Abstract:
A brazed bicycle frame and method for making. At least two bicycle frame half-shells are fabricated. A filler metal is then placed between the bicycle frame half-shells to form a two-part hollow frame section. The two-part hollow frame section is inserted into a hot volume at a temperature higher than the melting temperature of the filler metal but lower than the melting temperature of the two bicycle frame half-shells. The filler metal is allowed to melt. The filler metal is then allowed to cool and harden to form a rigid joint. Preferably, the bicycle frame half-shells each have a flange that facilitates alignment fixturing and assembly of the two-part hollow frame sections. Also it is possible for the filler metal and the bicycle frame half-shells to be placed in an extruded or formed grooved section. The grooved section also facilitates alignment fixturing and assembly of the two part hollow frame sections, and helps to strengthen the braze joint.

Description:
This application is a continuation-in-part of patent application Ser. No. 09/431,878 filed on Nov. 2, 1999, now U.S. Pat. No. 6,386,567, which is a continuation-in-part of patent application Ser. No. 09/049,266, filed on Mar. 27, 1998, now U.S. Pat. No. 5,975,550. 
    
    
     BACKGROUND OF THE INVENTION 
     The history of the bicycle goes back many years. A crude two-wheeled vehicle propelled by the feet was popular as early as the second half of the 17 th  century. Extensive developments to the design of the bicycle were made during the 19 th  century. At the end of the 19 th  century, the bicycle had become a serious means of transportation. In 1899, the U.S. production of about 1,000,000 bicycles a year was valued at $31,000,000. However, by 1909 the bicycle industry in the U.S. was nearly nonexistent due to the advent of the motorcycle and automobile. Bicycle riding was generally confined to children and to small groups of devotees, such as members of the League of American Wheelmen, organized in 1880 and the Century Road Club Association, organized in 1899. 
     It was not until the 1960&#39;s and 1970&#39;s and more recently in the 1990&#39;s that bicycling once again began to enjoy strong popularity. There are several modem reasons that may have resulted in this strong resurgence. Air pollution, traffic congestion, and the high cost of automobile fuel are all reasons that it makes sense to use a bicycle for transportation. Personal fitness is also a modem trend that is very popular. The bicycle is an outstanding device to use for physical exercise. 
     As the bicycle has developed and has become firmly established as part of our modem culture, its use has expanded in recent years. For example, in addition to the traditional road bicycle, mountain bikes and BMX bikes are now very popular. 
     Bicycle Frames 
     As bicycle frame technology has improved, bicycle designers have focused on making bicycle frames that are lightweight and strong. Similarly, bicycle designers are concerned about building bicycle frames in a cost effective and time efficient manner. Monocoque bicycle frames are extremely popular for road, mountain, and BMX bicycles. A monocoque structure is one in which the skin absorbs all or most of the stresses to which the structure is subjected. 
     There are two common methods for making a hollow monocoque bicycle frame. The first method is by extruding individual hollow tubular frame sections. These frame sections can then be cut to length, bent to a desired shape, coped, aligned and then individually welded together to produce a bicycle frame. Some of the major disadvantages to making bicycle frames in this manner are: 1) the manufacturer is limited by available extruded tubing material and sizes, 2) the thickness and cross section of the tube cannot vary with stress, 3) the amount and type of bending and coping that he is able to do to the extruded frame sections, and 4) the extra time it takes to individually align and weld each frame member together, and 5) the time necessary to align each frame after welding. 
     The second known method involves forming matching frame half-shells and then welding them together along their entire seam. The advantage of the second method over the first is that the cross sectional area of the welded frame sections can vary along their length. However, welding formed matching half-shells along their entire seam is a time consuming and complicated process. Because welding a bicycle frame is considered to be delicate work, welders have to be highly trained or high cost robotic welders are used to do an effective, consistent and esthetically acceptable job. Therefore, it is much more expensive to weld formed matching half-shells together than it is to extrude individual frame sections and then weld those together. 
     Brazing 
     Brazing is a method of joining together metals by inserting the entire work into a hot volume (such as a molten salt bath or a hot furnace) and using a filler metal with a melting point lower than that of the metals to be joined. Brazing is well known in the prior art. 
     What is needed is a more efficient method for making monocoque bicycle frames. 
     SUMMARY OF THE INVENTION 
     The present invention provides a brazed bicycle frame and method for making. At least two bicycle frame half-shells are fabricated. A filler metal is then placed between the bicycle frame half-shells to form a two-part hollow frame section. The two-part hollow frame section is inserted into a hot volume at a temperature higher than the melting temperature of the filler metal but lower than the melting temperature of the two bicycle frame half-shells. The filler metal is allowed to melt. The filler metal is then allowed to cool and harden to form a rigid joint. In one preferred embodiment the bicycle frame half-shells each have a flange that facilitates alignment fixturing and assembly of the two-part hollow frame sections. In another preferred embodiment the filler metal and the bicycle frame half-shells are placed in an extruded or formed grooved section. The grooved section also facilitates alignment fixturing and assembly of the two part hollow frame sections, and helps to strengthens the braze joint. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a bicycle frame in which the rear portion of the frame has been brazed. 
     FIG. 2 shows an upper frame half-shell and a lower frame half-shell and filler metal. 
     FIG. 3 shows the components shown in FIG. 2 brazed together. 
     FIGS. 4A-4D show a procedure for making a preferred embodiment of the present invention. 
     FIG. 5 shows another preferred embodiment of the present invention. 
     FIG. 6 shows another preferred embodiment of the present invention. 
     FIGS. 7-14 show a procedure for making another preferred embodiment of the present invention. 
     FIG. 15 shows another preferred embodiment of the present invention. 
     FIG. 16 shows a preferred two-part frame section being inserted into a molten salt bath. 
     FIG. 17 shows a preferred two-part frame section being heated by a torch. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Preferred embodiments of the present invention can be described by reference to FIGS. 1 -17. 
     Brazing a Bicycle Frame 
     FIG. 1 shows a side view of a first preferred embodiment of the present invention in which chain stay  2  and seat stay  4  of rear portion  6  of bicycle frame  8  have been brazed. FIG. 2 shows a detailed view of the components of seat stay  4  prior to it being brazed. To braze seat stay  4 , upper frame half-shell  9  and lower frame half-shell  10  are first cleaned. Then, braze filler metal  11  is placed between upper frame half-shell  9  and lower frame half-shell  10  and the two halves are assembled. In a preferred embodiment, the upper and lower frame half-shells are aluminum alloy and filler metal  9  is an aluminum brazing alloy. Connecting pins  12  help align and assemble upper frame half-shell  9  appropriately with lower frame half-shell  10 . After the two halves are assembled, seat stay  4  appears as shown in FIG.  3 . As shown in FIG. 16, seat stay  4  is then inserted into a heated volume at approximately 1,400 degrees Fahrenheit to melt the aluminum alloy braze filler metal  11 . In a preferred embodiment the heated volume is a molten salt bath. Seat stay  4  is then removed from the molten salt bath and it cools. Consequently, filler metal  11  re-hardens, brazing together upper frame half-shell  9  and lower frame half-shell  10 . 
     Similarly, front portion  103  of bicycle frame  8  can also be brazed from two halves. By referring to FIG. 2, the advantages of brazing are made very clear. The manufacturer is exact shape and thickness he needs for the bicycle frame section. Also, many frame sections and joints can be simultaneously and uniformly brazed at once in the same heated volume, saving time and money in the construction process. Furthermore brazing uniformly heats the frame sections minimizing distortion and eliminating the need for alignment after brazing. 
     Grooved Brazing Method 
     A second preferred embodiment is shown in FIGS. 4A-4D. As shown in FIG. 4A, grooved section  15  is aligned with upper frame half-shell  17  and lower frame half-shell  16 . A preferred grooved section  15  is shown in FIG.  4 D. In the second preferred embodiment, grooved section  15  is extruded 6061 aluminum and is approximately ¼ inch in diameter. Grooves  24 A and  24 B are rectangular and have a width of approximately 0.07 inch. Upper frame half-shell  17  and lower frame half-shell  16  are also preferably 6061 aluminum and are approximately 0.063 inch thick. As shown in FIG. 4A, the cross section of grooved section  15  is in the general shape of an H-section. Braze filler metal  19  is placed in grooves  24 A and  24 B. Braze filler metal  19  is preferably an aluminum brazing alloy. Upper frame half-shell  17  and lower frame half-shell  16  are then assembled together by inserting them into grooves  24 A and  24 B in grooved section  15  to form joined frame section  20 , as shown in FIG.  4 B. Grooved sections  15  holds upper frame half-shell  17  and lower frame half-shell  16  in assembled alignment as shown in FIGS. 4B and 4C. Note that in FIG. 4C, upper frame half-shell  17  and lower frame half-shell  16  bend at bend  18 . Grooved section  15  is pliable and therefore it can be bent so that it adjusts easily to the shape of the upper and lower halves. 
     The second preferred embodiment provides a significant time savings because grooved section  15  automatically aligns upper frame half-shell  17  so that it is positioned directly above lower frame half-shell  16 . In the second preferred embodiment, prior to applying heat to frame section  20 , upper frame half-shell  17  and lower frame half-shell  16  are secured together to ensure that their desired mating relationship does not alter during the brazing process. A preferred method of securing them together is with the use of clamps. Then, upper frame half-shell  17  and lower frame half-shell  16  are heated and are brazed together in a manner similar to that described in the first preferred embodiment. 
     Although FIGS. 4A-4C show grooved section  15  resembling an H-section in which the grooves are directly opposite one another, it is also possible to adjust the grooves so that they are at other angles. FIG. 5 shows grooved section  21  where the upper groove is angled to the left of the lower groove. FIG. 6 shows grooved section  22  in which the grooves are at 90 degrees to one another. 
     Flanged Half-Shell Brazing Method 
     A third preferred embodiment is shown in FIGS. 7-14. 
     Forming Flanged Half-Shells 
     In the third preferred embodiment, a flat section of any brazable sheet metal  30  (such as aluminum, stainless steel, or titanium) is formed into a half shell by mold  31 . In the preferred embodiment, sheet metal  30  is 6061 aluminum and is approximately 0.050 inch thick. Forming pressure is imparted to the top of sheet metal  30  causing it to assume the shape of mold  31  and become upper frame half-shell  32 , as shown in FIG.  8 . If necessary, excess aluminum is cut away, leaving flange  35  around upper frame half-shell  32 . Preferably, flange  35  extends approximately ¾ inch out from the outside edge of upper frame half-shell  32  to allow for clamping or the creation of other alignment, fixturing or assembly features. In a similar fashion a matching lower frame half-shell  34  is formed (FIG.  10 ). 
     Assembling then Brazing the Flanged Half-Shells 
     As shown in FIG. 10, upper frame half-shell  32  is aligned and assembled to lower frame half-shell  34 . Braze filler metal  36  is placed between upper frame half-shell  32  and lower frame half-shell  34 . FIG. 11 shows a front view of upper frame half-shell  32  secured together with clamps  37  to lower frame half-shell  34  with braze filler metal  36  in between. In a preferred embodiment, braze filler metal  36  is pasted between upper frame half-shell  32  and lower frame half-shell  34 . Clamps  37  are then tightened and upper frame half-shell  32  and lower frame half-shell  34  are heated and brazed together in a manner similar to that described in the first preferred embodiment. 
     Removing the Flange 
     After upper frame half-shell  32  and lower frame half-shell  34  have been heated and filler metal  36  has hardened, clamps  37  are removed, as shown in FIG.  12 . Trimming tool  38 , such as a router or end mill, is then run along the seam of the brazed two-part hollow frame section and flanges  35  are cut away. FIG. 13 shows a front view and FIG. 14 shows a perspective view of upper frame half-shell  32  brazed to lower frame half-shell  34  after flanges  35  have been trimmed away. 
     Of the three preferred embodiments discussed above, Applicants estimate that the third preferred embodiment provides the lowest cost bicycle frame manufacturing method. The same forming, brazing and trimming tools and procedures can be used for different sheet metal types (such as, titanium, aluminum, or stainless steel). Also, not only does the flange function as a temporary alignment, assembly and fixturing area, it further functions as a temporary placement area for the braze filler metal. For example, when the two part frame section is heated during the brazing process the flanges are able to contain the melted braze filler metal so that any excess melted braze filler metal is prevented from flowing onto the outer formed surfaces of the two part frame section. 
     While the above description contains many specifications, the reader should not construe these as limitations on the scope of the invention, but merely as exemplifications of preferred embodiments thereof. Those skilled in the art will envision many other possible variations are within its scope. For example, although it was stated that in the second preferred embodiment that upper frame half-shell  17  and lower frame half-shell  6  are clamped together to ensure that their desired mating relationship does not alter during the brazing process, it would also be possible to braze upper frame half-shell  17  and lower frame half-shell  16  together without using a separate clamping device. Friction provided by grooved section  15  would properly hold upper frame half-shell  17  and lower frame half-shell  16  in their proper mating relationship during brazing. Although FIG. 7 shows sheet metal  30  being formed by mold  31 , it is also possible to form flanged half-shells by machining them. However, the cost is much greater. Also, although FIG. 11 shows upper frame half-shell  32  and lower frame half-shell  34  clamped together, it would also be possible to crimp the flanges together. Or, the flanges could be held together with tabs. Or, the flanges could have mating holes and studs and the flanges could be snapped together. Although, FIG. 11 shows braze filler metal  36  pasted between upper frame half-shell  32  and lower frame half-shell  34 , this process could be simplified by the use of a brazing sheet whereby the braze filler metal sheet is roll bonded to the base metal sheet, thereby eliminating the need for a separate time consuming step of pasting filler metal between the half-shells. An advantage of the above preferred embodiments is found in the fact that at the junction between the upper frame half-shell and the lower frame half-shell there is a smooth seam. This contrasts with welding, which by nature of the process produces a seam that has a rippled appearance. As shown in FIG. 15, it is possible to further trim the seam of the brazed two-part hollow frame section to have a seam that is at the same level as upper frame half-shell  32  and lower frame half-shell  34  so that it will be virtually invisible after painting the hollow frame section. Also, although the above embodiments discussed how to braze the upper frame half-section to the lower frame half-section by melting a filler metal after the upper frame half-section and the lower frame half-section are inserted into a hot volume, it is also possible to braze the upper frame half-section and the lower frame half-section together by melting the filler metal with hand held torch  101  as shown in FIG.  17 . Disadvantages associated with torch brazing frame half-sections together are similar to the disadvantages associated with welding the frame half-sections together. For example, like welding, torch brazing formed matching half-shells along their entire seam is a time consuming and complicated process. It is considered to be delicate work, therefore torch brazers have to be highly trained or high cost robotic torch brazers are used to do an effective, consistent and esthetically acceptable job. Also, although the above preferred embodiments for brazing were discussed in relation to a bicycle frame, the above procedures could also be applied when building other types of monocoque structures. For example, these procedures could be used for building airplane wing sections or the hull or mast of a sailboat. Accordingly the reader is requested to determine the scope of the invention by the appended claims and their legal equivalents, and not by the examples which have been given.