We analyzed a sequence of multi-stage automatic cold forging processes composed of four axisymmetric processes followed by a non-axisymmetric process using rigid-plastic finite element based forging simulators. The forging sequence selected for an example involves a piercing process and a heading process accompanying folding or overlapping, which all make it difficult to simulate the processes. To reduce computational time and to enhance the solution reliability, only the non-symmetric process was analyzed by the three-dimensional approach after the axisymmetric processes were analyzed by the two-dimensional approach. It has been emphsized that this capability is very helpful in simulating the multi-stage automatic forging processes which are next to axisymmetric or involve several axisymmetric processes.

In the present work, the two-back stress model is proposed and continuum damage mechanics (CDM) is incorporated into the plastic constitutive relation in order to describe the plastic deformation localization and the damage evolution in a deforming continuum body. Coupling between damage mechanics and isothermal rate independent plasticity is performed using the kinematic hardening rule, which in turn is formulated by combining the nonlinear Armstrong-Frederick rule and the Phillips rule. The numerical analyses are carried out within h deformation theory. It is noted that the damage evolution within a work piece accelerates the plastic deformation localization such that the material with lower hardening exponent results in a rapid shear band formation. Moreover, the results from the numerical analysis reflected closely with the micro-structures around the fractured regime. The effects of the various hardening parameters on deformation localization are also investigated. As the nonlinear strain rate description in the back stress evolution becomes dominant, the strain localization becomes intensified as well as the damage evolution.

The shape of rectangular cup used for Ni-MH(Nickel-coated Metal Hydrogen) battery for hybrid car looks quite simple, but the forming process of extruding and setting up process design are highly difficult. Furthermore, there are few concrete reports on the rectangular deep drawn cup as part of hybrid vehicles till now. In this study, process design for rectangular cup in the multi-stage deep drawing process is carried out, and FE analysis is also preformed based on the result of the process design. From the simulation result, some unexpected problems such as earing, wrinkling and excessive thickness changes of the intermediate blank occurred. To overcome these failures, a series of modification for punch shape in the forming process design are completed and applied. Considering the modified punch shape in the multi-stage deep drawing process, additional FE analysis is also carried out and the simulation result is verified in view of the deformed shape, thickness change and effective strain distribution. The result of FE analysis with the improved process design confirmed not only reducing thinning of wall and possibilities of failure but also improving the quality of drawing product through the modification of punch shape.

Crash box is one of the most important automotive parts for crash energy absorption and is equipped at the front end of the front side member. The specific characteristics of aluminum alloys offer the possibility to design cost-effective lightweight structures with high stiffness and excellent crash energy absorption potential. This study deals with crashworthiness of aluminum crash box for an auto-body with the various types of cross section. For aluminum alloys, A17003-T7 and A17003-T5, the dynamic tensile test was carried out to apply for crash analysis at the range of strain from 0.003/sec to 200/sec. The crash analysis and the crash test were carried out for three cross sections of rectangle, hexagon and octagon. The analysis results show that the octagon cross section shape with A17003-T5 has higher crashworthiness than other cross section shapes. The effect of rib shapes in the cross section is important factor in crash analysis. Finally, new configuration of crash box with high crash energy absorption was suggested.

Alloy718 is the nickel-base super alloy well used as gas turbine components under severe operating conditions because of its high strength at high temperature and excellent creep resistance. In this study, a coupling bolt for the gas turbine component is manufactured by hot heading process instead of whole machining in order to improve the mechanical properties. Die shape for the hot heading has been designed by general design rule of hot forging and also optimal process condition has been investigated by finite element method. The initial billet temperature and the punch speed have been determined by $1150^{\circ}C$ and 600mm/s on the basis of finite element analysis, respectively. The coupling bolt has been manufactured by 200ton screw press and evaluated by experiment in order to investigate the mechanical properties. As a result of experiment, the mechanical properties such as hardness, tensile strength and creep behavior have been superior to those manufactured by machining.

The control of springback is very important in sheet metal forming since springback affects the dimensional inaccuracy of product. The object of this study is to design the manufacturing process for the improvement of the performance of seat rail by DP780. The influence of process variables such as bend angle and pad force on the springback has been firstly investigated through the comparison between the results of FE-analysis and trial out for initial design based on designer's experience. The process variables of the initial design have been modified in order to improve the dimensional accuracy of seat rail from the prediction of springback by FE-analysis. It was shown from experiment that the improved design satisfied the required specifications such as the dimensional accuracy and the strength of seat rail.

In this paper, experimental investigation has been performed to analyze the forming process of toothed or serrated sheets, which is used as strap engaging surface of the seal to secure together overlapping portions of steel or plastic strapping ligature. Serration formed on the strap engaging surface of the seal prevent from relative slipping between overlapping ligatures after closing the seal. The geometry of tooth on the strap engaging surface is directly related to the quality of securing overlapping ligatures together. Inclined indentation followed by scratching operation has been proposed and applied to the experiments. Punch entry and face angles are selected as process variables to see the influence of these variables on the tooth geometry. Five different punch entry angles have been applied to experiments and three different punch face angles have been selected for each case of punch entry angle. Clay is selected as model material for experiments. Experimental results are summarized in terms of tooth height, tooth width, and aspect ratio such as tooth height to width ratio, respectively.

The effects of blank shape on the safety of stamped parts are studied through the comparison of an optimal blank and the corresponding reference blank shape to show further advantage of the optimal blank. In order to carry out this study, stamping process has been analyzed and the forming history, e.g. accumulated effective strain and thickness has been incorporated in the crash analysis. The reference blank has been determined following to the actual industry guideline, and excessive material to the desired shape has been trimmed off before crash analysis for the objective comparison. Through the study, appreciable increase of impact safety has not been observed and the effective of blank shape is verified not to be significant.

A recent trend in automotive parts has been an integration of sub-assemblies with unified shapes. Tube structures also have been integrated to one body structure by using a near net shape forming instead of adopting welding. A cylindrical elastomer-forming process can be utilized to form a steel tube compressed in a radial direction. This process has some advantages compared to a hydro-forming or a swaging process in the viewpoint of a lower investment and a higher productivity. In order to predict a feasible specification of products within a work capability of the elastomer-forming equipment developed previously, effects of geometrical parameters of a tube on its shape accuracy are examined. Two characteristic parameters to account for the shape accuracy are chosen. One is the curvature radius at the corner part and the other is the straight ratio of the formed region. Careful examination of two parameters has led that the shape accuracy can be easily predicted by the regression equation obtained from the response surface method.