Apparatus for compression molding of composite parts starting from plates of composite material with a thermoplastic matrix

Abstract

To provide a compression molding device for manufacturing a composite-material part starting from a composite-material plate with a thermoplastic matrix.SOLUTION: There is provided a compression molding device, comprising: a fixed support structure 9; an upper half-die 10 provided with a first contoured surface corresponding to a profile of an upper surface of a part to be made; a lower half-die 12 provided with a second contoured surface 13 corresponding to a profile of a lower surface of the part to be made; holding means 15 carried by the support structure and configured to hold a plate 3 in a position interposed between the half-dies; and moving means for moving at least one of the half-dies from and towards the plate. The holding means includes two or more releasable gripper 16 that are configure to grip a separate portion of an outer edge 18 of the plate by friction, and to completely release or allow for completely releasing the plate itself when the plate is compressed between the half dies during molding.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] [CROSS-REFERENCE TO RELATED APPLICATIONS] This patent application claims priority to Italian Patent Application No. 102019000015509, filed September 3, 2019, the entire disclosure of which is incorporated herein by reference.

[0002] [Technical field] The present invention relates to a compression molding device for producing parts made of composite material, in particular for aeronautical applications, starting from a plate of composite material with a thermoplastic matrix. [Background technology]

[0003] As is known, composite materials are used in various industrial sectors, including the aeronautical industry. In particular, fiber-reinforced composite materials, commonly referred to as "prepregs," are known, which generally consist of a semi-finished product including a resin matrix and reinforcing fibers impregnated in the matrix. The fibers may be arranged in various configurations, such as in a single direction, in two or more directions with different orientations, or to form a woven fabric. The matrix is ​​used to secure the fibers together and possibly to other components during manufacturing.

[0004] Prepregs are usually provided in strip form and wound into rolls, and must be subjected to a thermal consolidation process, often under pressure, to achieve the desired mechanical properties.

[0005] The use of prepregs having a matrix of thermoplastic material in the aeronautical industry is known.

[0006] In this type of prepreg, the matrix resin has a high molecular weight, so that on the one hand it does not need to undergo a polymerization cycle and on the other hand it is not tacky.

[0007] A prepreg with a thermoplastic matrix can be considered, to a first approximation, as a finished product formed by a single sheet or plate. Therefore, to form a laminate, it is necessary to heat the thermoplastic prepreg layers so that at least the surfaces that contact the layers that make up the laminate melt, compress them under pressure, and then cool them. The temperature that must be reached for melting is the glass transition temperature T for amorphous thermoplastics. g and for semi-crystalline thermoplastics the melting point T f is.

[0008] In these cases, the equipment for manufacturing laminates based on thermoplastic prepregs must also provide heat to reach temperatures (which may be very high, depending on the material) that melt the resin and thus obtain adhesion between the various layers that make up the laminate; moreover, in the case of semi-crystalline thermoplastics, too rapid cooling can lead to amorphization of the part, with a consequent loss of performance properties.

[0009] Thermoplastic matrix composites have many advantages, such as: -Stable at room temperature. High elasticity. -Quick processing is possible. No autoclave required. ·Recyclable.

[0010] It is known, particularly in the aeronautical sector, to use compression molding machines to achieve the desired configuration of composite parts or components with a thermoplastic matrix.

[0011] In particular, such molding devices generally comprise a preheating station in which a pre-hardened flat plate of composite material with a thermoplastic resin matrix is ​​subjected to a heating operation to achieve softening, and a molding station in which the plate, pre-hardened and subsequently heated in the preheating station, is subjected to a compression molding operation to obtain the desired part or component.

[0012] The forming station essentially consists of: a fixed support structure; an upper half die having a lower contoured surface corresponding to the contour of the upper surface of the composite part to be produced by molding; a lower half die having an upper contoured surface corresponding to the contour of the lower surface of the composite part to be produced by molding; - retention means carried by the support structure in a fixed position and configured to hold the plate in position sandwiched between the upper and lower half dies throughout the forming operation; a moving means for moving at least one of the upper half die and the lower half die from the plate in a direction transverse to the plate itself and further towards the plate; Equipped with.

[0013] The retaining means are typically carried by the support structure and comprise fixing arms or springs which, in use, engage in respective through holes provided in the lateral ears of the plate to be formed. In particular, the plate to be formed is cut from a sheet of pre-hardened composite material with the desired number of lateral ears, which must then be fixed to the arms or retaining springs of the support structure of the forming apparatus. These lateral ears are perforated to allow the insertion of the arms or retaining springs.

[0014] After the forming operation, the ears are removed to obtain the desired final shape.

[0015] The use of this type of forming equipment leads to the formation of a relatively large amount of scrap and is obviously not compatible with composite materials, which are generally quite costly.

[0016] Because the starting plates are cut from a larger sheet of composite material, it is necessary to ensure that the shapes being cut out interdigitate (the "protrusions" of the shape to be cut out must "fit" into the "voids" of adjacent shapes) in order to produce as little scrap as possible. However, this is not always possible, and even if it were possible, the tabs created on each plate constitute an additional challenge to consider when trying to reduce waste.

[0017] The removal of ears from a molded part or component not only creates additional scrap, but also constitutes an additional operation that must be performed in the process to form the final part or component. Summary of the Invention

[0018] It is therefore an object of the present invention to provide a compression molding device for producing composite parts starting from a plate of composite material with a thermoplastic matrix, which makes it possible to eliminate the above-mentioned drawbacks of known types of molding devices in a simple and economical manner.

[0019] According to the present invention there is provided a compression moulding apparatus for producing parts from composite thermoplastic materials as set out in claim 1 and the claims dependent thereon. [Brief explanation of the drawings]

[0020] The present invention will now be described with reference to the accompanying drawings, which show example, but non-limiting embodiments. [Figure 1]1 is a schematic perspective view of a compression molding apparatus according to the invention during the production of a first example of a composite part, starting from a plate of composite material with a thermoplastic matrix, with some parts removed for clarity; [Figure 2] 2 is a schematic perspective view of a portion of the molding apparatus of FIG. 1 on an enlarged scale, with some parts removed for clarity; FIG. [Figure 3] 3 is an enlarged plan view of part of a support structure for the plate to be formed which forms part of the forming apparatus of FIG. 2; FIG. [Figure 4] FIG. 4 is an enlarged perspective view of a detail of FIG. 3. [Figure 5] 4 is a perspective view in reduced scale of the support structure of FIG. 3 and an actuator member of a forming device according to the invention configured to interact with the support structure itself; FIG. [Figure 6] 6A-6C are side views on a reduced scale of the detail of FIG. 4 at various stages of operation during interaction with the actuator member of FIG. 5; [Figure 7] 6A-6C are side views on a reduced scale of the detail of FIG. 4 at various stages of operation during interaction with the actuator member of FIG. 5; [Figure 8A] 1 is a side view of a further example of a part made of a composite material with a thermoplastic matrix that can be produced by a molding apparatus according to the teachings of the present invention. [Figure 8B] 1 is a side view of a further example of a part made of a composite material with a thermoplastic matrix that can be produced by a molding apparatus according to the teachings of the present invention. [Figure 8C] 1 is a side view of a further example of a part made of a composite material with a thermoplastic matrix that can be produced by a molding apparatus according to the teachings of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0021] In Figures 1 and 2, 1 indicates as a whole an example of a compression molding apparatus according to the invention, which is configured to produce a first example of a composite part or component 2, preferably for use in the aeronautical sector, starting from a flat plate 3 of a thermoplastic matrix composite material, in particular having a matrix based on a thermoplastic semi-crystalline or amorphous resin.

[0022] In the first case, the semi-crystalline thermoplastic resin may be, for example, polyether-ether-ketone, or PEEK. Alternatively, the semi-crystalline thermoplastic resin may be, for example, polyether-ketone-ketone, or PEKK. An example of an amorphous thermoplastic resin is represented by polyetherimide, or PEI.

[0023] The reinforcing fibers can be arranged in one or more unidirectional layers, in several layers with different orientations, or as a woven fabric.

[0024] The reinforcing fibers are preferably made of carbon, but it is also possible to use other types of reinforcing fibers known in the aeronautical field, such as glass fibers or a combination of glass fibers and carbon fibers.

[0025] It should be noted that the starting plate 3 for carrying out the forming operation is a pre-consolidated plate, i.e. it has been subjected in known manner to a prior consolidation operation in a hot press.

[0026] In the illustrated case, the starting plate 3 for producing the composite part 2 has the shape of a flat rectangle.

[0027] The composite part 2 produced by molding starting from the plate 3 has two laterally opposite flat horizontal portions 2a arranged on the same plane of arrangement and a central portion 2b having a substantially V-shaped profile formed by two oblique portions starting from the laterally opposite portions 2a and converging towards each other to a common edge (i.e., the peak of the V), preferably shaped like a flat horizontal strip (Figure 1).

[0028] In fact, the part 2 has a concave upper surface 4 in the central portion 2b and a convex lower surface 5 opposite the upper surface 4 and in the central portion 2b itself.

[0029] The molding device 1 comprises a preheating station 6, for example an infrared oven, in which the prehardened plates 3 are subjected to a heating operation in order to achieve softening of the prehardened plates 3, and a molding station 8 in which the prehardened plates 3, after being heated in the preheating station 6, are subjected to a compression molding operation in order to obtain the part 2.

[0030] The forming station 8 essentially comprises: a fixed support structure 9 (only partially visible in Figures 2, 3, 5, 6 and 7, as this is an innovation with respect to the known art); an upper half die 10 with a lower contoured surface 11 corresponding to the contour of the upper surface 4 of the composite part 2 to be produced by moulding; a lower half die 12 with an upper contoured surface 13 corresponding to the contour of the lower surface 5 of the composite part 2 to be produced by moulding; holding means 15 carried by the support structure 9 in a fixed position and adapted to hold the plate 3 in a sandwiched position between the upper half die 10 and the lower half die 12; a moving means (known per se and not shown) for moving one or both of the upper half die 10 and the lower half die 12 away from the plate 3 and towards the plate 3 in a direction A across the plate 3 itself; Equipped with.

[0031] In the illustrated case, the contoured surface 11 of the upper half die 10 has two laterally opposite flat horizontal portions 11a arranged on the same alignment plane and a central portion 11b which defines a protrusion having a substantially V-shaped outline, i.e. formed by two oblique portions which start from the laterally opposite portions 11a and converge towards each other to a common edge (i.e. the peak of the V) which is preferably shaped like a flat horizontal strip.

[0032] The undulating surface 13 of the lower half die 12 has a shape complementary to that of the undulating surface 11 of the upper half die 10 and has two flat horizontal portions 13a on either side of the lateral surface arranged on the same plane of arrangement, and a central portion 13b which defines a cavity having a substantially V-shaped outline, i.e., formed by two oblique portions which start from the either side of the lateral surface 13a and converge towards each other to a common edge (i.e., the peak of the V) which is preferably shaped like a flat horizontal strip.

[0033] The lateral portions 11a, 13a are intended to form the lateral portions 2a of the part 2, while the central portions 11b, 13b are intended to form the central portion 2b of the part 2 that is produced by molding.

[0034] It will be apparent that the part 2 shown herein is only one example of a composite part or component that can be produced by a molding apparatus in accordance with the teachings of the present invention, and that a variety of composite part shapes can be produced simply by varying the configuration of the contoured surfaces 11, 13 of the upper and lower half dies 10, 12, as will be explained below.

[0035] Advantageously, the holding elements 15 comprise respective releasable grippers 16 configured to grip separate portions of the outer edge 18 of the plate 3 by friction and to completely release or allow complete release of the plate 3 itself when the plate 3 is compressed between the upper half die 10 and the lower half die 12 during the forming operation.

[0036] In practice, the gripper 16 is configured to exert a holding force on the plate 3 that is smaller than the thrust that the plate 3 itself receives in the direction of withdrawal from the gripper 16 when compressed between the upper half die 10 and the lower half die 12.

[0037] In this way, the gripper 16 is configured to release the plate 3 and in use completely releases the plate 3, and more precisely completely releases the outer edge 18 of the plate 3 itself when the plate 3 is compressed between the upper half die 10 and the lower half die 12 in the forming operation.

[0038] As shown in Figures 2, 3 and 5, the support structure 9 comprises a frame element 20, in this case having a rectangular outer shape, having a plurality of attachment areas 21 for selectively fixing a desired number of grippers 16 which correlates with the shape of the plate 3 to be formed and the holding force desired to be obtained on the plate 3 itself.

[0039] In the illustrated case, two grippers 16 are used, which are fixed to each of the two short sides of the frame element 20 and which cooperate with laterally opposite portions of the outer edge 18 of the plate 3 .

[0040] As can be seen in Figures 2, 3, 5, 6 and 7, the gripper 16 is secured internally to the frame element 20 via a support arm 22 that is variable or extendable in length to accommodate the various contours of the plate being formed.

[0041] 2 to 7, each gripper 16 has two jaws 23, 24 hinged to one another about a common axis B parallel to the respective sides of the frame element 20 to which the gripper 16 itself is fixed, and the two jaws 23, 24 are movable between a closed state (FIGS. 4 and 7) and an open state (FIG. 6).

[0042] In particular, in the closed state, the jaws 23, 24 of each gripper 16 frictionally hold a respective portion of the outer edge 18 of the plate 3, while in the open state, the jaws 23 and 24 of each gripper 16 move away from each other compared to the closed state, allowing the plate 3 to be inserted or removed.

[0043] The hinge axis B of the jaws 23, 24 of each gripper 16 is perpendicular to the direction A and parallel to the respective side of the outer edge 18 of the plate 3 on which the jaws 23, 24 act.

[0044] With particular reference to the solution shown in Figures 4, 6 and 7, the jaw 23 of each gripper 16 is arranged below the jaw 24, is fixed to the respective support arm 22 and projects from the respective support arm 22 in the same direction of extension towards the inside of the frame 20, the jaws 23 having a substantially flat front working part 25 extending from the region of the hinge with the associated jaw 24 and defining a support for a respective part of the outer edge 18 of the plate 3.

[0045] The jaw 24 of each gripper 16 also extends from the hinge area with the associated jaw 23 and has a front acting portion 26 which is substantially V-shaped with the recess facing towards the jaw 23 itself and which cooperates with the associated plate 3 along a line or strip of the associated plate 3.

[0046] The hinge area between jaws 23 and 24 of each gripper 16 includes a pin 27 of axis B, with one or more arms 28 wrapped around pin 27 and secured to jaw 23, and one or more arms 29 also wrapped around pin 27 and secured to jaw 24.

[0047] Furthermore, each gripper 16 comprises actuator means 30 configured to load one or both of the associated jaws 23 , 24 towards a closing configuration and to define a holding force on the associated plate 3 .

[0048] In the illustrated case, the actuator means 30 of each gripper 16 comprises a spring 31, in particular having a cylindrical spiral, wound around the associated pin 27 and acting on the jaws 23, 24 via the respective arms 28, 29 to urge these jaws 23, 24 towards the closed state.

[0049] According to a possible alternative not shown, the actuator means 30 may comprise hydraulic or electric actuators with automatic adjustment of the closing force acting on the jaws 23 , 24 of each gripper 16 .

[0050] Furthermore, each gripper 16 is provided with an operating part 32 carried by one of the jaws 23, 24, extending rearward from the hinge region B relative to the respective working part 25, 26 and which can be operated from the outside to open the gripper itself.

[0051] In the illustrated case, the handle 32 is constituted by a plate which is fixed at its end 32a to the jaw 24 near the hinge region and which projects rearward in the manner of a cantilever from the jaw 24 itself. More precisely, the handle 32 of each gripper 16 has a free end 32b opposite the end 32a which starts from the hinge region and extends rearward of the jaw 23 so as to widen away from the jaw 23 and is slightly bent towards the jaw 23 itself.

[0052] With particular reference to Figures 5, 6 and 7, the forming apparatus 1 also comprises further actuator means 33 which act on the operating portion 32 of the gripper 16 to move the gripper 16 itself into the open position.

[0053] In the illustrated case, the actuator means 33 comprises a further frame element 34, preferably having a rectangular outer shape, which is displaceable from and towards the frame element 20 carrying the gripper 16 and which comprises a pushing portion 35 which simultaneously acts on the operating portion 32 of the gripper 16 itself.

[0054] In particular, the pushing portions 35 are preferably constituted by cylindrical elements which project perpendicularly in the manner of a cantilever from the frame elements 34 parallel to the direction A and which are located on the operating portions 32 of the grippers 16 and which are configured to act simultaneously on all operating portions 32 against the action of the respective springs 31 upon movement of the frame elements 34 towards the frame elements 20 in order to move the jaws 24 away from the respective jaws 23 and place the grippers 16 in the open state.

[0055] According to a possible alternative not shown, the actuator means 33 may comprise a plurality of actuator members, for example of the fluid type, acting individually on the operating parts 32 of the respective grippers 16 .

[0056] 8A, 8B and 8C show other possible examples, designated by the reference numerals 2', 2" and 2'", of composite parts or components that can be produced by the molding device according to the invention, starting from a plate of composite material with a thermoplastic matrix. It is clear that to obtain parts 2', 2", 2"', it may be necessary to modify the shape of the undulating surfaces 11, 13 of the half dies 10, 12 and to start from a plate with different contours and proportions than those of plate 3.

[0057] Part 2' in Figure 8A has a substantially S-shaped profile, while part 2'' in Figure 8B has a substantially U-shaped profile, and finally part 2''' in Figure 8C has a substantially U-shaped profile with flat lateral protrusions on either side extending in opposite directions from the free ends of the U.

[0058] The operation of the forming device 1 will be described below for the production of single parts 2 starting from respective pre-set plates 3 having a flat rectangular form.

[0059] In particular, the plate 3 is first subjected to a preheating operation in a preheating station 6 in order to soften the material from which the plate 3 is made.

[0060] The preheated plate 3 is then conveyed to the forming station 8 and fixed by the grippers 16 in the desired position between the upper half die 10 and the lower half die 12. More precisely, by lowering the frame element 34 along the direction A onto the frame element 20, the pushing parts 35 cooperate by pushing action with the operating parts 32 of the grippers 16, which are fixed to the frame element 20 itself (FIG. 6). The operating parts 32 of the jaws 24 are simultaneously lowered towards the respective jaws 23, causing the jaws 24 to rotate relative to the respective jaws 23 about the pins 27 until they reach the open state.

[0061] In this state, the plate 3 is inserted so that its outer edge 18 rests on the front part 25 of the jaw 23, and then the frame element 34 is moved upward again, which frees the operating part 32 of the jaw 24 so that the jaw 24 can rotate about the pin 27 until it reaches the closed position (Figures 2, 3, 4, 5, 7).

[0062] Once the plate 3 is positioned on the support structure 9 in a position sandwiched between the upper half die 10 and the lower half die 12, the actual forming operation can proceed by moving either or both of the half dies 10, 12 themselves towards the plate 3.

[0063] As soon as the plate 3 is compressed between the contoured surfaces 11 , 13 of the half dies 10 , 12 , the force exerted by the half dies on the plate 3 causes the plate 3 to release itself completely from the grippers 16 .

[0064] After the half dies 10, 12 are opened, the finished part 2 can be removed.

[0065] By examining the properties of a molding apparatus 1 constructed in accordance with the teachings of the present invention, the advantages that can be obtained with such a molding apparatus become apparent.

[0066] In particular, thanks to the fact that the starting plate 3 is clamped at its outer edge directly between the grippers 16 and is later released by the grippers 16 themselves when compressed between the two half dies 10, 12, the finished part 2 no longer has any fastening lugs that are initially provided and then removed after the forming operation. This allows for a significant reduction in scrap both when cutting the starting plate from the sheet of pre-consolidated composite material, since no fastening lugs need to be cut out, and after forming, since no material needs to be removed from the formed part.

[0067] Finally, it is evident that modifications and variations can be made to the forming device 1 described and illustrated herein without departing from the scope of protection defined by the claims.

Claims

1. A compression molding device (1) adapted to produce a composite part (2, 2', 2'', 2''') starting from a plate (3), in particular a flat plate, of a composite material with a thermoplastic matrix, comprising: a fixed support structure (9); an upper half die (10) with a first contoured surface (11) corresponding to the contour of the upper surface (4) of the part (2, 2', 2'', 2''') made of composite material to be produced by moulding; a lower half die (12) with a second contoured surface (13) corresponding to the contour of the lower surface (5) of the part (2, 2', 2'', 2''') made of composite material to be produced by moulding; holding means (15) carried by the support structure (9) in a fixed position and adapted to hold the plate (3) in a position sandwiched between the upper half die (10) and the lower half die (12); - a moving means for moving at least one of the upper half die (10) and the lower half die (12) from the plate (3) and further towards the plate (3) in a direction (A) across the plate (3) itself; An apparatus (1) comprising: the holding means (15) comprising two or more releasable grippers (16) that grip distinct portions of the outer edge (18) of the plate (3) by friction; The device (1) is characterized in that as soon as the plate (3) is compressed between the upper half die (10) and the lower half die (12) during molding, the force exerted by the upper half die (10) and the lower half die (12) on the plate (3) causes the plate (3) to completely release itself from the grippers (16).

2. 2. The device according to claim 1, wherein the grippers (16) are configured to exert a holding force on the plate (3) that is smaller than the thrust force that the plate (3) itself receives in the direction of withdrawal from the grippers (16) when compressed between the upper half die (10) and the lower half die (12).

3. 3. The apparatus according to claim 1 or 2, wherein the support structure (9) comprises a frame element (20) having a plurality of attachment areas (21) for selectively fixing a desired number of grippers (16) that correlates with the shape of the plate (3) to be formed and the holding force desired to be obtained on the plate (3) itself.

4. 4. The device according to claim 3, wherein the gripper (16) is fixed internally to the frame element (20) via a support arm (22) of variable or extensible length.

5. 5. The device according to claim 2, wherein each gripper (16) comprises two jaws (23, 24) hinged to one another and movable between a closed state in which they frictionally hold a respective portion of the outer edge (18) of the plate (3) and an open state in which they are moved apart to allow insertion or removal of the plate (3), and wherein each gripper (16) further comprises first actuator means (30), in particular elastic means (31), configured to apply a load to one or both of the jaws (23, 24) towards the closed state and to determine the holding force on the plate (3).

6. 6. The device according to claim 5, wherein one of the jaws (23, 24) of each gripper (16) has a substantially flat front action (25) defining a support for an associated portion of the outer edge (18) of the plate (3), and the other of the jaws (23, 24) of the gripper (16) has a substantially V-shaped front action (26) with a recess facing towards the one of the jaws (23, 24) so ​​as to cooperate with the associated plate (3) along a line or strip of the associated plate (3).

7. An apparatus as described in Claim 6, wherein the substantially flat front acting portion (25) and the substantially V-shaped front acting portion (26) extend from a common hinge area (B) of each of the jaw portions (23, 24) themselves.

8. 8. The device according to claim 7, wherein each of the grippers (16) comprises an operating portion (32) carried by one of the jaws (24) and extending rearward from the hinge region (B) relative to the respective front operating portion (26), and the device (1) further comprises second actuator means (33) acting on the operating portion (32) of the gripper (16) to move the gripper (16) itself into the open state.

9. The device according to claim 8, which relies on claim 5, which relies on claim 3 or 4, wherein the second actuator means (33) comprises a second frame element (34) displaceable from and towards the frame element (20) carrying the gripper (16), the second frame element (34) comprising a pushing portion (35) which simultaneously acts on the operating portion (32) of the gripper (16) itself.

10. 10. The apparatus according to any one of claims 1 to 9, further comprising heating means (6) for softening the plates (3) before subjecting them to a compressive action between the upper half die (10) and the lower half die (12).

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