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CN-115246035-B - Method for monitoring a laser machining process and associated laser machining system

CN115246035BCN 115246035 BCN115246035 BCN 115246035BCN-115246035-B

Abstract

The invention relates to a method for determining the depth of a vapor capillary during a laser machining process, comprising the steps of applying a machining laser beam to at least one workpiece for forming the vapor capillary, wherein the machining laser beam is deflected by a first deflection device on the workpiece along a machining path in a first scanning field, applying an optical measuring beam to the workpiece, wherein the optical measuring beam is deflected by a second deflection device on the workpiece along a detection path relative to the machining laser beam and is subsequently deflected by the first deflection device together with the machining laser beam, detecting distance measurement values along the detection path on the basis of the portion of the optical measuring beam reflected by the workpiece, determining the depth and/or the position of one of the vapor capillary on the basis of the detected distance measurement values, wherein the size of the detection area is determined on the basis of the position of the machining laser beam and/or on the basis of the deflection of the machining laser beam by the first deflection device. Furthermore, a laser processing system is proposed.

Inventors

  • WALDE TIM
  • R. MOSER
  • 1. Shikalban
  • D. Miletique

Assignees

  • 普雷茨特两合公司

Dates

Publication Date
20260505
Application Date
20220407
Priority Date
20210407

Claims (20)

  1. 1. A method for monitoring a laser machining process, comprising: Irradiating a processing laser beam (14) onto at least one workpiece (18 a, 18 b) for forming a vapor capillary, wherein the processing laser beam (14) is deflected on the workpiece (18 a, 18 b) by a first deflection device (26) along a processing path (70) within a first scan field (64) of the first deflection device (26), -Irradiating an optical measuring beam (36) onto the workpiece (18 a, 18 b), wherein the optical measuring beam (36) is deflected by a second deflection device (52) relative to the processing laser beam (14) and subsequently deflected together with the processing laser beam (14) by the first deflection device (26), wherein the optical measuring beam (36) is deflected on the workpiece (18 a, 18 b) along a detection path (82) in a detection region (76) by the second deflection device (52), wherein the second deflection device (52) has a second scanning field (66), Detecting distance measurement values along the detection path (82) on the basis of the portion of the optical measurement beam (36) reflected by the workpiece (18 a, 18 b), Determining the depth and/or position of the vapor capillary based on the detected distance measurement, Wherein the area of the detection region (76) on the workpiece (18 a, 18 b) and the position of the detection region (76) are adapted on the basis of the position (68) of the processing laser beam (14) in the first scan field (64), wherein the area of the detection region (76) is smaller than the area of the second scan field (66) of the second deflection device (52).
  2. 2. The method of claim 1, wherein the shape of the detection region (76) is matched further based on a position (68) of the processing laser beam (14) in the first scan field (64), and/or Wherein the position, area and/or shape of the detection zone (76) is adapted based on the processing speed along the processing path (70).
  3. 3. The method according to claim 1 or 2, further comprising determining a theoretical position (80) of the vapour capillary, and determining the position of the detection zone (76) based on the determined theoretical position (80) of the vapour capillary.
  4. 4. Method according to claim 1 or 2, wherein the processing laser beam (14) is moved along the processing path (70) without superposition of oscillating movements and/or, Wherein the processing laser beam (14) is moved along the processing path (70) only by deflection by means of the first deflection means (26) and/or, Wherein the laser processing head remains stationary relative to the workpiece during the laser processing process, by means of which the processing laser beam (14) impinges on the workpiece.
  5. 5. The method according to claim 1 or 2, wherein the closer the position (68) of the processing laser beam (14) is to the edge of the first scan field (64) and/or the greater the processing speed, the greater the area of the detection region (76) is determined.
  6. 6. The method according to claim 1 or 2, wherein the greater the processing speed, the greater the distance between the position of the detection zone (76) and the position (68) of the processing laser beam (14) is determined.
  7. 7. The method according to claim 1 or 2, wherein the position, shape and/or area of the detection region (76) is determined such that the position (68) of the processing laser beam (14) is located outside the detection region (76).
  8. 8. The method of claim 1 or 2, wherein the second scan field (66) is smaller than the first scan field (64).
  9. 9. The method according to claim 1 or 2, wherein the position (68) of the processing laser beam (14) is the current position of the processing laser beam (14) during the laser processing process, and/or Wherein the detection zone (76) is determined in real time.
  10. 10. The method according to claim 1 or 2, wherein the theoretical position (80) of the detection zone (76) and/or the vapour capillary is determined based on at least one of the following parameters: -a machining direction (74) of the machining laser beam, -a velocity vector of the machining laser beam, -a power of the machining laser beam (14), -a material and/or thickness of the at least one workpiece (18 a, 18 b), -a deflection angle of the first deflection means (26), -an optical path length of the machining laser beam (14) between a laser source (12) for the machining laser beam (14) and the at least one workpiece (18 a, 18 b), -an optical path length of the optical measuring beam (36) between a radiation source of the optical measuring beam (36) and the at least one workpiece (18 a, 18 b), -a focal position of the machining laser beam (14), -a focal position of the optical measuring beam (36), -a cross-sectional shape of the machining laser beam (14) in focus, -a cross-sectional shape of the optical measuring beam (36) in focus, -and-orientation of the laser machining system (10) and the at least one workpiece (18 a, 18 b) relative to each other.
  11. 11. The method according to claim 1 or 2, wherein the detection path (82) has a shape of the number "8", a spiral, a circle, a circular arc, a zigzag and/or a meander within the detection zone (76).
  12. 12. The method according to claim 1 or 2, wherein the detection region (76) is determined based on table values and/or in case an artificial neural network is used and/or based on a functional relationship.
  13. 13. The method according to claim 1 or 2, wherein the at least one workpiece (18 a, 18 b) comprises a battery cell and the irradiation of the processing laser beam (14) effects contact for the battery cell.
  14. 14. The method of claim 1, wherein the laser machining process is a laser welding process.
  15. 15. The method of claim 10, wherein the determination of the detection zone (76) comprises a determination of a location, a shape and/or an area of the detection zone (76).
  16. 16. The method of claim 10, wherein the orientation of the laser processing system (10) and the at least one workpiece (18 a, 18 b) relative to each other comprises an orientation of a laser processing head (16) of the laser processing system (10) and the at least one workpiece (18 a, 18 b) relative to each other.
  17. 17. A laser machining system (10), comprising: -a laser processing head (16) for irradiating a processing laser beam (14) onto at least one workpiece (18 a, 18 b) for forming a vapor capillary, wherein the laser processing head (16) comprises a first deflection device (26) for deflecting the processing laser beam (14) along a processing path (70) on the workpiece (18 a, 18 b) within a first scan field (64); -measuring means (34) for interferometric ranging, which are provided for irradiating an optical measuring beam (36) onto the at least one workpiece (18 a, 18 b), and which comprise second deflection means (52) for deflecting the optical measuring beam (36) on the workpiece (18 a, 18 b) along a detection path (82) relative to the machining laser beam (14) in a detection region (76), wherein the second deflection means (52) have a second scan field (66); coupling means (56) for coupling the optical measuring beam (36) into the laser processing head (16), which coupling means are arranged in front of the first deflection means (26) in the beam propagation direction of the processing laser beam (14) such that the optical measuring beam (36) can be deflected by the first deflection means (26) together with the processing laser beam (14), Wherein the measuring device (34) is configured for detecting distance measurement values along the detection path (82) on the basis of the portion of the optical measuring beam (36) reflected by the workpiece (18 a, 18 b), for determining the depth and/or the position (78) of the vapor capillary, and for matching the area of the detection region (76) on the workpiece (18 a, 18 b) and the position of the detection region (76) on the basis of the position (68) of the processing laser beam (14) within the first scan field (64), wherein the area of the detection region is smaller than the area of the second scan field (66) of the second deflection device (52).
  18. 18. The laser machining system according to claim 17, wherein the first deflection means (26) are arranged for deflecting the machining laser beam (14) along a first axis (x) by a first maximum deflection angle (28) and for deflecting the machining laser beam (14) along a second axis (y) by a predetermined second maximum deflection angle (29), wherein the first and second axes (x, y) are perpendicular to each other, Wherein the first scan field (64) is predefined by the first maximum deflection angle (28) and the second maximum deflection angle (29), wherein the first maximum deflection angle (28) and/or the second maximum deflection angle (29) is equal to or greater than 10 degrees.
  19. 19. The laser machining system of claim 17 or 18, wherein the measuring device (34) comprises a collimation device (48) for adjusting the focal position of the optical measuring beam (36), Wherein the measuring device (34) is arranged for controlling the collimating device (48) in order to adjust the focal position of the optical measuring beam (36) on the basis of the position of the optical measuring beam (36) within the first scan field (64) and/or within the second scan field (66) of the second deflection device (52).
  20. 20. The laser machining system of claim 17 or 18, wherein the measuring device (34) is or comprises an optical coherence tomography device.

Description

Method for monitoring a laser machining process and associated laser machining system Technical Field The present invention relates to a method for monitoring a laser machining process, in particular a laser welding process, and to a laser machining system, in particular a laser welding system, for monitoring a laser machining process. Background In a laser processing system (also referred to as a laser processing apparatus or simply apparatus), in order to process a workpiece, a processing laser beam emitted from a laser beam source or a laser fiber end is focused onto the workpiece to be processed. The machining may include laser beam welding. The laser processing system may include a laser processing head, such as a laser welding head, in which beam directing optics are integrated. For machining, a laser beam is irradiated onto the workpiece surface, wherein the laser beam is moved over the surface along a so-called machining path. Here, a vapor capillary, also called a Keyhole (Keyhole), is formed in the region between the workpiece surfaces (onto which the laser beam is irradiated) up to a certain depth within the workpiece. In the region of the vapor capillary, the material of the workpiece is heated so strongly by the irradiated laser power that the material evaporates. The vapor capillary is surrounded by a region of the material in a molten state. This region is called the puddle. The depth of the vapor capillary, i.e. the distance between the (raw) surface of the workpiece and the deepest part of the vapor capillary, is of great significance. The depth of the vapor capillary is, for example, related to the weld depth, i.e., the depth to which the material of the workpiece has melted during processing. Knowing the depth of the vapor capillary or the weld depth allows, on the one hand, to infer the strength of the welded connection, i.e. whether it has been welded deep enough, and, on the other hand, by knowing the depth of the vapor capillary, it can be ensured that the weld is not visible on the underside, i.e. that there is no undesired penetration of the weld. Thus, the depth of the vapor capillary, also known as keyhole depth, is a determining factor for the quality of the weld produced in laser beam welding. The deepest part of the vapor capillary is also called the keyhole bottom or the process substrate. For this reason, measurement of the depth of the vapor capillary during laser beam welding is of great significance. Recently, depth or distance measurement was achieved without contact by means of optical coherence tomography (english "optical coherence tomography", abbreviated as "OCT"). For this purpose, an optical measuring beam (also referred to as OCT measuring beam) of the optical coherence tomography apparatus impinges on the workpiece, and a portion of the optical measuring beam is reflected from the workpiece back into the optical coherence tomography apparatus. However, in order to be able to measure the depth of the vapor capillary reliably, it must be ensured that the optical measuring beam enters the vapor capillary at the deepest point and that the light reflected therefrom returns back into the optical coherence tomography apparatus. Typically, the position of the deepest part of the vapor capillary does not coincide with the position of the processing laser beam. The position, shape and size of the vapor capillary on the workpiece surface depend on the current parameters of the laser machining process. The parameters include, for example, a processing speed (also referred to as a feed speed), a processing direction, a power of a processing laser beam, a focal point size of the processing laser beam, a material of a workpiece, and the like. For example, an increase in the processing speed results in an increase in the distance between the location of the vapor capillary and the location of the processing laser beam. For this reason, positioning the OCT measuring beam on the workpiece in such a way that the deepest part of the vapor capillary can thus be reliably determined is one of the greatest challenges. If a so-called scanning system is used as a laser machining system for laser beam welding, in which the machining laser beam is moved through the machining path by means of a scanning mirror or other deflection unit, the problem is amplified again. Since chromatic aberration and angular variations of the processing laser beam and the OCT measuring beam relative to the objective lens and the workpiece cause the OCT measuring beam to be located at a different position on the workpiece than the processing laser beam. Furthermore, in scanning systems, especially in scanner-based welding systems, often operate at high processing speeds, so that typically the deviation between the position of the vapor capillary and the position or focal point of the processing laser is significantly greater than in fixed optical systems. This problem is exacerbated by the frequent changes in we