Method for evaluating an assembly made by welding parts made of thermoplastics

Description

Technical field

[0001] The present invention relates to a method for evaluating an assembly by welding of parts based on thermoplastic materials, a test piece and its associated uses and the associated welding system. Technical background

[0002] Parts made from thermoplastic materials have many applications, particularly in the aeronautics industry for the manufacture of fuselage skin parts, frames, or aircraft stringers. Alternatively, these parts can be used for space, automotive, or sports equipment.

[0003] These parts may include reinforcing fibers, for example carbon fibers and / or glass fibers, dispersed in a thermoplastic polymer matrix. These parts based on thermoplastic materials are commonly referred to as composite parts or composite material parts.

[0004] For some applications, it may be necessary to combine several composite parts, such as, for example, in the case of an aircraft fuselage, a skin panel, stiffeners and frames.

[0005] Various welding assembly processes (also called welding processes or manufacturing processes) by heating parts made from thermoplastic materials are known. A distinction is made between static welding processes and dynamic welding processes, in which the heating element moves relative to the parts to be welded. For example, the welding of the parts can be carried out by direct or indirect heating of the parts. Technologies based on the heating of an insert (or susceptor) previously deposited at the interface of the parts to be welded exist in particular. The parts can be welded by applying different types of heat sources. For example, the heat source can be obtained by induction, resistive effect, vibration, friction, ultrasound, use of a laser, hot gas flow or conduction from an external heat source.

[0006] By way of example, application PCT / FR2019 / 051775 filed on July 16, 2019 (unpublished) describes in particular a method of welding at least two rigid parts comprising a thermoplastic material and having respective surfaces to be welded, comprising: inserting an insert between the surfaces to be welded of the two parts; supplying heat by said insert; in which the insert moves relative to the parts to be welded during welding, in a welding direction D.

[0007] Depending on the welding process implemented and / or the type of parts to be welded, the quality of the weld joint must be assessed, and the welding parameters optimized, in order to determine whether the welding properties are satisfactory, particularly in terms of performance, efficiency, speed, integrity and homogeneity. Indeed, the implementation of such processes on an industrial scale and on large parts can have an impact on the reliability and repeatability of the quality of the weld joint, and requires satisfactory control of the heating of the parts to be welded. Optimizing the welding parameters also limits the disadvantages of certain welding assembly processes, including deformation, decompaction and / or delamination of the welded parts, lack of homogeneity of the weld joint, etc.

[0008] US patent 5,902,935 published on May 11, 1999 describes in particular a non-destructive method for evaluating the quality of welding of parts based on thermoplastic materials by using electromagnetic pulses to induce vibrations in the insert and by analyzing an acoustic signal obtained.

[0009] Welding technologies are also disclosed in the following documents: US application US 2014 / 0124125 A1 published on May 8, 2014, European application EP 2801472 A1 published on November 12, 2014 and the article by M. Hongoh et al., Japanese Journal of Applied Physics, Vol.45, No.5B, 2006, pp.4806-4811.

[0010] There is therefore a real need to provide a method for evaluating the welding assembly of parts based on thermoplastic materials; in particular the performance, efficiency, speed, integrity and / or uniformity of the welding.

[0011] There is also a real need to provide a method for evaluating the thermal profile of parts made from thermoplastic materials during their assembly by welding.

[0012] There is also a real need to provide a method for calibrating the welding parameters of parts made from thermoplastic materials.

[0013] There is also a real need to provide a qualification process for welding parts made from thermoplastic materials, particularly in the aeronautics sector.

[0014] There is also a real need to provide a method for monitoring a welding assembly, in particular the means and materials used, as production progresses. Summary of the invention

[0015] The invention relates firstly to a method for evaluating an assembly by welding of parts based on thermoplastic materials and having surfaces to be welded and respective free surfaces comprising: 1- the supply of a test piece comprising at least two pieces overlapping at least in part; at least one of the parts being a perforated reference part comprising at least one perforation in its thickness; 2- the provision of a welding installation comprising at least one heating element and at least one temperature sensor; 3- the supply of heat by the heating element; 4- the measurement of at least one internal temperature of the test piece by the temperature sensor at the perforation; in which the heating element and the temperature sensor move relative to the parts to be welded during welding, in a welding direction D.

[0016] In one embodiment, the heating element is an insert, said insert being inserted between the surfaces to be welded of the two parts to be welded.

[0017] In one embodiment, said insert is heated by induction, by resistive effect, by vibration, by friction, by ultrasound or by use of a laser by a flow of hot gas or by conduction from an external heat source; preferably by induction or by resistive effect; very preferably by induction or alternatively by resistive effect.

[0018] In one embodiment, the perforation is a perforation passing through all or part of the thickness of the reference perforated part.

[0019] In one embodiment, the perforation is a perforation of square section, rectangular section or circular section; preferably of circular section.

[0020] In one embodiment, the reference perforated part comprises at least two perforations aligned perpendicularly and / or at least two perforations aligned parallel to the welding direction D.

[0021] In one embodiment, the reference perforated part comprises at least a first perforated section, a second non-perforated section and a third perforated section; the perforated sections respectively comprising at least one perforation and framing the non-perforated section.

[0022] In one embodiment, the method further comprises measuring at least one temperature of the free surface of the reference perforated part (surface temperature).

[0023] In one embodiment, the surface temperature and the internal temperature are measured transversely and / or longitudinally, relative to the welding direction D.

[0024] In one embodiment, the method further comprises recording the temperature values.

[0025] In one embodiment, the method further comprises comparing the measured temperatures with reference temperatures.

[0026] In one embodiment, the method further comprises a step of calibrating the parameters of the welding assembly process.

[0027] The invention secondly relates to a method of assembling by welding at least one series of parts based on thermoplastic materials to be welded and having surfaces to be welded and respective free surfaces comprising: 1- the determination of the welding parameter of said parts to be welded, from the evaluation of the assembly by welding of a test piece forming a representative sample according to the evaluation method described opposite; and 2- the implementation of the assembly by welding of said parts to be welded.

[0028] The invention relates thirdly to a test piece for implementing the method for evaluating an assembly by welding of parts based on thermoplastic materials as described opposite, said test piece comprising at least two parts based on thermoplastic materials having surfaces to be welded placed at least partly opposite each other and respective free surfaces, at least one of the parts being a perforated reference part comprising at least one perforation.

[0029] The invention relates fourthly to the use of the test piece as described opposite for the evaluation of an assembly by welding of parts based on thermoplastic materials to be welded, the test piece being a representative sample of said parts; preferably for comparison with a reference, for the calibration of at least one welding parameter, for the calibration of at least one welding parameter and / or for monitoring a welding assembly process.

[0030] Fifthly, the invention relates to a welding system for carrying out the evaluation of a welding assembly comprising a test piece and a welding installation, as described opposite. Brief description of the figures

[0031] There figure 1 represents a schematic perspective view of a welding installation 1 which can be adapted for implementing the method according to the invention. figure 2represents a perspective view of a perforated part of reference 20. The figure 3 represents a perspective view of a perforated part of reference 30. The figure 4 represents a perspective view of a test piece comprising a perforated reference part 30 and a non-perforated reference part 40, according to the present invention. Figure 5 represents a perspective view of a first perforated section of a perforated part of reference 50. The figure 6 represents a perspective view of a portion of a test piece corresponding to the first perforated section of a perforated reference part 50 and to the corresponding section of the second reference part 60. The figure 7 represents a cross-sectional view of a test piece at an alignment of perforations of a reference perforated part 50 and the corresponding second reference part 60. The figure 8is an image of surface and interface temperatures of a specimen obtained by thermal camera at the intermediate zone. The figure 9 is a graphical representation of the surface and interface temperatures of a test piece as a function of time, measured by a thermal camera at the intermediate zone during assembly by welding using the method according to the invention. The figure 10 is a graphical representation of the heating, welding and surface temperatures of a test piece as a function of the setpoint setting, measured by a thermal camera at the intermediate zone during assembly by welding using the method according to the invention. Detailed description

[0032] The invention is now described in more detail and in a non-limiting manner in the following description. Definitions

[0033] The term "rigid part" means a part that does not deform or deforms only slightly under its own weight. The rigidity of the part can be characterized by a deformation test of a test piece of the part to be welded. The test piece used in the deformation test is to be distinguished from the test piece according to the present invention. The deformation test consists of preparing a test piece cut from the portion of the part to be tested having the smallest thickness (if variable thickness), said test piece having a length of 12 cm, a width of 1 cm. The rigidity is assessed by placing and centering the test piece on two supports 10 cm apart. Under standard conditions of temperature (18 °C) and pressure (1,013.10 -3 < Pa), the test piece has a maximum deflection at its center of 1 cm, corresponding to a relative deformation with respect to the length of 10% maximum.

[0034] The term "part to be welded" means a part made from thermoplastic materials, i.e. a part comprising at least one matrix of thermoplastic materials. The part may be a part having a single-block structure (single-layer part) or a part having a multi-layer structure (multi-layer part, for example from 2 to 150 layers). A multi-layer part may comprise layers of identical or different compositions. The term "composite material" means a material comprising reinforcing fibers in a matrix of thermoplastic material. The term "non-composite material" means a material without reinforcing fibers.

[0035] A "reference part" means a part corresponding to a representative sample of a part to be welded.

[0036] The term “welding product” means a product comprising at least two parts, as described opposite, welded together using a process suitable for the welding assembly of parts made from thermoplastic materials.

[0037] The term "reference welding product" means the test piece according to the present invention comprising at least two parts including a perforated reference part, as described opposite, welded together using a method suitable for the assembly by welding of parts based on thermoplastic materials.

[0038] Unless otherwise stated, all percentages relating to quantities stated are volume percentages. Method for evaluating a welding assembly

[0039] The present invention relates to a method for evaluating a welding assembly of parts based on thermoplastic materials and having surfaces to be welded and respective free surfaces. The method according to the invention is implemented using a welding installation and a test piece, as described below.

[0040] In a first aspect, the invention relates to a method for evaluating a welding assembly of parts based on thermoplastic materials and having surfaces to be welded and respective free surfaces comprising: 1- the provision of a test piece comprising at least two partially overlapping parts, as described below; at least one of the parts being a reference perforated part comprising at least one perforation in its thickness; 2- the provision of a welding installation comprising at least one heating element and at least one temperature sensor; 3- the provision of heat by the heating element; 4- the measurement of at least one internal temperature of the test piece by the temperature sensor at the perforation; in which the heating element and the temperature sensor move relative to the parts to be welded during welding, in a welding direction D.

[0041] The process is a dynamic welding process.

[0042] The method comprises a step of providing a test piece, as described below.

[0043] The method comprises a step of providing a welding installation, as described below, comprising at least one heating element and at least one temperature sensor. The heating element, as described below, is chosen from heating elements suitable for implementing a dynamic welding process, in particular by ultrasound, by induction, by vibration or by resistive effect. In a particular embodiment, the method may comprise the provision of a heating element being an insert and a step of inserting said insert between the surfaces to be welded of the two parts. Said insert may be heated by induction, by resistive effect, by vibration, by friction, by ultrasound or by use of a laser by a flow of hot gas or by conduction from an external heat source; preferably by induction or by resistive effect; very preferably by induction or alternatively by resistive effect.

[0044] The method comprises a step of measuring at least one internal temperature of the test piece by the temperature sensor at the perforation (internal temperature).

[0045] The provision of a test piece comprising at least one reference perforated part, which comprises at least one perforation, is particularly advantageous. Indeed, it allows the measurement of at least one internal temperature of the test piece at the perforation, and not only the measurement of at least one temperature of the free surface of the reference perforated part (surface temperature). The internal temperature of the test piece may differ depending on the type of perforation made in the thickness of the reference perforated part. Indeed, when the perforation passes completely through the reference perforated part (through perforation), the internal temperature measured is the temperature of the welding interface, that is to say at the interface of the two parts at their surfaces to be welded placed opposite each other (interface temperature).When the perforation only partially passes through the reference perforated part (blind perforation), the measured internal temperature is the temperature in the thickness of the reference perforated part at a given depth (internal temperature at a given depth).

[0046] The method may further comprise a step of measuring at least one temperature of the free surface of the reference perforated part (surface temperature).

[0047] Temperatures can be measured using at least one temperature sensor. Different embodiments are possible depending on the type of temperature sensors used. Surface and internal temperatures can be measured by the same temperature sensor. Alternatively, surface and internal temperatures can be measured by different temperature sensors.

[0048] The measurement zone may correspond to different zones, in particular the pre-heating zone, the heating zone, the intermediate zone between heating and compacting, the welding zone (compaction and mechanical holding) as well as the zones after compacting, depending on the position of the welding device relative to the perforations of the reference perforated part, in a welding direction D; preferably at the intermediate zone. By "heating zone" is meant the zone at which the parts to be welded are heated by the heating element, which causes the temperature of the parts to be welded to rise. The heating zone moves in conjunction with the movement of the heating element relative to the parts to be welded, in a welding direction D. In a particular embodiment, the heating zone corresponds to the superposition zone of the parts to be welded and the insert.The term "intermediate zone" means the zone immediately after the heating element has passed through, and in which the parts to be welded have reached a temperature suitable for welding (target temperature). The term "welding zone" means the zone where the parts are welded to each other, in particular by applying pressure. When the heating element is an insert, the internal temperature measured at the heating zone, with a through perforation positioned directly above the insert, is the temperature of the insert. The temperature measured at the intermediate zone, just after the heating zone, is the maximum interface temperature of the test piece.Measuring this temperature is particularly advantageous in that it makes it possible to determine the maximum temperature reached by the parts to be welded and whether this temperature is, for example, lower than the degradation temperature of the thermoplastic materials making up the parts. The temperature measured at the intermediate zone, just before the welding zone, is the temperature at the time of welding. Measuring this temperature is also particularly advantageous in that it makes it possible to correlate the quality of the weld joint, in particular its strength and integrity, with the welding temperature.

[0049] Internal and surface temperatures can be measured concurrently or successively.

[0050] Temperatures can be measured one-off or continuously.

[0051] The internal and surface temperatures can be measured transversely, i.e. in a direction perpendicular to the welding direction D and to the thickness of the parts to be welded, the surface temperature being measured at at least one solid (non-perforated) part and the internal temperature being measured at at least one hollow through or blind part (perforation). The temperatures can be measured punctually, with at least one measuring point for the surface temperature and at least one measuring point for the internal temperature. Alternatively, the temperatures can be measured continuously, preferably from one edge of the test piece to the other. Depending on the temperature sensor used, and their number, the temperatures can be measured simultaneously or successively.Transverse temperature measurement allows the variation of internal and / or surface temperatures over a cross-section of the specimen to be assessed, particularly between the center and the edges. This type of measurement allows the homogeneity of the internal and / or surface temperature to be assessed over the entire cross-section of the specimen, thermal variations at the edges (edge effects), etc.

[0052] Internal and / or surface temperatures can be measured longitudinally, continuously or punctually and repeatedly at regular intervals, i.e. in a direction parallel to the welding direction D and perpendicular to the thickness of the reference parts and passing alternately from the solid (non-perforated) parts to the hollow parts (perforations). Longitudinal temperature measurement makes it possible to evaluate the variation in internal and / or surface temperatures along the test piece as welding progresses. This type of measurement makes it possible to evaluate the evolution of the internal and / or surface temperature along the test piece during welding (advance of the welding means in relation to the test pieces), the thermal variations during welding, the thermal variations within the thickness as a function of the depth and position of the welding device in relation to the test piece.

[0053] Depending on the temperature sensor used, for example a thermal imaging camera, it is possible to measure both transverse and longitudinal temperatures simultaneously.

[0054] The method may include a preheating step, in particular of the area to be welded and / or the support, using any appropriate means. Preheating may be carried out using infrared lamps or a jet of hot air. The area to be welded and / or the support must be preheated to a temperature which must remain below the melting temperature of all the materials constituting the parts to be welded. Preheating makes it possible to better control the temperature of the welded interface, to limit the heat flow within the welded parts, and to control the crystallization of the materials, in particular in the welding area. Heating may be local, close to and at the right angles to the areas to be welded.

[0055] The method may comprise a step of bringing the surfaces to be welded of the two parts into contact by applying pressure to at least one of the two parts upstream of (i.e. in front of) and / or downstream of (i.e. behind) the position of the insert relative to the welding direction D.

[0056] The method may include a step of cooling the welded parts. This controlled cooling step may be necessary in particular for good crystallization of the polymer after welding. - The evaluation method described in the present invention also makes it possible to measure the temperatures in these preheating and cooling zones.

[0057] The method may further comprise a step of recording the measured surface and / or internal temperature values. This is particularly advantageous for the manufacture of aeronautical parts such as the fuselage because the recording of this data is necessary for the qualification of an aeronautical process.

[0058] The method may further comprise a step of comparing the measured surface and / or internal temperatures with reference surface and / or internal temperatures, in particular the expected theoretical surface and / or internal temperatures or the previously measured and validated surface and / or internal temperatures. For example, the reference temperatures may be the melting point of the thermoplastic matrix or its degradation temperature. The reference temperatures (expected theoretical temperatures or previously measured and validated temperatures) are to be distinguished from the temperatures measured by the method according to the invention, the second temperatures being compared with the first. During welding, this comparison makes it possible to determine whether the welding process complies with the usage requirements and whether the thermal profile of the test piece corresponds to the expected theoretical thermal profile or to the validated thermal profile.This comparison also makes it possible to qualify the welding process used, without the need to measure internal temperatures during the welding of the parts to be welded, of which the test piece is a representative sample. This is advantageous in the aeronautics sector, which applies very strict safety standards.

[0059] This comparison step may correspond in particular to the comparison of the measured temperatures with the weldability window of the welding assembly process. By "weldability window" is meant, for a particular parameter setting (or setpoint parameter setting), a process allowing the obtaining of surface and internal temperatures included in a temperature range delimited by the melting temperature and by the degradation temperature of the thermoplastic matrix. The parameter setting of the welding process corresponds to all of its setpoint parameters, the modification of a single one of which can have an impact on the surface and internal temperatures. In particular, the measured heating and welding temperatures are compared with the temperature range of the weldability window for a given parameter setting.If the heating temperature is below and / or the soldering temperature is above the temperature range, the welding process settings can be adapted so that the heating and soldering temperatures are within the solderability window.

[0060] The method may further comprise a step of calibrating the parameterization of the welding assembly process, namely the process of welding assembly of parts to be welded, of which the test piece is a representative sample. This step may be implemented in particular after measuring the surface and / or interface temperatures of the test piece and after comparing them with reference surface and / or interface temperatures. This step may occur in particular after comparing the measured heating and welding temperatures with the weldability window of the welding process. The calibration of at least one setpoint parameter of the welding process makes it possible to optimize the results, in particular in terms of performance, efficiency, speed, integrity and / or uniformity of the welding.The setpoint parameters can be chosen from the heating temperature, the surface temperature of the upper part to be welded, the speed of movement of the welding device between the surfaces to be welded of the two parts, the pressure applied to the parts to be welded, the cooling temperature and / or the regulation temperature of the parts to be welded, the proximity between the insert and the inductor (induction welding), the intensity and frequency of the magnetic field (induction welding), etc. During a production, the method according to the invention has the advantage of being able to compare and validate the performance of a welding installation at a given time with respect to the initial approved performance of this same installation. Welding process

[0061] The method for evaluating an assembly by welding a test piece can be integrated into a method for an assembly by welding at least one series of parts based on thermoplastic materials, of which the test piece is a representative sample.

[0062] In a second aspect, the invention relates to a method of assembling by welding at least one series of parts based on thermoplastic materials to be welded and having surfaces to be welded and respective free surfaces comprising: 1- the determination of the welding parameters of parts based on thermoplastic materials and having surfaces to be welded and respective free surfaces, from the evaluation of the assembly by welding of a test piece forming a representative sample according to the evaluation method described above; 2- the implementation of the assembly by welding of said parts to be welded.

[0063] The welding of the test piece and its evaluation may be carried out before the welding of at least one series of parts made from thermoplastic materials, of which the test piece is a representative sample. This preliminary evaluation makes it possible, in particular, to verify that the welding process settings are correct or, where appropriate, to calibrate them.

[0064] The welding of the test piece and its evaluation can be implemented after the welding of at least one series of parts made from thermoplastic materials, of which the test piece is a representative sample. This post-evaluation makes it possible in particular to verify that the welding process settings have not changed / deviated during its implementation.

[0065] When there are at least two series of parts made from thermoplastic materials to be welded, the welding assembly of the test piece and its evaluation may be implemented between two assemblies of parts made from thermoplastic materials, of which the test piece is a representative sample. This intermediate evaluation makes it possible in particular to verify the consistency of the welding process settings. Test tube

[0066] The method according to the invention comprises providing a test piece of the parts to be welded. The test piece currently designates an assembly comprising at least two parts including a perforated reference part. A reference part is a representative sample of a part to be welded, which comprises a free surface (external surface) and a surface to be welded (internal surface) placed opposite the surface to be welded of the other part to be welded.

[0067] In a third aspect, the invention relates to a test piece for implementing the evaluation method as described above, this test piece comprising at least two parts based on thermoplastic materials having surfaces to be welded placed at least partly opposite each other and respective free surfaces, at least one of the parts being a perforated reference part comprising at least one perforation.

[0068] The dimensions and shape of the parts forming the test piece may vary depending on the parts to be welded, the type of welding assembly process used, the operating mode, the implementation conditions, etc. Thus, a person skilled in the art will determine the characteristics of the test pieces to be used depending on the assembly process selected, depending on the parts to be welded, etc. The present invention is therefore not limited to test pieces comprising parts having determined shapes, dimensions and / or a percentage of overlap. Indeed, the test piece according to the present invention can be used with any type of suitable process for welding parts based on thermoplastic materials.

[0069] The test piece comprises at least two parts. These parts may be rigid in that they do not deform or deform only slightly under their own weight. Their rigidity may be characterized by a deformation test as defined above. In particular, the parts are also rigid under the thermal conditions of the welding operation, that is to say they are rigid before, during and after welding. Each part forming the test piece may have the characteristics of the corresponding part to be welded of which it forms a representative sample. Thus, by way of example, the reference part may be a part comprising non-composite materials or composite materials, a single-layer part or a multi-layer part.

[0070] Each reference part may be of any suitable shape, in particular each reference part is of parallelogram shape, preferably of square or rectangular shape, very preferably of rectangular shape.

[0071] Each part can be of any suitable dimension, including any suitable length, any suitable width, and any suitable thickness. 'Length' means the dimension parallel (longitudinal) to the welding direction. 'Width' means the dimension perpendicular (transverse) to the welding direction. The dimensions of a reference part can be 1 to 20% of the dimensions of the corresponding part to be welded.

[0072] The pieces forming the test piece overlap in whole or in part.

[0073] At least one of the parts forming the test piece is a reference perforated part comprising at least one perforation.

[0074] The perforation can pass completely through the reference perforated part (through perforation). Alternatively, it can pass only partially through the reference perforated part (blind perforation), to a greater or lesser depth.

[0075] The provision of a reference perforated part allows the measurement of at least one internal temperature, in addition to the optional measurement of the surface temperature at the free surface of the reference perforated part. Depending on the type of perforation made in the thickness of the reference perforated part, different internal temperatures can be measured. A through perforation allows the measurement of the interface temperature of the surfaces to be welded on the reference parts (interface temperature). A blind perforation allows the measurement of a temperature in the thickness of the reference perforated part at a given depth (internal temperature at a given depth).

[0076] The perforation may be any perforation of any suitable cross-section, in particular a square cross-section perforation or a rectangular cross-section perforation (groove) or a circular cross-section perforation (hole). The grooves may have any suitable orientation, in particular being oriented transversely, longitudinally or obliquely relative to the welding direction. Preferably, the perforations do not extend over the entire width or length of the perforated section. Indeed, such perforations could have a negative impact on the welding, and in particular cause heat dissipation, reduce the strength of the weld joints. In a particular embodiment, the reference perforated part comprises circular cross-section perforations.

[0077] The cross-section of each perforation must be necessary and sufficient to allow the measurement of the interface temperature, without having a significant effect on the thermal profile of the test piece, such as heat dissipation. When the perforation is of circular cross-section, it may have a diameter between 0.5 and 10 mm. The reference perforated part may comprise at least three sections, namely a first perforated section, a second non-perforated section and a third perforated section, the perforated sections respectively comprising at least one perforation and framing the non-perforated section. By "first section" is meant the section of the part which will be welded first, i.e. before the second and third sections, with respect to the welding direction D. By "third section" is meant the section which will be welded last, i.e. after the first and second sections, with respect to the welding direction D.It is advantageous to provide a reference perforated part comprising a non-perforated central section surrounded by two perforated sections. Indeed, temperature measurements at the perforated sections make it possible to ensure that the thermal profile of the test piece does not vary significantly during welding, thus allowing the extrapolation of the thermal profile of the non-perforated central section. In addition, this central section can be used to carry out additional tests, generally destructive or non-destructive testing, for example the mechanical resistance of the weld joint, visual analysis, microscopic analysis, physicochemical analysis.

[0078] The reference perforated part, in particular the first section and / or the third perforated section, may comprise at least two perforations, preferably at least three perforations, aligned perpendicular to the welding direction D. These perforations may be located at different locations aligned perpendicular to the welding direction D, such as in its center, near one of the edges, etc. In a particular embodiment, at least one of the perforated sections of the reference perforated part comprises at least three adjacent transverse perforations, including a first perforation located near one edge of the part, a second perforation located in its center and a third perforation located near the opposite edge of the part. This arrangement allows the measurement and comparison of temperatures at different locations across the width of the part and therefore the observation of the transverse thermal profile of the part.For example, when the perforations are located respectively in the center and on the opposite edges of the part, the measurement and comparison of temperatures allows the observation of temperature differences across the width of the part, and in particular edge effects.

[0079] The reference perforated part, in particular the first section and / or the third perforated section, may comprise at least two series of longitudinal perforations, preferably at least three series of perforations, aligned parallel to the welding direction D. By "longitudinal series of perforations" is meant series of perforations - particularly identical in shape, dimensions and transverse location - which are repeated regularly along a perforated section. This arrangement allows the measurement and comparison of temperatures at different locations along the length of the part and therefore the observation of the longitudinal thermal profile of the part and therefore of the welding along the part.

[0080] The adjacent transverse perforations and the series of longitudinal perforations may form a particular pattern, in particular a regular geometric pattern. The perforations may form a checkerboard pattern or a staggered pattern. When the pattern is regular, the distance between two adjacent transverse perforations and / or between two adjacent longitudinal perforations is uniform. The perforated sections of the perforated part may have the same pattern of perforations or different patterns, preferably the same pattern. In a particular embodiment, the perforated sections comprise a checkerboard pattern comprising three adjacent transverse perforations and at least three series of longitudinal perforations.

[0081] The reference perforated part may comprise different types of perforations, i.e. at least one through perforation and at least one blind perforation, preferably at least two blind perforations. Providing a reference perforated part with different types of perforation makes it possible to measure a temperature gradient from the free surface of the reference perforated part to the interface of the two parts to be welded.

[0082] The perforation may be free of any material. Alternatively, the perforation may comprise a transparent material allowing temperature measurement by a suitable temperature sensor, for example a thermal imaging camera as described below. Filling the perforation with a transparent material has the advantage of allowing internal temperature measurement, while acting as a thermal insulator to limit convective losses.

[0083] The second part forming the test piece may be a part to be welded or a representative sample thereof. The evaluation method according to the invention may be implemented using a test piece comprising only reference parts including the reference perforated part, corresponding to representative samples of the parts to be welded. Alternatively, the evaluation method according to the invention may be implemented using a test piece comprising a reference perforated part, corresponding to a representative sample of a first part to be welded, and a second part to be welded as such. In this embodiment, the reference perforated part is used in situ directly with the second to be welded.

[0084] The second reference part may be perforated or non-perforated; preferably non-perforated. The perforated part and the second part are preferably respectively the upper part and the lower part of the test piece. The terms "upper" and "lower" are defined in relation to their positioning on the welding installation, on which the parts to be welded are positioned for assembly.

[0085] A perforated part of reference 20 is shown in the figure 2 It comprises a first perforated section 21, a second central non-perforated section 22 and a third perforated section 23. The first section 21 and the third section 23 each comprise respectively four and ten longitudinal series of three circular section perforations 24.

[0086] A perforated part of reference 30 is shown in Figures 3 and 4. It comprises a first perforated section 31, a second central non-perforated section 32 and a third perforated section 33. The first section 31 comprises perforations of different sections, namely circular section perforations 34, square section perforations 35 and rectangular section perforations (grooves) oriented longitudinally 36, transversely 37 or obliquely 38. The third section 33 comprises a series of three circular section perforations 34.

[0087] In the figure 4 , the perforated reference part is associated with a second non-perforated reference part 40, of identical shape and dimensions.

[0088] A portion of the first perforated section of a reference perforated part 50 is shown in figures 5, 6 And 7The first section comprises circular section perforations 51 of different lengths, the perforations being through 513 or blind 511, 512. In the figures 6 And 7 , the first perforated portion of the perforated part of reference 50 is associated with the corresponding section of the second non-perforated part of reference 60, of identical shape and dimensions.

[0089] The reference parts, or at least one of the layers constituting them, may comprise a matrix based on thermoplastic materials. The layers may comprise the same thermoplastic materials or different types / grades of compatible thermoplastic materials.The thermoplastic materials may be chosen from polyamides (PA), for example polyphthalamide (PPA), PA 11, PA 12, PA 6, PA 1010, PA 66, PA 46 or a copolyamide; polysulfones; polyphenylene sulfide (PPS); polyimides, for example polyetherimides (PEI); polyaryletherketones (PAEK), for example polyetherketoneketones (PEKK) and / or polyetheretherketones (PEEK); polyethylene terephthalate; polyolefins, for example polypropylene; chlorinated polymers, for example polyvinyl chloride (PVC) and polyvinylidene fluoride (PVDF); acrylic or methacrylic polymers or their mixtures The thermoplastic material may be an amorphous, crystalline or semi-crystalline thermoplastic material.

[0090] Each reference part may consist essentially of, or consist of, thermoplastic material. Alternatively, each reference part may comprise a matrix amount of the thermoplastic material ranging from 20% to 75% by volume, preferably from 30% to 55% by volume, relative to the total volume of the part.

[0091] The reference parts, or at least one of the layers constituting them as reference, may further comprise functional additives, preferably functional additives chosen from surfactants, ultraviolet (UV) stabilizers, thermal stabilizers, biocidal agents, impact modifiers, expansive agents or mixtures thereof.

[0092] Reference parts may include 0 to 30% by volume of functional additives.

[0093] The reference parts, or at least one of the layers constituting them, may further comprise fillers, in particular fibrous fillers and / or non-fibrous fillers.

[0094] The non-fibrous fillers may be chosen from mineral fillers, in particular from alumina, silica, calcium carbonate, titanium dioxide, glass beads, carbon black, graphite, graphene, carbon nanotubes or mixtures thereof.

[0095] Fibrous fillers can be chosen from so-called chopped fibers or continuous reinforcing fibers. Reinforcing fibers are used in particular to stiffen parts.

[0096] The reinforcing fibers may be chosen from glass fibers, quartz fibers, carbon fibers, graphite fibers, basalt fibers, silica fibers, metal fibers, ceramic fibers, natural plant fibers, synthetic organic fibers, or mixtures thereof.

[0097] Each reference part may comprise from 25 to 80% by volume, preferably from 45 to 70% by volume, of reinforcing fibers, relative to the total volume of the part.

[0098] In a fourth aspect, the present invention relates to the use of the test piece as described above for the evaluation of a welding assembly process for parts based on thermoplastic materials to be welded, the test piece being a representative sample of said parts; preferably for comparison with a reference, for the calibration of at least one welding parameter, for the calibration of at least one welding parameter and / or for monitoring a welding assembly process. Solder joint

[0099] Apart from the parts to be welded, no other thermoplastic material is added during the welding process, particularly at the interface of the surfaces to be welded. The weld joint between the two parts to be welded is therefore formed by the thermoplastic material matrices of the parts themselves, particularly by interpenetration. Facility

[0100] The welding method is implemented using a welding installation. The welding installation for implementing the method for evaluating an assembly by welding a test piece as described above, may comprise: a support for carrying the test piece to be welded; at least one heating element, configured to heat the parts to be welded; at least one temperature sensor, configured to measure the surface and / or internal temperatures of the test piece; the heating element and the temperature sensor being configured to move relative to the reference parts to be welded during welding, in a welding direction D.

[0101] The evaluation method according to the invention can be implemented with any suitable conventional welding installation, in particular by adding a temperature sensor. A particularly suitable welding installation is the welding installation 1 described in application PCT / FR2019 / 051775 filed on July 16, 2019 (unpublished). A schematic perspective view of the installation 1 is shown in figure 1. The welding installation 1 according to the application PCT / FR2019 / 051775 comprises in particular a support (not shown) for carrying parts 2, 3 to be welded; an insert 4 comprising an induction-sensitive material located at the end of a first arm 8; a corresponding inductor 5; a spacer element 7 located at the end of a second arm 9; a vibrator 12; a temperature-controlled enclosure 14 supplied by a blowing pipe 15; compacting rollers 6 surrounded by a track. Such conventional installations can be adapted, in particular, by adding a temperature sensor. The installation comprises a support for carrying at least one of the parts forming the test piece; preferably the non-perforated reference part. This support preferably comprises a flat face or any other suitable shape intended to carry one of the parts forming the test piece.

[0102] The installation comprises a heating element. Any heating element suitable for implementing a dynamic welding process according to the invention may be used, in particular heating by induction, by resistive effect, by vibration, by friction, by ultrasound, by use of a laser, by hot gas flow or by conduction from an external heat source.

[0103] The heating element may be an insert. The insert is configured to be inserted between the surfaces to be welded of the two parts forming the test piece. The insert may be heated by any suitable heating means, including induction, resistive effect, vibration, friction, ultrasound, laser, hot gas flow, or conduction from an external heat source.

[0104] The insert includes a material suitable for the heating medium.

[0105] For induction welding, the insert comprises an induction-sensitive material and the insert is heated by induction (inductive effect). The inductive effect is generated by applying a magnetic field generated by an inductor. The induction-sensitive material may be a magnetic field susceptor or absorber material, preferably an induction-sensitive metallic material, very preferably a metallic material chosen from iron, steel (for example, stainless steel), aluminum, nickel-chromium, titanium, or combinations thereof. For resistive effect welding, the insert comprises a resistive conductive material, and the insert is heated by resistive effect (or Joule effect). The resistive conductive material may be chosen from nickel alloys, lead alloys, titanium alloys, manganese alloys, nickel-chromium alloys, iron-chromium-aluminum alloys, and nickel-copper alloys.The resistive effect is generated by applying an electric current.

[0106] For laser welding, the insert may be heated directly by at least one laser. Alternatively, the insert may comprise a network of optical fibers for directing the laser heating energy to the surfaces to be welded. For hot gas flow welding, the insert may be heated directly by the hot gas flow, for example by contact. Alternatively, the insert may comprise at least one pipe for circulating the hot gas flow in the insert.

[0107] For conduction welding, the insert can be heated by any suitable external heat source.

[0108] The insert is advantageously a plate. The insert has a thickness of 5 mm or less, preferably 0.3 to 5 mm; very preferably 0.3 to 3 mm, more preferably 0.5 to 1.5 mm, even more preferably 0.5 to 1 mm. By "thickness" is meant the dimension between the surfaces of the insert in contact with the surfaces to be welded. If the surfaces of the insert are not flat and parallel to each other, the thickness corresponds to the maximum dimension between these two surfaces. Such thicknesses ensure the rigidity of the insert, good heat transfer and low mechanical deformation of the rigid parts when the insert passes over it and makes it possible to weld rigid parts.

[0109] During welding, the insert moves relative to the parts to be welded, in a welding direction D. The relative movement of the insert relative to the parts to be welded can be carried out by moving only the parts to be welded (the insert remaining fixed relative to the support) or alternatively by moving only the insert relative to the support (the parts being fixed relative to the support).

[0110] The installation may further comprise at least one arm, at the end of which is located the welding device, namely the insert. The insert may be fixed integrally to the arm.

[0111] The installation includes at least one temperature sensor. This sensor allows the measurement of the surface temperatures of the parts forming the test piece, in particular the surface temperatures of the upper perforated part. This sensor also allows the measurement of the internal temperatures of the test piece, at the perforations of the perforated sections of the reference perforated part.

[0112] The sensors can be chosen from pyrometers, thermocouples, thermal cameras, etc. In a particular embodiment, the temperature sensor is a thermal camera. The thermal camera provides a real-time image of the reference perforated part. It is possible to define an acquisition zone within this image, the acquisition zone preferably corresponding to the intermediate zone placed between the heating zone and the welding zone.The use of a thermal camera is particularly advantageous in that it allows the measurement of all the temperatures of interest, both transversely and longitudinally, in particular the surface temperature of the reference perforated part; the interface temperature, in particular the maximum temperature at the interface of the parts to be welded at the intermediate zone just after the heating zone or the welding temperature in the intermediate zone just before the compaction zone; the internal temperature of the perforated part at a given depth; the temperature of the heating element if relevant, in particular the temperature of the insert for induction welding.

[0113] Temperature sensors can continuously or punctually measure the surface and internal temperatures of the parts to be welded.

[0114] The temperature sensor can be positioned at different areas, including the pre-heating area, the heating area, the intermediate area, the welding area, etc. The temperature sensor is preferably positioned at the intermediate area, after heating and before welding.

[0115] During welding, the temperature measuring sensor and the heating element move together relative to the workpieces to be welded, in the welding direction D. By the expression "move together" we mean move at the same time, in the same direction (here the welding direction D) and at the same speed.

[0116] When the heating element is an insert, the temperature sensor is attached to the arm on which the insert is fixed.

[0117] For induction welding, the installation may further comprise at least one inductor for generating a magnetic field.

[0118] During welding, the inductor can move relative to the parts to be welded, in a welding direction D. Advantageously, the insert and the inductor move together relative to the parts to be welded during welding, in the welding direction D.

[0119] The inductor can be attached to the insert arm.

[0120] The installation may further comprise at least one pressure application element, in particular at least one plating roller and / or at least one compacting roller. These pressure application elements may be positioned behind and / or in front of the insert relative to the welding direction D. The pressure application elements make it possible to apply pressure to the workpieces so that they are pressed against each other.

[0121] The installation may further comprise at least one thermal regulation block. The thermal regulation block makes it possible to reduce the temperature of the free surfaces of the welded part relative to the welding temperature, while maintaining the surfaces to be welded, and therefore the welding interface, at a temperature higher than the melting temperature of the thermoplastic polymer.

[0122] The thermal regulation block is preferably positioned behind the insert relative to the welding direction D and in front of the pressure application elements (if present).

[0123] This cooling step allows the temperature gradient within the welded part to be controlled, and limits, or even prevents, decompaction.

[0124] The installation may further include a temperature-controlled enclosure, delimiting two zones located respectively inside and outside this enclosure. This enclosure makes it possible to maintain an area of the parts at a specific temperature. This may be a recrystallization temperature, behind the insert relative to the welding direction D, in order to allow recrystallization in optimal conditions and to avoid post-curing of the parts after welding. This may involve cooling outside the welding zone.

[0125] The temperature-controlled enclosure is positioned at the welding zone, preferably in front of and / or behind the insert relative to the welding direction D.

[0126] During welding, the temperature-controlled enclosure and the insert can move together relative to the parts to be welded, according to the welding direction D. The temperature-controlled enclosure can be integral with the insert arm and / or the inductor (if present).

[0127] The temperature of the area delimited by the enclosure and / or the area located outside can be obtained by blowing in a fluid, preferably hot air or cold air respectively, using at least one blowing pipe.

[0128] The temperature-controlled enclosure can be delimited by means of a flexible skirt, possibly fixed to the periphery of a top plate. Welding system

[0129] According to a fifth aspect, the present invention relates to a welding system for carrying out the evaluation of a welding assembly comprising a test piece and a welding installation, as described above. Automation of travel

[0130] The movements of the heating element / welding device and / or the temperature sensor and / or the inductor (if present) and / or the pressure application elements and / or the temperature-controlled enclosure can be carried out automatically, by one or more robots, or alternatively manually by an operator.

[0131] Such embodiments are particularly advantageous for the assembly of fuselage parts in the aeronautical field because the control of the welding temperature is necessary for the qualification of an aeronautical process. Examples

[0132] The following examples illustrate the invention without limiting it. Supply of test piece according to the invention

[0133] The specimens used in the tests reported below include two parts made of thermoplastic materials and having respective surfaces to be welded and free surfaces including a perforated reference part.

[0134] The perforated parts of reference 20, as shown in the figure 2 , comprise a thermoplastic matrix based on PPS polymer (43% by weight), as well as woven carbon fibers. These parts have a thickness of approximately 1.86 mm, a length of approximately 500 mm and a width of approximately 35 mm. They comprise a first perforated zone 21 comprising four longitudinal series of three transverse perforations 24, a second central zone 22 without perforation and a third perforated zone 23 comprising ten longitudinal series of three transverse perforations. The perforations 24 are through and have a diameter of approximately 5 mm.

[0135] The second part (not shown) forming the test piece corresponds to a part identical to the reference part 20 of the Fig. 2 but showing no perforation.

[0136] Two different specimens were tested, namely a first specimen whose reference pieces comprise a PPS polymer-based thermoplastic matrix comprising 5HS woven carbon fibers; or a second specimen whose reference pieces comprise a PEKK (Kepstan 7002™) polymer-based thermoplastic matrix (37% by weight) comprising Hextow AS7 unidirectional carbon fibers. Supply of a welding installation

[0137] A welding installation, similar to that shown in the figure 1, including in particular a support, an insert fixed to the end of an arm, an inductor, a thermal camera (heating element) and a compaction roller is provided. The inductor and the thermal camera are integral with the arm of the insert and therefore move together with the insert.

[0138] The surface and internal temperatures of the specimen are measured in the intermediate zone, i.e. just after the heating zone and before the welding (compaction) zone. The surface temperatures are measured in the solid zones of the reference perforated part. The internal temperatures (at the interface between the two parts to be welded) are measured at the perforations. Implementation of the method according to the invention

[0139] The method according to the invention can be implemented according to different predetermined settings. The modification of at least one setpoint parameter, for example the temperature of the insert, makes it possible to modify the implementation of the welding of the test piece and to have an impact on its performance. In particular, the modification of at least one parameter will have an impact on the measured surface and internal temperatures. Measurement of surface and internal temperatures of the specimen formed by two reference pieces Kepstan 7002 ™ < / Hextow AS7

[0140] There figure 8is the real-time image of the reference perforated part 20 obtained with a thermal camera according to a determined setting. This image taken from above the reference perforated part 20 illustrates the temperature differences measured between the solid (non-perforated) parts and the hollow parts (perforations 24), where the surface temperatures and the interface temperatures (°C) are measured respectively. The interface temperatures at the third, sixth and ninth perforations are visible in light gray, while the surface temperature of the solid area surrounding the perforations is visible in dark gray, demonstrating that the surface temperature is lower than the interface temperatures.

[0141] There figure 9is a graphical representation of the surface and interface temperatures (°C) measured / recorded as a function of time, during the joint movement of the insert and the thermal camera, at the intermediate zone, just before the passage of the compacting device and therefore of the welding. The interface temperatures measured at the perforations have a value of approximately 360-390 °C, while the surface temperatures have a value of approximately 275 and 240 °C. Determination of the weldability window using a specimen with SHS / PPS woven reinforcement

[0142] There figure 10 is a graphical representation of the heating, welding and surface temperatures (°C) measured / recorded as a function of different settings of the evaluation process.

[0143] The temperature range of the weldability window is delimited by the melting point of the thermoplastic matrix (lower limit) and the degradation temperature of the thermoplastic matrix (upper limit). By measuring the surface and internal temperatures - including surface, heating and welding temperatures - at different settings, it is possible to determine the settings for which the surface and internal temperatures correspond to the weldability window, as shown in the figure 10 These settings can be used to weld the parts, of which the test piece is a representative sample.

Claims

1. Method for evaluating an assembly by welding of parts made of thermoplastic materials and having respective surfaces to be welded and free surfaces (2, 3), comprising: - 1- providing a test piece comprising at least two parts (20,30,40,50,60) that overlap at least in part; wherein at least one of the parts is a perforated reference part (20,30,50) comprising at least one perforation in its thickness; - 2- providing a welding installation (1) comprising at least one heating element and at least one temperature sensor; - 3- providing heat by means of the heating element; - 4- measuring at least one internal temperature of the test piece by means of the temperature sensor at the level of the perforation; wherein the heating element and the temperature sensor move in a welding direction D relative to the parts to be welded during welding (2,3).

2. Method according to claim 1, wherein the heating element is an insert (4), wherein the insert (4) is inserted between the surfaces to be welded of the two parts to be welded (2,3).

3. Method according to claim 2, wherein the insert is heated by induction, by resistance, by friction, by ultrasound, or by using a laser through a hot gas stream, or by conduction from an external heat source.

4. Method according to any of the preceding claims, wherein the perforation is a perforation that traverses the all or part of the thickness of the perforated reference part (20, 30, 50).

5. Method according to any of the preceding claims, wherein the perforation is a perforation with a square (35), rectangular (36,37,38), or circular (24,34,51,511,512,513) cross-section.

6. Method according to any of the preceding claims, wherein the perforated reference part (20,30,50) comprises at least two perforations that are aligned perpendicular to, and / or at least two perforations that are aligned parallel to, the welding direction D.

7. Method according to any of the preceding claims, wherein the perforated reference part (20,30,50) comprises at least one first section that is perforated (21,31), one second section that is not perforated (22,32), and one third section that is perforated (23,33); wherein the perforated sections respectively comprise at least one perforation and frame the non-perforated section.

8. Method according to any of the preceding claims, further comprising measuring at least one temperature of the free surface of the perforated reference part (20,30,50).

9. Method according to any of the preceding claims, wherein the surface temperature and the internal temperature are measured transversely and / or longitudinally relative to the welding direction D.

10. Method according to any of the preceding claims, further comprising recording the temperature values.

11. Method according any of the preceding claims, further comprising comparing the temperatures measured with reference temperatures.

12. Method according to any of the preceding claims, further comprising a step of calibrating parameters of the method for assembly by welding.

13. Method of assembly by welding of at least one series of parts based on thermoplastic materials and having respective surfaces to be welded and free surfaces (2,3), comprising: - 1- determining the settings for welding the parts to be welded (2,3) based on the evaluation of the assembly by welding of a test piece constituting a representative sample according to claims 1 to 12; and - 2- carrying out the assembly of the parts to be welded (2,3) by welding.

14. Test piece for the implementation of the method for evaluating an assembly by welding of parts made of thermoplastic materials (2,3), according to any of claims 1 to 12, wherein the test piece comprises at least two parts based on thermoplastic materials having surfaces to be welded that are at least partially placed opposite one another and the respective free surfaces (20,30,40,50,60), wherein at least one of the parts is a perforated reference part (20,30,50) comprising at least one perforation.

15. Use of the test piece according to claim 14 to evaluate an assembly by welding of parts based on thermoplastic materials to be welded (2,3), wherein the test piece is a representative sample of these parts (2,3).

16. Welding system for the implementation of an evaluation of an assembly by welding comprising: a test piece according to claim 14 and a welding installation (1); said welding installation (1) comprising: a support for the test piece to be welded; at least one heating element, configured to heat the parts to be welded (2,3); at least one temperature sensor, configured to measure the surface and interface temperatures of the test piece; and the heating element and the temperature sensor being configured to move in a welding direction D relative to the parts to be welded (2,3) during welding.