Investigation of Forming Process for High-Expansion-Ratio AL6061 Tube Using Rotary Swaging

As bicycle design continues to develop, consumers are not satisfied with just the convenience and power-saving features of bicycles, but they also demand a fancy appearance. To achieve dramatic deforming of bike frames, an extreme high-profile difference is required. Thus, this study used rotary swaging, which is the best forging method among shrink forming processes, as the preforming process. The tube diameter reduction rates of 0.28 and 0.31 were set as the main parameters, and the effects of feeding speed, feeding method, and friction factor on the formed tube were analyzed. The results indicated that a higher feeding speed results in a lower rate of tube thickness increase and a lower friction factor results in a lower rate of tube thickness increase. Regarding the effects of feeding methods, the automatic feeding method yielded better surface roughness than the manual method. However, the tube may interfere with the swaging dies, causing serious damage to the tube surface. In summary, the tube rotary swaging process can be conducted at tube diameter reduction rates of 0.28 and 0.31. However, owing to the roughly twofold increase in tube thickness to more than 4 mm in some areas, the tube cannot fully fit the die face at these reduction rates under the hydroforming process. The tube can only be completely fitted to the die face at tube diameter reduction rates below 0.24.