Method for manufacturing a double-skinned plate incorporating circulation channels and plate obtained thereby

Abstract

The invention relates to a method for manufacturing a double-skinned plate (1) incorporating channels (2) constituting at least one fluid circulation network or circuit, the method essentially comprising a first step of providing two flat aluminium sheets (3 and 3'), followed by a step of joining them together by laser welding, according to a linear pattern (4) tracing the pattern of the circulation channels (2), the two flat aluminium sheets (3 and 3') into a double-skinned plate (1), and finally a step of forming the circulation channels (2) by injecting a pressurised liquid or gaseous fluid (LP) between the two sheets (3 and 3'). This method is characterised in that it also comprises a step of flattening the plate (1) consisting of the two sheets (3 and 3') joined together by laser welding before the step of forming, by pressure deformation, the circulation channels (2).

Description

Description Title of the invention: Method for manufacturing a double-skinned plate incorporating circulation channels and plate obtained

[0001] The present invention relates to the field of temperature regulation equipment, in particular by direct contact, and in particular in the form of a plate, with a preferred application in the context of battery boxes for electric or hybrid vehicles.

[0002] The present invention relates more specifically to an improved manufacturing method for such a plate, an installation for its implementation, the plate obtained and a housing comprising it.

[0003] The batteries currently used in electric and hybrid vehicles require temperature regulation, particularly during their charging and discharging phases. This is particularly the case for Li-ion batteries, whose operating temperature must be maintained between 10°C and 30°C.

[0004] To achieve this temperature regulation, the most common solution is the use of a regulating or cooling plate in contact with the battery cells, and generally placed in the bottom of the battery case. This plate, with a double-skin aluminum structure, has passages in the form of channels, arranged in a network(s) and allowing the circulation of a heat transfer fluid, for example water with added glycol.

[0005] Three different manufacturing technologies are currently used to produce these plates, namely, i) assembly by brazing of two preformed aluminum sheets, ii) assembly by lamination of two aluminum sheets comprising an interlayer of ink whose pattern corresponds to the circulation channels and which allows local separation of the sheets during a subsequent hydroforming operation and iii) direct extrusion of the plate with the circulation channels (technique called "micro-port extrusion", limited applications and complex and delicate implementation).

[0006] The implementation of a brazing or rolling assembly process has the disadvantage of generating significant heating which can reduce the mechanical qualities of the aluminum, of consuming a lot of energy and of requiring a filler metal or a coating with a specific alloy for the sheets to be assembled (for brazing). In addition, the precise assembly of preformed sheets is difficult to achieve and the reminiscence of tensions and stresses induced by preforming in these sheets negatively impacts the final double-skinned plate, particularly in terms of contact between the plates during the brazing process. In addition, this process requires complex clamping tools to ensure sufficient quality of the joint.

[0007] Document DE 102017005325 discloses a method for manufacturing a double-skinned plate incorporating channels constituting at least one fluid circulation network or circuit (F). This plate constitutes a temperature control plate for a battery case.

[0008] The method as disclosed by this document DE essentially comprises a first step of providing two flat sheets of aluminum, or an aluminum-based alloy, then a second step of mutual assembly by laser welding, according to a linear pattern drawing the pattern of the circulation channels, of said two sheets into a double-skinned plate, and, finally, a third step of forming said circulation channels, by injecting a pressurized fluid between the two sheets so as to deform areas of one of the sheets, these deformed areas corresponding to said channels and extending between the welding lines of the linear pattern. This last operation is carried out in a forming mold in order to control the final shape of the channels obtained and limit unwanted deformations.

[0009] By implementing a preliminary assembly of the aluminum sheets by laser welding, the process known from this DE document makes it possible to overcome the main limitations of the aforementioned manufacturing technologies, laser welding not significantly modifying the mechanical properties of the sheets, consuming less energy and not requiring filler material.

[0010] However, even if the tensions and constraints are significantly reduced by this process, the fact remains that laser welding still involves certain distortions due to the phenomena of thermal expansion and asymmetric heating of the two sheets (one directly exposed to the laser beam, the other not), which are found in the final plate and affect its geometry and temperature behavior.

[0011] The main aim of the present invention is to overcome these remaining drawbacks.

[0012] To this end, it relates to a method as mentioned above, characterized in that it also comprises a step of flattening or smoothing the plate consisting of the two sheets assembled by laser welding, before the step of forming, by deformation under pressure, the circulation channels.

[0013] The invention will be better understood from the following description, which relates to preferred embodiments, given as non-limiting examples, and explained with reference to the appended schematic drawings, in which:

[0014] [Fig. 1] is a schematic representation of the three stages of the manufacturing process according to the state of the art corresponding to the aforementioned DE document;

[0015] [Fig. 2A],

[0016] [Fig. 2B] and

[0017] [Fig. 2C] respectively represent a top view of a laser welding station in the form of a gantry with two mobile laser heads in a plane in accordance with an embodiment of the invention (2A), a partial side elevation view at the level of a mobile laser head of the station of FIG. 2A (the latter being equipped with a first variant of mobile local clamping means) (2B), and a detailed and partially sectional view illustrating the formation of a weld line with the mobile laser head of FIG. 2B (2C);

[0018] [Fig. 3] represents a sectional view similar to that of Figure 2B, but illustrating the implementation of another variant of clamping means usable in relation to the station of Figure 2A;

[0019] [Fig. 4] schematically illustrates an intermediate planishing station in accordance with the invention, treating the plate blank before its forming;

[0020] [Fig.5A] is a partial sectional view of a forming mold trapping a plate during its forming operation, by injection of liquid or gas under pressure, and,

[0021] [Fig. 5B] is a detail view of a portion of the plate of Fig. 5A, illustrating the pressure forces present during the forming operation.

[0022] The invention therefore relates to a method for manufacturing a double-skinned plate (1) incorporating channels (2) constituting at least one fluid circulation network or circuit (F), in particular a temperature regulation plate for a battery case.

[0023] This method essentially comprises a first step of providing two flat sheets or plates (3 and 3') made of aluminum, or an aluminum-based alloy, then a step of mutual assembly by laser welding, according to a linear pattern (4) drawing the pattern of the circulation channels (2), of said two sheets (3 and 3') into a double-skinned plate (1), and, finally, a step of forming said circulation channels (2), by injecting a pressurized liquid or gaseous fluid (LP) between the two sheets (3 and 3') so as to deform zones (4') of at least one of the sheets (3, 3'), which correspond to said channels (2) and extend between the welding lines (4”) of the linear pattern (4). The assembly of the two sheets or plates by laser welding is carried out without specific preheating thereof.

[0024] According to the invention, this method also comprises a step of flattening or smoothing the plate (1) consisting of the two sheets (3 and 3') assembled by laser welding, before the step of forming (by deformation under pressure) the circulation channels (2).

[0025] Thanks to the invention, the deformations and stresses induced in the plate (1) by thermal expansion during the laser welding operation, in particular due to the differentiated expansion of the two plates due to their different exposure to the heat source (only one being directly impacted by the laser), are eliminated and said plate regains a flatness similar to the original flatness of the two sheets or plates constituting it.

[0026] In accordance with an advantageous variant of implementation of the invention, and as shown in Figure 4, the step of flattening or leveling the plate (1) constituted by the two sheets (3 and 3') assembled by welding, is carried out by leveling (for example by means of a leveler, of the servo-hydraulic or electromechanical type, with two trains or layers of rollers, upper and lower, as shown in Figure 4). This operation, during which the plate moves between two sets of rollers, thus makes it possible to remove folds, irregularities, flatness defects and tensions in the double-skinned plate (1), and therefore in and between the two sheets or sheets (3 and 3') constituting it.

[0027] Preferably, and in order to be able to a priori guarantee the elimination of any deformation and any flatness defect, the step of planing or flattening by planing a plate (1) comprises at least two successive passes in different directions (D) of passage or running (for the plate in the planing station). Preferably, and with a view to achieving a satisfactory compromise between speed of execution (productivity) and operational quality (elimination of stresses, deformations, defects), this planing step comprises two passes with different directions of passage. Advantageously, the directions (D) of passage or running of the different passes (two or more) are oriented between 30° and 90° relative to each other, or relative to each other.

[0028] By carrying out this planarization or flattening step in a specific station or machine as indicated above, with a low process time (only a few seconds per pass) and without using heat (no particular heating during this operation), the invention not only achieves a high level of planarity and eliminates potential stresses and deformations, but also limits the energy requirements for this step and has an almost zero carbon footprint (approximately zero CO2 emissions).

[0029] Concerning flatness, the invention aims for a defect of at most 1 cm per meter of length. However, since flatness in the clamped state is highly dependent on the clamping possibilities and the distance between the fixing points, the invention aims to achieve flatness of the order of mm, or even less, in specific areas depending on the clamping.

[0030] The assembly by welding of the two sheets or plates (3 and 3') of aluminum, advantageously in aluminum of the 3xxx or 5xxx series (easier to weld without the appearance of hot cracks), is for example carried out by means of a laser fiber with implementation of a remote welding technique using a galvanometric scanner allowing for high welding speed. Alternatively, a laser head mounted on a robotic arm can be used.

[0031] The energy density and focus of the laser beam, as well as the other parameters of the welding process, are adjusted so that the width of the weld line at the interface between the two sheets is between 0.7 and 1.0 mm. Since the weld lines can be several tens of meters long (serpentine channels and two lines per channel), it is necessary to be able to weld at high speed and high power, for industrial and economic reasons. Typically, minimum powers of the order of 1 kW and speeds of the order of 6 m / min, preferably 10 to 20 m / min, are required.

[0032] In accordance with a first embodiment of the invention, and as shown in Figure 2B, it may be provided that during the course of the laser welding step the two sheets (3 and 3') are kept pressed against each other locally on either side of the or each moving laser welding point (5), for example by means of a pair of support or clamping means (6) moved in synchronism with the associated welding beam (7). As shown, the two means move in concert with the laser beam and on either side of the latter, leaving between them a passage window for the scanning and welding beams, for example of the order of 60 to 100mm.

[0033] In accordance with a second embodiment of the invention, and as shown in Figure 3, it can be provided that during the course of the laser welding step the two sheets (3 and 3') are kept pressed against each other substantially on all their respective mutually facing surfaces, for example by vacuum suction clamping. This second mode does not require any mobile means with synchronized movement.

[0034] Finally, in accordance with a third embodiment, not specifically shown but combining the solutions of the first two embodiments above, it can be provided that during the course of the laser welding step the two sheets (3 and 3') are kept pressed or clamped against each other, on the one hand, globally and substantially on all their respective surfaces mutually facing each other, and, on the other hand, locally on either side of the or each point (5) of mobile laser welding.

[0035] It can be noted that each of these clamping methods allows thermal expansion of the sheets during welding, which makes it possible to significantly reduce the formation of gaps resulting from the differentiated thermal expansion caused by the application of energy in a significant and asymmetric manner, and leading to welding defects.

[0036] In relation to each of the three aforementioned embodiments, the assembly by welding is carried out progressively from a central interior region of the plate (1) towards the peripheral zones of the latter, by means of a single or at least two laser beam(s) (7) moved in a controlled manner.

[0037] Taking into account the energy density applied and to limit expansion phenomena, it may also be provided that, during the progress of the laser welding step of the two sheets (3 and 3'), at least one of them is subjected to a cooling action, for example by resting on a cooled welding table (10).

[0038] According to another aspect of the invention, and as illustrated in Figure 5A by way of example, the step of forming the circulation channels (2), under hydraulic pressure, is carried out by placing the flat plate (1) in a mold (8, 8') allowing deformation under internal pressure of the zones (4') of one (3) of the sheets (3, 3'), zones (4') which correspond to said channels (2) and which extend between the welding lines (4”) of the linear pattern (4), relative to the other (3') of said sheets (3, 3').

[0039] As shown more precisely in Figure 5B, it is advantageously provided that, during the course of the step of forming the channels (2) by injecting a liquid or gaseous fluid under pressure (LP) between the two sheets (3 and 3'), a pressure (PC) is exerted on the first sheet or sheet (3) comprising the zones to be deformed (4'), so as to keep it in intimate contact with the other or second sheet or sheet (3') at all the surface regions of this second sheet (3') other than the zones to be deformed (4'), in particular at the surface zones in strips extending on either side of the weld lines (4”). This second sheet (3') rests and is advantageously held on a flat surface and therefore does not undergo any deformation during the injection of the fluid under pressure (preservation of a flat external surface for this second sheet).

[0040] Hydroforming pressures suitable for this process are between 6 and 30 MPa, depending on the thickness of the aluminium sheets, the grade and the minimum bending radii to be produced.

[0041] Applying pressure (PC) outside the areas (4') to be deformed helps limit the stretching of the sheet material in these areas, and also helps prevent any warping of the final plate. This pressure must not, however, exceed the elastic limit of the aluminum.

[0042] The regions of the mold part (8) which come in particular into contact in the strip surface areas extending on either side of the weld lines, may, if necessary, be textured on the surface to increase the grip in the contact interfaces.

[0043] The invention also relates to an installation for implementing the method of manufacturing a double-skinned plate (1) incorporating channels (2) for circulating fluid (F), as described above.

[0044] Such an installation comprises at least: a welding station (9) with at least one, preferably at least two, laser beam(s) (7) moved in a controlled manner and with one or more means (6) for mutually clamping the two plates (3 and 3'), globally and / or locally, as well as advantageously a cooled welding table (10), a planing or flattening station, advantageously a planing station (11) with at least one roller planer and a forming mold device (8, 8') associated with a device for injecting liquid or pressurized gas (LP). To reduce the welding time, the station (9) may comprise two mobile laser heads, mounted on a gantry and guided by a scanner.

[0045] The invention also relates to a double-skinned plate (1), in particular a temperature-regulating plate for a battery case, formed by welding two aluminum sheets (3, 3') together and incorporating channels (2) constituting at least one network or circuit for circulating fluid (F), of the heat-transfer liquid type, said plate (1) being obtained by means of the method of aforementioned manufacturing, preferably using the installation mentioned above.

[0046] Finally, the invention further relates to a battery case, in particular for a motor vehicle, comprising a cover and a bottom, as well as possibly an intermediate separating wall, in contact with cells of this battery, case characterized in that at least one element among said cover, said bottom and, where appropriate, said wall, is formed by a double-skinned plate (1) with integrated circulation channels described above. A plate (1) according to the invention, possibly covered on its outer face with an overmolded layer of plastic material, can thus constitute by itself the cover and / or the bottom of such a case.

[0047] Of course, the invention is not limited to the embodiments described and shown in the attached drawings. Modifications remain possible, particularly from the point of view of the constitution of the various elements or by substitution of technical equivalents, without departing from the scope of protection of the invention.

Claims

Claims

1. Method for manufacturing a double-skinned plate (1) incorporating channels (2) constituting at least one fluid circulation network or circuit (F), in particular a temperature regulation plate for a battery case, this method essentially comprising a first step of providing two flat sheets or plates (3 and 3') made of aluminum, or an aluminum-based alloy, then a step of mutual assembly by laser welding, according to a linear pattern (4) drawing the pattern of the circulation channels (2), of said two sheets (3 and 3') into a double-skinned plate (1), and, finally, a step of forming said circulation channels (2), by injecting a pressurized liquid or gaseous fluid (LP) between the two sheets (3 and 3') so as to deform zones (4') of at least one of the sheets (3, 3'), which correspond to said channels (2) and extend between the welding lines (4”) of the linear pattern (4),method characterized in that it also comprises a step of flattening or smoothing the plate (1) constituted by the two sheets (3 and 3') assembled by laser welding, before the step of forming, by deformation under pressure, the circulation channels (2).,

2. Method according to claim 1, characterized in that the step of flattening or smoothing the plate (1) constituted by the two sheets (3 and 3') assembled by welding, is carried out by planing.

3. Method according to claim 1, characterized in that the step of planing or flattening by planing comprises at least two passes in different directions (D) of passage or scrolling, preferably two passes, with directions (D) of passage or scrolling oriented between 30° and 90° relative to each other.

4. Method according to any one of claims 1 to 3, characterized in that during the course of the laser welding step the two sheets (3 and 3') are kept pressed against each other locally on either side of the or each movable laser welding point (5), for example by means of a pair of support or clamping means (6) moved in synchronism with the associated welding beam (7), and in that the welding assembly is carried out progressively from a region central interior of the plate (1) towards the peripheral zones of the latter, by means of a single or at least two laser beam(s) (7) moved in a controlled manner.

5. Method according to any one of claims 1 to 3, characterized in that during the laser welding step the two sheets (3 and 3') are kept pressed against each other substantially on all their respective mutually facing surfaces, for example by vacuum suction clamping, and in that the welding assembly is carried out progressively from a central interior region of the plate (1) towards the peripheral zones of the latter, by means of a single or at least two laser beam(s) (7) moved in a controlled manner.

6. Method according to claims 4 and 5, characterized in that during the course of the laser welding step the two sheets (3 and 3') are kept pressed or clamped against each other, on the one hand, globally and substantially on all their respective mutually facing surfaces, and, on the other hand, locally on either side of the or each mobile laser welding point (5).

7. Method according to any one of claims 1 to 6, characterized in that the step of forming the circulation channels (2), under hydraulic pressure, is carried out by placing the flat plate (1) in a mold (8, 8') allowing deformation under internal pressure of the zones (4') of one (3) of the sheets (3, 3'), zones (4') which correspond to said channels (2) and which extend between the welding lines (4”) of the linear pattern (4), relative to the other (3') of said sheets (3, 3').

8. Method according to any one of claims 1 to 7, characterized in that, during the course of the step of laser welding of the two sheets (3 and 3'), at least one of them is subjected to a cooling action, for example by resting on a cooled welding table (10).

9. Method according to any one of claims 1 to 8, characterized in that, during the course of the step of forming the channels (2) by injecting a liquid or gaseous fluid under pressure (LP) between the two sheets (3 and 3'), a pressure (PC) is exerted on the sheet (3) comprising the areas to be deformed (4'), so as to keep it in intimate contact with the other sheet (3') at all the surface regions of this sheet (3') other than the areas to be deformed (4'), in particular at the surface areas in strips extending on either side of the weld lines (4”).

10. Installation for implementing the method for manufacturing a double-skinned plate (1) incorporating channels (2) for circulating fluid (F), according to any one of claims 1 to 8, said installation comprising at least: a welding station (9) with at least one, preferably at least two, laser beam(s) (7) moved in a controlled manner and with one or more means (6) for mutually clamping the two plates (3 and 3'), globally and / or locally, as well as advantageously a cooled welding table (10), a planing or flattening station, advantageously a planing station (11) with at least one roller planer and a forming mold device (8, 8') associated with a device for injecting liquid or gas under pressure (LP). [Claim 1 1 ] Double-skinned plate (1 ), in particular a temperature-regulating plate for a battery case, formed by welding two sheets (3, 3') of aluminum together and incorporating channels (2) constituting at least one network or circuit for circulating fluid (F), of the heat-transfer liquid type, said plate (1 ) being obtained by means of the manufacturing method according to any one of claims 1 to 9, preferably using the installation according to claim 10.

12. Battery case, in particular for a motor vehicle, comprising a cover and a bottom, as well as possibly an intermediate separating wall, in contact with cells of this battery, case characterized in that at least one element among said cover, said bottom and, where appropriate, said wall, is formed by a plate (1) with double skin and integrated circulation channels, according to claim 11.

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