Method for determining a welding penetration depth of a welding process

Abstract

The invention relates to a method for determining a welding penetration depth of a welding process, in particular a laser welding process, comprising the following method steps: a. carrying out a set-up process, wherein, in the set-up process, a predefined welding process is carried out and information relating to a vapour capillary (100) is determined, b. determining a measurement geometry (200, 202, 204) taking into account the information relating to the vapour capillary (100), c. carrying out a productive process, wherein the predefined welding process is carried out and a welding penetration depth is determined on the basis of measurements of the vapour capillary (100) which are carried out using the measurement geometry (200, 202, 204).

Description

[0001] 2024P00009WQ 26.08.2025

[0002] - 1 -

[0003] Method for determining the weld penetration depth of a welding process

[0004] The invention relates to a method for determining the penetration depth of a welding process, in particular a laser welding process.

[0005] When a processing laser beam is directed onto the surface of a workpiece, a vapor capillary, also known as a keyhole, forms in the area between the surface of the workpiece, where the laser beam is directed, and a certain depth within the workpiece. Within the vapor capillary, the workpiece material heats up so intensely due to the laser power that it vaporizes. The vapor capillary is surrounded by molten material, the weld pool. The depth of a vapor capillary formed during a laser welding process—that is, the distance between the unprocessed surface of the workpiece and the deepest point of the vapor capillary—is related to a

[0006] The vapor capillary depth is the depth to which the workpiece material is melted during processing. It is an indicator of the quality of the laser welding process.

[0007] When using an optical coherence tomograph for weld penetration depth measurement, setting the correct measurement position of the measuring beam is essential. The measuring beam must be directed onto the deepest point of the vapor capillary created by the processing laser beam in the workpiece to reliably measure the weld penetration depth. Precise positioning of the measuring beam on the base of the vapor capillary is necessary for accurate weld penetration depth measurement using an optical coherence tomograph. While it is known to determine the position of the deepest point of the vapor capillary, inaccuracies arise because the base of the vapor capillary is spatially extended, and its position and size are subject to fluctuations over time. 2024P00009WG 26.08.2025

[0008] - 2 -

[0009] From US patent 202310 036 545 A1, it is known to direct a measuring beam to different points inside and outside a phase change zone in order to obtain information about the welding process.

[0010] The object of the present invention is to provide a method with which the weld penetration depth can be determined more accurately.

[0011] According to the invention, this problem is solved by a method for determining the penetration depth of a welding process, in particular a laser welding process, comprising the following process steps:

[0012] Performing a setup process in which a specified welding process is carried out and information concerning a vapor capillary is determined,

[0013] Determining a measurement geometry taking into account the information concerning the vapor capillary,

[0014] Performing a production process in which the specified welding process is carried out and a weld penetration depth is determined based on measurements of the vapor capillary, which are carried out using the measuring geometry.

[0015] This makes it possible to select a measuring geometry optimized for the vapor capillary geometry or shape. During the setup process, it can be determined at which points or along which path the measuring beam should be used. The measuring geometry, i.e., the specification of how the measuring beam should move across the workpiece, can be selected so that even in the event of an (unintentional) change in the laser welding process, an accurate weld penetration depth can always be determined. For a given welding process, 2024P00009WQ 26.08.2025

[0016] - 3 - in particular, the material to be welded or the joining partners can be specified. The welding parameters of the laser welding process can also be specified. During the setup process and during the production process, a processing laser beam can be directed onto the surface of a workpiece, whereby the processing laser beam can be moved along a processing path across the surface of the workpiece.

[0017] The advantage of the method according to the invention lies in the fact that the measuring geometry compensates for temporal fluctuations of the vapor capillary and is therefore more robust to changes in the position of the vapor capillary. While the penetration depth can be successfully measured in most cases if a measuring geometry is not adapted to the vapor capillary, particularly its shape, if the measuring geometry is not adapted to the vapor capillary, it can happen that the edge region of the vapor capillary is also scanned, which means that measuring points have to be filtered out.

[0018] Since it is difficult to consistently pinpoint the deepest point of the constantly changing vapor capillary, the use of a measurement geometry ensures that measurements are taken in the vicinity of the presumed deepest vapor capillary depth. The measurement data can then be used to verify where the deepest vapor capillary depth is located. Continuous measurement of the penetration depth during the production process is possible. In principle, any one-dimensional or two-dimensional measurement geometry can be determined.

[0019] The acquisition of information concerning the vapor capillary can be carried out during the setup process and / or in the production process by means of coaxial camera observation or by X-ray tomography. However, it is particularly preferred if a measurement is carried out using optical coherence tomography (OCT). A measuring beam, in particular an OCT measuring beam, is directed onto the workpiece and a portion of the OCT measuring beam is reflected by the workpiece in 2024P00009WG 26.08.2025

[0020] - 4 - an optical coherence tomograph. In order to reliably measure the depth of the vapor capillary, it must be ensured that the measuring beam hits the deepest point of the vapor capillary and that the light reflected from there reaches the optical coherence tomograph.

[0021] During the setup process, information regarding the vapor capillary can be obtained by performing measurements of the vapor capillary using an OCT measuring beam. These measurements can then be repeated during the production process using an OCT measuring beam. The measurements are performed without contact. Defining a measurement geometry during the setup process ensures that the deepest point of the vapor capillary is targeted during production.

[0022] Information regarding the vapor capillary can include its shape, particularly its base. The shape of the vapor capillary can alternatively be referred to as its geometry or shape. In particular, a three-dimensional shape of the vapor capillary can be determined. Preferably, the height profile of the vapor capillary can be determined. If the shape of the vapor capillary is known, a suitable measurement geometry can be selected to ensure that the penetration depth can be reliably determined during subsequent measurements in a production process. Specifically, the shape of the vapor capillary base can be determined, and the measurement geometry can be defined taking the vapor capillary base into account. The vapor capillary base can be determined by recording the average depth of the measurement points or data.

[0023] Information regarding the vapor capillary can include the depth of the vapor capillary, the position of the deepest point of the vapor capillary (=deepest vapor capillary depth), and / or the extent of the vapor capillary. In particular, a lateral extent in at least one dimension can be determined. An extent in a horizontal plane can be determined. A lateral distance to the deepest point can be determined. Furthermore, the width and / or the 2024P00009WQ 26.08.2025

[0024] - 5 -

[0025] The diameter of the vapor capillary can be determined at its lowest point. The width and / or diameter of the vapor capillary can be determined, in particular, at a predetermined vertical distance from the lowest point.

[0026] Particular advantages arise when the measurement geometry is determined in such a way that it lies entirely within the vapor capillary, especially in the region of the vapor capillary base. This ensures that the penetration depth is determined exclusively within the vapor capillary base and that edge effects, such as when the OCT measuring beam detects a lateral wall of the vapor capillary, do not influence the correct determination. In principle, any complex one- and two-dimensional measurement geometries adapted to the vapor capillary base can be determined using the method according to the invention.

[0027] Furthermore, it can be provided that the measurement geometry is selected from a number of predefined measurement geometries. For example, a line scan can be specified as a predefined measurement geometry. It can also be provided that the predefined measurement geometry comprises several parallel line scans. Furthermore, it can be provided that the predefined measurement geometry has a circular or elliptical shape, with the center of the circle or ellipse corresponding to the position of the lowest point of the vapor capillary.

[0028] According to further training, it may be possible to adjust a predefined measurement geometry. For example, if a line scan is specified as the measurement geometry, the length of the line scan can be adjusted. If several parallel line scans are specified as the measurement geometry, the distance between the individual line scans can be adjusted. It is also conceivable to set and adjust the diameter of a circle as the measurement geometry or the vertices of an ellipse. 2024P00009WQ 26.08.2025

[0029] - 6 -

[0030] Particular advantages arise when the measuring geometry is oriented according to the feed vector of the welding process. This makes the method according to the invention applicable even to nonlinear welding processes.

[0031] The measurement geometry can be re-determined at predetermined events or time intervals. This allows for adjustments to the shape of the vapor capillary base, which changes over time. Possible causes for a changing vapor capillary shape include changing boundary conditions, such as contamination of the protective glass of the processing optics.

[0032] The measurement data acquired during the setup process of the OCT measurement can be displayed graphically. A measurement geometry can then be determined based on an analysis of the data displayed in this way.

[0033] Furthermore, it is conceivable to analyze a cluster of measurement data from the OCT measurement. For example, the deepest and densest cluster at measurement points within the expected weld penetration depth range can be identified. Subsequently, the extent of the identified cluster can be determined. Based on this extent, a suitable measurement geometry can be defined.

[0034] Automated determination of the measurement geometry is possible, in particular, when the measurement data is filtered, especially by sliding percentile filtering. Based on the filtered data, the depth of the vapor capillary and its extent, especially in the region of the vapor capillary base, can be determined relatively easily.

[0035] Further features and advantages of the invention will become apparent from the following detailed description of exemplary embodiments of the invention, with reference to the figures in the drawing, which shows essential details of the invention, as well as from the claims. The features shown therein are not necessarily to scale and are depicted in such a way that the inventive features 2024P00009WQ 26.08.2025

[0036] - 7 - can be made clearly visible. The various features can be implemented individually or in any combination in variants of the invention.

[0037] The schematic drawing shows exemplary embodiments of the invention in various stages of use, which are explained in more detail in the following description.

[0038] They show:

[0039] Fig. 1 is a highly schematic representation of a laser processing system;

[0040] Fig. 2 shows a top view of a schematic representation of a vapor capillary;

[0041] Fig. 3 shows a representation of a large number of measurement points determined during an OCT measurement;

[0042] Fig. 4 shows a representation of percentile filtering of the measurement data;

[0043] Fig. 5a shows a representation of a first measurement geometry;

[0044] Fig. 5b shows an alternative measurement geometry; and

[0045] Fig. 5c shows a representation of another alternative measurement geometry.

[0046] Figure 1 shows a laser processing system 10 with a laser processing arrangement 12, which includes a laser beam source 14 and a laser processing optic 16, comprising a focusing optic 18, for focusing a processing laser beam 20 onto a workpiece 22. 2024P00009WQ 26.08.2025

[0047] - 8 -

[0048] Furthermore, the laser processing system 10 includes a coherence tomograph 24, in particular an OCT tomograph. The laser processing system 10 also includes a detector 26. An observation beam 28 is directed onto the detector 26 by a mirror 30.

[0049] The processing laser beam 20 can be moved in the XY direction relative to the workpiece 22. This can be achieved, for example, by the laser processing optics 16 having a processing scanner that can deflect the processing laser beam 20 in the XY direction. Alternatively, the workpiece 22 can be arranged on a workpiece support that can be moved in the XY direction, or a laser processing head can be moved relative to the workpiece 22.

[0050] A control unit 31 can be set up to carry out or trigger the steps of the method according to the invention.

[0051] A measuring beam 46 (OCT measuring beam) can be emitted by a light source 44, in particular an S-LED of the coherence tomograph 24. The measuring beam 46 is directed onto the workpiece 22 by a scanner optic 48, hereinafter also referred to as scanner. In particular, a figure on the workpiece 22 is scanned by the scanner 48. Such a figure can be a measurement geometry. The measuring beam 46 is reflected by the workpiece 22 and directed by a beam splitter 50, so that the observation beam 28 is detected by the detector 26. The detector 26, which can be considered a component of the coherence tomograph 24, can therefore detect the measurement geometry scanned on the workpiece 22 by the scanner 48 and thus obtain information about the vapor capillary generated by the processing laser beam 20.

[0052] Figure 2 schematically shows a top view of a steam capillary 100 having a length L and a width B. A first steam capillary is created in a setup process by performing a predefined welding process. By measuring the steam capillary 100, information regarding the 2024P00009WC 26.08.2025 can be obtained.

[0053] - 9 -

[0054] The dimensions of the steam capillary 100 can be determined, which in turn can be used to define a measurement geometry that is used to determine the penetration depth of the steam capillary 100 in a production process. The steam capillary 100 can be measured using the OCT measuring beam 46. For example, several transversely offset measurement lines in the feed direction of the processing laser can be used. The measurement data acquired in this way can be displayed graphically, for example, as shown in Figure 3.

[0055] The horizontal axis indicates the measurement position, and the vertical axis indicates the measured depth. Figure 3 thus shows, in particular, a height profile of the steam capillary 100. The measurement points or data near the surface in region 102 represent a melt pool. The measurement points in region 104 represent the workpiece surface. The steam capillary 100 is located between them. The deepest steam capillary depth is found in region 106. This region is determined by searching for the deepest, densest cluster of measurement data 108. The base of the steam capillary is therefore located in region 106. The extent of the identified cluster in region 106, especially its lateral extent, can be determined. Furthermore, the position where the deepest steam capillary depth (deepest point of the steam capillary) is located can be determined.This information can be used to determine a suitable measurement geometry and measurement position.

[0056] Figure 4 shows a diagram 110, which was obtained by filtering, in particular by sliding percentile filtering, the measurement data 108. In this way, a height profile of the vapor capillary 100 is obtained. The extent 112, particularly in the region of a vapor capillary base 114, can be determined from the diagram 110. A measurement geometry to be determined should lie within this extent 112.

[0057] Figure 5a shows a first linear measurement geometry 200, which has a length LL. The length LL corresponds, for example, to the extent 112. The 2024P00009WQ 26.08.2025

[0058] - 10 -

[0059] The center point of the measuring geometry 200 is chosen at a distance Xc from the origin of the XY coordinate system (this is a simplified representation for this example; a real measuring geometry may also be shifted in the Y direction depending on the position of the steam capillary 100, if it does not extend along the X-axis with its longest dimension or is asymmetrically designed). It can be seen that the measuring geometry 200 is located entirely within the steam capillary 100. The center point of the measuring geometry 200 corresponds to the position of the deepest steam capillary depth determined during the setup process.

[0060] Figure 5b shows an alternative measurement geometry 202, which in this case has three parallel measurement lines 202 with a length LL and a center point at a distance Xc from the center of the XY coordinate system. The measurement lines are spaced Y apart. The parameters LL, Y, and Xc can be adjusted to reliably capture the area in which the weld penetration depth is to be determined.

[0061] Figure 5c shows another alternative measuring geometry 204, which is elliptical in shape. The center point 206, at a distance Xc from the center point of the XY coordinate system of the measuring geometry 204, corresponds to the position of the maximum depth of the steam capillary. The positions of the vertices Ys and Xs are chosen so that the measuring geometry 204 lies completely within the steam capillary, ensuring that the penetration depth can be reliably determined during measurements in production.

Claims

2024P00009WQ 26.08.2025 - 11 - Patent claims 1. Method for determining the penetration depth of a welding process, in particular a laser welding process, comprising the following process steps: a. Performing a setup process, wherein a predetermined welding process is carried out in the setup process and information concerning a vapor capillary (100) is determined; b. Determining a measurement geometry (200, 202, 204) taking into account the information concerning the vapor capillary (100); c. Performing a production process, wherein the predetermined welding process is carried out and a penetration depth is determined based on measurements of the vapor capillary (100) which are carried out using the measurement geometry (200, 202, 204).

2. Method according to claim 1, characterized in that information concerning the vapor capillary (100) is determined in the setup process by performing measurements of the vapor capillary (100) with an OCT measuring beam (46).

3. Method according to claim 1 or 2, characterized in that the measurements in the production process are carried out with an OCT measuring beam (46).

4. Method according to one of the preceding claims, characterized in that the shape of the vapor capillary, in particular of the vapor capillary base (114), is determined as information relating to the vapor capillary (100).

5. Method according to one of the preceding claims, characterized in that the information relating to the vapor capillary (100) is: 2024P00009WQ 26.08.2025 - 12 - The depth of the vapor capillary (100), the position of the deepest point of the vapor capillary and / or the extent of the vapor capillary is determined.

6. Method according to one of the preceding claims, characterized in that the measuring geometry (200, 202, 204) is determined such that it lies completely within the vapor capillary (100), particularly in the area of ​​the vapor capillary base (114).

7. Method according to one of the preceding claims, characterized in that the measuring geometry (200, 202, 204) is selected from a number of predetermined measuring geometries (200, 202, 204).

8. Method according to claim 7, characterized in that a predetermined measuring geometry (200, 202, 204) is adapted.

9. Method according to one of the preceding claims, characterized in that the measuring geometry (200, 202, 204) is (co-)oriented according to the feed vector of the welding process.

10. Method according to one of the preceding claims, characterized in that the measurement geometry (200, 202, 204) is determined again at predetermined events or at predetermined time intervals.

11. Method according to one of the preceding claims, characterized in that measurement data determined during the setup process of the OCT measurement are graphically displayed.

12. Method according to one of the preceding claims, characterized in that clusters of measurement data from the OCT measurement are analyzed. 2024P00009WQ 26.08.2025 - 13 - 13. Method according to one of the preceding claims, characterized in that a filtering, in particular sliding percentile filtering, of the measurement data is carried out.

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