Welding method for a suitable sealing membrane for a tank and corresponding device

Abstract

The invention relates to a welding process for a first and a second plate extending in a first plane along a processing line extending along a first axis in the first plane, employing a mobile welding device above the processing line comprising a welding torch capable of emitting a laser beam, the welding process comprising, for each point along the processing line: a first step (110) of determining a height difference along a second axis perpendicular to the first plane, between the upper surface of the first plate and the lower surface of the second plate; a second step (120) of modifying at least one welding parameter of the welding torch as a function of the determined height difference if the latter is greater than a predefined threshold; a third step (130) of welding the first and the second plates;a fourth step (140) of moving the mobile welding device. Figure 3;

Description

Title of the invention: Welding method for a sealing membrane adapted for a tank and corresponding device. Technical field

[0001] The present invention relates to the field of tanks intended for storing and / or transporting gas in a liquid state, for example liquefied natural gas (LNG), particularly for maritime or river transport or for an onshore reservoir. More specifically, the invention relates to a method for welding a sealing membrane adapted for such a tank. The invention also relates to the associated welding device. Technological background

[0002] Liquefied gas transport tanks have a capacity of several thousand cubic meters of liquid gas each, or even several tens of thousands of cubic meters. Liquefied gas transport vessels have holds specifically designed to contain these tanks, their holds often being divided into several tanks. Such a tank can also be constructed outside a ship for onshore storage of natural gas in its liquid state. The gas is kept in a liquid state, for example at -163°C (degrees Celsius) for LNG, at atmospheric pressure. It must therefore be leak-proof and thermally insulated. Consequently, the internal surface of such a tank is covered with a sealing membrane, generally made of an assembly of metal sealing plates (typically stainless steel) welded together, each sealing plate being part of the tank's sealing membrane.

[0003] To weld these metal plates together, a welding machine is used, in which an operator guides the edges of these sealing plates, arranged in pairs adjacent to one another (lap joint), using a guide rail. The operator starts a program on the machine, and the machine, equipped with a welding torch, welds the edges of the sealing plates as it moves along them, while constantly adjusting the distance between the welding torch and the workpiece using a positioning sensor mounted on the machine.

[0004] As is known, the assembly of these metal plates to form a sealing membrane is carried out by plasma welding or by TIG welding (Tungsten Inert Gas). TIG welding is an arc welding process using a tungsten electrode, with the addition of a filler metal if necessary. These welding processes generate a large amount of metal oxides on the edges of the plates. This can compromise the membrane's integrity over time (corrosion). Therefore, it is necessary to brush the welds after the welding stage. This step is lengthy and tedious.

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

[0006] However, laser welding has a very low tolerance for gap. In other words, to weld two metal plates together to form a sealing membrane, one edge of a metal plate, called the upper plate, is superimposed on one edge of another metal plate, called the lower plate, forming a line called the weld line. For optimal welding, it is desirable that the height between the lower surface of the upper plate and the upper surface of the lower plate be close to 0 mm. In other words, the gap between two metal plates should ideally be close to 0 mm. This is generally not the case, and this gap can vary from one pair of metal plates to another, and along the weld line for a given pair of metal plates. This gap can be a few tenths of a millimeter.Such variability in mounting clearances is prohibitive to the use of a laser welding process since such clearances hinder the proper distribution of heat at the welding point, thus preventing the metals of the two plates from being bonded together at that point.

[0007] The invention aims to overcome all or part of the problems mentioned above by proposing a new continuous laser welding process compatible with the variability of the mounting clearances of the metal plates, without human intervention. Such a process makes it possible to take advantage of the high productivity of laser welding while accommodating the mounting clearances.

[0008] To this end, the invention relates to a welding method for an edge of a first plate extending in a first plane and an edge of a second plate superimposed on the edge of the first plate along a processing line extending along a first axis in the first plane, employing a mobile welding device above the processing line comprising a welding torch capable of emitting a laser beam, the welding method comprising, for each point along the processing line: - a first step of determining a difference in height along a second axis perpendicular to the foreground, between the upper surface of the edge of the first plate and the lower surface of the edge of the second plate; - a second step of modifying at least one welding parameter of the welding torch according to the determined height difference if the determined height difference is greater than a predefined threshold; - a third stage of welding the edges of the first plate and the second plate; - a fourth step of moving the mobile welding device.

[0009] The height difference along the second axis represents the gap between the two edges of the plate to be welded. Thanks to the process of the invention, the gap is determined at each point along the processing line. When this gap exceeds a predefined value, for example, on the order of 0.1 or 0.2 millimeters, corresponding to a value for which optimal laser welding cannot take place, at least one welding parameter is modified to allow welding of the two plate edges. In other words, as soon as a gap between the two plates is detected, the welding process of the invention allows the adjustment of one or more welding parameters to ensure proper fusion of the plate metal necessary for the required weld quality.

[0010] In one embodiment of the invention, the welding process includes a step for recording the height difference after the first step for determining the height difference. This recording step has the advantage of allowing the height difference to be determined for part or all of the processing line before initiating the successive welding steps.

[0011] In the welding process according to the invention, at least one welding parameter comprises at least one of the following: the orientation of the laser beam relative to a normal to the foreground, the laser beam initiation, the laser beam power, and the laser beam pulse frequency. The modification step may thus include the modification of one or more of these parameters. The modification step of the welding parameter(s) makes it possible to control the application of the correct amount of energy per unit area to weld the two plates, despite the presence of a gap. This energy application depends on the local height difference between the two plates to be welded. As a result, the material heats up to the correct level to locally melt the material of the plates and, by this modification, compensates for the existence of the gap.

[0012] Furthermore, since this modification of the welding parameter(s) is performed for each detected height difference, the welding process of the invention allows a permanent modification of parameters and allows local adjustment of the amount of energy required to work in continuous mode.

[0013] Modifying the parameters mentioned above also simplifies the welding kinematics since they do not involve repositioning the welding head.

[0014] In the welding process according to the invention, at least one welding parameter comprises at least one of the following: the height between the welding torch and the treatment line, and the orientation of the welding torch relative to the normal to the foreground. In this embodiment, the welding head can vary in its orientation and / or its distance from the treatment line. The advantage is the ability to maintain an optimal welding angle, i.e., the laser beam is located within a cone of revolution whose apex coincides with the point to be welded, and forming an angle between 0° and 45°, preferably 15° to 30°, around the normal to the treatment line at the point to be welded.

[0015] Advantageously, the welding process according to the invention includes, prior to the first step of determining the height difference, a step of determining a distance between a reference point of the position sensor and at least one point on the second plate. This determination step makes it possible to evaluate the distance at which the welding torch is located relative to the processing line. This distance varies, in particular, when the plates to be welded include corrugations, or undulations, as may be the case for sealing membranes for tanks intended to store and / or transport liquefied gas.

[0016] Thus, if the determined distance differs from the distance determined for the previous point along the processing line, for example, indicating the passage of a corrugation, the welding process according to the invention may include a step of modifying the laser beam power according to the determined distance. This consideration of the distance to the processing line makes it possible to perform the weld with a vertical welding head at the same height by varying the focal point and the beam power. This adjustment is necessary because the laser beam is not perpendicular to the surface to be welded, resulting in a loss of energy from the laser. This results in a more oval focal spot, and the power delivered by the laser is spread over a larger area. Modifying the beam power makes it possible to counteract these effects.

[0017] Alternatively, if the determined distance differs from the distance determined for the previous point along the processing line, also a sign of a passage of a corrugation, the welding process according to the invention may include a step of orienting the laser beam according to the determined distance.

[0018] The steps of modifying the power of the laser beam as a function of the distance to the processing line are obviously cumulative with the step of modifying one or more welding parameter(s) as a function of the height difference determined locally.

[0019] The invention also relates to a mobile welding device intended to weld an edge of a first plate extending in a first plane and an edge of a second plate superimposed on the edge of the first plate along a processing line extending along a first axis in the first plane, the mobile welding device comprising a welding torch capable of emitting a laser beam and means for modifying at least one welding parameter of the welding torch as a function of a height difference along a second axis perpendicular to the first plane between the upper surface of the edge of the first plate and the lower surface of the edge of the second plate, if the height difference is greater than a predefined threshold.

[0020] In the mobile welding device according to the invention, at least one welding parameter includes at least one of the following: the orientation of the laser beam relative to a normal to the foreground, the movement of the laser beam, the power of the laser beam, the frequency of the pulses of the laser beam.

[0021] Advantageously, the mobile welding device of the invention further comprises a position sensor capable of measuring the height difference along the second axis perpendicular to the first plane, between the upper surface of the edge of the first plate and the lower surface of the edge of the second plate. The position sensor integrated into the welding device has the advantage of continuously measuring the height difference at any point along the processing line. This information is directly transmitted to the means for modifying the welding parameter(s), allowing them to be modified precisely at the moment when the welding torch welds at the point along the processing line exhibiting said height difference. This results in laser welding that adapts to the gaps between the two plates to be welded. Brief description of the figures

[0022] These features and advantages, and others, of the present invention will become more apparent from the following description, made with reference to the accompanying drawings, given by way of non-limiting examples, and on which:

[0023] Fig. 1 represents a cross-sectional view of a first metal plate and a second adjacent metal plate intended to be joined together by welding;

[0024] Fig. 2 represents a sealing membrane welding device according to the invention, implementing a welding step of a sealing plate with an adjacent sealing plate, in one embodiment of the invention;

[0025] Fig. 3 schematically represents the steps of the welding process of two metal plates according to the invention;

[0026] Fig. 4 is a cross-sectional representation of the step of determining the height difference between the two plates to be welded according to an example of an embodiment of the present invention;

[0027] Fig. 5 is a cross-sectional representation of the step of determining the height difference between the two plates to be welded according to another embodiment of the present invention;

[0028] Figure 6 schematically represents a welding torch with a laser beam, including a reflection module;

[0029] Fig. 7 represents an embodiment of the plate welding step of the welding process according to the invention;

[0030] Fig. 8 represents another embodiment of the plate welding step of the welding process according to the invention;

[0031] Figure 9 schematically represents the welding of two plates without assembly gap according to the process of the invention;

[0032] Fig. 10 schematically represents the welding of two plates with an assembly set according to the process of the invention. Description of the implementation methods

[0033] For the sake of clarity, the same elements will bear the same references in the different figures.

[0034] The features, variants, and different embodiments of the invention, as described or as they will be presented in the detailed description that follows, can be combined in various ways, provided that they are not incompatible or mutually exclusive. In particular, variants of the invention may be conceived comprising only a selection of features described hereafter in isolation from the other described features, if this selection of features is sufficient to confer a technical advantage and / or to differentiate the invention from the prior art.

[0035] Figure 1 shows a cross-sectional view of a first metal plate 11 and a second adjacent metal plate 21 intended to be joined together by welding. The first plate 11 extends in a first plane PL. An edge 22 of the second plate 21 is superimposed on an edge 12 of the first plate 11. along a processing line 30 extending along a first axis Y in the first plane PI. As can be seen in [Fig. 1], the first metal plate 11 and the second adjacent metal plate 21 intended to be joined together have an overlap zone 15. In this overlap zone, the first plate has a flat lateral portion 12. To allow such an overlap, the second plate 21 has a joggling 23, that is, a raised portion of a lateral edge of the second plate 21, so that the raised portion of the lateral edge of the second plate 21 overlaps the lateral edge 12 of the first plate 11 at its overlap zone 15. During the welding step, a weld line is made at the processing line 30 so as to hermetically seal the second plate 21 to the first plate 11.

[0036] For optimal welding, it is desirable that the height 31 between the lower surface 24 of the upper plate 21 and the upper surface 14 of the lower plate 11 be close to 0 mm. In other words, the gap between two metal plates 11, 21 should ideally be zero, i.e., equal to 0 mm. As mentioned previously, this is generally not the case. Not only can this gap vary from one pair of metal plates to another, but also, for a given pair of metal plates, this gap can vary along the processing line 30.

[0037] Figure 2 represents a welding device 7 for a sealing membrane according to the invention, implementing the welding process of a sealing plate with an adjacent sealing plate, according to the invention. This is a highly schematic representation for descriptive purposes of the invention. Generally, the distance between the position sensor 73 and the welding torch 72, i.e., the distance between the points identified A and B, is on the order of 2 to 15 cm.

[0038] The welding process of the invention implements the mobile welding device 7 above the processing line 30. The welding device 7 comprises a welding torch 72 capable of emitting a laser beam. The welding device 7 further comprises means 74 for modifying at least one welding parameter of the welding torch 72 as a function of a height difference 31 along a second axis Z perpendicular to the first plane PI 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 the determined height difference 31 is greater than a predefined threshold.

[0039] The welding device 7 may further include a position sensor 73 capable of measuring the height difference along the second axis Z perpendicular to the first plane, 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.

[0040] Alternatively, the welding device 7 may not be equipped with a position sensor. In this variant, the successive height differences 31 along the processing line are predetermined and recorded on a recording medium, located in the welding device or on a remote server. For each point on the processing line, the associated height difference 31 is accessible to the modification means 74 to enable the process of the invention to be carried out.

[0041] The welding device 7 can move along a rail 3 which follows the edge of the second plate 21, above the processing line 30.

[0042] Figure 3 schematically represents the steps of the welding process for two metal plates according to the invention. The welding process according to the invention comprises, for each point along the processing line 30: - a first step 110 of determining a height difference 31 along a second axis Z perpendicular to the first plane PI, 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; - a second step 120 of modification of at least one welding parameter of the welding torch 72 according to the height difference 31 determined if the determined height difference 31 is greater than a predefined threshold; - a third step 130 of welding the edges 12, 22 of the first plate 11 and the second plate 21. Step 130 is a clinker welding step of the edges of the plates 11,21 with the welding torch 72. During this welding step, the plates 11,21 are welded by fusion of material from the edge of the plate 21 onto the edge of the plate 11. - a fourth step 140 of moving the mobile welding device 7.

[0043] For a given point on the processing line 30, if the height difference 31 is 0 mm, then the edges 12, 22 are welded at that point. But if, for this point, the height difference 31 is not zero, step 120 of modifying at least one welding parameter of the welding torch is carried out. The modification of the welding parameter(s) depends on the determined height difference 31. The modification of the welding parameters will be detailed below.

[0044] The welding process of the invention is based on determining an assembly gap between the two edges of the plates to be welded and on adapting the welding parameters according to the determined assembly gap. This results in a continuous adaptation, for each point to be welded along the processing line, of the welding parameters as a function of the differential height 31 between the two plates at that point. This continuous adaptation, performed according to the environment encountered, ensures proper welding of the two edges of plates together regardless of the local differential height. The welding of the two plates 11,21 is achieved by melting material from the edges of the two plates, this melting being carried out as the welding device 7 advances along the rail 3.

[0045] In one embodiment of the invention, the welding process may include a step 115 for recording the height difference 31 after the first step 110 of determining the height difference 31 on a recording medium, located on the welding device or remotely on a server external to the welding device. Recording the height differences 31 along the processing line makes it possible to obtain the profile of the assembly gaps along the entire processing line. This embodiment is advantageous when the welding device is not equipped with a sensor and retrieves the height difference 31 values ​​prior to the modification step 120.

[0046] In other words, the welding process according to the invention requires, at at least one point on the processing line, the determination of the height difference 31 at that point. This determination can be made beforehand for that point or for all points on the processing line, for example, by first passing a position sensor over the processing line and recording the plurality of height differences 31. Or this determination of the height difference can be made point by point. This is the case with a welding device equipped with the position sensor 73. In this configuration, schematically represented in [Fig. 2], the position sensor 73 and the welding torch 72 are separated by a fixed distance 76, typically between 2 and 15 cm. At time t1, the position sensor 73 measures the height difference 31 at point A. At this time t1, the welding torch 72 welds at point B.The modification means 74 are connected, via a wired connection 75 or a wireless connection, to the position sensor 73 and the welding torch 72. The height difference 31 can be recorded on the recording medium or directly transmitted to the modification means 74 to modify at least one welding parameter according to the height difference 31 determined at point A. Since the travel speed of the welding device 7 is known, and following the determination of the height difference 31 at point A, the modification means 74 are configured to modify at least one welding parameter at time t2, corresponding to the instant when the welding torch 72 is above point A. Thanks to this configuration, only one pass of the welding device over the processing line is necessary to perform both the determination and welding steps.

[0047] Fig. 4 is a cross-sectional representation of the step of determining the height difference between the two plates to be welded according to an example of an embodiment of the present invention.

[0048] In this embodiment, the position sensor 73 is a non-contact sensor, for example a laser profilometer, also called a laser scanner. It is a profile sensor that can detect, measure and evaluate a two-dimensional profile, in the cutting plane, without physical contact on the two plates 11, 21.

[0049] In this embodiment, the position sensor 73 implements the following substeps:

[0050] - sending an initial optical signal to a point on the surface of the edge 22 of the plate, this initial optical signal being for example a laser pulse, - reception of a return optical signal corresponding to the initial optical signal, this return optical signal being for example a reflection of the laser pulse initially sent onto the surface of edge 22 of the plate, and - measurement of the distance between the reference point of the position sensor 73 and the point on the surface of the edge 22 of the plate as a function of the initial optical signal and the return optical signal. This measurement typically uses the time between the sending of the laser pulse and the reception of the reflected laser pulse.

[0051] The position sensor 73 thus determines a first distance 33 between a reference height of the sensor along the Z-axis and the upper surface of the edge 22. It also determines a second distance 32 between the reference height of the sensor and the upper surface of the edge 12. Knowing the thickness e of the edge 22 (typically on the order of 1.2 mm), it is thus possible to determine the differential height 31. For this purpose, the position sensor 73 may include a calculator capable of calculating the differential height 31 from the distances 32, 33 and the thickness e. Alternatively, the calculator may be located remotely from the position sensor 73 and integrated into the welding device 7 or on a remote server.

[0052] Fig. 5 is a cross-sectional representation of the step of determining the height difference between the two plates to be welded according to another embodiment of the present invention.

[0053] In this embodiment, the position sensor 73 is a sensor with physical contact. It may be an LVDT (Linear Variable Differential Transducer) type sensor, which is an electromechanical device that converts mechanical motion (here rectilinear) into a variable electrical current, indicating the length of the movement and therefore the height 32, or height 33 respectively. As in the example in [Fig. 4], knowing the thickness e of the edge 22 and the heights 32 and 33, it is thus possible to determine the differential height 31. If this differential height 31 is greater than a predefined threshold, typically a few tenths of a millimeter, for example 0.1mm or 0.2mm, at least one welding parameter is modified to ensure the proper execution of the welding step.

[0054] In the welding process according to the invention, the at least one welding parameter that can be modified in step 120 includes at least one of the following: the orientation of the laser beam relative to a normal to the foreground, the movement of the laser beam, the power of the laser beam, the frequency of the pulses of the laser beam.

[0055] Fig. 6 schematically represents a welding torch 72 with a laser beam, comprising a reflection module 57.

[0056] The welding torch includes a laser beam generator 56, projecting the laser beam 6 onto a reflecting module 57 at the free end of the welding torch 72. The welding torch 72 is shown in [Fig. 6] in a highly simplified manner to make the illustration easier to understand. In fact, the laser beam generator 56 is external to the welding torch 72, and it is the fiber 9 that carries the generated beam into the welding torch 72. The reflecting module 57 is, for example, a set of mirrors that deflects the path of the laser beam 6 exiting the beam generator along a direction DI lying in a plane parallel to the longitudinal direction L and the vertical direction V, or along a direction D2 lying in a plane parallel to the transverse direction T and the vertical direction V.The modification means 74, shown schematically here, are connected via the connection 75 (wired or wireless) to the laser beam generator 56 in order to adjust its power or pulse frequency. Similarly, the modification means 74 can act on the reflection module 57 to adjust the orientation of the laser beam relative to the normal to the first plane PL. Such an adjustment of the laser beam's orientation towards the upper plate allows the energy delivered by the laser beam to be applied to the material of the upper and / or lower plate in order to heat the material at the edge of the plate and compensate for the height difference 31. It is also possible to modify the beam path in the module 57 by adjusting the inclination of the mirrors; this changes the height of the focal point, thus allowing the optimum focal point to be obtained without changing the power.Alternatively, it is also possible to adjust the beam power according to the detected gap and the torch's height. Similarly, the modification means 74 can move the laser beam to create a scanning motion along the treatment line. This scanning allows heat to be applied on both sides of the treatment line to melt the material and bond the two plates together.

[0057] In another embodiment, in the welding process, at least one welding parameter includes at least one of the heights between the welding torch 72 and the processing line and the orientation of the welding torch 72 with respect to the normal to the foreground PI. Figures 7 and 8 are examples of implementation of this process.

[0058] Fig. 7 represents an embodiment of step 130 of welding the plates of the welding process according to the invention.

[0059] In this embodiment, the plates to be welded include corrugations extending over a surface of each plate. These corrugations, or undulations, are intended to provide flexibility to the membrane formed after welding the plates to accommodate the thermal contraction of the steel during the cooling of the tank. It is thus possible to define the surface of the plate by flat areas 51 and waves 52 as shown in [Fig. 7]. In its movement above the processing line 30, the welding device 7 is therefore required to pass over flat areas 51 and waves 52.

[0060] In the embodiment shown in [Fig. 7], the welding device 7 maintains a straight position during its movement along the Y-axis. Thanks to this configuration, the welding kinematics are simplified since the welding head remains vertical and at the same height. However, the welding device 7 encounters two scenarios. The first scenario is the flat area 51, represented by position (a). The distance between the welding torch and the plates to be welded does not vary. But the height difference 31 between the two plate edges can vary. At any point along the processing line on a flat area, at least one welding parameter is adjusted according to the height difference 31 determined at that point.

[0061] The second scenario is Fonde, represented by positions (b) and (c). The distance between the welding torch and the plates to be welded varies during the passage of the wave. However, the height difference 31 between the two plate edges can also vary. To this end, the welding process according to the invention may include, prior to the first step 110 of determining the height difference 31, a step 105 of determining a distance between a reference point of the position sensor 73 and at least one point on the second plate. This distance indicates the presence of a wave. Alternatively, a previously generated profile of the plates to be welded, for example by laser profilometry, may be made available to the computer. The computer can then determine, based on the distance between the plates and the welding torch on the one hand and on the height difference on the other, the adjustment of at least one welding parameter.For example, as can be seen for positions (b) and (c), at two different distances between the plates and the welding torch, the power of the laser beam 6 can be adapted.

[0062] Figure 8 represents another embodiment of the plate welding step. of the welding process according to the invention.

[0063] In this alternative embodiment, the welding device 7 also accommodates the two scenarios of a flat zone 51 (position (a)) and the passage of the wave (positions (b), (c), and (d)). In this variant, the welding head remains vertical and the welding angle is maintained at an optimal level, i.e., such that the laser beam lies within a cone of revolution whose apex coincides with the point to be welded, and forming an angle between 0° and 45°, preferably 15° to 30°, around the normal to the treatment line at the point to be welded. It is then the laser beam 6 that is oriented. This configuration allows the welding head to remain upright in order to limit movement and simplify the welding kinematics.

[0064] In addition, there is the possible variation of the height difference 31 between the two plate edges. As before, the welding process according to the invention may include, prior to the first step 110 of determining the height difference 31, a step 105 of determining a distance between a reference point of the position sensor 73 and at least one point on the second plate. This distance is an indicator of the positioning of the welding torch relative to the wave. Alternatively, a previously generated profile of the plates to be welded may be made available to the computer. The computer can then determine, based on the distance between the plates and the welding torch on the one hand and on the determined height difference on the other hand, the adjustment of at least one welding parameter.For example, as can be seen for positions (b), (c), and (d), at different orientations of the welding torch relative to the processing line 30, the orientation of the laser beam 6 is adapted for positions (b) and (d), while the laser beam 6 is vertical in position (c). Similar to what was explained previously, in addition to adapting the beam due to the presence of the wave on the processing line, the welding process applies a modification of at least one welding parameter for each point on the processing line where the height difference 31 is greater than the predefined value.

[0065] In the welding process according to the invention, the second step 120, which involves modifying at least one welding parameter of the welding torch 72, is implemented if the determined height difference 31 exceeds a predefined threshold. This predefined threshold may be 0 mm. In other words, as soon as assembly clearance is detected, step 120 is initiated.

[0066] In one embodiment of the invention, the predefined threshold is 0.01 mm. This threshold corresponds to the sensitivity of the position sensor 73 which measures the height difference 31.

[0067] In another embodiment of the invention, the predefined threshold is 0.1 mm. This threshold corresponds to a height difference beyond which optimal laser welding can no longer be ensured without modifying at least one welding parameter.

[0068] In yet another embodiment of the invention, the second step 120 of modifying at least one welding parameter of the welding torch 72 is carried out by applying a predefined modification of a set of welding parameters according to the determined height difference, the predefined modification of this set varying according to a predefined increment of the height difference, for example, 0.05 or 0.1 mm. In other words, as soon as the determined height difference exceeds the predefined threshold (for example, a threshold of 0.1 mm), step 120 is carried out. And in carrying out step 120, for a predefined increment of 0.1 mm, for a height difference between 0.1 and 0.2 mm, the welding process of the invention will apply a modification of a set of welding parameters within a first range.For a height difference between 0.2 and 0.3 mm, the welding process of the invention applies a modification of the same set of welding parameters in a second range. However, the invention also covers the case of modifying another set of welding parameters for a height difference of a larger increment.

[0069] An example of application will be described later on the basis of [Fig. 10].

[0070] Subsequently, the modification of the welding parameter(s) of the welding torch is performed based on the determined height difference 31. In other words, for each point on the processing line, an initial test assesses whether the predefined threshold is reached. If the predefined threshold is reached, at least one welding parameter of the welding torch is modified to compensate for this assembly clearance and ensure proper welding at that point.

[0071] In an advantageous embodiment of the welding process of the invention, step 120, which modifies the welding parameter(s) of the welding torch, depends on the height difference 31. This means that, depending on the height difference determined at a point, the applied welding correction, i.e., the modification of the welding parameter(s), may differ from one welding point to another. This feature makes it possible to adapt the amount of energy supplied to each welding point according to the level of joint clearance to obtain the metal fusion required for welding the two plates.

[0072] Based on Figures 9 and 10, possible examples of implementing step 120 of modifying welding parameters are given below in a non-limiting manner, dz corresponding to the determined height difference (also referenced as 31). In these examples, the following welding parameters are considered These methods allow for the welding of two plates with no assembly gaps: a laser beam with a power of 1750 W, and an orientation of the laser beam relative to a normal Z' to the first plane at an angle aO (for example, between 0° and 30°). The predefined threshold for triggering modification step 120 is 0.01 mm.

[0073] Figure 9 schematically represents the welding of two plates 11, 21 without gap according to the process of the invention. In this configuration, the welding device 7 moves above the processing line 30, and the process steps are carried out at each point of the processing line as the welding device 7 advances. For each point of the processing line 30, 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. In the example illustrated in Figure 9, this height difference is equal to 0 mm; there is no gap. The determined height difference is therefore not greater than the predefined threshold. There is no step to modify at least one welding parameter of the welding torch.

[0074] The third step 130 of welding the edges 12, 22 of the first plate 11 and the second plate 21 is carried out by means of a laser beam, for example set to a power of 1750 W, and followed by the fourth step 140 of moving the mobile welding device 7 to start again at the first step 110 at the next point of the processing line.

[0075] Figure 10 schematically represents the welding of two plates with a joint according to the process of the invention. In this configuration, and similarly to what was explained in the example of Figure 9, the welding device 7 moves above the processing line 30, and the process steps are carried out at each point of the processing line as the welding device 7 advances. For each point of the processing line 30, 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. In the example illustrated in Figure 10, this height difference 31 (hereafter referred to as dz) is non-zero. To illustrate the invention, we consider the case of a height difference greater than 0.01mm, i.e. above the predefined threshold.

[0076] Since the height difference exceeds the predefined threshold, step 120, which modifies at least one welding parameter, is initiated. For example, the welding parameters modified may be the following, depending on the height difference.

[0077] For 0 mm < dz < 0.1 mm, the modified welding parameter is the laser beam power, which increases from 1750 W to 2000 W. The laser beam orientation by The ratio to the normal Z' in the foreground remains at angle aO. The offset between the treatment line and the intersection with surface 14 of the line carrying the laser beam is 0 mm. In other words, the laser beam points on the treatment line.

[0078] For 0.1 mm < dz < 0.2 mm, the modified welding parameter is the laser beam power, which increases from 1875 W to 2125 W. Furthermore, the orientation of the laser beam relative to the normal Z' in the foreground is modified, changing from angle aO to angle al (as shown in local magnification in the upper right of [Fig. 10]). The offset (denoted d) between the processing line and the intersection with surface 14 of the line carrying the laser beam 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 allows the laser beam to access a metallic area of ​​the upper plate in order to raise its temperature locally and melt a portion of it, thus contributing to the formation of the weld bead. The angle modification can be achieved by changing the inclination of the mirrors of module 57.

[0079] For 0.2 mm < dz < 0.3 mm, the modified welding parameter is the laser beam power, which increases from 2000 W to 2250 W. As with the case of dz between 0.1 and 0.2 mm, the orientation of the laser beam relative to the normal Z' in the foreground is modified. Since the height difference between the two plates is greater, the angle al becomes larger than in the previous case, resulting in an offset d between the processing line and the intersection with the surface 14 of the line carrying the laser beam of approximately 1 mm. The offset d is greater compared to the previous example of a height difference between 0.1 and 0.2 mm. Because the height difference is greater than in the previous case, the gap to be filled is larger. It is therefore necessary to access more metallic material.By proceeding in this way, the laser beam, with a higher power, can ensure the fusion of enough material to form the weld bead between the two plates.

[0080] The numerical values ​​of the welding parameters are given here by way of example to explain the invention. However, the process of the invention is by no means limited to them. In particular, the beam powers can vary by + / - 10% to take into account the height difference 31, to which can be added the height variation between the area to be welded and the welding torch at the point of a wave passage. Moreover, depending on the detected height 33 and the fact that the thickness of the assembly in the vertical section in the ZX plane at the level of the wave (due to the curvature) is locally greater, the laser beam power is advantageously increased. In other words, the welding parameters to be modified can vary with a certain percentage depending on the height difference 31 encountered and a potential more or less significant variation of the area to be welded as the waves pass.

[0081] Other welding parameters can be modified, such as moving the laser beam in the plane perpendicular to the processing line, thus performing a laser beam sweep. The speed of this sweep can also be modified. This movement allows the laser beam to come into contact with the edge of the top plate, thereby providing a localized, point-like energy input to the edge of the top plate, near the processing line. As a result, the metal at this plate edge reaches its melting point and melts to form the weld bead.

[0082] Based on the description of the invention, a person skilled in the art understands that the welding process according to the invention relies on the continuous detection of assembly clearance and the continuous adaptation of the welding parameters according to the assembly clearance encountered by the mobile welding device at each welding point along the processing line. Advantageously, the values ​​of the welding parameters to be applied during the modification step 120, according to the height differences encountered, can be tabulated and saved on a medium accessible to the modification means 74 to ensure proper control of the welding device.

[0083] In a preferred embodiment, the welding process according to the invention relies on modifying a judicious combination of several welding parameters. The choice of parameters to be modified, as well as the range within which they are modified, depends on the determined height difference. At a given point, the greater the determined height difference, i.e., the larger the joint gap, the more difficult it is to guarantee a good weld between the two plates. The invention allows, without human intervention, in an automated and continuous manner, the production of a weld bead with good geometry and meeting the required conformity criteria to guarantee the weld between the two plates and its durability over time. This effect is achieved by varying the energy input per unit area along the processing line according to the evolution of the determined height difference.

[0084] Although the invention has been described in connection with several particular embodiments, it is clearly evident that it is by no means limited to them and that it includes all technical equivalents of the means described as well as their combinations if these fall within the scope of the invention.

[0085] The use of the verb "comprise", "comprendre" or "include" and its conjugated forms does not exclude the presence of other elements or other steps than those stated in a claim.

[0086] In the claims, any reference sign in parentheses shall not be interpreted as a limitation of the claim.

[0087] It will more generally be apparent to a person skilled in the art that various modifications can be made to the embodiments described above, in light of the information just disclosed to them. In the claims that follow, the terms used shall not be interpreted as limiting the claims to the embodiments set forth in this description, but shall be interpreted to include all equivalents that the claims aim to cover by virtue of their formulation and whose prediction is within the grasp of a person skilled in the art based on their general knowledge.

Claims

Demands

1. A welding method for an edge (12) of a first plate (11) extending in a first plane (PI) and an edge (22) of a second plate (21) superimposed on the edge (12) of the first plate (11) along a processing line (30) extending along a first axis (Y) in the first plane (PI), employing a mobile welding device (7) above the processing line (30) comprising a welding torch (72) capable of emitting a laser beam, the welding method being characterized in that it comprises, for each point along the processing line (30): - a first step (110) of determining a height difference (31) along a second axis (Z) perpendicular to the first plane (PI), 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);- a second step (120) of modifying at least one welding parameter of the welding torch (72) according to the height difference (31) determined if the determined height difference (31) is greater than a predefined threshold; - a third step (130) of welding the edges (12, 22) of the first plate (11) and the second plate (21); - a fourth step (140) of moving the mobile welding device (7).

2. Welding method according to claim 1, comprising a step (115) of recording the height difference (31) after the first step (110) of determining the height difference (31).

3. A welding method according to any one of claims 1 or 2, wherein at least one welding parameter comprises at least one of the following: the orientation of the laser beam relative to a normal to the foreground, the laser beam motion, the laser beam power, the laser beam pulse frequency.

4. A welding method according to any one of claims 1 to 3, wherein at least one welding parameter comprises at least one of the heights between the welding torch (72) and the line of treatment and orientation of the welding torch (72) relative to the normal in the foreground.

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

6. Welding method according to claim 5, comprising, if the determined distance differs from the determined distance for the previous point along the processing line, a step (150) of modifying the power of the laser beam as a function of the determined distance.

7. Welding method according to claim 5 or 6, comprising, if the determined distance differs from the distance determined for the previous point along the processing line, a step (160) of orienting the laser beam according to the determined distance.

8. Mobile welding device (7) for welding an edge (12) of a first plate (11) extending in a first plane (PI) and an edge (22) of a second plate (21) superimposed on the edge (12) of the first plate (11) along a processing line (30) extending along a first axis (Y) in the first plane (PI), the mobile welding device comprising: - a welding torch (72) capable of emitting a laser beam; - means for modifying (74) at least one welding parameter of the welding torch (72) as a function of a height difference (31) along a second (Z) axis perpendicular to the foreground (PI) 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 the height difference (31) is greater than a predefined threshold.

9. Mobile welding device (7) according to claim 8, wherein the at least one welding parameter comprises at least one of the following: the orientation of the laser beam relative to a normal to the foreground, the movement of the laser beam, the power of the laser beam, the frequency of the laser beam pulses.

10. Mobile welding device (7) according to claim 8 or 9, further comprising a position sensor (73) capable of measuring the height difference (31) along the second (Z) axis perpendicular to the first plane (PI), 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).

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