Conveyor with articulated frame for stamping a composite part having a thermoplastic matrix

Abstract

The invention relates to a conveyor (1) for a preform (2) made of a composite material having a thermoplastic matrix, said conveyor (1) comprising: - two guide branches (3a) and at least two free branches (3b), forming a flat and rigid outer frame (3); - an articulated inner frame (4) formed by two inner half-frames (4a) in a U-shape connected by a double articulation; - means for holding the preform (2) on this inner frame (4), and - adaptation means on the outer frame (3) allowing folding of the inner frame (4).

Description

[0001] DESCRIPTION

[0002] CONVEYOR WITH ARTICULATED FRAME FOR STAMPING A THERMOPLASTIC MATRIX COMPOSITE PART.

[0003] TECHNICAL FIELD

[0004] The invention relates to a conveyor used during the manufacture and shaping of a part made of thermoplastic matrix composite materials. More particularly, the present invention relates to the manufacture of composite parts used as structural parts in aircraft, these structural parts generally having a curvature and / or a complex structure. These curved and / or complex parts are conventionally produced by stamping.

[0005] PRIOR ART

[0006] The share of composite materials in aircraft is growing rapidly, with composite materials making it possible in particular to lighten the structure of aircraft, which were previously mainly made of metal parts, and thus to reduce kerosene consumption. In addition to their advantageous mechanical properties / density ratio, composite materials are generally resistant to corrosion, extreme temperatures and humidity.

[0007] In addition to these advantages, which are highly valued in the aeronautical field, there is a "custom" design that allows for high anisotropy of the mechanical properties of the manufactured part, which thus adapts to the mechanical stresses it will undergo. This "custom" design is based in particular on the choice of materials used in the composite material as well as their arrangement, such as linear carbon fibers to manufacture a part subjected to unidirectional stress or woven and stacked fibers to manufacture a part subjected to a stress field.

[0008] These fibers, linear or woven, constitute a fiber reinforcement which is contained in a matrix. The composite material is manufactured in plate according to the classic methods of the state of the art. For shaping by stamping, this is carried out hot: the composite plate is therefore first cut into preforms to the dimensions of the part to be stamped then heated before being shaped by stamping. The matrix is ​​generally a thermoplastic resin matrix, this having the advantage of deforming after heating while regaining its initial mechanical properties after cooling, unlike thermosetting resins whose mechanical properties in the solid state are irreversible and which cannot be remelted after their manufacture.

[0009] To stamp composite parts, it is therefore necessary to convey the preforms between the oven, in which they have been heated, and the stamping tool which comprises two complementary molds, the die and the punch. The preform being heated, it is malleable and can only be conveyed with a support. The conveying is generally carried out by a horizontal and rigid frame on which is fixed either a release film which will follow the preform during the entire stamping cycle, or springs which hold the preform, this frame ensuring the transport and maintenance of the preform during stamping.

[0010] However, although the release film resists heating temperature well, it has a limited elongation rate which is not suitable for stamping parts with a non-developable surface, i.e. parts whose surface cannot be "flattened" without tearing or stretching it.

[0011] Similarly, springs are difficult to adapt to the stamping of large preforms because they must have both a sufficiently high stiffness to support the weight of the preform and a sufficiently low stiffness to accompany the preform during the mold closing phase during stamping. In addition, depending on their position and the final shape of the part to be manufactured by stamping, the springs will have a different elongation which is difficult to predict.

[0012] Another disadvantage of flat stamping of preforms to produce curved parts lies in the topology of the molds: in fact, since the molds are curved and have a lower temperature than the preforms, the contact of the curved molds with the preforms occurs gradually and causes heterogeneous cooling of the surfaces in contact, and of the part in general, which can be the cause of geometric distortions during cooling and / or internal stresses in the part. DISCLOSURE OF THE INVENTION

[0013] The main objective of the invention is to improve the stamping of a preform made of composite material using a conveyor making it possible to improve the quality of the stamping and therefore of the parts produced.

[0014] To improve the quality of the stamping, the invention provides for adapting the conveyor to the topology of the part to be stamped by internal guidance and enabling the preform to be shaped by more uniform positioning of the latter relative to the molding surfaces of the stamping tool.

[0015] More specifically, the present invention relates to a conveyor for a preform made of a thermoplastic matrix composite material transporting this preform between a heating furnace and a stamping tool, this conveyor comprising two guide branches parallel to each other and at least two other free branches, the guide branches and the free branches forming a flat and rigid external frame.

[0016] The conveyor also includes:

[0017] - an articulated internal frame,

[0018] - means of holding the preform on this internal frame, and

[0019] - means of adaptation on the external frame allowing the internal frame to be folded; the internal frame being formed by:

[0020] - two internal half-frames in the shape of a “U” each with a base from which two support branches extend in the same plane, each internal half-frame being connected by its base to a guide branch of the external frame, and

[0021] - a double articulation, each articulation connecting a support branch of one internal half-frame to a support branch of the other internal half-frame.

[0022] Advantageously, the flat outer frame allows the preform to be heated flat, this heating then being uniform over the entire preform, allowing for uniform shaping by stamping and therefore better quality.

[0023] Advantageously also, the articulated internal frame allows the preform to approach the curvature of the stamping molds: the contact of the molds with the preform is then homogeneous and rapid over the entire preform, thus limiting temperature variations at the time of contact with the molds and therefore internal stresses in the part as well as its geometric distortion during cooling.

[0024] Advantageously, parts obtained by stamping with an articulated internal frame also have optimized mechanical performance because they contain few internal stresses. With the same mechanical strength, parts resulting from this stamping are therefore of reduced thickness, thereby reducing the weight of the part.

[0025] According to preferred embodiments taken alone or in combination:

[0026] - the outer frame is rectangular;

[0027] - tension springs hold the preform in the internal frame;

[0028] - the tension springs are attached to the support branches;

[0029] - the support branches of the internal half-frames are connected to each other by ball joints to form the double articulation;

[0030] - the support branches of the internal half-frames are connected to each other by hinges to form the double articulation;

[0031] - the double articulation has at least one support face;

[0032] - at least one safety pin is inserted into the double joint.

[0033] According to means of adaptation on the external frame allowing the folding of the internal frame:

[0034] - the bases of the internal half-frames are connected by pivot links to the external frame and the free branches of the external frame are telescopic to adapt the external frame to the folding of the articulated internal frame;

[0035] - the outer frame has adaptation springs between the guide branches and the internal half-frames.

[0036] The invention also relates to a stamping tool comprising two molds producing a die and a punch, at least one support cylinder and a conveyor with an articulated internal frame whose double articulation comprises at least one support face on which a support cylinder presses during the stamping of a composite preform. PRESENTATION OF THE FIGURES

[0037] Other characteristics and advantages of the invention will emerge from the non-limiting description which follows, with reference to the appended drawings in which:

[0038] Figure 1, a schematic representation seen from above of an example of a conveyor of a composite preform according to the invention;

[0039] Figure 2, Figure 3 and Figure 5, a schematic side view representation of the stamping tooling and conveyor during different stages of stamping the composite preform;

[0040] Figure 4 and Figure 6, a schematic sectional representation of the stamping tooling and conveyor during different stages of stamping the composite preform;

[0041] Figure 7 is a top view schematic representation of an example of a composite preform conveyor variant.

[0042] DETAILED DESCRIPTION

[0043] Figure 1 illustrates a conveyor 1 of a preform 2 made of composite material. This preform 2 is made up of fibers 2a contained in a matrix 2b. These fibers are oriented in the longitudinal direction X of the preform 2, the latter being shaped by stamping resulting in this embodiment example in a curvature of the preform 2 in the longitudinal direction (see figure 6). Stamping therefore makes it possible to produce a part from the preform. Depending on the desired shape of the part after stamping, other orientations of the fibers and / or orientations more complex than linear - for example laminates with unidirectional folds or fabrics - are produced in the preform depending on the mechanical constraints observed in the part to be produced.

[0044] To carry out the stamping of the preform 2, it is first heated so that it can be deformed without damaging its structure: a thermoplastic matrix 2b is therefore chosen. Indeed, thermoplastic materials have the advantage of deforming after heating and regaining their initial mechanical properties after cooling. This behavior makes it possible to heat a preform again to flatten it or send it to another stamping tool without causing any degradation of its mechanical performance.

[0045] The conveyor 1 therefore makes it possible to transport the preform 2 made of composite material with a thermoplastic matrix 2b between a heating furnace and a stamping tool (see figure 2). The conveyor 1 comprises two guide branches 3a parallel to each other and perpendicular to the longitudinal direction X of the preform 2, as well as two free branches 3b perpendicular to the guide branches 3a. The guide branches 3a and free branches 3b form a flat and rigid outer frame 3 of rectangular geometry in the plane P.

[0046] Conveyor 1 also includes:

[0047] - an internal 4-articulated frame;

[0048] - means for holding the preform 2 on this internal frame 4, and

[0049] - means of adaptation on the external frame 3 allowing the internal frame 4 to be folded.

[0050] The internal frame 4 is formed by two internal half-frames 4a in the shape of a “U” each with a base 4b from which two support branches 4c extend in the same plane. The support branches 4c are each connected to a support branch 4c of the other internal half-frame by a pivot connection 4d, the support branches 4c of the internal half-frames 4a being thus connected to each other by a double articulation. In addition, each internal half-frame 4a is connected by its base 4b to a guide branch 3a of the external frame 3.

[0051] In this embodiment illustrated in Figure 1, the preform 2 is held in the internal frame 4 by twelve tension springs 5a attached to the support branches 4c of the internal half-frames 4a. In addition, the support branches 4c are connected to each other by two ball joints 4d to form the double articulation. The preform 2 can also be connected to the bases 4b by springs.

[0052] Alternatively to the ball joints 4d, hinges can connect the support branches of the internal half-frames to achieve the double articulation of the conveyor 1. Furthermore, the internal frame 4 being articulated at the level of the ball joints 4d, the internal frame 4 can bend and thus initiate a curvature shaping of the preform 2 which has been previously heated and which is held by the tension springs 5a to the internal frame 4.

[0053] To accompany this folding of the internal frame 4, adaptation means interface the internal frame 4 with the external frame 3. The bases 4a of the internal half-frames 4a are then connected by pivot links 3c to the external frame 3 and the free branches 3b of the external frame 3 are telescopic over a zone 3d to adapt the dimensions of the external frame 3 to the folding of the articulated internal frame 4. This zone 3d is here aligned with the double articulation of the internal frame 4. Furthermore, a locking means, here a pin 3e, makes it possible to block the free branches 3b at a given length.

[0054] Figure 2 shows, in a section in plane A, a stamping tool 6 comprising two molds producing a die 6a and a punch 6b, a support cylinder 6c and the conveyor 1. The double articulation of the articulated internal frame 4 comprises a support face 4e on which the support cylinder 6c presses during the stamping of a composite preform 2. The cylinder 6c is integral with the punch 6b which is movable along an axis Z perpendicular to the plane P of the conveyor 1. In the initial configuration presented in figure 2, the conveyor 1 is brought between the molds and the internal frame 4 of the conveyor 1 which is flat: the shaping of the preform 2 has not yet begun.

[0055] In the step illustrated in Figure 3, the punch 6b descends to approach the die 6a and the support cylinder 6c pushes on the support face 4e, thus causing the internal frame 4 to fold. In this configuration, the internal half-frames 4a are no longer coplanar and thus form an angle a. Figure 4 illustrates this configuration according to a section in the plane B. The preform 2 begins from this moment to bend under the action of the folding of the internal frame 4 on itself while the preform 2 is not yet in contact with the molds 6a, 6b. This curvature of the preform 2 standardizes the distance from the preform 2 to the die 6a and to the punch 6b. This standardization of the distance advantageously allows almost simultaneous contact of the surface of said molds on the preform 2 and therefore regular and uniform shaping of the preform.Alternatively, the support cylinder 6c can directly press the double articulation of the internal frame (4) when the latter does not have a support face 4e. Figure 5 and Figure 6 illustrate a view in plane A and plane B respectively of the stamping tool 6 when the preform 2 is shaped. The punch 6b, the preform 2 and the die 6a form a stack, the preform 2 being sandwiched between the punch 6b and the die 6a. The preform 2 is then shaped by stamping in accordance with the molds formed by the punch 6b and the die 6a.

[0056] At the end of the stamping, the punch 6b moves away from the preform 2 and the conveyor 1 is extracted from the stamping tool. The preform 2 thus shaped is then removed from the conveyor 1 and can be used.

[0057] Figure 7 shows a variant of the conveyor 1 in which the means for adapting the internal frame 4 to the external frame 3 are constituted by adaptation springs 3f between the guide branches 3a of the external frame 3 and the bases 4b of the internal half-frames 4a. These adaptation springs 3f allow the internal half-frames 4a on the one hand to pivot relative to the external frame 3 and on the other hand to fold under the action of the support cylinder 6c on the support face 4a of the double articulation of the internal frame 4. In addition, the free branches 3b are no longer telescopic, the adaptation springs being capable of providing the elongation necessary for folding the internal frame 4.

[0058] During transport of the conveyor 1, the double articulation of the internal frame 4 is blocked by a safety pin 4f which prevents the folding of the internal half-frames 4a. The safety pin 4f is here inserted into one of the pivot links 4d, a pin being able to be inserted into each of the pivot links. Alternatively, any means of blocking the folding of the half-frames can be used such as a locking device of the double articulation or leaf springs between the internal half-frames.

[0059] The invention is not limited to the embodiments described and shown. Thus, the internal frame can be adapted so that two support cylinders on the double pivot connection allow double curvature shaping by stamping.

Claims

CLAIMS 1. Conveyor (1) for a preform (2) made of a thermoplastic matrix composite material transporting this preform (2) between a heating furnace and a stamping tool (6), this conveyor (1) comprising two guide branches (3a) parallel to each other and at least two free branches (3b), the guide branches and the free branches forming a flat and rigid outer frame (3), the conveyor (1) being characterized in that it also comprises: - an internal articulated frame (4); - means for holding the preform (2) on this internal frame (4); - means of adaptation on the external frame (3) allowing the internal frame (4) to be folded; the internal frame being formed by: - two internal half-frames (4a) in the shape of a “U” each with a base (4b) from which two support branches (4c) extend in the same plane, each internal half-frame (4a) being connected by its base (4b) to a guide branch (3a) of the external frame (3), and - a double articulation, each articulation connecting a support branch (4c) of an internal half-frame (4a) to another support branch (4c) of the other internal half-frame (4a).

2. Conveyor (1) according to claim 1, characterized in that the outer frame (3) is rectangular.

3. Conveyor (1) according to any one of claims 1 to 2, characterized in that tension springs (5a) hold the preform in the internal frame (4).

4. Conveyor (1) according to any one of claims 1 to 3, characterized in that the support branches (4c) of the internal half-frames (4) are connected to each other by ball joints (4d) to form the double articulation.

5. Conveyor (1) according to any one of claims 1 to 3, characterized in that the support branches (4c) of the internal half-frames (4) are connected to each other by hinges to form the double articulation.

6. Conveyor (1) according to any one of claims 1 to 5, characterized in that the double articulation comprises at least one bearing face (4e).

7. Conveyor (1) according to any one of claims 1 to 6, characterized in that the adaptation means on the outer frame (3) comprise pivot connections (3c) between the bases (4b) of the internal half-frames (4a) and the outer frame (3), the free branches (3b) of the outer frame (3) being telescopic to adapt the outer frame (3) to the folding of the articulated internal frame (4).

8. Conveyor (1) according to any one of claims 1 to 6, characterized in that the adaptation means on the outer frame (3) comprise adaptation springs between the guide branches (3a) of the outer frame (3) and the internal half-frames (4a).

9. Conveyor (1) according to any one of claims 1 to 8, characterized in that at least one safety pin (4f) is inserted into the double articulation.

10. Stamping tool (6) comprising two molds producing a matrix (6a) and a punch (6b) characterized in that it also comprises at least one support cylinder (6c) and a conveyor (1) according to claim 1 to 9, the support cylinder (6c) pressing the double articulation of the internal frame (4) of the conveyor (1) during the stamping of a composite preform.

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