Method for welding sheet metal parts

Abstract

This invention relates to a method for butt welding flat metal plates (1, 2) in a welding machine, wherein two metal plates (1, 2) are placed on a conveying device (37) by a feeding device and fixed by a holding device, the two edges (4, 5) of the two metal plates (1, 2) to be welded are placed adjacent to each other in a butt-fitting manner to form a gap as small as possible and welded together by a welding laser (6), wherein the gap width (7) is measured and the welding process is controlled by the measured value. According to the invention, the gap width (7) is measured by the reflected light method and the net gap width (9) is measured by the transmitted light method, which allows for a more accurate estimation of the missing area (8) and missing volume in the gap.

Description

Technical Field

[0001] This invention relates to a method for butt welding of metal sheet components, particularly but not limited to the method for butt welding of metal sheet components in automobile body manufacturing as described in the preamble of claim 1. Background Technology

[0002] To produce sheet metal parts in car body manufacturing, modern manufacturing methods are employed that take individual sheet metal sheets—at most, after edge treatment—and create welded parts, known as tailored sheet metal (TWB). In known welding processes, particularly laser welding, the sheet metal is fed into a fixed welding tool and welded. Today, manufacturers primarily take advantage of the fact that sheet metal can be composed of different material grades or sheet thicknesses. This allows subsequent parts to be adapted to future localized loads, which would otherwise require additional reinforcement components. In the current automotive industry, door rings are made using TWB. These door rings consist of up to eight individual components, where the gaps vary due to differences in shape and manufacturing tolerances, and the sheet thickness of each component also differs. Furthermore, different types of gaps can occur between different door rings, complicating efficient production. Mastering V-welding is the biggest challenge here.

[0003] Poor weld quality means that undesirable cracks will appear in the weld during door ring crash tests. For safety reasons, this risk cannot be taken in door ring production, as real-world crashes are fatal to the automotive industry and have severe consequences. To date, known methods involve adding filler wire to close variable gaps up to 0.3 mm. Depending on the welding task (the material of the parts being welded), dynamically closing variable gaps of up to approximately 1 mm with additional material (wire) and high weld quality is a challenge.

[0004] Among known welding methods, particularly laser welding, there are two approaches: In the first approach, the plates are precisely positioned, clamped, and welded together by a movable welding head. In the second approach, metal sheets are fed into a fixed welding tool and welded together. Both methods require high mechanical precision to handle gap widths currently limited to approximately 0.3 mm.

[0005] Patent document US5328083 describes a method and apparatus for performing this process; however, it does not disclose how to accurately position the welding tool relative to the current weld seam orientation. Therefore, inaccuracies in the metal plate and misalignments in the weld seam position can lead to incorrect welding.

[0006] European patent document EP 0817698 B1 describes a method for continuous butt welding of metal plates, wherein the relative positions of the metal plates and the precision of the weld joint are maintained within a specific tolerance range. This method intentionally omits the mechanically precise alignment of the metal plates to be welded. Instead, the gap width and gap position are determined by a sensor device, and a laser tool is guided along the butt joint of the two plates. Subsequently, a control loop can be used to continuously adjust the power of the weld beam and the cooling power (gas, water) required during the welding process. This system requires extensive maintenance.

[0007] A challenge in laser welding is that the gap conditions between different components can vary, resulting in A-type, V-type, parallel, and zero-gap gaps, or a mixture thereof. One known method for determining gap size is the reflected light method. In this method, a light source emits light into the gap, which is reflected by the metal surface and analyzed by a camera positioned on a metal sheet on the same side as the light source. Another known reflected light method is laser line evaluation, for example. This method is based on laser triangulation. For this purpose, a laser line is projected onto the surfaces of two metal sheets. The projected laser line is substantially perpendicular to the edge of the metal sheet forming the gap. Depending on the distance and the shape of the gap, the reflected laser line strikes the camera at a specific angle. The width of the gap can then be determined by evaluating the captured laser line.

[0008] However, this type of system cannot always provide the correct gap size. Especially when it cannot be guaranteed that the same side of the metal plate is always facing up, this measuring system may provide an incorrect gap size.

[0009] In particular, such systems typically only provide the gap width for the upper region of the gap, but can hardly draw any conclusions about the gap width for the lower region.

[0010] A large gap between two metal plates to be welded results in a loss of laser energy absorbed within the gap, as some of the laser beam passes through unimpeded. This loss can be mitigated to some extent by defocusing a single focal point. However, this inevitably reduces the maximum intensity of the laser beam. On the other hand, in the technically zero-gap case, the ability to perform through-weld welding—that is, the ability to completely penetrate the metal vapor capillary during laser welding—decreases. This can be partially compensated for by reducing the welding speed or increasing the laser power. In short, it can be said that in applications, there is a trade-off between gap-closing capability and through-welding capability. To ensure optimal productivity, the laser beam source operates at its designed power limits. Due to reaction time constraints, changing the welding speed during welding operations is not feasible in many plant designs. This typically leads to a decrease in productivity.

[0011] Several approaches have been investigated to address the issues of machinability, efficiency loss, and process reliability associated with wide weld gaps. For example, the concept of a single-focus scanning tracker follows a method of using a high-intensity laser beam with a small focal diameter (0.2 mm to 0.3 mm) to oscillate transversely to the weld feed. Variations in amplitude and laser power depend on the measured gap width. However, experiments using commercially available systems for welding sheet metal have shown that, due to the achievable frequencies, the period length of the oscillating motion cannot guarantee complete coverage of the surrounding molten material at high welding speeds of approximately 10 m / min. To produce acceptable welds, welding speeds must be drastically reduced, resulting in productivity losses regardless of whether a gap is present or zero.

[0012] Two-point optics in laser welding, which uses two spatially separated focal points on the workpiece, is a technology that has moved from the laboratory to the production line. Patent document DE 101 13 471B4 specifies that the laser beam has at least two focal points at the welding point or at a short spatial distance from the welding point. Here, the distance between the focal points is constantly changing based on measurements of various parameters during the welding process, particularly welding speed and welding quality. Patent document CN203124961 mentions laser processing equipment and relates to a rotating two-point optical laser processing head, including a laser emitter, a light guide tube for conveying the laser beam, and a focusing lens for focusing the laser beam. A beam splitter is connected to a drive unit capable of rotating the beam splitter.

[0013] A welding apparatus with a dual-point optical system is also described in EP 3 572 178 A1.

[0014] By using a dual-focus optical system, the distribution of laser energy on both sides of the weld can be flexibly improved, thus avoiding the problem of insufficient energy transfer from a single focus. Furthermore, the beam splitter is connected to the drive unit and can rotate accordingly. Rotation of the dual focus can be achieved by rotating the entire process optical system or by rotating the dual-focus optical module. The main advantage of this method is that the power distribution can be adapted to the assigned task and controlled according to process conditions, such as when the weld width is changed. This achieves high flexibility, and most importantly, high process stability and weld quality. However, studies show that, at the same power level, welding using dual-focus optics results in a shallower weld penetration than welding using only a single laser beam. However, from a manufacturing perspective, the optimal parameters for producing the desired weld are closely related to the economic factors of the entire process. Therefore, process efficiency and weld quality are the core characteristics of the welding method.

[0015] In the process of welding custom sheet metal parts, important criteria are, on the one hand, the overall production capacity of the factory, i.e., how many parts can be produced per hour with an acceptable scrap rate, and on the other hand, the additional materials required to ensure the quality of the entire processing and the expected quality of the welded metal sheet, with reasonable technical effort and filler metal.

[0016] The drawback of the above solutions and methods is that they typically only measure the gap width and gap location, without considering the geometry of the gap. Figure 3 This illustrates different gap geometries in this respect, which are primarily created by the cutting process. Even when two metal plates have a point of contact at the cross-section, resulting in a zero gap, there are areas where the metal plates do not contact. Ideally, the missing volumes in these areas should be filled with material during the welding process to achieve optimal weld results. However, for this to be achieved, it is necessary not only to determine or at least estimate the gap width at one location, but also to determine or at least estimate the gap geometry. In known methods, this is not the case; the gap width is determined only at one location, typically in an area near the surface of the metal plates. Summary of the Invention

[0017] Therefore, the technical problem to be solved by the present invention is to provide a method that can eliminate the above-mentioned disadvantages.

[0018] This technical problem is solved by the features described in claim 1. Variations of advantageous embodiments are provided in the dependent claims.

[0019] Therefore, according to the present invention, the gap width is measured using the reflected light method, and the net gap width is measured using the transmitted light method, thereby more accurately estimating the missing area and missing volume in the gap. The net gap width can be understood as the minimum distance between the edges of the two metal plates, that is, the internal net width area between the metal plates.

[0020] The preferred method of reflected light is the laser line method, which is a laser triangulation method in which a laser line is projected perpendicularly to the direction of the slit onto the surface of the metal sheet, and the shape of the line is evaluated.

[0021] In the transmitted light method, light passes through a slit and is measured on opposing metal plates by a camera. The net width (net slit) between the two metal plates can be determined by evaluating the image.

[0022] Therefore, in addition to measuring the gap width using the reflected light method, this invention can also visually measure the net gap between metal plates to be welded. Thus, the missing volume can be estimated, and the welding process can be controlled optimally.

[0023] It is preferable to also add filler wire during the welding process. With the improved gap measuring device, the optimal requirement for the additional material (filler wire) can be determined more effectively. By controlling the feed speed of the additional wire, the optimal amount of wire can be fed in, thus reducing the amount of filler wire required.

[0024] Therefore, the proposed method can reduce overall production costs.

[0025] In summary, the proposed method delivers better productivity and process quality compared to other known methods.

[0026] During the welding process, it is preferable to use imaging technology to evaluate the measurement results in order to determine the missing volume between the two edges.

[0027] Significantly, another light source and a correspondingly equipped camera are used to detect holes in the resulting weld.

[0028] The reflected light method preferably uses a monochromatic light source.

[0029] Advantageously, it allows for continuous measurement and evaluation of gap width and net gap width.

[0030] If the reflected light method is used to measure the gap width, and if necessary, the transmitted light method is also used to measure the net gap between the upper and lower sides of the metal plate (1,2), even better results can be obtained.

[0031] The method according to the invention is particularly suitable for producing custom panels in vehicle body manufacturing. Attached Figure Description

[0032] The present invention and the problems existing in current measurement methods will be further explained below with reference to embodiments and the accompanying drawings. In the drawings:

[0033] Figure 1 An example of the laser welding process according to the present invention is shown in a side view;

[0034] Figure 2 The edge of the metal sheet after the cutting process is shown in cross-section;

[0035] Figure 3 The possible shapes of the cut edge are shown in cross-section;

[0036] Figure 4 The gap between two metal plates in contact (without a clear gap) is shown in cross-section;

[0037] Figure 5 A cross-section is shown of two non-contact metal plates with a clear gap, and a gap lighting device, according to the prior art.

[0038] Figure 6 The slit measurement by transmitted light is shown in cross-section;

[0039] Figure 7 The gap between two non-contacting metal plates is shown in cross-section.

[0040] The same reference numerals in the figures refer to the same features in various cases. Detailed Implementation

[0041] Figure 1 An embodiment of the laser welding process 35 according to the invention is shown for processing metal plates 1, 2, which are placed, for example but not limited to, on a conveyor 37 movable along the transport direction TR. In a first process step, the metal plates 1, 2 are placed on the conveyor 37 by a feeding device (not shown) and held by a holding device (not shown). After this, the slit position and slit width are determined. This is achieved with the aid of a top camera 20, and optionally a bottom camera 21 may also be used. Furthermore, the two cameras 20, 21 are respectively provided with a lower illumination device 18 and an upper illumination device 19 in an opposing manner.

[0042] The space D between the two metal plates 1 and 2 depends on the layout of the metal plates to be welded. If the metal plates 1 and 2 have a rectangular layout, D can be kept small; if the metal plates 1 and 2 have a diamond layout, D can be chosen to be larger. In the second process step, with filler wire 10 added to filler wire unit 24, the metal plates 1 and 2 are joined into a welded metal plate 36 by welding laser 6. In the third process step, the quality of the weld is inspected from above by a fixed second quality system, which includes a top camera 22 and a bottom lighting device 31, and optionally can also be inspected from below by another fixed quality system (bottom camera 23 and top lighting device 32). Subsequently, after the fixing device (not shown) is disengaged, the welded metal plate 36 is removed from the conveyor belt.

[0043] Figure 2 The schematic diagram illustrates an example of the edge 5 of a cut metal plate 1, the plate having a thickness of T1. As a result of the cutting process, the edge 5 has a rolled-up area R after plastic deformation, an undeformed cut area S, a fractured area B, and burrs G. The ratio of S to B can vary considerably.

[0044] Figure 3The schematic diagram illustrates the possible shapes of the cut edges and different gap geometries. If the metal plate 1 on the left and the metal plate 2 on the right push against each other, the gap geometry between the two metal plates 1 and 2 changes depending on the direction of the edges due to plastic deformation during the cutting process. Furthermore, the gap geometry depends on whether the sheet thicknesses T1 and T2 of the two metal plates are the same. It is also clearly shown here that the gap geometry can vary significantly depending on the positions of the metal plates 1 and 2. The case where the two sides of metal plates 1 and 2 that are facing upwards during the cutting process also face upwards during the welding process results in a completely different gap geometry compared to the case where one or both of the sides facing upwards during the cutting process face downwards during the welding process.

[0045] Figure 4 A metal plate 1 with a thickness of T1 and an upper side 25 and a lower side 26 on the left, and a metal plate 2 with a thickness of T2 and an upper side 25 and a lower side 26 on the right, are shown in cross-section in the schematic diagram. The two metal plates 1 and 2 are in contact at the bottom of the rolled-up area on the left side 27 and the rolled-up area on the right side 28. Therefore, there is no gap in this area (no net gap). According to the prior art, the gap width 7 is determined by gap measurement using the reflected light method. This determined gap width 7 generally reflects the gap width at the upper part of the gap. The shaded area describes the missing area 8 between the two metal plates 1 and 2. Since the gap closes at the bottom, the missing area 8 can only be estimated very roughly by the measured gap width 7.

[0046] Figure 5 This illustrates a gap measuring device using the reflected light method. Two metal plates 1 and 2 are not in contact, thus creating a net gap. The net gap can be understood as the minimum distance between the two edges 4 and 5 of the metal plates when viewed in cross-section. Two light sources 11 and 12 illuminate the net gap, where multiple reflections of light 13 are received by camera 20. Light 14 is reflected in the upper region of the left edge 4, making it undetectable by the top camera 20. Light rays 15 and 16 are also reflected multiple times in the regions of the left edge 4 and right edge 5, also making them undetectable by camera 20. Through this process, the gap width 7 is determined in the upper region of the metal plates 1 and 2; however, this is typically different from the net gap width.

[0047] Figure 6The gap measurement of two metal plates 1 and 2 with a clear gap is now shown using the transmitted light method. Therefore, metal plate 1, with a thickness of T1 and having an upper side 25, a lower side 26, and an edge 4 on the left, and metal plate 2, with a thickness of T2 and having an upper side 25, a lower side 26, and an edge 5 on the right, are not in contact. A lower illumination device 18 emits light 17 through the gap from below, which is detected by a camera 20 at the top. This gap measurement using the transmitted light method measures the clear gap width 9, which is the minimum distance between the two edges 4 and 5.

[0048] Figure 7 The gap measuring device according to the present invention is now shown. Here, reflected light (such as...) is used simultaneously. Figure 5 (as shown) and transmission light methods (such as) Figure 6 (As shown) The gap is measured. In this example, the two metal plates 1 and 2 are not in contact. The gap width 7 is measured using the reflected light method on the upper region of metal plates 1 and 2. The net gap width 9 is determined using the transmitted light method. In this example, the reflected light and transmitted light are detected by a shared camera 20. Subtracting the net gap width 9 from the measured gap width 7 yields the dummy gap width 3. The dummy gap area 29 is the gap area under the dummy gap width 3. The dummy gap area 29 can be estimated using the dummy gap width 3 and the metal plate thicknesses T1 and T2. The net gap area 30 can be determined using the measured net gap width 9 and the known metal plate thicknesses T1 and T2. The sum of the estimated dummy gap area 29 and the determined net gap area 30 gives the missing area 8, which can be used to estimate the missing volume.

[0049] exist Figure 1 In this method, the reflected light method is used not only on the upper side of the metal plates 1 and 2, but also on the lower side. For this purpose, two light sources 38 and 39 are located below the metal plates. Light from light sources 38 and 39 is reflected from the metal plates and gaps and detected by the camera 21 at the bottom. Similarly, this camera 21 also detects the transmitted light from the upper lighting device 19.

[0050] List of reference numerals

[0051] 1. The metal plate on the left

[0052] 2. The metal plate on the right side

[0053] 3. Fake gap width

[0054] 4. Edge of metal plate

[0055] 5. Edge of metal plate

[0056] 6. Welding Laser

[0057] 7. Gap width measured using the reflected light method

[0058] 8. Missing area

[0059] 9. Net width of the gap

[0060] 10 Filler wire

[0061] 11, 12 Light Sources

[0062] 13 Light

[0063] 14. Light

[0064] 15. Light

[0065] 16. Light

[0066] 17 Light

[0067] 18. Below lighting fixture

[0068] 19. Above-ground lighting fixtures

[0069] 20 Top Cameras

[0070] 21 Bottom Camera

[0071] 22 Top Cameras

[0072] 23 Bottom camera

[0073] 24 Filler wire units

[0074] 25. Upper side of metal plate

[0075] 26. The underside of the metal plate

[0076] 27. Left side curl

[0077] 28. Right side curl

[0078] 29. Fake gap area

[0079] 30 Net gap area

[0080] 31. Lighting fixture below

[0081] 32. Above-ground lighting fixture

[0082] 35 Laser welding process

[0083] 36 Welded metal plates

[0084] 37 Conveying device

[0085] Light sources 38 and 39

[0086] TR transport direction

[0087] R Rolling Area

[0088] S-shaped cutting area

[0089] B. Fault Zone

[0090] G Burrs

[0091] D. Spacing between metal plates

[0092] Thickness of the metal plate on the left side of T1

[0093] Thickness of the metal plate on the right side of T2

Claims

1. A method of butt welding flat metal sheets (1, 2) in a welding machine, wherein, Two metal plates (1, 2) are placed on a conveying device (37) by a feeding device and fixed by a holding device, wherein the two edges (4, 5) of the two metal plates (1, 2) to be welded to each other are placed adjacent to each other in a butt joint manner to form a gap as small as possible, and are welded together by a welding laser (6), wherein the gap width (7) is measured and the welding process is controlled by the measured value, characterized in that the gap width (7) is measured by a reflected light method and the net gap width (9) is measured by a transmitted light method, and thereby the missing area (8) or missing volume in the gap is evaluated.

2. The method of claim 1, wherein, The reflected light method is the laser line method in laser triangulation.

3. The method according to claim 1 or 2, characterized in that, Filler wire (10) is provided to the laser welding process (35).

4. The method of claim 3, wherein, The supply of filler wire is controlled based on the assessed missing volume.

5. The method according to claim 1 or 2, characterized in that, Imaging techniques were used during the welding process to analyze the measurement results in order to determine the missing volume between the two edges (4, 5).

6. The method according to claim 1 or 2, characterized in that, After the welding process, the holes in the weld can be detected by the lighting device (31, 32) with corresponding cameras (22, 23).

7. The method according to claim 1 or 2, characterized in that, The reflected light method uses a monochromatic light source (11, 12).

8. The method according to claim 1 or 2, characterized in that, The gap width (7) and the net gap width (9) are continuously measured and analyzed.

9. The method according to claim 1 or 2, characterized in that, A shared camera (20) was used for both the reflected light method and the transmitted light method.

10. The method according to claim 1 or 2, characterized in that, The reflected light method is used to measure the gap width (7) on the upper and lower sides of the metal plates (1, 2).

11. The method according to claim 1 or 2, characterized in that, The transmitted light method is used to measure the net width (9) of the gap on the upper and lower sides of the metal plates (1, 2).

12. The application of the method according to any one of claims 1 to 11 in the production of custom panels in automobile body manufacturing.

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