bar of the power module and the second conductive bar is connected to the set of capacitors.

[0036] The invention also relates to an assembly comprising an inverter comprising at least one power module and an electric motor controlled by the inverter, the assembly comprising a device as previously described, and in which the first conductive bar is an alternating current output conductive bar of the power module and the second conductive bar is connected to a phase of the motor.

[0037] The invention finally relates to a method of welding two conductive bars comprising the steps of: - provision of a first conductive bar and a second conductive bar; - contacting by superposition of the first conductive bar and the second conductive bar, thus forming a superposition zone also called a connection zone, - formation of a weld bead by laser welding, the weld bead forming a crossing or overlap with itself or another weld bead.

[0038] In such a method, the formation of the weld bead may comprise the application and movement of a laser beam to the surface of one of the conductive bars in the connection zone, resulting in a weld bead which comprises a starting portion, a central portion, and a stopping portion, the depth of the weld being increasing in the starting portion, between a starting point of the starting portion and a starting point of the central portion, the depth of the weld being substantially constant in the central portion, and the depth of the weld being decreasing between a central portion end point and an end point of the stopping portion, and in which, the weld bead having a width L, a starting zone of the central portion is defined as the zone of the central portion following the starting point of the central portion over a length equal to the width of the weld bead,and an end zone of the central portion is defined as the zone of the central portion preceding the end point of the central portion over a length equal to the width of the weld bead, the displacement of the laser beam being such that the start zone of the central portion or the end zone of the central portion is an area of ​​overlap with another point of the weld bead or with another weld bead,

[0039]

[0040]

[0041]

[0042]

[0043] welding. Alternatively in such a method, one of the central portion start zone and the central portion end zone advantageously overlaps in whole or in part with the other of the central portion start zone and the central portion end zone or coincides with the end zone or the central portion start zone of another weld bead. BRIEF DESCRIPTION OF THE FIGURES Other advantages, aims and particular characteristics of the present invention will emerge from the following non-limiting description of at least one particular embodiment of the devices and methods which are the subject of the present invention, with reference to the appended drawings, in which: • [Fig.l] is a schematic perspective view of an example of application of the present invention; • [Fig.2] is a schematic view of a power module of an inverter and of its environment, which constitute a preferential application of the present invention; • [Fig.3] schematically illustrates in section an aspect of a weld by laser; • [Fig.4] schematically illustrates in section another aspect of a weld by laser; • [Fig.5] represents a first example of a welding pattern which can be made within the scope of the present invention; • [Fig.6] represents a second example of a welding pattern that can be made within the scope of the present invention; • [Fig.7] represents a third example of a welding pattern that can be made within the scope of the present invention; • [Fig.8] represents a fourth example of a welding pattern that can be produced within the framework of the present invention; • [Fig.9] represents a fifth example of a welding pattern which can be made within the scope of the present invention; • [Fig. 10] represents a sixth example of a welding pattern that can be produced within the framework of the present invention. DETAILED DESCRIPTION OF THE INVENTION This non-limiting description is given as an example of an embodiment. [Fig.l] represents an assembly which constitutes an example of application of the present invention. This assembly comprises a first conductive bar 1 and a second bar driver 2.

[0044] The first conductive bar 1 is an output conductive bar of a power module 3. The second conductive bar 2 is a conductive bar connected to a phase of an electric motor.

[0045] It is also at the level of the second conductive bar that the current can be measured, for example using a Hall effect sensor placed in the air gap of a magnetic core, which, in the example shown, is contained in the housing 4.

[0046] In order to be able to pass a current between the power module 3 and the corresponding phase of the electric motor, the first conductive bar 1 must be connected to the second conductive bar 2. As described above, this connection is generally made using a screw and a threaded insert which tighten the conductive bars in contact with each other. A screw connection requires added elements, it is complex to automate, adds mass to the assembly, and requires a certain volume. In the context of the present invention, the first conductive bar 1 and the second conductive bar 2 are positioned one on top of the other and brought into contact, in an overlapping zone called the connection zone 5. A weld is made by laser welding, in the connection zone.Laser welding makes it possible to create a mechanical and electrical connection between the conductive bars 1,2, the current passing throughout the contact zone between the conductive bars, in particular in the weld.

[0047] [Fig. 2] illustrates the fact that, in the context of an inverter controlling an electric motor, such welds between two conductive bars, in accordance with the present invention, can be made at several connections. In [Fig. 2], which is a schematic sectional view, it can be seen that in this context, there are several connection zones, 5 between two conductive bars. There is thus a connection zone 5 between the power module 3 and the conductive bar linked to a phase of the motor (conductive bar exiting at the housing 4), as illustrated in [Fig. 1]. There is another connection zone 5 between a set of capacitors 6 and the power module 3. There is still another connection zone between the set of capacitors 6 and the component preceding it, namely an electromagnetic compatibility filter, represented here by its output conductive bar 1 '.

[0048] [Fig.2] also shows that performing a laser weld leaves a free and flat face under the bonding area, which can allow cooling at the bonding level by conduction, for example with thermal paste.

[0049] A laser weld is made by applying a laser beam to the surface of a conductive bar in the bonding area. The laser creates locally very high heat which fuses the targeted materials. The laser is moved relative to the conductive bars, so as to form a weld bead, which may or may not be straight, depending on the relative movement between the laser and the conductive bars.

[0050] The width L of a weld bead may be, for example, between 0.1 mm and 2 mm, in particular between 0.3 and 1 mm, for example of the order of 0.4 mm or 0.5 mm. This width of the weld bead is defined according to the thermal resistance of the conductive bars thus connected.

[0051] [Fig. 3] illustrates in a sectional view (in this case according to the section plane AA shown in [Fig. 4]) the effect of laser welding in the connection zone 5. The section shown in [Fig. 3] intercepts the weld beads of the pattern of [Fig. 5] six times. Each weld bead corresponds to a merged zone 7 (which is called "the weld") which extends over the entire thickness of the first conductive bar 1, as well as in the thickness of the second conductive bar 2.

[0052] In other words, considering that the laser weld has a depth p, measured from the surface where the laser is applied (here the surface of the first conductive bar) to the level at which the laser has produced the melting of the material, to ensure a melting between the material of the first conductive bar and that of the second conductive bar, the depth p of the weld is greater than the thickness e of the part on which the laser is applied, that is to say here the first conductive bar.

[0053] [Fig. 4] illustrates a weld bead 8 produced by laser welding in order to connect a first conductive bar 1 and a second conductive bar 2 together. The weld bead 8 is straight, and was produced in the direction D (i.e. the laser scanned the surface of the parts in this direction D). [Fig. 4] is a schematic sectional view, along the weld bead 8.

[0054] As can be seen, due to the time taken to establish the laser power and the thermal inertia of the conductive bars (or other parts thus welded), the fused zone 7 takes a certain time, and therefore a certain distance along the length of the weld bead, to reach the desired weld depth p. Similarly, when welding is stopped, the weld does not stop perfectly immediately.

[0055] We therefore distinguish along the length of the weld bead, and according to its direction D of production: - a starting portion 9, located at the beginning of the weld bead and in which the depth of the weld (i.e. the depth of the fused zone 7) generally increases until reaching the desired depth; - a central portion 10, in which the depth of the weld is substantially constant, and corresponds substantially to the desired depth which allows fusion between the material of the first conductive bar 1 and that of the second conductive bar 2; - a stop portion 11, in which the thickness of the weld decreases.

[0056] By “substantially constant”, it is understood that the depth of the weld does not vary by more than 20% around its average depth.

[0057] The starting portion 9 begins with a starting point of the starting portion 12, which is the first point of the weld bead visible on the surface of the first conductive bar and ends with the starting point of the central portion 13. The central portion 10 therefore extends from the starting point of the central portion 13 to an end point of the central portion 14. Then, the stopping portion 11 extends from the end point of the central portion 14 to the end point of the stopping portion 15, which corresponds to the end of the bead formed by the weld visible on the surface of the first conductive bar.

[0058] A start zone ZD of the central portion is defined as the zone of the central portion following the start point of the central portion (13) over a length equal to the width L of the weld bead. An end zone ZF of the central portion is defined as the zone of the central portion preceding the end point of the central portion (13) over a length equal to the width L of the weld bead.

[0059] [Fig. 5] represents a first welding pattern according to an embodiment of the invention. By welding pattern is meant a set of one or more welding beads formed in the connection zone 5. A welding pattern may be present once or be repeated in said connection zone 5.

[0060] The pattern of [Fig.5] comprises two weld beads, namely a first weld bead 16 and a second weld bead 17.

[0061] The first weld bead is formed along a first direction D1, and the second weld bead is formed along a second direction D2.

[0062] Each weld bead 16, 17 has a general U-shape, with two lateral branches parallel to each other and a central branch perpendicular to the two parallel branches. The U-shapes formed by the two weld beads, which are of the same dimension, are oriented in opposite directions and nested within each other. Thus, the central branch of each U is crossed by a lateral branch of the other U. This crossing makes it possible to guarantee that an effective weld, with the desired depth for fusing the material of the second conduction bar, is produced over an effective weld width 18, taking into consideration the starting portions 9 and the stopping portions 11 in which the weld is incomplete.

[0063] In order to optimize the effective weld width 18, the pattern is configured so that the end zone of the central portion of the weld bead corresponds to the meeting and crossing zone of this bead with the other weld bead.

[0064] It will be noted that the first weld bead 16 and the second could have been made weld bead 17 in directions opposite to the directions DI and D2 indicated in [Fig.5]. In this case, the meeting between the two weld beads would have advantageously taken place in the start zone of the central portion.

[0065] [Fig. 6] shows another weld pattern that can be produced within the scope of the present invention. The pattern of [Fig. 6] also comprises a first weld bead 16 and a second weld bead 17. Each weld bead forms an “L”, the two Ls are of the same size, and the two weld beads 16, 17 cross each other twice to form a rectangle.

[0066] The portions of each weld bead which extend beyond the rectangle thus formed advantageously correspond to the starting portion 9 and to the stopping portion of each of the weld beads. Thus, at the level of the second conductive bar 2, the pattern fused by the laser in which the connection with the first conductive bar 1 is made corresponds exactly to the rectangle formed by the two “L”-shaped weld beads.

[0067] [Fig. 7] is another example of a weld pattern, which can be implemented within the scope of the present invention. The weld pattern of [Fig. 7] comprises three weld beads, namely: a first L-shaped weld bead 16, a second L-shaped weld bead 17, and a third weld bead 19 which is straight. The “L”s formed by the first weld bead 16 and the second weld bead 17 are formed symmetrically, with the two longer branches of the L parallel to each other, and the two ends of the shorter bars of the “L” facing each other. The third weld bead 19 extends perpendicular to the longer branches of the “L”-shaped weld beads and intersects them. In particular in the example shown, the end zone of the central portion of the first weld bead 16 coincides with the start zone of the central portion of the third weld bead 19.The end zone of the central portion of the second weld bead 17 coincides with the end zone of the central portion of the third weld bead 19.

[0068] By “coincides” we mean overlapping in whole or in part.

[0069] [Fig. 8] is another example of a weld pattern. The weld pattern of [Fig. 8] comprises a single weld bead, which forms a rectangle, or a square. However, the weld bead is configured so that it crosses (itself) at a crossing point coinciding with the start area of ​​the central portion and with the end area of ​​the central portion. Thus, the central portion 10 forms the rectangle or square, and the weld reaches the second conductive bar around the entire perimeter of the rectangle. This principle is applicable to any other closed shape of the weld bead.

[0070] [Fig.9] is another example of a weld pattern, which may be implemented within the scope of the present invention. The pattern comprises a single weld bead, which forms a closed pattern, here substantially in the shape of a rectangle. In this embodiment, the start area of ​​the central portion 13 coincides with the end area of ​​this same central portion. Thus, in general, the end of the weld bead meets its start, and an overlap, or covering, of the weld bead with itself is created. This ensures that the weld reaches the second conductive bar around the entire perimeter of the rectangle, or any other closed shape such as a square, a circle, an oval.

[0071] Weld beads included in each other can be formed according to the principle developed in [Fig.8] or advantageously in [Fig.9] (for example two or three squares or two or three circles of different sizes, one inside the other, and for example concentric).

[0072] Finally, [Fig. 10] shows another weld pattern, which is similar to that of [Fig. 5], except that instead of a side branch of each "U" formed by the weld beads crossing the central branch of the "U" formed by the other weld bead, when the side branch meets the central branch of the other weld bead, the stop portion is formed by overlapping or covering this other weld bead.

[0073] All the patterns presented above, and more generally all the patterns conceivable according to the present invention, can be repeated several times in the same connection zone.

[0074] The present invention thus allows the production of optimized laser welds between two conductive bars. The laser welds produced according to the present invention advantageously take into account the existence of portions of the weld bead where the weld is imperfect, at the beginning and at the end of the weld bead, to ensure that the weld is effective over the entire desired weld pattern. The welds produced in accordance with the principles described above make it possible to improve the surface actually joined between the two conductive bars. For example, it makes it possible to guarantee that the desired weld width is respected, or to form a weld which effectively connects the conductive bars in a complete closed pattern.

[0075] The invention finds a preferential application in the power connections in an inverter, in particular an inverter controlling an electric traction motor of a motor vehicle, as well as in the interfaces of this inverter with other components.

[0076] Nomenclature: • 1: first conductive bar • 2: second conductive bar • 3: power module • 4: accommodation • 5: connection zone • 6: set of capacitors • 7: merged zone • 8: welding bead • 9: starting portion of the welding bead • 10: central portion of the weld bead • 11: stop portion of the weld bead • 12: starting point of the starting portion • 13: starting point of the central portion • 14: end point of the central portion • 15: end point of the stopping portion • 16: first weld bead • 17: second weld bead • 18: effective weld width • 19: third weld bead

Claims

Claims

1. Device comprising a first conductive bar (1) and a second conductive bar (2), the first conductive bar (1) and the second conductive bar (2) being superimposed in a connection zone (5), said connection zone (5) comprising a laser weld which connects the two conductive bars (1, 2), the weld comprising a weld bead (8), characterized in that the weld bead (8) forms a crossing or an overlap with itself or another weld bead.

2. Device according to claim 1, the weld bead (8) consisting of a starting portion (9), a central portion (10), and a stopping portion (11), the depth of the weld being increasing in the starting portion (9), between a starting point of the starting portion (12) and a starting point of the central portion (13), the depth of the weld being substantially constant in the central portion (10), and the depth of the weld being decreasing between a central portion end point (14) and an end point of the stopping portion (15), and wherein, the weld bead having a width (L), a starting zone of the central portion is defined as the zone of the central portion following the starting point of the central portion (13) over a length equal to the width (L) of the weld bead,and an end zone of the central portion is defined as the zone of the central portion preceding the end point of the central portion (13) over a length equal to the width (L) of the weld bead, in which the start zone of the central portion (13) or the end zone of the central portion (14) is an area of ​​overlap with another point of the weld bead or with another weld bead.,

3. Device according to claim 2, in which one of the start zone of the central portion (13) and the end zone (ZF) of the central portion overlaps in whole or in part with the other of the start zone (ZD) of the central portion and the end zone (ZF) of the central portion (14) or overlaps in whole or in part with the end zone or the start zone of the central portion of another weld bead.

4. Device according to any one of claims 1 to 3, in which the weld comprises a weld bead (8) tracing a closed shape.

5. Device according to claim 4, in which the weld bead (8) forms a rectangle.

6. Device according to claim 5, in which the weld bead (8) forms a circle or an ellipse.

7. Devices according to any one of claims 4 to 6, in which the weld comprises several weld beads (16, 17, 19) each forming a closed shape, the weld beads being concentric.

8. A device according to claim 1 or claim 2, wherein the weld comprises two weld beads (16, 17), each weld bead forming an "L", the two weld beads (16, 17) crossing each other twice to form a rectangle.

9. A device according to claim 1 or claim 2, wherein the weld comprises two weld beads (16, 17), each weld bead forming a "U" of the same size as the U of the other weld bead, the U's being nested within each other so that a lateral branch of each U crosses a central branch of the other U.

10. Device according to any one of claims 1 to 3, in which the weld comprises three weld beads, namely two “L” shaped beads (16, 17) placed symmetrically, in the plane of the weld, facing each other, and a third weld bead (19) which is straight and which crosses the two L shaped weld beads.

11. Inverter comprising at least one power module (3) and a set of capacitors (6), the inverter comprising a device according to any one of the preceding claims in which the first conductive bar (1) is a direct current supply conductive bar of the power module (3) and the second conductive bar (2) is connected to the set of capacitors (6).

12. An assembly comprising an inverter comprising at least one power module (3) and an electric motor controlled by the inverter, the assembly comprising a device according to any one of claims 1 to 10 in which the first conductive bar (1) is an alternating current output conductive bar of the power module (3) and the second conductive bar (2) is connected to a phase of the motor.

13. Method of welding two conductive bars comprising the steps of: - providing a first conductive bar (1) and a second conductive bar (2); - contacting by superposition of the first conductive bar (1) and the second conductive bar (2), thus forming a superposition zone also called a connection zone (5), - forming a weld bead (8), by laser welding, the weld bead (8) forming a crossing or an overlap with itself or another weld bead.

14. A welding method according to claim 13 wherein forming the weld bead (8) comprises applying and moving a laser beam to the surface of one of the conductive bars (1, 2) in the bonding area (5), resulting in a weld bead which comprises a starting portion (9), a central portion (10), and a stopping portion (11), the depth of the weld being increasing in the starting portion (9), between a starting point of the starting portion (12) and a starting point of the central portion (13), the depth of the weld being substantially constant in the central portion (10), and the depth of the weld being decreasing between a central portion end point (14) and a stopping portion end point (15), and wherein, the weld bead having a width (L),a start zone (ZD) of the central portion is defined as the zone of the central portion following the start point of the central portion (13) over a length equal to the width (L) of the weld bead, and an end zone (ZF) of the central portion is defined as the zone of the central portion preceding the end point of the central portion (13) over a length equal to the width (L) of the weld bead, the method being characterized in that the movement of the laser beam is such that the start zone (ZD) of the central portion (13) or the end zone (ZF) of the central portion (14) is an area of ​​overlap with another point of the weld bead or with another weld bead.,

15. Welding method according to claim 13, wherein one of the start zone (ZD) of the central portion (13) and the end zone (ZF) of the central portion (14) overlaps in whole or in part with the other of the start zone (ZD) of the central portion (13) and the end zone (ZF) of the central portion (14) or coincides with the end zone or the start zone of the central portion of another weld bead.

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