Ribbonizing method and apparatus

Abstract: A ribbonizing apparatus and method for forming a fiber band from a plurality of fiber tows extending along respective fiber tow pathways. The ribbonizing apparatus includes an assembly for selectively heating at least a respective one of the plurality of fiber tows as the fiber tow extends along the fiber pathways. When not needed, the heat is removed from the fiber tow. A plurality of embodiments for accomplishing the method are contemplated.

Description: The present invention is related to composite structures manufacturing methods and apparatus for practicing such methods. More particularly, the present invention is directed to a method and apparatus for making pre-impregnated multi-filament tows or rovings into a flat ribbon of predetermined thickness and width that can be processed through a delivery head and placed onto a mandrel surface for forming tubular articles. In present fiber placement systems, fibrous rovings or tows, impregnated with a thermosetting resin, are wound in a helical pattern in a number of superimposed layers onto a mandrel to produce a tubular article. Various methods are known in the art of manufacturing composite structures, including hand lay-up, automated tape lay-up, filament winding, and fiber placement. The present invention applies to the area of fiber placement. Examples of such systems can be found in U.S. Patent Nos. 4,699,683 and 4,877,471, assigned to Boeing Company, Seattle, Washington. In addition EP-A-370 507 discloses a filament winding device, incorporating a ribbonizing apparatus according to the preamble of claim 1, which applies superimposed layers of fibrous rovings or tows, impregnating with a thermosetting resin, in a helical pattern onto a mandrel to produce a generally tubular article having varying contours, as well as a method of ribbonizing a plurality of fiber tows according to the preamble of claim 17. An object of the present invention is to improve the processes and apparatusses in which preimpregnated multi-filament tows, or rovings, are used. The improvements particularly are directed to the manner of controlling the ply thicknesses and widths of the tape lay-up. The following four mechanisms are utilized in a method and apparatus for forming a ribbon from a plurality of fiber tows: a spacing device; a heating device; a spreading device; and a cooling device. Three alternative embodiments are described which improve the ribbonizing process, viz., a tow lift system, a bi-metallic system, and an independent zone system. In a first embodiment, referred to as the tow lift system, means are provided to accommodate independent tow cutting and adding in a fiber delivery head, as disclosed in EP-A-370 507 and US-A-5,290,389. When a tow is cut from the band, the tows remain in contact with the heated bars, or tubes, of the ribbonizer. It is preferable to remove the stationary tows from contact with the heated tubes at that time. Three heater tubes are utilized in the first embodiment whereby the ribbonizing of each individual tow is independent of the other tows. Each tow has an actuation device such as an electric solenoid or pneumatic cylinder that actuates a rack and gear to raise the tows and make contact therewith with the ribbonizing bars. Such actuation can be selective by means of computer control. The entry spacing, tube heating, and tow cooling and be the same as that described with reference to the first embodiment. The tube that houses the heater is segmented so that individual rotation for each tow is possible. In a second embodiment, referred to as the bi-metallic system, individual tow cutting and adding is also accommodated. The ribbonizing actuator of this embodiment is two dissimilar metals bonded together. One metal acts as the heat source, and the other as the actuator. As power is applied, the metals heat, expand, and lengthen. With the material being assembled in a arc, the arc grows and presses the metals against a respective individual fiber tow. Between the heat of the metal and the pressure of the metal expanding the tow is spread to a desired width and thickness. In a third embodiment, again individual heaters are provided for the individual fiber tows. The heating element is wrapped around a insulator and has a abrasive resistant conductor placed over the heating element. The fiber tow passes over the conductor surface and is spread, as required. When the tow is required, its respective heater has power applied. When the tow is cut and remains stationary, the heater is turned off. In view of the foregoing description, the ribbonizing apparatus, according to the present invention, can be defined as including: (a) means defining a plurality of pathways for the plurality of fiber tows; and (b) means for selectively heating respective ones of the plurality of fiber tows as the fiber tows extend along respective ones of the pathways. Specifically according to the invention, the fiber tows have a predeterminate width and thickness, and the means for selectively heating include (i) means for transferring heat to respective ones of the plurality of fiber tows for controlling the width and the thickness of the fiber tows and (ii) means for terminating heat transfer to the respective ones of the plurality of fiber tows. More specifically, the means for selectively heating include means for effecting selective contact of the fiber tows with a source of heat. Further, the means for effecting selective contact of the fiber tows include means for moving selective ones of the fiber tows, in a direction transverse to the fiber tow path, for contact with the source of heat. Still further, in one embodiment, the plurality of fiber tows extend transversely of the fiber tow pathways, the source of heat include a heating bar extending transversely across the plurality of fiber tows, and the means for effecting selective contact include means for moving selective ones of the fiber tows for contact with the heating bar. In a particular embodiment of the invention, the means for effecting selective contact of the fiber tows include respective cam members which are selectively rotatable for engaging and moving respective fiber tows toward the source of heat and away from the source of heat. Further in accordance with this embodiment, the cam members have heat conductive portions for engaging the tows during movement of the respective fiber tows toward the source of heat, and have heat insulative portions for engaging the respective fiber tows when the fiber tows are removed from contact with the source of heat. Still further, each of the cam members is in driving connection with a respective power actuator assembly for rotating the cam members. Each of the power actuator assemblies include a linear actuator, such as an air-actuatable cylinder device, or other suitable actuator. Further, each of the cam members has a toothed segment, and the power actuator assembly includes a rack member in engagement with a respective toothed segment for rotating a respective cam member. More specifically according to this embodiment, a pair of cam members are provided for each of the fiber tows, spaced in the direction of a respective one of the fiber tow pathways, wherein the source of heat includes a heating element positioned between the pair of cam members and is adapted to be on an opposite side of the fiber tows from the pair of cam members. In another embodiment of the invention, the means for effecting selective contact of the fiber tows include respective bi-metallic elements positioned adjacent respective ones of the fiber tow pathways. Further according to this embodiment, each of the bi-metallic elements is connected to a source of power and is selectively heated for engaging respective fiber tows. Still further, a positioning roller and a cooling roller are provided, which are spaced in the direction of the fiber tow pathways, wherein each of the bi-metallic elements is mounted in a bowed configuration projecting in a direction between the positioning roller and the cooling roller. Specifically, according to an embodiment of the invention, the means defining a plurality of pathways include a plurality of bars around which the fiber tows extend, at least one of the bars having a heating element affixed thereto. The above and additional objects, characteristics, and advantages of the present invention will become apparent in the following detailed description of preferred embodiments, with reference to the accompanying drawing which is presented as a non-limiting example, in which: FIG. 1 is rear-side isometric view of a filament delivery system and a mandrel around which the filament is applied, thereby illustrating a typical fiber placement system; FIGS. 2a and 2b illustrates the tow lift system of the invention, FIG. 2a depicting an actuated position, and FIG. 2b depicting an unactuated position; FIG. 3 illustrates the bi-metallic embodiment of the invention; FIG. 4 illustrates a simplified zonal ribbonizing embodiment; and FIG. 5 illustrates a high-tech zonal ribbonizing embodiment; FIG. 1 illustrates a filament placement system 1 in which individual rovings or tows 2 are directed to a delivery bead 3, which is mounted onto a manipulator, and emerge at a delivery roller 4. The delivery roller applies the tows, formed into a band, onto a rotating mandrel 5. The fiber placement machine 6 includes a creel assembly for maintaining individual spook upon which the individual tows are wound, from which they are directed to the delivery head. Operation of the machine 6, including the delivery head 3, is controlled by a computer 7. Within the delivery head 3, a ribbonizer assembly can be provided, although the ribbonizer can, if desired, be placed anywhere along the fiber path 2 between the creel and the delivery head. By placing the ribbonizer in the head, however, the fiber path is less complicated, particularly with regard to certain ply orientations such as low angle winding. FIGS. 2-5 illustrate the embodiments of ribbonizing for individual tow control. In the embodiment of FIGS. 2a and 2b, the ribbonizer consists of several thermally conductive cams 20 that are rotatable around the heated tube 14, which hold the cartridge heater 15. A respective insulating pinion 21, made of Torlon®, e.g., holds each of the conductive cams 20 in place and mates with a respective rack 22. Respective air cylinders 23 or, alternatively, solenoids, actuate movement of the racks 22 in reciprocatory directions, thereby rotating the cams 20 which make contact with respective ones of the fiber tows 2, as needed. Random access control is provided via computer 7. FIG. 2a depicts the ribbonizing position of the assembly, whereby the tow 2 is forced against the heat conductive cams 20 and into engagement with the upper heater tube 14. FIG. 2b depicts the unactuated, non-ribbonizing, position of the assembly, whereby the tow would not make contact with either of the heat conductive cams 20 or the upper heater tube 14. FIG. 3 illustrates a further embodiment of the invention. The fiber tows 2 extend along the various elements of the delivery head, as described above. In the embodiment shown in FIG. 3, an additional positioning roller 27 is provided, aligned with the positioning/cooling roller 28. A bi-metallic strip 25 is anchored to a mounting base 24 and is positioned above the rollers 27, 28. The bi-metallic strip 25 extends between two fixed attachment points 26, 26, between which the bi-metallic strip bows downwardly. The fiber tow 2 passes between the bi-metallic strip 25 and the rollers 27, 28. The two rollers 27, 28 are positioned such that when the bi-metallic strip 25 expands, upon exposure to a heat source, the bowed bi-metallic strip, i.e., its tangent, is forced between the rollers 27, 28, thereby engaging and forcing the fiber tow 2 downwardly, making the tow spread. Power supply 29, schematically shown, is controlled by means of the computer 7 to cause the bi-metallic strip to expand. The cooling roller 28 cools the fiber tow 2 in a manner described above. In this embodiment, however, the cooling roller 28 plays a double role by maintaining the fiber tow 2 in a straight line so that ribbonizing can take place, as well as providing its normal cooling function. FIG. 4 illustrates a so-called "low-tech" means for independent tow ribbonizing. By means of separate beating elements, each tow 2 can be controlled independently. In this embodiment, a insulating base 33, made of Torlon®, e.g., or other suitable material, is provided which has the resistance heating element 32 wrapped around it. An upper cover 34 comprises a conductive metal having a abrasive resistive coating. The insulating base extends between a pair of side plates 30, 30 and above a base plate 31 connecting the supports at its ends. The power to the beating elements 32 is controlled by means of the computer 7. In FIG. 5, a so-called "high-tech" means for ribbonizing is illustrated. In this embodiment, a ceramic tube 39 is provided, having grooves for the respective fiber tows 2. In the bottom of each groove, a heating element is provided. The heating element comprises a wire 35 such as ni-chrome which is heated. An insulator 36 is provided to ensure that the wire does not short. A thermocouple 38 is implanted to monitor the heating. An abrasive resistance coating 37, of stainless steel, e.g., is placed over the wires 35 upon which the tows 2 pass over. The thermcouple 38 is linked to the computer 7 for providing the necessary control of the individual tow heating and cooling.

Claims: A ribbonizing apparatus for use with a plurality of fiber tows (2) in a fiber placement apparatus (6), said ribbonizing apparatus (6) comprising means defining a plurality of pathways for said plurality of fiber tows (2) characterized by means for selectively heating respective ones of said plurality of fiber tows (2) as said fiber tows (2) extend along respective ones of said pathways. The ribbonizing apparatus of claim 1, said fiber tows (2) having a predeterminate width and thickness, said means (14, 15, 32, 35) for selectively heating comprising (i) means for transferring heat to respective ones of said plurality of fiber tows for controlling said width and said thickness of said fiber tows and (ii) means (28) for terminating heat transfer to said respective ones of said plurality of fiber tows. The ribbonizing apparatus of claim 1, said means for selectively heating comprising means (14, 15, 32, 35) for effecting selective contact of said fiber tows with a source of heat. The ribbonizing apparatus of claim 3, said means for effecting selective contact of said fiber tows (2) comprising means (20, 21) for moving selective ones of said fiber tows (2), in a direction transverse to said fiber tow path, for contact with said source of heat (14, 15, 32, 35). The ribbonizing apparatus of claim 4, said plurality of fiber tows (2) extending transversely of said fiber tow pathways, said source of heat (14, 15, 32, 35) comprising a heating bar (14) extending transversley across said plurality of fiber tows (2), and said means for effecting selective contact comprising means for moving selective ones of said fiber tows (2) for contact with said heating bar (14). The ribbonizing apparatus of claim 3, said means for effecting selective contact of said fiber tows (2) comprising respective cam members (20) which are selectively rotatable for engaging and moving respective fiber tows (2) toward said source of heat (14, 15, 32, 35) and away from said source of heat (14, 15, 32, 35). The ribbonizing apparatus of claim 6, said cam members (20) having heat conductive portions for engaging said tows (2) during movement of said respective fiber tows (2) toward said source of heat (14, 15, 32, 35), and having heat insulative portions for engaging said respective fiber tows (2) when said fiber tows (2) are removed from contact with said source of heat (14, 15, 32, 35). The ribbonizing apparatus of claim 7, each of said cam members (20) being in driving connection with a respective power actuator assembly for rotating said cam members (20). The ribbonizing apparatus of claim 8, each of said power actuator assembly comprising an air-actuatable cylinder device. The ribbonizing apparatus of claim 8, each of said cam members (20) having a toothed segment, said power actuator assembly comprising a rack member in engagement with a respective toothed segment for rotating a respective cam member (20). The ribbonizing apparatus of claim 6, a pair of cam members (20) for each of said fiber tows (2), spaced in the direction of a respective one of said fiber tow pathways, said source of heat (14, 15, 32, 35) comprising a heating element (14) positioned between said pair of cam members and adapted to be on an opposite side of said fiber tows (2) from said pair of cam members (20). The ribbonizing apparatus of claim 3, said means for effecting selective contact of said fiber tows (2) comprising respective bi-metallic elements (25) positioned adjacent respective ones of said fiber tow pathways. The ribbonizing apparatus of claim 12, each of said bi-metallic elements (25) being connected to a source of power (29) and being selectively heated for engaging respective fiber tows (2). The ribbonizing apparatus of claim 13, further comprising a positioning roller (27) and a cooling roller (28) spaced in the direction of said fiber tow pathways, each of said bi-metallic elements (25) being mounted in a bowed configuration projecting in a direction between said positioning roller (27) and said cooling roller (28). The ribbonizing apparatus of claim 1, said means (14, 15, 32, 35) for selectively heating comprising a ceramic tube (39) having grooves for receiving respective ones of said plurality of fiber tows (2) and heating element (35) being provided within each of said grooves. The ribbonizing apparatus of claim 15, further comprising a thermocouple (38) within each groove for monitoring heating of said fiber tows (2). A method of ribbonizing a plurality of fiber tows extending along respective fiber tow pathways, characterized by the step of selectively heating at least one of said plurality of fiber tows differently to the remainder as said fiber tows extend along their said respective pathways. The method of claim 17, said fiber tows having a predeterminate width and thickness, said step of selectively heating comprising (i) transferring heat to respective ones of said plurality of fiber tows for controlling said width and said thickness of said fiber tows and (ii) terminating heat transfer to said respective ones of said plurality of fiber tows. The method of claim 17, said step of selectively heating comprising effecting selective contact of said fiber tow with a source of heat. The method of claim 19, said step of effecting selective contact of said fiber tow comprising moving selective ones of said fiber tows, in a direction transverse to said fiber tow path, for contact with said source of heat. The method of claim 17, said respective one of said plurality of fiber tows being heated during advancing movement of said fiber tow along said pathways. The method of claim 17, said step of selectively heating at least said respective one of said plurality of fiber tows being made in response to a signal that said fiber tow is to added to form said fiber band. The ribbonizing apparatus of claim 1, wherein said means (14, 15, 32, 35) for selctively heating respective ones of said plurality of fiber tows (2) consists of a source of heat to which said plurality of fiber tows (2) are exposed and means for selectively varying exposure a respective ones of said fiber tows (2) to said at least one source of heat (14, 15, 32, 35). The ribbonizing apparatus of claim 23, said means defining a plurality of pathways comprising a plurality of bars around which said fiber tows (2) extend, at least one of said bars having a heating element (32) affixed thereto. The method of claim 17, characterised by transporting said plurality of fiber tows along a predetermined pathway; said step of selectively heating said at least one of said plurality of fiber tows consisting of exposing said plurality of fiber tows to at least one source of heat and selectively varying exposure a respective ones of said fiber tows to said at least one source of heat. The method of claim 25, said step of transporting said fiber tows along a predeterminate pathway comprising transporting means said fiber tows among a plurality of bars, at least one of said bars having a heating element affixed thereto.

Inventors: FUJIMOTO KAZUTOSHI, GILL DEE R, JOHNSON JOHN A, NIELSEN JAMES P, SHEPHERD NOEL I, WEIS WILLIAM J, FUJIMOTO, KAZUTOSHI, GILL, DEE R., JOHNSON, JOHN A., NIELSEN, JAMES P., SHEPHERD, NOEL I., WEIS, WILLIAM J.
Applicants: HERCULES INC, HERCULES INCORPORATED
Application year: 1991
Main classification: B29B15
IPC codes: B29C70, B29C53, D02J13, B29C35, B29K105, B29L23