| In recent years,sheet metal forming technology has been widely used in aerospace and automotive industries,and has become the main way of manufacturing large and small parts in these industries.Sheet metal forming technology has been paid closely attention by many scholars at home and abroad,but there are also some technical problems,such as poor uniformity of deformation caused by uneven stress of sheet metal.How to improve the formability of sheet metal is one of the long-term goals in this field,and it is also an important basis to determine the quality and reliability of sheet metal forming.Magnetic medium is a new type of intelligent material,which has been applied in advanced manufacturing field.Its state can change instantaneously and reversibly with the action of external magnetic field.It can change between liquid,semisolid and quasi-solid under artificial control,so it is a very meaningful attempt to replace the traditional rigid punch as a soft die.At the same time,overlapping sheet forming is also one of the important ways to improve the formability of light alloy sheet.The friction force between the two sheets can provide the longitudinal stress for the target sheet,which can greatly delay the rupture of the sheet and improve the formability and deformation uniformity of the sheet.This paper combines the advantages of these two kinds of forming methods,and carries out the forming experiment with the help of magnetic medium after adding a layer of sheet metal to the outer side of the target sheet.In this paper,the effect of overlapping sheet conditions on the formability of magnetic force-transmitting medium for Al1060 aluminium sheet is studied,and a special device structure is developed.The results show that the forming behavior and forming ability of the aluminum sheet may be changed by adding an overlapping sheet.Compared with the condition without overlapping sheet,when the thickness of the overlapping sheet is 0.5mm,the maximum thinning rate reduces from 43.95% to 38.16%.It improves the deformation uniformity of the entire target aluminum sheet,and the forming performance also increases with it.Compared with the situation of 1mm overlapping sheet thickness under the same condition,the uniformities of the wall thickness distribution and forming properties of the resulting target aluminum sheet with a overlapping sheet thickness of 0.5mm are significantly better,it reveals the internal mechanism.It also establishes a theoretical model of the warp stress varies with angle,and provides scientific guidance for the improvement of light alloy forming performance and the expanding of the implementation about thin sheet magnetic media pressurized technology.Finally,the optimal overlapping sheet conditions were determined,and the effects of magnetic medium concentration,current intensity and lubrication between sheets on the overall forming were compared.The results show that: With the increase of current intensity or mass fraction of MRF,the ultimate limit of the target sheet is significantly increased when the double-layer sheets reach the forming limit,and the size of the cracking portion is decreased.As the mass fraction of the magnetron fluid increases from 56% to 80% with 3A field coil current,the rate of decrease of the wall thickness of the target sheet reached 15.75% and the ultimate limit height has increased by 8.74%.It can be seen that with stronger current intensity or higher mass fraction of the MRF,the improvement of the uniformity and coordination of the deformation of each part of the sheet is promoted.Meanwhile,the experimental results show that the thickness distribution and forming limit of the sheet metal without lubricant are better than that of the sheet metal with lubrication,which indicates that the friction between the two sheets can improve the forming performance of the target sheet metal.This study provides a scientific basis for improving the forming performance and comprehensive quality of low-plastic lightweight sheet. |
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