To study cracks, which are affected by bending formation, a hat-shape-forming experiment was conducted and breaking behavior was observed. Then, a prediction method using limited surface strain was investigated. In the case of high-bendability steel, after the occurrence of necking, breakage occurred. It was found that, in this type of breakage, the forming limit could be predicted using a conventional forming limit diagram (FLD), which means that there is limited strain at the middle of the thickness direction. On the other hand, in the case of low-bendability steel, cracks outside the bending surface occurred and grew, followed by breaking without necking. In this case, it was found that the forming limit could be predicted using limit surface strain, which could be obtained by finite element analysis (FEA) and an experiment using V-shape-bending test.
In the finite element analysis (FEA) of high-speed forming for rate-sensitive materials, the accuracy significantly depends on tensile testing data obtained at high-strain-rate. The measurement accuracy of the testing data depends on the design of the specimen geometry. In this study, the effects of important parameters of the specimen geometry, i.e., parallel length, the width of the parallel part, and the radius of the transition zone, on the measurement accuracy were investigated by dynamic explicit FEAs for three different sets of material parameters. The results of the FEAs
in the present study revealed the range of optimal specimen geometry. Additionally, the result showed that the consideration of work hardenability is important for the optimization of the specimen geometry. Finally, our prediction by the present simulations was experimentally verified by tensile test performed at high-strain-rate.
Recently, highly straight wire has been widely used in high-efficiency electronic and medical devices. A rotational blade straightener is particularly effective for straightening coiled wires because the straightener can bend wires along both the longitudinal and circumferential directions. However, it is difficult to straighten fine wires without the need for operators to adjust the straightener, and there is little research on wire straightening. We used fine stainless-steel(AISI 304) wires as experimental specimens. Currently, two blades are used to bend and counterbend a wire. Here, we describe two methods of wire straightening using a rotational blade straightener, and compare the new method with the current method. Intentional twisting is newly applied to wire straightening. We found that the twisting method is easier and more effective than the current bending method. Furthermore, the final straightness is greatly improved by tension annealing after rotational blade straightening.
We report the results of our experiments on and finite-element simulation of the electromagnetic free bulging of aluminum sheet metal. A single copper alloy plate is used in the experiments instead of a winding coil. The experiments are performed with a die of a 10mm circular hole with 2.0mm shoulder radius at 3.0kJ discharge energy. Then, both the formed height and thickness strain distribution of the sheet are measured. The height and strain distribution obtained by the FEM simulation are in close agreement with the experimental results. According to the simulation results, there is little movement of the sheet up to 3.3μs, which corresponds to the time of the maximum magnetic pressure. After 3.3μs, part of the sheet on the die shoulder causes a bending deformation because the sheet placed on the die hole begins to float, and then the sheet assumes the shape of a plastic hinge. In the time range from 5μs to 20μs, the sheet is always floating in parallel to the die hole at 190m/s, and then, a bending wave moves toward the center of the sheet at 330m/s, narrowing the floating region of the sheet. The sheet is deformed into a cone shape, and the bulging finishes at 27.5μs. Our simulation method is applicable to various materials.
Lubrication is one of the most important factors for improving the productivity of tandem cold rolling mills, as improved lubricity makes it possible to increase the rolling speed of thin steel strips and prevent chatter when rolling materials with high deformation resistance. A new hybrid lubrication system is proposed and its effectiveness is clarified. The system is based on a coolant recirculation system in combination with an added system for flexible lubrication control. The key to realizing stable coolant system operation is a control technology for plate-out oil film formation on strips under high-speed-rolling conditions. The new technology has been applied to the fabrication of a production tandem cold-rolling mill for thin steel strips. It successfully enables flexible controllability of lubrication conditions and achieves high-speed stable rolling, while maintaining an oil consumption rate equivalent to that of recirculation systems.
Mash seam welders are not applied in continuous cold rolling lines, because rolling fracture occurs under conditions of high reduction owing to the presence of residual steps at the edge of the lap seam. The flattening mechanism of residual steps has mainly been investigated. The shear force of crossing the upper and lower swaging wheels smoothens the steps without forming double-lapped defects. However, the theory of preventing double-lapped deformation remains unclear. On the basis of experimental analysis and FEM, in this report the effect of cross swaging on the flattening of mash seam welds is discussed. Double-lapped defects occur parallel to the sheet surface in the early stage of swaging, because bulging deformation at the edge of the lap seam cannot be prevented. The double-lapped deformation is prevented as follows: (1) Because of the high-temperature zone within the welded sheets after welding, shear deformation due to cross swaging occurs easier than bulging. (2) As tensile force in the longitudinal direction owing to thermal shrinkage occurs within the sheets immediately after welding, plastic flow in the longitudinal and thickness directions by cross swaging is enhanced.
Several metal flow joining methods have been developed since 1980 aimed at low cost and high productivity. In this study, we examine a new metal flow joining method that enables a shaft and ring to be combined without the need for any specialized punch. In this experimental study, 20-mm-diameter solid shafts and 40-mm-outer-diameter rings having a 20-mm-inner-diameter step at the 18.5-mm-inner-diameter center hole were used. The material combinations of the shaft/ring were S45C/SKD11, A5056/S45C, and S45C/A5056. The experiment was performed as follows. The shaft was inserted into the ring and pressed. Then, metal flowed between the contact faces. The gap between them was filled with the flowing metal, and then, they were joined by the high clamping pressure. The primary results were as follows. This joining method caused small amounts of metal flow because of the highly precise fitting between the shaft and ring. Therefore, they could be joined by small pressing strokes. In this experiment, the maximum joining efficiency (shaft return proof load/joining load) ranged from 25% to 35%. This new metal flow joining method appears to be highly useful in terms of low cost, high productivity, and non-mass production.