FR3039444A1 - OPTIMIZED LASER-ARC HYBRID WELDING PROCESS - Google Patents

Abstract

The method is for welding two plates (12) of thicknesses (E) greater than 8 mm, and having weld side edges (12C) parallel to each other. The weld bead is made by means of a hybrid welding tool (24) comprising: a laser emitter (26) emitting a laser (28) along a transmission axis (A), with a focal point ( 36) disposed in the thickness of the plates, and a MAG welding torch (29), having a gas diffusion nozzle (30) and at least one filler wire (32) extending to a free end (34). Considering a projection plane parallel to the upper surfaces (12A), the orthogonal projection of the focal point (36) and the orthogonal projection of the free end (34) of the filler wire (32) on this projection plane are spaced apart a distance (D) greater than or equal to 15 mm.

Description

Optimized laser-arc hybrid welding process

The present invention relates to a laser-arc hybrid welding process for assembling two steel plates together.

More particularly, the invention relates to a method of welding two steel plates with thicknesses greater than 8 mm.

Such steel plates are assembled for example to form together large walls, for example for the manufacture of naval structures.

Already known in the state of the art, a laser-arc hybrid welding process, for the assembly of two steel plates together along a weld line, wherein: - the two plates present respectively substantially coplanar upper surfaces and substantially coplanar lower surfaces, - the upper and lower surfaces of each plate define between them a thickness greater than 8 mm, - the plates each have a side edge weld, the lateral edges of the plates being arranged facing each other, and being substantially parallel to each other, a weld bead being formed along the weld line at these side weld edges, and - the welding being carried out by means of a hybrid welding tool comprising: a laser emitter, capable of emitting a laser along an emission axis, said laser having a focal point disposed between the upper and lower surfaces in the direction of the emission axis (A), and • a MAG welding torch, comprising a gas diffusion nozzle and at least one filler wire housed in the diffusion nozzle and extending to a free end.

A hybrid laser arc welding process is defined by many parameters that must be taken into consideration for good welding quality. Parameter examples are listed below.

A first parameter is the welding speed, i.e. the speed at which the hybrid welding tool is moved along the weld line. Other parameters concern the laser emitter, namely: the laser power, the optical fiber diameter, the optical ratio, the focal length, the spot diameter, the beam shaping comprising the number of spots and the delta between spots, power distribution and beam oscillation, optical quality, optical type (lens, mirror), wavelength, beam mode, beam quality and polarization. Other parameters concern the MAG welding torch, namely the current mode (continuous, pulsed or CMT), the voltage, the high current, the low current, the frequency, the pulsation time, the filler wire in particular. its type (solid wire or flux-cored wire), the diameter of the filler wire, the distance the wire protrudes from the end of the diffusion nozzle, the number of filler wires and the distance between the filler wires , filler wire material, and parameters relating to the diffused gas, including its composition, nozzle diameter, and diffusion rate. Other parameters of the method are the position of the focal point of the laser with respect to the upper surface of the plates, the position of the laser with respect to the weld line, the distance between the focal point of the laser and the free end of the wire the laser transmitter and welding torch relative to each other in the direction of movement laser emission axis and the upper surface of the parts to be welded, the angle of the welding torch relative to the upper surface of the parts to be welded, the angle of advance pulled / pushed, the cutting process of the edges the lateral edges (straight or V-shaped), the play before welding, the material to be welded, the thickness of the steel plates, etc.

It should be noted that the invention relates to a method of welding two steel plates whose side edges of welding are substantially parallel to each other. Such parallel side edges between them are also called "straight edges", as opposed to "V-shaped edges" that is to say side edges forming an angle between them. Indeed, it appears that, for the production of industrial parts of large dimensions, such V-shaped edges do not provide a satisfactory welding quality and / or a sufficiently homogeneous and / or reproducible welding.

A straight edge welding process is very different from a V-edge welding process, and does not give the same results. More particularly, the application of a method of welding V edges to straight edges does not give good results, and vice versa.

Furthermore, it should be noted that the invention is intended for industrial use, particularly to be applied to sheets of several meters, mass of the order of at least one ton. A welding process for such an industrial application has to be considered differently from a process of welding smaller samples, so that the parameterization of a welding process of such samples does not give any teaching for the parameterization of an industrial level welding process. More particularly, efficient parameterization for a sample welding process generally does not give good results for industrial application for large size sheets, and vice versa. The object of the invention is in particular to optimize an arc laser hybrid welding process for plates with thicknesses greater than 8 mm and of large dimensions, with straight lateral edges of welding. For this purpose, certain welding parameters have been modified contrary to the conventional teachings of the state of the art concerning the configuration of hybrid welding processes for the assembly of plates with thicknesses greater than 8 mm, with side edges. rights. For this purpose, the subject of the invention is in particular a hybrid laser-arc welding method, for assembling two steel plates together along a weld line, in which: the two plates present respectively substantially coplanar upper surfaces and substantially coplanar lower surfaces, - the upper and lower surfaces of each plate define between them a thickness greater than 8 mm, - the plates each have a lateral weld edge, the lateral edges of the plates being arranged in facing each other, and being substantially parallel to each other, a weld bead being made along the weld line, at these lateral weld edges, and - the weld bead is made by means of a hybrid welding tool comprising: a laser emitter, capable of emitting a laser along an emission axis, said laser having a focal point available between the upper and lower surfaces in the direction of the emission axis, and • a MAG welding torch, comprising a gas diffusion nozzle and at least one filler wire housed in the diffusion nozzle and extending to a free end, and wherein, considering a projection plane parallel to the upper surfaces, the orthogonal projection of the focal point and the orthogonal projection of the free end of the filler wire on this projection plane are spaced apart a distance greater than or equal to 15 mm.

While the state of the art, and even the usual principle of hybrid welding, recommends a laser-arc synergy with a short laser-arc distance, between 2 and 5 mm, for a steel thickness of the order of 10 mm, the invention provides a sequential effect of the laser transmitter and the welding torch rather than a simultaneous effect as taught by the state of the art, by providing a distance between the laser transmitter and torch greater than or equal to 15 mm.

The inventors have found that such a distance makes it possible to limit the risks of collapse of the welding bath of the welding torch between the lateral edges while ensuring a connection between the weld pool of the welding torch and the weld pool of the laser transmitter. This guarantees a stability of the solder bath over a long length of weld bead.

The welding method according to the invention also makes it possible to avoid reworking on the welding zones, and has a precision and efficiency of industrial level.

A welding method according to the invention may also have one or more of the following characteristics, taken alone or in any technically feasible combination: Said distance is between 15 and 20 mm. The distance between the upper surfaces and the focal point, in the direction of the emission axis, is between 2 and 6 mm, preferably equal to 4 mm. - The welding tool is moved along the weld line with a speed between 1 and 2.5 meters per minute (m / min), preferably substantially equal to 1.5 m / min. - The welding tool being moved in a direction of movement along the weld line, the laser emitter precedes the welding torch in this direction of movement. - The laser has a power between 8 and 12 kW. - The filler wire is a cored wire, preferably a metal powder wire or a rutile wire. - The laser is moved along the weld line oscillating around this weld line, with an oscillation amplitude of between 1 and 3 mm, preferably substantially equal to 2 mm, the oscillation frequency of the laser around the weld line is preferably substantially equal to 500 Hz. - The side weld edges are previously made by a laser cutting method of a lateral end of each plate. - The method comprises a prior step of selecting welding parameters according to characteristics of the plates to be welded. The invention will be better understood on reading the description which follows, given solely by way of example and with reference to the appended figures, in which: FIG. 1 represents a device for welding two steel plates between them, for the application of the welding method according to the invention; - Figure 2 shows schematically a welding tool of the welding device of Figure 1.

FIG. 1 shows a hybrid laser arc welding device 10 for assembling two steel plates 12 together.

The steel plates 12 are made of steels of yield strength greater than 350 MPa, for example steels of shade DH36, or of a close grade.

The welding device 10 is suitable for assembling steel plates 12 each having a thickness E greater than 8 mm. Each steel plate 12 has an upper surface 12A and a lower surface 12B, the upper surfaces 12A of the two plates 12 being substantially coplanar with each other, and the lower surfaces 12B of the plates 12 are also substantially coplanar with each other. The thickness E of each plate 12 is defined as the distance between its upper surface 12A and its lower surface 12B. This thickness E is for example 10 mm.

Each plate 12 has a lateral weld edge 12C, the side edges 12C of the two plates 12 being arranged facing one another.

The steel plates 12 are large, that is to say that their side edges 12C have a length greater than 1 meter.

According to the configuration of the method according to the invention, these lateral welding edges 12c are substantially parallel to each other. Such edges are called "straight edges".

The steel plates 12 are assembled together at these lateral weld edges 12C, forming, between these lateral weld edges 12C, a weld bead extending along a weld line 14.

In order to maintain the plates 12 during the welding process, the welding device 10 comprises two support plates 16 and 18.

Advantageously, one of the support plates 16 is fixed, and the other of the support plates 18 is movable along a transverse direction substantially perpendicular to the weld line 14, to move towards or away from the fixed support 16.

The welding device 10 comprises clamping means 20 capable of applying a force for bringing the moving plate 18 closer to or away from the fixed plate 16. These clamping means 20 comprise, for example, threaded rods passing through the plate. fixed 16 and the movable plate 18, the tightening being performed by screwing these threaded rods.

The fixed support plate 16 has a first stop 21, and the mobile support plate 18 has a second stop 22. The first 21 and second 22 stops are arranged opposite one another in the transverse direction, and are intended to receive between them the steel plates 12.

Thus, each steel plate 12 is disposed on a respective one of the fixed plates 16 and mobile 18, each in contact with one of the abutments 21, 22 respectively, and their welding edge 12C one facing the other in the transverse direction. These welding edges 12C are thus able to be clamped against each other when the clamping means 20 are activated.

The welding device 10 further comprises clamping means 23 for holding each plate 12 on the fixed plate 16 or mobile 18 corresponding. These clamping means 23 comprise for example electromagnets or alternatively pressure screws.

The welding device 10 also comprises a hybrid welding tool 24, shown in more detail in FIG. 2. The welding tool 24 comprises a laser emitter 26, capable of emitting a laser 28 along an axis of FIG. emission A. Note that, in the example described, the transmission axis A is substantially perpendicular to the plane of the upper surfaces 12A. The welding tool 24 also comprises a MAG-type welding torch 29, comprising a gas diffusion nozzle 30 and a filler wire 32 housed in the diffusion nozzle 30 and extending to a free end 34. Advantageously, the welding torch 29 is inclined with an angle of attack of the filler wire 32 between 20 and 30 ° relative to the upper surface 12A, to promote the removal of the weld pool in width.

This welding device makes it possible to produce a hybrid laser arc welding method according to the invention, parameterized for optimum welding quality.

For example, the laser emitter 26 is chosen to emit a laser of wavelength substantially equal to 1030 nanometers. This laser transmitter 26 comprises, for example, an optical fiber having a diameter of between 400 μm and 600 μm, with a length substantially equal to 30 μm. The laser has a power advantageously between 8 and 12 kw.

The laser has a focal point 36 whose position relative to the upper surfaces 12A of the two plates 12 is a parameter of the welding process. Advantageously, the distance DF between the plane of the upper surfaces 12A and the focal point 36, in the direction of the transmission axis A, is between 2 and 6 mm, preferably equal to 4 mm.

Such a focal point disposed at this distance DF of 4 mm is optimal for a good quality of welding. The welding tool is intended to be moved along the weld line 14 in a direction of displacement S. According to another parameter of the welding process according to the invention, the laser transmitter 26 precedes the welding torch 28 in this direction of displacement S. Thus, the weld pool has optimum wetting with a flat bead.

Another parameter of the welding process according to the invention is the selection of the type of the filler wire 32. Advantageously, the filler wire 32 is a cored wire, preferably a metal powder wire (for example the cored wire Metal Core Oerlikon FLUXOFIL M8) or a rutile thread (eg Rutilated Welding Alloys ROBOFIL KX71T1 cored wire). These types of wire make it possible to obtain satisfactory weld side bead morphologies, meeting the NF EN ISO 12932 standard of July 2013. These filler wires make it possible to optimize the wetting of the weld bead.

In order to guarantee the fusion in the weld bead along the entire length of the weld line 14, the laser touches the two plates 12 to be welded. For this purpose, several welding parameters, making it possible to widen the melted zone, in particular to obtain a width of 2 mm of this melted zone, are conceivable.

In particular, it is possible to increase the laser spot diameter, to perform a bi-spot laser welding, or to perform an oscillation of the laser around the weld line (wobbling).

The present invention proposes to optimize the choice of this parameter, by performing an oscillation of the laser emitter 26 around the weld line 14, with an oscillation amplitude of between 1 and 3 mm, preferably substantially equal to 2 mm. In addition, advantageously, the oscillation frequency of the laser emitter 26 around the weld line 14 is substantially equal to 500 hertz.

It should be noted that the oscillation of the laser 28, which is optimal with regard to the width of the melted zone, is also optimal for the solder games. Thus, this method according to the invention makes it possible to carry out a welding even in the case of a clearance of 0.4 mm between the lateral weld edges 12C, while respecting the quality criteria.

Furthermore, the welding speed adopted, that is to say the speed at which the welding tool 24 moves along the weld line is chosen between 1 and 2.5 m per minute, and preferably substantially equal to 1.5 m per minute.

The welding speed of 1.5 m per minute hold ensures a weld width of 2 mm in the laser zone to increase the playability and stability of the melt on the reverse side. In addition, this welding speed limits the maximum hardness of the heat affected zone to around 400 Hv. One of the most important parameters in hybrid welding is the distance D between the laser 28 and the MAG welding torch 29. According to the invention, and contrary to the conventional teachings of the state of the art, this distance D, which corresponds, considering a projection plane parallel to the upper surfaces 12A, to the distance between the orthogonal projection of the focal point 36 and the orthogonal projection of the free end 34 of the filler wire 32 on this projection plane, is greater or equal to 15 mm. Preferably, this distance D is between 15 and 20 mm.

This distance D makes it possible to limit the risks of collapse of the welding bath of the welding torch 29 in the bottom of the laser bead, while ensuring a connection between the two solder baths.

It appears that the welding process of the invention allows an optimal quality of the weld. In particular, the weld bead obtained has a good compactness and no crack is observed in macrography. More particularly, the use of a large distance D, greater than or equal to 15 mm makes it possible to control the quality of the cord on the back side, by limiting the fall of the solder bath.

These welds are made according to the acceptance criteria of the standard 13919-1 (laser welding standard) and not the norm 5817 (MAG welding standard), the welds meeting the strictest severity criteria.

In order to improve the quality of docking between the plates 12 prior to welding, and thus to improve the quality of the welding, the lateral weld edges 12C are advantageously prepared, prior to welding, by a laser cutting process. With this laser cutting method, it is possible to control the clearance between the plates 12 to be welded, in order to guarantee constant play, so as not to penalize the welding parameters.

This laser cutting process is for example carried out by means of the fixed support platforms 16 and mobile 18 previously described. The steel plates 12 are put in place on these support plates 16, 18 and held by the clamping means 24. Their opposite ends are then cut by means of a laser cutting tool to form the lateral edges 12C. . For example, the laser cuts of the two plates are made one after another with the same laser cutting tool.

The clamping means 24 are kept activated after the cutting, until the end of the welding, to limit any expansion of the plates 12 during the relaxation of the thermomechanical stresses due to cutting.

In a manner known per se, laser cutting is performed by means of a laser beam focused on the plate to be cut. The high power density causes a very rapid rise in temperature of the material, which then passes to the liquid state. Under the action of a gas, active (oxygen) or neutral (nitrogen), the molten metal is evacuated on the opposite side to the laser energy, creating the cutting bleed.

In the case of cutting under active gas, in particular under oxygen, an exothermic reaction is generated. Oxygen is then responsible for 50 to 70% of the cutting energy.

In the case of cutting under a neutral gas, the gas mainly has only two actions, namely to protect the cutting field in the liquid state of the oxidation, and to quickly expel the molten metal by mechanical effect.

Advantageously, in order to obtain lateral edges 12C of optimum shape, the laser cutting method according to the invention is a YAG laser cut (yttrium-aluminum garnet) under oxygen.

Alternatively, the method may be YAG laser cutting under nitrogen, CO2 laser cutting under oxygen, or any other laser cutting method possible.

Note that the invention is not limited to the embodiment described above, and could have various variants.

The method according to the invention is optimized for welding plates with thicknesses greater than 8 mm and with straight edges. More particularly, the method is optimized for DH36 grade steel plates with thicknesses substantially equal to 10 mm.

However, the method according to the invention is applicable to other materials and to other plate thicknesses, contrary to the methods known from the state of the art which are generally limited to a specific type of material, to a thickness precise and / or precise application, such a method of the state of the art does not allow to weld several materials and several thicknesses with the same equipment. The invention provides for increasing the versatility of the method, using the following steps. a) Firstly, a step of selecting the welding parameters according to the applications, the input parameters and the output target parameters, the geometry of the parts to be welded (edge to edge, T ... ), and / or metals to be welded. This selection step uses dedicated parameterization means, including in particular a database of the parameters of the assembly / welding defined according to the applications (material grades, parts to be welded, etc.), and modeling and simulation means. , with the parameters thus determined. b) A step is then made to determine (automatically) the effectors to be controlled, during which the number and position of the effectors (2, 3 ...), the choice of associated effectors and the mechanical / robotic system are determined. associated positioning and control, the modularity of the effectors, the composition of the electrodes and gases, the choice between sequential or simultaneous Arc and Laser, the appropriate effector head adaptable / modular / interchangeable, the type of wire used (poked / rutile ...), the scrolling speed, the choice of parameters on the source, the power, the orientation, the distance, the control system / speed temperature, etc. c) Finally, a step is provided for actuating and controlling the effectors using control means / software, using control / servo loops, zone / sample test loops, taking into account the relative positioning (to the nearest millimeter) of the parts to be welded and the effectors of welding.

It should be noted that the welding is preferably combined with other steps to optimize the welding, including cutting steps, conveying, use of robot / cobot, etc.

Finally, the welding can be optimized following inspections, including non-destructive testing (NDT), and / or by video image tracking, during welding or on the finished product.

Claims (10)

1. Hybrid laser-arc welding process, for assembling two steel plates (12) together along a weld line (14), wherein: - the two plates (12) respectively have substantially coplanar upper surfaces (12A) and substantially coplanar lower surfaces (12B), - the upper (12A) and lower (12B) surfaces of each plate define between them a thickness (E) greater than 8 mm, - the plates (12). ) each have a side weld edge (12C), the side edges (12C) of the plates (12) being arranged facing one another, and being substantially parallel to each other, a weld bead being made along of the weld line (14), at these side weld edges (12C), and - the weld bead is made by means of a hybrid welding tool (24) comprising: • a laser emitter (26) , capable of emitting a laser (28) along an emission axis (A), said laser (28) having a focal point (36) disposed between the upper (12A) and lower (12B) surfaces in the direction of the emission axis (A), and • an MAG welding torch (29), comprising a gas diffusion nozzle (30) and at least one filler wire (32) housed in the diffusion nozzle (30) and extending to a free end (34), characterized in that, in that considering a projection plane parallel to the upper surfaces (12A), the orthogonal projection of the focal point (36) and the orthogonal projection of the free end (34) of the filler wire (32) on this projection plane are spaced apart from each other. a distance (D) greater than or equal to 15 mm. The hybrid welding method according to claim 1, wherein said distance (D) is between 15 and 20 mm. Welding method according to claim 1 or 2, wherein the distance (DF) between the upper surfaces (12A) and the focal point (36) in the direction of the emission axis (A) is comprised between 2 and 6 mm, preferably equal to 4 mm. A welding method according to any one of the preceding claims, wherein the welding tool (24) is moved along the weld line (14) at a speed of between 1 and 2.5 meters per minute ( m / min), preferably substantially equal to 1.5 m / min. A welding method according to any one of the preceding claims, wherein the welding tool (24) is displaced in a direction of travel (S) along the weld line (14), the laser transmitter ( 26) precedes the welding torch (29) in this direction of movement (S). 6. Welding process according to any one of the preceding claims, wherein the laser (28) has a power of between 8 and 12 kW. The welding method according to any one of the preceding claims, wherein the filler wire (32) is a flux-cored wire, preferably a metal powder wire or a rutile wire. A welding method according to any one of the preceding claims, wherein the laser (28) is moved along the weld line (14) oscillating about this weld line (14), with an amplitude of oscillation between 1 and 3 mm, preferably substantially equal to 2 mm, the oscillation frequency of the laser (28) around the weld line (14) is preferably substantially equal to 500 Hz. A welding method according to any one of the preceding claims, wherein the weld side edges (12C) are previously made by a laser cutting method of a lateral end of each plate (12). 10. Welding process according to any one of the preceding claims, comprising a prior step of selecting welding parameters according to characteristics of the plates to be welded.