Method for monitoring and / or adjusting a laser welding process according to the geometry of a fusion or weld bead detected by OCT, and associated machining device and computer program product

Abstract

In a method for monitoring and / or regulating a laser welding process for welding two workpieces (2), preferably two rod-shaped conductors, composed of a metallic material, in particular copper or aluminum, by means of a machining laser beam (3), the machining laser beam is directed at end faces (4) of the workpieces (2) arranged side by side in order to melt out a melt pool (8) at the two end faces (4) and, in further process, a melt bead (9), which then solidifies into a weld bead (9'), during the laser welding process, a liquid melt pool (8) and / or a liquid melt bead (9) is scanned by means of an OCT measuring beam (10) in line scans (12), the actual geometry of the melt pool (8) and the melt bead (9) is determined from the line scans (12), and welding parameters are set, in particular regulated, as a function of deviations of the determined actual geometry of the melt pool (8) and the melt bead (9) from a predetermined target geometry. After the laser welding process, the solidified weld bead (9') is scanned by means of the OCT measuring beam (10) in line scans (10), the actual geometry of the weld bead (9') is determined from the line scans (12), and the quality of the weld bead (9') is monitored as a function of deviations of the determined actual geometry of the weld bead (9') from a predetermined target geometry.

Description

Technical Field

[0001] This invention relates to a method for monitoring and / or regulating a laser welding process for welding two workpieces, preferably two rod-shaped conductors, made of metallic materials, particularly copper or aluminum, by means of a processing laser beam directed at the side-by-side end faces of the workpieces, so as to melt a molten pool at both end faces and, in a further process, melt beads, which then solidify into weld beads. Preferably, the workpiece end faces to which the processing laser beam is directed are arranged side-by-side at the same height. The invention also relates to a processing machine suitable for carrying out this method and an associated computer program product. Background Technology

[0002] Copper-containing bent rod-shaped conductors, particularly so-called hairpins, are installed in electric machines, such as electric motors or generators. These rod-shaped conductors correspond to a predetermined electrical wiring arrangement and are soldered together to form an electromagnet. Electric motors typically have dozens, often hundreds, of bent rod-shaped conductors, which must be soldered together in pairs. It is important that the soldering provides a sufficient cross-section through which current can flow from one rod-shaped conductor to another (“connection area”). If the connection area is too small, significant ohmic heating, efficiency losses, or even machine failure occur during operation.

[0003] Rod-shaped conductors are welded together by means of a laser beam, which is typically directed at the end faces of two rod-shaped conductors arranged side-by-side and mostly in contact with each other. These end faces are melted by the introduced heat and, after solidification, joined together by solidified molten beads. Typically, the laser beam is always directed at the rod-shaped conductors with the same power for the same amount of time, thereby achieving a sufficiently large connection area.

[0004] However, contamination or roughness on the surface of the rod conductor can cause fluctuations in its reflectivity to the laser beam, thus affecting the actual energy input. Similarly, misalignment of the rod conductor (e.g., gaps or misalignment) or inaccurate laser beam positioning can alter the actual energy input. In cases of excessively low energy input, too little material is melted, resulting in excessively small weld beads that provide an insufficient weld area. Strong spatter formation during laser welding can also lead to excessively small weld beads with an inadequate weld area. The weld area can only be inspected subsequently by destructive testing or computed tomography (CT) or X-ray techniques. Therefore, visual inspection by a worker is typically performed, or periodic evaluation of randomly selected samples is conducted using CT or X-ray techniques. Reworking defective parts is very costly.

[0005] DE 10 2014 226 710 A1 discloses a method for monitoring hairpins using sensors that measure the extent of the molten pool and can identify whether the welding process is within predetermined boundaries. Furthermore, additional sensors can be used to inspect solidified welds and distinguish between good and bad welds.

[0006] In addition, DE 10 2014 113 283 A1 discloses a point distance sensor for coaxial measurement methods, particularly optical coherence tomography, to detect and analyze areas on a workpiece for quality inspection.

[0007] DE 10 2016 109 909 A1 describes an apparatus for process monitoring in laser processing, particularly in laser welding and deep penetration laser welding, by means of optical distance measurement. Here, distance measurement can be performed, for example, by optical coherence tomography. Summary of the Invention

[0008] The objective of this invention is to provide a method for monitoring a laser welding process for welding two workpieces, the method being easily, quickly, and non-destructively implemented, and to provide a method for adjusting the laser welding process to ensure a sufficiently large joint area at all times.

[0009] This task is addressed according to the invention described at the beginning by the following method: during the laser welding process, the liquid molten pool and liquid molten beads are scanned by means of an OCT (optical coherence tomography) measuring beam in at least one line scan; the actual geometry of the molten pool and / or molten beads is determined based on the at least one line scan; at least one welding parameter is adjusted, in particular, based on the deviation of the determined actual geometry of the molten pool and liquid molten beads from a predetermined nominal geometry; and / or after the laser welding process, the solidified weld beads are scanned by means of an OCT measuring beam in at least one line scan; the actual geometry of the weld beads is determined based on the at least one line scan; and the quality of the weld beads is monitored based on the deviation of the determined actual geometry of the weld beads from the predetermined nominal geometry.

[0010] According to the present invention, the actual geometry of the molten pool, molten beads, and / or solder beads is scanned by one or more line scans using an OCT measuring beam, and preferably at least one of the following actual geometric features of the molten pool, molten beads, and / or solder beads is determined thereby:

[0011] - Diameter and / or roundness of the molten pool

[0012] - The diameter, height, and / or curvature of the molten bead, and

[0013] - The diameter, height, and / or curvature of the solder ball.

[0014] The connection area can be determined or derived from the deviation between the actual geometry of the molten pool, molten beads, and / or weld beads and the predetermined nominal geometry.

[0015] If the actual diameter of the determined solidified molten bead is smaller than the nominal diameter intended for a perfect molten bead, or if the outer contour of the solidified molten bead is too non-circular, then the bonding area of ​​the solidified molten bead is too small and the bead is classified as defective. If the actual height of the determined solidified molten bead is smaller than the nominal height intended for a perfect molten bead, or if the actual curvature of the determined solidified molten bead deviates from the nominal curvature intended for a perfect molten bead, for example, from the nominal curvature of a spherical cap shape, then the bead is classified as defective.

[0016] If, during the laser welding process, at least one actual geometric feature of the determined molten pool or molten bead deviates from the predetermined nominal geometric feature, this deviation can be offset by changing the welding parameters. For example, if the actual diameter of the determined molten pool or the actual diameter of the molten bead is smaller than the nominal diameter predetermined for the corresponding measurement time point, extending the welding parameter "welding duration" can still achieve a sufficiently large connection area of ​​the solidified weld bead.

[0017] The OCT measurement beam is preferably performed with at least two different line scans, especially line scans that are perpendicular to each other, in order to detect the actual geometry in three dimensions.

[0018] If a solder ball is classified as defective, it can be automatically re-soldered or other actions, particularly an alarm, can be triggered. Direct re-soldering is not a wasteful reprocessing of the defective part.

[0019] A processing machine according to the invention for laser welding two workpieces, preferably rod-shaped conductors, made of metallic materials, particularly copper or aluminum, by means of a processing laser beam, comprising: a laser beam generator for generating a processing laser beam; a laser scanner for two-dimensionally deflecting the processing laser beam onto the side-by-side end faces of the two workpieces to melt a molten pool at both end faces and, in a further process, melt beads, which then solidify into weld beads (9'); and optical coherence tomography. An optical coherence tomography (OCT) apparatus, the optical coherence tomography apparatus being used to generate an OCT measurement beam, the measurement beam being directed by a laser scanner to the two end faces; an OCT scanner, the OCT scanner being arranged between the optical coherence tomography apparatus and the laser scanner, the OCT scanner causing the OCT measurement beam to be deflected two-dimensionally to the two end faces in order to scan the molten pool, molten beads and / or weld beads by means of the OCT measurement beam in at least one line scan; a machine control device, the machine control device being used to control the laser scanner and the OCT scanner; an evaluation device, the evaluation device being used to determine the actual geometry of the molten pool, molten beads and / or weld beads based on the at least one line scan; and a setting device, the setting device being used to set, in particular adjust, at least one welding parameter based on the deviation of the determined actual geometry of the molten pool and / or molten beads from a predetermined nominal geometry; and / or a monitoring device, the monitoring device being used to monitor the quality of the weld beads based on the deviation of the determined actual geometry of the weld beads from the predetermined nominal geometry. The machine control unit is programmed to control the OCT scanner during and / or after the laser welding process so as to scan the end face of the workpiece in at least one line scan by means of the OCT measuring beam.

[0020] Finally, the present invention also relates to a computer program product having a code medium adapted to implement all steps of the method according to the invention when the program is run on the machine control device of a processing machine. Attached Figure Description

[0021] Other advantages and advantageous designs of the subject matter of this invention will become apparent from the specification and drawings. The foregoing features, as well as the further listed features, can also be used individually or in any combination. The illustrated and described embodiments should not be construed as exhaustive, but rather as having exemplary features for summarizing the invention.

[0022] In the attached image:

[0023] Figure 1 A schematic diagram of a processing machine for laser welding two rod-shaped conductors according to the present invention is shown; and

[0024] Figure 2a , 2b The diagram shows the end faces of two rod-shaped conductors to be welded, each end face having a molten pool. Figure 2a ) and molten beads ( Figure 2b );as well as

[0025] Figure 3 The diagram shows the welded ends of two rod-shaped conductors, with solidified molten beads on the ends. Detailed Implementation

[0026] Figure 1 The processing machine 1, schematically shown, is used for laser welding of two workpieces made of metallic material by means of a processing laser beam 3, which here takes the form, for example, two bent rod-shaped conductors 2 (“hairpins”) made of copper. The two rod-shaped conductors 2 have the same end faces 4 to be welded with the same cross-section and are arranged side by side with their end faces 4 at the same height.

[0027] The laser processing machine 1 includes a laser beam generator 5 for generating a processing laser beam 3, a laser scanner 6 for two-dimensionally deflecting the processing laser beam 3 on the end face 4 of the workpiece 2 along the x and y directions, and an optical coherence tomography (OCT) device 7 for optically scanning the end face 4 of the workpiece 2. The laser scanner 6 may have, for example, a scanner mirror that can deflect about two axes, or two scanner mirrors that can each deflect about one axis.

[0028] like Figure 2a , 2b As shown, a common, initially planar molten pool 8 is melted at both end faces 4 by means of a processing laser beam 3. In the further welding process, molten beads 9 are formed from the molten pool, and then the molten beads solidify into weld beads. Figure 3 Two rod-shaped conductors 2 are shown welded together, with their end faces 4 connected to each other by solidified solder beads 9' in a material fit.

[0029] The OCT 7, in a known manner, includes an OCT light source (e.g., a superluminescent diode) for generating a light beam and an OCT beam splitter for splitting the beam into an OCT measurement beam 10 and an OCT reference beam. The OCT measurement beam 10 is transmitted to a measuring arm and strikes the end face 4 of the workpiece 2. The OCT measurement beam 10 is at least partially reflected on said end face and guided back to the OCT beam splitter, which is non-transmissive or partially transmissive in this direction. The OCT reference beam is transmitted to a reference arm and reflected by a mirror at the end of said reference arm. The reflected OCT reference beam is also guided back to the OCT beam splitter. The superposition of the two reflected beams is finally detected by a detector (OCT sensor) to determine the height information about the end face 4 of the workpiece 2, taking into account the length of the reference arm. This method is based on the fundamental principle of optical wave interference and achieves the detection of height differences along the axis of the measurement beam in the micrometer range.

[0030] OCT (small field of view) scanner 11 is arranged in the beam path of OCT measuring beam 8 so that the OCT measuring beam 10 is deflected two-dimensionally, i.e., along the x and y directions, on the end face 4 of workpiece 2 and thereby scans 12 with one or more lines. Figure 2a , 2b The end face 4 of the workpiece 2 is scanned. The OCT scanner 11 may have, for example, a scanner mirror that can deflect about two axes, or two scanner mirrors that can each deflect about one axis. A beam splitter is arranged obliquely in the beam path of the processing laser beam 3 and reflects the processing laser beam 3 and transmits the OCT measurement beam 10. The OCT measurement beam 10 (at the zero position of the two scanners 6, 11 coaxial with the processing laser beam 3) is coupled into the laser scanner 6 by the beam splitter (e.g., in the form of a dichroic mirror) 13 so as to point the OCT measurement beam 10 toward the end face 4 of the workpiece 2.

[0031] The line scan data of OCT 7 is transmitted to the evaluation device 14, which determines the actual geometry of the molten pool 8, molten beads 9, and solder beads 9' based on one or more line scans 12. Preferably, one of the following actual geometric features of the molten pool 8, molten beads 9, and solder beads 9' is determined as the actual geometry:

[0032] - Diameter d and / or roundness of molten pool 8

[0033] - The diameter D, height H, and / or curvature of the molten bead 9, and

[0034] - The diameter D', height H', and / or curvature of the solder ball 9'.

[0035] The determined actual geometry of the molten pool 8 and molten beads 9 is transmitted to the setting device 15, which adjusts, in particular, welding parameters, such as welding duration, according to the deviation between the determined actual geometry of the molten pool 8 and molten beads 9 and the predetermined nominal geometry. If, for example, the determined actual diameter d, D of the molten pool 8 or molten beads 9 is smaller than the nominal diameter predetermined for the corresponding measurement time point, extending the welding duration can still achieve a sufficiently large connection area of ​​the solidified weld beads 9'.

[0036] The determined actual geometry of the solidified solder ball 9' is transmitted to the monitoring device 16, which monitors the quality of the solder ball 9' based on the deviation between the determined actual geometry and the predetermined nominal geometry. If the deviation is outside the predetermined tolerance, the solder ball 9' is classified as defective, and the welded rod conductor 2 is removed. In the case of an excessively small connection area, the welded rod conductor 2 can be directly re-welded while still in the welding position until the connection area is within the tolerance.

[0037] The machine control unit 17 controls the movement of the scanners 6 and 11 and is programmed to control the OCT scanner 11 during and / or after the laser welding process so as to scan the end face 4 of the workpiece 2 with one or more line scans 12 by means of the OCT measuring beam 10.

Claims

1. A method for monitoring and / or regulating a laser welding process for welding two workpieces (2) made of metallic material by means of a processing laser beam (3), said processing laser beam being directed at the side-by-side end faces (4) of the workpieces (2) to melt a molten pool (8) at both end faces (4) and, in a further process, to melt a molten bead (9), which then solidifies into a weld bead (9'). Its features are, During the laser welding process, the liquid molten pool (8) and / or liquid molten beads (9) are scanned by means of an OCT measuring beam (10) with at least one line scan (12), the actual geometry of the molten pool (8) and / or the molten beads (9) is determined according to the at least one line scan (12), and at least one welding parameter is adjusted according to the deviation between the determined actual geometry of the molten pool (8) and / or the molten beads (9) and a predetermined nominal geometry.

2. The method according to claim 1, characterized in that, OCT scanning is performed using the OCT measurement beam (10) with at least two different line scans (12).

3. The method according to claim 1 or 2, characterized in that, Based on the at least one line scan (12), at least one of the following actual geometric features of the molten pool (8) and / or the molten bead (9) is determined: - The diameter and / or roundness of the molten pool (8), - The diameter, height and / or curvature of the molten bead (9).

4. The method according to claim 1 or 2, characterized in that, After the laser welding process, the solidified weld bead (9') is scanned with at least one line scan (12) using an OCT measuring beam (10). The actual geometry of the weld bead (9') is determined based on the at least one line scan (12), and the quality of the weld bead (9') is monitored based on the deviation between the determined actual geometry and the predetermined nominal geometry. The diameter, height, and / or curvature of the solder bead (9') are determined based on at least one line scan (12). If a solder ball (9') is classified as defective, the solder ball (9') is automatically re-soldered or another action is triggered.

5. The method according to claim 1 or 2, characterized in that, At least one welding parameter that was changed was the welding duration.

6. The method according to claim 1 or 2, characterized in that, The workpiece is made of copper or aluminum.

7. The method according to claim 1 or 2, characterized in that, The workpiece consists of two rod-shaped conductors.

8. The method according to claim 2, characterized in that, The at least two different line scans (12) are perpendicular to each other.

9. The method according to claim 4, characterized in that, The other action mentioned is to issue an alarm.

10. A processing machine (1) for laser welding two workpieces (2) made of metallic material by means of a processing laser beam (3), comprising: A laser beam generator (5) is used to generate the processing laser beam (3); A laser scanner (6) is used to deflect the processing laser beam (3) in two dimensions onto the side-by-side end faces (4) of two workpieces (2) so as to melt a molten pool (8) at the two end faces (4) and melt a molten bead (9) in a further process, which then solidifies into a weld bead (9'). An optical coherence tomography (OCT) device (7) is used to generate an OCT measurement beam, which is directed by the laser scanner (6) to the two end faces (4). An OCT scanner (11) is arranged between the coherence tomography device (7) and the laser scanner (6). The OCT scanner is used to deflect the OCT measurement beam (10) two-dimensionally onto the two end faces (4) so ​​as to scan the molten pool (8), the molten beads (9) and / or the weld beads (9') with at least one line scan (12) by means of the OCT measurement beam (10). A machine control device (17) for controlling the laser scanner (6) and the OCT scanner (11); Evaluation device (14) for determining the actual geometry of the molten pool (8), the molten bead (9) and / or the weld bead (9') based on the at least one line scan (12); Adjustment device (15), said adjustment device being used to adjust at least one welding parameter based on the deviation between the determined actual geometry of the molten pool (8) and / or the molten beads (9) and a predetermined rated geometry; and / or A monitoring device (16) is used to monitor the quality of the solder ball (9') based on the deviation between the determined actual geometry of the solder ball (9') and the predetermined nominal geometry; The machine control device (17) is programmed to perform the method according to any one of claims 1 to 9.

11. A computer program product having a code medium adapted to perform all steps of the method according to any one of claims 1 to 9 when the program is run on a machine control device (17) of a processing machine (1).

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