FR2981001A1 - Method for manufacturing three-dimensional composite material e.g. aeronautical structural part, involves stamping preform to provide desired form, and cooling stamped preform by maintaining stamped preform under pressure along with blank - Google Patents

Abstract

The method involves providing a blank that comprises a massive and/or three-dimensional form. A strand of reinforced fibers impregnated with thermoplastic resin is wound in surplus quantity. A preform is stamped to provide a desired form while evacuating surplus resin. The stamped preform is cooled by maintaining the stamped preform under pressure along with the blank. A winding tool (16) is arranged with a plate (13) for winding the strand.

Description

The invention relates to a method for manufacturing a composite material three-dimensional or massive such as for example a connecting rod, while giving it a high mechanical strength.

BACKGROUND OF THE INVENTION It is known to manufacture composite material parts by incorporating short reinforcing fibers into thermoplastic resin, and by forming the parts in press. With this method, the length of the fibers is limited to twenty or thirty millimeters, because these fibers are randomly oriented in the thermoplastic resin. This process, which is part of the so-called SMC (Sheet Molding Compound) processes, makes it possible to manufacture parts having a fiber density of between thirty and forty percent, in general, which corresponds to weakly loaded parts which consequently have a mechanical strength. relatively low. In practice, this method makes it possible to manufacture parts of regular and relatively small thickness, such as fairing or cowling parts for the automotive industry. According to another known method, a fabric of plane reinforcing fibers, which can have a relatively substantial thickness, is impregnated with thermoplastic resin before being installed in a press to be deformed so as to give it a curve. Several elements of this type can be manufactured before being glued to each other by hot stamping. It is for example possible to bring an L-section piece on a flat portion, to produce a three-dimensional piece with a T-section. This process, which was developed by the Carbon Forge company, makes it possible to manufacture pieces with longer fibers. (between fifty and one hundred millimeters), having a higher fiber density (between fifty-five and sixty percent). This method makes it possible to obtain a higher mechanical strength, especially since the orientation of the fibers is substantially controlled instead of being disordered.

In practice, this other method makes it possible to manufacture structural parts but having small dimensions, worth for example one hundred and fifty by one hundred and fifty millimeters, and shapes that must nevertheless be relatively simple.

OBJECT OF THE INVENTION The object of the invention is to provide a method for manufacturing parts made of thermoplastic matrix composite material, allowing the manufacture of highly loaded parts having complex and / or massive three-dimensional shapes and which can have significant dimensions. . SUMMARY OF THE INVENTION To this end, the subject of the invention is a process for manufacturing a composite material 20 having a solid and / or three-dimensional shape, comprising the steps of: winding at least one fiber strand while hot reinforcing agents impregnated with thermoplastic resin in surplus quantity, on coils of a tooling, to form a preform of the manufactured part; - Hot stamp this preform to give it a desired shape while removing the excess resin; Cool the die preform by holding it under pressure to form the blank. The invention thus makes it possible to produce a three-dimensional piece having a high density of fibers which are oriented along the path used during the winding, which contributes to increasing the mechanical strength while allowing the manufacture of three-dimensional and / or massive pieces. . The invention also relates to a method as defined above, in which a winding tool is used comprising a sole having a face provided with winding reliefs in the form of pads. The invention also relates to a method as defined above, in which the pads are retractable.

The subject of the invention is also a method as defined above, in which a separate winding tool and die tooling is used, and in which the preform is cooled before being transferred from the winding tooling to die-casting equipment. The invention also relates to a method as defined above, in which a heating type stamping tool is used. BRIEF DESCRIPTION OF THE FIGURES FIG. 1 is a view from above of a double rod manufactured with the method according to the invention; Figure 2 shows in perspective the winding of a reinforcing fiber strand around the reliefs of a winding tool to manufacture the rod of Figure 1 according to the invention; Figure 3 is a detail view showing in perspective a winding relief of the tool of Figure 2 in the form of a stud having a shoulder; Figure 4 is a sectional view showing a possibility of winding a reinforcing fiber strand around a shoulder stud; Figure 5 is a view showing a face of a stamping tool in which is installed a part being stamped.

DETAILED DESCRIPTION OF THE INVENTION The idea underlying the invention is to wind a strand around studs arranged in such a way that the path followed by the wound strand coincides with the ribs or reinforced zones of the part to be manufactured.

For this purpose, there is shown in the figures a winding tooling and a stamping tooling used for the manufacture of a double rod shown in Figure 1 by being marked with 1. In accordance with the invention, the manufacture of a piece having a different geometry of this double rod is provided with similar tools adapted to this other geometry. The double rod 1 comprises a central bearing 2 oriented along a main axis AP corresponding to an axis normal to the plane of Figure 1, and two lateral arms 3 and 4 oriented transversely extending along an axis AT perpendicular to the axis AP and departing from the central landing 2 in opposite directions. Each arm is terminated by a corresponding bearing, and these lateral bearings, marked by 6 and 7, are oriented parallel to the central bearing 2. Each of the three bearings has a generally cylindrical wall shape with a circular base, the central bearing having a diameter significantly greater than that of the lateral bearings. The arm 3 has a flat wall 9 extending in a plane normal to the main direction AP, that is to say in the plane of Figure 1, and two ribs 11 and 12 bordering the region 9. Each rib is a wall extending perpendicularly to the plane wall 9, and which connects the central bearing 2 to the lateral bearing 6. The two ribs 11 and 12 are located on either side of the transverse axis AT, which in turn passes through the central axis of each of the bearings 2, 6 and 7.

The central region 9 has a relatively small thickness relative to the height of the bearings along the main direction AP, while the lateral ribs 11 and 12 each have a height close to the height of the bearings.

The double rod of FIG. 1 has a shape which is symmetrical with respect to a plane normal to the transverse axis AT and containing the main axis AP which moreover coincides with the central axis of the main landing 2. Thus, the arm 4 is the symmetrical arm 3, so that it also includes two ribs of the same type. Furthermore, the double rod 1 is also symmetrical with respect to a plane containing the transverse axis AT and the main axis AP, and it is also symmetrical with respect to a plane normal to the main axis AP and containing the axis transversal AT. The winding tool 16 for producing this double rod 1 here comprises a plate or sole 13 having a flat upper face 14, this plate being provided with seven winding reliefs which are here pads, identified by the references 17 to 23. More concretely, the stud 17 corresponds to the bearing 6, the studs 18 and 19 correspond to the space between the ribs 11 and 12 of the arm 3, the stud 20 corresponds to the central bearing 2, the studs 21 and 22 correspond to the space located between the ribs of the arm 4, and the stud 23 corresponds to the bearing 7. As shown in Figure 2, a strand 24 of reinforcing fibers impregnated with thermoplastic resin is wound on this winding tool 16, around the pads 17-23, so as to follow a path that delimits at the same time the three bearings or clevises 2, 6, and 7, and the ribs 11 and 12 of the arm 3 and the corresponding ribs of the arm 4. The strand 24 of reinforcing fibers can occur under different fo rmes: it can be a set of fibers organized parallel to each other and constituting a kind of reinforcing fiber cord; it may also be a set of fibers braided with each other to form a flexible braid extending generally in a main direction, but consisting of spindle fibers oriented in multiple directions. The strand 24 impregnated with excess thermoplastic resin is wound around the different pads so that, as can be seen in FIG. 2, it completely surrounds the bearing 6 to then pass on the same side of the pads 18 and 19 before change side to surround one half of the central block 20 to then return on the same side of the pads 21 and 22 before completely surround the second side pad 7 to return in a symmetrical path to the first side pad 6, which corresponds to a complete turn. The strand 24 can thus be wound on several turns around the various pads, the number of turns being conditioned by the diameter of the section of the strand vis-à-vis the dimensions of the part to be manufactured. In the example of Figure 2 which is given mainly didactic to understand the trajectory of the strand, it is wound on a turn and a half.

As can be seen in the figures, the studs 17 and 23 are shoulder studs: these are studs of revolution comprising a cylindrical base extended by a coaxial stud of smaller diameter than the base. This form of the studs 17 and 23 makes it possible to make bearings or clevises whose inner surface is itself chamfered, that is to say that it comprises two zones having two different diameters. In particular, and as visible in FIGS. 3 and 4, the strand 24 can be wound over a large number of turns by being arranged so as to form a single circumferential layer 26 around the base of the stud 17, and two concentric circumferential layers 27 and 28 around the upper end of the stud 17 which has a significantly smaller diameter than its base. Thus, different solutions can be envisaged with regard to the winding of the strand on the winding tool 16, depending on the particularities of shapes that one wishes to obtain at the part to be manufactured. The strand 24 which is impregnated with excess thermoplastic resin is wound on the tool 16 hot, so as to have the flexibility required to allow accurate winding. Advantageously, the winding tooling 15 is of the heating type, and the winding as such can be achieved by means of a robotic arm. When the winding of the strand 24 is completely finished, it constitutes a preform of the part to be manufactured, and the whole is allowed to cool so that this preform solidifies in its proper form. When the preform is solidified, it is extracted from the winding tool. As such, the relief elements that constitute the pads 17-23 are advantageously provided retractable relative to the plate 13 which carries them. In this case, the detachment of the preform is obtained by controlling the retraction of the pads 17-23 before entering this preform to put it in place in a stamping tool or stamping corresponding. Such a tool, which is shown in FIG. 5 by being marked with 31, comprises a plate in which is machined an imprint, or more particularly a half-cavity of the outer shape of the double-rod 1 to be manufactured. This tool or die is installed in a press which carries at the end of its cylinder another die having on its internal face a fingerprint corresponding to the other half of the double rod to be manufactured. When the preform has been installed in the stamping tool, i.e. in one of the half-impressions, the stamping cycle can be started. The press is then controlled to bring the two matrices closer to each other, until a predetermined pressure is established for a predetermined duration.

This stamping operation is carried out hot for this purpose, the stamping tools are advantageously provided heating, and they are advantageously preheated to heat the preform before engaging the stamping cycle. During the maintenance of pressure by the press on the two hot stamping tools, the excess thermoplastic resin flows out of the body of the preform 32 of the double-rod to manufacture. For this purpose, the stamping tool 31 has a hollow region, marked by 33 and 34, and extending all around the footprint of the double rod that is used to manufacture. This or these hollow regions 33 and 34 are themselves surrounded by a flat surface 36 with a rectangular contour, and by which the two forging tools bear against one another when the press is controlled for this purpose. As illustrated schematically in Figure 5, the excess thermoplastic resin escapes from the preform during the stamping to be placed in the hollow zones 33 and 34 provided for this purpose. Because these hollow zones are located at the level of the joint plane delimited jointly by the two stamping tools when they bear against each other, the excess of thermoplastic resin then constitutes a burr 37 extending over all around the double rod manufactured at the joint plane of this rod, so that it can then easily be removed by sawing or otherwise. Advantageously, the stamping is performed in several operations, using different pairs of stamping tools, to gradually reduce the volume of the double rod to manufacture. For example, a first pair of die tools can be used to form a first blank from the preform by stamping it. Once this first blank is finished, the burr corresponding to the excess thermoplastic resin is removed before placing this first blank in another stamping tool of a second pair of dies, to further reduce its volume by generating a new burr corresponding to the excess of resin. A last pair of stamping tools can be used to further refine the geometry of the double rod, before removal of the last burr, which makes it possible to constitute the double rod in the form of a blank. As will be understood, the various stamping operations that are carried out hot, typically at a temperature of between one hundred and sixty and two hundred degrees Celsius, make it possible to evacuate the excess thermoplastic resin, but this heating gives rise to a softening temporary of the manufactured part. The part is advantageously cooled, at least partially before its transfer from a stamping tool to another stamping tool. In particular, after the last stamping operation, the tooling is allowed to cool as well as the part that it contains before demolding. This cooling is performed while maintaining the dies under pressure for the duration necessary for the solidification of the thermoplastic resin, which allows to extract from these matrices a double raw rod undeformed.

In general, the invention makes it possible to produce a three-dimensional piece having a high fiber density, which can reach fifty-five to sixty percent of fibers, and moreover, these fibers, which are in the form of a strand, are thus of continuous type and oriented according to the trajectory used during the winding. This winding contributes to imparting to the manufactured part a significant mechanical strength, in addition to allowing the manufacture of parts having a large volume and / or complex shape.

Concretely, the whole phase of winding of the fiber strand makes it possible to position and orient the fibers in a state very close to that which they will have in the finished part: the orientation of the fibers can thus be completely optimized with respect to the manufactured part. The stamping phase which follows the winding makes it possible to obtain a desired geometry with a high degree of precision. Furthermore, it is possible to place an insert in the preform so that it is integrated into the finished part being rigidly secured to the body of the finished part in order, for example, to facilitate the transfer of forces. Such an insert is typically an element of a nature other than the body of the part, such as a metal type insert.

Thus, this manufacturing method makes it possible to manufacture composite material parts initially made of steel or other, to replace them with parts made of composite material having a weight and / or a smaller volume and comparable mechanical strength.

As illustrated in the example of the figures, the method according to the invention makes it possible to manufacture parts having complex shapes, extending along the three dimensions, and which can also be massive either in localized regions, or on the whole of the room.

In the example of the figures, the part is obtained by winding a single strand of fibers. But in the case of a piece of more complex shape, it is quite possible to wind several strands corresponding for example to several parts of the part to be manufactured.

Claims (5)

REVENDICATIONS1. A method for manufacturing a composite material (1) having a solid and / or three-dimensional shape, comprising the steps of: - winding at least one reinforcing fiber strand (24) impregnated with thermoplastic resin in excess quantity, on winding reliefs (1723) of a tool (16), to form a preform (32) of the manufactured part (1); - Hot forging this preform (32) to give it a desired shape while evacuating the excess resin; - Cool the die preform by maintaining it under pressure to form the blank (1). 2. Method according to claim 1, wherein using a winding tool (16) having a sole having a face provided with winding reliefs (1723) in the form of pads. 3. Method according to claim 2, wherein the pads (17-23) are retractable. 4. Method according to one of the preceding claims, wherein one uses a winding tooling (16) and a stamping tooling (31) distinct, and wherein the preform (32) is cooled before being transferred from the winding tooling to the die tooling. 5. Method according to one of the preceding claims, wherein using a stamping tooling (31) of the heating type.