FR3071186A1 - METHOD FOR ASSEMBLING A PANEL AND A STRUCTURE PART - Google Patents

Abstract

A method of assembling a first piece (1) and a second piece (2), formed of a thermoplastic material, wherein the first piece (1) comprises energy directors (11), and wherein the steps are carried out in which: the two parts (1, 2) are pressed against each other, the parts (1, 2) are vibrated relative to each other in one direction main (XX '), so that the friction of the energy directors (11) of the first piece (1) on the surface (20) of the second piece (2) cause a rise in temperature sufficient to melt the material forming the energy directors (11) of the first piece (1) and the surface (20) of the second piece (2) in contact therewith and for welding the pieces (1, 2). Prior to pressing the pieces (1, 2) against each other, at least one bead of glue (3) is deposited on one of the two pieces so that the opposite faces (10, 20) each of the parts are brought into contact with said bead (3).

Description

The invention relates to a method of assembling two parts made of thermoplastic material, intended more particularly to form a body element of a motor vehicle.

In known manner, a vibration welding technique is used. A first room is provided with projecting elements, otherwise known as energy directors, and intended to come into contact with the second room. The two pieces are pressurized against each other so that the energy directors of the first piece are in contact with the surface of the second piece. The parts are then made to vibrate with respect to each other in a main direction, so that the friction of the energy directors of the first part on the surface of the second part causes a rise in temperature sufficient to bring about fuses the material forming the energy directors of the first part and the surface of the second part in contact with them and to weld the parts.

The vibration of the parts can be achieved by electromagnetic means acting on one of the chassis supporting one of the two parts and serving as a positioning support. Equivalently, it is also possible to use ultrasound acting on sonotrodes applied locally on one of the two parts to vibrate one part with respect to the other.

Because of the relatively short cycle times, of the order of ten seconds, this technology has a certain economic advantage.

However, if ultrasonic welding is suitable for small parts, its implementation becomes more complex when one seeks to fix large parts such as body parts. In fact, due to the greater flexibility of the parts, it becomes difficult to control the melting of all the energy directors distributed over the entire surface and there is then a loss of resistance in the welds. To combat these effects, the skilled person is led to increase the number of energy managers.

In addition, the use of certain thermoplastic materials such as polypropylene loaded with talc, does not promote the production of quality welds.

The object of the method according to the invention is to provide a solution to this problem.

This method of assembling a first and a second part formed from a thermoplastic material, provides that a first part comprises energy directors and comprises the stages during which:

we put the two parts under pressure against each other so that the energy directors of the first part are in contact with the surface of the second part we vibrate the parts with respect to each other in a main direction, so that the friction of the energy directors of the first part on the surface of the second part cause a rise in temperature sufficient to melt the material forming the energy directors of the first part and the surface of the second part in contact with them and to weld the parts.

This method is characterized in that, prior to the pressurization of the parts against each other, at least one bead of adhesive is deposited on one of the two parts so that, after the pressurization of the two pieces against each other, the opposite faces to each other of each of the pieces are brought into contact with said bead of glue.

Thus, after polymerization of the glue, the two parts are kept in contact with each other mainly by the glue. The welds made by vibration during the assembly process usefully strengthen the connection between the two parts.

This method also allows to position the two parts relative to each other in the cycle time, very short, necessary for the melting of the surfaces of the two parts, and to achieve the polymerization of the glue for a longer time without immobilizing the assembly means.

It also becomes possible to reduce the number of energy directors to the number just sufficient to maintain the parts, the time for the complete setting of the glue.

In addition, contrary to popular belief, the properties of the adhesive are not degraded by vibrations if the vibration of the parts is carried out in a very short time following the deposition of the adhesive bead, when the adhesive is still sufficiently fluid and elastic so that the chemical chains being formed are not broken by the shearing effect.

Finally, in certain configurations, it is useful to take advantage of the contribution of heat energy generated by the melting of the parts at the contact points formed by the energy directors, to initiate the operation of adhesive polymerization.

The device according to the invention can also comprise, in isolation, or in combination, the following characteristics:

The parts are welded by vibration less than 3 minutes after depositing the bead of glue.

After performing the welding of the parts by vibration, the adhesive is polymerized, leaving the two parts exposed to the ambient environment for a determined period.

the amount of heat generated during the welding of the parts is sufficient to initiate the adhesive polymerization reaction.

After carrying out the welding of the parts by vibration, the adhesive is polymerized by raising the temperature of the two parts for a determined period.

A crosslinkable adhesive is used, preferably of the two-component type.

A two-component adhesive of polyurethane, epoxy or methacrylate type is used.

The bead of glue is deposited at a determined distance from an energy director so that, after the two parts are pressurized against each other, the glue is distributed freely between the two parts without coming into contact with said energy manager.

The glue is deposited on the head of an energy director so that, after the two parts are pressurized against each other, the glue is distributed on both sides of said energy director.

The energy directors are formed by partitions, continuous or discontinuous, aligned in the main direction and form rows separated by a given distance (d1).

The bead of adhesive is deposited between two rows of energy directors, so that, after the two parts are pressurized against each other, the adhesive is distributed in all or part of the space between the two rows of partitions.

Apply the bead of glue so that the glue is evenly distributed outside the space between the two rows of partitions.

The energy directors are trapped in the bead of glue.

The first part and the second part are formed from compatible hot-melt materials comprising the following materials:

o Polypropylene (PP) possibly reinforced with glass fibers (type

PPGFL) or loaded with talc, or Acrylonitrile Butadiene Styrene (ABS).

The invention will be better understood on reading the description and the appended figures, which are provided by way of examples and have no limiting character, in which:

Figure 1 shows a reinforcement of a bodywork element seen from the front.

FIG. 2 represents a schematic sectional view of the two parts after the adhesive bead has been deposited and before the two parts are pressurized against each other, according to a first alternative embodiment.

Figure 3 shows the parts of Figure 2 after the vibration welding step (section along A-A).

Figure 4 shows a schematic sectional view (along A-A) of the assembly of the two parts, according to a second alternative implementation of the method

FIG. 5 represents a schematic sectional view (along A-A), of the assembly of the two parts, according to a third alternative for implementing the method.

Figure 1 illustrates a reinforcement of a vehicle body element formed of the superimposition after assembly, a first part 1, in the case of an inner reinforcement, and a second part 2 , in this case an outer skin.

These two parts are assembled using a vibration welding means bringing energy directors 11 (displayed by horizontal lines appearing under the second part 2), arranged on the surface 10 of the reinforcement outer 1, with the surface 20 of the outer skin 2, facing the inner reinforcement 1. The shape and arrangement of the energy directors 11 is determined by the characteristics of the parts to be welded.

In the example used as a support in Figure 1, the energy directors 11 are formed by partitions arranged in rows, oriented in a main direction XX ', and spaced from one another by value d _r This particular and non-limiting arrangement gives the energy directors 11 mechanical strength in the direction XX ', and makes it possible to limit their dimensioning to what is strictly necessary. The distance di between two rows can vary from ten millimeters to a few centimeters.

Mechanical means (not shown) ensure the relative maintenance, the pressurization of the two parts against each other during the actual vibration operation, as well as the setting of relative reciprocating movement in the direction XX 'of the two pieces in relation to each other.

The mechanical movement of the parts is preferably provided by electromagnets or, alternatively by sonotrodes arranged locally and set in motion by ultrasound. These sonotrodes allow to overcome design constraints related to the shape and position of the energy directors. In fact, the sonotrode forms the hooks by locally heating and deforming the material of the internal reinforcement 1 towards the external skin 2.

Figure 2 is a sectional view of the two parts according to A-A.

The inner reinforcement piece 1 (first piece) is formed of a compatible material, and preferably of the same kind, with the material forming the outer skin 1. The thickness e ₂ of the reinforcement piece is of the order of 2.5 mm.

The outer skin 2 (second part) is formed of a hot-melt material such as Polypropylene (PP), optionally reinforced with glass fibers (PPGFL type) or loaded with talc, or Acrylonitrile Butadiene Styrene (ABS). The thickness of the skin is around 4 mm.

By compatible here is meant the ability of the two materials to form a resistant weld after being brought one and the other to their melting temperature. This suggests that these melting temperatures are only a few degrees Celsius apart.

The energy directors 11, according to the embodiment of the invention illustrated in Figures 1 and 2, have a thickness e ₃ of the order of 0.7 mm to 0.8 mm and a height h ,, before the vibration operation, of the order of 1.8 mm to 2 mm.

The operating conditions to generate the localized melting of thermoplastic parts commonly used in the automotive industry, and in the particular case serving as support for this description are as follows: the pressure of application of the parts one against the other is of the order of 0.1 MPa to 0.5 MPa, and the vibration of the parts with respect to each other is carried out at a frequency of the order of 250 Hz, on an amplitude of about 0.8 mm to 1 mm, for a period of the order of 10 seconds.

Once the weld is completed, the position of the two parts relative to each other is frozen.

Figure 3 illustrates the respective positions of the two parts after welding. It can be seen that the height of the energy directors 11 has been reduced, and that the distance h ₂ between the faces 10 and 20 of the two parts 1 and 2 is no more than about 1 mm.

The first alternative embodiment of the invention illustrated in Figure 2 provides for depositing a bead of glue 3 in the space 12 between two rows of partitions 11 arranged on the first part 1, and remote one of the other from a distance d! on the order of 10mm. Preferably, the adhesive volume is adjusted to completely fill the space 12 between the two rows of partitions 21.

When the two parts are pressurized against each other, the face 20 of the second part 2 repels the glue 3 disposed beyond the height h _l5 and forces the latter to spread laterally . The excess glue can then escape through interruptions 13 arranged in a row of partitions or, as illustrated in FIG. 3, a volume of excess glue can be provided so that the glue overflows over the partition 11 and occupies the space outside space 12.

Figure 4 illustrates a second alternative embodiment, in which the bead of adhesive is deposited directly on the head 110 of the energy director 11, so that, after the pressurization of the two parts 1 and 2 l one against the other, the glue 3 is distributed on either side of the energy director 11 and encloses the latter. In order to strengthen the vibration weld, we can arrange, during this operation, to ensure that, when the parts are pressurized against each other, the adhesive is distributed equally and on the other of said energy director so that as little glue as possible remains at the interface between the head of the energy director and the face of the other part.

In the two alternative embodiments described above, the walls of the energy directors are trapped in the adhesive bead, which has the effect of reinforcing the mechanical resistance of the adhesive bead, and of the connection between the two parts 1 and 2. In addition, as will be seen later, the heat generated during the production of the weld is better distributed within the bead of glue with the effect of accelerating the crosslinking of the glue.

The third alternative embodiment, illustrated in Figure 5 provides, to deposit the adhesive at a sufficient distance from the energy directors 11, so that, when pressurizing the two parts 1 and 2 one against the other, the glue 3 is freely distributed between the faces 10 and 20 of each of the parts without coming into contact with an energy director 11.

Regardless of the alternative embodiments set out above, an adhesive compatible with the materials forming the parts 1 and 2 will be chosen.

Preferably, choose an adhesive or a polymer, crosslinkable, preferably two-component heat activatable, and optionally re-activatable with heat, allowing to obtain good results in terms of mechanical strength and resistance over time.

The polymerization of the adhesive can be done by leaving the two parts, once welded by vibration, exposed to the ambient environment for a determined period. The catalyst contained in one of the two components makes it possible to give the adhesive its final properties and to join the two parts in a robust manner.

It will be observed here that, during the polymerization of the adhesive, the two parts can be handled without altering the quality of the connection, due to the presence of the welds formed at the level of the energy directors. The glue can thus polymerize for a longer period of time, without immobilizing the assembly installation.

The calories generated during the soldering operation can be used to accelerate the initiation of the crosslinking reaction. This advantage cannot be obtained when the third alternative embodiment of the invention is chosen (Figure 5).

If an addition of heat is necessary, it is possible to arrange the two parts in a heated enclosure for a determined period of time to complete the polymerization of the glue. Alternatively, it is also possible to use directional heating means acting on reduced and localized surfaces, such as infrared means or hot pulsed air so as to reduce the thermal deformations of the parts and to limit the energy consumption. .

Two-component adhesives of the polyurethane, epoxy or methacrylate type give good results in this regard. One-component adhesive can also be used, the polymerization of which is ensured by contact with the moisture contained in it. ambiant air. In this context, we should avoid choosing the first embodiment of the invention in which the adhesive is trapped between the two rows of partitions and remains isolated from contact with ambient air. The third embodiment of the invention then seems preferable.

Finally, although their mechanical strength is lower, hotmelt or hotmelt reactive adhesives may also be suitable.

In all cases, it should be verified that the vibration operation is carried out when the adhesive is still sufficiently fluid. These optimal conditions are generally obtained when the vibration operation is carried out less than three minutes after depositing the bead of adhesive.

The implementation alternatives of the invention described above are in no way limiting and may be subject to variants, without departing from the subject of the invention as claimed.

NOMENCLATURE

Interior reinforcement (first piece).

Face of the interior reinforcement supporting the energy directors.

110 Head of the energy manager.

Energy director forming partitions arranged in rows.

Space between two rows of partitions.

Partition interruptions.

Outer skin (second piece).

Face of the outer skin coming into contact with the energy directors.

Glue bead.

XX 'Main direction.

Ιη Height of an energy director before vibration.

h ₂ Height of the residual space between the outer skin and the inner reinforcement after vibration.

ei Thickness of the interior reinforcement (first part).

e ₂ Thickness of the outer skin (second piece).

e ₃ Thickness of an energy director.

di Distance between two energy managers.

Claims (14)

1. Method of assembling a first part (1) and a second part (2), formed of a thermoplastic material, and intended to equip a motor vehicle, in which the first part (1) comprises directors of energy (11), and in which the steps are carried out during which: the two parts (1, 2) are put under pressure one against the other so that the energy directors (11) of the first part (1) are in contact with the surface (20) of the second part (2), the parts (1, 2) are made to vibrate with respect to each other in a main direction (XX ′), so that the friction of the energy directors (11) of the first part ( 1) on the surface (20) of the second part (2) cause a rise in temperature sufficient to melt the material forming the energy directors (11) of the first part (1) and the surface (20) of the second part (2) in contact with the latter and in order to weld the parts (1,2), characterized in that, before the parts (1, 2) are pressurized against each other, at least one bead of glue (3) is deposited on one of the two pieces so that, after the two pieces (1,2) are pressurized against each other, the opposite faces (10, 20) to each other of each of the parts are brought into contact with said cord (3). 2. Method according to claim 1, in which the parts are welded by vibration less than 3 minutes after having deposited the bead of adhesive. 3. The assembly method according to claim 1 or claim 2, wherein, after having performed the welding of the parts (1, 2) by vibration, the adhesive (3) is polymerized, leaving the two parts exposed (1, 2). to the surrounding environment for a specified period of time. 4. The assembly method according to claim 1 or claim 2, wherein the amount of heat generated during the welding operation of the parts (1, 2) is sufficient to initiate the polymerization reaction of the adhesive (3). 5. The assembly method according to claim 1 or claim 2, wherein, after having performed the welding of the parts (1, 2) by vibration, the adhesive (3) is polymerized by raising the temperature of the two parts (1,2 ) for a specified period. 6. The assembly method according to any one of claims 1 to 5, in which a crosslinkable adhesive (3) is used, preferably of the two-component type. 7. The assembly method according to claim 5, wherein a two-component adhesive (3) of polyurethane, epoxy or methacrylate type is used. 8. An assembly method according to any one of claims 1 to 7, in which the adhesive bead (3) is deposited at a determined distance from an energy director (11) so that, after setting pressure of the two parts (1, 2) against each other, the glue is freely distributed between the two parts (1, 2) without coming into contact with said energy director (11). 9. An assembly method according to any one of claims 1 to 7, in which the adhesive (3) is deposited on the head (110) of an energy director (11) so that, after setting pressure of the two parts (1, 2) against each other, the glue (3) is distributed on either side of said energy director. (11) 10. The assembly method according to any one of claims 1 to 7, wherein the energy directors (11) are formed by partitions, continuous or discontinuous, aligned in the main direction (XX ') and form rows. separated by a given distance (di). 11. The assembly method according to claim 10, in which the bead of adhesive (3) is deposited between two rows of energy directors (11), so that, after the two parts (1.2 ) one against the other, the glue (3) is distributed over all or part of the space (12) between the two rows of partitions. 12. The assembly method according to claim 11, in which the bead of glue (3) is deposited so that the glue is also distributed outside the space (12) between the two rows of partitions. 13. The assembly method according to any one of claims 9 to 12, in which the energy directors (11) are trapped in the adhesive bead (3). 14. The assembly method according to any one of the preceding claims, in which the first part (1) and the second part (2) are formed from compatible hot-melt materials comprising the following materials: Polypropylene (PP) possibly reinforced with glass fibers (PPGFL type) or loaded with talc, Acrylonitrile Butadiene Styrene (ABS).