Method for manufacturing a curved article, comprising elongated reinforcing elements.

© Patent holder (s):

Protension IP Assets BV in Delft.

* 72) Inventor (s):

Jacky Ferdinand Henriëtte Wetzels in Delft. Lucas Stefan van den Akker in Rotterdam.

© Patent issued:

29.04.2015 © Authorized representative:

Ir. AAG Land et al in THE HAGUE.

© Method for manufacturing a curved article, comprising elongated reinforcing elements.

© The invention relates to a method for manufacturing a curved article with improved properties, in particular ballistic properties. The method comprises positioning a plurality of elongated reinforcing elements, and an adhesive means onto a first mold member to create a structure; positioning a second mold member around the structure; applying a pressure such that an outer surface of the first mold member and an inner surface of the second mold member engage and pressurize the structure; heating the structure until the adhesive means have fused, melted or cured; depressurizing the structure; and removing the second mold member from the molded structure to obtain the article. A preferred method comprises dividing the molded structure in two or more parts to obtain two or more articles.

LC 2011653

This patent has been granted regardless of the attached result of the prior art research and written opinion. The patent corresponds to the documents originally filed.

Method for manufacturing a curved article, comprising elongated reinforcing elements

The invention relates to a method for manufacturing a curved article, comprising elongated reinforcing elements. The invention in particular relates to a method for manufacturing a curved armor article, such as a helmet, preferably a combat helmet, and a radome.

Curved articles, and in particular curved armor articles such as protective helmets, are typically made of composites of high strength reinforcing fibers embedded in a polymer adhesive matrix. Such armor articles offer adequate ballistic protection and lightweight properties. Drawn polymeric fibers based on aramid and ultra high molecular weight polyethylene in particular have shown good anti-ballistic properties.

In a typical state of the art method, a curved article is manufactured from a relatively flat preform by deforming the preform into a three-dimensional shape. This however produces scrap material and also wrinkles in the article, which may significantly affect ballistic performance and causes inconsistence of performance along different locations of the surface of the article.

In another known method, pieces of an intermediate sheet-like product of reinforcing fibers embedded in a suitable resin, or any other ballistic sheet material, is cut into shapes and then arranged on a mold to form a three-dimensional preform. The preform is then subjected to heat and pressure to form the curved armor article. This method however is time consuming and results in significant quantities of costly scrap material. Also, the use of a segmented preform negatively affects ballistic and other properties.

It has been proposed in WO 2008/128715 Al to produce a preform in a threedimensional shape resembling the shape of the article to be produced. A form stable preform shape is obtained by locally adhering at least a part of the fibrous reinforcing elements to each other. The preform is molded in a mold at elevated temperature and pressure to produce the anti-ballistic article. Although this known method at least partly solves the problem of wrinkling, the anti-ballistic performance of the produced curved article can be improved further.

An object of the present invention is to provide a method for manufacturing a curved article, such as a radome, without substantial wrinkling. Another object is to provide a method for manufacturing a curved armor article, in particular a combat helmet, with improved anti-ballistic properties.

This object is achieved according to the invention by a method in accordance with claim

1. According to the invention a method for manufacturing a curved article is provided, the method comprising positioning a plurality of elongated reinforcing elements, and an adhesive means onto a first mold member to create a structure; positioning a second mold member around the structure; applying a pressure such that an outer surface of the first mold member and an inner surface of the second mold member engage and pressurize the structure; heating the structure until the adhesive means have fused, melted or cured; depressurizing the structure; removing the second mold member from the molded structure; and dividing the molded structure in two or more parts to obtain two or more molded articles.

In an embodiment of the method, the method comprises the step of cooling the structure after the adhesive means have been fused, melted or cured. This is in particular useful when an adhesive means is used that needs to be cooled from a fused or molten state to solidify it, such as is the case for an adhesive means comprising a thermoplastic material for instance.

The method of the invention allows to obtain two or more molded articles without having to use a preform. The method further yields articles with improved (antiballistic) properties. This is believed to occur because of a combination of less wrinkling during pressurizing, if any, a much better control over the positioning of the elongated reinforcing elements in the structure, and a more accurate positioning of the elongated reinforcing elements in the molded articles. Also, wall thickness variations are reduced or even eliminated. Indeed, dividing the molded structure in parts to obtain the articles is performed only after the structure has been molded. In the molded structure, the elongated reinforcing elements are consolidated in their desired position by the fused, cooled or cured adhesive means, and their position is therefore not, or only negligibly, influenced by the dividing step. The architecture of the elongated reinforcing elements is so to say 'frozen in' and does not change appreciably during molding of the structure and articles.

A useful embodiment of the method in accordance with the invention comprises positioning the plurality of elongated reinforcing elements onto the first mold member under tension. This optionally also spreads and / or further draws the elongated reinforcing elements which is advantageous. In the molded structure, the elongated reinforcing elements are consolidated in their desired position by the fused, cooled or cured adhesive means, and the elongated reinforcing elements therefore substantially maintain their tension and / or spreading in the molded structure which benefits properties.

Elongated reinforcing elements suitable for use in the method of the invention may comprise (continuous) fibers, pre-impregnated fibers (prepregs) and / or drawn tapes or films, preferably slitted in a transverse direction to form tapes. Fibers are understood to include a body whose length is far greater than its transverse dimensions. Suitable fibers include monofilaments, multifilament yams, strips, ribbons and / or tapes, as well as other textile structures.

In an embodiment of the invention, a method is provided wherein the elongated reinforcing elements comprise glass fibers, carbon and graphite fibers, metal fibers, drawn polymeric fibers, such as aramid fibers, PBO fibers (Zylon®), M5® fibers, ultrahigh molecular weight polyethylene or polypropylene fibers or tapes, as well as natural fibers, such as flax and wood fibers, and / or combinations of said fibers.

The shape of the structure is substantially determined by the shape of the first mold member. Virtually any shape is possible, but for practical reasons spheroid-like structures are preferred. A spheroid-like shape in the context of this application comprises the usual definition of a shape approximating a sphere but not perfectly round, especially an ellipsoid that is generated by revolving an ellipse around one of its axes, but also comprises shapes made of sections of spheres, cylinders, and cones, for instance comprising a cylinder with end caps of hemispherical or torispherical shape, and any free shapes resembling a two-sided domed shape necessary to approximate the general shape and details of the final structure. The term spheroid-like is conveniently used throughout this application to denote such shapes by one word. The structures may be obtained by positioning a plurality of elongated reinforcing elements, and an adhesive means onto a first mold member having a spheroid-like shape. The second mold member has an interior surface that preferably defines an outside surface of the article, whereas an outside surface of the first mold preferably defines an inside surface of the article.

Dividing the molded structure in parts may be carried out by any means in the art. According to an embodiment of the invention, a method is provided wherein dividing the molded structure in two or more parts is done by mechanical, abrasive and / or melt cutting. Relatively simple and fast cutting methods may be applied since cutting is performed on a molded structure, and not on a fluffy preform, as may be usual in the state of the art.

The curved articles when divided and removed from the first mold member are in one embodiment ready for use. In another embodiment, they may need some finishing such as (divided) edge trimming. The amount of scrap material produced in carrying out the invented method is therefore very limited. In the known method in which a preform is positioned in a mold and compression molded, the preform needs to be oversized at its edges in order to accommodate any shifting of the preform with respect to the mold when the mold is closed.

The invented method allows to produce articles, curved in one or more directions, from elongated reinforcing elements directly without appreciable wrinkling. A curved article, in the context of this application, typically has an elevation with respect to a flat surface on which it is positioned of at least 1/5 of the largest linear dimension within the projected surface of the article on the flat surface. It should be noted that some parts divided from the structure may have a lesser that 1/5 elevation to largest linear dimension ratio.

By positioning a plurality of elongated reinforcing elements onto the first mold member in the shape and position required by the final articles, molding the structure and dividing it to obtain the articles, virtually any shape and orientation of the elongated reinforcement elements can be achieved. A reduced deformability of a preform, as applied in the state of the art method, no longer represents a limiting factor and virtually any shape and fiber architecture can be obtained. In such an embodiment the first mold member is provided in a shape that covers the shape of all the final articles at least once, elongated reinforcement is then positioned in the positions, quantity, orientation and material required for each article, the structure produced and then divided in two or more parts that correspond to the final articles. The articles may be sold separate, or they may form the parts of a modular assembly that is assembled later, for instance by a user. The two or more parts in this embodiment form the modules of the modular assembly.

According to the invention a plurality of elongated reinforcing elements is positioned onto a first mold. Suitable methods for positioning the elongated reinforcing elements comprise but are not limited to robotic fiber and tape placement, placement of fibers, tapes, and fabrics by hand or by laminating and textile machinery, filament winding, pultrusion, and combination of those methods. In a preferred embodiment of the method, the plurality of reinforcing elements is positioned onto the first mold member by filament and / or tape winding.

In filament or tape winding, the elongated reinforcing elements are typically dispensed from a number of spools, carried by a creel. The reinforcing elements are led to the outer surface of a first mold member that is rotated around a centrally disposed shaft. When the shaft projects from either apex side of the first mold member, the structure created by positioning the elongated reinforcing elements and the adhesive means onto the first mold member will generally have two polar openings at both sides of the first mold member when the shaft is removed after filament winding or after pressing. Such an opening may for instance be closed by fitting in a closing plug. When the winding shaft is removed before pressing, pressing may relocate the reinforcing elements on the first mold member towards the polar openings, thereby at least partly closing the polar openings. When the shaft projects from one side of the first mold member only, a structure may be created that has only one polar opening at the sides of the first mold member where the shafts projects. Such a filament winding method is referred to as polar winding and represents an embodiment of the invention. Pole free winding is another option, in which winding method a winding shaft is absent and the movement of the winding mold is effected magnetically or frictionally. In this case it is possible to obtain a structure without polar openings.

With filament or tape winding, the elongated reinforcing elements may be oriented in any desired directions across the surface of the first mold member, while a substantially wrinkle-free article with homogeneous properties may be obtained. In another embodiment of the invention, the first mold member is provided with a plurality of projections that allow to position at least a part of the reinforcing elements in a nongeodetic pattern onto the first mold member. A winding trajectory is geodetic when it spans the shortest distance between two points on the curved surface of the article, otherwise it is non-geodetic. Less extreme non-geodetic patterns may also be obtained by using surface friction provided by the first mold member and / or by the structure that is being produced.

The amount of elongated reinforcing elements that are positioned on the first mold member may be varied within a large range and the amount is generally such that the desired thickness and / or areal density of the articles to be produced is reached. Positioning the elongated reinforcing elements is preferably carried out such that the produced articles have constant properties over substantially their entire surface, in particular when the articles are anti-ballistic and / or transmittent to electromagnetic / radar / communications radiation / waves / signals.

The method according to the invention is particularly useful for the manufacture of articles that are curved in one or more directions. Preferred examples thereof include protective helmets, such as combat helmets, radomes, ballistic protection panels for body parts other than the head, such as body and shoulder pads, other protective articles for military and civil personnel, such as curved armor or constructive panels for automobiles or for helicopters for instance.

The first mold member may remain part of the molded structure from which the two or more articles originate. A preferred embodiment in accordance with the invention however provides a method comprising the step of removing the first mold member from the molded structure to obtain the two or more articles.

In a preferred method, two identical shell-like articles, such as two combat helmet shells for instance, are produced by positioning a plurality of elongated reinforcing elements, and an adhesive means onto a first mold member to create a spheroid-like structure; then positioning a second mold member around the structure; applying a pressure such that an outer surface of the first mold member and an inner surface of the second mold member engage and pressurize the spheroid-like structure; heating the spheroid-like structure until the adhesive means have fused, melted or cured; depressurizing the spheroid-like structure; removing the second mold member from the molded spheroidlike structure; and dividing the molded spheroid-like structure in two parts to obtain the two molded articles.

In the above described embodiment, the amount of waste can be minimized by defining the first and / or second mold shape such that two molded parts form an (approximately) anti-symmetric pair on the first mold after having divided the molded structure. The invented method allows to produce more than one part with one first mold member shape only, and one skilled in the art will have no difficulty in selecting the desired shape of the first mold member and / or second mold member as well as the pattern of dividing lines along the surface of the molded structure to obtain the parts with a minimum of waste scrap material. As a guideline, one skilled in the art may select a first mold member and / or second mold member and / or molded structure geometry having one plane of symmetry, such as a plane perpendicular to the axis of rotation of the first mold member, or a plane going through the axis of rotation of the first mold member, or an anti-symmetrical first mold member with respect to said planes, or even a first and / or second mold member having no symmetry at all. He may further select dividing lines running in one of said planes, or following another contour, as dictated by the rims or free ends of the parts to be produced, or dividing lines having anti-symmetry with respect to one of said planes. It is also possible to provide parts with cut-outs and the like.

There is a trend in the art of protective helmets and the like to offer modularity. Such modular protective helmets typically comprise a helmet shell, detachable ear pieces and a mandible that protects the face, although other modularity / make up may exist. The method in accordance with the invention is particularly suitable for producing such a modular helmet. Indeed, in such an embodiment, a first mold is provided in a shape that covers all the components at least once, elongated reinforcement is then positioned in the positions, quantity, orientation and material required for each component, the structure produced and then divided in parts that correspond to helmet shell, ear pieces and mandible, as required.

According to the invention, the method comprises positioning a plurality of elongated reinforcing elements, and an adhesive means onto a first mold member to create the structure. The adhesive means may comprise thermoplastic as well as thermosetting resins, or blends thereof. Suitable thermosetting resins include but are not limited to epoxide resins, phenolic resins, polyurethane resins, polyester resins, and the like. Suitable thermoplastic resins include but are not limited to styrene resins, such as polystyrene, ABS, MBS, polycarbonate resins, polyolefins such as polyethylene (LDPE, HDPE) and polypropylene, thermoplastic polyurethane resins, and natural or synthetic rubbers.

In an embodiment of the invented method, the adhesive means comprise a thermoplastic polymeric film material that is applied into the structure and / or onto an inner and / or outer surface of the structure. The polymeric film material melts when heating the structure and penetrates within the structure to embed at least part of the elongated reinforcing elements. Cooling the structure then solidifies the polymeric film material which binds the elongated reinforcing elements together to form a molded structure. The polymeric film material may extend over part of the structure, or alternatively may extend over substantially the entire inner and / or outer surface of the structure.

Another embodiment of the invented method uses an adhesive means that comprise a plurality of thermoplastic polymeric elongated elements that are positioned onto the first mold member together with the plurality of elongated reinforcing elements. The thermoplastic polymeric elongated elements are typically provided onto spools, that are applied onto some spool positions of the filament winding creel. The thermoplastic polymeric elongated elements melt when heating the structure and this molten material penetrates within the structure to embed at least part of the elongated reinforcing elements. Cooling the structure then solidifies the diffused thermoplastic polymeric elongated element material which binds the elongated reinforcing elements together to form a molded structure. The thermoplastic polymeric elongated elements preferably comprise thermoplastic polymer monofilaments that are combined with the elongated reinforcing elements in any conceivable way, for instance by comingling.

In yet another embodiment of the method according to the invention, the elongated reinforcing elements comprise drawn polymeric reinforcing elements, and the adhesive means comprise said drawn polymeric reinforcing elements. In this embodiment, the structure is preferably molded at a temperature between the melting point of the elongated reinforcing elements and 20 ° C below the melting point, more preferably 10 ° C below the melting point. This will fuse the drawn polymeric reinforcing elements together at least partly without too much affecting their mechanical properties.

Yet another embodiment of the invention provides a method wherein the adhesive means comprise a thermoplastic and / or thermosetting binder in the form of a powder, an emulsion, a dispersion or a solution. Applying a binder to the elongated reinforcing elements at least locally, letting the binder diffuse in the structure by heating, and solidifying the binder by curing and / or cooling adheres elongated reinforcing elements to each other. The binder may be any material having adhesive properties, and may be applied by spraying, dipping, and the like. In an embodiment, (part of) the elongated reinforcement elements are (partly) coated with the binder.

It is an advantage of the invented method that the amount of the adhesive means relative to the amount of elongated reinforcing elements in the molded structure (and articles) may be extremely low. Preferred embodiments of the invention use an amount of the adhesive means of less than 20% by weight, relative to the total amount of elongated reinforcing elements and the adhesive means, more preferably of less than 15% by weight, relative to the total amount of elongated reinforcing elements and the adhesive means, and most preferably of less than 12% by weight, relative to the total amount of elongated reinforcing elements and the adhesive means. A low relative amount of the adhesive means is beneficial to anti-ballistic properties of the produced articles.

According to the invention, a second mold member is positioned around the unmolded structure. The second mold member has an interior surface that defines an outside surface of the molded article and may be made of metal alloys suitable for molds and the required pressures. It may for convenient demolding comprise several closely fitting parts that together conform to the overall second mold member shape. After having applied the second mold member around substantially the complete structure, a pressure is applied such that an outer surface of the first mold member and an inner surface of the second mold member engage and pressurize the structure. Applying pressure can be done in several ways although some methods in accordance with embodiments described below have proven advantageous.

In a first embodiment of the method, the first mold member comprises a stiff body and a conformal cover and pressure is applied within the conformal cover such that an outer surface of the conformal cover and an inner surface of the second mold member engage and pressurize the structure. The stiff body can be a solid body, or may be a hollow body, in which embodiment the interior cavity of the first mold member is preferably pressurized to withstand process parameters. The interior cavity pressure can also be used to pressurize the conformal cover, by providing the first mold member's hollow body with orifices.

The first mold member is preferably stiff enough to substantially retain its form stability when subjected to the loads, occasioned by process parameters such as consolidating pressures, reinforcement element tensions and the like.

In another embodiment of the method, the second mold member comprises a stiff body and a conformal cover, and pressure is applied between the stiff body and the conformal cover such that an outer surface of the conformal cover and an outer surface of the first mold member engage and pressurize the structure. In this embodiment, the first mold member's surface defines the inner surface of the molded articles, which may be of advantage when this inner surface should have closely defined dimensions and shape. The outer surface of the conformal cover is defined as the surface facing away from the second mold member.

The use of a conformal cover provides the opportunity to mold articles with varying thickness, which may be of interest. This allows parts of the structure where elongated reinforcing elements are prone to change in orientation during positioning thereof on the first mold member's surface to be strengthened by adding more material and locally increase thickness.

For reasons of speed of production, it may be advantageous in an embodiment to use a first mold member that is rotation symmetric. Such a first mold member forms a surface of revolution around a central shaft. A further embodiment of the method according to the invention comprises using a first mold member that is non-symmetrical. This allows to obtain virtually any inner surface shape of the molded articles, in particular when the second mold member comprises a stiff body and a conformal cover, and pressure is applied between the stiff body and the conformal cover such that an outer surface of the conformal cover and an outer surface of the first mold member engage and pressurize the structure.

In a further embodiment of the method, the first mold member comprises an inflatable shell structure and pressure is applied within the shell structure such that an outer surface of the shell structure and an inner surface of the second mold member engage and pressurize the structure.

In yet another embodiment, the first mold member is made of a rubber polymer, taking a first mold member comprising a stiff core of for instance a metal alloy and a relatively thick shell of a rubber polymer around the core is preferred. In this embodiment, pressure may be applied onto the structure by simply bringing the first and second mold members towards each other under application of an external pressure. The pressure is built up by deformation of the relatively thick rubber shell. The thickness and hardness of the rubber shell may be chosen in dependence of the desired pressure level.

Another embodiment relates to a method in which the first mold member is made of a material having a thermal coefficient of expansion that differs from the thermal coefficient of expansion of the second mold member. The pressure in this embodiment is built up by heating and / or cooling of at least one of the mold members.

Still a further embodiment relates to a method wherein the structure is enclosed in an envelope within which envelope a vacuum is applied during heating. This embodiment not only provides increased pressure on the structure during fusing, melting or curing the adhesive means but also removes entrapped voids from the structure. The envelop, preferably a polymeric film envelope, does not need to be removed after molding but it may at least partly melt and form an integral part of the molded articles. It may also be wasted. In an even more preferred embodiment, the envelope is formed by the conformal cover of the first mold member and the interior surface of the second mold member.

For anti-ballistic purposes, the elongated reinforcing elements preferably have a tenacity of at least 2.0 N / tex, more preferably at least 2.5 N / tex ,, and most preferably at least 3.0 N / tex. The use of reinforcing elements with the indicated tenacities allows objects to be manufactured with good flexural stiffness and ballistic properties and high resistance to extraneous forces, such as required for helmets.

For anti-ballistic purposes, particularly preferred fibers to be used in the method according to the invention comprise drawn fibers prepared from ultra-high molecular weight polyethylene (UHMWPE). Such fibers are commercially available, for instance under the trade names Dyneema® (DSM) or Spectra® (Honeywell). Other particularly preferred fibers include aramid fibers, obtainable from Teijin under the trade name Twaron®, or Kevlar®, obtainable from Dupont, for instance. Suitable drawn tapes include Endumax® obtainable from Teijin.

According to the method of the invention, a pressure is applied such that an outer surface of the first mold member and an inner surface of the second mold member engage and pressurize the structure, as well as heating to heat the structure until the adhesive means have fused, melted or cured. The person skilled in the art will generally be able to choose a suitable combination of temperature, pressure and time to adequately consolidate the structure before dividing it in the articles.

Producing the unmolded structure will generally take a limited time, in particular when filament or tape winding is used. Pressurizing and heating to obtain the desired shape of the molded articles may typically be effected in 5 to 90 minutes, depending on the adhesive means used, and the thickness of the structure for instance.

Typical pressures applied to the unmolded structure may vary widely, and are typically within 5 to 100 MPa. It may have advantages to apply several distinct pressure levels in a stepwise fashion. A first moderate pressure level may for instance be applied to stabilize ('freeze in') the elongated reinforcing element architecture where after a second more elevated pressure is applied to obtain the desired shape, wall thickness, and density of the final molded structure and articles . It is also possible to apply a distinct temperature level for each pressure level.

Typical temperatures depend among others on the adhesive means used and are typically selected between room temperature and 250 ° C. After forming at the selected temperature and pressure, the molded structure is cured and / or cooled in case a thermoplastic binder is used before dividing it into parts.

The invention will now be explained in greater detail by means of the enclosed figures, without however being limited thereto. In the figures:

Figure 1 schematically shows a cross-sectional view of a first step in accordance with an embodiment of the method of the present invention;

Figure 2 schematically shows a cross-sectional view of a second step in accordance with an embodiment of the method of the present invention;

Figure 3 schematically shows a cross-sectional view of a third step in accordance with an embodiment of the method of the present invention;

Figure 4 schematically shows a cross-sectional view of a fourth step in accordance with an embodiment of the method of the present invention;

Figure 5 schematically shows a cross-sectional view of a fifth step in accordance with an embodiment of the method of the present invention;

Figure 6 schematically shows a cross-sectional view of a sixth step in accordance with an embodiment of the method of the present invention;

Figure 7 schematically shows a cross-sectional view of a seventh step in accordance with an embodiment of the method of the present invention;

Figure 8 schematically shows a perspective view of two articles, produced in accordance with an embodiment of the method of the present invention.

Referring to figures 1-8, the overall method of manufacturing two lightweight combat helmets (100a, 100b) is depicted. The manufacturing method begins with providing spools of reinforcing tape or fiber material on a creel, for instance UHMWPE antiballistic fiber yam, coated with a thermoplastic material such as HDPE. In this embodiment shown, the adhesive means is provided by the HDPE coating on the reinforcing fibers. The spools are mounted on a creel of a filament winding machine, known per se. A relatively low amount of HDPE of less than 12% by weight, relative to the total amount of the UHMWPE anti-ballistic fiber yams is used in this embodiment.

The UHMWPE anti-ballistic fiber yams are then led to a first mold member 1 via suitable guiding means (not shown). First mold member 1 has a spheroid-like shape, is supported by a central shaft 2, and comprises a stiff core 10 and a conformal cover 11. The stiff core 10 is made of a fiber reinforced composite, whereas the conformal cover is typically made of a rubber polymer, such as a silicone rubber. The wall thickness of the cover may be chosen in accordance with (pressure) requirements. It may be constant or vary across the surface of the cover 11. The cover 11 extends over substantially the complete outer surface 13 of the core 10 of first mold member 1 but is not connected to it, possibly apart from some parts in apex regions ( 14a, 14b) of the first mold member 1. The first mold member 1 is provided with polar openings at the apex regions (14a, 14b) through which openings the shaft 2 extends.

Shaft 2 is at both ends and in a known manner supported by rotatable clamps (not shown) provided on the filament winding machine. The clamps can be brought in rotation around a longitudinal axis 16 of the shaft 2, which will also rotate the first mold member 1 around said axis 16. The HDPE-coated UHMWPE anti-ballistic fiber yams are positioned onto the first mold member 1, in which process the orientation of the yams is controlled by the ratio of the speed of rotation around axis 16 and the speed of linear translation parallel to the longitudinal axis 16. Several layers of reinforcing elements are positioned onto the first mold member 1 (and on layers that were already positioned on the first mold member 1) to finally obtain a spheroid-like shaped structure 15, as shown in figure 2. By changing the orientation of the reinforcing elements within every layer and / or between layers, virtually any fiber architecture can be obtained.

In a next step, shown in figure 3, a second mold member 20 is provided around the filament wound structure 15. The second mold member 20 in the embodiment shown comprises 2 parts (20a, 20b) that closely fit together in the assembled state. Second mold member parts (20a, 20b) may be connected to each other by any suitable means, including mechanical connection means such as bolts (not shown). The second mold member 20 in the assembled state defines an interior cavity 21, defined and enclosed by the internal surfaces (21a, 21b) of mold parts (20a, 20b). The interior cavity 22 is shaped such that it conforms to the desired outside surface of the articles (100a, 100b) to be molded. The second mold member parts (20a, 20b) are provided with openings at the apex regions (14a, 14b) through which openings the shaft 2 can extend.

In a next step, shown in figure 4, pressure is applied within the conformal cover 11 which causes the interior surface 17a of the cover 11 to separate from the outer surface 13 of the core 10 of first mold member 1. Pressure may be applied by introducing a suitable medium 18, such as air, nitrogen gas, or oil in the area enclosed by the interior surface 17a of the cover 11. A convenient way to introduce the medium 18 under pressure into said area comprising providing a hollow shaft 2 that is provided with a number of orifices 19 in its wall at positions that terminate within said area. Alternative means do exist, such as exchanging the shaft 2 with hydraulic tubing, and / or introducing the medium by opening valves through hydraulic lines provided in (one of) the mold parts (20a, 20b), preferably at a junction of two of said mold parts. This is especially of advantage when an article is made by polar or pole free winding, and the article does not have a polar opening that needs to be closed. Yet another possibility comprises providing a hollow first mold member, filling an interior cavity of said first mold member with a medium under pressure, and introducing said medium under pressure into the area between the outer surface 13 of the core 10 of first mold member 1 and the interior surface 17a of the cover 11, preferably by providing the wall of the first mold member with orifices.

Due to the pressure exerted on the conformal cover 11 by medium 18, an outer surface 17b of the conformal cover 11 and an inner surface (21a, 21b) of the second mold member 20 engage and pressurize the structure 15 that is positioned in between.

Before, during and / or after pressurizing the structure 15, said structure 15 is heated until the adhesive means, ie the HDPE coating on the UHMWPE reinforcing fibers in the present embodiment, has melted and at least partly wetted the elongated reinforcing element, ie the UHMWPE anti-ballistic fiber yams in the present embodiment. The relatively low amount of HDPE coating of less than 20% by weight, more preferably less than 15% by weight, and most preferably less than 12% by weight, relative to the total amount of the UHMWPE anti-ballistic fiber yams provides a sufficient amount of molten adhesive to bond the UHMWPE anti-ballistic fiber yarns together.

Heating may be accomplished by any suitable means, such as providing a heated medium 18, or heating the first and / or second mold member by providing at least one of them with heating means, such as hydraulic, electrical, infrared or ultrasonic heating means, and the like, and combinations thereof.

In a next step, the consolidated structure 15 is cooled under pressure or after the pressure has been released, as shown in figure 5. Suitable cooling means include passive and active cooling means, adapted to cool the medium 18, and / or the first mold member 1, and / or the second mold member 20. Releasing the pressure (figure 5) causes the interior surface 17a of the (preferably elastic) cover 11 to return to the outer surface 13 of the core 10 of first mold member 1. This also causes the outer surface 17b of the cover 11 to retract from the internal surface of the second mold member 20, which internal surface is formed by the assembled internal surfaces (21a, 21b) of mold parts (20a, 20b).

In a next step, shown in figure 6, the second mold member parts (20a, 20b) are removed from the molded structure 15, which makes the outer surface 15b of the molded structure 15 accessible. Although not shown in figure 6, another embodiment may also remove the shaft 2, also before providing the second mold member.

According to the invention, the molded structure 15 is then divided along cutting line 23 throughout the total wall thickness 24 of the molded structure 15. This provides two molded parts (25a, 25b) that are readily removed from the shaft 2 by shifting each part in a direction (26a, 26b) along the shaft 2. Division of the molded structure 15 may be carried out by any suitable means, such as by mechanical and / or abrasive cutting means, water (or another medium) jetting means, laser cutting means, and the like. Separating the two parts (25a, 25b) from the shaft 2 also separates the two parts (25a, 25b) from the f irst mold member 1. In another embodiment, parts of the first mold member 1, such as an outer cover, may remain on the interior surface of parts (25a, 25b).

Although the molded structure 15 is may be broadly symmetrical (apart from details such as for instance ear pieces in case of helmets) with respect to symmetry plane 27, cutting is performed along cutting lines 23 that approximately follow the contour of the rim of the shaped parts (25a, 25b) to be produced. It is also possible that the molded structure is non-symmetrical or anti-symmetrical, and that identically shaped parts after cutting are rotated 180 ° with respect to each other around the winding axis (the axis of rotation), forming an anti-symmetric pair . In such an embodiment, the relatively long rear part of a helmet for instance would fit with and be adjacently positioned to the relatively short front side of the other helmet. This may decrease the amount of waste. Robotic cutting means provide any kind of cut lines and arrangement of parts onto the first mold member to be extracted from the molded and consolidated structure.

After removal of the two molded parts (25a, 25b), these parts may require some trimming, for instance along their cutting edges (28a, 28b), for instance by grinding, to obtain two identical final combat helmet shells (100a, 100b) that are ready for use.

Adding to the performance increase observed, the method in accordance with the invention offers advantages, such as the absence of wrinkles in the final article, the use of cheaper starting materials instead of the more expensive prepreg weaves and prepreg UD materials, freedom of combining different materials, a low amount of waste, an increased production speed, and the opportunity for far-reaching automation, and hence high levels of reproducibility.