Hole expansion using a flat-bottomed cylindrical punch was carried out to clarify the effects of piercing conditions on the fracture behavior of high-strength steel sheets. The results showed that the hole expansion rate λ negligibly changed with the piercing conditions in the case of a small initial hole diameter because of fracture from the inside of the edge of the hole. On the other hand, λ drastically changed in the case of a large initial hole diameter because of fracture from the edge of the hole. Moreover, by investigating the correlation between the quality of what around the hole and λ for a large initial hole diameter, it was clarified that λ of ferrite single-phase steel is affected by hardening behavior, and λ of ferrite-pearlite dual-phase steel is affected by the number of microvoids.
To produce magnesium alloy covers reinforced with ribs at a lower load, a new forging process, in which thin plates made of magnesium alloy are partially compressed using a servo press, is proposed. In this study, the features of the forming process are investigated by carrying out forging tests on the thin plates under various conditions. The ribs are simply formed at the back of the cover using the proposed process, but the contraction is generated at a place where two ribs intersect on the face of the cover. It is clarified that covers having a flat and smooth surface with no contraction are produced using the compressive process with a restriction in the height of the ribs. These results suggest the effectiveness of the proposed forging process.
Ni-plated steel wire used for springs in electrical appliances and other devices has good corrosion resistance. Surface gloss as well as lubricity is required in spring cold working. To achieve both surface gloss and lubricity, a liquid lubricant was used in the final pass while soap powder lubricant was used in former passes. This basic research has been conducted to investigate the relationship between surface gloss and processing parameters in the final pass. As reported in our previous paper, the surface gloss of Ni-plated steel wire increases with an increase in the approach semi angle of the die and the effects of the number of times of dilution in an emulsion type lubricant are minimal. Thus, it is important to investigate friction coefficient and die pressure, which can affect die life, and to reveal the key parameter for surface gloss. In this paper, friction coefficient and die pressure are evaluated by finite element method and the relationships between experimental surface gloss and processing parameters are discussed.
We previously proposed a two-step cold extrusion method that requires a relatively low punch pressure to form completely teethed gears. The method was found to be capable of forming gears with better quality than gear formed by the conventional method. In this paper we report on our study of the application of this forming method to the S15C low-carbon steel material that has been pretreated by carburization only, and as such has a high carbon content in its surface layer. The specifications of the spur gear examined were as follows: module m=1.25 and number of teeth Z=18. We found that this method is capable of forming gears with a high carbon content in their surface layer with a low punch pressure applied to a material that is of high deformation resistance and pretreated by carburization only. By using this method, the carburization process after gear forming can be replaced with induction hardening, which takes less time.
Gears shaped by the cold extrusion method through the reduction in the outer diameter of a workpiece showed burrlike irregularities in their end faces owing to the different rates of reduction in area at the dedendum and addendum. To use such gears in actual applications, it was necessary to remove such irregularities. In this study, by to reduce irregularities in the end faces, we shaped gears using a stepped mandrel and a toothed container, and by expanding the workpiece by pressing its inner surface outward. The specifications of the spur gears examined were as follows: module m=1.0 and number of teeth Z=26. The workpiece material was carbon steel. The large diameter of the mandrel was varied in order to evaluate the effects of the reduction in area. As a result, we obtained completely toothed gears that have fewer burrlike irregularities in their end faces with a low reduction in area. The pressure of the stepped mandrel (punch) required for this shaping is far below the strength of mandrel materials. Each gear was shaped even when a two-layered workpiece was used.
Sectional thickness profile control is 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 is performed by analyses using complicated models and FEM models. These analyses need a long elapse time even with the fastest computers, and are difficult to apply in actual mill operations. To solve such problems, an equation involving the transcription ratio of the roll profile and the inheritance ratio of the inlet profile is used. To obtain a highly accurate prediction, consistent ratios and other factors are needed for the equation. There are only a few studies of this equation in which such ratios are numerically discussed, especially with regard to prediction accuracy. In this paper, the accuracy of the profile prediction equation is discussed using a simple quasi-three dimensional rolling model that we developed. It is clear that the mechanical crown of the profile prediction equation must be defined anew, and that a combination of a quadratic curve and a high-order power curve is necessary for such an equation.
The deep drawability of tailored blanks (TBs) composed of thick and thin sheets is considerably lower than that of their component sheets, since the plane-strain stretching mode is more likely to occur in such TBs as a result of the movement of the weld bead line at the bottom of the cup during forming. To improve the deep drawability of TBs, a new forming technology using a counterpunch is proposed, where the movement of the weld bead line during forming is strongly constrained by the counterpunch pressure. From the results of square-cup drawing experiments on several types of TB of mild steel/high-strength steel sheets, it was found that the limiting cup height increases markedly with increasing counterpunch pressure. One good feature of this forming technology is that the action of counterpunch pressure is necessary only on the thick (or stronger) sheet part, not on the entire cup bottom.