We investigate the deformation behavior of a high-strength steel alloy in bore expansion both experimentally and analytically to clarify the effects of the material model (anisotropic yield function) on the predictive accuracy of finite element simulations of bore expansion. The test material used in the bore expansion test is a dual-phase steel alloy with a tensile strength of 780MPa. The elastic-plastic deformation behavior of the test material is precisely measured by biaxial tensile tests using cruciform specimens to determine the appropriate anisotropic yield function for the test material. The measured contours of plastic work and the directions of plastic strain rates are in good agreement with those predicted using Yld2000-2d with an exponent of 4. Moreover, forming simulations of and experiments on the bore expansion of the test material have been carried out. The anisotropic yield functions used in the simulation are von Mises, Hill’s quadratic and Yld2000-2d nonquadratic yield functions. Yld2000-2d with an exponent of 4 has given the closest agreement with the experimental results. Consequently, anisotropic yield functions significantly affect the predictive accuracy of the deformation behavior of a sheet in bore expansion.
There is limited application of magnesium alloys as metal-forming products because of their poor plastic deformability at normal temperatures and their high production cost. To promote products manufactured by metal forming, rolling technologies enabling the production of thin sheets with suitable mechanical properties and surface qualities are required. To investigate the optimum rolling condition, hot-rolled AZ31 sheets were experimentally rolled by four-pass warm rolling in a total reduction range of 76 % with or without lubrication states in the temperature range from 293 K to 573 K. Rolling behaviors such as rolling force, grain structures and grain orientations were investigated. Mechanical properties such as tensile strength, elongation and r value were measured by tensile tests. Then, bending tests and conical cup tests are conducted for sheet forming tests. Finally, the effect of warm rolling conditions on their mechanical properties and sheet formability are discussed.
A coil used in this seam welding has a large mechanical strength because it is fabricated from one copper alloy plate. When the coil has a small width and a small thickness, the welding of sheet metals can be performed using a low discharge energy in general. However, the coil is unfit for an experiment with a high discharge energy because the mechanical strength of the coil decreases with a decrease in coil cross-sectional area. Therefore, the proper selection of coil shapes is important, and the coil shape should be determined for the size of the sheet metals. The influence of coil width on welding an aluminum sheet to an aluminum sheet or a magnesium alloy sheet is confirmed. It becomes clear that a coil of 3 mm width is used only for the experiment with a low discharge energy because of its low durability and the influence of discharge circuit. To improve energy efficiency, the coil with enough cross-sectional area and many grooves of uniform depth is fabricated, and the effect is confirmed. A coil with grooves can weld sheet metals with a lower discharge energy compared with a coil without grooves.
To improve the joining range of ultra high strength steel and aluminum alloy sheets in self-pierce riveting, the determination of die shape was proposed. A self-pierce rivet is driven through the upper sheet and flared in the lower sheet with a die, and the rivet directly pierces into the sheets without drilling the sheets beforehand unlike conventional rivets. Insufficient driving though the upper sheet and fracture of the lower sheet occur owing to the high strength and low ductility of the ultra sheet, respectively. To prevent the occurrence of defects, the determination of a die shape for the depth of die projection and the depth of the die was proposed. The ultra high strength steel sheet having a tensile strength of 980MPa and an aluminum alloy sheet were successfully joined using a die with appropriate shapes.
In this paper, we describe a pushing-cut process using multiple pieces of a white-coated cardboard. In the cutting process of cardboards such as post cards, the cutting quality on wedged cardboards is empirically known to be affected by the piled-up pieces of the cardboards, friction coefficient, the thickness of the coated layer, the blade tip profile and other factors. In this work, the effects of mechanical conditions on the cardboard cutting characteristics were experimentally investigated by varying blade apex angle, the surface roughness of the blade, tip thickness and the number of piled-up pieces of cardboard. The following experimental results were obtained: (1) the breaking down and local minimum point of cutting line force were characterized using blade apex angle and tip thickness; (2) the position of the peaked line force for each layer depended on the number of piled-up pieces and its order; (3) an apex angle less than 42 degree is stable for the release of the breakdown layer, whereas an apex angle larger than 53 degrees is in a fairly sticky state and unstable for such release.
Friction for a large reduction in thickness in forging of plates was reduced by oscillating forging load. In this process, compressive load is partially released during the forming with a liquid lubricant to relubricate the outer portion of the plate. The gap between the die and the outer portion of the plate in each release is caused by the difference in elastic recovery between the die and the plate, and the liquid lubricant is automatically fed into the gap during the partial release of the load. In the compression of an aluminum alloy plate, the effects of the releasing ratio of the load and the number of releases on the reduction in compressive load were examined. Compressive load was reduced by load oscillation, and the thickness of the compressed plate was significantly decreased. The mechanism of automatic relubrication by the load oscillation was verified by inducing the corrosion of part of the gap in a forging experiment. It was found that load oscillation having an automatic relubrication function is effective in preventing the increase in the load in the forging of plates.
A method of manufacturing an axisymmetric cup with necked edges from an aluminum flat sheet metal by the numerical controlled spinning technique is presented. The first step entails forming a cup-shaped blank along the surface of a die from a flat circular sheet metal by numerical control spinning. The second step entails necking the opening edge of the cup-shaped blank without a die. Suitable conditions for the spinning processes without causing any defects, such as wall fractures and wrinkling, are sought and examined. The process conditions, which include the roll path configuration, the feed velocity of the roll and the revolution speed of the spinning machine spindle, are optimized for successful production. The findings confirm that the numerical controlled necking technique without a die enables us to manufacture necked cups with adequate accuracy and to use the data in the manufacture of other similar products.