Study On Forming Properties Of Pressurized Sheet Assisted By Magnetic Medium Under Different Loading Modes

With the development of science and technology,many new smart materials have been discovered or manufactured,and many of them are used in industrial production,which has brought great economic and social benefits.In this context,the development of smart materials is a new activity in the field of sheet flexible forming.Magneto-rheological fluid(MRF)is a suspension which is mixed by the micron and nano-sized soft magnetic particles whose magnetic conductivity is comparatively higher while magnetic viscosity is lower,the non-magnetic liquid and the additives.This suspension exhibits the Newton fluid characteristics under no magnetic field;however,it can transform from liquid to semi-solid or solid instantly when a certain magnetic field is applied.It is worthy of note that this change is instantaneous and reversible.Firstly,the composition and performance characteristics of MRFs were analyzed,and the required MRF was also purchased in this study.Secondly,the performance testing method of magnetic smart medium was proposed,and the corresponding special tooling structure was developed and properties of the medium were systematic tested and analyzed.Based on the finite element simulation,relationships between the diameter of the exciting convex die,the current intensity,the number of turns of the coil and the distribution of the magnetic field were given.Ultimately,the best technological plan was obtained through the optimization.Taking 304 stainless steel sheet as an example,the influences of MRF on forming height,forming limit and wall thickness distribution of sheet metal were systematically studied under different loading modes.Under different magnetic field,rheological properties of the MRF werechanged,which could realize the change of stress state and deformation behavior in the process of sheet metal forming.With the increase of current intensity,the sheet forming height increased,the thinning degree of various parts also increased,and the angle part thinning degree was the most serious under the same punch loading condition.Subsequently,forming process experiment of the double-pressured sheet assisted by the magnetic medium was carried out,and the structure of the back-pressure unit was developed,realizing the function of double side synchronous loading on the sheet.The research results showed that when the current increased from 0 A to 4 A,the height of sheet metal forming increased by 18.03 % correspondingly.When the punch load was 15 mm,the maximum wall thickness thinning rate decreased from 28 % to 22.6 %,and the forming height increased inversely.With the increase of magnetic field intensity,the wall thickness distribution and deformation uniformity of the sheet were improved under the effect of load transfer and adhesion of MRF.With the gradual maturity of the process theory,it is expected to open up a new idea for the study of the forming process of sheet metal flexible media.