BUTT WELDING WITH ULTRASHORT PULSE LASER BEAMS, AND OPTICAL ELEMENTS JOINED TOGETHER FROM INDIVIDUAL PARTS

Abstract

The present disclosure provides methods, devices, and systems for the butt welding of two, e.g., planar, workpieces composed of glass, e.g., quartz glass, by a pulsed laser beam, e.g., an ultrashort pulse (“USP”) laser beam, which is directed into the workpiece material parallel to the joining surface of the two workpieces and which is focused into the workpiece material in the region of the joining surface to locally melt the two workpieces in the region of their joining surface, wherein the laser focus of the laser beam focused into the workpiece material is moved in or counter to the beam direction of the laser beam to produce in the region of the joining surface a weld seam extending along the beam direction.

Claims

1. A method for butt welding two workpieces composed of glass, the method comprising: focusing at least one ultrashort pulse laser beam into the two workpieces parallel to a joining surface of the two workpieces and focusing the at least one ultrashort pulse laser beam into a region of the joining surface to locally melt the two workpieces in the region of their joining surface; and moving a laser focus of the ultrashort pulsed laser beam in or counter to a beam direction of the laser beam to produce in the region of the joining surface a weld seam extending along the beam direction.

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

3. The method of claim 1, wherein the movement of the laser focus in or counter to the beam direction is effected continuously or step-by-step.

4. The method of claim 3, wherein the movement of the laser focus in or counter to the beam direction is effected continuously at an advance speed of 0.5 mm/s to 100 mm/s.

5. The method of claim 3, wherein the movement of the laser focus in or counter to the beam direction is effected continuously at an advance speed of 5 mm/s to 30 mm/s.

6. The method of claim 3, wherein the movement of the laser focus in or counter to the beam direction is effected continuously at an advance speed of 20 mm/s.

7. The method of claim 1, wherein the weld seam has a seam diameter of 5 to 500 μm.

8. The method of claim 1, wherein the weld seam has a seam diameter of 50 to 100 μm.

9. The method of claim 1, wherein a transverse movement of the laser focus is also superimposed on the advance movement of the laser focus in or counter to the radiation direction of the laser beam.

10. The method of claim 1, wherein the ultrashort pulsed laser beam comprises a laser pulse packet consisting of individual pulses.

11. The method of claim 10, wherein the individual pulses in the pulse packet are identical.

12. The method of claim 1, wherein the laser beam impinges at right angles or obliquely on a workpiece side facing the laser beam.

13. The method of claim 1, wherein a plurality of weld seams are produced at a distance from one another along a joining line of the two workpieces.

14. The method of claim 1, wherein during the movement of the laser focus in or counter to the beam direction, the laser beam is not moved relative to the two workpieces.

15. The method of claim 1, wherein during the advance movement of the laser focus in or counter to the beam direction, the laser beam is moved relative to the two workpieces parallel or transversely with respect to a joining line of the two workpieces.

16. The method of claim 15, wherein a focus speed at which the laser focus is moved in or counter to the beam direction is greater than an advance speed at which the laser beam is moved parallel or transversely with respect to the joining line.

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

17. An optical element composed of glass, comprising two individual parts that are laser-welded to one another, wherein the two individual parts are laser-welded to one another by at least one weld seam extending in a thickness direction of the two individual parts.

18. The optical element of claim 17, wherein the weld seam extends at right angles or obliquely with respect to a surface of the optical element.

19. The optical element of claim 17, wherein the weld seam has a length of at least 50 μm.

20. The optical element of claim 17, wherein the weld seam is a continuous line or a repeatedly interrupted line.

21. The optical element of claim 17, wherein a plurality of weld seams extending in the thickness direction of the two individual parts are arranged at a distance from one another along the joining line of the two individual parts.

22. The optical element of claim 17, wherein the weld seam has a seam diameter of 5 to 500 μm.

Description

DESCRIPTION OF DRAWINGS

[0021] Further advantages and advantageous configurations of the subject matter of the invention are evident from the description, the claims and the drawing. Likewise, the features mentioned above and those presented further below can each be used by themselves or as a plurality in any desired combinations. The embodiments shown and described should not be understood as an exhaustive enumeration, but rather are of exemplary character for outlining the invention.

[0022] FIG. 1 is a schematic diagram of a laser processing machine for the butt welding of two laser-transparent workpieces together using a laser beam as described herein, one of the two workpieces being illustrated in a cut-away view in the region of vertical weld seams.

[0023] FIGS. 2A-2C are a series of schematic diagrams of a different vertical advance movements of the laser focus in the beam direction of the laser beam during butt welding to produce a weld seam, in a sectional view along the joining surface of the two laser-welded workpieces.

[0024] FIGS. 3A-3C are a series of photographs of a vertical weld seams that were produced in a monolithic glass block with the vertical advance movements of the laser focus as shown in FIGS. 2A-2C.

[0025] FIGS. 4A-4C are a series of schematic diagrams of different vertical advance movements of the laser focus counter to the beam direction of the laser beam during butt welding to produce a vertical weld seam, in a sectional view along the joining surface of the two laser-welded workpieces.

[0026] FIGS. 5A-5C are a series of photographs of vertical weld seams that were produced in a monolithic glass block with the vertical advance movements of the laser focus as shown in FIGS. 4A-4C.

DETAILED DESCRIPTION

[0027] 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 a laser beam 3. The two workpieces 2 are formed for example from, e.g., glass, quartz glass, polymer, glass ceramic, in crystalline fashion or from combinations thereof and/or with opaque materials.

[0028] 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 10 ps, e.g., in the form of femtosecond pulses, a horizontal workpiece table 6, on which the two workpieces 2 to be welded bear next to one another, and a laser processing head 8, which is movable in X-Y-directions and is height-positionable in the direction of the double-headed arrow 7 and has a focusing optical unit 9 for focusing the laser beam 3 emerging at the bottom of the laser processing head 8. As an alternative or in addition to the laser processing head 8 that is movable in X-Y-directions, the workpiece table 6 can also be moved in X-Y-directions.

[0029] During the butt welding of the two workpieces 2, the laser beam 3 is directed at right angles onto the workpiece top side 10a facing the laser processing head 8 and is focused into the workpiece material in the region of the common joining surface 11 of the two workpieces 2 to locally melt the two workpieces 2 in the region of the joining surface 11. In this case, the laser focus F of the laser beam 3 is moved in or counter to the beam direction 12 of the laser beam 3 to produce in the region of the joining surface 11 a vertical weld seam 13 extending in the beam direction 12. In this case, the laser focus F of the focused laser beam 3 is situated at the joining surface 11 or in proximity to said joining surface 11 in the volume of one of the two workpieces 2. Ideally, the process starts before the laser focus F to allow for power tolerances. Butt welding work is in the vicinity of or in very close proximity to the joining surface 11. The vertical weld seam 13 extends almost over the entire workpiece thickness and ends before the workpiece top side and underside 10a, 10b such that no escape of material arises and a clean process is conducted. This depends on the size of the weld seam 13 or the welding bubble. Instead of being directed at right angles to the workpiece top side 10a as in FIG. 1, the laser beam 3 can also be directed obliquely onto the workpiece top side 10a, such that the weld seam produced in the workpiece volume runs obliquely with respect to the workpiece top side 10a (e.g., 45° welding). The workpiece underside 10b of the two workpieces 2 can for example be coated, e.g., with a highly reflective coating. A plurality of vertical weld seams 13 can be produced at a distance from one another along the joining line 15 of the two workpieces. The joining line 15 can also run non-straight, instead of straight as shown in FIG. 1.

[0030] FIGS. 2A-2C schematically show different vertical advance movements of the laser focus F in the workpiece volume in the beam direction 12, wherein during this vertical advance movement of the laser focus F the laser beam 3 is stationary relative to the two workpieces 2. In FIG. 2A the laser focus F is moved in the beam direction 12 continuously (e.g., at a vertical advance speed of 20 mm/s) and in FIGS. 2B and 2C, the laser focus is moved step by step without pauses (FIG. 2B) and with a temporal pause (e.g., 2 seconds) between the steps (FIG. 2C). As shown in FIGS. 2A-2C, the laser beam 3 can impinge on the workpiece top side 10a at right angles or alternatively obliquely.

[0031] FIGS. 3A-3C are photographs of vertical weld seams 13 produced by the vertical advance movements of the laser focus F as shown in FIGS. 2A 2C in a monolithic glass block. As shown in FIGS. 3A-3C, both the continuous and the step-by-step movement of the laser focus F in the beam direction 12 result in a vertical weld seam 13 which is formed from solidification bubbles (which arise on account of local material densifications) or individual spot welds 14 and extends in the thickness direction D of the two workpieces 2 (as shown in FIG. 1). It should be emphasized here that an individual spot weld 14 can also be placed through individual spot welds 14 that have already been produced beforehand. In FIG. 3B the respective next individual spot weld 14 is produced in the material still hot from the preceding individual spot weld 14, whereas in FIG. 3C the respective next individual spot weld 14 is produced in the material that has already cooled down owing to the temporal delay with respect to the preceding individual spot weld 14. No appreciable difference can be ascertained between the weld seam 13 in material processed hot (FIG. 3B) and in cooled-down material (FIG. 3C). As a result, the continuous movement and the step-by-step movement of the laser focus F in the beam direction 12 give rise to a vertical weld seam 13. In this case, bubbles 14 arise during the solidification of the weld seam 13 on account of rapid expansion and cooling. The bubbles 14 are not desired, but are difficult to prevent.

[0032] FIGS. 4A-4C schematically show different vertical advance movements of the laser focus F in the workpiece volume counter to the beam direction 12, wherein during this vertical advance movement of the laser focus F, the laser beam 3 is stationary relative to the two workpieces 2. In FIG. 4A the laser focus F is moved counter to the beam direction 12 continuously (e.g., at a vertical advance speed of 20 mm/s) and in FIGS. 4B, 4C said laser focus is moved step by step without pauses (FIG. 4B) and with a temporal pause (e.g., 2 seconds) between the steps (FIG. 4C).

[0033] FIGS. 5A-5C are photographs of vertical weld seams 13 produced by the vertical advance movements of the laser focus F as shown in FIGS. 4A-4C in a monolithic glass block. As shown in FIG. 5A, the continuous movement of the laser focus F counter to the beam direction 12 results in a continuous, vertical weld seam 13 without discernible solidification bubbles or individual spot welds. In FIG. 5B welding occurs in material still hot from the preceding step, and in FIG. 5C welding occurs in material that has already cooled down due to the temporal delay with respect to the preceding step. FIGS. 5B and 5C each show a vertical weld seam 13 interrupted by solidification bubbles 14 with distinct cracks along the entire weld seam 13. As a result, only the continuous movement of the laser focus F counter to the beam direction 12 gives rise to a continuous, crack-free vertical weld seam 13 extending in the thickness direction D of the two workpieces 2.

[0034] During the vertical advance movement of the laser focus F in or counter to the beam direction 12, the laser beam 3 can also be moved relative to the two workpieces 2 in an advance direction running parallel or transversely with respect to the joining line 15, e.g., by the laser processing head 8 being correspondingly moved in the X-direction and Y-direction. In this case, however, the focus speed at which the laser focus F is moved in or counter to the beam direction 12 should be greater than the advance speed at which the laser beam 3 is moved in the advance direction.

[0035] By the butt welding methods described above, for example, individual mirror elements 2 (e.g., for a linear optical system) can be joined together to form a large mirror by one or more vertical weld seams being placed along the joining line. Moreover, poor horizontal weld seams can be corrected by vertical weld seams that are placed through a horizontal weld seam. The weld seam can also have a circular shape or other freeform contour. It is also possible to weld slightly curved surfaces with slight movement in the X-direction during Z-welding.

Other Embodiments

[0036] 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.