Method and tool for manufacturing a quadrilateral shell made of composite material

Abstract

The present invention relates to a method for manufacturing a quadrilateral shell having five sides and non-deployable three-sided connectors between said sides, said method comprising the steps of: i. cutting plies (210, 220) containing continuous fibers covering the five sides of the shell outside a three-sided connector zone; ii. obtaining four connector components (320) consolidated in the shape of said three-sided connector, each of said components comprising an integration zone (321) between said plies; iii. positioning and stacking the plies obtained in step i); iv. inserting the four consolidated components (320) into the three-sided connection zone by inserting the integration zone between two plies to obtain a preform; v. Performing consolidation of the stack of fiber plies by placing the preform in a tool (502, 602) and subjecting the assembly obtained in step iv) to a predetermined pressure / temperature cycle.

Description

[Technical Field]

[0001] The present invention relates to a method and tool for manufacturing a quadrilateral shell made of composite material.

[0002] The invention is primarily, but not exclusively, applied in the field of luggage for the manufacture of suitcases or trunks with rigid shells. [Background technology]

[0003] Referring to prior art FIG. 1, a suitcase or rigid trunk generally comprises two rectangular shells (100) of equal or different depths (only one of which is shown in this figure), which comprise five sides assembled by hinges and a closing mechanism.

[0004] Each shell has a base (101) and a flanged edge (102).

[0005] According to an exemplary embodiment, the shell is made of a thermoplastic polymer, reinforced or not with short or continuous fibers depending on the embodiment.

[0006] The so-called continuous fibers (110) extend from one free edge (191) of the shell to the other free edge (192). This definition of continuous reinforcement will be retained throughout this text.

[0007] If the shell is made of a composite material reinforced by continuous fibers, this is obtained, for example, by stacking fiber plies pre-impregnated with the polymer that constitutes the matrix, which are then molded and solidified in shape by a thermocompression process during a subsequent step.

[0008] US Pat. No. 5,629,999 describes an example of such a method for forming a stack of fiber plies by hot compression.

[0009] The connection zones (121, 122) between the faces of the shell, especially the three-sided connection zones (121) or "trunk corners", are critical zones in the implementation of this method, especially when the reinforcing fibers used have little or no plasticity at the molding temperature, or when the stiffness of the reinforcing fibers prevents them from following this complex contour.

[0010] The three-sided connection (121) generally describes the surface as a portion of a sphere or a portion of an ellipsoid.

[0011] First, it is difficult to conform these shapes without wrinkling the plies, especially at the corners (121) of the trunk, which are non-deployable zones.

[0012] It is difficult to apply pressure to these zones without using punches with movable or expandable parts and therefore complex tooling.

[0013] It is difficult to ensure uniform heating temperatures in these zones by implementing rapid heating and cooling tools such as those described in US Pat. No. 5,649,499.

[0014] Even if wrinkle formation is successfully avoided, for example by tensioning the fibers during molding, by successfully providing uniform heating and sufficient pressure for consolidation in the above zones, the phenomenon of polymer squeezing between the fibers may occur, which leads to localized deficiencies and the appearance of defects in the polymer matrix.

[0015] Thus, while the apparatus and method described in the '691 patent is generally satisfactory for producing shallow deep-drawn shells, such as protective shells for mobile phones, the cost of implementing the method remains high for continuous fiber reinforced shells with relatively deep drawn sections, such as those used in luggage applications.

[0016] Patent document 2 describes a luggage element comprising two shells made of polymer reinforced with polymer fibers. The shells are obtained by assembling polymer matrix panels reinforced with polymer fibers, more specifically the bottom panel, with the side panels in a thermocompression / overmolding operation. Thus, although each panel is individually reinforced with continuous polymer fibers, the resulting shell is not reinforced by a continuous reinforcement extending between the two free edges of the shell. [Prior art documents] [Patent documents]

[0017] [Patent Document 1] European Patent No. 2694277 [Patent Document 2] European Patent No. 3096643B1 Summary of the Invention [Means for solving the problem]

[0018] The present invention aims to overcome the drawbacks of the prior art and to this end relates to a method for manufacturing a quadrilateral shell with five faces having flanged edges and non-developable three-sided connections between said faces, said method comprising the following steps: i. cutting a ply containing continuous fibers, the fibers extending from one free edge of the shell to the other free edge, the ply being notched so as not to cover a three-sided connection zone; ii. obtaining four consolidated connection parts having the shape of the three-sided connection, each of the parts comprising an integration zone for insertion between the plies; iii. positioning and stacking the plies obtained in step i); iv. inserting the four consolidated parts into the three-sided connection zone by inserting the integration zone between two plies to obtain a preform; v. Consolidation of the stack of fibre plies is carried out by placing the preform in a tool and subjecting the assembly obtained in step iv) to a predetermined pressure-temperature cycle.

[0019] The fibre plies thus cover only the deployable zone and are easily installed in or on the tool without forming any wrinkles, nevertheless the composite part obtained is reinforced with continuous fibres extending from one free edge of the shell to the other, which ensures the stiffness and robustness of the shell.

[0020] The corners of the trunk are perfectly integrated after hardening without any visual defects.

[0021] The present invention is implemented according to the embodiments and variants described below, which should be considered individually or according to any technically valid combination.

[0022] According to one embodiment, the connection piece is made of a thermoplastic polymer and is obtained by a plastic injection molding process, a mass production process that is economical and reproducible with regard to the shapes obtained.

[0023] Alternatively, the connecting piece is obtained by a thermocompression process.

[0024] Advantageously, the polymers that make up the connecting parts are reinforced with short fibers, thus improving the mechanical resistance of these parts.

[0025] Advantageously, the polymers constituting the connecting piece are chosen so that the maximum consolidation temperature applied to the assembly during step v) is above the glass transition temperature of the polymer but below the melting point of the polymer, so that the shape of the three-sided connecting piece adapts to the shape of the shell during the consolidation step.

[0026] According to one embodiment, the connecting piece extends between the flanged edges of the molded shell, which allows for easier cutting of the plies.

[0027] According to one embodiment, step v) is carried out in a tool comprising a pair of punches and dies, the assembly obtained in step iv) being included between the punch and the die during step v).

[0028] According to another embodiment, step v) comprises covering the assembly obtained in step iv) with an impermeable tarpaulin and evacuating the space comprised between the tarpaulin and the tool.

[0029] The present invention will now be disclosed according to its preferred embodiments, which are in no way limiting, with reference to Figures 1 to 6. [Brief explanation of the drawings]

[0030] [Figure 1] FIG. 1 shows in perspective view an example of a part that can be produced by the method of the present invention. [Figure 2A] FIG. 2A shows a top view of an example of a cutout in a ply for manufacturing a part according to the method of the present invention. [Figure 2B] FIG. 2B shows a top view of another example of a ply cutout for the manufacture of a shell according to the method of the present invention. [Figure 3] FIG. 3 shows, in partial cross section, an example of the placement in a tool of a preform produced by the method of the invention. [Figure 4] FIG. 4 shows in a perspective view an embodiment of a connection piece for the implementation of the method of the invention. [Figure 5] FIG. 5 shows in cross section an example of a tool for the implementation of the method of the invention. [Figure 6] FIG. 6 shows in cross section another example of a tool for the implementation of the method of the invention. DETAILED DESCRIPTION OF THE INVENTION

[0031] According to one embodiment, the method and device of the present invention are implemented for the mass production of prior art rectangular shells made of a composite material comprising a thermoplastic polymer matrix reinforced with continuous fibers (290).

[0032] However, the invention is not limited to this embodiment and can be implemented using plies pre-impregnated with a thermosetting polymer.

[0033] For this purpose, the preform is made by layering fiber plies (210, 220) containing continuous fibers (290), at least one of said fiber plies (210, 220) comprising continuous fibers (290) that extend from one free edge (291) to another free edge (292) of the shell when said shell is manufactured according to the method of the invention.

[0034] By way of non-limiting example, the fiber plies may be composed of natural fibers, such as glass fiber, carbon fiber, flax, bamboo, or sisal fiber, or polymeric fibers, in the form of a woven or nonwoven fabric, coated with a thermoplastic polymer, co-blended with a thermoplastic polymer, or co-laminated with a thermoplastic polymer film.

[0035] The fiber plies are pre-cut so that the plies (210, 220) that extend over the entire surface of the shell and cover the five faces of the shell are provided with cutouts (221, 222) so that they do not cover the connection zones between the faces of the shell.

[0036] Referring to FIG. 2A, in one embodiment, the ply (210) is provided with a cutout (222) so as not to cover the connection zone between the flanged edges of the shell that the ply (210) is intended to cover, said cutout including a three-sided connection zone.

[0037] Referring to FIG. 2B, according to another embodiment, the ply (220) includes cutouts (221) at the corners of the three-sided connection zone or trunk between the surfaces that the ply (220) covers.

[0038] These embodiments are not limiting, and similar results can be achieved, for example, by alternating rectangular plies whose longer dimension extends along the Y axis with rectangular plies whose longer dimension extends along the X axis, to simplify the cutouts.

[0039] Referring to Figure 2B, the same principles apply to the configuration shown in this figure.

[0040] Regardless of the embodiment, the cutouts (222, 221) are adapted to the shape of the connection zones at the corners of the trunk of the final part, in particular the connection radii between the faces.

[0041] Referring to FIG. 2B, the cutout (221) in the ply (220) is shown as a circular cutout, however, if the target connection at the corner of the final shell trunk has a shape other than spherical, the cutout may have an elliptical or trilobal cross-sectional shape.

[0042] Due to the presence of these cutouts, the plies do not cover the non-developable zones of the final part, and they are easily applied onto or into a tool having the shape of the part to be manufactured by folding them along the fold lines (215, 225) to form flanged edges.

[0043] Advantageously, the dimensions of the plies are variable according to their position in the stack to take into account the variation in the joint radius between the faces according to the thickness of the shell to be produced.

[0044] The plies (210, 220) are layered in the shape of the shell to be produced on a punch-type tool with relief or on a hollow die-type tool.

[0045] Depending on the nature of the polymer that constitutes the matrix of the composite, the polymer is present in the ply in the form of a co-laminated film or a coating of co-mixed fibers, and depending on the joint radius between the faces of the shell, the folding of the ply is carried out by locally heating the ply in the folding zone, for example with a soldering iron or any other suitable means.

[0046] Advantageously, during layering, the plies are welded together by spots or weld lines so that the assembly is stable and easy to handle.

[0047] Referring to Figure 3, the connection between the plies (210, 220) in the connection zones corresponding to the cutout zones (221, 222) of the plies is performed by a connection part (320) in a tool (300), in which the die is provided with an imprint having the shape of a shell.

[0048] Said connection piece (320) has a shape similar to the connection surface in said connection zone between the faces of the shells and comprises a fixing portion (321) adapted to be embedded between the plies (210, 220) at the edge of the cutting zone (221, 222).

[0049] 4, according to one embodiment, the connection piece (320) comprises two parts (421, 422), separate or integral with each other, one of which (421) corresponds to the three-sided connection zone and the other (422) corresponds to the substantially deployable connection zone between the faces.

[0050] The fastening portion (321) is shown here as simple, but depending on the embodiment it may be provided with reliefs to perfect the grip between the plies.

[0051] According to one embodiment (not shown), the connecting piece comprises an arrangement for the installation of caster wheels for supporting the casing or for the passage of the arms of a telescopic handle.

[0052] The connecting parts can be of any kind, in particular made of plastic, metal or composite material.

[0053] Said connection parts are obtained by implementing methods adapted to their properties and are manufactured independently of the shell, so that they can be mass-produced in a manufacturing unit remote from that of the shell.

[0054] According to an advantageous embodiment, the connection part is made of a thermoplastic polymer and is obtained by plastic injection molding or by thermocompression.

[0055] According to one alternative of this embodiment, the connection piece is made of a thermoplastic polymer reinforced with short fibers.

[0056] According to an advantageous embodiment, the melting point of the polymer constituting the connecting part is higher than the melting point (in the case of a thermoplastic polymer) or the curing temperature (in the case of a thermosetting polymer) of the polymer impregnating the ply constituting the rest of the shell.

[0057] Advantageously, the glass transition temperature of the polymer that makes up the connecting parts is lower than the melting point or hardening temperature of the polymer that impregnates the plies that make up the rest of the shell, so that during consolidation or hardening of the assembly, the connecting parts have a certain plasticity that allows them to adapt their shape to the mould.

[0058] Referring to Figure 5, according to a first embodiment, the consolidation of the assembly including the laminate and the connecting parts is carried out in a mould comprising a pair of punches (501) and dies (502).

[0059] The punch and die are mounted on the platen, one on the moving part of the press.

[0060] The punch and / or die advantageously comprise a heating network comprising inductors (510) extending into the cavities made in the punch and die and distributed in such a way as to obtain a uniform heating temperature of the preform when said inductors are supplied with an alternating current having a frequency between 10 kHz and 100 kHz.

[0061] The spatial distribution of the inductors within the die or punch is obtained using thermal simulations that implement, for example, finite element calculations.

[0062] The punch and / or die are preferably made of a material with good thermal conductivity and high thermal effusivity, such as an aluminum alloy or a copper alloy.

[0063] This property is advantageous for rapid heating and rapid transfer of heat from the mold to the preform, but also contributes to obtaining uniformity of temperature on the surface of the punch or die that contacts the preform during consolidation.

[0064] Referring to FIG. 5, as shown in the detailed view, the walls of the cavity include a layer (515) made of a material that is sensitive to induction heating, such as ferromagnetic steel or a nickel alloy, examples of which are not limiting.

[0065] This layer (515) is approximately 1 mm thick.

[0066] According to one embodiment, the layer of material sensitive to induction heating (515) does not cover the entire surface of the cavity, but only the section of the cavity oriented towards the surface of the mold that will be in contact with the preform.

[0067] This property allows the heat to be directed towards the preform, resulting in a uniform distribution of the heating temperature of the preform without heating the entire mold.

[0068] According to another embodiment, the mold is made entirely from steel that is ferromagnetic at the desired molding temperature.

[0069] When an alternating current is applied to the inductor (510), the layer (515) that is sensitive to induction heating increases in temperature and transfers the heat to the die or punch, which in turn transfers the heat to the preform.

[0070] The mould also comprises cooling means (520) in the form of ducts through which a heat transfer fluid such as water, oil or gas circulates.

[0071] This cooling circuit allows for rapid cooling of the mold and consolidated preform, thereby shortening the production cycle.

[0072] According to one embodiment, the punch (501) comprises an inflatable bladder (530) and means (535) for inflating said bladder.

[0073] The mold further comprises means (540) for sealing between the punch (501) and the die (502) when the mold is closed, i.e. when the punch is brought into close proximity to the die using a press.

[0074] Thus, when the mold is closed, the preform is contained within a sealed cavity defined between the punch (501) and the die (502).

[0075] According to an embodiment more particularly adapted for the case where the plies (210, 220) comprise a thermoplastic polymer, a preform integrating the connecting part (320) is placed in a die (502) or on a punch (501).

[0076] Previously, the preform is assembled by assembling the plies (210, 220) and the connecting piece (320) directly in one of the mold's tools, ie punch or die, or in a separate tool.

[0077] In the case of plies pre-impregnated with a thermoplastic polymer, the plies are held together with each other and with the connecting components by weld spots or weld lines.

[0078] This pre-assembly of the preform is carried out manually or robotically.

[0079] The die is brought into close proximity with the punch to form a sealed cavity containing the preform.

[0080] According to one embodiment, the cavity is evacuated to a vacuum by suitable means (not shown).

[0081] In parallel, the inductor (510) is powered with an alternating current, which has the effect of heating the preform to a temperature at least equal to the melting point of the thermoplastic polymer with which the plies are impregnated.

[0082] These configurations allow the connection element (320) to retain its integrity at this temperature, but advantageously, according to one embodiment, if the connection element is made of an injection-molded polymer or formed by thermocompression, the glass transition temperature of the polymer that makes up the connection element (320) is below the melting point of the polymer that impregnates the ply.

[0083] Further pressure is applied to the preform by moving the punch towards the die and / or by inflating the bladder (530) of the punch.

[0084] This application of pressure makes it possible to calibrate the final thickness of the part and ensure a uniform distribution of the polymer thickness.

[0085] The connecting parts (320), when made of polymer, have a relatively high malleability, and when the additional pressure is applied, the pressure causes the connecting parts (320) to conform to the shape of the mold, thus ensuring an aesthetically perfect connection between the ply and the connecting parts.

[0086] The inductor is de-energized and heat transfer fluid is directed through duct 520, thereby cooling the mold and preform while still maintaining pressure on the preform.

[0087] Once the temperature of the preform is below the glass transition temperature of the polymer impregnating the plies, the mold can be opened and the part removed from the mold.

[0088] The cycle then continues with a new preform.

[0089] Using induction heating and forced cooling, this cycle can be completed in less than five minutes.

[0090] Referring to Figure 6, according to an exemplary embodiment, a tool for implementing the method of the present invention comprises: a convex or concave shape (602) on or in which a preform with a connection part is placed; a tarpaulin (630); and means (640) for sealing the space between said tarpaulin (630) and the tool (602).

[0091] Thus, the preform placed in or on the tool is contained in a sealed cavity between said tool and the tarpaulin (630).

[0092] This embodiment is well suited to, but not exclusive to, impregnating the plies of the preform with a thermosetting polymer.

[0093] As in the previous embodiment, the tool is provided with induction heating and cooling means.

[0094] Means (not shown) make it possible to evacuate the space contained between the tarpaulin (630) on which the preform is placed and the wall of the tool (602).

[0095] An intermediate piece (650) made of compressible material is placed between the tarpaulin (630) and the preform of the connecting piece.

[0096] The non-developable zone preform therefore ensures that the formation of wrinkles in the tarpaulin (630), more particularly in the connection zones, is limited to these non-developable zones, where they do not affect the quality of the final part due to the presence of the connection and intermediate parts (650). This property also allows the manufacturing costs of the tarpaulin (630) to be reduced.

[0097] According to this embodiment, with the preform placed on or in the tool and the tarpaulin in place, the inductor is powered by alternating current to bring the preform to the curing temperature (or melting point in the case of a thermoplastic polymer) of the polymer impregnated in the plies of the preform, while at the same time evacuating the space between the tarpaulin in which the preform is placed and the tool.

[0098] The tarpaulin provides uniform pressure to all the plies of the preform.

[0099] The pressure and temperature are maintained for the duration of the cure cycle, after which cooling means are used to cool the mold and the part thus produced, and the vacuum is then released to remove the part from the mold.

[0100] With reference to FIG. 5, those skilled in the art will appreciate that the illustrated tool can also be used to cure preforms that include plies impregnated with thermosetting polymers.

[0101] With reference to FIG. 6, those skilled in the art will appreciate that the illustrated tool can also be used for consolidating preforms that include plies impregnated with thermoplastic polymers.

[0102] The above description and embodiments show that the present invention achieves its intended purpose and allows continuous fiber reinforced composite parts in the form of deep deep drawn rectangular shells to be obtained from fiber plies pre-impregnated with thermoplastic or thermosetting polymers without resorting to complex draping or deep drawing techniques.

[0103] The method of the present invention is therefore adapted to the acquisition of such parts in the mass production of consumer goods such as luggage products.

Claims

1. 1. A method for manufacturing a quadrilateral shell having five faces with flanged edges (102) and non-developable three-sided connections (121) between said faces, said method comprising the following steps: i. cutting plies (210, 220) containing continuous fibers (290), the continuous fibers extending from a free edge (291) of the ply to another free edge (292), the ply being provided with cutouts (221, 222) so as not to cover a three-sided connection zone; ii) Obtaining four consolidated connection parts (320) having the shape of the non-deployable three-sided connection, each of the consolidated connection parts comprising an integration zone (321) for insertion between the plies; iii) Positioning and stacking the plies obtained in step i); iv. Inserting the four consolidated connection pieces (320) into the three-sided connection zone by inserting the integration zone between two of the plies to obtain a preform; v. placing said preform in a tool (502, 602) and carrying out consolidation by subjecting the preform obtained in step iv) to a predetermined pressure and temperature cycle; A method comprising:

2. The method described in claim 1, wherein the four solidified connecting parts (320) are made of a thermoplastic polymer.

3. The method described in claim 2, wherein the thermoplastic polymer constituting the four solidified connecting parts (320) is reinforced with short fibers.

4. The method of claim 1, wherein the four solidified connecting parts are obtained by plastic injection molding.

5. The method described in claim 1, wherein the four consolidated connecting parts (320) are obtained by a thermal compression method.

6. The method described in claim 2, wherein the thermoplastic polymers constituting the four consolidated connecting parts are selected so that the maximum consolidation temperature applied to the preform during step v) is higher than the glass transition temperature of the thermoplastic polymer but lower than the melting point of the thermoplastic polymer.

7. The method of claim 1, wherein after step v), the four solidified connecting parts (320) extend between the flanged edges of the rectangular shell.

8. The method described in claim 1, wherein the tool comprises a pair of punches (501) and dies (502), and the preform is contained between the punch and the die during step v).

9. 2. The method of claim 1, wherein step v) comprises covering the preform with an impermeable tarpaulin (630) and evacuating the space contained between the tarpaulin and the tool.

10. 2. The method according to claim 1, wherein the rectangular shell is configured to fit into a luggage element, and the connecting parts of the three-sided connection include a configuration for installing caster wheels for supporting the casing or for passing the arms of a telescopic handle.

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