FR2829416A1 - Method, for fabricating light metal honeycomb structure involves laser welding of corrugated or crenellated segments formed for a light metal strip - Google Patents

Abstract

The fabrication of a light metal honeycomb structure by laser welding consists of: (1) forming, by plastic deformation, several segments from a light metal strip with a predefined width corresponding to the thickness of the honeycomb structure, in order to give a corrugated or crenellated longitudinal profile to each segment; (2) feeding and positioning a first segment to a laser welding station; (3) feeding and positioning a second segment to the laser welding station so that the hollows of the corrugations or crenellations of the second segment coincide with the summits of the corrugations or crenellations of the first segment; (4) pressing the first and second segments against each other to put these hollows and summits into contact; (5) laser welding to form a linear transverse joint in each contact zone; (6) stopping the pressing action; (7) repeating the foregoing stages with each subsequent segment to form the complete honeycomb structure. Independent claims are also included for: (a) a device for the fabrication of a light metal honeycomb structure by laser welding; (b) a light metal honeycomb structure thus obtained; (c) a lightweight sandwich panel incorporating such a honeycomb structure.

Description

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 The present invention relates to a method for manufacturing a honeycomb structure of light metal by laser welding, in particular for the construction of lightweight sandwich panels of the type comprising a honeycomb structure core and two facing plates fixed respectively on each side of the soul. The present invention also relates to a device for carrying out this method and a honeycomb structural core of light metal obtained by said method.

Minutes du 6ème Colloque International sur le Soudage et la Fusion par Faisceaux d'Electrons et Laser-CISFFEL-15-19 juin 1998, Toulon, France). Cet article indique, page 297, que les panneaux sandwichs avec âme constituée par une structure en nid d'abeille sont onéreux, ne résistent pas au feu et ne sont pas soudables. Cet article décrit donc un procédé et un appareillage pour la fabrication de panneaux sandwichs en acier, dans lesquels l'âme est constituée par plusieurs bandes ajourées en acier, qui sont disposées de chant, parallèlement les unes aux autres et maintenues dans cette position avec un espacement approprié par des moyens temporaires de calage et de serrage, pendant qu'une tôle supérieure en acier et une tôle inférieure en acier sont successivement fixées par soudage au laser respectivement sur les tranches supérieure et inférieure desdites bandes ajourées en acier. Light sandwich panels or lightweight structural panels (PSL) and their applications in many areas of the art are now well known (see for example the article "LASER WELDING OF STEEL SANDWICH PANELS", by P. PATOU et al, pages 291 to 298 of Volume 1 of

Minutes of the 6th International Symposium on Welding and Fusion by Electron Beams and Laser-CISFFEL-15-19 June 1998, Toulon, France). This article states, page 297, that honeycomb-core sandwich panels are expensive, non-fireproof and non-weldable. This article therefore describes a method and an apparatus for the manufacture of steel sandwich panels, in which the core is constituted by several perforated steel strips, which are arranged in singing, parallel to each other and held in this position with a suitable spacing by temporary clamping and clamping means, while a steel upper plate and a lower steel plate are successively fixed by laser welding respectively on the upper and lower edges of said perforated steel strips.

 However, honeycomb structures of light metal such as aluminum or an aluminum alloy are already known. A first technique of manufacturing these honeycomb structures is illustrated schematically in Figure 1 of the accompanying drawings. An aluminum strip 1 having a relatively large width W is unwound from a roll 2 and is then cut into rectangular sheets, such as sheet 3, having a relatively large width W and length L. Several parallel bands of adhesive 4 are then deposited longitudinally on the upper face of each sheet 3 and the sheets 3 and lined with adhesive strips are stacked in a package 5 until said package reaches a desired thickness T. The adhesive strips 4 are deposited on the successive sheets 3 of such

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 so that the adhesive strips of any sheet are offset laterally by half a step from the adhesive strips of the previous sheet and the next sheet. In other words, in the package 5, the adhesive strips are arranged in staggered rows. Then, each package 5 is cut transversely into several packages, such as the package 6, having a dimension l equal to the thickness 1 desired for the honeycomb structure. Then, each package 6 is subjected to a stretching operation. For this purpose, the upper sheet 6a and the lower sheet 6b of each package 6 are subjected to traction forces directed in opposite directions, as indicated by the arrows F1 and F2, so as to obtain the honeycomb structure 7 desired.

 Lightweight honeycomb structures made by this first technique and lightweight sandwich panels incorporating such honeycomb structures have a number of disadvantages. The bonded joints of the honeycomb core have a relatively poor strength because the drawing operation mentioned above has the effect of weakening their strength. The two facing plates can not be attached to the honeycomb core by welding or brazing because the high temperature at which the honeycomb core would be subjected during the welding or soldering operation would further weaken or even destroy the glued joints of the honeycomb core. The two facing plates are therefore usually attached to the honeycomb core by gluing. The aging over time of bonded bonds is a major problem of this type of assembly because it depends on the quality of the glues used.

 In addition, the aforementioned stretching operation is difficult to achieve and it is difficult to obtain a honeycomb structure 7 whose cells have a regular and uniform geometry on the entire surface of the structure, when the package 6 from which the structure is formed comprises a large number of sheets or strips of light metal and / or when the sheets or strips of light metal constituting the package 6 have a relatively large thickness. The sheets or strips of light metal, in particular aluminum, used for the manufacture of honeycomb structures according to this first technique therefore usually have a thickness of less than 0.2 mm. As a result, the honeycomb structures produced by this first technique have an insufficient level of resistance.

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 for certain applications, such as for the construction of chassis of motor vehicles, rail, nautical or aeronautical, for the construction of technical floors in buildings or for the realization of shock absorbing elements that can be integrated into the design of various structures, and in general for all applications that require lightweight sandwich panels incorporating such honeycomb structures to have a high resistance to fatigue, tensile, compressive, shear, bending or shocks.

 In addition, the honeycomb structures obtained by this first technique are sensitive to corrosion. Indeed, the bonded bonds of the honeycomb structure prohibit any treatment against corrosion, such as for example by dipping in chemical or electrolytic baths.

 A second technique has also been proposed for the manufacture of honeycomb structures of various metals, such as aluminum, stainless steel and titanium (see US 5,437,936, US 5,609,288 and EP). 0 703 841). This second technique differs from the first technique described above with reference to Figure 1, essentially by the fact that the adhesive strips 4 are replaced by laser welded joints. Again, after the sheets or strips of metal have been laser-welded two by two, the resulting sheet or strip package is subjected to a drawing operation to obtain a honeycomb structure.

 Compared to the first manufacturing technique using glued joints, this second technique of manufacturing with laser welded joints makes it possible to improve the properties of the honeycomb structure with regard to durability and resistance to corrosion ( the honeycomb structure can indeed be treated against corrosion by soaking in chemical or electrolytic baths).

 However, again, the drawing operation does not make it possible to use sheets or metal strips having a relatively large thickness for the manufacture of the honeycomb structure. Thus, the three documents mentioned above indicate that the thickness of the metal sheets or strips is between 0.025 and 0.152 mm, usually between 0.05 and 0.127 mm. As a result, the honeycomb structures produced by this second technique and the sandwich panels

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 incorporating such honeycomb structures still have insufficient strength for the above-mentioned applications, which requires that the sandwich panels have high strength in use.

 In addition, because of the small thickness of the sheets or metal strips constituting the honeycomb structure, the realization of laser welded joints is extremely delicate because the depth of penetration of the laser beam must be controlled with great precision. If the depth of penetration is insufficient, we will obtain welded joints with a resistance too low. Conversely, if the depth of penetration is too great, it is possible to form welded joints connecting more than two sheets or metal strips at a time and preventing the structure from deploying correctly during the subsequent drawing operation.

 In addition, still because of the small thickness of the sheets or metal strips constituting the honeycomb structure, it is not possible to weld metal inserts in the cells of said structure. Indeed, the metal inserts usually used to connect the sandwich panels to each other in a complex structure or to connect some of the sandwich panels to a suitable support structure, or to connect other elements to the sandwich panels, have a thickness much larger material than the metal sheets or strips constituting the honeycomb structure. As a result, the power that would be required to weld such metal inserts into the cells of the honeycomb structure would be too great for the metal sheets or strips constituting said structure and would result in a cutting of said metal sheets or strips to the place of the desired welds.

 The object of the present invention is therefore to provide a method for manufacturing, by laser welding, a honeycomb structure from a strip of light metal, for example aluminum or aluminum alloy, which can if desired, have a much greater thickness than that of the metal sheets or strips which can be used in the two aforementioned known processes, and which makes it possible to obtain, if desired, a honeycomb structure having a resistance mechanical much larger than that of honeycomb structures obtained by known methods.

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 The subject of the invention is therefore a process for manufacturing a lightweight metal honeycomb structure by laser welding, characterized by the steps of: a). forming, by plastic deformation, several segments of a light metal strip having a predefined width corresponding to the desired thickness of the honeycomb structure, to provide a corrugated or crenellated longitudinal profile to each segment of the metal strip lightweight ; b). bringing and positioning a first corrugated or crenulated longitudinal profile segment of the light metal strip to a laser welding station; c). bringing and positioning a second segment with a corrugated or crenellated longitudinal profile of the light metal strip at the laser welding station, such that the recesses of the corrugations or crenals of said second segment are in agreement with the peaks of the corrugations or crenals of said first segment ; d). clamping said first and second segments against each other so as to set the valleys of the corrugations or crenals of said second segment in contact with the peaks of the corrugations or crenals of said first segment; e). forming, by laser welding, a transverse linear welded joint in each contact zone between the apices and recesses of the corrugations or crenals of said first and second segments, for fixing said first and second segments together; f). to stop said clamping; g). repeat steps c) and f) with each subsequent segment of the light metal strip, as many times as necessary until the resulting honeycomb structure has a desired size corresponding to an integer multiple of 1 amplitude of the corrugations or crenals of the segments of the light metal strip, and to remove the honeycomb structure of the welding station.

 Since in the process according to the invention the segments of the metal strip are waved or crenulated before the segments of the strip are welded in pairs to each other, it is no longer necessary to perform a drawing operation or deployment of a package of metal strips as was the case in known processes, drawing or deployment operation which required the use of thin metal strips,

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 therefore easily deformable, so that the tensile forces used during the drawing or deployment operation does not weaken the strength of previously bonded joints or welded seams. With the method according to the invention, it becomes therefore possible to use, if desired, segments of metal strips having a much greater thickness than in the case of known methods.

The thickness of the segments of the light metal strip can be as large as 1 mm or more, and it is only limited by the power of the forming means used to give each segment of the strip its wavy or crenellated shape.

- le sectionnement de la bande continue de métal léger est effectué pendant que le ou les segments est ou sont dans un état serré ; - le sectionnement de la bande continue de métal léger est effectué avant l'étape de formation des joints soudés linéaires transversaux pour les segments d'ordre pair, et après l'étape de formation des joints soudés linéaires transversaux pour les segments d'ordre impair. The method according to the invention may furthermore have one or more of the following features: the step of forming by plastic deformation consists in passing a continuous strip of light metal between two toothed wheels whose teeth have a profile corresponding to said longitudinal profile corrugated or crenellated; the continuous strip of light metal is advanced between the two toothed wheels in steps of a length corresponding to the desired length for each of said segments of the continuous strip of light metal, and after each step the continuous strip of light metal is cut to detach the most forward segment; the continuous strip of light metal is cut by means of the laser used to form said transverse linear welded joints;

the sectioning of the continuous strip of light metal is carried out while the segment or segments is or is in a tight state; the cutting of the light metal continuous strip is carried out before the step of forming the transverse linear welded joints for the even order segments, and after the step of forming the transverse linear welded joints for the odd order segments .

 The invention also relates to a device for the manufacture of a honeycomb structure of light metal by laser welding, characterized by: a). forming means for forming, by plastic deformation, a plurality of segments of a light metal strip having a predefined width corresponding to the desired thickness of the honeycomb structure, to provide a corrugated or crenellated longitudinal profile at each segment of the light metal band;

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b). a laser welding station; c). means for sequentially bringing said segments with a corrugated or crenellated longitudinal profile to the laser welding station and for positioning said segments each time in such a way that the hollows of the corrugations or crenals of the segment lastly brought and positioned at the laser welding station are in concordance with the vertices of the corrugations or crenals of the segment previously brought and positioned at the laser welding station; d). clamping means for clamping together the segments supplied and positioned at the laser welding station so as to each time the hollows of the corrugations or crenals of the segment last brought and positioned at the laser welding station in contact with the peaks of the corrugations or crenals of the previously brought and positioned segment of the laser welding station; e). said laser welding station having means capable of forming a transverse linear welded joint in each contact zone between the peaks and valleys of the corrugations or crenches brought into contact by the clamping means
The device according to the invention may furthermore have one or more of the following features: it comprises a supply reel carrying, rolled up on it, a continuous strip of light metal of said predefined width, and said deformation forming means comprise two toothed wheels whose teeth have a profile corresponding to said corrugated or castellated longitudinal profile, and which are arranged between the supply reel and the laser welding station so as to act respectively on the opposite faces of the continuous strip of light metal passing the two wheels toothed during its movement from the supply reel to the laser welding station, at least one of the two gears being connected to rotating drive means; the rotational drive means comprise a motor; said supply and positioning means comprise said toothed wheels, a first fixed guide which extends from the exit side of the nip zone of the two gears to the entrance of the laser welding station, and a second guide that is mobile between a first position in which it extends the

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 first fixed guide and forms with the surface of a support plate a guide tunnel for said segments successively brought to the laser welding station, and a second position in which the second guide is spaced from said support plate, said support plate being arranged such that said segments are edged on the surface of the support plate; said clamping means comprise a support plate which is carried by the support plate and which extends along a first side of the second guide when the latter is in its first position, a movable clamping plate which extends parallel to the backing plate on a second side of the second guide, and actuating means for moving the movable clamping plate towards and away from the backing plate when the second guide is in its second position; - The movable clamping plate carries, on its face facing the support plate, a plurality of positioning projections adapted to engage tightly in some of the corrugations or crenals of the first segment of the continuous strip of light metal brought to the welding station laser when the movable clamping plate is moved for the first time to the support plate by the actuating means; the bearing plate bears, on its face facing the movable clamping plate, a plurality of positioning elements which each have a concave shape complementary to the shape of a vertex of the corrugations or crenals of the segments of the continuous strip of light metal and which are able to receive some of the peaks of the corrugations or crenals of the segment recently brought to the laser welding station; the support plate is movable in a direction parallel to the longitudinal direction of the segments of the light metal continuous strip between a first position in which the said positioning elements are situated respectively opposite the positioning projections carried by the plate; mobile clamping each time an odd order segment is brought to the laser welding station, and a second position which is shifted from the first position by a distance corresponding to half a step of the corrugations or crenals of the segments of the strip continuous light metal every time an even order segment is brought to the laser welding station;

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 the movable clamping plate carries holding gripping means capable of grasping and retaining the first segment of the continuous strip of light metal fed to the laser welding station, when the movable clamping plate is moved for the first time towards the support plate, such that said first segment and any subsequent segment, which was subsequently secured by welding to the first segment or to an intermediate segment, can be moved together with the movable clamping plate away from the plate support for enabling the second guide to be placed in its first position and bringing a new segment of the continuous light metal strip between the support plate and the segment or segments attached to the movable clamping plate; said means for forming the transverse linear welded joints comprise a laser having a focusing head which is directed towards the face of the support plate opposite to the face of the support plate facing towards the mobile clamping plate, and said support plate comprises, for the passage therethrough of the laser beam, a light which has a corrugated or crenal shape, whose corrugations or crenals have an amplitude greater than the width of the light metal strip and a pitch corresponding to that of the corrugations or crenals of the segments of said light metal strip; the laser is carried by a support which is movable at least in a first direction perpendicular to the support plate and in a second direction perpendicular to the first direction and parallel to the supply direction of the segments of the light metal strip at the laser welding station; the carrier carrying the laser is also movable in a third direction perpendicular to said first and second directions; the focusing head of the laser comprises scanning means arranged to force the laser beam to scan in a third direction perpendicular to said first and second directions.

 the laser is mounted in a fixed position and is connected by an optical fiber to the focusing head which can be moved in three directions, namely a first direction perpendicular to the support plate, a second direction perpendicular to the first direction and parallel to the longitudinal direction of the segments of the

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 light metal strip at the laser welding station, and a third direction perpendicular to the first and second directions.

 The subject of the invention is also a honeycomb structure made of light metal obtained by the process according to the invention as defined above, as well as a light sandwich panel comprising a core with a honeycomb structure made of metal. light and two light metal facing plates, which are respectively fixed on each side of the core, the latter having a honeycomb structure manufactured by the method according to the invention.

- la figure 5 est une vue à échelle agrandie du détail V de la figure 4H ; - la figure 6 est une vue en perspective éclatée d'un panneau sandwich léger incorporant une structure en nid d'abeille selon l'invention. Other characteristics and advantages of the invention will emerge more clearly on reading the following description of an embodiment of the invention given by way of example with reference to the appended drawings, in which: FIG. 1 is a view in perspective illustrating schematically the successive steps of a known method of manufacturing a honeycomb structure; - Figure 2 shows schematically a device according to the invention for the manufacture of a honeycomb structure; FIG. 3 is a front view of a support plate forming part of the device of FIG. 2; - Figures 4A to 4H are partial views of the device of Figure 2, illustrating successive steps of the method according to the invention for the manufacture of a honeycomb structure;

FIG. 5 is an enlarged view of the detail V of FIG. 4H; - Figure 6 is an exploded perspective view of a lightweight sandwich panel incorporating a honeycomb structure according to the invention.

 Referring to FIG. 2, an embodiment of a device 10 according to the invention can be seen for the manufacture of a lightweight metal honeycomb structure. The device 10 essentially comprises shaping means 11 for giving a corrugated or castellated longitudinal profile to a strip 12 made of light metal, for example aluminum or aluminum alloy, advancing and guiding means 13 for bringing sequentially and positioning successive segments of the strip 12 shaped by the forming means 11 at a welding station at

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 laser 14, and clamping means 15 capable of clamping the segments of the strip 12 which have been brought and positioned at the welding station 14, each time a new segment is brought and positioned at said welding station.

 In the embodiment shown in Figure 2, the device 10 includes a supply reel 16 which carries a reserve of light metal strip 17 in the form of a roll. The forming means 11 comprise a pair of gears 18 and 19 which are arranged between the supply reel 16 and the welding station 14, respectively on either side of the path of the strip 12 of light metal unwound from the In this case, the two toothed wheels 18 and 19 constituting the forming means 11 advantageously have both a forming function to give the strip 12 the desired corrugated or corrugated longitudinal profile and a driving function for unwind the strip 12 from the supply reel 16 and bring said strip, in corrugated or crenated form, into the welding station 14.

 The band 12 has a width which is for example between 4 mm and 50 mm and which is equal to the desired thickness of the honeycomb structure to be manufactured.

 The forming means 11, the advancing and guiding means 13, the clamping means 15 and the supply spool 16 are mounted on a common support plate 21 which is part of a frame of the device 10. In FIGS. and 3, there is shown a system of reference axes XYZ, whose horizontal axis X is parallel to the direction of advance of the strip 12 and the vertical axis Z is perpendicular to the plane of FIG. case, Figure 2 is a plan view of the device 10 and the plate 21 is horizontal. However, the plate 21 could just as easily be arranged vertically.

 The support plate 21 carries drive means, such as, for example, a geared motor unit 22, able to rotate at least one of the two toothed wheels 18 and 19. For example, the toothed wheel 18 is fixed to the shaft output 23 of the geared motor unit 22, while the toothed wheel 19 is mounted idle on an axis 24. However, if necessary, the toothed wheel 19 could also be rotated by the geared motor unit 22 via a transmission appropriate.

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 Preferably, the spacing of the two toothed wheels 18 and 19 can be adjusted according to the thickness of the strip 12. For example, the axis 24 of the toothed wheel 19 can be carried by a carriage (not shown) which can be moved relative to the support plate 21 in a direction parallel to the Y axis, as indicated by the double arrow F3, under the action of a clamping system (not shown), for example a clamping system screw, with manual or motorized control.

 The teeth of the two toothed wheels 18 and 19 have a profile corresponding to the desired profile for the corrugations or crenals to be formed on the strip 12. If the tops of the teeth and the interdental hollows of the two toothed wheels have a rounded profile, at the output of the forming means 11 the strip 12 will have a corrugated longitudinal profile having substantially the shape of a sinusoid. However, it may be preferred that the teeth of the two toothed wheels 18 and 19 have a trapezoidal or substantially trapezoidal profile, in order to give the band 12 a crenellated longitudinal profile, which makes it possible to obtain a good contact surface against surface (instead linear tangential contact in the case of a sinusoidal longitudinal corrugated profile) between the peaks and troughs of the segments of the strip 12 which are brought and positioned as will be seen later in the welding station 14. Preferably, the two inserted wheels 18 and 19 are detachably mounted on the pins 23 and 24 so that they can be exchanged with other pairs of toothed wheels having tooth profiles and / or numbers of teeth different from those gears 18 and 19, depending on the shape and / or dimensions of the corrugated or crenellated profile desired for the strip 12 of light metal.

 In addition to the two gears 18 and 19, the advancing and guiding means 13 comprise a pair of fixed guides 25 and 26 and a movable guide 27, which extend parallel to the axis X. The two guides 25 and 26 extend from the exit side of the nip zone of the two gears 18 and 19 to the inlet of the welding station 14. Preferably, the two guides 25 and 26 are mounted on the support plate 21 of such that their spacing is adjustable so as to be adjustable as a function of the amplitude of the corrugations or crenals of the corrugated or crenellated profile of the strip 12. The guide 27 is constituted by a U-section section, which can be moved by actuating means not shown in a direction parallel to the Z axis between a first position in which the guide 27 extends the

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 channel formed between the two guides 25 and 26 and forms with the surface of the support plate 21 a guide tunnel for the segments of the strip 12 successively brought to the welding station 14, and a second position in which the guide 27 is spaced apart of said support plate 21.

 The clamping means 15 comprise a support plate 28 which is carried by the support plate 21 and which extends along a first side of the guide 27 when the latter is in its first position, a movable clamping plate 29 which extends parallel to the support plate 28 on a second side of the guide 27, and actuating means 31, partially shown in Figure 2, to move the movable clamping plate 29 in a direction parallel to the Y axis, towards and away from the support plate 28 as indicated by the double arrow F4, when the guide 27 is in its second position. The actuating means 31 may comprise for example at least one linear actuator such as a hydraulic or pneumatic cylinder or a screw jack driven by an electric motor step. The movable clamping plate 29 is guided on the support plate 21 between two guides 32 and 33 which extend parallel to the axis Y. The guide 32, located on the inlet side of the welding station 14, is a fixed guide while that the guide 33 is preferably adjustable in a direction parallel to the axis X, so as to be adjustable in spacing relative to the guide 32 as a function of the length of the segments of the strip 12 successively brought to the welding station 14, therefore according to one of the two dimensions of the surface of the honeycomb structure to be manufactured.

 The movable clamping plate 29 carries, on its face facing the support plate 28, a plurality of positioning projections 34 adapted to engage tightly in some of the corrugations or crenals of the first segment SI of the strip 12 fed to the welding station 14, when the movable clamping plate 29 is moved for the first time to the support plate 28 by the actuating means 31. The movable clamping plate 29 further carries gripping and retaining means 35 capable of gripping the first segment SI of the strip 12 when the movable clamping plate 29 is moved for the first time to the support plate 28, and to retain said first segment SI against said movable clamping plate 29 for the duration of the process of manufacture of the honeycomb structure. For example, the gripping and retaining means 35 may consist of ratchets that are mounted

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 pivoting on the movable clamping plate 29 about an axis parallel to the axis X, each pawl being adapted to snap behind the first segment SI of the band 12 in one of the recesses of the corrugations or crenals of said first segment SI, as shown in Figure 5. Preferably, each pawl 35 is biased by a spring (not shown) to its latching position. Thus, each time that the movable clamping plate 29 is moved in one or the other direction of the double arrow F4 by the actuating means 31, the first segment S1 and any subsequent segment subsequently fixed by welding to this first segment SI or an intermediate segment can be moved together with the movable clamping plate 29 is away from the support plate 28 to allow the introduction of the guide 27 in its first position and the supply of a new segment of the strip between the support plate 28 and the segment or segments attached to the movable clamping plate 29, or to the support plate 28, to allow clamping, between the two plates 28 and 29, segments attached to the plate 29.

 The bearing plate 28 carries, on its face facing the movable clamping plate 29, a plurality of positioning elements 36 which each have a concave shape complementary to the shape of a vertex of the corrugations or crenals of the segments of the strip 12. The support plate 28 is movably mounted on the support plate 21 in a direction parallel to the X axis between a first position in which the positioning elements 36 are located respectively opposite the positioning projections 34 carried by the movable clamping plate 29 whenever an odd order segment is fed to the welding station 14, and a second position is shifted from the first position by a distance corresponding to half a step of the corrugations or crenals of the segments of the strip 12 each time an even order segment is brought to the welding station 14. A linear actuator (not shown) can be provided to move the support plate 28 from its first to its second position and vice versa.

 Preferably, the two plates 28 and 29 of the clamping means 15 can be interchanged with other similar plates whose number and / or shape of the positioning protrusions 34 and positioning elements 36 are adapted to the length of the segments. the strip 12 and / or the shape and pitch of the corrugations or crenals of the segments of said strip.

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 At the welding station 14 is a laser 37 having a focusing head 38 which is directed towards the face of the support plate 28 opposite to that which faces the movable clamping plate 29. The support plate 28 comprises a light 39 for passing therethrough of the beam of the laser 37. As shown in FIG. 3, the light 39 has a wavy or crenellated shape, whose corrugations or crenals have an amplitude greater than the width of the strip 12 and a pitch corresponding to that of the corrugations or crenals of the segments of said strip 12.

 Different types of laser can be used for the laser 37, such as solid lasers (YAG laser), diode lasers, or gas lasers (CO2 laser). A nozzle (not shown) connected to an inert gas source may be attached or disposed around the focusing head 38 of the laser 37 to supply an inert protective gas to the welding zone.

 The laser 37 is carried by a support (not shown), such as for example a gantry, which can perform at least two movements, namely a first movement in a direction parallel to the Y axis, as indicated by the double arrow F5 in FIG. 2, and a second movement in a direction parallel to the X axis, as indicated by the double arrow F6 in FIG. 2. In a first embodiment, the support of the laser 37 may furthermore perform a third movement in a direction parallel to the Z axis. The three movements of the laser support 37 are respectively controlled by motors (not shown) such as electric stepper motors, which are connected to a central control unit (not shown) which controls the various motors and actuators of the device 10 according to the invention. In particular, the two motors that control the movements of the laser support 37 along the two axes X and Z are controlled by the central control unit so that the laser beam emitted by the laser 37 describes a trajectory 41 (FIG. ) which has a rectangular waveform corresponding to the mean line of the light 39 of the support plate 28. It will be noted that the two motors controlling the movements of the laser support 37 along the two axes X and Z could be controlled by the central control unit such that the trajectory described by the laser beam has a sinusoidal or substantially sinusoidal waveform having the same period as the rectangular waveform of the trajectory 41.

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 In another embodiment, the laser support 37 may be movable only in directions parallel to the X and Y axes, and the laser focusing head 38 may include scanning means (not shown) arranged to force the laser beam. to scan in a direction parallel to the Z axis under the action of a suitable engine. Again, the motor controlling the displacement of the support of the laser 37 along the axis X and the motor controlling the scanning along the axis Z are controlled by the central control unit so that the beam emitted by the laser 37 describes a trajectory having a rectangular waveform such as the trajectory 41 of FIG. 3, or a trajectory having a sinusoidal or substantially sinusoidal waveform.

 The device according to the invention operates in the following manner. First, the guide 27 is placed in its first position between the support plate 28 and the movable clamping plate 29, the support plate 28 is placed in its first position in which its positioning elements 36 are located opposite the positioning protrusions 34 of the movable clamping plate 29, the laser 37 is brought into the position shown in solid lines in FIG. 2 and a coil 16 provided with a roll 17 of a light metal band , for example aluminum, is placed on the support plate 21. Then, the front end of the strip 12 is engaged between the two toothed wheels 18 and 19 and the geared motor unit 22 is turned on so as to rotate the two toothed wheels 18 and 19 respectively in the directions indicated by the arrows F7 and F8 in FIGS. 2 and 4A. As a result, the two toothed wheels 18 and 19 advance the strip 12 in the direction of the X axis and, simultaneously, give to said strip 12, by plastic deformation, a corrugated or crenellated profile. The band 12 thus shaped then passes between the two guides 25 and 26, then in the guide 27. When the front end of the band 12 reaches a position corresponding to a desired length for the first segment of the band 12, for example in a position close to the end of the movable clamping plate 29 on the side of the guide 33, a suitable sensor or proximity sensor (not shown) placed in this position, such as a photocell or a microcontact, sends a stop signal to the central control unit, which then causes the gearmotor unit 22 to stop and, immediately after, the retraction of the guide 27 to its second position in

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 which it is no longer between the support plate 28 and the movable clamping plate 29, as shown in Figure 4B.

 Then, the central control unit activates the actuating means 31 associated with the movable clamping plate 29 so as to move the latter in the direction of the arrow F9 (FIG. 4C) so as to clamp the first segment SI of the strip 12 during the displacement of the plate 29, the positioning protrusions 34 of this plate 29 and the positioning elements 36 of the support plate 28 come into contact with each other. taken with some of the corrugations of the first segment SI of the band 12 in order to precisely position said segment SI and tighten it firmly between the two plates 28 and 29. At the same time, the catches 35 come to grip the segment SI to maintain it against the movable clamping plate 29.

 Then, the central control unit causes the laser 37 to move in the direction of the arrow F 10 (FIG. 4C) in order to engage the front end of the focusing head 38 of the laser in the first vertical part 39a (FIG. 3) of the light 39 of the support plate 28, and to bring said front end in the immediate vicinity of the strip 12. Then, the central control unit momentarily activates the laser 37 and moves the latter in a parallel direction to the Z axis for a distance at least equal to the width of the strip 12, as indicated in 4 la in Figure 3, to cut the strip 12 to detach the SI segment.

 Then, the central control unit activates the actuating means 31 associated with the movable clamping plate 29 so as to move the latter and the segment SI in the direction of the wire arrow (FIG. 4D) by an amount sufficient to that the guide 27 can be brought back to its first position between the plates 28 and 29. At the same time, the central control unit causes the laser 37 to move in the direction opposite to the arrow FIO of FIG. 4C, FIG. an amount just sufficient to pull the front end of the focusing head 38 of the laser 37 out of the first vertical portion 39a of the lumen 39 of the backing plate 28.

 Then, the central control unit activates the actuator associated with the guide 27 in order to bring the latter back to its first position between the two plates 28 and 29 as shown in FIG. 4E, and it activates at the same time the actuator

<Desc / Clms Page number 18>

 associated with the support plate 28 so as to move the latter in the direction of the arrow F12 by an amount corresponding to half a pitch of the corrugations or crenals of the segment SI. The laser 37 is also displaced by the same amount in the direction of the arrow F12. Then, the central control unit turns on again the geared motor unit 22 to advance the band 12 between the two guides 25 and 26 and in the guide 27, in a direction parallel to the axis X, while putting in the form of said strip 12 under the action of the two toothed wheels 18 and 19, until the aforementioned detector or sensor detects that the front end of the second segment S2 of the strip 12 has reached a position in which this end is substantially aligned with the corresponding end of the SI segment. At this moment, the hollows of the corrugations or crenals of the segment S2 are respectively in agreement with the peaks of the corrugations or crenals of the segment SI, and the central control unit causes the gearmotor group 22 to stop.

 Then, the central control unit activates the actuator associated with the guide 27, so as to retract the latter as shown in FIG. 4F, then it activates the actuating means 31 associated with the movable clamping plate 29, so that to clamp together the two segments S1 and S2 between the two plates 28 and 29 as indicated by the arrow F13 in Figure 4G. Then, the central control unit causes the laser 37 to move in the direction of the arrow F14 in order to engage the focusing head 38 of the laser in the first vertical portion 39a of the light 39 of the support plate 28. Then, the central control unit causes the laser 37 to move along the Z and X axes, from the position shown in solid lines to the position shown in dashed lines in FIG. 4G so that the laser beam describes the trajectory 41 shown in Figure 3. At the beginning of the path 41, that is to say in its first vertical portion which is in agreement with the first vertical portion 39a of the light 39, the power of the laser 37 is set to a relatively large value for severing the band 12 as indicated at 41a, in order to detach the second segment S2. Then, the power of the laser can be adjusted to a relatively lower value, sufficient for welding, to form, in agreement with each of the following vertical portions of the lumen 39, a transverse linear welded seam in each contact zone between them. vertices and valleys of the first and second segments SI and S2, as indicated at 41b to 411 in

<Desc / Clms Page number 19>

 Figure 5). For welding, the power of the laser 37 can be adjusted so that the welding is carried out in partial penetration, that is to say on the entire thickness of the segment S2 and on a part of the thickness of the SI segment. However, the power of the laser can be advantageously adjusted so that the welding is carried out in total penetration, that is to say on a depth corresponding to the sum of the thicknesses of the two segments S1 and S2, as shown in FIG. In the latter case, thanks to the wavy shape of the segments S1 and S2, there is no risk that the segment SI is also welded to the movable clamping plate 29 to the right of each welded joint, including the right projections In this regard, it will be observed in FIG. 5 that each positioning protrusion 34 has a height h smaller than the depth of the corrugations or crenals of the segment SI.

Similarly, when the hollows of the corrugations of the next segment S3 of the strip 12 are welded to the vertices of the corrugations of the segment S2, there is no risk that the joints welded between the segments S2 and S3 interfere with the segment SI .

 After the welded joints 41a to 411 have been formed, the central control unit activates the actuating means 31 associated with the movable clamping plate 29 so as to move the latter in the direction indicated by the arrow F15 on the FIG. 4H, in an amount sufficient for the guide 27 to be brought back to its first position between the two plates 28 and 29.

 Then, the operations described with reference to FIGS. 4E to 4H are repeated to effect the welding of the third segment 83 of the strip 12 on the second segment S2, except that in this case the support plate 28 is moved in the opposite direction to that of the arrow F12 of FIG. 4E of a half-pitch of the corrugations or crenals of the segment S2, and that the laser 37 is moved from the position shown in dotted lines to the position shown in solid lines in FIG. 4G, to form successively the welded joints 441 to 41a, the sectioning of the band 12 at 41a to detach the segment S3 is here performed at the end of the welding operation.

 For the next segment of the band 12, ie the fourth segment S4, the operations are repeated in exactly the same manner as those described with reference to FIGS. 4E to 4H with respect to the segment S2, and so on. for the following segments of the strip 12. The operations described above are continued until the honeycomb structure thus formed has, in the direction of the Y axis,

<Desc / Clms Page number 20>

 a desired dimension corresponding to an integer multiple of the amplitude of the corrugations or crenals of the segments S1, S2, S3, S4 ... of the band 12.

 Then, the honeycomb structure thus obtained is removed from the welding station 14. For this, after moving the movable clamping plate 29 in the direction of the arrow F15, it is necessary to release the segment SI which is attached to the plate 29 by the pawls 35. The release of the segment SI can be performed for example by means of a pusher (not shown) operated manually or automatically using an actuator controlled by the central control unit, said pusher being able to act simultaneously on all pawls 35 to bring them to an erased position in which they release the SI segment.

 Reference is now made to FIG. 6, which is a fragmentary exploded perspective view of a lightweight sandwich panel 50 comprising a core 51 of honeycomb structure made of light metal, for example aluminum or aluminum alloy. and two facing plates 52 and 53, also of light metal, for example aluminum or aluminum alloy. As shown, the core 51 is composed of several segments S1, S2, S3 ... SIC ... of a strip of light metal, which have been put into a corrugated or crenellated form and welded in pairs by means of of the device 10 of Figure 2. The two facing plates 52 and 53 can be fixed respectively on each side of the core 51 by conventional methods, such as by gluing or brazing.

Example 1
Several samples of sandwich panels with honeycomb core were made of an alloy of aluminum and magnesium, state Oit111, hot rolled, supplied by the company ALMET-PECHINEY under the reference AG3 5754, whose chemical composition is of 96% by weight of Al, 3% by weight of Mg and 1% by weight of Si, Fe, Cu, Mn, Cr, Zn and Ti.

 The honeycomb core 7 of the samples was made in accordance with the known method described above with reference to FIG. 1, from strips of said aluminum and magnesium alloy having a thickness of 60 μm. The glue used was a glue marketed by STRUCTIL under the reference ST 1035.

The glue strips 4 had a width of about 3mm and a spacing pitch of about 6.7mm from the middle in the middle of two adjacent strips of glue. The

<Desc / Clms Page number 21>

 The honeycomb structure 7 obtained after drawing had a thickness t of 13 mm, and each of its cells had substantially the shape of a hexagon of which two opposite sides each had a length of about 3 mm and whose remaining four sides each had a length of about 3.7 mm.

 The two facing plates of each sample were cut from a sheet of said aluminum and magnesium alloy having a thickness of 1.5 mm and were bonded to the honeycomb core 7 by means of the adhesive mentioned above. , reference ST 1035. The samples thus obtained had a total thickness of 16 mm and a bulk density of 0.60 g / cm 3 (measured on a parallelepiped-shaped sample of 60 × 60 × 16 mm 3).

Example 2
Several samples of sandwich panels with honeycomb core were made of the same alloy of aluminum and magnesium as for example 1.

 The honeycomb core 51 was manufactured in accordance with the method according to the invention from a strip 12 of said alloy having a thickness of 0.5 mm and a width of 13.6 mm. The corrugations of the segments S1, S2, S3 ... of the strip 12 had an amplitude of 10 mm, a pitch of about 34.6 mm, and a substantially trapezoidal shape with horizontal high and low bearings having a length of 5 mm. mm and connecting to oblique flanks approximately 4.13 mm long, inclined at 60 with respect to the top and bottom bearings, by rounded portions having a radius of about 5.7 mm.

 The laser used for the welding of the segments SI, S2, S3 ... and for the cutting of the strip 12 was a continuous laser TRUMPF HI 4006D having a rated power of 4 kW and connected by an optical fiber of diameter 600 μm and length 50 m to a focusing and welding head having a focal length of 150 mm and giving a focal spot of 450 μm in diameter. For welding, the power of the laser was set at 3.2 kW and the laser beam moving speed at 18 m / min. However, by adjusting the power of the laser to a higher value, it is possible to increase the speed of displacement of the laser beam, thus reducing the time of use of the laser, which is an important factor with regard to the cost of the laser. manufacture of the core 51. For the cutting of the strip 12, the

<Desc / Clms Page number 22>

 Laser power was set at about 3 kW and an inert gas was projected under relatively high pressure (about 106 Pa) over the welding area.

 The two facing plates 52 and 53 of each sample were cut from a sheet of said aluminum and magnesium alloy having a thickness of 1.2 mm and were bonded to the honeycomb core 51 by means of the above-mentioned adhesive, reference ST 1035. The samples thus obtained had a total thickness of 16 mm and a bulk density of 0.57 g / cm 3 (measured on a parallelepiped-shaped sample of 70 × 70 × 16 mm 3).

 The samples of Examples 1 and 2 were submitted on the one hand to static tests under different modes of stress and on the other hand to endurance tests. The static tests were carried out first at room temperature (25 C) and with a relative humidity of 50% RH, then at a temperature of 70 C with a humidity of 100% RH. The endurance tests were performed at room temperature (25 C) with a moisture content of 50% RH.

a). des essais de cisaillement, selon la norme ASTM C273-94, sur des échantillons de forme générale parallélépipédique ayant un volume initial V 0 égal à 3 200 x 50 x 16 mm3, les efforts de cisaillement étant appliqués aux plaques de parement des échantillons dans des directions opposées parallèles aux côtés les plus longs (200 mm) desdites plaques de parement ; b). des essais de compression à plat, selon la norme ASTM C365-94, sur des échantillons de forme générale parallélépipédique ayant un volume initial Vo égal à 60 x 60 x 16 mm3 pour les échantillons de l'exemple 1 et égal à 70 x 70 x 16 mm3 pour les échantillons de l'exemple 2, les efforts de compression étant appliqués perpendiculairement aux plaques de parement desdits échantillons ; et c). des essais de flexion 4 points, selon la norme ASTM C393-94, sur des échantillons de forme générale parallélépipédique ayant un volume initial Vo égal à

3 300 x 60 x 16 mm3, l'une des deux plaques de parement des échantillons reposant sur deux points d'appui espacés d'une distance d de 260 mm et une charge étant appliquée à l'autre plaque de parement en deux points situés entre les deux points d'appui précités et espacés de ceux-ci d'une distance d/4 égale à 65 mm. The static tests consisted of:

at). shear tests, according to ASTM C273-94, on parallelepiped-shaped general samples having an initial volume V 0 equal to 3200 x 50 x 16 mm3, the shear stresses being applied to the facing plates of the samples in opposite directions parallel to the longer sides (200 mm) of said facing plates; b). flat compression tests, according to the ASTM C365-94 standard, on parallelepiped-shaped general samples having an initial volume Vo equal to 60 × 60 × 16 mm 3 for the samples of example 1 and equal to 70 × 70 × 16 mm 3 for the samples of Example 2, the compression forces being applied perpendicular to the facing plates of said samples; and c). 4-point bending tests, according to ASTM C393-94, on parallelepiped-shaped general samples having an initial volume Vo equal to

3,300 x 60 x 16 mm3, one of two sample facing plates resting on two support points spaced a distance d of 260 mm and one load applied to the other facing plate at two points located between the two abutting points and spaced therefrom by a distance d / 4 equal to 65 mm.

<Desc / Clms Page number 23>

 The endurance tests consisted of 4-point bending tests, according to the same ASTM C393-94 standard and samples having the same shape and initial volume 25 C-50% RH 70 C-100% RH as for static 4-point bending tests. Bending forces were applied to the two-point sample facing plates and two load application points having the same d and d / 4 spacings as for static bending tests, and the load was varied. sinusoidally applied with a load ratio Rp equal to 0.1 and a frequency f equal to 5 Hz.

 The results of the static tests and endurance tests are shown respectively in Tables 1 and 2 below.

TABLE 1

<Tb>
<tb> Tests <SEP> V0
<tb> static <SEP> C0 <SEP> C1 <SEP># / C0 <SEP># (C1) <SEP> C0 <SEP> C1 <SEP># / C0 <SEP># (C1)
<tb> Tests <SEP> of <SEP># M = 1,52MPa <SEP># M = 2, <SEP> 60MPa <SEP> + 71% <SEP> 4% <SEP> TM = 1, <SEP> 34MPa <SEP> TM = 1, <SEP> 27MPa-5%
<tb> Shear <SEP> G = 134MPa <SEP> G = 738MPa <SEP> + 450% <SEP> 11% <SEP> G = 41MPa <SEP> G = 90MPa <SEP> + 120%
<tb><SEP> assay of <SEP># M = 3, <SEP> 07MPa <SEP># M = 12, <SEP> 7MPa <SEP> + 314% <SEP> 0, <SEP> 6% <SEP > cM = 2, <SEP> 85MPa <SEP> aN4 = <SEP> 1 <SEP> 2, <SEP> 4MPa <SEP> + 335% <SEP> 1%
<tb> Compression
<tb> to <SEP> flat <SEP> E = 837MPa <SEP> E = I, <SEP> 48GPa <SEP> + 77% <SEP> 13% <SEP> E = 1, <SEP> 032GPa <SEP> E = 1, <SEP> 55GPa <SEP> + 50% <SEP> 28%
<tb> Assay <SEP> of <SEP> F = 2, <SEP> 5mm <SEP> F = 8, <SEP> Omm <SEP> + 220% <SEP> 38% <SEP> F = 2, <SEP > 07mm <SEP> F = 2.20mm <SEP> + 6%
<tb> Bending <SEP> 4
<tb> points <SEP> -c = 1, <SEP>63MPa't = 3, <SEP> 0IMPa <SEP> + 85% <SEP> 10% -r = 1, <SEP> 49MPa <SEP> T = 0, <SEP> 84MPa-44%
<Tb>
TABLE 2

<Tb>
<tb> Endurance tests <SEP><SEP> C0 <SEP> C1
<tb> ChargeMAX <SEP> ChargeMAX
<tb><SEP> Test Conditions <SEP> N <SEP> N
<tb> (Newton) <SEP> (Newton)
<tb> (Newton) <SEP> (Newton)
<tb> 1 <SEP> 400 <SEP> 4 <SEP> 700 <SEP> 000
<tb> 1500 <SEP> 1 <SEP> 000 <SEP> 000
<tb> 25 C-50% <SEP> RH <SEP> 1 <SEP> 750 <SEP> 246 <SEP> 000
<tb> Bending <SEP> 4 <SEP> points <SEP> 2 <SEP> 000 <SEP> 80 <SEP> 000 <SEP> 2 <SEP> 000 <SEP>> 1 <SEP> 000 <SEP> 000
<tb> V0 = 300x60x16mm3 <SEP> 2 <SEP> 400 <SEP> 17 <SEP> 000 <SEP> 2 <SEP> 400 <SEP> 1 <SEP> 000 <SEP> 000
<tb> d / 4 = 65mm <SEP> 3000 <SEP> 900 <SEP> 000
<tb> Report <SEP> of <SEP> load <SEP>: <SEP> Rp = 0, <SEP>! <SEP> 4000 <SEP> 280 <SEP> 000
<tb> Sinusoidal <SEP> cycle <SEP> f = 5Hz <SEQ> 4500 <SEP> It <SEP> 000
<tb> 5000 <SEP> 500
<Tb>

<Desc / Clms Page number 24>

In Tables 1 and 2, the CO entries are for the sandwich panel samples made according to Example 1, while the CI entries are for the sandwich panel samples made according to Example 2; the inputs / CO represent the difference (in%) between the test results concerning the samples of Example 2 (entries C1) and the test results concerning the samples of Example 1 (CO entries); the A (CI) inputs represent the standard deviations of the test results for the samples of Example 2; the symbol T represents the maximum shear stress causing a separation of the facing plates from the honeycomb core of the samples or rupture of the glued or welded joints of said core during the shear tests; the symbol G represents the apparent shear modulus; the symbol CM represents the maximum compressive stress; the symbol E represents the compression module of the honeycomb core; the symbol F represents the length of the arrow in the middle of the length of the samples deformed by bending; the symbol T represents the shear stress in the core of the samples, which caused the facing plates to peel away from the core or rupture of the bonded or welded joints of said core of the samples during the bending tests; loadMAX and N represent respectively the maximum load and the number of cycles which caused a separation of the facing plates from the core of the samples or a rupture of the glued or welded joints of said core during the endurance tests.

 In conclusion, from a mechanical point of view, the static tests demonstrate the high potential of sandwich panels (CI) according to the invention compared with known sandwich panels (CO): a). + 300% for the maximum stress in compression; b). + 220% for the maximum deflection allowed by the flexural structure; c). + 450% for the apparent shear modulus; d). for these three modes of loading, a substantial gain in the energy absorbed by the deformation.

 These results suggest an improvement in collision resistance, also called crash resistance.

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The general endurance behavior of the sandwich panels (C1) according to the invention is better than that of the known sandwich panels (CO), because, at equal number of cycles, they are able to withstand higher loads. In addition, the scale of the charges is greater for the panels (C1) according to the invention than for known panels (CO).

 Note also that the improvement of the mechanical properties of the sandwich panels (CI) according to the invention is accompanied by a decrease (about 5%) of the apparent density of said panels (CI) relative to the known panels (CO) , despite a substantial increase in the thickness of the aluminum strips from which the honeycomb core of the panels is made (0.5 mm for IC panels instead of 60 u. m for CO panels) and despite a relatively small decrease in the thickness of the facing plates (1.2 mm for IC panels instead of 1.5 mm for C0 panels). The reduction in weight, of equal volume, and the significant improvement in the mechanical properties of resistance and endurance, which are allowed by the invention, are particularly advantageous in industries such as, for example, the automotive, aeronautical or space industries, where both weight reduction and improved resistance and endurance of building materials are sought.

 It goes without saying that the embodiment of the invention which has been described above has been given by way of purely illustrative and non-limiting example, and that many modifications can be made by those skilled in the art. without departing from the scope of the invention. Thus, for example, the forming of the strip 12 could be performed, particularly in the case where the strip 12 has a large thickness, by means of two pairs of toothed wheels arranged successively between the coil 16 and the pair of guides 25 and 26, namely a first pair of gears for preforming and a second pair of gears for finishing forming. Alternatively, the forming of the band 12 could be effected by means of a press interposed between the coil 16 and the pair of gears 18, 19, the latter then serving only to advance the band 12 shaped toward the welding machine 14.

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 Instead of being performed by means of the laser 37, the severing of the band 12 in several segments can be performed by mechanical shearing means.

 In another variant, the strip 12 can be shaped and cut into several segments S1, S2, S3... In a first machine, and the segments can then be successively welded two by two in a second machine. transfer being provided to seize one by one the segments at the output of the first machine and to bring them and position them in the second machine.

 In another embodiment, instead of the pawls 35, it is possible to use, for example, a vacuum system for grasping and holding the first segment S1 against the movable clamping plate 29.

 In another embodiment, instead of moving the laser 37 along the three axes X, Y, Z, it is possible to use a laser mounted in a fixed position and connected by an optical fiber to a focusing and welding head. which can be moved along the three axes X, Y, Z.

Claims (22)

A method of manufacturing a lightweight metal honeycomb structure (51) by laser welding, characterized by the steps of: a). forming, by plastic deformation, several segments (S1, S2, S3 ...) of a strip (12) of light metal having a predefined width corresponding to the thickness of the honeycomb structure, to give a profile longitudinal corrugated or crenellated at each segment of the light metal band; b). bringing and positioning a first segment (SI) of corrugated or crenated longitudinal profile of the light metal strip to a laser welding station (14); c). bringing and positioning a second segment (S2) with a longitudinal or crenellated profile of the light metal strip at the laser welding station, such that the hollows of the corrugations or crenals of said second segment are in agreement with the peaks of the corrugations or crenals of said first segment; d). clamping said first and second segments (S1, S2) against each other so as to place the corrugations or crenellations of said second segment in contact with the peaks of the corrugations or crenals of said first segment; e). forming, by laser welding, a transverse linear welded joint (41a, 41b, 41c ...) in each contact zone between the peaks and valleys of the corrugations or crenals of said first and second segments, for fixing said first and second second segments to each other; f). to stop said clamping; g). repeat steps c) and f) with each subsequent segment (S3, S4 ...) of the light metal strip as many times as necessary until the resulting honeycomb structure has a dimension desired corresponding to an integer multiple of the amplitude of the corrugations or crenals of the segments of the light metal strip, and to remove the honeycomb structure of the welding station.  2. Method according to claim 1, characterized in that the step of forming by plastic deformation consists of passing a continuous strip (12) of light metal between two toothed wheels (18,19) whose teeth have a profile corresponding to said longitudinal profile corrugated or crenellated. <Desc / Clms Page number 28>  3. Method according to claim 2, characterized in that the continuous strip (12) of light metal is advanced between the two toothed wheels (18,19) in steps of a length corresponding to the desired length for each of said segments (SI , S2, S3 ...) of the continuous strip of light metal, and after each step the continuous strip of light metal is cut to detach the most forward segment.  4. Method according to claim 3, characterized in that the continuous strip (12) of light metal is cut by means of the laser (37) for forming said transverse linear welded joints (41a, 41b, 41c ...).  5. Method according to claim 4, characterized in that the cutting of the continuous strip (12) of light metal is performed while the segment or segments is or are in a tight state.  6. Method according to claim 5, characterized in that the cutting of the continuous strip (12) of light metal is performed before the step of forming the transverse linear welded joints for even order segments (S2, S4. .), and after the step of forming the transverse linear welded points for the odd order segments (S3, S5 ...).  7. Device for the manufacture of a honeycomb structure (51) made of light metal by laser welding, characterized by: a). forming means (11) for forming, by plastic deformation, a plurality of segments (S1, S2, S3 ...) of a strip (12) of light metal having a predefined width corresponding to the desired thickness of the structure honeycomb, to give a corrugated or crenellated longitudinal profile to each segment of the light metal strip; b). a laser welding station (14); c). means (11, 13, 34, 36) for sequentially bringing said corrugated or crenellated longitudinal profile segments to the laser welding station (14) and for positioning said segments each time such that the hollows of the corrugations or crenals of the segment recently brought and positioned at the laser welding station are in agreement with the peaks of the corrugations or crenals of the segment previously brought and positioned at the laser welding station; <Desc / Clms Page number 29>  d). clamping means (15) for clamping together the segments supplied and positioned at the laser welding station (14) so as to each time place the hollows of the corrugations or crenals of the segment last brought and positioned at the laser welding station in contact with the vertices of the corrugations or crenals of the previously brought and positioned segment of the laser welding station; e). said laser welding station (14) comprising means (37) capable of forming a transverse linear welded joint (41a, 41b, 41c ...) in each contact zone between the peaks and valleys of the corrugations or crenels in contact with each other by the clamping means (15).  8. Device according to claim 7, characterized in that it comprises a supply reel (16) carrying, wound on it, a continuous strip (12) of light metal of said predefined width, and in that said forming means ( 11) by plastic deformation comprise two toothed wheels (18,19) whose teeth have a profile corresponding to said corrugated longitudinal profile or crenellated and which are arranged between the supply reel (16) and the laser welding station (14) so as to acting respectively on the opposite faces of the continuous strip (12) of light metal passing the two gears (18,19) during its movement from the supply reel (16) to the laser welding station (14), at least one of the two gears being connected to rotating drive means (22).  9. Device according to claim 8, characterized in that the rotary drive means (22) comprise a motor.  10. Device according to claim 8 or 9, characterized in that said feeding and positioning means (11, 13, 34, 36) comprise said gear wheels (18, 19), a first fixed guide (25, 26). which extends from the exit side of the nip region of the two gears to the entrance of the laser welding station (14), and a second guide (27) which is movable between a first position in which it extends the first fixed guide (25,26) and forms with the surface of a support plate (21) a guiding tunnel for said segments (S1, S2, S3 ...) successively fed to the laser welding station (14) and a second position in which the second guide (27) is spaced apart from said support plate (21), said support plate being arranged such that said segments are edged on the surface of the support plate. <Desc / Clms Page number 30>  11. Device according to claim 10, characterized in that said clamping means (15) comprise a bearing plate (28) which is carried by the support plate (21) and which extends along a first side of the second guide (27) when the latter is in its first position, a movable clamping plate (29) which extends parallel to the support plate (28) on a second side of the second guide (27), and actuating means (31) for moving the movable clamping plate (29) towards and away from the bearing plate (28) when the second guide (27) is in its second position.  12. Device according to claim 11, characterized in that the movable clamping plate (29) carries on its side facing the support plate (28), a plurality of positioning projections (34) adapted to engage closely in some of the corrugations or crenals of the first segment (SI) of the continuous strip (12) of light metal fed to the laser welding station (14), when the movable clamping plate (29) is moved for the first time to the plate support (28) by the actuating means (31).  13. Device according to claim 12, characterized in that the support plate (28) carries on its side facing the movable clamping plate (29), a plurality of positioning elements (36) which each have a complementary concave shape in the shape of a vertex of the corrugations or crenals of the segments of the continuous strip (12) of light metal and which are adapted to receive some of the peaks of the corrugations or crenals of the segment recently brought to the laser welding station (14).  14. Device according to claim 13, characterized in that the support plate (28) is movable in a direction (X) parallel to the longitudinal direction of the segments (S1, S2, S3 ...) of the continuous strip ( 12) of light metal between a first position in which said positioning elements (36) are located respectively opposite the positioning projections (34) carried by the movable clamping plate (29) each time a segment of odd order (SI, S3 ...) is fed to the laser welding station (14), and a second position which is shifted from the first position a distance corresponding to half a step of the corrugations or crenals of the segments of the strip continuous light metal each time an even order segment (S2, S4 ...) is fed to the laser welding station (14). <Desc / Clms Page number 31>  15. Device according to any one of claims 11 to 14, characterized in that the movable clamping plate (29) carries gripping and retaining means (35) able to grasp and retain the first segment (SI) of the continuous strip (12) of light metal fed to the laser welding station (14), when the movable clamping plate (29) is moved for the first time to the support plate (28), so that said first segment (S1) and any subsequent segment, which was subsequently secured by welding to the first segment or to an intermediate segment, can be moved together with the movable clamping plate (29) away from the support plate (28). ) to enable the second guide (27) to be placed in its first position and to feed a new segment of the continuous light metal strip between the support plate (28) and the segment (s) attached to the movable plate clamping (29).  16. Device according to any one of claims 11 to 15, characterized in that said means (37) for forming transverse linear welded joints

 (41a, 41b, 41c) comprise a laser (37) having a focusing head (38) which is directed towards the face of the backing plate (28) opposite the face of the backing plate facing the plate movable clamping device (29) and in that said support plate (28) comprises, for the passage therethrough of the laser beam (37), a light (39) which has a corrugated or crenellated shape, whose corrugations or crenals have an amplitude greater than the width of the strip (12) of light metal and a pitch corresponding to that of the corrugations or crenals segments of said strip of light metal.  Device according to claim 16, characterized in that the laser (37) is carried by a support which is movable at least in a first direction (Y) perpendicular to the support plate (28) and in a second direction ( X) perpendicular to the first direction and parallel to the supply direction of the segments (S1, S2, S3 ...) of the strip (12) of light metal laser welding station (14).  18. Device according to claim 17, characterized in that the support carrying the laser (37) is also movable in a third direction (Z) perpendicular to said first and second directions (Y and X).  19. Device according to claim 17, characterized in that the focusing head (38) of the laser (37) comprises scanning means arranged to <Desc / Clms Page number 32>  causing the laser beam to scan in a third direction (Z) perpendicular to said first and second directions (Y and X).  20. Device according to claim 16, characterized in that the laser is mounted in a fixed position and is connected by an optical fiber to the focusing head which can be moved in three directions (X, Y, Z), namely a first direction (Y) perpendicular to the support plate (28), a second direction (X) perpendicular to the first direction and parallel to the longitudinal direction of the segments (S1, S2, S3 ...) of the strip (12) of light metal at the laser probing station (14), and a third direction (Z) perpendicular to the first and second directions (Y and X).  21. Honeycomb structure (51) of light metal, characterized in that it is obtained by the method according to any one of claims 1 to 6.  22. A lightweight sandwich panel (50) comprising a honeycomb core (51) made of light metal and two light metal facing plates (52, 53), which are fixed respectively on each side of the core, characterized in that the core (51) is a honeycomb structure manufactured by the method according to any one of claims 1 to 6.