Improvement in Material Flow During Non-Isothermal Warm Deep Drawing of Non-Heat Treatable Aluminum Alloy Sheets

Automotive industries are very much interested in implementing warm forming technology for fabrication of light weight auto-body panels using aluminum alloys without localized thinning or splitting. A non-heat treatable and low formable AA5754-H22 aluminum alloy sheet was selected in the present work, and a laboratory scale warm deep drawing test set-up and process sequences were designed to improve material flow through independent heating of punch and dies. Significant enhancement in cup depth was observed when the temperature of punch and dies were set to 30°C and 200°C respectively. Thermo-mechanical finite element model of the non-isothermal deep drawing test was developed successfully to study the improvement in material flow incorporating Barlat-89 yield theory using temperature dependent anisotropy coefficients and Cowper-Symonds hardening model of AA5754-H22 material. It was found that a non-isothermal temperature gradient of approximately 93°C was established within the blank from the center to flange at the start of deformation, and subsequent evolution of temperature gradient helped in improving material flow into the die cavity. The effect of temperature gradient on forming behavior in terms of cup height, ear profile and thinning development across flange, cup wall, and blank center were predicted and validated with experimental results.