Methods for controlling a joining process

Abstract

A method suitable for controlling a joining process in which a first joining partner (11) and a second joining partner (12) are joined by laser beam welding, wherein depth information in an area influenced by the laser beam welding is determined and evaluated using optical coherence tomography, wherein a contour of a joint (20) and / or a width (s) of a joining gap (21) between the first joining partner (11) and the second joining partner (12) is measured in a continuous OCT measurement before and / or during the laser beam welding, and the information thus obtained is used for controlling and quality assurance of the welding process, characterized in that, when a measurement artifact (43) occurs due to a secondary, indirect reflection (43) of the OCT measuring beam (41) from a component edge of the second joining partner (12), a width (s) of a possible joining gap (21) is determined.

Description

The invention relates to a method according to the features of claim 1 for regulating a joining process.It is known that components to be joined are often subject to gaps in the butt joint. These gaps have a disadvantageous effect on the quality of the weld seam and lead to increased process and quality fluctuations and very disadvantageously to reject rates when the components are welded.It is known from the prior art to detect and detect the joint or the component position by means of optical systems, for example on a camera basis, in order to expel the components before the subsequent welding for upstream reworking if an undesired gap is identified, which, however, in turn disadvantageously entails increased processing outlay.DE 10 2012 210 012 A1 describes a method for laser remote welding of two coated metal sheets, wherein a laser beam is directed by means of a scanner device onto the metal sheets to be connected to one another and is guided on these metal sheets. It is provided that the sheets are connected to one another by generating a front fillet weld at an overlap joint, wherein the continuous weld seam generation is detected by a camera device and, on the basis of an automatic evaluation of the recorded images, the path of the laser beam is optionally corrected and adapted to a desired weld seam course.DE 10 2014 117 157 A1 describes a method for joining workpieces by means of a machining beam of a joining device, having a machining optical unit with actively driven deflection units for guiding and with optical elements movable at least to a part for focusing the machining beam onto the surface of a first and / or a second of the workpieces to be joined, comprising joining the first with the second workpiece at an overlap joint with generation of a spatially limited melt pool by means of the machining beam, wherein the machining beam carries out a spatially oscillating movement defined by oscillation parameters during the joining, one or more height positions with respect to the perpendiculars are detected in each case on a top side section of the first workpiece adjoining a machining position to be machined by the machining beam at the overlap joint and a top side section of the second workpiece adjoining the machining position at the overlap joint, evaluating the height positions with regard to the determination of a height difference between the upper side sections of the first and second workpiece adjacent to the machining position at the overlapping joint, and the energy input of the machining beam into the upper side section of the workpiece located higher at the machining position is increased with increasing height difference at the overlapping joint and is decreased with decreasing height difference, wherein a setting of a plurality of process parameters including oscillation parameters of the oscillating movement and a defocusing of the machining beam takes place based on a programmed process model which is dependent at least on a material composition of the workpieces to be connected, a height of the gap, the thicknesses of the workpieces and a positioning of the workpieces in space and relative to one another, wherein at least one oscillation parameter of the oscillating movement of the machining beam is determined in such a way, coupling the oscillations of the machining jet into melt waves formed on the surface of the melt bath, so that molten material flows out of the melt bath at the machining position into a gap formed at the overlapping joint between the two workpieces.DE 10 2023 112 857 A1 discloses a computer-assisted method for adapting processing parameters of a laser processing machine as a function of a characteristic joint cross section of a contact joint between two workpieces to be joined of a workpiece arrangement, comprising the method steps: positioning a sensor of a measurement system in a predetermined target processing position of a processing optics of the laser processing machine at the contact joint by aligning the sensor with a target processing coordinate along a predetermined target processing path of the workpiece arrangement; creating an arrangement profile of the workpiece arrangement by scanning a surface of the workpiece arrangement in a measurement plane transversely to the target processing path; determining the characteristic joint cross section of the workpieces of the workpiece arrangement by evaluating the arrangement profile; and adapting the processing parameters as a function of the determined characteristic joint cross section. The invention also relates to a measuring arrangement and to a production system.DE 10 2021 002 040 A1 discloses a method and a welding device for connecting a first workpiece to a second workpiece by laser welding. The welding device is designed to apply a laser beam to the workpieces and has an output device of an optical coherence tomography system. The output device is designed for outputting a measurement beam of the coherence tomography system. By means of the measurement beam, a size of a gap formed between the workpieces during the laser welding can be detected. The coherence tomography system has at least one deflection mirror which is designed to deflect the measurement beam. By means of the at least one deflecting mirror, the measuring beam can be applied to respective narrow sides of the workpieces arranged overlapping one another at least in regions. At the same time, a broad side of one of the workpieces, which adjoins the narrow side of this workpiece, can be acted upon by the laser beam.DE 10 2023 118 058 A1 discloses a computer-supported classification method for a joining geometry of a contact joint between two workpieces to be joined of a workpiece arrangement, comprising the method steps: positioning a sensor of a measurement system in a predetermined machining position of a machining optics of a laser processing machine at a joint of the workpiece arrangement; creating a geometry profile of the workpiece arrangement by scanning a surface of the workpiece arrangement at the joint in a measurement plane transversely or perpendicular to a main direction of extension of the contact joint; determining the joining geometry by evaluating and comparing the geometry profile with stored reference profiles to determined joining geometries. The invention also relates to a production method and a production system.It is an object of the invention to provide a device and a method for reliably regulating the joining process.The object is achieved by a method for regulating a joining process, in which a first joining partner and a second joining partner are joined to one another by laser beam welding, depth information in a region influenced by laser beam welding being determined and evaluated by means of optical coherence tomography.In such a method, it is proposed that a contour of a joint and / or a width of a joint gap between the first joining partner and the second joining partner is measured within the laser welding system before and / or during a laser beam welding process in a continuous OCT measurement, and the information thus obtained is used to control the welding process.In the invention, with the aid of OCT technology (OCT: Optical Coherence Tomography), an approach is implemented in laser beam welding in order to measure the contour / geometry of the joint (e.g. butt joint) when carrying out a continuous OCT measurement, e.g. with the aid of a measurement line having a plurality of measurement points perpendicular to the joint.Advantageous embodiments of the invention are the subject matter of the dependent claims.The method according to the invention provides that, when a measurement artifact occurs due to a secondary, indirect reflection of the OCT measurement beam from a component edge and / or contour of the second joining partner, a width of a possible joining gap is determined. If the OCT measurement beam is reflected by the component edges of both joining partners, it is possible to establish whether there is a joining gap and, if this is the case, how wide the joining gap is.If there is no joining gap, the difference between primary and secondary reflection becomes smaller the smaller the distance of a measurement point from the joint.If the OCT measurement beam reaches the joint, primary and secondary reflections coincide, i.e. they provide the same distance value in the depth direction.If, on the other hand, there is a joining gap, the primary and the secondary reflection always supply different distance values. When a measurement artifact occurs due to a secondary, indirect reflection of the OCT measurement beam from a component edge of the second joining partner, the width of the possible joining gap can be determined, in particular along the joint geometry to be welded. If the OCT measurement beam approaches the joining gap, it is no longer reflected at all as soon as it is directed into the joining gap. If the last measurement point is considered before this occurs, a good approximation value for the width of the joining gap is obtained from the difference of the distance values in the depth direction from primary and secondary reflection.Information about a contour of the joint or / and a width of the joint gap obtained from the continuous OCT measurement can advantageously be used to influence parameters of the welding process, in particular the welding position, the welding power, a welding speed and / or a defocusing of the laser beam. The influencing can take place in real time. Alternatively, an OCT measurement can be carried out first and the data obtained therefrom can be used to set the parameters of the welding process, for example by means of an NC controller.In a further embodiment of the proposed method, it can be provided that the information of the joining gap is used in combination with other OCT measurement values generated from the welding process, in particular those measurement values assigned to the capillary / welding depth and surface topography, for quality assurance of the laser welding process, and the unmated and / or joined component is evaluated on the basis of set i.o. / n.i.o. limit values and is discharged when these are exceeded.The following advantages are associated in particular with the method according to the invention:An active online process control of the welding process is made possible by the determination of an increased joining gap in that an adaptation of the process parameters and of the welding position takes place, which can be stored in a database for different states, for example.Waste in production operation can be reduced by the method. At the same time, the possibility of a revision is created in order to correct errors.By means of a welding process adapted according to the invention, the quality of the connection or weld seam can be improved considerably.A simple measurement covers a plurality of position parameters, for example the seam position, component height, component offset, gap width, etc., by the additional evaluation of the measurement artifact.The process according to the invention can reduce cycle time. In the proposed method, the OCT technology is made usable as a universal QS system for the weld seam positioning by using an OCT scanner as an online and post depth measurement unit.The method according to the invention enables increased flexibility in technology and standardization of technology and can be carried out using current plant and system technology.The measurement can be used flexibly for different joints (overlapping joint, butt joint, fillet joint, etc.) and chamfer angles, wherein a particular suitability for butt joints exists.The method has a high flexibility with respect to materials and material thicknesses (i.e. both in the case of thin and thick sheet metal connections). A particular suitability of the method has been established for the welding of transmission parts.Exemplary embodiments of the invention are explained in more detail below with reference to drawings.The following are shown: FIG. 1 shows a schematic illustration of an exemplary laser welding device, FIG. 2 shows the measuring principle in the case of a joint joint without a joint gap, and FIG. 3 shows the measuring principle in the case of a joint joint with a joint gap.FIG. 1 shows a schematic illustration of the laser welding device 30 used, wherein the x-axis is a local welding feed direction 51, i.e. with respect to the current location of the weld. The z-axis is a depth direction 53. the y-axis is a also local transverse direction 52.An upper joining partner 11 and a lower joining partner 12 lie against one another forming a butt joint. In the exemplary embodiment shown, both joining partners 11, 12 are hollow cylinders, so that the global welding feed direction is circular.To generate a welding laser beam 34, the laser welding device 30 comprises a welding laser 31 which generates laser light and feeds this laser light to a welding optics 32 arranged above the arrangement of the two joining partners 11, 12. By deflecting mirrors 33 arranged in the welding optics 32, a welding laser beam 34 is directed onto the joining partners 11, 12. The high-energy radiation melts the material of the joining partners 11, 12. A bath of melt is formed around the point of impingement of the welding laser beam 34, which subsequently solidifies to form a weld seam.The welding optics 32 continuously guides the welding laser beam 34 along the circular joint line in the welding feed direction 51 during the welding, so that a weld seam 20 running in the welding feed direction 51 is formed.The laser welding device 30 further comprises an OCT measurement beam unit 40 which generates an OCT measurement beam 41 which is directed at the current location of the weld. There, OCT measurements are carried out with the OCT measurement beam 41 along a measurement line, not shown in the drawing, having a plurality of measurement points. For this purpose, the OCT measurement beam 41 is continuously moved repeatedly back and forth, as shown by the double arrows in FIG. 1. As a result, the OCT measurement beam 41 is reflected by the first joining partner 11 and by the second joining partner, as will be explained in more detail with reference to FIGS. 2 and 3. In FIG. 1, this is illustrated by way of example by the primary OCT measurement beam 42 reflected by the first joining partner and the secondary OCT measurement beam 43 reflected by the second joining partner.FIG. 2 shows the two joining partners 11, 12 in an idealised joint 20 in which there is no joining gap 21. FIG. 3 shows the two joining partners 11, 12 in a joint 20 in which there is a joining gap 21 between the joining partners 11, 12. In both exemplary embodiments, an edge of the first joining partner 11 has a flank angle δ with respect to the joint 20.The OCT measurement beam 41 is directed at a measurement point 22. The OCT measurement beam 41 is reflected by the measurement point 22 as a primary reflected OCT measurement beam 42. Because of the flank angle δ, the OCT measurement beam 41 is also deflected toward the second joining partner 12 and reflected by the latter as a secondary reflected OCT measurement beam 43.In both FIGS. 2 and 3, a diagram is shown with the measurement values obtained from the primary OCT measurement beam 42 reflected by the first joining partner and from the secondary OCT measurement beam 43 reflected by the second joining partner.According to the invention, with the aid of this multiple reflection, as a result of a flank angle δ (such as, for example, a chamfer of a component edge) of the first joining partner 11 and a back-reflecting component edge of the second joining partner 12, conclusions about a possible joining gap 21 are generated. Here, at least two measurement signals are generated for each measurement point 22. The first, primary measurement signal 42 is generated at the first joining partner 11 by direct reflection at the flank angle δ of the chamfer. The second, secondary measurement signal 43 (measurement artifact) is based on an OCT measurement beam 41 deflected to the side from the flank angle δ of the chamfer of the first joining partner 11 and on the reflection of the OCT measurement beam 41 at the component edge of the second joining partner 12.This secondary measurement signal 43 and its depth position is dependent on the distance a of the second joining partner 12 from the bevel / component edge / component surface of the first joining partner 11.If an unwanted joining gap 21 now occurs at the joint 20, the secondary measurement signal 43 measures a path length extension around the width s of the joining gap 21 between the two joining partners 11, 12.By means of an algorithm, this width s can be used in real time and / or downstream for regulating the welding process (welding position, welding power, welding speed, defocusing, NC control, etc.).List of reference characters11 first joining partner 12 second joining partner 20 joint 21 joint gap 22 measurement point 30 laser welding device 31 welding laser 32 welding optics 33 deflection mirror 34 welding laser beam 40 OCT measurement beam unit 41 OCT measurement beam 42 primary reflected OCT measurement beam, primary measurement signal, direct reflection 43 secondary reflected OCT measurement beam, secondary measurement signal, measurement artifact 51 welding feed direction 52 transverse direction 53 depth direction δ flank angle a distance s width

Claims

Method suitable for regulating a joining process, in which a first joining partner (11) and a second joining partner (12) are joined to one another by laser beam welding, depth information in a region influenced by laser beam welding being determined and evaluated by means of optical coherence tomography, a contour of a joint (20) and / or a width (s) of a joining gap (21) between the first joining partner (11) and the second joining partner (12) being measured before and / or during the laser beam welding in a continuous OCT measurement, and the information obtained in this way being used for regulating and quality assurance of the welding process, characterized in that, when a measurement artifact (43) occurs, a secondary measurement defect occurs, In an embodiment, a width (s) of a possible joint gap (21) is determined by indirect reflection (43) of the OCT measurement beam (41) from a component edge of the second joint partner (12).Method according to Claim 1, characterized in that information about a contour of the joint (20) and / or a width (s) of the joint gap (21), which information is obtained from the continuous OCT measurement, is used to influence parameters of the welding process, a welding position, a welding power, a welding speed and / or a defocusing of the welding laser beam (34).Method for regulating a joining process according to at least one of the preceding claims, characterized in that the information of the joining gap is used in combination with other OCT measurement values generated from the welding process, those measurement values assigned to the capillary / welding depth and surface topography, for quality assurance of the laser welding process, and the unmated and / or joined component is evaluated on the basis of set i.o. / n.i.o. limit values and is discharged if these are exceeded.

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