Method for laser beam welding two components

Abstract

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

Description

[0001] Description

[0002] Process for laser beam welding two components

[0003] Technical area

[0004] The invention relates to a method for laser beam welding two components, which reduces the risk of leaky welds. The method according to the invention is suitable, for example, for joining bipolar plates of fuel cells, where the joints have relatively long welds whose tightness must be ensured.

[0005] State of the art

[0006] US 2006 / 0054664 A1 discloses a method for laser welding two components having the features of the preamble of claim 1. In particular, embodiments of a welding path with multiple weld seams are also known from this document, in which the weld seams (only) touch or cross in certain areas.

[0007] Furthermore, DE 102019215 181 A1 by the applicant discloses a method for laser welding two components. This method is characterized in that two components arranged side by side with respect to the direction of incidence of laser beams are joined by melting the material of the two components by a laser beam at a distance from the joining area of ​​the components, resulting in a common melting area in the joining area. In other words, this means that the known method creates a single, typically relatively wide weld seam for joining the two components. This is intended to reduce the risk of a leaky weld seam, caused, for example, by gaps occurring between the two components, and to achieve a high-quality weld seam. Disclosure of the Invention

[0008] The method according to the invention for laser beam welding two components with the features of claim 1 has the advantage that the probability of leakage in the connection area between the two components is further reduced and particularly high-quality weld paths can be produced.

[0009] The invention is based on the idea of ​​connecting the components along the connecting region producing a weld path by means of at least two separate weld seams, in such a way that the weld seams along the weld path form self-contained cells or sections, wherein the at least two weld seams are produced with respect to one and the same point on the weld path in such a way that the material of the weld path produced first has already at least partially solidified in order to avoid a collision between two liquid weld pools. Such a design and arrangement of at least two weld seams reduces the probability of a leak occurring in the connecting region, since for a leak to occur the at least two weld seams in the region of a cell would have to be leaking at the same time. Such a case is relatively unlikely. In addition, since points at which the individual weld seams cross or...Since the contact areas make up a very small portion of the weld path, and since the weld seam has already at least partially solidified, irregularities in this weld seam are reduced when creating the other weld seam, as there is no collision or mixing with material from the weld seam created later, the probability of a leaky joint area is very low. In particular, this avoids complex interactions between the weld pools of the weld seams.

[0010] Against the background of the above explanations, it is therefore provided in a method according to the invention for laser beam welding two components with the features of claim 1 that the at least two weld seams are produced with a time offset at least in the regions where the at least two weld seams touch, so that the material of a produced weld seam is at least partially, preferably completely, solidified when the at least one laser beam reaches the region to form another weld seam.

[0011] Advantageous further developments of the method according to the invention for laser beam welding two components are listed in the subclaims.

[0012] A particularly advantageous method that enables the weld seams of the welding path to be formed quasi-simultaneously, but spatially spaced from one another, using a multiple spot, provides for the at least two weld seams to be produced simultaneously in time and preferably at a spatial distance relative to the extension of the welding path. Preferably, the at least two weld seams are produced in parallel in time but at a spatial distance, so that a first weld seam is produced first in time in the direction of the extension of the welding path, followed spatially by a second or further weld seam, but temporally parallel.

[0013] Another advantageous embodiment of the method provides for additional regions to be created along the weld path in which the at least two weld seams are spaced apart. This enables, for example, particularly wide weld paths with advantageous mechanical connection properties and electrical contact properties of the two components compared to a single weld seam.

[0014] A further preferred embodiment of the method provides that the at least two weld seams overlap or cross each other.

[0015] There are numerous possibilities regarding the geometry of the weld seams. With a view to relatively simple beam guidance, it is preferably provided that, viewed in the direction of the weld path, either exclusively straight weld seams are formed, or a combination of at least one straight weld seam and at least one weld seam with a sinusoidal or circular arc segment, or a combination consisting of at least two weld seams with a sinusoidal or circular arc segment.

[0016] A further development of the described geometry of the weld seams provides that in the case of the formation of at least two sinusoidal or circular arc-shaped weld seams, these are formed identically and, viewed in the direction of the weld path and / or perpendicular to the direction of the weld path, have an offset from one another.

[0017] The shape of the weld path can also be varied as desired. However, it is preferred that the at least two weld seams produce a straight weld path or a weld path that is curved at least in some areas.

[0018] Furthermore, it is preferably provided that the two welds are created by at least one laser beam, which has a different power and / or a different spot diameter and / or a different focal plane for forming the respective weld. While this means that systematically occurring leaks in the area of ​​one weld cannot be avoided due to the welding parameters underlying this weld, these leaks typically cannot occur there due to the different (welding) parameters selected for forming the other weld. Thus, this measure further reduces the probability of simultaneous occurrence of leaky welds.

[0019] An advantageous embodiment of the method provides that the at least one laser beam has at least two spots, wherein the at least two spots have a predetermined distance that is described by a distance vector. Preferably, a laser beam is split into two partial laser beams, each with one spot. This contributes to the at least two weld seams being able to be produced particularly easily and quickly. It is particularly advantageous that the predetermined distance can be constant in amount and / or direction relative to the weld path when producing the weld seams. The distance between the laser spots remains constant. The angle of the twist line between the laser spots and the weld path remains constant. However, the distance of the laser spots to the weld path preferably does not remain constant.It has proven advantageous for a first spot of the at least two spots to be a master spot and a second spot of the at least two spots to be a slave spot, with the slave spot following the master spot at a predetermined and preferably constant distance during the formation of the weld path. Following means in particular that the slave spot follows the master spot like a shadow, but not by the slave spot repeatedly sweeping over the points swept over by the master spot. The distance remains unchanged as a relative connecting vector between the master spot and the slave spot. A distance that is constant in amount and direction has the advantage that it is technically easy to implement. Alternatively or additionally, it is advantageous for the at least two spots to rotate, pivot, or oscillate around a spot axis during the creation of the weld seams. This makes it easy to create the described contours of the weld seams.Preferably, the spot axis is aligned substantially perpendicular to a surface of the components. The spot axis is an axis in the middle between the at least two laser beams that generate the at least two spots, with the spot axis being substantially parallel to the laser beams. If a beam splitter generates the two partial beams from one laser beam (double spot), these partial beams diverge slightly and are thus only substantially parallel. Consequently, the spot axis also runs substantially parallel to the partial beams.

[0020] The method according to the invention for laser beam welding two components described so far is preferably used for joining bipolar plates of fuel cells.

[0021] Further advantages, features and details of the invention will become apparent from the following description of preferred embodiments of the invention and from the drawings.

[0022] Brief description of the drawings Fig. 1 shows a schematic side view of a connection area of ​​two components arranged one above the other in the area of ​​a laser weld seam,

[0023] Fig. 2 is a plan view of the connecting area of ​​Fig. 1 to explain the basic inventive concept,

[0024] Fig. 3 in analogy to Fig. 2 a representation of a first preferred embodiment of weld seams,

[0025] Fig. 4 is a section in plane IV—IV of Fig. 3,

[0026] Fig. 5 to

[0027] Fig. 9 shows in plan view corresponding to Fig. 3 different shapes of welds when using two or three welds,

[0028] Fig. 10 is a plan view of a welding path with a partially curved course,

[0029] Fig. 11 is a plan view of a first variant of a welding track, and

[0030] Fig. 12 a plan view of a second variant of a welding track.

[0031] Embodiments of the invention

[0032] Identical elements or elements with the same function are provided with the same reference numbers in the figures.

[0033] Fig. 1 shows a schematic side view of a partial section of a connecting region VB of two, in particular, plate-shaped components 1, 2, which are connected to one another along a weld path SB when the components 1, 2 are arranged one above the other. The two components 1, 2 are arranged in contact with one another on sides facing one another. Purely as an example, the two components 1, 2 have the same thickness or material strength. Furthermore, the two components 1, 2 are made of similar materials or materials that can be welded to one another. The components 1, 2 are preferably bipolar plates of a fuel cell.

[0034] The welding path SB is generated by a laser beam device 100, which is designed to generate two separate weld seams SN1 and SN2 using, for example, two laser beams LS1 and LS2. For this purpose, as shown, the laser beam device 100 can have 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. Alternatively (not shown), the laser beam device 100 can also have two separate laser beam sources for generating the two laser beams LS1 and LS2. Furthermore, the optical device 101 serves to guide the two laser beams LS1 and LS2 along the arrow 103 along the components 1, 2 to generate the welding path SB, wherein the two laser beams LS1 and LS2 are guided perpendicular to the plane of the two components 1, 2.The two components 1, 2 are arranged one above the other with respect to the direction of incidence of the laser beams LS1 and LS2 onto the components 1, 2, i.e., the two laser beams LS1 and LS2 impinge on the first component 1 from the side facing away from the second component 2. It can also be provided that the laser beams LS1 and LS2 impinge on the first component 1 not perpendicularly, but at an oblique angle.

[0035] The two laser beams LS1 and LS2 strike the components 1, 2 at different times and / or locations. The laser beams LS1 and LS2 can have different power levels or energy densities and / or different spot diameters and / or different focal planes. Furthermore, it can be seen in particular from Fig. 3 that there is a spatial distance b or a temporal offset t between the two laser beams LS1 and LS2 with respect to the creation of the two weld seams SN1 and SN2 in the direction of arrow 103, i.e. with respect to a point on the weld path SB. This spatial distance b orThe time offset t is so large that the material of the weld seam SN 1 , SN2 produced first at one point has already solidified at least partially, preferably completely, when the other weld seam SN2, SN1 is produced at this point, if this point is an area 17 at which the two weld seams SN1 , SN2 touch or cross.

[0036] Fig. 2 shows a further basic idea of ​​the method according to the invention, in which two weld seams SN1 and SN2 are produced by means of at least one laser beam LS1, LS2, which weld seams form the weld path SB, the two weld seams SN1 and SN2 forming closed cells Z1 to ZN, in the section of the weld path SB shown, seven cells Z1 to Z7. Purely as an example, the cells Z1 to ZN are formed in that the weld seam SN1 is designed as a straight weld seam SN1, while the weld seam SN2 has first sections 11 which run parallel at a distance from the weld seam SN1 and second sections 12 which run at right angles to the first sections 11 and connect the first sections 11 of the first weld seam SN1 with the second weld seam SN2. This results in rectangular cells Z1 to ZN in plan view.

[0037] It should also be noted that the shape of cells Z1 to ZN can deviate from the rectangular shape as desired. The only important thing is that cells Z1 to ZN are formed as closed cells Z1 to ZN. Cells Z1 to ZN of a welded track SB can also have different sizes and / or shapes.

[0038] If a weld seam SN1 or SN2 is leaking in the area of ​​one of the cells Z1 to ZN, which is illustrated in Fig. 2 using the example of cells Z2 and Z4 by the gaps 14, the weld path SB is still tight overall in a direction indicated by the double arrow 15 and running perpendicular to the weld path SB, because the cells Z1 to Z7 or the weld path SB are delimited by the two weld seams SN1 and SN2, and because in the area of ​​the two cells Z2 and Z4 only one of the two weld seams SN1 and SN2 is leaking. Furthermore, in an abstract sense, the probability of a leak in a weld seam SN1 or SN2 in the area of ​​a cell Z1 to Z7 can be specified with a factor p1 or p2. The probability that both weld seams SN1 and SN2 are leaking in the area of ​​one and the same cell Z1 to Z7 is p1 x p2.Since this product is always smaller than each factor p1, p2 taken individually, the probability of a leaky weld line SB occurring is reduced for closed cells Z1 to Z7.

[0039] Since the formation of the welding path SB shown in Fig. 2, consisting of the rectangular cells Z1 to ZN, is difficult to realize in practice, advantageous welding paths SB which are relatively easy to realize in practice and which make use of the inventive concept are described below.

[0040] 3, 4 and 5. It can be seen therein that the two weld seams SN1 and SN2, viewed in the direction of the weld path SB, are each composed of circular arc sections running in different directions or curvatures or are sinusoidal, but are otherwise of the same design. It can also be seen that the two weld seams SN1 and SN2 have a changing distance a from one another, such that first regions 16 are created in which the two weld seams SN1 and SN2 are spaced apart from one another, and second regions 17 in which the two weld seams SN1 and SN2 touch or overlap one another. According to the invention, this is achieved in that, as already explained above, the two weld seams SN1 and SN2 are created by the at least one laser beam LS1, LS2 at a time and / or location offset from one another.

[0041] The two identically designed weld seams SN1 and SN2 according to Fig. 5 are basically designed correspondingly to the two weld seams SN1 and SN2 according to Fig. 3. In contrast to Fig. 3, the two weld seams SN1 and SN2 according to Fig. 5 have an overlap in the direction of the double arrow 18, perpendicular to the direction of the weld path SB. This causes the two weld seams SN1 and SN2 to cross. As a result, closed cells Z are created even if the two weld seams SN1 and SN2 are slightly shifted or offset from one another as viewed in the direction of the double arrow 18. Furthermore, the circular-arc-shaped or sinusoidal path sections of the weld seams SN1 and SN2, viewed in the direction of the weld path SB, can each have a shorter length compared to Fig. 3, so that smaller cells Z1 to ZN are created.As already mentioned, the two weld seams SN1 and SN2 can also be created using a single laser beam LS1, LS2 using a double spot optics with a fixed (spot) distance b. This is possible because the geometries of the two weld seams SN1, SN2 are identical, but spatially offset. However, the distance b can also be variable. The only important thing is that in an area 17 the material of an already created weld seam SN1 is at least partially, preferably completely, solidified when the laser beam LS2 reaches the area 17 to create the other weld seam SN2.

[0042] Fig. 6 illustrates the case in which a first weld seam SN1, as shown in Fig. 3, is combined with a second weld seam SN2, which is formed in a straight line. This also creates second regions 17 along the weld path SB, in which the two weld seams SN1 and SN2 partially overlap or at least touch each other.

[0043] Fig. 7 illustrates a borderline case in which the two weld seams SN1 and SN2 of the weld path SB, preferably generated with a temporal offset, at least touch each other, preferably overlapping in regions in the direction of the double arrow 18 perpendicular to the direction of the weld path SB. In this case, the cells Z1 to ZN shrink to a size of zero. The configuration according to Fig. 7 has the advantage of being particularly easy to implement, since no complex beam guides are required for the at least one laser beam LS1, LS2.

[0044] However, the invention is not limited to the use of (only) two weld seams SN1 and SN2. Thus, Fig. 8 shows the case in which two weld seams SN1 and SN2 are combined according to the arrangement in Fig. 3 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 touches the second weld seam SN2. Thus, second regions 17 are formed both between the first weld seam SN1 and the second weld seam SN2, and between the second weld seam SN2 and the third weld seam SN3. This further increases the probability of the weld path SB being tight in the direction of the double arrow 18 running perpendicular to the weld path SB, since in the event of a leak in the region of a cell Z1 to ZN, all three weld seams SN1, SN2, and SN3 running perpendicular to the weld path SB would have to be leaky in the region of this cell Z1 to ZN.

[0045] Fig. 9 illustrates a case in which, similar to Fig. 5, three intersecting weld seams SN1, SN2, and SN3 are formed, each of which, viewed in the direction of the weld path SB, is offset from one another or is arranged out of phase with one another. Here, too, analogous to Fig. 8, all three weld seams SN1, SN2, and SN3 would have to leak simultaneously over a small portion of the length of the weld path SB to cause a leaky weld path SB.

[0046] Finally, Fig. 10 shows, using the example of two weld seams SN1 and SN2, that these are arranged symmetrically to a straight line of symmetry 20 running between the two weld seams SN1 and SN2. Such straight lines of symmetry 20 (not shown) are also present in the arrangements in Figs. 3, 5 and 9. The welding path SB in Fig. 10 also has, in addition to two straight welding path sections 21 and 22, a curved welding path section 23 shaped in the shape of a quarter circle, which connects the two welding path sections 21 and 22 to one another. The illustration in Fig. 10 is intended to illustrate that, overall, any desired course of welding paths SB can be generated by appropriately shaped or arranged welding path sections 21 and 22.

[0047] It should be noted again that the geometries of the weld seams SN1, SN2, and SN3 are identical in the weld paths SB shown in Figs. 8 to 9, i.e., they can be converted into one another by shifting. This is advantageous when creating the weld seams SN1, SN2, and SN3 using a single laser beam LS1, LS2 and an optic with a fixed distance b between the spots.

[0048] The method described so far can be modified or altered in a variety of ways without deviating from the inventive concept. It is not absolutely necessary for the at least two weld seams SN1, SN2, and SN3 to be identical, for example, each sinusoidal. When using sinusoidal weld seams SN1, SN2, or SN3, for example, they can have different period lengths and / or their period length or amplitude can change along the weld path SB.

[0049] Figure 11 shows a first variant of a welding path SB with a first weld seam SN1 and a second weld seam SN2, which are generated simultaneously by means of two spots formed from a laser beam. For this purpose, the laser beam is first split and then strikes the component at two spatially spaced points (“spots”) 24 and 25. The first weld seam SN1 touches the second weld seam SN2 at contact points 27. The first weld seam SN1 is generated by a master spot 24 and the second weld seam SN2 by a slave spot 25. The master spot 24 and the slave spot 25 have a predetermined distance 26, wherein the predetermined distance 26 is constant in magnitude during the generation of the two weld seams SN1, SN2 and has a constant angle to the welding path SB in its direction. The two weld seams SN1, SN2 are spatially offset but otherwise identical weld seams SN1, SN2 on straight sections of the weld path.The welding path SB is generated in the direction of arrow 103. In the direction of arrow 103, the master spot 24 generates the first weld seam SN1. At the same time, the second weld seam SN2 is generated by the slave spot 25 at a distance from the master spot 24. Figure 11 also shows that different predetermined distances 26 between the master spots 24 and the slave spot 25 are possible. The predetermined distances 26 can be selected in discrete steps. The welding path SB consists of a first weld seam SN1 and a second weld seam SN2, which consist of two identical, periodic geometries that are spatially offset. The periodic geometry is preferably a sine function. The predetermined distance 26 as a connecting vector between the master spot 24 and the slave spot 25 is selected such that it describes the spatial offset of the two periodic geometries relative to one another.Weld SN2 is therefore derived from weld SN1 when weld SN1 is locally shifted by a distance of 26. Therefore, there are several possibilities for selecting the distance 26, some of which are shown in Figure 11. It is often advantageous to choose the shortest possible distance that leads to the desired geometry.

[0050] Figure 12 shows a second variant of a welding path SB with a first weld seam SN1 and a second weld seam SN2, which are generated simultaneously by means of two spots formed from a laser beam. For this purpose, the laser beam is first split and then strikes the component at two spatially spaced points ("spots") 24 and 25. The first weld seam SN1 intersects the second weld seam SN2 at intersection points 28. The first weld seam SN1 is generated by a master spot 24 and the second weld seam SN2 by a slave spot 25. The master spot 24 and the slave spot 25 have a predetermined distance 26, wherein the predetermined distance 26 is constant in magnitude during the generation of the two weld seams SN1, SN2 and has a constant angle to the welding path SB in its direction. The two weld seams SN1, SN2 are spatially offset but otherwise identical weld seams SN1, SN2 on straight sections of the shit track.The welding path SB is generated in the direction of arrow 103. In the direction of arrow 103, the master spot 24 generates the first weld seam SN1. At the same time, the second weld seam SN2 is generated by the slave spot 25 at a distance from the master spot 24. Figure 12 also shows that different predetermined distances 26 between the master spots 24 and the slave spot 25 are possible. The predetermined distances 26 can be selected in discrete steps. The welding path SB consists of a first weld seam SN1 and a second weld seam SN2, which consist of two identical, periodic geometries that are spatially offset. The periodic geometry is preferably a sine function. The predetermined distance 26 as a connecting vector between the master spot 24 and the slave spot 25 is selected such that it describes the spatial offset of the two periodic geometries relative to one another.Weld SN2 is therefore derived from weld SN1 when weld SN1 is locally shifted by distance 26. Therefore, there are several ways to select distance 26, some of which are shown in Figure 12. It is often advantageous to choose the shortest possible distance that leads to the desired geometry.

Claims

Claims 1. 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) to form at least one weld seam (SN1, SN2), wherein the two components (1, 2) are arranged one above the other with respect to a direction of incidence of the at least one laser beam (LS1, LS2) onto the two components (1, 2), and wherein at least two weld seams (SN1, SN2, SN3) are produced, which contact each other at least in places in regions (17) along a weld path (SB) formed by the at least two weld seams (SN1, SN2, SN3), characterized in that the at least two weld seams (SN1, SN2, SN3) are produced with a time offset (t) at least in the regions (17) at which the at least two weld seams (SN1, SN2, SN3) touch each other so that the material of a produced weld seam (SN1, SN2, SN3) is at least partially, preferably completely solidified,when at least one laser beam (LS1, LS2) reaches the area (17) to form another weld seam (SN1, SN2, SN3).

2. Method according to claim 1, characterized in that the at least two weld seams (SN1, SN2, SN3) are produced simultaneously and preferably with a spatial distance (b) with respect to the extension of the weld path (SB).

3. Method according to claim 1 or 2, characterized in that additionally further regions (16) are produced along the welding path (SB), in which the at least two weld seams (SN1, SN2, SN3) have a distance (a) from one another. Method according to one of claims 1 to 3, characterized in that the at least two weld seams (SN1, SN2, SN3) overlap or cross one another. Method according to one of claims 1 to 4, characterized in that, viewed in the direction of the weld path (SB), either exclusively rectilinear weld seams (SN1, SN2, SN3), or a combination of at least one rectilinear and at least one sinusoidal or circular arc-shaped weld seam (SN1, SN2, SN3), or a combination consisting of at least two sinusoidal or circular arc-shaped weld seams (SN1, SN2, SN3) are formed. Method according to claim 5, characterized in that, in the case of the formation of at least two sinusoidal or circular arc-shaped weld seams (SN1, SN2, SN3), these are formed identically and, viewed in the direction of the weld path (SB) and / or perpendicular to the direction of the weld path (SB), have an offset from one another.Method according to one of claims 1 to 6, characterized in that a rectilinear weld path (SB) is produced by means of the at least two weld seams (SN1, SN2, SN3). Method according to one of claims 1 to 6, characterized in that a weld path (SB) that is at least partially curved is produced by means of the at least two weld seams (SN1, SN2, SN3). Method according to one of claims 1 to 8, characterized in that. that the at least two weld seams (SN1, SN2, SN3) are produced by at least one laser beam (LS1, LS2) which has a different power and / or a different spot diameter and / or a different focal plane for forming the respective weld seam (SN1, SN2, SN3). Method according to one of claims 1 to 9, characterized in that the at least one laser beam (LS1, LS2) has at least two spots, wherein the at least two spots have a predetermined distance (26). Method according to claim 10, characterized in that the predetermined distance (26) between the at least two spots is constant in amount and / or direction during the production of the weld seams (SN1, SN2, SN3) relative to the welding path (SB).Method according to one of claims 10 or 11, characterized in that a first spot of the at least two spots is a master spot (24) and a second spot of the at least two spots is a slave spot (25), wherein the slave spot (25) follows the master spot (24) at the predetermined distance (26) during the formation of the weld path (SB). Method according to one of claims 10 to 12, characterized in that the at least two spots turn or rotate or oscillate about a spot axis during the production of the weld seams (SN1, SN2, SN3). Method according to one of claims 1 to 13, characterized in that bipolar plates of a fuel cell are welded together thereby.

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