Analysis Of Material's Mechanical Behavior In The Deformation Zone Of Closed-Extruding Fine Blanking

Closed extruding fine blanking is a new fine blanking technology that can process materials with big thickness and low plasticity utilizing three-dimensional compressive stress,which promotes plasticity magnificently,within deformation cavity.Basic mechanical issues,including the relations between plasticity and three dimensional stress;forming stress calculations and problems of simulation accuracy for which fracture criteria should be chosen were mainly studied in this essay.The study above will lay the foundation of the development of closed extruding fine blanking which is highly engineering applicable.Firstly,in order to acquire the extent of plasticity promotion caused by three dimensional compressive stress,experiment simulations of closed upsetting and normal upsetting based on duralumin were carried out,and the promotion extent of plasticity was preliminarily and quantitatively proposed by surface damage distribution and theoretical calculation.Similar method was applied to closed-extruding fine blanking to make mechanical analysis of the materials inside cavity,with flow resistance stress being calculated.Slip line field was also established to calculate the blanking force.Thus forming quality can be predicted in terms of how much blanking force is needed under good plasticity conditions.Secondly,6 common ductile fracture criteria were chosen and normal tensile test,torsion test were conducted to calculate the fracture critical values.Meanwhile,stress-strain data was utilized to fit the extrapolation rheological model of material's during fine blanking,which was then embedded into Deform2 D by Absoft FORTRAN.Materials with different filling rate(100% and 90%)were chosen to simulate the forming process with different fracture criteria.Damage and other fracture factors were considered to judge those criteria and the one which fits closed extruding fine blanking best was selected.Based on the correct criterion,heat transforming was studied.Finally,physical experiment was carried out.The results show that the surface damage of duralumin has reduced by 2/3 due to high flow resistance stress under three dimensional compressive stress environment;The blanking force should be around 440~500KN of 20# steel of 100% filling rate;Ludwik flow stress model and Normalized C&L ductile fracture criterion match closed-extruding fine blanking most correctly;temperature rise during forming is limited which influencesvery little on forming;physical experiment is similar to simulation which can increase simulation precision and can also pave a way for secondary development for FEA software,meanwhile reference of design and optimization of mold can be acquired.