FR3022479A1 - LASER WELDING APPARATUS FOR ASSEMBLING POLYMERIC PIECES - Google Patents

Abstract

The invention relates to a laser welding apparatus for assembling polymeric material parts, comprising a source for emitting a laser beam and a clamping device (1) superimposed on the parts, said clamping device being configured to exert, on the surface of one of the pieces, a bearing on an area of said surface not impacted by the laser beam, the clamping device (1) comprising a support and a rolling member (6) having a degree of freedom movement in own rotation relative to the support so as to be able to move by rolling on said surface, characterized in that the rolling member (6) comprises at least one additional degree of freedom of movement in rotation relative to the support.

Description

FIELD OF THE INVENTION The present invention relates in particular to a device and a method for joining parts by laser welding. More particularly, the assemblies of parts made of polymeric plastic materials, including thermoplastics, and in particular transparent or translucent parts, are aimed at. A preferred application relates to the automotive industry for the manufacture of parts of headlights or other beam projection and / or signaling elements. TECHNOLOGICAL BACKGROUND The industry, and especially the automotive industry, employs more and more specific design parts, sometimes with complex shapes. In some cases, typically for headlights or the like, the polymer material parts have a three-dimensional geometry. During manufacturing processes, it may be necessary to assemble several parts together to obtain the final monobloc system. Welding techniques employing a laser beam are known for this purpose. Generally, the parts to be assembled are superimposed and placed on a lower bearing surface. The welding device moves over this superposition so as to produce, with given parameters (eg feed rate, beam concentration and power), a weld bead at the interface between the rooms. The beam can be focused at this interface. A difficulty lies in the realization of this assembly by welding in view of the complexity of the parts and / or the need not to alter them during their joining. Document US-A1-2006 / 0144509 discloses an apparatus for welding molded thermoplastic parts comprising a source of a laser-type light beam and a device for holding the parts applied against each other. The latter device employs a wheel adapted to exert a bearing on the surface of one of the 35 pieces near the place where the laser beam applies heat to the parts to be welded, the wheel adjoining the beam. A disadvantage is that this technique can degrade the workpiece to which the wheel is applied which is damaging, especially when a quality surface condition is required, which is the case for functional or aesthetic optical parts. It should be understood that it is necessary for the wheel to strongly press on one of the parts to be welded so that the parts are in contact over the entire weld area. At the same time, the support of the wheel must be located to operate precisely near the beam and to marry the shapes of the room which it follows the surface. It is difficult or even impossible according to this prior art to exert sufficient effort for effective maintenance of parts during welding without damaging them.

The invention solves all or part of the disadvantages of current techniques. SUMMARY OF THE INVENTION One aspect of the invention relates in particular to a laser welding apparatus for assembling polymeric material parts, comprising a laser beam emission source and a superimposed clamping device. , said clamping device being configured to exert, on the surface of one of the parts, a bearing on an area of said surface not impacted by the laser beam, the clamping device comprising a support and a rolling member having a degree of freedom of movement in own rotation relative to the support so as to be able to move by rolling on said surface. Advantageously, this apparatus is such that the rolling member comprises at least one additional degree of freedom of movement in rotation relative to the support.

This arrangement improves the mobility of the rolling member on the workpiece. Indeed, the invention offers a capacity for adapting the position of the rolling member during its movement on the surface of the part. In this way the rolling member can move with rolling contact without friction or very little. On the manufactured parts, the result is an optimization of the final surface state because the part to which the rolling member applies is much less subject to scratches. In addition, the invention can advantageously follow the shapes of the parts to be welded so that the clamping effect of the rolling member is more continuous than before, even on highly curved parts. According to a non-limiting possibility, the at least one additional degree of freedom of movement in rotation comprises a pivot axis oriented in a direction perpendicular to a tangent to the rolling member at the point of contact of the rolling member on the area. In this situation, the additional degree of freedom is directly related to the direction in which the average reaction force of the workpiece to be welded during the support of the rolling member takes place. In an advantageous variant, the degree of additional freedom in rotation is limited. This avoids a rotational movement beyond a sufficient angular sector and prevents any inadvertent movement that could affect the advance of the rolling member on the surface of the workpiece.

In another embodiment, a plurality of rolling members are provided to distribute the clamping force at several locations around the laser beam. These members may be carried by a single support piece, for example forming a frame around the area where the laser beam is projected. The invention also relates to a laser welding method for assembling two polymeric pieces comprising the following steps: superimposing respective zones of the pieces; clamping the pieces by the surface of one of the pieces, exerting a bearing on an area of said surface not impacted by the laser beam by a rolling member; emission of a laser beam by a source so as to weld an interface portion of the two parts and simultaneous movement of the rolling member 20 and the laser beam relative to the two parts, the rolling member applying on the surface of one of the parts so as to move with a freedom of movement in own rotation, characterized in that the rolling member is left free in rotation according to an additional freedom of movement. The invention also relates to an assembly unit comprising an apparatus according to the invention, and at least two parts to be assembled in superposition and / or a base support for receiving said parts. BRIEF INTRODUCTION OF THE FIGURES Other features, objects and advantages of the present invention will be apparent from the following detailed description, and / or from the accompanying drawings given by way of non-limiting examples and in which: Figure 1 shows a perspective view of a first embodiment of the invention; FIG. 2 is a profile view of the embodiment of FIG. 1; FIG. 3 shows a sectional view along the lines A-A of FIG. 2 and an example of the relative position of a beam and of the clamping device; Figure 4 is a sectional view along the lines B-B of Figure 2; FIG. 5 illustrates another embodiment of the invention; - Figure 6 shows another configuration of the invention.

DETAILED DESCRIPTION Before going into detail of preferred embodiments of the invention with reference to the drawings in particular, other optional features of the invention, which can be implemented in combination in any combination or in combination with each other. alternatively, are indicated below: the at least one additional degree of freedom of movement in rotation comprises a pivot axis 8 directed in a direction perpendicular to a tangent to the rolling member 6 at the point of contact of the rolling member 6 on the surface; The pivot has a bounded angular deflection; the angular deflection is limited to an angular sector of less than 30 ° and preferably of 20 °; the support comprises a bearing 4 in which the pivot is located; the rolling member 6 is mounted on a bracket 5 configured to form the degree of freedom of movement in its own rotation; - The bearing 4 and the bracket 5 comprise stops cooperating so as to form the bounded angular deflection; the direction 9 of the degree of freedom of movement in its own rotation is perpendicular to the direction of the additional degree of freedom of movement in rotation; the rolling member 6 is a wheel; the wheel comprises a convex curvilinear tread profile, preferably in a portion of a circle; - The rolling member 6 has two additional degrees of freedom in rotation; The rolling member 6 is spherical; - The rolling member 6 is mounted in ball joint. - The clamping device 1 comprises a plurality of rolling members 6; the rolling members 6 are arranged so as to surround at least part of the laser beam 19; The rolling members 6 are uniformly spaced in a circle around the bundle 19; The support comprises a base 17 in which the rolling members 6 are mounted, the base 17 having a central hole 18 opening configured to pass the laser beam 19; the surface of the rolling member 6 adapted to be brought into contact with the surface of one of the parts is made of a material having a HRC hardness of greater than 56. the bearing member (s) and the source being arranged with in such a way that the rolling member is at a distance from the trajectory of the laser beam emitted by said source. Thus, the point of the rolling member intended to be in contact with the surface is at a distance from the trajectory of the laser beam emitted by said source and therefore at a distance from the zone impacted by the beam. An application of the invention is the production of elements from plastic parts. This will include thermoplastic polymers and parts may have all geometric configurations. Preferably, these parts 15 are in the form of thin layers, that is to say that they have a much smaller thickness in front of at least one other dimension. For example, a lighthouse optic element, in overall hull form, can be obtained by the invention. This assembly involves the at least partial overlap of two parts so as to allow a weld at their interface. This weld is advantageously obtained by localized heating to exceed the melting point of the material of at least one of the parts. The heating in question is produced by a light beam 19, advantageously laser, the room or parts through which the beam 19 being passed to be transmissive of the light in question (preferentially used transparent or translucent parts, for example in polycarbonate). Advantageously, the beam is focused so that its focus is on or near the interface between the parts to be welded. Thus, the caloric intake is limited outside this interface and the heating is concentrated at the location of the weld.

By way of example, the parts to be assembled can be received and maintained on a mounting bench on which they are superimposed. The beam 19 is carried by a welding head supporting the light source, the head being controlled in advance, for example along a three-dimensional path, to form a continuous weld seam or not between the two parts.

The beam 19 is typically of the laser type (acronym for "light amplification by stimulated emission of radiation", amplification of light by stimulated emission of radiation). The welding efficiency is impacted by possible contact defects between the two parts to be welded. To ensure good contact at the interface of the parts, the invention also implements a clamping device 1. The latter exerts a bearing on the surface (opposite to the interface piece / piece) of one of the 5 pieces. This support is preferably located and located near the place of the weld. For example, the support is shifted laterally of the beam 19 in the direction of advance of the latter during welding. As an illustration, this offset may be less than a value of 2 to 5 cm. To achieve the support without seriously damaging the surface quality of the workpiece, the support is preferably effected by limiting the friction, by means of a rolling member 6, such as a wheel. Advantageously, the wheel follows the path of the beam 19 during welding, with a proper rotation around its axis 9 of symmetry. In order to optimize the action of the rolling member 6 and to limit or even eliminate the degradation of the surface of the part to be welded, the invention proposes a welding apparatus which adds a freedom of movement to the body welding. A first example is illustrated in Figures 1 to 4. In this example, as in that of Figure 5, a single rolling member 6 is illustrated. It is understood that this case is not limiting and that the teaching of the invention, in particular with reference to this embodiment, can be applied to a plurality of rolling members 6. Moreover, The apparatus of the invention may comprise more than one laser beam. Figure 1 shows an example of the clamping device 1 adapted to generate a support on one of the parts to be assembled. Within the welding apparatus, this device can be integrated into an assembly with a laser beam source, this assembly being movable as welding takes place, relative to the parts to be assembled. The clamping device 1 has in the example an arm 3 connected, by an upper end, to a fixing portion 2 adapted to bring the device to the rest of the movable welding assembly. At its lower end, the arm 3 receives a bearing 4 which is preferably the locus of a hinge, here in the form of a pivot of rotation axis 8. This articulation allows a movement of the lower part of the device 1 relatively to the part comprising the arm 3. The lower part comprises, as in Figure 1, a bracket 5 carrying at its lower end, a shaft 10 on which is rotatably mounted, the rolling member 6 here in the form of a wheel .

Figures 3 and 4 show an example of this mounting of the wheel on the shaft 10, via a shoulder of the shaft and a retention by a nut. This example is schematic and any other arrangement allowing a clean rotation of the wheel about the axis 9 is possible. On the other side of the bracket 5, a shaft 10 is received in the bearing 4, via a bearing arrangement 7.

It will be understood that the rolling member 6 then has two rotational mobilities. One is provided by its own rotation about the axis 9, the other by the pivot along the axis 8. According to one possibility, the axes 8 and 9 are perpendicular but this is not mandatory.

For example, the axis 9 may be inclined so that the wheel does not fit in a vertical plane and / or parallel to the beam 19 and / or perpendicular to the force of the support on the surface. It is advantageous that the axis 8 is directed in the direction of the reaction force produced by the surface of the workpiece to be welded to the rolling member 6 during clamping. The contact of the rolling member 6 on the workpiece being usually punctual and the direction of the axis 9 may correspond to the direction of a straight line perpendicular to the tangent to the wheel at the point of contact with the workpiece. Still in a nonlimiting manner, the axes 8 and 9 are not concurrent. The axis 8 may be located in a plane further forward in the direction of advance of the apparatus during welding. This favors the maintenance of the trajectory of the rolling member 6. This offset emerges, for example, from FIGS. 2 and 3. To prevent the incursion of the rolling member 6 into angular sectors that are too oblique relative to the plane perpendicular to its axis 9 the degree of additional freedom of movement formed by the axis pivot 8 can be limited to a bounded angular sector. This angular limitation is, in the embodiment of Figures 1 and 4, produced by the cooperation of stops respectively formed on the shaft of the bracket 5 and the bearing 4. In Figure 3, the bearing 4 has an opening 12 s' extending in a plane perpendicular to the axis 8. The shaft of the bracket 5 comprises a stop 13 30 inserted into this opening 12, the ends of the latter limiting the relative angular movement. For example, a travel of less than 30 °, especially 20 °, preferably centered on the direction of advance of the apparatus may be suitable. Figures 3 and 4 show moreover that the axis 9 at the right of which occurs the support 35 of the wheel on the workpiece may be in the same plane as the axis of the beam 19 laser.

Moreover, the plane defined by the axis 9 and the bearing point of the rolling member 6 on the workpiece may be parallel to the axis 8. Preferably, the rolling member 6 has a hardness HRC (according to the Rockwell hardness standard) greater than 50, and preferably greater than or equal to 56. It is advantageously made of steel. While one would have thought that the rolling member 6, due to a virtually punctual support on the workpiece, could degrade it even more strongly by being hard, the invention has highlighted, at the contrary, a high hardness promotes frictionless rolling and without degradation of the workpiece. In the case where the rolling member 6 is a wheel, the latter advantageously has a convex curvilinear profile on the tread, as is apparent from Figures 3 and 4. A profile in a circle portion is preferred. The contact on the workpiece is all the more precise in this configuration. The rolling member 6 may also be a sphere as in the examples of Figures 5 and 6. The invention also does not exclude combining rolling members 6 of 15 different shapes, wheels and spheres in particular. In Figure 5, the rolling member 6 is a single sphere. It is rotatably mounted in a base 17 fixed to the arm 3. For example, the base 17 comprises a first 14 and a second 15 connectable parts and defining an overall interior volume of housing of the sphere, the latter protruding from the housing by a Hole 16 traversing the second portion 15. It will be understood from this embodiment that the rolling member 6 may have more than one additional rotational mobility. In this case, in addition to the proper rotation corresponding to the follow-up of the advance movement of the rolling member 6 in contact with the surface of the workpiece, there are two additional mobilities and a ball joint is formed. It may be advantageous to distribute the clamping support around the bundle 19, as shown in FIG. 6. The clamping device 1 comprises a base 17 in which several rolling members 6 are mounted, for example in the form of spheres, with a ball joint with 3 degrees of freedom in rotation. It could also be wheels with two degrees of freedom in rotation. The spheres protrude, as in the case of Figure 5, towards the surface of the workpiece here following a same plane. Two arms 3 serve to support the base 17. The base 17 is configured to position the rolling members 6 around the beam 19. The base 17 of Figure 6 is a closed form completely surrounding the beam 19, with a passage in form Hole 18 in the center for said beam 19. The base 17 may have an annular shape. The rolling members 6 may be evenly distributed around the base 17. By way of illustration, the passage at the center of the base 17 may be circular, in particular with a diameter of 1 to 3 mm greater than that of the beam 19. at the entrance to the hole 18. Still by way of example, balls of the order of 1.5 to 2.5 mm may be suitable in this example. Note that the mounting of the rolling members 6 or on the rest of the clamping device 1 may include other mobilities, such as a damping. In addition, in the case of FIG. 6, a pivot between the arms 3 can make it possible to improve the adaptation of the contact of the rolling members 6 to the part to be welded, this pivot being able to be of axis perpendicular to the advance of the clamping device 1 during welding. The invention is not limited to the previously described embodiments but extends to all embodiments in accordance with his spirit.

3022479 10 REFERENCES 1. Clamping device 2. Clamping part 3. Arm 4. Bearing 5. Stem 6. Rolling member 7. Bearing 8. Rotating shaft 9. Rolling shaft 10. Shaft 11. Bearing surface 12. Opening 13. Stop 14. First housing part 15. Second housing part 16. Hole 17. Base 18. Hole 19. Beam

Claims (20)

REVENDICATIONS1. Laser welding apparatus for assembling polymeric material parts, comprising a laser beam emission source and a superimposing clamping device (1), said clamping device being configured to exert on the surface one of the parts, a support on an area of said surface not impacted by the laser beam, the clamping device (1) comprising a support and a rolling member (6) having a degree of freedom of movement in its own rotation relative to the support so as to be able to move by rolling on said surface, characterized in that the rolling member (6) has at least one additional degree of freedom of movement in rotation relative to the support. 2. Apparatus according to the preceding claim wherein the at least one additional degree of freedom of movement in rotation comprises an axis pivot (8) directed in a direction perpendicular to a tangent to the rolling member (6) at the point of contact of the rolling member (6) on the surface. 3. Apparatus according to the preceding claim wherein the pivot has a bounded angular deflection. 4. Apparatus according to the preceding claim wherein the angular deflection is limited to an angular sector of less than 30 ° and preferably 20 °. 5. Apparatus according to one of claims 2 to 4 wherein the support comprises a bearing (4) in which is located the pivot. 6. Apparatus according to one of the preceding claims, wherein the rolling member (6) is mounted on a bracket (5) configured to form the degree of freedom of movement in own rotation. 7. Apparatus according to the two preceding claims in combination and in combination with one of claims 3 or 4, the bearing (4) and the bracket (5) comprise stops cooperating to form the bounded angular deflection. 8. Apparatus according to one of the preceding claims wherein the direction (9) of the degree of freedom of movement in own rotation is perpendicular to the direction of the degree of freedom of movement additional rotation. 9. Apparatus according to one of the preceding claims wherein the rolling member (6) is a wheel. 10. Apparatus according to the preceding claim wherein the wheel (6) comprises a convex curvilinear tread profile, preferably in a portion of a circle. 3022479 12 11. Apparatus according to claim 9 or 10, wherein the wheel (6) comprises an axis (9) of symmetry around which it is rotatable to roll on said surface, and wherein the at least one degree of freedom of movement additional rotation comprises an axis pivot (8), said pivot axis (8) and said axis (9) of symmetry being perpendicular. 12. Apparatus according to claim 1 wherein the rolling member (6) has two additional degrees of freedom in rotation. 13. Apparatus according to the preceding claim wherein the rolling member (6) is spherical. 10 14. Apparatus according to the preceding claim wherein the support comprises a housing in which the rolling member (6) is mounted in ball joint. 15. Apparatus according to one of the preceding claims wherein the clamping device (1) comprises a plurality of rolling members (6). 16. Apparatus according to the preceding claim wherein the rolling members (6) are arranged to surround at least in part the beam (19) laser. 17. Apparatus according to the preceding claim wherein the rolling members (6) are uniformly spaced in a circle around the beam (19). 18. Apparatus according to the preceding claim, the support comprising a base (17) in which the rolling members (6) are mounted, the base (17) having a central hole (18) opening configured to let the beam (19). laser. 19. Apparatus according to one of the preceding claims wherein the surface of the rolling member (6) adapted to be brought into contact with the surface of one of the parts is a material having an HRC hardness greater than 56. 20. Laser welding process for assembling two polymeric parts 25 comprising the following steps: superimposition of respective zones of the parts; - Tightening parts by the surface of one of the parts, exerting a bearing on an area of said surface not impacted by the beam (19) laser by a rolling member (6); 30 - emission of a laser beam (19) by a source so as to weld an interface portion of the two parts; - Simultaneous movement of the rolling member (6) and the laser beam (19) relative to the two parts, the rolling member (6) applying to the surface of one of the parts so as to move with a freedom of movement. movement in clean rotation, characterized in that the rolling member (6) is left free to rotate according to an additional freedom of movement.