Abstract
In tube forming, differences in deformation characteristics between thin- and thick-walled tubes must exist. Experimental results using metal tubing with an outer diameter (D) of 8 mm are discussed in this study. Cross-shaped tube hydroforming of 0.5-mm- and 0.8-mm-thick specimens was examined. Protruded long branches were formed under a range of constant fluid pressures and relatively large axial feeding, approximately 4D. The 0.8-mm-thick specimens had a wider range of faultless forming conditions than the 0.5-mm-thick specimens. There seemed to be a boundary in thickness between 0.8 mm (0.10D) and 0.5 mm (0.06D). In addition, the contact condition between the tubular specimen and die strongly affected forming results. An MoS2 spray and PTFE sheets were used as lubricants to examine the effects of friction on axial feeding force and tube deformation. The highest axial feeding force was recorded under the forming condition of 0.8-mm-thick tubing and an MoS2 spray without PTFE sheets. The magnitude of forming pressure had a marginal effect on feeding force. The formed length of branches depended on forming pressure and lubrication.
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