U.S. patent application number 15/652597 was filed with the patent office on 2017-11-02 for arrow or crossbow bolt shafts having a profiled inner diameter.
This patent application is currently assigned to Feradyne Outdoors, LLC. The applicant listed for this patent is Feradyne Outdoors, LLC. Invention is credited to William Edward Pedersen, Jon Arthur Syverson.
Application Number | 20170314898 15/652597 |
Document ID | / |
Family ID | 58158128 |
Filed Date | 2017-11-02 |
United States Patent
Application |
20170314898 |
Kind Code |
A1 |
Syverson; Jon Arthur ; et
al. |
November 2, 2017 |
Arrow or Crossbow Bolt Shafts Having a Profiled Inner Diameter
Abstract
Composite arrow or crossbow bolt shafts have a hollow core,
where the inner diameter of the shafts vary along the length of the
shaft, but the outer diameter of the shafts remains constant. The
hollow inner core may vary gradually in size along the length of
the shaft, or it may vary in discrete stepped portions so that the
shaft is more hollow in some portions in comparison to others. The
hollow composite shafts may be manufactured by wrapping a tapered
or stepped inner mandrel with fibers of a composite material and
curing that composite material, or by triaxially braiding composite
fibers around a tapered or stepped inner mandrel before curing
those composite fibers.
Inventors: |
Syverson; Jon Arthur;
(Cloquet, MN) ; Pedersen; William Edward; (Duluth,
MN) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Feradyne Outdoors, LLC |
Superior |
WI |
US |
|
|
Assignee: |
Feradyne Outdoors, LLC
Superior
WI
|
Family ID: |
58158128 |
Appl. No.: |
15/652597 |
Filed: |
July 18, 2017 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
15242240 |
Aug 19, 2016 |
|
|
|
15652597 |
|
|
|
|
62208220 |
Aug 21, 2015 |
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F42B 6/04 20130101 |
International
Class: |
F42B 6/04 20060101
F42B006/04; F42B 10/02 20060101 F42B010/02 |
Claims
1. A method of manufacturing an arrow or crossbow bolt shaft,
comprising: shaping an inner mandrel so that an outer diameter of
the inner mandrel varies along the length of the inner mandrel;
wrapping the inner mandrel with wrapping material; heating the
inner mandrel and the wrapping material to form a shaft around the
inner mandrel; removing the inner mandrel from the interior of the
shaft; and mechanically processing the shaft to shape the shaft to
its desired final dimensions.
2. The method of claim 1, wherein shaping the inner mandrel
comprises turning the inner mandrel on a lathe.
3. The method of claim 1, wherein the wrapping material comprises
fibers of one or more materials.
4. The method of claim 3, wherein the fibers of one or more
materials comprise carbon fibers, stainless steel fibers, spring
steel fibers, steel fibers, titanium fibers, magnesium fibers,
aluminum fibers, linearized polyethylene or spectra fibers, silicon
carbide fibers, cellulose fibers, or fiberglass fibers.
5. The method of claim 4, wherein the wrapping material comprises
thermoset resin or thermoplastic resin.
6. The method of claim 5, wherein: the wrapping material comprises
a dry carbon fiber mat that has been coated with liquid thermoset
resin; and wrapping the inner mandrel with wrapping material
comprises manually wrapping the coated carbon fiber mat around the
inner mandrel.
7. The method of claim 6, wherein heating the inner mandrel and the
wrapping material comprises placing the inner mandrel and the
coated carbon fiber mat in a press and molding the coated carbon
fiber mat at an elevated temperature.
8. The method of claim 5, wherein: the wrapping material comprises
a thermoplastic, pre-impregnated carbon fiber tape and one of a
polypropylene type or a nylon tape; and wrapping the inner mandrel
with wrapping material comprises wrapping the pre-impregnated
carbon fiber tape around the inner mandrel and then wrapping the
polypropylene tape or the nylon tape around the carbon fiber
tape.
9. The method of claim 8, wherein heating the inner mandrel and the
wrapping material comprises placing the inner mandrel wrapped with
the tapes into an oven and curing the tapes at an elevated
temperature.
10. The method of claim 4, wherein: the wrapping material comprises
a self-adhesive, pre-impregnated carbon fiber fabric; and wrapping
the inner mandrel with the wrapping material comprises wrapping the
fabric around the inner mandrel.
11. The method of claim 1, wherein mechanically processing the
shaft comprises sanding or grinding the shaft to its desired final
dimensions.
12. The method of claim 11, wherein sanding or grinding the shaft
to its desired final dimensions comprises sanding or grinding the
shaft until the shaft has a constant outer diameter along the
entire length of the shaft.
13. The method of claim 12, further comprising coating the shaft
having its desired final dimensions with a thin polymeric tube or
fabric to reduce the friction on the exterior of the shaft.
14. The method of claim 13, wherein the thin polymeric tube or
fabric comprises polypropylene, polyethylene, vinyl, or nylon.
15. The method of claim 1, wherein the inner mandrel comprises
steel, aluminum, or titanium.
16. A method of manufacturing an arrow or crossbow bolt shaft,
comprising: shaping an inner mandrel so that the outer diameter of
the inner mandrel varies along a length of the inner mandrel;
tri-axially braiding fibers of one or more materials around the
inner mandrel; heating the inner mandrel and the tri-axially
braided fibers to form a shaft around the inner mandrel; and
removing the inner mandrel from the interior of the shaft.
17. The method of claim 16, wherein the fibers of one or more
materials comprise carbon fibers, titanium fibers, stainless steel
fibers, spring steel fibers, steel fibers, aluminum fibers,
cellulose fibers, fiberglass fibers, silicon carbide fibers, or
magnesium fibers.
18. The method of claim 17, wherein the carbon fibers are
high-modulus carbon fibers or intermediate-modulus carbon
fibers.
19. The method of claim 16, wherein tri-axially braiding fibers of
one or more materials around the inner mandrel comprises varying a
speed at which the inner mandrel moves longitudinally during the
tri-axial braiding of the fibers around the inner mandrel.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional of U.S. patent application
Ser. No. 15/242,240 filed Aug. 19, 2016, which claims the benefit
of U.S. Provisional Patent Application No. 62/208,220 filed Aug.
21, 2015, which are herein incorporated by reference in their
entirety.
FIELD OF EMBODIMENTS OF THE PRESENT INVENTION
[0002] Embodiments of the present invention relate to arrow or
crossbow bolt shafts, collectively referred to as "shafts," having
a profiled inner diameter, as well as methods of manufacturing such
shafts. More particularly, the present invention is directed to
shafts with a hollow core and a varying inner diameter, and methods
of manufacturing such shafts.
BACKGROUND OF EMBODIMENTS OF THE INVENTION
[0003] Arrows and crossbow bolts with composite carbon shafts have
recently become increasingly popular. Commonly, such composite
shafts are manufactured around an inner core--a metal rod known as
an "inner mandrel." The inner mandrel is a metal rod or cylinder
typically made from steel or aluminum, and has a uniform, smooth
outer diameter. These composite shafts are often made of materials
such as carbon fiber--usually, a carbon fiber sheet or mat that is
impregnated with a resin and then wrapped around the metal inner
mandrel.
[0004] After being wrapped around the inner mandrel, the carbon
fiber sheet can be itself wrapped with a polymer, such as nylon or
polypropylene, to hold the carbon fiber sheet in place during
manufacture. The wrapped inner mandrel is then cured in an oven,
which liquefies the resin and bonds the carbon fibers, forming the
composite shaft. The material of the polymeric wrapping is designed
to shrink when exposed to the heat of the oven in which the wrapped
inner mandrel is cured, providing compressive stress which forces
air and gases out of the composite while curing. After the shaft is
removed from the oven, the inner mandrel is removed, and the
exterior of the composite shaft can be machined or ground to the
desired outer dimensions and appearance.
[0005] Composite shafts manufactured using these methods are
generally strong, in order to minimize the shafts bending,
breaking, or splintering upon impacting a target. Additionally,
such composite shafts are lightweight, allowing the arrow or
crossbow bolt to fly faster and retain more kinetic energy during
flight.
[0006] We have discovered that there exists a need for a composite
arrow or crossbow bolt shaft with a constant outer diameter but
varying thickness, which allows the bolt shaft's center of mass to
be varied arrow or crossbow, as well as a need for manufacturing
techniques for such shafts. We have also discovered that there
exists a need for improvements to the structural integrity of known
shafts, as well as improvements of the vibration damping properties
of known shafts to retain more kinetic energy during flight. We
have further discovered that such improvements can be made through
the use of various combinations in the selection of material
components and manufacturing processes for such shafts.
SUMMARY OF EMBODIMENTS OF THE INVENTION
[0007] Embodiments of the invention are directed to an arrow or
crossbow bolt shaft that includes a shaft inner diameter that
varies along a length of the shaft, a shaft outer diameter of that
remains constant along the length of the shaft, and a hollow core
including an outer diameter that varies along the length of the
shaft. By varying the inner diameter of the shaft along the length
of the shaft, the location of shaft's center of mass can be varied
in a manner that can affect the shaft's aerodynamic properties,
in-flight capabilities, and strength. Additionally, controlling the
inner profile of the arrow or crossbow bolt shaft allows for
control of the stiffness and strength characteristics of the shaft
assembly.
[0008] In certain embodiments, the shaft inner diameter and hollow
core outer diameter vary along the entire length of the shaft.
[0009] In certain embodiments, the hollow core outer diameter and
the shaft inner diameter vary continuously along the length of the
shaft. In other embodiments, the shaft is a stepped shaft including
a plurality of portions, and each of the plurality of portions has
a constant shaft inner diameter that is different than a shaft
inner diameter of each of the other portions.
[0010] In certain embodiments, a stepped shaft includes at least
three portions. In certain embodiments, each of the plurality of
portions of the stepped shaft has the same length. In other
embodiments, at least one of the plurality of portions of the
stepped shaft has a different length than another of the plurality
of portions of the stepped shaft.
[0011] In certain embodiments, a stepped shaft includes a tapered
portion, in which the shaft inner diameter and hollow core outer
diameter vary continuously along the length of the tapered
portion.
[0012] In certain embodiments, the center of mass of the shaft is
closer to a tip portion of the shaft than to a tail portion of the
shaft. In certain further embodiments, the center of mass of the
shaft is between approximately 10% and approximately 20% front of
center. In still further embodiments, the center of mass of the
shaft is approximately 13% front of center.
[0013] The shaft includes fibers of one or more materials. The
materials may be carbon fibers, stainless steel fibers, spring
steel fibers, steel fibers, titanium fibers, magnesium fibers,
aluminum fibers, linearized polyethylene or spectra fibers, silicon
carbide fibers, cellulose fibers, or fiberglass fibers. The carbon
fibers may be high modulus carbon fibers or intermediate modulus
carbon fibers.
[0014] Embodiments of the shaft include thermoset resin or
thermoplastic resin. The thermoset resin can be an epoxy,
polyester, vinylester, phenolic, or urethane. The thermoplastic
resin can be polyether ether ketone (PEEK), polymethyl methacrylate
(PMMA), acrylic, nylon, or polyethylene.
[0015] Embodiments of the invention are directed to methods of
manufacturing arrow or crossbow bolt shafts, including shaping an
inner mandrel to have an outer diameter that varies along the
length of the inner mandrel, wrapping the inner mandrel with
wrapping material, heating the inner mandrel and the wrapping
material to form a shaft around the inner mandrel, removing the
inner mandrel from the interior of the shaft, and mechanically
processing the shaft to shape the shaft to its desired final
dimensions.
[0016] In certain embodiments, shaping the inner mandrel includes
turning the inner mandrel on a lathe.
[0017] The wrapping material includes fibers of one or more
materials. The materials may be carbon fibers, stainless steel
fibers, spring steel fibers, steel fibers, titanium fibers,
magnesium fibers, aluminum fibers, linearized polyethylene or
spectra fibers, silicon carbide fibers, cellulose fibers, or
fiberglass fibers. The carbon fibers may be high modulus carbon
fibers or intermediate modulus carbon fibers.
[0018] In certain embodiments, the wrapping material includes a dry
carbon fiber mat that has been coated with liquid thermoset resin,
and wrapping the inner mandrel with wrapping material includes
manually wrapping the coated carbon fiber mat around the inner
mandrel. In further embodiments, heating the inner mandrel and the
wrapping material includes placing the inner mandrel and coated
carbon fiber mat in a press and molding the coated carbon fiber mat
at an elevated temperature.
[0019] In certain embodiments, the wrapping material is a
thermoplastic, pre-impregnated carbon fiber tape and either a
polypropylene or nylon tape, and wrapping the inner mandrel with
wrapping material includes wrapping the pre-impregnated carbon
fiber tape around the inner mandrel and then wrapping the
polypropylene or nylon tape around the carbon fiber tape. In
further embodiments, heating the inner mandrel and the wrapping
material includes placing the inner mandrel wrapped with the tapes
into an oven and curing the tapes at an elevated temperature.
[0020] In certain embodiments, the wrapping material include a
self-adhesive, pre-impregnated carbon fiber fabric, and wrapping
the inner mandrel with wrapping material includes wrapping the
fabric around the inner mandrel.
[0021] In certain embodiments, mechanically processing the shaft
includes sanding or grinding the shaft to its desired final
dimensions. In further embodiments, sanding or grinding the shaft
to its desired final dimensions includes sanding or grinding the
shaft until the shaft has a constant outer diameter along the
entire length of the shaft. In further embodiments, the shaft,
having its desired final dimensions, is coated with a thin
polymeric tube or fabric to reduce the friction on the exterior of
the shaft. In still further embodiments, the thin polymeric tube or
fabric includes polypropylene, polyethylene, vinyl, or nylon.
[0022] In certain embodiments, the inner mandrel includes steel,
aluminum, or titanium.
[0023] Embodiments of the present invention are directed to methods
of manufacturing arrow or crossbow bolt shafts. The methods include
shaping an inner mandrel so that the outer diameter of the inner
mandrel varies along the length of the inner mandrel, tri-axially
braiding fibers of one or more materials around the inner mandrel,
heating the inner mandrel and the tri-axially braided fibers to
form a shaft around the inner mandrel, and removing the inner
mandrel from the interior of the shaft. The fibers of one or more
materials may be carbon fibers, stainless steel fibers, spring
steel fibers, steel fibers, titanium fibers, magnesium fibers,
aluminum fibers, linearized polyethylene or spectra fibers, silicon
carbide fibers, cellulose fibers, or fiberglass fibers. The carbon
fibers may be high modulus carbon fibers or intermediate modulus
carbon fibers.
[0024] In certain embodiments, tri-axially braiding fibers of one
or more materials around the inner mandrel includes varying the
speed at which the inner mandrel moves longitudinally during the
tri-axial braiding of the fibers around the inner mandrel.
BRIEF DESCRIPTION OF THE DRAWINGS
[0025] FIG. 1A is a side view of a composite shaft design with a
tapered inner diameter and a constant outer diameter.
[0026] FIG. 1B is a cross-sectional view of a portion of the shaft
design of FIG. 1A.
[0027] FIG. 2A is a side view of a composite shaft design with a
stepped inner diameter and a constant outer diameter.
[0028] FIG. 2B is a cross-sectional view of a portion of the
composite shaft design of FIG. 2A.
[0029] FIG. 3A is a perspective view of an inner mandrel used in a
manufacturing process for a composite shaft.
[0030] FIG. 3B is a perspective view of the inner mandrel of FIG.
3A being wrapped with a composite material during the manufacturing
process for a composite shaft.
[0031] FIG. 4 is a side view depicting tri-axial braiding of fibers
around a tapered inner mandrel.
[0032] FIG. 5 is a top view depicting the movement of the bobbins
tri-axially braiding fibers around the tapered inner mandrel of
FIG. 4.
[0033] FIG. 6 depicts the interwoven tri-axially braided fibers
resulting from the process depicted in FIGS. 4 and 5.
DETAILED DESCRIPTION OF THE INVENTION
[0034] The present invention is directed to arrow and crossbow bolt
shafts and methods for manufacturing such shafts. For the purposes
of the present invention, both arrow shafts and crossbow bolt
shafts will be referred to collectively as "shafts."
[0035] FIGS. 1A and 1B illustrate an embodiment 100 of a composite
shaft 105 having a hollow core 110. The shaft 105 has a constant
outer diameter surrounding the hollow core 110, but the thickness
(and the inner diameter) of the shaft 105 gradually varies along
the length of the shaft 105. Specifically, the thickness of the
shaft 105 is greater (and the inner diameter of the shaft smaller)
at the tip end 105a than it is at the tail end 105b.
Correspondingly, the outer diameter of the hollow core is greater
at the tail end 110b than it is at the tip end 105a, as the shaft
105 decreases in thickness. In this embodiment 100, the thickness
of the composite shaft 105 gradually and steadily decreases from
the tip end 105a to the tail end 105b (for the purposes of the
present invention, a so-called "tapered" shaft design), even as the
outer diameter of the composite shaft 105 remains constant.
[0036] In the embodiment 100 depicted in FIGS. 1A and 1B, the
greater thickness of the composite shaft 105 at the tip end 105a
than at the tail end 105b results in the shaft 105 having a center
of mass that is closer to the tip end 105a than to the tail end
105b.
[0037] A shaft with a center of mass closer to the tip end than the
tail end is referred to as a shaft that is "front of center." The
percentage to which a shaft is "front of center" is equal to the
percent difference between the physical midpoint. of the shaft (by
length) and the center of gravity of the shaft, as compared to the
total length of the shaft. The front of center percentage value can
be calculated using the following equation, where "L" represents
the total length of the shaft, and "B" represents the distance from
the tail end of the shaft to the center of mass of the shaft:
Front of Center % = ( B L - 0.5 ) * 100 % ##EQU00001##
[0038] In some embodiments, the center of mass of the shaft 105 may
be between about 5% and about 20% front of center, or between about
10% and 15% front of center. In certain embodiments, the center of
mass of the shaft 105 is about 13% front of center.
[0039] As the center of mass moves closer to the tip end of the
shaft (i.e., as the percent front of center of the shaft
increases), the shaft 105 will have better stability during flight,
as the increased distance between the fletchings on the tail of the
shaft 105 and the center of gravity of the shaft 105 allow the
fletchings to more effectively stabilize the shaft 105 in flight,
straightening the shaft 105 by rotating the shaft 105 around its
center of pressure. However, as the percentage front of center
value of the shaft 105 increases, the shaft 105 will dive more
quickly due to the greater weight distribution in the nose end 105a
of the shaft 105, limiting the distance that the shaft 105 can fly.
In contrast, a shaft 105 with a lower percentage front of center
value will be less stable during flight, but will hold its
trajectory better and fly longer distances.
[0040] FIGS. 2A and 2B illustrate another embodiment 200 of a
composite shaft 205 having a hollow core 210. In this embodiment
200, like the embodiment 100 depicted in FIGS. 1A and 1B, the shaft
205 also has a constant outer diameter. However, instead of
gradually tapering in thickness like the embodiment 100 depicted in
FIGS. 1A and 1B, the shaft 205 of embodiment 200 includes three
distinct portions 205a, 205b, and 205c. In each one of the portions
205a, 205b, and 205c, the shaft 205 has a thickness that is
constant, but different than the thickness of each of the other
portions. For the purposes of the present invention, such a design
200 is known as a "stepped" shaft.
[0041] The shaft 205 is thickest in the portion 205a nearest the
tip of the shaft 205, less thick in the middle portion 205b, and
the least thick in the portion 205c nearest to the tail end of the
shaft 205. Correspondingly, the hollow core 210 of the shaft has
its largest outer diameter in the tail portion 210c, a smaller
outer diameter in middle portion 210b, and an even smaller outer
diameter in nose portion 210a. Like the embodiment 100 depicted in
FIGS. 1A and 1B, the stepped shaft embodiment 200 has a center of
gravity that is front of center.
[0042] In embodiment 200 displayed in FIGS. 2A and 2B, the stepped
shaft 205 has three portions 205a, 205b, and 205c. However, in
other embodiments, a stepped shaft may have two, three, four, or
another number of distinct stepped portions. Furthermore, in some
embodiments, the length of each portion may be equal to the length
of each of the other portions of the stepped shaft, while in other
embodiments, each portion of the stepped shaft may have a different
length. For example, in one embodiment, a stepped shaft composed of
three portions may have first and second portions having the same
length, with the third portion having a different length than those
first and second portions. In another embodiment, however, the
third portion will have the same length as the first and second
portions of that stepped shaft. By "tuning" the number of stepped
portions in the shaft, as well as the relative length of these
stepped portions of the shaft, a manufacturer of such shafts can
adjust the vibration frequency of the shaft design.
[0043] In some embodiments, some portions of the shaft are stepped,
while other portions of the same shaft are tapered. For example, in
one embodiment, a shaft has three portions, where the first and
third portions are stepped portions, each of these stepped portions
of the shaft having a constant thickness different than the other
stepped portion of the shaft (but identical outer diameters).
However, in a second portion of the shaft located between the
stepped first and third portions, the thickness of the shaft tapers
gradually and continuously down from a higher thickness in the
first portion of the shaft to a lower thickness in the third
portion of the shaft.
[0044] In embodiments 100 and 200 of the invention depicted in
FIGS. 1A-1B and 2A-2B, the shafts 105 and 205 include one or more
types of fibers. In these embodiments, the different types of
material fibers used to construct the shafts 105 and 205 may be
non-metallic or metallic fibers, including carbon fibers, titanium
fibers, stainless steel fibers, spring steel fibers, steel fibers,
aluminum fibers, cellulose fibers, fiberglass fibers, silicon
carbide fibers, magnesium fibers, and linearized polyethylene or
spectra.
[0045] To obtain an arrow or crossbow bolt shaft having a desired
selection of material and mechanical properties, a designer may
select desired material types and relative quantities of fibers
from which to manufacture a shaft. High-modulus carbon fibers
(having a modulus of about 400 gPa) can be used to construct a
shaft having relatively high stiffness and strength, few defects,
and small carbon fibers. Using intermediate-modulus carbon fibers
(having a modulus of about 285 gPa), on the other hand, will result
in a shaft that has relatively lower stiffness and/or strength in
comparison to a shaft made of high-modulus carbon fibers, but that
increases the margin for error in an archer's accuracy. For
example, the lower stiffness of an intermediate-modulus carbon
fiber shaft aids in negating the effects of the so-called "archer's
paradox" (the name given to the phenomenon in which an arrow
travels straight at a target at which a bow is pointed, even though
the arrow shaft must be pointed to the side of the target as it
rests against the bow)--a property known as the "dynamic spine" of
the shaft.
[0046] Metallic fibers, such as titanium or magnesium fibers,
impart different properties to a composite shaft. For example,
titanium or magnesium fibers can be hexagonally close-packed
together because of the orientation of the titanium or magnesium
atoms within the metal lattice. Such metallic fibers aid with
vibration damping upon release, resulting in a reduced loss of
kinetic energy during flight from wobbling/vibration of the arrow
or crossbow bolt. This reduced in-flight loss of kinetic energy,
due to the vibration damping properties of the metallic fibers,
ensures that the shaft strikes its target with greater velocity and
energy, resulting in increased penetrating power and effectiveness.
Furthermore, metallic fibers, such as titanium and steel, have
relatively high toughness, causing the metal fibers of the
composite shaft to absorb energy upon impact and reducing the
probability that the shaft will fracture or break.
[0047] To obtain a shaft having the desired combination of
stiffness, strength, toughness, vibration damping, and other
properties, a mix of carbon fibers and metallic fibers can be used
to construct composite shaft embodiments of the present invention.
Different material types and changes in the relative amounts of the
different fiber materials may be used to adjust the desired
characteristics of a composite shaft. In one embodiment of the
invention, for example, a composite shaft may be manufactured from
20% vibration-damping fibers (such as titanium and/or magnesium
fibers), which decrease vibration and wobbling and provide
toughness to the shaft, and 80% carbon fibers, which give the shaft
stiffness and strength.
[0048] The composite shafts of the present invention are
manufactured by forming the shafts around an inner mandrel, which
is then removed from the interior of the shaft, leaving behind the
hollow composite arrow or crossbow bolt shaft. In various
embodiments, the inner mandrel may be made from, for example,
aluminum, steel, or titanium. FIG. 3A illustrates an exemplary
inner mandrel 300. The outer diameter of inner mandrel 300 varies
in size along the length of inner mandrel 300, and the tapered
profile of inner mandrel 300 corresponds to the outer diameter of
the hollow inner core of a composite shaft that is formed around
inner mandrel 300. The inner mandrel 300 can be shaped by turning
the inner mandrel 300 on a lathe so that its outer diameter has the
desired profile for the hollow inner core of a composite shaft to
be manufactured around the inner mandrel 300. The inner mandrel 300
can be a tapered mandrel, a stepped mandrel, or a combination of
the two.
[0049] Various manufacturing processes can be utilized to
manufacture the composite shafts of the present invention. In a
first set of embodiments of the manufacturing processes, after an
inner mandrel 300 has been shaped to the desired profile, one or
more composite materials are wrapped around the inner mandrel 300.
This process is depicted in FIG. 3B, in which composite tape 310 is
being wrapped around inner mandrel 300, with inner mandrel 300
being tightly gripped in place by a machine during wrapping of the
tape 310. The wrapping of tape 310 is typically an automated
process performed by a machine. The machine for wrapping tape 310
may be a center-less tape wrapping machine or a "lathe" type
wrapping machine.
[0050] By altering the angle at which the tape 310 wraps around
inner mandrel 300, a designer may control the strength and other
mechanical properties of the composite shaft that is manufactured
around inner mandrel 300. The two main forces acting on such shafts
are: 1) tensional/compressional forces, which act longitudinally
along the main axis of a shaft, and which are caused, for example,
by a shaft striking a target head on; and 2) buckling forces, which
act radially outward from the longitudinal axis of an shaft, and
which result from the shaft striking a target at an angle (and not
directly head-on).
[0051] Wrapping the tape 310 more radially around inner mandrel 300
causes the resulting composite shaft to have more radial support,
allowing the shaft to better resist the buckling forces described
above. In some embodiments, therefore, the tape 310 is wrapped at a
more radial angle at the tip portion of the shaft, giving more
radial support to the shaft at the point nearest to where the shaft
strikes a target and helping that portion of the shaft resist the
buckling forces generated when the shaft strikes a target at an
angle. In areas of the shaft further from the tip end of the shaft,
the tape 310 may be wrapped at a more longitudinal angle around
inner mandrel 300, causing the shaft to have more longitudinal
support in those areas and be better able to resist the
tensional/compressional forces generated along the main axis of the
shaft.
[0052] To further vary the capabilities and properties of the
shaft, additional tape 310 may be laid along the length of the
inner mandrel 300 to provide additional axial stiffness, or wrapped
radially around desired portions of the inner mandrel 300 to
provide additional radial support. Two or more different tapes 310,
each made of fibers of different materials and/or different fiber
sizes can also be used in a single composite shaft, so that the
resulting shaft has the combination of properties desired by a
designer.
[0053] In some embodiments, the composite tape 310 is
pre-impregnated ("pre-preg") composite tape which is impregnated
with a thermoplastic. The thermoplastic may be a resin, and the
thermoplastic resin may be made of polyether ether ketone (PEEK),
polymethyl methacrylate (PMMA), acrylic, nylon, and/or
polyethylene.
[0054] In some embodiments of the pre-preg tape manufacturing
process, after the pre-preg tape 310 has been wrapped around inner
mandrel 300, a polypropylene or nylon tape is then wrapped around
the pre-preg composite tape 310. Inner mandrel 300 and the layers
of tape 310 wrapped around it are then placed in an oven, and cured
at an appropriate temperature for the particular thermoplastic
resin used in the pre-preg tape 310. As inner mandrel 300 and the
wrapped layers of tape 310 bake in the oven, the polypropylene or
nylon tape shrinks, applying compressive force to the pre-preg tape
310 and inner mandrel 300 and forcing air out of the entire
pre-preg tape 310 and inner mandrel 300 assembly, resulting in a
composite shaft having a varying inner profile being formed around
inner mandrel 300.
[0055] In some other embodiments of the pre-preg tape manufacturing
process, instead of wrapping the pre-preg tape 310 and inner
mandrel 300 with nylon or polypropylene tape, the pre-preg tape 310
and inner mandrel 300 can be placed in an autoclave. The pressure
and temperature are then elevated within the autoclave, curing the
pre-preg tape 310 and forcing air out of the entire pre-preg tape
310 and inner mandrel 300 assembly, resulting in a composite shaft
having a varying inner profile being formed around inner mandrel
300.
[0056] In a second type of embodiments of the manufacturing
process, inner mandrel 300 is manually wrapped with a dry composite
fiber mat that is then coated with liquid thermoset resin--a
process known as a "wet layup" process. The liquid thermoset resin
can be an epoxy, polyester, vinylester, phenolic, and/or urethane
thermoset resin. The thermoset resin is forced to infiltrate the
fabric of the composite fiber mat wrapped around the inner mandrel
300, and then the wrapped inner mandrel is placed into a press and
molded at an elevated temperature to create a composite shaft
around inner mandrel 300. In some embodiments, the elevated
temperature at which the wrapped, soaked fabric is molded is
approximately 200 degrees Fahrenheit.
[0057] In a third type of embodiments of the manufacturing process,
the composite shaft can be manufactured around inner mandrel 300
using a process known as "roll wrapping." In the roll wrapping
process, a woven composite fabric that is pre-impregnated with a
thermoplastic resin, such as polyether ether ketone (PEEK),
polymethyl methacrylate (PMMA), acrylic, nylon, or polyethylene, is
wrapped around inner mandrel 300 by rolling inner mandrel 300
between two plates. The pre-impregnated woven composite fabric is
self-adhesive, causing the pre-preg woven composite fabric to
adhere to inner mandrel 300 for further processing. The pre-preg
woven fabric adhered to inner mandrel 300 can then be wrapped with
nylon or polypropylene tape and cured, as described above, or can
be cured in an autoclave, also as described above.
[0058] Whether the composite shaft is manufactured using the
pre-preg tape, wet layup, or roll wrapping methods described above,
after curing the composite shaft, inner mandrel 300 is removed from
the interior of the shaft, leaving a composite tube having a
profiled hollow interior (whether tapered, stepped, or a
combination of the two). The exterior of the composite shaft can
then be sanded, ground, or otherwise machined so that the composite
shaft has the final exterior dimensions desired by the
manufacturer--for example, a constant outer diameter along the
length of the composite shaft.
[0059] After the composite shaft has been sanded or ground to the
desired final exterior dimensions, in some embodiments, the
composite shaft is coated with a thin polymeric tube or fabric to
reduce the coefficient of friction on the exterior surface of the
composite shaft. In some embodiments, the polymeric tube or fabric
includes polypropylene, polyethylene, vinyl, or nylon.
[0060] In addition to the various wrapping, curing, and
sanding/grinding manufacturing processes described above, in other
embodiments of the present invention, the composite shaft is
manufactured using a triaxial braiding process.
[0061] FIGS. 4 and 5 depict an embodiment of a triaxial braiding
manufacturing process to assemble a composite shaft 400 made up of
triaxially braided fibers 425, 435, and 445. Fibers 425, 435, and
445 are braided around a profiled inner mandrel 410, which moves in
direction 450 along the longitudinal axis of inner mandrel 410
through the triaxial braiding apparatus. Inner mandrel 410 can be a
tapered mandrel, a stepped mandrel, or a combination of the
two.
[0062] As illustrated by the embodiment of the manufacturing
process depicted in FIG. 4, threads 425 are unspooled off of
bobbins 420a and 420b and braided at a first angle to the
longitudinal axis of inner mandrel 410, threads 435 are unspooled
off of bobbins 430a and 430b and braided at a second angle to the
longitudinal axis of inner mandrel 410, and threads 445 are
unspooled off of longitudinal thread guides 440a and 440b parallel
to the longitudinal axis of inner mandrel 410. While the exemplary
illustration of FIG. 4 depicts only two bobbins 420a and 420b
unspooling threads 425, two bobbins 430a and 430b unspooling
threads 435, and two longitudinal thread guides 440a and 440b, a
triaxial braiding assembly for manufacturing composite arrow or
crossbow bolt shafts will have a greater number of bobbins 420a-b
and 430a-b and longitudinal thread guides 440a and 440b surrounding
inner mandrel 410, and a correspondingly greater number of threads
425, 435, and 445 being triaxially braided onto inner mandrel 410.
The particular number of bobbins and longitudinal thread guides
utilized in the triaxial braiding manufacturing process depends on
the size of inner mandrel 410 upon which the threads are being
braided.
[0063] As inner mandrel 410 moves along its longitudinal axis 450
through the triaxial braiding plane 460, threads 425, 435, and 445
are unspooled from bobbins 420a-b and 430a-b and longitudinal
thread guides 440a and 440b and converge together into a braid
within zone 470. And as inner mandrel 410 moves along its
longitudinal axis 410 through the triaxial braiding plane 460,
bobbins 420a-b and 430a-b rotate around inner mandrel 410 on the
triaxial braiding plane 460 in a spiraling pattern, as depicted by
FIG. 5. FIG. 5 is a top-down view of inner mandrel 410 in the
triaxial braiding apparatus, illustrating bobbin 420 moving along
spiraling path 428 around inner mandrel 410 on triaxial braiding
plane 460 to braid thread 425 onto inner mandrel 410, and bobbin
430 moving along spiraling path 438 in the opposing direction
around inner mandrel 410 on triaxial braiding plane 460 to braid
thread 435 onto inner mandrel 410.
[0064] While the exemplary illustration in FIG. 5 only depicts two
bobbins 420 and 430 discussed above, a triaxial braiding assembly
for manufacturing composite arrow or crossbow bolt shafts will have
a greater number of bobbins 420 and 430 surrounding inner mandrel
410 and moving along paths 428 and 438, with the particular number
of bobbins depending on the size of inner mandrel 410.
[0065] By varying the speed at which inner mandrel 410 moves along
its longitudinal axis 450 through the triaxial braiding plane 460
in comparison to the speed at which bobbins 420 and 430 rotate
around inner mandrel 410 on the triaxial braiding plane 460 along
paths 428 and 438, a manufacturer of composite shaft 400 can adjust
the angle of the threads 425 and 435 in the composite shaft 400 in
comparison to the longitudinally oriented threads 445. By slowing
the relative speed of the longitudinal movement 450 of inner
mandrel 410, threads 425 and 445 will be relatively more radially
oriented, providing more radial support for composite shaft 400 to
resist buckling forces caused by the shaft 400 striking a target
off-center. Conversely, by increasing the relative speed of the
longitudinal movement 450 of inner mandrel 410, threads 425 and 445
will be relatively more longitudinally oriented, providing more
axial support for composite shaft 400 to resist
tensional/compressional forces along the longitudinal axis of the
composite shaft 400.
[0066] FIG. 6 illustrates an exemplary embodiment of a triaxial
braiding pattern of fibers 425, 435, and 445, resulting from the
triaxial braiding process depicted in FIGS. 4 and 5. While fibers
425 and 435 are depicted in FIG. 6 as being interwoven at a
consistent 45 degree angle in comparison to longitudinal fibers
445, as discussed above, fibers 425 and 435 may be braided at
varying angles to longitudinal fibers 445 at different points in
the composite shaft 400. For example, the fibers 425 and 435 may be
more radially oriented (to provide more support against buckling
forces) at the tip portion of the shaft 400, but more
longitudinally oriented at the tail portion of the shaft 400.
[0067] In addition to varying the angles of fibers 425 and 435 as
discussed above, fibers 425, 435, and 445 may include fibers of one
or more different materials. For example, fibers 425, 435, and 445
may include high-modulus or intermediate-modulus carbon fibers,
titanium fibers, stainless steel fibers, spring steel fibers, steel
fibers, aluminum fibers, cellulose fibers, fiberglass fibers,
silicon carbide fibers, magnesium fibers, and linearized
polyethylene or spectra. In one exemplary embodiment, fibers 425,
435, and 445 are made of 20% vibration-damping fibers (such as
metallic titanium and/or magnesium fibers), which decrease
vibration and wobbling and provide toughness to the shaft 400, and
80% carbon fibers, which give the shaft 400 stiffness and strength.
Fibers 425, 435, and 445 may also vary in their thickness, which
also affects the strength, stiffness, and other properties of the
composite shaft 400.
[0068] After the tri-axial braiding process is completed to form a
braided pattern, as shown in FIG. 6, the composite shaft 400 is
cured. In some embodiments, fibers 425, 435, and 445 are
pre-impregnated with a thermoplastic resin, such as polyether ether
ketone (PEEK), polymethyl methacrylate (PMMA), acrylic, nylon, or
polyethylene. In these embodiments, the pre-impregnated fibers 425,
435, and 445 of composite shaft 400 can be wrapped in polypropylene
or nylon tape and then cured in an oven, or the pre-preg fibers
425, 435, and 445 can be cured in an autoclave under elevated
temperature and pressure.
[0069] In other embodiments, in which the fibers 425, 435, and 445
are not pre-impregnated with a thermoplastic, the fibers 425, 435,
and 445 of the composite shaft 400 can be coated with liquid
thermoset resin in a wet layup process. The thermoset resin may be
epoxy, polyester, vinylester, phenolic, or urethane. After the
thermoset resin infiltrates fibers 425, 435, and 445, the
tri-axially braided fibers 425, 435, and 445 and the profiled inner
mandrel 410 are placed into a press and molded at an elevated
temperature to create a composite shaft 400 around inner mandrel
410. In some exemplary embodiments, the elevated temperature at
which the wrapped, soaked braided fibers 425, 435, and 445 are
molded is approximately 200 degrees Fahrenheit.
[0070] After the fibers 425, 435, and 445 of the composite shaft
400 are cured, inner mandrel 410 is removed from the interior of
composite shaft 400, leaving a hollow, profiled interior in the
composite shaft 400, the hollow core of composite shaft 400 having
an outer diameter that corresponds to the outer diameter of the
profiled inner mandrel 410. The triaxial braiding manufacturing
method allows the fibers 425, 435, and 445 to be woven around inner
mandrel 410 to form a composite shaft 400 having a constant,
uniform outer diameter, reducing the need to sand or grind the
composite shaft 400 after the curing process has completed, and
avoiding material waste. In some embodiments, the composite shaft
400 is then coated with a thin polymeric tube or fabric to reduce
the coefficient of friction on the exterior surface of the
composite shaft 400. In some embodiments, the polymeric tube or
fabric includes polypropylene, polyethylene, vinyl, or nylon.
* * * * *