LASER WELDING OF TRANSPARENT WORKPIECES

Abstract

Methods and devices for laser welding of mutually overlapping workpieces by pulsed laser beams, for example, Ultrashort-pulsed (USP) laser beams, are provided. In one aspect, a method includes directing a pulsed laser beam through one workpiece onto the other workpiece and moving the pulsed laser beam in a feed direction relative to the two workpieces to produce a weld seam between the two workpieces bearing against one another. A deflection back and forth of the pulsed laser beam directed transversely or parallel to the feed direction is superposed on the pulsed laser beam moved in the feed direction.

Claims

1. A method of laser welding of two mutually overlapping workpieces by a pulsed laser beam, the method comprising: directing the pulsed laser beam through a first workpiece onto a second workpiece, the first and second workpieces mutually overlapping each other; and moving the pulsed laser beam in a feed direction relative to the first and second workpieces to produce a weld seam between the first and second workpieces, wherein a deflection back and forth of the pulsed laser beam directed transversely or parallel to the feed direction is superposed on the pulsed laser beam moved in the feed direction.

2. The method of claim 1, wherein at least one of the first workpiece or the second workpiece is formed from at least one of glass, polymer, or glass ceramic.

3. The method of claim 2, wherein the at least one of the first workpiece or the second workpiece is formed partially with an opaque material.

4. The method of claim 1, wherein at least one of the first workpiece or the second workpiece has a transparency of at least 90% at a laser wavelength of the pulsed laser beam.

5. The method of claim 1, wherein the first and second workpieces are moved exclusively in the feed direction and at the same time the laser beam is deflected back and forth exclusively transversely or parallel to the feed direction.

6. The method of claim 1, wherein the first and second workpieces are moved with a constant feed velocity in the feed direction.

7. The method of claim 1, wherein the first and second workpieces are moved with a feed velocity with acceleration in the feed direction.

8. The method of claim 1, wherein the laser beam is deflected back and forth periodically with an identical amplitude transversely to the feed direction to produce the weld seam.

9. The method of claim 1, wherein the weld seam is in a form of a zigzag line or a sine curve.

10. The method of claim 1, wherein one or more pulses of the pulsed laser beam have at least one parameter chosen such that a nonlinear absorption process occurs during the laser welding in at least one of the first workpiece or the second workpiece.

11. The method of claim 1, wherein the pulsed laser beam comprises an Ultrashort-pulsed (USP) laser beam in a form of USP laser pulses.

12. A laser processing machine for laser welding of two mutually overlapping workpieces, the laser processing machine comprising: a laser configured to generate a pulsed laser beam; a scanner configured to deflect the pulsed laser beam transversely or parallel to a feed direction; and a machine controller configured to control the scanner such that a deflection back and forth of the pulsed laser beam directed transversely or parallel to the feed direction is superposed on a movement of the laser beam relative to the two mutually overlapping workpieces in the feed direction.

13. The laser processing machine of claim 12, wherein at least one of the two mutually overlapping workpieces has a transparency of at least 90% at a laser wavelength of the pulsed laser beam.

14. The laser processing machine of claim 12, wherein the laser comprises an Ultrashort-pulsed (USP) laser for generating a USP laser beam in a form of USP laser pulses.

15. The laser processing machine of claim 12, further comprising: a workpiece mover configured to move the two mutually overlapping workpieces in the feed direction, wherein the machine controller is configured to control the workpiece mover and the scanner such that the laser beam is moved relative to the two mutually overlapping workpieces in the feed direction and the deflection back and forth of the laser beam directed transversely or parallel to the feed direction is superposed on the movement.

16. The laser processing machine of claim 12, wherein the machine controller is configured to control the scanner such that a weld seam is produced between the two mutually overlapping workpieces that abut on one another.

17. The laser processing machine of claim 16, wherein the weld seam is in a form of a zigzag line or a sine curve.

18. The laser processing machine of claim 12, wherein the machine controller is configured to control the scanner such that a focus of the pulsed laser beam is in a volume of one of the two mutually overlapping workpieces, the volume being below or above a joining area of the one of the two mutually overlapping workpieces.

19. The laser processing machine of claim 12, wherein one or more pulses of the pulsed laser beam have parameters chosen such that a nonlinear absorption process occurs during the laser welding in at least one of the two mutually overlapping workpieces.

20. The laser processing machine of claim 12, wherein the scanner is formed by at least one of an electro-optical deflector, an acousto-optical deflector, a piezo-adjustable deflector, or a deflector based on microelectromechanical system (MEMS).

Description

DESCRIPTION OF DRAWINGS

[0018] FIG. 1 schematically shows a laser processing machine for laser welding of two laser-transparent workpieces by means of a laser beam, the upper workpiece being partly cut away in its illustration.

[0019] FIGS. 2A and 2B show two different weld seams according to the invention on two laser-welded workpieces, the upper workpiece being partly cut away in its illustration.

[0020] FIG. 3 shows the polarization contrast intensity of a rectilinear weld seam and a zigzag weld seam on two laser-welded workpieces, in each case in a plane view of the lap joint of the two laser-welded workpieces.

DETAILED DESCRIPTION

[0021] The laser processing machine 1 shown in FIG. 1 serves for laser welding of two mutually overlapping workpieces 2a, 2b by means of a laser beam 3, where at least the upper workpiece 2a in FIG. 1, in particular also the other, lower workpiece 2b, has a transparency of at least 90% at the laser wavelength and is formed for example from glass, in particular quartz glass, from polymer, glass ceramic, in a crystalline fashion or from combinations thereof and/or with opaque materials.

[0022] 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, in particular less than 10 ps, a movement unit (e.g., a workpiece mover such as a workpiece table) 6, which is movable in the x-y-direction, for jointly moving the two workpieces 2a, 2b to be welded, and also a scanner 7 for two-dimensionally deflecting the laser beam 3 on the two workpieces 2a, 2b to be welded.

[0023] The scanner 7 is for example a microscanner (e.g., a galvanometer scanner) with a high-Na microscope objective. In this case, the USP laser pulses 5 emitted by the USP laser 4 are deflected by a galvanometer scanner 7, the beam deflection of which is imaged via a telescope (not shown) into the region of the focal plane of the microscope objective. The laser beam 3 can be deflected by the scanner 7 in two transverse axes, and the deflected laser beam 3 is imaged by means of the telescope onto the microscope objective of the scanner 7, said microscope objective being situated just in front of the workpiece to be processed. Alternatively, the beam deflection can also be effected by means of deflectors that are electro-optical, acousto-optical, piezo-adjustable or else based on microelectromechanical system (MEMS) technology.

[0024] During the laser welding of the two workpieces 2a, 2b, the laser beam 3 is directed through the upper workpiece 2a in FIG. 1 onto the lower workpiece 2b and is movede.g., by means of movement of the movement unit 6relative to the two workpieces 2a, 2b along a here rectilinear feed trajectory 8 in order that the two workpieces 2a, 2b are locally melted at their joining areas 9a, 9b abutting on one another and are thus connected to one another. A deflection back and forth (double-headed arrow 11) of the laser beam 3 directed transversely, here at right angles, to the respective feed direction 10 is superposed on the laser beam 3 moved along the feed trajectory 8, in order thereby to produce a weld seam 12 in the shape of, e.g., a zigzag or serpentine line on the top side 8. In this case, advantageously, the laser focus of the focused laser beam 3 is not situated on the joining area, but rather in the volume of the second workpiece 2b near its joining area 9b. The weld seam 12 can be embodied as a regular zigzag line (FIG. 2A) or as a sine curve (FIG. 2B) as a result of the superposition of a uniform feed movement and a periodic transverse deflection of the laser beam 3.

[0025] The weld seam 12 in the shape of a zigzag or serpentine line brings about on average lower stresses than a rectilinear weld seam, where stress maxima occur in a manner separated from one another. Microscopic displacements (strains) on account of the change in volume of the workpiece material cannot accumulate along a preferred direction and thus cannot predefine a breaking line. The stresses that are laser-induced during the pass of the laser beam 3 are reduced or redistributed, with the result that a higher strength is achieved in comparison with conventional laser welding.

[0026] A deflection back and forth of the laser beam 3 directed parallel to the respective feed direction 10, instead of transversely as shown, can also be superposed on the laser beam 3 moved along the feed trajectory 8, in order thereby to produce a longitudinal weld seam (not shown) on the top side 8.

[0027] The following laser parameters can be chosen: [0028] laser wavelength between 200 and 5000 nm, [0029] repetition rate of the laser pulses between 1 kHz and 500 GHz, [0030] laser pulse duration between 10 fs and 500 ps, [0031] focusing and pulse energy such that the fluence in the focus zone is greater than 0.01 J/cm.sup.2.

[0032] The modification threshold given a pulse duration of approximately 1 ps and a laser wavelength of approximately 1 m here in the case of glass, for example, is approximately 1 to 5 J/cm.sup.2 in the volume, and approximately 0.1-0.5 J/cm.sup.2 at the surface.

[0033] One measure of the laser-induced stresses (stress birefringence) is the polarization contrast intensity, which is illustrated in FIG. 3 by way of example for the case of a rectilinear weld seam (curve a) and the weld seam in the shape of a zigzag or serpentine line according to the invention (curve b). In the case of the rectilinear weld seam (a), the induced stress is comparably high over the entire modified region and indicates a uniform, continuous stress distribution. The weld seam (b) in the shape of a zigzag or serpentine line exhibits on average lower stress maxima with intensity peaks occurring in a manner separated from one another, as a result of which the strength of the laser-bonded connection is increased.