FR3072898A1 - PROCESS FOR MANUFACTURING A PIECE OF COMPOSITE MATERIAL - Google Patents

Abstract

A method of manufacturing at least one composite material part, the method comprising the following successive steps: - providing a first forming tool (20) heated to a temperature above the melting point of the thermoplastic material (13), - arranging at least one reinforcing layer and a thermoplastic material (13) in the first forming tool (20); - closing the first forming tool (20) and applying a first pressure in said first forming tool (20); - opening the first forming tool (20) and transferring the non-consolidated part to a second forming tool (22), said second forming tool (22) having a temperature lower than the melting temperature of the thermoplastic material (13) ; - Consolidate the unbound part and then out the consolidated part (46) of the second forming tool (22).

Description

The present invention relates to a method of manufacturing at least one piece of composite material comprising a matrix of thermoplastic material and at least one reinforcing layer comprising fibers.

Such manufacturing processes are known. Such a method is used in particular for manufacturing a composite part for a motor vehicle.

A conventional solution consists in using a prepreg reinforcement element manufactured prior to the manufacture of the part. The prepreg reinforcing element is for example a fabric of reinforcing fibers impregnated with a thermoplastic material. The prepreg reinforcing elements are produced in a conventional manner continuously in a double-band press, in which a strip of fabric of reinforcing fibers and a strip of thermoplastic material circulate. The press comprises a heated zone, in which the two strips are brought into contact and arranged to melt the thermoplastic material so as to impregnate the fabric with the thermoplastic material, and a second cold zone which makes it possible to consolidate the reinforcing element. This process makes it possible to manufacture only plates of prepreg material having a constant thickness and a single orientation of fibers or a single weave of fabric. These plates are then cut to the shape of parts to be manufactured and shaped.

In a variant, the thermoplastic material and the fiber reinforcement layer are first placed in a mold to heat the plastic material so that it permeates the fibers, then the part is cooled in order to consolidate it. Such a production process thus requires heating the mold and then allowing each part produced by this mold to cool, which considerably increases production times, which can go up to several hours, in particular because of the time required to heat the mold again. mold which was cooled during the production of the previous part.

Such a production process thus requires heating the mold and then allowing each part produced by this mold to cool, which considerably increases production times, in particular because of the time required to reheat the mold which has been cooled during production. from the previous play.

One of the aims of the invention is to overcome this drawback by proposing a method for manufacturing a piece of rapid composite material while ensuring their final quality.

To this end, the subject of the invention is a method of manufacturing at least one part made of composite material comprising a matrix of thermoplastic material and at least one reinforcing layer comprising fibers, the method comprising the following successive steps:

- providing a first forming tool movable between an open position and a closed position, said first forming tool being heated to a temperature above the melting temperature of the thermoplastic material,

- have at least one reinforcing layer and a thermoplastic material in the first forming tool in the open position;

- Close the first forming tool and apply a first pressure in said first forming tool so that the thermoplastic material impregnates the fibers of the reinforcing layer in order to form an unconsolidated part;

- Open the first forming tool and transfer the unconsolidated part to a second forming tool, said second forming tool having a temperature below the melting temperature of the thermoplastic material;

- consolidate the non-consolidated part in the second forming tool; and

- remove the consolidated part from the second forming tool.

The manufacturing process according to the invention notably makes it possible to speed up the manufacturing process of a part made of composite material starting from dry fibers and reducing the time required between two production cycles. In fact, the manufacturing process allows the first forming tool to be left at the desired temperature without having to cool it and then heat it again during the production of two successive parts.

According to particular embodiments of the invention, the method also has one or more of the following characteristics, taken in isolation or according to any technically possible combination (s):

- The first forming tool comprises a first molding cavity and the second forming tool comprises a second molding cavity having the shape of the part to be manufactured;

the second forming tool comprises a device for injecting a molding material, the method comprising a step of injecting a molding material into the second molding cavity on the consolidated part before it leaves the second tool forming;

- The first molding cavity has the developed or undeveloped shape of at least part of the part to be manufactured;

- the reinforcing layer and the thermoplastic material are placed in a mold cavity of a mold, said mold being placed in the first forming tool and then in the second forming tool;

- Before placing the reinforcing layer and the thermoplastic material in the first forming tool, the method comprises a step of cutting the reinforcing layer to the shape of at least part of the part to be manufactured;

- the fibers of the reinforcing layer extend in at least two different orientations;

the part made of composite material comprises several reinforcing layers, the method comprising, before placing the reinforcing layers and the thermoplastic material in the first forming tool, the following successive steps:

- Cut the reinforcing layers, so that each has dimensions less than or equal to the corresponding dimensions of the part to be manufactured; and

- stack and join together the cut reinforcing layers;

- The cut reinforcement layers have at least two different orientations of fibers or at least two different textile weaves;

- Before placing the reinforcing layers and the thermoplastic material in the first forming tool, the method comprises a step of preheating the materials;

- several parts are manufactured, the first forming tool being maintained at the temperature above the melting temperature of the thermoplastic material between the outlet of a first non-consolidated part of the first forming tool, and the arrangement of at least one reinforcement layer and a thermoplastic material in the first forming tool for the production of a second non-consolidated part;

- a pressure higher than the ambient pressure is applied in the second forming tool;

- The first pressure is less than 15 bars, and is preferably less than 10 bars; and

- the time of a cycle spent in the first forming tool and / or the second forming tool is between 40 s and 70 s, and is advantageously equal to 55 s.

Other characteristics and advantages of the invention will appear on reading the description which follows, given solely by way of example and made with reference to the appended drawings, in which:

- Figure 1 is a perspective view of a finished part obtained by the method according to the invention;

- Figure 2 is an illustration of the steps for obtaining the reinforcing layers according to an embodiment of the invention;

- Figure 3 is a top view illustrating the cutting of the reinforcing layers;

- Figures 4 to 7 are schematic representations of the forming tools during successive stages of the manufacturing process according to the invention;

- Figure 8 is a schematic representation of a variant of the forming tools according to an embodiment of the invention; and

- Figure 9 is a schematic representation of an example of stacking of reinforcing layers and of composite material according to an embodiment of the invention.

The method according to the invention is suitable for manufacturing parts made of composite material, for example a part of a motor vehicle seat as shown in FIG. 1 or other parts such as door reinforcements, automobile structure reinforcements, aerodynamic fairings, load floors, etc. The part 10 comprises a matrix 12 of thermoplastic material 13, and at least one reinforcing layer 14 comprising fibers 16.

The matrix 12 is made of polypropylene (PP), polyamide (PA), polyethylene terephthalate (PET) or other thermoplastic.

The fibers 16 of the reinforcing layer 14 are for example glass fibers, or carbon fibers, aramid fibers, natural fibers or the like. The reinforcing layer 14 can also comprise a mixture of these fibers. Such fibers are chosen to strengthen the part, which allows for example to reduce its thickness while retaining its mechanical properties. Thus, the part 10 made of composite material is lightened compared to a part made only of plastic material while having satisfactory mechanical properties.

As shown in Figure 1, the part 10 has for example a three-dimensional shape whose body is formed by the reinforcing layer 14 impregnated by the matrix 12. Additional parts can be molded onto the body, such as ribs 17 and / or attachment zones 18.

Each part 10 is produced in a forming device 19, comprising a first forming tool 20 and a second forming tool 22. The first and second forming tools 20, 22 are movable between an open position, in which the material or materials of the matrix 12 and the material or materials of the reinforcing layer or layers 14 can be arranged in the forming tools 20, 22 and a closed position in which the forming tools 20, 22 act on the materials 12, 14 to form the part 10 to be produced.

According to a first embodiment shown in Figures 4 to 7, the forming tools 20, 22 are molds. The molds are advantageously isothermal molds. In a variant shown in Figure 8, the forming tools 20, 22 are presses with heating plates adapted to receive at least one mold.

The different stages of the process for manufacturing a part 10 with the forming tools 20, 22 according to the first embodiment will now be described.

According to one embodiment and with reference to FIG. 2, firstly, a reinforcing layer 14 and layers of thermoplastic material 13 are unwound from storage rollers 24 and positioned one on the other, the layer of reinforcement 14 being for example sandwiched between the layers of thermoplastic material 13. They are then passed between two hot rollers 26 which apply pressure to the layers while heating them in order to form a stack 28 from the reinforcement layer 14 and layers of thermoplastic material 13. According to a variant, the stack 28 comprises several layers of reinforcement 14 and of thermoplastic material 13, for example arranged alternately one on the other.

With reference to FIG. 3, the stack 28 is then cut by a cutting device 30 into several complexes 31 each formed from a part of the stack 28 and comprising at least one reinforcing layer 14 and a layer of thermoplastic material 13. The stack 28 can also be made up of layers of mixed materials containing reinforcing fibers, and a thermoplastic material, for example in the form of streaked reinforcing fibers, or fabrics made from reinforcing fibers and thermoplastic fibers.

The stack 28 can also be made of fabrics of reinforcing fibers powdered with a thermoplastic matrix.

The cutting device 30 is adapted to cut the complexes 31 so that each of these complexes 31 has a dimension less than or equal to a corresponding dimension of the part 10 to be manufactured. The cut complex 31 advantageously has the shape of the part 10 to be manufactured. Alternatively, the complex 31 is punched to the shape of the part 10 to be manufactured. This cutting makes it possible in particular to reduce waste, because the thermoplastic material 13 outside the cuts can be recycled for future manufacturing. In fact, in certain known methods, the parts made of composite material are cut after the fibers have been impregnated with the matrix. In this case, the waste consists of fibers already impregnated, this waste not being reusable.

FIG. 9 illustrates different configurations of the reinforcing layers 14 in a complex 31.

In the configuration shown at the top of FIG. 9, the cut complexes 31 comprise a first 32, a second 34 and a third reinforcing layer 36, these three layers comprising glass fibers 16 which are advantageously a mixture of glass fibers 16 extending in a first orientation and fibers 16 extending in a second orientation substantially perpendicular to said first orientation. Each reinforcing layer 32, 34, 36 is for example arranged between two layers of the thermoplastic material 13. In a variant, the glass fibers 16 of the first, second and third reinforcing layers 32, 34 and 36 extend only in the first orientation. In another variant, the glass fibers 16 of the first, second and third reinforcing layers 32, 34 and 36 extend only in the second orientation.

In another configuration represented in the middle of FIG. 9, the cut complexes 31 comprise a first 32 and a second 34 reinforcing layers, these two layers comprising glass fibers 16 which are advantageously a mixture of glass fibers 16 extending in a first orientation and of fibers 16 extending in a second orientation substantially perpendicular to said first orientation. Alternatively, the glass fibers 16 of the first and second reinforcing layers 32, 34 extend only in the first orientation. In another variant, the fibers 16 of the first and second reinforcing layers 32, 34 extend only in the second orientation. Between the first and second reinforcing layers 32 and 34 is disposed a third reinforcing layer 36 comprising glass fibers 16 which are advantageously a mixture of fibers 16 extending in a third orientation which has an angle of 45 ° relative to the first orientation and of glass fibers 16 extending in a fourth orientation substantially perpendicular to said third orientation. In a variant, the glass fibers 16 of the third reinforcing layer 36 extend only in the third orientation. In another variant, the glass fibers 16 of the third reinforcing layer 36 extend only in the fourth orientation. Each reinforcing layer 32, 34, 36 is for example arranged between two layers of the thermoplastic material 13. It is also possible to use reinforcing layers having unidirectional woven fibers, multiaxial fibers (“Non Crimp Fabric” in English) , or layers of glass fibers having random orientations.

Still in another configuration shown at the bottom of FIG. 9, the cut complexes 31 comprise a first 32 and a second reinforcing layer 34 comprising carbon fibers 16. The first and second layers 32 and 34 are advantageously each a mixture of fibers of carbon 16 extending in a first orientation and of carbon fibers 16 extending in a second orientation substantially perpendicular to said first orientation. Alternatively, the carbon fibers 16 of the first and second layers 32 and 34 extend only in the first orientation. In another variant, the carbon fibers 16 of the first and second layers 32 and 34 extend only in the second orientation. Between the first and second reinforcing layers 32 and 34 is disposed a third reinforcing layer 36 comprising glass fibers 16 which are advantageously a mixture of glass fibers 16 extending in said first orientation and of glass fibers 16 s' extending in said second orientation. In a variant, the glass fibers 16 of the third layer 36 extend only in said first orientation. In another variant, the glass fibers 16 of the third layer 36 extend only in said second orientation. Each reinforcing layer 32, 34, 36 is for example arranged between two layers of the thermoplastic material 13.

The reinforcing layers 14 and the layers of thermoplastic material 13 cut from each complex 31 are then joined, for example by sewing or stitching so as to locally secure the layers of reinforcing fibers 14 and the layers of thermoplastic material 13.

According to one embodiment of the invention, before placing the complex 31 in the first forming tool 20, the method comprises a step of preheating the complex 31 to a temperature below the temperature of the melting of the composite material 13. This preheating step is carried out for example by passing the complex 31 in an oven with infrared radiation. Such a preheating step makes it possible to reduce the time necessary to heat the complex 31 in the first forming tool 20 and thus reduce the cycle time in this forming tool.

Referring to FIG. 4, the first forming tool 20 comprises a first molding cavity 38. In a variant, the first forming tool 20 comprises a plurality of first molding cavities 38 for the simultaneous production of several pieces 10. The first molding cavities 38 are for example four in number. The surface of the first molding cavities 38 is advantageously treated by a deposition of a fluorine resin layer or by a plasma deposition of an organosilicon layer in order to avoid adhesion of the thermoplastic material 13 to the surface of the first molding cavity 38. The first molding cavity 38 has for example a substantially planar shape. Advantageously, the first cavity 38 has the shape of at least part of the part 10 to be manufactured.

The first forming tool 20 is heated to a temperature higher than the melting temperature of the thermoplastic material 13. It is heated by heating means integrated in the first forming tool 20, for example by electrical resistances, infrared rays, by radiation or microwave.

In the case where the thermoplastic material 13 is PA66, the temperature of the first molding cavity 38 is between 275 ° C and 315 ° C, and is advantageously between 280 ° C and 300 ° C.

The first forming tool 20 is able to apply a first pressure in the first molding cavity 38. The first pressure is less than 15 bars, and is preferably less than 10 bars.

The second forming tool 22 includes a second molding cavity 40 and an injection device 42 for molding material. In a variant, the second forming tool 22 comprises a plurality of second molding cavities 40. The number of second molding cavities 40 is equal to the number of first molding cavities 38.

The second molding cavity 40 has the shape of at least part of the part 10 to be manufactured.

The second forming tool 22 has a temperature below the melting temperature of the thermoplastic material 13. It is cooled by a cooling device. Such a device comprises for example conduits arranged in the vicinity of the second molding cavity 40 of the second forming tool 22. A cooling fluid, for example water or oil, circulates in the conduits in order to cool the second mold cavity 40.

In the case where the thermoplastic material 13 is PA66, the temperature of the second molding cavity 40 is between 145 ° C and 165 ° C, preferably substantially equal to 150 ° C, and is advantageously equal to 150 ° C.

The second forming tool 22 is able to apply a second pressure in the second molding cavity 40. The second pressure is between 15 bars and 50 bars, advantageously between 20 bars and 30 bars.

As shown in Figure 4, at least one complex 31 is disposed in the first molding cavity 38, the first forming tool 20 being in its open position.

According to another embodiment, instead of producing a complex 31 as described above, only the reinforcing layers 14 are cut and the thermoplastic material 13 is introduced into the first forming tool 20 in the form of a powder , for example sprayed on the reinforcing layers 14 arranged in the first molding cavity 38.

As a variant, coiled fibers or cut fabrics comprising thermoplastic fibers and reinforcing fibers are cut and then introduced into the first forming tool 20.

With reference to Figure 5, the first forming tool 20 is then closed. The first pressure is applied in the first molding cavity 38 so that the thermoplastic material 13 permeates the fibers 16 of the reinforcing layer 14 in order to form an unconsolidated part 44.

The time that the reinforcing layers 14 and of the composite material 13 spend in the first forming tool 20 is for example between 40 s and 70 s, and is advantageously equal to 55 s.

Thus, in the first molding cavity 38, the thermoplastic material 13 liquefies and impregnates the fibers 16 of the reinforcing layer or layers 14 under the effect of heat and pressure in the first molding cavity 38. The part non-consolidated 44 obtained is flexible or plastically deformable.

Then, the first forming tool 20 is opened, and the non-consolidated part 44 is transferred to the second forming tool 22, as visible in FIG. 6. The transfer is fast enough for the non-consolidated part 44 to remain deformable when it enters the second molding tool 22. This transfer time is less than 20 s, and is preferably less than 10 s.

According to a preferred embodiment of the invention, successive parts 10 are produced continuously. The first forming tool 20 is maintained at a temperature above the melting temperature of the thermoplastic material 13 between the outlet of a first non-consolidated piece 44 of the first forming tool 20 and the arrangement of at least one reinforcing layer 14 and a thermoplastic material 13 in the first forming tool 20 for the production of a second non-consolidated part 44. Thus, the first forming tool 20 is not cooled between two stages of opening and closing, and the production of parts 10 is accelerated.

Referring to Figure 7, the second forming tool 22 having a temperature below the melting temperature of the thermoplastic material 13, the thermoplastic material 13 solidifies and the non-consolidated part 44 then consolidates in the second mold cavity 40 and forms a consolidated part 46. Such a part has the mechanical characteristics, for example of rigidity, desired for the use of the part 10.

The second pressure is applied in the second molding cavity 40. The second pressure makes it possible in particular to reduce the porosity of the thermoplastic material 13 of the non-consolidated part 44.

The time that the non-consolidated part 44 spends in the second forming tool 22 is in particular between 40 s and 70 s, and is advantageously equal to 55 s.

In a variant, before the exit of the consolidated part 46 from the second forming tool 22, the method comprises an overmolding step using the injection device 42. This overmolding step comprises the injection of a molding material onto the consolidated piece 46 in the second molding cavity 22 in order to create the shape of the desired final piece 10 without additional step after the exit of the consolidated piece 46 from the second molding tool 22. This overmolding step is used for example to create the reinforcing ribs 17 or attachment zones 18 on a seat of a motor vehicle.

After consolidation in the second molding cavity 40, the consolidated part 46 has left the second forming tool 22.

Referring to Figure 8, a second embodiment of the method of manufacturing a part 10 with the forming tools differs from the first embodiment in that the reinforcing layers 14 and the thermoplastic material 13 are arranged in a cavity molding 38 of a mold 48. The mold 48 is first placed in the first forming tool 20 to form the non-consolidated part 44, and then, without opening the mold 48, is transferred to the second forming tool 22 in order to consolidate the non-consolidated part 44. This mode makes it possible in particular to avoid the oxidation of the part 10.

The molding cavity 38 has for example the shape of at least part of the part 10 to be manufactured. As a variant, the molding cavity 38 can be substantially flat and a possible shaping of the part 10 occurs during an additional shaping step after the consolidated part 46 has come out of the mold 48 out of the second forming tool 22.

Thanks to the invention described above, the time spent on manufacturing a part made of composite material is reduced, which increases production efficiency. In addition, the method makes it possible to obtain a finished part when it leaves the mold. Such a part does not require an additional finishing step.

According to conventional methods for manufacturing thermoplastic prepregs continuously, it is only possible to obtain plates comprising a single reinforcing armor having fibers extending in one of the unique directions (for example 0/90). These classic plates are standardized, having a unique shape, often rectangular. According to the invention, it is possible to obtain more flexibility on the thickness and orientation of the reinforcing fibers during the manufacture of the composite part. This is particularly advantageous for manufacturing the components with reinforced parts.

In addition, it is no longer necessary to reheat and then cut the composite plate in order to obtain the final part, which consumes less energy and creates less waste.

Claims (14)

1. - Process for manufacturing at least one part (10) of composite material comprising a matrix (12) of thermoplastic material (13) and at least one reinforcing layer (14) comprising fibers (16), the method comprising the following successive stages: - providing a first forming tool (20) movable between an open position and a closed position, said first forming tool (20) being heated to a temperature above the melting temperature of the thermoplastic material (13), - placing at least one reinforcing layer (14) and a thermoplastic material (13) in the first forming tool (20) in the open position; - close the first forming tool (20) and apply a first pressure in said first forming tool (20) so that the thermoplastic material (13) permeates the fibers (16) of the reinforcing layer (14) in order to form an unconsolidated part (44); - Open the first forming tool (20) and transfer the non-consolidated part (44) to a second forming tool (22), said second forming tool (22) having a temperature below the melting temperature of the thermoplastic material (13); - consolidate the non-consolidated part (44) in the second forming tool (22); and - take out the consolidated part (46) from the second forming tool (22). 2. - The manufacturing method according to claim 1, wherein the first forming tool (20) comprises a first molding cavity (38) and the second forming tool (22) comprises a second molding cavity (40) having the shape of the part (10) to be manufactured. 3. - The manufacturing method according to claim 2, wherein the second forming tool (22) comprises an injection device (42) of a molding material, the method comprising a step of injecting a material of molding in the second molding cavity (40) on the consolidated part (46) before it leaves the second forming tool (22). 4. - The manufacturing method according to claim 2 or 3, wherein the first molding cavity (38) has the developed or undeveloped form of at least part of the part (10) to be manufactured. 5. - manufacturing method according to claim 1, wherein the reinforcing layer (14) and the thermoplastic material (13) are arranged in a mold cavity of a mold (48), said mold being disposed in the first tool forming (20) then in the second forming tool (22). 6, - The manufacturing method according to any one of claims 1 to 5, wherein, before placing the reinforcing layer (14) and the thermoplastic material (13) in the first forming tool (20), the method comprises a step of cutting the reinforcing layer (14) in the form of at least part of the part (10) to be manufactured. 7, - The manufacturing method according to any one of claims 1 to 6, wherein the fibers (16) of the reinforcing layer (14) extend in at least two different orientations. 8, - The manufacturing method according to any one of claims 1 to 7, wherein the part (10) of composite material comprises several reinforcing layers (14), the method comprising, before arranging the reinforcing layers (14) and the thermoplastic material (13) in the first forming tool (20), the following successive steps: - Cut the reinforcing layers (14), so that each has dimensions less than or equal to the corresponding dimensions of the part (10) to be manufactured; and - stack and join together the cut reinforcement layers (14). 9, - The manufacturing method according to claim 8, wherein the reinforcing layers (14) cut have at least two different orientations of fibers (16) or at least two different textile weaves. 10, - The manufacturing method according to any one of claims 1 to 9, wherein, before having the reinforcing layers (14) and the thermoplastic material (13) in the first forming tool (20), the method comprises a material preheating step. 11, - The manufacturing method according to any one of claims 1 to 10, wherein several parts are manufactured, the first forming tool (20) being maintained at the temperature above the melting temperature of the thermoplastic material (13) between the exit of a first non-consolidated part (44) from the first forming tool (20), and the arrangement of at least one reinforcing layer (14) and a thermoplastic material (13) in the first forming tool ( 20) for the production of a second non-consolidated part (44). 12, - The manufacturing method according to any one of claims 1 to 11, wherein a pressure greater than the ambient pressure is applied in the second forming tool (22). 13, - The manufacturing method according to any one of claims 1 to 12, wherein the first pressure is less than 15 bars, and is preferably less than 10 bars. 14, - The manufacturing method according to any one of claims 1 to 13, 5 wherein the time of a cycle spent in the first forming tool (20) and / or the second forming tool (22) is between 40 s and 70 s, and is advantageously equal to 55 s.