Mechanical assembly made of continuous fiber-reinforced thermoplastic composite and overmolded, and method for manufacturing such an assembly

Abstract

The invention relates to a mechanical assembly (E) comprising: - at least a first tubular part (1) made of thermoplastic composite reinforced with continuous fibers with a fiber content of less than 2%, said first composite part (1) being in the form of a winding of successive layers (1a) of continuous fibers impregnated with a consolidated thermoplastic matrix, the winding of the fibers being carried out around an axis of the first composite part (1) and at angles to the axis between -90° and 90° and different between at least two layers; - a second thermoplastic part (2) over-injected into / around at least a portion of the first composite part (1). Figure for the abstract: Fig. 7

Description

Title of the invention: Mechanical assembly made of thermoplastic composite reinforced with continuous fibers and overmolded, and method of manufacturing such an assembly Technical field

[0001] The present invention relates to the field of manufacturing a mechanical assembly comprising thermoplastic parts reinforced with continuous fibers, well known to those skilled in the art under the acronym CFRT for "Continuous Fiber Reinforced Thermoplastic".

[0002] Continuous fibers are understood to mean fibers that have a significant length relative to the dimensions of the part or final product, in particular a few centimeters, as opposed to short fibers generally of the order of a few millimeters. In other words, these are fibers of such a length that they cannot be injected in any way whatsoever, that is to say, cannot be supplied other than by means of a textile or a preform. Prior art

[0003] In the prior art, there are various methods and devices for manufacturing complex mechanical parts from thermoplastic. These methods include stamping, molding, plastic injection, composite fiber winding and overmolding techniques.

[0004] Continuous or long fiber reinforced thermoplastic composite (CFRT) parts are known and commonly used for their combination of strength, stiffness, and light weight. CFRTs are used in a range of applications from automotive to aerospace, where material performance is critical.

[0005] Continuous or long fiber CFRTs have increased strength and stiffness compared to short fibers, because the loads are distributed more efficiently and since the fiber length is no longer the limiting factor on the mechanical properties of the part (modulus and stress load) as is the case with short fiber composites.

[0006] CFRT parts can be manufactured using a filament winding process, where fibers combined with a polymer, for example fibers impregnated with thermoplastic resin, are wound around a guide. These parts are then pressurized and heated to form a rigid and strong composite part. However, these CFRT parts are limited in terms of shape complexity and functionality.

[0007] It is also known in the prior art to use overmolding techniques to add additional features or to improve the mechanical properties of a part. However, overmolding CFRT parts can be difficult due to the rigid and non-malleable nature of CFRT. In addition, overmolding can cause the CFRT part to collapse or deform during the injection process, which can affect the quality and performance of the finished part.

[0008] Another difficulty lies in maintaining the position of a CFRT insert in a mold during the over-injection process since differences in thermal expansion between the CFRT insert and the over-molding material can cause deformations.

[0009] The pressure and speed of the thermoplastic injection flow can also move the insert from its initial position, especially if the insert is lightweight or if the mold design is not optimal for holding it firmly in place.

[0010] Furthermore, the plastic injection technique is widely used for the manufacture of mechanical parts due to its ability to create complex shapes with high dimensional precision. However, this technique has certain constraints, particularly in the limited possibilities of thickness variation, and of following specific demolding axes, thus limiting the freedom of design.

[0011] Although manufacturing techniques are widely used, they have limitations in terms of design complexity, material performance and production efficiency. Therefore, there is a need to overcome these limitations.

[0012] It is also known to produce preforms in the form of composite thermoplastic matrix plates or flat preforms which are cut to the desired shape. These plates or flat preforms are heated until the thermoplastic melts and are then introduced into a tool allowing stamping to the desired shape.

[0013] Subsequently, additional features are injection molded, for example, shape details, ribs or edge finishes.

[0014] This technique, however, has the disadvantage of generating cutting waste which must be managed, and is especially not suitable for the production of complex parts with hollow bodies. Statement of the invention

[0015] One of the aims of the invention is therefore to overcome the limitations of the previous techniques by providing a mechanical assembly combining the use of thermoplastic composite materials with hollow bodies reinforced with continuous fibers, and thermoplastic overmolding, to achieve high levels of strength, lightness and freedom of form, while maintaining an implementation cost compatible with mass markets such as the automobile or sports and leisure sectors for example.

[0016] For this purpose, a remarkable mechanical assembly has been developed in that it comprises: - at least one first part with a closed section, i.e. hollow / tubular, made of thermoplastic composite reinforced with so-called continuous fibres with a wefting of less than 2%, preferably less than 0.5%, said first composite part being in the form of a winding of successive layers of continuous fibres, for example of different natures (carbon, glass, etc.), impregnated with a consolidated thermoplastic matrix, the winding of the fibres being carried out around an axis of the first composite part and at angles relative to the axis of between -90° and 90° and different between at least two layers; - a second thermoplastic part over-injected into / around at least a portion of the first composite part.

[0017] The invention has the advantage of being able to produce, for example, functional sleeves of CFRT tubes, in particular for producing connecting parts. Other advantageous applications can be imagined, such as the production of a CFRT skeletal core for a handlebar, or a bicycle frame for example.

[0018] Curl in a thermoplastic composite reinforced with so-called continuous fibers refers to the waviness or deviation of the fibers from their direction parallel to the surface against which they are applied, i.e., away from said surface. It is essentially a measure of the curvature or sinuosity of the fibers in the matrix of the material in a plane orthogonal to the application surface. A curl of 0% indicates that the fibers are perfectly parallel to the application surface, without any orthogonal deviation. In contrast, a curl greater than 0% means that the fibers have some waviness or deviation in the plane orthogonal to the application surface. Curl affects several properties of composites, including their strength, stiffness, thermal conductivity, and their behavior during solidification and cooling.

[0019] According to the invention, the overmolding of a first part in thermoplastic composite reinforced with continuous fibers with a fogging of less than 2% allows: - increased strength and stiffness: When the fibers are parallel or nearly parallel to the application surface, they are able to support loads more directly and efficiently, resulting in increased strength and stiffness of the composite material in the direction of the fibers; - to improve the surface condition of the part, unlike a coating greater than 2% which would generate areas rich in matrix / resin depending on the weaving / braiding / winding pattern, which would present a shrinkage which could degrade the surface condition as well as the surface properties of the part; - less deformation and shrinkage: A deformation of less than 2% allows to reduce deformations and shrinkage of the material during solidification and cooling, because there is less "play" in the fiber structure.

[0020] This configuration offers several other advantages. In addition to increasing the modulus of elasticity of the assembly obtained thanks to the embedding and the connection due to the overinjection, it offers significant freedom of form.

[0021] The invention also makes it possible to propose sections with an amplified moment of inertia, thus improving resistance to normal forces and bending moments.

[0022] This design makes it possible to obtain a mechanical assembly with excellent resistance to traction, compression and torsion. This is made possible by winding successive layers of fibers impregnated with a consolidated thermoplastic matrix around an axis at specific angles, as well as by the compatibility between the thermoplastic matrix of the first part and that of the thermoplastic of the second over-injected part.

[0023] The invention also has environmental advantages. The CFRT matrix and the injected thermoplastic are recyclable, which helps to reduce the environmental impact of the final product.

[0024] This compatibility creates optimal adhesion between the insert and the overmolding material, which avoids the risk of delamination or formation of weak zones between the two materials, and allows for better distribution of loads and stresses across the composite, which is crucial for the mechanical performance of the finished part.

[0025] This compatibility between the matrices is also thermal, which makes it possible to minimize the differences in thermal expansion, and therefore the movements of the insert (first part).

[0026] The second over-injected part provides additional rigidity and increased resistance to mechanical stress, in addition to allowing the incorporation of additional features such as connecting elements, hooks, etc.

[0027] According to a particular embodiment, the mechanical assembly comprises at least a third part made of thermoplastic composite reinforced with continuous fibers with a molding of less than 2%, and the second part made of thermoplastic is also over-injected into / around at least a portion of the third part.

[0028] This adds a layer of complexity to the whole, offering more possibilities for the integration of functionalities and shapes. The second part in over-injected thermoplastic forms a chemical or mechanical bond between two CFRTs.

[0029] In this latter configuration, several modes can be envisaged.

[0030] For example, and in order to increase the strength of the assembly in specific areas, such as critical plastic deformation areas, and depending on specific needs, the second thermoplastic part and / or the third thermoplastic part composite comprises at least one area reinforced with continuous fiber strands or ribbons with a weft of less than 2%, preferably held on a panel by stitching to allow the fiber strands with a complex, non-linear geometry to be held in place, in order to follow the geometry of the final part.

[0031] For the remainder of the description, the term "wick" refers to a set of continuous threads or fibers, covered or not, twisted or not, said threads or fibers forming a bundle, these threads being able to be made of materials of different natures, possibly impregnated. It can even be a ribbon with an integrated matrix.

[0032] This definition of "wick" is used to avoid confusion of vocabulary with "sewing thread". The insert can be said to be dry and in the form of a textile base then overmolded in the mechanical assembly, or else said to be consolidated with the textile base embedded in a thermoplastic matrix.

[0033] Advantageously, the third part has portions of thermoplastic overmolded surfaces comprising hollow or raised elements to promote the adhesion of the second thermoplastic part and also participate in the transmission of forces between these parts.

[0034] In order to maximize the transmission of forces between the second thermoplastic part and the third composite part, the hollow elements are open so as to be crossed by portions of the second thermoplastic part.

[0035] The recessed elements or the raised elements preferably comprise undercut sections, for example dovetail sections, to maximize the holding of the second thermoplastic part with the third composite part.

[0036] Preferably, and to direct the flow of over-injected thermoplastic in a desired direction, for example so that the thermoplastic arrives well above the part to be overmolded, the first and / or the third part may have arrangements for guiding the injection flow. These arrangements may be of any suitable type such as a groove, walls, ribs or obstacles provided on the surface of said part, forcing the flow of thermoplastic to take a preferential path.

[0037] According to another example, the third composite part is also of closed section and in the form of a winding of successive layers of continuous fibers impregnated with a consolidated thermoplastic matrix, the winding of the fibers being carried out around an axis of the third composite part and at angles relative to the axis between -90° and 90° and different between at least two layers.

[0038] This configuration makes it possible to produce, by means of the second over-injected thermoplastic part, a mechanical connection between two CFRT tubes.

[0039] In certain configurations, and in particular when the second thermoplastic part is over-injected around a tubular portion, the mechanical assembly according to the invention comprises so-called “anti-collapse” means, considered to be lost and positioned inside the tubular portions around which the second thermoplastic part is over-injected, and against which the hollow / tubular portions are pressed.

[0040] These lost means can be of any type and any suitable material, and are called "anti-collapse" because they have participated in locally preventing the collapse of the structure during the overmolding process. They therefore improve the reliability of the manufacturing and also make it possible to further and locally increase the resistance of the assembly to mechanical stresses.

[0041] This configuration also offers the advantage of reducing the price of the injection tooling by avoiding the use of slides for example.

[0042] Advantageously, the anti-collapse means comprise portions of variable sections, for example portions narrowed or brought closer to the axis of the hollow / tubular portion, such as an inclined portion, a groove or a flat for example, having made it possible to achieve a so-called “desired” collapse of the hollow / tubular portions against the anti-collapse means during over-injection.

[0043] This makes it possible to reinforce the tensile / compression / torsional force absorption between the hollow / tubular portion, the anti-collapse means and the second over-injected thermoplastic part.

[0044] This also makes it possible to have an external surface of the second over-injected part which can be flush with an external surface of the hollow / tubular portion.

[0045] According to a particular embodiment, the anti-collapse means are in the form of a plug thus allowing the closure of the closed section portion, possibly comprising a functionalized portion projecting outside the closed section portion, to form for example a connection between two composite parts.

[0046] The overmolding of hollow composite bodies used in the invention makes it possible to circumvent certain traditional constraints of plastic injection. In particular, it offers the possibility of creating non-removable shapes, shapes with curved straight sections and volumes with variable thickness, etc.

[0047] The invention also makes it possible to reduce the cost of the injection tooling, since it is no longer necessary to carry out as many movements in the molds to produce so-called "open" zones.

[0048] According to another characteristic, the anti-collapse means can integrate a metal insert engaged with the second over-injected thermoplastic part in order to further solidify the mechanical connection between the different parts of the assembly, and contribute to resistance to mechanical stress.

[0049] The mechanical assembly may also comprise an expandable element such as an intumescent seal or a material that can be activated chemically or under the effect of heat, for example generated during overmolding or before injection, positioned between the anti-collapse means and the hollow / tubular portion, which has in particular increased in volume during the overinjection of the second thermoplastic part, in order to further improve the strength of the assembly.

[0050] According to a particular embodiment, the second thermoplastic part is over-injected around the entirety of the first composite part and / or the third composite part.

[0051] This characteristic of the invention makes it possible to obtain a mechanical assembly having a core formed by the first part in CFRT and an envelope in injected thermoplastic. The mechanical assembly thus obtained has mechanical properties increased by the continuous fibers, offering a resistance comparable to, or even superior to, that of metals in the directions of the fibers and depending on the nature of the fibers.

[0052] The first composite part and / or the third composite part has variable sections at the level of the portions around which the second part is over-injected.

[0053] This allows, for example, that an external surface of the second overmolded part can be flush with an external surface of the first composite part and / or the third composite part.

[0054] Advantageously, the second part is over-injected into a groove formed in the first part and / or the third part and having made it possible to guide the injection flow in a desired direction, for example to maintain the first composite part, or the third composite part in position during the over-injection process. This can also be of aesthetic interest by making it possible to ensure that the injection flow does not move the insert, i.e. the first composite part, or the third composite part, at the level of the visible surface of the mechanical assembly, which itself could be textured.

[0055] The invention also relates to a method for producing a mechanical assembly as mentioned above, remarkable in that it consists of: - positioning in a mold at least a portion of a first tubular part made of thermoplastic composite reinforced with long fibers with a damping of less than 2%, said first composite part being in the form of a winding of successive layers of continuous fibers associated with a polymer, for example fibers impregnated with a consolidated or non-consolidated thermoplastic matrix, co-mixed with polymer fibers, powdered with polymer, etc. the winding of the fibers being carried out around an axis of the first composite part and at angles to the axis between -90° and 90° and different between at least two layers; - over-injecting thermoplastic into / around at least a portion of the first composite tubular part, to form a mechanical assembly comprising a first composite part and a second thermoplastic part over-injected into / around the first part.

[0056] Thus, this structured method offers increased efficiency during the production process, as well as improved repeatability, which reduces production costs and waste. Furthermore, the overmolding operation of the first CFRT part is carried out in a single step, without using a polymer preform. Production rates are therefore improved.

[0057] According to another embodiment, the method consists of also positioning in the same mold at least a second part made of thermoplastic composite reinforced with continuous fibers with a damping of less than 2%, and of over-injecting thermoplastic also into / around at least a portion of the second composite part, to form a mechanical assembly comprising the second part made of thermoplastic over-injected around the first composite part and at least a third composite part.

[0058] According to particular embodiments, the second composite part has a yoke comprising strands or ribbons of continuous fibers with a wefting of less than 2%, preferably held on the yoke by stitches, the yoke being said to be dry and in the form of a textile base, or else said to be consolidated with a textile base embedded in a thermoplastic matrix.

[0059] Or, the second composite part is in the form of a tubular part produced by winding successive layers of continuous fibers associated with a polymer, the winding of the fibers being carried out around an axis of the tubular part and at angles relative to the axis between -90° and 90° and different between at least two layers.

[0060] The advantage that arises from these different modes is the speed of execution, with a single over-injection step.

[0061] Preferably, the second composite part has excess thicknesses so that said second composite part rests on either side of the mold to hold it in position during over-injection of the thermoplastic.

[0062] Depending on the nature of the mechanical assembly to be produced, and if the over-injection is carried out around hollow / tubular portions, the method may comprise a step consisting of positioning, before the over-injection, anti-collapse means inside the hollow / tubular portion(s) around which the second thermoplastic part is over-injected.

[0063] The anti-collapse means may be lost, i.e. they remain in the mechanical assembly produced but, of course, they can be removable, for example of the slider type, eclipsable core, inflatable bladder, sand, incompressible material, pressurized fluid maintained by one or more plugs, possibly lost, and the method then comprises a step consisting of subsequently removing said anti-collapse means.

[0064] According to another advantageous characteristic, the method may comprise, before the over-injection step, a step consisting of positioning retractable stops in the mold to orient the flow of over-injected thermoplastic in a desired direction, for example so that the thermoplastic plastic arrives well above the part to be over-molded. Brief description of the drawings

[0065] [Fig. 1] is a schematic representation of the first tubular part of the mechanical assembly, made of thermoplastic composite reinforced with so-called continuous fibers with a thickness of less than 2%.

[0066] [Fig.2] illustrates an exemplary embodiment of the invention, consisting of functionalizing a CFRT tube;

[0067] [Fig.3] is a sectional view of the assembly of [Fig.2].

[0068] [Fig.4] illustrates another example of a mechanical assembly according to the invention, consisting of a bicycle fork pivot.

[0069] [Fig.5] is a sectional view of an assembly according to another embodiment, consisting of connecting two CFRT tubes.

[0070] ] is a schematic representation of a yoke implemented in the invention, comprising strands or ribbons of continuous fibers with a weft of less than 2%, and in particular less than 0.5%, held on the yoke by stitches.

[0071] [Fig.7] is another example of an embodiment of a mechanical assembly according to the invention, consisting of a bicycle handlebar.

[0072] [Fig.8] is another example of an embodiment of a mechanical assembly according to the invention, consisting of a bicycle frame.

[0073] [Fig.9] illustrates the installation of anti-collapse means and an insert inside the portion around which thermoplastic is over-injected.

[0074] [Fig. 10] is a schematic, sectional view illustrating the positioning of the retractable stop to guide the injection flow.

[0075] [Fig. 11] is a view similar to that of [Fig. 10], the stop having been retracted

[0076] [Fig. 12] represents an example of a second composite part having arrangements for guiding the injection flow.

[0077] [Fig. 13] illustrates, before overmolding, the positioning of the second part composite of [Fig. 12] around a bicycle head tube.

[0078] [Fig. 14] illustrates an anti-collapse means which has made it possible to achieve a desired collapse.

[0079] [Fig. 15] illustrates the production of a mechanical assembly (E) having a core formed by the first part in tubular CFRT and an envelope in injected thermoplastic, the assembly having an undercut shape. Detailed description of the invention

[0080] With reference to Figures 1 to 15, the present invention relates to a mechanical assembly (E) remarkable for its hybrid construction combining thermoplastic composites reinforced with continuous fibers and thermoplastic over-injection processes.

[0081] This invention finds potential applications in various fields, such as the automotive industry, aerospace, shipbuilding, the bicycle industry and other sectors where lightweight, strong and durable components are required.

[0082] The aforementioned assembly (E) comprises a first tubular part (1) made of thermoplastic composite reinforced with continuous fibers. With reference to [Fig.l], this first part (1) is designed to offer excellent mechanical resistance, increased lightness and durability compared to traditional materials. The composite is formed by winding successive layers (la) of continuous ribbons or fibers, impregnated with a consolidated thermoplastic matrix.

[0083] The continuous fibers are arranged around an axis of the first composite part (1), and their orientation varies between -90° and 90° relative to this axis. This variation in angle between the successive layers (la) makes it possible to optimize the distribution of loads and to improve the resistance to multidirectional stresses. In addition, the fogging, that is to say the deviation of the fibers from their direction parallel to the surface against which they are applied, is kept below 2% to guarantee optimal mechanical performance.

[0084] The mechanical assembly (E) then comprises a second part (2) made of thermoplastic which is over-injected into and / or around at least a portion of the first composite part (1).

[0085] In this way, the second thermoplastic part (2) is firmly integrated into the first composite part (1), and ensures a reliable mechanical and chemical bond between the two materials. Over-injection offers great flexibility in terms of design, making it possible to create complex geometries and meet specific needs.

[0086] The over-injection of the second thermoplastic part (2) makes it possible, for example, to produce functional end pieces on the first part (1) which is a CFRT tube, see figures 2 and 3.

[0087] According to different embodiments, this technique also makes it possible to mechanically bond the first composite part (1) with a third composite part (3).

[0088] Figures 4 and 5 illustrate the mechanical connection of a first part (1) made of composite, in the form of a CFRT tube, with one or more third parts (3) made of composite, also in the form of a CFRT tube (3a) formed by the winding of successive layers of continuous ribbons or fibers, impregnated with a consolidated thermoplastic matrix, with angles ranging between - 90° and 90° relative to the axis and with a damping of less than 2%. The mechanical connection being achieved by means of the second part (2) over-injected around at least a portion of each tube (1, 3a). [Fig.4] illustrates for example the production of a mechanical assembly (E) of the bicycle fork type.

[0089] In practice, the tubes (1, 3a) are positioned in the same mold and the thermoplastic is over-injected around at least a portion of each tube, in a single step.

[0090] According to another example, the third composite part (3) may comprise areas reinforced with an overmolded insert (3b), as shown in [Fig.6], containing wicks (3c) or ribbons of continuous fibers, with a weft of less than 2%, held on the insert (3b) by stitches (3d).

[0091] For the remainder of the description, the term "wick" refers to a set of unidirectional threads or fibers, covered or not, twisted or not, said threads or fibers forming a bundle, these threads being able to be made of materials of different natures, possibly impregnated. It can even be a woven ribbon with an integrated matrix.

[0092] The insert (3b) can be said to be dry and in the form of a textile base then overmolded in the mechanical assembly, or else said to be consolidated with the textile base embedded in a thermoplastic matrix.

[0093] For example, with reference to [Fig.7], the invention then makes it possible to produce a mechanical assembly (E) comprising a first part (1) made of composite, in the form of a CFRT tube to form a bicycle handlebar, a third part (3) made of composite reinforced by inserts (3b) as mentioned above to form a handlebar stem, the whole linked by a second part (2) made of thermoplastic over-injected around the stem and at least one part of the handlebar. According to a particular embodiment, the second part (2) made of thermoplastic over-molds the entirety of the first part (1) made of composite and the third part (3) made of composite, which makes it possible to obtain a mechanical assembly (E) having a core formed by the first part made of CFRT and an envelope made of injected thermoplastic.

[0094] [Fig. 15] also illustrates the production of a mechanical assembly (E) having a core formed by the first part (1) in tubular CFRT and a thermoplastic envelope (2) injected around the entire first part (1). In this example, we also illustrate the possibility that the first part (1) in composite can have variable sections at the level of the portions around which the second part (2) is over-injected. This makes it possible to produce mechanical assemblies (E) with hollow bodies and undercuts. This possibility frees up the design of the parts, usually limited by the constraints of injection. Such a part would need to be injected in two parts, then welded.

[0095] Thus, according to the invention, in addition to being injectable into a simple mold, and having a continuous fiber core, the shapes of the assembly can be undercut.

[0096] In practice, the first composite part (1) and the third composite part (3) are positioned in the same mold and the thermoplastic is over-injected around at least a portion of each part, in a single step.

[0097] According to another example illustrated in [Fig.8], this technique makes it possible to produce a mechanical assembly (E) in the form of a bicycle frame comprising CFRT tubes as first parts (1), mechanically connected by second parts (2) made of thermoplastic over-injected at least around an end portion of the tubes, one of which is for example reinforced with the aforementioned over-molded insert (3b), forming a third part (3), for example positioned at the level of the steering socket.

[0098] In practice, the first composite part (1) and the third composite part (3) are positioned in the same mold and thermoplastic is over-injected around said parts to bond them, in a single step, and form the mechanical assembly (E).

[0099] To ensure the success of the over-injection process, the invention proposes the use of anti-collapse means (4) positioned inside the hollow / tubular portions around which the second thermoplastic part (2) is over-injected. These anti-collapse means (4) ensure that the hollow / tubular portions retain their shape during over-injection, thus avoiding any unwanted collapse.

[0100] With reference to figures 2, 3 and 5, the anti-collapse means (4) may be in the form of a plug allowing the hollow / tubular portion to be closed, and possibly comprising a functionalized portion projecting outside the hollow / tubular portion.

[0101] In these figures, it can be seen that the first part (1) made of composite in the form of a CFRT tube comprises, for example, portions of variable diameter so that the external surface of the second part (2) over-injected can be flush with an external surface of the first part (1) made of composite. This also makes it possible to reinforce the tensile / compression / torsional force between the tubular portion and the second part (2) in over-injected thermoplastic.

[0102] In the same way, the anti-collapse means (4) advantageously comprise portions of variable sections (4a) to reinforce the tensile / compression / torsional force absorption between the anti-collapse means (4) and the second part (2) made of over-injected thermoplastic.

[0103] Preferably and with reference to [Fig. 14], the anti-collapse means (4) have means which have made it possible to achieve a so-called “desired” collapse of the hollow / tubular portions against the anti-collapse means (4) during overinjection. These means are illustrated for example in the form of four flats (4b) regularly distributed around the circumference of the plug.

[0104] With reference to [Fig.9], the anti-collapse means (4) can also integrate a metal insert (5) engaged with the second part (2) made of over-injected thermoplastic in order to further solidify the mechanical connection between the different parts of the assembly, and contribute to the resistance to mechanical stresses.

[0105] According to an advantageous characteristic, and with reference to figures 10 and 11, retractable stops (6) can be introduced into the mold (7) to direct the flow of over-injected thermoplastic. These retractable stops (6) are designed to direct the thermoplastic precisely, ensuring a homogeneous distribution of the thermoplastic, for example to hold the first composite part (1), or the third composite part (3) in position during the over-injection process. This can also be of aesthetic interest by making it possible to ensure that the injection flow does not move the insert, i.e. the first composite part (1), or the third composite part (3), at the level of the visible surface of the mechanical assembly (E). This stop (6) can be designed to be retracted manually (controlled), or automatically depending on the pressure and depending on the injection phase (dynamic or holding).The fact that the stop (6) is retractable means that there is no aesthetic impact or loss of volume in the finished part.

[0106] With reference to Figures 12 and 13, and for the same purpose, the first part (1) and / or the third part (3) may have arrangements (8) for guiding the injection flow. These arrangements (8) may be of any suitable type such as a groove, walls, ribs or obstacles provided on the surface of said part, forcing the flow of thermoplastic to follow a preferential path. For example, with reference to Figures 12 and 13, the arrangements (8) are illustrated in the form of grooves in which the insert (1b) is located. The third consolidated composite part (3) is then positioned around two CFRT tubes (1) and in a mold (7), and thermoplastic is over-injected around the assembly to form, for example, a bicycle head tube.

[0107] Another solution, for example when it is a question of ensuring that a third part comprising the consolidated composite insert (1b) remains firmly pressed in the right place, would be to locally increase the thickness of said third part to accelerate the flow of thermoplastic at this place.

[0108] It is clear from the above that the invention does indeed provide a mechanical assembly combining the use of thermoplastic composite materials with hollow bodies reinforced with continuous fibers, and thermoplastic overmolding, to achieve high levels of strength, lightness and freedom of form, while maintaining an implementation cost compatible with mass markets such as the automobile industry or sports and leisure, for example.

Claims

Claims

1. Mechanical assembly (E) characterized in that it comprises: - at least a first tubular part (1) made of thermoplastic composite reinforced with so-called continuous fibers with a wefting of less than 2%, said first composite part (1) being in the form of a winding of successive layers (la) of continuous fibers impregnated with a consolidated thermoplastic matrix, the winding of the fibers being carried out around an axis of the first composite part (1) and at angles relative to the axis between -90° and 90° and different between at least two layers; - a second thermoplastic part (2) over-injected into / around at least a portion of the first composite part (1).

2. Mechanical assembly according to claim 1, characterized in that it comprises at least a third part (3) made of thermoplastic composite reinforced with continuous fibers with a fogging of less than 2%, and in that the second part (2) made of thermoplastic is also over-injected into / around at least a portion of the third part (3).

3. Mechanical assembly (E) according to one of the preceding claims, characterized in that the second part (2) made of thermoplastic and / or the third part (3) made of composite comprises at least one reinforced zone with at least one overmolded insert (3b) comprising wicks (3c) or ribbons of continuous fibers with a misting of less than 2% held on the insert (3b) by stitching (3d).

4. Mechanical assembly (E) according to claim 2, characterized in that the third composite part (3) is tubular and in the form of a winding of successive layers (la) of continuous fibers impregnated with a consolidated thermoplastic matrix, the winding of the fibers being carried out around an axis of the third composite part (3) and at angles relative to the axis between -90° and 90° and different between at least two layers.

5. Mechanical assembly (E) according to one of the preceding claims, characterized in that it comprises anti-collapse means (4) positioned inside hollow / tubular portions around which the second thermoplastic part (2) is over-injected, and against which the hollow / tubular portions are pressed.

6. Mechanical assembly (E) according to claim 5, characterized in that the anti-collapse means (4) comprise portions of variable sections (4a) having made it possible to achieve a desired collapse of the hollow / tubular portions against the anti-collapse means (4) during over-injection.

7. Mechanical assembly (E) according to one of claims 5 to 6, characterized in that the anti-collapse means (4) are in the form of a plug allowing the hollow / tubular portion to be closed, and possibly comprising a functionalized portion projecting outside the hollow / tubular portion.

8. Mechanical assembly (E) according to one of the preceding claims, characterized in that the second thermoplastic part (2) is over-injected around the entirety of the first composite part (1) and / or the third composite part (3).

9. Mechanical assembly (E) according to one of the preceding claims, characterized in that the first part (1) and / or the third part (3) has arrangements (8) for guiding the injection flow.

10. Method for producing a mechanical assembly (E) according to claim 1, characterized in that it consists of: - positioning in a mold (7) at least a portion of a first tubular part made of thermoplastic composite reinforced with long fibers with a damping of less than 2%, said first composite part (1) being in the form of a winding of successive layers (la) of continuous fibers associated with a polymer, the winding of the fibers being carried out around an axis of the first composite part (1) and at angles relative to the axis between -90° and 90° and different between at least two layers; - over-injecting thermoplastic into / around said tubular portion, to form a mechanical assembly (E) comprising a first part (1) made of composite and a second part (2) made of thermoplastic over-injected into / around the first part (1).

11. Method according to claim 10, characterized in that it consists of: - also positioning in the same mold (7) at least a second part made of thermoplastic composite reinforced with so-called continuous fibers with a fogging of less than 2%; - also over-injecting thermoplastic into / around at least a portion of the second composite part, to form a mechanical assembly (E) comprising the second part (2) made of thermoplastic over-injected around the first composite part (1) and at least a third composite part (3).

12. Method according to one of claims 10 to 11, characterized in that it consists of: - also positioning in the same mold (7) at least one yoke (3b) comprising wicks (3c) or ribbons of continuous fibers with a misting of less than 2% held on the yoke (3b) by stitches (3d); - also over-injecting thermoplastic around the yoke (3b).

13. Method according to one of claims 10 to 12, characterized in that before the over-injection, the method comprises a step consisting of positioning anti-collapse means (4) inside one or more hollow / tubular portions around which the second thermoplastic part (2) is over-injected.

14. Method according to one of claims 10 to 13, characterized in that it consists of positioning in the mold (7) retractable stops (6) to direct the flow of over-injected thermoplastic.

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