Method using a laser for welding between two metallic materials or for sintering of powder(s), application for making bipolar plates for PEM fuel cells

Abstract

A method for welding between two metallic plates, including: (a) fitting a solid plate without openings, configured to be transparent at at least one emission wavelength of a laser beam (F) emitted by a laser (L), between the laser (L) and at least one contact zone between the metallic plates to be welded; (a1) inerting of the contact zone via a netural gas, where the neutral gas circulates in channels delimited by the contact zone between the metallic plates and by the solid plate; (a2) exerting pressure on the two metallic plates to apply them against one another in the contact zone to be welded, where the application pressure is exerted by the solid plate directly in contact with one of the two metallic plates to be welded; and (b) emission of a laser beam, through the solid plate, to perform welding of the metallic plates in the contact zone.

Claims

1. A method of welding between two metallic plates, comprising: (a) fitting a solid plate without openings, configured to be transparent at at least one emission wavelength of a laser beam (F) emitted by a laser (L), between said laser (L) and at least one contact zone between the metallic plates to be welded; (a1) inerting of the at least one contact zone via a neutral gas; wherein the neutral gas circulates in channels delimited by the at least one contact zone between the metallic plates and by the solid plate; (a2) exerting pressure on the two metallic plates to apply them against one another in the at least one contact zone to be welded, wherein the application pressure is exerted by the solid plate directly in contact with one of the two metallic plates to be welded; and (b) emission of a laser beam, through the solid plate, to perform welding of the metallic plates in the at least one contact zone.

2. The method according to claim 1, wherein the neutral gas is argon and/or nitrogen.

3. The method according to claim 1, wherein the emission (b) is carried out with the laser beam perpendicular to the solid plate.

4. The method according to claim 1, wherein the emission (b) is carried out with the laser beam perpendicular to the at least one contact zone to be welded.

5. The method according to claim 1, wherein material used for the solid plate employed is selected from the following materials: glass, polymer, transparent ceramic, and/or ytterbium-doped scandium oxide to limit absorption.

6. A method of making bipolar plates suitable for fuel cells, comprising: implementing the method according to claim 1.

Description

DETAILED DESCRIPTION

(1) Other advantages and features of the invention will become clearer on reading the detailed description of the invention given for purposes of illustration, and nonlimiting, referring to the following figures, where:

(2) FIG. 1 is a schematic cross-sectional view of a bipolar plate for PEM fuel cells with welded joints,

(3) FIG. 2 is a schematic cross-sectional view of laser welding equipment according to the prior art for making a bipolar plate according to FIG. 1;

(4) FIG. 3 is a schematic cross-sectional view of laser welding equipment according to the invention for making a bipolar plate according to FIG. 1;

(5) FIG. 4 is a schematic cross-sectional view of laser sintering equipment according to the invention for making a sintered coating on the surface of a bipolar plate according to FIG. 3;

(6) FIG. 5 is a schematic cross-sectional view of laser sintering equipment according to the invention for making a sintered metal component.

(7) For clarity, the same references denoting the same elements of welding equipment and of a bipolar plate of a PEM fuel cell according to the prior art and according to the invention are used for all FIGS. 1 to 5.

(8) It is to be noted that the various elements according to the prior art and according to the invention are shown only for clarity, and they are not to scale.

(9) The terms “top” and “bottom” referring to the pressure plates are to be considered in a configuration with the plates to be welded positioned horizontally and the laser beam positioned vertically.

(10) FIGS. 1 and 2 have already been discussed in detail in the preamble. Therefore they are not described below.

(11) FIG. 3 shows laser welding L with encapsulation of sheets 2, 3 to be assembled together by means of pressure plates 8, 10.

(12) The bottom plate 8 serves as a base on which the sheets 2, 3 to be assembled are positioned.

(13) The solid top plate 10 will sandwich the sheets 2, 3 with pressure for maintaining a contact force between the surfaces of the sheets at the level where the joints 4 are to be made.

(14) As can be seen in FIG. 3, the solid plate 10 according to the invention is transparent to the wavelength(s) of the welding laser L. This solid plate 10 therefore does not have to be provided with well-defined multiple openings, in contrast to plate 9 according to the prior art.

(15) Thus, the beam F of the laser L can pass through plate 10 at any point of the latter in order to provide a continuous or spot weld seam in the required joint zones 4. These zones may be complex in their shape and/or their accessibility. They may be, for example, zones between the channels 5, 6, 7, on the perimeter of the openings for gas supply, on the outer perimeter of the sheets 2, 3, and so on.

(16) Advantageously, during welding, the beam F of the laser L is oriented perpendicular to the transparent plate 10 and the welded zone 4. This makes it possible to avoid having design constraints for the refractive index of the material to be used for plate 10 to avoid a change of direction of the beam F.

(17) The transparent plate 10 may be of glass, of polymer of the acrylic type or of ceramic of the zinc selenide (ZnSe) type. The ceramic may be doped (ytterbium-doped scandium oxide) to limit absorption of the radiation of the laser beam.

(18) The refractive index of plate 10 is advantageously of the order of 1.

(19) The transparent plate 10 without openings makes it possible to define, with plate 8 forming the base, an internal space that is easy to make hermetic. Thus, this space may be filled with an inerting gas G of the nitrogen or argon type, as shown in FIG. 3. The welded zones 4 are thus completely immersed in the inerting gas G that circulates and is confined in the channels delimited by plates 2, 3 and 8, 10.

(20) FIG. 4 illustrates another embodiment employing a transparent plate without openings 10 according to the invention.

(21) Plate 10 will close a container 11 and thus form a space into which an inerting gas G is injected.

(22) The container 11 contains both a bipolar plate 1 and a metal powder P deposited on the surface of the plate so as to obtain a sintered coating 12.

(23) The beam F of the laser L can pass at any point through the transparent plate 10 and reach the powder in very precise zones of the powder to be sintered and thus obtain a uniform sintered coating 12 on the surface of plate 1.

(24) FIG. 5 illustrates another way of obtaining a sintered metal component starting with a container similar to that in FIG. 4 and a transparent plate without openings 10 according to the invention.

(25) The beam F of the laser L can pass at any point through the transparent plate 10 and reach the powder P in very precise zones of the powder to be sintered, to obtain a metallic part of a desired shape.

(26) Other variants and advantages of the invention may be achieved while remaining within the scope of the invention.

(27) For example, if in the execution of welding for obtaining a bipolar plate, the plate that is transparent to the wavelengths of the laser also serves as a pressure plate for keeping the two metal plates in contact in the zones to be welded, it might very well be envisaged that the transparent plate does not have this function of applying pressure and that the latter is provided by other means.

(28) The invention is not limited to the examples that have just been described; it is notably possible to combine together features of the examples illustrated, within variants that are not illustrated.

REFERENCES CITED

(29) [1]: Marcinkoski J, James B D, Kalinoski J A, Podolski W, Benjamin T, Kopasz J. “Manufacturing process assumptions, used in fuel cell system cost analyses.” J Power Sources 196, 2011, 5282-5292 [2]: Cazes, “Welding with high-energy beams: electron beam and laser.” Techniques de I′Ingénieur 1994, B7, 740