METHOD FOR CLOSING AN INJECTION MOLD USING CAP SAFETY STRIPS

Description

Technical Field

[0001] The present invention relates to the general field of manufacturing parts of revolution such as gas turbine housings. Previous technique

[0002] In the aeronautical field, the aim is to reduce the mass of engine components while maintaining high levels of mechanical properties. For example, in an aeronautical turbomachine, the fan casing, which defines the contour of the engine's air intake and houses the rotor supporting the fan blades, is now made of composite material.

[0003] The manufacturing process for a blower housing made of composite material begins with the winding of a fiber reinforcement onto a mandrel whose profile matches that of the housing to be produced. The fiber reinforcement can be created, for example, by three-dimensional or multi-layer weaving, as described in US patent 8,322,971. This fiber reinforcement is then shaped into a single piece comprising a tubular portion and flanges corresponding to the housing's mounting points. The manufacturing process continues with the densification of the fiber preform using a polymer matrix. This involves impregnating the preform with a resin and then polymerizing the resin to obtain the final part.

[0004] The invention relates more particularly to a manufacturing method in which the impregnation of the fibrous preform is carried out by the injection molding process known as RTM (Resin Transfer Molding). According to this process, the fibrous preform is enclosed in a rigid mold of fixed geometry comprising a mandrel or drum around which the fibrous preform is wound and a counter-mold which is placed on top of the fibrous preform and whose shape corresponds to the desired part of revolution. The resin is injected under controlled pressure and temperature into the mold after the walls of the two mold parts have been brought together and a vacuum has been created if necessary. Once the resin has been injected, it is polymerized by heating the mold. After injection and polymerization, the final part is demolded and trimmed to remove excess resin, and the chamfers are machined to obtain the desired part, for example, a housing.Since the preform is bulky when it is wound onto the mandrel, meaning that it has an excess thickness compared to the theoretical thickness of the finished part, the closing of the mold also ensures the function of definitively compacting the preform to bring it to its final thickness.

[0005] There figure 1 This illustrates an RTM 300 injection mold comprising a drum or mandrel 310 around which a fibrous preform 30 is wound, and a counter-mold formed by a plurality of angular sectors 320. The mold is closed by the angular sectors 320, which ensure the compaction of the preform. A method for closing such a mold is described in particular in US patent 2018 / 370082, which discloses the preamble to claim 1.

[0006] However, closing the mold with such angular sectors proves to be a delicate operation. Indeed, as illustrated on the figure 2A First, every other sector is placed, each locally compacting the fibrous preform. The fibrous preform 30 exhibits blisters 31 near the ends of each angular sector 320 because it is no longer compacted. The mold closure continues with the positioning of the remaining angular sectors between the sectors already positioned, as illustrated in the figures. figures 2B And 2C During the placement of these sectors, the bulges 31 are pushed against the edges of the already positioned sectors because the preform is displaced from the center of the sector by compaction. Furthermore, the shape of the sectors and the direction of mold closure mean that a space remains between the sectors until the very last moment of mold closure. Some of the bulges 31 then enter this space and are ultimately pinched between the edges of adjacent sectors, as shown in the figure. figure 2C The pinched fibers of the preform lead to the creation of defects known as "pinch fibers" on the finished part. These pinched fibers appear on the finished part—that is, after the resin is injected into the preform and transformed into a matrix—as raised bumps on the external surface of the part. To achieve a satisfactory surface finish, these bumps are sanded, which disrupts the continuity of the fibers or strands within the part and, consequently, significantly reduces its mechanical properties. Description of the invention

[0007] The invention aims to provide a solution that avoids the aforementioned drawbacks.

[0008] This goal is achieved in particular through a process for closing an injection mold for manufacturing a part of revolution in composite material, the mold comprising: a mandrel supporting a fibrous preform obtained by winding a fibrous strip, the mandrel comprising an annular wall whose outer surface profile corresponds to that of the inner surface of the part to be manufactured, a plurality of angular sectors comprising an annular base intended to come into contact with the fibrous texture, the annular base extending between first and second longitudinal edges along an axial direction and between first and second lateral edges along a circumferential direction, the annular base of each sector having a shape corresponding to the shape of the part of revolution to be manufactured, the method comprising the successive positioning and fixing of the angular sectors on the mandrel, the annular base of each sector compacting the portion of fibrous preform present opposite, the lateral edges of the annular base of each angular sector being in contact with the lateral edges of the annular base of the adjacent sectors, characterized in that, before the positioning and fixing of the angular sectors on the mandrel, strips are placed on the exposed surface of the fibrous preform, each strip covering an area of ​​the fibrous preform located opposite a junction area between two lateral edges of the annular base of two adjacent angular sectors and in that each strip has a shape corresponding to the shape of the annular base of the two adjacent angular sectors at the junction area.

[0009] Thus, according to the process of the invention, the fibrous preform is protected from potential pinching between two adjacent angular sectors during mold closure. Indeed, the strips covering the preform in areas corresponding to the junction zones between the sectors prevent the portion of the preform present at the bulges from being pushed against the lateral edges of the angular sectors, thereby avoiding any pinching of the preform between the lateral edges of two adjacent sectors. Consequently, the appearance of "pinch fiber" defects on the finished part is prevented. It is therefore possible to compact the preform with each of the angular sectors without affecting the mechanical properties of the finished part.

[0010] According to a particular feature of the injection mold closing method of the invention, the strips are made of a composite material comprising a fibrous reinforcement densified by a matrix. The fibrous reinforcement of each strip may comprise carbon fibers, glass fibers, or a mixture of carbon and glass fibers. The matrix may be obtained from a resin or thermosetting or thermoplastic material.

[0011] According to another particular feature of the method of closing an injection mold of the invention, the strips are made of metallic material.

[0012] According to another particular feature of the method of closing an injection mold of the invention, in which each strip has a thickness less than or equal to 0.2mm.

[0013] According to another particular feature of the method of closing an injection mold of the invention, angular sectors are first positioned and fixed on the mandrel at a determined distance from each other so as to leave a space between two angular sectors, the remaining angular sectors then being positioned and fixed on the mandrel in the spaces left between the angular sectors already fixed.

[0014] According to another particular feature of the method of closing an injection mold of the invention, each angular sector has first and second grooves present respectively on the first and second lateral faces, the grooves extending along the axial direction, a sealing gasket being housed both in the first groove of a first lateral face of an angular sector and in the second groove of a second lateral face of an adjacent angular sector.

[0015] The invention also relates to a method for manufacturing a part of revolution made of composite material comprising: the production by three-dimensional or multi-layer weaving of a fibrous texture in the form of a strip, the winding of the fibrous texture on several superimposed turns on a mandrel of an injection mold so as to form a fibrous preform, the injection mold comprising a plurality of angular sectors, the closing of the injection mold in accordance with the invention, the densification of the fibrous preform by a matrix so as to obtain a part of revolution in composite material comprising a fibrous reinforcement densified by a matrix, the demolding of the part in composite material. Brief description of the drawings

[0016] [ Fig. 1 ] There figure 1 is a schematic perspective view of an injection mold according to the prior art, [ Fig. 2A ] There figure 2A is a partial radial cross-sectional view showing a mold closing stage of the figure 1 , [ Fig. 2B ] There figure 2B is a partial radial cross-sectional view showing another stage of mold closure of the figure 1 , [ Fig. 2C ] There figure 2C is a partial radial cross-sectional view showing another stage of mold closure of the figure 1 , [ Fig. 3 ] There figure 3 is a schematic perspective view of a blower housing made of composite material, [ Fig. 4 ] There figure 4 is a schematic perspective view of an injection mold according to an embodiment of the invention, [ Fig. 5 ] There figure 5 is a schematic perspective view showing an angular sector of the mold of the figure 4 , [ Fig. 6 ] There figure 6 is another schematic perspective view showing an angular sector of the mold of the figure 4 , [ Fig. 7 ] There figure 7 is a schematic perspective view showing a strip of the mold of the figure 4 , [ Fig. 8 ] There figure 8 is another schematic perspective view showing a strip of the mold of the figure 4 , [ Fig. 9A ] There figure 9A is a partial radial cross-sectional view showing the beginning of the positioning of an angular sector during the closing of the mold of the figure 4 , [ Fig. 9B ] There figure 9B is a partial radial cross-sectional view showing the mold of the figure 4 farm, [ Fig. 10 ] There figure 10 is a radial and axial cross-sectional view of the mold of the figure 9B . Description of the implementation methods

[0017] The invention applies generally to any gas turbine housing made of organic matrix composite material.

[0018] The invention will be described below in the context of its application to a blower housing for an aeronautical gas turbine engine.

[0019] There figure 3 Figure 10 shows a perspective view of a blower housing that can be manufactured using a mold and a method according to the invention. Such a housing is centered on a longitudinal axis XX and comprises an annular wall 11 delimited upstream by an upstream flange 12 and downstream by a downstream flange 13 (upstream and downstream being defined with respect to the direction of gas flow in the gas turbine). The internal surface 14 of the annular wall 11 is intended to delimit the air inlet duct in the gas turbine and / or to support panels (acoustic attenuation, abradable, etc.).

[0020] There figure 4 This is a schematic perspective view of a mold according to the invention during the closing process. Such a mold can be used for impregnating a fibrous preform using a Resin Transfer Molding (RTM) process to manufacture a blower housing 10 such as the one previously shown. The fibrous preform can be made by three-dimensional weaving of a strip-shaped fibrous texture with fibers, for example, of carbon, glass, aramid, or ceramic, and the impregnation matrix can be made of a polymer, for example, epoxy, bismaleimide, or polyimide.

[0021] The mold 100 is rotatably mounted on a drive shaft (not shown) centered on the axis XX, and includes a mandrel 110. The axial direction DA and radial direction DR will be defined with respect to this axis XX, the axial direction DA being parallel to the axis XX and the radial direction DR being perpendicular to the axis XX. Reference will also be made to a circumferential direction DC which, as shown in the figure 4 , corresponds to a direction that is tangent to any circle centered on the axis XX. This direction is perpendicular to both the axial direction DA and to a radial direction DR.

[0022] The mandrel 110 comprises an annular wall 111 in the form of a barrel supporting a fibrous preform 20 formed by winding a fibrous strip, and two lateral flanges 112. The mandrel 110 is held on its drive axis by means of spokes 113.

[0023] The flanges 112 form a support intended to receive the folded parts of the preform 20 wound on the mandrel 110, and which are intended to form the upstream flanges 12 and downstream flanges 13 of the blower housing 10.

[0024] The mold 100 further includes a counter-mold composed of several angular sectors 120 (here six in number) assembled in a sealed manner on the mandrel 110. In the example described here, the sectors are locked together in a sealed manner by locking keys 130 which maintain a flat gasket between the sectors (not shown in the figure 4 According to one embodiment, the sectors can be directly locked together by bolting using angled screws. In this case, the seal between the sectors is achieved by compacting a gasket housed in grooves on the lateral edges of the sectors, as explained below.

[0025] The angular sectors 120 are assembled onto the side flanges 112 by clamping screws 131 passing through orifices 122 present in the sectors 120 and screwed into tapped holes 1120 present on the side flanges 112. The screws 131 allow the assembly of the sectors 120 onto the flanges 112 and the adjustment of the compaction pressure which is applied to the fibrous preform 20.

[0026] In the example described here, the angular sectors 120 are locked together by clamping screws 141 passing through holes 132 in the locking keys 130 and screwed into tapped holes 128 on the angular sectors 120 or into bolts integrated into the tooling. A key 130 is fixed between two adjacent sectors 120 by two rows of screws 141 extending longitudinally along the ends of each sector 120. The locking keys 130 are assembled radially from the outside, once the sectors 120 are mounted on the mandrel 110. In this way, the keys ensure circumferential clamping of the sectors 120 together.

[0027] O-rings (not shown) positioned on the flanges 112 ensure the seal between the sectors 120 and the mandrel 110.

[0028] THE figures 5 et 6 illustrate an angular sector 120. Each angular sector 120 comprises an annular base 121 intended to come into contact with the fibrous texture 20. The annular base extends between first and second longitudinal edges 122 and 123 along the axial direction DA and between first and second lateral edges 124 and 125 along the circumferential direction DC, the first lateral edge 124 of the annular base 121 of an angular sector 120 being in contact with a second lateral edge 125 of the annular base of an adjacent angular sector ( figure 9B ).

[0029] The annular base 121 has a shape corresponding to that of the devolution part to be manufactured. In the example described here, the annular base 121 has an evolving shape along the axial direction DA corresponding to the evolving profile of the housing to be manufactured. More precisely, the annular base 121 includes a hollow portion 1212 corresponding to the shape of an overthickness 22 present on the preform 20 and intended to form a retention zone in the final housing ( figure 10 ). The hollow portion extending along the entire length of the annular base 121 in the circumferential direction DC.

[0030] The first lateral edge 124 of the annular base 121 of each angular sector 120 has a lower portion 1240. The second lateral edge 125 of the annular base 121 of each angular sector has a lower portion 1250.

[0031] Each angular sector 120 further comprises a first lateral face 1241 parallel to the radial direction DR and present in the extension of the first lateral edge 124 of the annular base 121, and a second lateral face 1251 parallel to the radial direction DR and present in the extension of the second lateral edge 125 of the annular base 121. This facilitates the fixing of the sectors 120 on the mandrel 110.

[0032] Furthermore, first and second grooves 1242 and 1252 may be present on the first and second lateral faces 1241 and 1251, respectively, with the grooves extending along the axial direction DA. A sealing gasket 150 is housed both in the first groove 1242 of the first lateral face 1241 of an angular sector and in the second groove 1252 of the second lateral face 1251 of an adjacent angular sector. This provides a seal between the sectors and allows the sectors to be locked directly together without the use of wrenches and flat gaskets as described above.

[0033] According to the invention, strips 200 are positioned on the exposed surface of the fibrous preform 20 before the injection mold 100 is closed by the angular sectors 120. More specifically, a strip 200 is placed at each location on the exposed surface of the preform 20 that is intended to be opposite a junction zone between two lateral edges of the annular base of two adjacent angular sectors ( figure 4 ). Each strip 200 has dimensions suitable for covering this area. In the example described here, each strip 200 has, along the axial direction DA, a width I 200 at least equal to the width I 121 of the annular base 121 of each angular sector 120 and a length L 200 allowing the strip 200 to extend along the circumferential direction DC beyond the lateral edges 124 and 125 of two adjacent angular sectors ( figures 4 , 7 et 8 The length of the straps may be less than the width of the fibrous preform when the pinching risk zones are not present across the entire width of the preform. According to an alternative embodiment, several straps may be arranged adjacently along the axial direction DA.

[0034] As illustrated on the figures 7 et 8 Each strip 200 has a shape corresponding to the shape of the annular base of the two adjacent angular sectors at the junction zone. More precisely, the outer surface 202 of each strip intended to come into contact with the annular bases of two adjacent angular sectors has a convex portion 2020 whose shape fits perfectly with the recessed portion 1212 present on the annular base 121 of each angular sector 120. Correspondingly, the inner face 201 of each strip 200 has a recessed portion 2010 that matches the shape of the recessed portion 1212 present on the annular base 121 of each angular sector 120. The portions 2010 and 2020 extend along the entire length of each strip in the circumferential direction DC.

[0035] According to one aspect of the invention, the 200 series strips are made of composite material from a fibrous reinforcement densified by a matrix. Various types of composite materials and manufacturing processes can be used. The strips can be manufactured from preforms produced by: draping of unidirectional or bidirectional plies of carbon fibers, glass fibers or a mixture of carbon and glass fibers, each ply being pre-impregnated with a matrix precursor such as an epoxy resin for example, infusion of an epoxy resin into a dry fibrous texture obtained for example by draping of unidirectional or bidirectional plies, draping of unidirectional or bidirectional plies of carbon fibers, glass fibers or a mixture of carbon and glass fibers, each ply being pre-impregnated with a resin or thermoplastic material such as polyetheretherketone (PEEK), polyetherketoneketone (PEKK) polyaryletherketones (PAEK), polyetherimide (PEI).

[0036] The preform of the strip is then shaped and heat-treated to transform the resin or thermosetting material (polymerization) or thermoplastic material (heating then cooling) into a matrix.

[0037] The shaping of the preform of the strip can be advantageously carried out by molding on the annular base 121 of an angular sector 120, which ensures that the strip will perfectly conform to the shape of the annular base when the mold is closed.

[0038] The stiffness of the strip is adjusted so that it has sufficient flexibility not to break when deformed by the angular sector fixed first as explained below.

[0039] The strips can also be made of metallic material, in particular by sheet metal stamping or additive manufacturing (for example by nickel electrodeposition) following the same shape as that of the annular base of the angular sectors.

[0040] Each strip made of composite or metallic material has a thickness E p200 less than or equal to 0.2mm in particular so as not to form too large an impression in the fibrous preform when closing the mold.

[0041] THE figures 9A et 9B illustrate the positioning of an angular sector during the closing of mold 100. More precisely, on the figure 9A A final angular sector 1206 is being positioned between two angular sectors 1201 and 1205, which have already been positioned, in order to complete the closure of the mold 100. According to one feature of the mold closing method of the invention, every other angular sector is first placed and fixed, and then the closure is completed by closing the gaps between two angular sectors with the remaining sectors. Other mold closing configurations are, however, possible.

[0042] On the figure 9A The fibrous preform 20 has bulges 21 in the vicinity of the lateral edge 125 of the angular sector 1205 and the lateral edge 124 of the angular sector 1201 due to its compaction by these angular sectors. According to the invention, a strip 200 is present on the exposed surface of the preform 20 at the level of each bulge 21. At this stage of the mold closing, the strips 200 are deformed at the level of the bulges 21 under the effect of the compaction force imposed by the angular sectors already positioned (sectors 1205 and 1201 on the figure 9A ).

[0043] The mold closure continues with the positioning and fixing of the last angular sector 120 6 as illustrated on the figure 9B During the placement of this sector, the bulges 21 cannot penetrate the space present between the angular sectors due to the presence of the bands 200. The bands 200 prevent the portion of preform present at the level of the bulges 21 from being pushed against the lateral edges of sectors 120 5 and 120 1, which prevents any pinching of the preform between the lateral edges of two adjacent sectors.

[0044] As can be seen on the figure 10 Once the mold is closed, each strip 200 perfectly follows the shape of the annular base 121 of each angular sector 120 of the mold 100. In the example described here, each strip 200 has, along the axial direction DA, a shape identical to that of the profile of the annular bases 121 of the adjacent angular sectors between which it is placed. Each strip 200 has, in particular, on its outer surface a convex portion 2020 whose shape adapts to the shape of the recessed portion 1212 present on the annular base 121 of each angular sector 120 and corresponding to the shape of an overthickness 22 present on the preform 20 and intended to form a retention zone in the final housing.

[0045] With the strips according to the invention, the appearance of "pinch fiber" type defects on the finished part is avoided. It is thus possible to compact the preform 20 with each of the angular sectors 120 without affecting the mechanical properties of the finished part.

[0046] The manufacture of the crankcase 10 shown on the figure 3 The process begins with the creation of a fibrous texture through three-dimensional weaving between warp and weft yarns. "Three-dimensional weaving" or "3D weaving" refers to a weaving method in which at least some of the weft yarns interlock with warp yarns across multiple layers of warp yarns, or vice versa. The fibrous texture may have an interlock weave. "Interlock" weaving refers to a weave in which each layer of weft yarns interlocks with several layers of warp yarns, with all yarns in the same weft column moving in the same direction within the plane of the weave. Other weave structures are possible. The yarns used may include carbon fiber, glass fiber, or silicon carbide fibers. The fibrous texture is in the form of a strip that is wound several times around the mandrel 110 of the mold 100 to form the fibrous preform 20.

[0047] The mold 100 is then closed by means of the angular sectors 120 described previously, these sectors also compacting the preform 20.

[0048] The next step involves densifying the fibrous preform by filling its porosity with the matrix material. This is achieved by injecting the liquid matrix precursor, such as a resin, throughout the preform within the mold. The transformation of the precursor into an organic matrix, namely its polymerization, is carried out by heat treatment, generally by heating the mold, after removing any solvent and cross-linking the polymer. The preform remains in the mold, which has a shape corresponding to that of the part to be produced. The organic matrix can be obtained from epoxy resins, such as high-performance epoxy resins, or from liquid precursors of carbon or ceramic matrices.

[0049] The densification of the fibrous preform can be achieved using the well-known resin transfer molding (RTM) process. This involves injecting a thermosetting resin into the internal space of the mold containing the fibrous preform. A pressure gradient is typically established within this internal space between the resin injection point and the resin discharge ports to control and optimize resin impregnation of the preform. Once the resin has been injected throughout the preform, it is polymerized by heat treatment according to the RTM process.

[0050] After injection and polymerization, the part is demolded.

[0051] The part is finally trimmed to remove excess resin and the chamfers are machined to obtain a housing 10 with a shape of revolution as illustrated on the figure 3 .

Claims

1. A method for closing an injection mold (100) for the manufacture of a revolution part made of composite material, the mold comprising: - a mandrel (110) supporting a fiber preform (20) obtained by winding of a fiber web, the mandrel comprising an annular wall (111), the profile of the external surface of which corresponds to that of the inner surface (14) of the part to be manufactured, - a plurality of angular sectors (120) comprising an annular base (121) intended to come into contact with the fiber texture (20), the annular base extending between first and second longitudinal edges (122, 123) along an axial direction (DA) and between first and second side edges (124, 125) along a circumferential direction (DC), the annular base of each sector having a shape corresponding to the shape of the revolution part to be manufactured, the method comprising the successive positioning and fixing of the angular sectors (120) on the mandrel (110), the annular base (121) of each sector compacting the fiber preform portion present oppositely, the side edges (124 , 125) of the annular base (121) of each angular sector (120) being in contact with the side edges (124, 125) of the annular base (121) of the adjacent sectors, characterized in that, before the positioning and fixing of the angular sectors on the mandrel, strips (200) are placed on the exposed surface of the fiber preform (20), each strip (200) covering an area of the fiber preform located facing a junction area between two side edges (124, 125) of the annular base (121) of two adjacent angular sectors (120) and in that each strip has a shape corresponding to the shape of the annular base of the two adjacent angular sectors at the junction area.

2. The method according to claim 1, wherein the strips (200) are made of composite material comprising a fiber reinforcement densified by a matrix.

3. The method according to claim 2, wherein the fiber reinforcement of each strip comprises carbon fibers or glass fibers or a mixture of carbon and glass fibers.

4. The method according to claim 2 or 3, wherein the matrix is obtained from a thermosetting or thermoplastic resin or material.

5. The method according to claim 1, wherein the strips are made of metal material.

6. The method according to any one of claims 2 to 5, wherein each strip (200) has a thickness less than or equal to 0.2 mm.

7. The method according to any one of claims 1 to 6, wherein angular sectors (120) are first positioned and fixed on the mandrel (110) at a determined distance from each other so as to arrange a space between two angular sectors, the remaining angular sectors (120) then being positioned and fixed on the mandrel (110) in the spaces arranged between the already fixed angular sectors.

8. The method according to any one of claims 1 to 7, wherein each angular sector (120) includes first and second grooves (1242, 1252) present respectively on the first and second side faces (1241, 1251), the grooves extending along the axial direction (DA), a seal (150) being housed both in the first groove (1242) of a first side face of an angular sector and in the second groove (1252) of a second side face of an adjacent angular sector.

9. A method for manufacturing a revolution part made of composite material (30) comprising: - the production by three-dimensional or multilayer weaving of a fiber texture in the form of a web, - the winding of the fiber texture on several turns superimposed on a mandrel (110) of an injection mold (100) so as to form a fiber preform (20), the injection mold comprising a plurality of angular sectors (120), - the closing of the injection mold (100) in accordance with any of claims 1 to 8, - the densification of the fiber preform (20) by a matrix so as to obtain a revolution part made of composite material (30) comprising a fiber reinforcement densified by a matrix, - the demolding of the composite material part.