Method for end-side laser welding

Abstract

The invention relates to a method for the end-side laser welding of a joint of two joining flanges fixed to one another, belonging to a joining fitting (1, 1.1) made of a steel material, at least one of which is equipped with a metal coating having an evaporation temperature below the melting temperature of the steel material, the method is carried out in such a way that the joining flanges (1, 1.1) of the two joining fittings (1, 1.1) are fixed to each other during the laser welding at an angle which opens in the direction facing away from the joint side to which the laser is applied, whereby a degassing gap (5) is provided between the joining flanges (3, 3.1), which degassing gap expands in the direction of the introduction of heat, through which degassing gap the coating material (8, 9) is discharged. 8.1) as a result of the introduction of heat.

Description

[0001] This application is a divisional application of the invention application with an application date of March 19, 2018, an application number of 201880018706.7, an international application number of PCT / EP2018 / 056833, and an invention name of “Method for end-side laser welding”.

[0002] The invention relates to a method for the end-side laser welding of a joint of two mutually fixed joining flanges, which are two joining fittings made of steel, wherein at least one joining flange is provided with a metal coating having an evaporation temperature below the melting temperature of the steel.

[0003] There are numerous applications in which joining flanges of metal parts, which are fixed to one another with their flat sides, are welded to one another from the end at their joints (end sides of the joining flanges extending parallel to one another). In many cases, laser welding is used for this purpose. The joining flanges of the joining fittings can be end regions adjoining one another in the longitudinal extension direction of the joint, for example end regions of sheet metal workpieces or regions bent or flanged specifically for forming joining flanges of such workpieces. For the end-side welding, the joining flanges are fixed against one another in a suitable manner, for example by means of suitable clamping devices, more precisely until the welding is carried out.

[0004] From the document DE102013107228B3, laser welding of the end faces of the joining flanges of two joining fittings is known, wherein the joining fittings are steel sheet parts. The laser welding method known from this document provides that less energy is input to the central area of ​​the weld and higher energy is input to the edge area adjacent thereto, which is located inside the joint. In order to be able to weld on the desired joint width, the welding laser beam oscillates back and forth transversely to the feed direction. For this previously known method, the different energy introductions required on the cross section of the weld are also introduced by means of the movement of the welding laser beam, more precisely or in the form of: extending the dwell time of the laser beam and / or increasing the energy of the laser beam in the edge area of ​​the weld, in which the welding should be carried out by a higher energy input. It is thereby achieved that the weld zone in the edge area can be introduced relatively deeply into the joint.

[0005] When welding sheet steel parts, the problem mainly arises in the vehicle body area, when the sheet metal is equipped with a metal coating. Here, the metal coating can be an anti-corrosion coating, such as a zinc coating. Usually, this zinc coating is designed as hot-dip galvanizing or electrolytic galvanizing. The problem that arises when joining such sheet metal parts is that the melting point and evaporation temperature of the metal coating are significantly lower than the melting temperature of the steel. The consequence of this is that when two workpieces are fusion-welded, where at least one joining part is a metal coating with an evaporation temperature above the melting temperature of the steel, as is the case, for example, in the zinc coating, the coating material evaporates explosively and spontaneously due to the heat input necessary for fusion welding. In the case of zinc coating, it is also called zinc degassing. The result is an increase in spatter, where parts of the molten weld pool are also drawn out and lead to an increase in the porosity in the weld. This porosity can be explained by the unimpeded degassing of the evaporated zinc. In addition, internal stresses are generated in the weld due to the welding process. In combination with the given diffusion possibilities, the remaining liquid zinc may make the weld brittle due to the so-called "liquid metal embrittlement" (LME). Such welds therefore often fail to meet other strength requirements imposed on the welded components, in particular when vibrations or dynamic loads are involved, since the risk of cracking is increased due to material embrittlement.

[0006] In the welding process known from document DE 10 2013 107 228 B3, the gap size between the joint flanges of the joint fittings is maintained during the fusion welding of galvanized metal sheets. This gap size must not be too large or too small. In order to maintain the gap size over the length of the joint, correspondingly high requirements are placed on the clamping device. In addition, it is inevitable in this method that part of the laser energy is lost, more precisely, the part of the laser beam that passes through the gap between the joint fittings.

[0007] Document WO2016 / 169791A1 discloses a method by which two such joint fittings can be welded to each other in the region of their joint flanges by end-side laser welding, while reducing the problem of zinc degassing. For this previously known method, the weld pool is kept liquid for a longer time by oscillating the laser beam at a frequency between 80 Hz and 1000 Hz transversely to the feed direction. In addition, a certain amount of power is introduced into the weld pool by the laser beam oscillation. Both measures contribute to a controlled degassing process through the weld pool. However, the required welding depth also increases with increasing sheet thickness. As a result, it becomes increasingly difficult to carry out a complete or controlled degassing process when there are two zinc-coated joint fittings, because the zinc travels an increasingly long distance to the surface. Even if the joint fittings can be laser welded on the end side by this method, at least one of the parts has a coating with an evaporation temperature below the melting temperature of the steel, in particular the feed speed is also limited by the necessary laser oscillation transversely to the feed direction. In mass production, more time must be provided for the laser welding process accordingly.

[0008] Therefore, starting from the discussed prior art, the technical problem to be solved by the present invention is to improve the method for end-side laser welding of a joint of two mutually fixed joining flanges, which are two joining parts made of steel, so that welding can be carried out more quickly with a larger feed and more effective coating degassing than in the method known from WO2016 / 169791A1, while avoiding pore formation and LME.

[0009] This technical problem is solved by a method of the type described at the outset, wherein the joining flanges of two joining fittings used in a laser welding process are fixed so as to enclose an angle with each other that is open in a direction away from the joint side subjected to laser action, thereby providing a degassing gap between the joining flanges that expands in the direction of heat introduction, through which evaporation products of the coating material formed by the heat introduction are discharged.

[0010] The term "joint flange" used within the scope of the present invention is that edge section of a joint fitting, via which the joint fitting is connected to the joint flange of another joint fitting. Thus, that section of a joint fitting represents its joint flange, which, starting from the adjoining joint, corresponds to the penetration depth of the material melted by welding.

[0011] For this method, the joint fitting is not fixed in parallel with its mutually facing sides, as is known in the prior art, but is fixed to enclose an angle. The angle opens in the direction away from the joint side to which the laser is applied. Laser welding is performed in the position where the joint flanges are fixed to each other. Due to the angled arrangement of the joint flanges, a degassing gap is provided, which extends outward from the position where the welding seam is currently continuously melted in the depth direction and expands in width. The evaporation products of the coating material formed by the heat introduction are discharged through the degassing gap. This does not mean that no evaporation products are discharged from the coating material in the direction of the laser-loaded side, but that the evaporation products are at least mostly discharged in a controlled manner through the degassing gap. In order to discharge the degassing products, a path is obtained by the aforementioned geometry and size of the degassing gap, which enables the evaporation products to overcome a smaller resistance than degassing through the weld pool. Therefore, at least most of the evaporation products are discharged through the degassing gap, more precisely, away from the joint area. In the method according to the present invention, the total laser energy can be introduced into the material to be melted.

[0012] It is accepted that within the scope of this embodiment, it is described for the first time that the two joining flanges to be welded on the end sides are not arranged parallel to each other. According to the mainstream view, "the parallel arrangement of the joining flanges must have a sufficient width" is a guarantee that welding burn-through will not occur. It was therefore surprisingly determined that even when the joining flanges are arranged at an angle to each other as described above to form a degassing gap, no burn-through is observed at the same laser intensity setting and the quality of the weld formed is significantly better. This is due to the cleverly designed degassing path, which allows the evaporation products of the metal coating to be discharged in the propagation direction of the laser beam and not in the opposite direction (for which the evaporation products must cross the liquid weld pool). However, the joining parts are adjacent to each other in the area of ​​the joint, for example with mutually facing joint edges. The loss of laser energy is thus minimized. Therefore, in this method, it is basically not necessary for the weld pool to remain liquid for a longer time.

[0013] The aforementioned angled arrangement of the mutually facing joining flanges for forming the degassing gap allows a design of the joining flanges in which the joining flanges, in their mutually fixed arrangement, are adjacent to each other only by line contact or approximate line contact for carrying out the joining process. As a result, the evaporation products of the metal coating can already be conducted through the degassing gap when using fusion welding. At the same time, the line contact and the weld pool generated along the line contact form an effective barrier to the evaporation products of the coating. By directing the laser beam at the joints abutting against each other, the coating surface is preheated in the depth direction of the weld seam formed based on the inclined arrangement of the sides of the joining flanges facing each other, which is achieved by the laser beam and its reflection on the sides of the joining parts facing each other and / or by a weld pool "eroded" along the depth, which has a heat front that precedes itself. In this way, the joining flange and in particular the metal coating are heated and brought to the evaporation temperature of the metal coating, and the steel then melts in this area.

[0014] The degassing gap formed by the aforementioned mutual fastening of the joint flanges provides a path through which the degassing products are discharged, which takes place automatically due to the pressure generated during evaporation. In the method according to the invention, the melt is essentially free of evaporation products, so that the weld seam is either completely porous or has very few pores. The quality of the weld seam formed is therefore very good and meets the highest static requirements even under oscillations and dynamic loads. Since the degassing of the metal coating in this method does not take place through the weld pool, in principle the weld pool does not need to remain liquid longer than is required for melting the steel to achieve a controlled degassing process. Based on this, the laser beam can be moved at a correspondingly high feed speed in this method. Studies have shown that the method can be implemented at a feed speed of more than 10 m / min.

[0015] The arrangement of the sides of the joint flanges facing each other to form a degassing gap at an angle can be achieved by the corresponding arrangement of the joint fittings in the straight joint flange. It is also feasible that at least one of the two joint fittings is bent or arched in the area of ​​its joint flange, and the joint of the closed arched portion is a joint fixed to each other on the joint of the other joint fitting for the laser welding process. In addition, it is advantageous that the joint flanges can be clamped in an angled arrangement by simple devices when the joint flanges are arranged with each other. They are different from the prior art and do not need to be clamped on the sides adjacent to each other in parallel. More precisely, one of the two joint flanges can be fixed, and the other joint flange is pressed against the one joint flange in order to form the desired line contact, so as to compensate for possible tolerances.

[0016] The advantage of this method is not only that a particularly good weld quality and a possible high welding speed can be achieved even when welding metal-coated joint fittings, but also that the joint flange only needs to have a width corresponding to the depth of the weld. The joint flange can therefore be kept particularly narrow. This can reduce the weight of the component formed by the joint fitting, for example a vehicle structure. At the same time, the installation space required by such a component is reduced, which is a considerable advantage especially for compact motor vehicles. Due to the mutually inclined arrangement of the joint flanges for forming the degassing gap, they can be formed by curved component edges, which in turn reduces the installation space required by the component.

[0017] The aforementioned advantages of degassing are achieved when the angle enclosed by the joint flanges is very small, for example only 1°, preferably between 6° and 8°. The opening angle of the degassing gap should not be chosen to be too large, so that a weld with a sufficiently deep root can be produced. Therefore, the joint flanges are generally arranged with respect to each other to form a degassing gap so as to form an angle of no more than 20°, since at larger angles the strength is correspondingly reduced.

[0018] For carrying out the laser welding method, it is not necessary to require that the material thickness of the joining parts must have a certain amount. In fact, the certain amount is determined according to other requirements for the component to be manufactured.

[0019] Studies have shown that the degassing process can be facilitated when the laser beam is directed at the joint area of ​​the mutually fixed joint of the two joint flanges at an angle transverse to the feed direction. The reason for this is that more and more reflections occur on the mutually facing surfaces of the joint flanges in the area of ​​the degassing gap, which leads to less energy loss and a correspondingly more intense preheating before the actual melting of the surface area of ​​the metal coating. In addition, it can be observed that when using a laser, energy can be introduced deeper into the material than when not using a laser. According to the assumption, the joint flanges arranged at an angle to each other are combined with the use of a laser to achieve improved reflection properties, which makes it possible to introduce energy deeper into the material at the same laser efficiency compared to conventional methods. Under this influence, it can be achieved that the weld to be formed enters the joint plane by itself. In other words, a uniform weld is formed between two joint accessories arranged at an angle to each other, basically according to the contour curve of the joint accessories. The angle at which the laser beam is tilted transverse to the feed direction should not be greater than 25°. When tilted more sharply, the weld can sometimes no longer be constructed with the necessary depth at a larger feed.

[0020] Since the evaporation products of the metal coating are directed away from the surface impinged by the laser, the laser optics and other adjacent devices are also protected from weld pool splashes etc. However, it is expedient to provide an air flow across the welding beam over the joining area, by which any evaporation products that may have formed on the side are blown away and thus contamination of the laser and adjacent devices is prevented.

[0021] In addition, the laser beam can be reciprocated in an oscillating manner transversely to the feed direction according to the longitudinal extension direction of the joint, as described in WO 2016 / 169791 A1. This measure keeps the weld pool liquid for a longer time and the weld pool dynamics introduced into it have a positive effect on avoiding the formation of pores in the weld. If the laser beam is guided in an oscillating manner transverse to the feed direction, steel parts with a metal coating can also achieve results that meet this requirement, wherein the metal coating has a melting point above the melting point of the steel. By the oscillation of the laser beam and the weld pool dynamics introduced into the weld pool thereby, the continuous phase formed by the metal coating during the fusion welding process is first destroyed and then evenly and therefore finely dispersedly distributed in the weld. The displacement amplitude during this oscillating laser beam movement generally corresponds to two-thirds of the width of the joint surface formed by the mutually fixed joint.

[0022] In addition to the non-penetrating, i.e. vertical arrangement of the laser in the feed direction, the joint zone can also be preheated in the feed direction, more precisely by directing the laser beam at an angle away from the vertical, more precisely obliquely in the feed direction, to the joint zone. In this case, an angle of inclination between 5° and 45° relative to the vertical on the joint zone is considered suitable. Due to this angular position, the laser beam is directed at the joint zone in a penetrating manner in the feed direction. The laser beam then pushes a larger heat front in front of it, which is particularly meaningful when joining joint parts with metal coatings, whose metal coatings have an evaporation temperature that is lower than the melting point of the steel. The metal coating on the upper side of the joint then evaporates at least to a large extent, after which the steel melts. Overall, this reduces the sag of the joint and improves the quality of the weld.

[0023] The present invention is described below according to an embodiment with reference to the accompanying drawings. In the accompanying drawings:

[0024] Figure 1a-1c : Two joint fittings for end-side laser welding ( Figure 1a ) In the initial stage of forming a weld pool at one point in the joint area to start the welding process ( Figure 1b ) and during the duration of welding ( Figure 1c )

[0025] Figure 2a-2c : Before the material starts to melt ( Figure 2a ), in the initial stage of forming the weld pool ( Figure 2b ) and after the welding process is completed ( Figure 2c ) is an enlarged cross-sectional view of the welding process shown in FIG. 1 ,

[0026] Figure 3a-3c : With series Figure 1a-1c Corresponding welding diagrams for joint fittings with different geometric designs and

[0027] Figure 4 :With Figure 3a-3c The welding diagram corresponds to the macroscopic grinding diagram of the two joint parts.

[0028] Figure 1a The edge sections of two joint fittings 1, 1.1 are shown, the rest of which is not shown in detail. The joint fittings 1, 1.1 are sheet steel parts, which are used, for example, for the production of structural parts for vehicles. The joint fittings 1, 1.1 are hot-dip galvanized and therefore have a metallic coating, namely a zinc coating. Figure 1a In the position of the two joint fittings shown in Fig. 1, the joint edges 2.2, 2.3 facing each other abut against each other. Therefore, the two joint fittings 1, 1.1 are in line contact with each other. Figure 1aThe upper section of the shown part of the middle joint fitting 1.1 forms a joint flange. The extension of the joint flange 3, 3.1 is Figure 1a The two joint fittings 1, 1.1 are arranged at an angle of about 10° to each other in order to achieve the aforementioned line contact on the joint edges facing each other. As a result of this arrangement, the surfaces 4, 4.1 of the joint fittings 1, 1.1 facing each other are angled to each other and enclose a gap 5. The gap width increases from the joint edges 2.2, 2.3 fixed to each other in abutting relationship in the direction away from the joint 2, 2.1.

[0029] exist Figure 1a In the arrangement of the two joint fittings 1, 1.1 shown in the figure, the two joint fittings 1, 1.1 are fixed in a clamping device (not shown) for the purpose of producing the end-side welding for joining the two joint fittings 1, 1.1. The joint fittings 1, 1.1 are preferably fixed to each other in such a way that the joint edges 2.2, 2.3 abutting against each other are under a certain preload.

[0030] In order to join the two joining parts 1, 1.1 to one another, the laser beam 6 is directed toward the joint 2, 2.1 (see Figure 1b ). The laser beam 6 is defocused. However, laser focusing can also be considered at this location. The diameter of the laser spot is Figure 1b This is clearly visible in the diagram of . Due to the heat input to the two joints 2, 2.1, the zinc coating on the joints 2, 2.1 evaporates, after which the steel begins to melt. This also applies to this location, where the zinc coating is only present on the mutually facing sides 4, 4.1 of the joint fittings 1, 1.1 and the zinc coating is no longer present on the end sides of the joints 2, 2.1, for example due to previous processing steps, such as trimming of the joint fittings. The weld pool is denoted by the reference numeral 7. Due to the action of the laser beam and the continuous heat input caused by it, the weld pool 7 autonomously erodes from the joints 2, 2.1 into the joint fittings 1, 1.1, that is, the weld pool finds its own path. The expansion of the weld pool 7 in the depth direction, which is located forward, forms a heat front, which heats the zinc coating on the mutually facing sides of the joint fittings 1, 1.1. Since the evaporation temperature of the zinc coating is lower than the melting temperature of the steel, the zinc coating begins to evaporate before the steel melts or the process is completely or partially completed. Through the gap 5, also referred to as the degassing gap in the present embodiment, the evaporated products of the zinc coating are conducted along the path with the least resistance. This is a path through the degassing gap 5 away from the weld pool 7, such as Figure 1b As shown by the block arrows in the figure. Since the evaporated products are guided along the direction of diffusion of the weld zone into the depth of the weld, the weld zone is similar to self-erosion into the depth to a certain extent. In this method, the work of constructing the weld in depth does not need to overcome the counterflow of the evaporated products of the metal coating.

[0031] Figure 1c The joint region is shown after welding has been substantially completed. It can be seen that the weld pool 7 has penetrated sufficiently deeply into the joint parts 1 , 1 . 1 . The zinc coating on the mutually facing sides 4 , 4 . 1 of the joint parts 1 , 1 . 1 also evaporates out of the weld pool 7 through the degassing gap 5 .

[0032] series Figures 2a to 2c The above-described method is once again described with reference to an enlarged detail of the region of mutually adjoining connection edges 2.2, 2.3 of two connection fittings 1, 1.1. Figures 1a to 1c The joining method described in Figures 2a to 2c In the embodiment of the invention, the laser beam 6.1 is directed obliquely transversely to its feed direction at the two joints 2, 2.1. As mentioned above, although the two joint parts 1, 1.1 are in contact with each other in the area of ​​the joint edges 2.2, 2.3 facing each other, there are actually small gap sections between the two joint parts 1, 1.1 due to the inevitable material inhomogeneities. This causes parts of the laser beam to pass through these openings (such as Figure 2a ) and reflected on the mutually facing surfaces 4, 4.1 inside the degassing gap 5. The penetration of the laser beam on the surfaces 4, 4.1 (due to the tilted laser beam 6.1) heats the zinc coating 8, 8.1 on the mutually facing surfaces of the joint parts 1, 1.1. Figure 2b The laser beam ends its passage through the inevitably existing gap when the material begins to melt in the area of ​​the mutually abutting joint edges 2.2, 2.3 (shown in FIG) and the weld pool 7 is formed. Due to preheating and the heat front extending around the weld pool 7, the zinc coating 8, 8.1 in the immediate vicinity of the weld pool 7 has already melted and usually either completely or at least largely evaporated, after which the weld pool melts in the area with the steel. This is particularly the case in this case, when the zinc coating 8, 8.1 does not extend or only partially extends in the mutually facing joint edges 2.2, 2.3 of the joining parts 1, 1.1 and therefore extends primarily on the mutually facing surfaces 4, 4.1 of the joining parts 1, 1.1. This can be achieved, for example, by a pre-trimming process of the corresponding joining parts 1, 1.1 on their end sides. Figure 2b The dashed line shows the isotherm I, which shows the evaporation temperature of the zinc coating 8, 8.1. The temperature of the weld pool 7 is higher than the temperature of the isotherm I shown, which precedes the penetration of the weld pool 7 in the depth direction. Accordingly, before the weld pool 7 diffuses, the zinc coating 8, 8.1 evaporates at least partially, after which these parts of the steel melt. The evaporation products are led out of the weld pool 7 via the path obtained by the degassing gap 5, as shown in FIG. Figure 2b As shown schematically.

[0033] Figure 2c The weld seam formed is shown. Figure 2cThe weld seam depth shown in is at the same time the width of the joint flange 3 , 3 . 1 as part of the joint fitting 1 , 1 . 1 .

[0034] series Figures 3a to 3c The joining of two further joining fittings 1.2, 1.3 is schematically shown. Figures 1a to 1c In the embodiment of the invention, the joint fittings 1, 1.1 are both designed flat and arranged at an angle to each other, while the joint fittings 1.2, 1.3 of the joint fitting 1.3 are designed to be curved in the area of ​​their joint flanges 3.2. In this embodiment, the degassing gap is provided by the curved structure of the joint flange 3.2 in that a line contact between the joint fittings is formed at their curved ends. However, it is also conceivable at this location that the two joint fittings are designed to be curved and are fixed to each other oppositely by means of line contact at the corresponding outer radius ends or curved ends. Welding process and series Figures 1a to 1c or Figures 2a to 2c The same is implemented as described in .

[0035] Figure 4 The macroscopic grinding image of a weld seam is shown, which is produced according to the welding method described in the previous figure. The image shows that the molten material has an ideal shape and is free of pores.

[0036] In order to check the load capacity of such a weld, the bumper is made of two zinc-coated sheet steel parts welded to each other at the end. The component is a profile with a channel-shaped cross section, the open side of which is closed by a steel sheet. The two parts are welded to each other at the end, as described in the previous figure. The thickness of the sheet steel part used is 2 mm. The welding depth is between 2.5 mm and 3 mm. Drop tests carried out on this component with a drop height of 3 m and a drop mass of more than 500 kg did not lead to the destruction of the weld. However, in all the tests carried out, the base material used failed at several locations, but the weld did not fail. This result is surprising, because in other cases, the weld is usually a weak point for such components, especially under dynamic loads.

[0037] The present invention is described based on the embodiments. Without departing from the scope of the claims, those skilled in the art will obtain other various feasible solutions for implementing the present invention.

[0038] Reference numerals list

[0039] 1, 1.1, 1.2, 1.3 Joint accessories

[0040] 2.2.1 Connector

[0041] 2.2, 2.3 Joint edges

[0042] 3, 3.1, 3.2 Joint flange

[0043] 4.4.1 Surface

[0044] 5 Gap / Degassing Gap

[0045] 6.6.1 Laser beam

[0046] 7. Welding Pool

[0047] 8.8.1 Zinc coating

[0048] I isotherm.

Claims

1. A method for end-side laser welding of a joint (2, 2.1) of two mutually fixed joining flanges, the two mutually fixed joining flanges belonging to two joining fittings (1, 1.1, 1.2, 1.3) made of steel, wherein at least one of the two joining fittings has a metal coating, the metal coating having an evaporation temperature below the melting temperature of the steel, wherein: Each joining flange has two side faces facing opposite directions, the two side faces terminate at the end sides of the joining flange, each end side extends between the two side faces, and wherein one of the two end sides of each joining flange is positioned to face one of the two end sides of another joining flange, the method comprising: the joining flanges (1, 1.1, 1.2, 1.3) of the two joining fittings (1, 1.1, 1.2, 1.3) are arranged during the laser welding process to enclose an angle between them that is open in the direction of the joint side facing away from the laser beam loading the end side of the laser welding joint, thereby providing a degassing gap (5) that expands in the direction of heat introduction between the joining flanges (3, 3.1, 3.2), and conducting evaporation products of the coating material (8, 8.1) formed due to the heat introduction through the degassing gap; wherein, when the joint flanges of the two joint fittings are arranged, the two joint fittings are adjacent to each other in the region of the joint edges facing each other of the joint, and a gap is formed between the joint edges facing each other in the longitudinal extension direction of the joint; and Laser welding the end faces of the joining flanges by means of a laser beam, the feed direction being in the longitudinal extension direction of the joint, the laser beam being oriented obliquely transversely to the longitudinal extension direction of the joint, so that a weld seam is formed in the connection region of the joint connecting the two joining flanges to one another; A portion of the laser beam passes through the slit opening and is reflected on the mutually facing sides of the two joining flanges in the degassing gap, thereby heating the metal coating of at least one of the two joining parts in the area within the degassing gap, so that at least most of the metal coating melts or at least most of it evaporates, and then the weld pool and the steel material in this area in the degassing gap melt.

2. The method according to claim 1, characterized in that The joining flanges (3, 3.1, 3.2) are fixed to one another in the region of their mutually facing joint edges (2.2, 2.3) by means of line contact in order to carry out laser welding.

3. The method according to claim 1, characterized in that The joint flanges (3, 3.1, 3.2) are fixed to each other at an angle of between 1° and 20°.

4. The method according to claim 1, characterized in that The laser spot striking the joint (2, 2.1) is arranged such that its diameter is greater than the maximum gap width between the joining flanges (3, 3.1, 3.2) fixed to one another in the region of the joint (2, 2.1), the degassing gap (5) gradually increasing in width from the maximum gap width.

5. The method according to claim 1, characterized in that The laser beam (6.1) is directed to the joining area of ​​the joint (2, 2.1) at an inclination angle of no more than 25 degrees transversely to the feeding direction.

6. The method according to claim 1, characterized in that On the side of the joint impinged by the laser beam, an air flow is provided which flows transversely to the direction of the laser beam and is guided through the laser beam.

7. The method according to claim 1, characterized in that The laser beam oscillates back and forth transversely to the feed direction according to the longitudinal extension direction of the joint.

8. The method according to claim 7, characterized in that The oscillation frequency of the laser beam does not exceed 1000 Hz.

9. The method according to claim 7, characterized in that The displacement amplitude of the oscillating movement of the laser beam does not exceed two thirds of the width of the joint surface formed by the mutually fixed joints.

10. The method according to claim 1, characterized in that The joint (2, 2.1) is designed to preheat the melted joining zone gradually in the feed direction before melting.

11. The method according to claim 10, characterized in that The laser beam is directed towards the joining zone penetratingly at an angle of between 5° and 45° relative to the vertical.

12. The method according to claim 1, characterized in that The metal coating of at least one joint fitting is a zinc coating (8, 8.1).

13. The method according to claim 1, characterized in that The width of the joining zone to be melted is smaller than the width of the joint surface formed by the mutually fixed joints (2, 2.1), and the laser beam (6, 6.1) is guided in such a way that the outer edge areas are not melted at the two joints (2, 2.1) in order to form a weld pool support in each case.

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