Necking Prediction in Tube Hydroforming by Stress-Based Forming Limit Diagrams

Path-independent stress based forming limit diagrams for anisotropic materials along with the Hill 48 yield function; power law strain hardening and isotropic hardening are derived. Bifurcation analyses via solving equilibrium equations of a pointed vertex on subsequent yield loci are utilized. The presented practical forming limit diagrams (FLSDs) show more acceptable agreements with experimental data compared with those obtained by other methods. A typical neck detection macro in APDL is developed by FEA simulation for a free bulge tube hydroforming to confirm the significant simplicity and straightforwardness of the mentioned FLSD.

Hydroforming Simulation and Experiment on Al 5083 T-Shapes

The hydroforming process to manufacture Al 5083 T-shapes with desired protrusion height and uniform thinning rate was evaluated by means of numerical simulation in this work. The optimization of process parameters and the prediction of forming effect were then carried out. Subsequently, the practical forming was performed based on the simulation results. It was obvious that the simulation results agreed well with the experimental ones. In addition, the streamline on the surface which formed in the hydroforming process was observed in the experiment.

Upsetting of Ultrafine-Grained Bulk Al-Mg Alloy Consolidated by Hydrostatic Extrusion

Deformation characteristics and forming limit of ultrafine-grained bulk Al-Mg alloy were examined with upsetting process. The Al-7.5%Mg alloy produced by cryogenic milling and HIP was subjected to hot hydrostatic extrusion as a final consolidation in fabricating the ultrafine-grained bulk material. Upsetting was performed to study their mechanical characteristics in a practical forming process. The extruded specimen showed that the pores remained in spite of the HIP had been collapsed and almost eliminated. The effective removal of the distributed pores resulted in significant increase of formability by preventing early cracking. Metallographic investigations showed that the size of grain remained below a few hundred nanometer scale in the processes.

Dispersion of Glass Powder and Characterization of Thick Film for AC Plasma Display Panels

Bi-based glass pastes were prepared in the mixed organic solvents (α-terpineol and texanol) with different kinds and concentrations of organic dispersant such as fish oil , phosphate ester and poly methyl methacrylate (PMMA). The rheological stability of glass pastes was characterized by using a rheometer and adsorption behavior of organic additives for the glass powders was carried out by using a thermal gravimetric analyzer (TGA).The Bi-based glass pastes exhibited the most stable rheological behavior at an addition of phosphate ester of 0.5 in mass %, due to the steric repulsive force acting on the surface of glass powers with adsorbing the organic additives. This study allowed significant delay of the sedimentation time and suppressed generation of micropores during practical forming process by a screen printing method.