Method for measuring a vapour capillary of a welding process

Abstract

A method for measuring a vapor capillary (102) of a welding process, in particular a laser welding process, comprises the following method steps: a. carrying out a predefined welding process, in particular a laser welding process, which produces a vapor capillary (102), whereby a machining beam is directed onto a workpiece (22) and the machining beam and the workpiece (22) are moved relative to one another in the feed direction; b. carrying out a depth measurement with a measuring beam (46) while the welding process is being carried out, wherein the measuring beam (46) is moved in a measuring scan (104-112) parallel to the feed direction in the region of the vapour capillary (102), c. carrying out multiple depth measurements with the measuring beam (46) while the welding process is being carried out, wherein multiple measuring scans (104-112) are carried out parallel to the feed direction and offset transversely to the feed direction.

Description

[0001] Method for measuring a vapor capillary of a welding process

[0002] The invention relates to a method for measuring a vapor capillary of a welding process, in particular a laser welding process, in which a predetermined welding process generating a vapor capillary, in particular a laser welding process, is carried out by directing a processing beam onto a workpiece and moving the processing beam and workpiece relative to each other in the feed direction. A depth measurement is carried out with a measuring beam during the execution of the welding process, wherein the measuring beam is moved parallel to the feed direction in the region of the vapor capillary.

[0003] 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 maximum 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

[0004] 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.

[0005] 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 machining 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.

[0006] From DE 10 2021 000 151 A1, a method for determining the depth of a vapor capillary formed during the production of a weld is known, wherein the weld is produced by laser welding along a feed direction. A reference measurement is performed in which a reference beam scans a surface of a component being welded along the feed direction, thereby acquiring reference values ​​that characterize the respective height of the surface at successive reference points along the feed direction.Subsequently, laser welding is carried out, in which the weld seam is produced and a capillary depth measurement is performed, in which a measured value is recorded at successive measuring points along the feed direction, which characterizes the respective depth of the vapor capillaries that are created during the production of the weld seam and move along the feed direction at the respective measuring point.

[0007] This procedure is carried out without first determining where the greatest capillary depth is expected. Therefore, there is a risk that the capillary depth measurement will be performed at a location that does not encompass the greatest capillary depth.

[0008] The object of the present invention is to provide a method for measuring a vapor capillary to determine its maximum capillary depth. This object is achieved according to the invention by a method for measuring a vapor capillary of a welding process, in particular a laser welding process, comprising the following steps: a. Executing a predetermined welding process generating a vapor capillary, in particular a laser welding process, by directing a processing beam onto a workpiece and moving the processing beam and the workpiece relative to each other in the feed direction; b. Performing a depth measurement with a measuring beam during the execution of the welding process, wherein the measuring beam is moved in a measuring scan parallel to the feed direction in the region of the vapor capillary, the method being characterized in that c.Several depth measurements are carried out with the measuring beam during the execution of the welding process, whereby several measurement scans are performed parallel to the feed direction and offset transversely to the feed direction.

[0009] The inventive method thus performs at least two, i.e., two or more, depth measurements in different positions offset from the feed direction, so-called transverse offset positions, during a welding process, particularly a laser welding process. A depth measurement parallel to the feed direction is performed in a measurement scan, which can also be referred to as a line scan or longitudinal scan. In a measurement scan, a measured value is acquired at successive measuring points along the feed direction, which characterizes the respective depth of the vapor capillaries that are formed during the production of the weld and move along the feed direction at the respective measuring point.

[0010] According to the invention, several longitudinal scans are performed with an offset transverse to the feed direction. The greatest capillary depth may be located at the position where the workpiece is machined with the processing jet. However, due to different boundary conditions, such as heat conduction effects, gas effects, or errors or deviations in the adjustment of the measuring system and the processing jet system, the greatest capillary depth may also be offset from this position. If measurement scans are performed at different transverse offset positions, there is a greater probability of determining the greatest capillary depth. The steps described above are preferably carried out in a setup process.If the position with the greatest capillary depth is determined during this setup process, the specified welding process can then be carried out in a production process and the depth measurement can only be performed in the area of ​​the previously determined position, in particular the transverse offset position, of the greatest capillary depth.

[0011] For a given welding process, the material to be welded and / or the joining partners can be specified. The welding parameters of the (laser) welding process can also be specified.

[0012] During the setup process and during the production process, a processing beam, in particular a processing laser beam, can be directed onto the surface of a workpiece, whereby the processing beam can be moved along a processing path, i.e., in the feed direction, across the surface of the workpiece. According to the invention, a measurement strategy is chosen that is based on line scans in the feed direction. To correct for any transverse offset of the greatest capillary depth relative to the processing path, several line scans or longitudinal scans with an offset transverse to the feed direction are performed. From the individual scans, the scan with the greatest capillary depth can be determined. A longitudinal position of this longitudinal scan, at which the deepest capillary depth is found, can also be determined. This information can be used to subsequently measure the capillary depth in a production process.

[0013] The method according to the invention can be applied to both linear and non-linear welding processes, e.g., circles. In non-linear welding processes, the orientation of the depth measurement, i.e., the measurement scan, is aligned with the feed vector of the welding process, in particular the welding jet. The method according to the invention does not require a cross-scan, in which one line must be positioned relative to a second line. This approach is prone to errors because both transverse and longitudinal scans can be performed at positions where no vapor capillary is present.

[0014] Area scans capture many measurement points outside the vapor capillary. This is particularly problematic with short welds, such as those commonly found in electromobility. For example, with a weld duration of 50 milliseconds, only about 25 scans can be performed. If many measurement points are located outside the vapor capillary, it is impossible to determine the optimal measurement position, i.e., the position of greatest capillary depth. The method according to the invention is therefore advantageous compared to area scans.

[0015] It is particularly preferred if the depth measurements are performed using optical coherence tomography (OCT). An OCT measuring beam can be directed onto the workpiece, and a portion of the OCT measuring beam can be reflected from the workpiece into an optical coherence tomograph. 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. To achieve this, according to the invention, several parallel, offset measurement scans are performed with an OCT measuring beam. OCT measurements are performed without contact.

[0016] During the welding process, multiple depth measurements, i.e., measurement scans, can be performed at the same transverse offset position. A measurement scan typically takes significantly less time than the welding process itself. This allows sufficient time to perform several measurement scans at the same transverse offset position to obtain more accurate information regarding the vapor capillary depth. This also allows for adjustments resulting from the movement of the welding jet across the workpiece, which in turn moves the vapor capillary. For example, a welding duration, determined by the welding jet's on-time, might be one second. A depth measurement (measurement scan) could, for instance, be performed within one millisecond.This means that within one millisecond, the measuring beam is moved across the workpiece, for example along a line scan, and a large number of measurement points are recorded. For example, 10 parallel scans, i.e., scans offset from each other, can be performed. These 10 scans would therefore only take about 10 milliseconds. Thus, it would be possible to perform approximately 100 scans at each offset position.

[0017] The measurement results from scans performed at the same transverse offset position can be superimposed. Based on these superimposed scans, the greatest capillary depth for this transverse offset position can be determined. This depth is determined, for example, at the point where the densest cluster of measurement points / results is found. During the superimposition process, it can be taken into account that the vapor capillary moves across the workpiece, and therefore the scans performed at a transverse offset position are offset in the feed direction.

[0018] According to one method variant, the number of laterally offset measurement scans, the length of the measurement scans, and / or the spacing of the measurement scans perpendicular to the feed direction can be specified. Furthermore, it is conceivable that the number and / or spacing of the measurement scans perpendicular to the feed direction is determined as a function of the focal spot diameter of the processing beam. For a focal spot diameter of the processing beam, particularly a laser focal spot diameter, of 100 micrometers and a lateral spacing (transverse offset) of 10 micrometers, a number of 11 measurement scans can be determined. Alternatively or additionally, the number and lateral spacing of the measurement scans can be determined if the focal spot diameter of the measurement beam, particularly the OCT measurement beam, is known. For example, the lateral spacing of the measurement scans can be set equal to the radius of the OCT measurement beam.Determining the parameters of the depth measurements, in particular the number of measurement scans that are carried out transversely offset from each other, and the distance between the measurement scans, especially depending on a focal spot diameter, can be automated.

[0019] The distance between two adjacent measurement scans, i.e., the transverse offset, is preferably < 10 micrometers, particularly preferably < 5 micrometers. The measurement scans are preferably performed in a defined sequence, for example, from negative to positive Y-axis direction, if the Y-axis direction corresponds to the transverse direction.

[0020] The number of measurement scans performed per transverse offset position can be determined depending on the duration of the welding process.

[0021] The transverse offset position with the greatest capillary depth can be determined. This transverse offset position can be used for capillary depth measurement in a production process.

[0022] Alternatively or additionally, a height profile of the vapor capillary can be determined by interpolating the measurement results from scans taken at different transverse offset positions. This has the advantage of allowing for a more precise determination of the maximum capillary depth.

[0023] Further advantages arise when the position in the feed direction with the greatest capillary depth is determined. If this position is known, measurements during the production process only need to be taken around it. This means that shorter depth measurements, and especially shorter measurement scans, can be performed. It also ensures that depth measurements during the production process are taken exclusively within the steam capillary. In a setup process, on the other hand, the length of the depth measurement, especially the length of a measurement scan, can be selected so that areas outside the actual steam capillary are also covered.

[0024] As previously mentioned, the specified welding process can be carried out in a production environment, and a depth measurement or scan parallel to the feed direction can be performed only at the previously determined transverse offset position with the greatest capillary depth. This saves time for depth measurements in the production process, as fewer and shorter depth measurements (shorter scans) are required. In some cases, it may be sufficient to perform only spot depth measurements in the production process.

[0025] 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 show essential details of the invention, and from the claims. The features shown therein are not necessarily to scale and are depicted in such a way that the inventive features are clearly visible. The various features can be implemented individually or in any combination in variants of the invention.

[0026] The schematic drawing shows exemplary embodiments of the invention in various stages of use, which are explained in more detail in the following description.

[0027] They show:

[0028] Fig. 1 is a highly schematic representation of a laser processing system;

[0029] Fig. 2 is a schematic representation of a weld seam with a vapor capillary;

[0030] Fig. 3 shows different depth profiles from performed measurement scans. Figure 1 shows a laser processing system 10 with a laser processing arrangement 12, which has 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.

[0031] 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.

[0032] 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.

[0033] A control unit 31 can be set up to carry out or trigger the steps of the method according to the invention.

[0034] 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, the scanner 48 scans a figure on the workpiece 22. Such a figure can be, in particular, a line-shaped measurement scan. The measuring beam 46 is reflected by the workpiece 22 and directed by a beam plate 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 determine information concerning the vapor capillary generated by the processing laser beam 20.Figure 2 shows a top view of a weld 100 produced by moving a processing beam, in particular a processing laser beam 20, in the feed direction, which here corresponds to the X-direction, over a workpiece 22. At the point where the processing beam strikes the workpiece 22, material of the workpiece 22 is melted, forming a vapor capillary 102. To determine depth information about the vapor capillary 102, in particular to enable the determination of the maximum capillary depth, measurement scans 104, 106, 108, 110, and 112 are performed with a measuring beam 46. Measurement scans 104 to 112 are performed parallel to the feed direction. Measurement scans 104 to 112 are performed transversely to the feed direction at the transverse offset positions -Y2, ​​-Y1, Y0, Y1, and Y2. The distance between adjacent measurement scans 104 to 112 is d. In particular, measurement scans 104 to 112 are performed equidistantly.The length of a measurement scan 104 to 112 is specified by L. In the illustrated embodiment, the length L is greater than the length of the vapor capillary 102. This ensures that edge regions of the vapor capillary 102, as well as areas of the melt or solidified melt, are also captured. The measurement scans 104 to 112 are performed with a measuring beam 46, which moves parallel to the feed direction. The time required for depth measurements performed using measurement scans 104 to 112 is significantly shorter than the duration of a laser processing process. This allows multiple measurement scans 104 to 112 to be performed at a single transverse offset position -Y2, ​​-Y1, Y0, Y1, Y2. By interpolating the measurement scans 104 to 112 performed at the different transverse offset positions -Y2 to Y2, and the depth information obtained from them, a height profile of the vapor capillary 102 can be generated.

[0035] Figure 3 shows the height profiles of measurement scans 104 to 112. For each transverse offset position -Y2 to Y2, two height profiles are shown as examples. From the superposition of the measurement scans at the same transverse offset position, or the measurement results, the greatest capillary depth Zmax,-Y2, Zmax,-Y1, Zmax,Y0, Zmax,YI, Zmax,Y2 for this transverse offset position can be determined. Furthermore, it can be determined at which position in the feed direction or longitudinal direction this greatest capillary depth was measured, namely at the locations Xzmax,-Y2, Xzmax,-Yi, Xzmax.Yo, Xzmax.Yi, Xzmax,Y2.

[0036] Furthermore, it is possible to determine at which transverse offset position -Y2 to Y2 the greatest capillary depth was measured. If the measurement scans 104 to 112, or the measurement results of the scans 104-112, are interpolated, a more precise transverse offset position at which the greatest capillary depth occurs can also be determined. In a subsequent production process, a depth measurement can then be carried out in the region of this determined greatest capillary depth.

Claims

Patent claims 1. Method for measuring a vapor capillary (102) of a welding process, in particular a laser welding process, comprising the following steps: a. Executing a predetermined welding process, in particular a laser welding process, which generates a vapor capillary (102), by directing a processing beam onto a workpiece (22) and moving the processing beam and the workpiece (22) relative to each other in the feed direction; b. Performing a depth measurement with a measuring beam (46) during the execution of the welding process, wherein the measuring beam (46) is moved in a measuring scan (104-112) parallel to the feed direction in the region of the vapor capillary (102), characterized in that c. Several depth measurements are performed with the measuring beam (46) during the execution of the welding process, wherein several measuring scans (104-112) are performed parallel to the feed direction and transversely offset to the feed direction.

2. Method according to claim 1, characterized in that during the execution of the laser welding process several measurement scans (104-112) are carried out at the same transverse offset position (-Y2, -Y1 , Y0, Y1 , Y2).

3. Method according to one of the preceding claims, characterized in that the measurement results of the measurement scans performed at the same transverse offset position (-Y2, -Y1 , Y0, Y1 , Y2) are superimposed.

4. Method according to one of the preceding claims, characterized in that the number of transversely offset measurement scans (104-112), which The length (L) of the measurement scans (104-112) and / or the distance (d) of the measurement scans (104-112) perpendicular to the feed direction is specified.

5. Method according to one of the preceding claims, characterized in that the number and / or the distance (d) of the measurement scans (104-112) transverse to the feed direction is determined as a function of a focal spot diameter of the processing beam.

6. Method according to one of the preceding claims, characterized in that the number and / or the distance (d) of the measurement scans (104-112) transverse to the feed direction is determined as a function of a focal spot diameter of the measurement beam.

7. Method according to one of the preceding claims, characterized in that the number of measurement scans (104-112) performed per transverse offset position (-Y2, -Y1 , Y0, Y1 , Y2) is determined as a function of the duration of the welding process.

8. Method according to one of the preceding claims, characterized in that the transverse offset position (-Y2, -Y1 , Y0, Y1 , Y2) with the greatest capillary depth is determined.

9. Method according to one of the preceding claims, characterized in that a height profile of the vapor capillary (102) is determined, wherein an interpolation is performed between the measurement results of the measurement scans (104-112) at different transverse offset positions (-Y2, -Y1 , Y0, Y1 , Y2).

10. Method according to one of the preceding claims, characterized in that the position in the feed direction with the greatest capillary depth is determined. - 14 - 11. Method according to one of the preceding claims, characterized in that the specified welding process is carried out in a production operation and a depth measurement parallel to the feed direction is carried out only at the previously determined transverse offset position (-Y2, -Y1 , Y0, Y1 , Y2) with the greatest capillary depth.

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