Method for laser beam welding two components

Abstract

The invention relates to a method for laser beam welding two components (1, 2), in which the material of the two components (1, 2) is melted by means of at least one laser beam (LS1, LS2) in order to form at least one weld seam (SN1, SN2), the two components (1, 2) being arranged one above the other with respect to the direction of incidence of the at least one laser beam (LS1, LS2) onto the two components (1, 2).

Description

Technical Field

[0001] The invention relates to a method for laser beam welding of two components, in which the risk of leaky welds is reduced. The method according to the invention is suitable, for example, for connecting bipolar plates of fuel cells to one another, wherein the connection has a relatively long weld whose leaktightness is to be ensured. Background Art

[0002] US 2006 / 0054664 A1 discloses a method for laser beam welding of two components having the features of the preamble of claim 1. In particular, this document also discloses an embodiment of a welding path having a plurality of weld seams, wherein the weld seams (only) partially touch or intersect.

[0003] Furthermore, DE 102019215181 A1 of the applicant discloses a method for laser beam welding of two components, which is distinguished by the fact that two components arranged next to each other with respect to the direction of incidence of the laser beam are connected in such a way that the material of the two components is melted by the laser beam at a distance from the connection region of the components, so that a common melting region is obtained in the connection region. In other words, this means that the known method produces a single, usually relatively wide weld seam to connect the two components. As a result, the risk of leaky weld seams, for example due to gaps that occur between the two components, should be reduced and a weld seam of high quality should be achieved. Summary of the invention

[0004] The method according to the invention for laser beam welding of two components with the features of claim 1 has the advantage that the probability of leaks in the connecting region between the two components is further reduced or a welding path of particularly high quality can be produced.

[0005] The invention is based on the idea of ​​connecting the components to one another by at least two independent welds along a connection region where a welding track is produced, more precisely in such a way that the welds along the welding track form a closed unit or section, wherein at least two welds are produced with respect to the same location of the welding track in such a way that the material of the first produced welding track has already at least partially solidified in order to avoid a collision of two liquid weld pools. Such a construction and arrangement of the at least two welds reduces the probability of leaks in the connection region, since for leaks to occur, at least two welds must be leaky at the same time in the region of a unit. This situation is relatively unlikely. In addition, since the location at which the individual welds intersect or touch only constitutes a very small sub-region of the welding track and the irregularities of the welds are reduced when producing the further welds there due to the already at least partially solidified welds (since no collision or thorough mixing with the material of the weld produced later can occur), the probability of leaky connection regions is very low. In particular, complex interactions between the weld pools of the welds can be avoided thereby.

[0006] Therefore, against the background of the above explanations, in the method according to the invention for laser beam welding of two components having the features of claim 1, it is provided that at least two welds are produced with a time offset at least in the region where at least two welds touch, so that when at least one laser beam reaches the region to form a further weld, the material of the produced weld is at least partially, preferably completely, solidified.

[0007] Advantageous developments of the method according to the invention for laser beam welding of two components are listed in the dependent claims.

[0008] A particularly advantageous method, which enables the formation of weld seams of a welding track by means of multiple points almost simultaneously, but at a spatial distance from one another, provides that at least two weld seams are produced simultaneously in time and preferably at a spatial distance relative to the extension of the welding track. Preferably, it is provided that at least two weld seams are produced in time in parallel, but at a spatial distance, so that in the direction of the extension of the welding track, the first weld seam is produced first in time and the second or further weld seam is produced spatially following, but in time in parallel.

[0009] Another advantageous embodiment of the method provides that, along the welding path, a further region is additionally produced in which at least two weld seams are spaced apart from one another. Compared to a single weld seam, this enables, for example, a particularly wide welding path with advantageous mechanical connection properties and electrical contact properties of the two components.

[0010] A further preferred embodiment of the method provides that at least two weld seams overlap or intersect one another.

[0011] There are a number of possibilities for the geometry of the weld seam. Preferably, in view of relatively easy beam guidance, provision is made to form only straight weld seams, or a combination of at least one straight weld seam and at least one sinusoidal or circular segment-shaped weld seam, or a combination of at least two sinusoidal or circular segment-shaped weld seams, viewed in the direction of the welding path.

[0012] A development of the described geometry of the weld seams provides that, when forming at least two sinusoidal or circular segment-shaped weld seams, these weld seams are formed identically and have an offset relative to one another, viewed in the direction of the weld path and / or perpendicularly thereto.

[0013] The shape of the welding path can also be varied in any manner in principle. Preferably, however, provision is made to produce a straight welding path or at least a partially curved welding path by means of at least two weld seams.

[0014] Furthermore, it is preferably provided that the two weld seams are produced by at least one laser beam which has different powers and / or different spot diameters and / or different focal planes for producing the respective weld seams. Thus, although leaks which occur systematically in the region of a weld seam cannot be avoided due to the welding parameters on which the weld seam is based, such leaks will generally not occur there due to the different selection of the (welding) parameters for producing the other weld seam. This measure therefore additionally reduces the probability of leaky weld seams occurring simultaneously.

[0015] An advantageous embodiment of the method provides that at least one laser beam has at least two points, wherein at least two points have a predetermined spacing, which is described by a spacing vector. Preferably, a laser beam is divided into two sub-laser beams, each having a point. This helps to be able to produce at least two welds particularly easily and quickly. It is particularly advantageous here that the predetermined spacing can be constant in magnitude and / or direction relative to the welding track when producing the weld. The spacing between the laser points remains constant. The angle of the torsion line between the laser point and the welding track remains constant. However, preferably, the spacing of the laser point from the welding track does not remain constant. It has been found to be advantageous that the first of the at least two points is a main point and the second of the at least two points is a slave point, wherein the slave point follows the main point at a predetermined and preferably constant spacing when forming the welding track. Here, "following" means in particular that the slave point follows the main point in the form of a shadow, but wherein the slave point does not re-sweep the point swept by the main point. Here, the spacing as the relative connection vector between the main point and the slave point remains unchanged. A spacing that is constant in terms of magnitude and direction has the advantage that this can be easily realized technically. As an alternative or in addition, it is advantageous if the at least two points are rotated or swiveled or oscillated about a point axis during the production of the weld seam. This makes it possible to easily produce the described profile of the weld seam. Preferably, the point axis is oriented substantially perpendicular to the surface of the component. The point axis is an axis in the center between the at least two laser beams that produce the at least two points, wherein the point axis is substantially parallel to the laser beams. If the beam splitter produces two sub-beams from one laser beam (double spot), these sub-beams are slightly offset from each other and are therefore only substantially parallel. Therefore, the point axis also extends substantially parallel to the sub-beams.

[0016] The method according to the invention for laser beam welding of two components described in this way is preferably used for connecting bipolar plates of fuel cells. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Further advantages, features and details of the present invention are obtained from the following description of preferred embodiments of the present invention and with reference to the accompanying drawings. In which:

[0018] Figure 1 The connecting region of two components arranged one above the other in the region of a laser weld seam is shown in a schematic side view.

[0019] Figure 2 Shows Figure 1 A top view of the connection area of ​​, for illustrating the basic concept of the present invention,

[0020] Figure 3 Similar to Figure 2 A first preferred embodiment of a weld seam is shown,

[0021] Figure 4 Shows Figure 3 The cross-sectional view in plane IV-IV of

[0022] Figures 5 to 9 Corresponding to Figure 3 The top view shows the different shapes of the weld when two or three welds are used.

[0023] Fig.10 A top view of a welding trajectory with a partially curved profile is shown,

[0024] Fig.11 A top view showing a first variation of a welding trajectory; and

[0025] Fig.12 A second variant of a welding path is shown in a top view. DETAILED DESCRIPTION

[0026] Identical or functionally identical elements are provided with the same reference symbols in the figures.

[0027] Figure 1 A schematic side view shows a partial section of a connection region VB of two, in particular plate-shaped, components 1, 2 which are connected to one another along a welding track SB with the components 1, 2 arranged one above the other. The two components 1, 2 are arranged on the sides facing one another in abutting contact relative to one another. Purely by way of example, the two components 1, 2 have the same thickness or material thickness. Furthermore, the two components 1, 2 consist of the same type of material or of a material that can be welded to one another. Preferably, the components 1, 2 are bipolar plates of a fuel cell.

[0028] The welding track SB is generated by a laser beam device 100, which is designed to generate two independent weld seams SN1 and SN2 by means of two laser beams LS1 and LS2, for example. For this purpose, as shown, it is provided that the laser beam device 100 has an optical device 101, by means of which the two laser beams LS1 and LS2 are generated or decoupled from a single laser beam source 105. As an alternative (not shown), the laser beam device 100 can also have two independent laser beam sources to generate the two laser beams LS1 and LS2. In addition, the optical device 101 is used to guide the two laser beams LS1 and LS2 to generate the welding track SB along the components 1 and 2 along the arrows 103, wherein the two laser beams LS1 and LS2 are guided perpendicularly to the planes of the two components 1 and 2. The two components 1 and 2 are arranged one above the other with respect to the incident directions of the laser beams LS1 and LS2 on the components 1 and 2, that is, the two laser beams LS1 and LS2 are projected onto the first component 1 from the side facing away from the second component 2. In this case, it can also be provided that the laser beams LS1 and LS2 do not impinge on the first component 1 perpendicularly, but at an oblique angle.

[0029] The two laser beams LS1 and LS2 are irradiated onto the components 1, 2 with an offset in time and / or position. In this case, the laser beams LS1 and LS2 can have different powers or energy densities and / or different spot diameters and / or different focal planes. Figure 3 In particular, it can be seen that there is a spatial spacing b or a time offset t between the two laser beams LS1 and LS2 with respect to the production of the two weld seams SN1 and SN2 in the direction of the arrow 103, that is, with respect to the location on the welding trajectory SB. This spatial spacing b or time offset t is so large that if the location is a region 17 in which the two weld seams SN1, SN2 touch or intersect, the material of the weld seams SN1, SN2 first produced at this location is already at least partially, preferably completely solidified when the other weld seams SN2, SN1 are produced at this location.

[0030] exist Figure 2, a further basic concept of the method according to the invention is shown in , wherein two weld seams SN1 and SN2 are produced by means of at least one laser beam LS1, LS2, which form a welding track SB, wherein the two weld seams SN1 and SN2 form closed units Z1 to ZN, seven units Z1 to Z7 in the shown section of the welding track SB. The units Z1 to ZN are formed purely by way of example in that the weld seam SN1 is constructed as a straight weld seam SN1, while the weld seam SN2 has a first section 11 and a second section 12, which extends parallel to the weld seam SN1 at a distance, and which extends at a right angle to the first section 11 and connects the first section 11 of the first weld seam SN1 to the second weld seam SN2. As a result, rectangular units Z1 to ZN are obtained in a top view.

[0031] In addition, it is mentioned that the shape of the units Z1 to ZN can deviate from a rectangular shape as desired. However, it is essential that the units Z1 to ZN must be designed as closed units Z1 to ZN. The units Z1 to ZN of the welding track SB can have different sizes and / or shapes.

[0032] If the weld seam SN1 or SN2 now has a leak in the region of one of the units Z1 to ZN, this Figure 2 In the example of the units Z2 and Z4, the gap 14 will be used to illustrate that the welding track SB continues to be sealed in the direction marked by the double arrow 15 and extending perpendicularly to the welding track SB, because the units Z1 to Z7 or the welding track SB are limited by the two weld seams SN1 and SN2, and because only one of the two weld seams SN1 and SN2 is not sealed in the area of ​​the two units Z2 and Z4. In addition, it is applicable from an abstract perspective that the probability of the non-sealing of the weld seams SN1 or SN2 in the area of ​​the units Z1 to Z7 can be expressed by the coefficient p1 or p2. Therefore, the probability that the two weld seams SN1 and SN2 are not sealed in the area of ​​the same unit Z1 to Z7 is p1×p2. Since this product is always smaller than each coefficient p1, p2 itself, the probability of a non-sealed welding track SB is reduced for the closed units Z1 to Z7.

[0033] Due to Figure 2 The construction of the welding track SB composed of rectangular units Z1 to ZN shown in FIG. 1 is difficult to realize in practice, so an advantageous and relatively easy to realize welding track SB in practice will be described below, which adopts the concept of the present invention.

[0034] So first refer to Figure 3 , Figure 4 as well as Figure 5. It can be seen here that, viewed in the direction of the welding trajectory SB, the two weld seams SN1 and SN2 are each composed of arc segments extending in different directions or curvatures or are sinusoidally constructed, but are otherwise identically constructed. It can also be seen that the two weld seams SN1 and SN2 have a varying spacing a relative to each other such that a first region 16 and a second region 17 are generated, in which the two weld seams SN1 and SN2 are spaced apart relative to each other, and in which the two weld seams SN1 and SN2 are in contact with or overlap each other. This is achieved according to the invention in the following manner: as already explained above, the two weld seams SN1 and SN2 are generated by at least one laser beam LS1, LS2 offset in time and / or position relative to each other.

[0035] according to Figure 5 The two identically constructed weld seams SN1 and SN2 are basically the same as those according to Figure 3 The two weld seams SN1 and SN2 are constructed correspondingly. Figure 3 Different, according to Figure 5 The two weld seams SN1 and SN2 overlap in the direction of the double arrow 18, perpendicular to the direction of the welding trajectory SB. This causes the two weld seams SN1 and SN2 to intersect. As a result, a closed unit Z is produced even if the two weld seams SN1 and SN2 are arranged slightly shifted or offset relative to each other as viewed in the direction of the double arrow 18. In addition, compared to Figure 3 , the arc-shaped or sinusoidal path sections of the weld seams SN1 and SN2 each have a shorter length when viewed in the direction of the welding path SB, so that smaller units Z1 to ZN are produced.

[0036] As already mentioned, the two weld seams SN1 and SN2 can also be produced by means of a single laser beam LS1, LS2 by means of a two-spot optics with a fixed (spot) spacing b. This is possible because the two weld seams SN1, SN2 have the same geometry, but are arranged offset in space. The spacing b can also be designed variably. However, it is important that the material of the weld seam SN1 that has already been produced is at least partially, preferably completely, solidified in the region 17 when the laser beam LS2 reaches the region 17 for producing the further weld seam SN2.

[0037] Figure 6 It shows that the corresponding Figure 3 1 and 2. The first weld seam SN1 of the diagram is combined with a second weld seam SN2 of a straight line. Here, a second region 17 is also produced along the welding path SB, in which the two weld seams SN1 and SN2 partially overlap but at least touch each other.

[0038] Figure 7A limiting case is shown in which the two weld seams SN1 and SN2 of the welding trajectory SB, which are preferably generated with a time offset, at least touch and preferably partially overlap in the direction of the double arrow 18 perpendicular to the direction of the welding trajectory SB. In this case, the units Z1 to ZN shrink to zero size. Figure 7 The embodiment of has the advantage that it is particularly easy to implement since no complex beam guidance for the at least one laser beam LS1 , LS2 is necessary.

[0039] However, the invention is not limited to the use of (only) two welds SN1 and SN2. Figure 8 The following situation is shown in Figure 3 The two weld seams SN1 and SN2 arranged in a manner of FIG. 1 are combined with a third weld seam SN3, which is arranged on the side of the second weld seam SN2 facing away from the first weld seam SN1 and contacts the second weld seam SN2. Therefore, the second region 17 is constructed not only between the first weld seam SN1 and the second weld seam SN2, but also between the second weld seam SN2 and the third weld seam SN3. As a result, the probability of further improving the sealing of the welding track SB is achieved along the direction of the double arrow 18 extending perpendicularly to the welding track SB, because in the case of leaks in the area of ​​the units Z1 to ZN, all three weld seams SN1, SN2 and SN3 extending perpendicularly to the welding track SB in the area of ​​the units Z1 to ZN must be leaky.

[0040] exist Fig. 9 The following situation is shown in Figure 5 Three mutually intersecting weld seams SN1, SN2 and SN3 are formed, which are respectively arranged offset or phase-shifted relative to each other when viewed in the direction of the welding path SB. Figure 8 , all three weld seams SN1 , SN2 and SN3 must be leaky simultaneously over a smaller portion of the length of the weld track SB to result in a leaky weld track SB.

[0041] Finally, in Fig.10 In the figure, two weld seams SN1 and SN2 are used as an example, and the two weld seams are arranged symmetrically with respect to the symmetry line 20 between the two weld seams SN1 and SN2. This symmetry line 20, which is not shown, also exists in Figure 3 , Figure 5 and Fig. 9 In addition, Fig.10 The welding path SB in FIG. 1 also has, in addition to the two rectilinear welding path sections 21 and 22 , a curved welding path section 23 , which is designed in the form of a quarter circle and connects the two welding path sections 21 and 22 to one another. Fig.10The illustration of SH is intended to illustrate that overall any desired course of the welding path SB can be produced by correspondingly shaped or arranged welding path sections 21 and 22 .

[0042] It should be pointed out again that Figures 8 to 9 In the welding track SB shown in , the geometry of the weld seams SN1, SN2 and SN3 is identical, that is, can be transferred into each other by displacement. This is advantageous when the weld seams SN1, SN2, SN3 are produced by means of a single laser beam LS1, LS2 and an optical device with a fixed spacing b between the points.

[0043] The method described in this way can be modified or altered in various ways without departing from the inventive concept. It is not mandatory for at least two weld seams SN1, SN2 and SN3 to be identically configured, for example, each sinusoidally configured. When using sinusoidal weld seams SN1, SN2 or SN3, these weld seams can, for example, also have different period lengths and / or their period length or amplitude can vary along the welding trajectory SB.

[0044] Fig.11 A first variant of a welding trajectory SB having a first weld seam SN1 and a second weld seam SN2 is shown, which are produced simultaneously by means of two spots formed by a laser beam. For this purpose, the laser beam is first divided and then irradiated onto the component at two spatially spaced spots (“Spots”) 24 and 25. The first weld seam SN1 contacts the second weld seam SN2 at a contact point 27. Here, the first weld seam SN1 is produced by the main spot 24 and the second weld seam SN2 is produced by the secondary spot 25. The main spot 24 and the secondary spot 25 have a predetermined spacing 26, wherein the predetermined spacing 26 is constant in magnitude and has a constant angle relative to the welding trajectory SB in terms of its direction when the two weld seams SN1, SN2 are produced spatially offset on a straight section of the welding trajectory, but otherwise identical weld seams SN1, SN2. The welding trajectory SB is produced in the direction of the arrow 103. In the direction of the arrow 103, the main spot 24 produces the first weld seam SN1. At the same time, a second weld seam SN2 is produced at a distance from the main point 24 via the secondary point 25 . Fig.11Furthermore, it is shown that different predetermined distances 26 between the main point 24 and the secondary point 25 can be realized. The predetermined distance 26 can be selected in discrete steps. The welding trajectory SB consists of a first weld seam SN1 and a second weld seam SN2, which consist of two identical periodic, spatially offset geometric shapes. Preferably, the periodic geometric shapes are sinusoidal functions. The predetermined distance 26 is selected as a connecting vector between the main point 24 and the secondary point 25 so that it describes the spatial offset of the two periodic geometric shapes relative to each other. If the weld seam SN1 is locally displaced by the distance 26, then the weld seam SN2 can be obtained from the weld seam SN1. Therefore, there are multiple feasible options for selecting the distance 26, in Fig.11 Some of these possibilities are shown in . It is generally advantageous to select the shortest possible spacing that results in the desired geometry.

[0045] Fig.12 A second variant of a welding trajectory SB having a first weld seam SN1 and a second weld seam SN2 is shown, which are produced simultaneously by means of two spots formed by a laser beam. For this purpose, the laser beam is first divided and then irradiated onto the component at two spatially spaced points (“Spots”) 24 and 25. The first weld seam SN1 intersects the second weld seam SN2 at an intersection point 28. Here, the first weld seam SN1 is produced by the main point 24 and the second weld seam SN2 is produced by the secondary point 25. The main point 24 and the secondary point 25 have a predetermined spacing 26, wherein the predetermined spacing 26 is constant in magnitude and has a constant angle relative to the welding trajectory SB in terms of its direction when the two weld seams SN1, SN2 are spatially offset but otherwise identical weld seams SN1, SN2 on a straight section of the welding trajectory. The welding trajectory SB is produced in the direction of the arrow 103. In the direction of arrow 103 , the main point 24 generates a first weld seam SN1 . At the same time, a second weld seam SN2 is generated at a distance from the main point 24 via the secondary point 25 . Fig.12 Furthermore, it is shown that different predetermined spacings 26 between the main point 24 and the secondary point 25 can be realized. The predetermined spacing 26 can be selected in discrete steps. The welding trajectory SB consists of a first weld seam SN1 and a second weld seam SN2, which consist of two identical periodic, spatially offset geometric shapes. Preferably, the periodic geometric shapes are sinusoidal functions. The predetermined spacing 26 is selected as a connecting vector between the main point 24 and the secondary point 25 so that it describes the spatial offset of the two periodic geometric shapes relative to each other. If the weld seam SN1 is locally displaced by the spacing 26, the weld seam SN2 is then obtained from the weld seam SN1. There are therefore a number of possible options for selecting the spacing 26, in which Fig.12Some of these possibilities are shown in . It is generally advantageous to select the shortest possible spacing that results in the desired geometry.

Claims

1. A method for laser beam welding two components (1, 2), in, The material of the two components (1, 2) is melted by means of at least one laser beam (LS1, LS2) to form at least one weld seam (SN1, SN2), wherein the two components (1, 2) are arranged one above the other with respect to the direction of incidence of the at least one laser beam (LS1, LS2) on the two components (1, 2), and wherein at least two weld seams (SN1, SN2, SN3) are produced, which are in contact at least partially in a region (17) along a welding track (SB) formed by the at least two weld seams (SN1, SN2, SN3), It is characterized in that The at least two welds (SN1, SN2, SN3) are produced with a time offset (t) at least in the region (17) where the at least two welds (SN1, SN2, SN3) are in contact, so that when the at least one laser beam (LS1, LS2) reaches the region (17) to construct the further welds (SN1, SN2, SN3), the material of the produced welds (SN1, SN2, SN3) is at least partially, preferably completely, solidified.

2. The method according to claim 1, It is characterized in that The at least two weld seams (SN1, SN2, SN3) are produced simultaneously and preferably at a spatial distance (b) relative to the extent of the welding track (SB).

3. The method according to claim 1 or 2, It is characterized in that A further region (16) is additionally produced along the welding path (SB), in which the at least two weld seams (SN1, SN2, SN3) are at a distance (a) from one another.

4. The method according to any one of claims 1 to 3, It is characterized in that The at least two weld seams (SN1, SN2, SN3) overlap or intersect each other.

5. The method according to any one of claims 1 to 4, It is characterized in that When viewed along the direction of the welding trajectory (SB), only straight welds (SN1, SN2, SN3) are constructed, or a combination of at least one straight weld and at least one sinusoidal or circular arc segment weld (SN1, SN2, SN3) is constructed, or a combination of at least two sinusoidal or circular arc segment welds (SN1, SN2, SN3) is constructed.

6. The method according to claim 5, It is characterized in that When constructing at least two sinusoidal or circular segment-shaped weld seams (SN1, SN2, SN3), these weld seams are constructed identically and are offset relative to one another when viewed in the direction of the welding path (SB) and / or perpendicularly to the welding path (SB).

7. The method according to any one of claims 1 to 6, It is characterized in that A straight welding path (SB) is produced by means of the at least two weld seams (SN1, SN2, SN3).

8. The method according to any one of claims 1 to 6, It is characterized in that An at least partially curved welding path (SB) is produced by means of the at least two weld seams (SN1, SN2, SN3).

9. The method according to any one of claims 1 to 8, It is characterized in that The at least two weld seams (SN1, SN2, SN3) are produced by at least one laser beam (LS1, LS2) having different powers and / or different spot diameters and / or different focal planes to form the respective weld seams (SN1, SN2, SN3).

10. The method according to any one of claims 1 to 9, It is characterized in that The at least one laser beam (LS1, LS2) has at least two points, wherein the at least two points have a predetermined distance (26).

11. The method according to claim 10, It is characterized in that When producing the weld seam (SN1, SN2, SN3), the predetermined distance (26) between the at least two points is constant in magnitude and / or direction relative to the welding trajectory (SB).

12. The method according to any one of claims 10 or 11, It is characterized in that The first point of the at least two points is a main point (24), and the second point of the at least two points is a slave point (25), wherein, when forming the welding track (SB), the slave point (25) follows the main point (24) at a predetermined distance (26).

13. The method according to any one of claims 10 to 12, It is characterized in that During the production of the weld seam (SN1, SN2, SN3), the at least two points are rotated or swiveled or vibrated about a point axis.

14. The method according to any one of claims 1 to 13, It is characterized in that The method is used to weld bipolar plates of fuel cells to each other.

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