Rtm injection method and mold using symmetrical crush resistant segments
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- SAFRAN AIRCRAFT ENGINES SAS
- Filing Date
- 2021-05-26
- Publication Date
- 2026-06-19
AI Technical Summary
During the closing process of existing injection molds, the fibers of fiber preforms are easily squeezed, leading to poor mold sealing and defects such as "squeezed fibers" on finished parts.
The injection mold design includes first and second series of corner segments, each with a protruding and recessed lower portion on its lateral edge, ensuring that the fiber preform is uniformly compressed when the mold is closed, avoiding squeezing.
This effectively avoids the squeezing of fiber preforms when the mold is closed, improves the mold sealing and the quality of finished parts, and reduces the defect rate.
Smart Images
Figure CN115697682B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the general field of manufacturing axisymmetric components, such as gas turbine housings. Background Technology
[0002] In the aerospace industry, there is a desire to reduce the mass of engine components while still maintaining their high mechanical properties. For example, in aero turbine engines, fan housings are now made of composite materials, defining the profile of the engine's air intake flow, and housing the rotor that supports the fan blades.
[0003] The manufacture of a composite fan housing begins with the mounting of fiber reinforcement wound around a mandrel, the profile of which is itself molded to the profile of the housing to be manufactured. For example, the fiber reinforcement can be produced by three-dimensional or multi-layer weaving as described in patent US 8,322,971. This fiber reinforcement forms a tubular fiber preform with flanges corresponding to the flanges of the housing. Manufacturing continues by densifying the fiber preform with a polymer matrix, including impregnating the preform with resin and the polymer resin to obtain the finished part.
[0004] This invention relates more particularly to a manufacturing mode in which the impregnation of a fiber preform is achieved by an injection molding method called RTM (Resin Transfer Molding). According to this method, the fiber preform is enclosed in a rigid mold having a fixed geometry, the rigid mold comprising a mandrel or roller and a reverse mold on which the fiber preform is wound, the reverse mold being disposed on the fiber preform and its shape corresponding to the desired axisymmetric part, and resin is injected into the mold under controlled pressure and temperature after the walls of the two parts of the mold are brought together and a vacuum has been created in the mold, if necessary. Once the resin is injected, its polymerization is carried out by heating the mold, and after injection and polymerization, the finished part is demolded, then trimmed to remove excess resin, and chamfered to obtain the desired part, such as a housing.
[0005] Because the preform is too large when it is wound on the mandrel, that is, it has a thickness that is excessive relative to the theoretical thickness of the finished part, the closure of the mold also provides the function of final clamping of the preform to give the preform its final thickness.
[0006] Figure 1 An RTM injection mold 300 is shown, comprising a mandrel or roller 310 and a reverse mold, on which a fiber preform 30 is wound, and the reverse mold is formed by a plurality of corner segments 320. Mold closure is achieved by the corner segments 320, which ensure the compression of the preform. A method for closing this type of mold is specifically described in document US 2018 / 370082.
[0007] However, the closure of the mold for this type of corner sector has proven to be a delicate operation. In fact, as... Figure 2A As shown, the first segment of the two is placed, each of which partially compresses the fiber preform. The fiber preform 30 has a protrusion 31 near the end of each corner segment 320 because it is no longer compressed. With the... Figure 2B and 2C The positioning of the remaining corner segments between the already positioned segment segments, as shown, continues with the mold closing. During the installation of these segment segments, as the preform is extruded from the center of the segment by compression, the protrusion 31 is extruded and abuts against the edge of the already positioned segment. Furthermore, the shape of the segment segments and the mold closing direction ensure that there is space between the segment segments until the very last moment of mold closure. Then, a portion of the protrusion 31 penetrates into this space so that it is finally pressed between the edges of adjacent segment segments, as shown. Figure 2C As shown. The fibers of the extruded preform can cause mold deterioration, poor mold sealing, and, in particular, defects known as "extruded fibers" in the finished parts. Summary of the Invention
[0008] The purpose of this invention is to provide a solution to avoid the compression of fibers in preforms during the closing of the injection mold.
[0009] Specifically, this objective is achieved through an injection mold used to manufacture axisymmetric components of composite materials, the injection mold comprising:
[0010] - A mandrel designed to support a fiber preform formed by winding, the mandrel including annular walls whose outer surface profile corresponds to the profile of the inner surface of the part to be manufactured.
[0011] - Multiple counter-die corner segments, assembled on a mandrel, are designed to close the die and compress a fiber preform wound on the mandrel. Each corner segment includes an annular base intended to contact the fiber preform. The annular base extends axially between a first longitudinal edge and a second longitudinal edge, and circumferentially between a first transverse edge and a second transverse edge. The first transverse edge of the annular base of the corner segment contacts the second transverse edge of the annular base of the adjacent corner segment.
[0012] The feature is that the plurality of corner fan segments include a first series of corner fan segments and a second series of corner fan segments, wherein the first and second lateral edges of each corner fan segment in the first series each include a protruding lower portion forming a first non-zero angle relative to the radial direction, and the first and second lateral edges of each corner fan segment in the second series each include a recessed lower portion forming a second non-zero angle relative to the radial direction, wherein the first angle and the second angle have the same range.
[0013] The protruding and recessed lower portions present on each corner segment allow for the pushing aside or "pushing away" of the preform portion protruding from the outer side of the lateral edge of the corner segment. Since the portions of the lateral edge of each corner segment in contact with the fiber preform in the middle of the segment—that is, the protruding and recessed lower portions—are parallel to the closing direction, i.e., parallel to the radial direction, there is no space between the two segments when closed. Therefore, the risk of squeezing the yarn, and thus the preform, is considerably reduced. Thus, it is possible to press the preform firmly against each corner segment without the risk of squeezing the preform at the joint between two adjacent segments.
[0014] According to a specific feature of the mold of the present invention, each corner segment in the first and second series includes: a first lateral surface and a second lateral surface, the first lateral surface being parallel to the radial direction and existing in a continuation of the first lateral edge of the annular base, and the second lateral surface being parallel to the radial direction and existing in a continuation of the second lateral edge of the annular base. This allows for a smaller protrusion angle.
[0015] According to another specific feature of the mold of the invention, the first non-zero angle relative to the radial direction formed by the protruding lower portion of the lateral edge of the corner segment in the first series of segments is between 18° and 45°.
[0016] Another object of the present invention is a method for closing an injection mold for manufacturing axisymmetric components of composite materials, the mold comprising:
[0017] - A mandrel supporting a fiber preform obtained by winding a fiber tape, the mandrel including annular walls whose outer surface profile corresponds to the profile of the inner surface of the part to be manufactured.
[0018] - Multiple corner fan segments, each including an annular base intended to contact the fiber texture, the annular base extending between a first longitudinal edge and a second longitudinal edge in the axial direction, and between a first transverse edge and a second transverse edge in the circumferential direction.
[0019] The method is characterized in that a plurality of corner fan segments include a first series of corner fan segments and a second series of corner fan segments, wherein the first and second lateral edges of each corner fan segment in the first series of fan segments each include a protruding lower portion forming a first non-zero angle relative to the radial direction, and the first and second lateral edges of each corner fan segment in the second series of fan segments each include a recessed lower portion forming a second non-zero angle relative to the radial direction, the first angle and the second angle having the same range, and the method is characterized in that the method includes continuously positioning and attaching each corner fan segment to a mandrel, wherein the annular base of each fan segment is pressed against the fiber preform portion present thereto, and during positioning, the lateral edges of the annular bases of the corner fan segments in the first series of fan segments remain in contact with the lateral edges of the annular bases of the corner fan segments in the second series of fan segments already attached to the mandrel.
[0020] According to a specific feature of the method of the present invention, the corner segments in the second series of segments are first positioned and attached to the mandrel at a predetermined distance from each other, so as to provide space between the two corner segments in the second series of segments, and the corner segments in the first series of segments are then positioned and attached to the mandrel in the space provided between the corner segments in the second series of segments.
[0021] According to another specific feature of the method of the present invention, each corner segment in the first and second series of segments includes a first lateral surface and a second lateral surface, the first lateral surface being parallel to the radial direction and existing in the continuation of the first lateral edge of the annular base, and the second lateral surface being parallel to the radial direction and existing in the continuation of the second lateral edge of the annular base.
[0022] Another specific feature of the method according to the invention is that the first non-zero angle relative to the radial direction formed by the protruding lower portion of the lateral edge of the corner segment in the first series of segments includes between 18° and 45°. Attached Figure Description
[0023] Figure 1 This is a schematic perspective view of an injection mold based on existing technology.
[0024] Figure 2A It shows the closure Figure 1 A partial radial sectional view of the steps of the mold.
[0025] Figure 2B It shows the closure Figure 1 A radially sectional partial view of another step in the mold process.
[0026] Figure 2C It shows the closure Figure 1 A radially sectional partial view of another step in the mold process.
[0027] Figure 3This is a schematic perspective view of a fan housing made of composite materials.
[0028] Figure 4 This is a schematic perspective view of an injection mold according to an embodiment of the present invention.
[0029] Figure 5 It shows Figure 4 A schematic perspective view of the corner sector in the first series of sector segments of the mold.
[0030] Figure 6 It shows Figure 4 A schematic perspective view of the corner sector in the second series of sector segments of the mold.
[0031] Figure 7 yes Figure 4 A radial sectional view of the injection mold, in which the first series of corner segments are located.
[0032] Figure 8A It is shown in Figure 4 A radial sectional view of the portion where the corner sector begins positioning during mold closure.
[0033] Figure 8B It shows Figure 8A A partial radial sectional view of the positioning progress of the corner sector.
[0034] Figure 8C It is shown Figure 4 A partial radial sectional view of the closed mold. Detailed Implementation
[0035] This invention is generally applicable to any gas turbine housing made of organic matrix composite materials.
[0036] Hereinafter, the invention will be described within the scope of its application to the fan housing of an aero gas turbine engine.
[0037] Figure 3 A perspective view of a fan housing 10, which can be manufactured using the molds and methods according to the invention, is shown. This type of housing is centered on a longitudinal axis XX and includes an annular wall 11 defined upstream by an upstream flange 12 and downstream by a downstream flange 13 (upstream and downstream defined relative to the flow direction of the airflow in the gas turbine). The inner surface 14 of the annular wall 11 is intended to define the inlet flow in the gas turbine or to support panels, housings, etc., used to define this flow.
[0038] Figure 4This is a schematic perspective view of the mold according to the invention during closure. This type of mold can be used for impregnation via a fiber preform method of RTM (“Resin Transfer Molding”) type to manufacture a fan housing 10 as previously presented. Fiber preforms can be produced by three-dimensionally weaving a fiber texture in the form of strips using fibers, such as carbon, glass, aramid, or ceramic, and the impregnation matrix can be a polymer, such as epoxy resin, bismaleimide, or polyimide.
[0039] The mold 100 is rotatably mounted on a drive shaft (not shown) centered on axis XX, and includes a mandrel 110. Hereafter, an axial direction D will be defined relative to this axis XX. A and radial D R Direction, axial direction D A Parallel to axis XX, and radially in direction D R Perpendicular to axis XX. Also referencing the circumferential direction D. C ,like Figure 4 As shown, this circumferential direction corresponds to the direction tangent to any circle centered on the axis X–X. This direction is perpendicular to the axial direction D. A and radial direction D R .
[0040] The mandrel 110 includes an annular wall 111 in the shape of a roller and two transverse flanges 112, the annular wall 111 supporting a fiber preform 20 formed by winding a fiber strip. The mandrel 110 is held on its drive shaft by spokes 113.
[0041] Flange 112 forms a support member intended to receive a folded-back portion of the preform 20 wound on mandrel 110, and the support member is intended to form the upstream flange 12 and the downstream flange 13 of the fan housing 10.
[0042] Mold 100 further includes a reverse mold comprising a plurality of corner segments 120 and 160, which are assembled in a sealed manner on mandrel 110 and locked together in a sealed manner by a locking key 130, which maintains a flat seal between the segments (in Figure 4 (Not shown in the image). According to a variant embodiment, these segments can be directly locked together by bolting with inclined screws. In this case, as explained later, a seal between the segments is achieved by pressing a seal housed in a groove present on the lateral edge of the segment.
[0043] More precisely, the multiple corner fan segments include a first series of corner fan segments 120 (three in this case) and a second series of corner fan segments 160 (three in this case) that are alternately positioned around the spindle 110.
[0044] Angle segments 120 and 160 are respectively assembled onto the transverse flange 112 by clamping screws 131, which pass through openings 122 and 162 respectively present in the segments and are screwed into threaded holes 1120 present in the transverse flange 112. Screws 131 allow segments 120 and 160 to be assembled onto the flange 112 and allow adjustment of the clamping pressure applied to the fiber preform 20. The threaded holes can be replaced by nuts inserted into a retainer, which facilitates maintenance in the case of aluminum molds.
[0045] In the embodiment described herein, corner segments 120 and 160 are locked together by clamping screws 141 that pass through an opening 132 in a locking key 130 and are screwed into threaded holes 126 and 161 respectively in corner segments 120 and 160. The key 130 is attached between two adjacent segments 120 and 160 by two rows of screws 141 extending longitudinally at the ends of each segment. The locking key 130 is assembled radially from the outside once the segments are assembled onto the mandrel 110. In this way, the key ensures that segments 120 and 160 are circumferentially clamped together.
[0046] An O-ring seal (not shown) positioned on flange 112 ensures a seal between sectors 120 and 160 and spindle 110.
[0047] Figure 5 An angle sector 120 from a first series of angle sector segments according to an embodiment of the present invention is shown. Each angle sector 120 includes an annular base 121 intended to contact the fiber texture 20. The annular base is in the axial direction D A It extends between the first longitudinal edge 122 and the second longitudinal edge 123, and in the circumferential direction D C Extending between the first lateral edge 124 and the second lateral edge 125, the first lateral edge 124 of the annular base 121 of the corner fan segment 120 contacts the second lateral edge 165 of the annular base of the adjacent corner fan segment 160 in the second series of corner fan segments, while the second lateral edge 125 of the annular base 121 of the corner fan segment 120 contacts the first lateral edge 164 of the annular base of the adjacent corner fan segment 160 in the second series of corner fan segments. Figure 8C The first lateral edge 124 of the annular base 121 of each corner sector 120 includes a protruding lower portion 1240 in the form of a ramp, which is relative to the radial direction D. R Forming the first non-zero angle β 1240 Similarly, the second lateral edge 125 of the annular base 121 of each corner sector includes a protruding lower portion 1250 in the form of a ramp, which is relative to the radial direction D. R Forming the second non-zero angle β 1250First angle β 1240 Second angle β 1250 Having the same range Figure 8A ).
[0048] Figure 6 An angle sector 160 from a second series of angle sector segments according to an embodiment of the present invention is shown. Each angle sector 160 includes an annular base 161 intended to contact the fiber texture 20. The annular base is located in the axial direction D. A It extends between the first longitudinal edge 162 and the second longitudinal edge 163, and in the circumferential direction D C Extending between the first lateral edge 164 and the second lateral edge 165, the first lateral edge 164 of the annular base 161 of the corner fan segment 160 contacts the second lateral edge 125 of the annular base of the adjacent corner fan segment 120 in the first series of corner fan segments, while the second lateral edge 165 of the annular base 161 of the corner fan segment 160 contacts the first lateral edge 124 of the annular base of the adjacent corner fan segment 120 in the first series of corner fan segments. Figure 8C The first lateral edge 164 of the annular base 161 of each corner sector 160 includes a recessed lower portion 1640 in the form of a ramp, which is relative to the radial direction D. R Forming the first non-zero angle β 1640 Similarly, the second lateral edge 165 of the annular base 161 of each corner sector includes a recessed lower portion 1650 in the form of a ramp, which is relative to the radial direction D. A Forming the second non-zero angle β 1650 First angle β 1640 Second angle β 1650 Having the same range Figure 8A Angle β 1240 β 1250 β 1640 and β 1650 They all have the same range.
[0049] Figure 7 A method for closing a mold 100 according to an embodiment of the present invention is shown, the mold having corner segments 120 of a first series of fan segments and corner segments 160 of a second series of fan segments. In this embodiment, the corner segments 160 of the second series of fan segments are first positioned. After the preform 20 has been compressed, the corner segments 160 are attached to the mandrel 110 of the mold 100 at spaced-apart positions to allow the corner segments 120 of the first series of fan segments to be inserted between the two corner segments 160 during the completion of mold closure. Once the corner segments 160 are positioned and attached to the mandrel 100, the corner segments 120 of the first series of fan segments are placed and attached.
[0050] Figures 8A to 8C The positioning of the corner sector 120 in the first series of sector segments is shown during the completion of mold 100 closure. More precisely, in Figure 8A In this process, the final corner fan segment 1203 of the first series is positioned between two corner fan segments 1601 and 1603 of the second series that have already been positioned, in order to complete the closure of the mold 100. Due to their protruding construction and their contact with the complementary recessed portions of adjacent fan segments during the positioning of fan segment 1203, the protruding lower portions 1240 and 1250, respectively present on the lateral edges 124 and 125 of the fan segments, will push away or "drive away" the portion of the preform 20 protruding outside the lateral edge 165 of the corner fan segment 1603, and the portion of the preform 20 protruding outside the lateral edge 164 of the corner fan segment 1601. Since in the middle of the fan segment, the portions of the lateral edges of each corner fan segment that contact the fiber preform 20, i.e., the protruding lower portions 1240 and 1250 and the recessed lower portions 1640 and 1650, are parallel to the closing direction, i.e., parallel to the radial direction D. R When closed, there is no space between the two segments. Therefore, the risk of squeezing these yarns and the resulting preforms is significantly reduced.
[0051] exist Figure 8B In the process, it was observed that the protruding portions 1240 and 1250 of the corner sector segment 1203 contact the recessed portions 1640 and 1650 of the corner sector segments 1601 and 1603, respectively, which begins at the start of the installation of the corner sector segment 1203. This very early contact during the positioning of the sector segments is made possible by the engagement of the two lateral edges, each having a recessed portion and a protruding portion as described above, with the two lower portions having complementary bevels.
[0052] Therefore, the preform 20 can be pressed together with each corner segment 120 without the risk of the preform 20 being squeezed between two adjacent segments, such as Figure 8C As shown in the image.
[0053] Each corner sector 120, 160 further includes a direction D parallel to the radial direction. R and the respective first lateral surfaces 1241, 1641 existing in the continuation of the respective first lateral edges 124, 164 of the respective annular bases 121, 161, and parallel to the radial direction D R And each second lateral surface 1251, 1651 existing in the continuation of each second lateral edge 125, 165 of each annular base 121, 161.
[0054] According to a specific feature of the invention, a first non-zero angle β relative to the radial direction is formed by the protruding lower portions 1240 and 1250 of the first lateral edge 124 and the second lateral edge 125 of the corner sector segment 120, respectively. 1240 and β 1250 It is included between 18° and 45°.
[0055] Figure 3 The manufacture of the housing 10 shown begins with the creation of a fibrous texture through three-dimensional weaving of warp and weft yarns. Here, "through three-dimensional weaving" or "3D weaving" refers to a weaving pattern in which at least some of the weft yarns are connected to several layers of warp yarns, or vice versa. The fibrous texture may have an interlocking weaving pattern. Here, "interlocking weaving" refers to a weaving pattern in which each layer of weft yarns is connected to several layers of warp yarns, wherein all yarns of the same weft yarn column have the same movement in the plane of the pattern. Other weaving patterns may be considered. The yarns used may in particular be carbon fiber, glass, or silicon carbide yarns. The fibrous texture has the shape of a strip that is wound several times around the mandrel 110 of the mold 110 to form the fibrous preform 20.
[0056] Then, by closing the mold 100 through the aforementioned corner segments 120 and 160, these segments further compress the preform 20.
[0057] Next, the fiber preform is densified, which involves filling the pores of the fiber preform with the material constituting the matrix. For this purpose, a matrix precursor liquid, such as a resin, is injected into the entire preform present in a mold. The conversion of the precursor to an organic matrix is achieved by heat treatment, typically by heating the mold after removing any solvent (if applicable) and curing the polymer; that is, by polymerizing the polymer, the preform is held constant in the mold, which has a shape corresponding to the part to be produced. Organic matrices are particularly available from epoxy resins, such as commercially available high-performance epoxy resins, or liquid precursors of carbon or ceramic matrices.
[0058] Densification of fiber preforms can be achieved using a known transfer molding method called RTM (“Resin Transfer Molding”). This method involves injecting a thermosetting resin into the internal space of a mold containing the fiber preform. Typically, a pressure gradient is established within this internal space between the injection point and the exit point of the resin to control and optimize the impregnation of the preform through the resin. Once the resin has been injected into the entire preform, it is polymerized through heat treatment according to the RTM method.
[0059] After injection and polymerization, the part is demolded. Finally, the part is trimmed to remove excess resin and chamfered to obtain a shell 10 with an axisymmetric shape, such as... Figure 3 As shown in the image.
Claims
1. An injection mold for manufacturing axisymmetric components of composite materials, the injection mold comprising: - A mandrel designed to support a fiber preform formed by winding, the mandrel including annular walls whose outer surface profile corresponds to the profile of the inner surface of the part to be manufactured. - Multiple counter-die corner segments, assembled on a mandrel and designed to form the die and press a fiber preform wound on the mandrel, each corner segment including an annular base intended to contact the fiber preform, the annular base extending axially between a first longitudinal edge and a second longitudinal edge and circumferentially between a first transverse edge and a second transverse edge, the first transverse edge of the annular base of the corner segment contacting the second transverse edge of the annular base of the adjacent annular segment. The feature is that the plurality of corner fan segments include a first series of corner fan segments and a second series of corner fan segments. Each of the first series of corner fan segments has a first lateral edge and a second lateral edge that each includes a protruding lower portion forming a first non-zero angle relative to the radial direction. Each of the second series of corner fan segments has a first lateral edge and a second lateral edge that each includes a recessed lower portion forming a second non-zero angle relative to the radial direction. The first angle and the second angle have the same range. The protruding and recessed lower portions present on each corner fan segment allow for pushing away or "driving away" of preform portions protruding outside the lateral edges of the corner fan segments. Each of the first series of corner fan segments and the second series of corner fan segments includes a first lateral surface that is parallel to the radial direction and exists in the continuation of the first lateral edge of the annular base, and a second lateral surface that is parallel to the radial direction and exists in the continuation of the second lateral edge of the annular base.
2. The injection mold according to claim 1, wherein, Each corner segment includes a first groove and a second groove respectively existing on a first transverse surface and a second transverse surface, the first groove and the second groove extending in the axial direction, and a washer is accommodated in both the first groove on the first transverse surface of the corner segment and the second groove on the second transverse surface of the adjacent corner segment.
3. The injection mold according to claim 1, wherein, The first non-zero angle formed by the protruding lower portion of the lateral edge of the first series of angular fan segments relative to the radial direction is between 18° and 45°.
4. A method for closing an injection mold for manufacturing an axisymmetric component of a composite material, the mold comprising: - A mandrel supporting a fiber preform obtained by winding a fiber tape, the mandrel including annular walls whose outer surface profile corresponds to the profile of the inner surface of the part to be manufactured. - Multiple corner fan segments, including an annular base intended to contact the fiber texture, the annular base extending axially between a first longitudinal edge and a second longitudinal edge, and circumferentially between a first transverse edge and a second transverse edge. The method is characterized in that the plurality of corner fan segments include a first series of corner fan segments and a second series of corner fan segments. Each corner fan segment in the first series has a first lateral edge and a second lateral edge each comprising a protruding lower portion forming a first non-zero angle relative to the radial direction. Each corner fan segment in the second series has a first lateral edge and a second lateral edge each comprising a concave lower portion forming a second non-zero angle relative to the radial direction. The first and second angles have the same range. Furthermore, the method includes continuously positioning and attaching each corner fan segment to a mandrel, with the annular base of each fan segment pressing against the fiber preform portion thereon during the positioning period. In the first series of corner fan segments, the lateral edge of the annular base of the corner fan segment remains in contact with the lateral edge of the annular base of the corner fan segment in the second series of corner fan segments that has been attached to the mandrel. The lower portions present on each corner fan segment, which are respectively protruding and recessed, will allow the preform portion protruding on the outer side of the lateral edge of the corner fan segment to be pushed away or "driven away". Each corner fan segment in the first series and the second series includes a first lateral surface that is parallel to the radial direction and exists in the continuation of the first lateral edge of the annular base, and a second lateral surface that is parallel to the radial direction and exists in the continuation of the second lateral edge of the annular base.
5. The method according to claim 4, wherein, The corner fan segments in the second series are first positioned and fixed on the mandrel at a predetermined distance from each other to provide space between the two corner fan segments in the second series. Then, in the space provided between the corner fan segments in the second series, the corner fan segments in the first series are positioned and attached to the mandrel.
6. The method according to claim 4 or 5, wherein, The first non-zero angle formed by the protruding lower portion of the lateral edge of the first series of angular fan segments relative to the radial direction is between 18° and 45°.