Welding method for welding sealing membrane of storage tank and corresponding welding device

Abstract

The invention relates to a welding method and a corresponding welding device for welding a sealing membrane of a storage tank. A welding method uses a welding device movable above a machining line along which a first plate and a second plate extending in a first plane are welded, the machining line extending along a first axis in the first plane, the welding device comprising a welding torch adapted to emit a laser beam.

Description

Technical Field

[0001] This invention relates to the field of storage tanks intended for storing and / or transporting liquefied gases (e.g., liquefied natural gas (LNG)), particularly to the field of marine or river transport and land-based storage tanks. More specifically, this invention relates to a method for welding sealing membranes suitable for such storage tanks. The invention also relates to related welding apparatus. Background Technology

[0002] Storage tanks used for transporting liquefied gases have capacities ranging from thousands to tens of thousands of cubic meters. Ships used for transporting liquefied gases have specially adapted bilges to accommodate these tanks, which are often partitioned to form multiple tanks. Such tanks can also be manufactured for both shipboard and land-based storage of liquefied natural gas. For example, in the case of LNG, the gas in the tank remains liquid at -163°C under atmospheric pressure. Therefore, the tank must be sealed and insulated. Consequently, the inner surface of such tanks is covered with a sealing membrane, which typically consists of an assembly of metal (usually stainless steel) sealing plates welded together, each plate forming part of the tank's sealing membrane.

[0003] The welding machine is used to weld these metal plates together. The operator must use guide rails to guide the welding machine along the edges of these sealing plates, which are placed adjacent to each other (this is called fillet welding / assembly). The operator starts the program on the welding machine, which is equipped with a welding torch and welds the edges of the sealing plates as it moves along the edges. The distance between the welding torch and the parts to be welded is continuously adjusted using positioning sensors mounted on the welding machine.

[0004] Known methods for assembling these metal plates to form a sealing film include plasma welding or tungsten inert gas (TIG) welding. TIG welding is an arc welding process that uses a tungsten electrode (with filler metal if necessary). This welding process generates a large amount of metal oxides on the edges of the sealing plate, which, in the long run, reduces the integrity of the film due to corrosion. Therefore, it is necessary to brush the weld seam after the welding step. This step has proven to be lengthy and tedious.

[0005] One solution for improving productivity is laser welding. Laser welding involves raising the temperature of metal to a precise value, causing the metal to reach its melting point and begin to melt. Laser welding is based on extremely concentrated light that initiates the melting of the metal. This light is emitted at a specific wavelength. For example, in fiber laser welding, the wavelength can be 1064 nanometers.

[0006] However, laser welding has very small tolerances in terms of assembly gap. In other words, to weld two metal plates together to form a seal, the edge of the upper metal plate is overlapped on the edge of the lower metal plate to form a processing line. For optimal welding, it is desirable that the height difference between the lower surface of the upper plate and the upper surface of the lower plate be close to 0 mm. In other words, it is advantageous that the gap between the two metal plates be close to 0 mm. This is usually not the case, and the gap can vary from one pair of metal plates to another along the processing line used to process the pair. This gap can be approximately a fraction of a millimeter. This variability in the assembly gap is unacceptable in laser welding because it hinders the proper distribution of heat at the weld point, thus preventing the metals of the two plates from joining at that point. Summary of the Invention

[0007] This invention aims to alleviate some or all of the aforementioned problems by proposing a novel continuous laser welding method that is compatible with the variability of the assembly gaps of metal sheets without human intervention. This method enables the benefits of the high productivity of laser welding by adapting to the assembly gaps.

[0008] Therefore, the object of the present invention is a welding method using a welding apparatus movable above a processing line to weld the edges of a first plate extending in a first plane and the edges of a second plate stacked on the edges of the first plate along the processing line, the processing line extending along a first axis in the first plane, the welding apparatus including a welding torch adapted to emit a laser beam, and the welding method comprising, for each point along the processing line:

[0009] - First step: Determine the height difference between the upper surface of the edge of the first plate and the lower surface of the edge of the second plate along the second axis perpendicular to the first plane;

[0010] - Second step: If the determined height difference is higher than the predefined threshold, then modify at least one welding parameter of the welding torch according to the determined height difference;

[0011] - Third step: Weld the edges of the first and second plates;

[0012] - Fourth step: Move the movable welding device.

[0013] The height difference along the second axis represents the assembly gap between the edges of the two plates to be welded. According to the method of the invention, the assembly gap is determined at each point along the processing line. If the assembly gap is greater than a predefined value (e.g., approximately 0.1 mm or 0.2 mm, corresponding to a value where optimal laser welding is impossible), at least one welding parameter is modified to enable welding of the edges of the two plates. In other words, once the assembly gap between the two plates is detected, the welding method according to the invention can adjust one or more welding parameters to ensure proper melting of the metal in the plates necessary to guarantee the desired weld quality.

[0014] In one embodiment of the invention, the welding method includes a storage step for storing the height difference after a first step of determining the height difference. This storage step has the advantage that it allows the height difference to be determined for the entire or part of the processing line before subsequent welding steps are performed.

[0015] In the welding method according to the invention, at least one welding parameter includes at least one of the following: the orientation of the laser beam relative to the normal of the first plane, the movement of the laser beam, the power of the laser beam, and the pulse frequency of the laser beam. Therefore, the modification step may include modifying one or more of these parameters. The step of modifying one or more welding parameters enables control of the correct energy input per unit surface area for welding two plates, regardless of the presence or absence of an assembly gap. This energy input depends on the local height difference between the two plates to be welded. Therefore, the material is heated to the correct level for locally melting the material of the plates, and the presence of an assembly gap is compensated for by this modification.

[0016] Furthermore, by modifying one or more welding parameters for each detected height difference, the welding method according to the invention enables continuous modification of one or more parameters and allows for localized adjustment of the amount of energy required for continuous operation.

[0017] The above modifications to one or more parameters also simplify welding kinematics because they do not involve repositioning the weld joint.

[0018] In the welding method according to the invention, at least one welding parameter includes at least one of the following: the height between the welding torch and the processing line, and the orientation of the welding torch relative to the normal of the first plane. In this variation, the orientation of the welding head and / or its distance from the processing line can be changed. An advantage is the ability to maintain an optimal welding angle, i.e., the laser beam is located in a cone whose apex coincides with the point to be welded, forming an angle between 0° and 45°, preferably between 15° and 30°, around the normal of the processing line at the point to be welded.

[0019] Advantageously, the welding method according to the invention includes a determining step prior to the first step of determining the height difference: determining the distance between a reference point of a position sensor and at least one point on the second plate. This determining step enables the assessment of the distance of the welding torch relative to the processing line. In particular, as in the case of sealing membranes for storage tanks intended for storing and / or transporting liquefied gases, this distance varies when the plate to be welded includes corrugations (also called corrugations).

[0020] Therefore, the welding method according to the invention may include the following steps: if the determined distance differs from the distance determined for a previous point along the processing line (e.g., through a wavy mark), then modifying the power of the laser beam according to the determined distance. Taking the distance to the processing line into account allows welding at the same height using a vertical welding head by changing the focus and power of the beam. This adjustment is necessary because the laser beam is not perpendicular to the surface to be welded, resulting in energy loss from the laser. This results in a more elliptical focal spot shape, and the power provided by the laser is distributed over a larger spot. Modifying the laser power allows these effects to be counteracted.

[0021] Alternatively, the welding method according to the invention may include the following steps: if the determined distance is different from the distance determined for the previous point along the processing line (which is also the mark of the ripples), then the laser beam is directed according to the determined distance.

[0022] The step of modifying the laser beam power based on the distance from the processing line is obviously an addition to the step of modifying one or more welding parameters based on a locally determined height difference.

[0023] The present invention also relates to a movable welding apparatus designed for welding the edges of a first plate extending in a first plane and the edges of a second plate stacked on the edges of the first plate along a processing line extending along a first axis in the first plane. The movable welding apparatus includes a welding torch adapted to emit a laser beam and a modification member for modifying at least one welding parameter of the welding torch based on the height difference when the height difference between the upper surface of the edge of the first plate and the lower surface of the edge of the second plate along a second axis perpendicular to the first plane is greater than a predefined threshold.

[0024] In the movable welding apparatus according to the invention, at least one welding parameter includes at least one of the following: the orientation of the laser beam relative to the normal of the first plane, the movement of the laser beam, the power of the laser beam, and the pulse frequency of the laser beam.

[0025] Advantageously, the movable welding apparatus according to the invention further includes a position sensor adapted to measure the height difference between the upper surface of the edge of the first plate and the lower surface of the edge of the second plate along a second axis perpendicular to the first plane. The position sensor incorporated into the welding apparatus has the advantage of continuously measuring the height difference at all points along the processing line. This information is directly transmitted to a modification member for modifying one or more welding parameters, allowing the precise timing of welding at the point on the processing line where the welding torch has the height difference to be adjusted. This enables laser welding to adapt to assembly gaps between the two plates to be welded. Attached Figure Description

[0026] These and other features and advantages of the invention will become more apparent from the following description given with reference to the accompanying drawings, which are provided by way of non-limiting example, in which:

[0027] Figure 1 A cross-sectional view of a first metal plate and a second metal plate intended to be assembled by welding a first metal plate and an adjacent second metal plate together is shown.

[0028] Figure 2 An apparatus for welding a sealing film according to an embodiment of the present invention is shown, the apparatus employing the step of welding a sealing plate to an adjacent sealing plate;

[0029] Figure 3 This is a diagram illustrating the steps of a method for welding two metal plates according to the present invention;

[0030] Figure 4 This is a cross-sectional view of the step of determining the height difference between two plates to be welded in one embodiment of the present invention;

[0031] Figure 5 This is a cross-sectional view of the step of determining the height difference between two plates to be welded according to another embodiment of the present invention;

[0032] Figure 6 This is a diagram showing a welding torch that uses a laser beam and includes a reflective module;

[0033] Figure 7 An embodiment of the steps for welding a plate according to the method of the present invention is shown;

[0034] Figure 8 Another embodiment of the steps for welding a plate according to the method of the present invention is shown;

[0035] Figure 9 This diagram illustrates welding two plates without assembly gaps using the method according to the invention;

[0036] Figure 10 The diagram illustrates welding two plates with an assembly gap using the method according to the invention. Detailed Implementation

[0037] For clarity, the same elements are labeled with the same reference numerals in the various figures.

[0038] The features, variations, and embodiments of the invention described or to be described in the following detailed description can be associated with each other in various combinations, provided that such features, variations, and embodiments are not incompatible or mutually exclusive. Variations of the invention are particularly conceivable if the selection of features is sufficient to provide a technical advantage and / or to distinguish the invention from the prior art, and therefore may only have the selection of features separate from the other described features, as described below.

[0039] Figure 1 A cross-sectional view is shown of a first metal plate 11 and an adjacent second metal plate 21 intended to be assembled together by welding. The first plate 11 extends in a first plane P1. The edge 22 of the second plate 21 overlaps the edge 12 of the first plate 11 along a machining line 30 extending along a first axis Y in the first plane P1. Figure 1 As can be seen, the first metal plate 11 and the adjacent second metal plate 21, intended to be assembled together, have an overlapping area 15. In this overlapping area, the first plate includes a planar edge 12. To achieve this overlap, the second plate 21 includes a tenon 23 (i.e., a protruding portion of the lateral edge of the second plate 21) such that the protruding portion of the lateral edge of the second plate 21 overlaps the lateral edge 12 of the first plate 11 at the overlapping area 15. A welding step creates a weld line at the processing line 30, thereby assembling the second plate 21 and the first plate 11 in a sealed manner.

[0040] To achieve optimal welding, it is desirable that the height difference 31 between the lower surface 24 of the upper plate 21 and the upper surface 14 of the lower plate 11 is close to 0 mm. In other words, ideally, the gap between the two metal plates 11, 21 must be zero, i.e., equal to 0 mm. As mentioned above, this is not usually the case. This gap can vary not only from one metal plate to another, but also, for a given pair of plates, along the machining line 30.

[0041] Figure 2 A welding apparatus 7 for welding a sealing film according to the invention is shown, the welding apparatus 7 employing the method of welding a sealing plate to an adjacent sealing plate according to the invention. This illustration is highly illustrative for the purpose of disclosing the invention. The distance between the position sensor 73 and the welding torch 72 (i.e., the distance between point A and point B) is typically about 2 cm to 15 cm.

[0042] The welding method according to the invention employs a welding apparatus 7 capable of moving above a processing line 30. The welding apparatus 7 includes a welding torch 72 adapted to emit a laser beam. The welding apparatus 7 also includes a modification member 74 for modifying at least one welding parameter of the welding torch 72 based on the height difference 31 along a second axis Z perpendicular to the first plane P1 and between the upper surface 14 of the edge 12 of the first plate 11 and the lower surface 24 of the edge 22 of the second plate 21, if such a height difference 31 is higher than a predefined threshold.

[0043] The welding apparatus 7 may also include a position sensor 73, which is adapted to measure the height difference between the upper surface 14 of the edge 12 of the first plate 11 and the lower surface 24 of the edge 22 of the second plate 21 along a second axis Z perpendicular to the first plane.

[0044] Alternatively, the welding apparatus 7 may not be equipped with a position sensor. In this variant, the continuous height difference 31 along the processing line is predetermined and stored on a storage medium in the welding apparatus or on a remote server. The height difference 31 associated with each point on the processing line can be accessed by the modification member 74 to enable the use of the method according to the invention.

[0045] The welding device 7 can move along the track 3, which is above the processing line 30 and along the edge of the second plate 21.

[0046] Figure 3 This diagram illustrates the steps of a method for welding two metal plates according to the present invention. For each point along the processing line 30, the welding method according to the present invention includes:

[0047] - First step 110: Determine the height difference 31 between the upper surface 14 of the edge 12 of the first plate 11 and the lower surface 24 of the edge 22 of the second plate 21 along the second axis Z perpendicular to the first plane P1;

[0048] - Second step 120: If the determined height difference 31 is higher than the predefined threshold, then modify at least one welding parameter of the welding torch 72 according to the determined height difference 31;

[0049] - Third step 130: Welding the edges 12, 22 of the first plate 11 and the second plate 21. Step 130 is a step of performing fillet welding on the edges of the plates 11, 21 using a welding torch 72. During this welding step, the plates 11, 21 are welded by melting the material of the edge of the plate 21 onto the edge of the plate 11.

[0050] - Fourth step 140: Move the movable welding device 7.

[0051] For a given point on processing line 30, if the height difference 31 is 0 mm, then edges 12 and 22 are welded at that point. However, if the height difference 31 at that point is not zero, then step 120 is performed to modify at least one welding parameter of the welding torch. The modification of one or more welding parameters depends on the determined height difference 31. The modification of one or more welding parameters is described in detail below.

[0052] The welding method according to the invention is based on determining the assembly gap between the edges of the two plates to be welded, and adjusting one or more welding parameters according to the determined assembly gap. This results in the continuous adjustment of the welding parameters at each welding point along the processing line, based on the height difference 31 between the two plates at that point. This continuous adjustment, depending on the encountered environment, ensures that the edges of the two plates are correctly welded together regardless of the local height difference. As the welding device 7 advances along the track 3, the two plates 11, 21 are welded by melting the material at the edges of the two plates.

[0053] In a variation of the invention, the welding method may include step 115 after the first step 110 of determining the height difference 31: storing the height difference 31 on a storage medium in the welding apparatus or on a server outside the welding apparatus. Storing the height difference 31 along the processing line generates the profile of the assembly gap along the entire processing line. This variation is advantageous if the welding apparatus does not have a sensor and the value of the height difference 31 is recovered before modifying step 120.

[0054] In other words, the welding method according to the invention requires determining the height difference 31 at at least one point on the processing line. This can be predetermined for that point or for all points on the processing line, for example, by pre-determining by having a position sensor pass above the processing line and storing multiple height differences 31. The height differences can now be determined point-by-point. This is the case with a welding apparatus equipped with a position sensor 73. In this configuration, as... Figure 2As schematically shown, position sensor 73 and welding torch 72 are spaced apart by a fixed distance 76, typically between 2 cm and 15 cm. At time t1, position sensor 73 measures a height difference 31 at point A. At this time t1, welding torch 72 performs welding at point B. Modification component 74 is connected to position sensor 73 and welding torch 72 via a wired connection 75 or a wireless connection. The height difference 31 can be stored on a storage medium or directly transmitted to modification component 74 to modify at least one welding parameter based on the height difference 31 determined at point A. The moving speed of welding device 7 is known, and after determining the height difference 31 at point A, modification component 74 is configured to modify at least one welding parameter at time t2 corresponding to the time when welding torch 72 is above point A. Due to this configuration, the determination and welding steps can be performed only once by having the welding device pass over the processing line.

[0055] Figure 4 This is a cross-sectional view of the step of determining the height difference between two plates to be welded in one embodiment of the present invention.

[0056] In this embodiment, the position sensor 73 is a non-contact sensor, such as a laser profilometer (also known as a laser scanner). This is a profile sensor that can detect, measure, and evaluate a two-dimensional profile in a cross-sectional plane without physical contact with the two plates 11, 21.

[0057] In this embodiment, the position sensor 73 performs the following sub-steps:

[0058] - An initial optical signal is sent to a point on the surface of the edge 22 of the board; this initial optical signal is, for example, a laser pulse.

[0059] - Receive the return optical signal corresponding to the initial optical signal, such as the reflection of a laser pulse from the surface of the edge 22 of the initial impact plate, and

[0060] - The distance between the reference point of position sensor 73 and a point on the surface of the edge 22 of the plate is measured based on the initial and returned optical signals. This measurement typically uses the time between the emitted laser pulse and the received reflected laser pulse.

[0061] Therefore, position sensor 73 determines a first distance 33 between a reference height of the sensor along axis Z and the upper surface of edge 22. Position sensor also determines a second distance 32 between the reference height of the sensor and the upper surface of edge 12. The thickness e of edge 22 is known (typically approximately 1.2 mm), thus the height difference 31 can be determined. For this purpose, position sensor 73 may include means capable of calculating the height difference 31 based on distances 32, 33 and thickness e. Alternatively, the calculation means may be located remotely from position sensor 73 and integrated into welding apparatus 7 or a remote server.

[0062] Figure 5 This is a cross-sectional view of the step of determining the height difference between two plates to be welded in another embodiment of the invention.

[0063] In this embodiment, the position sensor 73 is a physical contact sensor. The position sensor may be an LVDT (Linear Variable Differential Sensor), an electromechanical device that converts mechanical movement (in this case, linear movement) into a changing current, which indicates the length of the movement performed, and thus indicates height 32 or height 33. (As in...) Figure 4 In the example, the thickness e of edge 22 and the heights 32 and 33 are known, so the height difference 31 can be determined. If the height difference 31 is higher than a predefined threshold, typically a few tenths of a millimeter (e.g., 0.1 mm or 0.2 mm), at least one welding parameter is modified to ensure that the welding steps are performed correctly.

[0064] In the welding method according to the invention, at least one welding parameter that can be modified in step 120 is at least one of the following: the orientation of the laser beam relative to the normal of the first plane, the movement of the laser beam, the power of the laser beam, and the pulse frequency of the laser beam.

[0065] Figure 6 The figure shows a welding torch 72 that generates a laser beam and includes a reflection module 57.

[0066] The welding torch includes a laser beam generator 56, which projects a laser beam 6 onto a reflective module 57 at the free end of the welding torch 72. Figure 6The diagram is shown in a highly simplified manner to reduce the depiction of the welding torch 72. In reality, the laser beam generator 56 is actually outside the welding torch 72, and it is the fiber 9 that feeds the generated beam into the welding torch 72. The reflecting device 57 is, for example, a set of mirrors that deflects the trajectory of the laser beam 6 leaving the laser beam generator in direction D1 in a plane parallel to the longitudinal direction L and the vertical direction V, or in direction D2 in a plane parallel to the transverse direction T and the vertical direction V. The modification member 74, schematically depicted here, is connected to the laser beam generator 56 via a wired or wireless connection 75 to adjust the power or frequency of the laser beam generator's pulses. Similarly, the modification member 74 can act on the reflecting module 57 to adjust the orientation of the laser beam relative to the normal of the first plane P1. This adjustment of the laser beam's orientation toward the upper plate allows the energy delivered by the laser beam to impact the material of the upper and / or lower plates, heating the material at the edges of the plates and compensating for the height difference 31. Similarly, the beam path in module 57 can be modified by changing the tilt of the reflector; this modifies the height of the focal point, allowing for optimal focus without modifying the power. Alternatively, the beam power can also be modified based on the detected gap and the height of the welding torch. Likewise, modifying component 74 can move the laser beam to generate a scanning motion along the processing line. Scanning enables heating of both sides of the processing line to melt the material, thereby bonding the two plates together.

[0067] In another embodiment of the welding method, at least one welding parameter includes at least one of the following: the height between the welding torch 72 and the processing line, and the orientation of the welding torch 72 relative to the normal of the first plane P1. Figure 7 and Figure 8 An example of this method is shown.

[0068] Figure 7 An embodiment of step 130 of welding a plate in the welding method according to the present invention is shown.

[0069] In this embodiment, the plates to be welded include corrugations extending across the surface of each plate. These corrugations are designed to impart flexibility to the film formed after welding the plates, accommodating the thermal shrinkage of the steel as the tank cools. Therefore, as... Figure 7 As shown, the surface of the plate can be defined by the planar region 51 and the corrugated portion 52. Therefore, when the welding device 7 moves above the processing line 30, the welding device 7 passes through the planar region 51 and the corrugated portion 52.

[0070] exist Figure 7In the illustrated embodiment, the welding device 7 remains in a straight position as it moves along the Y-axis. Due to this configuration, welding kinematics are simplified because the welding head remains vertical and at the same height. However, the welding device 7 encounters two situations. The first situation involves the planar region 51 indicated by position (a). The distance between the welding torch and the plate to be welded does not change. However, the height difference 31 between the edges of the two plates may change. At each point along the planar region of the processing line, at least one welding parameter is adjusted based on the height difference 31 determined at that point.

[0071] In the second case, the corrugated portion is represented by positions (b) and (c). The distance between the welding torch and the plate to be welded changes during the passage of the corrugated portion. However, the height difference 31 between the edges of the two plates may also change. For this purpose, the welding method according to the invention may include step 105 before the first step 110 of determining the height difference 31: determining the distance between the reference point of the position sensor 73 and at least one point on the second plate. This distance indicates the presence of the corrugated portion. Alternatively, the profile of the plate to be welded, pre-generated, for example by laser profilometry, can be provided to a calculator device, which can then determine the adjustment of at least one welding parameter based on both the distance between the plate and the welding torch and the height difference. For example, as can be seen at positions (b) and (c), the power of the laser beam 6 can be adjusted at two different distances between the plate and the welding torch.

[0072] Figure 8 Another embodiment of the steps for welding a plate in the welding method according to the present invention is shown.

[0073] In this other embodiment, the welding device 7 also encounters two cases regarding the planar region 51 (position (a), and passing through the wavy section at positions (b), (c), and (d)). In this variant embodiment, the welding head remains vertical and the welding angle is kept optimal, i.e., the laser beam is located in a cone whose apex coincides with the point to be welded, forming an angle between 0° and 45°, preferably between 15° and 30°, around the normal of the processing line at the point to be welded. The laser beam 6 is then oriented. This configuration allows the welding head to remain straight, limiting movement and simplifying welding kinematics.

[0074] In addition, the height difference 31 between the edges of the two plates may vary. As previously described, the welding method according to the invention may include step 105 before the first step 110 of determining the height difference 31: determining the distance between the reference point of the position sensor 73 and at least one point on the second plate. This distance is an indication of the position of the welding torch relative to the corrugation. Alternatively, a pre-generated profile of the plate to be welded may be provided to a calculator. The calculator can then determine the adjustment of at least one welding parameter based on both the distance between the plate and the welding torch and the determined height difference. For example, as can be seen for positions (b), (c), and (d), the orientation of the laser beam 6 is adjusted for positions (b) and (d) at different orientations of the welding torch relative to the processing line 30, while the laser beam 6 is vertical at position (c). In a similar manner to that already explained above, in addition to adjusting the beam due to the presence of the corrugation on the processing line, the welding method applies a modification of at least one welding parameter for each point on the processing line where the height difference 31 is greater than a predefined value.

[0075] In the welding method according to the invention, if the determined height difference 31 is higher than a predefined threshold, a second step 120 is performed to modify at least one welding parameter of the welding torch 72. This predefined threshold can be 0 mm. In other words, step 120 begins once an assembly gap is detected.

[0076] In a variant of the invention, the predefined threshold is 0.01 mm. This threshold corresponds to the sensitivity of the position sensor 73 that measures the height difference 31.

[0077] In another variation of the invention, the predefined threshold is 0.1 mm. This threshold corresponds to a height difference such that optimal laser welding can no longer be achieved without modifying at least one welding parameter.

[0078] In another variation of the invention, the second step 120 of modifying at least one welding parameter of the welding torch 72 is performed by applying a predefined modification of a set of welding parameters based on a determined height difference, the predefined modification of the gap varying according to a predefined increment of the height difference (e.g., 0.05 mm or 0.1 mm). In other words, step 120 is performed once the determined height difference exceeds a predefined threshold (e.g., a threshold of 0.1 mm). When performing step 120, for a predefined increment of 0.1 mm and a height difference between 0.1 mm and 0.2 mm, the welding method of the invention applies modifications within a first range to a set of welding parameters. For a height difference between 0.2 mm and 0.3 mm, the welding method of the invention applies modifications within a second range to the same set of welding parameters. However, the invention also includes cases where another set of welding parameters is modified for a larger height difference increment.

[0079] The following is for reference. Figure 10 An application example is described.

[0080] Based on the determined height difference 31, one or more welding parameters of the welding torch are modified. In other words, for each point on the processing line, a first test assesses whether a predefined threshold has been reached. If the predefined threshold has been reached, at least one welding parameter of the welding torch is modified to compensate for the assembly gap and ensure proper welding at the welding point.

[0081] In an advantageous embodiment of the welding method according to the invention, step 120, which modifies one or more welding parameters of the welding torch, depends on the height difference 31. This means that, based on the height difference determined at a point, the applied welding correction (i.e., the modification of one or more welding parameters) can vary from one welding point to another. This allows the amount of energy transferred at each welding point to be adjusted according to the degree of assembly gap to obtain the metal melting required for welding the two plates.

[0082] The following text is for reference only. Figure 9 and Figure 10 Possible embodiments of step 120, which modifies the welding parameters, are described in a non-limiting manner, where dz corresponds to the determined height difference (also labeled 31). In these examples, the following welding parameters are considered to enable welding of two plates without an assembly gap: a laser beam power of 1750 W and an orientation of the laser beam relative to the normal Z' of the first plane at an angle α0 (e.g., between 0° and 30°). A predefined threshold for triggering step 120 is 0.01 mm.

[0083] Figure 9 This diagram illustrates the welding of two plates 11, 21 without assembly gaps using the method according to the invention. In this configuration, the welding device 7 moves above the processing line 30, and as the welding device 7 advances, the steps of the method are performed at each point on the processing line. During the first step 110, the height difference 31 between the upper surface 14 of the edge 12 of the first plate 11 and the lower surface 24 of the edge 22 of the second plate 21 is determined at each point on the processing line 30. Figure 9 In the example shown, the height difference is 0 mm, and there is no assembly gap. Therefore, the determined height difference does not exceed a predefined threshold. There is no step performed to modify at least one welding parameter of the welding torch.

[0084] The third step 130, which involves welding the edges 12, 22 of the first plate 11 and the second plate 21, is performed by means of a laser beam set to, for example, a power of 1750W. This is followed by the fourth step 140, which involves moving the movable welding device 7 to perform the first step 110 again at the next point on the processing line.

[0085] Figure 10 This is a diagram showing the welding of two plates with an assembly gap using the method of the present invention. In this configuration, and in a similar manner as explained in the case of the example of Figure 9 the welding device 7 moves above the processing line 30, and when the welding device 7 advances, the steps of the method are performed at each point on the processing line. During the first step 110, the height difference 31 between the upper surface 14 of the edge 12 of the first plate 11 and the lower surface 24 of the edge 22 of the second plate 21 is determined at each point on the processing line 30. In Figure 10 the example shown, this height difference 31 (hereinafter denoted as dz) is non-zero. To illustrate the present invention, consider the case where the height difference is greater than 0.01 mm (i.e., higher than a predefined threshold).

[0086] If the height difference is higher than the predefined threshold, the step 120 of modifying at least one welding parameter is started. Depending on the height difference, the modified one or more welding parameters may be as follows.

[0087] For 0 mm < dz ≤ 0.1 mm, the modified welding parameter is the power of the laser beam, which increases from 1750 W to 2000 W. The orientation of the laser beam with respect to the normal Z' of the first plane remains at the angle a0. The offset between the processing line and the intersection of the straight line of the laser beam and the surface 14 is 0 mm. In other words, the laser beam points to the processing line.

[0088] For 0.1 mm < dz ≤ 0.2 mm, the modified welding parameter is the power of the laser beam, which increases from 1875 W to 2125 W. In addition, the orientation of the laser beam with respect to the normal Z' of the first plane is modified from the angle a0 to the angle a1 (as shown in a larger scale in the upper right corner of Figure 10 ). The offset (denoted as d) between the processing line and the intersection of the straight line of the laser beam and the surface 十四 is approximately 0.5 mm. In other words, the laser beam no longer points to the processing line. The laser beam points to the edge of the upper plate. This offset enables the laser beam to approach the metal area of the upper plate to locally increase the temperature of this metal area and melt a part of this metal area to contribute to the formation of the weld bead. The angle can be modified by modifying the tilt of the mirror of the module 57.

[0089] For 0.2 mm < dz ≤ 0.3 mm, the modified welding parameter is the power of the laser beam, which increases from 2000 W to 2250 W. When dz is between 0.1 mm and 0.2 mm, the orientation of the laser beam relative to the normal Z’ of the first plane is modified. The greater the height difference between the two plates, the greater the angle a1 becomes compared to the previous case, thereby obtaining an offset d of approximately 1 mm between the processing line and the intersection of the straight line of the laser beam with the surface 14. The offset d is greater compared to the previous example of the height difference between 0.1 mm and 0.2 mm. The height difference is greater than that in the previous case, and the assembly gap to be compensated is greater. Thus, it is necessary to obtain more metal. Proceeding in this way, a laser beam with a higher power can ensure melting sufficient material to form a weld between the two plates.

[0090] The numerical values of the welding parameters are given here by way of example to explain the present invention. However, the method of the present invention is in no way limited to these numerical values. In particular, the beam power can vary by + / - 10%, and to take into account the height difference 31, the height variation between the welding area and the welding torch when passing through the undulation can be added to the height difference 31. Additionally, based on the detected height 33 and the fact that the thickness of the component is locally greater in the vertical section in the plane ZX at the undulation (due to the curvature), the power of the laser beam is advantageously increased. In other words, one or more of the welding parameters to be modified can vary by a certain percentage according to the height difference 31 encountered and the greater or lesser potential variation of the welding area when passing through the undulation.

[0091] Other welding parameters (such as the movement of the laser beam in a plane perpendicular to the processing line) can be modified, thereby constituting a scan of the laser beam. The scan speed can also be modified. This movement enables the laser beam to contact the edge of the upper plate to constitute a local and confined input of energy at the edge of the upper plate, near the processing line. As a result, the metal at the edge of the plate reaches its melting point and melts to form a weld bead.

[0092] Based on the description of the present invention, those skilled in the art will understand that the welding method according to the present invention relies on the continuous detection of the assembly gap and the continuous adjustment of one or more welding parameters according to the assembly gap encountered by the movable welding device at each welding point along the processing line. According to the height difference encountered, the values of one or more welding parameters to be applied during the modification step 120 can be advantageously tabulated and stored on a medium accessible to the modification member 74 to ensure the correct control of the welding device.

[0093] In a preferred embodiment, the welding method according to the invention relies on a judicious combination of modified welding parameters. The selection of the parameters to be modified and the range of modification depend on the determined height difference. At a given point, the larger the determined height difference (i.e., the larger the assembly gap), the more difficult it is to ensure a good weld between the two plates. The invention enables the automatic and continuous generation of weld beads with good geometry that meet the consistency criteria required to ensure the weld between the two plates and their durability over time, without human intervention. This effect is achieved because the energy input per unit surface area along the processing line varies according to the determined height difference.

[0094] Although the invention has been described in conjunction with specific embodiments, it is obvious that the invention is by no means limited to these specific embodiments, and the invention includes all technical equivalents and combinations thereof of the described components if such technical equivalents and combinations thereof fall within the scope of the invention.

[0095] The use of the verbs “comprising” or “including” and their variations does not exclude the presence of elements or steps other than those mentioned in the claims.

[0096] In the claims, any reference numerals between parentheses shall not be construed as limiting the claims.

[0097] Generally, it will be more apparent to those skilled in the art that various modifications can be made to the embodiments described above based on the teachings already disclosed to them. The terminology used in the claims should not be construed as limiting the claims to the embodiments disclosed in this specification, but must be interpreted to include all equivalents that the claims are intended to cover, as their formulation and implications are obvious to those skilled in the art based on their background knowledge.

Claims

1. A welding method using a welding device (7) movable above a processing line (30) to weld along the processing line (30) the edge (12) of a first plate (11) extending in a first plane (P1) and the edge (22) of a second plate (21) stacked on the edge (12) of the first plate (11), the processing line (30) extending along a first axis (Y) in the first plane (P1), the welding device comprising a welding torch (72) adapted to emit a laser beam, the welding method being characterized in that, for each point along the processing line (30), the welding method comprises: - First step (110): Determine the height difference (31) between the upper surface (14) of the edge (12) of the first plate (11) and the lower surface (24) of the edge (22) of the second plate (21) along the second axis (Z) perpendicular to the first plane (P1); - Second step (120): If the determined height difference (31) is higher than the predefined threshold, then modify at least one welding parameter of the welding torch (72) according to the determined height difference (31); - Third step (130): Weld the edges (12, 22) of the first plate (11) and the second plate (21); - Fourth step (140): Move the movable welding device (7).

2. The welding method according to claim 1, wherein, The welding method includes step (115) after the first step (110) of determining the height difference (31): storing the height difference (31).

3. The welding method according to claim 1 or 2, wherein, The at least one welding parameter includes at least one of the following: the orientation of the laser beam relative to the normal of the first plane, the movement of the laser beam, the power of the laser beam, and the pulse frequency of the laser beam.

4. The welding method according to any one of claims 1 to 3, wherein, The at least one welding parameter includes at least one of the following: the height between the welding torch (72) and the processing line, and the orientation of the welding torch (72) relative to the normal of the first plane.

5. The welding method according to any one of claims 1 to 4, wherein, The welding method includes step (105) prior to the first step (110) of determining the height difference (31): determining the distance between a reference point of the position sensor and at least one point on the second plate.

6. The welding method according to claim 5, wherein, The welding method includes step (150): if the determined distance is different from the distance determined for the previous point along the processing line, the power of the laser beam is modified according to the determined distance.

7. The welding method according to claim 5 or 6, wherein, The welding method includes step (160): if the determined distance is different from the distance determined for a previous point along the processing line, then the laser beam is directed according to the determined distance.

8. A movable welding device (7) for welding along a processing line (30) to the edge (12) of a first plate (11) extending in a first plane (P1) and the edge (22) of a second plate (21) stacked on the edge (12) of the first plate (11), the processing line (30) extending along a first axis (Y) in the first plane (P1), the movable welding device comprising: - A welding torch (72) suitable for emitting laser beams; - Modification component (74) for modifying at least one welding parameter of the welding torch (72) according to the height difference (31) between the upper surface (14) of the edge (12) of the first plate (11) and the lower surface (24) of the edge (22) of the second plate (21) along the second axis (Z) perpendicular to the first plane (P1) when the height difference (31) is higher than a predefined threshold.

9. The movable welding device (7) according to claim 8, wherein, The at least one welding parameter includes at least one of the following: the orientation of the laser beam relative to the normal of the first plane, the movement of the laser beam, the power of the laser beam, and the pulse frequency of the laser beam.

10. The movable welding apparatus (7) according to claim 8 or 9, wherein, The movable welding device further includes a position sensor (73) adapted to measure the height difference (31) between the upper surface (14) of the edge (12) of the first plate (11) and the lower surface (24) of the edge (22) of the second plate (21) along the second axis (Z) perpendicular to the first plane (P1).

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