US 20030051795 A1
An improved filament winding method and apparatus for fabrication of composite material products is based on a mechanism that rotates filaments around a non-rotating mandrel. The primary filaments in predetermined patterns tend to move on the mandrel and thus such filaments are fixed in position relative to the mandrel by over-wrapping them with secondary filaments applied over the primary filaments. The winding mechanism functions by rotating filament spools around a non-rotating mandrel rather than rotating the mandrel to pull the filaments onto the mandrel. The mandrel is axially translated through the center of the winding mechanism or the winding mechanism is translated over a stationary mandrel which is supported in such a manner as to provide for such translation.
1. A method of fabricating a fiber reinforced composite structure from at least two sets of filaments from a filament supply applied to a non-rotating mandrel support surface chosen to match a desired shape of said composite structure, said method comprising the steps of:
placing at least one or more first fiber sets in any non-secured but predetermined orientations of from zero to essentially ninety degrees on said support surface; and
over-wrapping said first fiber set(s) with at least one additional fiber set, which additional set extends around the mandrel support surface and secures said first fiber set in said predetermined orientations.
2. The method in accordance with
impregnating said fiber sets with a matrix material which solidifies said fiber sets into said desired shape; and
removing said impregnated fiber structure from said mandrel support surface whereby said matrix material and said fibers have an inside shape that matches the outside shape of the support surface.
3. The method of
applying the fiber from said bobbins to said mandrel by relative motions between said filament supply and said mandrel.
4. The method of
rotating and/or translating one or more spool sets relative to said longitudinal axis of said mandrel.
5. The method of
arraying said spool set and said bobbins in a predetermined pattern around said mandrel.
6. The method in accordance with
applying said fiber filament from a fixed location relative to said support surface.
7. The method of
controlling said movement of said spool sets such that at least one of said sets is non rotational while said set still moves axially along said longitudinal axis of said non-rotating mandrel.
8. The method of
removing the mandrel from the composite structure by collapsing said mandrel.
9. The method of
supporting said sets of spools such that the position of said sets are fixed relative to each other in the direction corresponding to the axial direction of said mandrel.
10. Filament winding apparatus for fabricating fiber reinforced composite structures from at least two sets of filaments to be applied to a non-rotating support surface chosen to match the desired shape of said composite structure, said apparatus comprising:
first means for placing at least one or more first fiber sets in any non-secured but predetermined orientations from zero to ninety degrees on said support surface;
second inner means located within the first fiber set placing means and having located therein an opening for receiving a filament support surface; and
filament control means including said second means for over-wrapping said first fiber set(s) with at least one additional fiber set, which additional set extends around the support surface and secures said first fiber set in said predetermined orientations on said support surface.
11. Apparatus for fabricating fiber reinforced composite structures in accordance with
means for impregnating said fiber sets with a matrix material which solidifies said fiber sets into said desired shape prior to removal from said support surface.
12. The apparatus in accordance with
means for holding said mandrel in a stationary position; and
means for applying the fiber sets to said stationary mandrel by spool sets which are moved relative to the stationary mandrel.
13. The apparatus of
a plurality of circular spool sets which are in side by side relation with each other and all sharing a common center aligned with said longitudinal axis of said mandrel; and
each of said spool sets having bobbins adapted to receive wound spools of said fiber filaments together with fiber application rings centrally located within said spools and also having the same common center as said circular spool sets.
14. The apparatus of
means for rotating one or more spools around the mandrel and also moving said spool sets along said longitudinal axis relative to said mandrel at a controlled rate such that a circumferential helix of said secondary filaments fixes and secures said primary filaments in place along said mandrel.
15. The apparatus of
means for arraying said spools in a spaced pattern which surrounds said mandrel.
16. The apparatus in accordance with
means for applying said fiber filament from a fixed location relative to said support surface.
17. The apparatus of
means for controlling said movement of said spool sets such that at least one of said sets is non rotational while still moving axially along said longitudinal axis.
18. The apparatus of
means for removing the mandrel from the composite structure by collapsing said mandrel.
19. Filament winding apparatus for fabricating fiber reinforced composite structures from a plurality of sets of filaments to be applied to a non-rotating mandrel support surface chosen to match the desired shape of said composite structure, said apparatus comprising:
first outer circular means having spools of wound filaments thereon for placing at least one or more first fiber sets in any non-secured but predetermined orientations from zero to ninety degrees on said mandrel support surface;
second inner means located within the first fiber set placing means and having located therein filament openings for guiding filaments from said outer circular means to the inner surface of said second means for secondary filament placement and over-wrapping of said primary filaments on the surface of said mandrel support for securing said primary filaments in place on said mandrel; and
means for controlling the movement of said first and second filament supply means such that the primary and secondary filaments supply means are rotated around said non-rotating mandrel and both said first and second means translate together as a fixed unit back and forth along the longitudinal axis of said mandrel while applying concentric layers of filaments in said predetermined orientations around each layer on said mandrel support surface.
20. The filament winding apparatus of
a plurality of circular spool sets which are in side by side relation with each other and all sharing a common center aligned with said longitudinal axis of said mandrel; and
each of said spool sets having bearing races and bearings located between the inner surfaces of adjacent spool sets which allow adjacent spool sets to be controlled independently of each other during said filament layer application.
 On May 29, 2001 the United States Patent Office received a copy of—and assigned serial No. 60/294,195 to—a Provisional Patent Application (PPA) filed by the same inventor hereof. That PPA is incorporated herein by this reference as though set out here in full. Additionally, the PPA is being supplemented by this Regular Patent Application (RPA). Applicant expressly reserves all rights and privileges flowing from the PPA and its earlier official filing date and contents thereof. This RPA follows and is supported by the PPA.
 This invention relates to filament winders used to apply filaments to a support surface such as a mandrel. More specifically, the field of this invention relates to the fabrication of filament reinforced composite products. Additionally the field of this invention relates to winding of filaments and relative motion between filament winding machinery and a mandrel. The field of the winding method of the invention envisions computer control of mandrels, spools and associated filament winding apparatus for the improved formation of diverse composite material structures.
 My invention interfaces and operates in conjunction with various filament winding and composite material forming technologies. Set out below are brief descriptions of certain relevant terms which further the understanding of the invention. These terms provide a basis for a detailed teaching of the improvements of this invention in the relevant arts. Such terms are not intended to replace the claims but rather serve as helpful guides in understanding my novel improvements in these arts.
 Fiber reinforced composites are materials consisting of a multitude of fibers which are surrounded and encased in a matrix. The desired properties of the composite may be structural, electrical, thermal or magnetic. These diverse properties are achieved by the appropriate selection of the matrix and fiber materials and by the orientation and quantities of these selected constituents.
 The matrix material performs functions such as maintaining the fibers in a set position after the matrix has set or cured, transferring forces between adjacent fibers, providing environmental protection for the fibers and providing resistance to fluid penetration. Examples of matrix materials include polymers such as epoxies, metals, ceramics, refractory materials such as carbon and graphite, and elastomeric materials such as rubber.
 Fibers used in composites include such materials as glass, carbon, metal, jute, and ceramics. The fibers are frequently as small as 5 mm in diameter and may be grouped into yarns or filaments of from one to over 40,000 fibers.
 An object that forms the inside shape of the composite part that is being fabricated. It may be extracted after the part is fabricated or in some cases, the mandrel may remain inside the composite part. The shape may be irregular and the mandrel may be either straight or curved as required for the configuration of the part being fabricated. The axial direction of the mandrel is herein taken to be the longitudinal axis of the mandrel. Fiber or filament orientations are referenced to the axial direction with the axial direction taken as 0 degrees and the circumferential direction as 90 degrees.
 Pultrusion is a process for fabricating long slender composite parts of constant cross section by pulling the fiber reinforcements through a heated die where the fibers are wet out with uncured resin either prior to the die or while in the die. Heat supplied from the die causes the resin to cure thus producing a solid composite having the same shape as the die opening.
 Braiding is a process for producing an interlaced textile where the interweaving of the yarns is a result of passing the yarns over and under yarns approaching from the opposite direction. The yarns which form this braid are generally supplied to two counter rotating feeds.
 Fabrication of fiber reinforced plastic composites has become a major worldwide industry. The modern fibers or reinforcing filaments now available allow components to have physical properties far in excess of their metal counterparts. By selection from among a wide variety of filaments such as glass, carbon, arimide, polyethylene, ceramic or metal, and by careful control of the orientation of these filaments, it is possible to achieve a wide range of physical properties.
 Properties that can be tailored include stiffness, strength, thermal conductivity, thermal expansion, weight, electromagnetic energy absorption, etc. These various fibers were traditionally imbedded or encased in a plastic matrix but even the matrix technology has been broadened to now include matrices such as metal, ceramic, carbon and glass.
 Braiding machines are an alternative to reinforced filaments, but such machines have their drawbacks. While braiding machines do not suffer from the need to secure the filaments by wrapping, they do suffer from a limited ability to control fiber distribution. Often a craftsman must control many variables such as angles, speed, tension and other related factors in a given task. Braiding machines do not offer the versatility that such a designer desires. Moreover, braiding is limited by a very slow operating speed compared to the faster and more versatile filament winding technology.
 The two most efficient methods for fabricating composite components are generally considered to be filament winding and pultrusion. The pultrusion process is more limited in the part configurations that can be fabricated and the matricies that can be used. The filament winding process traditionally was based on attaching filaments to a mandrel and then pulling the band of filaments through a bath of resin as the mandrel rotated. Fiber orientation was controlled by translating the bath and fiber band guide along the mandrel as the mandrel rotated. By coordination of the translation and rotation, the fiber angle was controlled. This process is very efficient and has been used to fabricate such items as pipes, pole vault poles and rocket motor cases.
 A disadvantage of existing filament winding machines is that they have a limited ability to control the orientation of the filaments. When fabricating long shapes, they can not apply filaments in the axial direction as the filaments would simply fall out of position. This is a serious limitation when fabricating advanced composite materials, such as carbon fiber reinforced composite tubes, since the axial stiffness of the finished tube is seriously degraded by only a few degrees of deviation from the axial direction.
 A second problem with existing filament winding machines is that they can not change the filament winding angle without spreading this change over a large axial distance. This limitation is a result of the inability to stop the filaments from sliding in the axial direction. This is a disadvantage in that it limits the ability of the composites designer to specify the desired orientations and requires him to settle for a machine imposed solution.
 A third disadvantage is that the filaments must very gradually reverse direction in such a manner as to wrap around the mandrel sufficiently to prevent them from sliding back down the mandrel. This results in a filament buildup at the location where the machine reversed direction. This buildup is generally either left as excess material or is cut from the final part but is wasted material in either case. A further disadvantage that this drawback causes is that it prohibits short layers for use with overlaying layers, as the buildup at the ends of the shorter layers will cause a bump in the overlaying plies. Such a bump is both unsightly and can also cause structural weakness.
 The invention relates both to apparatus for, and methods of, forming composite materials based upon a novel over-laying of a primary set of filaments by a wound second set of filaments which secures the primary filaments in place in a desired pattern. The method of fabricating a fiber reinforced composite structure involves the steps of using at least two sets of filaments which are applied to a support surface that is chosen to match the desired shape of a finished composite structure.
 In accordance with my invention I choose to place my first fiber set in a non-secured but predetermined orientation on a support surface, such as a mandrel, for example. Let us say that the mandrel is chosen to form a unique sailboat mast having particularly rigorous design criteria. Moreover, assume that this mast requires many axial filament strands, which strands tend to fall away from the mandrel surface as soon as they are being applied.
 In my invention, I over-wrap the first fiber set with at least one additional fiber set, which additional set extends around the mandrel and immediately follows behind and secures the first fiber set to the mandrel in accordance with predetermined orientations.
 In my novel approach such predetermined orientations range from zero to essentially ninety degrees on said support surface. As an example, let us assume that the composites designer is presented with a specification to suit the sailboat mast requirements. Once the mast has achieved the required layers of filament—perhaps in the order of twenty layers or so—these filament sets are impregnated with a matrix material which solidifies, and when cured, hardens the wound fiber sets into the desired mast shape. This structure has very precisely controlled fiber orientations for superior strength and reliability. When a supplier is today faced with liability for any and all catastrophes, such precise filter alignment is mandatory. Please keep in mind that even a few degrees variation from the desired design goal vastly deteriorates the strength and reliability of the finished part.
 In my embodiment I have also provided a way of removing the impregnated fiber structure from the mandrel support surface in order to assure that the matrix material and the impregnated fibers have an inside shape that matches the outside shape of my mandrel. In my apparatus for performing my novel method, I have achieved a versatility which allows my mandrel to be either in a stationary position or to move relative to my source(s) of filament supply. When using spool sets for applying filaments, I have the added capability to meet designer's requirements since the spools both rotate and translate relative to the mandrel. Indeed, all of the rotating spools may move axially relative to the mandrel, and may serve to apply axial layers along the longitudinal axis of the mandrel. These capabilities are important features of this my invention.
 In my apparatus I have established arrays for the spool sets which I employ for laying down the fibers. Such spool sets are normally in a uniform pattern around my mandrel. In conjunction with these spool sets, I have fixed locations for applying certain filaments as needed for versatility in meeting the diverse design requirements for composite material application of the technology of today. Since the outside shape of the mandrel fixes the inside shape of the composite material being formed, I employ, as an option, a collapsing mandrel in order to secure an easy and efficient release of the formed composite material.
 This improved filament winding invention, presents a diverse number of options for securing any given number of yarns to a mandrel as required including axial fiber layers. Multiple fiber passes, each yielding a layer of given orientations from zero to ninety degrees relative to the longitudinal axis of a mandrel provides valuable freedom in composite material designs. The resulting improvements achieved by this novel invention substantially eliminate many of the above noted disadvantages of prior art filament winding or braiding machines, thus allowing the composites designer to produce structurally efficient products while fabricating them in an efficient manner.
 Several objects and advantages of the invention are to enable filament winding of products without resorting to excessive wraps around the mandrel, to allow the use of short plies or layers to be used in combination with longer layers, and to allow selection of a zero to ninety degree orientations of the filaments relative to the mandrel axis. My range thus includes axial layers that run along the longitudinal axis of the mandrel and also can run transverse to that axis.
 Still further objects and advantages include the ability to use inexpensive mandrels as will become readily apparent from the following detailed description. Additional objects and advantages of the invention are to apply the filaments without a plastic resin thus allowing subsequent impregnation by a matrix of the designer's choice.
FIG. 1 is a perspective view of a machine constructed in accordance with the invention;
FIG. 2 is a perspective view of a filament application subassembly or zone for the machine in FIG. 1;
FIG. 3 includes FIG. 3A and FIG. 3B which are respectively a simplified diagram showing application of primary and secondary over-laying filaments to a mandrel by techniques of either dry or pre-impregnated filaments.;
FIG. 4 is an end view of the machine in FIG. 1;
FIG. 5 is a side view of machine in FIG. 1; and
FIG. 6 is a top view of the machine in FIG. 1.
FIG. 1 is a perspective view of a machine 100 constructed in accordance with my invention. A base plate 25 supports the filament winding mechanism 50 and translating supports 75 for the mandrel 15. The winding mechanism 50 consists of rotating rings 21 through 24 with attached spools 1 through 4 of filaments. The rings 21, etc. can be rotated by the motors 5 through 8 which are, in turn, controlled by a computer which is not shown. Such computer controlled machines are well known in this art and need no further description. The mandrel supports 14 and 16 are keyed into the base plate 25 with a dove tail thus allowing them to translate as directed by a motor 8 running through a pinion 9 and acting on a rack 10 attached to the base plate 25.
FIG. 2 is perspective view of a typical ring subassembly. Ring 22 provides support for four spool brackets 31. Each spool bracket 31 has one spool, or bobbin, 2 of wound filaments 29 with a friction restraint to provide tensioning for the filaments 29 as they are pulled from the spools 2. The filaments 29 pass through holes 27 in the outer ring 22 and then through holes 28 in the innermost filament control ring 30. After passing through rings 22 and 30, the filaments 29 are available to wrap onto the mandrel 15 (FIG. 1) which is not shown in this FIG. 2. Filament control ring 30 is supported by four spokes 32 that are threaded into rings 22 and 30 respectively. Ring 22 has a bearing race 33 in each axial face. Ring 22 may be driven by a belt 26 (FIG. 1) that runs in groove 34 under speed control from a servo motor 8 (not shown in FIG. 2).
FIG. 3 includes FIGS. 3A and 3B which are respectively a simplified section of winding on a mandrel section and a block diagram of filament winding options and decision controls. FIG. 3A shows several primary filament 129 a, 129 b, etc. running axially along the longitudinal axis 49 of mandrel 15. These primary filaments would tend to fall or scoot around on mandrel 15 when laid down in an axial or zero degree direction as shown. In accordance with this invention, however, my spool sets such as that of FIG. 2 follow closely behind the primary filaments 129 and immediately over-wrap a secondary filament winding 139 that secures the primary filaments in place. The inner ring 30 allows my secondary filaments 139 to be immediately behind the primary filaments 129 and thus secures them in place on the mandrel 15 with precisely controlled orientations.
FIG. 3B is a simplified block diagram of my method which shows that either dry or pre-impregnated fibers may be laid down on a mandrel as desired. Also shown is a matrix filament and a pre-impregnated step that allows either type filament to secure the primary filaments in place on a mandrel. In this flow chart type drawing, bobbins 120 provide the primary filaments which at 122 are applied to mandrel 15 as shown in FIG. 3A. Bobbins 121 provide the secondary filaments 139 which at 123 secure the primary filaments 129 by over-wrapping them.
 At decision step 124, a determination is made as to whether or not the filaments were pre-impregnated. If not, then at step 125, the filaments are impregnated. Both operational both paths then lead to a curing of the matrix at 126. Step 127 removes the composite structure.
 My mandrel 15 is collapsible to provide for removal of the impregnated fiber structure from the mandrel support surface whereby the matrix material and the fibers have an inside shape that matches the outside shape of the mandrel support surface.
FIG. 4 is an end view of the machine 100 of FIG. 1. This end view shows the position of mandrel 15 relative to the filament positioning ring 30. Note that both the center of the circular surface mandrel 15, and the inner and outer rings 22 and 30 all share a common center. Spools 1 are attached to ring 21 with similar brackets—such as 31 shown in FIG. 2—except that they are shorter as necessary to provide clearance under the spools 2 that are attached to adjacent ring 22. Ring 18 is a non-rotating support ring that has a bearing race on the hidden side. Each ring has a bearing race that matches that in the facing ring. The rings thereby support each other with the ball bearings in these races and with the outer non-rotating support rings 18 being anchored by fixed supports 26.
 This end view of FIG. 4 also shows how one set of spools may be held in a fixed position relative to the mandrel. Computer control for the various spool sets can achieve a rotation from zero on up to higher speeds as necessary. At zero speed the spool set 1, for example, becomes fixed in place, and in that instance would be laying down four filaments that run axially along the mandrel 15. Obviously the number of spools and their orientation as shown in these drawings is a matter of choice and should not be taken as limiting. As a typical example, four spools only are shown, when in actual practice, each such set may involve up to forty spools.
FIG. 5 shows a side view of the machine. As there shown one sees that the spools are generally in the same transverse plane as the filament supply rings such as ring 30 of FIG. 2. Such a location, however, is not to be taken as limiting because such spools may be otherwise located.
FIG. 6 shows a top view of the winding machine. This view shows that the spools 1 and 2 are in a common rotating plane but spools set 1 is rotating on a smaller diameter than spool set 2. This is best shown perhaps, in FIG. 3. Bar 20 connects mandrel support bases 16 such that the bases are held at a set end to end distance. Note that bolts 28 anchor plate 20 and can be adjusted to set the spacing of the two bases 16 to accommodate different length mandrels 15.
1 spool—or bobbin—of filaments
2 spool of filaments
3 spool of filaments
4 spool of filaments
14 mandrel support base
16 mandrel support
17 mandrel clamp
18 support ring
25 base plate
26 ring support plate
30 filament control ring
31 spool bracket
33 bearing race
34 belt groove
 The operation of this invention differs from conventional composite filament winders in several ways. In this invention, the mandrel 15 does not rotate because the machine 100 causes the filaments 29, FIG. 2, to be wrapped around the non-rotating mandrel 15. I have achieved operational flexibility by mounting spool sets such as 1, 2, 3 etc. on respective outer rings 21, 22, 23, etc. Each outer ring is one of a pair of concentric rings 30 for each zone, and both rings of the pair are spoke connected such that both rings of a pair rotate around a mandrel 15 (FIG. 1) that is positioned relative to the innermost ring 30. My spool, or bobbin, sets are in a side by side relationship and are controlled independently of each other by a computer in any well known manner. Several respective sets of filaments can thus be applied sequentially and almost simultaneously.
 The outermost spool 2 location, FIG. 2, allows filaments 29 to be brought through holes 37 in the outer ring 22 and admitted into and through openings 28 in the inner filament control ring 30. By passing the yarns through holes 28 in the inner ring 30, the yarns, or filaments, 29 can be laid down in close and controlled proximity to the surface of a mandrel that is positioned within the opening of the inner ring 30. Advantageously, the mandrel 15, FIG. 1, is essentially a roll that fits snugly within the inner ring 30 While shown as concentric toroids, or rings, the inner and outer geometric configurations, of course need not be circular, but may be varied in shape in accordance with the particular composite structure being formed. Different shaped mandrels may thus be accommodated within the filament control apparatus of appropriate shape.
 Use of a mandrel-surrounding filament control means such as inner ring 22 and the outer ring 30 allows the filament 29 to be position controlled just prior to the filament 29 being wound onto the mandrel 15. My apparatus thus achieves a high degree of accuracy in filament placement. Moreover, as shown in FIG. 2, spokes 32 fix inner ring 30 relative to outer ring 22, and such spokes can be of varying length and interchangeable so as to allow different shapes for the innermost filament application set, or zone. By simply changing the inner ring configuration—or even leaving it out entirely—different filament shapes may be laid down on complex shaped mandrels and yet form various types of composite material structures by closely controlled filament applications.
FIG. 2 illustrates a typical inner and outer ring pair subassembly in accordance with my invention. The ring 22 supports the spools by use of brackets 31 and outer ring 22 also holds the internal filament positioning ring 30. The outer ring 22 is driven by a belt (11, FIG. 1) riding in groove 34 located on the exterior of the ring 22. Ring 22 is held in position by the ball bearings (not shown) that ride in the races 33 on each side of the ring face.
 As a ring pair is rotated and the mandrel is moved axially, several filaments 29, in accordance with the number of spools 2 and openings 27, 28 of a given bobbin set, will be drawn onto the mandrel in helical patterns. Angles of the helix can be adjusted from substantially circumferential to axial along the longitudinal axis of the mandrel 15 by controlling the mandrel translation and the rotation speed of the ring pair 22, 30. By using servo motors such as 5, 6 (FIG. 1) to create these motions, the helix angles can be computer controlled to allow high quality fabrication of complex fiber architectures that might be specified by an advanced composites designer.
 The winding machine 100 shown in these drawings utilizes four sets of ring subassemblies or zones. Such zones are in side by side orientation with a common center located on the geometric center of the mandrel 15. More or less numbers of rings 22 might be used as appropriate to the objectives of the composites fabricator. In this machine 100 each of the rings constitutes a zone where filaments can be controlled independently of the adjacent zones. By loading the spools on the two inner rings or zones with a high grade structural yarn such as carbon filaments and the two outer rings or zones with a very low denier glass, the machine will be capable of applying, for example, structural carbon in any desired pattern including axial.
 My improved capability is a result of using one of the two exterior rings (with the light weight glass yarns) to apply a substantially circumferential helix over the carbon yarns as the carbon is drawn onto the mandrel. This over-wrapping helix or winding secures or fixes the filaments from the inner zones by pressing them against the previously deposited yarns and or the mandrel. The use of the two outermost zones for over-wrapping or fixing the yarns of the inner zones thus allows my novel machine to function equally well in either direction of translation relative to the mandrel.
 The use of the external rotating rings to secure the yarns in position allows the structural yarns to be applied without wrapping them around the mandrel prior to reversing the translation. This permits short layers, reduction of waste, fabrication of composite structures with high axial content and local ply build-up for internal reinforcements in areas of high concentrated force loading. The process is equally effective when used with structural yarns in a helix rather than axial orientation in that it allows soft helix angles, as well as quickly changing helix angles, and it eliminates the need to slowly change the helix angle at the end of the translation.
 Another feature of the machine is the use of rings to help control the yarn positions just prior to depositing them on the mandrel. These rings can function similar to the wiper rings on a braiding machine in that the yarns can pass between the rings. Unlike the wiper rings on a braiding machine, the rings can also be made with holes as shown in FIG. 2 such that the yarns pass through the holes for more precise positioning of the yarns. This can be done by allowing the rings to rotate with the mechanism controlling the yarns in each zone.
 Another embodiment of the invention is to hold the mandrel in a fixed location and move the winding assembly back and forth over the mandrel. This can be a substantial advantage when fabricating long composite structures such as sailboat masts as it reduces the amount of floor space that is required.
 While my invention has been described with reference to particular examples of some preferred embodiments, it is my intention to cover all modifications and equivalents within the scope of the following claims. It is therefore requested that the following claims, which define my invention, be given a liberal interpretation commensurate with my contribution to the relevant technology.