Until recently, the only products that can be formed using a conventional cold-roll forming machine are those with cross-sectional profiles constrained to a single width along the longitudinal axis. Products with cross sections of various widths in the longitudinal direction, namely, flexible cross sections, were conventionally fabricated by the press forming method. The servo cold-roll forming machine was developed to yield products with cross-sectional profiles of various widths in the longitudinal direction. This new flexible cold-roll forming method has a number of technical, economical, and ecological advantages such as higher production efficiency, lower initial cost, and wider range of product sizes and materials that can be processed. In this paper, the newly developed servo cold-roll forming machine and the products formed by this machine are introduced.
A compression method for sheet metal was developed, and a compression-tension test under high-speed deformation was performed on three kinds of dual-phase steel sheet, such as those with tensile strength grades of 590MPa, 780MPa and 980MPa. Strain rate range was changed from 7.0×10-3[1/s] to 100[1/s]. From the results, the following conclusions were drawn. (1) The dual-phase high-strength steel sheet shows a strain rate dependence on the Bauschinger effect. (2) The strain rate dependence on the Bauschinger effect in the dual-phase steel sheet can be formulated. (3) There is no consistency in the strain rate history dependence on the Bauschinger effect for the dual-phase steel sheet.
Over the past decades, hot stamping technology has been gradually applied to the production of ultra high-strength automotive components. Although automotive components such as bumpers, door impact beams, center pillar reinforces have been produced by hot stamping and installed in many cars worldwide, this promising technology has not spread as much as expected. One of the major reasons is its high production cost caused by the low productivity of this technology. In this study, we propose a new hot stamping technology characterized by high productivity, which significantly reduces the cycle time of stamping and minimizes or omits laser trimming and piercing.
Sectional thickness profile control has been one of the important size control demands for highly accurate flat products. Profile prediction is necessary for setting up profile control devices in flat rolling mills. The profile prediction of flat products has been performed by analyses using complicated models and FEM models. These analyses need long elapse time even with the newest computers, and are difficult to apply in actual mill operations. To solve such problems, the equation involving the transcription ratio of the roll profile and the inheritance ratio of the inlet profile has been used. To obtain highly accurate prediction, consistent ratios and other factors are needed for the equation. There are only a few studies concerning this equation in which such ratios are numerically discussed especially with regard to prediction accuracy. In this study, a simplified quasi-three-dimensional rolling model is developed for the profile prediction of real-sized flat products using conventional PCs with a short elapse time. The accuracy of the developed model seems as good as the previous models. With the model, the transcription ratios for real-sized flat products can be calculated and the accuracy of the profile prediction equation can be discussed.
A systematic study on the effects of solute carbon and cementite density on ductility was conducted in low-carbon Al-killed steel with 0.022 mass% C. The results obtained are as follows; 1) Total elongation was impaired by the presence of solute carbon. The deterioration is mainly caused by a decrease in local elongation; however, uniform elongation is hardly affected by solute carbon. The dynamic strain aging due to solute carbon is considered to impair local elongation, because necking is promoted by local softening when strain rate increases locally. 2) Total elongation is impaired by the presence of intragranular cementites, but is hardly affected by grain boundary cementites. Uniform elongation decreases clearly with increasing density of intragranular cementites, which is caused by a significant increase in yield strength. Furthermore, since intragranular cementites form voids, they may impair local elongation due to ductile fracture. However, when their density becomes high, in other words, they become significantly small, a slight improvement in local elongation is observed. Grain boundary cementites have no effects on the tensile properties of low-carbon Al-killed steel within the scope of the present study.
In this paper, we describe a pushing-cut process using a stack of two polycarbonate (PC) sheets. The cutting line force of a 30° single, or 30°/90° facet blade on the stacked PC sheets was measured, and the cutting deformation of PC sheets was observed using a CCD camera in order to reveal the effect of a stocked structure on the deformation flow of PC sheets. The side view of the PC sheets was observed with respect to indentation of the blade by varying the height of the blade tip and the thickness of the PC sheets. The following results were obtained: (1) the breaking down and local maximum point of the cutting line force were characterized using the ratio of blade tip height h to the sheet thickness t; (2) the sheared profiles described by the inclined angleβ, the elevation angle γ and the necked height ηn were also characterized using the ratio h/t; (3) the sheared profile was classified into three modes with respect to γ and ηn/t when h/t was varied; (4) upper-bound and lower-bound cutting load responses were observed near the local maximum point owing to unstable slipping between the worksheet (upper layer) and the underlay.
The effect of strain gradient on the stretch flange deformation limit of steel sheets was investigated by hole expansion test under some forming conditions and by FEM. Hole expansion ratio was changed by changing initial hole diameter and punch shapes. It was clarified that limit deformation strain increases as it does not depend on initial hole diameter or punch shape, and thus strain gradient increases. The strain gradient along the direction toward the maximum principal strain did not affect limit deformation strain. The limit deformation thickness strain of the stretch flange portion could be changed by changing strain gradient. The sensitivity of the effect of strain gradient on limit deformation strain tended to increase as material yield ratio increased. These results suggest that the formability of stretch flange deformation area should be determined from not only the maximum principle strain but also the strain gradient and blanking clearance.
A method of spreadsheet calculation of plane strain slip line field solutions by the matrix operator method is presented. Excel and its add-in software ‘solver′ are used for determining the values of variables satisfying the boundary value problems of slip line fields. Two examples of known slip line fields of smooth die compression and indentation problems are calculated to determine if the Excel calculation can give correct results, by comparing with the previous data obtained by Collins and Dewhurst. Our results are in agreement with Collins and Dewhurst's data, confirming that the Excel calculated values are correct. CAD software is used to draw slip line fields and hodographs on the basis of spreadsheet numerical data and found to be suitable for drawing slip line fields and hodographs easily and rapidly.