The microforming of surface cavities is a promising method of creating a functional surface on a metal workpiece. In a previous report, basic ideas on a method for and characteristics of metal-formed surface cavities as information transmitters were described. In this study, for small samples or small areas for storing information, the possibility of miniaturizing surface cavities is explored in terms of metal forming and the decoding of the 2D bar code with a PC-based optical measuring system. Dots with a 16-fold higher density of 840 DPI and a pitch of 30 μm on a mirror-finished metal plate were successfully metal-formed and decoded. The limitation of the miniaturization was the need to limit the diameter of surface cavities within 120% of the pitch of the dots. In addition, the effect of the surface roughness of the workpiece was examined to confirm the applicability of this method. Hairline-finished or abraded test pieces were successfully decoded with an enhanced inclination of lighting angles and/or additional image processing for enhancing the optical contrast between the background and the dotted cavities.
For the clearance compensation effect under an unbalanced clearance condition, the effect is related to not only the horizontal force but also the shearing force. At various stages of the design of tool sets, punch length and blankholder condition are important factors. In this paper, we discuss the influences of punch length and blankholder condition on the compensating mechanism through the elastic-plastic finite element method. The results of this study clarified the following. The clearance compensation effect depends on the horizontal force and the shearing force even if the punch length and blankholding condition are varied. When the punch length becomes long using a blankholder, the effect is enhanced. Though, the increasing rate of the effect becomes small with punch length. The use of a blankholder strengthens the effect owing to the bending moment by the shearing force.
The formability of hydroforming of tubes was improved by controlling an internal pressure path for the wrinkling. In the former stage of hydroforming, wrinkles occur at a relatively low pressure, and then the wrinkles are eliminated by increasing the pressure in the latter stage. Local thinning caused by bulging is prevented by the occurrence of wrinkling in the former stage; thus, the tube does not burst. The formability for the wrinkling control is also improved by delaying contact with the die, because local thinning occurs owing to the restriction of material flow induced by such contact. For the wrinkling control, a hydroforming process of steel tubes with a box die was performed in both finite element simulation and experiment, and the range of the pressure path without defects was determined. Moreover, the forming range was extended by eliminating large wrinkles with impulsive pressure. It was found that the wrinkling control for the tube hydroforming is effective in improving the formability.
A new plastic joining method of fixing bars with a hot forged plate is proposed. The bars at room temperature are directly joined to the high-temperature plate using a press. The optimum conditions of the proposed plastic joining method are examined using SCM435 bar and S45C plate on a mechanical press. By adjusting the indentation pressure to below the yield stress of the bar at room temperature during plastic joining, it is possible to attach the bar to the plate without buckling or fattening the bar. The bonding stress (shearing stress) between the bar and the plate is obtained in the range of 70-160 MPa depending on the die clearance, plate temperature or plate thickness. The bonding mechanism of the proposed plastic joining method is discussed from the viewpoints of adhesion of the bar-plate and the clamp stress associated with the thermal stress of the plate.
For the past decade, hot stamping technology has been gradually applied to the production of super high strength automotive parts. Although auto-parts such as bumpers, door impact beams, center pillar reinforces have been produced by hot stamping and installed in many cars all over the world, this promising technology has not spread as much as was expected. One of the major reasons is the high production costs owing to the low productivity of this technology. In this study, we investigate the effect of forming conditions on the shape fixability of hot stamped hat-type parts. On the basis of the obtained results, we introduce a new hot-stamping technology characterized by a markedly high productivity.