| Special-shaped thin-walled aluminum alloy sheet metal parts' shaping has become an urgent technical problem to be solved in the development of automobile lightweight technology.As A typical part in the automotive field,the aluminum alloy box-shaped parts have deepened the forming difficulty due to the large difference in deformation of various parts.The new sheet hydroforming process with controlled rim pressure is an advanced new technology of flexible die forming.This paper will study a new hydrodynamic deep drawing(HDD)process that can form an ideal part.This process add controlled rim pressure on the outer edge of the sheet flange,thereby reducing the sheet thinning rate and changing the position of the wall thickness constant line,which can reduce the thinning rate of the sheet,change the position of the wall thickness constant line.Taking the concave bottom box of 5A06 aluminum alloy as the research object,the forming process of the part is studied by finite element numerical simulation.For the concave bottom part which is not easy to form,in the initial stage of HDD,the pre-bulging process is set up to analyze the influence of the matching relationship between different pre-bulging height and pre-bulging pressure on the defect form,thinning rate and fitability of the concave bottom part.Combined with the idea of finite element discretization,a new method for characterizing the modulus of part is proposed.The simulation results show that the reasonable matching relationship between pre-bulging height and pre-bulging pressure can effectively reduce the crack and wrinkles at the concave bottom.And In the range of appropriate reduction rate,the sheet can be formed against the punch to the maximum extent.Based on the pre-bulging pressure 6 MPa and pre-bulging height 6 mm,the loading curves of liquid chamber pressure are studied.And the influence of different liquid chamber pressures on the form of part defects and the section thickness distribution at the diagonal and the center line of the straight side are analyzed.Thus A reasonable liquid chamber pressure 30 MPa is determined.The simulation results show that reasonable liquid chamber pressure can effectively control the crack at the round corner of the part and the wrinkle at the edge under the premise of ensuring the forming quality of the top of the concave bottom.Thereby,the wall thickness distribution is evenly uniform,and the forming effect of the box is obviously improved.The effect of HDD with controlled rim pressure on the different shape sheets of the concave bottom box is studied.And a method of rim pressure application by setting local coordinate system in numerical simulation software is proposed.The influence of different rim pressures on the defect form,wall thickness invariant lines and sheet boundary flow after forming different shapes of sheets is revealed.The simulation results show that the application of rim pressure has a certain extent to improve the defects of different forms.At the same time,it can effectively suppress the excessive thinning of the sheet.With the increase of rim pressure,the wall thickness constant lines of different shape sheets move down to the bottom of the box.So the wall thickness distribution is more uniform,and at the same time the flow amount of the sheet boundary motion is increased.compared with the other two shapes of the sheet material,the difference between the flow amount of the straight side portion and the rounded portion of the circular cut bow shape sheet is small,and the wrinkling problem of the straight side portion is effectively weakened.The concave bottom box-shaped member with better forming effect can be obtained under rim pressure 15 MPa. |
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