Method for assessing a weld seam produced on a workpiece during a laser welding process using a laser beam and welding device for carrying out the method

Abstract

Method (1) for assessing a weld seam (5) produced on a workpiece (4) during a laser welding process (2) by means of a laser beam (3), wherein a welding device (6) having a laser beam optics (7) and a measuring beam optics (8) configured to perform continuous optical coherence tomography, as well as a workpiece (4) and two or more joining partners (9, 10) stacked on top of one another in a predeterminable position relative to the welding device (6) are provided, wherein a laser welding process (2) is established in which the welding device (6) is moved relative to the workpiece (1) in a surface-parallel welding direction (11), or vice versa, and a weld seam (5) is produced on the workpiece (4) using a laser beam (3) provided by the laser beam optics (7), wherein a continuous optical coherence tomography is performed during the laser welding process (2) by means of the measuring beam optics (8),in the context of which capillary depth measurement values (12) of a vapor capillary (13) forming on the workpiece (4) during the laser welding process (2) and / or of a welding influence zone (14) surrounding the vapor capillary (13) and surface depth measurement values (17) serving as a reference for the capillary depth measurement values (12) of two surface sections (18) arranged outside the vapor capillary (13) and outside the welding influence zone (14) of a surface (19) of the workpiece (4) facing the measuring beam optics (8) are determined, and wherein- the determined capillary depth measurement values (12) are continuously divided into separate capillary depth information blocks (20) and the determined surface depth measurement values (17) are continuously divided into separate surface depth information blocks (21), wherein a block size of these blocks (20, 21) is determined by a predeterminable interval size (22), a predeterminable time period and / or a predefined weld seam length is determined,- wherein a statistical capillary characteristic (23) is derived from each of the capillary depth information blocks (20), - wherein a statistical surface characteristic (24) is derived from each of the surface depth information blocks (21), - wherein a ratio of the surface characteristic (24) to the capillary characteristic (23) is used as an evaluation criterion for assessing the weld seam (5) produced on the workpiece (4) in an interval (22) during the laser welding process (2) by means of the laser beam (3), characterized in that - at least one or in each case one limit value (25) is derived from the surface depth information blocks (21), - wherein the derived at least one limit value (25) or the limit values (25) are continuously applied at intervals to the capillary depth information blocks (20), and those capillary depth measured values (12) of a capillary depth information block (20),which exceed the at least one limit value (25) or the limit values (25), serve as an evaluation criterion for assessing the weld seam (5) produced on the workpiece (4) by means of the laser beam (3) in an interval (22) during the laser welding process (2).

Claims

[1] Method (1) for assessing a weld seam (5) produced on a workpiece (4) during a laser welding process (2) by means of a laser beam (3), - wherein a welding device (6) with a laser beam optics (7) and with a measuring beam optics (8) designed to carry out a continuous optical coherence tomography and a workpiece (4), two or more joining partners (9, 10) stacked on top of one another, are provided in a predeterminable relative position to the welding device (6), - wherein a laser welding process (2) is established, in which the welding device (6) is moved in a surface-parallel welding direction (11) relative to the workpiece (1), or vice versa, and a weld seam (5) is produced on the workpiece (4) by means of a laser beam (3) provided by means of the laser beam optics (7), wherein - during the laser welding process (2), a continuous optical coherence tomography is carried out by means of the measuring beam optics (8), in the context of which capillary depth measurement values (12) of a vapor capillary (13) forming on the workpiece (4) during the laser welding process (2) and / or of a welding influence zone (14) surrounding the vapor capillary (13) and surface depth measurement values (17) serving as a reference for the capillary depth measurement values (12) of two surface sections (18) of a surface (19) of the workpiece (4) facing the measuring beam optics (8) are determined, and wherein - the determined capillary depth measured values (12) are continuously divided into separate capillary depth information blocks (20) and the determined surface depth measured values (17) are continuously divided into separate surface depth information blocks (21), wherein a block size of these blocks (20, 21) is determined by a predeterminable interval size (22), a predeterminable time period and / or a predeterminable weld seam length, - wherein a statistical capillary characteristic (23) is derived from each of the capillary depth information blocks (20), - wherein a statistical surface characteristic (24) is derived from each of the surface depth information blocks (21), - wherein a ratio of the surface characteristic (24) to the capillary characteristic (23) is used as an evaluation criterion for assessing the weld seam (5) produced on the workpiece (4) by means of the laser beam (3) in an interval (22) during the laser welding process (2), characterized by , that - at least one or each limit value (25) is derived from the surface depth information blocks (21), - wherein the derived at least one limit value (25) or the limit values (25) are continuously applied at intervals to the capillary depth information blocks (20), and those capillary depth measured values (12) of a capillary depth information block (20) which exceed the at least one limit value (25) or the limit values (25) serve as an evaluation criterion for assessing the weld seam (5) produced on the workpiece (4) in an interval (22) during the laser welding process (2) by means of the laser beam (3). [2] Method (1) according to one of the preceding claims, characterized bythat at least one physical characteristic of the laser beam (3) provided by means of the laser beam optics (7) is controlled during the laser welding process (2) as a function of an assessment, provided by the method (1), of the weld seam (5) produced on the workpiece (4) during the laser welding process (2). [3] Welding device (6) comprising a laser beam optics (7) and a measuring beam optics (8) configured to carry out a continuous optical coherence tomography, wherein the welding device (6) is configured to carry out the method (1) according to one of the preceding claims.

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