FR2749535A1 - Composite thermoplastic part for automobiles incorporating glass fibre strands - Google Patents

Abstract

A method of making parts for automobiles consists of heating at least one plaque of glass fibre reinforced thermoplastic and pressing into shape uses plaques forming at least one layer (22) of a thermoplastic material and at least one layer (2) having strands (6) of glass fibres (8) in contact with a thermoplastic material. Each fibre (8) is embedded in the thermoplastic in the strand. Also claimed are automobile parts made this way.

Description

 The invention relates to parts for a motor vehicle made from composite plates, and to methods of manufacturing these parts.

 A method is known for manufacturing a part for a motor vehicle which uses several composite plates. Each plate is in one piece and has layers of polypropylene between which glass fibers are arranged. In this process, the plates are preheated, then stacked on top of each other and stamped. This step assembles the plates together and forms the part, giving it the desired configuration. Glass fibers increase the mechanical resistance of the part while allowing a certain elastic bending. To this end, the method is used to manufacture bumper beams.

 However, it can be seen that in the finished part, the glass fibers are not sufficiently in contact with the polypropylene matrix, the polypropylene not having reached and impregnated certain portions of the fibers. This defect is revealed by the existence of white areas on the glass fibers visible from the outside faces of the part, which contrast with the areas of the fibers colored by the polypropylene. This poor contact of the fibers with the polypropylene means that the mechanical resistance of the part is then insufficient. The part can therefore rupture prematurely or under relatively moderate stress. This contact fault has its origin in the composite plates used, in which it is already detectable.

 In the process for manufacturing these plates, a stack is produced continuously comprising two sheets of polypropylene and glass fibers placed between the two sheets, for example in a random orientation. The stack is passed through a press where it is brought to a temperature at least equal to the melting temperature of polypropylene, and where it is pressed. The polypropylene melts and comes into contact with the glass fibers. After cooling, a composite plate is obtained in one piece. The plate is then cut to the desired dimensions.

 An object of the invention is to provide a method of manufacturing a part, in which the glass fibers are suitably impregnated with the thermoplastic material, in order to produce parts having improved resistance and flexibility for a weight equal to that parts from the above process.

 In order to achieve this goal, there is provided according to the invention a method of manufacturing a part for a motor vehicle, comprising the successive steps consisting in: - heating at least one plate comprising at least one layer comprising glass fibers and a thermoplastic material; and - stamping the plate or plates to form the part, in which the plate or plates comprise at least one layer comprising a thermoplastic material and at least one layer comprising strands of glass fibers in contact with a thermoplastic material, the fibers of each strand being embedded in thermoplastic material in the strand.

 Thus, in the plates used to implement the method, the contact between the glass fibers and the thermoplastic material is from the outset satisfactory. Consequently, good contact is also ensured between the fibers and the thermoplastic material in the part produced by the process. It has no white areas. Parts are therefore produced having improved resistance and flexibility for a weight equal to that of the parts resulting from the aforementioned known method.

 Advantageously, the strands extend in a common direction, which improves the flexibility of the part.

 The layer comprising the strands may include wires extending in a direction perpendicular to the direction of the strands. The wires help preserve the arrangement of the strands in a common direction during the stamping step.

 Preferably, the strands constitute a fabric.

 Thus, the arrangement of the strands is more conserved during stamping. Furthermore, the mechanical resistance of the part and its flexibility in the two perpendicular directions defined locally by the plane of the fabric are improved.

 Advantageously, the or at least one of the plates comprising strands, has reduced dimensions compared to those of another plate of the stack.

 Thus, the part is reinforced only in the most stressed places during its use.

 According to the invention, a part for a motor vehicle is also provided, comprising at least one layer comprising glass fibers and a thermoplastic material, the part comprising at least one layer comprising a thermoplastic material and at least one layer comprising strands of fibers of glass in contact with thermoplastic material, the fibers of each strand being embedded in the strand in thermoplastic material.

 This part is obtained by means of the method of the invention.

 It may advantageously be a bumper beam, a lighthouse surround, a fan unit support, an engine compartment shutter screen, or a seat back element .

Other characteristics and advantages of the invention will become apparent on reading the following description of a preferred embodiment and of variants given by way of non-limiting examples. In the accompanying drawings: - Figure 1 is a longitudinal sectional view of an installation for manufacturing composite plates used in the method according to the invention; - Figure 2 is a cross-sectional view of a strand comprising glass fibers and thermoplastic fibers used in the installation of Figure 1; - Figure 3 is a partial perspective view in section of a composite plate used in the embodiment of the method according to the invention; - Figure 4 is a partial perspective view of a first bumper beam according to the invention; - Figure 5 is an enlarged view of the detail
D of Figure 4 showing the edge of the beam; - Figure 6 is a perspective view of a second bumper beam according to the invention; - Figure 7 is a partial perspective view of a third bumper beam according to the invention; and - Figure 8 is a partial perspective view in section of a composite plate used in a second embodiment of the method according to the invention;
We will first describe the manufacture of composite plates which will then be used in this embodiment of the method according to the invention. Figure 1 shows an installation for the continuous implementation of a process for manufacturing composite plates. This process includes the following successive steps.

During a first step, a stack is produced comprising five layers superimposed on each other. The stack comprises two layers 2, 4 of fabric constituting the upper and lower faces of the stack. Referring to Figure 2, this fabric consists of strands 6 of weft and warp woven in a conventional manner. Each strand 6 comprises glass fibers 8 and polypropylene fibers 10. Such a fabric is sold under the name of "Twintex" by the company
Vetrotex. Two of the layers of the stack consist of two respective sheets 12, 14 of polypropylene adjacent to the respective fabric layers 2, 4. The fifth layer of the stack consists of glass fibers 16, or glass mats, arranged in a random orientation between the two polypropylene sheets 12, 14 at the center of the stack.

The stack thus comprises from bottom to top a layer of fabric 4, a polypropylene sheet 14, glass fibers 16, a polypropylene sheet 12 and a layer of fabric 2. This stacking is carried out continuously on a conveyor belt from strips of fabric, polypropylene sheets and glass fibers unrolling without interruption. The weft threads of the fabric extend in the direction of travel during the manufacture of the plate.

 In a second step, the stack passes through a double-band press 18 of conventional type. This press presses the stack according to its thickness and brings the stack to a temperature equal in this case to 210 OC.

In all cases, this temperature is at least equal to the melting temperature of the polypropylene. Thus, the polypropylene fibers 10 of the strands 6 of the fabric melt and permeate the adjacent glass fibers 8 in these strands. Thus, the glass fibers 8 of the strands are embedded in the polypropylene. Furthermore, the sheets 12 and 14 melt and impregnate the glass fibers of the layer 16 disposed between them. These sheets also impregnate externally the strands of glass fibers of the fabric of the layers 2, 4. After fusion, the two polypropylene sheets 12, 14 and the glass fibers 16 no longer form a single layer. At the outlet of the press, the glass fibers of the layer 16 and of the fabric layers 2, 4 are therefore impregnated with polypropylene which constitutes a matrix with which they form a body.

 Referring to Figures 1 and 3, there is obtained after cooling a continuous composite plate 20 in one piece having in the center a layer 22 comprising polypropylene and glass fibers 16 impregnated with polypropylene. On either side of this layer, the plate comprises two layers of fabric 2, 4 constituting the two opposite faces of the plate. In the fabric, the strands 6 now include glass fibers 8 embedded in the strand in polypropylene resulting from the melting of the polypropylene fibers 10. The strands are impregnated, on the outside of the strands, with the polypropylene of layer 22 The plate thus comprises a polypropylene matrix and a glass fiber reinforcement. The plate in this case has a width of 1 m and a thickness of 3.7 mm.

The use of fabric for the manufacture of the composite plate results in that, from the manufacture of the plate, the glass fibers of the strands are suitably impregnated with the polypropylene and positioned in the plate. The plate has no white areas at the fibers. The subsequent stamping of the plate will not significantly modify this impregnation and this positioning.

 This plate is intended to be stamped during the manufacturing process of a part for a motor vehicle according to the invention, an embodiment of which will now be described. With reference to FIGS. 4 and 5, this embodiment aims at the manufacture of a bumper beam 24. This beam has a U-shaped profile and is intended to be interposed in a known manner between the skin of the bumper and an element of the chassis of the vehicle.

It is designed to flex elastically for a frontal impact at a speed equal to 4 km / h. In the present embodiment, the method comprises the following steps.

 Four identical composite plates 20 are cut to the appropriate dimensions as mentioned above. Then, the plates are preheated to soften the polypropylene. These plates are superimposed between them to produce a stack so that the layers of fabric 2, 4 of the adjacent plates come into mutual contact. Then, this stack is placed in a stamping mold and the stack is stamped, which has the effect of assembling the plates together by deforming them to form the beam of desired shape.

 A beam is thus obtained comprising uniformly along its thickness four layers 22 each comprising polypropylene and glass fibers 16 impregnated with polypropylene. These layers are separated from each other by a pair of layers of fabric 2, 4. The two opposite faces on either side of the thickness of the beam are constituted by a layer of fabric 2, 4. In the fabric , the strands 6 comprise glass fibers embedded in the strand in polypropylene.

The part thus comprises a polypropylene matrix and reinforcements of glass fibers. All these layers are attached to each other and form a single block.

 The layers of fabric are present on the two opposite faces of the beam as well as at the center of its thickness. The layers of fabric adjacent to the external face 23 of the beam (towards the outside of the vehicle) improve the resistance of the beam in compression. The layers of fabric adjacent to the internal face 25 of the beam (towards the interior of the vehicle) improve the tensile strength of the beam. The layers of fabric close to the center of the thickness of the beam improve the resistance of the beam in shear. The beam thus obtained has improved tensile strength and longitudinal flexibility.

 A variant of this mode of implementation of the manufacturing process makes it possible to obtain the beam of FIG. 6 (shown shorter than in reality). In this variant, to make the stack, three plates of a conventional type are superimposed comprising a layer comprising polypropylene and glass fibers. These three plates have the same dimensions with each other. A fourth layer of the stack, constituting one face of the stack, comprises a composite plate 20 according to the invention, this plate having reduced dimensions compared to those of the other three plates of the stack. This plate is dimensioned and positioned with respect to the other plates to constitute the central zone of the external face at the front of the beam, as shown in FIG. 6 on which this zone has been hatched for understanding. Four other plates of the aforementioned conventional type and of adapted reduced dimensions complete the fourth layer of the stack at the edges of the plate 20. All the plates of the stack have the same thickness. In addition, the plate 20 was produced by choosing the fabric and the quantity of glass fibers of the layer 16 so that the total glass content by weight of the plate 20 is substantially equal to that of the other plates of the stack. , typically around 40%. It is thus possible to preheat the plates at the same temperature and for the same duration, for example in the same oven, without fear that one of the plates will be overheated relative to the others until the polypropylene burns. The rest of the process is unchanged.

 A beam 26 is thus obtained in which the portion reinforced by means of the two fabrics 2, 4 is limited to a central zone before the part, at a place particularly stressed in compression during a frontal impact of the vehicle. At this zone, the thickness of the beam, starting from the external face, has a layer of fabric, a layer 22 comprising polypropylene and glass fibers in contact with it, a layer of fabric, then three layers similar to layer 22. In the other areas of the part, the thickness of the beam has four layers similar to layer 22.

 FIG. 7 shows a third beam 28 produced according to another variant implementation of the method. This time, the ends of the branches of the "U" are bent outwards. The zones near the ends 30 of the branches of the "U" are produced by means of a stack of four plates 20 as in FIG. 5, the other parts of the beam being formed by means of conventional plates as mentioned above. Here, the reinforced portion is therefore limited to the areas close to the ends 30 of the branches of the "U". In this zone, the structure of the beam according to its thickness is similar to that of FIG. 5. In the other zones, the thickness of the beam has four layers similar to layer 22.

 FIG. 8 shows a composite plate 120 used in another variant implementation of the method, replacing plate 20. The method of manufacturing this plate is close to that of plate 20. This time, we replace the two layers of fabric 2, 4 by two layers 102, 104 comprising strands 6 arranged parallel to each other in the direction of travel of the plate. (The strands are also marketed by the company Vetrotex under the name of Twintex.) The tablecloths further include threads 132, for example made of polyesters, extending in a direction perpendicular to the direction of the strands 6. These threads are interlaced with the strands 6, in order to hold the strands in place. The wires preserve the arrangement of the strands during the manufacture of the plate, then during stamping during the manufacture of the beam.

 The composite plate 120 obtained after cooling has three layers. The central layer 122 is identical to the layer 22 of the plate 20. On either side of this central layer, the plate comprises two layers constituting the two opposite faces of the plate and comprising the strands 6 and the wires 132. Here again, the strands 6 now comprise glass fibers 8 embedded in the strand in polypropylene resulting from the melting of the polypropylene fibers 10. The strands 6 are impregnated on the outside of the strands with the polypropylene of layer 22. This plate can be used to make the three aforementioned beams.

 Of course, many modifications can be made to the invention without departing from the scope thereof.

 Thus, it is possible to use a thermoplastic material other than polypropylene, for example a polyester.

 The composite plate (s) may be made up in different ways depending on the stack which made it possible to manufacture them. The plate may comprise a single layer comprising strands 6 or, on the contrary, at least three layers comprising strands 6. The strands 6 comprising glass fibers may be present in a single layer comprising glass fibers or, conversely, in each layer comprising glass fibers. Thus, in FIG. 1, the layer 16 could consist of strands 6. The fabric comprising these strands could comprise as much warp yarn as weft yarn (balanced fabric), or more weft yarns (extending along the direction of travel during the manufacture of the plate) as warp threads, for example in a 4/1 proportion.

 The plates of Figures 3 and 8 may include several successive layers 22 interposed between the two layers of fabric.

 The glass fibers 16 of the layer 22 may be arranged in a common direction parallel to the direction of travel. It may be cut fibers.

 In the plates 20, 120, the fabric layer may have reduced dimensions compared to those of another layer of the plate so that the fabric layer will be limited to a portion of the plate.

 The method of manufacturing the part from a composite plate can be implemented by stamping a single plate according to the invention, or two or more plates.

 The method of manufacturing a part for a motor vehicle is not limited to beams and may make it possible to manufacture, for example, a headlight surround, a fan unit support, an engine compartment shutter screen, or a seat back element. .

Claims (13)

Claims  1. A method of manufacturing a part for a motor vehicle, comprising the successive steps consisting in: - heating at least one plate (20; 120) comprising at least one layer comprising glass fibers and a thermoplastic material; and - stamping the plate or plates to form the part (24, 26, 28), characterized in that the plate or plates comprise at least one layer (22; 122) comprising a thermoplastic material and at least one layer (2, 4 ; 102, 104) comprising strands (6) of glass fibers (8) in contact with a thermoplastic material, the fibers of each strand being embedded in thermoplastic material in the strand.  2. Method according to claim 1, characterized in that the strands (6) constitute a fabric.  3. Method according to claim 1, characterized in that the strands (6) extend in a common direction.  4. Method according to claim 3, characterized in that the layer comprising the strands (6) comprises son (132) extending in a direction perpendicular to the direction of the strands.  5. Method according to one of claims 1 to 4, characterized in that the plate (20; 120) comprises two layers (2, 4; 102, 104) comprising strands and constituting the upper and lower faces of the plate.  6. Method according to claim 5, characterized in that the plate further comprises at least one layer (22) comprising thermoplastic material and glass fibers (16), this layer extending between the two layers comprising the strands.  7. Method according to one of claims 1 to 6, characterized in that it comprises the steps consisting in: - heating at least two plates (20; 120) and making a stack of the plates together; and - stamping the stack to form the part.  8. Method according to claim 7, characterized in that it comprises the step consisting in heating several plates, some or only some of these plates comprising strands (6) in which the glass fibers are embedded in thermoplastic material.  9. Method according to claim 8, characterized in that the or at least one of the plates (20) comprising strands, has reduced dimensions compared to those of another plate of the stack.  10. Method according to one of claims 8 to 9, characterized in that the plate or plates (20) comprising strands, has a glass content by weight and a thickness substantially equal to that of another plate of the stacking.  11. Part (24; 26; 28) for a motor vehicle, comprising at least one layer comprising glass fibers and a thermoplastic material, characterized in that the part comprises at least one layer (22; 122) comprising a thermoplastic material and at least one layer (2, 4; 102, 104) comprising strands (6) of glass fibers (8) in contact with thermoplastic material, the fibers of each strand being embedded in the strand in thermoplastic material.  12. Part according to claim 11, characterized in that the layer (2, 4) or one of the layers comprising strands, is limited to a portion of the part.  13. Part for a motor vehicle, characterized in that it is manufactured by means of the method according to one of claims 1 to 10.