During the forming process of sheet metals, the drawbead in the die face controls a restraining force so that the sheet flows into the die cavity with tension. In order to investigate a drawgbead restraining force and a pre-strain just after drawbeads which are essential in the finite element analysis of form-ing processes, the friction test and drawing test are employed. The experiments performed with a cir-cular bead stepped bead double circular bead and circular-and-stepped bead in the various forming conditions and bead sizes show that the restraining force varies linearly with the blank holding force. bead radius blank thickness and friction but the pre-strain nonlinearly does with them.

An expert drawbead model is developed for the finite element analysis of stamping processes. The expert model calculates drawbead restraining forces and bead-exit thinnings with the forming condi-tions and drawbead size. The drawbead restraining forces and bead-exit thinnings of a circular draw-bead and stepped drawbead are computed by mathematical models and corrected by the multiple lin-ear regression method based on experimental measurements. The squared drawbead preventing the sheet from drawing-in inside die cavity is assumed to have a very huge drawbead restraining force and no pre-strain just after drawbead. The combined beads are considered as a combination of basic draw-beads such as circular a drawbead stepped drawbead and squared drawbead so that the drawbead restraining forces and bead-exit thinnigs are basically sum of those of basic drawbeads.

In order to analyze the tensile deformation characteristics of laser welded tailored blanks. laser welded blanks of different thikness and strength combinations were prepared and tensile tests were done. The tensile elongation along the direction perpendicular to weld line of laser welded blanks was reduced as increasing the deformation restraining force (strength X thicknes) ratio between two welded sheets and fracture occurred at weaker side of base sheets if void ration of welded sheets and fracture occurred at weaker side of base sheets if void ratio of weld section was less than 45% The tensile elongation along weld line reached above 90% of the elongation of base material if welding was done perfectly. Total elongation along the direction perpendicular to weld line was able to be predicted by force equilibrium and power law behavior of base sheets and it was related with the deformation of stronger sheet and formability of weaker side.

In order to analyze the stretch flange forming characteristics of tailored blanks. laser welded blanks of different thickness and strength combinations were prepared and hole expansion tests were done. The stretch flange formability of laser welded blanks was reduced as increasing the deformation restraining force($strength{\times}thickness$) ratio between two welded sheets. Simulation of stretch forming mode deformation and comparson with experimental results showed that the stretch flange formabili-ty was influenced not only by the difference of the deformation restraining forces between two base sheets but also by the difference of the deformation restraining forces between base sheet and weld. Therefore the stretch flange formability was reduced more rapidly than tensile elongation as increas-ing the deformation restraining force ration. It was also found that simulation of stretch flange forming was more accurate when material properties of weld was given.

In this paper the bending collapse characteristics of 6XXX series aluminum rectangular tubes were studied with a pure bending collapse test rig which could apply the pure bending moment without imposing additional shear and tensile forces. Under the pure bending moment, there occured three kinds of bending collapse modes-local buckling delayed buckling and tensile failure-depending on the a, b, t (depth width thickness) and material properties. Experimental results are compared with the results of finite element method and other methods.

In this study an attempt was made to simulate the coextrusion process of the cladded finned tube manufacturing by extrusion of plasticine. The effects of the billet and the plate inserted between the ingot and extrusion die on the variation of clad thickness of the extruded tube were studied. The results showed that cladded tube with uniform thickness can be obtained by a proper combination of clad thickness of billet and the plate. The relative strength of the billet and clad materials did not affect significantly on the variation of the clad thickness of the extruded tubes.

The present study is concerned with the hydrostatic extrusion process of copper-clad aluminium bar to investigate the bonding conditions as well as the basic flow characteristics. Considering the bonding mechanism of bi-metal contact surface as cold pressure welding the normal pressure and the contact surface expansion are selected as process parameters governing the bonding conditions, in this study the critical normal pressure required for the local extrusion-the protrusion of virgin surfaces by the surface expansion at the interface-is obtained using a slip line method and is then used as a criteron for the bonding. A rigid plastic finite element method is used to analyze the steady state extrusion process. The interface profile of bi-metal rod is predicted by tracking the paths of two particles adja-process. The interface profile of bi-metal rod is predicted by tracking the paths of two particles adja-cent to interface surface. The contact surface area ration and the normal pressure along the interface are calculated and compared to the critical normal pressure to check bonding. It is found that the model predictions are generally in good agreement with the experimental observations. The compar-isons of the extrusion pressure and interface profile by the finite element with those by experi-ments are also given.

This study is concerned with the thermo-biscoplastic finite element analysis of hot tube extrusion through square dies with a mandrel. The problem is treated as a non-steady state and the ALE description is used due to abruptly turning flow at the die aperture. Since the contact heat transfer coefficient and the friction factor are required in the analysis experiments are also carried out to determine the values, In order to apply ceramics to an extrusion die the study is focussed on under-standing the characteristics of the process. The simulated results provide the useful informations such as metal flow temperature distribution stress state etc. The elastic analysis of the dies is carried out to obtain the stress state of the ceramic dies.

Identification of forming limits of sheet metals is an important task to be done before the sheet metal forming processes. The information of the forming limit is indispensable for design of deformed shapes and related forming processes. This procedure becomes more important than ever as the auto-body becomes complicated and the number of auto-body parts is reduced for lower production cost. To identify the forming limit of sheet metals stretching with a hemispherical punch has gained popularity because of the convenient experimental procedure. The stretching experiment however has localized deformation or the shear band is originated from the non-unifrom deformation in the critical circum-stance instead of the absolute criterion. More accurate information of the forming limit therefore could be obtained by a more appropriate experiment to the real process. In this papaer an experiment program is devised to practivally identify the forming limits of sheet metals for auto-body parts. The experiment program contains not only stretching but deep-drawing Both forming experiments use the same hemispherical punch while they use different specimens. Deep-drawing experiments use speci-mens cut out in circular arc on both sides of circular blank to make it torn during the deep-drawing They also use speciments cut out straight in one side of a circular blank to make it deformed unevenly which causes local deformation during the deep-drawing. The experimental result demonstrates that the forming limit diagrams in the two cases show difference in their effective magnitude. The forming limit curve from deep-drawing is located lower than that from stretching. It is noted from the result that the deep-drawing process causes acceleration of localized deformation in comparison with the stretching process. From the experimental result the maximum value of forming limit could be pre-dicted for safe design.