Operant Friction Coefficient of Prephosphated Galvanneal under Punch Stretching

Finite element analysis of the limiting dome height (LDH) test has been conducted in order to determine the operant (or effective) friction coefficient pertaining to prephosphated galvanneal under punch stretching conditions. Simulation results indicate that an effective friction coefficient (μ) of about 0.05, which is substantially lower than the experimentally measured drawbead friction coefficient of 0.11, would be necessary to obtain the experimentally observed LDH formability enhancement with prephosphated galvanneal coating over a drawing quality steel substrate. The work also demonstrates that the effect of friction on dome height and minor strain at failure depends on specimen width and substrate strength level, with the relationship being quite nonlinear. The apparent difference in friction behavior between punch stretching and draw bead conditions raises concerns about the use of a single friction coefficient in computer simulation models that are widely used today for up-front die feasibility analysis.