Method and device for laser welding

Abstract

The invention relates to a method for the laser welding of at least two workpieces (10, 12), comprising the steps of: - providing a first workpiece (10) and a second workpiece (12); - producing at least one laser spot (16) on the first workpiece (10) and / or the second workpiece (12), wherein the at least one laser spot (16) has an in particular circular core region (18) and an in particular annular ring region (20); - moving the at least one laser spot (16) at a welding speed (v) on the first workpiece (18) and the second workpiece (20) in order to produce a molten bath (22); - changing a power distribution between the core region (18) and the ring region (20) depending on a position of the at least one laser spot (16) on the first workpiece (10) and / or on the second workpiece (12) and / or depending on the welding speed (v) of the at least one laser spot (16) and / or depending on at least one welding variable at the position of the at least one laser spot (16).

Description

[0001] Title: Method and device for laser welding

[0002] Description

[0003] The invention relates to a method and a device for laser welding. Furthermore, the invention relates to a computer-readable storage medium, a computer program, and a data carrier signal.

[0004] It is known that in laser welding the laser power is increased when machining along a preferred direction in order to reduce the process time. It is also known that the laser power is reduced when machining transversely to the preferred direction, e.g. when cornering, so that a constant power input into the workpiece is guaranteed due to a reduced welding speed or feed speed. This is intended to ensure that the welding depth remains constant even at different welding speeds. The object of the invention is to provide a method for laser welding which has short process times and consistent machining quality, in particular when machining along and transversely to the preferred direction.

[0005] The object underlying the invention is achieved by a method having the features of claim 1. The method for laser welding at least two workpieces comprises the following steps:

[0006] Providing a first workpiece and a second workpiece .

[0007] Generating at least one laser spot on the first workpiece and / or the second workpiece, wherein the at least one laser spot has a, in particular circular, core region and a, in particular annular, ring region preferably surrounding the core region.

[0008] Moving the at least one laser spot at a welding speed across the first workpiece and the second workpiece to create a molten pool. Heat is preferably introduced into the first workpiece and / or second workpiece, so that the workpieces are joined together along a weld seam.

[0009] Changing a power distribution between the core region and the ring region depending on a position of the at least one laser spot on the first workpiece and / or on the second workpiece and / or depending on the welding speed of the at least one laser spot and / or depending on at least one welding variable at the position of the at least one laser spot.

[0010] By changing the power distribution, the welding process can be adjusted to changing welding conditions, such as the position of the laser spot, the welding speed, or the welding variables. Consequently, in addition to a consistent welding depth, consistent welding quality can be ensured, even under changing welding conditions. This process therefore offers a particularly high degree of flexibility in laser welding. Furthermore, a reduction in spatter and pores can be achieved.

[0011] It is advantageous to adjust the power distribution during laser welding. This allows real-time response to changing welding conditions.

[0012] It is also advantageous if the switching time between successive power distributions is a maximum of 20 ms. Due to this short switching time, even short welding processes, especially shorter than 1 s, can be effectively adapted.

[0013] According to a development of the method, the at least one laser spot can be generated by means of an optical multifiber. The optical multifiber can be designed as a 2-in-1 fiber. The 2-in-1 fiber can preferably have a fiber core diameter ratio of core to ring in a range between 1:2 and 1:9, in particular between 1:4 and 1:6. The fiber core diameter is preferably 50 gm and the fiber ring diameter is preferably 200 gm.

[0014] An advantageous development of the invention provides that the adjustment of the power distribution between the core region and the ring region is carried out by means of a wedge switch (cf. e.g. in WO2011124671A1).

[0015] The wedge switch can preferably be moved over the entire range from 0 to 100% by means of a stepper motor configured for this purpose over a maximum of 80 separately controllable steps (or positions), in particular over a maximum of 60 steps. The step duration between two adjacent steps or positions can, due to the step spacing, be, for example, a maximum of t = 360 gs. In this way, the wedge switch can be configured such that the switching time between successive power distributions is a maximum of 20 ms.

[0016] An alternative development of the invention provides that the power distribution between the core region and the ring region is adjusted by splicing a first input fiber with a core region of a multifiber and at least one second input fiber with at least one ring region of the multifiber. Accordingly, the core region and the ring region are fed from different laser modules (see, for example, WO2014118516A1).

[0017] The welding variable preferably has one or more, in particular all, of the following variables: material of the first workpiece and / or of the second workpiece and / or workpiece geometry of the first workpiece and / or of the second workpiece and / or gap width between the first workpiece and the second workpiece and / or surface quality, in particular average roughness, of the first workpiece and / or of the second workpiece and / or occurrence and / or amount of spatter during laser welding and / or position tolerances, in particular lateral component offset, of the first workpiece and / or of the second workpiece and / or total power during laser welding and / or focus position of a laser beam and / or beam diameter of a laser beam on the first workpiece and / or the second workpiece and / or intensity of a laser beam and / or fluence of a laser beam.

[0018] If spatter occurs, a material-dependent optimum value can be set for the power distribution between the core and ring areas. For a material such as copper, this is a core-to-ring power ratio in a range between 20:80 and 50:50. It is advantageous if the optimum value is adjustable.

[0019] It is advantageous if the at least one welding variable is recorded during laser welding by means of a measuring device, in particular an optical one. The process can therefore be adapted as needed in real time. The measuring device can preferably be designed as a camera-based sensor system, in particular VisionLine Detect. The position and position deviations of individual parts to be welded can be recorded by means of the measuring device. Alternatively, an interferometrically based sensor system, in particular VisionLine OCT Detect, can also be used. An advantageous development of the invention provides that when the power distribution of the core region and the ring region of the at least one laser spot is changed, a total power as the sum of the power of the core region and the ring region of the at least one laser spot is also changed.Accordingly, the process can also be individually adapted to local welding requirements or joining situations.

[0020] A further advantageous development of the invention provides that, when the movement speed of the laser spot is reduced, the power distribution is changed in such a way that the average laser power density in the core area is reduced and / or the average laser power density in the annular area is increased. Accordingly, a consistent welding result can be achieved even when cornering tightly or slowly.

[0021] A further advantageous development of the invention provides that, when the movement speed of the laser spot is increased, the power distribution is changed in such a way that the average laser power density in the core area increases and / or the average laser power density in the annular area decreases. Accordingly, a consistent welding result can be achieved even during fast longitudinal movements.

[0022] It is advantageous if, at the start of a laser processing operation, the power distribution is set such that the average laser power density in the core area is greater than the average laser power density in the ring area. It is additionally or alternatively advantageous if, at the end of a laser processing operation, the power distribution is set such that the average laser power density in the core area is smaller than the average laser power density in the ring area. This makes it possible to achieve an optimal welding result at the start, in particular through less spatter and short process times, or at the end, in particular through fewer pores and short process times.

[0023] It is also advantageous if the power distribution is adjusted such that the average laser power density oscillates between the core region and the ring region. Consequently, melt pool dynamics can be improved.

[0024] A further advantageous development of the invention provides that, for improved gap bridging, the laser power density is increased in the ring region and / or decreased in the core region depending on the gap width between the first workpiece and the second workpiece. The larger the gap width, the greater the laser power density in the ring region and / or the lower the laser power density in the core region. Consequently, an optimal joining result can be achieved even with a large gap width between the first and second workpiece.

[0025] Preferably, for improved gap bridging between the first workpiece and the second workpiece, the power distribution is changed such that an average laser power density in the core region is reduced and / or an average laser power density in the ring region is increased.

[0026] It is also advantageous if changing the

[0027] Power distribution between the core area and the ring area is carried out using artificial intelligence and / or machine learning.

[0028] It is advantageous if the core region has a plurality of core section regions. It is advantageous if the ring region has a plurality of ring region sections. It is advantageous if the core region and the ring region are directly adjacent to one another. Alternatively, it is conceivable to provide a gap separating the core region and the ring region. For the purposes of the invention, the core region and the ring region refer to the laser spot imaged on the workpiece, the core region and the ring region being formed in the focus position on the workpiece.

[0029] Alternatively, it is conceivable that two overlapping, preferably coaxially arranged, laser spots with different diameters are provided to form a core region and a ring region, wherein the core region is provided in the region of the overlap and the ring region is provided outside the overlap.

[0030] The object underlying the invention is also achieved by a laser welding device for laser welding at least two workpieces with the features of claim 13. The laser welding device is designed to carry out the method described above.

[0031] To generate the laser spots, a laser with a beam quality of SPP (beam parameter product) less than or equal to 4 mm*mrad (millimeters * milliradians) can be used. To generate the laser spots, a NIR (near infrared) laser (multi-mode) with a power greater than or equal to 4 kW, in particular greater than 8 kW, preferably 12 kW, can be used.

[0032] Alternatively, a laser with a wavelength in the visible range (VIS laser), particularly green or blue, can be used.

[0033] According to a further development of the method, the at least one laser spot can be moved by means of a scanner optics system. The scanner optics can have an imaging ratio of 1.7:1. The scanner optics can preferably be equipped with an optical sensor, e.g., a camera. Accordingly, gap tolerances or positional deviations can be detected, so that the power distribution can be adjusted in real time. The scanner optics can preferably be designed to be ultralight in order to shorten non-productive times.

[0034] It is advantageous if the method is used for welding hairpins and / or battery casings.

[0035] The object underlying the invention is also achieved by a computer-readable storage medium having the features of claim 14. The computer-readable storage medium comprises instructions which, when executed by a computer, cause the computer to carry out the method described above.

[0036] The problem underlying the invention is also solved by a computer program having the features of claim 15. The computer program comprises instructions which, when executed by a computer, cause the computer to carry out the method described above.

[0037] The object underlying the invention is also achieved by a data carrier signal having the features of claim 16. The data carrier signal transmits and / or characterizes the previously described computer program.

[0038] The description further includes a use of the method for laser welding for a welding process which is shorter than 5 s, in particular shorter than 3 s, preferably shorter than 2 s, and preferably shorter than 1 s.

[0039] Further details and advantageous embodiments of the invention can be found in the following description, on the basis of which embodiments of the invention are further described and explained.

[0040] It shows :

[0041] Fig. 1 is a schematic plan view of workpieces to be joined;

[0042] Fig. 2 is a schematic side view of the workpieces to be joined according to Fig. 1;

[0043] Fig. 3 is a diagram illustrating the welding process according to Fig. 1 and 2 with a power profile of the core region and the ring region as well as the welding speed of the laser spot. To illustrate the method according to the invention, a first workpiece 10 and a second workpiece 12 which are to be welded together are shown by way of example in Fig. 1 and 2. The first workpiece 10 furthermore has a first base section 10A and a first cover section 10B which are likewise to be welded together. The second workpiece 12 furthermore has a second base section 12A and a second cover section 12B which are likewise to be welded together. Alternatively, it is conceivable that the workpieces 10, 12 are formed in one piece and are to be welded together and / or that a base section 10A, 12A and a cover section 10B, 12B are to be welded together.In this case, the base section 10A, 12A can form the first workpiece and the cover section 10B, 12B can form the second workpiece.

[0044] During laser welding, a laser spot 16 is generated on the first workpiece 10 and / or the second workpiece 12 by means of a laser beam 14. The laser beam 14 is designed such that the laser spot 16 imaged on the first workpiece 10 and / or the second workpiece 12 has a circular core region 18 and an annular ring region 20 surrounding the core region 18.

[0045] In Fig. 2, the laser beam 14 is shown in a simplified form, with the core region 18 and the ring region 20 already formed along the laser beam 14. It is conceivable that the core region 18 and the ring region 20 are formed in this way, in particular with a sharp separation, only in the focus position or in the laser spot 16. Overlaps and blurring of the two regions 18, 20 may occur along the laser beam 14.

[0046] The laser spot 16 is moved over the first workpiece 10 and the second workpiece 12 at a welding speed v, which is shown in Fig. 3. A molten pool 22 is created by the energy input of the laser beam 14. Different times t0 - t7 of a welding process are shown in Fig. 1 and 2, with the laser spot 16 being provided at different locations. Accordingly, the laser spot 16 runs from top left (t0) to top right (t0) and crosses a gap 24 (t1) provided between the first workpiece 10 and the second workpiece 12. The laser spot 16 then makes a corner move (t0). The laser spot then moves in a preferred direction (t3) to bottom right (t0). The corner moves (t0, to), the gap bridging (ts) and the preferred direction (t7) are repeated again until a completed round has been completed.

[0047] The different points in the welding process are characterized by different welding variables. The requirements differ at the beginning of the welding process (to), at the end of the welding process (after t7), during gap bridging (t7, ts), and / or during cornering (t2, t4, t6).

[0048] According to the invention, the power distribution between the core region 18 and the ring region 20 is adjusted depending on location and / or time and / or depending on at least one welding variable during laser welding. Fig. 3 shows the power distribution over time. Alternatively, the power distribution can be mapped over location, with one or more coordinates being displayed on the y-axis. Both variants can be

[0049] Procedures can be used together or individually.

[0050] The power distribution is preferably determined by a ratio between the average laser power density of the core region 18, hereinafter referred to as core power P K and the average laser power density of the ring area 20, hereinafter referred to as ring power P R designated .

[0051] The workpieces 10, 12 and / or the welding process are designed such that the welding variables change rapidly, in particular with a time interval of less than 50 ms, in particular less than 30 ms. Accordingly, it is advantageous if the switching time between two consecutive power distributions of the core power and the ring power is a maximum of 20 ms. The welding process (t1 to after t7) can preferably last a maximum of 3 s, in particular a maximum of 2 s, preferably a maximum of 1 s.

[0052] At time to the welding speed is v 0 . For this reason it is advantageous if the core power P K in the core area 18 greater than the ring power P R in the ring area 20 is .

[0053] The welding speed v is increased until the time ti at which the gap 24 is bridged. For improved gap bridging of the gap 24, it is advantageous if the ring power P R in the ring area 20 greater than the core power P K in the core area 18. The total power is defined as the sum of the core power P K of the core area 18 and the ring power P R of the ring region 20 is at least substantially constant.

[0054] At time t2 a cornering movement is carried out during which the welding speed v is reduced. Due to the changing welding speed v it is advantageous if the core power P K greater than the ring power PR is .

[0055] At time ta, the welding speed v reaches a maximum, since a straight movement of the laser beam along a preferred direction is carried out. Due to the higher welding speed v, it is advantageous if the power in the core region 18 is greater than in the ring region 20. Furthermore, it is advantageous if the total power increases in contrast to the start of the welding process ( t0 ) and / or the gap bridging ( t1 ) and / or the cornering ( t2 ).

[0056] The change in the power distribution between the core power P K and the ring power P R can preferably be provided accordingly at the further times (t4-t7).

[0057] At the end of the welding process (after t7) it is also advantageous if the ring power P R greater than core power P K is .

[0058] Between the times t4 and ts it is indicated in Fig . 3 that in order to improve the melt bath dynamics the core power P K and the ring power P R oscillate. It is advantageous if the core power P K oscillates by the amount by which the ring power P R oscillates. In this case, the power distribution is variable and the total power is constant. It is also conceivable that for a short time the core power P K the ring power P R Furthermore, it is conceivable that the power distribution and / or the ring power P R and / or core performance P K and / or the total power oscillates. Such oscillation can preferably also be provided at other times.

[0059] 1 and 2, the first workpiece 10 and the second workpiece 12 are made of the same material. Therefore, the power curve and the welding speed curve v for the first workpiece 10, i.e. t o - t 1 and t s - t 7, and the second workpiece 12, i.e. t 1 - t s, are identical with regard to the corresponding welding variable. Alternatively, it is conceivable for these to be made of different materials, so that the power distribution and / or the total power changes for the corresponding workpiece 10, 12 or material of the workpiece 10, 12. The power distribution and / or the total power is also adaptable due to a change in the workpiece geometry and / or the gap width and / or the surface quality and / or the occurrence and / or a maximum amount of spatter.

[0060] To determine the at least one welding variable in real time, an optical and / or tactile measuring device (not shown) can preferably be provided. Furthermore, a control unit (not shown) can be provided, which is configured to adapt the power distribution of the core region 18 and the ring region 20 and / or their total power during laser welding depending on the at least one welding variable detected by the measuring device, in particular with a maximum switching time of 20 ms.

Claims

Patent claims 1. A method for laser welding at least two workpieces (10, 12), comprising the steps: - Providing a first workpiece (10) and a second workpiece (12); - generating at least one laser spot (16) on the first workpiece (10) and / or the second workpiece (12), wherein the at least one laser spot (16) has a, in particular circular, core region (18) and a, in particular annular, ring region (20); - moving the at least one laser spot (16) at a welding speed (v) on the first workpiece (18) and the second workpiece (20) to produce a molten pool (22); - Changing a power distribution between the core region (18) and the ring region (20) depending on a position of the at least one laser spot (16) on the first workpiece (10) and / or on the second workpiece (12) and / or depending on the welding speed (v) of the at least one laser spot (16) and / or depending on at least one welding variable at the position of the at least one laser spot (16).

2. The method according to claim 1, wherein the adjustment of the power distribution occurs during laser welding.

3. Method according to claim 1 or 2, wherein a switching time between successive power distributions is a maximum of 20 ms.

4. Method according to claim 1, 2 or 3, wherein the adjustment of the power distribution between the core region (18) and the ring region (20) is carried out by means of a wedge switch.

5. The method according to claim 1, 2 or 3, wherein a first input fiber is spliced ​​with a core region (18) of a multiple fiber and at least one second input fiber is spliced ​​with at least one ring region (20) of the multiple fiber, and wherein the adjustment of the power distribution between the core region (18) and the ring region (20) is carried out by changing the power at the respective input fibers.

6. Method according to one of the preceding claims, wherein the at least one welding variable comprises one or more, in particular all, of the following variables: - material of the first workpiece (10) and / or the second workpiece (12), - workpiece geometry of the first workpiece (10) and / or the second workpiece (20), - gap width between the first workpiece (10) and the second workpiece (12), - surface quality of the first workpiece (10) and / or the second workpiece (12), - Occurrence and / or quantity of spatter during laser welding, - Position tolerances, in particular lateral component offset, of the first workpiece (10) and / or the second workpiece (12), - Total performance of laser welding, - Focus position of a laser beam (14) , - beam diameter of a laser beam (14) on the first workpiece (12) and / or the second workpiece (20), Intensity of a laser beam (14) , - fluence of a laser beam (14) .

7. Method according to one of the preceding claims, wherein at least one welding variable is recorded during laser welding by means of a measuring device, in particular an optical and / or tactile measuring device.

8. Method according to one of the preceding claims, wherein when changing the power distribution of the core region (18) and the ring region (20) of the at least one laser spot (16), a total power as the sum of the power of the core region (18) and the ring region (18) of the at least one laser spot (16) is also changed.

9. Method according to one of the preceding claims, wherein when the movement speed (v) of the laser spot (16) is reduced, the power distribution is changed such that an average laser power density in the core region (18) is reduced and / or an average laser power density in the ring region (20) is increased.

10. Method according to one of the preceding claims, wherein upon an increase in the movement speed (v) of the laser spot (16), the power distribution is changed such that an average laser power density in the core area (18) increased and / or a medium laser Power density in the ring area (20) reduced.

11. Method according to one of the preceding claims, wherein at the start of a laser processing operation the power distribution is set such that an average laser power density in the core region (18) is greater than an average laser power density in the ring region (20), and / or wherein at the end of a laser processing operation the power distribution is set such that an average laser power density in the core region (18) is smaller than an average laser power density in the ring region (20).

12. Method according to one of the preceding claims, wherein the power distribution is adjusted such that the average laser power density between the core region (18) and the ring area (20) oscillates.

13. Method according to one of the preceding claims, wherein for improved gap bridging depending on a gap width between the first workpiece (10) and the second workpiece (12) the laser power density is increased in the ring region (20) and / or reduced in the core region (18).

14. Method according to one of the preceding claims, wherein changing the power distribution between the core area (18) and the ring area (20) using artificial intelligence and / or machine learning.

15. Laser welding device for laser welding at least two workpieces (10, 12), wherein the laser welding device is configured to carry out the method according to one of the preceding claims.

16. A computer-readable storage medium comprising instructions which, when executed by a computer, cause the computer to carry out the method according to at least one of claims 1 to 14.

17. A computer program comprising instructions which, when executed by Execution of the computer program by a computer causes the computer to carry out the method according to at least one of claims 1 to 14.

18. A data carrier signal that transmits and / or characterizes the computer program according to claim 17.

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