Investigations On Soft-drawing Deep Forming Process Of Box Shaped Part Using A Magnetorheological Fluid (MRF)

The special-shaped thin wall sheet metal components have been widely used in the aerospace and automobile manufacturing fields which are most non axisymmetric structures.The box shaped part is one of the typical representatives.Its forming difficulty is much more complex than that of the cylindrical part,which is mainly due to the uneven distribution of stress along the circumferential direction,and the large deformation of all parts.A type of fairing is a box shaped thin-walled,and the sidewalls have smaller rotation angles.The conventional deep drawing method needs four times deep drawing(every pass with annealing)to achieve the whole component forming,but it is difficult to meet the requirement because of the surface quality defects.At the same time,because of the geometric structure characteristics of the hollow thin shell,the control difficulty of the deformation uniformity and the forming quality is great.Magnetorheological fluid(MRF)is one of the new intelligent materials widely used in advanced manufacturing field in recent years.Its state and performance can be changed instantaneously and reversally with the external magnetic field.It's a new attempt to make magnetorheological fluid(MRF)as a transfer medium for soft die forming assisted sheet forming.It can give full play to the comprehensive advantages and characteristics of liquid medium,semisolid and solid state transfer media,and play a role of directional quantitative controlled loading.In this paper,the magnetic medium is used to study the deep drawing process of the soft mold of the box parts,and the special structure is designed and developed.The results of square box showed that the wall thickness of the diagonal section of the box shaped parts,from the bottom center to the flange,was decreased first and then increased,and the thinning maximum site distribution is in punch fillet area.With the increase of current intensity,the overall deformation increased and the uniformity of box reduced.Compared with that of 0 A,deep drawing forming limit of 6 A is increased by 21.74 %,the springback is only 0.52 mm,and the attaching capability was improved,meanwhile,the size of precision is also significantly improved.The experimental results of deep drawing process of rectangular box showed that,although the process conditions were different,the thinning of the wall thickness in the bottom corner area was the largest.When the current was increased from 0 A to 3 A,the maximum thinning rate was reduced from 29.6 % to 20.1 %,and the overall deformation uniformity of all parts was significantly improved,the springback was also greatly reduced,and the forming limit and forming quality were also improved.As a result,the new force medium represented by magnetorheological fluid enriches the existing technical system of sheet metal forming and opens up a new way of thinking.