Method and device for welding a thermoplastic polymer part onto a base containing thermoplastic polymer

Abstract

Title: Method and Device for Welding a Thermoplastic Polymer Part to a Thermoplastic Polymer Base. The invention relates to a method for welding a weldable element (2) to a base (3), the weldable element (2) having an interface surface (21) of thermoplastic polymer intended to be welded to a welding zone (31) of the base (3), the welding zone (31) of the base (3) being made of thermoplastic polymer capable of being welded to the thermoplastic polymer of the interface surface (21) of the weldable element (2), the method comprising a step of heating the weldable element (2) and the base (3), followed by a step of pressing the weldable element (2) onto the base (3). Figure for the abstract: Fig. 1

Description

Title of the invention: Method and device for welding a thermoplastic polymer part to a base containing thermoplastic polymer

[0001] The field of the invention is that of the design and manufacture of welded thermoplastic parts.

[0002] The invention relates more particularly to a method and a device for producing a part composed of two parts made of thermoplastic polymer assembled to each other by welding.

[0003] It is known to assemble a part made of polymer material onto an element made of composite material by gluing. This involves providing material (the glue), and makes it possible to obtain good mechanical performance.

[0004] In the field of the invention, thermoplastic welding of two composites of the same thermoplastic nature is known.

[0005] For example, a device for welding two thermoplastic composite plates to each other comprises heating means and pressing means.

[0006] The heating means comprise a radiant block intended to heat and emit infrared radiation.

[0007] The device also comprises two plates between which the welding is carried out.

[0008] Each tray is configured to carry one of the two plates to be welded. These plates to be welded, carried by the trays, are positioned so as to create an overlap between a part of one of the plates, and a part of the other of the plates. Welding is carried out between these two parts positioned opposite each other.

[0009] Initially, the plates are moved away from each other and a free volume is provided between the plates, and thus between the welded plates, to allow the insertion of the radiant block which, once heated, causes the heating of the plates to be welded at the level of their surface exposed to the infrared radiation of the radiant block.

[0010] Then the radiant block is removed and the trays are closed against each other quickly. The trays are pressed against each other so that a weld joint formed between the plates is consolidated, then the trays are moved apart from each other slowly to allow the removal of the plates welded to each other.

[0011] There is a need to improve such a technique, and more specifically to enable the welding of small-sized thermoplastic plastic elements onto thermoplastic composite plates, while exhibiting mechanical performance at least equal to that of glued type assemblies.

[0012] There is also a need for such an assembly technique which can be rapid and automated, and in particular faster than a gluing process while not requiring the addition of additional material.

[0013] The invention aims in particular to meet these needs of the prior art.

[0014] More specifically, the invention aims to propose a method and a device welding a part made of thermoplastic polymer material to another part made of thermoplastic polymer material, of larger size.

[0015] The invention also aims to provide such a method and such a device which make it possible to obtain an assembly of a mechanical quality at least equal to that of assemblies by gluing.

[0016] The invention also aims to provide such a device and such a method which make it possible to carry out an assembly more quickly than a method according to the prior art and which does not require the addition of material.

[0017] These objectives, as well as others which will appear subsequently, are achieved thanks to the invention which has as its subject a method of welding an element to be welded on a base, the element to be welded having an interface surface made of thermoplastic polymer intended to be welded on a welding zone of the base, at least the welding zone of the base being made of thermoplastic polymer capable of joining by welding with the thermoplastic polymer of the interface surface of the element to be welded, the method comprising a step of heating the element to be welded and the base, then a step of pressing the element to be welded on the base, the thermoplastic polymer of the interface surface having a first temperature limit corresponding to a temperature from which the thermoplastic polymer of the interface surface is in a molten state,the thermoplastic polymer of the welding zone having a second temperature terminal corresponding to a temperature from which the thermoplastic polymer of the interface surface is in a molten state; , characterized in that the heating step comprises a main heating sub-step consisting of: - heating the interface surface to a temperature above the first temperature limit, and - heat the welding zone to a temperature lower than the second temperature terminal; and in that, at the end of the heating step, the element to be welded has stored a quantity of heat equal to or greater than a quantity of heat necessary to bring, during the pressing step, the temperature of the welding zone to the melting temperature of the thermoplastic polymer of the welding zone of the base, and allow molecular creep between the interface surface and the welding zone.

[0018] Thanks to the method according to the invention, it is possible to carry out an assembly of an element to be welded on a base by means of local welding of the respective thermoplastic polymer materials, making it possible to obtain in a short time an assembly of a mechanical quality at least equal to that of assemblies by bonding.

[0019] Indeed, thanks to the interface surface which is brought to a temperature higher than the first temperature limit, and to the welding zone which is brought to a temperature lower than the second temperature limit, then during the pressing step, a temporary (molecular creep) and local fusion occurs at the interface between the element to be welded and the base thanks to the quantity of heat stored by the base locally at the interface surface.This welding allows the quality of the base material not to be affected because the radiation treatment is local and superficial.

[0020] Tests have demonstrated that the mechanical performance of such an assembly is at least equal to that of glued-type assemblies. In addition, no, or at least little, damage to the base has been observed, particularly in terms of post-welding delamination or ply slippage.

[0021] This process makes it possible not to generate particulate or molecular pollution, particularly present during the supply of material, for example for brazing, or for bonding.

[0022] This process can be automated in addition to being very quick to execute.

[0023] The interface surface may be made of a semi-crystalline or amorphous thermoplastic polymer, and the base welding zone may be made of a semi-crystalline or amorphous thermoplastic polymer.

[0024] If the thermoplastic polymer is semi-crystalline, the temperature limit corresponds to the melting temperature of said semi-crystalline thermoplastic polymer.

[0025] If the thermoplastic polymer is amorphous, the temperature limit corresponds to the glass transition temperature of said amorphous thermoplastic polymer.

[0026] According to a preferred solution, during the main heating sub-step, the interface surface is heated to a temperature lower than 120%, preferably lower than 116%, of the melting temperature of the semi-crystalline thermoplastic polymer of the interface surface of the element to be welded.

[0027] Advantageously, during the main heating sub-step, the interface surface is heated to a temperature greater than 110% of the melting temperature of the semi-crystalline thermoplastic polymer.

[0028] According to another preferred characteristic, during the main heating sub-step, the welding zone is heated to a temperature greater than 90%, preferably essentially greater than 99% of the melting temperature of the semi-crystalline thermoplastic polymer of the base welding zone.

[0029] According to an advantageous solution, during the heating step, the heating of the welding zone is carried out by focusing the heating on the welding zone.

[0030] In this way, the base material is preserved outside the welding zone.

[0031] In particular, it is avoided to heat the perimeter of the welding zone, or at least to limit this heating, to avoid modifying the structural properties of the material of the perimeter of the welding zone.

[0032] According to an advantageous variant, the heating step comprises a final heating sub-step, following the main heating sub-step, and during which the heating of the welding zone is increased to the second terminal or beyond the second temperature terminal.

[0033] By means of such a final heating sub-step, the fact that between the end of heating and the contacting of the element to be welded and the base during pressing, there is a non-compressible time interval producing a perceptible cooling of the welding zone is compensated. These are heat losses by convection.

[0034] According to another embodiment variant, during the final heating sub-step, the heating of the interface surface is increased relative to a temperature reached during the main heating sub-step.

[0035] In this case, if the thermoplastic polymer of the interface surface is a semi-crystalline thermoplastic polymer, the interface surface is brought to a temperature strictly lower than 135% of the melting temperature of the thermoplastic polymer, and preferably lower than 130% of this melting temperature.

[0036] Degradation of the thermoplastic material is thus avoided.

[0037] According to this other variant, the interface surface is also heated to compensate for the time interval occurring between the effective end of the heating and the moment when contact occurs between the element to be welded and the base during the pressing phase.

[0038] According to an advantageous embodiment, the main heating sub-step comprises: - a preliminary phase of temperature increase of a surface temperature of the interface surface and the welding zone; - a final phase of stabilization of the surface temperature of the interface surface and the welding zone.

[0039] Thanks to such a main heating sub-step, a homogenization of the surface temperature is achieved at the interface surface and the zone of welding following the preliminary temperature rise phase.

[0040] This improves the welding quality obtained over the entire interface surface and the welding zone.

[0041] The invention also relates to a device for welding an element to be welded to a base, the element to be welded having an interface surface made of thermoplastic polymer intended to be welded to a welding zone of the base, the welding zone of the base being made of thermoplastic polymer capable of joining by welding with the thermoplastic polymer of the interface surface of the element to be welded, the device comprising means for heating the element to be welded and the base, and means for pressing the element to be welded against the base, the thermoplastic polymer of the interface surface having a temperature terminal, called the first temperature terminal, corresponding to a temperature from which the thermoplastic polymer of the interface surface is in a molten state, the thermoplastic polymer of the welding zone having a temperature terminal, called the second temperature terminal,corresponding to a temperature from which the thermoplastic polymer of the interface surface is in a molten state, characterized in that the heating means comprise two separate heating sub-assemblies, including a first heating sub-assembly for heating the element to be welded and a second heating sub-assembly for heating the base, , and in that, during a main heating sub-step, the first heating sub-assembly is configured to produce heating at a temperature higher than the first temperature limit, and the second heating sub-assembly is configured to produce heating at a temperature lower than the second temperature limit.

[0042] The welding device makes it possible to implement the method described above, and makes it possible to present its advantages.

[0043] According to an advantageous characteristic, the device comprises a mask for focusing the heating, or a concentrator of radiative beams, on the welding zone of the base.

[0044] Such a focusing mask or such a concentrator makes it possible to concentrate the heating on the welding zone, and to tend to avoid heating the periphery of the welding zone of the base.

[0045] According to a preferred characteristic, the device comprises an element holder configured to carry an element to be welded, the element holder comprising a peripheral wall surrounding a cavity for receiving the element to be welded, the peripheral wall having a peripheral pressing surface intended to extend around the interface surface of the element to be welded received in the receiving cavity, in the continuity of this interface surface.

[0046] Thanks to such an element holder, a fining of the element to be welded is avoided, or at least limited, following its pressing on the base. Indeed, the pressure applied between the two elements when they are brought into contact tends to cause the polymer of the element to be welded, which is in the molten state, to flow.

[0047] It is also permitted to maintain the structural quality of the base around the welding area.

[0048] Other characteristics and advantages of the invention will appear more clearly on reading the following description of different preferred embodiments of the invention, given as illustrative and non-limiting examples, and the appended figure: • [Fig.l] [Fig.l] is a schematic representation of a device for welding an element to be welded to a base, this device implementing a method according to the invention.

[0049] With reference to [Fig.l], the welding device 1 according to the invention is described below.

[0050] This welding device 1 is designed to implement the welding method which will be described later.

[0051] The welding device 1 is designed to allow the welding of an element 2 to be welded onto a base 3.

[0052] The element 2 to be welded has an interface surface 21.

[0053] This interface surface 21 is, according to the present embodiment, flat. However, it is conceivable that this interface surface 21 is not flat.

[0054] The base 3 has a welding zone 31.

[0055] According to the present embodiment, this welding zone 31 is flat. However, as for the interface surface 21, it is conceivable that the welding zone 31 is not flat.

[0056] The interface surface 21 and the welding zone 31 each have a shape adapted to their welding. This interface surface 21 and this welding zone 31, to optimize their welding, have a rigorously complementary shape. However, a potential difference in relief between the two shapes is conceivable, for example to create a housing between the interface surface 21 and the welding zone 31.

[0057] During welding, the interface surface 21 of the element 2 to be welded is intended to be welded to the welding zone 31 of the base 3.

[0058] The surface 21 of the element 2 to be welded is made of thermoplastic polymer.

[0059] More generally, the element 2 to be welded can be entirely made of thermoplastic polymer.

[0060] The welding zone 31 of the base 3 is made of thermoplastic polymer. This thermoplastic polymer of the welding zone 31 is in particular capable of joining by welding with the thermoplastic polymer of the interface surface 21 of the element 2 to be welded.

[0061] The base 3 may be entirely made of thermoplastic polymer.

[0062] However, preferably, the base 3 is a composite material.

[0063] As a result, the base 3 can comprise a matrix which is then made of thermoplastic polymer.

[0064] In this case, the composite base 3 may have a plurality of layers including a surface layer which is then made of thermoplastic polymer, so that the welding zone 31 is made of thermoplastic polymer.

[0065] These thermoplastic polymers can be amorphous or semi-crystalline thermoplastic polymers.

[0066] The thermoplastic polymer couples may in particular be the following, respectively for the welding zone 31 and for the interface surface 21: - polyamide / polyamide, - polyphenylene sulfide / polyphenylene sulfide, - polyetheretherketone / polyetheretherketone, - polyetheretherketone / polyetherimide, - polyetherimide / polyetherimide.

[0067] The thermoplastic polymer of the interface surface has a temperature limit, called the first temperature limit, which corresponds to a temperature from which the thermoplastic polymer of the interface surface is in a molten state.

[0068] Similarly, the thermoplastic polymer of the welding zone has a temperature terminal, called the second temperature terminal, which corresponds to a temperature from which the thermoplastic polymer of the interface surface is in a molten state.

[0069] If the thermoplastic polymer is semi-crystalline, the temperature limit then corresponds to the melting temperature of said semi-crystalline thermoplastic polymer.

[0070] If the thermoplastic polymer is amorphous, the temperature limit then corresponds to the glass transition temperature of said amorphous thermoplastic polymer.

[0071] The welding device 1 comprises a frame for supporting its various components described below.

[0072] The device 1 also comprises: - means for heating the element 2 to be welded and the base 3; - pressing means 4 of the element 2 to be welded against the base 3.

[0073] The device 1 also comprises a carriage 6.

[0074] This carriage 6 is mounted movably on an axis 61.

[0075] The axis 61 extends transversely to a pressing axis of the element 2 to be welded against the base 3.

[0076] The carriage 6 comprises motor means 62 making it possible to motorize the movement of the carriage 6 along the rail 61.

[0077] The heating means previously mentioned are carried by the carriage 6.

[0078] These heating means more precisely comprise two distinct heating sub-assemblies.

[0079] The heating means comprise in particular a first heating subassembly 51 for heating the element 2 to be welded, and a second heating subassembly 52 for heating the base 3.

[0080] The first heating subassembly 51 and the second heating subassembly 52 comprise emitters 50 of infrared radiation.

[0081] Alternatively, the emitters 50 of infrared radiation can be replaced by other means of emitting heating radiation such as lasers.

[0082] These emitters 50 are positioned on one side of a carriage 6 to be able to emit radiation in the direction of the element 2 to be welded, and on another side of the carriage 6, opposite the first side, to emit radiation in the direction of the base 3.

[0083] As explained below, the emitters 50 of the first heating subassembly 51 are designed to be operated and controlled independently of the emitters 50 of the second heating subassembly 52.

[0084] According to the present embodiment, the device 1 further comprises means for measuring a surface temperature of the interface surface 21 and the welding zone 31.

[0085] These measuring means comprise a first pyrometer 71 and a second pyrometer 72.

[0086] The first pyrometer 71 and the second pyrometer 72 are carried by the carriage 6. As illustrated in [Fig.l], these pyrometers 71, 72 are oriented to carry out a measurement respectively of the interface surface 21 and of the welding zone 31.

[0087] These pyrometers, shown schematically, can integrate end mirrors to move the electronics away from the transmitters 50.

[0088] The device 1 also comprises a holding table 40 for the base 3. This holding table 40 makes it possible to hold the base 3 during the pressing of the element 2 to be welded by the pressing means 4.

[0089] As detailed below, the welding method comprises a heating step and then a pressing step. During the heating step, the carriage 6 is inserted between the element 2 to be welded and the base 3, to allow heating of the interface surface 21 and the welding zone 31, then the carriage 6 is shifted to allow the element 2 to be welded to be pressed against the base 3.

[0090] According to the embodiment shown, the device 1 further comprises a mask 8 for focusing the heating on the welding zone 31 of the base 3.

[0091] This focusing mask 8 has a through cavity of truncated cone shape allowing the passage of infrared radiation produced by the emitters 50 of the second heating sub-assembly 52 in the direction of the welding zone 31.

[0092] This focusing mask 8 can for example be made of ceramic.

[0093] This focusing mask 8 is coupled to the carriage 6 so that it can be removed when the carriage 6 is shifted to the side of the pressing axis of the element 2 to be welded towards the base 3.

[0094] According to an embodiment not shown, the device may comprise a concentrator of radiative beams as an alternative to the focusing mask.

[0095] Still according to the present embodiment shown, the device 1 further comprises an element holder 9. This element holder 9 is coupled to the pressing means 4.

[0096] This element holder 9 is configured to carry the element 2 to be welded.

[0097] The element holder 9 comprises a main part 91 and a peripheral wall 92.

[0098] The element holder 9 delimits a cavity for receiving the element 2 to be welded. The wall peripheral 92 surrounds the receiving cavity of the element 2 to be welded.

[0099] Furthermore, the peripheral wall 92 has a peripheral pressing surface 93 which is intended to extend around the interface surface 21 of the element 2 to be welded received in the receiving cavity. This peripheral surface 93 extends in the continuity of the interface surface 21.

[0100] Advantageously, the peripheral wall 92 is mounted to move relative to the main part 91.

[0101] In this case, the pressing means 4 are configured to apply a differentiated pressing force to the main part 91 and to the peripheral wall 92.

[0102] In this case, the pressing means 4 can be configured to exert a greater pressing force at the peripheral wall 92 than the pressing force exerted on the main part 91.

[0103] In this way, during pressing, a fining of the element 2 to be welded is avoided or limited and the quality of the base 3 is maintained.

[0104] The welding process is now described below.

[0105] The welding method is a method of welding the element 2 to be welded onto the base 3.

[0106] This welding method comprises a step of heating the element 2 to be welded and the base 3.

[0107] Subsequent to the heating step, the method comprises a step of pressing element 2 to be welded onto base 3.

[0108] The heating step comprises a main heating sub-step.

[0109] This main heating sub-step consists of: - heating the interface surface 21 to a temperature higher than the first temperature limit, and - heating the welding zone 31 to a temperature lower than the second temperature terminal.

[0110] At the end of the heating step, the element 2 to be welded has stored a quantity of heat equal to or greater than a quantity of heat necessary to bring, during the pressing step, the temperature of the welding zone 31 to the melting temperature of the thermoplastic polymer of the welding zone 31 of the base 3, and to allow molecular creep between the interface surface 21 and the welding zone 31.

[0111] In the case where the thermoplastic polymers of the interface surface 21 and of the welding zone 31 are semi-crystalline thermoplastic polymers, the first temperature terminal and the second temperature terminal correspond to the respective melting temperatures of these thermoplastic polymers.

[0112] In the case where the thermoplastic polymers of the interface surface 21 and of the welding zone 31 are amorphous thermoplastic polymers, the first temperature terminal and the second temperature terminal correspond to the respective glass transition temperatures of these thermoplastic polymers.

[0113] In the case where the thermoplastic polymer(s) of the interface surface 21 and / or of the welding zone 31 are of the semi-crystalline type, then the following parameters are applicable:

[0114] During the main heating sub-step, the interface surface 21 is heated to a temperature lower than 120%, preferably lower than 116%, of the melting temperature of the semi-crystalline thermoplastic polymer of the interface surface 21 of the element 2 to be welded.

[0115] Advantageously, during the main heating sub-step, the interface surface is heated to a temperature greater than 110% of the melting temperature of the semi-crystalline thermoplastic polymer.

[0116]

[0117] During this main heating sub-step, the welding zone 31 is heated to a temperature greater than 90%, preferably greater than 99%, of the melting temperature of the semi-crystalline thermoplastic polymer of the welding zone 31 of the base 3.

[0118] In other words, the interface surface 21 is brought just beyond the first temperature limit, while the welding zone 31 is brought just below the second temperature limit.

[0119] According to the present embodiment, the heating step further comprises a terminal heating sub-step.

[0120] This final heating sub-step, which follows the main heating sub-step, is intended to compensate for the fact that between the end of the heating and the actual start of pressing the element 2 to be welded against the base 3, there is a non-compressible time interval during which the interface zone 21 and the welding zone 31 decrease in temperature.

[0121] This time interval corresponds in particular to the time necessary to remove the carriage 6 and begin pressing.

[0122] To this end, during the final heating sub-step, the heating of the welding zone 31 is increased to the melting temperature, or to a temperature higher than the melting temperature of the thermoplastic polymer of the welding zone 31 of the base 3.

[0123] During the final heating sub-step, the heating of the interface surface 21 may also be increased relative to a temperature reached during the main heating sub-step.

[0124] In other words, a heating peak is produced prior to the removal of the carriage 6 and the start of pressing the element 2 to be welded against the base 3.

[0125] Preferably, a maximum of three seconds elapse between the end of heating and the start of pressing. Beyond this, undesirable overheating of the materials is necessary. Of course, the aim is to shorten this period as much as possible.

[0126] During the main heating sub-step, the surface temperatures of the interface surface 21 and the welding zone 31 are stabilized.

[0127] Also, the main heating sub-step includes: - a preliminary phase of increasing the temperature of the interface surface 21 and the welding zone 31; - a final phase of stabilization of the surface temperature of the interface surface 21 and the welding zone 31.

[0128] During the preliminary temperature rise phase, the interface surface 21 and the welding zone 31 see their temperature increase under the effect of the infrared radiation from the emitters 50 up to a pre-programmed set temperature which is different and distinct depending on the interface surface 21 and the welding zone 31.

[0129] The method advantageously implements a step of real-time control of the surface temperatures of the interface zone 21 and the welding zone 31. These surface temperatures are controlled using the first pyrometer 71 and the second pyrometer 72.

[0130] As soon as one of the interface surface 21 or the welding zone 31 has reached the set temperature, it is expected that the other of the interface surface 21 and the welding zone 31 has also reached its set temperature. The preliminary temperature rise phase is then completed and it has moved on to the final stabilization phase.

[0131] During this final stabilization phase, the respective set temperatures are maintained so that there is a homogenization of the surface temperatures at all points of the interface surface 21 and at all points of the welding zone 31.

[0132] During the heating step, the heating of the welding zone 31 is carried out by focusing the heating on the welding zone 31.

[0133] This focusing is notably carried out using the focusing mask 8 previously described.

[0134] The device 1 and the method previously described make it possible to carry out welding of the element 2 to be welded to the base 3 which has mechanical assembly performances at least equal to those of glued type assemblies.

[0135] Tests and analyses have demonstrated, for example in the case where the base is a composite, that there is little or no damage to the thermoplastic composite plate or part and in particular no post-welding delamination or ply slippage.

[0136] This process makes it possible not to generate particulate or molecular pollution.

[0137] The device 1 makes it possible to carry out welding which is notably faster than a gluing assembly process and which makes it possible not to require material, and which is also automatable.

Claims

Claims

1. Method for welding an element (2) to be welded to a base (3), the element (2) to be welded having an interface surface (21) made of thermoplastic polymer intended to be welded to a welding zone (31) of the base (3), the welding zone (31) of the base (3) being made of thermoplastic polymer capable of joining by welding with the thermoplastic polymer of the interface surface (21) of the element (2) to be welded, the method comprising a step of heating the element (2) to be welded and the base (3), then a step of pressing the element (2) to be welded onto the base (3), the thermoplastic polymer of the interface surface having a temperature terminal, called the first temperature terminal, corresponding to a temperature from which the thermoplastic polymer of the interface surface is in a molten state, the thermoplastic polymer of the welding zone having a temperature terminal, called the second temperature terminal,corresponding to a temperature from which the thermoplastic polymer of the interface surface is in a molten state, characterized in that the heating step comprises a main heating sub-step consisting of: - heating the interface surface (21) to a temperature higher than the first temperature limit, and - heating the welding zone (31) to a temperature lower than the second temperature limit, and in that, at the end of the heating step, the element (2) to be welded has stored a quantity of heat strictly greater than a quantity of heat necessary to bring, during the pressing step, the temperature of the welding zone (31) to the second temperature limit, and to allow molecular creep between the interface surface and the welding zone.,

2. Method according to the preceding claim, characterized in that during the main heating sub-step, the interface surface (21) is heated to a temperature lower than 120%, preferably lower than 116%, of the melting temperature of the semi-crystalline thermoplastic polymer of the interface surface (21) of the element (2) to be welded.

3. A method according to any preceding claim, ca- characterized in that during the main heating sub-step, the welding zone (31) is heated to a temperature greater than 90%, preferably greater than 99%, of the melting temperature of the semi-crystalline thermoplastic polymer of the welding zone (31) of the base (3).

4. Method according to any one of the preceding claims, characterized in that during the heating step, the heating of the welding zone (31) is carried out by focusing the heating on the welding zone (31).

5. Method according to the preceding claim, characterized in that the heating step comprises a final heating sub-step, following the main heating sub-step, and during which the heating of the welding zone (31) is increased to the second temperature limit or beyond the second temperature limit.

6. Method according to the preceding claim, characterized in that during the final heating sub-step, the heating of the interface surface (21) is increased relative to a temperature reached during the main heating sub-step.

7. Method according to any one of the preceding claims, characterized in that the main heating sub-step comprises: - a preliminary phase of increasing the temperature of a surface temperature of the interface surface (21) and the welding zone (31); - a final phase of stabilizing the surface temperature of the interface surface (21) and the welding zone (31).

8. Device (1) for welding an element (2) to be welded to a base (3), the element (2) to be welded having an interface surface (21) made of thermoplastic polymer intended to be welded to a welding zone (31) of the base (3), the welding zone (31) of the base (3) being made of thermoplastic polymer capable of joining by welding with the thermoplastic polymer of the interface surface (21) of the element (2) to be welded, the device (1) comprising means for heating the element (2) to be welded and the base (3), and means for pressing (4) the element (2) to be welded against the base (3), characterized in that the heating means comprise two separate heating sub-assemblies, including a first heating sub-assembly (51) for heating the element (2) to be welded and a second heating sub-assembly (52) for heating the base (3), and in that that, during a main heating sub-step: - the first heating subassembly (51) is configured to produce heating at a temperature higher than a first temperature limit corresponding to a temperature from which the thermoplastic polymer of the interface surface is in a molten state; - the second heating subassembly (52) is configured to produce heating at a temperature lower than a second temperature limit corresponding to a temperature from which the thermoplastic polymer of the welding zone is in a molten state.

9. Device (1) according to the preceding claim, characterized in that it comprises a mask (8) for focusing the heating, or a concentrator of radiative beams, on the welding zone (31) of the base (3).

10. Device (1) according to any one of claims 8 and 9, characterized in that it comprises an element holder (9) configured to carry an element (2) to be welded, the element holder (9) comprising a peripheral wall (92) surrounding a cavity for receiving the element (2) to be welded, the peripheral wall (92) having a peripheral pressing surface (93) intended to extend around the interface surface (21) of the element (2) to be welded received in the receiving cavity, in the continuity of this interface surface (21).

Images