FR3014730A1 - REINFORCING SHEET FOR MOLDING COMPOSITE PARTS - Google Patents

Abstract

Reinforcement sheet comprising a plurality of substantially continuous reinforcing fibers. The reinforcing sheet has at least one zone in which at least one fiber forms at least one corrugation in the plane of the sheet so as to promote the stretching of the reinforcing sheet in this area.

Description

The invention relates to the technical field of products and semi-products for molding a piece of reinforced plastics material. In particular the invention relates to a reinforcing sheet for producing a semi-product made of plastic.

In the automotive field for example, many parts must combine mechanical strength and low weight. To do this, it is known to replace steel parts by plastic parts, thermosetting or thermoplastic. Various molding processes of plastic parts are known: - compression process (for thermosetting materials such as SMC); - thermoforming process (compression with a thermoplastic material); - injection process (for thermoplastics). - Resin transfer process (RTM) It is known to use reinforced plastics (thermosetting or thermoplastic). These materials consist of reinforcing fibers mixed with a polymer resin. These reinforcements comprise glass or carbon fibers, for example. These fibers can be cut (ends of fiber of variable length between 2 mm and 50 mm) or, conversely, continuous. To obtain high mechanical performance, continuous fibers, for example unidirectional or in the form of fabric, are frequently used. These reinforcements have the advantage of improving the mechanical characteristics of the plastic part in which they are incorporated.

The majority of manufacturing processes for composite parts require the reinforcement to be placed on the mold before making the parts. However, it is very difficult to drape non-developable surfaces with these unidirectional or woven reinforcements. The use of little extensible reinforcing sheets thus requires a lot of draping time of the mold surfaces. It is then often necessary to make a preform, which is then available in the mold before use of the resin. This process therefore requires a preparatory shaping step (preforming), which lengthens the manufacturing time and therefore increases the manufacturing cost of the reinforced plastic part. Reinforcements in the form of cut fibers, arranged in sheets which are used, for example, in SMC or "mat" type materials, have the advantage of constituting a deformable reinforcement, even on non-developable surfaces. However, these types of reinforcement arrangements have low mechanical characteristics compared to materials containing reinforcements in the form of continuous fibers (fabric or unidirectional). In addition, the creep of SMC materials during molding tends to create a low reproducibility anisotropy within the material and poor homogeneity of characteristics and thicknesses.

The use of continuous fibers in a material improves the mechanical characteristics, but the manufacturing cycle time of the part is often lengthened by the complexity of depositing the reinforcements, either in the mold or on a preform (draping). Indeed, for a material reinforced by a network of unidirectional and rectilinear continuous fibers, the lay-up of a complex non-developable three-dimensional shape is not possible by the implementation of a single reinforcing sheet and of one piece, but will be through the precise positioning of several smaller pieces (patches) cut, each covering a smaller area, drapable locally. The reinforcements being extremely rigid in the direction of the fibers, it is almost impossible to lengthen them in the direction of the fibers without breaking them.

The invention relates to a reinforcing sheet making it possible to overcome these drapability constraints, in that it comprises a set of substantially continuous reinforcing fibers, and in that at least one zone of the reinforcing sheet comprises at least one at least one fiber forming at least one corrugation in the plane of the sheet so as to promote the stretching of the reinforcing sheet in this area. The deformability of this reinforcing sheet, and the semi-product incorporating such a reinforcing sheet, is thus favored. The distribution of continuous fiber undulations in the reinforcing sheet makes it possible to create degrees of freedom that can be expressed during the setting of reinforcing sheets.

Such a reinforcing sheet thus facilitates draping of the mold, by its intrinsic ability to deform, while maintaining a high mechanical strength through continuous reinforcements (uncut). With such a material it is possible to limit or even eliminate the preforming step before molding.

According to the invention, at least one of the fibers may have: at least one wavelength ripple different from the other fibers; and / or at least one wave of amplitude different from the other fibers; and / or - at least one out-of-phase corrugation with corrugations of at least one other fiber; and / or - a different main direction of at least one other fiber. In addition, at least one of the fibers may be juxtaposed on at least one other fiber. According to one embodiment, the reinforcing fibers have parallel main directions in the plane of the sheet.

According to the invention, the reinforcing sheet may comprise fibers without undulation at the ends, and comprises fibers with more and more corrugation closer to the center of the reinforcing sheet. In another embodiment, reinforcing fibers form at least one corrugation in a plane different from the plane of the sheet. Finally, the reinforcing fibers can be held in place by sewing or other means of assembly (gluing, dusting ...). The invention also relates to a sheet of plastics material for molding, comprising a polymer resin and a reinforcing sheet according to the invention. The invention also relates to an assembly of plastic sheets comprising at least two plastic sheets according to the invention. According to the invention, the main direction of fiber orientation may differ from one sheet to another. The invention also relates to a method for producing a plastic sheet for molding according to the invention, in which the following steps are carried out: reinforcing fibers are unwound; at least one corrugation is formed on each unrolled fiber by means of a movable deposition head; The reinforcing fibers of plastic are impregnated. The invention also relates to a process for producing a piece of thermoplastic or thermosetting material reinforced by means of an injection molding. This method comprises the following steps: at least one reinforcing sheet according to the invention is placed in a mold; The mold is closed and a thermoplastic or thermosetting material is injected into the mold; and - the part thus obtained is demolded. The invention also relates to a method for producing a piece of thermosetting or thermoplastic material reinforced by means of compression molding. This method comprises the following steps: a plastic sheet according to the invention or an assembly of plastic sheets according to the invention is placed in a mold; the mold is closed and a pressure and a temperature are applied; and - the part thus obtained is demolded. According to one embodiment of the methods for producing a thermoplastic piece according to the invention, the reinforcing sheet is draped over a mold shape before the mold closing step. The invention will be better understood on reading the description which follows, with reference to the appended drawings in which: FIG. 1 illustrates an example of a reinforcing sheet, seen from above, according to the invention. Figure 2 illustrates examples of waviness in the plane of the sheet. Figure 3 illustrates the possibility of extension in the plane of the sheet, a fiber in the main direction (DP) of the fiber.

Figure 4 illustrates a reinforcing sheet, viewed from above, whose fibers are sewn to each other. Figure 5 illustrates a portion of an assembly of three overlapping reinforcing sheets with variations in wavelength, amplitude, phase, spacing and direction of the fibers.

FIG. 6 illustrates a semi-finished product sheet consisting of reinforcements and a molding resin matrix according to the invention. Figure 7 illustrates an assembly of several reinforcing sheets according to the invention. FIG. 8 illustrates a part of two reinforcing sheets of an assembly superimposed with principal directions (DP1 and DP2) of orientation of the fibers different from one sheet to another, here perpendicular. Figures 9, 10 and 11 illustrate a portion of a reinforcing sheet according to the invention, with variations in wavelength, amplitude, phase, spacing and direction of the fibers.

FIG. 12 illustrates an embodiment according to which the reinforcing sheet comprises fibers that are non-waving (therefore straight) at the ends, and comprises fibers with more and more corrugation while approaching the center of the reinforcing sheet.

Referring to FIG. 1, the reinforcement sheet (FR) according to the invention comprises a set of reinforcing fibers (FIR), the fibers being continuous fibers, and at least one zone comprising at least one fiber forming at least one a corrugation (OND) in the plane of the sheet so as to promote the stretching of the reinforcing sheet in said area to improve drapability upon introduction into a mold. The drapability of a reinforcing sheet defines the capacity of this reinforcing sheet to conform to the shape of a mold, without generating folds (by excess material), or without generating stretching (due to lack of material). As illustrated in FIG. 2, a fiber forms at least one undulation, when it is not rectilinear, and thus offers an overall degree of freedom of stretching along its principal direction, between a position forming a ripple towards a rectilinear position (RECT): the fiber is "unrolled, decouples, straightens, tends", towards a rectilinear form, from which the fiber can (almost) no longer lengthen (because of its nature of reinforcement it resists stretching by elongation). This is called waving any displacement of the shape of the fiber relative to a rectilinear shape (RECT). An example of fiber having corrugations is a fiber forming one or more sinusoids.

These corrugations thus add a degree of freedom of extension of the sheet in the main direction (DP) of the fiber (FIG. 3). Preferably, the corrugations have an amplitude greater than 5 mm in the plane of the reinforcing sheet. The term "substantially continuous fiber", as opposed to a staple fiber, is a reinforcing fiber having a length greater than 50mm, preferably greater than 100mm. Ideally, a substantially continuous fiber is an uninterrupted fiber within the reinforcing sheet to which it belongs. In the description, a substantially continuous fiber is referred to as "continuous fiber". The fibers of the reinforcing sheet form a sheet being integral with each other. One way to make the reinforcing fibers integral, is to sew them to each other as shown schematically in Figure 4, by means of wire (FIL) holding for example. It is also possible to sew the corrugated reinforcing fibers on a "mat" type sheet, which may itself be of the same material as the reinforcing fibers (glass fibers, carbon fibers, aramid fibers, etc.). The reinforcing fibers can also be made integral by pre-impregnating them with a resin by means of a powder coating technique. According to an exemplary embodiment, the wavelength of the corrugations is between 10mm and 200mm, preferably between 50mm and 100mm, and the amplitude of the corrugations is between 10mm and 200mm, preferably between 50mm and 100mm. Depending on the desired degree of drapability, which depends in particular on the shape of the end piece for which the backing sheet is intended, certain parameters of the corrugations are varied. Thus, the reinforcing sheet according to the invention may comprise at least one fiber having: at least one wavelength ripple different from the other fibers; and / or at least one wave of amplitude different from the other fibers; and / or at least one out-of-phase corrugation with corrugations of at least one other fiber; and / or a different main direction of at least one other fiber. Figures 9, 10 and 11 illustrate various factors of variation of the corrugations on a portion of a reinforcing sheet according to the invention: variations in wavelength, amplitude and spacing of the fibers. FIG. 8 illustrates a part of two reinforcing sheets of an assembly superimposed with principal directions (DP1 and DP2) of orientation of the fibers different from one sheet to another, here perpendicular. According to one embodiment (not shown), at least one of the fibers is juxtaposed on at least one other fiber, for example by phase shift, thus making it possible to increase the thickness of the reinforcing sheet. According to another embodiment illustrated in FIGS. 4 and 6, the fibers have parallel main directions in the plane of the sheet, that is to say that they lie in the same plane without crossing each other. According to this configuration, the spacing (e) between two adjacent fibers (between their parallel corrugations) can be between 0mm and 20mm, preferably between 0mm and 5mm. It is also possible to vary the type of corrugations between several places of the reinforcing sheet. The wave pattern is thus variable on the surface of the reinforcing sheet. The aim is to obtain more deformable areas by stamping than others, and areas having improved performance with respect to mechanical strength. The greater the amplitude of the corrugations, the more the product is likely to deform by stamping. Thus, FIG. 9 shows an alternation of rectilinear and corrugated fiber zones, the rectilinear zones being preferably at the leaf end and with more and more corrugation approaching the center of the reinforcing sheet. Figure 10 also shows combined wavelength and amplitude variations. Figure 11 also shows combined variations of spacing and principal direction. According to another embodiment, some fibers form at least one corrugation in a plane different from the plane of the sheet, that is to say in the thickness of the sheet. An advantage of this embodiment is that it is possible to bind the different layers of reinforcements in the thickness, also having corrugations in the plane of the layer. This makes it possible to produce products that are less sensitive to different delamination phenomena. Delamination is a decohesion of the layers of reinforcements. It appears when the parts are subjected to strong deformations. The reinforcing fibers may be glass fibers, carbon fibers, aramid fibers, metal fibers (steel, aluminum, copper, nickel, etc.), plant fibers (flax, hemp, etc.) , basalt fibers, thermoplastic fibers (PP, PA, PET, UHMWPE ...), ceramic fibers, or a combination of these types of fibers (all types of fibrous reinforcements or in the form of bands). According to one embodiment, the fibers and / or the reinforcing sheet are held in place by sewing on a support, such as a fabric, a mat or a plastic film. This semi-product can be used with a resin injection molding process when the mold is closed. The invention also relates to a plastic sheet (FMP) for molding (manufacture of composite parts) comprising a plastic material (MP), thermoplastic resin or thermosetting resin, and a reinforcing sheet (FR) according to the invention. invention (Figure 6). This plastic sheet is a semi-product. A semi-finished product is a semi-finished product from which a finished part is manufactured by molding. The plastic sheet according to the invention may comprise a support (FS), a film of polyethylene for example or other polymer, on at least one face. In general, this film is positioned on both sides. It allows to support the resin on which the reinforcing fibers are available. It may be advantageous to preimpregnate the reinforcing fibers prior to placing them on the film. Preferably, the resin is a thermoplastic or thermosetting material. This resin may contain additives chosen from: mineral fillers, spherical fillers or cut reinforcing fibers. This is to improve the performance and / or the cost of the plastic sheet. The thickness E of a plastic sheet according to the invention is between 0.1 mm and 10 mm; and preferably between 0.5mm and 3mm. The invention also relates to a complex semi-product, an assembly, consisting of several sheets of plastic material according to the invention. The superposition of several of these sheets makes it possible to obtain a complex semi-product in the form of a thick sheet, as illustrated in FIG. 7. According to one embodiment, the fibers of the same sheet are extend substantially in the same direction in the plane of the sheet, and the fiber wave pattern (amplitude, pitch, phase shift, spacing, main direction) differs from one sheet to another as illustrated in FIG. 5. Figure 5 illustrates a portion of an assembly of three sheets of reinforcements superimposed with variations in wavelength, amplitude, phase and principal direction (DP1, DP2 and DP3) of the fibers. These changes in the corrugation between each sheet during their superposition makes it possible to obtain a product having homogeneous characteristics in certain zones, or specific (drapability, mechanical reinforcement) in localized zones.

The invention also relates to a method for manufacturing a plastic sheet according to the invention. The method comprises the following steps: reinforcement fibers are unwound; at least one corrugation is formed on at least one unrolled fiber by means of a movable deposition head; the reinforcing fibers of plastic are impregnated. The reinforcements are thus arranged according to a definite ripple depending on the speed of advance on the continuous production installation and movements (speed, sweep, etc.) of the mobile head (s). of deposit. According to this method, it is possible to impregnate, with thermosetting resin for example, the reinforcing fibers before or after the formation of the corrugations. In the case of a unitary impregnation of each fiber wick through an impregnation chamber, the latter allows to wet the fibers with the resin. The characteristics of the final material depend greatly on the quality of the impregnation. The impregnation can be improved if the chamber is evacuated with air. A calibrated nozzle makes it possible to fix the fiber / resin content by dewatering the resin before leaving the chamber. The locks are then corrugated and placed on a first support film before being covered with a second support film. The semi-finished product thus obtained can be rolled up and stored. Generally, a support film is provided on at least one of the surfaces of the sheet to support the reinforcing sheet and to obtain the separating effect between the coiled layers. In order to obtain the different types of sheets according to the invention, the fibers can be unrolled substantially in the same direction; - juxtapose (partially overlap) the reinforcing fibers in the plane of the sheet. The goal is to steer the continuous reinforcements so as to improve the formability of the plastic sheet (semi-finished product) obtained. According to a particular variant, the reinforcing sheet is produced by placing the fibers in corrugations in phase shift, preferably in phase opposition, thereby making it possible to produce a thicker semi-product.

More generally, one can, within a same sheet, vary the ripple parameters (amplitude, phase, pitch, spacing ...). According to another embodiment, is added to the corrugations contained in the plane of the sheet, at least one corrugation out of the plane of the sheet, to achieve a three-dimensional assembly in the thickness of the semi product. This particularity makes it possible to improve the overall performances and the homogeneity of the characteristics of the semi-product and to avoid the inter-layer delamination which may appear during extreme stresses.

The invention also relates to a method for manufacturing an assembly of sheets of plastics material according to the invention. Several layers of semifinished product (reinforcing sheet according to the invention) are superimposed to form a new complex semi-product for use in the compression molding or RTM process to obtain a finished part.

Preferably, at least two plastic sheets according to the invention are superimposed so that the corrugation pattern of the reinforcing fibers is different from one sheet to another. The semi-finished product is then cut into shapes of dimensions adapted to the part to be produced.

A "complex" semi-product is obtained by stacking several of these semi-products. The main axes of each semi-product will be deliberately misaligned or not depending on the expected final characteristics of the part. The invention also relates to a process for producing a part made of reinforced thermoplastic material by means of injection molding or resin transfer, in which the following steps are carried out: at least one reinforcing sheet is placed in a mold according to invention; the mold is closed and a thermoplastic material is injected into the mold. the part thus obtained is demolded.

The invention also relates to a method for producing a part made of thermosetting material reinforced by means of a compression molding (SMC), in which the following steps are carried out: a pre-impregnated reinforcement sheet according to the invention is placed in a mold or an assembly of plastic sheets according to the invention; the mold is closed (which is heated) and a pressure is applied, the material is heated to initiate the crosslinking of the resin; and -10- - the piece thus obtained is demolded. According to one or the other of the methods for producing a plastic part according to the invention, it is possible to drape the reinforcing sheet on a form of the mold (preforming) 5 before the step of closing the mold.

Claims (14)

REVENDICATIONS1. Reinforcing sheet comprising a set of reinforcing fibers, characterized in that the fibers are substantially continuous fibers, and in that at least one zone of the reinforcing sheet comprises at least one fiber forming at least one corrugation in the plane of the sheet so as to promote the stretching of the reinforcing sheet in said zone. 2. Reinforcing sheet according to claim 1, wherein at least one of the fibers has: at least one wave of wavelength different from the other fibers; and / or at least one wave of amplitude different from the other fibers; and / or at least one out-of-phase corrugation with corrugations of at least one other fiber; and / or - a different main direction of at least one other fiber. 3. Reinforcement sheet according to one of the preceding claims, wherein at least one of the fibers is juxtaposed on at least one other fiber. 4. Reinforcing sheet according to one of claims 1 and 2, wherein the reinforcing fibers have parallel main directions in the plane of the sheet. 5. Reinforcing sheet according to one of the preceding claims, wherein the reinforcing sheet comprises fibers without ripple at the ends, and comprises fibers with more and more corrugation closer to the center of the reinforcing sheet. 6. Reinforcing sheet according to one of the preceding claims, wherein reinforcing fibers form at least one corrugation in a plane different from the plane of the sheet. 7. Reinforcing sheet according to one of the preceding claims, wherein the reinforcing fibers are held in place by stitching or by gluing or dusting. 8. Plastic film for molding, comprising a polymer resin, characterized in that it comprises a reinforcing sheet according to one of the preceding claims. 9. Assembly of plastic sheets comprising at least two plastic sheets according to claim 8. An assembly according to claim 9, wherein the principal direction of fiber orientation differs from one sheet to another. 11. A method of manufacturing a plastic sheet for molding according to claim 8, characterized in that the following steps are carried out: - reinforcing fibers are unwound; at least one corrugation is formed on each unwound fiber, by means of a movable removal head; the reinforcing fibers of plastic are impregnated. Process for producing a part made of thermoplastic or thermosetting material reinforced by means of an injection molding, characterized in that it comprises the following steps: at least one reinforcing sheet according to one of Claims 1 is placed in a mold. at 7; the mold is closed and a thermoplastic or thermosetting material is injected into the mold; and the part thus obtained is demolded. 13 Process for producing a part made of thermosetting or thermoplastic material reinforced by means of a compression molding, characterized in that it comprises the following steps: a plastic sheet according to claim 8 or an assembly of plastic sheets according to one of claims 9 and 10; the mold is closed and a pressure and a temperature are applied; and the part thus obtained is demolded. Process for producing a thermoplastic part according to one of Claims 12 or 13, in which the reinforcing sheet is draped over a shape of said mold before the step of closing the mold.