Sheet metal forming simulations are now widely used for predicting forming defects in the design of drawing dies for automotive panels. As a countermeasure against defects, however, performing a variety of simulations currently leads to the requirement of many man-hours since designers repeat the process of trial and error on the basis of their experience. A numerical optimization methodology has been recently applied to stamping in research. The optimization of forming conditions, such as the drawing bead force of actual parts and the blank size, has resulted in difficulties because it involves a large number of constraints such as formability and cost. Moreover, the objective function has multiple peaks. In this study focus on the independence of variables and develop a new method of searching the best feasible solution in the case of complicated design problems such as automotive panels. There are two steps in the developed method. 1) The optimization process is applied to the design variables with strongly related objective functions. 2) All design variables are optimized by considering all objective functions. This method was compared with optimization techniques such as simulated annealing. More optimal solutions for automotive parts can be obtained by applying the proposed method.

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The spiral extrusion processing method that forms an inner spiral multi-grooved tube by hot extrusion is proposed. The spiral extrusion processing method is a compound die extrusion method that installs a rotary plug at the exit of the die mandrel of porthole dies. In this paper, the effects of extrusion conditions and rotary plug shape on groove torsion angle, section groove angle and groove depth in the inner spiral multi-grooved tube are investigated. As a result, a good inner spiral multi-grooved tube is formed in which extrusion temperature and extrusion ram speed are low. Even if the working height of the rotary plug increases, only the outer diameter of the extruded inner spiral multi-grooved tube increases, and therefore, it is understood that the predetermined inner spiral multi-grooved tube is not provided.

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Femtosecond laser is a type of ultrashort-pulse laser. Ultrashort-pulse laser irradiation generates high-pressure plasma and shock waves at the surface of the target. If the target is irradiated in water, the shock waves are enough to deform the target plastically. The authors proposed a new microjoining method using the shock waves accompanied by femtosecond laser irradiation. A thin wire was mounted in a fit bore drilled in a plate, and the laser was focused around the edge of the wire end face. The wire was deformed by shock waves generated by many laser pulses. After the laser irradiation, the deformed wire prevented the release of the plate, as well as the rivet connection. Some model tests were performed to examine forming properties and joining strength. Laser pulse energy, spot diameter and laser spot position influenced the deformed shape and joining strength. In the case of irradiation close to the wire edge, the deformed shape and joining strength varied. They were made stable by transferring the laser spot intermittently.

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The evolution of structural anisotropy in metallic hollow sphere (MHS) compacts during uniaxial compression in elevated temperatures is examined by experimentation as well as numerical simulation, in which an anisotropic continuum model for the compaction of powder packing is applied. The contacts between MHSs are enlarged with the reduction in the height of the compacts during firing, although the contact areas in the lateral direction are smaller than those in the vertical direction. The calculated results are in good agreement with the experimental data. A quasi-static compression test at room temperature for the sintered bodies is also conducted to reveal the correlation of their strength with the reduction in height during firing. It is shown that the bodies whose height is reduced over a certain value during firing have sufficient strength regardless of sintering temperature and time. Optimum sintering conditions to obtain firm MHS bodies can be estimated by the present method of simulation.

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A numerical simulation of the split Hopkinson pressure bar impact compression test is performed to verify the experimental technique for obtaining a more accurate stress-strain curve. The extrapolation method of eliminating the frictional effect of the tool-specimen interface from the stress-strain curve is numerically verified when the curve including oscillatory wave is appropriately smoothed. Furthermore, regarding the technique where the round headed striker bar is used to suppress oscillation in stress waves, the proper test condition is numerically inspected. One appropriate method in determining the radius is presented, where the maximum strain obtained from the dimension of the specimen is conformed with that calculated from the stress pulse. In the case where the reflected wave contains oscillatory components, if strain-rate is calculated from the difference between the input pulse and the transmitted pulse, a more accurate relationship between stress and strain is obtained in a small-strain region.

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A resistance heating process of a side wall for warm and hot spline forming of cups was developed to manufacture high tensile strength steel gears. The side wall of the cup was heated by the electrification to decrease the forming load and to increase the formability. Since the cross-sectional area of the side wall having a uniform wall thickness is uniform, the heating of the side wall by the resistance heating becomes uniform. The inhomogeneous contact between the electrode and side wall was improved by inserting copper foils in the interface, and thus the temperature distribution in the hoop direction became uniform. The uniformity of the temperature distribution in the axial direction was improved by decreasing the total area of the contact between the electrode and side wall and by increasing the number of contacts. The side wall of the cup was successfully shaped into a gear by the warm and hot spline forming process using resistance heating.

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