APPLICATION OF THE FINITE-ELEMENT METHOD TO A DESIGN OF OPTIMIZED TOOL GEOMETRY FOR THE OSU FORMABILITY TEST

A new, plane-strain, sheet-formability test (the O,S,U, Formability Te st, OSUFT) has been recently proposed, and it has shown many improveme nts over the limiting dome height (LDH) test. However, the prototype t ool geometry was initially determined arbitrarily for the experiment s o that an enhancement of the tool geometry was made with dual purpose: to design the tool geometry to generate consistent plane-strain state up to failure under various lubrication states and different testing materials and, at the same time, to make the testing equipment cost as low as possible so that the test may be readily available for small- and medium-scale stamping companies, The latter demands a compact tool geometry to minimize the required press capacity, while the former re quires wider blanks that increase the punch load, Considering these co nflicting conditions, computer simulation technique using three-dimens ional finite-element method was introduced, rather than performing num erous die tryouts, to design the optimal tool geometry from simulative trial and error, By reducing the size of the entire tool and controll ing the width-to-length ratio of the blank, an enhanced tool geometry was found that generates stable plane-strain state up to failure and s till features low required load capacity for materials with r-values u p to 2.0, friction coefficient ranges of 0,15 to approximately 0.35, a nd thicknesses up to 1.5 mm, The bending-dominant failure due to small er radii of the tool was avoided, Comparison of LDH simulation showed that the enhanced configuration of the test will produce more proporti onal strain path and larger plane-strain area near the predicted failu re region, It was also predicted that the testing results will be less sensitive to the lubrication state on the tool surface and the materi al anisotropy of the sheet, which will contribute to a better repeatab ility of the test, Experiments revealed that the optimized tool showed significantly less scatter in measurement compared with that of the L DH and the original O.S.U. formability tests.