RICHTER, Jed (324 Park Road, Isle of Wight, Cowes Hampshire PO31 7NN, GB)
GILL, Adrian (8 Osborne Road, Isle of Wight, East Cowes PO32 6RX, GB)
HEDGES, Andrew (22 Malmesbury Road, Southampton Hampshire SO15 5FR, GB)
RICHTER, Jed (324 Park Road, Isle of Wight, Cowes Hampshire PO31 7NN, GB)
GILL, Adrian (8 Osborne Road, Isle of Wight, East Cowes PO32 6RX, GB)
| CLAIMS 1. A method for manufacturing a composite material article, the method comprising - providing a mould (4), - placing at least one layer (1) of bulk fiber material on the mould (4), - placing, at an edge of the bulk fiber material layer (1), a flange element (2) partially overlapping the bulk fiber material layer (1), and partially extending so as to form a flange, and - curing bulk resin on the mould (4), where the bulk fiber material layer (1) has been impregnated with the bulk resin, with the flange element (2) placed at the edge of the bulk fiber material layer (1). 2. A method according to claim 1, wherein the article is elongated, and wherein two flange elements (2) are placed at respective longitudinal edges of the bulk fiber material layer (1). 3. A method according to any one of the claims 1-2, wherein the composite material article is a spar cap (Kc) for a spar (Ka) for a wind turbine blade. 4. A method according to any one of the claims 1-3, wherein the flange element (2) is a pultruded element. 5. A method according to any one of the claims 1-4, wherein the flange element (2) is a solid, pre-cured, elongated corner element. 6. A method according to claim 5, wherein the flange element (2) is, when placed at the edge of the bulk fiber material layer (1), held in place by a plurality of clamps (3). 7. A method according to any one of the claims 1-4, wherein the flange element (2) is in a composite material comprising flange fibers and a flange resin which is partially cured when the flange element (2) is placed at the edge of the bulk fiber material layer (1). 8. A method according to claim 7, wherein the flange resin is cured to be solidified simultaneously with the curing of the bulk resin. 9. A method according to any one of the claims 7-8, wherein the flange element (2) is, when placed at the edge of the bulk fiber material layer (1), held in place by a corner mould (3). 10. A method according to claim 9, wherein the corner mould (3) is attached to the mould (4) on which the bulk fiber material layer (1) is placed. 1 1. A wind turbine blade manufactured according to any of the preceding claims. |
TECHNICAL FIELD AND BACKGROUND
The invention relates to a method for manufacturing a composite material article.
Reference is made to fig. la showing a cross-section of a wind turbine blade. Some wind turbine blade types comprise a composite material spar Ka extending in the longitudinal direction of the blade, and presenting a rectangular cross-section. This spar can be manufactured separately and then introduced into the blade assembly together with blade shells Kb. Two opposing walls of the spar serve as spar caps Kc, joined by the two remaining walls serving as webs Kd. The caps and webs can be manufactured separately, and then joined to form the spar.
Reference is made to fig. lb showing a sectioned perspective view of a part of an apparatus for manufacturing the spar caps according to a known method. The method comprises using a female mould Kl, in which cap composite material K2, e.g. including carbon fiber and epoxy, is provided. The material is arranged so as to form the entire cap including corner flanges K21 for later bonding to the webs of the spar.
Automated deposition systems, such as automatic fiber placement (AFP) machines are known as making the manufacturing of composite material products more efficient. They can involve moving a fiber placement head past a mould and depositing fiber tows on the mould, see e.g. US6692681B1, US2007044896A1 or WO2005105641 A2.
Manufacturing composite material articles with flanges, such as the corner flanges K21 in fig. lb, can be difficult. A small radius at the corner of the mould used can provide a challenge in making sure fibers and resin reach all the way into the corner so that no voids or pockets are provided. Particularly if automated fiber placement is desired for the manufacturing, the corners at the flanges K21 can provide problems. It is simply difficult to place material in such concave corners using automated fiber placement.
SUMMARY
It is an object of the invention to improve composite material article
manufacturing. It is also an object of the invention to improve composite material article manufacturing using automated deposition systems. It is a further object of the invention to improve manufacturing of composite material articles with small radius curvatures, in particular while avoiding voids and pockets at the curvatures.
These objects are reached with a method according to claim 1. Thus, the invention relates to a method for manufacturing a composite material article, the method comprising
- providing a mould,
- placing at least one layer of bulk fiber material on the mould,
- placing, at an edge of the bulk fiber material layer, a flange element partially overlapping the bulk fiber material layer, and partially extending so as to form a flange, and
- curing bulk resin on the mould, where the bulk fiber material layer has been impregnated with the bulk resin, with the flange element placed at the edge of the bulk fiber material layer.
It should be noted that impregnating the bulk fiber material with the bulk resin, can be done before placing the bulk fiber material layer on the mould, such as when using pre-impregnated fibers, (prepreg), or after placing the bulk fiber material layer on the mould, such as when using a so called resin infusion process.
The invention provides for the corner flange details to be manufactured separately from a composite material article's bulk or main structure. This enables separate processes to be used for the flanges and the bulk region, which is particularly useful when the bulk region has a simple geometry, such as substantially flat. The bulk flat region is then left as a simple geometrical structure, and can be laid up by an AFP system, (e.g. involving tape lay, prepreg, or fibes laid dry and then infused). Alternatively, the bulk region material can be laid on the mould manually.
It should be noted that one or more further fiber material layers can be placed in the mould after the flange elements have been placed at the edge of the bulk fiber material layer.
Advantageous embodiments are defined in the dependent claims 2-10, and also described below.
The composite material article can be a spar cap for a spar for a wind turbine blade, where the spar extends in the longitudinal direction of the blade. The spar can comprise opposing walls to serve as spar caps, joined at their longitudinal edges by webs. Thereby, two flange elements can be placed at respective essentially parallel edges of the bulk fiber material layer, for forming two flanges for bonding the spar cap to the webs.
The flange element can be a pultruded element, preferable a composite material element. Alternatively, the flange element can be manufactured by some other suitable method. Thus it could be a composite item made on a mould from pre- impregnated fibers (prepreg) or with an infusion resin technique. The flange element can be a solid, pre-cured, elongated corner element, i.e. a composite material element in which the resin has been fully cured, before it is placed in the mould.
Alternatively, the flange element can be in a composite material comprising flange fibers and a flange resin which is partially cured when the flange element is placed at the edge of the bulk fiber material layer. Thereby, the flange resin can be cured to be solidified simultaneously with the curing of the bulk resin.
The invention also provides a wind turbine blade according to claim 1 1.
DETAILED DESCRIPTION OF DRAWINGS AND PREFERRED EMBODIMENTS
Below, the invention will be described with reference to the drawings, in which fig. la, referred to above, shows a cross-section of a wind turbine blade, fig. lb, referred to above, shows a sectioned perspective view of a part of an apparatus for manufacturing wind turbine blade spar caps according to a known method, fig. 2 and fig. 3 show respective sectioned perspective views of parts of apparatuses for manufacturing spar caps according to respective embodiments, and fig. 4 shows a further cross-section of a wind turbine blade.
Reference is made to fig. 2 showing a sectioned perspective view of a part of an apparatus for manufacturing an article in the form of a spar cap according to an embodiment of the invention. In this method, spar cap material 1 ,
comprising a plurality of layers of fiber material, herein also referred to as bulk fiber material, which is pre-impregnated with a resin, herein also referred to as a bulk resin, is placed on a mould 4. Thereafter, two flange elements 2 are deposited at respective longitudinal edges of the spar cap material 1, so that they partially overlap the spar cap material 1 , and partially extend so as to form flanges, for bonding the spar caps to webs of the spar. The flange elements are pre-fabricated, pultruded, elongated composite corner elements, held in place by a plurality of clamps 3. A vacuum bag (not shown) is applied over the spar cap material as well as the flange elements 2 for curing the spar cap material. Thereafter the bulk resin is cured, whereby the flange elements 2 are bonded to the spar cap material by means of the bulk resin.
Preferably, the spar geometry is adapted to allow for the flange elements 2 to present constant cross-sections. By making the corner geometry consistent for the majority of the spar, a continuous manufacturing process can be used, e.g. pultrusion. The flange elements, e.g. in the form of pultrusions, could be fully or, as exemplified below, partially cured, and they could comprise
thermosetting or thermoplastic.
Reference is made to fig. 3, showing a sectioned perspective view of a part of an apparatus for manufacturing the spar caps according to another embodiment of the invention. In this method, two corner moulds 3 are provided for support of the flange elements 2. The flange elements 2 are in a composite material comprising fibers and a resin, herein also referred to as flange fibers and flange resin, which is partially cured when the flange elements are placed at the spar cap material. A vaccum bag (not shown) is applied over the flange elements 2 as well as the spar cap material 1 , and the flange resin is cured to be solidified simultaneously with the curing process of the bulk resin. This solution may give improved shape control and connection to the spar cap material 1 due to the flexible nature of partially cured pultrusion.
Preferably, the flange elements 2 have mostly biaxial fibres, with some UD (uni-directional) if required. Alternatively, mostly or only UD could be provided in the flange elements 2. The material for the flange elements could be for example carbon or glass fibres. The invention allows for a small radius (for example approximately 10mm) at the spar corners, which allows for a continuous profile from the root to the tip of the spar. If desired, the flange elements 2 can be machined to give less height towards spar (blade) tip. The spar cap material 1 could be for example UD carbon with some biaxial carbon or glass fibres. The invention makes automated fiber deposition suitable for the spar cap material 1. As can be seen in fig. 2 and fig. 3, along the longitudinal edges of the spar cap, side chamfers are provided on the deposited spar cap material 1, and the upper surfaces of the side chamfers support the flange elements 2 when they are placed on the mould.
It should be noted that the invention is suited for manufacturing any composite material item, e.g. with an elongated shape, where it is desired to obtain one or more flanges on the item. Fig. 4 shows a cross-section of a wind turbine blade, in which an extra web 7, is provided between the main spar Ka and a trailing edge of the blade. The extra web comprises flanges 71 for bonding it to the shells Kb of the blade, and these flanges could be provided as flange elements 2 as described above.