Takamichi Iwata

Formability Improvement Technique for Heated Sheet Metal Forming by Partial Cooling

A forming process for heated sheet metal, such as hot-stamping, has limited use in deformable shapes. Higher temperature areas which have not yet come into contact with dies are more easily deformed; therefore, local deformation occurs at these areas which leads to breakage. To improve the formability of heated sheet metal, a deformation control technique utilizing the temperature dependence of flow stress is proposed. This technique can suppress local deformation by partial cooling around potential cracking areas to harden them before forming. In order to apply this technique to a variety of product shapes, a procedure to determine a suitable initial temperature distribution for deep drawing and biaxial stretching was developed with a coupled thermal structural simulation. In this procedure, finite elements exceeding forming limit strain are highlighted, and an initial temperature distribution is defined with areas of decreased temperature around the elements to increase their resistance to deformation. Subsequently, the partial cooling technique was applied to a deep drawing test with a heated steel sheet. The results of the experiment showed that the proposed technique improved 71% in the forming limit depth compared with results obtained using a uniform initial temperature distribution.

Surface evaluation method and stamping simulation for surface deflection of automotive outer panels

In designing dies of automotive outer panels, the most difficult process is to modify surface deflection. To fabricate high-quality outer panels without modifying dies, it is important to develop an evaluation method and a numerical analysis method for surface deflection of outer panels. In this study, we have developed a new evaluation method that uses the maximum value of curvature calculated using reflecting curves in the surface. This new evaluation method made the examiners evaluation to conform with the digital evaluation. The evaluation results with the new method shows better agreement with the sensory value than those with the conventional methods. We have proposed the new analysis method to predict surface deflection correctly. By the proposed simulation method, plastic deformation is calculated in consideration of stress in thickness direction, and restriking conditions have been examined. We have applied our methods to the fabrication of automotive outer panels, and verified that these are useful and practical.In designing dies of automotive outer panels, the most difficult process is to modify surface deflection. To fabricate high-quality outer panels without modifying dies, it is important to develop an evaluation method and a numerical analysis method for surface deflection of outer panels. In this study, we have developed a new evaluation method that uses the maximum value of curvature calculated using reflecting curves in the surface. This new evaluation method made the examiners evaluation to conform with the digital evaluation. The evaluation results with the new method shows better agreement with the sensory value than those with the conventional methods. We have proposed the new analysis method to predict surface deflection correctly. By the proposed simulation method, plastic deformation is calculated in consideration of stress in thickness direction, and restriking conditions have been examined. We have applied our methods to the fabrication of automotive outer panels, and verified that these are us...

Studies on seven-membered ring derivatives. Part VI. Conformation of (+)-6β-bromo-3,8-dimethyldecahydrozaulen-5-one

Conformational change involving interconversion between two twist-chair conformers in (+)-6β-bromo-3,8-dimethyldecahydroazulen-5-one has been investigated by means of circular dichroism measurements in various solvents. A method for the calculation of the relative conformer population in such a flexible molecule from these measurements has been devised and applied to the ketone. The result obtained is in agreement with that expected from conformational analysis.