For manufacturing twisted products, we proposed a new extrusion process using stepwise assembled dies that are divided the radial direction of billet. In this study, we tried to apply the proposed extrusion process to the production of a hollow shaft with a helical tooth on the outside/inside. Furthermore, we built an extrusion system whose various processing conditions are controlled by a personal computer. The fundamental characteristics are investigated by carrying out an extrusion test using a colour clay on a hollow shaft with a helical tooth produced by the proposed process. The twist depends on the flow angle of the material of the die aperture. The method successfully produces a tooth whose twist continuously changes in the extrusion direction of the extrusion system. These results show that the proposed extrusion process is effective in producing twisted products.
The standardization of the split Hopkinson pressure bar compression test is attempted to determine stress-strain curves at high constant strain rates, say 1000 s-1, for four types of sheet metal specimen under conditions of uniaxial stress using an extrapolation method. The extrapolation method which is a variant of the well-known Cook and Larke extrapolation method has been established for determining curves of dynamic resistance to homogeneous deformation, i.e., intrinsic stress-strain curves. We use laminated circular plate specimens with four initial ratios of constant diameter to height that is equal to the thickness multiplied by the number of the plate laminated. It is also shown that one of eight striker bars with different kinds of tapered cylindrical shapes enables constant strain rate testing throughout the deformation of specimens. The analysis of the experimental results is conducted as follows: First, the mean stress containing friction effects are graphed against strain. Secondly, curves are cross-plotted with the mean stress as the ordinate and current diameter/height (d/h) ratio as the abscissa for various strains. The extrapolation of a curve back to zero d/h in the figure is expected to be the intrinsic flow stress free of the effect of friction.
Combined extrusion forging is effective in load reduction and process simplification. However, combined forging is not used widely. The reason for this seems to be the load and metal flow being difficult to assume. Many research studies have been conducted to solve this problem. Although it is considered that extrusion load and metal flow are affected by the shape ratio of a billet (ho/do), research on this subject is insufficient. In this study, the effects of the shape ratio of a billet on metal flow and extrusion load in forward can-backward can combined extrusion forging were examined by experiment and analysis. The metal flow is affected by the shape ratio of a billet. When the shape ratio is 1.5, the rate of change in extruded length changes. When the shape ratio is 0.4, extruded length is proportional to the stroke. Extrusion load increases with the shape ratio of a billet. The forward and backward extruded lengths and the combined extrusion load can be predicted from the diameter, height and flow stress of a billet and the reduction in what area.
In this study, the effects of the shape ratio of a billet on metal flow and extrusion load in forward rod-backward rod combined extrusion forging were examined by experiment and analysis. Metal flow is affected by the shape ratio of a billet. When the shape ratio is 1.5, the rate of change in extruded length changes. When the shape ratio is 0.4, extruded length is proportional to the stroke. Extrusion load increases with the shape ratio of a billet. The internal crack generated in forward rod-backward rod combined extrusion forging grew with stroke. An estimation method for void volume in the deformed work piece by Archimedes' principle was applied to the analysis of the rod-rod combined extruded work piece of aluminum alloy at each stroke. The critical stroke at which a void was generated could be determined from the relationship between stroke and void volume. A ductile fracture criterion was obtained by the critical stroke and FE simulation. By using the obtained ductile fracture criterion and FE simulation, the critical stroke could be determined.
In this paper, we discuss the possibilities of burr-free blanking and deep drawing of sintered metal fiber sheets. In the blanking, the experimental results showed that a conventional blanking technique can reduce the height of the burr under the conditions of small tool clearance. However, there is still small burr. Then, the authors proposed a new method that can realize burr-free blanking of the sheet. The method proved to be effective also for the dimensionally accurate blanking of the sheet. In the deep drawing, it was found that a technique using a die with a fixed blank holder can realize high-aspect-ratio drawing of the sheet. Moreover, with the use of the holder, a deep-drawn product with no defect like folds can be produced consistently by making the gap between the blank-holding plate and die nearly equal to the thickness of the sheet to be drawn.
As automobile weight reduction is an urgent issue in reducing CO2 from automotive emission, we produce an ultra high-tensile-strength steel strip in a tandem hot strip mill by high-reduction rolling. However in the implementation of high-reduction rolling for an ultra high-tensile-strength steel strip, one serious problem was slippage when the head end did not grip rolls in the finishing latter stand. We confirmed that the head end shape became a bump and the new head end thickness control technology was realized; that is the head end of the rolled slip is thinned down to a thickness less than the programmed thickness like a wedge in the previous stand and it maintains gripping capability in the next stand.
A femtosecond laser is a type of ultrashort-pulse laser. Femtosecond laser irradiation induces high-pressure plasma and shock waves at the surface of a target. Under some irradiation conditions, such shock waves are enough to deform the target plastically. Laser peen forming is a type of sheet metal forming using this deformation by shock waves. The author adopted laser peen forming using femtosecond laser for thin-sheet-metal bending. Generally, shock waves induced in air are much smaller than those induced in water, and thus; are unfavorable for plastic deformation. However, the shock waves induced by a femtosecond laser were enough to bend a thin sheet metal even in air. Elastic prebending was adopted during the process. Bending angle was increased by applying prebending. The effects of laser irradiation conditions on bending efficiency were investigated. The large spot diameter and high fluence improved bending efficiency.
The deformation behavior of the three-roll-type ring rolling is complicated, and no study has yet explained its features. A long computational time is required in the case of applying a full Lagrangian 3-D mesh. In this study, 3-D CAE analysis was applied to three-roll-type ring rolling by using both a Lagrange mesh and Arbitrary Lagrangian Eulerian (ALE) mesh. Both the deformed shape of the cross section and the forward slip shape on the side of the ring showed good agreement with results of the experiment and ALE analysis, the CAE analysis result obtained using the Lagrangian mesh showed a double-bulge shape in cross section. The forward slip shape in the center of the outer ring caused by a difference in the circumference velocity of the drive roll was observed in three-roll-type ring rolling, where the analysis and experiment results showed good agreement. The calculation time for the ALE mesh also became half of that for the Lagrange mesh. Thus, ALE analysis is useful for the CAE analysis of three-roll-type ring rolling.