In axisymmetric tube reducing of thin sheet metal tubes, the reduction ratio of diameter is an important factor in the process design. For very thin sheet metal tubes, tube reducing cannot be successfully employed due to wrinkling of the edge portion of a tube as well as due to buckling of its rest portion.
In the present study, thin sheet metal tubes are subjected to internal pressure during the tube reducing process in order to increase the forming limits, i.e. to increase the reduction ratio of diameter. Analysis is made for the sound flow deformation in nonsteady tube reducing considering the normal anisotropy. Experiments are carried out for brass tubes. From the experimental results there exists an optimal range of semi-cone angle of the die to avoid both the circumferential wrinkling at the edge and the side buckling of the tube. There is a good agreement in forming load between analysis and experiments. The present study shown to give an effective guide line in design the tube reducing process for very thin-walled sheet metal tubes. However, it is suggested that an analysis for instability should be made to design the process more effectively.
