WO2018115619A1

WO2018115619A1 - Sonotrode with non-linear cooling channels

Info

Publication number: WO2018115619A1
Application number: PCT/FR2017/053363
Authority: WO
Inventors: David Tresse; Jérôme Brizin; Stéphane GUILLIER
Original assignee: Compagnie Plastic Omnium
Priority date: 2016-12-22
Filing date: 2017-12-04
Publication date: 2018-06-28
Also published as: EP3558645A1; FR3061063A1; MA47065A

Abstract

The invention concerns a sonotrode (2) for welding two parts made from plastic material, the sonotrode being made in one piece and comprising: - at least one inlet opening (16, 20, 26; 36; 46), - at least one outlet opening (18, 22, 28; 38; 48), and at least one conduit (12, 14, 24; 32; 40) forming an inner channel communicating with the inlet and outlet openings such that the sonotrode comprises at least one fluid circuit extending from the inlet opening, through the inner channel and to the outlet opening, the inner channel having a non-linear shape suitable for optimising the heat exchange with the fluid travelling through same.

Description

Sonotrode with non-linear cooling channels

The invention relates to the field of welding plastic parts, more specifically motor vehicle parts. More particularly, the invention relates to a sonotrode adapted to perform such welding operations.

Motor vehicle parts, such as for example a bumper or a floor, comprise a plurality of plastic elements, for example made of a thermoplastic material, fixed to each other by welding.

In order to carry out these welding operations, it is possible to use a sonotrode. The sonotrode means a device preferably taking elongated form, for example rod-shaped or cylindrical, connected to an ultrasound generator. This sonotrode receives ultrasound from the ultrasound generator, at a frequency generally between 20 kHz and 40 kHz, and restores the vibration energy in its end in contact with the materials to be welded.

The sonotrode includes an end for welding two plastic elements in contact with each other. The restitution of the vibratory energy locally causes the excitation of the molecules of the material, releasing energy and causing a rise in temperature to melt the two plastic elements at the contact zone with the sonotrode so to weld the two elements together. After stopping the ultrasound, it is necessary to wait until the plastic begins to cool before removing the sonotrode otherwise the quality of the weld will be affected.

The large number of elements to be welded to each other on certain parts of a motor vehicle leads to having to perform a large number of welds while respecting a production rate as fast as possible. However, the repetition of the welds leads to a gradual heating of the sonotrode. When the sonotrode has accumulated a certain amount of heat, it is necessary to leave it longer in place at a weld zone. Indeed, in case of withdrawal too fast and especially if the temperature is still high locally, the melt would generate son. This waiting time is detrimental to performance.

It is therefore advantageous to set up a device for cooling the sonotrode and preventing it from rising in temperature.

It has been proposed in the prior art to equip the welding device with a tube supplied with compressed air and directed towards the free end of the sonotrode, that is to say the end comprising the part which will be in contact with the material to be welded.

However, such a device only allows local cooling of the sonotrode, at the outlet of the compressed air, with consequently an exchange surface restraint. The regions of the sonotrode not being connected to the tube supplied with compressed air, but in which the heat of the material to be welded diffuses, will then undergo a heating. This solution is then of little interest in terms of cooling the sonotrode.

Another solution envisaged consists in drilling a set of linear holes in the body of the sonotrode in order to create a fluid circuit inside the sonotrode, a circuit supplied with compressed air.

However, such a device has several disadvantages.

Firstly, it is difficult to drill the sonotrode over a large length because of the difficulty of making large boreholes. In addition, such drilling may have the effect of weakening the sonotrode. Finally, this method only makes it possible to create a circuit whose channels are rectilinear. In this case, either the circuit is present only in a limited area of the sonotrode, or the rectilinear channels must be organized to make a path, with the addition of plugs on some openings which complicates the maintenance of tightness with vibration. The cooling of the sonotrode is not optimal.

A solution for creating a circuit having a complex structure (that is to say composed of non-rectilinear channels) consists in producing a sonotrode in several blocks which are drilled according to different drilling angles and then assembling the different blocks to create the sonotrode. However, this requires perfect alignment of the different blocks, otherwise it will partially or completely close the fluid circuit. In addition, the sonotrode being a device traversed by vibrations, this structure in several blocks can lead to embrittlement of the sonotrode.

An object of the invention is to eliminate, or at least to limit substantially all or part of the aforementioned drawbacks.

For this purpose, the subject of the invention is a sonotrode for welding two plastic parts, characterized in that the sonotrode is made in one piece, and in that it comprises:

at least one inlet port,

at least one exit orifice, and

at least one conduit forming an internal channel communicating with the inlet and outlet ports so that the sonotrode comprises at least one fluid circuit extending from the inlet port, through the internal channel and up to the outlet orifice, the internal channel having a non-linear shape capable of optimizing the heat exchange with the fluid flowing through it.

Thus, there is obtained a sonotrode comprising a cooling capacity superior to the prior art because the shape of the circuit will allow a better heat exchange between the sonotrode and the cooling fluid and thus generate the cooling of a larger volume of the sonotrode, and also facilitate the creation and maintenance of a turbulent regime of the cooling fluid, which improves the heat exchange and therefore cooling with respect to a laminar flow regime. It is even conceivable that the sonotrode does not heat at all despite the repetition of the welds.

In addition, this sonotrode is made in a single block, which allows to maintain a solid structure and despite the presence of an internal cooling circuit of a shape capable of generating and maintaining turbulence in the fluid flowing through it.

Optionally, the sonotrode according to the invention may comprise one or more of the following characteristics:

the duct is capable of generating and maintaining turbulences in the fluid flowing through it;

the conduit has a shape chosen from the double helix form or the lattice form;

the sonotrode comprises a hollow volume between 5% and 60% of the total volume of the sonotrode, preferably between 8% and 40%, even more preferably between 20% and 34%;

the sonotrode comprises an exchange surface area of between 5,000 and 50,000 mm ² , preferably between 6,500 and 35,000 mm ² , even more preferentially between 11,000 and 25,000 mm ² ;

the duct is able to be traversed by a gas, preferably air;

the sonotrode is produced by additive manufacturing, and

- The sonotrode is made of titanium, aluminum or steel, with or without heat treatment.

We will now present three embodiments of the invention in support of the appended figures, for the same external sonotrode dimensions, which are provided by way of example and are not limiting in nature, in which:

- Figure 1 is a perspective view of a sonotrode according to the invention;

FIG. 2 is a perspective view of a duct according to a first embodiment of the invention;

FIG. 3 is a perspective view of a variant of the duct of FIG. 2;

FIGS. 4 and 5 are perspective views of a duct according to a second embodiment of the invention, and

FIGS. 6 and 7 are perspective views of a duct according to a third embodiment of the invention;

Referring now to Figures 1 and 2 which show a sonotrode 2 comprising a main body 4 and two ends 6 and 8. The sonotrode can be made of metal, for example titanium, aluminum or steel, or in any other material adapted to its function, with or without heat treatment.

An upper end 6 of the sonotrode 2 is able to connect the sonotrode with an ultrasound generator. A lower end 8 of the sonotrode 2 is adapted to be in contact with plastic elements to be welded. For this, the lower end 8 may be V or angle allowing the sonotrode to cover the areas to be welded, or, as shown in Figure 2, include several rows (the number may vary) of teeth 10 allowing the sonotrode to pass through the first thickness of plastic material at the areas to be welded.

The sonotrode 2 may comprise two ducts 1 2 and 14 forming internal channels for the circulation of a cooling fluid, for example compressed air, inside the sonotrode 2, as shown in FIG. 12 comprises an inlet port 1 6 and an outlet port 18. The conduit 14 comprises an inlet port 20 and an outlet port 22. These orifices can of course be reversed, the orifices 1 8 and 22 becoming orifices inlet and the orifices 16 and 20 becoming outlet orifices. These orifices can lead to the side walls of the main body 4 of the sonotrode 2.

The two ducts 1 2 and 14 are wound around each other to form a structure in the form of a double helix, each of the propellers having a pitch identical to the other. This identity of step is visible in FIG. 2, but also in FIG. 3, on which it can be seen that the pitch Pi of the helix 12 is identical to the pitch P ₂ of the propeller 14. This identity allows the ducts to be distributed. 1 2 and 14 uniformly over the length of the sonotrode 2. The pitch of the propellers may be different. This double-helix structure makes it possible to distribute the ducts 12 and 14 widely in the volume of the sonotrode, thus generating an exchange surface that can cool a large part of the volume of the sonotrode and this geometry with curvatures also makes it possible to create more easily turbulence in the cooling fluid, for example compressed air, circulating in the conduits 12 and 14. In addition, for the same fluid flow rate, the internal channel may have a diameter smaller than a sonotrode according to the invention. prior art (in the prior art the minimum diameter is imposed by the constraint of having to drill deeply, ie with a drill of sufficiently large diameter) and the flow regime is therefore more easily turbulent.

In order to be able to produce a sonotrode 2 comprising channels having the structure illustrated in FIG. 2, the sonotrode 2 may be, like all the sonotrodes described hereinafter, carried out by three-dimensional printing (3D), a technique allowing to build the sonotrode 2 layer after layers and thus create a sonotrode 2 of a single holding and comprising conduits 12 and 14. These conduits 12 and 14 extend over approximately 70% of the length of the sonotrode 2 and on average 40% of its width.

In this embodiment, the empty volume of the sonotrode 2 is equal to 8,265 mm ³ for a total volume of 100,428 mm ³ , ie a percentage of hollow zones equal to 9% of the total volume of the sonotrode. The heat exchange surface is equal to 6 609 mm ² .

FIG. 3 represents an alternative embodiment of the duct of FIG. 2. The sonotrode according to this variant comprises only one duct 24 forming an internal channel and consequently a single inlet orifice 26 and a single outlet orifice 28. The Conduit 24 forms, like the conduits 12 and 14 of Figure 2, a structure in the form of a double helix. An end loop 30 then replaces the ends of the conduits 12 and 14 opening on the orifices 18 and 22.

In this variant embodiment, the empty volume of the sonotrode 2 is equal to 8 869 mm ³ for a total volume of 100 428 mm ³ , ie a percentage of hollow zones equal to 9.7% of the total volume of the sonotrode. The heat exchange surface is equal to 7 093 mm ² .

The channel 24 extends about 70% of the length of the sonotrode 2 and averages over 40% of its width.

In what follows, two other embodiments of the invention will be described with reference to FIGS. 4 to 7. In these figures, elements similar to those of the preceding figures are designated by identical reference numerals.

In a second embodiment illustrated in FIGS. 4 and 5, the sonotrode 2 may comprise a duct 32 forming an internal channel connected to two orifices 36 and 38 for entering and leaving cooling fluid.

The conduit 32 comprises a plurality of rectilinear portions 33 extending parallel to each other in a direction parallel to a longitudinal axis A. The portions 33 are located equidistant from each other and form a circle in a parallel cutting plane to a transverse axis B. This arrangement, which may vary from that of Figures 4 and 5, allows to evenly distribute the hollow areas in the sonotrode 2 to optimize the cooling of the latter. The portions 33 are connected to each other via two circular portions 34 located substantially at the openings 36 and 38 and extending in a direction perpendicular to the longitudinal axis A. The fluid circuit extends over approximately 80% of the length of the sonotrode 2 and on average 60% of its width.

In this embodiment, the empty volume of the sonotrode is equal to 17 259 mm ³ for a total volume of 100 428 mm ³ , ie a percentage of hollow zones equal to 20.8% of the total volume of the sonotrode. The heat exchange surface is itself equal to 11 828 mm ² .

In a third embodiment of the invention illustrated in FIGS. 6 and 7, the sonotrode may comprise a trellis-shaped conduit 40 connected to two input and output orifices (not shown), which duct forms an internal diffusion circuit. cooling fluid.

Like the duct 32, the duct 40 comprises a plurality of straight portions 42 extending parallel to each other in a direction parallel to the longitudinal axis A. The portions 42 are located equidistant from one another and form a network having a shape adapted to the region of the sonotrode in which they are located. For example, in the upper part of the sonotrode near the end 6, the portions 42 form a cylindrical network. In the lower part of the sonotrode near the end 8, the portions 42 form a network whose section in a plane parallel to the axis B has the shape of a rectangular parallelepiped. This arrangement, which may vary from that of FIGS. 6 and 7, makes it possible to uniformly distribute the hollow zones in the sonotrode 2 in order to optimize cooling of the latter.

The rectilinear portions 42 are connected to each other via connecting portions 44 extending in directions forming an angle of between 30 ° and 60 °, preferably substantially equal to 45 ° aveda direction in which extend the straight portions 42. The angles formed at the junction between the portions 42 and 44 make it easier to produce the sonotrode in additive manufacturing and also have the advantage of easily generating large turbulences of the cooling fluid flowing through the duct 40 .

In this embodiment, the duct extends about 80% of the length of the sonotrode 2 and about 80% of its width.

In this embodiment, the empty volume of the sonotrode 2 is 25 352 mm ³ for a total volume of 100 428 mm ³ , a percentage of hollow zones equal to 33.8% of the total volume of the sonotrode. The heat exchange surface is equal to 19 078 mm ² .

In operation, compressed air (or any other coolant) is injected into the sonotrode duct (s) during operation. Having on the one hand one or more ducts extending over a length of between 70% and 80% of the length of the sonotrode 2 and over a width of between 40% and 80% of the width of the sonotrode 2 and on the other hand a conduit structure for generating and maintaining turbulence in the fluid flow along its path can effectively cool the sonotrode 2 or even to avoid heating of the latter in operation. This makes it possible to maintain a very high rate of production of plastic parts comprising elements to be welded to each other. other.

The invention is not limited to the embodiments presented and other embodiments will become apparent to those skilled in the art.

For example, it is conceivable to have different conduit shapes than those described above while maintaining similar cooling properties.

Nomenclature

^1st embodiment

2: sonotrode

4: main body

6: upper end

8: lower end

10: teeth

12: 1 ^st leads

14: ^2nd conduit

16: ^1, port ¹ leads

18: ^2nd orifice of the first duct

20: ^1st orifice of the ^2nd duct

22: ^2nd orifice of the ^2nd duct

24: single conduit

26: ^1st orifice of the single conduit

28: ^2nd orifice of the single conduit

30: terminal loop

Pi: no duct 12

P ₂ : no conduit 14

^2nd embodiment

32: led

33: straight portions

34: circular portions

36: ^1st orifice of the duct

38: ^2nd orifice of the duct

A: longitudinal axis

B: transverse axis

^3rd embodiment

40: led

42: straight portions

44: portions of connection

A: longitudinal axis

B: transverse axis

Claims

claims

Sonotrode (2) for welding two plastic parts, characterized in that the sonotrode is made in one piece, and in that it comprises:

at least one inlet port (16, 20, 26; 36; 46),

at least one outlet orifice (18, 22, 28; 38; 48), and

at least one conduit (12, 14, 24; 32; 40) forming an internal channel communicating with the inlet and outlet ports so that the sonotrode comprises at least one fluid circuit extending from the port of input, through the inner channel and up to the outlet, the inner channel having a nonlinear shape adapted to optimize the heat exchange with the fluid flowing through it.

Sonotrode (2) according to claim 1, wherein the duct (12, 14, 24; 32; 480) is capable of generating and maintaining turbulence in the fluid flowing through it.

Sonotrode (2) according to any one of the preceding claims, wherein the conduit (12, 14, 24; 40) has a shape selected from the double helix form or the lattice form.

Sonotrode (2) according to any one of the preceding claims, comprising a hollow volume between 5% and 60% of the total volume of the sonotrode, preferably between 8% and 40%, even more preferably between 20% and 34%.

Sonotrode (2) according to any one of the preceding claims comprising an exchange surface area of between 5,000 and 50,000 mm ² , preferably between 6,500 and 35,000 mm ² , even more preferably between 11,000 and 25,000 mm ² .

Sonotrode (2) according to any one of the preceding claims, wherein the conduit (12, 14, 24; 32; 40) is able to be traversed by a gas, preferably air.

Sonotrode (2) according to any one of the preceding claims, the sonotrode being produced by additive manufacturing.

Sonotrode (2) according to any one of the preceding claims, the sonotrode being made of titanium, aluminum or steel, with or without heat treatment.