The Research On Inhomogeneous Plastic Flow Of Metal Sheet In Drawing

Cylindrical parts need trimming process due to the earing defectsproduced after drawing. It’s necessary to set aside enough trimmingallowance when calculating sheet size. Yet excessive trimming willincrease baiting size. That will expand deformation degree, increasecracking risk and scrap rate then sheet metal waste will be caused. On theother hand, trimming value is too small, It is easy to bring aboutinsufficient drawing height and higher scrap rate. The fundamental causeof earing is inhomogeneous plastic flow. In this paper, theinhomogeneous plastic flow can be dealt with from two aspects: First, theresearch for cause of inhomogeneous plastic flow in sheet metal formingprocess to master earing formation law. Second, according to the earingformation law, we budget the height of trimming value of workpiece, sothat the trimming value can be controlled to a minimum,Thus it canenhance utilization rate of plate and reduce production cost.We apply the anisotropy and strain hardening theory to analyzing thestress of deformation zone, thus indicating that the larger anisotropyparameter of plane r is, the greater inhomogeneous plastic flow degree ofmetal and the higher ear height. Strain hardening can lead to yield surfaceexpansion, relieve the sheet anisotropy in drawing process and lower theinhomogeneous degree of sheet plastic flow, thus narrowing earingheight.The results of drawing test show that the larger the anisotropyparameter of plate plane is, the more obvious the inhomogeneousplastic flow of sheet and the higher earing rate; Strain hardening candecrease the inhomogeneous plastic flow of metal sheet and inhibit eargrowth. The results are consistent with theoretical analysis. The resultsshow that trimming value is only1/10~1/4of that in productionpractice.T he trimming value is overhigh in production practice, whichleads to materials waste. According to the calculation, the size of billetdetermined by this method can save1.5%~2.6%raw materials.