WO2023061782A1

WO2023061782A1 - Laser welding method

Info

Publication number: WO2023061782A1
Application number: PCT/EP2022/077364
Authority: WO
Inventors: Oliver BOCKSROCKER; Nicolai Speker; Tim Hesse
Original assignee: Trumpf Laser- Und Systemtechnik Gmbh
Priority date: 2021-10-15
Filing date: 2022-09-30
Publication date: 2023-04-20
Also published as: DE102021126749A1

Abstract

The invention relates to a method for laser welding two, preferably metal, components (19, 12), wherein a pulsed laser beam (18) is directed onto a surface (20) of one of the components (10) such that the material of the components (10, 12) is melted in the area of a weld seam (23) to be produced, wherein the laser beam (18) has an intensity profile that has an annular intensity maximum and a local intensity minimum in its centre, wherein the intensity in the intensity minimum is at least 10% smaller than in the intensity maximum (30), and wherein a depth (34) of the produced weld seam (23) is at most as large as a width (36) of the weld seam.

Description

laser welding process

Background of the Invention

The invention relates to a method for laser welding two components, with a pulsed laser beam being directed onto a surface of one of the components, so that the material of the components is melted in the area of a weld seam to be created.

Such methods are known in principle from the prior art. The weld seam penetrates one of the components and extends into the other component, so that the components are connected to one another.

The pulse durations used in so-called "stiching" are in the nanosecond range. Laser beams with a Gaussian or Tophat-like intensity profile are often used for this purpose. However, the high intensity in the center of these laser beams causes significant evaporation of material from the weld pool. This leads to turbulence in the weld pool Ultimately, this increases the susceptibility to errors in the welding process.

The aforementioned problems also arise in welding processes with continuous or quasi-continuous laser beams. In the case of deep-penetration welding processes, which are fundamentally known from the prior art, the depth of the weld seam produced is significantly greater than its width. As a result, a single weld seam has only a small connection cross-section. In order to achieve the desired mechanical strength or electrical conductivity, several weld seams are typically placed next to one another. This lengthens the manufacturing time and increases the manufacturing costs.

object of the invention

It is an object of the invention to specify a method with which components can be welded efficiently and with high quality.

Description of the invention

This object is achieved according to the invention by a method according to claim 1. Advantageous variants are specified in the subclaims and the description.

According to the invention, a method for laser welding two components is provided. The components are typically metal sheets or foils. In particular, a foil can be welded to a metal sheet. A thickness of the components can be less than 3 mm, in particular less than 2 mm. The components can have the same thickness or different thicknesses. The components are preferably each made of a metallic material. The components can be made of similar materials, i. H. an alloy with the same main alloying element. The main alloying element can be iron, copper or aluminum, for example. In particular, the components can consist of the same material. In special cases, more than two, for example three or four, components can be welded together.

Typically, the components overlap each other over a large area. Due to the surface overlapping of the components, the flat sides of the adjoining ones become flat components arranged together. In particular, there can be an overlap joint or a parallel joint. The weld seam penetrates at least a first of the components and extends into the second component and possibly further components, so that the components are connected to one another.

To weld the components, a pulsed laser beam is directed onto a surface of one of the components (also referred to as the first component). As a result, the material of the components is melted in the area of a weld seam to be created. The melting of the material below the surface, in particular the material of the second component, takes place primarily through thermal conduction. In other words, it is a heat conduction welding process.

According to the invention, the laser beam has an intensity profile that has a ring-shaped intensity maximum and a local intensity minimum in its center. In other words, the intensity of the laser beam initially increases radially outwards, starting from the center. From the ring-shaped intensity maximum, the intensity drops further outwards until the outer edge of the laser beam is reached. In the ring-shaped intensity maximum, the intensity can be constant or variable in the circumferential direction. In other words, the ring-shaped intensity maximum can be described by the entirety of the respective local intensity maximums of all radial directions.

In the intensity minimum, the intensity is at least 10%, preferably at least 20%, particularly preferably at least 30%, very particularly preferably at least 40% less than in the intensity maximum. If the intensity of the ring-shaped intensity maximum changes in the circumferential direction, a minimum intensity in the area of the intensity maximum can be used for comparison. An, in particular arithmetic, mean value over the intensities or the median of the intensities along the ring-shaped intensity maximum is preferably used for the comparison. Furthermore, according to the invention, a depth of the weld seam produced is at most as great as a width of the weld seam. In other words, the aspect ratio of depth to width of the weld seam is at most 1:1. The depth of the weld seam is preferably at most two thirds, particularly preferably at most half of the width of the weld seam. The depth of the weld seam can be a maximum of 3 mm, in particular a maximum of 2 mm. The weld seam preferably does not reach as far as an end surface of the second component that is remote from the surface of the first component on which the laser beam impinges.

Due to the minimum intensity in the center of the laser beam, the evaporation of material in the middle of the weld pool can be avoided or at least reduced. Movements, in particular turbulent flows, in the weld pool can be avoided or at least reduced. As a result, a particularly uniform melting can be achieved and consequently a particularly uniform weld seam can be obtained. In addition, it can be achieved that the depth of the weld seam can be set particularly precisely and, in particular, changes only extremely slightly along the direction in which the weld seam extends (in the feed direction).

Due to the large width of the weld seam, a large connection cross section is obtained. This increases the mechanical strength and electrical conductivity of the weld seam. The number of weld seams required can be reduced as a result. This reduces the overall process time for connecting the components. In particular, the interaction time with the laser beam is also reduced, which can be advantageous for the properties of the components or the assembly of the components.

Furthermore, the large width and precisely adjusted depth of the weld seam allows precise mixing of the materials of the two components. The quality, in particular the mechanical strength or electrical conductivity, of the weld seam is further improved as a result. A gradient of the intensity profile from the intensity maximum radially outward is particularly preferably greater in terms of absolute value than from the intensity maximum radially inward, in particular by at least 10%, preferably by at least 25%. In other words, the intensity drops more sharply radially outward from the intensity maximum than radially inward toward the intensity minimum. As a result, the size or extent of the melted area can be set particularly precisely. Even with different surface qualities, the desired size or extent of the weld pool or weld seam can be obtained very precisely. The maximum intensity can be between 80% and 90%, in particular around 86%, of the diameter of the laser beam. For comparison, the gradients are basically determined at the same radial distance from the intensity maximum.

The components can be made of different materials. In particular, the components can consist of dissimilar materials with different main alloying elements. The main alloying elements can be iron, copper or aluminium, for example. The method according to the invention makes it possible to weld such different materials efficiently and with high quality. In particular, the method according to the invention reduces the formation of intermetallic or brittle phases. As a result, the weld seam produced has high strength, high ductility and low electrical resistance.

A cross-section of the weld may have the shape of a plano-convex lens. The weld seam is preferably delimited, facing away from the surface, by a convexly curved arc, which in particular can be elliptical, preferably round. In other words, the cross section of the weld seam corresponds to a section of an oval, preferably an ellipse, particularly preferably a circle. The weld seam is thus rounded at its lower end in the depth direction. The need-based mixing of the joining partners can be further improved as a result. Especially when welding dissimilar items materials, the resulting proportion of brittle phases can be further reduced by this shape of the weld seam.

A pulse duration of a pulse of the laser beam can be at least 10 ps, preferably at least 20 ps. In this way it can be achieved that the material of the components is melted on a sufficiently large area.

The pulse duration can be at most 1 s, preferably at most 0.5 s. This reduces the heat input into the components. In addition, short interaction times with the laser beam can promote needs-based mixing in the weld pool. Particularly in the case of components of dissimilar materials, this can additionally reduce the formation of brittle phases.

Typically, all pulses have the same pulse duration. This simplifies the implementation of the method.

A pulse energy of a pulse of the laser beam can be at least 100 mJ, preferably at least 200 mJ. This enables large areas to be melted. As a result, a large connection area of the weld seam can be achieved. In addition, this can help to obtain the desired depth-to-width aspect ratios of at most 1:1. Typically, all pulses have the same pulse energies. This simplifies the implementation of the method.

According to a preferred variant, the intensity minimum of the laser beam can be present at least over the entire welding depth. An intensity minimum that extends in the propagation direction of the laser beam and is located in the center of the intensity profile of the laser beam can be achieved, for example, by pinching the fiber guiding the laser beam, as described in WO 2019/150071. In such a case, after leaving the fiber, the intensity minimum can be present at any position in the propagation direction of the laser beam. The intensity minimum extended in the beam propagation direction increases the tolerances in the direction of the optical axis of the laser beam. The laser beam can be formed with a plurality of partial beams, at least some of which are arranged along the ring-shaped intensity maximum. In other words, the partial beams are arranged azimuthally along the intensity maximum. This increases flexibility when shaping the laser beam or intensity profile. At least one further partial beam of the laser beam can be arranged in the area of the central intensity minimum. The partial beams are preferably generated by laser light sources that are independent of one another. As a result, the configuration of the intensity profile can be further refined. At least two of the partial beams can have different laser powers. In particular, it can be provided that the laser powers of the partial beams are changed independently of one another. As a result, for example, a greater intensity can be set at the front in the direction of advance and this intensity profile can be retained in a simple manner when the direction of advance changes. The laser light sources may include a fiber laser.

Alternatively, it can be provided that the laser beam is emitted by a laser light source which has an active laser fiber whose mode field can be changed by introducing mechanical stress. The mode order can be adjusted by changing the mechanical load on the active laser fiber. No optical elements need to be exchanged for this. This allows the intensity profile to be easily adapted to different materials to be welded. The laser light source can include a disk laser.

Further alternatively, the laser beam may be emitted by a laser fiber having a core fiber and a ring fiber. Laser light from different laser light sources is preferably introduced into the core fiber and into the ring fiber. In this way, the drop in intensity in the intensity minimum can be adjusted in a particularly simple manner. The beam parameter product of the laser beam can be at least 0.38 mm*mrad. The beam parameter product of the laser beam can be at most 100 mm*mrad, preferably at most 32 mm*mrad, in particular in the case of a laser light source with a changeable mode field. Furthermore, the beam parameter product, in particular when using a laser fiber with a core fiber and a ring fiber or when the laser beam is formed by several partial beams, can be at most 0.6 mm*mrad.

The beam diameter of the laser beam can be at least 10 μm and/or at most 1200 μm on the surface of the first component. The beam diameter on the surface can be at least 30 μm and/or at most 300 μm, preferably at most 70 μm, particularly when using a laser fiber with a core fiber and a ring fiber or when the laser beam is formed by several partial beams. Furthermore, the beam diameter on the surface, in particular in the case of a laser light source with a changeable mode field, can be at least 50 μm.

The fluence of the laser beam can be at most 1000 J/mm ² , in particular at most 300 J/mm 2 . The intensity of the laser beam can be at most 20 kW/mm ² , in particular at most 10 kW/mm ² . The aforementioned maximum values relate in particular to a preferably arithmetic averaging over the cross section of the laser beam.

A wavelength of the laser beam can be at least 800 nm and/or at most 1200 nm. In other words, the laser beam can be an infrared laser beam. In particular, the wavelength can be 1030 nm or 1070 nm.

Alternatively, the wavelength of the laser beam can be in the visible light range. In particular, the wavelength can be at least 400 nm and/or at most 450 nm; the laser beam can therefore be blue. Alternatively, the wavelength can be 515 nm; the laser beam can therefore be green. An average laser power of the laser beam can be at least 10 W, in particular at least 50 W, and/or at most 2000 W, in particular at most 700 W, in particular with arithmetic averaging over time. A pulse peak power of the individual laser pulses can be at least 100 W, in particular at least 500 W, and/or at most 20 kW, in particular at most 7 kW.

A pulse frequency can be at least 25 Hz, in particular at least 250 Hz, and/or at most 8 kHz, in particular at most 800 Hz.

A feed rate can be at least 10 mm/s, in particular at least 100 mm/s, and/or at most 5 m/s, in particular at most 2 m/s.

The laser beam used for welding can be emitted by a laser light source which has scanner optics. Alternatively, the laser beam can be emitted from a laser light source with flying focusing optics. The scanner optics or focusing optics can have an imaging ratio of at least 1:1, preferably at least 1.5:1, and/or at most 5:1, preferably at most 2:1. The imaging ratio indicates the enlargement of the beam diameter through the optics. The imaging ratio m can be calculated from the ratio of the focal length f of a lens and a collimation focal length fc as m=f/fc.

The depth of the weld seam can be at least 1.5 times, preferably at least twice, particularly preferably at least three times the thickness of that component on whose surface the laser beam impinges. In this way it can be achieved that the weld seam has a sufficiently large width in the contact area of the components, so that in other words the connection cross section is formed in the desired size. Preferably, a cross section through the laser beam has the same extent in two mutually perpendicular directions. This simplifies the control of the welding process.

The intensity maximum is particularly preferably in the form of a circular ring. This allows welding in any direction with identical properties.

Alternatively, the annular intensity maximum can be polygonal. A polygonal design of the intensity maximum is particularly useful when the laser beam consists of several partial beams. The polygonal intensity minimum has at least three, preferably at least four, corners. In particular, the polygonal intensity minimum can have six, eight or twelve corners. A circular shape can be approximated in this way

Further advantages of the invention result from the claims, the description and the drawing. According to the invention, the features mentioned above and those detailed below can each be used individually or collectively in any desired, expedient combination. The embodiments shown and described are not to be understood as an exhaustive list, but rather have an exemplary character for the description of the invention.

Detailed description of the invention and drawings

The invention is illustrated in the drawing and is described using exemplary embodiments. Show it:

1 shows a schematic sectional representation of the welding of two components using a method according to the invention, a laser beam being emitted by a laser light source with an active laser fiber whose mode field can be changed by mechanical loading;

FIG. 2 shows a schematic representation of the intensity profile of the laser beam in the welding method of FIG. 1 with a first ring mode;

FIG. 3 shows a schematic representation of the intensity profile of the laser beam in the welding method of FIG. 1 with a different ring mode;

4 shows a laser light source, which emits a laser beam from a core fiber and a ring fiber, for a welding method according to the invention, in a schematic sectional representation;

5 shows a schematic cross section through a laser beam composed of several partial beams for a welding method according to the invention.

FIG. 1 shows a snapshot of the welding of a first component 10 to a second component 12. Here, flat sides of the two components 10, 12 are arranged adjacent to one another, so that the two components 10, 12 overlap one another over an area. The two components 10, 12 each consist of a metallic material. In the present case, the components 10, 12 consist of dissimilar materials; for example, the first component 10 can be made of an aluminum alloy and the second component 12 can be made of a copper alloy. The two components can have different thicknesses. A thickness 14 of the first component 10 can be 0.15 mm, for example. A thickness 16 of the second component 12 can be 0.3 mm, for example.

To weld the two components 10 , 12 , a pulsed laser beam 18 is directed onto a free surface 20 of the first component 10 . A pulse duration of the laser beam 18 can be 100 ps. A pulse energy of a pulse of the laser beam 18 can be 500 mJ. A wavelength of the laser beam 18 can be 1030 nm. A beam diameter 22 of the laser beam 18 at the point of impact on the surface 20 can be 850 μm. The material of the components 10, 12 is melted by the heat introduced by the laser beam 18 in the area of the weld seam 23 to be created.

In the exemplary embodiment of FIG. 1, the laser beam 18 is emitted by a laser light source 24 with an active laser fiber 26 . The mode field of the laser beam 18 can be changed by changing the mechanical load on the active laser fiber 26 . For this purpose, the laser light source 24 can have an actuator 28 .

In order to weld the components 10, 12, a ring mode is activated by suitably loading the laser fiber 26. The intensity distribution of the laser beam 18 at the point of impact on the surface 20 is shown in FIG. A grayscale representation of the intensities in the cross section of the laser beam 18 is shown at the bottom left. The profiles of the intensities I are plotted in cross sections along the X-axis and Y-axis through the laser beam 18 at the top left and bottom right.

The laser beam 18 has an intensity maximum 30 in the form of a circular ring, which surrounds a local intensity minimum 32 in the center of the laser beam 18 . The intensity can have certain fluctuations in the azimuthal direction along the intensity maximum 30 . In the central intensity minimum 32, the intensity here is about half as large as the median of the intensities in the intensity maximum 30. From the intensity maximum 32 radially outwards, the intensity falls faster than radially inwards. This will make the Laser beam 18 sharply delimited radially outwards. In contrast, the intensity decreases more slowly towards the intensity minimum 32 .

When welding with the laser beam according to FIG. 2, the pulse peak power can be 1581 W. Average laser power can be 454W. The pulse frequency can be 250 Hz. The pulse duration can be 1150 ps. The pulse energy can be 1.8J. The feed speed can be 1.5 m/min.

FIG. 3 shows the intensity distribution of the laser beam 18 when the components 10, 12 are welded when another ring mode is activated. In this ring mode, the intensity fluctuates less in the azimuthal direction along the circular intensity maximum 30 than in FIG.

When welding with the laser beam according to FIG. 3, the peak pulse power can be 1635 W. Average laser power can be 470W. The pulse frequency can be 250 Hz. The pulse duration can be 1150 ps. The pulse energy can be 1.8J. The feed speed can be 1.5 m/min.

In the welding method according to the invention, the weld seam is created in such a way that a depth 34 of the weld seam 23 (measured in the direction of propagation of the laser beam 18) is smaller than a width 36 of the weld seam 23 (measured perpendicularly to the direction of propagation of the laser beam 18), see Figure 1. Here the Depth 34 approximately one third of the width 36. The depth 34 of the weld seam 22 can be 0.3 mm, for example. When welding the components 10, 12, the intensity minimum 32 can preferably be present over the entire welding depth.

On its side facing away from the surface 20, ie toward the second component 12, the weld seam 23 is formed by a convex arc 38, here bounded by an arc of a circle. The cross section of the weld seam 23 therefore has the shape of a plano-convex lens or a segment of a circle. The weld seam 23 does not extend completely through the second component 12 . In particular, the weld seam 23 does not extend to an end face 39 of the second component 12 which faces away from the first component 10 .

FIG. 4 shows a laser light source arrangement 40 which can be used in place of the laser light source 24 of FIG. 1 for welding the components 10, 12. The laser light source arrangement 40 has a laser fiber 42 with a core fiber 44 and a ring fiber 46 . The ring fiber 46 surrounds the core fiber 44. A laser beam 18 is formed in its center by laser light exiting from the core fiber 44 and in its radially outer region by laser light exiting from the ring fiber 46.

Laser light from separate laser light sources 48, 50 is fed into the core fiber 44 and the ring fiber 46. Appropriate activation of the laser light sources 48, 50 ensures that the intensity of the laser beam 18 is lower in the center than in a ring-shaped area surrounding the center. In other words, the laser light emerging from the ring fiber 46 generates an annular maximum intensity which encloses a central intensity minimum which is essentially generated by the laser light emerging from the core fiber 44 .

FIG. 5 shows a cross section through a laser beam 18 which is formed from a plurality of partial beams 52, 54. The partial beams 52 form an annular intensity maximum. In the present case, the partial beams 52 are arranged on corner points of a polygon, here a hexagon. The partial beam 54 is provided for controlling the intensity of a central intensity minimum. If a particularly low intensity is desired in the center, the partial beam 54 can also be omitted. It is understood that more or fewer than six sub-beams 52 can be used. Likewise, several partial beams 54 could be used in the center. Further ring-shaped layers of partial beams could also be provided (not shown in more detail). The partial beams 52, 54 can each be emitted from separate laser light sources. In particular, the intensities of the partial beams 52 can be set independently of the intensity of the partial beam 54 and, if necessary, changed during welding. In addition, it can be provided that at least one of the partial beams 52 has a different intensity than other partial beams 52. The different intensities of the partial beams 52 can be changed depending on a feed direction and/or feed speed.

In summary, the invention relates to methods for laser welding, in which a laser beam has a lower intensity in its center than in an annular area that surrounds the center. The laser beam is directed onto a first component to be welded. The material of the first and a second component (located behind the first component in the beam propagation direction) is melted by thermal conduction. The intensity profile with the central intensity minimum and the annular intensity maximum reduces the evaporation of material from the weld pool as well as movements in the weld pool. The welding takes place in such a way that the depth of the weld seam is at most as great as the width of the weld seam. Facing away from a free surface, a cross section of the weld seam is preferably delimited by a uniformly curved arc.

Reference sign list first component 10 second component 12

Thickness 14 of the first component 10

Thickness 16 of the second component 12

laser beam 18

surface 20

beam diameter 22

Weld 23

Laser light source 24 active laser fiber 26

actuator 28

Intensity maximum 30

Intensity minimum 32

depth 34

width 36

arch 38

end face 39

Laser light source assembly 40

Laser fiber 42

core fiber 44

ring fiber 46

Laser light sources 48, 50

Partial beams 52, 54

Claims

Method for laser welding two, preferably metallic, components (19, 12), wherein a pulsed laser beam (18) is directed onto a surface (20) of one of the components (10), so that the material of the components (10, 12) in Area of a weld seam (23) to be created is melted, the laser beam (18) having an intensity profile which has a ring-shaped intensity maximum (30) and a local intensity minimum (32) in its center, the intensity in the intensity minimum (32) being at least 10 % is smaller than the intensity maximum (30), and a depth (34) of the created weld (23) is at most as large as a width (36) of the weld. Method according to Claim 1, characterized in that a gradient of the intensity profile from the intensity maximum (30) radially outward is greater in terms of absolute value than from the intensity maximum (30) radially inward. Method according to one of the preceding claims, characterized in that the depth (34) of the weld seam (23) is at most two thirds, preferably at most half, of the width (36) of the weld seam (23). Method according to one of the preceding claims, characterized in that the components (10, 12) consist of different materials.

5. The method according to any one of the preceding claims, characterized in that the weld seam (23) facing away from the surface (20) is delimited by a convexly curved arc (38), which is in particular elliptical, preferably round.

6. The method according to any one of the preceding claims, characterized in that a pulse duration of a pulse of the laser beam (18) is at least 10 ps, preferably at least 20 ps, and/or that the pulse duration is at most 1 s, preferably at most 0.5 s .

7. The method according to any one of the preceding claims, characterized in that a pulse energy of a pulse of the laser beam (18) is at least 100 mJ, preferably at least 200 mJ.

8. The method according to any one of the preceding claims, characterized in that the minimum intensity is present over the entire welding depth.

9. The method according to any one of claims 1 to 8, characterized in that the laser beam (18) is formed with a plurality of partial beams (52, 54), at least some of which are arranged along the ring-shaped intensity maximum (30), preferably wherein at least one of the Partial beams (54) is arranged in the area of the minimum intensity (32).

10. The method according to claim 9, characterized in that the partial beams (52, 54) are generated by laser light sources that are independent of one another.

- 19 - Method according to claim 9 or 10, characterized in that at least two of the partial beams (52, 54) have different laser powers, in particular that the laser powers of the partial beams (52, 54) are changed independently of one another. Method according to one of Claims 1 to 8, characterized in that the laser beam (18) is emitted by a laser light source (24) which has an active laser fiber (26) whose mode field can be changed by introducing mechanical stress. Method according to one of Claims 1 to 8, characterized in that the laser beam (18) is emitted by a laser fiber (42) with a core fiber (44) and a ring fiber (46), preferably in the core fiber (44) and in the Ring fiber (46) laser light from different laser light sources is introduced. Method according to one of the preceding claims, characterized in that the depth (34) of the weld seam (23) is at least 1.5 times, preferably at least twice, particularly preferably at least three times the thickness (14) of that component (10). , on whose surface (20) the laser beam (18) strikes. Method according to one of the preceding claims, characterized in that a cross section through the laser beam (18) has the same extent in two mutually perpendicular directions, in particular the intensity maximum (30) being circular or polygonal.