Method of manufacturing bicycle frame by die casting and bicycle frame manufactured thereby

摘要

A bicycle frame comprises tubes closed at their ends and lugs for connecting the tubes to form the frame, which lugs are formed by die casting in dies in which the tubes are arranged so as to integrally surround the closed ends of the tubes by the die-cast lugs. The tubes are previously formed at their ends with tapered portions each extending from that corresponding to an extreme end of a boss of the lug surrounding the end of the tube toward an extreme end of the tube. The outer surfaces of the bosses of the die-cast lugs are in substantially constant outer diameter or slightly tapered, thereby, in conjunction with the tapered portions of the tube, eliminating stress concentrations at the extreme ends of the bosses of the lugs, and saving the amount of the die-cast metal resulting in light weight bicycles which can save driving power and cost of manufacture.