Tube bulge forming for one-piece fabrication of multi-joint head tubes for Ti-alloy-body bicycles

Abstract

The tube bulge forming process is a very effective means to manufacture a complex part as one piece, without the need for additional processes, such as welding and joining. Since one-piece components can endure higher applied loads, they should be considered in the design and manufacture of structural parts. The head tube of a bicycle is one such example, being a four-directional multi-joint component that is also subjected to the highest external load of all bicycle parts. A head tube is therefore ideally fabricated as a singular piece using a suitable process such as tube bulge forming. Commercial Ti-3Al-2.5V alloy tube was selected for this study, as it represents a standard material for Ti-alloy-body bicycles. Finite element simulation is used to predict defects resulting from inappropriate gas blowing conditions and to calculate the optimum forming conditions. Based on the results of finite element analysis and practical experiment, an optimized pressure curve for the bulging of a bicycle head tube is proposed. The effect of microstructural change by deformation is also investigated to predict possible defects in the large-scale deformation of bulged head tubes.