Harrison, N., Ilinich, A., Friedman, P., Singh, J. et al., "Optimization of High-Volume Warm Forming for Lightweight Sheet," SAE Technical Paper 2013-01-1170, 2013, doi:10.4271/2013-01-1170.
Traditional warm forming of aluminum refers to sheet forming in the temperature range of 200°C to 350°C using heated, matched die sets similar to conventional stamping. While the benefits of this process can include design freedom, improved dimensional capability and potentially reduced cycle times, the process is complex and requires expensive, heated dies. The objective of this work was to develop a warm forming process that both retains the benefits of traditional warm forming while allowing for the use of lower-cost tooling. Enhanced formability characteristics of aluminum sheet have been observed when there is a prescribed temperature difference between the die and the sheet; often referred to as a non-isothermal condition. This work, which was supported by the USCAR-AMD initiative, demonstrated the benefits of the non-isothermal warm forming approach on a full-scale door inner panel. Finite element analysis was used to guide the design of the die face and blank shape. The forming cell developed for the automated production trials included demonstrations of pre-heating, automation, and formability and established process repeatability, cycle time, and the formability window. Successful parts were formed with a sheet temperature in the window of 250°C ± 10°C on a room temperature die face using material from two material suppliers. The work demonstrated that non-isothermal warm forming can enable sufficient formability to stamp a one-piece door inner panel from commodity aluminum alloys using a lower cost process that is more consistent with conventional stamping than previous warm forming proposals.