Abstract:
A method for manufacturing a bicycle wheel rim includes: (a) providing a first mold assembly which includes an inner mold and an outer mold, the outer mold having an annular first forming face to surround an annular second forming face of the inner mold; (b) disposing annularly a first prepreg preform that overlie annularly and respectively the annular first and second forming faces; (c) causing the first and second forming faces to press the concaved faces and thermoforming the first prepreg preform to obtain an annular outer rim part; (d) forming a second prepreg preform into an annular inner rim part; and (e) combining the annular outer rim part with the annular inner rim part to form a wheel rim.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    This invention relates to a method for manufacturing a bicycle wheel rim, more particularly to a method for manufacturing a bicycle wheel rim with better production yield and thermal resistance. 
         [0003]    2. Description of the Related Art 
         [0004]    Components of a bicycle are constantly lightened in order to increase riding speed. Therefore, conventional aluminum wheel rims are gradually replaced by wheel rims made of a carbon fiber composite material. 
         [0005]      FIG. 1  shows a conventional method for manufacturing a wheel rim  63  made of a carbon fiber composite material. The wheel rim  63  with an inner rim part  632  and an outer rim part  631  is integrally formed by disposing a carbon fiber composite material between an air bag  61  and a silicon mold  62  followed by thermoforming. The air bag  61  is susceptible to high temperature damage which can cause the wheel rim  63  unable to be formed. Therefore, resins with low forming temperature are used in the carbon fiber composite material to form the wheel rim  63 . However, the resins with low forming temperature are likely to be damaged by heat generated by brake pad friction, and thus the wheel rim  63  has unsatisfactory long term durability. Besides, form error is a great problem for the wheel rim  63  since two soft materials, the air bag  61  and the silicone mold  62 , are used as molds. Moreover, since the outer and inner rim part  631 ,  632  are simultaneously formed, damage to one of the outer and inner rim part  631 ,  632  will cause discard of the complete wheel rim  63 , thereby resulting in lower production yield. 
         [0006]      FIG. 2  shows another conventional method for manufacturing a wheel rim. The method shown in  FIG. 2  is similar to the aforesaid method shown in  FIG. 1  except that a metal mold assembly  65  is used to replace the silicone mold  62 . The metal mold assembly  65  includes a core mold element  651  and two annular mold elements  652  which are spaced apart from each other axially. A carbon fiber composite material is disposed between an air bag  64  and the metal mold assembly  65  for thermoforming. Form error in this method is reduced due to rigidity of the metal mold assembly  65 . In this conventional method, the core mold element  651  has a first region that abuts against the two annular mold elements  652  to force the two annular mold elements  652  to equally expand the carbon fiber composite material. In the metal mold assembly  65 , after the wheel rim is formed, the core mold element  651  is difficult to remove from the annular mold elements  652  due to the large friction between the core mold element  651  and the annular mold elements  652 . Meanwhile, this method also has thermal resistance and production yield problems as encountered in the prior art show in  FIG. 1 . 
       SUMMARY OF THE INVENTION 
       [0007]    The object of the present invention is to provide a method for manufacturing a bicycle wheel rim and a bicycle wheel rim made therefrom. 
         [0008]    According to one aspect of the present invention, there is provided a method for manufacturing a bicycle wheel rim that includes an annular inner rim part and an annular outer rim part. The method includes the following steps:
       (a) providing a first mold assembly which includes an inner mold and an outer mold extending annularly around the inner mold, the outer mold having an annular first forming face to surround an annular second forming face of the inner mold;   (b) disposing annularly a first prepreg preform between the annular first and second forming faces, the first prepreg preform having a substantially H-shape in cross section and including two back to back disposed concaved faces that overlie annularly and respectively the first and second forming faces;   (c) causing the first and second forming faces to press the concaved faces and thermoforming the first prepreg preform to obtain the annular outer rim part;   (d) forming a second prepreg preform into the annular inner rim part; and   (e) combining the annular outer rim part with the annular inner rim part to form the wheel rim.       
 
         [0014]    According to another aspect of the present invention, there is provided a bicycle wheel rim made from the aforesaid method. The bicycle wheel rim includes an annular inner rim part including an annular body with a substantially hollow triangle shape in cross section, the annular body being tapered radially from an outer end thereof to an inner end thereof; and an annular outer rim part having a substantially H-shape in cross section, and including two back-to-back disposed concaved faces, one of the concaved faces receiving and abutting against the outer end of the annular body. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]    Other features and advantages of the present invention will become apparent in the following detailed description of the preferred embodiments with reference to the accompanying drawings, of which: 
           [0016]      FIG. 1  is a sectional view illustrating a conventional method for manufacturing a bicycle wheel rim; 
           [0017]      FIG. 2  is a sectional view showing another conventional method for manufacturing a bicycle wheel rim; 
           [0018]      FIG. 3  is a flow chart of the first preferred embodiment of a method for manufacturing a bicycle wheel rim; 
           [0019]      FIG. 4  is a sectional view of the first preferred embodiment showing a step of forming an annular outer rim part using a first mold assembly; 
           [0020]      FIG. 5  is a sectional view of the first preferred embodiment illustrating a step of forming an annular outer rim part and uniting the annular outer and inner rim parts; 
           [0021]      FIG. 6  is a sectional view of a wheel rim manufactured by the first preferred embodiment; 
           [0022]      FIG. 7  is a flow chart of the second preferred embodiment of a method for manufacturing a bicycle wheel rim; and 
           [0023]      FIG. 8  is a sectional view of the second preferred embodiment illustrating a step of forming an annular inner rim part in a second mold. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0024]    Before the present invention is described in greater detail, it should be noted that like elements are denoted by the same reference numerals throughout the disclosure. 
         [0025]      FIGS. 3 ,  4 , and  5  illustrate the first preferred embodiment of a method for manufacturing a wheel rim of this invention. The wheel rim includes an annular inner rim part  4 ′ and an annular outer rim part  3 ′ surrounding the annular inner rim part  4 ′ (see  FIG. 6 ). The method of the first preferred embodiment includes forming the annular outer rim part  3 ′ using a first mold assembly, removing the first mold assembly, and forming the annular inner rim part  4 ′ using a second mold and the annular outer rim part  3 ′ and simultaneously connecting the annular outer and inner rim parts  3 ′,  4 ′. 
         [0026]    The first mold assembly used to form the annular outer rim part  3 ′ includes an outer mold  21  having an annular first forming face, an inner mold  22  having an annular second forming face, and two side modes  23 . The outer mold  21  is made from metal, and the inner mold  22  is made from rubber. The outer mold  21  extends annularly around the inner mold  22  such that the annular first forming face surrounds the annular second forming face. The annular first forming face has an annular first end face  213  and two first lateral faces  214 . The annular second forming face has an annular second end face  221  and two second lateral faces  222 . The annular first and second end faces  213 ,  221  confront each other in a radial direction. The first lateral faces  214  extend radially outward from two opposite sides of the first end face  213 , and the second lateral faces  222  extend radially inward from two opposite sides of the second end face  221 . 
         [0027]    The outer mold  21  further includes two annular mold elements  212  that are spaced apart from each other axially, and a core mold element  211  disposed between the annular mold elements  212 . The annular mold elements  212  respectively define the first lateral faces  214  and cooperatively define the first end face  213 . The core mold element  211  is movable between a wedging position and an un-wedging position, and is tapered radially and toward the first end face  213 . The core mold element  211  is spaced apart from the annular first end face  213  by a distance in the wedging position. 
         [0028]    A first prepreg preform  3  made from fiber and resin is disposed annularly between the annular first and second forming faces. The first prepreg preform  3  has a substantially H-shape in cross section and includes two back to back disposed concaved faces that overlie annularly and respectively the first and second forming faces. The two side modes  23  are then disposed on two axially opposed sides of the outer and inner modes to press the first prepreg preform  3  against the respective lateral faces  214 ,  222  of the outer and inner modes  21 ,  22 . Specifically, in the first mold assembly in which the core mold element  211  is disposed in the wedging position, the first and second forming faces of the outer and inner molds  21 ,  22  press the concaved faces of the first prepreg preform  3 . 
         [0029]    Thereafter, a thermoforming is conducted at 180° C. to form the first prepreg preform  3  into the annular outer rim part  3 ′. 
         [0030]    After thermoforming, the core mold element  211  is firstly removed followed by removing the annular mold elements  212 . After the outer mold  21  is removed, the inner mold  22  and the side molds  23  are then removed in sequence. 
         [0031]    A second prepreg preform  4  covered on and contacts an entire surface of an inflated air bag  25  and the outer rim part  3 ′ are placed in a second mold. The second mold  24  includes a mold body  241  having an inner surface  242  to define a cavity. The inflated air bag  25  covered with the second prepreg preform  4  is disposed in the cavity. 
         [0032]    In the first preferred embodiment, the outer rim part  3 ′ is used as a mold in this step and annularly surrounds and contacts the second prepreg preform  4 . In the second mold  24 , the inflated air bag  25  pressures the second prepreg preform  4  to press the second prepreg preform  4  against the inner surface  242  of the mold body  241  and against the outer rim part  3 ′. Thermoforming is carried out to form the second prepreg preform  4  into the annular inner rim part  4 ′ and simultaneously to unite the inner rim part  4 ′ with the outer rim part  3 ′ so as to form a wheel rim shown in  FIG. 6 . 
         [0033]    As shown in  FIG. 6 , the wheel rim includes the annular inner rim part  4 ′ and the annular outer rim part  3 ′. The annular inner rim part  4 ′ includes an annular body with a substantially hollow triangle shape in cross section, and surrounds the inflated air bag  25 . The annular body is tapered radially from an outer end  41 ′ thereof to an inner end  42 ′ thereof. The annular outer rim part  3 ′ has a substantially H-shape in cross section and includes two annular side walls  31 ′ and an annular connecting wall  32 ′ connecting the two annular side walls  31 ′. The side walls  31 ′ has two outer part  311 ′ extend radially outward from two opposite sides of the connecting wall  32 ′, and two inner parts  312  extend radially inward from the two opposite sides of the connecting wall  32 ′. The inner parts  312 ′ together with the connecting wall  32 ′ define a first concaved face  35 ′ which receives and abuts against the outer end  41 ′ of the annular body of the annular inner rim part  4 ′. The outer parts  311 ′ together with the connected wall  32 ′ define a second concaved face  34 ′. The second concaved face  34 ′ defines a tire retaining space  33 ′. The first and second concaved faces  34 ′ and  35 ′ are back-to-back disposed. The annular outer rim part  3 ′ further includes two fixing parts  313 ′ each of which extends toward the tire retaining space  33 ′ from an end portion of the outer part  311 ′ of a respective one of the annular side walls  31 ′ to fix a tire received in the tire retaining space  33 ′. 
         [0034]    In practical use, an inner tube of a bicycle wheel is placed into the tire retaining space  33 ′ and is inflated. After inflation, the inner tube is fixed to the outer rim part  3 ′ by the fixing parts  313 ′. 
         [0035]      FIGS. 7 and 8  show the second preferred embodiment of a method for manufacturing a wheel rim of this invention. The second preferred embodiment is similar to the first preferred embodiment except that, in the step of forming the annular inner rim part  4 ′, the annular outer rim part  3 ′ is not used as a mold so that formation of the annular inner rim part  4 ′ and connection of the annular outer and inner rim part  3 ′,  4 ′ are conducted in separate steps. 
         [0036]    Specifically, in the second preferred embodiment, the second mold  24  further includes a cover mold element  243 . After the second prepreg preform  4  covered on the inflated air bag  25  is placed in the cavity of the mold body  241 , the cover mold  243  then covers the mold body  241 . The inflated air bag  25  pressures the second prepreg preform  4  to press the second prepreg preform  4  against the inner surface  242  of the mold body  241  and against the cover mold  243 . Thermoforming is carried out to form the second prepreg preform  4  into the annular inner rim part  4 ′. 
         [0037]    Finally the annular inner rim part  4 ′ and the annular outer rim part  3 ′ are connecting using thermoforming procedure so as to form the wheel rim. 
         [0038]    In this invention, since the annular outer rim part  3 ′ is formed before the annular inner rim part  4 ′, a thermal resist resin material can be used as the resin of the first prepreg perform  3  without encountering the problem of the damage to the inflated air bag  25  in the prior art. Therefore, the wheel rim of this invention exhibits superior thermal resistance. 
         [0039]    Moreover, since the annular outer rim part  3 ′ and the annular inner rim part  4 ′ are manufactured separately, discard of a complete wheel rim due to defect of one of the annular outer and inner rim part  3 ′,  4 ′ can be eliminated, thereby resulting in an increase in production yield and a decrease in manufacturing costs. 
         [0040]    Since the core mold element  211  is tapered, the same can be easily moved to the un-wedging position, e.g., moved away from the annular mold elements  212 . 
         [0041]    While the present invention has been described in connection with what are considered the most practical and preferred embodiments, it is understood that this invention is not limited to the disclosed embodiments but is intended to cover various arrangements included within the spirit and scope of the broadest interpretation and equivalent arrangements.