LAUSR

Abstract Adhesion between blank and die is the main reason for seizure and short tooling life during metal forming processes at elevated temperatures. This study applied novel complex-structured composite coatings, NC/NiBN and NC/WC:C, to the hot forming die flange and radius to reduce the use of lubricant. The high-temperature adhesion resistance and hot forming properties of the hybrid coated dies were tested and correlated with the microstructure and mechanical properties of the contacted blank/tool surfaces. The results show that the coated dies experienced little adhesion at elevated temperatures, consequently, ultra-low coefficients of friction of 0.11 against steel and 0.10 against Al at 350 °C were obtained. The minimum weight of lubricant per unit area required for a successful deep drawing of AA6082 was quantified by hot forming tests at various temperatures, and it was reduced by 83% at 400 °C. Complete lubricant-free deep drawing was achieved with limited blankholding force and forming temperature. Based on this experimental data and theoretical analysis of two disparate stress states, a model comparing the frictional state of material surfaces using the geometric features on formed parts is proposed.