Laser welding process

Abstract

Title: Laser welding process Laser welding process, in which a weld bead (30) is produced by a laser on a target from a starting zone (34) to a target zone (37) by sending laser light in a targeted manner onto the target from the starting zone (34) to the target zone (37), characterized in that the laser light is distributed in the starting zone (34) and / or in the target zone (37) of the weld bead (30) into a main spot (35, 39) and at least one auxiliary spot (36, 40) for heating an environment in the area of ​​incidence of the main spot (35, 39) on the target and in that during the welding operation between the starting zone (34) and the target zone (37) only a main spot (41) is formed which is guided onto the target along the weld bead (30) Figure for the abstract: Fig. 2a

Description

Title of the invention: Laser welding process State of the art

[0001] A method for welding parts using a laser beam is known from DE 10 2011 004 116 A1. For this purpose, the laser beam moves along a junction zone of the parts, the material of the parts, particularly metallic materials, being melted in the junction zone. A second, secondary laser beam is also provided, which heats a zone downstream of the melt. These measures can improve the welding result.

[0002] According to WO 2011 / 151818 Al, a laser system is known in which, by means of a coherent beam combination (Coherent Beam Combining), therefore with phase modulation of the individual beams, a phase optical grating and thus a laser radiation pattern can be produced. Description of the invention

[0003] The invention relates to a laser welding process, in which a weld bead is produced by a laser on a target from a starting zone to a target zone, by sending laser light in a targeted manner on the target, going from the starting zone to the target zone, characterized in that the laser light is distributed in the starting zone and / or in the target zone of the weld bead into a main spot and at least one auxiliary spot for heating an environment in the area of ​​incidence of the main spot on the target and in that during the welding operation only a main spot is formed between the starting zone and the target zone, which is guided on the target along the weld bead.

[0004] The laser welding process according to the invention has the advantage of producing a main spot and at least one auxiliary spot of a laser beam only in a start zone and an end zone of a weld bead.

[0005] Experience has shown that improving the welding result is achieved by using a main laser beam and one or more laser beams, particularly in the start and end zones of the weld bead. This is because, in the start zone, a significant temperature rise occurs when the laser beam is activated at the beginning of the welding operation, resulting in a steep temperature gradient around the weld point. During a sudden heating at the beginning of the fusion operation, particularly localized heating, metals can evaporate, creating what are known as weld spatters in liquid or solid metallic particles, which are expelled from the molten metal pool. The quality of the The weld bead is weakened, and weld spatter can be deposited near the weld bead, potentially leading to unintended electrical contacts between current-carrying tracks. The auxiliary laser beam reduces this temperature gradient, and by heating the area around the main spot at the beginning of the weld pool, such weld spatter is very effectively prevented.

[0006] Similarly, the sudden interruption of a laser beam at the end of the welding operation results in a steep temperature gradient. If the weld pool cools too rapidly at the end of the weld bead, a so-called weld crater can form. Such a weld crater can significantly reduce the quality of the weld bead. Uniform heating by auxiliary spots all around the main spot can very effectively prevent such a weld crater. This is because the auxiliary laser beam, or the effect under the auxiliary laser, heats the area surrounding the main spot, resulting in a temperature gradient around the weld point that is itself flatter than when the total laser power is concentrated on a single main spot.

[0007] The aforementioned damage to the weld bead occurs outside the start zone and the target zone with a lower probability, making it possible to concentrate the laser power on the main spot, which performs the welding operation. This is because, during continuous welding, the heat flux from the weld point into its surroundings is already sufficient to provide adequate heat input to the immediate environment of the weld point and to maintain a limited temperature gradient. Therefore, it is advantageous to concentrate all available laser power on the weld point itself.

[0008] It is therefore advantageous to fuse the auxiliary spot with the main spot after the start zone of the weld bead and to reform one or more auxiliary spots only before the end zone of the weld bead. This allows the advantages of distributing a laser beam into a main spot and at least one auxiliary spot in the start and end zones to be utilized, while the full laser power is available to perform the welding operation, and the welding operation can therefore be carried out in the shortest possible time. This avoids defects, particularly at the ends of the weld bead, while also allowing the welding operation to be performed smoothly and reliably.

[0009] According to an improvement, it is advantageous to form the main spot and at least one auxiliary spot by means of a laser using an optical unit that can be controlled for a combination of coherent beams. This allows for a simple shape of the main spot and the auxiliary spot(s). In particular, it is possible to dynamically create the spots so that the auxiliary spots approach and converge with the main spot, and then, in a zone at the end of the weld bead, diverge again from the main spot. An additional laser module is then not required to create the auxiliary spots.

[0010] To properly form the weld bead, it has been found that a number between four and twenty auxiliary spots, in particular between four and eight auxiliary spots, provides advantages with regard to a uniform distribution of heat.

[0011] It is also advantageous to shape the length of a starting zone or target zone so that this length represents a maximum of five times, and in particular twice, the width of the weld bead. This allows the use of auxiliary spotlights to be limited to an area where this distribution offers advantages.

[0012] It is also advantageous that the main spot has a diameter of 50 to 150 pm, in particular 75 to 100 pm, and the auxiliary pots a diameter of 25 pm to 150 pm, in particular 50 to 100 pm, since by choosing this width a reliable weld bead can be formed between metallic parts.

[0013] For a welding operation start zone, a distance of between 100 pm and 400 pm between the main spot and the auxiliary spot has been found to be advantageous. To enable dynamic guidance of the auxiliary spot relative to the main spot, the speed of movement of the auxiliary spots can be independent of that of the main spot.

[0014] According to one embodiment, several auxiliary spots are produced which are arranged respectively at a distance given in advance from the center of the main spot, in particular at a distance between 100 and 450 pm, most particularly at a distance of 125 and 175 pm.

[0015] For certain applications, it can also be advantageous for the main spot and auxiliary spots to be directly adjacent or to overlap at the edges so as to form a defined pattern consisting of the main and auxiliary spots. This ensures a given quality of the welded joint in advance. The main spot has twice, and in particular at least five times, the radiant power of at least one auxiliary spot, so that the welded strip in a central area of ​​the main spot reaches its greatest depth.

[0016] It is also advantageous for the diameter of at least one auxiliary spot on the target to vary with time or with a displacement of the main spot. In order to obtain adaptation to a desired conformation of the weld bead. The invention aims to in addition to an installation to carry out the process, in which a control unit is provided, which locates the start zone and / or the target zone of the weld bead.

[0017] Corresponding advantages also arise from a computer program product comprising instructions which, when the program is executed by a computer, cause the installation to perform a process according to the invention.

[0018] Drawings.

[0019] Examples of embodiments of the invention are shown in the drawing and are explained in more detail in the description that follows.

[0020] To the drawings:

[0021] Fig. 1 represents an installation according to the invention for carrying out the process;

[0022] Figure 2a represents a first example of an embodiment for the distribution of spots main and auxiliary components along the weld bead;

[0023] Fig. 2b shows a detail of the distribution between main spot and auxiliary spots according to Fig. 2a;

[0024] Figures 3 to 6 represent various embodiment examples for an auxiliary and main spot conformation in the start zone and respectively the target zone of the weld bead.

[0025] Method of execution of the invention

[0026] Figure 1 represents a laser 10 of a laser welding installation, the laser 10 directing a laser beam 11 onto a target 12. The target 12 consists, for example, of metallic elements arranged side by side, which are to be joined by a weld bead 13 indicated by a dashed line. For this purpose, the laser beam 11 produces a molten pool 14 in the material of the target 12, which, upon cooling, creates the weld bead 13 and joins the individual metallic elements of the target together. By means of optics 15, preferably controllable, the laser beam 11 is directed precisely onto the target 12. The laser beam 11 is thus controlled by a control device 16 which guides the laser beam 11 from a starting point 17 of the weld bead 13 to an ending point 18 of the weld bead 13.In one embodiment, observation of the welding operation can be carried out by a camera 19 so that control by the control device 16 can be carried out according to the welding operation taken by the camera 19. The laser beam is guided for this purpose in the direction 20 of the arrow from the starting point 17 to the ending point 18.

[0027] The control device 16 is designed to perform, particularly in a starting zone near the starting point 17 and in an ending zone near the ending point 18 of the weld bead, a variable distribution of the laser beam energy between a main spot and at least one auxiliary spot, or where applicable, several auxiliary spots. This eliminates disruptive welding effects. beginning and end of weld bead 13. Because a beam conformation deviating from a central spot is applied only at the beginning and end of the welding operation, the rest of the weld bead is not affected by the variable energy distribution. Outside the beginning and end zones, the laser power is instead concentrated onto a main beam. This allows the beam conformations in the beginning and end zones of weld bead 13 to be adapted to different operating requirements and different materials used, without requiring dismantling of the installation.

[0028] In one embodiment, several laser light sources having a steerable optical unit can be concentrated, each assigned either to a main spot or to a main spot and one or more auxiliary spots. In another embodiment, this can also be achieved with only one laser light source in which, in a suitable manner, the laser beam produces either only the main spot or one or more auxiliary spots in addition to the main spot.

[0029] In an advantageous embodiment, beam formation with a dynamic or highly flexible energy distribution is achieved using a fiber laser with individual phases, which are superimposed by coherent beam combination, a process known as coherent beam combining. By means of phase modulation of the individual beams, a phase-shifting optical grating is thus formed, enabling not only beam motion but also beam conformation, focus formation, and intensity modulation of the laser beam. In particular, it is possible to create a primary spot and one or more auxiliary spots for this purpose. Rapid beam matching in the megahertz range is thus possible.

[0030] Figure 2a shows an example of an embodiment of a weld bead 30 extending from a starting point 31 to an ending point 43. A starting zone 34 is delimited by a dashed line 33 relative to the starting point 31, which preferably represents several times, at least twice, in particular at least five times, and optionally also six times, the width of the weld bead 30. In the vicinity of the weld bead 32, Figure 2a symbolically represents a pattern of the laser beam in which a main spot 35 is surrounded by several auxiliary spots 36.

[0031] Correspondingly, a target zone 37 of the weld bead 32 is represented in the vicinity of the end point 43 by a dashed line 38, symbolically representing an alternative pattern for the distribution between a main spot 39 and an auxiliary spot 40. Along the weld bead 30, between the dashed lines 33 and 38, a normal zone of the weld bead 30 is represented, in which welding is carried out only with a main spot 41.

[0032] In a first embodiment, switching can be made directly between the represented patterns of the laser distribution at the boundary between the starting zone 34 and the normal zone 42, as well as between the normal zone 42 and the target zone 37. In an alternative embodiment, however, it is also possible for the auxiliary spots in the starting zone 34 to move closer to the main spot 35 as they move further and further away from the starting point 31, such that the single main spot 41 is created due to the approach at the transition to the normal zone. Correspondingly, the auxiliary spots, from the main spot at the transition 38 to the end zone 37, can be dynamically decoupled from the main spot 35.

[0033] Figure 2b shows the main and auxiliary spots of Figure 2a in detail. The corresponding distribution on Figure 2b is preferably arranged to prevent weld spatter at the beginning of the welding operation. By heating the environment, the temperature gradient of the main spot 35 relative to its environment is lowered by the auxiliary spots 36, thus preventing the formation of weld spatter. The configuration of parameters, such as the size and power of the main spot 35 and the auxiliary spots 36, depends on the conformation of the weld bead of the material or materials to be welded; for example, when using different materials, it depends on the conformation of the material, such as its surface properties, as well as other environmental parameters.In particular, the following can be modified: the number of auxiliary spots 36, a focal diameter 50 of the main spot 35, a focal diameter 51 of the auxiliary spots 36, a distance 52 between the main spot 35 and the auxiliary spot 36, the radiation power of the main spot 35 and the radiation power of the auxiliary spots 36. The speed at which the main spot 35 and the auxiliary spots 36 move on the target 12 can also be adjusted.

[0034] It has proven advantageous for the number of auxiliary spotlights to be between 4 and 20, in particular between 4 and 8, for the focal diameter 50 of the main spotlight to be from 50 to 150 pm, in particular from 75 to 100 pm, for the focal diameter 51 of the auxiliary spotlights to be from 50 to 150 pm, in particular from 50 to 100 pm, for the distance between the main spotlight 35 and the auxiliary spotlight 36 to be from 100 to 300 pm, in particular from 100 to 200 pm, for the power of the main spotlight to be from 100 watts to 12 kilowatts, in particular from 500 kilowatts to 10 kilowatts, and for the power of the auxiliary spotlight to be from 100 watts to 6 kilowatts, in particular from 500 watts at 5 kilowatts. A main and auxiliary spot advance speed is preferably between 1 and 200 mm per second, and in particular between 5 and 100 mm per second.

[0035] The proposed distance between the main spot and auxiliary spots can be reduced from the starting point 31 until passing through the normal zone 42 so that, during movement along the weld bead 32 to be created, the speeds of The movement of the main and auxiliary spotlights should be different in order to make it possible to bring the auxiliary spotlights closer to the main spotlight.

[0036] Fig. 3 represents a variant of the pattern in which, from a main spot 60, auxiliary spots 61, 62 are provided in two directions respectively, so that the auxiliary spots 61, 62 make an angle 65 at the apex of which the main spot 60 is arranged.

[0037] In another embodiment in [Fig.4], a regular grid of auxiliary spots 64 can also be constituted between which a main spot 63 is provided, where appropriate on a front side of the grid field in the direction of the welding progression.

[0038] For an end zone of the welding operation, as shown in [Fig. 5], in a first embodiment, a so-called trailing beam is provided, in which a main spot 70 precedes, followed by two or more auxiliary spots 71, 72, in this case two auxiliary spots. The molten pool 73 is shown in the vicinity of the main spot 70 and the auxiliary spots 71, 72, with the main spot moving along the arrow 74 until the weld bead ends. In another embodiment, it is also possible to exchange the position of the main spot and the auxiliary spots, respectively, with respect to the welding direction. This makes it possible to increase the depth of the weld bead in a stepped manner using the partial beams.

[0039] Following the auxiliary spots, at the end of the weld bead, comes the main spot, as shown in [Fig. 5], so that it is possible to deflect or slow down the flow of the molten pool in order to minimize a key parameter for the formation of a weld crater. In this case as well, the distance to the main spot and the power of the auxiliary spots must be adjusted experimentally if necessary.

[0040] An alternative embodiment, particularly for advancing to the end of the weld bead, is shown in [Fig. 6], where a main spot 80 develops from the beginning of the end zone to the end of the weld bead, and the laser stops in the direction 81 of the arrow. In this embodiment, four auxiliary spots 82 are formed first, then seven auxiliary spots 83, and then eight auxiliary spots 84. These auxiliary spots move further away from the main spot 80 as one approaches the end of the weld bead and gain increasing power relative to the main spot. Alternatively, for example, only six, and then nine auxiliary spots are possible.Thus, during the formation of the 84 auxiliary spots, a uniform heating of the environment of the main spot occurs in order to reduce a thermal gradient, and thus, when the main spot is switched off, the formation of a weld crater is avoided. Preferably, 4 to 20 auxiliary spots are planned, particularly 4 to 8 auxiliary spots. The distance from the end to the main spot is from 100 to 400 pm, particularly from 100 to 300 pm.

Claims

Demands

1. A laser welding method, wherein a weld bead (30) is produced by a laser (10) on a target (12) from a starting zone (34) to a target zone (37) by directing laser light from the starting zone (34) to the target zone (37) onto the target (12), characterized in that the laser light is distributed in the starting zone (34) and / or in the target zone (37) of the weld bead (30) into a main spot (35, 39) and at least one auxiliary spot (36, 40) for heating an environment in the area of ​​incidence of the main spot (35, 39) on the target (12), and in that during the welding operation, only a main spot (41) is formed between the starting zone (34) and the target zone (37), which is guided onto the target (12) along the weld bead. (30) of welding.

2. A method according to claim 1, characterized in that the main spot (35, 39) and at least one auxiliary spot (36, 40) are formed by a laser (10) by means of an optical unit that can be controlled for a coherent beam combination.

3. A method according to any one of the preceding claims, characterized in that between four and 20, in particular between four and eight, auxiliary spots are formed.

4. A method according to any one of the preceding claims, characterized in that a length of the starting zone (34) and / or the target zone (37) represents at most five times, in particular twice, the width of the weld bead (30).

5. A method according to any one of the preceding claims, characterized in that the main spot (35, 39) has a diameter of 50 to 150 pm, in particular 75 to 100 pm, and the auxiliary pots (36, 40) have a diameter of 25 pm to 150 pm, in particular 50 to 100 pm.

6. A method according to any one of the preceding claims, characterized in that several auxiliary spots (36, 40) are produced, which are arranged respectively at a given distance in advance from the center of the main spot, in particular at a distance between 100 and 450 pm, most particularly at a distance of 125 and 175 pm.

7. Method according to claim 6, characterized in that the distance of the auxiliary spots to the center of the main spot and / or a speed of movement of the auxiliary spots varies with time or with a movement of the main spot.

8. A method according to any one of claims 1 to 5, characterized in that the main spot and auxiliary spots are directly adjacent or intersect at the edges so as to form a defined pattern made up of main and auxiliary spots.

9. A method according to any one of the preceding claims, characterized in that the main spot has twice, in particular at least five times, the radiating power of at least one auxiliary spot.

10. A method according to any one of the preceding claims, characterized in that the diameter of at least one auxiliary spot on the target varies with time or with a displacement of the main spot.

11. Installation for carrying out the process according to any one of the preceding claims comprising a laser (10) for combining coherent beams and comprising a control unit for locating the starting zone (34) and / or the target zone (37) of the weld bead (30).

12. Computer program product comprising instructions which, when the program is executed by a computer, cause the installation according to claim 11 to perform the process according to any one of claims 1 to 10.

Images