FR2584106A1 - METHOD FOR MANUFACTURING THREE-DIMENSIONAL STRUCTURES BY NEEDLEING PLANE LAYERS OF SUPERIMPOSED FIBROUS MATERIAL AND FIBROUS MATERIAL USED FOR THE IMPLEMENTATION OF THE PROCESS - Google Patents

Abstract

PLANAR STRIPS 20 OF FIBROUS MATERIAL ARE OVERLAYED ON A TRAY 10 NEEDLEING EACH NEW STRIP ON THE PREVIOUS ONE UNTIL THE DESIRED THICKNESS IS OBTAINED, AND THE DISTANCE BETWEEN THE TRAY AND THE NEEDLES IS CHANGED EVERY TIME. IS BROUGHT ON THE STACKING, TO MANUFACTURE A SUBSTANTIALLY UNIFORM NEEDLE THROUGHOUT THE THICKNESS OF THE STRUCTURE. THE TRAY AND THE NEEDLES ARE MUTUALLY SPACED EACH EACH OF A NEW STRIP, EQUAL TO THE THICKNESS OF THE STRIP WHEN NEEDED.

Description

Method for manufacturing three-dimensional structures by needling

  The present invention relates to the manufacture of three-dimensional structures formed by superimposed planar layers of fibrous material bonded together by needling. The field of application of the invention is more particularly, but not exclusively, the manufacture of three-dimensional reinforcement structures intended for the production of parts made of composite material by densification of the reinforcement structures, in particular for manufacturing brake discs, composite tiles , etc. A known method of manufacturing planar structures by needling superimposed layers of fibrous material is described in the utility certificate FR 2 196 966. According to this known method, planar unidirectional layers are superimposed by being crossed and then needled. Although no limitation is given as to the number of superimposed layers, this document is silent on the means to be used to achieve a thick structure with homogeneous characteristics throughout the structure. The patent FR 2 414 574 describes a process for manufacturing fibrous reinforcement for brake discs by forming felt rings by needling, stacking the rings on top of each other until the desired thickness is obtained, and maintenance of the stack for densification. It is indicated that all of the stacked rings can be needled,

  but without describing the procedure.

  The two documents mentioned above, as well as US Pat. No. 3,772,115 in fact disclose needling techniques for small thicknesses, and it turns out that these techniques are not as such transposable for large thicknesses. One reason is that, from a certain penetration in the superimposed layers, the needles lose their aggressiveness due to the blocking of their roughness by pieces of fibers torn from the layers of material already crossed; the needles cannot then correctly fulfill their function, making it impossible to obtain the same needling characteristics throughout the thickness of the stack. However, for materials intended to be exposed to severe thermomechanical stresses, it is important to maintain the properties constant throughout the mass so, by

  example, to avoid delamination.

  Also, according to one of its aspects, the present invention has-

  does it aim to provide a method for producing thick three-dimensional structures by needling superimposed planar layers with a constant needling density in

the entire thickness.

  This object is achieved by a process according to which, in accordance with the invention, flat strips of fibrous material are superimposed on a plate by needling each new strip on the previous one until the desired thickness is obtained, and the distance between the plate and the needles are modified each time a new strip is brought onto the stack, so as to achieve a substantially uniform needling in

the entire thickness of the structure.

  The plate and the needles are separated from each other, each time a new strip is brought in, by a distance equal to

  the thickness of the strip once needled.

  At each needling pass, the needles pass through several superimposed bands. Also, in order to obtain a homogeneous material throughout its thickness, finishing needling passes are carried out after the feeding and needling of the last strip, so that the needling density in the upper layers is substantially equal to that in the other layers. After each finishing pass, the platter and the needles are moved to each other as if a new strip has been fed. Because they perform part of their course in the air during the finishing passes, the needles are more aggressive towards the upper layers of the stack than if they had previously had to cross other layers with capping more or less important of their roughness. For this reason, the number of finishing passes is preferably less than that necessary to arrive until the point where the needles no longer reach the last layer of the stack. According to another of its aspects, the present invention relates to a fibrous material capable of being used for the implementation of the method. The choice of fibrous material is guided by the intended application, while ensuring that the needled texture lends itself to the densification operation, that is to say has a

fairly large open porosity.

  For example, the strip of material may comprise at least one layer formed of single staple fibers, obtained by carding or a layer of continuous fibers obtained by coating

  cables or wires followed by a pre-needling.

  When greater mechanical strength is required, a complex made of a fabric (canvas or satin) may be used, on which a web of fibers has been needled, a fabric made of warp and weft of threads formed of continuous filaments or discontinuous, or a fabric consisting of a warp of threads formed of continuous or discontinuous filaments and in a weft of

spinning wick.

  Furthermore, the material must be suitable for needling, which is hardly the case for carbon or ceramic fibers used in the composition of the composite materials currently used for applications requiring high thermomechanical strength. In the latter case, at least part of the constituent fibers of the material are carbon or ceramic precursor fibers which lend themselves well to needling and which are subsequently transformed into carbon or ceramic fibers by

treatment of the structure.

  Other features and advantages of the process according to

  the invention will emerge on reading the description given below

  after, for information, but not limitation, with reference to the accompanying drawings in which: - Figure 1 is a view illustrating, very schematically a device for implementing the method according to the invention, and - Figures 2 to 4 illustrate, in section, different stages in the production of a structure with the method according to the invention. On a horizontal plate 10 are fed, one by one, strips 20 of fibrous material of width and length

  determined according to the dimensions of the structure to be produced.

  The strips 20 are stacked on top of each other and linked between

  them by needling by means of a needle board 12.

  This is located above the plate 10 and extends parallel to one of the sides of the plate 10, and over a length substantially equal to that of this side, with the needles 13

  directed vertically downwards.

  The needle board 12 is integral with a drive device (not shown) which, in a manner well known per se,

  communicates to the hands a vertical reciprocating movement.

  The needle board 12 and the stack of strips 20 are movable relative to each other in the horizontal direction and in the vertical direction. Horizontally, the plate 10 is by

  example movable relative to a support table 14, perpendicular to

  rement to the board 12, under the action of drive means (not shown) mounted on the table 14. Vertically, the mutual displacement of the plate 10 and the board 12 is for example achieved by driving the table 14 by means worm or other coupling device with a motor (not shown) fixed to the

  needle board support frame.

  The fabrication of a structure is carried out as follows.

  A first strip of material is placed on the plate, then a second is superimposed on it and is needled on the first, the needle board 12 being continuously driven in an alternating vertical movement while the plate is moved horizontally over a length at less equal to that of the strips 20 to scroll these over their entire length opposite the board 12. When the plate 10 has reached an end of its travel, a new strip 20 is stacked on the previous ones then the table 14 is lowered by a distance corresponding to the thickness e of a needled strip before making a new needling pass by moving the plate 10 to the other end of its travel. This is done by supplying the plate 10 with new strips at each end of its horizontal travel, until reaching the height

desired for structure.

  Each penetration of the needles, the roughness (or barbs) of the latter entrain fibers of the material of the crossed bands, which fibers make the vertical connections.

between the overlapping bands.

  Figures 2 and 3 show the needles respectively in the high position and in the low position. The needles penetrate the texture to a depth equal to several times the thickness of a needled strip (for example 8 times). The needling depth is kept constant throughout the operation due to the gradual lowering of the structure relative to the needles. In order to be able to needle the first strips on the plate 10, it is necessary to provide means making it possible to prevent the needles 13 from abutting against the hard surface of the plate 10. For this purpose, the plate 10 is covered with a coating 11 in which the needles can penetrate without being damaged and without bringing back particles or

  fibers within the structure to be manufactured.

  The coating 11 can for example consist of a sheet 11a of reinforced elastomer (for example of Hypalon "reinforced with a" Nylon "fabric) fixed to the plate 10 and on which is glued a layer llb formed of a base felt (for example

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  polypropylene felt) of sufficient thickness so that the needles, during the first needling pass can penetrate the planned needling depth without touching the plate 10. On the base felt is another sheet 11c, by example in polyvinyl chloride. During needling, the sheet 11c is crossed by the needles but prevents too much fiber from the material of the strips 20 from becoming encrusted in the base felt and complicating

  removal of the completed structure.

  It will be noted, as a variant, that it is possible either to keep the plate stationary horizontally and therefore to move the needle board, or to carry out the needling on a perforated plate with perforations corresponding to the needles of the board 12. In this In this case, it is not useful to provide the tray with a surface coating such as the coating 11. The tray is stationary relative to the needle board in the horizontal direction and therefore it is the stacking of strips which is moved horizontally on the table with each needling pass. In order to obtain a constant needling density throughout the thickness of the structure, it is necessary to carry out finishing needling passes after the last strip has been put in place and needled. We proceed as if new bands were put in place. Because the needles then cross a certain distance d in the air before reaching the structure and reaching the end of descent (Figure 4), their roughness is less blocked than if they had to cross the same distance d through the fibrous material. The needles thus exhibit increasing aggressiveness during the finishing passes. To avoid then a more dense needling in the upper layers, the number of finishing passes carried out (for example four) is less than that (eight) which would have been necessary to arrive until the moment when the

  needles no longer reach the last deposited strip.

  The strip of fibrous material may be present under

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  different forms, in particular depending on the intended application. Thus, the fibrous material can be at least partially constituted by a layer of staple fibers obtained by carding (carding web), or by a layer of continuous fibers obtained by crossing unidirectional layers of continuous cables or wires and needling at low density. (pre-needling) of the plies together. In the latter case, the crossing may be carried out as known per se by coating; one of the plies of unidirectional cables or wires is supplied continuously while another ply of unidirectional cables or wires is superimposed on it back and forth in a direction perpendicular to the movement of the first ply. Due to the relative displacement between the unidirectional plies, three superimposed plies are in fact obtained, forming between them angles different from

 , for example about 60.

  When a higher mechanical strength is requested from the structure, in particular as a function of the desired properties of the final composite material to be manufactured, the fibrous material consists of at least one woven layer for example: - a complex consisting of a fabric of continuous threads or discontinuous (satin or fabric) on which a web of staple fibers obtained by carding (carding veil) or a web of continuous fibers has been needled with a low needling density, these plies being deposited on the fabric by coating, - a single fabric consisting of warp and weft of threads formed of continuous or discontinuous filaments, or - a single fabric consisting of warp of threads formed of continuous or discontinuous filaments and weft of a wick of

spinning.

  The fibers constituting the materials described above can be any natural, artificial or synthetic, organic or mineral fiber, as it is or heat treated, the choice of the nature of the fibers depending on

the intended application.

  As regards the production of reinforcement structures for composite materials intended to withstand significant thermomechanical forces, the most interesting fibers are carbon fibers and ceramic fibers (alumina, silicon carbide, etc.) as well as the fibers precursors of these fibers or any fibers constituting an intermediate between fibers

  precursors and fibers completely heat treated.

  When the three-dimensional structure is produced wholly or in part from precursor or intermediate fibers, it subsequently undergoes heat treatment

  intended to give fibers the optimal mechanical properties.

  This last way of proceeding makes it possible not to break the fibers during needling in the case where the heat treated fibers have too high moduli and too low transverse resistances to be needled without

  damage, as is the case with carbon and ceramic fibers.

  Thus, the materials described above can be made at least in part with carbon or ceramic precursor fibers, the possible remainder of the fibers being carbon or

ceramic.

  For example, the fibrous material intended for needling consists of a complex formed from a fabric of high-strength carbon fibers pre-needled with a veil of carding fibers from P.A.N. (polyacrylonitryl, carbon precursor) stabilized. In this complex, the fabric provides the desired mechanical strength while the fiber web allows non-destructive needling of the superimposed bands because the barbs of the needles, covering themselves with P.A.N. stabilized, do not seriously injure carbon fibers. For the sake of economy, the fabric will be chosen as light as possible, taking into account the desired mechanical properties, for example with a surface mass of between 100

and 600 g / m2.

  In the previous example, it is of course possible to independently replace fibers and / or carbon precursors with fibers and / or ceramic precursors. And, conversely, a fabric of carbon or ceramic precursor fibers can be combined with

  a carbon or ceramic fiber card veil.

  Likewise, carbon or ceramic fibers and carbon or ceramic precursor fibers can be combined by forming, independently of each other, the warp and the weft of a fabric made up, in warp, of continuous filament yarns or discontinuous and, in the weft, of a spinning wick or

continuous or discontinuous filaments.

Claims (13)

  1. A method of manufacturing three-dimensional structures formed by superimposed flat layers of fibrous material bonded together by needling, characterized in that: flat strips of fibrous material are superimposed on a plate by needling each new strip on the previous one up to obtaining the desired thickness, and the distance between the plate and the needles is modified each time a new strip is brought to the stack, so as to perform a substantially uniform needling throughout the thickness of the structure.   2. Method according to claim 1, characterized in that the plate and the needles are mutually separated, each time a new strip is brought in, by a distance equal to the thickness of the band once needled.   3. Method according to any one of claims 1 and 2,   characterized in that the stack of layers or the set of needles is moved relative to each other, a new strip being superimposed on the structure during manufacture each time the stack of layers or the all   needles reaches one end of its course.   4. Method according to any one of claims 1 to 3,   characterized in that finishing needling passes are made after the last strip has been brought in and needled, so that the needling density in the upper layers is substantially equal to that in the other layers. 5. Method according to claim 4, characterized in that the number of finishing passes is less than that necessary to arrive until the point where the needles no longer reach the last layer of the stack.   6. Fibrous material intended for the implementation of the process   according to any one of claims I to 5, characterized in that   that it is at least partly made up of unidirectional layers of crossed and pre-needled cables or wires 8 4 106 between them.   7. Material according to claim 6, characterized in that   the sheets are crossed at angles of about 60.   8. Material according to any one of claims 6 and 7,   characterized in that the sheets consist, independently of one another, of cables or wires, the fibers of which are made of a material chosen from carbon, ceramics, precursors   carbon and ceramic precursors.   9. Fibrous material intended for the implementation of the process   according to any one of claims I to 5, characterized in that   that it comprises at least one woven layer.   10. Material according to claim 9, characterized in that it is at least partly constituted by a fabric of continuous threads or   discontinuous on which a card web is pre-needled.   11. Material according to claim 10, characterized in that the fabric and the card web consist, independently of one another, of fibers of a material chosen from carbon, ceramics, carbon precursors and the ceramic precursors.   12. Material according to claim 9, characterized in that it is at least partly constituted by a fabric whose warp is formed of continuous or discontinuous threads and the weft of a spinning wick. 13. Material according to claim 12, characterized in that the warp and the weft are constituted, independently of one another, by fibers of a material chosen from carbon, ceramics, carbon precursors and precursors of ceramics.