The present invention is related to a method and an apparatus for welding the front fork of a bicycle, and more particularly to a method and an apparatus which utilizes two high-frequency heating means to weld the front fork of the bicycle.
The main structure of the general front fork of a bicycle includes a hollow, substantially rectangular joint having a central bore therethrough and two oval-shaped openings respectively on the opposite sides of the central bore; a hollow handlebar stem with one end fixed into the central bore; and two fork blades with respective one ends fixed into the respective openings. According to the above-described front fork, the other end of the handlebar stem is used to connect with a handlebar of the bicycle, and the respective other ends of the fork blades are used to pivotally connect to the two ends of the hub of the front wheel.
When people ride a bicycle, they usually incline forward and grasp the handlebar grips to support almost the entire weight of their upper body so they can easily propel the bicycle by the action of their feet upon the pedals. Therefore, it is extremely important in a bicycle, especially a road-racing bicycle, that the handlebar, the front fork, and the front wheel are capable of bearing reasonably large loads. If the rider has an accident in which any one of the above-mentioned portions is broken, it will cause the rider to fall down, hitting the ground with his head foremost.
The front fork is the weakest portion of all because it is constructed of three elements jointed together. Those who are ordinarily skilled in the art have done much experimentation trying to make the jointed parts of the front fork stay firmly combined together as one substantially integral part, even during violent vibration and impact. Nowadays, the general method used to achieve this goal is the welding process.
One type of welding process which may be used is electric welding. However, in order to completely seal the junctures in the joint between the crosspiece, the handlebar stem, and the fork blades using an electric welding process, one must use many weld metals and expend a great deal of time. Thus, the spot welding technique, which merely fuses several spot areas of the junctures between the parts, is prevalent among the bicycle manufacturers. Although spot welding is more economical, the stability of the front fork decreases to an extent that is undesirable.
Another one of the welding processes which was developed to solve the above-mentioned problem is copper welding. Its welding procedures include: first placing copper into the hollow crosspiece; inserting the handlebar stem and the fork blades into the openings of the crosspiece properly; and then applying the welding torch to the predetermined positions which one desires to weld. In this method, the copper is first melted due to the fact that its melting temperature is lower than the front fork, and then it begins to flow into the gaps existing in the junctures between the crosspiece, the handlebar stem, and the fork blades as a result of the capillarity effect. Therefore, after the welded portions cool down, the crosspiece, the handlebar, and the fork blades are firmly combined together as an integral part.
Actually, copper welding provides the advantages of security and also saves time. However, unfortunately, the capillarity effect of copper is significantly affected by temperature. If one of the junctures between the crosspiece, the handlebar stem, and the fork blades reaches the melting temperature of the copper before the others, most of the melting copper will flow to that juncture, causing too much copper to accumulate on that juncture so that the copper overflows out of the joint. This overflowing phenomena happens not only when one juncture reaches the melting temperature of copper first, but also whenever the three junctures exist at different temperature conditions. Thus, the overflowing phenomena frequently happens in the manufacturing process of the front fork of the bicycle as a result of the different thicknesses between the tube walls of the handlebar stem and the fork blade. In general, the wall thickness of the handlebar stem is about 2.4 to 2.8 mm, and that of the fork blade is about 1.2 mm. Since the wall thickness of the handlebar stem is at least two times that of the wall thickness of the fork blade, it is difficult in the conventional welding process to control the temperatures of the junctures to maintain equality. Therefore, in many cases, it is necessary to supplement extra copper onto the portions which are not covered by the copper, or to rub out the copper overflow after the welding is finished. Moreover, this situation significantly affects the development of automatic production, the structural strength of the front fork, and the ultimate appearance of the finished bicycle.
The above-described copper welding technique may also utilize a high-frequency heating system to accomplish the heating procedure, which helps reduce the cost of manufacture. However, since the conventional high-frequency heating system uses an induction coil surrounding the outer surface of the front fork for heating therefrom, it contributes to the temperature problem described above, and this problem remains to be solved.
A method and an apparatus for welding the front fork of a bicycle according to the preferred embodiment of the present invention intends to improve upon the abovedescribed disadvantages.