Research on the Effects of the Movable Die and its Counter Force on Sheet Hydroforming

摘要

An improved Sheet Hydro-forming process was proposed,which was investigated in Institute of Metal Research,Chinese Academy of Sciences.ASAME system and FEM are used to analyze the forming process to explain some results that were found in the experiment.In the simulation,the effect of the movable die on the maximum principal stress is investigated in detail by using the FEM code LS-DYNA.For this case,the movable die changes the distribution of the maximum principal stress.For the sheet hydroforming without the movable die,the principal stress near the shoulder of the movable die arrives to the maximum value when t=0.0033s suddenly.But for the sheet hydroforming with the movable die,the maximum principal stress still lies in the die radius.The principal stress near the shoulder of the movable die is smaller.At the last stage contacting with the die,for the case without the movable die,the maximum principal stress near the shoulder of movable die is larger than that of the sheet hydroforming with the movable die.Moreover,the stress distribution near the shoulder of movable die for the case without the movable die is complicated.It is instable and very easy to occur wrinkling.The movable die delays the maximum thickness strain to the contacting die stage.So the formability of sheet metal can be remarkably improved by adopting the movable die.On a certain extent,the uniform distribution of thickness can be realized by increasing the counterforce of movable die.The minimum thickness reduction moves outside which is very helpful for the uniform thickness distribution.In this paper,two kinds of materials,soft steel and stainless steel,were investigated.