Patent Description:
The present invention relates to compression molding.

There are various methods for fabricating a part using composite materials, such as fiber-reinforced plastics. One such method is compression molding. In compression molding, a raw material(s) is placed in a mold, and then heated and compressed.

In the case of fiber-reinforced composite materials, fiber and resin (or fiber pre-preg) is placed in a mold. Depending on the geometry of the part being formed, and the stresses to which it is subjected during use, either chopped, randomly oriented, or continuous fiber that is pre-formed to the mold may be used. The mold remains closed for a period of time and goes through a heating and cooling cycle based on the resin used. This ensures that the resin has time to flow through the mold, thus filling any voids. During this time, the resin hardens to produce a solid molded-plastic part.

The use of fiber-reinforced composites in compression molding presents certain challenges. For example, the presence of voids compromises the strength of a part. Voids can occur, for example, if the resin does not achieve an acceptably low viscosity before it begins to harden. Moreover, it can be problematic to flow resin to portions of the mold having very small features, or features that are out-of-plane with respect to the bulk of the part. Additionally, although the resin matrix plays an important role in the integrity of the part, enhanced strength is due primarily to the presence of fibers. Consequently, even if a finished part includes minimal voids, if the fibers are not appropriately distributed, the strength of the part can be compromised.

<CIT> discloses an as molded glass fiber reinforced plastic panel having an integrally formed rib and an exposed smooth surface free of visual surface distortion. The glass fiber reinforced plastic panel comprises chopped glass strands having an average length of not more than one inch extending into said rib to reinforce the rib, continuous glass strands having an average length of at least two inches interposed between said chopped strands and said exposed surface, the continuous strands bridging the rib, and the juncture of said rib with said panel being defined by sharp, essentially fillet-free corners in that any lead-in radius is less than the order of magnitude of approximately <NUM> inch.

<CIT> refers to a structural component made out of long-fiber reinforced thermoplastic material (LFT) with integrated continuous fiber (CF)-reinforcement. It includes at least three individually integrated, shaped CF-profiles, which form a three-dimensional intersection point. In this, at least one CF-profile lies in an upper plane, at least one CF-profile lies in a lower plane of the intersection point and at least one CF-profile extends continuously in a vertical direction between these CF-profiles of the upper and of the lower main plane. The CF-profiles are connected to one another by shaping of the LFT-mass at the intersection point in a force-transmitting manner. At several points, loads are exerted on the CF-profiles, wherein such three-dimensionally applied loads are capable of being optimally supported.

The present invention provides a method for use in compression molding that avoids some of the drawbacks of the prior art. The method in accordance with the present teachings utilizes "non-flowing continuous" fibers and "flowing continuous" fibers. In some embodiments, a method for "laying-up" fiber bundles is provided. In some embodiments not being part of the scope of the invention, a layup comprising fiber bundles is provided. In some embodiments, the method of the present invention is used to provide improved fiber-reinforced composite parts via compression molding. The methods and compositions disclosed herein are particularly useful for forming parts that includes off-axis, out-of-plane, or small, intricate features.

During the course of molding beams having relatively small (compared to the beam) cavities at either end, the inventors discovered that fiber bundles that are about the same length as the beam did not flow into the cavities, although the resin did. In fact, these relatively long continuous fiber bundles tend not to flow at all. The inventors found, however, that when relatively shorter-length fiber bundles were added to the mold along with the longer fiber bundles, the relatively shorter fibers preferentially flowed into and filled the cavities. Although these shorter fiber bundles were "non-continuous" with respect to the major feature -the beam- they were "continuous" with respect to the minor feature -the cavities. That is, the shorter fiber bundles were slightly longer than the cavities.

These shorter fibers/fiber bundles, which are continuous with respect to one or more minor features of a mold (but not with respect to a major feature of the mold) are referred to herein and the appended claims as "flowing continuous" fibers or fiber bundles, for the reason noted. The relatively longer fiber bundles, which extend the length of a major feature of the mold and will not "flow" in a compression-molding process, are referred to herein and the appended claims as "non-flowing, continuous" fiber or fiber bundles. It is notable and important that flowing, continuous fiber, as that term is used herein, is not the same as "chopped fiber. " Typically, although not necessarily, chopped fiber is shorter in length than the flowing continuous fibers, as a function of size of the minor feature. Moreover, chopped fiber assumes a random orientation in the mold (and in the molded part), whereas in embodiments of the invention, the flowing fiber is specifically aligned for maximum strength and stiffness.

It was found that, as long as the flowing, continuous fibers are of sufficient length to extend beyond the confines of the cavity that they are filling, such flowing fibers entwine themselves with the non-flowing continuous fiber via overlap and, of course, the resin matrix itself. The flowing, continuous fibers tend to align with the direction of resin flow, which increases the strength and stiffness of small features.

The inventors recognized that the strategic placement of "vents," typically at a remote end of a minor feature, promotes flow of fibers into the minor feature. More particularly, the vents help in establishing and maintaining a relatively lower pressure region in the minor feature(s) relative to the major feature(s). This pressure differential promotes flow of resin, and appropriate-length fibers (i.e., the flowing continuous fiber) with it.

A method in accordance with the present teachings utilizes a female mold, wherein the female mold includes at least one major feature having a long axis and at least one minor feature having a length less than <NUM> percent of a length of the major feature. The method comprises:.

In another embodiment not being part of the scope of the claims of the invention, a method comprises:.

In yet another embodiment not being part of the scope of the claims of the invention, a method comprises:.

In still another embodiment not being part of the scope of the claims of the invention, a method comprises:.

The following embodiments of lay-ups for compression molding are not part of the scope of the claims of the invention and are only described for illustrative purposes. In some embodiments, compositions comprising layups for compression molding as described in the methods are provided. Specifically, in some embodiments, a lay-up for compression molding utilizing a female mold, the female mold including a least one major feature having a long axis, and at least one minor feature, the layup comprising:.

In some other embodiments, a lay-up for compression molding utilizing a female mold, the female mold including a least one major feature having a long axis, and at least one minor feature, the layup comprising:.

In yet some additional embodiments, a lay-up for compression molding utilizing a female mold, the female mold including a least one major feature having a long axis, and at least one minor feature, the layup comprising:.

In still further embodiments, a lay-up for compression molding utilizing a female mold, the female mold including a least one major feature having a long axis, and at least one minor feature, the layup comprising:.

And yet in some further embodiments, the methods and compositions are used to form fiber-composite parts via a compression molding process.

Summarizing, the invention, as claimed, depicted and described, comprises the use of non-flowing continuous fiber bundle(s) and flowing continuous fiber bundle(s) in a method for compression molding. Various embodiments of the present invention comprise the following features, in any (non-conflicting) combination, among other features disclosed herein:.

Compression molding, well known in the art, utilizes a female mold and a male mold, applying heat and pressure to form a molded part. Relative to the prior art, methods described herein provide improvements in compression-molded parts comprising fiber composites.

Referring now to <FIG>, in method <NUM> in accordance with the invention, the volume and length of the flowing continuous fiber bundle(s) are determined in task S601. The length of a flowing continuous fiber bundle(s) is based on the length of the typically relatively smaller cavities/feature(s) (hereinafter "minor features") that depend from the major features(s), plus the amount of overlap that is desired between the flowing fiber and the non-flowing fiber. In other words, the "overlap" is a measure of how far the flowing fibers will extend beyond the minor feature. The desired overlap is based, at least in part, on the type/location of stresses to which the final fiber-composite part will be subjected. As a practical minimum, the flowing continuous fiber should overlap the non-flowing continuous fiber by at least ten percent of the length of the flowing fiber. Thus, by way of example, if the flowing continuous fiber has a length of <NUM> millimeters, it should overlap the non-flowing fibers by at least <NUM>. More preferably, flowing fibers should overlap non-flowing by <NUM> percent or more of the length of the flowing fibers. With respect to a maximum overlap, as the length of the flowing continuous fiber increases, it will reach a length at which it does not flow; that is, it is non-flowing continuous fiber. That length, and the corresponding amount of overlap, is determined via simple experimentation.

As implied by the foregoing, the volume of the flowing continuous fiber bundles will be greater than the volume of the features they are intended to form, because the flowing continuous fibers will extend beyond the features that they form.

In operation <NUM>, the volume and length of the non-flowing continuous fiber bundles are determined. This can be done in several ways, one of which is (i) determining the volume of the major feature or features of the part to be fabricated, and (ii) subtracting, from the major feature volume, the "overlap" volume, which is the volume of flowing continuous fibers that extend beyond the minor feature(s). Another way to perform this determination is to subtract the volume of the flowing fibers from the total volume of the part.

A major feature is the largest feature, or one of several features that are about the same size and that dominate, in terms of size, any other features of a mold. The major feature will typically have a maximum dimension, which is referred to herein as its length, which will determine the length of the non-flowing continuous fiber bundle(s) for that major feature. That is, the length of the non-flowing continuous fiber bundle(s) is substantially equal to the largest dimension of the major feature. If there is more than one major feature, and the major features have different lengths, then the non-flowing continuous fiber bundle(s) associated with the different major features will have different lengths. The volume of a major feature is determined in the usual fashion (e.g., length x width x height for rectangular-shaped features, cross sectional area x length for cylindrical/semi cylindrical features, etc.).

After the volume of the major feature is determined, the overlap volume is subtracted therefrom, providing the minimum required volume of the non-flowing continuous fiber bundle plus the resin (or the non-flowing continuous fiber prepreg).

The major feature(s) will often be significantly larger than the minor features of the mold. Consequently, the flowing continuous fiber bundle(s) in mold will typically be shorter than the non-flowing continuous fiber bundle(s). For the majority of parts, the length of the flowing continuous fibers/bundle(s) will be less than <NUM> percent of the length of non-flowing continuous fibers/bundle(s).

Per operation S603, the fiber bundles are placed in the female mold. The flowable continous fiber bundle(s) is placed proximal to the minor features.

Based on the layup provided by method <NUM>, a fiber-composite part can be formed, per method <NUM> (<FIG>). In accordance with operation S701, the male mold is brought into contact with the female mold, which contains a lay-up, as provided by method <NUM>. The molding materials (i.e., the fiber and resin or fiber prepreg) are then subjected to elevated temperatures and pressures in operation <NUM>. As the resin reaches its melt temperature, the pressure causes the flowing fiber bundles to move towards regions of lower pressure. Such lower pressure regions will be the minor features; that is, open cavities, vented cavities, or sections of the mold that have a smaller volume percentage of molding material than adjacent mold sections. The process is continued for a period of time and goes through a heating and cooling cycle based on the resin being used. In operation S703, the two mold halves are separated and the final part is removed, such as via ejector pins or other known techniques.

The interplay between these three factors (i.e., pressure, heat, and time), the alignment of molding material (with respect to the cavities, etc.), the position and size of vents, and the use of flowable continuous fiber bundles are the primary variables that can be used to control the flow and alignment of fibers to achieve the functional requirements of the fabricated part.

In accordance with the present teachings, during layup, non-flowing continuous fiber bundles are aligned with the long axis of the major feature they are intended to occupy. In some embodiments, flowing continuous fiber bundles are also aligned with the long axis of a major feature, and sited proximal to the minor feature that the fibers are intended to occupy. In the embodiments of the invention, however, the flowing continuous fiber bundles are aligned with the expected direction of flow (of resin) into the minor feature, to the extent that differs from the long axis of the major feature. The expected direction of flow can be determined by CFD (computational fluid dynamics).

The fibers suitable for use herein are typically in the form of resin-impregnated bundles ("pre-preg"), which typically include thousands of individual fibers, in the form of "towpreg. " As used herein, the term "fiber bundle" means an amount of fibers in the range of <NUM> to about <NUM>,<NUM> fibers. The fiber bundles are typically more or less cylindrical arrangements (i.e., cylindrical tows). However, in some alternative embodiments, rectangular, ovular, flat tows, or tape can be used. Fiber bundles are distinguishable from tape based on the aspect ratio of width to thickness (i.e., cross section). Tape will typically have a ratio of width to thickness in the range of <NUM> to <NUM>, whereas the fiber bundles used in conjunction with some embodiments of the invention will have a ratio of width to thickness in the range of <NUM> to <NUM>. The fiber bundles are usually circular, but oval form factors are not atypical.

Fibers suitable for use in conjunction with the invention include any type of fiber that can withstand the operating temperatures of a compression molding process (as a function of resin selection). For example, and without limitation, suitable fiber include: carbon, glass (A, C, E, S, D types), aramid, ceramic, natural, metal, cellulose, among others. The fibers within the towpreg can have any diameter, which is typically but not necessarily in a range of <NUM> to <NUM> microns. The cross-sectional shape of the fiber can be circular, oval, trilobal, polygonal, etc. The fiber can have a solid core or a hollow core. The fiber can be formed of a single material, multiple materials, and can itself be a composite. The fiber can include an exterior coating such as, without limitation, sizing, to facilitate processing. In some embodiments, multiple types of fiber can be used to produce a single part.

As previously mentioned, in some embodiments, prepreg, which is fiber that is pre-impregnated with resin, is used in conjunction with the invention. However, in some other embodiments, fiber and resin are delivered separately to the mold or as a comingled yarn. Any resin system that flows when subjected to heat and pressure is suitable for use in conjunction with embodiments of the invention. More preferably, embodiments of the invention use a thermoplastic resin, such as, 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), polyamide (PA), polyethylene terephthalate (PET), polyphenylene sulfide (PPS), polyphenylsulfone (PPSU), polyphosphoric acid (PPA), polypropylene (PP), polysulfone (PSU), polyurethane (PU), polyvinyl chloride (PVC), etc..

The minor features formed using the present method can be exceedingly small. Wall thicknesses as small as <NUM> millimeters and having a length-to-thickness ratio of over <NUM>:<NUM> have been demonstrated. The minor features can have any shape. In some embodiments, the minor features will require the flowed fibers to bend in excess of <NUM> degrees.

<FIG> depicts part <NUM>, molded in accordance with the present method. Part <NUM> includes beam <NUM> and legs <NUM>. The beam is a "major feature" and each leg is a "minor feature. " <FIG> depicts the orientation of fibers in part <NUM>. Non-flowing continuous fibers <NUM> span the length of beam <NUM>. Flowing continuous fibers <NUM> extend fully into legs <NUM> and out some distance into beam <NUM>. Although both fibers <NUM> and <NUM> appear to be on the surface of part <NUM>, it will be understood by those skilled in the art that the fibers depicted in this figure, and the many more that are not depicted, are distributed through the thickness of the beam <NUM> and legs <NUM>.

The ends of flowed continuous fiber <NUM> that intermingle with non-flowed continuous fiber <NUM> aligns with the direction of flow (i.e., aligned with the long axis of the beam). Fibers <NUM> are omitted from one of the legs for clarity.

<FIG> depicts the layup of the fiber bundles. Of course, the fiber bundles are placed in the female mold; for pedagogical purposes, they are superimposed on the finished part (as for <FIG>). Fiber bundles include eight fiber bundles <NUM> of non-flowing, continuous, unidirectional fiber for strength and stiffness in bending, and eight fiber bundles <NUM> of flowing continuous fiber. To the extent possible, fiber bundles <NUM> are sited proximal to the features they are intended to fill.

<FIG> depicts part <NUM> having an "x" shape. Part <NUM> consists of two long beams <NUM> and four cupped receivers <NUM> at each end of the two beams. Long beams <NUM> are "major features" and the cupped receivers <NUM> are "minor features. " <FIG> depicts the orientation of fibers in part <NUM> (fibers are omitted from two of the receivers for clarity). Non-flowing continuous fibers <NUM> span the length of beam <NUM>. Flowing continuous fibers <NUM> extend fully into receivers <NUM> and out some distance into associated beam.

Thus, flowing continuous fibers <NUM> flow axially along each base beam <NUM>, and fan outward to fill the widening geometry of each receiver <NUM>. The fibers flow upward and beyond <NUM> degrees as they conform to the female mold. It is notable the thickness of receivers <NUM> vary from thick, to thin, and then returning to thick. The flowing fibers in receivers <NUM> are substantially aligned with the axial direction of the beams, providing bending strength to curved receivers <NUM>.

<FIG> depicts the layup of the fiber bundles. Fiber bundles include two long fiber bundles <NUM> of non-flowing, continuous, unidirectional fiber. In the illustrative embodiment, one of the fiber bundles <NUM> overlaps the other. In some other embodiments (not depicted), fiber bundles <NUM> could be bent. One end of such bent fiber bundles could be disposed near the end of either beam and bend around the center of the "x" to terminate at any other beam end. Additionally, part <NUM> is made using eight fiber bundles <NUM> of flowing continuous fiber. Once again, fiber bundles <NUM> are proximal to the features they are intended to fill.

<FIG> depicts part <NUM> comprising beam <NUM> and boss <NUM>; the former is the major feature and the latter is the minor feature. <FIG> depicts first embodiment 300A of part <NUM>. Non-flowing continuous fibers <NUM> span the length of beam <NUM>. Flowing continuous fibers 308A extend fully into boss <NUM> and out some distance into beam <NUM>.

<FIG> depicts the layup of the fiber bundles for the embodiment depicted in <FIG>. The fiber bundles include fiber bundle <NUM> of non-flowing, continuous, unidirectional fiber for strength and stiffness in bending, and two fiber bundles 307A of flowing continuous fiber. Fiber bundles 307A are sited near to cavity <NUM> that will create boss <NUM>. As depicted in <FIG>, for this embodiment, fibers in fiber bundles 307A enter the cavity "head first," creating embodiment 300A of part <NUM>.

<FIG> depicts second embodiment 300B of part <NUM>. Non-flowing continuous fibers <NUM> span the length of beam <NUM>. Flowing continuous fibers 308B extend fully into boss <NUM> and out some distance into beam <NUM>. However, unlike embodiment 300A, each flowing fiber 308B flows from the center of the fiber into cavity <NUM>. This fiber arrangement will imbue embodiment 300B with a greater ability to withstand compressive stress or axial impact stress on boss <NUM> than the fiber arrangement of embodiment 300A. <FIG> depicts the layup of fiber bundles for the embodiment depicted in <FIG>. The two bundles 307A of flowing fiber are replaced by a single, longer fiber bundle 307B.

<FIG> depicts rod end <NUM> having eye-shaped head or ring <NUM> and integral shank <NUM>. Head <NUM>, which is a "minor feature," includes circular opening <NUM>. <FIG> depicts the orientation of fibers in part <NUM>. Non-flowing continuous fibers <NUM> span the length of shank <NUM>. Flowing continuous fibers <NUM> extend fully and intermingle in head <NUM> and protrude some distance into the fibers in shank <NUM>. In this particular embodiment, (non-flowing) spiral preform fiber bundle <NUM> is positioned around opening <NUM>. This imbues the rod end <NUM> with high hoop strength. As in previous embodiments, the portion of flowing continuous fibers <NUM> that mingle with non-flowing continuous fibers <NUM> align with the direction of flow along shank <NUM>.

<FIG> depicts the layup of the fiber bundles to produce the embodiment depicted in <FIG>. The fiber bundles include fiber bundle <NUM> of non-flowing, continuous, unidirectional fiber for strength and stiffness in bending, fiber bundles <NUM> of flowing continuous fiber, and spiral preform <NUM>. In accordance with the illustrative method, fiber bundles <NUM> are sited proximal to cavity <NUM> that will create head <NUM>.

<FIG> depicts fork <NUM>, including handle ("major feature") <NUM> and tines ("minor feature") <NUM>. <FIG> depicts first embodiment 500A of part <NUM>. In this embodiment, as usual, non-flowing continuous fibers <NUM> span the length of handle <NUM>. Flowing continuous fibers <NUM> extend fully into tines <NUM> and protrude some distance into fibers <NUM> in handle <NUM>.

<FIG> depicts the layup of the fiber bundles to produce the embodiment depicted in <FIG>. The fiber bundles include fiber bundle <NUM> of non-flowing, continuous, unidirectional fiber for strength and stiffness in bending, and two fiber bundles <NUM> of flowing continuous fiber. In accordance with the illustrative method, fiber bundles <NUM> is sited near to the cavity <NUM> that will create tines <NUM>.

<FIG> depicts second embodiment 500B of fork <NUM>. Once again, non-flowing continuous fibers <NUM> span the length of handle <NUM>. Flowing continuous fibers <NUM> extend fully into tines <NUM> and out some distance into non-flowing fibers <NUM> in the handle. As best seen in <FIG>, embodiment 500B includes u-shaped fiber preform <NUM>, in addition to non-flowing continuous fiber bundle <NUM> and flowing continuous fiber bundles <NUM>. Compared to embodiment 500A, embodiment 500B of fork <NUM>, by virtue of fiber preform <NUM>, would be better able to withstand a stress that pulls tines <NUM> apart.

As previously mentioned, the strategic placement and use of vents in the mold promotes flow of flowing continuous fibers into minor features. The mold for part <NUM> (<FIG>) is naturally vented because the cavities that form the minor features are open until the last moment when they shut off at the end of the legs. The same is true for the mold for part <NUM> (<FIG>). For both of molds, the entire end face of the minor features (i.e., legs <NUM> and cupped receivers <NUM>) are vented until the very end.

For the mold for part <NUM> (<FIG>), vent <NUM> is situated at the end of the minor feature (i.e., boss <NUM>). The mold for part <NUM> (<FIG>) is vented, via vent 409A, at the "top" of ring <NUM>. As desired, the region at which flowing continuous fibers <NUM> from the bundles <NUM> entangle one another can be controlled based on where on the ring the vent appears. Offsetting the location of a vent, such as vent 409B, creates uneven flow of fiber around the ring. This will affect the primary location at which the fibers from the two bundles <NUM> entangle one another. Relative to other locations around the ring, the point of entanglement will be somewhat weaker. Consequently, if enhanced tensile strength is required in a particular region, such as the top of the ring, the point of entanglement is advantageously shifted away from that location. For the mold for part <NUM> (<FIG>), a vent (vents 509A and 509B) are situated at the end of each tine <NUM>.

There is an amount of natural venting provided by the small gap between mold halves. However, to ensure that a minor feature is filled with resin and fiber, vents are typically used in accordance with the present teachings. The vents are typically small holes, such as in the range of about of <NUM> to about <NUM>. The vents are kept relatively small to prevent excessive materials loss and to prevent fiber from entering the vents. In some embodiments, multiple vents are used. Vents self-clear on each cycle because the resin in them re-melts and flows from the vent.

In light of the present disclosure, those skilled in the art will understand how to increase the ability of a part to withstand stresses at specific regions thereof by overlapping flowing and non-flowing continuous fibers and additionally, in some embodiments, using a preform having a particularly geometry. Directionally, increasing the overlap between flowing and non-flowing continuous fibers will increase the ability of a part to withstand stress.

Part <NUM> (depicted in <FIG>) was molded, via compression molding, and load tested. Several samples of part <NUM> were formed in accordance with the invention (samples <NUM>-<NUM>) and several samples of the part were formed in accordance with the prior art. The results are reported in Table <NUM>, below.

For the examples (i.e., samples <NUM>-<NUM>), the part was formed from sized tow-preg (bundles of pre-impregnated fiber). Such sized bundles are referred to as "preforms. " Each preform contained <NUM>,<NUM> carbon fibers (Plasitcomp, Inc. , MN) impregnated with PA (polyamide) <NUM>. For the comparative examples (i.e., Samples <NUM>-<NUM>), the part was formed from chopped tow-preg containing the same type of fibers and resin.

The chopped prepreg was not significantly shorter than the preforms of flowing continuous fiber. The difference is in the manner in which the material is laid-up in the mold. Chopped prepreg is randomly oriented throughout the mold, whereas the preforms that provide the non-flowing continuous fiber and those that provide the flowing continuous fiber are placed and oriented in a specific manner, as previously described.

The conditions (i.e., temperature and pressure cycling) are primarily a function of the resin used. Each sample was heated from ambient temperature to <NUM> °F under <NUM> psi of pressure. Once at <NUM> °F, the pressure applied to each specimen was increased to <NUM> psi. While holding <NUM> psi of pressure, the temperature was increased to <NUM> °F and held for five minutes. After this holding time, the heat was removed while pressure was maintained, thus cooling the samples until they returned to solid state.

The quantity and size of the preforms required to form the part must be determined. That is accomplished by: (i) determining the volume of the specific regions of the part; (ii) determine what "type" of preform (i.e., non-flowing continuous or flowing continuous) is required for each such specific region; and (iii) calculating the required quantity of each type of preform.

Referring again to <FIG>, part <NUM> includes five different regions: beam <NUM> and four legs <NUM>. As previously described, beam <NUM> will be formed from non-flowing continuous fibers, whereas the smaller and off-axis legs <NUM> will be formed from flowing continuous fibers.

All dimensions in millimeters (mm or mm<NUM>).

The relatively significant overlap (<NUM>-<NUM>= <NUM>) provided by the (<NUM>) length of the flowing continuous fiber was desirable for the anticipated function of the part and the stresses to which the part will be subjected.

The calculated quantity of fiber is rounded-up to next integer. This apparent overfilling of the mold is not undesirable, since there are some losses of material (resin) to flash. Typically, overfilling of a mold by about <NUM> to about <NUM>% of the mold's overall volume yields adequate quality in a finished part.

Table I depicts the results of load testing. The loading-bearing capacity of part <NUM>, when fabricated in accordance with the present teachings, improved by <NUM>% on average relative to its load-bearing capacity when formed using chopped fiber. The maximum load was determined by a universal testing machine built by Instron, setup with compression platens (i.e., for the application of downwardly directed force). The samples were situated in the center of the bottom platen, with the beam on top and legs underneath, thus creating four contact points on the bottom platen. A loading apparatus was affixed to the top platen to load the samples in three-point bending, the two support points supplied by the legs and the third loading point supplied by the loading apparatus on the top platen. The loading apparatus applied force to the minor axis of the top beam surface. Flowed specimens failed in the beam center, whereas chopped specimens failed at the leg-beam joint.

Claim 1:
A compression-molding method, the method utilizing a female mold, the female mold including a least one major feature having a long axis, and at least one minor feature, the minor feature having a length less than <NUM> percent of a length of the major feature, the method comprising:
disposing, in the female mold, at least one non-flowing continuous fiber bundle comprising first fibers and a first resin, wherein the at least one non-flowing continuous fiber bundle has a first length and aligns with the long axis, and has an aspect ratio of width to thickness in a range of about <NUM> to about <NUM>;
disposing, in the female mold, at least one flowing continuous fiber bundle at a first location that is proximal to the at least one minor feature, wherein the at least one flowing continuous fiber bundle comprises second fibers and a second resin, has a second length that is less than <NUM> percent of the first length, has an aspect ratio of width to thickness in a range of about <NUM> to about <NUM>; and
venting the minor feature to flow, from the first location to a second location that is at least partially within the at least one minor feature, the second fibers and the second resin in an amount sufficient to fill the one minor feature, and wherein the second fibers align with an expected direction of flow of the second resin.