Patent Description:
This disclosure relates generally to molding complex parts, particularly those with very small, thin, or intricate features, with the invention relating to a corresponding method for molding and to a corresponding compression mold.

It is often desirable to fabricate parts from fiber-composite materials. A fiber composite part includes fibers that are dispersed within a matrix, formed from a resin. The matrix surrounds and supports the fibers by maintaining their relative positions, in addition to preventing the fibers from abrasion and environmental attack. The fibers impart their mechanical and physical properties to enhance those of the matrix. The combination is synergistic; the composite possesses material properties unavailable from the individual constituents, such as a very high strength-to-weight ratio.

A variety of different molding processes are available to form fiber-composite parts, such as compression molding, filament winding, pultrusion, wet layup, and transfer molding. In this regard for example, <CIT> discloses a fiber-composite part having a core consisting of short fibers in a resin matrix and an outer circumferential region consisting of long fibers in a resin matrix; <CIT> discloses a resin transfer molding process wherein two different resins are sequentially added to a mold cavity, the second resin to be injecting having a higher viscosity than the first and the sequential injection of resin protects an article that has been inserted in the mold cavity; <CIT> discloses a transfer/injection molding apparatus, with the charge to the apparatus is formed so that fibers are randomly oriented within substantially parallel horizontal planes, ensuring that the fibers remain parallel to the direction of the initial flow into the cavity of the molding apparatus; <CIT> discloses a molding method for making brush ware and <CIT> discloses a resin transfer molding process that prevents the formation of a void in a mold package that seals electronic parts. There are, however, challenges to using such processes for fabricating complex parts with very small, thin, or intricate features, particularly those requiring substantial strength and stiffness.

The present invention is set out in the appended set of claims and provides a method for molding and a corresponding compression mold. The present invention is for fabricating fiber-reinforced parts having very small, thin, or intricate features, as well as desired properties. Such parts might have feature sizes that are too small/thin to accommodate bent preforms, yet, at the same time, require continuous fibers for strength and stiffness.

In accordance with the present teachings, preforms are placed on a portion of a mold cavity. A preform is a sized, or sized and shaped bundle of fiber. In the illustrative embodiment, the bundle of fiber contains thousands of fibers, and is typically referred to as "tow. " In the illustrative embodiment, the fibers in the tow are (pre-) impregnated with a polymer resin; the tow is then called "towpreg" or "prepreg tow.

The preforms are compressed and heated, which melts the resin therein. In the illustrative embodiment, the compression is applied by a plunger that moves linearly within a plunger cavity, wherein the stroke axis (direction) of the plunger is oriented at least <NUM> degrees out-of-plane with respect to a major surface of the mold cavity. In the illustrative embodiments, the major surface of the mold cavity is substantially orthogonal to the plunger's stroke axis.

Embodiments of the invention enable a level of control of fiber movement/placement that is not possible with prior-art molding processes that utilize a plunger. In the prior art, particularly with injection-molding processes, chopped fiber is used as feedstock. As the chopped fiber is forced into a mold via a plunger, it rotates and turns based on the movement of resin through the mold cavity, as well as collisions with a complex and random matrix of other fibers. In embodiments of the invention, however, the feed comprises a majority of relatively long fibers (i.e., fibers that are comparable to the length of a major axis of the part being formed). It is believed that the use of long fibers stabilizes the underlying fiber structure of the part because the fibers are kept under some degree of tension due to features of the process, such that the fibers do not strictly follow the flow of the liquid resin. Rather, fiber position and orientation in the mold cavity and, hence, the final part, are controlled, to a substantial degree, by characteristics of the fiber (e.g., length, orientation in the plunger cavity, etc.), rather than the liquefied resin.

In embodiments of the method, the preforms are oriented such that:.

For preforms that align with one or more planes that are parallel to a major surface of the mold cavity, in some embodiments of the method:.

Fibers tend, to some degree, to align with the direction of flow through the mold cavity. Also, fibers flow to areas of relatively lower pressure. Consequently, the inventors realized that fibers, when appropriately sized, can be directed into very thin, small, or otherwise intricate features, or their final orientation in the part can be engineered. Key parameters in that regard is the size of the fiber (i.e., comparable to the size of the small feature) as well as the selective placement and actuation of vents, which can alter the flow of resin and fiber through the mold cavity.

In accordance with some embodiments, the final location of fibers in a mold cavity during plunger-driven compression molding, and, hence, their final location in the part being fabricated, can be controlled through the use of one or more of the following parameters, as a function of application specifics:.

The feedstock (i.e., preforms) is placed in the plunger cavity. In some embodiments, the preforms are stacked in successive layers in the plunger cavity. After the resin has melted (due to applied heat/energy), advancing the plunger through the plunger cavity forces fiber and melted resin into the mold cavity. In some embodiments, vents are opened and closed multiple times during a single plunger stroke. The use of the vents enables pressure to be selectively reduced in desired regions of a mold cavity, which will facilitate directing the flow of resin and fiber to such reduced-pressure regions.

In accordance with some embodiments of the method, sequencing the actuation of the vents enables different layers/groups of preforms in the stack thereof to be directed to different areas of the mold cavity.

For example, consider a mold cavity in which there is a first vent proximal to a first feature of the mold cavity and a second vent proximal to a second feature of the mold cavity. To selectively direct fiber to the first feature, the first vent is opened. To selectively direct fiber to the second feature, the second vent is opened some time after the first vent. If, for example, the first feature of the mold cavity is a relatively small compared to the overall size of the mold cavity, the fibers intended for that region will be smaller than those directed to the major regions of the mold cavity. More particularly, these smaller fibers will be comparable to the size of the first (relatively small) feature. Typically, the smaller fibers will be somewhat longer than the feature to facilitate overlap between those fibers with longer fibers in the major regions of the cavity. Such overlap enhances part strength.

Typically, the first vent does not need to be closed before opening the second vent. In particular, as the first feature fills with fiber and resin, the pressure required to force more material into that feature increases dramatically. Thus, once the second vent opens, material will flow towards the second feature, since the pressure will be lower there a fiber and resin will readily flow thereto. In this example, the opening of the first vent and, after a period of time, the opening of the second vent, both occur during a single plunger stroke.

Furthermore, the orientation of fibers in the mold cavity and, hence, the final part, can be influenced by the orientation of the preforms. Such orientations include the orientation of the preforms (fibers): (<NUM>) relative to the stroke direction of the plunger, and/or (<NUM>) relative to the axes of the mold. Controlling fiber orientation using these parameters enables off-axis directions of a part to be strengthened.

Moreover, based on the aforementioned ability to control the end location of fibers in the mold cavity, a modulus gradient (i.e., a gradient in Young's modulus) can be established through a part. This can be accomplished, for example, using preforms that differ in fiber type (e.g., some including carbon fiber, others including glass fiber, etc.), and by appropriately organizing them in the stack within the plunger cavity. In conjunction with the selective actuation of vents, the different materials wind up at different locations in the mold cavity.

Alternatively, a modulus gradient can be created by controlling the fiber volume fraction. For example, a first group of preforms can be formed such that the fiber volume fraction is relatively greater than that of a second group of preforms (i.e., there is relatively less resin, as a percentage of the total constituents in the first group of preforms than in the second group of preforms). Using the aforementioned mentioned technique of selective actuation of vents, in conjunction with appropriately stacking the first and second groups of preforms in the mold cavity, the resin and fiber from the first group of preforms can be directed to a first location in the mold, and the resin and fiber from the second group of preforms can be directed to a second location in the mold. This results in the creation of a relatively more fiber-rich region in the first location of the mold, and, hence, the final part, thereby creating the aforementioned modulus gradient.

Also, the strength and stiffness of selected areas of a part can be controlled by using preforms having different lengths. Those parameters can be altered as a function of the extent of fiber overlap in specific regions of the part (i.e., the amount by which longer fibers in the main portion of the part overlap with potentially smaller fibers in a smaller/intricate feature of the part. Once again, this is implemented through the use and selective actuation of vents, and appropriate stacking of preforms having fibers of different lengths and, in some applications, different orientations with respect to the plunger cavity and/or mold cavity.

In summary, some embodiments of the invention utilize a plunger that is out-of-plane with respect to a mold cavity in conjunction with molds for the fabrication of parts via compression molding. Vents are used to assist in directing the movement of fibers to specific regions of the mold cavity. Although vents and plungers are known in the prior art, typically for use in injection molding, such use is distinct from embodiments of the invention. Unlike the prior art, applicants disclose, for some embodiments:.

In accordance with the present teachings, preforms are placed in the plunger cavity. The lowest layer of preforms rests on a portion of the mold cavity. The plunger's stroke axis is out-of-plane to a major surface of the mold cavity. In the illustrative embodiment, the plunger's stroke axis is <NUM> degrees out-of-plane (i.e., orthogonal) to a major surface of the mold cavity. In some other embodiments, the plunger's stroke axis is greater than <NUM> degrees out-of-plane to a major surface of the mold cavity. By virtue of the orientation of plunger/plunger cavity with respect to the mold, initial movement of fibers in the mold cavity (as the fiber moves away from its position in the stack), is via a shear force.

In particular the invention provides, according to claim <NUM>, a method for molding comprising:.

In a first embodiment thereof, the method comprising cooling the fibers and resin to create a composite part.

In a second embodiment thereof, ordering, in a stack, further comprises providing a first spatial orientation to the first group of preforms and a second spatial orientation to the second group of preforms in the plunger cavity.

In a third embodiment, and further to the second embodiment, the first spatial orientation and the second spatial orientation are individually selected from the group consisting of axially aligned with respect to the plunger cavity, transversely aligned with respect to the plunger cavity, axially aligned with respect to the mold cavity, transversely aligned with respect to the mold cavity.

In a fourth embodiment, and further to the second embodiment, the first group of preforms and the second group of preforms are transversely aligned with respect to the plunger cavity, and are neither orthogonal nor parallel to one another.

In a fifth embodiment, the first characteristic is selected from the group consisting of a length of the fibers of the preforms, a composition of the fibers of the preforms, and a fiber volume fraction of the preforms.

In a sixth embodiment, the plurality of preforms are arranged in a stack in the plunger cavity, wherein the first group of preforms are relatively lower in the stack and closer to mold cavity than the second group of preforms, so that the fibers from the first group of preforms flow through the mold cavity before fibers from the second of preforms.

In an seventh embodiment, the first region comprises a feature that is relatively smaller than any feature associated with the second region.

In a ninth embodiment the first group of preforms has a spatial orientation different than the second group of preforms with respect to at least one of either the plunger cavity and the mold cavity.

In a tenth embodiment, the method comprising adding a preform to the mold cavity before liquefying the resin.

In a eleventh embodiment, a major portion of the fibers having a length that is substantially as long as a major axis of the mold cavity.

In a twelfth embodiment, the method comprising cooling mold cavity after the fibers and resin have flowed through the mold cavity.

In a thirteenth embodiment, , the plunger cavity is oriented out-of-plane by at least <NUM> degrees with respect to a longest axis of the mold cavity.

The invention is furthermore providing a compression mold as defined in claim <NUM>.

Additional embodiments of the invention comprise any other nonconflicting combination of features recited in the above-disclosed embodiments.

The following terms, and their inflected forms, are defined for use in this disclosure and the appended claims as follows:.

Other than in the examples, or where otherwise indicated, all numbers expressing, for example, quantities of ingredients used in the specification and in the claims are to be understood as being modified in all instances by the term "about. " Accordingly, unless indicated to the contrary, the numerical parameters set forth in the following specification and attached claims are understood to be approximations that may vary depending upon the desired properties to be obtained in ways that will be understood by those skilled in the art. Generally, this means a variation of at least +/- <NUM>%.

Also, it should be understood that any numerical range recited herein is intended to include all sub-ranges encompassed therein. For example, a range of "<NUM> to <NUM>" is intended to include all sub-ranges between (and including) the recited minimum value of about <NUM> and the recited maximum value of about <NUM>, that is, having a minimum value equal to or greater than about <NUM> and a maximum value of equal to or less than about <NUM>.

The fiber bundles that are sized or sized and shaped to form preforms for use herein includes thousands of individual fibers, typically in multiples of a thousand (e.g., <NUM>, <NUM>, <NUM>, etc.). Such fiber bundles are typically called "tow. " In some embodiments, the fibers in the tow are impregnated with a polymer resin; such material is referred to as "towpreg" or "prepreg tow. " Although all of the towpreg depicted in the Figures are cylindrical (i.e., have a circular cross section), they can have any suitable cross-sectional shape (e.g., oval, trilobal, polygonal, etc.).

The individual fibers can have any diameter, which is typically, but not necessarily, in a range of <NUM> to <NUM> microns. Individual fibers can include an exterior coating such as, without limitation, sizing, to facilitate processing, adhesion of binder, minimize self-adhesion of fibers, or impart certain characteristics (e.g., electrical conductivity, etc.).

Each individual fiber can be formed of a single material or multiple materials (such as from the materials listed below), or can itself be a composite. For example, an individual fiber can comprise a core (of a first material) that is coated with a second material, such as an electrically conductive material, an electrically insulating material, a thermally conductive material, or a thermally insulating material.

In terms of composition, each individual fiber can be, for example and without limitation, carbon, glass, natural fibers, aramid, boron, metal, ceramic, polymer filaments, and others. Non-limiting examples of metal fibers include steel, titanium, tungsten, aluminum, gold, silver, alloys of any of the foregoing, and shape-memory alloys. "Ceramic" refers to all inorganic and non-metallic materials. Non-limiting examples of ceramic fiber include glass (e.g., S-glass, E-glass, AR-glass, etc.), quartz, metal oxide (e.g., alumina), aluminasilicate, calcium silicate, rock wool, boron nitride, silicon carbide, and combinations of any of the foregoing. Furthermore, carbon nanotubes can be used.

Any thermoplastic can be used in conjunction with embodiments of the invention. Exemplary thermoplastic resins useful in conjunction with embodiments of the invention include, without limitation, acrylonitrile butadiene styrene (ABS), nylon, polyaryletherketones (PAEK), polybutylene terephthalate (PBT), polycarbonates (PC), and polycarbonate-ABS (PC-ABS), polyetheretherketone (PEEK), polyetherimide (PEI), polyether sulfones (PES), polyethylene (PE), polyethylene terephthalate (PET), polyphenylene sulfide (PPS), polyphenylsulfone (PPSU), polyphosphoric acid (PPA), polypropylene (PP), polysulfone (PSU), polyurethane (PU), polyvinyl chloride (PVC). An exemplary thermoset is epoxy.

The equipment used in conjunction with embodiments of the present invention have some similarities to a process known as "transfer molding. " <FIG> depicts conventional apparatus <NUM> for forming a part via a transfer-molding process.

Apparatus <NUM> includes mold <NUM>, mold cavity <NUM>, transfer pot <NUM>, sprue <NUM>, plunger <NUM>, heaters <NUM>, and ejector pin <NUM>, arranged as shown. A feed, which is usually a plastic/resin, is placed in transfer pot <NUM>. Plunger <NUM> is moved downwardly into transfer pot <NUM>, compressing the plastic in the mold. Heaters <NUM> heat the mold to a temperature that is sufficient to melt the plastic. The liquid plastic then flows through sprue <NUM> under pressure and into mold cavity <NUM>. Sprue(s) <NUM> (there may be several) is typically a small cylindrical opening that leads from transfer pot <NUM> to mold cavity <NUM>. After the part is formed and the mold is opened, ejector pin <NUM> is used to push the part out of mold cavity <NUM>. By virtue of the structural arrangement of the apparatus <NUM>, such as the presence of the sprues, fiber, particularly continuous fiber, is typically not used in conjunction with this transfer molding process. To the extent that the feed includes any fiber, it is usually "chopped" fiber, so that it could fit through the sprue.

<FIG> depicts scoop <NUM>. The scoop includes handle <NUM>, body <NUM>, and fingers or tines <NUM>. Scoop <NUM> is very thin and has a relatively elongated form. For a part having such a configuration, it is important that part stiffness and strength are oriented in the direction of the long axis of the handle. This reduces any tendency for the part to snap under flexion, such as could occur, for example, if tines <NUM> were immobilized in the ground and excessive upward or downward pressure is applied at handle <NUM>. It is also necessary that the tines are well connected to the handle via body <NUM> in strength and stiffness.

<FIG> and <FIG> depict mold <NUM> for making scoop <NUM>. The mold includes mold cavity <NUM>', including cavity portions <NUM>', <NUM>', and <NUM>' for forming respective portions of the scoop; that is, handle <NUM>, body <NUM>, and tines <NUM>. Plunger <NUM> is received by plunger cavity <NUM> in mold <NUM>, and is arranged to move linearly therein. Note that stroke axis B-B of plunger <NUM> is out-of-plane with respect to mold cavity <NUM>'. In fact, stroke axis B-B is out-of-plane and orthogonal with respect to cavity portions <NUM>' and <NUM>'.

In mold <NUM>, as in many molds consistent with the present teachings:.

The material that is used to form the part; that is, preforms <NUM>', are positioned within plunger cavity <NUM> on a portion of mold cavity <NUM>'; in this embodiment, on portion <NUM>'. The embodiment shown in <FIG> depicts a first arrangement of preforms <NUM>', wherein the preforms are oriented horizontally, which is out-of-plane and, in fact, orthogonal with respect to the plunger's stroke axis, B-B (i.e., the direction/axis along which plunger <NUM> moves). Furthermore, preforms <NUM>' are axially aligned with mold cavity <NUM>'; that is, they are aligned with axis A-A.

The number of preforms <NUM>' that are required for fabricating scoop <NUM> (or any part) is determined by matching the mass of the preforms to the mass of the fabricated scoop. In this embodiment, the length of preforms <NUM>' matches the width of plunger cavity <NUM>. The preforms could be shorter, but relatively longer fibers ultimately result in better material properties for the finished part.

<FIG> depicts a representation of the orientation of the fibers (from preforms <NUM>') in the molded part; that is, scoop <NUM>. During fabrication, fibers tend to flow along the direction of the long axis of the part, which is axis A-A in this embodiment. For this particular part, the fibers follow the long axis of handle <NUM> before fanning out through body <NUM> of scoop <NUM>, and ultimately flowing into tines <NUM>. The fibers overlap, as illustrated, for example, at locations <NUM> and <NUM>, which provides considerable stiffness and strength to the scoop <NUM>. It will be appreciated that there are many more fibers, and many more incidents of overlap thereof, in an actual part made in accordance with the present teachings.

Furthermore, the degree of fiber overlap can be varied based on fiber length and parameters that affect the final position of the fibers in the mold cavity, such as vents. That is, sequencing the actuation of vents <NUM> during the stroke of the plunger <NUM> can provide a staged delivery of fibers. <FIG> depicts vent <NUM>; one such vent is fluidically coupled to the terminus of each tine (only one is depicted in <FIG>) of the mold-cavity. Vents and their operation are discussed in greater detail in conjunction with <FIG>, later in this specification.

<FIG> depicts, for the same mold <NUM>, preforms <NUM>", which are arranged in a second arrangement that is different from the first arrangement shown in <FIG>. In particular, preforms <NUM>" are oriented vertically, which is "axially aligned" with respect to the plunger's stroke-axis B-B. Since, in mold <NUM>, plunger cavity <NUM> is longer than it is wide, preforms <NUM>" may be longer than preforms <NUM>' of <FIG>. As previously noted, longer fibers, such as are present in preforms <NUM>" relative to preforms <NUM>', typically result in better material properties for the finished part.

Once again, vents (not depicted in <FIG>) are used to facilitate the movement of fibers to specific regions (e.g., the tines, etc.) and control the extent of overlap with other fibers.

<FIG> depicts a representation of the orientation of the fibers (from preforms <NUM>") in scoop <NUM>. As in the embodiment depicted in <FIG>, the fibers tend to align with the long axis of the part, and overlap, as illustrated at location <NUM>, for example.

<FIG> depicts, a third arrangement of preforms in mold <NUM>, wherein relatively shorter preforms <NUM>' are oriented horizontally and axially aligned with mold cavity <NUM>' (i.e., parallel to axis A-A), and preforms <NUM>" are oriented vertically, axially aligned with the plunger cavity (i.e., parallel to axis B-B), and are positioned on top of preforms <NUM>'.

For very thin features, such as are present in scoop <NUM>, it can be beneficial to use such a combination of shorter fibers and longer fibers. The shorter fibers more reliably fill any thin/small/intricate features. Meanwhile, the longer and shorter fibers intermingle and overlap, thereby coupling the thin/intricate feature to the rest of the part.

For example, in scoop <NUM>, if mold filling is an issue, fibers from shorter preforms <NUM>' at the bottom of the feed stack would flow first into cavity portion <NUM>' (the tines), and more easily fill this portion than would longer fibers from preforms <NUM>". Although not depicted, vents, as previously discussed, are advantageously fluidically coupled to the terminus of each of the tines (i.e., mold-cavity portion <NUM>'). Referring now to <FIG>, longer fibers 216f" from preforms <NUM>" located higher in the feed stack would mix with shorter fibers 216f' from preforms <NUM>', overlapping, such as at location <NUM>, to connect the tips of tines <NUM> to the rest of scoop <NUM>.

<FIG> depicts mold cavity <NUM>' without the surrounding mold <NUM>. Vents <NUM>-<NUM>, <NUM>-<NUM>, and <NUM>-<NUM> are individually fluidically coupled to the terminus of a respective tine. There are instances in which it will be desirable to have fiber of a first characteristic fill some but not all of the tines of the mold cavity, whereas fiber having a second characteristic fills the remaining tines.

For example, one or more of the tines may differ in length from the other tines, or one or more of the tines may experience greater stresses during use than other of the tines. In such cases, the longer tines or tines experiencing greater stresses would benefit from relatively longer fibers, or fibers made from a relatively stronger material, or from material having a relatively higher fiber-volume fraction.

To direct two (or more) groups of preforms having fibers that differ in some characteristic to different locations in a mold requires that the two (or more) groups of preforms be stacked in an appropriate order in the plunger cavity. Thus, when the plunger is actuated (to force fiber and liquefied resin into the mold cavity), and an appropriate one or more vents are actuated (to create a decrease in pressure at certain discrete regions of the mold cavity), fibers from the group of preforms lowest in the plunger cavity enter the mold cavity (along with liquefied resin) and flow to such discrete regions. After those discrete regions fill, and with the plunger still moving downwardly, and one or more different vents actuating, fiber from the next group of preforms in the stack (along with liquefied resin) enters the mold cavity and flow to fill other portions of the mold cavity that are at reduced pressure.

With continuing reference to <FIG>, and referring also to the timing diagram of <FIG>, "Vent-<NUM>" corresponds to vent <NUM>-<NUM>, "Vent-<NUM>" corresponds to vent <NUM>-<NUM>, and "Vent-<NUM>" corresponds to vent <NUM>-<NUM>. Vent-<NUM> and Vent-<NUM> control portions of the mold cavity that correspond to "the outer tines," and Vent-<NUM> controls the portion of the mold cavity that corresponds to "the central tine. " The central tine is to be filled first, followed by the outer tines, then the rest of the mold cavity. An appropriate amount of a first type of preforms for filling the central tine is placed at the bottom of the plunger cavity. An appropriate amount of a second type of preforms for filling the outer tines is placed on top of the first type of preforms. Additional preforms would be placed on top of the second type of preforms for filling the balance of the body (<NUM>') and handle (<NUM>') portions of the mold cavity.

At time T<NUM>, the plunger (e.g., plunger <NUM>, <FIG>) is actuated, moving downwardly to force fibers and now-liquefied resin into mold cavity <NUM>'. Also at time T<NUM>, Vent-<NUM> is actuated (i.e., opened). Actuation of this vent creates relatively lower pressure in the central tine as compared to the outer tines. Consequently, fibers and resin flow to fill the central tine. By time T<NUM>, the central tine has filled with resin and the appropriate type of fiber, and Vent-<NUM> and Vent-<NUM> are actuated to create relatively lower pressure in the outer tines versus the central tine and other regions of the mold cavity. Note that the plunger is still moving downwardly, forcing fiber and liquefied resin into the mold cavity. Although <FIG> depicts Vent-<NUM> being closed at time T<NUM>, that is not necessary, since as a region fills with material , the pressure it would take to force further fiber into the region increases significantly. The fiber and resin will thus preferentially flow elsewhere; in this case, to the outer tines.

Actuation of later-opened vents (such as Vent-<NUM> and Vent-<NUM>) can be controlled passively, using relief valves on the vents, for example. In such an embodiment, when the pressure in the mold cavity exceeds some value (as discrete regions fill while fiber and resin continue to be forced into the mold cavity), the relief valve actuates, thereby opening the initially closed vent. Alternatively, the vents can be actively controlled, such as by using position control on the plunger and controlling for volume. That is, knowing how much material is forced into the mold cavity per unit movement of the plunger, and how much material must be delivered to fill portions of the mold cavity that are to be filled first, one can determine the requisite change in position of the plunger to deliver that amount of material. Thus, once the plunger moves the determined amount, a second set of vents are actuated.

<FIG> depicts mold cavity <NUM>", which is another embodiment of a mold for making scoop <NUM> of <FIG>. In addition to having a vent at the terminus of each tine, mold cavity <NUM>" includes four vents <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM>, and <NUM>-<NUM>, two of which are fluidically coupled to each side of body portion <NUM>' of the mold cavity. These vents can be used to create a crossing overlap between fibers in the tines and fibers in other portions of the scoop.

<FIG> depicts a timing diagram that illustrates a mold-filling process. For this example, it is assumed that the tines receive one type of fiber, and the rest of the mold receives a second type of fiber. The fibers that are primarily intended for the tines are about <NUM> times longer than the tines. The fibers that are primarily intended for the balance of the mold cavity are about <NUM> times the length of the tines. A first group of preforms having fibers intended for the tines are placed into the plunger cavity, followed by a second group of preforms having fibers intended for the rest of the mold cavity. Relatively shorter preforms <NUM>' and relatively longer preforms <NUM>" shown stacked in the plunger cavity in <FIG> is illustrative.

The amount of fiber and resin in the first group of preforms is sufficient to fill the tines. The second group of preforms includes the fiber and resin required to fill the rest of the mold cavity.

By time T<NUM>, the resin in at least the first (lower) group of preforms is liquefied. At time T<NUM>, the plunger as well as Vent-<NUM>, Vent-<NUM>, and Vent-<NUM> are actuated. The relatively lower pressure in the tines draws the relatively shorter fibers from the first group of preforms into the tines.

At time T<NUM>, Vent-<NUM>, Vent-<NUM>, Vent-<NUM>, and Vent-<NUM> are actuated, created low pressure regions to the sides of mold body portion <NUM>'. The plunger continues its downward movement, forcing fiber from the second group of preforms as well as liquefied resin into the mold cavity. The portion of these longer fibers that reside in body portion <NUM>' tend to curve toward either of the sides thereof, crossing the portion of fibers extending from the tines. As previously discussed, the vents need not be closed when the cavity portions they control are filled since it would take a substantially increased pressure to force additional material into those regions.

<FIG> depicts bracket <NUM>. The bracket includes body <NUM>, four horizontal tabs <NUM>, fastener holes <NUM>, two vertical tabs <NUM>, and rod-receiving holes <NUM>. Bracket <NUM> can be used, for example, to connect a rod end to a control surface. The rod is received by rod-receiving holes <NUM>. Fastener holes <NUM> mount bracket <NUM> to a surface with screws, bolts, pins, etc. Vertical tabs <NUM> and horizontal tabs <NUM> are orthogonal to one another. It is desirable to have good bending stiffness in each of tabs <NUM> and <NUM> and for all of such tabs to be well connected to one another in strength and stiffness.

<FIG> and <FIG> depict mold <NUM> for making bracket <NUM>. The mold includes mold cavity <NUM>'. Plunger <NUM> moves linearly along stroke axis B-B (<FIG>) in the plunger cavity in mold <NUM>. Otherwise hidden lines of mold <NUM>' are depicted to show how the part is situated in the mold. Parting lines on the mold have been omitted. Once again, stroke axis B-B of plunger <NUM> is out-of-plane with respect to mold cavity <NUM>' and, in particular, to body portion <NUM>' and horizontal tab portions <NUM>' thereof. Mold <NUM> also includes sliding pins (not depicted for the sake of clarity) to create holes <NUM> and <NUM>.

As depicted in <FIG>, the preforms that will form the part are organized to have two different orientations in the plunger cavity. Preforms <NUM>' at the bottom of the stack of bundles are aligned with axis A-A, which is the long axis of mold cavity <NUM>'. In other words, fiber bundles <NUM>' are axially aligned with respect to mold cavity <NUM>'. Preforms <NUM>" at the top of stack are aligned with axis C-C, which is transverse to the long axis of mold cavity <NUM>'.

<FIG> depicts a representation of the orientation of the fibers (from preforms <NUM>' and <NUM>") in bracket <NUM>. As implied above, the fibers from the preforms flow into mold cavity <NUM>' in the order in which they are positioned in the plunger cavity, those on the bottom (i.e., on the surface of mold cavity <NUM>') flowing first.

Thus, fibers 316f' from lower, axially-aligned preforms <NUM>' will preferentially fill horizontal tab portions <NUM>' (<FIG>) of the mold cavity first, which are generally aligned with axis A-A. Fibers 316f" from transversely oriented preforms <NUM>" begin filling mold cavity <NUM>' after all fibers 316f' from preforms <NUM>' have flowed into the mold cavity. The intent is to have fibers 316f" filling vertical tabs <NUM>. The transverse orientation of fibers 316f" is not to promote flow toward vertical tabs <NUM>; rather, it is to facilitate an overlap with axially running fibers 316f'.

Preforms follow the path of least resistance, which typically means flowing along the long axis of the mold cavity and towards regions of lowest pressure. The latter parameter -pressure- can be altered through the use of strategically located vents, as previously disclosed. This technique can be used to selectively direct the flow of resin and fibers to a particular location.

Thus, in the present embodiment, vents (not depicted) are situated to vent pressure at the terminus of horizontal tab portions <NUM>' and at the top of vertical tab portions <NUM>' of the mold cavity (<FIG>). In some embodiments of the invention, after fibers 316f' from preforms <NUM>' flow to horizontal tabs portions <NUM>', the vents controlling the pressure at those locations are closed and the vents controlling the pressure at the tip of vertical tab portions <NUM>' are opened. This creates a region of relatively lower pressure at the tips of the vertical tab portions of the mold cavity, and resin/fibers preferentially flow toward those locations.

As a consequence of vertical tabs <NUM>, it is likely that gravity will result in resin/fiber flowing preferentially to horizontal tab portions <NUM>' and then, as the level of resin rises, fibers/resin will eventually flow to vertical tab portions <NUM>'. Although some mixing will occur, fibers 316f" from bundles <NUM>" will primarily end up in vertical tabs <NUM>, aligned with the axis C-C (see <FIG>).

Mixing between fiber orientations occurs near the middle of bracket <NUM>, such as at location <NUM>. This facilitates strong connections between all features of bracket <NUM>. And overlap between fibers flowing around holes <NUM> in different directions, such as at location <NUM>, results in good hoop strength for those features.

Fiber bundles at other angles (i.e., not aligned with axes A-A or C-C) could also be included. In some embodiments, axially aligned preforms <NUM>' are made from carbon fiber towpreg and transversely aligned preforms <NUM>" are made from glass fiber towpreg, both incorporating the same resin. This results in vertical tabs <NUM> being more compliant than horizontal tabs <NUM>. Moreover, fiber volume fraction could be varied across the stack to engineer different material properties for different portions of bracket <NUM>.

In a further embodiment, part strength is increased in select areas using a preform that is placed in mold cavity <NUM>' prior to flowing the preforms into the mold cavity. For example, if an amount of hoop strength is required that is greater than what is nominally expected from the methods disclosed herein (i.e., that which results from the overlap of flowing fibers coming from both sides of fastener holes <NUM>), a helical, spiral, or circular fiber-bundle preform, such as preform <NUM>, is placed around one or more of holes <NUM>. The flowing fibers from the method described herein overlap and couple to preform <NUM> and connect it to the rest of the part during the molding process.

In accordance with the present method, to fabricate scoop <NUM> (<FIG>) or bracket <NUM> (<FIG>), the mold parts are combined (closed), except for the plunger, leaving the plunger cavity open. The final weight of the part is estimated from part volume and the density of the composite material. Maximum length(s) for the fibers are determined as a function of its intended location and orientation in the mold cavity. The maximum length for preforms is determined as a function of its orientation in the plunger cavity. Preforms are created by cutting towpreg in appropriate lengths, recognizing that the allowable length of a fiber, as calculated based on its orientation in the mold, might be longer than its actual length, as determined and permitted based on the size of the plunger cavity.

All fibers are weighed to check that the weight of the fiber/resin matches the expected final part weight. The total weight of the preforms can slightly exceed the expected part weight since some of the resin, and even fiber, will flow into the vents of the mold.

Preforms are then stacked in the plunger cavity in the requisite order and orientation. The plunger is then placed in the plunger cavity. The entire mold, including the plunger cavity, plunger, and mold cavity are heated. In some embodiments, cartridge heaters or the like, which are inserted through holes into the mold, are used to heat the plunger, the plunger cavity, and the mold cavity. In some other embodiments, the mold is situated on a heated platen, which is used to heat the mold. For large molds, an insulating blanket can be placed around the mold to reduce radiative and convective heat losses. In most embodiments in which plural groups (different types) of preforms are used, there is no need to differentially heat the different groups of preforms. Depending on the manner in which the preforms are stacked, after mixing in the plunger cavity of different fibers from different preforms is minimal. To the extent it may, in certain applications, be desirable to melt one type of preform before another type, this can be accomplished by operating the mold cavity at a higher temperature than the plunger/plunger cavity.

After heating, the plunger is pressed against the preforms, thereby compressing the fibers and resin and forcing them into the mold cavity. After an appropriate amount of time under heat and pressure in accordance with compression molding protocols, heating ceases. In some embodiments, the mold is actively cooled, such by passing air, water, steam, or oil through cooling channels. After cooling, the mold is disassembled, as necessary, to remove the composite part formed by this process.

Claim 1:
A method for molding, comprising:
ordering, in a stack within a plunger cavity (<NUM>), first and second groups of preforms (<NUM>', <NUM>", <NUM>', <NUM>"), each group comprising plural preforms (<NUM>', <NUM>", <NUM>', <NUM>"), each preform (<NUM>', <NUM>", <NUM>', <NUM>") comprising resin-coated fibers (216f', 216f", 316f', 316f"), wherein the first group of preforms (<NUM>', <NUM>') and the second group of preforms (<NUM>", <NUM>") differ from one another as to at least one characteristic;
liquefying the resin;
advancing a plunger (<NUM>, <NUM>) through the plunger cavity (<NUM>) to force, into a mold cavity (<NUM>', <NUM>", <NUM>'), fibers (216f', 216f", 316f', 316f") and resin from the two groups of preforms (<NUM>', <NUM>", <NUM>', <NUM>"); and
actuating, in sequence, a first vent (<NUM>-<NUM>) and then a second vent (<NUM>-<NUM>, <NUM>-<NUM>), wherein:
the first vent (<NUM>-<NUM>) is fluidically coupled to a first region of the mold cavity (<NUM>', <NUM>", <NUM>'),
the second vent (<NUM>-<NUM>, <NUM>-<NUM>) is fluidically coupled to a second region of the mold cavity (<NUM>', <NUM>", <NUM>'),
actuation of the first vent results (<NUM>-<NUM>) in preferential flow of fiber (216f', 216f", 316f', 316f") to the first region,
actuation of the second vent (<NUM>-<NUM>, <NUM>-<NUM>) results in preferential flow of fiber (216f', 216f", 316f', 316f") to the second region, and wherein the ordering of preforms (<NUM>', <NUM>", <NUM>', <NUM>") in the stack and the sequencing of actuation of the vents (<NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM>) are coordinated so that fibers (216f', 316f') from the first group of preforms (<NUM>', <NUM>') flow to the first region and fibers (216f", 316f") from the second group of preforms (<NUM>", <NUM>") flow to the second region.