CA2211556A1 - Method for making honeycomb core composite articles - Google Patents
Method for making honeycomb core composite articlesInfo
- Publication number
- CA2211556A1 CA2211556A1 CA002211556A CA2211556A CA2211556A1 CA 2211556 A1 CA2211556 A1 CA 2211556A1 CA 002211556 A CA002211556 A CA 002211556A CA 2211556 A CA2211556 A CA 2211556A CA 2211556 A1 CA2211556 A1 CA 2211556A1
- Authority
- CA
- Canada
- Prior art keywords
- composite
- composite skin
- honeycomb core
- skin
- precured
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Abandoned
Links
Classifications
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
- B29C70/00—Shaping composites, i.e. plastics material comprising reinforcements, fillers or preformed parts, e.g. inserts
- B29C70/04—Shaping composites, i.e. plastics material comprising reinforcements, fillers or preformed parts, e.g. inserts comprising reinforcements only, e.g. self-reinforcing plastics
- B29C70/28—Shaping operations therefor
- B29C70/30—Shaping by lay-up, i.e. applying fibres, tape or broadsheet on a mould, former or core; Shaping by spray-up, i.e. spraying of fibres on a mould, former or core
- B29C70/34—Shaping by lay-up, i.e. applying fibres, tape or broadsheet on a mould, former or core; Shaping by spray-up, i.e. spraying of fibres on a mould, former or core and shaping or impregnating by compression, i.e. combined with compressing after the lay-up operation
- B29C70/342—Shaping by lay-up, i.e. applying fibres, tape or broadsheet on a mould, former or core; Shaping by spray-up, i.e. spraying of fibres on a mould, former or core and shaping or impregnating by compression, i.e. combined with compressing after the lay-up operation using isostatic pressure
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
- B29C70/00—Shaping composites, i.e. plastics material comprising reinforcements, fillers or preformed parts, e.g. inserts
- B29C70/04—Shaping composites, i.e. plastics material comprising reinforcements, fillers or preformed parts, e.g. inserts comprising reinforcements only, e.g. self-reinforcing plastics
- B29C70/06—Fibrous reinforcements only
- B29C70/08—Fibrous reinforcements only comprising combinations of different forms of fibrous reinforcements incorporated in matrix material, forming one or more layers, and with or without non-reinforced layers
- B29C70/088—Fibrous reinforcements only comprising combinations of different forms of fibrous reinforcements incorporated in matrix material, forming one or more layers, and with or without non-reinforced layers and with one or more layers of non-plastics material or non-specified material, e.g. supports
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
- B29C70/00—Shaping composites, i.e. plastics material comprising reinforcements, fillers or preformed parts, e.g. inserts
- B29C70/04—Shaping composites, i.e. plastics material comprising reinforcements, fillers or preformed parts, e.g. inserts comprising reinforcements only, e.g. self-reinforcing plastics
- B29C70/28—Shaping operations therefor
- B29C70/40—Shaping or impregnating by compression not applied
- B29C70/42—Shaping or impregnating by compression not applied for producing articles of definite length, i.e. discrete articles
- B29C70/44—Shaping or impregnating by compression not applied for producing articles of definite length, i.e. discrete articles using isostatic pressure, e.g. pressure difference-moulding, vacuum bag-moulding, autoclave-moulding or expanding rubber-moulding
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
- B29C70/00—Shaping composites, i.e. plastics material comprising reinforcements, fillers or preformed parts, e.g. inserts
- B29C70/04—Shaping composites, i.e. plastics material comprising reinforcements, fillers or preformed parts, e.g. inserts comprising reinforcements only, e.g. self-reinforcing plastics
- B29C70/28—Shaping operations therefor
- B29C70/40—Shaping or impregnating by compression not applied
- B29C70/42—Shaping or impregnating by compression not applied for producing articles of definite length, i.e. discrete articles
- B29C70/44—Shaping or impregnating by compression not applied for producing articles of definite length, i.e. discrete articles using isostatic pressure, e.g. pressure difference-moulding, vacuum bag-moulding, autoclave-moulding or expanding rubber-moulding
- B29C70/443—Shaping or impregnating by compression not applied for producing articles of definite length, i.e. discrete articles using isostatic pressure, e.g. pressure difference-moulding, vacuum bag-moulding, autoclave-moulding or expanding rubber-moulding and impregnating by vacuum or injection
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
- B29C70/00—Shaping composites, i.e. plastics material comprising reinforcements, fillers or preformed parts, e.g. inserts
- B29C70/68—Shaping composites, i.e. plastics material comprising reinforcements, fillers or preformed parts, e.g. inserts by incorporating or moulding on preformed parts, e.g. inserts or layers, e.g. foam blocks
- B29C70/86—Incorporated in coherent impregnated reinforcing layers, e.g. by winding
- B29C70/865—Incorporated in coherent impregnated reinforcing layers, e.g. by winding completely encapsulated
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29D—PRODUCING PARTICULAR ARTICLES FROM PLASTICS OR FROM SUBSTANCES IN A PLASTIC STATE
- B29D24/00—Producing articles with hollow walls
- B29D24/002—Producing articles with hollow walls formed with structures, e.g. cores placed between two plates or sheets, e.g. partially filled
- B29D24/005—Producing articles with hollow walls formed with structures, e.g. cores placed between two plates or sheets, e.g. partially filled the structure having joined ribs, e.g. honeycomb
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29D—PRODUCING PARTICULAR ARTICLES FROM PLASTICS OR FROM SUBSTANCES IN A PLASTIC STATE
- B29D99/00—Subject matter not provided for in other groups of this subclass
- B29D99/001—Producing wall or panel-like structures, e.g. for hulls, fuselages, or buildings
- B29D99/0014—Producing wall or panel-like structures, e.g. for hulls, fuselages, or buildings provided with ridges or ribs, e.g. joined ribs
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B32—LAYERED PRODUCTS
- B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
- B32B3/00—Layered products comprising a layer with external or internal discontinuities or unevennesses, or a layer of non-planar form; Layered products having particular features of form
- B32B3/10—Layered products comprising a layer with external or internal discontinuities or unevennesses, or a layer of non-planar form; Layered products having particular features of form characterised by a discontinuous layer, i.e. formed of separate pieces of material
- B32B3/12—Layered products comprising a layer with external or internal discontinuities or unevennesses, or a layer of non-planar form; Layered products having particular features of form characterised by a discontinuous layer, i.e. formed of separate pieces of material characterised by a layer of regularly- arranged cells, e.g. a honeycomb structure
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B32—LAYERED PRODUCTS
- B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
- B32B37/00—Methods or apparatus for laminating, e.g. by curing or by ultrasonic bonding
- B32B37/14—Methods or apparatus for laminating, e.g. by curing or by ultrasonic bonding characterised by the properties of the layers
- B32B37/146—Methods or apparatus for laminating, e.g. by curing or by ultrasonic bonding characterised by the properties of the layers whereby one or more of the layers is a honeycomb structure
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29L—INDEXING SCHEME ASSOCIATED WITH SUBCLASS B29C, RELATING TO PARTICULAR ARTICLES
- B29L2031/00—Other particular articles
- B29L2031/60—Multitubular or multicompartmented articles, e.g. honeycomb
- B29L2031/608—Honeycomb structures
Abstract
A method for making a honeycomb core composite article includes forming a honeycomb core (24) and a precured composite skin (20) having a core edge (32) and a restraint edge (30), respectively. The precured composite skin (20) is placed in combination with a rigid mold member having a mold surface (12s) and the honeycomb core (24) is mated with the precured composite skin (20) to form a mated subassembly (36). An uncured composite skin (22) is laid over the mated subassembly (36) such that a peripheral portion (44) of the uncured composite skin (22) extends beyond the restraint edge (30) by a distance X and such that the peripheral portion (44) is in superposed abutting engagement with the mold surface (12s). The honeycomb core (24), the precured composite skin (20) and the uncured composite skin (22) define a composite lay-up (10) over which a vacuum bag (14) is disposed. The resultant mold cavity (60) is evacuated to urge the vacuum bag (14) against the uncured composite skin (22) thereby effecting engagement of the peripheral portion (44) with the restraint edge (30) and the mold surface (12s). The composite lay-up (10) is then cured to form the completed honeycomb core composite article. The method produces a honeycomb core composite article wherein the honeycomb core (24) thereof is accurately located and substantially distortion-free.
Description
Description Method For Making Honeycomb Core Composite Articles Technical Field The present invention relates to manufacturing honeycomb core composite articles, and more particularly, to an improved method of manufacturing such composite articles wherein the honeycomb core thereof is accurately located and substantially distortion-free.
Background Of The Invention Composite articles incorporating honeycomb cores are commonly utilized for fabricating aerospace structures due to their advantageous strength to weight ratio. Honeycomb core (HC) composite articles are typically comprised of upper and lower composite skins, i.e., fiber reinforced resin matrix laminates, that are separated and stabilized by the honeycomb core. Due to the high bending stiffness and compressive strength properties of HC composite articles, i.e., the honeycomb core functions as a shear web and spaces the composite skins from the bending neutral axis, HC composite articles have particular utility in aerospace applications such as aircraft fuselage panels and door structures. The high strength and low weight of such construction results in lower overall aircraft system weight.
HC composite articles may be fabricated utilizing various composite forming methods. The most commonly employed technique involves the use of a vacuum bag molding assembly wherein an impervious membrane or "vacuum bag" is employed for consolidating the composite skins and ensuring proper adhesion thereof to the centrally disposed honeycomb core. More specifically, the lower composite skin, honeycomb core, and upper composite skin are sequentially laid in a rigid mold member so that the honeycomb core is overlaid by the upper and lower composite skins. The upper and lower composite skins are formed from uncured "prepreg" or "B-stage"
laminates comprised of a fiber reinforcement such as graphite, aramide or fiberglass fibers disposed in a binding matrix such as epoxy, phenolic or other similar organic resinous material. Film adhesive, which is applied to the honeycomb core prior to the lay-up, forms the bonds between the upper and lower composite laminates and the honeycomb core. The vacuum bag is disposed over the rigid mold member and sealed thereto so as to form a mold cavity which is occupied by the uncured composite lay-up. The mold cavity is then evacuated and additional pressure and temperature are applied via an autoclave oven to cure the lay-up. The combination of vacuum and external pressure functions to consolidate the composite skins, remove air and volatiles from the resin binder, and apply the necessary compaction pressure to ensure full and uniform adhesion of the lay-up.
Difficulties commonly encountered during the fabrication of HC
composite articles relate to shifting and/or distortion of the honeycomb core under compaction pressure. While the honeycomb core is relatively stable in the direction of the individual cells, i.e., the cells provide significant buckling stability, it will be appreciated that pressure applied transversely of the cells may cause distortion and/or shifting, e.g., accordioning, of the honeycomb core due to the inadequate strength thereof in a lateral direction. This is more clearly understood by reference to Fig. 1 a wherein a lay-up of upper and lower composite skins 100,102, and a honeycomb core 104 is disposed in a vacuum bag molding assembly 108. The vacuum bag 110 is shown applying a lateral component of pressure P along the ramped edges of the honeycomb core, which lateral pressure component causes the local collapse and distortion of the honeycomb core edges. Fig. 1b shows a top view of the cured HC composite article wherein the distortion, indicated by dashed lines 112, is exaggerated for illustrative purposes .
Attempts to overcome problems of distortion and shifting have included stabilization techniques wherein the edges of the honeycomb core, i.e., several rows of honeycomb cells about the entire periphery, are stabilized by the application of film adhesive or filled with a low density syntactic foam. Once cured, the film adhesive and/or the foam-filled cells serve to retard the accordioning of the honeycomb core.
U .S. Patents 4,680,216 and 5,354,195 discuss honeycomb core stabilization techniques and various materials useful therefor. While these techniques have been marginally successful in limiting distortion of the honeycomb core (on the order of about .64 cm to .95 cm (.25 in to .375 in), such materials are substantially parasitic and are not practical for applications wherein minimization of overall aircraft weight is a critical design criterion. Furthermore, these stabilization options are not acceptable for applications wherein accurate and distortion-free core location is highly critical. For example, applications requiring the use of ~ radar absorbent (i.e., carbon-loaded) honeycomb core to defeat enemy radar require far more exacting manufacturing tolerances than those which can be produced by prior art stabilization techniques. If shifting of the radar absorbent honeycomb core should occur during the manufacturing process, radar coverage on the aircraft could be compromised.
Other attempts to yield a distortion-free core have included the use of restraint devices formed or assembled about the periphery of the molding assembly. Fig. 2a depicts a vacuurn bag molding assembly wherein rows of vertically protruding pins 120 are affixed to a rigid mold member 122 and disposed in adjacent relation to the HC
composite article 124 to be formed. As the upper composite skin 126 is laid over the honeycomb core 128, the pins 120 are caused to engage a peripheral portion 130 of the upper composite skin 126, i.e., pierce the composite fabric, to prevent lateral displacement thereof during the molding/compaction process. A bridging effect is thereby created in the upper composite skin 126, i.e., between the uppermost corner 132 of the honeycomb core 128 and the mating surface 134 of the lower composite skin 136, to react lateral compaction pressure and, consequently, prevent distortion of the honeycomb core 128. While this technique is suitable for high tolerance applications, e.g., LO
applications, the protruding pins 120 are a source of high maintenance, i.e., requiring periodic cleaning and repair, pose a hazard to the operator, and create difficulties when sealing the vacuum bag 138 to the rigid mold member 122. Regarding the latter, the vacuum bag 138 must be sealed outboard of the protruding pins 120, thus requiring the additional step of disposing a protective elastomer strip 139 over the protruding pins 120 to prevent damage to the vacuum bag 138.
A similar approach is shown in Fig. 2b wherein a perforated or apertured metal strip 140 is substituted for the protruding pins 120. The peripheral portion 130 of the upper composite skin 126 is laid over the apertured metal strip 140 such that under compacting pressure the apertures 142 thereof capture or grip the peripheral portion 130 to prevent lateral displacement of the upper cornposite skin 126. This CA 02211~6 1997-07-2~
approach yields similar results to the above-described pinned con~iguration.
however. Iaborious cleanin(J is required tO remove e~cess resin from the aperlUreS 1~7 prior ~o initialing the ne.Yt cure cycle.
Yet another method ~'or yielding a distortion-free HC composile arlicle is 5 described in Brayden et al. ~.S. Pa~em ~,7~7~651. The metho~:i hl~ol~es Ihe introduction of pressurized air or gas~ such as that produced b- an auloclave~ on the back-side of the upper t'ace plies of the HC composite article. and parlicularly on ~he face plies overlaying a ramped porlion of the honeycomb core. The back-pressure effects an equalizing or reacting force ~vhich prevents lateral movement and I () distortion of the hone comb core. The moid assembly IS equipped ~ith a press~lre port which introduces pressurized air or gas ~o the volume or cav it- occupied b~ the honeycomb core and belween the face plies. The honeycomb core inc!udes perforations in the cell ~valls to permit communication of pressure fi-om one ~ell lo an adjacen~ cell and ultimately ~o ~he entire back-side of the upper face ~lies. While l 5 this technique offers a unique soluIion, ~he COSt associated with mold modifica~ions and the laborious set-up associated with creating an closed internal system for internally pressurizing the HC composite article is fiscally disadvantageous.
A need therefore e~cists to provide an improved method of manufacluring HC
composite articles which provides accurate and distortion-free core location and70 minimizes repair and/or maintenance of the molding assembly.
Disclosure Of Invention It is an object of the present invention to provide a method for manufacturing HC composite articles wherein the honeycomb core thereof is accurately located and ~5 substantially distortion-free.
lt is another object of the present invention to provide a method for manufacturing HC composite articles wherein modifications to and maintenance of the molding assembly are minimi7.od.
These and other objects are achieved by a method for making HC composite 30 articles including the steps of: forming a honeycomb core having a core edge,placing a first composite skin in combination with a rigid mold member having a mold surface, mating the honeycomb core to the first composite skin thereby forrning a mated subassembly, laying-up a second composite skin over the mated subassembly, which second composite skin is an uncured composite skin and which 35 honeycomb core, first composite skin and second composite skin~ in combination, define a composite lay-up, disposing a vacuum bag over the composite lay-up thereby forming a mold cavity between the mold surface and the vacuum bag, AMEh;DED SH~ET
-evacua~ing the mold cavity to urge the vaCuum bag against the second composite skin for compacting the same against the ma~ed subassembl~v. and curing the composite la~-up to form the honeycomb core composite article. The method is further characterized by the steps of .t'orming the first composite skin prior to the . placing slep so ~hat the t'irst composite skin is a precured composite skin having a restr~int edge~ disposing the second composite skin in combination with the mated subassembl-i such that a peripheral portion of the second composite skin e.~l;tends bevond the restraint edge bv a distance ~ and, furthermore. so that the peripheral portion is in superposed abutting engagemen~ with the mold s-lrf.lce ot' the rigi :!
10 mold member~ and ~vherein the evacuating slep causes the v acuum bag to et'~ct enga ~ement of the peripheral portion ~vith the restrain. edge and the rnold surface tor preventing laleral displacement of the second composite sl~in upon curing ot' the composite la!-up.
The t'oregoing and other objects. fealures and advantages or'the present 1~ invention ~ill become more apparent in light of the following A~IEl~l~,E~ S~
detailed description of exemplary embodiments thereof, as illustrated in the accompanying drawings.
Brief Description Of The Drawings A more complete understanding of the present invention and the attendant features and advantages thereof may be had by reference to the following detailed description of the invention when considered in conjunction with the following drawings wherein:
Figs. 1 a and 1 b depict a honeycomb core (HCj composite article being formed in a vacuum bag molding assembly and the resultant distortion of the honeycomb core under molding assembly pressure;
Figs. 2a and 2b depict prior art molding apparatus for preventing distortion o~ a vacuum-formed HC composite article;
Fig. 3 depicts an exploded partial cross-sectional view of a HC
composite lay-up employing the teachings of the present invention;
Fig. 4 depicts the HC composite artic!e manufactured by the method of the present invention, and more particularly, the consolidation of the lay-up by a vacuum bag molding assembly.
Best Mode For carrying Out The Invention Referring now to the drawings wherein like reference characters identify corresponding or similar elements throughout the several views, Fig. 3 depicts an exploded partial cross-sectional view of a honeycomb core (HC) composite lay-up 10 disposed between a rigid mold member 12 and a vacuum bag 14 which, in combination, form a vacuum bag mold assembly 16. The composite lay-up 10 includes precured and uncured composite skins 20, 22, and a honeycomb core 24 disposed therebetween.
The honeycomb core 24 may be any of the conventionally used open cellular honeycombs such as aluminum, phenolic or NOMEX (~
(NOMEX is a registered trademark of Hexcel Corp., Chatsworth, CA for an aramid fiber or fabric). For applications wherein weight is a critical design criterion, a lightweight honeycomb core having a density of about 28.84 Kg/m3 (1.8 Ibs/ft3) is preferred. Generally, honeycomb core is purchased in bulk and machined to the desired shape and size using Numerically Controlled (NC) machining apparatus. While the honeycomb core 24 is shown to have a ramped surface 26 to gradually transfer shear loads to the precured and uncured composite CA 02211~6 1997-07-2~
skins 20~ 22~ it will be understood that the ~eachings of the present in-ention are equally applicable to honevcomb cores having a right-angled conficTuration The precured composite skin ~0 is comprised of fiber reinforced resin matri~ composite laminates having a fiber reinforcement such as graphite~ aramide S or fiberglass fibers disposed in a binding matri~ such as epo.Yv. phenolic or other similar organic resinous material. Preferably, two composite laminates havin( a total thickness of at least about .038 cm (.015 in) are laid-up in a mold assembl~r and cured to form a cured composite panel. Any conventional t'abric;ltiol1 metll()d.
such as vacuum forming. resin transfer molding, Ol matcllecl metal molding ma~
be used to form and cure the composite panel. The prel'erred melhod. however.
utilizes a v~cuum bag mold assembly wherein the same rigid mold member l ~
employed for forming the HC composite lay-up is used ~'or t'orming the precured composite skin 20. Once cured, at least one end of the cured composite panel is trimmed~ thus forming the precured first composite skin '0. The trimming I S operation also produces ~ restraint edge 30 having a right-anglea confi(T~Ira~i()n ~0'. The utility of this construction will become eviden~ when discussing ~he subsequent processing steps.
The precured first composite skin 20 is then returned to the rigid mold member 12 and the honeycomb core 24 is mated therewith to form a mated subassemblv 36 (see Fig. 4). Furthermore, the honeycomb core '~ is disposed in superposed relation with the precured composite slcin ~0 so that the restraint edge 30 e~tends beyond the edge 32 of the honeycomb core 24. The portion of the precured composite skin 20 e~tending beyond the core edge 32 defines an upwardly facing mating surface 38 which will, in subsequent steps~ be disposed in combination with and bonded to the uncured composite skin 22. The mating step additionally includes the application of a bonding adhesive 34a to one or both of the mating surfaces, i.e., to either the honeycomb core 24 or the precured composite skin 20, for bonding the core to the precured composite skin 20. In the preferred embodiment, the bonding adhesive 34a is co-cured with the completed composite lay-up l0, i.e., concurrent with the curing step (cure cycle) described hereinbelow. However, it is also contemplated that the bonding operation may be performed prior to subsequent processing steps, e.g., as a independent operationrequiring a unique cure cycle. The preferred bonding adhesive 34a is a film adhesive such as EA 9690 manufactured by Hysol Corp located in Pittsburgh, CA.
The uncured composite skin 22 is comprised of one or more l~min~tes of uncured preimpregnated fiber reinforced composite material having a fiber reinforcement such as graphite, aramide or fiberglass fibers disposed in a binding CA 02211~6 1997-07-2~
matrix such as epo~cy~ phenolic or other similar organic resinous material. In the preferred embodiment a bonding adhesive '4b. such as Hysol 9690 film adhesive~
is first applied to the e~posed upper surfàce 40 or' the hone- comb core ~4 in preparation for the lay-up of the uncured composite sLiin 22. The adhesive 3~b S facilitates the bonding of the uncured composite sL;in " to the lloneycomb core ~4, however~ it will be appreciated that the uncured binding matri~ i.e.~ resin of the uncured composite skin ?7, m~y adequately wet the honeycomb core surface during the cure cycle to et'fect a suitable bond~ thereby eliminatin~J the need for the bonding adhesive 3~b. _ The uncured composite skin " is laid over the mated subass~mbl- 36 all(l is precompacted using con~entional debulklng techniques to ensure intima~e contact with the e~posed upper honeycomb core surface 40 and the mating surface 3~ of the precured composite skin '0. Furthermore~ the uncured composite skin 22 is appropriately sized so as to permit a peripheral portion 4~i S thereof to e~tend bevond the restraint edge 30 of the precured composite sliin ~0.
Moreover~ the peripheral portion 44 is in superposed abutting engagement with the mold surface I 's of the rigid mold member 1 ' and e~tends a distance X
beyond the restraint edge 30. Preferably, the peripheral portion 44 e~ctends at least 1.9 cm (.75 in) beyond the edge 30 and, more preferably, about ~.5 cm (1 in) '0 beyond the edge 30.
The vacuum bag 1~ is disposed over the completed composite lay-up 10 and sealed to the rigid mold member 12, or to itself~ 1~ti~ in~ a conventional sealer strip 50 such as "Prestite" (Prestite is a brand name of a semi-adhesi~e compliant material produced by 3M located in St. Paul, MN for a semi-adhesive 25 compliant). Optionally, a separator or release film 52 and a breather ply 54 may be interposed between the uncured composite skin " and the vacuum bag 14.
The separator film 52 facilitates release of the vacuum bag 14 after curing the composite lay-up 10 while the breather ply 54 facilitates the removal of air andvolatiles from the uncured A~/iENL~ED SHEET
composite skin 22 during the cure cycle. Representative materials are specified in the below-described example. In the described embodiment, the use of the release film 52 and breather ply 54 are preferred, however, the composite lay-up 10 is minimally comprised of ~.
the honeycomb core 24, the precured composite skin 20, and the uncured composite skin 22.
The completed vacuum bag molding assembly 16 shown in Fig. 4 forms a sealed mold cavity 60, i.e., between the rigid mold member 12 and the vacuum bag 14, which is in fluid communication with a vacuum pump 62. The vacuum pump 62 functions to evacuate the mold cavity 60 of gaseous fluids, i.e., air and volitales, and to create a pressure differential for urging the vacuurn bag 14 against the uncured composite skin 22. Concomitantly, the peripheral portion 44 of the uncured composite skin 22 is forced into engagement with the restraint edge 30 of the precured composite skin 20 and against the mold surface 12s.
The vacuum bag molding assembly 16 is then placed in an autoclave oven (not shown) wherein the composite lay-up 10 is exposed to additional pressure and temperature for curing. For the described embodiment, the autoclave oven applies a pressure of about 3.72 x107-4.46 x 107N/m2 (25 - 30 Ibs/in2) to the lay-up and elevates the temperature thereof to about 121 - 232~C (250 - 450~ F) degrees for a period of about 120 - 180 mins.
During the vacuum forming step, i.e., evacuation of the mold cavity 60, and subsequent curing step, the peripheral portion 44 of the uncured composite skin 22 engages the restraint edge 30 of the precured composite skin 20 so as to provide a mechanical interlock therebetween. The restraint edge 30 functions to inhibit the lateral displacement of the uncured composite skin 22 and, consequently, cause a bridging effect therein in the region overlaying the ramped honeycomb surface 26. As discussed supra, the bridging effect functions to react the lateral component of pressure P applied by the vacuum bag 14. Concomitantly, the contacting interface Cl between the peripheral portion.44 and the mold surface 12s, provides additional restraint toward the objective of inhibiting lateral displacement. That is, the frictional force along the contacting interface Cl augments the restraint capacity of the restraint edge 30. Accordingly, by inhibiting lateral displacement and, consequently, the catenary displacement of the uncured composite skin 22, shifting and/or distortion of the honeycomb core 24 is minimized.
While the completed HC composite article may be used in the configuration produced by the foregoing process steps, the cured composite lay-up may be trimmed along line TL to net dimension to form a horleycomb core composite article having a uniform thickness peripheral flange 70. Preferably, the restraint edge 30 and the peripheral portion 44 are removed during this operation. Accordingly, the trimming operation removes the abrupt contour transition produced by the restraint edge 30 which enhances the strength of peripheral flange 70 for subsequent fastening and/or bonding operations.
The restraint edge 30 and the mold surface 12s are tooling surfaces which are functionally equivalent to the prior art pinned and perforated metal strip configurations, however, it will be appreciated that the formation of these tooling surfaces is far less labor intensive.
The restraint edge 30 is formed in conjunction with the manufacturing process and becomes and integral part of the finished HC composite article. Furthermore, the only additional step involves the formation of the precured composite skin 20. Insofar as it is advantageous to precure a composite laminate for the purposes of improving laminate quality and strength, the method of the present invention will have no adverse cost effect on the manufacturing process when such improved quality and strength are desired. For example, the precured composite skin 20 may be formed under a pressure of 1.1 1 X 1 o8 N/m2 (75 Ibs/in2) to improve the fiber volume content, i.e., increase the fiber to resin ratio, and, consequently, the strength of the composite laminate. Such increased fiber volume is not achievable using conventional co-cure methods, i.e., wherein both composite skins are uncured before entering the autoclave oven, insofar as high compaction pressures cannot be transferred via the low density honeycomb core.
With regard to fabricating the rigid mold member 12 to include the mold surface 1 2s, which is slightly enlarged for superpositioning of the peripheral por~ion 44, it will be appreciated that fabricating such an additional area surface is inconsequential in terms of time and labor.
It will also be appreciated that the hazards and periodic maintenance of the prior art tooling surfaces are entirely eliminated by CA 02211~6 1997-07-2~
the method of the present invention. Thal is. the present method does not introduce hazardous ;ooling surfaces e.g., pins~ or other tooling surraces. e.g.apertures w hich require periodic cleaning.
S l~AM~
~ honevcomb core (HC) composite article was ~bricated using the teachinus of the inven~ion as follows. A sheet ot 1.8 Ibs/ft3 NO~IEX~) honevcomb core was machined tO a thickness dimension of 3.0 cm ~ l .18 in). alld ;
length and width dimension o~ 60.1 cm ( '~ in)~ respectivelv. rhe ed~es ot the honeycomb core ~vere beveled to it'orm a 30~ ramp angle about the entire periphery. The honevcomb core was then cleaned with alcohol alld dried in an oven at 65.5~ C ( 1~0~ F) for a period of 1~0 minutes.
A firs~ composite skin was formed by cutting two plies of K~VLAR@~
~lber reinforced composite material (KEVLAR(~ is a regis~eted trademark of E.L.
l S du Pont de ~emours ~ Co. Iocated in Wilmington. DE for an aromatic poiyamideof high tensile strength) to a length and width dimension of 66.0~ cm (26 in).
respectivelv. The plies were sequentially laid in a rigid mold member of a vacuum bag molding assembly. A Fluorinated Ethylene-Propylene (FEP) separator film and a breather piy formed from a compliant porous material such as N- 10 (the FEP film and N- 10 ply were obtained from Airtech International located in Carson. CA) were respectively applied to the lay-up. A vacuum bag was applied to the lay-up and sealed to the rigid mold member using Prestite adhesive.
The completed vacuum bag molding assembly was then placed in an autoclave oven to cure the plies. In the autoclave oven, the composite plies were step-cured for a period of 180 mins to a peak pressure and temperature of 1.1 1 X 1 o8 ~/m2(75 lbs/in2) and 1 82.2~C (360~ F), respectively. The lay-up resulted in a curedcomposite panel having a thickness dimension of .038 cm (.015 in). The cured composite panel was then trimmed about its periphery to form a precured composite skin having a restraint edge. The net size of the precured composite skin was approximately 63.5 cm (25 in) square.
The precured composite skin was returned to the rigid mold member and a first layer of Hysol 9690 film adhesive was applied to the entire exposed surface.
The prior-formed honeycomb core was then mated upon and centered over the precured composite skin so that the A~ E~ ~J ~Ht-rT
restraint edge extended approximately 2.54 cm (1 in) beyond the edge of the honeycomb core. A second layer of Hysol 9689 film adhesive was then applied to the exposed upper surface of the honeycomb core.
An uncured composite skin comprising two plies of KEVLAR(~) material was laid over the mated subassembly, i.e., the honeycomb core and the precured composite skin, so that a peripheral portion of the uncured composite skin extended 2.54 cm (1 in) beyond the restraint edge of the precured composite skin. The uncured composite skin was debulked using conventional vacuum debulking apparatus for 5 minutes. An FEP separator film and an N-10 breather ply were sequentially laid over the uncured composite skin. A vacuum bag was then placed over the uncured composite skin and sealed to the rigid mold member, thereby forming a completed vacuum bag molding assembly. The mold cavity was evacuated so as to apply atmospheric pressure (full vacuum) via the vacuum bag to the underlying composite lay-up. The peripheral portion of the uncured composite skin was thereby simultaneously forced into engagement with the restraint edge of the precured composite skin and the mold surface of the rigid mold member, respectively.
The vacuum bag molding assembly was then placing in an autoclave oven and step-cured as follows. The autoclave pressure was raised to 1.49 X 107 N/m2 (10 Ibs/in2) and autoclave temperature was elevated to 93.3~ C (200~F) for a first hold phase of 60 minutes.
Approximately 30 minutes into the first hold phase, the autoclave pressure was gradually increased to 3.72 x 107 N/m2 (25 Ibs/in2).
Following the first hold phase, the temperature was gradually raised to 182.2~C (360 ~F) and held at a second hold phase (final cure phase) for 120 minutes.
The honeycomb core of the resultant composite article was found to be substantially distortion-free and accurately located relative to the composite skins.
The above described method may be used alone or in combination with various core stabilization techniques such as those described in U.S. Patents 4,680,216 and 5,354,195. Furthermore, debulking operations may be performed between each of the above described lay-up steps to improve the efficacy of the resultant bonds.
W 096/22878 PCTrUS95/01099 Although the invention has been shown and described with respect to exemplary embodiments thereof, it should be understood by those skilled in the art that the foregoing and other changes, omissions and additions may be made therein and thereto, without departing from the spirit and scope of the present invention.
Background Of The Invention Composite articles incorporating honeycomb cores are commonly utilized for fabricating aerospace structures due to their advantageous strength to weight ratio. Honeycomb core (HC) composite articles are typically comprised of upper and lower composite skins, i.e., fiber reinforced resin matrix laminates, that are separated and stabilized by the honeycomb core. Due to the high bending stiffness and compressive strength properties of HC composite articles, i.e., the honeycomb core functions as a shear web and spaces the composite skins from the bending neutral axis, HC composite articles have particular utility in aerospace applications such as aircraft fuselage panels and door structures. The high strength and low weight of such construction results in lower overall aircraft system weight.
HC composite articles may be fabricated utilizing various composite forming methods. The most commonly employed technique involves the use of a vacuum bag molding assembly wherein an impervious membrane or "vacuum bag" is employed for consolidating the composite skins and ensuring proper adhesion thereof to the centrally disposed honeycomb core. More specifically, the lower composite skin, honeycomb core, and upper composite skin are sequentially laid in a rigid mold member so that the honeycomb core is overlaid by the upper and lower composite skins. The upper and lower composite skins are formed from uncured "prepreg" or "B-stage"
laminates comprised of a fiber reinforcement such as graphite, aramide or fiberglass fibers disposed in a binding matrix such as epoxy, phenolic or other similar organic resinous material. Film adhesive, which is applied to the honeycomb core prior to the lay-up, forms the bonds between the upper and lower composite laminates and the honeycomb core. The vacuum bag is disposed over the rigid mold member and sealed thereto so as to form a mold cavity which is occupied by the uncured composite lay-up. The mold cavity is then evacuated and additional pressure and temperature are applied via an autoclave oven to cure the lay-up. The combination of vacuum and external pressure functions to consolidate the composite skins, remove air and volatiles from the resin binder, and apply the necessary compaction pressure to ensure full and uniform adhesion of the lay-up.
Difficulties commonly encountered during the fabrication of HC
composite articles relate to shifting and/or distortion of the honeycomb core under compaction pressure. While the honeycomb core is relatively stable in the direction of the individual cells, i.e., the cells provide significant buckling stability, it will be appreciated that pressure applied transversely of the cells may cause distortion and/or shifting, e.g., accordioning, of the honeycomb core due to the inadequate strength thereof in a lateral direction. This is more clearly understood by reference to Fig. 1 a wherein a lay-up of upper and lower composite skins 100,102, and a honeycomb core 104 is disposed in a vacuum bag molding assembly 108. The vacuum bag 110 is shown applying a lateral component of pressure P along the ramped edges of the honeycomb core, which lateral pressure component causes the local collapse and distortion of the honeycomb core edges. Fig. 1b shows a top view of the cured HC composite article wherein the distortion, indicated by dashed lines 112, is exaggerated for illustrative purposes .
Attempts to overcome problems of distortion and shifting have included stabilization techniques wherein the edges of the honeycomb core, i.e., several rows of honeycomb cells about the entire periphery, are stabilized by the application of film adhesive or filled with a low density syntactic foam. Once cured, the film adhesive and/or the foam-filled cells serve to retard the accordioning of the honeycomb core.
U .S. Patents 4,680,216 and 5,354,195 discuss honeycomb core stabilization techniques and various materials useful therefor. While these techniques have been marginally successful in limiting distortion of the honeycomb core (on the order of about .64 cm to .95 cm (.25 in to .375 in), such materials are substantially parasitic and are not practical for applications wherein minimization of overall aircraft weight is a critical design criterion. Furthermore, these stabilization options are not acceptable for applications wherein accurate and distortion-free core location is highly critical. For example, applications requiring the use of ~ radar absorbent (i.e., carbon-loaded) honeycomb core to defeat enemy radar require far more exacting manufacturing tolerances than those which can be produced by prior art stabilization techniques. If shifting of the radar absorbent honeycomb core should occur during the manufacturing process, radar coverage on the aircraft could be compromised.
Other attempts to yield a distortion-free core have included the use of restraint devices formed or assembled about the periphery of the molding assembly. Fig. 2a depicts a vacuurn bag molding assembly wherein rows of vertically protruding pins 120 are affixed to a rigid mold member 122 and disposed in adjacent relation to the HC
composite article 124 to be formed. As the upper composite skin 126 is laid over the honeycomb core 128, the pins 120 are caused to engage a peripheral portion 130 of the upper composite skin 126, i.e., pierce the composite fabric, to prevent lateral displacement thereof during the molding/compaction process. A bridging effect is thereby created in the upper composite skin 126, i.e., between the uppermost corner 132 of the honeycomb core 128 and the mating surface 134 of the lower composite skin 136, to react lateral compaction pressure and, consequently, prevent distortion of the honeycomb core 128. While this technique is suitable for high tolerance applications, e.g., LO
applications, the protruding pins 120 are a source of high maintenance, i.e., requiring periodic cleaning and repair, pose a hazard to the operator, and create difficulties when sealing the vacuum bag 138 to the rigid mold member 122. Regarding the latter, the vacuum bag 138 must be sealed outboard of the protruding pins 120, thus requiring the additional step of disposing a protective elastomer strip 139 over the protruding pins 120 to prevent damage to the vacuum bag 138.
A similar approach is shown in Fig. 2b wherein a perforated or apertured metal strip 140 is substituted for the protruding pins 120. The peripheral portion 130 of the upper composite skin 126 is laid over the apertured metal strip 140 such that under compacting pressure the apertures 142 thereof capture or grip the peripheral portion 130 to prevent lateral displacement of the upper cornposite skin 126. This CA 02211~6 1997-07-2~
approach yields similar results to the above-described pinned con~iguration.
however. Iaborious cleanin(J is required tO remove e~cess resin from the aperlUreS 1~7 prior ~o initialing the ne.Yt cure cycle.
Yet another method ~'or yielding a distortion-free HC composile arlicle is 5 described in Brayden et al. ~.S. Pa~em ~,7~7~651. The metho~:i hl~ol~es Ihe introduction of pressurized air or gas~ such as that produced b- an auloclave~ on the back-side of the upper t'ace plies of the HC composite article. and parlicularly on ~he face plies overlaying a ramped porlion of the honeycomb core. The back-pressure effects an equalizing or reacting force ~vhich prevents lateral movement and I () distortion of the hone comb core. The moid assembly IS equipped ~ith a press~lre port which introduces pressurized air or gas ~o the volume or cav it- occupied b~ the honeycomb core and belween the face plies. The honeycomb core inc!udes perforations in the cell ~valls to permit communication of pressure fi-om one ~ell lo an adjacen~ cell and ultimately ~o ~he entire back-side of the upper face ~lies. While l 5 this technique offers a unique soluIion, ~he COSt associated with mold modifica~ions and the laborious set-up associated with creating an closed internal system for internally pressurizing the HC composite article is fiscally disadvantageous.
A need therefore e~cists to provide an improved method of manufacluring HC
composite articles which provides accurate and distortion-free core location and70 minimizes repair and/or maintenance of the molding assembly.
Disclosure Of Invention It is an object of the present invention to provide a method for manufacturing HC composite articles wherein the honeycomb core thereof is accurately located and ~5 substantially distortion-free.
lt is another object of the present invention to provide a method for manufacturing HC composite articles wherein modifications to and maintenance of the molding assembly are minimi7.od.
These and other objects are achieved by a method for making HC composite 30 articles including the steps of: forming a honeycomb core having a core edge,placing a first composite skin in combination with a rigid mold member having a mold surface, mating the honeycomb core to the first composite skin thereby forrning a mated subassembly, laying-up a second composite skin over the mated subassembly, which second composite skin is an uncured composite skin and which 35 honeycomb core, first composite skin and second composite skin~ in combination, define a composite lay-up, disposing a vacuum bag over the composite lay-up thereby forming a mold cavity between the mold surface and the vacuum bag, AMEh;DED SH~ET
-evacua~ing the mold cavity to urge the vaCuum bag against the second composite skin for compacting the same against the ma~ed subassembl~v. and curing the composite la~-up to form the honeycomb core composite article. The method is further characterized by the steps of .t'orming the first composite skin prior to the . placing slep so ~hat the t'irst composite skin is a precured composite skin having a restr~int edge~ disposing the second composite skin in combination with the mated subassembl-i such that a peripheral portion of the second composite skin e.~l;tends bevond the restraint edge bv a distance ~ and, furthermore. so that the peripheral portion is in superposed abutting engagemen~ with the mold s-lrf.lce ot' the rigi :!
10 mold member~ and ~vherein the evacuating slep causes the v acuum bag to et'~ct enga ~ement of the peripheral portion ~vith the restrain. edge and the rnold surface tor preventing laleral displacement of the second composite sl~in upon curing ot' the composite la!-up.
The t'oregoing and other objects. fealures and advantages or'the present 1~ invention ~ill become more apparent in light of the following A~IEl~l~,E~ S~
detailed description of exemplary embodiments thereof, as illustrated in the accompanying drawings.
Brief Description Of The Drawings A more complete understanding of the present invention and the attendant features and advantages thereof may be had by reference to the following detailed description of the invention when considered in conjunction with the following drawings wherein:
Figs. 1 a and 1 b depict a honeycomb core (HCj composite article being formed in a vacuum bag molding assembly and the resultant distortion of the honeycomb core under molding assembly pressure;
Figs. 2a and 2b depict prior art molding apparatus for preventing distortion o~ a vacuum-formed HC composite article;
Fig. 3 depicts an exploded partial cross-sectional view of a HC
composite lay-up employing the teachings of the present invention;
Fig. 4 depicts the HC composite artic!e manufactured by the method of the present invention, and more particularly, the consolidation of the lay-up by a vacuum bag molding assembly.
Best Mode For carrying Out The Invention Referring now to the drawings wherein like reference characters identify corresponding or similar elements throughout the several views, Fig. 3 depicts an exploded partial cross-sectional view of a honeycomb core (HC) composite lay-up 10 disposed between a rigid mold member 12 and a vacuum bag 14 which, in combination, form a vacuum bag mold assembly 16. The composite lay-up 10 includes precured and uncured composite skins 20, 22, and a honeycomb core 24 disposed therebetween.
The honeycomb core 24 may be any of the conventionally used open cellular honeycombs such as aluminum, phenolic or NOMEX (~
(NOMEX is a registered trademark of Hexcel Corp., Chatsworth, CA for an aramid fiber or fabric). For applications wherein weight is a critical design criterion, a lightweight honeycomb core having a density of about 28.84 Kg/m3 (1.8 Ibs/ft3) is preferred. Generally, honeycomb core is purchased in bulk and machined to the desired shape and size using Numerically Controlled (NC) machining apparatus. While the honeycomb core 24 is shown to have a ramped surface 26 to gradually transfer shear loads to the precured and uncured composite CA 02211~6 1997-07-2~
skins 20~ 22~ it will be understood that the ~eachings of the present in-ention are equally applicable to honevcomb cores having a right-angled conficTuration The precured composite skin ~0 is comprised of fiber reinforced resin matri~ composite laminates having a fiber reinforcement such as graphite~ aramide S or fiberglass fibers disposed in a binding matri~ such as epo.Yv. phenolic or other similar organic resinous material. Preferably, two composite laminates havin( a total thickness of at least about .038 cm (.015 in) are laid-up in a mold assembl~r and cured to form a cured composite panel. Any conventional t'abric;ltiol1 metll()d.
such as vacuum forming. resin transfer molding, Ol matcllecl metal molding ma~
be used to form and cure the composite panel. The prel'erred melhod. however.
utilizes a v~cuum bag mold assembly wherein the same rigid mold member l ~
employed for forming the HC composite lay-up is used ~'or t'orming the precured composite skin 20. Once cured, at least one end of the cured composite panel is trimmed~ thus forming the precured first composite skin '0. The trimming I S operation also produces ~ restraint edge 30 having a right-anglea confi(T~Ira~i()n ~0'. The utility of this construction will become eviden~ when discussing ~he subsequent processing steps.
The precured first composite skin 20 is then returned to the rigid mold member 12 and the honeycomb core 24 is mated therewith to form a mated subassemblv 36 (see Fig. 4). Furthermore, the honeycomb core '~ is disposed in superposed relation with the precured composite slcin ~0 so that the restraint edge 30 e~tends beyond the edge 32 of the honeycomb core 24. The portion of the precured composite skin 20 e~tending beyond the core edge 32 defines an upwardly facing mating surface 38 which will, in subsequent steps~ be disposed in combination with and bonded to the uncured composite skin 22. The mating step additionally includes the application of a bonding adhesive 34a to one or both of the mating surfaces, i.e., to either the honeycomb core 24 or the precured composite skin 20, for bonding the core to the precured composite skin 20. In the preferred embodiment, the bonding adhesive 34a is co-cured with the completed composite lay-up l0, i.e., concurrent with the curing step (cure cycle) described hereinbelow. However, it is also contemplated that the bonding operation may be performed prior to subsequent processing steps, e.g., as a independent operationrequiring a unique cure cycle. The preferred bonding adhesive 34a is a film adhesive such as EA 9690 manufactured by Hysol Corp located in Pittsburgh, CA.
The uncured composite skin 22 is comprised of one or more l~min~tes of uncured preimpregnated fiber reinforced composite material having a fiber reinforcement such as graphite, aramide or fiberglass fibers disposed in a binding CA 02211~6 1997-07-2~
matrix such as epo~cy~ phenolic or other similar organic resinous material. In the preferred embodiment a bonding adhesive '4b. such as Hysol 9690 film adhesive~
is first applied to the e~posed upper surfàce 40 or' the hone- comb core ~4 in preparation for the lay-up of the uncured composite sLiin 22. The adhesive 3~b S facilitates the bonding of the uncured composite sL;in " to the lloneycomb core ~4, however~ it will be appreciated that the uncured binding matri~ i.e.~ resin of the uncured composite skin ?7, m~y adequately wet the honeycomb core surface during the cure cycle to et'fect a suitable bond~ thereby eliminatin~J the need for the bonding adhesive 3~b. _ The uncured composite skin " is laid over the mated subass~mbl- 36 all(l is precompacted using con~entional debulklng techniques to ensure intima~e contact with the e~posed upper honeycomb core surface 40 and the mating surface 3~ of the precured composite skin '0. Furthermore~ the uncured composite skin 22 is appropriately sized so as to permit a peripheral portion 4~i S thereof to e~tend bevond the restraint edge 30 of the precured composite sliin ~0.
Moreover~ the peripheral portion 44 is in superposed abutting engagement with the mold surface I 's of the rigid mold member 1 ' and e~tends a distance X
beyond the restraint edge 30. Preferably, the peripheral portion 44 e~ctends at least 1.9 cm (.75 in) beyond the edge 30 and, more preferably, about ~.5 cm (1 in) '0 beyond the edge 30.
The vacuum bag 1~ is disposed over the completed composite lay-up 10 and sealed to the rigid mold member 12, or to itself~ 1~ti~ in~ a conventional sealer strip 50 such as "Prestite" (Prestite is a brand name of a semi-adhesi~e compliant material produced by 3M located in St. Paul, MN for a semi-adhesive 25 compliant). Optionally, a separator or release film 52 and a breather ply 54 may be interposed between the uncured composite skin " and the vacuum bag 14.
The separator film 52 facilitates release of the vacuum bag 14 after curing the composite lay-up 10 while the breather ply 54 facilitates the removal of air andvolatiles from the uncured A~/iENL~ED SHEET
composite skin 22 during the cure cycle. Representative materials are specified in the below-described example. In the described embodiment, the use of the release film 52 and breather ply 54 are preferred, however, the composite lay-up 10 is minimally comprised of ~.
the honeycomb core 24, the precured composite skin 20, and the uncured composite skin 22.
The completed vacuum bag molding assembly 16 shown in Fig. 4 forms a sealed mold cavity 60, i.e., between the rigid mold member 12 and the vacuum bag 14, which is in fluid communication with a vacuum pump 62. The vacuum pump 62 functions to evacuate the mold cavity 60 of gaseous fluids, i.e., air and volitales, and to create a pressure differential for urging the vacuurn bag 14 against the uncured composite skin 22. Concomitantly, the peripheral portion 44 of the uncured composite skin 22 is forced into engagement with the restraint edge 30 of the precured composite skin 20 and against the mold surface 12s.
The vacuum bag molding assembly 16 is then placed in an autoclave oven (not shown) wherein the composite lay-up 10 is exposed to additional pressure and temperature for curing. For the described embodiment, the autoclave oven applies a pressure of about 3.72 x107-4.46 x 107N/m2 (25 - 30 Ibs/in2) to the lay-up and elevates the temperature thereof to about 121 - 232~C (250 - 450~ F) degrees for a period of about 120 - 180 mins.
During the vacuum forming step, i.e., evacuation of the mold cavity 60, and subsequent curing step, the peripheral portion 44 of the uncured composite skin 22 engages the restraint edge 30 of the precured composite skin 20 so as to provide a mechanical interlock therebetween. The restraint edge 30 functions to inhibit the lateral displacement of the uncured composite skin 22 and, consequently, cause a bridging effect therein in the region overlaying the ramped honeycomb surface 26. As discussed supra, the bridging effect functions to react the lateral component of pressure P applied by the vacuum bag 14. Concomitantly, the contacting interface Cl between the peripheral portion.44 and the mold surface 12s, provides additional restraint toward the objective of inhibiting lateral displacement. That is, the frictional force along the contacting interface Cl augments the restraint capacity of the restraint edge 30. Accordingly, by inhibiting lateral displacement and, consequently, the catenary displacement of the uncured composite skin 22, shifting and/or distortion of the honeycomb core 24 is minimized.
While the completed HC composite article may be used in the configuration produced by the foregoing process steps, the cured composite lay-up may be trimmed along line TL to net dimension to form a horleycomb core composite article having a uniform thickness peripheral flange 70. Preferably, the restraint edge 30 and the peripheral portion 44 are removed during this operation. Accordingly, the trimming operation removes the abrupt contour transition produced by the restraint edge 30 which enhances the strength of peripheral flange 70 for subsequent fastening and/or bonding operations.
The restraint edge 30 and the mold surface 12s are tooling surfaces which are functionally equivalent to the prior art pinned and perforated metal strip configurations, however, it will be appreciated that the formation of these tooling surfaces is far less labor intensive.
The restraint edge 30 is formed in conjunction with the manufacturing process and becomes and integral part of the finished HC composite article. Furthermore, the only additional step involves the formation of the precured composite skin 20. Insofar as it is advantageous to precure a composite laminate for the purposes of improving laminate quality and strength, the method of the present invention will have no adverse cost effect on the manufacturing process when such improved quality and strength are desired. For example, the precured composite skin 20 may be formed under a pressure of 1.1 1 X 1 o8 N/m2 (75 Ibs/in2) to improve the fiber volume content, i.e., increase the fiber to resin ratio, and, consequently, the strength of the composite laminate. Such increased fiber volume is not achievable using conventional co-cure methods, i.e., wherein both composite skins are uncured before entering the autoclave oven, insofar as high compaction pressures cannot be transferred via the low density honeycomb core.
With regard to fabricating the rigid mold member 12 to include the mold surface 1 2s, which is slightly enlarged for superpositioning of the peripheral por~ion 44, it will be appreciated that fabricating such an additional area surface is inconsequential in terms of time and labor.
It will also be appreciated that the hazards and periodic maintenance of the prior art tooling surfaces are entirely eliminated by CA 02211~6 1997-07-2~
the method of the present invention. Thal is. the present method does not introduce hazardous ;ooling surfaces e.g., pins~ or other tooling surraces. e.g.apertures w hich require periodic cleaning.
S l~AM~
~ honevcomb core (HC) composite article was ~bricated using the teachinus of the inven~ion as follows. A sheet ot 1.8 Ibs/ft3 NO~IEX~) honevcomb core was machined tO a thickness dimension of 3.0 cm ~ l .18 in). alld ;
length and width dimension o~ 60.1 cm ( '~ in)~ respectivelv. rhe ed~es ot the honeycomb core ~vere beveled to it'orm a 30~ ramp angle about the entire periphery. The honevcomb core was then cleaned with alcohol alld dried in an oven at 65.5~ C ( 1~0~ F) for a period of 1~0 minutes.
A firs~ composite skin was formed by cutting two plies of K~VLAR@~
~lber reinforced composite material (KEVLAR(~ is a regis~eted trademark of E.L.
l S du Pont de ~emours ~ Co. Iocated in Wilmington. DE for an aromatic poiyamideof high tensile strength) to a length and width dimension of 66.0~ cm (26 in).
respectivelv. The plies were sequentially laid in a rigid mold member of a vacuum bag molding assembly. A Fluorinated Ethylene-Propylene (FEP) separator film and a breather piy formed from a compliant porous material such as N- 10 (the FEP film and N- 10 ply were obtained from Airtech International located in Carson. CA) were respectively applied to the lay-up. A vacuum bag was applied to the lay-up and sealed to the rigid mold member using Prestite adhesive.
The completed vacuum bag molding assembly was then placed in an autoclave oven to cure the plies. In the autoclave oven, the composite plies were step-cured for a period of 180 mins to a peak pressure and temperature of 1.1 1 X 1 o8 ~/m2(75 lbs/in2) and 1 82.2~C (360~ F), respectively. The lay-up resulted in a curedcomposite panel having a thickness dimension of .038 cm (.015 in). The cured composite panel was then trimmed about its periphery to form a precured composite skin having a restraint edge. The net size of the precured composite skin was approximately 63.5 cm (25 in) square.
The precured composite skin was returned to the rigid mold member and a first layer of Hysol 9690 film adhesive was applied to the entire exposed surface.
The prior-formed honeycomb core was then mated upon and centered over the precured composite skin so that the A~ E~ ~J ~Ht-rT
restraint edge extended approximately 2.54 cm (1 in) beyond the edge of the honeycomb core. A second layer of Hysol 9689 film adhesive was then applied to the exposed upper surface of the honeycomb core.
An uncured composite skin comprising two plies of KEVLAR(~) material was laid over the mated subassembly, i.e., the honeycomb core and the precured composite skin, so that a peripheral portion of the uncured composite skin extended 2.54 cm (1 in) beyond the restraint edge of the precured composite skin. The uncured composite skin was debulked using conventional vacuum debulking apparatus for 5 minutes. An FEP separator film and an N-10 breather ply were sequentially laid over the uncured composite skin. A vacuum bag was then placed over the uncured composite skin and sealed to the rigid mold member, thereby forming a completed vacuum bag molding assembly. The mold cavity was evacuated so as to apply atmospheric pressure (full vacuum) via the vacuum bag to the underlying composite lay-up. The peripheral portion of the uncured composite skin was thereby simultaneously forced into engagement with the restraint edge of the precured composite skin and the mold surface of the rigid mold member, respectively.
The vacuum bag molding assembly was then placing in an autoclave oven and step-cured as follows. The autoclave pressure was raised to 1.49 X 107 N/m2 (10 Ibs/in2) and autoclave temperature was elevated to 93.3~ C (200~F) for a first hold phase of 60 minutes.
Approximately 30 minutes into the first hold phase, the autoclave pressure was gradually increased to 3.72 x 107 N/m2 (25 Ibs/in2).
Following the first hold phase, the temperature was gradually raised to 182.2~C (360 ~F) and held at a second hold phase (final cure phase) for 120 minutes.
The honeycomb core of the resultant composite article was found to be substantially distortion-free and accurately located relative to the composite skins.
The above described method may be used alone or in combination with various core stabilization techniques such as those described in U.S. Patents 4,680,216 and 5,354,195. Furthermore, debulking operations may be performed between each of the above described lay-up steps to improve the efficacy of the resultant bonds.
W 096/22878 PCTrUS95/01099 Although the invention has been shown and described with respect to exemplary embodiments thereof, it should be understood by those skilled in the art that the foregoing and other changes, omissions and additions may be made therein and thereto, without departing from the spirit and scope of the present invention.
Claims (13)
1) A method for making a honeycomb core composite article comprising the steps of:
forming a honeycomb core (24) having a core edge (32):
placing a first composite skin (20) in combination with a rigid mold member (12) having a mold surface (12s);
mating said honeycomb core (24) to said first composite skin (20) thereby forming a mated subassembly (36) and so that said first composite skin extends beyond an edge (30) said core edge (32);
laying-up a second composite skin (22) over said mated subassembly (36), said second composite skin (22) being an uncured composite skin (22) so that said honeycomb core (24), said first composite skin (20) and said second composite skin, in combination, define a composite lay-up (10);
disposing a vacuum bag (14) over said composite lay-up (10) thereby forming a mold cavity (60) between said mold surface (12s) and said vacuum bag (14);
evacuating said mold cavity (60) to urge said vacuum bag (14) against said second composite skin (22) for compacting the same against said mated subassembly (36); and curing said composite lay-up (10) to form the honeycomb core composite article;
wherein the method is characterized by the steps of:
forming the first composite skin (20) prior to said placing step so that said first composite skin is a precured composite skin (20) having a restraint edge (30);
disposing said second composite skin (22) in combination with said mated subassembly (36) such that a peripheral portion (44) of the second composite skin (22) extends beyond said restraint edge (30) by a distance X
and, furthermore, so that said peripheral portion (44) is in superposed abutting engagement with the mold surface (12s) of the rigid mold member (12); and wherein said evacuating step causes said vacuum bag (14) to effect engagement of said peripheral portion (44) with said restraint edge (30) and said mold surface (12s) for preventing lateral displacement of said second composite skin (22) upon curing of the composite lay-up (10).
forming a honeycomb core (24) having a core edge (32):
placing a first composite skin (20) in combination with a rigid mold member (12) having a mold surface (12s);
mating said honeycomb core (24) to said first composite skin (20) thereby forming a mated subassembly (36) and so that said first composite skin extends beyond an edge (30) said core edge (32);
laying-up a second composite skin (22) over said mated subassembly (36), said second composite skin (22) being an uncured composite skin (22) so that said honeycomb core (24), said first composite skin (20) and said second composite skin, in combination, define a composite lay-up (10);
disposing a vacuum bag (14) over said composite lay-up (10) thereby forming a mold cavity (60) between said mold surface (12s) and said vacuum bag (14);
evacuating said mold cavity (60) to urge said vacuum bag (14) against said second composite skin (22) for compacting the same against said mated subassembly (36); and curing said composite lay-up (10) to form the honeycomb core composite article;
wherein the method is characterized by the steps of:
forming the first composite skin (20) prior to said placing step so that said first composite skin is a precured composite skin (20) having a restraint edge (30);
disposing said second composite skin (22) in combination with said mated subassembly (36) such that a peripheral portion (44) of the second composite skin (22) extends beyond said restraint edge (30) by a distance X
and, furthermore, so that said peripheral portion (44) is in superposed abutting engagement with the mold surface (12s) of the rigid mold member (12); and wherein said evacuating step causes said vacuum bag (14) to effect engagement of said peripheral portion (44) with said restraint edge (30) and said mold surface (12s) for preventing lateral displacement of said second composite skin (22) upon curing of the composite lay-up (10).
2) The method according to claim 1 further characterized in that said step of mating said honeycomb core (24) to said precured composite skin (20) includes the substep of applying a film adhesive (34a) between said honeycomb core (24) and said precured composite skin (20).
3) The method according to claim 2 further characterized by the step of applying a bonding adhesive (34b) between said mated subassembly (36) and said uncured composite skin (22).
4) The method according to claim 1 further characterized in that said uncured composite skin (22) is laid-up such that said distance X is greater than about 1.9 cm (.75 in).
5) The method according to claim 1 further characterized by the step of trimming the cured honeycomb core composite article so that said restraint edge (30) and said peripheral portion (44) are removed.
6) The method according to claim 1 further characterized in that said step of forming said precured composite skin (20) forms said precured composite skin (20) so that the thickness thereof is greater than about .038 cm (.015 in) and so that said restraint edge (30) defines a right angled configuration (30').
7) The method according to claim 1 further characterized in that said step of forming said precured composite skin (20) includes the substeps of vacuum forming a lay-up of composite laminates in said rigid mold member (12), and trimming said vacuum-formed lay-up to form said restraint edge (30) of said precured composite skin (20).
8) The method according to claim 1 further characterized by the step of applying a release film (52) in combination with said uncured composite skin (22).
9) The method according to claim 8 further characterized by the step of applying a breather ply (54) in combination with said release film (52).
10) A method for according to claim 4 further characterized in that said step of forming said precured composite skin (20) includes forming said precured composite skin (20) so that the thickness thereof is greater than about .038 cm (.015 in), and wherein the method is further characterized by the step of trimming the honeycomb core composite article so that said restraint edge (30) and said peripheral portion are removed.
11) The method according to claim 10 further characterized in that said step of forming said precured composite skin (20) includes the substeps of vacuum forming a lay-up of composite laminates in said rigid mold member (12), and trimming said vacuum formed lay-up to form said restraint edge (30) of said precured composite skin (20).
12) The method according to claim 10 further characterized by the step of applying a release film (52) in combination with said uncured composite skin (20).
13) The method according to claim 10 further characterized by the step of applying a breather ply (54) in combination with said release film (52).
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA002211556A CA2211556A1 (en) | 1995-01-27 | 1995-01-27 | Method for making honeycomb core composite articles |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA002211556A CA2211556A1 (en) | 1995-01-27 | 1995-01-27 | Method for making honeycomb core composite articles |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2211556A1 true CA2211556A1 (en) | 1996-08-01 |
Family
ID=4161123
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002211556A Abandoned CA2211556A1 (en) | 1995-01-27 | 1995-01-27 | Method for making honeycomb core composite articles |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA2211556A1 (en) |
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| CN110065245A (en) * | 2019-05-06 | 2019-07-30 | 衡阳泰豪通信车辆有限公司 | A kind of integrated molding cabin structure and its forming method having stealthy function |
| CN110142985A (en) * | 2019-05-16 | 2019-08-20 | 江阴海达橡塑股份有限公司 | A kind of paving and solidification integral type core model and its application method |
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| CN114919241A (en) * | 2022-05-10 | 2022-08-19 | 宁波曙翔新材料股份有限公司 | Box-shaped composite material forming process suitable for paper honeycombs with large thickness |
| CN115384127A (en) * | 2022-07-25 | 2022-11-25 | 成都飞机工业（集团）有限责任公司 | Honeycomb sandwich composite material part and preparation method thereof |
-
1995
- 1995-01-27 CA CA002211556A patent/CA2211556A1/en not_active Abandoned
Cited By (8)
| Publication number | Priority date | Publication date | Assignee | Title |
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| CN110065245A (en) * | 2019-05-06 | 2019-07-30 | 衡阳泰豪通信车辆有限公司 | A kind of integrated molding cabin structure and its forming method having stealthy function |
| CN110142985A (en) * | 2019-05-16 | 2019-08-20 | 江阴海达橡塑股份有限公司 | A kind of paving and solidification integral type core model and its application method |
| CN110142985B (en) * | 2019-05-16 | 2024-04-19 | 江阴海达橡塑股份有限公司 | Paving and curing integrated core mold and application method thereof |
| CN113725623A (en) * | 2021-08-30 | 2021-11-30 | 湖南航天环宇通信科技股份有限公司 | Antenna reflecting surface with back rib and forming method thereof |
| CN114919241A (en) * | 2022-05-10 | 2022-08-19 | 宁波曙翔新材料股份有限公司 | Box-shaped composite material forming process suitable for paper honeycombs with large thickness |
| CN114919241B (en) * | 2022-05-10 | 2024-04-16 | 宁波曙翔新材料股份有限公司 | Box-shaped composite material forming process suitable for honeycomb containing large-thickness paper |
| CN115384127A (en) * | 2022-07-25 | 2022-11-25 | 成都飞机工业（集团）有限责任公司 | Honeycomb sandwich composite material part and preparation method thereof |
| CN115384127B (en) * | 2022-07-25 | 2024-01-12 | 成都飞机工业（集团）有限责任公司 | Honeycomb sandwich composite material part and preparation method thereof |
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| Date | Code | Title | Description |
|---|---|---|---|
| FZDE | Discontinued |