| Deep drawing and forming is an important process in sheet metal processing,which is widely used in various industrial fields such as automobile,machinery and electronics.Blank holder force is an important parameter in the deep drawing and forming process,and reasonable selection of blank holder method and application of blank holder force load is an important guarantee to improve the sheet forming performance and complete the forming process smoothly.The electro-permanent magnet blank holder and deep drawing forming process is a new sheet forming process with the magnetic suction force provided by the electro-permanent magnet cushion as the blank holder force.The electro-permanent magnet blank holder and deep drawing forming process involves a variety of physical fields such as electromagnetic,thermal,structural and plastic forming,etc.The interaction of these physical fields has an important impact on the forming process,and the study of related issues has theoretical and practical significance.Firstly,the internal structure and demagnetization working principle of the electropermanent magnet cushion were analyzed,and the spatial magnetic circuit was studied to obtain the main factors affecting the magnitude of magnetic suction force of the electropermanent magnet cushion.On this basis,a set of electro-permanent magnet blank holder and deep-drawing forming dies that can be used in a single-action press was designed.Secondly,the multi-physical fields involved in the electro-permanent magnet blank holder and deep drawing and forming process were analyzed,and the simulation analysis method of sequential coupling of multi-physical fields was used to analyze the relationship curve between the magnetic suction force of the electro-permanent magnet cushion and the magnetizing current;the structural deformation of the electro-permanent magnet cushion after magnetizing and blank holding and the law of blank holding distribution to the slab were simulated and analyzed;the thermal structural coupling analysis was carried out,and under the natural convection condition,the temperature rise of the cushion not affect its normal use,but the thermal deformation of the cushion lead to uneven distribution of the blank holder force on the slab.Again,the effect of structural deformation of the electro-permanent magnet cushion during the blank holding process on the forming effect was analyzed by taking the deepdrawing forming of cylindrical parts as an example,and the results showed that the structural deformation of the electro-permanent magnet cushion change the distribution of the blank holder force on the slab,but have little effect on the forming effect.The thermal deformation of the electro-permanent magnet cushion leads to uneven distribution of the blank holder force,which in turn leads to uneven sheet flow in the flange area of the slab and affects the forming process and the forming results of the cylindrical part.The electropermanent magnet cushion can significantly reduce its temperature rise under forced convection conditions and can effectively improve the uneven distribution of the cushion blank holder force.When the magnetic field area of the electro-permanent magnet cushion is used as the forming area,the transverse dimension of the die structure can be significantly reduced and improve the electro-permanent magnet cushion usable area,and it has no effect on the deep drawing of the slab.Finally,the deep drawing and forming experiments were carried out using an electropermanent magnet blank holder die,and well form cylindrical parts were drawn using the optimum magnetizing current value obtained from the simulation analysis.Under certain demagnetization conditions,the temperature rise of the electro-permanent magnet cushion was measured and the deep drawing and forming experiments were carried out,and the experimental results were basically consistent with the finite element analysis results,which verified the accuracy of the electro-permanent magnet cushion thermal field simulation. |
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