Mold assembly for manufacturing a composite part with a stiffener, method of manufacturing a composite part and composite part with a stiffener

Abstract

A mold assembly for manufacturing a composite part with a stiffener, the mold assembly includes a bottom mold configured to form a first surface of the composite part, wherein the bottom mold has at least one elongated recess configured to form a stiffener in the composite part; a feeder unit having a shape corresponding to the at least one elongated recess, wherein the feeder unit is configured to fit at least partially into the at least one elongated recess; and a top mold configured to form a second surface of the composite part opposite to the first surface. Also a method of manufacturing a composite part using such a mold assembly, which includes draping a flat laminate over the bottom mold and pushing portions of the laminate into the at least one elongated recess.

Claims

1. A method of manufacturing a composite part including a stiffener, the method comprising: providing a bottom mold having at least one elongated recess in a molding surface of the bottom mold; draping a flat laminate onto the bottom mold; driving a feeder unit onto the laminate, wherein the feeder unit pushes a portion of the laminate into the at least one elongated recess; pressing a top mold onto the laminate; and hardening the laminate, wherein the bottom mold forms a first surface of the composite part, the at least one elongated recess forms a stiffener in the composite part, and the top mold forms a second surface of the composite part opposite to the first surface, wherein the molding surface is curved in at least one of: a radial direction extending from a center of the molding surface, such that the molding surface forms a circular shape and the at least one elongated recess extends from the center of the molding surface; and a vertical direction, such that the molding surface bends downward.

2. The method according to claim 1, wherein driving the feeder unit comprises: pushing an insert mounted to a fixture of the feeder unit together with the portion of the laminate at least partially into the at least one elongated recess, and releasing the insert from the fixture.

3. The method according to claim 2, wherein driving the feeder unit further comprises removing the feeder unit from the laminate and the bottom mold.

4. The method according to claim 1, wherein driving the feeder unit comprises: driving a blade portion of the feeder unit together with the portion of the laminate into the at least one elongated recess, and removing the feeder unit from the laminate and the bottom mold before pressing the top mold onto the laminate.

5. The method according to claim 1, further comprising: inserting a reinforcing device into the at least one elongated recess, wherein the reinforcing device includes an elongated slit, and wherein driving the feeder unit comprises pushing the portion of the laminate into the elongated slit of the reinforcing device.

6. The method according to claim 1, further comprising: draping a laminate patch onto the laminate at least at portions of the laminate corresponding to the elongated recess.

7. The method according to claim 1, wherein the upper mold is curved in both the radial direction and the vertical direction and wherein side edges of the at least one elongated recess extend perpendicularly to the molding surface.

8. The method according to claim 1, wherein a depth of the at least one elongated recess increases with increasing distance from the center of the molding surface.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Preferred embodiments of the invention are now explained in greater detail with reference to the enclosed schematic drawings, in which

(2) FIG. 1 schematically illustrates a perspective view of a mold assembly and certain details thereof;

(3) FIGS. 2 and 3 schematically illustrate perspective views of a mold assembly at subsequent process situations;

(4) FIGS. 4 and 5 schematically illustrate cross-sections of a detail of a mold assembly at subsequent process situations;

(5) FIGS. 6 and 7 schematically illustrate cross-sections of a detail of a mold assembly in different exemplary configurations;

(6) FIG. 8 schematically illustrates a perspective view of a composite structure;

(7) FIG. 9 illustrates an exemplary flow diagram of a method of manufacturing a composite part including a stiffener; and

(8) FIG. 10 schematically illustrates an aircraft.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(9) FIG. 1 schematically illustrates a perspective view of a part of a mold assembly 100. The mold assembly 100 comprises a bottom mold 110 that is configured to form a first surface of a composite part 10 (FIG. 8). The composite part 10 can be manufactured, which will be outlined in more detail below, by draping a flat laminate 200 onto the bottom mold 110 the laminate may be any thermoplastic or thermoset fiber reinforced sheet.

(10) The illustrated bottom mold 110 has a molding surface (upper and visible surface in FIG. 1) that is curved in at least one direction, particularly in two directions. One curvature is around a center axis C, i.e., the bottom mold 110 is of a circular shape. In addition, from a center of the bottom mold (where center axis C intersects with bottom mold) the bottom mold 110 bends downwards, i.e., is curved in a second direction. The second curvature has to be contemplated in each cross-section running through center axis C. Such cross-section of the bottom mold 110 forms a portion of a circle or ellipse, which has a center at a position on center axis C below the top of bottom mold 110.

(11) The flat laminate 200 is larger than the bottom mold 110, i.e., has a larger diameter (in horizontal direction in FIG. 1), in order to be draped over the entire bottom mold 110. However, due to the curvature of the bottom mold 110, the laminate will not fit at an outer rim of the bottom mold 110. This effect is used to form integrated stiffeners 15, 16 (FIGS. 5 to 7) into the composite part 10. To do so, the bottom mold 110 comprises at least one elongated recess 115 configured to form such stiffener 15, 16.

(12) As illustrated in the two details in FIG. 1 of the elongated recesses 115, a depth D1, D2 of the elongated recess 115 increases with increasing distance from the center C of curvature of the at least one curved surface. In other words, the elongated recess 115 as a smaller depth D1 at a position on the bottom mold 110 closer to the center axis C and has a larger depth D2 further away from the center axis C with a maximum at the bottom end of the bottom mold 110.

(13) Only as an example, if the bottom mold 110 is of a circular shape around center axis C and its cross-section forms a 40° portion of a circle on each side of the center axis C, the bottom mold can have a radius of 1.4 meters at its bottom rim, while the flat laminate has a radius of 1.414 meters. If 8 stiffeners shall be formed in the composite part, each stiffener can have a maximum depth D2 of 48 mm.

(14) FIGS. 2 and 3 schematically illustrate perspective views of a mold assembly 100 at subsequent process situations. Specifically, in order to form the stiffeners 15, 16 in the composite part 10, the flat laminate 200 has to be put into the at least one elongated recess 115 after draping the flat laminate 200 over the bottom mold 110. This may be achieved by a feeder unit 120 of the mold assembly 100. The feeder unit 120 has a shape corresponding to the at least one elongated recess 115. In the specific illustrated case, 8 stiffeners shall be formed, so that 8 elongated recesses 115 are in the bottom mold 110. The corresponding feeder unit 120 has a star form with 8 arms. Each of the arms of the feeder unit 120 is curved at its bottom edge in correspondence to the curvature of the bottom mold 110 as well as the elongated recess 115.

(15) The feeder unit 120 is moved onto the bottom mold 110 and further into a position where at least a part of the feeder unit 120 fits into the at least one elongated recess 115. Thereby, a portion of the laminate 200 is pushed into the at least one elongated recess 115 by the feeder unit 120, as illustrated in the lower part of FIG. 3.

(16) Still with respect to FIG. 3, the mold assembly 100 can further comprise a top mold 140 configured to form a second surface of the composite part 10 opposite to the first surface, wherein the first surface is the one including the stiffeners 15, 16. The top mold 140 may either comprise a plurality of openings, so that the top mold 140 can be placed over the draped laminate 200, while each arm of the feeder unit 120 fits through one opening of the top mold 140. The bottom mold 110 and top mold 140 can now be used to apply a pressure to the laminate 200 for hardening. Alternatively, the feeder unit 120 is removed and the top mold 140 forms a sphere without openings covering the entire draped laminate 200.

(17) The pushing of the laminate 200 into the elongated recesses 115 is now explained in more detail with respect to FIGS. 4 to 7. For instance, the feeder unit 120 may comprise a fixture 125 (FIG. 5), to which an insert 210 (FIGS. 2 and 4) is mounted. When the feeder unit 120 is moved towards the bottom mold 110, the insert 210 pushes the portion of the laminate 200 into the at least one elongated recess 115, the result of which is illustrated in FIG. 5. The portion of the laminate 200 surrounds most of the circumference of the insert 210, with the exception of the upper side of the insert 210 which faces the fixture 125 of the feeder unit 120.

(18) The insert 210 can be dimensioned to press fit the portion of the laminate 200 into the elongated recess 115, so that the recess 115 is completely filled by the laminate 200 and the insert 210, and the stiffener 15, 16 will later be free of voids. As is illustrated in FIG. 4, the elongated recess 115 can have a cross-sectional shape corresponding to a desired outer surface of the stiffener 15, 16. Only as examples, a cross-sectional shape of a rectangle 116 and a cross-sectional shape of substantially U-form 117 is shown in FIG. 4. In other words, the bottom end 116, 117 of the elongated recess may either have sharp corners or a round shape, respectively. It is to be understood that the resulting stiffener may also have widening portions at a distal end or elsewhere, which can be formed by a corresponding recess and optionally an insert of flexible material, which pushes the laminate in the widened portion of the recess.

(19) Furthermore, the insert 210 can be released from the fixture 125 by a mechanism pushing the insert 210 out of the fixture 125, which is illustrated in FIG. 5. Alternatively, the insert 210 may be released from the fixture 125 simply by a press fit in the recess 115, which creates a higher frictional force on the insert 210 than in the fixture 125. Also alternatively, an insert 211 (as in the right part of FIG. 7) may be pushed into the recess 115 that extends over the upper surface of the laminate 200 when draped over the bottom mold 110. This extending insert 211 facilitates pressing the laminate 200 into the recess 115 during hardening for an improved continuous form of the stiffener 15, 16.

(20) An alternative and simpler way of pushing the laminate 200 into the recesses 115 may be achieved by a blade portion of the feeder unit 120 arranged at the bottom end of the feeder unit 120 (not explicitly illustrated in the drawings). Such blade portion functions as the insert 210, but is part of or fixed to the feeder unit 120. Thus, when removing the feeder unit 120, the blade portion is also removed from the portion of the laminate 200 in the elongated recess 115. This allows manufacturing of stiffeners 15, 16, which have a width of substantially double the thickness of the laminate 200. Using a thin blade portion (not illustrated), the laminate 200 can be pushed into the recess 115 without an insert.

(21) The stiffener 15, 16 may further be formed using a reinforcing device 220, 221 (FIG. 6) configured to be inserted into the at least one elongated recess 115. The reinforcing device 220 can be of a U-form, the outer circumference of which coincides with the inner surface of the recess 115. Another type of reinforcing device 221 may be supplemented with at least one flange extending over a portion of the bottom mold 110 adjacent to the elongated recess 115, when the reinforcing device 221 is inserted into the recess 115. The flange may be tapered towards its outer ends. Any flange provides for a good integration into the composite parts 10.

(22) In any case, the reinforcing device 220, 221 includes an elongated slit, which provides the same functionality as the elongated recess 115. Since the reinforcing device 220, 221 may be formed of a different material than the laminate 200, the stiffener 15, 16 can be provided with any property required for the particular composite part 10. The reinforcing device 220, 221 may also be made of the same material as the laminate 200 or may be made of a pre-consolidated or semi-cured material. This allows improving precision of the dimensions of the stiffener 15, 16.

(23) Referring to FIG. 7, at the upper part of the laminate 200 two bend portions of the laminate will contact one another or contact the insert 210, 211. Thus, the composite part 10 is not closed and could be vulnerable due to a non-continuous surface. This may be improved by draping a laminate patch 230, 235 (see also FIG. 8) onto the laminate 200 at least at portions of the laminate 200 corresponding to the elongated recess 115. Such patch 230 closes the upper side of the composite part 10 along the elongated recess 115. A top patch 235 may close any gap in the center of the composite parts 10, if the stiffeners reach to the center C.

(24) FIG. 8 schematically illustrates a perspective view of a composite structure 10. On the left-hand side of FIG. 8 the composite structure 10 is illustrated broken up, so that the inside of the spherical composite structure 10, and particularly one of the stiffeners 15, 16, is visible. On the outside of the composite structure 10, the portions of the laminate 200, which are bend on the outside part of the stiffeners 15, 16 are covered by respective patches 230, 235. The portions 12 of the composite structure 10 between a pair of stiffeners 15, 16 have the shape corresponding to the bottom mold 110 and top mold 140. Likewise, the outer (upper) surface of the patches 230, 235 can be formed by the top mold 140.

(25) FIG. 9 illustrates an exemplary flow diagram of a method of manufacturing a composite part 10 including a stiffener 15, 16. The method starts in step 300 with providing a bottom mold 110 having at least one elongated recess 115. In an optional step 305 a reinforcing device 220, 221 can be inserted into at least one of the at least one elongated recess 115.

(26) The manufacturing method continues in step 310 with draping a flat laminate 200 onto the bottom mold 110, and in step 320, with driving a feeder unit 120 onto the laminate 200. The feeder unit 120 pushes a portion of the laminate 200 into the at least one elongated recess 115 or into a slit of a reinforcing device 220, 221, if present in the elongated recess 115.

(27) Furthermore, the laminate 200 may be supplemented with a laminate patch 230, 235 draped in step 325 onto the laminate 200 at least at portions of the laminate 200 corresponding to the elongated recess 115. Particularly, the laminate patch 230, 235 is draped onto a side of the laminate 200 facing away from the bottom mold 110.

(28) The draped laminate 200 and optionally the laminate patch 230, 235 is then pressed in step 330 by a top mold 140 pressing the laminate 200 towards the bottom mold 110. This pressing may also act on an insert 210 inserted between the portion of the laminate 200 pushed into the elongated recess 115. This facilitates filling the recess 115 completely by the laminate 200.

(29) Finally, the laminate 200 is hardened in step 340 to form the composite part 10. Specifically, the bottom mold 110 forms a first surface of the composite part 10, the at least one elongated recess 115 forms a corresponding stiffener 15, 16 integrated in the composite part 10, and the top mold 140 forms a second surface of the composite part 10 opposite to the first surface.

(30) FIG. 10 schematically illustrates an aircraft 1 comprising at least one composite part 10. Specifically, the illustrated aircraft 1 comprises a rear bulkhead 10 made from a composite material. Conventional rear bulkheads were made from several metal components mounted together. Using the method and composite part 10 of the present disclosure significantly reduces the time to manufacturing such rear bulkhead 10 and further reduces the weight of such bulkhead 10.

(31) It is to be understood that other portions of the aircraft 1, such as doors, parts of the wing, parts of the fuselage, etc., may be formed by a composite part 10 as herein disclosed.

(32) The above description of the drawings is to be understood as providing only an exemplary embodiment of the present invention and shall not limit the invention to this particular embodiment.

(33) While at least one exemplary embodiment of the present invention(s) is disclosed herein, it should be understood that modifications, substitutions and alternatives may be apparent to one of ordinary skill in the art and can be made without departing from the scope of this disclosure. This disclosure is intended to cover any adaptations or variations of the exemplary embodiment(s). In addition, in this disclosure, the terms “comprise” or “comprising” do not exclude other elements or steps, the terms “a” or “one” do not exclude a plural number, and the term “or” means either or both. Furthermore, characteristics or steps which have been described may also be used in combination with other characteristics or steps and in any order unless the disclosure or context suggests otherwise. This disclosure hereby incorporates by reference the complete disclosure of any patent or application from which it claims benefit or priority.