Methods and laser welding devices for deep welding a workpiece

1. A method for deep welding a workpiece, the method comprising:

irradiating a surface of the workpiece using a first laser beam and a second laser beam, wherein, in a workpiece surface plane, a first beam width B 1 of the first laser beam is greater than a second beam width B 2 of the second laser beam, and wherein the second laser beam is directed onto an area of the workpiece surface plane within an area of the workpiece surface plane onto which the first laser beam is directed,

wherein an intensity of the first laser beam alone is sufficient to produce a keyhole in the workpiece and the keyhole produced in the workpiece has a capillary width KB in the workpiece surface plane, wherein KB is substantially equal to B 1 , and B 2 ≤0.75*KB, wherein BPP 1 is a beam parameter product (BPP) of the first laser beam and BPP 2 is a beam parameter product of the second laser beam, wherein BPP 1 >BPP 2 , and wherein a high BPP represents a low beam quality;

guiding the first and second laser beams in a multicore fiber having at least one core fiber and a ring fiber, wherein the first laser beam is guided in the ring fiber and the second laser beam is guided in the core fiber, and the first and second laser beams exit from a fiber end of the multicore fiber before the workpiece;

directing the first and second laser beams by a common optical unit onto the workpiece; and

imaging the fiber end with the common optical unit in a common focus on or in the workpiece, wherein the common optical unit comprises a collimation lens and a focusing lens.

2. The method of claim 1 , wherein the first laser beam and the second laser beam have a same focal position or have focal positions spaced apart from one another by less than 1 mm in a direction perpendicular to the surface of the workpiece.

3. The method of claim 1 , wherein focal positions of the first and second laser beams are located in the workpiece surface plane or below the workpiece surface inside the keyhole.

4. The method of claim 1 , wherein BPP 1 >2*BPP 2 .

5. The method of claim 1 , wherein a first laser power L 1 of the first laser beam is less than or equal to a second laser power L 2 of the second laser beam.

6. The method of claim 5 , wherein L 2 >2*L 1 .

7. The method of claim 1 , wherein a first focusing angle W 1 of the first laser beam is less than or equal to a second focusing angle W 2 of the second laser beam.

8. The method of claim 1 , wherein for a smallest width KD of the keyhole in a top quarter closest to the workpiece surface, and for a greatest width G 2 of the second laser beam in the top quarter of the keyhole 0.8*KD>G 2 .

9. The method of claim 8 , wherein 0.6*KD >G 2 .

10. The method of claim 1 , further comprising aligning the first laser beam and the second laser beam coaxially to have a common beam axis.

11. The method of claim 10 , wherein the common beam axis extends substantially perpendicularly to the workpiece surface.

12. The method of claim 1 , wherein the multicore fiber is a two-in-one fiber having a core fiber and a ring fiber, wherein the first laser beam is guided in the ring fiber and the second laser beam is guided in the core fiber, and the first and second laser beams exit from a fiber end of the two-in-one fiber.

13. The method of claim 1 , wherein the common optical unit consists of a collimation lens and a focusing lens.

14. The method of claim 1 , further comprising generating an original laser beam from a common laser source, wherein a first part of the original laser beam is eccentrically coupled into the ring fiber and forms the first laser beam, and a second part of the original laser beam is coupled into the core fiber and forms the second laser beam.

15. A laser welding device, designed for carrying out a method of deep welding a workpiece, the method comprising:

guiding a first laser beam and a second laser beam in a multicore fiber having at least one core fiber and a ring fiber, wherein the first laser beam is guided in the ring fiber and the second laser beam is guided in the core fiber, and the first and second laser beams exit from a fiber end of the multicore fiber before the workpiece,

directing the first and second laser beams by a common optical unit onto the workpiece, wherein the common optical unit comprises a collimation lens and a focusing lens;

imaging the fiber end with the common optical unit in a common focus on or in the workpiece,

irradiating a surface of the workpiece using the first laser beam and the second laser beam, wherein, in a workpiece surface plane, a first beam width B 1 of the first laser beam is greater than a second beam width B 2 of the second laser beam, and wherein the second laser beam is directed onto an area of the workpiece surface plane within an area of the workpiece surface plane onto which the first laser beam is directed,

wherein an intensity of the first laser beam alone is sufficient to produce a keyhole in the workpiece and the keyhole produced in the workpiece has a capillary width KB in the workpiece surface plane, wherein KB is substantially equal to B 1 , and B 2 <0.75*KB, wherein BPP 1 is a beam parameter product (BPP) of the first laser beam and BPP 2 is a beam parameter product of the second laser beam, wherein BPP 1 >BPP 2 , and wherein a high BPP represents a low beam quality.

16. The method of claim 15 , wherein BPP 1 >2*BPP 2 .

17. The method of claim 15 , wherein BPP 1 >4*BPP 2 .

18. A method for deep welding a workpiece, the method comprising:

irradiating a surface of the workpiece using a first laser beam and a second laser beam,

wherein, in a workpiece surface plane, a first beam width B 1 of the first laser beam is greater than a second beam width B 2 of the second laser beam, and wherein the second laser beam is directed onto an area of the workpiece surface plane within an area of the workpiece surface plane onto which the first laser beam is directed,

wherein an intensity of the first laser beam alone is sufficient to produce a keyhole in the workpiece and the keyhole produced in the workpiece has a capillary width KB in the workpiece surface plane, wherein KB is substantially equal to B 1 , and B 2 <0.75*KB, and

wherein a first focusing angle W 1 of the first laser beam is less than or equal to a second focusing angle W 2 of the second laser beam.

19. The method of claim 18 , wherein the second laser beam has a better beam quality than the first laser beam.

20. The method of claim 18 , further comprising:

guiding the first and second laser beams in a two-in-one fiber having a core fiber and a ring fiber, wherein the first laser beam is guided in the ring fiber and the second laser beam is guided in the core fiber, and the first and second laser beams exit from a fiber end of the two-in-one fiber before the workpiece;

directing the first and second laser beams by a common optical unit onto the workpiece; and

imaging the fiber end with the common optical unit in a common focus on or in the workpiece, wherein the common optical unit comprises a collimation lens and a focusing lens.

21. The method of claim 1 , wherein BPP 1 >4*BPP 2 .

22. A laser welding device, designed for carrying out a method of deep welding a workpiece, the method comprising:

irradiating a surface of the workpiece using a first laser beam and a second laser beam,

wherein, in a workpiece surface plane, a first beam width B 1 of the first laser beam is greater than a second beam width B 2 of the second laser beam, and wherein the second laser beam is directed onto an area of the workpiece surface plane within an area of the workpiece surface plane onto which the first laser beam is directed,

wherein an intensity of the first laser beam alone is sufficient to produce a keyhole in the workpiece and the keyhole produced in the workpiece has a capillary width KB in the workpiece surface plane, wherein KB is substantially equal to B 1 , and B 2 <0.75*KB, and

wherein a first focusing angle W 1 of the first laser beam is less than or equal to a second focusing angle W 2 of the second laser beam.