Method for depositing an anti-reflective metallic layer onto a metallic substrate for subsequent laser welding between said metallic substrate and a surface of a metallic part

Abstract

The invention relates primarily to a method for depositing an anti-reflective metallic layer (4) onto a metallic substrate (3) for subsequent laser welding between said metallic substrate (3) and a metallic workpiece (5). This method comprises at least one supersonic projection step of metallic powder particles (14) onto a face (15) of the metallic substrate (3) at a temperature below the melting point of said metallic powder particles (14) and at a speed exceeding 350 meters per second. The projection of the powder particles (14) is carried out at a pressure between 20 and 37 bar, at a temperature between 30 and 60% of the melting point of the metallic powder particles, and at a distance from the metallic substrate (3) between 10 and 70 millimeters. Figure to be published with the abbreviation: Figure 1

Description

Title of the invention: Method for depositing an anti-reflective metallic layer onto a metallic substrate for subsequent laser welding between said metallic substrate and a surface of a metallic part. TECHNICAL FIELD OF THE INVENTION

[0001] The technical field of the invention is that of the welding assembly of two metal parts.

[0002] The present invention relates more specifically to laser welding of two metal parts together. TECHNOLOGICAL BACKGROUND OF THE INVENTION

[0003] Welding two metal parts together using an infrared laser—with a wavelength of approximately 1060 nanometers—allows, when the laser beam is applied to the metal surface of one of the two parts to be welded, the heat from the laser beam to be transferred to said metal parts in order to melt them locally. The weld joint between these two parts is formed during cooling, resulting in the hardening of the molten portion.

[0004] This technique nevertheless has drawbacks. Indeed, some metallic materials are highly reflective at the wavelength of laser radiation, and therefore do not absorb most of the energy supplied by the laser. It is therefore necessary to use particularly powerful, high-energy lasers and / or lasers with a shorter wavelength. SUMMARY OF THE INVENTION

[0005] In this context, the invention relates to a laser welding process for two metal parts together which offers better energy efficiency.

[0006] The invention further aims at a limited supply of raw material.

[0007] To this end, the invention relates to a method of depositing an anti-reflective metallic layer on a metallic support for the purpose of a subsequent laser welding operation between said metallic support and a metallic part, which method comprises at least one supersonic projection step of metallic powder particles onto a face of the metallic support at a temperature below the melting temperature of said metallic powder particles and at a speed above 350 meters per second, the projection of powder particles being carried out at a pressure between 20 and 45 bars, at a temperature between 30 and 60% of the melting temperature of the metallic powder particles and at a distance from the metallic support between 10 and 70 millimeters.

[0008] The process of the invention may also include the following optional features considered individually or in all possible technical combinations. - The projection of powder particles is carried out at a temperature between 680 and 770 °C and at a pressure between 28 and 37 bar. - The projection of powder particles is carried out at a pressure between 33 and 37 Bars, at a temperature between 730 and 770 °C and at a distance from the metal support between 30 and 50 millimeters. - The projection of powder particles is carried out at a pressure of 35 Bars, at a temperature of 750 °C and at a distance of 40 millimeters from the metal support. - The projection stage is carried out by linear movement substantially parallel to the face to be covered of the metal support at a speed of between 150 and 250 millimeters per second in between one and four passes. - The linear movement speed is between 170 and 190 millimeters per second, preferably 185 millimeters per second. - The projection of metallic powder particles is carried out at a pressure of 35 Bars, at a temperature of 750 °C and at a distance of 40 millimeters from the metallic support and according to two passes of linear displacement. - The projection speed is between 500 and 1000 meters per second, preferably greater than 600 meters per second. - The average size of the metal powder particles is between 5 and 80 micrometers in average size. - The average size of the metal powder particles is between 20 and 60 micrometers, preferably 40 micrometers. - The anti-reflective metallic layer has a thickness of between 50 and 170 micrometers. - The metal powder particles are stainless steel. - The metal support is made of copper, aluminum or steel.

[0009] Another aspect of the invention relates to a metallic support coated on at least one of its faces with an anti-reflective metallic layer made of metallic powder particles deposited by supersonic projection at a temperature lower than the melting temperature of said metallic powder particles, and intended to be welded onto a metallic part by a laser welding operation, which anti-reflective metallic layer has a maximum roughness Rz of between 50 and 100 micrometers according to standards NF EN ISO 21920-1 and NF EN ISO 21920-2.

[0010] The support of the invention may also include the following optional features considered individually or according to all possible technical combinations. - The anti-reflective metallic layer has an arithmetic mean roughness Ra between 1 and 15 micrometers according to standards NF EN ISO 21920-1 and NF EN ISO 21920-2. - The anti-reflective metallic layer has an average arithmetic roughness Ra between 7 and 15 micrometers according to the standard. - The anti-reflective metallic layer has a maximum roughness Rz between 60 and 80 micrometers and an arithmetic mean roughness Ra between 10 and 12 micrometers according to standards NF EN ISO 21920-1 and NF EN ISO 21920-2. - The anti-reflective metallic layer has a thickness of between 50 and 170 micrometers. - The metal powder particles are made of stainless steel or nickel. - The metal support is made of copper, aluminum or steel.

[0011] The invention finally relates to a method of welding a metal support as described above, obtained by the deposition process as described above, on a surface of a metal part, which method includes at least one step of positioning the metal support on the surface of the metal part, the anti-reflective metal layer being disposed opposite the metal part, and a step of applying a welding power by laser radiation on the anti-reflective metal layer of the metal support to effect the weld between said metal support and the metal part.

[0012] The invention and its various applications will be better understood by reading the following description and examining the accompanying figures. BRIEF DESCRIPTION OF THE FIGURES

[0013] Other features and advantages of the invention will become apparent from the reading of the following description, with reference to the attached figures, which illustrate: [Fig.1] The [Fig.1] illustrates a schematic cross-sectional view of a laser welding point between two metal parts according to the invention; [Fig.2] Fig.2 illustrates a cross-sectional view of the metal part under a microscope at 100X magnification, the surface of which is covered with an anti-reflective metallic layer deposited by supersonic projection of metal powder particles; [Fig.3] Fig.3 illustrates the view of [Fig.2] at 300X magnification; [Fig.4] The [Fig.4] is a top view of the [Fig.2], showing the deposition of the anti-reflective metallic layer on the metal part to be welded; [Fig.5] The [Fig.5] illustrates four curves representing the roughness Rz of the anti-reflective metallic coating layer as a function of the projection pressure, each curve representing a different number of passes on the metallic part to be coated with the metallic coating; [Fig.6] The [Fig.6] illustrates four curves representing the roughness Ra of the anti-reflective metallic coating layer as a function of the projection pressure, each curve representing a different number of passes on the metallic part to be coated with the metallic coating; [Fig. 7] Figure 7 illustrates two metallic reflectance curves as a function of wavelength, one curve representing the metal part without the anti-reflective coating, and the other with the anti-reflective coating applied. DETAILED DESCRIPTION

[0014] It is first specified that in the figures, the same references designate the same elements regardless of the figure in which they appear and regardless of the form of representation of these elements. Similarly, if elements are not specifically referenced in one of the figures, their references can easily be found by referring to another figure.

[0015] It is also specified that the figures represent variants of the invention but that there may be other embodiments which meet the definition of the invention.

[0016] In many industrial fields, the welding of metal parts together is a daily operation, so there is a continuous need to improve welding processes and supports from an economic and ergonomic point of view.

[0017] By way of non-limiting example, making electrical connections between electrically conductive parts is a particularly common operation and generally requires the use of metallic connectors whose physical and geometric properties are adapted to electron transport, with optimized resistance to the passage of electric current. Thus, connectors made of copper, aluminum, or low-alloy coated steel are commonly used, these metals being excellent electrical conductors.

[0018] According to another non-limiting example, welding operations are particularly suitable for assembling metal plates—and more specifically metal sheets—to create cooling systems. These metal plates or sheets are generally made of copper, which is an excellent thermal conductor.

[0019] For the production of such assemblies of metal parts, laser welding offers numerous advantages. The welding cycles are carried out in very short cycles, ensure good weld quality and have a low implementation cost.

[0020] The metallic parts are nevertheless reflective, and this is all the more true as the wavelength of the laser used is high. Curve 12 of [Fig. 7] shows by For example, the reflection rate of a copper metal support surface as a function of the wavelength of the laser used: without appropriate treatment of this surface, it appears that welding with a blue or green laser (wavelength of the order of 532 nm) is possible, the reflection of the laser beam on the metal surface being here of the order of 30%, while welding with an infrared laser (wavelength of the order of 1000 nm) is impossible, the reflection of the laser beam on the metal surface being here of the order of 90%.

[0021] However, the use of infrared lasers is simpler and less expensive. It is therefore more practical to apply a surface treatment to the laser application surface of the metallic substrate to modify its reflective properties.

[0022] According to the invention and with reference to [Fig. 1], in order to improve the absorption of the energy transmitted by the laser, an anti-reflective metallic layer 4 is deposited locally on an upper face 15 of the metal support 3 which is to be welded to another metal part 5 - more precisely on a surface area of ​​the upper face 15 of the support 3 intended to be in the direction of the laser radiation, which upper face 15 is opposite the lower weld face of said support 3 which comes into contact with said metal part 5. Advantageously, the anti-reflective metallic layer 4 is made of nickel or stainless steel.

[0023] In fact, during the welding operation, the laser beam is emitted against the upper surface 15 at the level of the metallic layer 4 of the metallic support 3, itself in contact with the metallic part 5 to be welded to said support 3, and most of the laser energy - typically around 60% - is absorbed by the anti-reflective layer 4, diffused into the metallic support 3 and into the metallic part 5 in the form of heat 7. See for this purpose curve 13 of [Fig.7].

[0024] In other words, a small part of the beam is reflected by the anti-reflective layer 4 deposited on the upper surface 15 of the support 3. The metal support 3 and the metal part then undergo a localized high temperature rise, above the melting temperature of the materials, which will allow the appearance of a zone of the weld 6 which will solidify upon cooling (as soon as the laser is no longer applied to the upper surface 15 of the metal support 3) to allow the assembly of the support and the metal part 3, 5. This anti-reflective metal layer 4 thus makes it possible to limit the power required of the laser and to improve the weld quality.

[0025] To produce its anti-reflective function and with reference to Figures 2 to 4, the metallic layer 4 covering the upper surface 15 of the support 3 has a minimum roughness to allow diffuse reflection of the laser radiation at the surface of said metallic layer 4. Diffuse reflections associated with a high level of roughness of the metallic layer 4 lead to an increase in the

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[0033] absorption power of laser radiation by the surface 15 of the support 3 and allow welding between the metal support 3 and the metal part 5, at the level of the area 6. The roughness of a surface is expressed according to several parameters, and in particular the arithmetic mean roughness Ra and the maximum roughness Rz. The average roughness Ra is expressed according to the formula^ _ ] °where it represents The absolute value of a deviation i of the profile of the anti-reflective layer 4, while the roughness Rz, which indicates the maximum height of the profile of the anti-reflective layer 4, is calculated by selecting five zones of said profile of the anti-reflective layer 4, measuring for each zone the difference between the highest peak and the lowest trough, and averaging these five measurements. The roughness Rz thus provides, relative to the average roughness Ra, information on the maximum height of the peaks and the maximum depth of the valleys of the roughness profile of the anti-reflective layer 4, which are favorable to increasing the absorption capacity of laser radiation. Roughness Ra and Rz are determined according to standards NF EN ISO 21920-1, NF EN ISO 21920-2 and where applicable NF EN ISO 21920-3. To allow diffuse reflection of the laser at the upper surface 15 of the anti-reflective layer 4, the latter must have a minimum average roughness Ra, which is on the order of the wavelength of the laser used for welding. In this case, for an infrared laser with a wavelength on the order of a micrometer (pm), the average roughness Ra must be greater than or equal to 1 pm. Advantageously, the average roughness Ra of the anti-reflective layer 4 is between 1 and 15 pm, and preferably between 7 and 15 pm, and even more preferably between 10 and 12 pm. This provides sufficient roughness to ensure good absorption of the infrared laser, while limiting the thickness of the anti-reflective layer 4, which is typically between 50 and 170 microns. Furthermore, the maximum roughness Rz of the anti-reflective layer 4 is between 50 and 100 pm, and preferably between 60 and 80 pm. This ensures optimized absorption of laser radiation by the anti-reflective layer 4. With reference to [Fig.2] to 6, a process for depositing an anti-reflective metallic layer 4 on the upper face 15 of a metallic support 3 will now be described. The anti-reflective metallic layer 4 is obtained by supersonic projection of metallic powder particles 14 onto the surface 15 of the metallic support 3, which will cause plastic deformation of the upper surface 15 receiving said powder particles 14 and allow their implantation in the support 3. The metal powder particles 14 are, for example and advantageously, made of stainless steel. Alternatively, the metal powder particles 14 are made of nickel. Preferably, the average particle size of the metal powder 14 is between 5 and 80 pm, more preferably between 20 and 60 pm, and more preferably around 40 pm, in order to obtain the desired roughness, i.e. an average roughness Ra between 1 and 15 pm, and preferably between 7 and 15 pm, and more preferably between 10 and 12 pm, as well as a maximum roughness Rz between 50 and 100 pm, and preferably between 60 and 80 pm.

[0034] The projection speed of the metal powder particles 14 is greater than 350 meters per second (m / s), preferably between 500 and 1000 m / s, and even more preferably greater than 600 m / s.

[0035] Furthermore, the distance between the upper surface 15 of the metal support 3 receiving the projected powder 14 and a nozzle for projecting the metal powder particles 14 is between 10 and 70 millimeters (mm), preferably between 30 and 50 mm, and even more preferably around 40 mm.

[0036] In addition, the pressure at the outlet of the projection nozzle is between 20 and 45 bars, preferably between 28 and 37 bars, even more preferably between 33 and 37 bars and even more preferably in the order of 35 bars.

[0037] Furthermore, the metal powder particles 14 are projected at a temperature below the melting temperature - typically below 60% of the melting temperature of the metal powder particle material 14 - to maximize the acceleration of the powder particles while limiting excessive heating and possibly thermal deformation of the metal support 3, and to allow sufficient roughness of the anti-reflective layer 4, but at a sufficiently high temperature - typically at least 30% of the melting temperature of the metal powder particle material 14 - to promote the lowering of their mechanical properties and allow their plastic deformation upon impact with the upper surface 15 of the metal support 3, to ultimately allow optimal adhesion of the powder particles 14 to the surface 15 of the metal support 3.

[0038] By way of preferred example, for stainless steel powder particles 14, the temperature of said projected metal powder 14 is between 680 and 770°C, preferably between 730 and 770°C and even more preferably in the order of 750°C.

[0039] These parameters of temperature, speed and pressure of projection and projection distance ensure good implantation of the metallic powder particles 14 on the surface 15 of the metallic support 3 with the roughness values ​​Ra and Rz sought and indicated above in the description.

[0040] In order to optimize the homogeneity of the metallic layer 4 deposited on the application surface 15 of the laser of the metallic support 3, the linear speed, parallel to said surface 15 of the metallic support 3 on which the metallic powder 14 is deposited, is between 150 and 250 mm / s, preferably between 170 and 190 mm / s and even more preferably in the order of 185 mm / s.

[0041] Figures 5 and 6 illustrate curves 8, 9, 10, 11, 16, 17, 18, 19 representing respectively the maximum roughness Rz and the average roughness Ra of anti-reflective coatings as a function of the projection pressure of the metal powder, the projection being carried out with metal particles at a distance of 40 mm from the surface of the metal substrate at a temperature of 750°C

[0042] It appears that the average roughness Ra and the maximum roughness Rz of the anti-reflective metallic layer 4 is dependent on the application pressure of the metallic powder particles 14 but also on the number of passes, a pass being defined by a passage of the metallic powder projection nozzle 14 over the surface 15 of the metallic support 3 to cover it with a first layer of agglomerated metallic powder.

[0043] Thus, a two-pass process consists of coating the first layer of agglomerated metal powder with a second layer of metal powder. In other words, there are as many passes as there are superimposed layers forming the anti-reflective layer 4.

[0044] Curves 8, 9, 10, and 11 in [Fig. 5] correspond to the maximum roughness Rz as a function of the pressure of the anti-reflective layers 4, respectively for four layers (four passes), three layers (three passes), two layers (two passes), and one layer (one pass). Curves 16, 17, 18, and 19 in [Fig. 6] correspond to the average roughness Ra as a function of the pressure of the anti-reflective layers 4, respectively for four layers (four passes), three layers (three passes), two layers (two passes), and one layer (one pass).

[0045] Unexpectedly and particularly advantageously, it appears that at a pressure of 35 bar, the average roughness Ra and the maximum roughness Rz increase for the two-pass layer (curves 10 and 18), while these roughnesses decrease or remain stable for the other one-, three-, or four-pass layers. Even more advantageously, it appears that at 35 bar, the differences in average roughness Ra and maximum roughness Rz between the two-pass layer (curves 10 and 18) and the four-pass layer (curves 9 and 17) are not significant.

[0046] Thus, since the efficiency of infrared laser energy absorption depends on the roughness Ra and Rz of the anti-reflective layer 4, it has been demonstrated that with a projection of metallic powder particles 14 at a projection temperature of 750°C, a projection pressure of 35 bar and a distance from the metallic support A 40 mm thick, two-layer (two-pass) anti-reflective coating 4 exhibits the same absorption capacity as a four-layer (four-pass) anti-reflective coating 4. The use of powdered metallic particles 14 is therefore limited and controlled without altering the diffuse reflective capacity of the metallic anti-reflective coating 4.

[0047] The invention ultimately enables the implementation of a welding process for the metal support 3, described above and obtained by the process of the invention, on a metal part 5, which process includes at least one step of positioning the metal support 3 on the surface of the metal part 5, the anti-reflective metal layer 4 being disposed on a deposition face opposite to the lower welding face of the support which comes into contact with the surface of the metal part, and a step of applying a laser beam welding power to the anti-reflective metal layer 4 of the metal support 3 to perform the weld between said metal support 3 and the metal part 5.

Claims

Demands

1. A method for depositing an anti-reflective metallic layer (4) onto a metallic support (3) for the purpose of a subsequent laser welding operation between said metallic support (3) and a metallic part (5), which method comprises at least one supersonic projection step of metallic powder particles (14) onto a face (15) of the metallic support (3) at a temperature below the melting temperature of said metallic powder particles (14) and at a speed above 350 meters per second, the projection of powder particles (14) being carried out at a pressure between 20 and 45 bar, at a temperature between 30 and 60% of the melting temperature of the metallic powder particles and at a distance from the metallic support (3) between 10 and 70 millimeters.

2. A method according to claim 1, characterized in that the projection of powder particles is carried out at a temperature between 680 and 770 °C and at a pressure between 28 and 37 bars.

3. Method according to claim 1 or 2, characterized in that the projection of powder particles (14) is carried out at a pressure between 33 and 37 Bars, at a temperature between 730 and 770 °C and at a distance from the metal support (3) between 30 and 50 millimeters.

4. Method according to the preceding claim, characterized in that the projection of powder particles (14) is carried out at a pressure of 35 Bars, at a temperature of 750 °C and at a distance from the metal support (3) of 40 millimeters.

5. A method according to any one of the preceding claims, characterized in that the projection step is carried out by linear movement substantially parallel to the face (15) to be covered of the metallic support (3) at a speed of between 150 and 250 millimeters per second in between one and four passes.

6. A method according to the preceding claim, characterized in that the linear displacement speed is between 170 and 190 millimeters per second, preferably 185 millimeters per second.

7. A method according to any one of claims 1 and 6, characterized in that the projection of metal powder particles (14) is carried out at a pressure of 35 Bars, at a temperature of 750 °C and at a distance from the metal support (3) of 40 millimeters and according to two linear displacement passes.

8. A method according to any one of the preceding claims, characterized in that the projection speed is between 500 and 1000 meters per second, preferably greater than 600 meters per second.

9. A method according to any one of the preceding claims, characterized in that the average size of the metal powder particles (14) is between 5 and 80 micrometers average size.

10. A method according to the preceding claim, characterized in that the average size of the metal powder particles (14) is between 20 and 60 micrometers, preferably 40 micrometers.

11. A method according to any one of the preceding claims, characterized in that the anti-reflective metallic layer (4) has a thickness of between 50 and 170 micrometers.

12. A method according to any one of the preceding claims, characterized in that the metal powder particles (14) are stainless steel.

13. A method according to any one of the preceding claims, characterized in that the metal support (3) is made of copper, aluminum or steel.

14. Metallic support (3) coated on at least one of its faces with an anti-reflective metallic layer (4) made of metallic powder particles (14) deposited by supersonic projection at a temperature lower than the melting temperature of said metallic powder particles, and intended to be welded onto a metallic part (5) by a laser welding operation, which anti-reflective metallic layer (4) has a maximum roughness Rz between 50 and 100 micrometers according to standards NF EN ISO 21920-1 and NF EN ISO 21920-2.

15. Support (3) according to the preceding claim, characterized in that the anti-reflective metallic layer (4) has an arithmetic mean roughness Ra between 1 and 15 micrometers according to standards NF EN ISO 21920-1 and NF EN ISO 21920-2.

16. Support (3) according to the preceding claim, characterized in that the anti-reflective metallic layer (4) has a roughness arithmetic mean Ra between 7 and 15 micrometers according to the standard.

17. Support (3) according to any one of claims 15 and 16, characterized in that the anti-reflective metallic layer (4) has a maximum roughness Rz of between 60 and 80 micrometers and an arithmetic mean roughness Ra of between 10 and 12 micrometers according to standards NF EN ISO 21920-1 and NF EN ISO 21920-2.

18. Support (3) according to any one of claims 15 to 17, characterized in that the anti-reflective metallic layer (4) has a thickness of between 50 and 170 micrometers.

19. Support (3) according to any one of claims 15 to 18, characterized in that the metal powder particles (14) are made of stainless steel or nickel.

20. Support (3) according to any one of claims 15 to 19, characterized in that the metal support (3) is made of copper, aluminum or steel.

21. A method of welding a metal support (3) according to claims 14 to 20 obtained by the method according to claims 1 to 13, onto a surface of a metal part (5), which method comprises at least one step of positioning the metal support (3) on the surface of the metal part (5), the anti-reflective metal layer (4) being disposed on the opposite side of the metal part, and a step of applying laser radiation welding power to the anti-reflective metal layer (4) of the metal support (3) to effect the weld between said metal support (3) and the metal part (5).

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