The hydraulic bulge forming of tubular components.

The bulge forming process is a method for shaping tubular components using an internal hydrostatic pressure combined with an axial compressive force. Initial investigations involved carrying out an extensive literature survey to determine the components which could be formed and the types of machines which have been used. Subsequent to this, initial tests were carried out using a previously designed die and tool block in conjunction with a compression testing machine. In these tests copper tubes were formed into expander/reducers and cross pieces by manual adjustment of the axial force and internal pressure.Having obtained experience of the difficulties associated with this die and toolblock, and the loading requirements necessary for theforming process, a new bulge forming machine was designed. The design of the machine was based on the following main criteria: (i) The machine should be free standing and self contained. (ii) The axial deformation of the ends of the tube blank should besynchronised to allow the bulge to form centrally on the tube. (iii) The internal bulge forming pressure should be externallycontrollable during the forming process. (iv) The design should incorporate facilities for subsequent automatic control using a micro-processor/computer. On the basis of these requirements, a machine was designed, built andcommissioned.After correcting a few problems encountered in the commissioning of the machine, a series of tests were carried out, forming tee and cross pieces from copper tube of two different wall thicknesses. These were found to be fairly easy to produce on this new machine. From the resulting components, formed at various combinations of internal pressure and axial compressive force, the limits for a successful forming operation were established. Further analysis of these components was then undertaken to evaluate the effects of the internal pressure and axial compressive force on the bulge height and the wall thickness in the deformation zone. From these results, which have been illustrated graphically, the greatest effect on the resulting bulge can seen to be the axial compressive force.An extension of a theoretical analysis has also been presented, which predicts the wall thickness distribution around the bulge zone. Comparison of these predictions with the experimental wall thickness distributions shows fairly good agreement, especially at the root and tip of the side branch.