The possibility of controlling the bending angle in press V-bending using shot peening (SP) in the die was confirmed using aluminum alloy A5052 with 1 mm thickness. The bending radius and angle were 10 mm and 90°, respectively. After press bending, the bending angle is greater than 90°. By controlling air pressure and shot mass, the bending angle was reduced using SP. The reduction in bending angle using SP was greater when SP was performed during press loading than after unloading. Under the conditions of this experiment, the reduction in bending angle using SP was small for thicknesses of 2 mm or greater. Future experiments will be planned to use a direct-pressure system with a high shot velocity.

There are two main types of body-frame structures for automobile bodies: monocoque structures, which are made by welding several panel parts together, and space-frame structures, which are made by joining closed-section tubes together. Space-frame structures have high strength and stiffness. Therefore, that can reduce vehicle weight. Furthermore, if the dimensions of the rectangular cross section of the curved tube can be varied in the longitudinal direction, further weight reduction is expected. The bent tube with variable cross section can be formed by the existing method, hydroforming. However, hydroforming requires large dies that fit the shape of the product, and the forming machine is large and expensive, because of the large clamping force required. In this paper, we adopt the roll forming method, which is smaller than the conventional method, has smaller forming load, and can form square tubes continuously. Then, we propose the novel die-less tube bending method in which the straight circular tube is continuously bent and formed into various cross section by means of the rectangular opening formed by the four forming rolls installed in two directions. Using a prototype device, we verified that the bent tube with variable cross section in the longitudinal direction can be formed.

For a better understanding of the effect of the strength difference between soft and hard phases on the Bauschinger effect of dual-phase (DP) steels, we experimentally investigated two types of DP steel, i.e., one with a large strength difference and the other with a small difference. Reversed simple-shear tests revealed that the steel with a larger strength difference showed earlier re-yielding under reverse loading; thus, the strength difference between phases enhances the Bauschinger effect. Furthermore, the actual morphology of the steel with a larger strength difference was reproduced in a finite element model of which hard and soft phases were represented by high and low flow stresses, respectively. By changing the flow stress for the hard phase, the effect of the strength difference was analyzed by finite element analyses. In the simulations, the observed difference of the Bauschinger effect was qualitatively reproduced. It was also shown that strains given to the soft phase in the vicinity of the hard phase are relatively low and those areas first re-yield immediately after reverse loading. This was pronounced in the case with a larger strength difference. The earlier re-yielding for the larger strength difference is possibly ascribe to not only the higher back stresses but also the lower strains.

In this study, we evaluate defects generated during press forming using an ultrasonic phased array. The ultrasonic phased array can capture the occurrence of defects better than measurements using a single probe because it can display the measurement results as a two-dimensional image. A phased array probe was attached to a die using the magnetic force of a magnet, and ultrasonic waves were irradiated to the flange of a cylindrical drawing to evaluate the occurrence of flange wrinkles. When ultrasonic waves were irradiated parallel to wrinkle waves, the wrinkles could be recognized even if the irradiation position was changed. When the wrinkles with a height of about 0.5 mm occurred, the wrinkles could be evaluated for a sheet metal with a thickness of 0.5 mm even with a lubricant of 0.2 ml/s and a processing speed of 50 spm. For a sheet metal with a thickness of 1 mm, the wrinkles could be evaluated by reducing the processing speed to 30 spm with the lubricant usage of 0.2 ml/s.

Ultrafine-grained steels have high strength but small elongation. However, M1.7 small screws with a cross recess could be successfully formed without cracking by cold heading using ultrafine-grained steels. Typically, soft steels are selected to avoid recess cracking to produce a screw with a recess. Ultrafine-grained steels exhibit good formability with respect to compression working, despite being hard steels. In this research, the formability of ultrafine-grained steels was investigated on the basis of true stress-true strain curves. Finite Element Method simulations revealed significant strain generation near the recess during screw forming. Very low carbon ultrafine-grained steels exhibit extremely high fracture stress and fracture strain. The fracture strain is larger than that generated near the recess in a screw. head. As a result, ultrafine grained steels simultaneously achieve outstanding formability and high strength. These features allowed for a reduction in CO₂ emissions by half in the screw manufacturing process as it eliminates the need for quenching and tempering.

Achieving high surface brightness and high processability necessitates the development of a lubricant with suitable extreme-pressure (EP) agents to prevent seizures and heat scratches on strip surfaces. Despite its significance, a comprehensive investigation of the mechanisms by which EP agents function within lubricant oils during cold rolling remains insufficient. In this study, we aim to elucidate the effect of EP agents with varying molecular structures on oil film formation, utilizing micro-Fourier transform infrared spectroscopy (micro-FTIR) in conjunction with ball-on-disk testing. The findings reveal that the molecular structure of EP agents significantly impacts oil film formation, attributable to their condensation behaviors at the entry side of the Hertzian contact area and their distinct viscosity characteristics.

On the basis of geometric numeration in explosive welding, the collision angle and the velocity of the collision point, which are joining parameters, in magnetic pulse welding were obtained by free deformation analysis without collision deformation analysis. The collision angle and the velocity of the collision point on a joining region in a welded sheet were found by comparing positions of them with the joining region in the welded sheet. The study demonstrated the effect of gap length on the joining parameters and a joining process，resulting in the convex deformation of the A1050-H24 moving sheet and the removal of a metal jet. In the joining region, the range of collision angles is from 2.6° to 31.3° and the range of velocities of the collision point is from 7.5 km∙s^-1 to 0.48 km∙s^-1. The small collision angle and the high velocity of the collision point depend on the plastic hinge appearing at the early stage in the convex deformation of the moving sheet. It has been clarified that the joining parameters can be calculated by incorporating geometric numeration into the convex shape of the moving sheet.

The effects of die temperature, die gap, plunger speed and molten metal temperature on the flow length of A1070 pure aluminum in a thin die gap were investigated. The die gaps were 0.5, 0.8 and 1.0 mm. The plunger speeds were 0.2, 0.4, 0.6 and 0.8 m/s. The die temperatures were 30, 70, 110 and 150 °C.The molten metal temperatures were 680, 730 and 780 °C. When the die gap was 0.5 mm, the flow length was largest when the die temperature was 30 °C and the plunger speed was 0.2 m/s, which is contrary to conventional expectations. However, when the die gap was 1.0 mm, the flow length increased as the die temperature and plunger speed increased, which aligns with previously reported results. It became clear that when the die gap was 0.5 mm, the effects of die temperature and plunger speed on flow length were opposite to those for a die gap wider than 0.5 mm. The cause of this phenomenon is discussed in terms of the adhesion and peeling of the solidification layer used.