Assembly of parts made of thermoplastic material and method for mounting such parts by thermoplastic riveting

Description

TECHNICAL FIELD

[0001] The invention relates to an assembly of composite parts with a thermoplastic matrix, and to a method of assembling such parts by thermoplastic riveting. It relates more particularly to the assembly of parts with a thermoplastic matrix with high mechanical performance (resistance, deformation, etc.), used in particular, but not exclusively, in aeronautics.

[0002] In the aeronautics field, riveting intended to assemble parts must achieve a flawless joint, in particular without the risk of opening by shearing. In this field, various joining methods are used for metal or composite material parts. Conventionally, metal parts are generally joined by screws and nuts. For example, patent document FR 2 622 257 describes such metal riveting of large panels with pre-drilling and pre-riveting at regular intervals.

[0003] Regarding the assembly of composite materials, several other techniques are also being developed: by reinforcing the panels to be welded and using metal fasteners, possibly after a bonding step; by "sewing" type joining with a thread having high tensile strength (based on "kevlar", glass or carbon fibers, etc.) and a suitable type of needle. In patent document DE 102004055592 the composite material components are preheated before being sewn with threads selected according to the material of the components, the heated area then being compressed to maintain the thickness of the entire components.

[0004] These known techniques are commonly referred to in English as: stitching, tufting, lock stitching, or Z-pinning. Advantageously, the seam can be reinforced by injecting resin after the jointing has been completed. However, these techniques are difficult to apply to thermoplastic materials, which exhibit significant rigidity at room temperature. STATE OF THE ART

[0005] On passenger doors of commercial aircraft based on a stiffened structure / pressurized panel architecture, the interface between the flanges of the stiffened structure and the panel ensures resistance to tearing induced by pressurized loading of the panel. The non-propagation of defects (such as delamination resulting from barely visible impact damage, abbreviated to "BVID") may appear within the composite material constituting the architecture.

[0006] Solutions have been found to improve the assembly of thermosetting composite material parts, but these solutions are not suitable for thermoplastic composite material parts. A method for assembling thermoplastic parts called TAP (acronym for "Therally Assisted Pinning" in English terminology), recommends heating needles above the melting temperature of the resin and then piercing the two thermoplastic parts to be assembled. The end of the needle that protrudes from the other side of the two thermoplastic parts is then cut off, the portion of the needle remaining in the thickness of the material used to join the two parts. This method has the disadvantage of promoting resin-metal contact, which has poor tear resistance, which is a particularly critical point in fields where the parts are subject to high mechanical stresses, particularly in the aeronautics or space sector.

[0007] Another solution, presented in US patent document 5,186,776, advocates a method of riveting a composite material by means of metal pins inserted into the heated composite material and subjected to ultrasonic vibrations, this pin preferably being inserted with a cylindrical tool surrounding the pin. But the use of ultrasound is only suitable for metal pins and also has the disadvantage of resin-metal contact.

[0008] Another solution, developed in patent documents GB 2 205 374 or EP 0 392 568, consists of orienting the reinforcing fibers in a rivet made of thermoplastic material at high temperature and assembling the parts by appropriate heat treatment. This solution does not guarantee high tear resistance. STATEMENT OF THE INVENTION

[0009] The invention aims to overcome these drawbacks and to do this, the invention provides for the use of a riveting joint made of plastic material compatible with thermoplastic matrix composite parts while having characteristics of high mechanical resistance, in particular tear resistance.

[0010] More specifically, the present invention relates to an assembly of composite parts with a thermoplastic matrix. Such an assembly comprises a plurality of riveting points made by sewing assembly links made of a material compatible with the material of the parts, these links being embedded in said zones and passing through them from one side to the other, along zones of the parts overlapping by superimposing two faces of these zones arranged opposite each other. Each zone has another opposite face which remains visible with the part. In this assembly system, the assembly links are made of a composite material based on thermoplastic resin. And these links are constituted at least in part by a stitching stitch (or tufting) made from thread formed of fiber aramid coated with resin.

[0011] The term "part" is generic and refers to a panel, a fairing, a skin, a beam, a frame, a rail, a crosspiece, a veil, a support or any other element to be assembled.

[0012] According to preferred embodiments: the assembly link is made of a composite material chosen from a resin reinforced with continuous fibers, a resin reinforced with fibers of cut lengths, in particular short or long depending on the composite material of the assembled parts and / or the thickness of these parts, the resin being advantageously cut on site after insertion, and carbon nanotubes; the assembly link is in a form chosen from a strand, a staple coupling two adjacent strands by a resin made of continuous fibers, an insert and a combination of strand, staple and / or stitch, at least one stitched stitch being in this assembly link; advantageously, these different types of links coexist in the same assembly of parts;the parts are made of high-performance aeronautical or space-grade physical laminates, in particular with a thermoplastic matrix based on PPS (polyphenylene sulfide), PEEK (polyetheretherketone), PEKK (polyetherketoneketone), PEI (polyetherimide), PAI (polyamide imide), or PI (polyimide) depending on the excellence of the qualities to be prioritized (resistance to compression, impact, chemical agents, temperature, etc.), advantageously reinforced with glass, boron, carbon fibers or any other woven or non-woven reinforcing fiber material; the areas of the parts to be assembled can be located in any part of these parts, both at the edge and in internal and central parts, and independently of one or the other part. ;

[0013] The invention also relates to a method of assembling parts by thermoplastic riveting using transversely drilled heating panels, this method taking place according to the following steps: covering the parts by superimposing two faces of two facing zones, each part having another opposite face which remains visible; placing on each face of the visible zone a pierced heating panel so that the holes are positioned opposite; heating the areas of the parts from their opposite faces by the heating panels to a penetration temperature of a drilling tip to initiate the fusion of the areas of the superimposed faces, the areas being able to represent the entirety of the parts; inserting at least one drilling tip through a first heating panel, with successive drilling of the first and second parts so as to create at least one cylindrical bore; withdrawing the drilling tip, this withdrawal being able to be carried out by continuous movement in the same direction ("forward movement") or in the opposite direction ("reverse movement");inserting an assembly link made of a composite material based on thermoplastic resin into each cylindrical bore up to the visible face of the second part, this link being constituted at least in part by a stitch formed in a pique made from aramid fiber coated with resin a; removing the pierced heating panels and installing in their place a consolidation tool by heating under pressure, to fuse the constituent material of the assembly link with that of the parts, then cooling. ;

[0014] According to preferred implementation methods: the assembly link made of thermoplastic material is a reinforcing element which has a shape complementary to the cylindrical bore; in this case, a cut of the assembly link protruding from the visible face of the first part is carried out after the removal of the first heating panel and before the installation of the consolidation tooling; the assembly link made of thermoplastic material is the formation of a stitch between two threads by the passage of a sewing needle in the cylindrical bore.

[0015] According to particularly advantageous implementation modes, the method according to the invention can provide for: automate steps of simultaneous assembly of several parts to be assembled, in particular a grid for drilling the parts can be used for simultaneous drilling of the parts by the drilling tips; in the case where the assembly link is a reinforcing element, to drive this element following the drilling tip which comes out of the thermoplastic material by moving in the direction of its introduction; generate a countersunk head on the first zone from the corresponding geometry of the drilling tip, the countersunk head being extended by the drilling in order to facilitate the insertion of the assembly link, the reinforcing element or the stitching point, and arrange a punching hollow in the second heating panel placed against the visible face of the second part, in order to anchor the reinforcing element on this face by forming a bead after compression and heating.

[0016] The thermoplastic riveting assembly is reinforced by the geometry of the cylindrical bores: diameter, distance between the bore lines, distance between the bores of the same line. This assembly is also reinforced by the characteristics of the strands or the staple legs: nature of the resin of the material, identical or physico / chemically compatible with the material of the parts to be assembled; typology of the continuous or adapted length fibers, and their sufficient metallic charge to allow electrical continuity. The materials used for the assembly parts are of the same nature, either similar or at least physico / chemically compatible.

[0017] This process can be applied in particular to the reinforcement of the assembly of parts already joined by welding, induction, gluing or any equivalent means, during construction, maintenance or repair.

[0018] The invention also relates to equipment with high mechanical resistance, such as an aircraft or satellite structure (in particular: aircraft door, boxes (mast, wing, landing gear compartment, rudder, etc.), fuselage, wing or airframe of aircraft and satellites, panels, etc.) comprising an architecture with a stiffened structure and pressurized panel made of composite material, in which structures and panels are assembled according to the assembly of parts defined previously, in particular by implementing the method described above. PRESENTATION OF FIGURES

[0019] Other data, characteristics and advantages of the present invention will appear on reading the non-limited description which follows, with reference to the appended figures which represent, respectively: there figure 1 , a view of an example of carrying out steps of the method of assembly by thermoplastic riveting of two parts made of thermoplastic material; the figure 2 , a variant of the process of the figure 1 using a stitch; the figure 3 , a view of a riveting according to an exemplary embodiment of the invention using a staple; and the figure 4 , a variant of the process of the figure 1 using a cylindrical strand bore with a countersunk head and a domed end using a riveting tool.

[0020] In the figures in this text, identical or similar elements are identified by the same reference sign which refers to the passage(s) of the description which mention(s) it. DETAILED DESCRIPTION

[0021] There figure 1presents an example in seven main steps of the assembly method according to the invention by thermoplastic riveting of two parts 2a, 2b of aircraft door architecture made of thermoplastic material. In this example, the parts 2a, 2b are assembled by their end zones delimited by their edges 10a and 10b, but the method can be applied to the assembly of parts in zones located in the center of these parts. The thermoplastic material here is PEEK (polyether-phenylene ether-ketone). This riveting involves the use of a drilling tip 1, two drilled heating panels 3a and 3b for the passage of the drilling tip 1, as well as two undrilled heating panels 30a and 30b.

[0022] This process takes place in the following steps: step 1: superposition of the edges 10a and 10b of the parts 2a, 2b made of thermoplastic material, these edges 10a, 10b then each having: an apparent edge face 11a, 11b, and a non-apparent central edge face 12a, 12b attached to the other central edge face 12b, 12a; and placement on each apparent edge face 11a, 11b of a pierced heating panel 3a, and 3b; the holes P2 and P3 are - in the example - perpendicular to the edge faces 11a, 11b and 12, 12b, but may be inclined relative to these faces, in particular in the orientation range between 30 and 90°; step 2: heating by the pierced heating panels 3a and 3b, of the edges 10a and 10b of the two pieces of thermoplastic material 2a, 2b, this heating being carried out at a temperature a few degrees higher than the melting point of the thermoplastic material; the fusion between the non-visible central faces 12a and 12b is thus gradually initiated;steps 3 and 4: insertion of a drilling tip 1 (arrow F0) through the drilled heating panels 3a and 3b, with almost simultaneous drilling of a first edge 10a then of a second edge 10b of the two PEEK parts in order to produce a cylindrical bore 5 with a circular base in the example; then the drilling tip 1 is removed either by moving in the same direction as when it was introduced (in "forward motion") as in the example, or by moving in the opposite direction (in "reverse motion"); step 5: replacement of one of the drilled heating panels (the first panel 3b in this embodiment example), by an undrilled heating panel 30b, in order to allow uniform heating of the two edges 10a and 10b; then replacement of the second drilled heating panel 3a, thus uncovering the visible edge face 11a;a strand 6 made of thermoplastic matrix composite material, PEEK in the example, is then inserted into the cylindrical bore 5 by means of a tool 60 (arrow F1); step 6: the strand 6 is cut on site to the correct height - i.e. barely protruding from the edge face 11a - by means of a tool 61 (arrow F2); step 7: an undrilled heating panel 30a is placed on the exposed face 11a, also covering the cut strand 6; then the two undrilled heating panels compress and heat the two edges 10a and 10b of the thermoplastic material parts; thus, this heating makes it possible to fuse the two non-visible central faces 12a and 12b as well as, advantageously, the high-performance mechanical reinforcement laminated material (in PEEK and carbon fibers in the example) of the assembly parts with that of the two edges 10a and 10b.;

[0023] There figure 2 presents a variant of the process of the figure 1concerning the use of a stitch, made using two threads 14 and 15. These threads are made of fibers coated with thermoplastic resin, the fibers being in aramid of the "kevlar" type in the example, which have high tensile strength. Alternatively, the "kevlar" fiber can be replaced by carbon or glass fibers. Steps 1 to 4 of the figure 1 are identical to those of the method using a strand. Then, to use a stitching stitch, a sewing needle 13 is inserted into the cylindrical bore 5 on the side of the edge 10a (step 5'). The sewing needle 13 carries the thread 14, and this thread 14 is knotted with the other thread 15 which runs along the edge 10b (step 6'). Other types of sewing stitches can also be used (lock stitch, etc.).

[0024] There figure 3illustrates an example of use of a staple 20, within the framework of the method of assembly by thermoplastic riveting of the two edges 10a and 10b of the parts made of thermoplastic material. A staple 20, made of thermoplastic material with continuous fibers, is inserted simultaneously into two adjacent bores 5 (cf. figure 1 , step 4) of thermoplastic riveting according to the invention, by means of its two legs 21 and 22. The central joining part 23 of the clip 20 is flattened during heating against the edge 10b by the heating panels 30a and 30b.

[0025] Schematic views of the figure 4 present a variation of the last stages of the process of the figure 1 , using a particular cylindrical bore 5' to insert (arrow F3) the strand 6. This bore 5' is made by a drilling tip (cf. figure 1) whose geometry is adapted by a conical end shape in order to create a corresponding flared entry countersunk head 40 (step 4'). Thanks to this flared entry 40, the insertion of the strand 6 is facilitated and its anchoring reinforced, as described below. After insertion, the strand 6 is cut so as to leave an excess end portion overhanging the face 11a. A "curving" of its other end is carried out by means of a riveting tool which forms a riveting hollow 41 in the heating panel 30'b (step 4'). By compression and heating using the panels 30a and 30'b, the other end of the strand 6 is curved into the shape of a half-spherical bead 62 (step 7'). The flared entry 40 and the riveting hollow 41 thus allow optimized anchoring of the strand 6, the excess material occupying the free space of the hollows 40 and 41, thus creating widened ends of the strand 6.

[0026] The invention is not limited to the embodiments described and shown. Thus, in the heating system, the heating part may be the drilling tip instead of the heating panels. Or, undrilled heating panels may supplement the drilling heating panels during the process steps.

[0027] The cylindrical bores made in the heating panels can be circular, polygonal or oblong in base.

[0028] The flared bore entries can also be made by any machining means: milling, routing, turning, etc.

[0029] Furthermore, the assembly link may be made of a composite material based on thermoplastic resin reinforced by any known and suitable load element.

Claims

1. An assembly of composite parts (2a, 2b) with a thermoplastic matrix, comprising a plurality of riveting points formed by assembly links (6; 14, 15 ; 20) made of a material compatible with the material of the parts, these ties being embedded in zones (10a, 10b) and passing right through them along the said zones of the parts overlapping by superimposing two faces (12a, 12b) of these zones (10a, 10b) arranged opposite each other, each zone (10a, 10b) having another opposite face (11a, 11b) which remains visible with the part (2a, 2b), wherein the assembly ties (6 ; 14, 15; 20) are made of a composite material based on thermoplastic resin, and in that these links (6; 14, 15; 20) are constituted at least in part by a stitched seam made from aramid fiber thread coated with resin passing right through the zones (10a, 10b) with an orientation of between 30° and 90° relative to their faces (11a, 11B, 12a, 12b).

2. The assembly as claimed in claim 1, wherein the assembly tie (6; 14, 15; 20) is made of a composite material selected from continuous fiber-reinforced resin, chopped-length fiber-reinforced resin and carbon nanotubes.

3. The assembly as claimed in claim 1 or 2 wherein the assembly tie (6; 14, 15; 20) is in a form selected from a strand (6), a staple (20) coupling two adjacent strands by a continuous fiber resin, an insert and a combination of strand, staple and / or stitch, at least one stitch of backstitch (14, 15) being in this assembly tie.

4. The assembly as claimed in any one of the preceding claims, wherein the parts (2a, 2b) consist of laminates based on PPS (polyphenylene sulfide), PEEK (polyetheretherketone), PEK (polyetherketoneketone), PEI (polyetherimide), PAI (polyamide imide) and PI (polyimide).

5. An assembly method for thermoplastic matrix composite parts (2a, 2b) according to any of the preceding claims by thermoplastic riveting, this method being carried out according to the following steps: - overlapping the parts (2a, 2b) by superimposing two faces (12a, 12b) of facing regions (10a, 10b), each part (2a, 2b) having another opposite face (11a, 11b) which remains visible with the part (2a, 2b); - placing a perforated heating panel (3a, 3b) on each exposed zone face (11a, 11b) so that the perforations are positioned opposite each other; - heating the zones (10a, 10b) of the parts (2a, 2b) from their opposite faces (11a, 11b) by transversely drilled heating panels (3a, 3b) to a temperature below the melting point of the thermoplastic matrix material of the parts to initiate melting of the zones (10a, 10b) of the superimposed faces (12a, 12b); - insertion of at least one piercing tip (1) through a first heating panel (3a), with successive piercing of the first (2a) and second (2b) parts so as to create at least one cylindrical bore (5; 5'); - removal of the drilling tip (1), which can be carried out by continuous movement in the same direction ("forward motion") or in the opposite direction ("reverse motion") ; - insertion of an assembly link (6; 14, 15; 20) made of composite material based on thermoplastic resin into each cylindrical bore (5, 5') up to the visible face (12b) of the second part (10b), this link being constituted at least in part by a stitch formed into a quilt (14, 15) made from aramid fiber coated with resin; - removal of the perforated heating panels (3a, 3b) and installation in their place of a pressurized heating consolidation tool (30a, 30b), to fuse the material making up the assembly link (6; 14, 15; 20) with that of the parts (2a, 2b), then cooling.

6. The assembly method as claimed in the preceding claim, in which the assembly bond (6) of thermoplastic material is a reinforcing element which has a shape complementary to the cylindrical bore (5; 5').

7. The assembly method as claimed in the preceding claim, in which a cut in the assembly bond (6, 20) protruding from the visible face (12a) of the first part (10a) is made after removal of the first heating panel (3a, 3b) and before installation of the consolidation tooling (30a, 30b).

8. The assembly method according to any one of claims 6 or 7, wherein in the case where the assembly link (6, 6') is a reinforcing element, this element is driven following the piercing tip (1) which emerges from the thermoplastic material (10a, 10b) moving in the direction of its introduction.

9. The assembly method as claimed in claim 5, in which the assembly bond of thermoplastic material is the formation of a stitch (14, 15) between two threads by the passage of a sewing needle (13) through the cylindrical bore (5).

10. The assembly method as claimed in any one of claims 5 to 9, in which provision is made for automating the simultaneous assembly steps of several parts to be assembled.

11. The assembly method as claimed in claim 1, in which a workpiece drilling grid (2a, 2b) is used for simultaneous drilling of the workpieces (2a, 2b) by the drilling tips (1).

12. The assembly method as claimed in any one of claims 5 to 11, wherein a countersunk head (40) is generated from the corresponding geometry of the drill tip, the countersunk head (40) being extended by the bore (5').

13. The assembly process as claimed in any one of claims 5 to 12, in which a bonding recess (41) is formed in the second heating panel (30'b) positioned against the visible face (11b) of the second part (2b), in order to anchor the reinforcing element (6) to this face (11b), forming a bead (62) by compression and heating.

14. High-strength equipment comprising an architecture with a stiffened structure and a pressurized panel made of composite material, characterized in that structures and panels (2a, 2b) are assembled in accordance with the assembly of parts according to any one of claims 1 to 4, by implementing the process according to any one of claims 5 to 13.