WO2010019697A1

WO2010019697A1 - Mold system and method for making helmet

Info

Publication number: WO2010019697A1
Application number: PCT/US2009/053590
Authority: WO
Inventors: Lawrence J. Dickson
Original assignee: ArmorSource LLC
Current assignee: ArmorSource LLC
Priority date: 2008-08-12
Filing date: 2009-08-12
Publication date: 2010-02-18
Anticipated expiration: 2011-02-12

Abstract

A method for forming a resin-fiber composite shell includes introducing a resin-fiber pre-preg packet between a rigid cavity (10) and a rigid core (22). A flexible member (24) is introduced between the rigid cavity and the rigid core. The flexible member has a first side and a second side that is opposite the first side. The resin-fiber pre-preg packet (36) is positioned on the first side of the flexible member. A fluid is introduced between the flexible member and one of the cavity wall and the core wall for applying a substantially uniform pressure on the second side of the flexible member. The first side of the flexible member applies the substantially uniform pressure to the resin-fiber pre-preg packet for forming the resin-fiber pre-preg packet into a shape of one of the cavity wall and the core wall.

Description

MOLD SYSTEM AND METHOD FOR MAKING HELMET

[0001] This application claims the benefit of U.S. Provisional Application No.

61/088,044, filed August 12, 2008, which is hereby incorporated by reference.

Background

[0002] The present invention relates to the field of articles of manufacture made from resin-fiber composites and methods for making such articles. More particularly, the invention relates to a ballistic helmet comprising an impact resistant composite shell, a mold for making the helmet, and a method for producing the helmet.

[0003] Helmets having impact resistance and in particular ballistic resistance are known in the art. However, attempts are continually underway to improve the impact and ballistic resistance of such helmets. A variety of helmets and methods for making helmets are described in publications such as US Patent Nos. 4,199,388; 4,953,234 and 5,112,667. These patents disclose using fiber-resin composite materials to create improved helmet shells. In particular, US Patent No. 4,953,234 describes an improved helmet using polyethylene fibers in a polymer matrix. The composite shell is made by assembling together pre-preg packets where each pre-preg packet containing a multitude of pre-preg layers. Each pre-preg layer in turn has a multitude of unidirectional coplanar fibers embedded in a polymeric matrix, with adjacent fiber layers in the pre-preg packets situated at various angles relative to each other. The ballistic resistant material described in these patents exemplifies known ballistic materials having penetration resistance.

[0004] Even though ballistic materials produced using resin-fiber composites are known, conventional processing techniques are limited by the level of pressure they can uniformly apply during crucial stages of processing. A conventional helmet mold typically consists of a two-piece, matched-metal die. The rigid pieces of the die internest when closed and heat and pressure are applied to a resin-fiber pre-preg placed within. As a result, resin flows from the resin-fiber pre-preg into the gap between the internested rigid pieces. Conventional helmet molding methods are not dynamic operations, however, that use molds designed to respond to resin flow by applying continuous pressure uniformly throughout the entire molding process. Rather, since the gap between the internested rigid pieces in a conventional mold is fixed, once sufficient flow of resin is achieved the pressure applied to the resin-fiber pre-preg is released. Consequently, conventional helmet molding methods are limited because high pressures are obtained only during initial stages of processing.

[0005] The present invention improves upon conventional helmet manufacturing by offering responsive molds and novel production methods that can be used with state of the art resin- fiber composite ballistic materials to optimize the ballistic performance of helmets produced. The mold designs and methods described herein solve deficiencies associated with conventional helmet manufacturing techniques by allowing high pressure to be continuously and uniformly applied to a resin-fiber helmet pre-form during all stages of molding.

Summary

[0006] In one embodiment, a method for forming a resin-fiber composite shell includes introducing a resin-fiber pre-preg packet between a rigid cavity and a rigid core. A flexible member is introduced between the rigid cavity and the rigid core. The flexible member has a first side and a second side that is opposite the first side. The resin-fiber pre-preg packet is positioned on the first side of the flexible member. A fluid is introduced between the flexible member and one of the cavity wall and the core wall for applying a substantially uniform pressure on the second side of the flexible member. The first side of the flexible member applies the substantially uniform pressure to the resin- fiber pre-preg packet for forming the resin-fiber pre-preg packet into a shape of one of the cavity wall and the core wall. Brief Description of the Drawings

[0007] In the accompanying drawings which are incorporated in and constitute a part of the specification, embodiments of the invention are illustrated, which, together with a general description of the invention given above, and the detailed description given below, serve to exemplify the embodiments of this invention.

[0008] FIGURE 1 illustrates a cross-section view of a mold that has a rigid cavity operatively connected to an expandable member, which contains an inward- forming reaction ring, in accordance with one embodiment of an apparatus illustrating principles of the present invention;

[0009] FIGURE 2 illustrates a cross-section view of a mold that has a rigid cavity operatively connected to an expandable member, which contains an outward- forming reaction ring, in accordance with one embodiment of an apparatus illustrating principles of the present invention;

[0010] FIGURE 3 illustrates an alternate embodiment of a cross-section view of a mold; and

[0011] FIGURE 4 illustrates another alternate embodiment of a cross-section view of a mold.

Detailed Description of Illustrated Embodiment

[0012] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used in the description of the invention herein is for describing particular embodiments only and is not intended to be limiting of the invention. As used in the description of the invention and the appended claims, the singular forms "a," "an," and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. AU publications, patent applications, patents, and other references mentioned herein are incorporated by reference in their entirety. [0013] Unless otherwise indicated, all numbers expressing quantities of ingredients, properties such as molecular weight, reaction conditions, and so forth as used in the specification and claims are to be understood as being modified in all instances by the term "about." Accordingly, unless otherwise indicated, the numerical properties set forth in the following specification and claims are approximations that may vary depending on the desired properties sought to be obtained in embodiments of the present invention. Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the invention are approximations, the numerical values set forth in the specific examples are reported as precisely as possible. Any numerical values, however, inherently contain certain errors necessarily resulting from error found in their respective measurements.

[0014] As used herein, "substantially void-free" means at least 50% of the bulk structure of the molded composite, obtained after the molding operation is complete, does not contain any voids or have any gas or air pockets present.

[0015] As used herein "optimized ballistic properties" means that by design the ballistic performance of the molded composite structure is tailored to a particular use and meets the ballistic performance criteria that have been established for the particular use.

[0016] Composite Shells and Helmets

[0017] Methods described herein produce a resin-fiber composite shell that is substantially void-free and has optimized ballistic properties throughout. The resin-fiber composite shell has a hemispherical shape and is produced by a method comprising expanding a flexible member within a hemispherical-shaped rigid cavity that contains one or more resin-fiber pre-preg packets. The flexible member and the hemispherical-shaped rigid cavity are attached so that the flexible member expands into and fills the hemispherical-shaped rigid cavity. In this configuration the flexible member and the hemispherical-shaped rigid cavity comprise two parts of a mold suitable for carrying out the methods described herein.

[0018] A single resin-fiber pre-preg packet or a multitude of packets are placed in the rigid cavity. During molding the resin- fiber pre-preg packets are disposed between the surface of the flexible member and the concave surface of the substantially hemispherical-shaped rigid cavity. The rigid cavity is heated to a temperature suitable for processing the resin-fiber pre-preg packets into a composite material. A hydraulic medium is used to expand the flexible member, which can be pressurized to pressures of from about 14 psi to over 100,000 psi.

[0019] Upon pressurization with the hydraulic medium, the flexible member expands and contacts the resin-fiber pre-preg packets. The resin-fiber pre-preg packets are reacted and compressed between the surface of the flexible member and the surface of the substantially hemispherical-shaped rigid cavity. At the elevated temperatures and pressures employed, resin from the resin-fiber pre-preg packets flows into the interfacial region between the flexible member and the substantially hemispherical-shaped rigid cavity to fill the space between these two surfaces. Both elevated temperatures and pressures are maintained throughout the entire molding process.

[0020] As previously indicated, a conventional mold is a matched-metal die made from two rigid pieces. The pieces internest with a fixed gap existing between the two rigid surfaces. As a result of the fixed gap, when different thicknesses or different amounts of pre-preg materials are used in different regions of the mold, by design for example, the molding surfaces of conventional molds may pinch at the high points where the pre-preg materials are thickest. When this happens, the greatest molding pressures are applied only at the places where the mold pinches. Consequently, the bulk composite structure is exposed to non-uniform pressure during molding, which leads to non- uniformities in the composite structure and in ballistic performance.

[0021] This does not happen when molds and methods of the present invention are used because the amount of pressure applied to all regions of the pre-preg material is not determined by the width of the gap existing between two rigid surfaces. Rather, a flexible member is used to apply pressure to the pre-preg material uniformly. A mold having a flexible member makes dynamic molding operations possible, since the flexible member can respond to varying thickness of pre-preg material or to changes in resin flow by applying uniform pressures to all regions of the mold simultaneously and throughout all stages of molding. After molding is complete and the mold cools, a substantially void free, impact resistant, hemispherical-shaped, resin-fiber composite shell is produced.

[0022] In certain instances, it may be desirable to use more or thicker pre-preg packets in areas of a helmet that form the side regions as compared to areas that form the crown region. This is because field studies show fewer ballistic events occur to the crown region compared to the rest of the helmet due to its location. Furthermore, since it is known that lighter ballistic garments provide advantages to a wearer by increasing the wearer's mobility and lessening his or her fatigue, a helmet having less resin-fiber composite in the crown region but more everywhere else would be advantageous. A helmet having resin-fiber composite material selectively removed only from the crown area, formed in a process where continuous pressure is applied uniformly throughout the entire structure, would produce a lighter helmet exhibiting minimal detrimental changes in overall ballistic performance.

[0023] Methods employing a hydraulic medium to shape a helmet resemble hydroforming in limited respect. Hydroforming is a specialized stamping process that uses high pressure hydraulic fluid at room temperature to press a continuous metal sheet or tube into a die. Hydroformation allows malleable metals to be manipulated to produce lightweight, structurally stiff, strong pieces with complex shapes that are otherwise difficult or impossible to make using standard solid stamping techniques. However, hydroforming is done with metals at room temperature. Furthermore, the metals used in hydroforming operations do not undergo a phase change to form the structure. In contrast, the fiber-resin composites made using hydraulic pressure according to the present invention are molded at elevated temperatures. Unlike in hydroforming, the solid resin from the pre-preg material melts and undergoes a phase change in order to form a composite structure. Also, rather than being in direct contact with a pressurized hydraulic fluid as typically occurs during hydroforming, resin fiber pre-preg material is reacted against a flexible member that is pressurized with hydraulic fluid. [0024] Pre-Preg Packets

[0025] The resin-fiber composite shell is formed, according to certain embodiments of the methods herein described, by using heat and constant pressure to compress together one or more resin-fiber pre-preg packets. Any commercially available resin-fiber pre-preg packets can be used in conjunction with the methods herein described to produce suitable resin- fiber composite shells. Resin-fiber pre-preg packets can be flat. Alternatively, the pre-preg packets can be pre-formed, for example in a pre-molding step, into a pre-form that is partially hemispherical in shape. Specifically, the resin-fiber pre- preg packets can be pre-formed into a helmet-shaped pre-form in a pre-molding step. Resin-fiber pre-preg packets are made from one or more continuous sheets that, optionally, have perforations, patterns, pre-cuts, pre-creases, or formed into pinwheel configurations in a pre-cutting step. This may aid with the pre-preg packets more easily adopting a three-dimensional shape upon molding without forming additional creases or folds or extraneous overlapping of material.

[0026] Resin-fiber sheets comprising the resin- fiber pre-preg packets contain ballistic fibers within a polymer matrix (e.g., Dyneema from DSM Corp., Spectra Shield from Honeywell International, etc). Ballistic fibers suitable for fabrication of pre-preg packets vary widely and include organic or inorganic fibers having a tensile strength of at least about 5 grams/denier, a tensile modulus of at least about 30 grams/denier, and an energy-to-break of at least about 20 joules/gram. The tensile properties may be measured by an Instron Tensile Testing Machine by pulling a 10 in. (25.4 cm) length of fiber clamped in barrel clamps at a rate of 10 in/min. (25.4 cm/min). Specifically, fibers that are suitable include those having tenacity equal to or greater than about 10 g/d, a tensile modulus equal to or greater than about 150 g/d, and an energy-to-break equal to or greater than about 8 joules/gram. Other fibers contemplated as suitable include those having a tenacity equal to or greater than about 20 g/d, a tensile modulus equal to or greater than about 500 g/d, and an energy-to-break equal to or greater than about 30 joules/grams.

[0027] Polymers suitable for fabrication of pre-preg packets also vary widely and include thermoplastic resins and thermosetting resins. Exemplary thermoplastic resins contemplated maybe selected from various classes of thermoplastic polymers including but not limited to polyurethanes, polyethylenes, polyolefins, polypropylenes, polyesters and thermoplastic elastomers. Exemplary thermosetting resins contemplated may be selected from various classes of thermosetting polymers including but not limited to polyvinyl butyrols (PVB), polyesters, vinyl esters, PVB-phenolics, epoxies, and urethanes.

[0028] In certain embodiments, a resin-fiber pre-preg packet comprises a plurality of resin-fiber sheets. Furthermore, each resin-fiber sheet may comprise one or more fiber layers embedded in a polymer matrix. Still further, each of the fiber layers may be comprised of a unidirectional array of coplanar and substantially parallel fiber bundles. The bulk direction of alignment of the substantially parallel fiber bundles making up each of the fiber layers in the polymer matrix is oriented in such a way, so that it is different from the bulk direction of alignment of any neighboring layer of coplanar fiber bundles. The difference between the directions of orientation for any two neighboring layers may have an angle associated with them of from about 0 to about 180 degrees.

[0029] For certain exemplary embodiments, from about 2 to about 250 resin-fiber pre-preg packets comprise the resin-fiber composite shell, hi other exemplary embodiments, from about 5 to about 50 resin-fiber pre-preg packets comprise the resin- fiber composite shell. For certain exemplary embodiments, from about 2 to about 20 resin-fiber sheets comprise each resin-fiber pre-preg packet, hi other exemplary embodiments, from about 5 to about 20 resin-fiber sheets comprise each resin-fiber pre- preg packet.

[0030] Mold Systems

[0031] Mold systems (molds) described herein are useful for forming a resin-fiber composite shell. The mold has a rigid cavity substantially hemispherical in shape, and a flexible member that is capable of expanding to fill the substantially hemispherical- shaped rigid cavity. The flexible member and the rigid cavity are parts of the mold operatively connected together. The flexible member and the rigid cavity are attached, positioned relative to one another, such that the flexible member expands into and fills the rigid cavity when it is pressurized with a hydraulic medium. Being connection in this way, the flexible member and the rigid cavity are two parts of a mold that is useful for carrying out the methods herein described.

[0032] An embodiment of the molds provided herein is a mold for forming a resin-fiber composite helmet. In this embodiment, for example, the mold has a flexible member attached to a helmet-shaped rigid cavity, hi a similar manner to that described, the rigid cavity is heated and the flexible member is expanded within the helmet-shaped rigid cavity. Subsequently, one or more resin-fiber pre-preg packets, placed in the rigid cavity and disposed between the surface of the flexible member and the concave surface of the helmet-shaped rigid cavity, are compressed and are molded into a resin-fiber composite helmet that is substantially void-free and that has optimized ballistic properties suitable for specifically designed applications.

[0033] As previously indicated, a conventional helmet mold is typically a matched-metal die that has two rigid pieces that internest and that have a void or air gap existing between the two rigid pieces when the mold is closed. Resin-fiber pre-preg material is place between the rigid pieces and it is held in place in the gap region when the mold is closed and pressure is applied. As a result of the fixed gap configuration, when different thicknesses or quantities of pre-preg material are used in different regions of the mold, a conventional mold may pinch at the high points and apply greatest pressures at areas where the pre-preg material is thickest or present in greatest amounts. Consequently, non-uniform pressures are applied to the bulk resin-fiber pre-preg material during the molding cycle leading to non-uniform ballistic performance in the resulting composite structure.

[0034] Another result of the fixed gap configuration in conventional molds is that variable pressures may be applied during different stages of the molding process. For example, when pre-preg material used in a molding operation is initially thicker than the fixed gap width, the pre-preg material starts off being placed under very high pressure when the mold is closed. However, after sufficient heat is applied, the initial thickness of pre-preg material decreases as resin flows out of the pre-preg material into the surrounding regions of the mold. When this occurs, the thickness of the pre-preg material may end up being less than the width of the fixed gap. Because the rigid surfaces of the mold are as close as their rigid nature will allow them to be, the high pressure initially applied to the pre-preg material is released. Consequently, high molding pressures are applied to the pre-preg material only during the initial stages of molding.

[0035] Unlike with the conventional helmet molds that have a fixed gap configuration, the molds for making composite shells and helmets described herein utilize a flexible member pressurized with a hydraulic medium so that it expands within a hemispherical-shaped rigid cavity. In this way, the flexible member expands and compresses pre-preg material against the surface of the rigid cavity wall. Because the member is flexible and not rigid, the surface of the member adjusts throughout the molding operation to various changes that occur to the shape and thickness of the pre- preg material being molded as a result of resin flow. This keeps the surface of the flexible member in constant contact with the pre-preg material so that constant pressure is maintained on the pre-preg material throughout. By dynamically responding to the resin flow associated with compression molding, molds of the present invention apply very high pressures continuously throughout every stage of the molding process. This produces substantially void-free, hemispherical-shaped resin- fiber composite shells that exhibit optimal performance, and which can be used to make superior helmets with enhanced ballistic properties.

[0036] Another advantage to the molds described herein is the versatility that they provide. Consider the limitations associated with the conventional matched-metal die type molds having two rigid parts and a fixed gap between the rigid molding surfaces. The thickness of the gap and the design of the rigid molding surfaces are typically determined based on specifications associated with particular products that the mold will be used to produce. Therefore, when a conventional mold is used an operator is required to change out most or all of the components of the mold when a different product is desired. This is unlike the molds of the present invention, where the space between the two molding surfaces (the rigid cavity surface and the flexible member) depends upon how much the flexible member is pressurized. As a result, one mold configuration may be used to mold several different types of products. Thus, it is contemplated that an operator may only need to change the pressure applied or the pre-preg material used to form one product versus another. Consequently, the molds described herein are more versatile than conventional molds, since different products may be produced using a single mold. This saves the operator both in time and costs of production associated with changing out a mold entirely.

[0037] Rigid Cavity and Core

[0038] The rigid, concave cavity is hemispherical in shape. The cavity provides a surface where the resin-fiber composite shell is made and acts as a template for forming the outside surface or exterior shape of the composite shell or helmet. Thus, it is generally made to have the precise shape of the desired object. Accordingly, in certain exemplary embodiments, the rigid cavity is in the shape of a helmet and is used to produce helmet-shaped composite shells.

[0039] The rigid cavity is made from a material robust enough to withstand forces associated with being in contact with a flexible member that is pressurized with hydraulic medium, without undergoing deformation. Materials used to construct the rigid cavity are also capable of withstanding elevated temperatures for an extended period of time, since these are conditions typically used in the molding procedures. Furthermore, it is desirable to make the rigid cavity from a material that conducts heat, since this will facilitate effective transfer of heat to the resin-fiber pre-preg packets during molding. Heat can be applied during molding by using a separate heat source. Optionally, the rigid cavity contains or can be fitted with a heat source as part the construction. In certain exemplary embodiments, the rigid cavity is made from, for example, a block of steel, aluminum, or brass.

[0040] Optionally, in certain embodiments, a rigid core is also part of the mold construction, hi these embodiments, the rigid core attaches to both the flexible member and the rigid cavity. The rigid core and the rigid cavity connect to each other, sandwiching the flexible member between their surfaces. The surface of the rigid core that is in contact with the flexible member may be flat. Alternatively, the surface of the rigid core that is in contact with the flexible member may protrude outward, either partially or wholly, and internest with the rigid cavity, hi this configuration, the mold in- part resembles a conventional two-piece matched-metal die. When the mold is closed, the rigid core attaches to and forms a seal with the flexible member. However, the seal is only formed around the perimeter of the flexible member leaving the middle portion of the member free to expand when pressurized with hydraulic medium.

[0041] The rigid core may also be fitted with tubes, channels, and valves that are appropriate for controlling flow and pressurization of a hydraulic medium. A pump and a reservoir for a hydraulic medium may also be provided as part of the rigid cavity, the rigid core, or as a completely separate component that is individually connected to the mold. Materials used to construct the rigid core are also capable of withstanding elevated temperatures for an extended period of time, since these are the conditions typically used in the molding procedures. As with the rigid cavity, it is desirable to make the rigid core from a material that conducts heat, since this facilitates effective transfer of heat to the resin-fiber pre-preg packets during molding. Furthermore, heat can be applied during molding by using a separate heat source integrated with the rigid core, the rigid cavity, or both. Optionally, the rigid core, the rigid cavity, or both have or can be fitted with a heat source as part of its construction. In certain exemplary embodiments, the rigid core is made from, for example, a block of steel, aluminum, or brass.

[0042] Flexible Member

[0043] The flexible member is an elastic membrane, an elastic bag, an elastic balloon, an elastic bladder, etc., which is capable of expanding and can be pressurized with a suitable hydraulic fluid. The flexible member is large enough so that upon expansion it can fill the substantially hemispherical shaped rigid cavity. The flexible member provides a surface where the resin-fiber composite shell is made and acts as a template for forming the inside surface of the composite shell. The flexible member is made from material robust enough to withstand being pressurized with hydraulic fluid without rupturing and is capable of withstanding elevated temperatures for an extended period of time, commensurate with conditions used during molding. Furthermore, the flexible member is chemically compatible with the type of hydraulic fluid used. [0044] Specifically, in certain embodiments, the flexible member is made, for example, from a thermally stable, resilient rubber which does not dissolve in hydraulic fluid. Some suitable rubbers in this regard are elastomeric materials commercially available from the Mosites Rubber Company Inc., Fort Worth, Texas, which include Buna-N, Butyl, Chloroprene, Chlorinated Polyethylene, Chlorosulfonated Polyethylene, EPT or EPDM, Epichlorohydrin, Ethylene Acrylic, Ethylene Propylene/Silicone, Fluorocarbon Fluorosilicone, Natural, Polyacrylic, SBR, Silicone, and Urethane rubbers.

[0045] In certain embodiments, the flexible member is an impermeable, single layer, elastic membrane that stretches over the hemispherical-shaped rigid cavity when the mold is closed. The flexible member forms a seal with and attaches around the perimeter of the cavity. In this closed configuration, the flexible member seals the rigid cavity shut and the mold resembles a drum. When closed, the mold has an inside area and an outside area separated by the elastic membrane. When the outside area of the mold is pressurized with a hydraulic medium to a pressure greater than the pressure inside the mold, the pressure differential causes the flexible member to stretch towards the area of lower pressure. Because the flexible member is elastic, it expands into the rigid cavity.

[0046] Embodiments where the flexible member is partitioned into two or more sections that can be separately pressurized with hydraulic fluid are also contemplated. The separate sections can be pressurized to either the same or different pressures. In embodiments of the method where two or more sections of the flexible member are to be pressurized to different pressures, the different member sections can be distinct chambers completely separate from one another that are individually attached to separate hydraulic systems and can then be pressurized to different pressures. Alternatively, the flexible member can be comprised of a single, continuous membrane made with discrete sections that either have different thicknesses or are made from different materials that have different elastic properties. A continuous member having such discrete sections can exhibit different levels of expansion relative to one another that, for example, may depend upon how thick the different sections are or on the types of material that they are made from. In this way, a single hydraulic system can be used to pressurize a single membrane and produce the same results as if a single member with two distinct chambers attached to two separate hydraulic systems were used.

[0047] Embodiments having a flexible member partitioned into two or more distinct chambers or into two or more sections that can be separately pressurized with hydraulic fluid may be used, in accordance with methods herein described, to produce resin-fiber composite shells and helmets that have non-uniform thicknesses but uniform ballistic performance. The non-uniformity of the thickness is a design feature of the helmet based on the proposed end use for the product. One design feature, for example, could be to produce lighter products with suitable or superior ballistic performance. Weight reduction can be achieved by selectively removing resin fiber composite only from helmet areas because it is known from field studies that ballistic events occur less frequently in this area. Therefore, a helmet designed to have less resin-fiber composite only in the crown region is desirable. Consequently, a mold for producing such helmets would allow helmets to be lightened without detrimentally impacting their overall utility.

Also contemplated is an embodiment using a mold having a flexible member partitioned into two sections, where one section of the flexible member is used to form the crown of the helmet and another section of the flexible member is used to form the rest of the helmet. The mold embodiment contemplated may be utilized so that the two distinct sections of the flexible member are pressurized to different pressures to produce a helmet with different amounts of resin-fiber composite material in the crown region versus the rest of the helmet. Specifically, we believe a mold as described above, having a flexible member partitioned into two sections, may be used in a method where the section of the flexible member associated with the crown of the helmet would be pressurized at a higher pressure than would be the section of the flexible member associated with the rest of the helmet. Accordingly, as the mold is heated and the different sections of the member pressurized to compress the pre-preg material, more resin will flow out of the area associated with the crown region of the helmet rather than areas of the helmet which are not under such high pressure. As a result, a helmet will be produced that is thinner in the crown region than it is in other areas of the helmet. Optionally, excess resin from the crown region could be removed during the molding operation using a resin overflow valve, to produce a helmet that is also lighter than a comparable helmet made using conventional molds.

[0048] Methods

[0049] Methods described and exemplified herein are for forming a resin-fiber composite shell, hi one embodiment, the method comprises expanding a flexible member within a hemispherical-shaped rigid cavity containing at least one and, optionally, more than one resin- fiber pre-preg packet. The resin-fiber pre-preg packets are disposed between the flexible member and the surface of the hemispherical-shaped rigid cavity, hi this way, a hemispherical shaped resin-fiber composite shell is produced from the resin- fiber pre-preg packet.

[0050] hi another embodiment, the method for making a hemispherical shaped resin-fiber composite shell comprises the following steps: (1) providing a substantially hemispherical-shaped rigid cavity, operatively connected to a flexible member that is capable of expanding to fill the rigid cavity; (2) placing one or more resin- fiber pre-preg packets in the rigid cavity; (3) heating the rigid cavity; and (4) expanding the flexible member within the rigid cavity to compress the resin-fiber pre-preg packet against the surface of the substantially hemispherical-shaped rigid cavity. In this way a hemispherical-shaped resin-fiber composite shell is produced from the resin-fiber pre- preg packet.

[0051] Methods also described and exemplified herein involve forming a resin- fiber composite helmet and producing a high performance ballistic helmet, m one embodiment, the method for forming a resin-fiber composite helmet comprises expanding a flexible member within a helmet-shaped rigid cavity. The rigid cavity contains at least one and, optionally, more than one resin-fiber pre-preg packet. The resin-fiber pre-preg packets are disposed between the flexible member and the surface of the helmet-shaped rigid cavity. In this way, a resin-fiber composite helmet is produced from the resin-fiber pre-preg packet. The helmet produced is substantially void-free and has optimized ballistic properties throughout. [0052] In another embodiment, a method for producing a high performance ballistic helmet involves using a mold comprised of a flexible member attached to a rigid cavity, the method comprising inducing uniform high pressure against a helmet pre-form by expanding the flexible member within the rigid cavity during a molding cycle to result in a high performance ballistic helmet molded at extremely high pressure in a very uniform process.

[0053] In another embodiment, a method of forming a ballistic structure involves using a mold comprising a flexible member attached to a rigid template designed to form a surface of the ballistic structure, the method comprising inducing uniform high pressure against a ballistic pre-form by expanding the flexible member against the rigid template to compress the ballistic perform between the flexible member and the rigid template during a molding cycle to result in a high performance ballistic structure molded at extremely high pressure in a very uniform process.

[0054] The flexible member as described above, which includes an elastic membrane or an elastic bag or balloon, is expanded by pressurization with a hydraulic medium. During operation, the flexible member is pressurized to a pressure of from about 14 to about 100,000 psi. For certain embodiments, the flexible member is pressurized to a pressure of about 14 to about 30,000 psi. The hydraulic medium is a fluid having a low compressibility such that force is transferred through the fluid with minimal loss. Suitable hydraulic mediums for use with the methods herein described include, for example, synthetic compounds, mineral oil, water, petroleum-based hydraulic oils, and water-based hydraulic mixtures. As with the flexible member and the rigid cavity, suitable hydraulic mediums are robust enough to withstand extended periods of time at the elevated pressures and elevated temperatures associated with the conditions used in the molding procedures. Furthermore, the hydraulic medium is chosen to be compatible with the type of material used to make the flexible member so that the flexible member does not dissolve, swell, or breakdown structurally when exposed to the hydraulic medium.

[0055] As previously indicated, embodiments of the method are contemplated having the flexible member partitioned into two or more sections that can be pressurized separately. The separate sections are pressurized to either the same or different pressures. Specifically, we consider embodiments where different sections of the flexible member are pressurized to different pressures and where the different sections of the flexible member are attached to separate hydraulic systems to carry out pressurization to different pressures. Alternatively, it is contemplated that separate sections of the flexible member are attached to separate hydraulic systems, where the separate hydraulic systems contain different hydraulic mediums having different compressibility. Consequently, the different hydraulic mediums may respond differently and may transfer different amounts of compressive force, by way of the partitioned flexible member, to the different areas of the mold and associated resin-fiber pre-preg packets. Thus, resin-fiber composite shells and helmets having non-uniform thicknesses can be formed, which have distinctly defined areas of predetermined thicknesses by design. The non-uniform thick resin-fiber composite shells and helmets can designed based on an end use planned for the product and one of ordinary skill will understand what locations and variations in thickness for the non-uniformities are acceptable for resin- fiber composites that are suitable for various ballistic purposes.

[0056] For certain embodiments, steps of the methods involve heating the mold, for example the rigid cavity in embodiments where the mold is constructed from a block of steel, and, optionally, maintaining the rigid cavity at a predetermined temperature. Applying heat during molding facilitates the processing of pre-preg material into resin- fiber composite shells and helmets by enabling resin to flow from the resin-fiber pre-preg packets into the interface between the flexible member and the hemispherical shaped rigid cavity. The temperature that the rigid cavity is heated to and, optionally, maintained at depends upon several factors, including the nature of the resin material present in the resin-fiber pre-preg packets and the design requirements associated with achieving a particular optimized ballistic performance for a particular product. One of ordinary skill will understand how temperatures which are employed in various molding methods can be adjusted based on these factors.

[0057] Typically, resin flow is initiated by reaching the glass transition temperature of the polymer present in the resin material. However, some resin formulations may need to reach higher temperatures. For example, in certain instances the resin melt temperature may need to be reached for suitable resin flow to occur during molding. Resin flow is related to the resin viscosity, which depends on both the heat and pressure applied. Therefore, in certain cases where low pressures are preferred for forming resin-fiber composite shells and helmets, it may be advantageous to heat the mold, for example the rigid cavity in embodiments where the mold is constructed from a block of steel, to higher temperatures. Conversely, in cases where resin decomposition or resin reaction is likely and high temperatures are undesirable, pressures used in the molding operation may be increased to have suitable resin flow during molding. For specific embodiments of the methods herein described, the mold, for example the rigid cavity in embodiments where the mold is constructed from a block of steel, is heated to temperatures of from about 180° F to about 750° F. In other embodiments, the mold is heated to temperatures of from about 180° F to about 450° F.

[0058] For certain embodiments, the steps of the methods involve drawing vacuum on the substantially hemispherical-shaped rigid cavity while expanding the flexible member. For example, when the rigid cavity is constructed from a block of steel, the rigid cavity may be equipped with a vacuum channel that allows a vacuum to be drawn on the cavity portion of the rigid die during the molding process. A vacuum pump, which is either an integrated part of the mold or is an external unit that is separate from the mold, may be connected to the vacuum channel to draw the vacuum. Drawing vacuum on the rigid cavity before expanding the flexible member may help stabilize resin-fiber pre-pre material located within the cavity, and may prevent the pre-preg material from shifting prior to compression. Drawing vacuum while expanding the flexible member to compress the resin-fiber pre-preg material ensures removal of gases and other volatiles produced as a result of molding. Because gases and other volatiles are removed under vacuum, they do not become entrapped in the re-solidified resin once it cools. Thus, substantially void-free resin-fiber composite structures, shells, and helmets can be formed. A vacuum may also be used to remove resin overflow during the compression stage of molding. Thus, drawing vacuum during molding may facilitate the production of lighter weight ballistic helmets. [0059] While the molds and methods described herein involve expanding a flexible member within a rigid cavity to compress pre-preg material between the flexible member and the surface of the rigid cavity, these are only specific embodiments and others are contemplated. For example, for embodiments where a rigid core is part of the mold construction, contemplated are methods and molds that involve compressing pre- preg material between the flexible member and the surface of the rigid core. For this exemplary mold, the configuration is set-up opposite that of the mold configurations previously described. Pre-preg material is loaded in the mold, for example, by draping it over the rigid core, and the flexible member is attached along the periphery to the rigid cavity. Inside and outside areas of the mold in this opposite configuration are likewise reversed compared with the molds previously described. The mold is pressurized with hydraulic medium from the side of the flexible membrane which faces towards the rigid cavity. As a result, the flexible member does not expand within the rigid cavity to compress pre-preg material, but instead squeezes around and up against the rigid core in order to compress pre-preg material between these two surfaces to form a desired ballistic structure.

[0060] Prophetic Examples

[0061] The present invention will be understood by those skilled in the art by referenced to the accompanying drawing. While preferred embodiments of the present invention are described with reference to the accompanying Figures 1-2, these figures illustrate only preferred embodiments and should not limit the scope of the present invention.

[0062] Mold Configuration 1

[0063] Figure 1 shows a cross-sectional view of a helmet mold configuration according to Example 1. The mold has a rigid cavity operatively connected to an expandable member and contains an inside-forming reaction ring. The expandable member in this configuration is a single layer of an elastic membrane.

[0064] It should be pointed out that, for best performance, sharp edges associated with the rigid pieces of the mold which come into contact with the flexible member should be smoothened in such a way that the flexible member is not pinched or punctured at such edges during molding operation.

[0065] Referring now to Figure 1

[0066] The bottom part of the mold, representing the rigid cavity, is shown at 10.

The rigid cavity in this example is constructed from a block of steel and has a substantially hemispherical-shaped surface shown at 12, which is clearly visible when the mold is open. The rigid cavity contains a vacuum port that allows gases and other volatiles or excess resin to be removed during a molding operation. The vacuum port is shown at 14. A rubber mold seal is shown at 16. A removable reaction ring that allows resin-fiber pre-preg material movement during molding is shown at 20.

[0067] The top part of the mold is shown at 22, and in this example it is constructed from a block of steel. The top part of the mold includes a rigid core, which in this example protrudes outward so that it internests with the rigid cavity when the mold is closed. The top part of the mold also includes a flexible member that is capable of expanding to fill the substantially hemispherical-shaped rigid cavity. The flexible member expands and is used to react against the pre-preg material. For example, the flexible member 24 may expand about 1/2" before contacting the pre-preg material. An exemplary flexible member that is a single layer of an elastic membrane made from rubber is shown at 24. The top part of the mold also contains a hydraulic fluid management system including ports for managing the hydraulic fluid; the hydraulic inlet and outlet ports are shown at 26 and 30 and the hydraulic medium is shown at 32.

[0068] The member retaining ring is shown at 34. A helmet pre-form to be molded is shown at 36. The helmet pre-form 36 includes at least one resin-fiber pre-preg packet. The helmet pre-form is positioned in the mold relative to the removable reaction ring, shown at 20, so that the helmet is formed on the inside of the reaction ring. In this example, the removable reaction ring is not beveled and this will result in the rim of the helmet being formed between two rigid surfaces (the rigid cavity and the inside surface of the reaction ring). A void or air space sufficient to draw vacuum during the molding process is shown at 40. [0069] Mold Configuration 2

[0070] Figure 2 shows a cross-section view of a cross-sectional view of a helmet mold configuration according to Example 2. The mold has a rigid cavity operatively connected to an expandable member and contains an outside-forming reaction ring. The expandable member in this configuration is a single layer of an elastic membrane.

[0071] It should be pointed out that, for best performance, sharp edges associated with the rigid pieces of the mold which come into contact with the flexible member should be smoothened in such a way that the flexible member is not pinched or punctured at such edges during molding operation.

[0072] Referring now to Figure 2

[0073] The bottom part of the mold, representing the rigid cavity, is shown at 110.

The rigid cavity in this example is constructed from a block of steel and has a substantially hemispherical-shaped surface shown at 112, which is clearly visible when the mold is open. The rigid cavity contains a vacuum port that allows gases and other volatiles or excess resin to be removed during a molding operation. The vacuum port is shown at 114. A rubber mold seal is shown at 116. A removable reaction ring is shown at 120.

[0074] The top part of the mold is shown at 122, and in this example it is constructed from a block of steel. The top part of the mold includes a rigid core, which in this example protrudes outward so that it internests with the rigid cavity when the mold is closed. The top part of the mold also includes a flexible member that is capable of expanding to fill the substantially hemispherical-shaped rigid cavity. The flexible member expands and is used to react against the pre-preg material. An exemplary flexible member that is a single layer of an elastic membrane made from rubber is shown at 124. The top part of the mold also contains a hydraulic fluid management system including ports for managing the hydraulic fluid; the hydraulic inlet and outlet ports are shown at 126 and 130 and the hydraulic medium is shown at 132. [0075] The member retaining ring is shown at 134. A helmet pre-form to be molded is shown at 136. The helmet pre-form is positioned in the mold relative to the removable reaction ring, as shown at 20, so that the helmet is formed on the outside of the reaction ring. Unlike with Example 1, in Example 2 the removable reaction ring is beveled and all parts of the helmet are formed between the flexible member and a rigid surface (whether the rigid cavity or the outside surface of the reaction ring).

[0076] Method of Molding - Mold Configuration 1

[0077] The example is directed to a method of molding a helmet using the mold described in Example 1 having a bottom part and a top part. The bottom part contains the rigid cavity and is used to essentially form the exterior shape of the helmet and it is generally made to the precise shape of the desired helmet. The top part contains a rigid core and a flexible member that can be pressurized with a hydraulic medium and used as a reaction point to compress a helmet pre-form to form a ballistic helmet.

[0078] Referring now to Figure 1

[0079] To mold the helmet using the mold of Example 1 , the helmet pre-form 36 is placed into the bottom piece 10 of the mold (i.e., the rigid cavity). The pre-form 36 can be flat or it can be pre-molded at low pressures in order to de-bulk the helmet prior to the high pressure molding. Once the pre-form 36 is loaded into the mold, a removable reaction ring 20 is secured in placed. The reaction ring ensures that a void 40 is maintained in the mold to provide room for the helmet pre-form 36 to expand during high pressure molding. The void 40 is also sufficiently sized to allow a vacuum to be drawn during the molding process, through the vacuum port 14. Applying a vacuum during molding is preferred but is not required.

[0080] The single layer of an elastic membrane that is the flexible member 24 that is shown in this configuration, and which is part of the top piece of the mold 22, is attached by a member retaining ring 34. The member retaining ring 34 secures the flexible member 24 along its perimeter to the rest of the top piece of the mold 22. Since the flexible member 24 is only secured to the top piece of the mold 22 along the perimeter, the flexible member 24 can move up and down in conjunction with the top piece of the mold 22 and it can also expand outward from the rigid core and into the rigid cavity as it pressurizes with hydraulic medium 32. The top piece of the mold 22 and the flexible member 24 nest within the bottom piece of the mold 10, which contains the helmet pre-form 36 and the mold is placed under sufficient pressure so that the two pieces come together and the mold closes during the molding cycle.

[0081] The mold is heated while being pressurized. Temperatures and pressures are selected that are appropriate for the type of helmet resin-fiber material used and one of ordinary skill in the art will recognize that the temperatures and pressure employed are selected based on the type of material used to make the helmet while also considering the end ballistic performance desired. Generally though, the higher the pressure the better will be the ballistic performance. The helmet mold is typically heated to temperatures of from about 18O⁰F to about 750⁰F, and most commonly from about 18O⁰F to about 45O⁰F. The hydraulic medium 32 is introduced through a hydraulic inlet port 26, while the hydraulic outlet port 30 remains closed. The flexible member 24 is pressurized with the hydraulic medium 32 to pressures of from about 14 psi to about 100,000 psi, and most commonly to pressures of from about 3000-10000 psi. The pressurization of the elastic member 24 with the hydraulic medium 32 causes the elastic member 24 to expand into the hemispherical shaped rigid cavity 12 and to compress the helmet pre-form 36 into its final helmet shape.

[0082] After a suitable time, the helmet mold is cooled as appropriate for the end of the molding cycle. The hydraulic medium 24 is evacuated through the hydraulic outlet port 30, causing the flexible member 24 to pull away from the newly molded helmet 36. The mold is then opened. The top piece of the mold 22 is pulled away from the bottom piece of the mold 10 and the reaction ring 20 is removed. The newly molded helmet 36 can then be removed from the rigid cavity 10.

[0083] Referring now to Figure 3

[0084] The mold system (mold) illustrated in Figure 3 represents an alternate embodiment of the present invention, hi this embodiment, the mold system includes a bottom part 210 of a mold, which represents the rigid cavity, and a top part 222 of the mold, which represents the rigid core. In this embodiment, the flexible member 224 is positioned substantially closer to the helmet pre-form 236, which includes at least one resin-fiber pre-preg packet, than the embodiments illustrated in either Figures 1 or 2. In one example, the flexible member 224 only flexes about 1/8", as opposed to the about 1/2" flex of the flexible member 24 in Figure 1.

[0085] The mold system illustrated in Figure 3 also illustrates an alternate embodiment of the inlet port 226. In this embodiment, the inlet port introduces the fluid at a substantially central location 250 in the cavity of the bottom part 210. The embodiment of Figure 3 illustrates the inlet port 226 delivering the fluid at the substantially central location 250, and the embodiments of Figures 1 and 2 illustrate the inlet ports 26, 30, 126, and 130 introducing the fluid relatively closer to side walls of the cavity of the bottom portion 10, 110. However, it is to be understood the fluid may be delivered to any location along the flexible member 24 (see Figure 1), 124 (see Figure 2), and 224 (see Figure 3).

[0086] Referring now to Figure 4

[0087] The mold system (mold) illustrated in Figure 4 represents an alternate embodiment of the present invention. In this embodiment, the mold system includes the helmet pre-form 336 (e.g., resin-fiber pre-preg material) on the top part 322 of the mold, which represents the rigid core of the mold. Therefore, in this embodiment, the resin- fiber pre-preg material 336 is between the flexible member 324 and the top part 322 of the mold (rigid core). In this embodiments, illustrated in Figures 1—3, on the other hand, the resin-fiber pre-preg material 36, 136, 236 is between the respective flexible members 24, 124, 224 and the respective bottom parts 10, 110, 210 of the molds (rigid cavities).

[0088] The unique methods and mold configurations described and exemplified herein provides for applying continuous and uniform pressures onto a resin-fiber helmet pre-form during each step of the molding procedure. The methods and mold configurations herein allow very high pressures to be applied to the helmet during processing and also, optionally, allow vacuum to be drawn on the mold during the molding process. Helmets can be produced using these mold configurations and methods that have very few voids and that have ballistic properties that may be optimized, by design, to suit a particular use. These helmets may have enhanced ballistic performance in comparison with control helmets produced using various conventional molds and conventional molding processes. Enhancing the ballistic performance of resin-fiber composites by using the mold configurations and the methods for processing herein described, in this way allows ballistic helmets to be constructed that provide better ballistic protection versus control helmets at equal weights as the helmets made by conventional techniques. The molds and processes described herein may also allow current ballistic standards to be met by helmets that are lighter than control helmets produced by conventional means.

[0089] While the present invention has been illustrated by the description of embodiments thereof, and while the embodiments have been described in considerable detail, it is not the intention of the applicants to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications will readily appear to those skilled in the art. Therefore, the invention, in its broader aspects, is not limited to the specific details, the representative apparatus, and illustrative examples shown and described. Accordingly, departures may be made from such details without departing from the spirit or scope of the applicant's general inventive concept.

Claims

LWe claim:

1. A method for forming a resin-fiber composite shell, the method comprising: introducing a resin-fiber pre-preg packet between a rigid cavity and a rigid core; introducing a flexible member between the rigid cavity and the rigid core, the flexible member having a first side and a second side that is opposite the first side, the resin-fiber pre-preg packet being positioned on the first side of the flexible member; and introducing a fluid between the flexible member and one of the cavity wall and the core wall for applying a substantially uniform pressure on the second side of the flexible member, the first side of the flexible member applying the substantially uniform pressure to the resin-fiber pre-preg packet for forming the resin-fiber pre-preg packet into a shape of one of the cavity wall and the core wall.

2. The method of claim 1 , wherein the step of introducing the resin-fiber pre- preg packet includes: introducing the resin-fiber pre-preg packet to contact the cavity wall.

3. The method of claim 1 , wherein the step of introducing the resin-fiber pre- preg packet includes: introducing the resin-fiber pre-preg packet to contact the core wall.

4. The method of claim 1 , further including: expanding the flexible member toward the resin-fiber pre-preg packet after the fluid is introduced.

5. The method of claim 4, further comprising heating the hemispherical- shaped rigid cavity prior to expanding the flexible member.

6. The method of claim 5, wherein heating the hemispherical-shaped rigid cavity includes heating to a temperature of from about 180° F to about 750° F.

7. The method of claim 1 , wherein forming the resin-fiber pre-preg packet into a shape of one of the cavity wall and the core wall includes: forming the resin-fiber pre-preg packet into a hemispherical-shaped helmet substantially void-free.

8. The method of claim 1 , wherein: each pre-preg packet comprises a plurality of resin-fiber sheets; each sheet comprises one or more fiber layers embedded in a polymer resin matrix; and each fiber layer comprises a unidirectional array of coplanar and substantially parallel fiber bundles, wherein the direction of alignment of the substantially parallel fiber bundles comprising each fiber layer in the polymer matrix is oriented at an angle of from about 0-180 degrees relative to the direction of orientation of the substantially parallel fiber bundles comprising a neighboring fiber layer.

9. The method of claim 1, wherein the step of introducing the fluid includes introducing a hydraulic medium.

10. The method of claim 1, wherein the step of introducing the fluid includes pressurizing a volume between the flexible member and the resin-fiber pre-preg packet between about 14 psi and about 100,000 psi.

11. The method of claim 1 , wherein the step of introducing the fluid includes : introducing the fluid into two or more separately expandable sections of the flexible member.

12. The method of claim 11, wherein the step of introducing the fluid into two or more separately expandable sections includes: pressurizing each separately expandable section to a different pressure.

13. The method of claim 1 , wherein the step of introducing the fluid includes : introducing the fluid at a substantially central location in the cavity.

14. A method for making a helmet-shaped resin-fiber composite shell comprising: providing a helmet-shaped rigid cavity, the helmet-shaped rigid cavity being operatively connected to a flexible member capable of expanding to fill the helmet- shaped rigid cavity; placing at least one resin-fiber pre-preg packet in the substantially helmet-shaped rigid cavity; heating the helmet-shaped rigid cavity; and expanding the flexible member within the substantially helmet-shaped rigid cavity to compress the plurality of resin-fiber pre-preg packets against the surface of the helmet- shaped rigid cavity for producing a helmet-shaped resin-fiber composite shell.

15. The method of claim 14, wherein the step of placing includes: placing from about 2 to about 250 resin-fiber pre-preg packets in the substantially helmet-shaped rigid cavity.

16. The method of claim 14, further comprising applying vacuum to the substantially helmet-shaped rigid cavity while expanding the flexible member.

17. The method of claim 14, wherein the expanding includes: expanding the flexible member about 1/8".

18. A mold system for forming a helmet, the mold system comprising, a substantially helmet-shaped rigid cavity; a rigid core; a flexible member between the cavity and the core; and a fluid port fluidly communicating with a fluid chamber on a first side of the flexible member, fluid introduced into the fluid chamber via the fluid port exerting a substantially uniform pressure on a resin-fiber pre-preg packet positioned on a second side of the flexible member for forming the resin-fiber pre-preg packet into a shape of one of a wall of the cavity and a wall of the core.

19. The mold system of claim 18 wherein the rigid cavity and the rigid core are made of steel.

20. The mold system of claim 18 wherein the rigid cavity is substantially hemispherical shaped.

21. The mold system of claim 20 wherein the rigid cavity is substantially helmet shaped.

22. The mold system of claim 18 further comprising a retaining ring securing the flexible member to the rigid core, wherein the retaining ring secures the flexible member to the rigid core along the perimeter of the flexible member.

23. The mold of claim 18, wherein the rigid core is sized to internest in the cavity.

24. The mold system of claim 23 further comprising a reaction ring disposed between the flexible member and the rigid cavity, wherein the reaction ring is positioned to form a void between the rigid cavity and the rigid core when the rigid cavity and the rigid core are internested.

25. The mold system of claim 24 wherein the reaction ring is shaped to direct the resin-fiber toward the flexible member as the pressure is exerted on the resin.

26. The mold system of claim 24 wherein the reaction ring is shaped to define a space between the reaction ring and the cavity wall.

27. The mold of claim 18, wherein the flexible member is an elastomeric rubber.

28. The mold of claim 27, wherein the elastomeric rubber is selected from the group consisting of Buna-N, Butyl, Chloroprene, Chlorinated Polyethylene, Chlorosulfonated Polyethylene, EPT, EPDM, Epichlorohydrin, Ethylene Acrylic, Ethylene Propylene/Silicone, Fluorocarbon Fluorosilicone, Natural, Polyacrylic, SBR , Silicone, and Urethane rubbers.