EP0678604A1 - Process and machine for the manufacture of a block-like reinforcement for a piece of composite material - Google Patents

Abstract

The composite framework structure is a block (B) formed by a continuous succession of plates (30), to be embedded in a hardened matrix. Each plate has layers of filament grids overlaid in parallel in each layer and partially parallel and at an angle to other layers, held together by a locking filament (Fl) which also holds the plates (30) together. <IMAGE>

Description

The present invention relates to a method for producing a block-shaped reinforcement for a piece of composite material, formed of said reinforcement embedded in a hardened matrix, said reinforcement comprising layers of superimposed wire (carbon, glass, boron, in particular), and a machine for implementing said method, as well as a frame and a piece of composite material thus obtained.

More particularly, although not exclusively, such pieces of composite material will be used, after machining, in the aeronautical, space and nuclear fields by virtue of their excellent properties of resistance to mechanical and / or thermal stresses.

Many processes are known for obtaining parts of composite material, and in particular their reinforcement. Generally, we start by making the reinforcement from fibers (son), in particular mineral, distributed in at least two directions, after which we introduce the matrix material into the reinforcement, and harden said material to forming said matrix and, thus, said composite part.

More specifically, in the present case, the term “block” denotes an object whose thickness or height represents at least a large fraction of its longitudinal dimensions (length, width; diameter).

For the production of such blocks, according in particular to patents US-A-3,955,602 and US-A-4,218,276, it is necessary to materialize the vertical direction, corresponding to the thickness or to the height of the block, by rods, in particular metal, between which plies of wire horizontal are introduced and compacted. Such a procedure requires the use of a large number of such rods, which must be replaced by wire at the end of the superposition of the horizontal layers of wire. It is therefore a restrictive and inflexible principle.

A similar process is described in patent FR-2,531,459, in which there is formed, initially, a network of rods or rigid rods, between which is deposited a wire forming successive layers superimposed in planes transverse to the direction of the chopsticks. Likewise, after the desired reinforcement has been produced, the rods are replaced by wire of the same kind, by driving them out beforehand from the armature using a long needle, which then hooks a wire and pulls it through the frame to replace the strip which has just been driven out. It can be understood that this method requires complex, bulky equipment (the armature must be reassembled to release a location for releasing the needles), and fragile (the needle must have a length corresponding to that of the rods). Correlatively, the height of the parts obtained by this process is necessarily limited. Moreover, this process, more flexible than the previous ones for the orientation of the horizontal layers, requires, on the one hand, to calibrate the lengths of deposited wire and, on the other hand, to also materialize the vertical direction in the form of a network of metal rods.

The present invention aims to avoid these drawbacks, and relates to a method for producing a block-shaped reinforcement for a piece of composite material, thanks to which it is no longer necessary to use metal rods to materialize the vertical direction (thickness or height of the block) and, ultimately, to replace them. Furthermore, the tools necessary for implementing the method are considerably simplified.

To this end, the method for producing a block-shaped reinforcement for a piece of composite material, formed of said reinforcement embedded in a hardened matrix, is remarkable, according to the invention, in that said block is constituted by continuously forming a succession of superimposed plates, each plate itself comprising superposed plies of wire produced by arranging, for each ply, straight sections of wire at least substantially parallel to one another, the straight sections of wire each ply extending in a direction, either parallel or crossed with respect to the direction of the straight wire sections of any other ply of the plate, and by joining together all of the superposed plies using '' a wire crossing said plies, and in that each plate is secured to the immediately underlying plate by the wire for securing the superimposed plies of the plate in question and to the immediately overlying plate by the connecting wire of the superimposed layers of said overlying plate.

Thus, it is possible to produce an armature in the form of a large block (height or thickness) from a succession, produced continuously and "in situ", of woven plates (wefting), connected together by transverse stitching.

Advantageously, the superimposed plies of each plate are compacted by mechanical pressure, and, in order to maintain the state of compaction thus obtained of said plies, the wire for securing the plies is stitched without knotting through said plies, forming stitching points on at least the major part of the surface of said plies having, after compaction, a density of the sections of wire which constitute them sufficient to frictionally retain said securing wire.

In particular, each of said straight wire sections can be stretched between two fixing points in position of the ends of said section.

Preferably, each fixing point in position is materialized by a pin, around which passes the junction between two sections of straight wires of the same direction and opposite directions.

According to another characteristic of the invention, after the production of a plate, all of the pins are detached from said plate and raised by a distance corresponding to the thickness of said plate.

According to yet another characteristic of the invention, the lowest plate of the block is produced on a support of flexible material, such as a foam of synthetic material.

The present invention also relates to a machine for implementing the process which has just been described, of the type comprising a frame provided with a base and uprights for mounting at least one mobile frame along said uprights, capable of to receive a wire removal tool, movable in a plane transverse to said uprights, remarkable, according to the invention, in that it comprises an additional frame, movable along said uprights, provided with pins for hooking said sections of wire straight.

Although other shapes, in particular cylindrical, can be envisaged (with corresponding frames, in particular circular), for the realization in particular of a block of rectangular shape, said additional frame has a quadrangular shape, each side of said frame comprising a series of said pins.

In this case, advantageously, each series of pins is mounted on a rotary axis for its retraction.

Preferably, each pin has a hook shape, the free end portion of which is curved outward.

According to another characteristic of the machine of the invention, the wire removal tool has a rigid tube extended by a flexible tube, the wire passing through said tubes.

Furthermore, the machine can include a stitching head having a rotary support at the lower end of which is mounted a needle, associated with a presser foot.

The figures of the appended drawing will make it clear how the invention can be implemented.

FIG. 1 is a diagrammatic view, in elevation, of an example of a machine for implementing the method according to the invention, the left half of which corresponds to a screening phase (wire removal) and the right half to a stitching phase.

Figure 2 is a schematic perspective view of a quadrangular frame carrying the wire hooking pins.

Figure 3 is a schematic perspective view of the wire removal tool, on its frame, of the machine of the invention.

Figure 4 shows an enlarged detail of the machine of Figure 1.

The machine 1 of FIG. 1 comprises a frame 2 provided with a base 3 and uprights 4, connecting the base 3 and the roof part 5 of the machine. The uprights 4, four in particular, can be made, as shown, in the form of threaded rods, and allow the mounting of movable frames 6,7 along said uprights, parallel to the direction Z. Although, for reasons clarity of the drawing, this is not shown, each frame 6,7 comprises a motor which drives, by a chain, four nuts, each corresponding to a threaded rod, which allow a translation of these frames in the direction Z (advantageously vertical ).

More particularly, the lower frame 6, as can best be seen in FIG. 2, has a quadrangular shape, each side 8A, 8B, 8C, 8D of the frame 6 comprising a series of pins 9, each series of pins being mounted on a rotary axis 10A, 10B, 10C, 10D. Said axes are connected to four bevel gears 11, arranged in the corners. One of the outputs of these bevel gearboxes is connected to a geared motor 12. A contact (not shown) fixed on this output makes it possible to stop the motor at the screen position of the hooks. Furthermore, at the corners of the sides 8A-8D, the lugs 13 for mounting the frame 6 are shown on the uprights 4. As can be seen better in FIG. 4, each pin 9 has a hook shape, the part of which free end 9A is bent outward, to facilitate the dithering of the wire, preventing it from rising and the pins from being retracted by rotation in the direction of the arrow P in FIG. 4.

The upper frame 7 comprises two carriages 14,15 which can move in the plane, transverse to the direction Z, defined by the two directions X, Y (see FIG. 3). The lower carriage 14 (Figure 3) comprises a bar 16, extending in the direction X, along which can move the wire removal tool 17, under the action of a motor 18, via a drive belt not shown. Furthermore, the bar 16 is movable in the direction Y, orthogonal to the direction X, its ends rolling on guide rails 19,20, fixed to the frame 7, under the action of drive belts 21,22, animated by a motor 23 also integral with the frame 7. The wire removal tool 17 can thus move in the directions X, Y at any point on the plane limited by the rails 19,20.

More particularly, the wire removal tool has a rigid tube 24 extended by a flexible tube 25, the wire F passing through said tubes 24, 25 coming from a coil 26 (FIG. 1).

In addition, the upper carriage 15 carries a stitching head 27 having a rotary support at the lower end of which is mounted a needle 28, preferably associated with a presser foot (not shown).

It will be noted that a wire removal tool and a stitching head which are particularly suitable for use in a machine of this type are described in detail in the French patent application, filed on April 18, 1994, in the name of the applicant, for "Method and machine for producing a plate-shaped reinforcement for a piece of composite material".

This machine is controlled by a numerically controlled director consisting of an axis card capable of driving eight motors plus sixteen inputs and sixteen all-or-nothing outputs. This card is installed in a computer which is used to send the card the data necessary for the execution of a block.

A block B is produced in the following manner, according to the invention.

A foam support 29 of a suitable height is placed on the base 3 of the machine. The two frames 6 and 7 are placed in relative position, so that the wire removal tool 17 places the wire F in the hooks 9. This can in particular be carried out in accordance with the method described in the French patent application referenced above. , and is schematically illustrated in FIG. 2.

A rasterization program is executed, which controls the removal of the plies of wire until the hooks are fully lined with sections of wire. This corresponds to a plate 30 (Figure 4) with a height of about 3 cm, for example.

Then, the transverse bar 16, carrying the carriage (FIG. 3) on which the wire removal tool 17 is fixed, retracts into the front or rear position in order to leave it placed at the stitching head 27.

The stitching is then carried out in particular in the manner described in the above-referenced French patent application, which compacts the tablecloths deposited. At the same time, each plate 30 is secured to the immediately underlying plate by the fastening wire F1 of the superimposed plies of the plate in question and to the immediately overlying plate by the fastening wire F1 of the superimposed plies of said plate overlying (Figure 4).

The rotation of the axes 10A-10D carrying the hooks 9 is then controlled, which has the effect of unhooking the sections of screened wire F which remain fixed by the sections of wire F1 stitched on the sheets previously deposited.

We can then reassemble the lower frame 6 of the height of the layers of wire deposited, corresponding to a plate, and complete the rotation of the axes 10A-10D in order to be able to start the screening operation again (depositing of wire). Each plate thus comprises superposed plies of wire produced by arranging, for each ply, straight sections of wire at least substantially parallel to one another, the straight sections of wire of each ply extending in a direction, ie parallel , or crossed with respect to the direction of the straight wire sections of any other ply of the plate, and all of the superimposed plies are joined together using a wire passing through said plies.

Furthermore, the superimposed plies of each plate 30 are compacted by mechanical pressure and, to maintain the state of compaction thus obtained of said plies, the connecting wire F1 of the plies is stitched without knotting through said plies, forming points of stitching on at least the major part of the surface of said plies having, after compaction, a density of the sections of wire which constitute them sufficient to frictionally retain said securing wire. In this respect, the screening wire F can constitute from 40 to 60% and the joining wire F1 from 1 to 10% of the total volume of the part (reinforcement plus matrix).

The block will therefore rise in stages. It consists of a succession of "sections" (plates) linked together by the stitching levels.

When the desired height is reached, the block is then removed from the machine by removing it from the lower foam 29 and taking away the foam 29A which is torn off.

The size of the blocks produced on the machine can be, for example, 800 mm x 800 mm x 2000 mm, or a mass of 1300 kg (linked to the capacity of the machine).

In the current application, this block (reinforcement or woven substrate neither impregnated nor densified) is cut into slices by sawing on a band saw, like a tree trunk, in order to obtain "boards" comprising the majority of wires perpendicular to the length of the board, to promote thermal conduction between the two faces.

Thus, the process of the invention makes it possible to produce a preform or fibrous reinforcement (before impregnation and densification) of large dimension (height) from a succession of woven plates (wefting), connected together by stitching.

The large block produced can then be cut into different elements or small blocks or plates, depending on the type of application (use) envisaged (due to the good consistency of the vertical direction Z of the stitching).

One of the interesting applications is the obtaining of a block whose thermal conductivity in a carbon / carbon direction is very high. For this, the percentage of fibers (threads) is increased in a desired direction. In addition, pitch fibers (whose conductivity is higher than that of graphite) can be used.

The blocks thus produced make it possible to replace the graphite commonly used in the nuclear field, for example.

In this case, plates having a high transverse thermal conduction (Z) are obtained by increasing the density of transverse wires (stitching) (relatively low in the XY plane of the part).

The downtime of the machine between two parts is very low since the starting operation is very simple. Very fine meshes can be produced, since the thickness of the vertical wires is small, of the order of 0.2 mm, and the pitch of the vertical wires only depends on the programming of the displacements of the stitching head and not complex tools (allowing the production of blocks with fine pitch). This process also makes it possible to place the horizontal layers of wire in any orientation in the plane (we are no longer limited to two or three directions, because the wire removal tool is programmed and it can move in the desired direction).

As already indicated, one of the products which can be obtained by this process is a thermally more conductive material than graphite and less brittle. This conduction must be obtained between the two faces of the material.

Claims (15)

Method for producing a block-shaped reinforcement for a piece of composite material, formed of said reinforcement embedded in a hardened matrix,
characterized in that said block (B) is formed by continuously forming a succession of superimposed plates (30), each plate itself comprising superposed layers of wire produced by arranging, for each layer, sections of straight wire at least substantially parallel to each other, the straight wire sections of each ply extending in a direction, either parallel or crossed with respect to the direction of the straight wire sections of any other ply of the plate, and by joining together all of the superimposed sheets using a wire passing through said sheets, and in that each plate (30) is joined to the plate immediately underlying by the connecting wire (F1) of the sheets superimposed on the plate in question and on the immediately overlying plate by the connection wire of the superimposed layers of said overlying plate. Method according to claim 1,
characterized in that the superimposed plies of each plate (30) are compacted by mechanical pressure, and, to maintain the state of compaction thus obtained of said plies, the securing wire (F1) of the plies is stitched without knotting through said plies , by forming stitches on at least the major part of the surface of said plies having, after compaction, a density of the sections of wire which constitute them sufficient to frictionally retain said securing wire. Method according to claim 1 or claim 2,
characterized in that each of said straight wire sections (F) is stretched between two fixing points in position (9) of the ends of said section. Method according to claim 3,
characterized in that each fixing point in position is materialized by a pin (9), around which the junction passes between two sections of straight wires of the same direction and opposite directions. Method according to claim 4,
characterized in that, after the production of a plate (30), all of the pins (9) are detached from said plate and raised by a distance corresponding to the thickness of said plate. Process according to any one of Claims 1 to 5,
characterized in that the lowest plate (30) of the block (B) is produced on a support (29) of flexible material, such as a foam of synthetic material. Machine for implementing the method according to any one of Claims 1 to 6, of the type comprising a frame provided with a base and uprights for mounting at least one mobile frame along said uprights, capable of receiving a wire removal tool, movable in a plane transverse to said uprights,
characterized in that it comprises an additional frame (6), movable along said uprights (4), provided with hooking pins (9) of said straight wire sections (F). Machine according to claim 7,
characterized in that said additional frame (6) has a quadrangular shape, each side (8A-8D) of said frame comprising a series of said pins (9). Machine according to claim 8,
characterized in that each series of pins (9) is mounted on a rotary axis (10A-10D) for its retraction. Machine according to claim 9,
characterized in that each pin (9) has a hook shape, the free end part (9A) of which is bent outwards. Machine according to any one of Claims 7 to 10,
characterized in that the wire removal tool (17) has a rigid tube (24) extended by a flexible tube (25), the wire (F) passing through said tubes (24, 25). Machine according to any one of Claims 7 to 11,
characterized in that it comprises a stitching head (27) having a rotary support at the lower end of which is mounted a needle (28), associated with a presser foot. Reinforcement for a piece of composite material, formed of said reinforcement embedded in a hardened matrix,
characterized in that it is produced according to the method according to any one of claims 1 to 6. Piece of composite material, formed of a frame embedded in a hardened matrix,
characterized in that said reinforcement is produced according to the method according to any one of claims 1 to 6. Elementary product,
characterized in that it is obtained by sawing or cutting a block produced in accordance with the method according to any one of claims 1 to 6.

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