EP4334073A1

EP4334073A1 - Method for monitoring a laser welding process, and associated laser welding system

Info

Publication number: EP4334073A1
Application number: EP22727798.5A
Authority: EP
Inventors: Tom Walde; Rüdiger MOSER; Stefan Birmanns; Fabian Becker; Igor Shkarban; Livia Barazzetti; Maurizio Kempf
Original assignee: Precitec GmbH and Co KG
Current assignee: Precitec GmbH and Co KG
Priority date: 2021-05-03
Filing date: 2022-05-03
Publication date: 2024-03-13
Also published as: WO2022233870A1; US20240227065A1; DE102021111349A1; CN117729983A

Abstract

The invention relates to a method for monitoring a laser welding process, said method comprising the following steps: carrying out the laser welding process by emitting a laser beam onto at least one workpiece to form a welded joint, the laser beam being guided along a processing path by a deflection device; collecting sensor data by at least two sensors during the laser welding process; and determining, on the basis of the collected sensor data and at least one processing parameter of the laser welding process, whether the welded joint has a defect. The invention also relates to an associated laser welding system.

Description

Method for monitoring a laser welding process and associated laser welding system

The present invention relates to a method for monitoring a laser welding process, in particular for determining whether a welded connection formed by the laser welding process has a defect, and a laser welding system that is set up to carry out the method.

Background and prior art

In a laser welding system, also referred to as a laser welding system or system for short, the laser beam emerging from a laser beam source or from the end of a laser conducting fiber is irradiated and focused on the workpieces with the aid of beam guiding and focusing optics to weld workpieces. The laser welding system can include a laser welding head in which the beam guiding and focusing optics are integrated. The laser beam is moved along a so-called processing path over the surface of the workpiece, whereby a vapor capillary, also known as a keyhole, forms in an area between the surface on which the laser beam is radiated and down to a certain depth within a workpiece. In the area of the vapor capillary, the material of the workpiece heats up so much due to the irradiated laser power that it vaporizes. The vapor capillary is surrounded by a molten pool in which the material is in a molten state. When the material cools down, a weld seam forms, which forms the welded connection between the welded workpieces, whereby the welded workpieces can also be referred to as a (single) component.

In order to ensure the quality of the weld seam or the welded joint, it is necessary to monitor the laser welding process. This is because defects can occur in a weld seam which cannot be tolerated in relation to the properties of the component. For example, if there is a gap between the welded workpieces, these may have to be discarded as rejects. Particularly in the case of a gap without bridging, a mechanical and/or electrical connection may not be present or may be insufficient. Often these defects cannot be seen with the naked eye or microscope, which is why sensor data are usually used to evaluate the welded joint. Current monitoring solutions include in-process and post-process monitoring and monitoring systems. In-process monitoring is also used to control the laser welding process. The monitoring of The laser welding process and the weld seam quality can already be observed today using a large number of individual monitoring systems. A weakness of these individual monitoring systems is that they each use different physical variables, eg geometric features in a camera image, thermal radiation and process lighting, for evaluation and analysis and evaluate them separately from one another. However, which physical parameters are best suited for quality monitoring depends on the combination of material and process in each individual case.

Based on the error criteria specified in each case, it can be recognized whether the welded connection has an error. Based on the detected defects, the weld can be classified as "okay" or "good weld", i.e. the welded workpieces are suitable for further processing or for sale, or as "bad" or "bad weld", i.e. the welded ones Workpieces are rejects and must be classified. The detection of defects and the subsequent classification of the welded connection is carried out separately and independently in the individual monitoring systems.

The detection of defects and the classification of the welded joint should be as reliable and automated as possible. As a rule, however, all the monitoring systems mentioned have what is known as a “sham committee”. These are welded workpieces that are classified as rejects by a monitoring system, but are actually OK. As a rule, however, it is more disadvantageous if welded workpieces are classified as OK by a monitoring system, but in reality they are not OK. This case is referred to as an "escape".

Disclosure of Invention

It is an object of the present disclosure to specify a method for monitoring a laser welding process, with the aid of which defects in a welded joint formed by the laser welding process can be determined reliably, quickly, easily and automatically.

It is an object of the present disclosure to provide a method for monitoring a laser welding process, by means of which incorrect classification of welded workpieces can be prevented or at least reduced. In particular, it is an object of the present invention to provide a method for monitoring a specify the laser welding process, with which both a false reject and an escape quota can be minimized in the classification of welded workpieces.

It is also an object of the present disclosure to specify a laser welding system configured to perform the method.

These objects are solved by the subject matter of the independent claims. Advantageous embodiments and further developments are the subject of the corresponding dependent claims.

The present disclosure is based on the concept of monitoring a laser welding process for welding workpieces, i.e. determining whether a weld joint formed by the laser welding process has a defect, by correlating sensor data from at least two sensors. The determination of whether the welded joint has a defect can be made based in particular on sensor data from a number of sensors and optionally also based on at least one processing parameter of the laser welding process. The determination of whether the welded connection has a defect and the monitoring of the laser welding process are therefore carried out by means of a combined and/or correlated evaluation of the sensor data from a number of sensors and optionally data relating to the at least one processing parameter of the laser welding process. Accordingly, the determination of whether the welded connection has a defect is based not only on sensor data from a single sensor, but also on sensor data from a number of sensors or additionally on data from the at least one processing parameter. Determining whether the weld joint has a defect is used to evaluate the quality of the weld joint. The procedure described can significantly improve the basis for evaluating the quality of the welded joint and reduce the risk of incorrect evaluation, i.e. incorrect classification of the welded workpieces. In this way, the rate of false rejects and escapes can be reduced.

According to a first aspect of the present disclosure, a method for monitoring a laser welding process is specified, the method comprising the steps of: carrying out the laser welding process by radiating a laser beam onto at least one workpiece to form a welded joint, the laser beam being deflected by a deflection device along a processing path is performed, detecting sensor data by at least two sensors during the laser welding process, and determining whether the weld joint has a defect, based on the detected sensor data, eg in particular based on a correlation and/or combination of the recorded sensor data. Preferably, the determination of whether the welded connection has a defect is also based on at least one processing parameter of the laser welding process or on a correlation and/or combination of the recorded sensor data and the at least one Be working parameters. In other words, determining whether the welded connection has a defect can be based on the recorded sensor data and at least one processing parameter of the laser welding process.

According to a second aspect of the present disclosure, a laser welding system is specified that is set up to carry out a laser welding process by irradiating the laser beam onto the at least one workpiece, and to carry out the method for monitoring the laser welding process according to embodiments of the present disclosure. The laser welding system comprises a laser welding head for radiating a laser beam onto at least one workpiece to form a welded joint, the laser welding head comprising a deflection device for guiding the laser beam along a processing path, at least two sensors, each of the sensors for acquiring corresponding sensor data during the laser welding process is set up, and a control unit set up to carry out a method according to one of the embodiments described herein.

The weld may be formed between portions or portions of a single workpiece or between at least two workpieces. The welded connection can be formed by a weld seam formed when the laser beam is irradiated, which can also be referred to as a weld bead. The deflection device can also be referred to as a scanning device, scanner unit or scanner. The laser welding system can also be referred to as a scanner system. The laser welding head can also be referred to as a scanner welding head. The laser welding process can also be referred to as a laser beam welding process. Determining whether the welded connection has a defect can also be referred to as defect determination for short.

When carrying out the laser welding process, process radiation is usually emitted from an interaction area between the laser beam and the workpiece. The interaction area can in particular comprise a vapor capillary formed when the laser beam is irradiated and a molten pool surrounding it. The process radiation in a visible wavelength range can also be referred to as process lights or plasma radiation. The process radiation in an infrared wavelength range can also referred to as temperature, infrared or thermal radiation. The process radiation generally also includes a portion of the laser beam that is reflected when the laser beam is radiated onto the at least one workpiece, which portion can also be referred to as a back reflection.

The sensor data can be based on radiation, i.e. on optical measurement data. In other words, radiation emanating from the workpiece and/or coupled into the laser welding head can be detected as sensor data, for example process radiation and/or a back-reflected measuring beam and/or imaging radiation. If process radiation is detected as the sensor data, at least one of the two sensors can include a photodiode and/or be set up to detect a radiation intensity in a specified wavelength range or at a specified wavelength.

The radiation emanating from the workpiece can be coupled into the laser welding head and can be superimposed on the irradiated laser beam at least in sections (i.e. in particular against the direction of propagation of the irradiated laser beam). The radiation can be decoupled from the beam path or beam path of the laser beam, e.g. by a first coupling device or a first beam splitter, preferably after passing through the deflection device. In other words, the first beam splitter can be arranged in front of the deflection device in the propagation direction of the incident laser beam. The radiation coupled out of the beam path of the laser beam can then be divided, e.g. by a second coupling device or by a second beam splitter, in order to impinge on the first sensor and the second sensor.

The laser welding head, through which the laser beam is radiated onto the workpiece, and the workpiece are preferably arranged stationary relative to one another at least during the laser welding process, ie during the formation of the welded joint. Thus, during the laser welding process, the laser beam is preferably deflected along the processing path solely by the deflection device. The processing path can correspond to a course of a desired weld seam. However, the present disclosure is also applicable to laser welding systems in which the workpiece is moved during the laser welding process by an axis system, for example. For example, the laser welding head can be attached to a robot. In this case, the deflection device can deflect the laser beam, with the robot moving at the same time or synchronously. Cycle time can be saved as a result. In this case, the laser welding system can have a higher-level control unit that coordinates the movements of the robot and the deflection device. The deflection of the laser beam along the processing path can be superimposed on an oscillating movement of the laser beam, which can also be referred to as a wobbling movement. An oscillating movement of the laser beam around an actual machining position along the machining path is generally referred to as a wobbling movement, the amplitude of which can speak approximately to the width of a resulting weld seam. A processing speed can be defined as a speed at which the laser beam is irradiated and deflected along the processing path. A superimposed wobbling movement of the laser beam can be ignored. When the laser beam wobbles, the processing speed can be referred to as an average speed of the laser beam along the processing path. Alternatively, the processing speed can be defined as a speed of the current processing position along the processing path.

One or more of the mentioned aspects can have one or more of the following optional features:

The deflection device can be set up to deflect the laser beam within a scanning field of the deflection device on the at least one workpiece.

If the weld is determined to have a defect, the weld and/or the welded workpiece may be classified as a bad weld, a bad weld, and/or a reject. If it is determined that the weld joint has no defect, the weld joint and/or the welded workpiece can be classified as a "good weld" and/or as "okay". A welded joint incorrectly classified as a "good weld" can be referred to as an "escape". A welded joint incorrectly classified as a scrap can be referred to as a "false scrap".

The processing parameter taken into account when determining the error can include at least one of the following parameters: an alignment of the laser welding head to the at least one workpiece, an angle of incidence of the laser beam on the at least one workpiece, a position of the laser beam within a scanning field of the deflection device, a deflection of the laser beam by the deflection device from a zero position, a focus position of the laser beam, a focus diameter of the laser beam, a focus shape of the laser beam, a processing speed, a processing direction, a Velocity vector of the laser beam along the processing path, a position of the at least one workpiece within the scanning field of the deflection device, a position of the processing path within the scanning field of the deflection device, a material and/or a thickness of the workpiece, an adjustment speed of a deflection element of the deflection device, a position and /or an adjustment angle of a deflection element of the deflection device.

The error can be determined based on target values for the processing parameters. The target values can be specified during the laser welding process, in particular during the formation of the welded connection. The target values can be provided in real time for error determination. The setpoint values can be time-resolved or time-dependent and/or time-independent setpoint values, in particular averaged over the laser welding process. The target values can be provided, for example, by a control unit of the laser welding head, in particular a control unit of the deflection device, or by the higher-level control unit, i.e. they are preferably not measured.

The at least two sensors for acquiring the sensor data can include at least two of the following sensors: a first intensity sensor, preferably comprising a photodiode, set up to acquire first intensity data of a radiation intensity of the process radiation emitted during the laser welding process in a visible wavelength range; a second intensity sensor, preferably comprising a photodiode, set up to acquire second intensity data of a radiation intensity of the process radiation in an infrared wavelength range; a third intensity sensor, preferably comprising a photodiode, set up to acquire third intensity data of a radiation intensity of a laser radiation reflected back from a surface of the workpieces; a sensor, preferably a photodiode, set up to acquire fourth intensity data of a radiation intensity of the laser beam in order to determine a current radiated power of the laser beam; an image sensor, preferably a camera, set up to capture image data or to record an image of a surface of the workpiece; a distance sensor, preferably an optical coherence tomograph, set up to acquire distance data of a distance between the laser welding head radiating the laser beam and the workpiece and/or set up to acquire distance data of a depth of a vapor capillary produced during the laser welding process and/or set up to acquire Surface profile data of a surface of a weld formed by the laser welding process. The power of the laser beam can also be referred to as laser power. The image sensor is preferable arranged coaxially, ie coaxially to the beam path of the laser beam or to the optical axis of the laser welding head. The process radiation or the radiation detected by at least one of the sensors can preferably be separated from the laser beam by a beam splitter, such as a dichroic mirror.

The acquisition of the sensor data can include at least two of the following steps: acquisition of first intensity data of a radiation intensity of the process radiation emitted in a visible wavelength range, acquisition of second intensity data of a radiation intensity of the process radiation emitted during the laser welding process in an infrared wavelength range, acquisition of third intensity data of a Radiation intensity of a laser beam reflected back by the at least one workpiece at a wavelength of the laser beam, acquisition of fourth intensity data of a radiation intensity of the irradiated laser beam at a wavelength of the laser beam to determine a current irradiated laser power, acquisition of image data by recording an image and/or video of a surface of the workpiece, acquiring surface profile data of the surface of the weld, and acquiring distance data of a distance to the work piece and/or a depth of a vapor capillary generated during the laser welding process.

Accordingly, the recorded sensor data can include at least two, in particular two different, of the following sensor data: Image data including at least one image of a surface of the at least one workpiece and/or an image of the vapor capillary and/or the melt pool, measured values of a radiation intensity of the process radiation in in a specified wavelength range or at a specified wavelength, measured values of a radiation intensity of the process radiation in a visible wavelength range, measured values of a radiation intensity of the process radiation in an infrared wavelength range, measured values of a radiation intensity of the laser radiation reflected back from the workpieces, measured values of a radiation intensity of the incident laser beam , surface profile data of the weld, measurements of a distance to the workpiece, and measurements of the depth of the vapor capillary created during the laser welding process.

According to preferred embodiments, the at least one processing parameter comprises at least one parameter of the deflection device, for example the position and/or the adjustment angle of the deflection element of the deflection device, the angle of incidence of the laser beam on the at least one workpiece, the position of the laser beam within the scanning field of the deflection device, the Deflection of the laser beam by the deflection device from a zero position, the position of the laser beam within the scan field Deflection device, the position of the at least one workpiece within the scanning field of the deflection device, the position of the processing path within the scanning field of the deflection device, and/or the adjustment speed of a deflection element of the deflection device. By including at least one of these processing parameters of the deflection device when determining whether the weld seam has a defect, the reliability and quality of the defect determination can be improved. This is particularly advantageous for laser welding systems in which the error determination is based on radiation, in particular the process radiation, which runs at least in sections through optical elements of the laser welding system, for example the deflection device and focusing optics, for example an F-Theta lens. Processing parameters of the deflection device, such as the position of a deflection element of the deflection device, can have an influence on the sensor data recorded for error determination, i.e. for example on the process radiation for recording the first to third intensity data, the optical measuring beam for recording the distance data, the surface profile data and /or on capturing the image data. In particular, processing parameters of the deflection device can influence a signal level of the corresponding sensor data. The focusing optics are usually only optimized for the wavelength of the laser beam. Therefore, when passing through the focusing optics, chromatic aberration can occur with radiation having a different wavelength than the wavelength of the laser beam. By including and taking into account the processing parameters mentioned when determining the error, the influence of the focusing optics and the deflection device on the sensor data when determining the error can be reduced.

The sensor data and the data of the processing parameter, in particular the target values of the processing parameter, preferably correspond, e.g. in terms of time and/or space. This may mean that the data was collected or recorded during the same specified period of time or at the same place. Furthermore, this can mean that corresponding data or values are available for specified points in time within a specified period of time. For this purpose, the sensor data and/or the data of the processing parameter can be recorded or recorded with the same sampling frequency. Alternatively, the data can be interpolated, or data can be discarded.

Determining whether there is a fault in the welded connection can take place while the laser welding process is being carried out, in particular in real time, and/or after the laser welding process has been carried out. Accordingly, the method for monitoring a laser welding process can be designed as an in-process or post-process method. The acquisition of the sensor data and / or determining whether an error in the Welded connection is present, can be carried out continuously and / or repeatedly during the implementation of the laser welding process.

Determining whether the welded joint has a defect may include determining whether the welded joint has at least one of the following defects: a missing or insufficient physical or electrical and/or mechanical connection through the welded joint between welded workpieces and/or a Gap between welded workpieces. For example, it may be determined that the weld has a defect if the conductivity of the electrical connection through the weld is equal to or less than a predetermined conductivity threshold. Further, the weld may be determined to have a defect if the size of the gap between workpieces welded in the lap or parallel butt is equal to or greater than a gap threshold.

Determining whether the welded connection has a defect can be carried out using algorithms and/or using a machine learning method, in particular using an artificial neural network.

Determining whether the welded joint has a defect may include: separately evaluating the sensor data for each of the at least two sensors, combining the evaluations by a logical operation, and determining whether the welded joint has a defect based on the combined evaluation. The separate evaluation of the sensor data for each of the at least two sensors can take place in each case taking into account the at least one processing parameter. Alternatively, the sensor data for one or some of the at least two sensors can be evaluated taking into account the at least one processing parameter.

For example, the sensor data for at least one of the sensors can be evaluated separately to the effect that it is determined whether, based on the sensor data of this sensor, the welded connection alone has a defect. This can be done in a conventional manner for error determination. For example, a photodiode can be used to measure an intensity curve of the process radiation emitted during the laser welding process in a visible wavelength range corresponding to the process lighting and in an infrared wavelength range corresponding to the heat radiation and an intensity curve of the laser radiation that is reflected back, and based on this, a corresponding intensity signal is generated. The intensity signals can then be analyzed separately from one another, for example by comparing the respective intensity signal with corresponding reference curves or envelope curves is compared. Based on the error criteria specified in each case, it can be recognized whether the welded connection has an error according to the evaluation of the respective intensity signal. Error criteria can be defined, for example, as a function of an integral of the curves over the envelope curves or of falling below or exceeding the envelope curves. In the case of an image of the melt pool as sensor data, geometric features of the melt pool, in particular the shape, size and/or position of the melt pool, can be recognized by means of image processing. Based on deviations from specified geometries, it can be detected here whether the welded joint has a defect.

The results of the separate evaluations can then be linked using a logical "and" operation. This can reduce the odds or probability of escapes. Alternatively or additionally, the results can be linked by a logical “or” operation. This can reduce the rate or probability of false rejects.

A first group of sensors, whose results of the separate evaluations are linked "and", and a second group of sensors, whose results of the separate evaluations are linked "or", each have at least two sensors, and the first group and the second group can have at least one sensor that is not included in the respective other group. Thus, when using more than two sensors, for example three sensors, a combination of the two evaluation methods is possible in order to reduce escapes and false rejects at the same time.

The laser welding process can be controlled based on the defect determination, in particular if it has been determined that the welded connection has a defect, by adjusting or setting at least one processing parameter, in particular the laser power, the processing speed and/or the focal position of the laser beam. For example, a correlation of the detected sensor signals can be used to control the laser power. In a further example, a focus position of the laser beam can be adjusted or adjusted based on the detected sensor signals, in particular based on a correlation and/or combination of the detected sensor signals, by means of a variable z-collimation. The regulation can be done by the control unit of the laser welding system or a higher-level control unit. The determination of whether the weld has a defect can be made during the performance of the laser welding process. Adjusting at least one processing parameter may include adjusting the same processing parameter based on which the error determination was performed, and/or adjusting another processing parameter of the laser welding process, wherein the other processing parameter is not the same as that used to determine the error.

The sensor data used for error determination can be raw data. Determining whether the welded connection has a defect can therefore be carried out without pre-processing the recorded sensor data. For example, an artificial neural network can determine whether the welded joint has a defect directly based on the raw data. This can also be referred to as “end-to-end” processing. As a result, the error determination can be carried out more reliably and quickly. Furthermore, the error determination can be carried out in real time and the monitoring of the laser welding process and the control of the laser welding process can be carried out more reliably and precisely.

Alternatively, the sensor data from the at least two sensors can be pre-processed or pre-evaluated before the fault is determined. This can be done, for example, by a processing unit of the laser welding system. The processing unit can have an FPGA (“Field Programmable Gate Array”). The functionality of the processing unit can be implemented by the control unit or the processing unit can be integrated into the control unit. In particular, the sensor data can be linked to the at least one processing parameter in such a way that the data correspond in time. For example, the recorded sensor data, in particular one or more of the first to fourth intensity signals, can be linked to at least one processing parameter of the deflection device, e.g an adjustment angle of a deflection element of the deflection device, a speed of a position change and/or an adjustment speed of the deflection element of the deflection device. As a result, the speed of the subsequent evaluation of the sensor data and the processing parameters and the error determination can be optimized or increased.

The deflection device can be set up to deflect the laser beam by at least a first deflection angle along a first axis. Preferably, the deflection device is additionally set up to deflect the laser beam by a second deflection angle along a second axis, the first and second axes being arranged at an angle to one another, for example perpendicular to one another. The maximum first deflection angle and/or the maximum second deflection angle of the deflection device can each be equal to or greater than 10 degrees, in particular 10 up to 20 degrees. If the deflection device has mirrors as deflection elements, these maximum deflection angles correspond to maximum mirror angles of at least 5 degrees, in particular 10 degrees, since the laser beam is deflected by twice the mirror angle.

The scanning field of the deflection device can be defined as a region on the workpiece or on the workpiece surface and/or can be predetermined by a maximum first and a maximum second deflection angle of the first deflection device. A length and/or a width of the scan field can be equal to or greater than 50 mm. The scan field can, for example, have a size of more than 50 mm×50 mm, in particular equal to or larger than approximately 100 mm×200 mm or 250 mm×150 mm, on the workpiece. According to embodiments, the scan field has an elliptical shape. In this case, the length of the scan field can indicate the length of the major axis of the ellipse and the width of the scan field can indicate the length of the minor axis of the ellipse. From the steering device can be designed as a large field scanner.

In order to bring about the deflection of the laser beam, the deflection device can have a first movable mirror and a second movable mirror. The first moveable mirror may be rotatable about a first axis of rotation and the second moveable mirror may be rotatable about a second axis of rotation, the first axis of rotation and the second axis of rotation being at an angle, e.g. at an angle between 45° and 135°. in particular of about 75 ° or 90 ° to each other. For this purpose, the mirror or the first and second mirrors can be designed as galvanometer mirrors, or galvo mirrors for short. Alternatively, the deflection device can have a movable mirror that can be rotated or pivoted about at least two axes. Accordingly, the deflection device can be designed as a galvanometer or galvo scanner. Alternatively, the deflection device can have MEMS-based, piezoelectric and/or inductive drives. Alternatively, the deflection device can be designed as a prism scanner or lens scanner.

The laser welding system, in particular the laser welding head, can include a first coupling device for coupling the laser beam into the deflection device and for coupling out the radiation emanating from the workpiece from a beam path of the laser beam. The first coupling device can be arranged in front of the deflection device in the propagation direction of the incident laser beam. Furthermore, the laser welding system, in particular the laser welding head, can comprise a second coupling device for dividing the radiation coupled out of the beam path of the laser beam. The second Coupling device can be set up to direct part of the radiation onto a first of the at least two sensors and another part of the radiation onto a second of the at least two sensors.

The laser welding system, in particular the laser welding head, can include collimation optics for adjusting the focal position of the laser beam. The collimation optics can be adjusted along an optical axis of the collimation optics and/or along a beam propagation direction of the laser beam in order to set the focus position of the laser beam. The collimation optics can comprise two or more lenses, the distances between which can be changed, at least in part. The adjustment can be motorized. The control unit can control the collimation optics to adjust the focal position of the laser beam.

The laser welding system, in particular the laser welding head, can also include focusing optics for focusing the laser beam. The focusing optics can include two or more lenses, the distances between which can be changed at least in part in order to set or change the focus position. The focusing optics can in particular be directed in order to focus the laser beam on the workpiece, in particular on a surface of the at least one workpiece. The focusing optics can include an F-Theta lens or be designed as such. The F-Theta lens can be telecentric.

The control unit can be set up to control the laser welding system, in particular the laser welding head, the at least two sensors, the deflection device, the focusing optics, the collimation optics and/or a laser source for generating the laser beam, in order to control the laser welding process and the method for monitoring the La to carry out the welding process.

Furthermore, the laser welding system can have an interface in order to transmit the sensor data and data of the processing parameters, in particular desired values, to an external control unit or the superordinate control unit, for example an external computer.

In addition, the laser welding system can have a ring light. The ring light can have separately switchable segments. With the help of the ring light, an image or video with a high contrast can be obtained by the image sensor. Using the ring light, a very high-contrast image can be recorded using a so-called "shape-by-shading" process. In addition, the laser welding system can have a line generator for triangulation. The image sensor can be generated using by the line generator lines generated on the surface of the at least one workpiece detect a geometry of the surface and/or a geometry of a weld seam formed by the laser welding process. Based on this, the image sensor can capture geometry data as sensor data.

The at least one workpiece can include one of the following elements: a battery, a battery cell, a battery pack, a battery connection, an arrester and/or a part of these elements. For example, the at least one workpiece can include a battery cell and an arrester. An electrical connection between the battery cell and the conductor can be established by means of the weld seam formed by the laser welding process.

Brief description of the drawings

The invention is described in detail below with reference to figures.

1 shows a schematic view of a laser welding system according to embodiments of the present disclosure;

2 shows a schematic view illustrating a scanning field of a deflection device of a laser welding system according to embodiments of the present disclosure;

3 shows a flow diagram of a method for monitoring a laser welding process according to embodiments of the present disclosure;

4 shows a schematic view of several workpiece groups in a scan field of a deflection device of a laser welding system according to embodiments to illustrate a method for monitoring a laser welding process according to embodiments of the present disclosure.

Detailed description of the drawings

Unless otherwise noted, the same reference numbers are used below for the same elements and those with the same effect. 1 shows a schematic view of a laser welding system according to embodiments of the present disclosure.

The laser welding system 10 includes a laser welding head 12 for radiating and directing a laser beam 14 onto at least one workpiece. The laser welding system 10 is set up to carry out a laser welding process for welding the at least one workpiece. According to the embodiment shown in FIG. 1, the laser welding system 10 is set up to weld two workpieces 16a, 16b to one another. The two workpieces 16a, 16b are arranged in a lap joint and the laser beam 14 is irradiated onto the workpiece 16a lying on top, but the present disclosure is not limited to this. The workpieces 16a, 16b can also be arranged, for example, in a parallel joint or in a butt joint, and the laser beam 14 can be irradiated onto both workpieces 16a, 16b. According to embodiments, the welding of the at least one workpiece can comprise a welding of parts or regions of an individual workpiece. In this case, the workpieces 16a, 16b shown in Figure 1 can be considered as parts or portions of this single workpiece.

The workpieces 16a, 16b are welded by irradiating the laser beam 14 onto the workpieces 16a, 16b and moving the laser beam 14 along a predetermined machining path 18 on the workpieces 16a, 16b. The machining path 18 can be arranged on one of the workpieces 16a, 16b. According to embodiments, the processing path can be arranged on both or on a boundary between the workpieces 16a, 16b. The specified processing path 18 indicates the course of a desired weld seam. The weld seam forms the weld connection to be formed by the laser welding process between the workpieces 16a, 16b. When the laser beam is radiated onto the workpieces 16a, 16b, a vapor capillary, also referred to as a keyhole, forms in an area between the surface of the workpieces 16a, 16b onto which the laser beam is radiated, down to a certain depth within the workpieces 16a, 16b , out. In the area of the vapor capillary, the material of the workpiece heats up so much due to the irradiated laser power that it vaporizes. The vapor capillary is surrounded by a melt pool in which the material is melted. As the material cools, the weld seam that forms the weld joint is formed.

The laser welding system 10 can be coupled to a laser source 20 for generating the laser beam 14 , also referred to as a processing laser beam, in order to couple the laser beam 14 into the laser welding head 12 . The laser source 20 can be embodied as a single-mode laser, as a solid-state laser or as a fiber laser. The laser beam 14 is a Optical fiber 21 is transmitted from the laser source 20 to the laser welding head 12 and is coupled into the laser welding head 12 from one end of the optical fiber 21, for example by means of a fiber coupler (not shown). A collimation optics 22 arranged after the fiber coupler is set up to collimate the laser beam 14 emerging divergently from the end of the optical fiber 21 . The focal position of the laser beam 14 can be adjusted or corrected with the aid of the collimation optics 22 . The axis along which a focal position of the laser beam 14 can be adjusted can correspond to an optical axis of the laser welding head 12, in particular an optical axis of a focusing lens system 24. This axis can also be referred to as the z-axis. Accordingly, the collimator optics 22 can be referred to as (variable) z-collimator optics or, for short, as (variable) z-collimation. The focus position can be adjusted by adjusting a lens of the collimator optics 22 along the optical axis of the collimator optics 22 or a beam axis of the laser beam 14 . The collimating optics 22 can have a motor unit (not shown) for adjusting the lens. The collimator optics 22 can be controlled by a superordinate control unit (not shown) of the laser welding system 10 or the control unit 48 . With the aid of the z-collimation, the focus position of the laser beam 14 can be suitably set as a function of the sensor signals from the sensors described below.

Laser welding system 10 also includes a first coupling device 23a for coupling laser beam 14 into laser welding head 12 or into deflection device 26. First coupling device 23a is designed as a beam splitter and includes, for example, a dichroic mirror that emits light with the wavelength of laser beam 14 substantially reflects and substantially transmits light of a different wavelength than that of the laser beam 14, i.e. the mirror is substantially transparent to light of a different wavelength than that of the laser beam 14. Process radiation, which is detected as sensor signals by the sensors described below, can be separated from the laser beam 14 after passing through the deflection device 26 with the aid of the first coupling device 23a. In addition, the laser welding head 12 includes focusing optics 24 for focusing the laser beam 12 on the at least one workpiece 16a, 16b, in particular on a surface of the at least one workpiece 16a, 16b. According to embodiments, the focusing optics 24 can be embodied as an F-Theta lens.

In order to change the position of the laser beam 14 on the at least one workpiece 16a, 16b, and in particular to guide the laser beam 14 along the processing path 18, the laser welding system 10 also includes a deflection device 26 for deflecting or Deflection of the laser beam 14 relative to the at least one workpiece 16a, 16b. From the deflection device 26 is set up to move or deflect the laser beam 14 along two axes x, y. According to embodiments, the two axes x, y can be perpendicular to one another and define an xy plane that is arranged parallel to a surface of the at least one workpiece 16a, 16b, but the present disclosure is not limited to this. The deflection device 26 can also be referred to as a scanner unit or scanner.

The processing path 18 can be traversed by the laser beam 14 with the aid of the deflection device 26 . A processing speed can be defined as a speed at which the laser beam 14 is irradiated and deflected along the processing path 18 . Any superimposed wobble movement of the laser beam 14 can be ignored. When the laser beam wobbles, the processing speed may be referred to as an average speed of the laser beam 14 along the processing path.

2 shows a schematic view illustrating a scan field of the deflection device 26. The deflection device 26 is set up to deflect the laser beam 14 along the x-axis by a first deflection angle and to deflect the laser beam 14 along the y-axis by a second divert deflection angle. The deflection device 26 has a zero position with respect to the x-axis and with respect to the y-axis, for which the laser beam 14 assumes a zero position along the respective axis. The zero position of the x-axis and the zero position of the y-axis can be viewed together as the center point or center 32 of a scan field 34 of the deflection device 26 who the. The center 32 of the scan field 34 may correspond to an undeflected position of the laser beam 14, i.e. a (general) null position of the laser beam 14. In the non-deflected position of laser beam 14, laser beam 14 can run between laser welding head 12 and the at least one workpiece 16a, 16b coaxially with an optical axis of laser welding head 12 and/or an optical axis of focusing optics 24.

A maximum first deflection angle 28 along the x-axis (ie rotation about the y-axis) and a maximum second deflection angle 30 along the y-axis (ie rotation about the x-axis) give an edge of the scan field 34 on the surface of the at least one work piece 16a, 16b, within which the deflection device 26 can deflect the laser beam 14 with respect to the at least one workpiece 16a, 16b. According to embodiments, the deflection device 26 is designed as a large field scanner. For example the maximum first deflection angle 28 and/or the maximum second deflection angle 30 may be greater than 10 degrees. The first and second maximum deflection angles 28, 30 can be predetermined by design. Alternatively, an F-theta objective set as the focusing optics 24 can limit the maximum deflection angles 28 , 30 .

In FIG. 2, the scan field 34 is shown as having a rectangular shape, but the present disclosure is not so limited. The scan field 34 can also have a circular or an elliptical shape. In this case, the rectangle shown in FIG. 2 can be regarded as a rectangle with the largest area inscribed in the elliptical first scan field.

In order to bring about the deflection of the laser beam 14, the deflection device 26 comprises at least one deflection element. According to embodiments, the deflection device 26 comprises two movable mirrors 36a, 36b (see FIG. 1) as a deflection element, which can be rotated or adjusted about different axes of rotation. The mirrors 36a, 36b can be designed as galvanometer mirrors. In this case, the deflection device 26 can be referred to as a galvanometer scanner or galvo scanner. According to alternative embodiments that are not shown, the deflection device comprises a movable mirror as the deflection element, which mirror can be adjusted about at least two axes. The position or the adjustment angle of the at least one deflection element therefore determine the deflection of the laser beam 14 from the zero position 32, the position of the laser beam 14 in the scan field 34 and the angle of incidence 25 of the laser beam 14 on the at least one workpiece 16a, 16b. In this case, the angle of incidence 25 is defined as the angle between a normal to the surface and the laser beam 14 .

A control unit (not shown) of deflection device 26, which can also be the control unit of laser welding system 10, can be set up to transmit current target values of at least one processing parameter of the laser welding process to control unit 48 of laser welding system 10 during the laser welding process at least one processing parameter can include, for example, one of the following parameters of deflection device 26: the angle of incidence 25 of laser beam 14, the position of laser beam 14 in the scanning field of deflection device 26, a deflection of laser beam 14 by deflection device 26 from zero position 32, the processing speed , a processing direction, a speed vector of the laser beam 14 along the processing path 18, and a position or adjustment, an adjustment angle and/or an adjustment speed of the at least one deflection element of the deflection device 26, for example the mirror 36a, 36b. According to embodiments, the laser welding head 12 and/or the at least one workpiece 16a, 16b can also be moved relative to one another, preferably between two consecutive laser welding processes. For example, the at least one workpiece 16a, 16b can be moved relative to the laser welding head 12 by a first movement unit (not shown). Alternatively or additionally, the laser welding head 12 can be moved relative to the at least one workpiece 16a, 16b by a second movement unit (not shown). The second movement unit can be designed as a robot, for example, and the laser welding head 12 can be attached to the robot. During a laser welding process, ie during the formation of a weld seam, the laser welding head 12 or the laser welding system 10 preferably remains stationary relative to the at least one workpiece 16a, 16b.

When the laser welding process is carried out, the laser beam 14 and the at least one workpiece 16a, 16b are emitted from an interaction region. The area of interaction can in particular include the vapor capillary and the melt pool. The process radiation in a visible wavelength range can also be referred to as process lights or plasma radiation. The process radiation in an infrared wavelength range can also be referred to as thermal radiation. The process radiation also includes a portion of the portion of the laser beam 14 that is reflected when the laser beam 14 is radiated onto the at least one workpiece 16a, 16b. This reflected portion can also be referred to as a back reflection.

A portion 19 of the process radiation is coupled back into the laser welding head 12 or the laser welding system 10 and runs at least in sections superimposed with the laser beam 14. Starting from the at least one workpiece 16a, 16b, this portion 19 of the process radiation enters the focusing optics 24 Laser welding head 12 and is also deflected by the deflection device 26. The portion 19 is then coupled out of the path of the laser beam 14 by the first coupling device 23a. The radiation intensity of this portion 19 is detected by sensors at predetermined wavelengths or in predetermined wavelength ranges, as described in detail below.

The position of the at least one deflection element of the deflection device 26 and thus the angle of incidence 25 of the laser beam 14 on the at least one workpiece 16a, 16b have an influence on the spectral distribution of the radiation intensity of the process radiation component 19 and of the optical measuring beam 43 and on the acquisition of image data , as below is described. The position of the at least one deflection element of the deflection device 26 and the angle of incidence 25 of the laser beam 14 on the at least one workpiece 16a, 16b therefore also determine a signal level of the sensor data output by the corresponding sensors.

The laser welding system 10 has a number of sensors for acquiring sensor data during the laser welding process. The sensors can also be referred to as sensors. The sensor system is preferably integrated into the laser welding head 12 or attached to it. In the embodiment shown in FIG. 1 , the laser welding system 10 has a measuring device 40 for interferometric distance measurement or for optical distance measurement using an optical measuring beam 42 . The measuring device 40 is set up to measure a distance between the laser welding head 12 and the at least one workpiece 16a, 16b during the laser welding process and/or to measure a depth of the vapor capillary. The measuring device 40 is set up to transmit distance data to the control unit as sensor data. The distance data may include measured distance values and/or measured depth values. The measuring device 40 can also be set up to record or scan a surface profile of a surface of the weld seam formed by the laser welding process. This can be done in particular after the laser welding process has been carried out. Capturing the surface profile can also be referred to as post inspection of the weld or weld bead. The measuring device 40 can be set up to transmit corresponding surface profile data to the control unit as sensor data.

According to embodiments, the measuring device 40 comprises an optical coherence tomograph or can be embodied as an optical coherence tomograph. In other words, the distance measurement can be based on optical coherence tomography (OCT). This type of distance measurement is based on the principle of using the coherence properties of light with the help of an interferometer. For this purpose, the optical measuring beam 42 is radiated onto the at least one workpiece 16a, 16b. The portion of the optical measuring beam 42 reflected back by the at least one workpiece 16a, 16b is superimposed with light from a reference arm (not shown) and caused to interfere. By evaluating the superimposed light, information about the distance from the at least one workpiece 16a, 16b, the surface profile of the weld seam or the depth of the vapor capillary can be obtained.

The laser welding system 10 includes a second coupling device 23b for coupling the optical measurement beam 42 into the laser welding head 16 and for superimposing of the optical measuring beam 42 with the laser beam 14. The second coupling device 23b is designed as a beam splitter and comprises, for example, a dichroic mirror, which essentially reflects light with the wavelength of the optical measuring beam 42, and light with a different wavelength than that of the optical measuring beam 42 essentially lets happen. The optical measuring beam 42 is thus reflected and deflected by the dichroic mirror of the second coupling device 23b and passes through the dichroic mirror of the first coupling device 23a in order to be coupled into the laser welding head 12 or into the deflection device 26 . After passing through the deflection device 26 and the focusing optics 24, the optical measuring beam 24 impinges on the surface of the at least one workpiece 16a, 16b.

The laser welding system 10 also includes a sensor unit 44 for measuring a radiation intensity of the process radiation coupled into the laser welding head 12 . For this purpose, the laser welding system 10 has a third coupling device 23c, which is set up to direct part of the process radiation into the sensor unit 44 . The third coupling device 23c is designed as a beam splitter and has, for example, a partially transparent mirror, so that the process radiation partially passes through the third coupling device 23c.

The sensor unit 44 has intensity sensors (not shown) for acquiring intensity data. A first intensity sensor of the sensor unit is set up, for example, to measure a radiation intensity of the process radiation that has entered the sensor unit 44 in a visible wavelength range and to output a first intensity signal based thereon. The first intensity sensor is set up to measure the radiation intensity of the plasma radiation. Based on this, the process lighting can be evaluated. The first intensity signal can include measured values of the radiation intensity of the process radiation in the visible wavelength range. The measured values can be transmitted to the control unit 48 as first intensity data.

A second intensity sensor is set up, for example, to measure a radiation intensity of the process radiation in the infrared wavelength range and to output a first intensity signal based thereon. The second intensity sensor is set up to measure the radiation intensity of the infrared or temperature radiation. Based on this, the melt pool dynamics can be evaluated. The second intensity signal can include measured values of the radiation intensity of the process radiation in the infrared wavelength range. The measured values can be transmitted to the control unit 48 as second intensity data. A third intensity sensor is set up, for example, to measure a radiation intensity of the process radiation at a wavelength of the laser beam and based on this to output a first intensity signal. The third intensity sensor is set up to measure the radiation intensity of the back reflection. The third intensity signal can include measured values of the radiation intensity of the process radiation at the wavelength of the laser beam. The measured values can be transmitted to the control unit 48 as third intensity data.

The sensor unit 44 is not limited to a combination of the first to third intensity sensors, but may include only one or two of these intensity sensors. The intensity sensors are preferably designed as photodiodes.

In the embodiment shown in Fig. 1, the laser welding system 10 also includes a fourth intensity sensor 38 for detecting or determining an irradiated power of the laser beam 14. The fourth intensity sensor 38 is set up to measure a radiation intensity at the wavelength of the laser beam 14 and based on this to output an intensity signal. The intensity signal can include measurements of the radiation intensity. Based on the measured radiation intensity, the current or irradiated or used power of the laser beam 14 can be determined. The fourth intensity sensor 38 is set up to transmit fourth intensity data to the control unit. The measured values can be transmitted to the control unit 48 as fourth intensity data. Alternatively, the intensity data can include determined values of the radiated power of the laser beam 14 .

In contrast to the third intensity sensor of the sensor unit 44, the fourth intensity sensor does not receive the radiation intensity of the back reflection. As shown in FIG. 1, the intensity sensor 38 is arranged in such a way that the portion of the laser beam 14 emerging from the collimating optics 22 that was not reflected and deflected by the first coupling device 23a impinges on the fourth intensity sensor 38. The fourth intensity sensor 38 thus measures the radiation intensity of laser radiation of the laser beam 14 that was not previously reflected by the at least one workpiece 16a, 16b. The measured radiation intensity is therefore not influenced by the processes in the interaction zone between the laser beam 14 and the at least one workpiece 16a, 16b. The radiated power of the laser beam 14 can therefore be determined and checked on the basis of this measured radiation intensity. Furthermore, the laser welding system 10 includes an image sensor 46 which is set up to generate image data. The image sensor 46 can also be referred to as a vision system. The image sensor 46 can include a camera (not shown), for example, or can be embodied as a camera. The image sensor 46 is set up to measure a radiation intensity of radiation

47 to be detected from the surface of the at least one workpiece 18a, 18b. The radiation 47 can include light in the visible wavelength range and/or in the infrared wavelength range, and can in particular include part of the process radiation that has passed through the third coupling device 23a. The radiation 47 can be directed onto the image sensor 46 by a fourth coupling device 23d. The fourth coupling device 23d can comprise a mirror. The image sensor 46 is set up to detect an intensity of the radiation 47 . Since in the laser welding system 10 shown in FIG. 1 the radiation 47 runs at least partially overlapping, in particular coaxially, with the laser beam 14, the arrangement of the image sensor 46 shown in FIG. 1 can also be referred to as a coaxial arrangement.

The image sensor 46 is set up in particular to detect the intensity of the radiation 47 with frequency and/or spatial resolution and to record an image of the surface of the at least one workpiece 16a, 16b based on the detected intensity. In particular, the image can show a region of the surface of the at least one workpiece 16a, 16b with the vapor capillary and the molten pool. The image can be color or grayscale. The image sensor 46 can be set up to record images continuously or repeatedly during the laser welding process. The image sensor 46 is set up to transmit the recorded image or images to the control unit 48 as image data. The image sensor 46 can be set up to record a video of the surface of the at least one workpiece 16a, 16b. In this case, a frame of video can be viewed as an image. The image sensor 46 can perform image (pre-)processing of the recorded image before it is transmitted to the control unit.

The disclosure is not limited to the configuration of the laser welding system 10 or the laser welding head 12 shown in FIG. 1 . In particular, the laser welding system 10 or the laser welding head 12 can comprise only two or three of the sensors 38 , 40 , 44 and 46 .

The control unit 48 is set up to receive the sensor data and is set up to receive target values of the at least one machining parameter. The control unit

48 is set up to determine, based on the sensor data from at least two of the sensors and based on the at least one processing parameter, whether the Laser welding process trained weld joint has a defect. The control unit 48 is also set up to control the laser welding head 12, in particular the deflection device 26 and the collimation optics 22, in order to carry out the laser welding process. Alternatively, this functionality can be implemented by a control unit of the laser welding head 12, for example the control unit of the deflection device 26, or by the higher-level control unit. The control unit 48 is set up to control the laser welding system 10, in particular the laser welding head 12 and the sensors, in order to carry out the method for monitoring the laser welding process.

3 shows a flow diagram of the method for monitoring a laser welding process according to embodiments of the present disclosure. The method can be carried out by the laser welding system 10 according to FIG. 1 .

The method includes performing the laser welding process according to embodiments of the present disclosure by irradiating a laser beam onto at least one workpiece to form a welded joint (SI). The laser beam is guided along a processing path by a deflection device. The laser welding process can be carried out, for example, by the laser welding system 10 according to FIG. 1 for welding the two workpieces 16a, 16b.

During the laser welding process, sensor data are recorded by at least two sensors (S2). The at least two sensors can include the two sensors of the laser welding system 10 of FIG. 1 . For example, the at least two sensors can include the first to third intensity sensors. According to embodiments, the sensor data is recorded in real time during the laser welding process and includes current sensor data from the respective sensors.

As a further step (S3), the method includes determining whether the welded joint formed by the laser welding process has a defect, based on the sensor data recorded. It is preferably determined whether the welded joint formed by the laser welding process has a defect, additionally based on at least one processing parameter of the laser welding process. According to embodiments, it is determined whether the welded connection has a defect based on target data of the at least one processing parameter that were recorded or recorded during the laser welding process, in particular during the formation of the welded connection. Determining whether the welded joint has a defect can also be referred to as defect determination for short. According to embodiments, the determination of whether the welded connection has a defect is carried out by means of machine learning methods, in particular using an artificial neural network. For example, it may be determined that the weld has a defect if the conductivity of the electrical connection through the weld between the workpieces 16a, 16b is equal to or less than a predetermined conductivity threshold. Further, the weld may be determined to have a defect if the size of the gap between lap welded workpieces 16a, 16b is equal to or greater than a gap threshold.

According to embodiments, the error is determined after the laser welding process has been carried out. If the weld is determined to have an imperfection, the weld or workpiece may be classified as bad, poor weld, and/or scrap. If it is determined that the weld joint has no defect, the weld joint or the welded workpiece can be classified as "pass" and/or as a good weld.

Defect determination and thus also classification of the welded workpieces are thus carried out by combining the sensor data from a number of sensors and data relating to the at least one processing parameter of the laser welding process. This increases the reliability of error determination. The procedure described can significantly increase the basis for evaluating the quality of the welded joint and reduce the risk of incorrect classification of the welded workpieces. In particular, this can reduce the risk of false rejects and escapes.

According to preferred embodiments, the at least one processing parameter is the angle of incidence 25 of the laser beam 14 on the at least one workpiece 16a, 16b, the position of the laser beam 14 within the scan field 34 of the deflection device 26, the deflection of the laser beam 14 by the deflection device 26 from the zero position 32, the position of the at least one workpiece 16a, 16b within the scan field 34 of the deflection device 26, the position of the processing path 19 within the scan field 34 of the deflection device 26, the adjustment speed of the deflection element of the deflection device 26, the position and/or the adjustment angle of the deflection element of the deflection device 26. Furthermore, according to embodiments, the sensor data of the at least two sensors include the first to third intensity data of the first to third intensity sensors of the sensor unit 44, wherein the first to third intensity data during the laser welding process include measured values of the radiation intensity of the process radiation.

As described above with reference to Figs. 1 and 2, the position of the at least one deflection element of deflection device 26 or the angle of incidence 25 of laser beam 14 on at least one workpiece 16a, 16b can determine a signal level of the sensor data output by the corresponding sensors, in particular the first to third intensity data.

Furthermore, the focusing optics 24, in particular in the case of an F-Theta lens, can have an influence on the signal levels. The focusing optics 24 is usually only optimized for the wavelength of the laser beam 14 . The focusing optics 24 can therefore cause chromatic aberration to radiation having a different wavelength than the wavelength of the laser beam 14 . This effect is intensified by a large deflection of the laser beam 14 from the zero position 32 by the deflection device 26 .

By including and taking into account at least one of the processing parameters mentioned when determining the error, the influences of the focusing optics 24 and the deflection device 26 on the sensor data can be taken into account when determining the error. In this way it can be avoided that variable or changing signal levels of the sensor data, which originate for example from different positions in the scan field, lead to an unreliable fault determination. The signal level can indicate an average signal level of the recorded sensor data or the measured values of the radiation intensity. The signal level can be defined in particular as the mean value over time of the measured values of the radiation intensity.

Other processing parameters that can be included in the error determination can include: an alignment of the laser welding head to the at least one workpiece, a focal position of the laser beam, a focal diameter of the laser beam, a focal shape of the laser beam, a processing speed, a processing direction, a material and/or a thickness of the at least one workpiece.

With reference to Fig. 1, the alignment of the laser welding head 14 to the at least one workpiece 16a, 16b, the processing speed, the processing direction, the material, the thickness of the at least one workpiece 16a, 16b can be controlled by the control unit (not shown) of the laser welding head 12, for example the control unit of the deflection device 26 (not shown) and/or by the higher-level control unit (not shown) of the Laser welding system 10 are transmitted to the control unit 48. The focal position of the laser beam 14, the focal diameter of the laser beam 14 and the focal shape of the laser beam 14 can be transmitted from the collimating optics 22 or the control unit of the laser welding head 12 to the control unit 48.

By considering the material, in particular the material properties, or the thickness of the at least one workpiece, it can be ensured in particular that the error determination can be reliably carried out even after a batch change of the workpieces. The surface quality is one of the material properties. This is described, among other things, by the reflection and coupling behavior of the material for the laser beam. A different surface quality can have an impact when changing batches of workpieces if the reflection and coupling behavior differ between two batches. The focal position, the focal diameter, the focal shape, the material and the thickness of the at least one workpiece and the processing speed also have an influence on the radiation intensity of the process radiation emitted during the laser welding process. If these processing parameters are taken into account in the error determination, the error determination can be carried out more reliably.

The correlated signals can also serve as input parameters for laser welding process control. If the defect determination is carried out during the laser welding process, the laser welding process can be regulated based on the result of the defect determination by adapting at least one processing parameter, in particular the processing speed, the laser power and/or the focus position of the laser beam, or is set. If, for example, it has been determined that the welded joint that has already been formed does not produce any or an insufficient electrical or mechanical connection between the workpieces, the laser power can be increased during the laser welding process and/or the processing speed can be reduced.

With reference to FIG. 1 , the regulation can be performed by the control unit 48 or by the superordinate control unit of the laser welding system 10 .

Based on the result of the error determination, a subsequent laser welding process can also be controlled. FIG. 4 shows a schematic view of several workpiece groups in a scanning field of a deflection device of a laser welding system according to embodiments to illustrate a method according to embodiments of the present disclosure. FIG. 4 illustrates how the method for monitoring laser welding processes is carried out on a number of workpiece groups. Three workpiece groups G1, G2, G3 of the same type are welded one after the other by the same laser welding process according to embodiments of the present disclosure. The method for monitoring the laser welding process according to FIG. 3 is carried out for each laser welding process, ie for each of the three workpiece groups G1-G3. As shown, each of the workpiece groups G1-G3 includes two workpieces to be welded, but the present disclosure is not limited thereto.

Each of the three workpiece groups G1-G3 is located at a different position in the scan field 34 of the deflection device 26 of the laser welding system 10 according to FIG. 1. The processing path to be followed to form the weld seam is therefore also located at a different position in the scan field 34 of the deflection device 26. The three workpiece groups GI GS include workpieces of the same type and the same laser welding process is to be carried out for each of the workpiece groups G1-G3.

As can be seen, with a stationary arrangement of the laser welding head 12 when welding the three workpiece groups G-1G3, the deflection of the laser beam 14 depends on the position of the respective workpiece group G1-G3 in the scan field 34 and thus on the position of the respective processing path in the scan field 34 Accordingly, the angle of incidence of the laser beam 14 and thus a proportion of the process radiation coupled into the laser welding head 12 differs between the workpiece groups G1-G3. For example, a smaller proportion of the process radiation is coupled into the laser welding head 12 for the workpiece group Gl and G3 than for the workpiece group G2, since the angle of incidence for the workpiece groups Gl and G3 is greater than for the workpiece group G2. As a result, in particular, the signal levels of the first to third intensity data vary between the workpiece groups G1-G3.

According to embodiments, the position of the respective workpiece group G1-G3, the position of the respective processing path for the workpiece groups G1-G3, the angle of incidence of the laser beam 14, the deflection of the laser beam 14 from the zero position and/or the position of the laser beam 14 in the scan field 34 of the deflection device 34 when determining whether the weld joint formed by the respective laser welding process has a defect is taken into account. This can ensure that the varying signal levels of the sensor data do not lead to an unreliable error determination. The position of a machining path within the scan field 34 can be defined as the position of the center of the machining path in the scan field. Furthermore, according to embodiments, the laser welding process on the workpiece groups G1-G3 is regulated based on the error determination for a previous laser welding process. If, for example, it was determined for the workpiece group G1 welded first that the welded connection has a defect, the laser welding process for welding the workpiece groups G2 and/or G3 can be regulated accordingly. For example, the laser power, the focal position of the laser beam 14 and/or the processing speed can be adjusted.

The present disclosure relates to a system for material processing using a laser beam, in particular a laser welding system, which includes a so-called laser welding head and a sensor system, preferably a laser welding head with integrated sensor system. The signals from the sensors of the sensor system are combined and evaluated in such a way that not only the signals from the individual sensors but also a correlation of the signals from a number of sensors can be used to evaluate the quality of the weld or the welding process. In this way, errors can be detected automatically and reliably with minimal false rejects or with a minimal escape rate. Information from the laser welding head, in particular a scanner unit (e.g. position, speed) can also be included in this correlation evaluation. The sensor system includes at least two of the following sensors, for example: photodiodes to evaluate the process lighting, the melt pool dynamics and the back reflection, photodiodes to determine the laser power currently used, optical coherence tomography, and visual image recording and image processing (camera). The sensors can be connected to the laser welding head. This type of procedure allows the signals to be displayed in real-time, conveniently combined with the results of the welds and correlated with one another, with the correlation being able to be established, for example, by using neural networks or other suitable methods, e.g. from the field of artificial intelligence . In addition, by acquiring and correlating sensor data from a number of sensors, insights and information regarding the need for maintenance of the laser welding system can also be obtained.

Claims

patent claims

1. Method for monitoring a laser welding process, the method comprising the steps:

Carrying out (Sl) the laser welding process using a laser welding head, which radiates a laser beam (14) onto at least one workpiece (16a, 16b) to form a welded connection, the laser beam (14) being guided by a deflection device (26) along a processing path (18 ) to be led,

Detection (S2) of radiation emanating from the workpiece and coupled into the laser welding head as sensor data by at least two sensors (38, 40, 44, 46) during the laser welding process, with the radiation running at least partially superimposed on the laser beam (14) and subsequently Passing the deflection device (26) from the beam path of the laser beam (14) is decoupled in order to hit the at least two sensors (38, 40, 44, 46); and

Determining (S3) whether the welded connection has a defect, based on the recorded sensor data and at least one processing parameter of the laser welding process.

2. The method of claim 1, further comprising the step of:

classifying the welded workpiece (16a, 16b) as scrap if it is determined that the weld joint has a defect.

3. The method according to any one of the preceding claims, wherein the processing parameter comprises at least one of the following parameters: an alignment of a laser welding head (12) irradiating the laser beam (14) with respect to the at least one workpiece (16a, 16b), an angle of incidence of the laser beam on the at least a workpiece, a focal position of the laser beam (14), a focal diameter of the laser beam (14), a focal shape of the laser beam (14), a processing speed, a processing direction, a speed vector of the laser beam (14) along the processing path (18), a material and/or a thickness of the at least one workpiece (16a, 16b), and at least one parameter of the deflection device (26), in particular a position of the laser beam (14) within a scan field (34) of the deflection device (26), a deflection of the laser beam (14) by the deflection device (26) from a zero position (32), the position of the processing path (18) within the Scan field (34) of the deflection device (26), an adjustment speed of a deflection element of the deflection device (26), and/or an adjustment angle of a deflection element of the deflection device (26).

4. The method according to any one of the preceding claims, wherein the at least two sensors (38, 40, 44, 46) include at least two of the following sensors: a first intensity sensor, preferably including a photodiode, wherein the first intensity sensor is set up to detect first Intensity data of a radiation intensity of a process radiation emitted during the laser welding process in a visible wavelength range; a second intensity sensor, preferably comprising a photodiode, the second intensity sensor being set up to acquire second intensity data of a radiation intensity of the process radiation in an infrared wavelength range; a third intensity sensor, preferably comprising a photodiode, the third intensity sensor being set up to acquire third intensity data of a radiation intensity of a laser radiation reflected back from a surface of the at least one workpiece (16a, 16b); a fourth intensity sensor (44), preferably comprising a photodiode, the fourth intensity sensor being set up to acquire fourth intensity data of a radiation intensity of the laser beam (14) in order to determine an irradiated laser power; an image sensor (46), preferably comprising a camera, wherein the image sensor is set up to capture image data by recording an image of a surface of the at least one workpiece (16a, 16b); and a distance sensor (40), preferably comprising an optical coherence tomograph, the distance sensor being set up to acquire distance data of a distance to the at least one workpiece (16a, 16b) and/or set up to acquire distance data of a depth of a material generated during the laser welding process Vapor capillary and/or set up to acquire surface profile data of a surface of a weld seam formed by the laser welding process.

5. The method according to any one of the preceding claims, wherein the acquisition of the sensor data comprises at least two of the following:

Acquisition of first intensity data of a radiation intensity of a process radiation emitted during the laser welding process in a visible wavelength range, acquisition of second intensity data of a radiation intensity of the process radiation emitted during the laser welding process in an infrared wavelength range, acquisition of third intensity data of a radiation intensity of one of the at least one workpiece ( 16a, 16b) back-reflected laser radiation,

acquisition of fourth intensity data for determining an irradiated laser power, Capturing image data by capturing an image of a surface of the at least one workpiece (16a, 16b), and

Detection of distance data of a distance between a laser welding head 12) radiating the laser beam (14) and the at least one workpiece (16a, 16b) and/or a depth of a vapor capillary produced during the laser welding process and/or of surface profile data of a surface of a surface formed by the laser welding process Weld.

6. The method according to any one of the preceding claims, wherein the determination of whether there is a defect in the welded connection takes place in real time while the laser welding process is being carried out and/or after the laser welding process has been carried out.

A method according to any one of the preceding claims, wherein it is determined whether the weld joint has one of the following defects: a missing or insufficient electrical and/or physical connection through the weld joint and/or a gap between welded workpieces (16a, 16b).

8. The method according to any one of the preceding claims, wherein the determination of whether the welded connection has a defect is carried out using algorithms and/or using a machine learning method, in particular using an artificial neural network.

9. The method according to any one of the preceding claims, wherein determining whether the welded joint has a defect comprises: evaluating the sensor data separately for each of the at least two sensors (38, 40, 44, 46),

combining the scores by a logical operation, and determining whether the weld has a defect based on the combined score.

10. The method according to any one of the preceding claims, further comprising:

Controlling the laser welding process when it has been determined that there is a defect in the weld joint by adjusting at least one processing parameter.

11. The method according to any one of the preceding claims, further comprising: pre-processing, in particular by means of an FPGA, the sensor data of the at least two sensors (38, 40, 44, 46).

12. The method according to any one of the preceding claims, wherein the deflection device (26) has a maximum deflection angle of greater than 10 degrees, in particular 20 degrees, and/or wherein the deflection device (26) has a scan field (34), its length and/or width is equal to or greater than 50 mm.

13. Laser welding system (10), comprising: a laser welding head (12) for radiating a laser beam (14) onto at least one workpiece (16a, 16b) to form a welded joint, the laser welding head (12) having a deflection device (26) for guiding the laser beam (14) along a processing path (18), at least two sensors (38, 40, 44, 46), each of the sensors (38, 40, 44, 46) for detecting the emanating from the workpiece and into the laser welding head coupled-in radiation is set up as sensor data during the laser welding process, and a control unit (48) which is set up to carry out a method according to one of the preceding claims.

14. Laser welding system (10) according to claim 13, wherein the control unit (48) is set up to regulate the laser welding process, in particular by adjusting the laser power and/or the focus position of the laser beam (14), based on the determination of whether the welded connection has an error.

15. Laser welding system (10) according to one of claims 13 or 14, wherein the laser welding head (12) comprises at least one of the following elements: a first coupling device (23a) for coupling the laser beam (14) into the deflection device (26) and for Decoupling the radiation emanating from the workpiece from a beam path of the laser beam (14), the first coupling device (23a) being arranged in front of the deflection device (26) in the direction of propagation of the irradiated laser beam (14); a second coupling device (23b) for dividing the radiation coupled out of the beam path of the laser beam (14) in order to direct part of the radiation to a first of the at least two sensors and another part of the radiation to a second of the at least two sensors; collimation optics (22) for adjusting the focal position of the laser beam (14), and an F-Theta lens (24) for focusing the laser beam (14) onto the at least one workpiece (16a, 16b).