Study On Double - Side Hydraulic Bulging Device And Technology Of Micro - Pipe

The rising demands of micro-tubular components presented by the electronic, medical and micro-system technology require efficient mass production methods for hollow-shaped micro-components. Micro-tube hydro-forming has great potential to mass-produce such micro-components. Tube thickness is at least in the sub-millimeter range, so grain size and grain orientation have an immensely important influence on material properties, plastic deformation law and forming process of micro parts. This is called size effect, and it is size effect that makes micro tubes low plasticity and poor formability. For the problem above, SS304 micro tubes as research object were used in this paper, first some theory about plastic micro forming was introduced, then study on the two-sides micro tube hydro-forming process was done. In this paper, the tensile tests and bulging tests were used to investigate the size effects on the material properties of SS304 micro tubes and influence of tube thickness and grain size on the formability of SS304 micro tubes. It was found that 1) the flow stress of SS304 micro tubes increases with tube thickness while the plasticity deteriorates with decrease of wall thickness and 2) the relationship between the ratio of bursting pressure to ultimate strength and the ratio of outer diameter to wall thickness of the SS304 micro tubes significantly deviates from that relationship of the macro tube. In this study,a micro tube hydro-forming system is developed for Two-sides hydro-forming of the SS304 micro tubes, and the effect of external pressure on the formability of the SS304 micro tubes was studied, it was found that external pressure has a positive effect on the improvement of formability of SS304 micro tubes. The change of microstructure of SS304 micro tubes during hydro-forming are very important to the study of hydro-forming process. In order to find out the change of microstructure of the hydro-formed SS304 micro tubes, a modeling method of a 3D polycrystalline model and multi-scale finite element model are proposed, as well as a method of the displacement boundary condition inheritance of macro pipe to micro crystal model.