Study On Reducing Drawing Of Ear With Variable Taper Blank-holder

Because of the anisotropy of the mechanical properties of the cold rolled steel plate,the uneven ear making occurs at the drawing edge.Ear defects not only reduce the utilization rate of sheet metal,but also reduce the finished product rate of parts.Reducing the drawing of ear is mainly achieved by adjusting the rolling process of sheet metal,changing the shape of blank,using variable clearance,variable pressure edge force and so on.The current research on the relationship between mechanical properties of sheet metal and ear making mainly focuses on the R of thick anisotropy index of sheet metal and the yield strength of material,while the research on the relationship between hardening index n affecting stress and strain during deformation and drawing ear making is less.Flat holder ring is generally used in the drawing process to edge the blank to prevent wrinkle and rupture.Compared with the flat holder ring,the taper blank holder can improve the wrinkle resistance and deformation degree of the blank.In this paper,according to the anisotropy of sheet metal,different taper is set in different directions of blank to edge pressing,that is,variable-taper blank holder is adopted.In the direction of slower material flow speed,the "wave peak" of the ear making is set with smaller taper,and in the direction where the material flow speed is faster,the"wave valley" of the ear making is set with larger taper,which makes the fluidity of the blank in each direction tend to be uniform.The relationship between hardening index n and ear-making was studied by measuring the n of hardening index of sheet metal in seven directions of DC04 cold rolled steel plate by unidirectional tensile test.Taking the cylindrical drawing as the research object,the influence of process parameters of variable-taper blank holder,pressure and blank deformation on ear-making rate was studied by using ABAQUS software.Results show that:(1)In the direction where the hardening index is small,the sheet material will form the "wave valley" of ear making,while the sheet material in the direction where the hardening index is larger will form the"wave peak" of ear making.(2)The larger taper is arranged in the smaller direction of hardening index and the smaller taper is arranged in the larger direction of hardening index.The lower ear-making rate can be obtained by using variable-taper blank holder.When the maximum taper of the variable-taper blank holder is 27° and the minimum taper is 20°,the minimum ear making rate is only 1.65%.(3)The variable-taper blank holder can not only reduce the ear-making rate but also change the ear-making type.For parts that require multi-pass drawing,the ear rate can be significantly reduced by using the taper flange drawing.(4)Blank deformation has little effect on the ear-making rate of cylindrical parts that are drawn deep by the variable-taper blank holder.When the drawing coefficient is reduced from 0.625 to 0.5,the ear making rate is changed from 1.84%to 3.13%.