FIBER PRECURSOR

Abstract

The present invention provides an improved fiber precursor, and methods for employing such to enhance the structural reinforcement of composite structures. The precursor is comprised of one or more fibrous filaments positioned within the precursor so that the filaments within each fiber are oriented at an angle offset from the axis of the length of the precursor. The offset of these filaments can be accomplished, for example, by twisting a plurality of filaments into a continuous spiral to form the precursor, or by wrapping a collection of colinear filaments about a central core, or by braiding plurality of filaments to form the precursor. The angle of offset at which the twisted, braided or wrapped fibers are positioned can be varied as a function of the twisting, braiding or wrapping process (angle of wrap, tension upon the twisting or wrapping fibers, degree of rotational twisting applied to the fibers per length of precursor, etc.). The offset angle can be arbitrarily chosen to achieve the desired shear properties based upon the particular composite structure, the manufacturing method(s) being employed, and the environment in which the precursor will be utilized.

Claims

1. A fiber precursor comprising: a plurality of twisted fibers arranged to form a continuous cylindrical element, wherein the fibers are predominantly aligned to twist at a fixed angle offset from a longitudinal axis of the continuous cylindrical element.

2. The fiber precursor of claim 1, wherein the fibers comprise comingled resin fibers and reinforcement fibers.

3. The fiber precursor of claim 2 wherein the resin fibers comprise thermoplastic fibers.

4. The fiber precursor of claim 2 wherein the reinforcement fibers comprise carbon fibers.

5. The fiber precursor of claim 1, wherein the fibers are twisted about the longitudinal axis to form the continuous cylindrical element.

6. The fiber precursor of claim 1, wherein the fixed angle is offset from the longitudinal axis by 45 degrees.

7. The fiber precursor of claim 1, wherein the plurality of twisted fibers comprises about 1,000 to about 50,000 fibers.

8. A method for fabricating fiber precursor, comprising the step of: twisting, about a central axis, a plurality of fibers so that the fibers become predominantly aligned to a fixed angle offset from the central axis and form a continuous cylindrical element having a longitudinal axis along the central axis.

9. The method of claim 8 wherein the fibers comprise comingled resin fibers and reinforcement fibers.

10. The method of claim 9 wherein the resin fibers comprise thermoplastic fibers.

11. The method of claim 9 wherein the reinforcement fibers comprise carbon fibers.

12. The method of claim 8 wherein the fixed angle of offset from the central axis is 45 degrees.

13. The method of claim 8 wherein the plurality of fibers comprises between 1,000 and 50,000 fibers.

14. A fiber precursor comprising: a straight core having a longitudinal axis and being comprised of a first bundle of a plurality of colinear fibers; and at least one additional bundle of a plurality colinear fibers wrapped around the straight core so as to form a coil about the straight core, wherein the coil comprises a plurality of sections wherein each section of the coil is offset from the longitudinal axis of the straight core by a fixed angle wherein the fixed angle for each section is the same fixed angle.

15. The fiber precursor of claim 14 wherein the first bundle and the at least one additional bundle have circular cross-sections having a cross-sectional diameter.

16. The fiber precursor of claim 15 wherein the cross-sectional diameter of the first bundle is substantially equal to the cross-sectional diameter of the at least one additional bundle.

17. The fiber precursor of claim 15 wherein the cross-sectional diameter of the first bundle is greater than the cross-sectional diameter of the at least one additional bundle.

18. The fiber precursor of claim 15 wherein the cross-sectional diameter of the at least one additional bundle is greater than the cross-sectional diameter of the first bundle.

19. The fiber precursor of claim 14 wherein the first bundle has a rectangular cross-section and the at least one additional bundle has a circular cross-section.

20. The fiber precursor of claim 14 wherein the first bundle has a rectangular cross-section and the at least one additional bundle comprises a flexible tape.

21. The fiber precursor of claim 14 wherein the first bundle and the at least one additional bundle comprise comingled resin fibers and reinforcement fibers.

22. The fiber precursor of claim 21 wherein the resin fibers comprise thermoplastic fibers.

23. The fiber precursor of claim 21 wherein the reinforcement fibers comprise carbon fibers.

24. The fiber precursor of claim 14 wherein the fixed angle is 45 degrees.

25. A method for fabricating a fiber precursor, comprising the step of: wrapping at least one bundle comprised of a plurality colinear fibers around a straight core comprised of a bundle of colinear fibers having a longitudinal axis, so form at least one coil with the at least one bundle about the straight core wherein each section of the at least one coil is offset from the longitudinal axis of the straight core by a fixed angle wherein the fixed angle for each section is the same fixed angle.

26. The method of claim 25 wherein the at least one bundle wrapped about the straight core and the bundle comprising the straight core each have circular cross-sections each having a cross-sectional diameter.

27. The method of claim 26 wherein the at least one bundle wrapped about the straight core and the bundle comprising the straight core have a substantially equal cross-sectional diameters.

28. The method of claim 26 wherein the cross-sectional diameter of the at least one bundle wrapped about the straight core is greater than the cross-sectional diameter of the bundle comprising the straight core.

29. The method of claim 26 wherein the cross-sectional diameter of the bundle comprising the straight core is greater than the cross-sectional diameter of the at least one bundle wrapped about the straight core.

30. The method of claim 25 wherein the at least one bundle wrapped about the straight core has a rectangular cross-sectional and the bundle comprising the straight core has a circular cross-section.

31. The method of claim 25 wherein the at least one bundle wrapped about the straight core comprises a flexible tape and the bundle comprising the straight core has a rectangular cross-section.

32. The method of claim 25 wherein the at least one bundle wrapped about the straight core and the bundle comprising the straight core comprise comingled resin fibers and reinforcement fibers.

33. The method of claim 32 wherein the resin fibers comprise thermoplastic fibers.

34. The method of claim 32 wherein the reinforcement fibers comprise carbon fibers.

35. The method of claim 32 wherein the fixed angle is 45 degrees.

36. A fiber precursor comprising: three or more bundles of a plurality colinear fibers interlaced with one another so as to form an interlocking, repeating pattern.

37. The fiber precursor of claim 36, wherein the plurality of colinear fibers comprises comingled resin fibers and reinforcement fibers.

38. The fiber precursor of claim 37 wherein the resin fibers comprise thermoplastic fibers.

39. The fiber precursor of claim 38 wherein the reinforcement fibers comprise carbon fibers.

40. The fiber precursor of claim 37, wherein the interlocking, repeating pattern is a flat braid.

41. The fiber precursor of claim 40, wherein the flat braid is a regular braid.

42. The fiber precursor of claim 36, wherein the interlocking, repeating pattern is a three-dimensional braid.

43. The fiber precursor of claim 42, wherein the three-dimensional braid is a tubular braid.

44. The fiber precursor of claim 36, wherein the plurality of colinear fibers comprises about 1,000 to about 50,000 fibers.

45. A method for fabricating a fiber precursor, comprising the step of: interlacing three or more bundles of a plurality colinear fibers so as to form a repeating pattern.

46. The method of claim 45 wherein the plurality of colinear fibers comprise comingled resin fibers and reinforcement fibers.

47. The method of claim 46 wherein the resin fibers comprise thermoplastic fibers.

48. The method of claim 46 wherein the reinforcement fibers comprise carbon fibers.

49. The method of claim 45 wherein the repeating pattern is a flat braid.

50. The method of claim 49 wherein the flat braid is a regular braid.

51. The method of claim 45 wherein the repeating pattern is a three-dimensional braid.

52. The method of claim 51 wherein the three-dimensional braid is a tubular braid.

53. The method of claim 45 wherein the plurality of colinear fibers comprises about 1,000 to about 50,000 fibers.

54. An additive manufacturing process, comprising the steps of: heating a fiber precursor selected from the group consisting of a plurality of fibers arranged to form a continuous cylindrical element, wherein the fibers are predominantly aligned to a fixed angle offset from a longitudinal axis of the continuous cylindrical element; a straight core having a longitudinal axis and being comprised of a first bundle of a plurality of colinear fibers and at least one additional bundle of a plurality colinear fibers wrapped around the straight core so as to form a coil about the straight core, wherein each section of the coil is offset from the longitudinal axis of the straight core by a fixed angle wherein the fixed angle for each section is the same fixed angle, and three or more bundles of a plurality of colinear fibers interlaced with one another so as to form an interlocking, repeating pattern to a temperature at which the fiber precursor becomes nominally plastic; and depositing the heated fiber precursor upon a build surface in a controlled pattern.

55. The additive manufacturing process of claim 54 wherein the depositing of the heated fiber precursor in the controlled pattern creates a three-dimensional object.

56. The additive manufacturing process of claim 54 wherein the heated fiber precursor is cooled prior to being heated.

57. The additive manufacturing process of claim 54 wherein the heated fiber precursor is deposited via a nozzle.

Description

DESCRIPTION OF THE DRAWINGS

[0012] The features, aspects, and advantages of the present invention will become better understood with regard to the following description, appended claims, and accompanying drawings in which:

[0013] FIG. 1 is a perspective view of equipment typically utilized to perform TFP.

[0014] FIG. 2 is a perspective view of an exemplary apparatus for twisting fibers to form an improved fiber precursor.

[0015] FIGS. 3A and 3B depict the process of wrapping a central fiber core with a fiber bundle having a substantially circular cross-section to form an improved fiber precursor.

[0016] FIGS. 4A and 4B depict an alternate process of wrapping a central fiber core with a fiber bundle having a substantially circular cross-section to form an improved fiber precursor.

[0017] FIGS. 5A, 5B and 5C depict the process of wrapping a central fiber core with a flexible tape to form an improved fiber precursor.

[0018] FIGS. 6A, 6B and 6C depict an alternate process of wrapping a central fiber core with a flexible tape to form an improved fiber precursor.

[0019] FIG. 7 depicts a section of an improved fiber precursor formed by braiding three bundles.

[0020] FIG. 8 is a cross-sectional view of an additive manufacturing manifold.

DETAILED DESCRIPTION

[0021] FIG. 2 is a perspective view of an exemplary apparatus adapted to mechanically twist comingled fibers to form a fiber precursor in accordance with a particular embodiment of the instant invention. As shown a collection of fibers 202, typically consisting of about 1000 to about 50,000 individual fibers are drawn forward at a continuous rate, V.sub.1 (as indicated by arrow 204) through the action of roller sets 206 and 208. The fibers are twisted at a continuous rate (for this example, in a clockwise direction at a rate of .sub.1 as indicated by arrow 210) as they are drawn forward so as to cause the collection of fibers to form twisted precursor 212. Twisted precursor 212 is then passed through die 214 which serves to trim any stray fibers 216 from the precursor. The rate at which the fibers are drawn forward (V.sub.1) in combination with the rate at which the fibers are twisted (.sub.1), and the distance between roller sets 206 and 208 determines the angle of offset (.sub.T) the twisted fibers assume with respect to the longitudinal axis 218 of precursor 212.

[0022] Increasing V.sub.1 will reduce offset angle .sub.T, increasing twisting rate .sub.1 will increase .sub.T, and reducing in the distance (d.sub.r) between roller sets 206 and 208 decreases .sub.T. These variables can be altered depending upon the desired offset angle, the physical characteristics of the fibers being drawn, the desired density of the resulting precursor, as well as other considerations that might arise based upon the specific apparatus being employed to perform the formation of the precursor and the environmental conditions in which it is being formed.

[0023] As stated above, the particular offset angle, .sub.T, can be varied by manipulating V.sub.1, .sub.1, and d.sub.r. Although the offset angle is not restricted to any particular value, well-known and generally accepted design theory for fiber composites, such as those set forth in Chou, T., Microstructural Design of Fiber Composites, Thermoplastic behavior of laminated composites, pp. 39-46, FIG. 2.4 (Cambridge University Press 1992), which is incorporated by reference herein, prescribe that an offset angle of 45, with respect to the plane of the substrate surface to which the precursor is affixed, would maximize the shear property of the resultant precursor/substrate structure. Note that the surface of the substrate would be aligned with the longitudinal axis of precursor affixed thereto in the manner illustrated in FIG. 1, and that this alignment results in the twisted fibers of precursor 212 being offset from the plane of the substrate surface by angle .sub.T. Consequently, a precursor comprised of twisted fibers having an offset angle .sub.T of 45 would be desirable for applications where the maximization of shear strength is the desired outcome.

[0024] Comingled fibers 202 utilized to form the twisted precursor are typically comprised of both reinforcing fibers and thermoplastic resin fibers. Reinforcing fibers include fibers comprised of materials such as carbon, glass, aramid, ultra-high molecular weight polyethylene (UHMPE), boron, steel, copper, and carbon nanotubes. Thermoplastic resin fibers include fibers comprised of materials such as nylon 66, nylon 6, nylon 12, polypropylene (PP), polyethylene (PE), polyester, polyether ether ketone (PEEK), polyphenylene sulfide (PPS), polyetherimide (PEI), and polyvinylidene difluoride (PVDF). The distribution of these two types of fibers within the twisted precursor is critical with respect to the resultant precursor/substrate structure, as this ratio determines the fiber/volume make-up of that structure. This ratio can be adjusted based upon the particular application and environment for which the precursor/laminate structure is being fabricated. However, regardless of the particular ratio, it is desirable to ensure that there is a uniform distribution of the thermoplastic resin fibers among the reinforcing fibers within the precursor. This uniform distribution provides for a precursor that exhibits predictable, consistent characteristics throughout the fabrication process of the structure, and consistent performance with respect to mechanical properties, such as shear strength, once incorporated into the structure.

[0025] An additional embodiment of the invention is illustrated in FIG. 3A. As shown, a straight core 302, having a diameter of .sub.C1, is fabricated from a bundle of colinear fibers. Straight core 302 is then wrapped with colinear fiber bundle 304, which has a diameter of .sub.SR1, so as to form a coil about the straight core with the wrapped colinear bundle. The wrapping is performed at a fixed angle of .sub.1 with respect to the longitudinal axis of straight core 302, so that each section of the coil is offset from the longitudinal axis of the straight core by an angle of .sub.1. This results in the fabrication of a wrapped precursor 306 having an effective diameter of (.sub.C1+2.sub.SR2). Assuming wrapped precursor 306 is affixed to the surface of a substrate in a manner similar to that illustrated in FIG. 1, the angle, .sub.1, at which bundle 304 is wrapped around straight core 302 would be the angle at which the axes of the colinear fibers within bundle 304 would be offset from the plane of the substrate surface. FIG. 3B provides a cross-sectional view of wrapped precursor 306. As with the first embodiment of the invention, the fibers within straight core 302 and bundle 304 are comprised of comingled fibers (both reinforcing fibers and thermoplastic resin fibers). The distribution of these two types of fibers being chosen to suit the particular application and environment for which the precursor is being fabricated.

[0026] The diameters of the straight core and colinear fiber, as well as the wrapping angle can be varied as needed for particular applications. In FIG. 4A, straight core 402, comprised of comingled fibers, having a diameter of .sub.C2 is wrapped at angle .sub.2 with comingled colinear bundle 404, which has a diameter of .sub.SR2. As shown, .sub.C2 is approximately three times .sub.SR2. The additional tensile strength imparted to a precursor/substrate structure by affixing wrapped precursor 406 thereto is directly proportional to the diameter of straight core 402. Similarly, the additional shear strength imparted to a precursor/substrate structure by affixing wrapped precursor 406 thereto is directly proportional to the diameter of wrapped bundle 404 and angle of the wrapping. FIG. 4B provides a cross-sectional view of wrapped precursor 406. Embodiments of this invention are not limited to precursors or fiber bundles having a substantially circular cross-section. For example, a flexible tape having a rectangular cross-section could be fabricated from a grouping of comingled, colinear fibers (typically about 1,000 to about 50,000 individual fibers). FIG. 5A provides a cross-sectional and top view of such a tape. Tape 502 has a width of w.sub.T and a thickness of t.sub.T. As shown in FIG. 5B, straight core 504, comprised of comingled fibers, having a diameter of .sub.C3 is wrapped at angle .sub.3 with tape 502 to form precursor structure 506. FIG. 5C provides a cross-sectional view of wrapped precursor 506.

[0027] FIGS. 6A-C provide an illustration of yet another embodiment of the invention, similar to that depicted in FIGS. 5A-C. FIG. 6A shows flexible tape 602 (fabricated from a bundle of comingled, colinear fibers or through a slurry bath or melt extrusion impregnation) and having a width w.sub.T and a thickness t.sub.T. Tape 602 is wrapped around straight core 604 at angle .sub.4 to form precursor 606. However, straight core 604 is shown in FIG. 6B to have a rectangular cross-section of width w.sub.C and height h.sub.C. Straight core 604 is fabricated from a bundle of comingled, colinear fibers that have been formed into rectangular solid, either by heating the bundle so as to melt all or some of the thermoplastic resin fibers within the comingled bundle that comprises straight core 604, or by the addition of a resin or other binder. As shown in FIG. 6C, precursor 606 has a rectangular cross-section with a height (h.sub.C+2t.sub.T) and a width of (w.sub.C+2t.sub.T).

[0028] It will be understood that although FIGS. 6A-C depict a straight core having a rectangular cross-section, other cross-sectional geometries could be utilized in further embodiments of the invention (triangular, oval, trapezoidal, etc.). Furthermore, the core need not be a straight core. Embodiments having curved cores, circular cores, or cores of other complex configurations are within the scope of the present invention. In addition, the wrapped core embodiments of FIGS. 3A-B, 4A-B, 5A-C and 6A-C are not limited to a single bundle or single layer being wrapped about a core. Multiple layers of identical, or dissimilar bundles can be wrapped about a core to suit the particular application and environment in which the precursor will be utilized.

[0029] Yet another embodiment of the invention is depicted in FIG. 7. In this embodiment, a braided precursor (700) is formed from three bundles (702, 704 and 706) of colinear fibers (reinforcement fibers, or comingled bundles of reinforcement fibers and thermoplastic resin fibers) which are braided together. This braiding serves to vary the angle at which the direction of the colinear fibers within each bundle are offset from the longitudinal axis of the overall braided precursor. As shown, the offset angle varies from .sub.MAX (which can approach 90 depending upon the braiding pattern) to .sub.MIN (which is shown to be 0 for the embodiment illustrated in FIG. 7). This variation of the offset angle results in the braided precursor exhibiting both significant tensile strength (a function of the portions of braided bundles having an offset angle approaching 0, and significant shear strength (a function of the portions of braided bundles having an offset angle approaching .sub.MAX). The braiding pattern shown in FIG. 7 is known as a regular braid and is considered a flat braid. Other, more complex flat braid patterns (such as the regular triaxial, diamond biaxial, diamond triaxial, and Hercules), as well as three-dimensional braid patterns (such as tubular or helical braiding) are well known in the textile art and could be utilized to create precursors in accordance with the instant invention.

[0030] Each of the embodiments of the precursor invention discussed above have been described as being primarily utilized in the fabrication of precursor structure. These structures typically require additional manufacturing processes, such as injection molding, autoclave curing, out-of-autoclave (OOA) curing, liquid molding and hot pressing, to be performed upon the precursor/substrate structures before a finished product or component is created.

[0031] The precursors disclosed may also be employed in manufacturing processes not requiring the introduction of, or attachment to, a substrate. For example, the twisted precursor of FIG. 2 could be created using a ratio of thermoplastic resin fibers to reinforcing fibers that resulted in a precursor having physical properties suited for use in an additive manufacturing process, such as fused filament fabrication (FFF). An example of an FFF deposition manifold 800 is shown in FIG. 8.

[0032] In FFF, a precursor filament 802 is deposited from a deposition nozzle 804 onto build surface 806. A twisted precursor (such as the one illustrated in FIG. 2), a wrapped precursor (FIGS. 3B, 4B, 5B, 6B), or a braided precursor (FIG. 7), properly dimensioned to be fed through manifold 800 via filament tube 808, would pass through cooling block 810 and heating block 812. The cooling, and then successive heating of precursor filament 803 causes the precursor to undergo thermal and mechanical changes. The temperatures of the blocks 810 and 812 and the resin-to-reinforcement fiber ratio of precursor filament 802 are chosen so that precursor filament 802 is a plastic state as it is deposited upon the build surface. When in a plastic state, the precursor filament can be formed into a shape and will retain that shape. The plastic state for various materials is well known to one skilled in the art and not described in detail herein. Deposition proceeds in a controlled pattern on the build surface to construct a 3D object from successive layers of precursor filament.

[0033] Although the invention herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present invention. It is therefore to be understood that numerous modifications may be made to the illustrative embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims.