To improve the forming performance of the deep drawing and the uniformity of wall thickness and then to improve the whole sheet quality, this paper puts the magnetic intelligent materials into the die as a force transmission medium to play a flexible back pressure role in the sheet deep drawing process, and develops a special experimental setup. The magnetic field affects the rheological properties of magnetorheological fluid (MRF) in the sheet deep drawing process, which changes the stress state and the deformation behavior. The research which takes the 304 stainless steel sheet whose thickness is 0.8 mm as an experimental object shows that, the forming performance of the sheet drawn with the MRF can be significantly improved with the increase of magnetic field intensity. Compared with conventional deep drawing, when the electric current of the coil is 2 A, the forming height limit of the sheet in the deep drawing process based on the pressure of magnetic medium increases by 26.3%, and the whole uniformity of wall thickness is improved obviously, which can effectively inhibit the possibility of the wrinkling defect in the flange. Thus, the sheet deep drawing process based on the pressure of magnetic medium is a potential research direction that may achieve the major breakthrough and progress.
The method of embedded cold-pressing joining could achieve the joining of sheets with different thickness and the joining of dissimilar sheets. Besides, it could meet the lightweight request easily. This article expounded the joining mechanism of this method deeply. To expound the joining mechanism of this method, this article has taken aluminum and stainless steel as examples. In addition, numerical stimulation studies of different hole types' connecting processes had shown that it was easier to reach plastic yield conditions for aluminum and deform it under the same load conditions. The deformation achieved was significantly greater than that for stainless steel. The width increment of the joining parts increased with the increase of the load pressures; however, the thickness changes of the joining parts behaved in an opposite manner. When the pressing volume of the punch reached 2.4 mm, with the width increment of aluminum sheets of the square hole reaching 2.78 mm, which was the maximum width increment, followed by the hexagonal hole, and the round hole being a minimum. Hole type had a small influence on the width of stainless steel sheets. The experimental results of different hole type joining process indicated that compared with round hole and hexagonal hole, the filling of the square hole was relatively difficult. In case of unreasonable process schemes, defects such as ''fake joining,'' ''offset loading'' and ''hole deformation'' would occur. Thus, this article provided a theoretical basis for the scheme establishment and quality control of the embedded cold-pressing joining process.
Sealing problems, subsequent cleaning processes and poor force transmission effect etc. series of problems which strongly restrict the development and application of traditional medium pressure-based sheet forming technology. To overcome these problems, the magnetorheological fluid (MRF) can be used as the alternative force transmission medium. In this study, the deep drawing process of a 304 stainless steel sheet using MRF was investigated. The die cavity was filled with MRF and electric current was used to quantitatively adjust the magnetic fields distribution, which then controls the deformation behavior of the forming sheet. As compared to the conventional deep drawing process, experimental results clearly show that significant improvement in the produced sample quality was obtained when using the MRF with the electric current of 2 A. These improvements include: the height of the boundary circle reduces by 20%, the wall thickness distribution is more uniform, the rebound ratio correspondingly reduces from 9.6% to 0.67%, and the degree of sticking mode and the size precision are significantly increased. The results of this study provide scientific guidance to solve the bottleneck in the traditional deep drawing forming technology. The potential applications of the MRF-based new deep drawing technology to improve the product quality were explored.
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