Abstract:
A method for disassembling two ultrasonically welded elements, one of the elements comprising, at a surface opposite the other element, an energy director that concentrates the heating during ultrasonic welding and forms a material junction between the two assembled elements after the ultrasonic welding. The method includes the steps of positioning a wire between the two assembled elements, so as to be secant to the energy director, said wire having suitable mechanical characteristics allowing it to cut the junction formed by the energy director and moving the wire between the two assembled elements so as to cut said junction.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of the French patent application No. 11 60366 filed on Nov. 15, 2011, the entire disclosures of which are incorporated herein by way of reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    The present invention relates to a method for disassembling two ultrasonically welded elements as well as an element that can be ultrasonically welded to another element making it possible to implement said method. The invention is more particularly suitable for separating a holder or part of a holder ultrasonically welded to a wall. 
         [0003]    According to one known embodiment illustrated in  FIGS. 1 to 3 , a holder  10  comprises a body  12 , in the form of a cylindrical pellet with a front surface  14 , that can be pressed against and connected to a wall  16  of an aircraft. The body  12  is extended by a rod  18  that makes it possible to connect a “light” element, in particular less than  2  kg, to the structure of the aircraft, for example such as an electrical cable, a tube, an insulating pad, cabin furniture, etc. 
         [0004]    The holder  10  is made from a composite material, for example thermoplastic resin, which may or may not be reinforced with fibers. 
         [0005]    The wall  16  of the aircraft is also made from a composite material, and for example comprises fibers embedded in a thermosetting resin matrix. According to the embodiment illustrated in  FIGS. 2 and 3 , the wall  16  comprises a coating  20  made from a thermoplastic material. Advantageously, the structure of the wall and its coating are co-polymerized, which makes it possible to obtain a solid connection between the coating and the wall. 
         [0006]    As illustrated in  FIG. 3 , the holder  10  is fastened to the wall  16  using an ultrasonic welding method. 
         [0007]    According to this technique, the holder is in contact with a vibration transmitter and its front surface  14  is pressed against the wall. Subsequently, by applying vibrations, heat is created at the interface between the holder and the wall up to their melting temperatures, allowing the molecular chains of the two elements in contact to mix in a diffusion area  22 . After the vibrations have stopped and cooling has taken place, a solid junction is obtained. 
         [0008]    To concentrate the heating, the front surface of the holder comprises at least one protruding shape called an energy director  24 . As illustrated in  FIG. 1 , an energy director describes a ring approximately concentric to the body of the holder with a triangular section and a height in the vicinity of 1.5 mm. After the vibrations have stopped, the energy director  24  is deformed and forms a junction  26  between the holder and the wall, as illustrated in  FIG. 3 . 
         [0009]    This assembly technique is in particular described in documents EP-2.004.388 and EP-1.423.256. 
         [0010]    Following such an assembly, it may be necessary to reinstall a holder, for example if it is broken or due to a defective initial assembly. However, ultrasonic welding is a practically irreversible assembly technique. It is particularly irreversible inasmuch as the energy director(s) do not have the same geometry as before the assembly, and no longer have a pointed shape making it possible to concentrate the vibrational energy. 
         [0011]    To disassemble the holder, a first solution consists of using a cutting and heating tool such as a blade and sliding it between the holder and the wall so as to destroy the junction  26 . This solution is not fully satisfactory, as the risks of damaging the wall made from the composite material are high due to the geometry of the blade-shaped tool and the heat produced by the latter. 
         [0012]    Another solution consists of using an ultrasonic knife, which is inserted between the holder and the wall in order to destroy the junction  26 . As before, this solution is not fully satisfactory, as the risks of damaging the composite material wall are high. 
         [0013]    Another solution consists of cutting out the holder using a rotating tool. This rotating tool has a cylindrical shape with at least one cutting edge at a front surface and an opening to allow the passage of the rod  18  of the holder, which may be used as axis of rotation. This tool also comprises two radial handles allowing it to be maneuvered. 
         [0014]    This rotating tool makes it possible, through machining such as end milling, to remove material and thereby eliminate the holder. 
         [0015]    Unlike the first two solutions, this solution makes it possible to limit the risks of damage to the wall. However, the surface of the wall may be scratched after this disassembly operation. 
         [0016]    Document U.S. Pat. No. 5,591,364 proposes positioning a wire near the junction formed ultrasonically, then circulating an electric current in the wire so as to cause heating by Joule effect in order to cause the junction to soften. According to this document, the wire is stationary. As before, this solution is not fully satisfactory, as the risks of damage to the composite material wall are high due to the heating caused by the wire. Furthermore, the solution is not easy to implement inasmuch as it is difficult to position the wire correctly relative to the junction. 
       SUMMARY OF THE INVENTION 
       [0017]    Consequently, the present invention aims to offset the drawbacks of the prior art by proposing a method for disassembling two elements assembled by ultrasound facilitating the disassembly and limiting the risks of damage to the wall. 
         [0018]    To that end, the invention relates to a method for disassembling two ultrasonically welded elements, one of the elements comprising, at a surface opposite the other element, an energy director that concentrates the heating during ultrasonic welding and forms a material junction between the two assembled elements after the ultrasonic welding, wherein the method comprises of positioning a wire between the two assembled elements, so as to be secant to the energy director, said wire having suitable mechanical characteristics allowing it to cut the junction formed by the energy director, and move the wire between the two assembled elements so as to cut said junction. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]    Other features and advantages will emerge from the following description of the invention, which is provided solely as an example, in reference to the appended drawings, in which: 
           [0020]      FIG. 1  is a perspective view of one example of a holder according to the prior art, more particularly showing an energy director before assembly, 
           [0021]      FIG. 2  is a cross-section illustrating the holder of  FIG. 1  pressed against a wall before assembly, 
           [0022]      FIG. 3  is a cross-section illustrating the holder and the wall of  FIG. 2  after assembly by ultrasonic welding according to the prior art, 
           [0023]      FIG. 4A  is a cross-section of a holder according to a first alternative of the invention, 
           [0024]      FIG. 4B  is a front view of the holder of  FIG. 4A , 
           [0025]      FIG. 5  is a cross-section illustrating a holder according to the invention secured to a wall by ultrasonic welding, 
           [0026]      FIG. 6A  is a cross-section of a holder according to another alternative of the invention, 
           [0027]      FIG. 6B  is a front view of the holder of  FIG. 6A , 
           [0028]      FIG. 7  is a perspective view of a holder according to another alternative of the invention, 
           [0029]      FIG. 8A  is a cross-section of the holder of  FIG. 7  along the broken line A-A secured to a wall, and 
           [0030]      FIG. 8B  is a cross-section of the holder of  FIG. 7  in a plane containing a groove, after insertion of a wire making it possible to separate it from the wall. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0031]      FIG. 5  shows a holder  30  secured to a wall by ultrasonic welding. 
         [0032]    According to one application and solely as an example, the holder  30  comprises a body  32 , in the form of a cylindrical pellet with a front surface  34  capable of being pressed against and connected to a wall  36  of the aircraft. The body  32  is extended by a rod  38  that can make it possible to connect a “light” element, in particular less than  2  kg, to the structure of the aircraft, for example such as an electrical cable, a tube, an insulating pad, cabin furniture, etc. 
         [0033]    The holder  30  is made from a composite material, for example thermoplastic resin, which may or may not be reinforced with fibers. 
         [0034]    The wall  36  of the aircraft is also made from a composite material, and for example comprises fibers embedded in a thermosetting resin matrix. According to the embodiment illustrated in  FIG. 5 , the wall  36  comprises a coating  38  made from a thermoplastic material. Advantageously, the structure of the wall and its coating are copolymerized. 
         [0035]    The holder  30  is secured to the wall  36  by ultrasonic welding. 
         [0036]    Of course, the invention is not limited to this example, and may be applied to other technical fields, other elements that are assembled by ultrasonic welding, the elements being made from materials compatible with this assembly method. 
         [0037]    In general, a first element, for example such as a holder, is connected to a second element, for example such as a wall, by ultrasonic welding, and one of the elements comprises a front surface  34  with at least one energy director  40 . 
         [0038]    In a known manner, an energy director  40  has a protruding shape relative to the front surface  34  with a reduced contact surface so as to concentrate the vibrational energy, and thus the heating. 
         [0039]    According to one embodiment, an energy director  40  is in the shape of a ring approximately concentric to the body of the holder with a triangular section and a height in the vicinity of 1.5 mm. However, the invention is not limited to this energy director geometry. Thus, according to another example, the front surface  34  may comprise three energy directors each in the shape of a cone. 
         [0040]    Generally, the front surface comprises at least one energy director with a reduced contact surface before assembly so as to concentrate the vibrational energy, and therefore the heating, during ultrasonic welding, and which forms a material junction  42  between the two assembled elements after the ultrasonic welding. 
         [0041]    The energy director  40  and the assembly method by ultrasonic welding will not be described further, as they are known by one skilled in the art, and are in particular described in documents EP-2.004.388 and EP-1.423.256 which are incorporated herein by reference. 
         [0042]    According to the invention, one of the two elements assembled by ultrasonic welding, in particular the holder  30 , comprises a wire  44  whereof one portion is included in the energy director  40  during manufacture thereof, said wire  44  having suitable mechanical characteristics, in particular in terms of torsional and shear strength, making it able to cut the junction  42  formed by the energy director  40 . 
         [0043]    This wire  44  may be metal or fibrous. 
         [0044]    According to one embodiment, the wire  44  is made from a nonflammable and non-electrically conducting fibrous material, for example such as braided glass fiber, with a small diameter, in the vicinity of 0.50 to 1 mm, to provide a scale. 
         [0045]    Alternatively, the wire  44  may be made from an electrically conducting material. 
         [0046]    The nature and diameter of the wire  44  are adjusted by one skilled in the art, in particular as a function of the material of the energy director  40 , so as to be able to cut the junction  42  formed by the latter after the ultrasonic welding assembly. 
         [0047]    Advantageously, in the energy director  40 , the portion of the wire  44  is arranged in a plane substantially parallel to the front surface  34 . 
         [0048]    The wire  44  passes through the energy director at least once and comprises portions arranged on either side of the portion included in the energy director. In the presence of several energy directors, a single wire  44  may pass through all of the energy directors. Alternatively, it is possible to provide several wires, each passing through one or more energy directors. 
         [0049]    According to the embodiment illustrated in  FIGS. 4A and 4B , the wire  44  passes twice through the energy director. According to the embodiment illustrated in  FIGS. 6A and 6B , the wire  44  passes once through the energy director. 
         [0050]    According to the invention, the wire  44  comprises at least one portion  46  that can be grasped to be able to maneuver it. 
         [0051]    According to a first alternative illustrated in  FIGS. 4A and 4B , the wire  44  comprises two portions  46 ,  46 ′ that can be grasped. 
         [0052]    According to another alternative, illustrated in  FIGS. 6A and 6B , the wire  44  comprises a portion  46  that can be grasped and another portion  48  that is stationary relative to one of the two assembled elements, in particular connected to the holder. According to this alternative, the wire  44  comprises clipping means at a first end and means for connecting the wire to one of the two assembled elements, in particular the holder, at a second end. 
         [0053]    The portion(s) capable of being grasped correspond to the ends of the wire  44 . 
         [0054]    In order to facilitate gripping of the wire, the portions  46 ,  46 ′ capable of being grasped comprise gripping means. Depending on the case, the gripping means may be a loop formed by the wire  44 , or tabs secured to the wire. As an example, the tabs are made from hard plastic or made up of a piece of cardboard inside which the wire  44  is glued. 
         [0055]    Other solutions may be considered to facilitate gripping of the wire. 
         [0056]    In the case of a holder made from a thermoplastic material, made by plastic injection molding, the wire  44  is inserted into the mold before the injection of the material. If necessary, the wire may be locally coated with an anti-adhesive film of the polytetrafluoroethylene type, to limit the risks of sticking of the thermoplastic material. 
         [0057]    The fact that a portion of the wire is included in the energy director allows the wire  44  to be connected to the element to be welded, which does not create any modifications in the ultrasonic welding assembly method, which is in line with that used to weld the wireless holders  44  of the prior art. 
         [0058]    Preferably, the wire is at a distance from the contact surface of the energy director  40  so as not to interfere with the ultrasonic welding operation. Advantageously, the wire is positioned in the portion of the energy director close to the front surface  34 , corresponding to one third of its height. 
         [0059]    To disassemble the holder  30 , the operator grasps one or two portions  46 ,  46 ′ of the wire  44  and exerts a force so as to cause a rotary movement of the or some of the portions of the wire  44  around the junction  42  formed by the energy director  40 . This rotational movement of the wire causes cutting of the junction and separation of the two previously assembled elements. 
         [0060]    According to the alternative illustrated in  FIGS. 4A and 4B , the rotational movement is done approximately over a half turn (180°). According to the alternative illustrated in  FIGS. 6A and 6B , the rotational movement is done approximately over one complete revolution (360°). 
         [0061]    Since the wire is made from a stronger material than that of the junction  42 , the latter is cut by the wire. 
         [0062]    Alternatively, it is possible to circulate an electric current in the wire  44 , so as to cause heating of the wire by Joule effect, which favors the cutting action of the wire  44 . Unlike the prior art, the disassembly essentially results from the cutting action of the wire and not its heating, which in fact only favors the cutting action. This heating is not sufficient by itself to obtain the rupture of the junction. 
         [0063]    In  FIGS. 7 ,  8 A and  8 B, a holder  30  is shown according to another alternative. As before, according to one embodiment, a holder  30  comprises a body  32  in the form of a cylindrical pellet with a front surface  34  that can be pressed against and connected to a wall  36  of the aircraft. 
         [0064]    At its front surface  34 , it comprises at least one energy director  40 . 
         [0065]    According to this alternative, the holder  30  comprises at least one groove  50  making it possible to position at least one wire  44  between the support  30  and the wall  36  on which it is fastened. This groove has a section suitable to slide a wire between the holder  30  and the wall  36  on which it is fastened. 
         [0066]    The groove  50  is secant with the energy director  40  at least at one point. Advantageously, as illustrated in  FIG. 7 , the groove  50  emerges at the peripheral surface  52  of the holder  30 . According to one embodiment, the groove  50  extends along a line corresponding to a diameter. 
         [0067]    Preferably, at a point of intersection with a groove, the energy director  40  comprises a notch  54 . According to one embodiment illustrated in  FIG. 7 , the notch  54  extends over the entire height of the energy director  40  and forms a slit. Alternatively, the notch  54  extends only over part of the height of the energy director, more particularly one third of its height from the front surface  34 , and forms a needle eye in which the wire  44  can be inserted. 
         [0068]    Thus, according to the alternative illustrated in  FIGS. 7 ,  8 A and  8 B, the wire  44  may not comprise any portion included in the energy director  40  during its production. 
         [0069]    The wire used to separate the elements assembled by ultrasonic welding can be connected to the holder using any suitable means. Alternatively, it may not be connected to the holder and a same wire may be used to separate several holders successively. 
         [0070]    Whatever the alternative, at least one of the assembled elements comprises means for positioning at least one wire  44  between two assembled elements, so as to be secant to the energy director. To separate the two elements, it is then necessary only to move the wire between the two assembled elements so as to cut the junction(s)  42  formed by the energy director after the ultrasonic welding. 
         [0071]    As is apparent from the foregoing specification, the invention is susceptible of being embodied with various alterations and modifications which may differ particularly from those that have been described in the preceding specification and description. It should be understood that I wish to embody within the scope of the patent warranted hereon all such modifications as reasonably and properly come within the scope of my contribution to the art.