Use of variable beam parameters to control a melt pool

1. A method for forming an article, comprising:

forming a melt pool;

exposing the melt pool to an optical beam comprising at least one beam characteristic;

forming a keyhole cavity in the melt pool, the keyhole cavity comprising at least one keyhole cavity property;

modifying the at least one beam characteristic in response to a change in the keyhole cavity property;

generating the optical beam in an optical beam delivery device including an optical fiber having a first length and a second length, the second length having two or more confinement regions, the optical beam delivery device further including a perturbation device configured to alter a bend radius of the first length;

launching the optical beam into the first length; and

guiding the optical beam into the second length,

wherein the modifying the at least one beam characteristic comprises:

activating the perturbation device to modify one or more beam characteristics of the optical beam in one or more of the first length, and the second length, and

confining at least a portion of the modified one or more beam characteristics of the optical beam within the two or more confinement regions of the second length.

2. The method of claim 1 , wherein a first amount of spatter is ejected from the melt pool after forming the melt pool and before the modifying the at least one beam characteristic, and

wherein a second amount of spatter is ejected from the melt pool after the modifying the at least one beam characteristic.

3. The method of claim 1 , wherein the modifying the at least one beam characteristic results in at least partial collapse of the keyhole cavity.

4. The method of claim 1 , wherein by the modifying the at least one beam characteristic, the optical beam comprises at least two different beam characteristics.

5. The method of claim 4 , wherein the modifying the at least one beam comprises switching between the at least two different beam characteristics.

6. The method of claim 5 , wherein the switching between the at least two different beam characteristics is performed at a frequency in a range from about greater than 0 Hz to about 1000 Hz.

7. The method of claim 1 , wherein the first length has a first refractive-index profile (RIP) and the second length has a second RIP,

wherein the first RIP differs from the second RIP.

8. The method of claim 7 , wherein the activating the perturbation device oscillates the one or more beam characteristics of the optical beam in one or more of the first length and the second length between at least two of a plurality of other beam characteristics at a frequency in a range of from greater than about 0 Hz to about 1000 Hz.

9. The method of claim 1 , wherein the at least one keyhole cavity property is at least partially determinative of forming an amount of spatter.

10. The method of claim 1 , further comprising forming a first amount of spatter before the modifying the at least one beam characteristic, and forming a second amount of spatter after the modifying the at least one beam characteristic.

11. The method of claim 10 , wherein the second amount of spatter is different than the first amount of spatter.

12. The method of claim 11 , wherein the second amount of spatter is less than the first amount of spatter.

13. The method of claim 11 , further comprising determining a first attribute of the first amount of spatter and determining a second attribute of the second amount of spatter.

14. The method of claim 1 , wherein the at least one keyhole cavity property comprises a cross-sectional area of the cavity.

15. The method of claim 1 , wherein the modifying the at least one beam characteristic is performed continuously over a range of values.

16. The method of claim 1 , wherein the modifying the at least one beam characteristic is performed by oscillating between a plurality of discrete values.

17. The method of claim 1 , wherein the at least one beam characteristic includes a beam parameter product (BPP).

18. The method of claim 1 , wherein the at least one keyhole cavity property comprises a detectable signature.

19. The method of claim 18 , further comprising providing a detectable signature of the at least one keyhole cavity property to a sensor configured to generate a signal in response to sensing a signature of a keyhole cavity property.

20. The method of claim 19 , further comprising providing the signal to a processor, wherein the processor is in communication with the sensor and with the optical beam delivery device, wherein the processor is configured to access a memory that stores data and instructions, and wherein the processor is configured to execute the instructions, wherein the instructions comprise:

retrieving a stored value from the data stored by the memory, the stored value corresponding to a known property of a keyhole cavity characteristic;

converting the signal generated by the sensor to a signature value corresponding to the keyhole cavity characteristic;

calculating a difference between the stored value and the signature value; and

wherein the modifying the at least one beam characteristic further comprises modifying the at least one beam characteristic when the difference is greater than a predetermined threshold value.

21. The method of claim 20 , wherein the detectable signature comprises a first spatter volume.

22. The method of claim 1 , further comprising depositing at least a portion of the melt pool on a build layer.

23. The method of claim 1 , wherein the forming the melt pool comprises a step in an additive manufacturing process.

24. The method of claim 1 , further comprising forming at least a portion of the melt pool as a weld.

25. The method of claim 1 , wherein the forming the melt pool comprises a step in a laser-welding process.

26. A method for changing an amount of spatter during laser-melting a material, comprising:

forming a melt pool,

ejecting a first amount of spatter from the melt pool;

exposing the melt pool to an optical beam comprising at least one beam characteristic;

modifying the at least one beam characteristic in response to the ejecting the first amount of spatter;

generating the optical beam in an optical beam delivery device including an optical fiber having a first length and a second length, the second length having two or more confinement regions, the optical beam delivery device further including a perturbation device configured to alter a bend radius of the first length;

launching the optical beam into the first length; and

guiding the optical beam into the second length,

wherein the modifying the at least one beam characteristic comprises:

activating the perturbation device to modify one or more beam characteristics of the optical beam in one or more of the first length, and the second length, and

confining at least a portion of the modified one or more beam characteristics of the optical beam within the two or more confinement regions of the second length.

27. The method of claim 26 , further comprising ejecting a second amount of spatter from the melt pool after the modifying the at least one beam characteristic, wherein the second amount of spatter is less than the first amount of spatter.