Patent Publication Number: US-2021170700-A1

Title: Fiber-composite bicycle frame article formed on molded mandrel

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to U.S. Provisional patent Application Ser. No. 62/944,915, filed Dec. 6, 2019, the entirety of which is hereby incorporated herein by reference for all purposes. 
    
    
     BACKGROUND 
     A bicycle frame or other bicycle components may be constructed from a variety of materials. Carbon- and other fiber-composite frames are desirable due to their light weight, high strength, high stiffness, and vibration-damping characteristics. Some fiber-composite bicycle frames are constructed by joining elongate, fiber-composite tubes (top tube, down tube, seat tube, etc.) at fiber-composite receiving joints (bottom bracket joint, head-tube joint, seat-tube joint, etc.). To facilitate customized bicycle-frame manufacture, it may be desirable to form the bicycle frames with variable joint angles, interior sizes and/or shapes, and exterior sizes and/or shapes. 
     SUMMARY 
     Some aspects of this disclosure are directed to methods for the manufacture of a fiber-composite article for a bicycle frame or other bicycle component. Such methods use an outer mold configured to define an outer surface of the fiber-composite article and an inner mold configured to define an inner surface of the fiber-composite article. One method comprises: securing in the inner mold a supportive armature for a space-filling mandrel, the mandrel being configured to occupy a space within the inner surface of the fiber-composite article during lay up and curing of the fiber-composite article; forming the mandrel by injection molding a solidifiable fluid into the inner mold, around the armature, the solidifiable fluid being configured to form a solidified, molded material; applying a fiber composition to the mandrel; securing the mandrel with the fiber composition in the outer mold. The method further comprises heating the fiber composition in the outer mold to form the fiber-composite article and concurrently heating the solidified, molded material. In this manner, the fiber composition is compressed into the outer mold due to expansion of the solidified, molded material. 
     Another method comprises fabricating the inner mold and securing in the inner mold a supportive armature for a space-filling mandrel. The mandrel is configured to occupy a space within the inner surface of the fiber-composite article during lay up and curing of the fiber-composite article. The method further comprises forming the mandrel by injection molding into the inner mold, around the armature; applying a fiber composition to the mandrel; securing the mandrel with the fiber composition in the outer mold; and heating the fiber composition in the outer mold to form the fiber-composite article. 
     Another aspect of this disclosure is directed to a fiber-composite article for a bicycle frame or other bicycle component. The article comprises an outer surface and an inner surface embossed with a texture of an inner release tape applied to a molded mandrel. The molded mandrel defines the shape of the inner surface. 
     The Summary above is provided in order to introduce in simplified form a selection of concepts that are further described in the Detailed Description. The Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows aspects of an example bicycle frame. 
         FIG. 2  illustrates a cross section of an example fiber-composite bicycle-frame article. 
         FIG. 3  shows aspects of an example method to manufacture a fiber-composite article. 
         FIG. 4  shows aspects of an example armature suitable for the manufacture of a fiber-composite bottom bracket joint of a bicycle frame. 
         FIG. 5  shows aspects of the example armature of  FIG. 4 , secured in an example inner-mold portion. 
         FIG. 6  shows aspects of an example inner mold comprising the inner-mold portion of  FIG. 5 . 
         FIGS. 7 and 8  show aspects of an example mandrel formed using the armature of  FIG. 4  and the inner mold of  FIG. 6 . 
         FIG. 9  shows aspects of the mandrel of  FIGS. 7 and 8  with an applied fiber composition, secured in an example outer-mold portion. 
         FIG. 10  shows aspects of an example outer mold comprising the outer-mold portion of  FIG. 9 . 
         FIG. 11  shows an example fiber-composite article after removal of the elements of the armature of  FIG. 4 . 
         FIG. 12  shows an example fiber-composite article after removal of the armature elements and molded mandrel segments. 
         FIG. 13  shows aspects of an example injection-molded mandrel for a seat-tube joint, in a corresponding inner-mold portion. 
         FIG. 14  shows aspects of an example injection-molded mandrel for a head-tube joint, in a corresponding inner-mold portion. 
     
    
    
     DETAILED DESCRIPTION 
     As noted above, a bicycle frame may include a plurality of elongate tubes coupled by fiber-composite receiving joints. In one approach, a receiving joint is formed in a mold that defines the inner and outer surfaces of the receiving joint. In particular, a portion of the inner surface may be defined by an inflatable bladder or other resilient structure. In some instances, however, lack of rigidity of the resilient structure may result in unacceptable dimensional tolerances for the inner surface of the receiving joint. In some instances, it may be difficult to control the pressure that the resilient structure exerts on the fiber-composite material under curing conditions. Furthermore, the inflatable-bladder may develop folds that allow fiber composition to pool up while curing, causing the texture of the folds (which may be stress inducing) to be transferred to the inner surface the fiber-composite article. Varying the bladder material may reduce the incidence of fold formation in some implementations, but at the expense of additional manufacturing complexity. 
       FIG. 1  shows aspects of an example bicycle frame  10 . The bicycle frame includes a plurality of fiber-composite articles in the form of frame segments  12  and receiving joints  14 . The illustrated frame segments include top tube  12 A, seat tube  12 B, down tube  12 C, seatstay  12 D, and chainstay  12 E. The illustrated receiving joints include bottom-bracket joint  14 A, head-tube joint  14 B, and seat-tube joint  14 C. Additional articles that may comprise fiber-composite material include a stem or fork. 
     Any fiber-composite article may include inner and outer surfaces of arbitrary topology. As shown by example in the cross-sectional view of  FIG. 2 , a fiber-composite article  16 , such as a frame segment  12  or receiving joint  14 , will generally comprise an inner surface  18  and an outer surface  20 . At any locus of a fiber-composite article, the separation between the inner and outer surfaces defines a wall thickness T. The wall thickness may be constant or variable over different loci of the fiber-composite article. In some examples, the wall thickness may be small in comparison to the overall dimensions of the fiber-composite article. For instance, fiber-composite frame segments  12 , may span hundreds of millimeters (mm) but have a wall thickness of about 5 mm or less. 
     In these and other examples, a fiber-composite article may take the form of a relatively thin envelope. A fiber-composite envelope may surround, retain, and/or marshal one or more structural members—tubes, rods, and/or rails, for example—that are received into the inner surface of the fiber-composite article. In the example of  FIG. 1 : bottom-bracket joint  14 A surrounds and retains seat tube  12 B, down tube  12 C, and chainstay  12 E; head-tube joint  14 B surrounds and retains top tube  12 A and down tube  12 C; and seat-tube joint  14 C surrounds and retains top tube  12 A, seat tube  12 B, and seatstay  12 D. Alternatively or in addition, a fiber-composite envelope may surround, retain, and/or marshal various mechanical hardware. In the example of  FIG. 1 : bottom-bracket joint  14 A retains, and marshals bottom bracket  22  and spindle  24 ; head-tube joint  14 B retains and marshals fork  26  and headset  28 A and  28 B; and seat-tube joint  14 C retains and marshals seat post  30 . 
       FIG. 3  shows aspects of an example method  32  to manufacture a fiber-composite article including, but not limited to, the fiber-composite articles described herein. The method employs an outer mold configured to define an outer surface of the fiber-composite article and an inner mold configured to define an inner surface of the fiber-composite article. The method also employs a space-filling mandrel configured to occupy a space within the inner surface of the fiber-composite article during lay up and curing of the fiber-composite article. 
     At  34  of method  32  a digital model of the desired fiber-composite article is created. The digital model is configured to represent at least the inner and outer surfaces of the fiber-composite article. The digital data structure of the digital model is not particularly limited. The digital model may include one or more CAD files, in some examples. In embodiments where the desired fiber-composite article is a receiving joint of a bicycle frame, the digital model may be customized to provide the desired bicycle-frame geometry and/or ride characteristics. 
     At  36  an outer mold that defines the outer surface of the fiber-composite article is fabricated according to the digital model created at  34 . The outer mold may be fabricated in two or more separable portions that are assembled together to enable molding of a substantially continuous outer surface of the fiber-composite article. In some examples, the outer mold may be subtractively machined (e.g., milled). In some examples, the outer mold may be additively manufactured (e.g., 3D printed). 3D printing, in some instances, may reduce the cost of mold making for short-run bicycle-frame configurations, which may be customized to a rider&#39;s desired bicycle-frame geometry and/or ride characteristics. In some examples, the milling and/or 3D printing is controlled automatically according to the features defined in the digital model. 
     The outer mold may be formed from any material that, in its formed state, is suitably rigid and dimensionally stable over the temperature range at which the fiber-composite article will be cured (vide infra). The outer mold may be formed from a metal or high-temperature thermoplastic or thermosetting polymer, for instance. In some examples, each separable outer-mold portion may include an o-ring groove. In examples in which o-ring grooves are included, the o-ring grooves of opposing separable outer-mold portions may be co-registered. In some examples, at least one outer-mold portion may include a ‘flash gap’ configured to allow a small amount of resin flow into the o-ring groove during curing, so as to provide substantially leak-free pressurization of the fiber composition while curing (vide infra). 
     At  38  an inner mold that defines the inner surface of the fiber-composite article is fabricated according to the digital model created at  34 . The inner mold may be fabricated in two or more separable portions that are assembled together to enable molding of a substantially continuous inner surface of the fiber-composite article. In some examples, the inner mold may be subtractively machined (e.g., milled). In some examples, the inner mold may be additively manufactured (e.g., 3D printed). 3D printing, in some instances, may reduce the cost of mold making for short-run bicycle-frame configurations, which may be customized to a rider&#39;s desired bicycle-frame geometry and/or ride characteristics. In some examples, the milling and/or 3D printing is controlled automatically according to the features defined in the digital model. The inner mold may be formed from any material that, in its formed state, is suitably rigid and dimensionally stable. The inner mold may be formed from a metal or thermoplastic or thermosetting polymer, for instance. 
     At  40  a supportive armature for a sacrificial, space-filling mandrel is fabricated, the mandrel being configured to occupy the space within the inner surface of the fiber-composite article during the lay up and curing of the fiber-composite article. The armature is a rigid structure. The armature includes a plurality of locating features configured to receive (or, alternatively, to be received into) corresponding locating features of the inner and outer molds. The armature may comprise any rigid material or combination of rigid materials. Examples include steel, aluminum, and high-strength polymer materials, such as polyacetal—e.g., Delrin. Generally speaking, the armature is configured to support the mandrel in the outer mold and to increase the dimensional stability of the mandrel, the balance of which is comprised of an injection-molded polymer material. In some examples, the armature may be configured to provide other manufacturing advantages, as described hereinafter. 
     In some examples, the armature includes one rigid element or a series of rigid elements—e.g., two or more rigid elements detachably coupled to each other. In examples in which the fiber-composite article is a bicycle-frame joint, the one or more rigid elements may include a hub and one or more nubs. The one or more nubs may align to a corresponding one or more segments of the bicycle frame when the hub is positioned in the bicycle-frame joint.  FIG. 4  shows aspects of an example armature  42  suitable for the manufacture of a fiber-composite bottom bracket joint of a bicycle frame. In this example, the armature elements align to the different bicycle frame tubes to be received into the fiber-composite article. More particularly, hub  44  is positioned at a bottom bracket position of the bottom bracket joint, nub  46  aligns to a down-tube position, nub  48  aligns to a seat-tube position, and nub  50  aligns to a chainstay position of the bicycle frame. In examples in which the fiber-composite article is a head-tube joint of the bicycle frame, the hub is positioned at a head-tube position of the head-tube joint, and the one or more nubs align to a top tube and a down tube of the bicycle frame. In examples in which the fiber-composite article is a seat-tube joint of the bicycle frame, the hub is positioned at a seat-tube position of the seat-tube joint, and the one or more nubs align to a top tube and a seatstay of the bicycle frame. 
     At  52  of  FIG. 3 , the armature is secured in the inner mold, and the sacrificial, space-filling mandrel is formed by injection molding around the armature, inside the inner mold. The mandrel is the solid structure around which the fiber composition of the fiber-composite article will be layed up. In some examples, the armature may be secured by co-registry of the corresponding locating features of the armature and of the inner mold, as noted above.  FIG. 5  shows armature  42  secured in a corresponding inner-mold portion  54 A. 
     The substance injection molded around the armature may include any solidifiable fluid configured to form a solidified, molded material that is substantially dimensionally stable over the temperature range at which the fiber-composite article will be cured. In some examples, the injection-molded material may undergo some amount of thermal expansion when heated from ambient temperature to the temperature range at which the fiber-composite article will be cured (vide infra). In this manner, the injection-molded material may exert pressure on the fiber composition during subsequent molding of the fiber-composite article. In some examples, the desired amount of thermal expansion may be within a range of 1 to 20% by volume. In some examples, the desired amount of thermal expansion may be within a range of 1 to 10% by volume. In some examples, the desired amount of thermal expansion may be within a range of 5 to 10% by volume. Other ranges of thermal expansion are also envisaged. 
     In some examples, a coefficient of thermal expansion of the solidified, molded material is greater than the coefficient of thermal expansion of the armature. Accordingly, the detailed configuration of the armature may be manipulated as a process variable in order to fine tune the expansion of the mandrel at curing temperatures. More specifically, any increase in the volume occupied by the armature of the mandrel is accompanied by a commensurate decrease in the volume of injection-molded material. Although the injection-molded material may expand significantly when heated, the armature may expand very little, due to its material composition. Accordingly, it is possible to reduce the degree to which the mandrel expands simply by increasing the volume occupied by the armature, without changing the composition of the injection-molded material. In addition, the size and shape of the armature can be engineered so that the negative space within the mandrel that forms upon removal of the armature (vide infra) simplifies removal of the molded mandrel segments as well. 
     Typically, the solidifiable fluid from which the injection-molded material solidifies comprises a polymerizable and/or cross-linkable component. In some examples, the injection-molded material may comprise silicone (i.e., a polysiloxane). In some examples, the injection-molded material may comprise a polyacrylic or a polyurethane. In some examples, the injection-molded material may be configured to reduce or substantially exclude entrained air. In other examples, however, the solidifiable fluid may comprise a controlled amount of a foaming agent in addition to the polymerizable and/or cross-linkable component. 
       FIG. 6  shows the assembled inner mold  56  comprising inner-mold portions  54 A and  54 B, which enclose the armature. Both inner-mold portions include a thru-hole  58  configured for a machine screw. Returning briefly to  FIG. 4 , the machine screw may screw into a screwthread  60  of armature  42  to secure the separable portions  54  of inner mold  56  to armature  42  and thereby secure the separable portions together. 
       FIG. 7  shows mandrel  62 , comprising armature  42  with injection-molded material  64  adhering thereon, after inner-mold portion  54 B is lifted away.  FIG. 8  shows mandrel  62  after inner-mold portion  54 A is lifted away. 
     At  66  of  FIG. 3 , the injection-molded material is segmented to facilitate eventual removal of the injection-molded material from the fiber-composite article. In some examples, segmentation of the injection-molded material may include slicing, scoring, and/or perforating the injection-molded material. In some examples, the injection-molded material is sliced so as to quarter the mandrel all the way through to the armature. Additional cuts may be made all the way around certain sections, to aid in removal around hard angles or complex surfaces. The cuts may terminate before the end of each section (e.g., in a range of about one to five millimeters before) in order to prevent the injection-molded material from detaching from the armature prior to, or during, the molding process. 
     At  68  of  FIG. 3 , an inner release layer is applied to the mandrel. In some examples, the inner release layer may comprise a fluid lubricant. In some examples, the inner release layer may comprise a release tape, such as poly(tetrafluoroethylene)—e.g., Teflon tape. In some examples, the release tape may be an adhesive tape that allows the injection-molded material to expand during curing of the fiber-composite article but keeps the injection-molded material from sticking to the fiber-composite article. In some examples, the release tape may reduce the transfer of undesired texture (artifacts of machining or 3D printing) from the inner mold onto the inner surface of the fiber-composite article. 
     At  70  of  FIG. 3 , a fiber composition is applied to the mandrel. In some examples, the fiber composition comprises a fiber-based textile that includes a curable (i.e., polymerizable and/or cross-linkable) resin. The fiber-based textile may take the form of a relatively narrow strip or tape, for example, which is applied in plural layers. The fibers of the fiber-based textile may comprise one or more natural or synthetic fibers. In some examples, the fibers of the fiber-based textile comprise high-strength carbon fibers. In some examples, the curable resin comprises a thermosetting resin. In some examples, the curable resin is applied externally to the fiber-based textile as the textile is applied to the mandrel. In other examples, the fiber-based textile is supplied with the curable resin already included therein (e.g., resin-impregnated or pre-impregnated carbon-fiber textile). In still other examples, the fiber-based textile may include a thermoplastic—e.g., a high-strength, high-performance thermoplastic such as polyetheretherketone (PEEK). 
     The quantity of fiber composition applied to mandrel may be such as to fill (but not overfill) the gap between the inner and outer surfaces of the fiber-composite article, as defined, respectively, by the inner and outer molds. In examples in which the fiber composition comprises a fiber-based textile, plural layers of the fiber-based textile may be layed upon and/or wrapped around the mandrel in order to achieve the desired thickness. In some examples, the desired number of layers of the fiber-based textile may be the maximum number that allows the portions of the outer mold to seal with the fiber-coated mandrel inserted between the outer-mold portions. 
     At  72  of  FIG. 3 , an outer release layer is applied to any or all of the outer-mold portions. In some examples, the outer release layer may comprise a fluid lubricant, such as a ‘mold-release’ agent. In some examples, the outer release layer may comprise a release tape, such as poly(tetrafluoroethylene) tape. In some examples, an adhesive-backed mold insert may be used in addition to or in lieu of a fluid lubricant or release tape. 
     At  74  of  FIG. 3 , the mandrel with the applied fiber composition is secured in the outer mold. In some examples, the mandrel may be secured by co-registry of the corresponding locating features of the armature and of the outer-mold portions, as noted above. In examples in which the opposing outer-mold portions include an o-ring groove, an o-ring may be inserted in the o-ring groove at this stage of manufacture. An o-ring may also be applied to any armature element that aligns to the o-ring groove, to complete the seal inside the outer-mold cavity. The outer-mold portions are then secured together around the mandrel. The outer-mold portions may be joined under compressive force—e.g., held together using one or more screws or clamps, and/or retained in a vice or press, such as a temperature-controlled press. 
       FIG. 9  shows mandrel  62  with the applied fiber composition  74  secured in outer-mold portion  76 A. This drawing also shows o-ring groove  78 .  FIG. 10  shows the assembled outer mold  80  comprising outer-mold portions  76 A and  76 B, which enclose the mandrel and applied curable fiber composition. Both outer-mold portions include a thru-hole  82  configured for a machine screw. Returning again to  FIG. 4 , the machine screw may screw into a screwthread  60  of armature  42  to secure the separable portions  76  of outer mold  80  to armature  42  and thereby secure the separable portions together. 
     At  84  the fiber composition is heated in the outer mold to form the fiber-composite article—e.g., by curing the fiber composition. In particular, the outer mold may be heated to a setpoint curing temperature for a predetermined curing time, in order to effect curing. In some examples, the outer mold is heated in a temperature-controlled oven. In some examples, the outer mold includes temperature-control componentry, such as a heating wire or heating tape and a thermocouple or other temperature sensor. The temperature control componentry may be coupled operatively to an electronic temperature controller and thereby configured to provide the setpoint temperature for the predetermined time. In some examples, as noted above, the outer mold may be retained in a temperature-controlled press that compresses the outer-mold portions and concurrently transfers heat to the outer mold and fiber composition therein. In some examples, a setpoint curing temperature may be between 60 and 180° C., more particularly about 100 to 150° C., and still more particularly, about 135° C. Concurrently, the mandrel including the solidified, molded material is heated. During such heating, the fiber composition is compressed into the outer mold due to expansion of the solidified, molded material. In particular, expansion of the injection-molded material of the mandrel compresses the plural layers of the fiber composition and forces the layers against the outer mold, yielding an adherent and substantially void-free structure having the desired inner and outer topology and desired high strength. After heating, the separable outer-mold portions are separated and the fiber-composite article is released from the outer mold. 
     At  86  of  FIG. 3 , the detachable armature elements are separated and removed from the fiber-composite article. In some implementations, the armature elements may be removed in a specific order. For instance, the rods and rails may be removed from their respective nubs, and then the hub may be removed from the injection-molded host. FIG.  11  shows the formed, fiber-composite article  88  after removal of the armature elements. Injection-molded material  90  is still visible in the drawing. 
     At  92  of  FIG. 3 , the molded mandrel material is removed from the inner surface of the fiber-composite article—e.g., in plural segments if the mandrel has been divided or perforated. When removing the injection-molded material from the fiber-composite article, end portions that were left uncut at  66  may either be cut or ripped off of the fiber-composite article.  FIG. 12  shows the formed, fiber-composite article  88  after removal of all armature elements and injection-molded segments of the mandrel. In some examples, the inner surface  94  of the fiber-composite article may be embossed with a texture of an inner release tape applied to the molded mandrel. 
     The method of  FIG. 3  is equally applicable to other fiber-composite bicycle-frame components besides the bottom-bracket joint shown in  FIGS. 4 through 12 .  FIG. 13  shows an injection-molded mandrel  62 ′ for a seat-tube joint in a corresponding inner-mold portion  54 A′.  FIG. 14  shows an injection-molded mandrel  62 ″ for a head-tube joint in a corresponding inner-mold portion  54 A″. It will be noted that fiber-composite receiving joints of a bicycle frame may be joined to the frame tubes or other members in any suitable manner, such as with a resin-based adhesive compatible with the fiber-composite material. Further, the tube nubs that are part of the receiving joints can have mechanical features for facilitating connection to one or more elongate frame tubes (e.g., a segment that protrudes into a frame tube). Further still, the outer size and/or shape of the nubs may be configured to match the tubes so that when joined together, the overall joint construction appears to be monolithic. Despite the emphasis herein on fiber-composite articles for a bicycle-frame, the above method of manufacture can be applied to various bicycle components that are not strictly part of the frame and to virtually any fiber-composite envelope or other article. 
     It will be understood that the configurations and methods described herein are provided by way of example, and that these examples are not to be considered in a limiting sense because numerous variations, extensions, and omissions are also envisaged. Any of the various acts of an above method may be performed in the sequence illustrated, in other sequences, in parallel, or omitted. 
     The subject matter of the present disclosure includes all novel and non-obvious combinations and sub-combinations of the various configurations, methods, properties, and other features disclosed herein, as well as any and all equivalents thereof.