Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K26/00—Working by laser beam, e.g. welding, cutting or boring
  • B23K26/02—Positioning or observing the workpiece, e.g. with respect to the point of impact; Aligning, aiming or focusing the laser beam
  • B23K26/04—Automatically aligning, aiming or focusing the laser beam, e.g. using the back-scattered light
  • B23K26/044—Seam tracking
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K26/00—Working by laser beam, e.g. welding, cutting or boring
  • B23K26/02—Positioning or observing the workpiece, e.g. with respect to the point of impact; Aligning, aiming or focusing the laser beam
  • B23K26/04—Automatically aligning, aiming or focusing the laser beam, e.g. using the back-scattered light
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K26/00—Working by laser beam, e.g. welding, cutting or boring
  • B23K26/08—Devices involving relative movement between laser beam and workpiece
  • B23K26/10—Devices involving relative movement between laser beam and workpiece using a fixed support, i.e. involving moving the laser beam
  • B23K26/103—Devices involving relative movement between laser beam and workpiece using a fixed support, i.e. involving moving the laser beam the laser beam rotating around the fixed workpiece
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K26/00—Working by laser beam, e.g. welding, cutting or boring
  • B23K26/20—Bonding
  • B23K26/21—Bonding by welding
  • B23K26/24—Seam welding
  • B23K26/28—Seam welding of curved planar seams
  • B23K26/282—Seam welding of curved planar seams of tube sections

Definitions

• the present invention relates to a method and a device for carrying out the welding of two pieces placed end to end in the assembly position by a welding beam.
• the technique concerned may also be suitable for other point welding processes, such as those using the plasma torch, TIG, MIG, MAG, or electron beam type.
• the invention applies in particular to the welding of sections of tube intended to produce pipelines for the transport of hydrocarbons, in particular on the seabed.
• This welding can take place under difficult conditions, as is the case on a barge which is subjected to the movements communicated by the sea and to numerous vibrations generated by the equipment and the motors which it carries.
• a welding machine has already been designed comprising a fixed laser source which is arranged at a distance from the sections of tube to be connected and the beam of which is guided, using articulated optical path means, up to a laser head which carries a focusing device and which is fixed on a turntable around the axis of the tube sections held edge to edge by their ends.
• the plate is rotated by means of a first electric motor around the tube sections, by adjusting the position of the laser head by axial translation by means of a second electric motor.
• a first electric motor around the tube sections, by adjusting the position of the laser head by axial translation by means of a second electric motor.
• Such a device is described in French patent 93 04642 published under the number 2 704 166.
• Laser welding requires extremely precise positioning of the laser beam focused on the joint to be welded, i.e. +/- 0.2 mm.
• the joint tracking setting usually uses an eddy current sensor that is attached to the laser head.
• This joint tracking system guides the laser head but not the laser beam itself. Consequently, any defect in alignment of the optical path induces a difference between the position of the laser beam and the joint to be welded, which risks causing a defective weld, the kinematics of the laser beam cannot be deduced simply from the kinematics of the laser head.
• the eddy current sensor does not allow the joint to be detected in an edge-to-edge assembly without play.
• the present invention aims to achieve direct and precise control of the welding beam and its impact by controlling its position, where the welding plasma is formed, at the position of the joint to be welded.
• the subject of the invention is a method of welding two pieces placed end to end in the assembly position according to an assembly joint to be welded by means of a spot beam welding head, in particular with a laser beam.
• the joint is observed continuously, by means of a shooting device integral with the welding head, by moving the assembly of the welding head and the camera along the joint and by detecting the orthogonal position of the joint for each position of the assembly of the welding head and the camera, the impact position of said beam is continuously observed on said parts, and the configuration of an optical path for guiding said beam is controlled by slaving the impact position to the joint position detected in the control of a translation of the assembly of the welding head and the camera orthogonally to the joint.
• the image taking device can be constituted in particular by a camera, or more particularly, for locating a laser beam, by a CCD camera or an infrared camera.
• a welding plasma is thus monitored by slaving its position on the joint as a function of the joint position detected; in other words, the laser beam itself, and not the laser head only, is positioned on the joint to be welded, in real time. This makes it possible to obtain a positioning accuracy of the laser beam, therefore of the welding plasma created, which is sufficient to ensure good welding, unlike the prior techniques.
• the assembly of the welding head and of the imaging device is moved along the entire assembly joint and a mapping of the orthogonal positions of the joint with respect to a straight line parallel to the joint line, and during a subsequent welding phase, welding is carried out with servo-control of the position of the welding plasma during a second movement of the assembly the welding head and the camera along the joint, the welding beam then being in operation.
• the mark preferably consists of a band forming a collar
• the positioning of the assembly of the welding head and of the camera is obtained by an axial displacement relative to the axis of the tube sections
• the establishment of the mapping and the welding are obtained by an orbital movement around the tube sections.
• a collar has an axial mark, therefore along a generatrix of the parts, which determines by reference an initial position of the assembly of the welding head and of the camera during the orbital movement.
• an anti-dazzle screen and a filter are arranged between the camera and the welding plasma. This makes it possible to obtain a correct view of the mark during this welding phase and to attenuate and filter the plasma for a more precise detection of the latter.
• the optical observation beam of the image-taking device is divided into two parts separated in space, which are sent respectively to the vicinity of the mark and to that of the seal or of the plasma. welding. This allows the use of a low field objective, providing good precision, even in the case where the mark and the weld joint or the plasma are separated by a large distance.
• the invention also relates to a device for implementing the method defined above.
• the image taking device comprises a CCD type sensor, disposed upstream of the laser head with respect to the displacement along the assembly joint in order to leave the desirable place for the laser head downstream.
• the welding head it is advantageous for the welding head to include a focusing device with a beam return mirror mounted for rotation about its optical axis.
• the welding beam is advantageously guided using an optical path articulated to a laser head comprising a focusing device which is fixed on a turntable around the axis of the sections of tube held edge to edge by their ends.
• an optical path preferably comprises a first part, starting from the laser source, the means of which are arranged in floating mounting with all the degrees of freedom on a fixed plate, and a second part leading the beam from the first part to a focusing device which is fixed on a rotating plate which can rotate around the tube sections relative to the fixed plate.
• the floating assembly can in particular be achieved by means of a ball bearing placed on the fixed plate and supporting a device with free translation in the direction perpendicular to the fixed plate.
• a sliding connection involving for example polytetrafluoroethylene pads or an air cushion device, or a displacement table in XY coordinates with rotation.
• the first part of the optical path comprises an arm mounted with free articulation relative to an axis parallel to the fixed plate so as to obtain a variable inclination of said arm relative to the fixed plate.
• This first part of the optical path may include an arm, the two ends of which are mounted in rotation with respect to each other about the axis of the arm, this making it possible to obtain one of the degrees of freedom, here in rotation.
• FIG. 1 schematically represents the essential elements of a particular installation for implementing the invention
• Figure 2 illustrates the constitution of a mark
• Figure 3 is a flow diagram of a particular embodiment of the method according to the invention in the case where it involves a learning phase
• Figures 4 and 5 show, respectively in axial view and in radial view, the arrangement of the welding head and that of the camera in the direction of the joint to be welded
• - Figure 6 is a schematic side view of a welding device according to the invention, illustrating in particular the means of constituting the optical path of the laser beam to the welding plasma, in a preferred application for the welding of sections of tube held end to end
• Figure 7 is a perspective view of the welding device of Figure 6
• Figure 8 is a top view of the device of Figure 6
• FIG. 9 is a detailed view of FIG. 6.
• the invention relates to welding by a point impact beam, more particularly a laser beam, between two parts 22 and 23 which are placed end to end as illustrated in particular in FIG. 4, in an assembly position where they are joined together according to a joint to be welded 3.
• the laser beam 4 is driven in displacement along the joint 3. It is focused on this joint by means of a focusing head 43.
• the focusing must correctly align the laser beam 4 on the joint 3, otherwise the weld would not be good. We consider here that it is necessary to ensure a positioning at + or - 0.2 mm to obtain a correct weld, which is not possible when we are content to adjust only the position of the focusing head in case the we see that the beam is misaligned.
• the invention therefore proposes to provide a real-time control of the point of impact of the welding beam 4 as a function of the exact position of the joint perpendicular to the joint line which is crossed by the beam during the welding operations.
• the joint is observed continuously to detect its position, using a shooting device integral with the welding head, we proceed to a learning phase during which a mapping of the position of the joint is established for each position of the assembly of the welding head and of the camera along the joint, and, simultaneously or delayed, continuously observes the impact of the welding beam and its position is controlled by controlling a translation of the assembly of the welding head and of the image taking device orthogonally to the joint, that is to say perpendicular to the movement of the welding head along the joint line, as a function of the joint position detected according to said mapping.
• the position of the image of the welding plasma on the screen is controlled according to the position of the joint provided by the mapping, taking into account the distance separating the point of observation of the joint and that of the point of impact where the welding plasma is formed.
• the first movement corresponding to a learning phase
• the position of the joint is mapped
• the welding head is controlled by adjusting the position of the welding beam relative to to the joint by slaving according to this mapping.
• an optical marker 6 is advantageously used (see FIG. 3), formed in the form of a linear strip, which is fixed to one of the parts 22 or 23 along the joint 3.
• the mapping is made up of the distance measured continuously between the seal 3 and the mark 6 and the position of the head 43 is controlled so that the distance between the welding plasma and the mark 6 copies that of the seal for each position along the path of the seal when the head in the welding phase.
• the mark 6 illustrated in Figure 2 has a transverse mark 7, which identifies an initial position for the movements to be made along the joint.
• the longitudinal position can also be identified at any time using an encoder sensitive to angular intervals during the rotation of the welding head when welding tubes assembled end to end, or when it is moved in a plane in other applications, such as the welding of flat sheets edge to edge.
• FIG. 1 An installation for the implementation of the method of the invention. It includes a digital camera 8, for example a CCD camera, which simultaneously observes the mark 6 and the joint 3 or the welding plasma.
• a computer 9 preferably comprising a display screen 11, receives and processes data from the camera 8 as well as position data supplied to it by the servo motor 12 in orthogonal position and by the motor 13 for movement along of the joint.
• the computer establishes from this data the mapping of the position of the joint with respect to the reference frame and it develops and supplies to a variator 15 controlling the servo motor 12, displacement orders carrying out the adjustment of the orthogonal servo position, by through an entry / exit card 14.
• the mark is advantageously placed at a short distance from the seal, for example 20 mm, so as to have good size images of the seal, of the mark and of the plasma.
• the observation beam of the camera can be divided into two beams, for example by means of prisms or mirrors, from which we can distinguish, by techniques known per se, on the one hand the information relating to the reference, on the other hand that relating to the position of the welding beam or to that of the joint itself.
• FIG. 5 comes in addition to FIG. 4 to reveal the camera 47, referenced 8 in FIG. 1.
• This camera is mounted fixed on the same frame as the focusing head 43 of the figures.
• An anti-glare screen 48 is placed in the vision beam of the camera, in front of the plasma created in the vicinity of the joint 3 between the parts 22 and 23 during the welding phase, so as to clearly distinguish a reference mark illustrated at 46, which normally is not very bright. It is also possible to place a retractable filter 49 which makes it possible to refine the image of the plasma observed.
• a nozzle 51 is interposed in a conventional manner on the path of the focused laser beam, at the entrance to a visual confinement enclosure delimited by the screen 48.
• Figures 6 to 9 show an installation applying the method and the device according to the invention in the context of barge welding of tube sections placed end to end, in particular for the realization and laying of pipes for transporting hydrocarbons.
• the device of the invention comprises a fixed support 21, which supports a fixed laser source 27, which is arranged at a distance from the sections of tube to be connected 22 and 23.
• the laser welding beam coming from this source is guided by an optical path articulated towards a welding head 43 which is fixed on a plate 24 rotatably mounted in the plate 21.
• the rotating plate 24 is arranged coaxially with respect to the two sections 22 and 23 and it is driven in rotation about their axis 25 by a motor 26.
• the two sections of tube constituting the parts to be welded are maintained in the assembly position by any appropriate means, generally either by claws or external gripping collars, or by gripping systems with inflatable pads or suction cups introduced inside. . They are joined in jointed assembly position by their respective end faces.
• a first part is distinguished, starting from the laser source 27, which constitutes a floating assembly with all the degrees of freedom relative to the fixed plate 21, and a second part which follows to conduct the beam to the focusing head 43 carried by the turntable 24.
• the first part of the optical path comprises an arm 28, of fixed length, materialized by two tubular elements sliding relative to one another.
• a deflection mirror 29 is mounted for rotation about the vertical axis of a bent part 32, at the end of which is arranged another deflection mirror 33 rotating on horizontal axis.
• the beam is thus returned in a vertical direction, that is to say perpendicular to the fixed plate 21.
• the rotation of the mirror 29 allows an inclination of the arm 28 relative to the fixed plate 21.
• the assembly of arms 28 and 32 and of mirrors 29 and 33 is mounted in free translation in the vertical direction by sliding on a vertical rail secured to a vertical frame 35. At the upper end of the latter, a deflection mirror 30 directs the beam towards the second part of the optical path.
• This mirror 30 is mounted to rotate about a vertical axis so as to rotate the second part of the optical path relative to the first part parallel to the plate 21.
• the vertical frame 35 is mounted on the plate 21 with the possibility of free translation in two directions in the plane of the plate 21 and of free rotation along a vertical axis. This can be achieved by means of a ball bearing 36 rolling on a mat of balls arranged in the plate 21. It is also possible to use air cushions or pads made of low-slip polytetrafluoroethylene. As a variant, the same effects can also be obtained by means of an X-Y displacement table with a rotation system.
• the second part of the optical path comprises a telescopic arm 37 which receives the beam returned by the mirror 30 and which ensures a translational movement along its axis. It has at its end a pair of deflection mirrors 38 and 39 which serve to admit the beam into an arm 41, which is of fixed length.
• the arm 41 has at its other end a deflection mirror 42 which is rotatably mounted on a frame 45 for directing the beam on the focusing device 43.
• the latter is carried by a secondary frame 44 (FIG. 9) which is mounted mobile in vertical translation, under the control of the servo motor, relative to the frame 45 which is itself fixed on the rotary plate 24. It may also be useful to mount the focusing head 43 in rotation on the frame 44, around the vertical axis of rotation of the mirror 42, so as to adjust the angle of inclination of the beam in the plane of the joint 3 as desired.
• FIGS. 6 and 9 implies a continuous reference mark for lateral positioning which is constituted by a collar 46 carried by the section of tube 22, and the camera 47 is mounted on the frame 45.
• a first step 52 the laser head is positioned behind the mark 7 (fig. 2) by means of the motor 26 for driving the plate 24. the servo motor to search for the collar 46 in the field of the camera. When the collar is located, it is framed so as to perceive the joint 3.
• step 53 the learning phase is carried out by triggering an orbital path of the plate 24 around the sections 22 and 23.
• the collar-seal distance is continuously recorded as a function of the angular position of the plate, and when the mark 7 is again detected, the motor 26 is stopped and it goes into control mode.
• the collar is followed which is very regular, which limits the movements managed by the servo motor.
• step 54 the computer performs a processing of the acquired information by evaluating the missing data (joint not identified) or doubtful and the best analytical adjustment of the joint-collar distance is performed by interpolation. If necessary, a new learning phase can be ordered to refine the mapping.
• the welding is carried out.
• the laser head is positioned at the rear of mark 7 and the orbital movement is triggered.
• the servo system is switched to piloting mode of the welding beam, to ensure that the welding plasma is permanently repositioned directly above the joint to be welded throughout the movement orbital.
• the screens are placed in front of the camera and laser shooting is controlled. The servo continuously corrects the joint-collar distance from the recorded values provided by the learning map.
• the method according to the invention is also suitable for carrying out in addition a phase of quality control of the weld by analyzing the defects of the plasma, for example by examination of its shape or by detection of its possible extinction.
• the invention is in no way limited to the embodiment and it is possible to make modifications or variants.
• it can be applied to all spot beam welding operations requiring great positioning accuracy of the welding beam on the joint to be welded, however also it is easy to adapt to the control of a beam carrying out the welding. between two flat sheets kept in the edge-to-edge assembly position along a straight rectilinear joint line.
• the image taking device can be designed to distribute the visual observation of position detection into two different optical paths, or it can comprise two different devices, for observing the joint and the welding plasma respectively.
• the field of vision of the camera (47) can be divided by means of prisms or mirrors.
• a vision camera infrared to observe the welding plasma, the position of the plasma being determined by the epicenter of the image obtained.

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• Physics & Mathematics (AREA)
• Optics & Photonics (AREA)
• Engineering & Computer Science (AREA)
• Plasma & Fusion (AREA)
• Mechanical Engineering (AREA)
• Laser Beam Processing (AREA)

Applications Claiming Priority (3)

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• 1996
  • 1996-08-08 FR FR9610144A patent/FR2752180B1/fr not_active Expired - Lifetime
• 1997
  • 1997-08-06 US US09/147,651 patent/US6084203A/en not_active Expired - Lifetime
  • 1997-08-06 AU AU39456/97A patent/AU3945697A/en not_active Abandoned
  • 1997-08-06 WO PCT/FR1997/001459 patent/WO1998006533A1/fr not_active Application Discontinuation
  • 1997-08-06 EP EP97936746A patent/EP0921896A1/de not_active Ceased
• 1999
  • 1999-02-04 NO NO990514A patent/NO990514D0/no not_active Application Discontinuation

Non-Patent Citations (1)

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