BUTT WELDING OF TWO WORKPIECES WITH AN ULTRASHORT PULSE LASER BEAM, AND ASSOCIATED OPTICAL ELEMENTS

Abstract

The present disclosure provides methods, devices, and systems for the butt welding of two, e.g., planar, workpieces, by at least one pulsed laser beam, e.g. an ultrashort pulse (“USP”) laser beam, which is focused into the workpiece material to locally melt the two workpieces in the region of their joining surface. The laser focus of the laser beam focused into the workpiece material is moved transversely with respect to the beam direction of the laser beam to produce in the region of the joining surface a weld seam extending transversely with respect to the beam direction of the laser beam.

Claims

1. A method for butt welding two workpieces, the method comprising focusing at least one ultrashort pulse laser beam into the two workpieces to locally melt the two workpieces in a region of a joining surface; and moving a laser focus of the pulsed laser beam transversely with respect to a beam direction of the laser beam to produce in the region of the joining surface a weld seam extending transversely with respect to the beam direction of the laser beam.

2. The method of claim 1, further comprising moving surfaces of the two workpieces to be joined into contact along a joining surface.

3. The method of claim 1, wherein the pulsed laser beam is directed in parallel to the joining surface, or at right angles to a top side of the workpieces, or both.

4. The method of claim 1, wherein the laser focus of the laser beam focused into the two workpieces is moved longitudinally, or transversely, or both longitudinally and transversely, with respect to the joining surface to produce the weld seam in the region of the joining surface.

5. The method of claim 1, wherein the laser beam has a Gaussian beam profile or a beam profile based on a ring-shaped angular distribution.

6. The method of claim 5, wherein the laser beam has a Bessel shaped beam profile.

7. The method of claim 1, wherein the laser beam is directed obliquely with respect to a top side of the workpieces, or with respect to the joining surface, or both.

8. The method of claim 1, wherein a plurality of laser beams that are offset with respect to one another, are focused into the two workpieces in the region of the joining surface.

9. The method of claim 8, wherein the plurality of laser beams are offset transversely with respect to the beam direction and parallel with respect to one another.

10. The method of claim 8, wherein laser foci of the plurality of laser beams are offset one behind another in the beam direction.

11. The method of claim 8, wherein a repetition rate of at least one of the pulsed laser beams is between 1 kHz and 500 GHz.

12. The method of claim 1, wherein a pulse duration of the pulsed laser beam is between 10 fs and 500 ps.

13. The method of claim 1, wherein to produce a transverse movement, the laser beam is pivoted back and forth in an oscillating manner or is rotated about an axis parallel to a direction of incidence.

14. The method of claim 1, wherein the laser focus of the laser beam is moved in the beam direction, counter to the beam direction, or both.

15. The method of claim 1, wherein the pulsed laser beam comprises an ultrashort pulse laser having pulse durations of less than 50 ps.

16. An element formed from at least two planar workpieces which are laser-welded to one another and which are joined together at at least one joining surface, comprising at least one weld seam in the region of the joining surface, which runs in a longitudinal direction and/or in a transverse direction with respect to the joining surface.

Description

DESCRIPTION OF DRAWINGS

[0019] FIG. 1 is a schematic diagram of a laser processing machine for butt welding two workpieces together using a laser beam, as described herein.

[0020] FIGS. 2A-2C are a series of schematic diagrams of a sectional view of two planar workpieces that are welded to one another by a Gaussian laser beam, the laser focus of which is moved transversely with respect to the joining surface (FIG. 2A), parallel to the joining line on the top side (FIG. 2B), and transversely with respect to the joining surface and parallel to the joining line on the top side (FIG. 2C); and

[0021] FIGS. 3A-3C are a series of schematic diagrams of a sectional view of two planar workpieces that are welded to one another by an inclined, Gaussian laser beam (FIG. 3A), a ring-shaped laser beam (FIG. 3B), and three Gaussian laser beams (FIG. 3C) running parallel next to one another.

DETAILED DESCRIPTION

[0022] The laser processing machine 1 shown in FIG. 1 serves for the butt welding of two planar workpieces 2 bearing against one another in a butt joint, by means of a laser beam 3. The two workpieces 2 are formed for example from glass, quartz glass, polymer, glass ceramic, crystals, or from combinations thereof, and/or with opaque materials, and/or are coated therewith.

[0023] The laser processing machine 1 includes a USP laser 4 for generating the laser beam 3 in the form of USP laser pulses 5 having pulse durations of less than 500 ps, e.g., in the form of femtosecond pulses, and a laser processing head 6, which is movable in X-Y-Z-directions and has a focusing optical unit 7 for focusing the laser beam 3 emerging at the bottom of the laser processing head 6. Alternatively or additionally, the assembly composed of the two workpieces 2 that are to be welded can also be moved in X-Y-directions.

[0024] The focusing optical unit 7 can spatially and/or temporally adapt the beam profile of the laser beam 3. For this purpose, the focusing optical unit 7 can comprise, e.g., a spatial light modulator and/or acousto-optical deflectors (AOD). In the focusing optical unit 7, the absorption region can be actively adapted, for example by beam shaping elements, e.g., diffractive optical elements, spatial light modulators or AOD. This can also take place highly dynamically during the butt welding itself. As an alternative or in addition to the temporal modulation of the pulse parameters or to the generation of pulse trains directly from the laser, the focusing optical unit 7 can additionally modify the temporal absorption dynamic characteristic by short laser pulse trains or bursts, and thereby vary the absorption and/or melting geometry directly or vary the melting geometry indirectly by an adapted cooling dynamic characteristic. The indirect adaptation of the cooling dynamic characteristic may, for example, necessitate adapting the cooling rate such that the final fictive temperature of the glass is modified under the influence of the density change and thus the induced stress. The laser beam 3 can be offset relative to the optical axis by means of the focusing optical unit 7.

[0025] During the butt welding of the two workpieces 2, the laser beam 3 is directed at right angles or virtually at right angles towards the workpiece top side 2a facing the laser processing head 6 and is focused into the workpiece material in the region of the common joining surface 8 of the two workpieces 2 to locally melt the two workpieces 2 in the region of the joining surface 8. In this case, the laser focus F of the laser beam 3 is moved at right angles to the beam direction 9 of the laser beam 3 to produce in the region of the joining surface 8 a weld seam 10.sub.1, 10.sub.2 extending at right angles to the beam direction 9 of the laser beam 3. In this case, the weld seam can extend transversely with respect to the joining surface 8 (transverse seam 10.sub.1) or longitudinally or parallel with respect to the top-side joining line 11 of the two workpieces 2 (longitudinal seam 10.sub.2). In the case of the longitudinal movement, the laser focus F can be situated in the material of one of the two workpieces 2 at the joining surface 8 or in proximity to the joining surface 8. In the case of the transverse movement, the laser focus F moves from the workpiece material of one workpiece 2 into the workpiece material of the other workpiece 2 and passes through the joining surface 8 in the process. A combined longitudinal and transverse movement of the laser focus is also possible in order thus to produce for example a weld seam in the shape of a wavy line or zigzag.

[0026] FIGS. 2A-2C each show a sectional view of two planar workpieces 2 which are welded to one another by a pulsed laser beam 3 having e.g. a Gaussian beam profile. The laser beam 3 is radiated in parallel to the joining surface 8 and at right angles onto the workpiece top side 2a. The laser beam 3 focused into the workpiece material melts a melting zone 12 in the shape of a drop in the workpiece material around the laser focus F.

[0027] In FIG. 2A, the laser focus F is moved at right angles to the joining surface 8 in direction A and across the joining surface 8 to produce a weld seam 10.sub.1 running across the joining surface 8. Instead of the shown linear transverse movement of the laser beam 3 in direction A, the laser beam 3 can also be rotated about an axis parallel to its direction of incidence to produce a ring-shaped weld seam which intersects the joining surface 8 twice. As a further alternative, the laser beam 3, in addition to its shown linear transverse movement in direction A, can also be rotated about an axis parallel to its direction of incidence to produce a cycloidal weld seam or a wider weld seam that intersects the joining surface 8.

[0028] In FIG. 2B, the laser focus F is moved parallel to the joining line 11 on the top side in direction B to produce in the region of the joining surface 8 a weld seam 10.sub.2 running along the joining surface 8.

[0029] In FIG. 2C, the laser focus F is both moved back and forth (double-headed arrow C) in an oscillating manner at right angles to the joining surface 8 and moved parallel to the joining line 11 on the top side and in the direction B to produce a weld seam 10.sub.3 in the shape of a wavy line or zigzag, for example, in the region of the joining surface 8. Instead of the translational transverse movement of the laser beam 3 in direction A, the laser beam 3 can also be pivoted back and forth in an oscillating manner or be rotated about an axis parallel to its direction of incidence. In the latter case, the rotation of the laser beam 3 superimposed on the linear advance movement produces a cycloidal weld seam or a wide weld seam in direction B.

[0030] FIG. 3A differs from FIG. 2A in that here the laser beam 3 is radiated in obliquely with respect to the joining surface 8 and with respect to the workpiece top side 2a and is moved transversely with respect to the beam direction of the laser beam 3 in direction A. The angle α between laser beam 3 and joining surface 8 is e.g. 10° to 20°. This inclined laser beam 3 makes it possible to bypass possible defects 13 at the workpiece surface 2a or at the joining surface 8 and nevertheless to achieve a good welding result. Instead of the shown translational transverse movement of the laser beam 3 in direction A, the inclined laser beam 3 can also be pivoted back and forth in an oscillating manner or be rotated about an axis parallel to its direction of incidence.

[0031] FIG. 3B differs from FIG. 3A in that here the laser beam 3 has a beam profile based on a ring-shaped angular distribution, e.g. a Bessel shape. This beam profile or the Bessel shape has significant beam portions outside the optical axis of the laser beam 3. As a result, it is possible to minimize the effect of possible defects 13 at the workpiece surface 2a or at the joining surface 8 and to achieve a good welding result. The laser beam 3, instead of being radiated in obliquely as in FIG. 3B, can also be radiated in at right angles onto the workpiece top side 2a as in FIG. 2A. In that case, too, the disturbing influence of surface defects 13 at the butt joint is reduced (albeit not in the full angular range).

[0032] FIG. 3C differs from FIG. 2A in that here a plurality of, e.g., three, pulsed laser beams 3 having an e.g. Gaussian beam profile are radiated in. The laser beams 3 are offset parallel with respect to one another in direction 3, and their laser foci F are offset one behind another in the beam direction 9. The laser beams 3 are moved across the joining surface 8 at right angles to the joining surface 8 jointly in direction A to produce a plurality of weld seams 10.sub.1 offset parallel in the depth direction. This plurality of laser beams 3 likewise makes it possible to obtain good welding results, even in the event of defects 13 being present in the workpieces 2.

[0033] Instead of the translational transverse movement of the laser beam 3 in direction A as shown in FIGS. 3A to 3C, the inclined laser beam 3 in FIGS. 3A and 3B and respectively the plurality of laser beams 3 can also be pivoted back and forth in an oscillating manner or be rotated about an axis parallel to the direction of incidence.

[0034] In addition to the transverse and longitudinal movements of the laser beam 3 as shown in FIGS. 2A-2C and 3A-3C, the laser focus F of the laser beam 3 can also be moved in and counter to the beam direction in order thus to produce a weld seam that varies in the workpiece depth.

OTHER EMBODIMENTS

[0035] A number of embodiments of the present disclosure have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the present disclosure. Accordingly, other embodiments are within the scope of the following claims.