A Quick Cycle Time Sensitivity Analysis of Boron Steel Hot Stamping

Several vehicle platforms involving the hot stamping of manufactured parts are launched every year. Mass production represents a key step in the manufacturing process of an actual hot stamping part. In this step, the cycle time (consisting of cooling time (t1) and handling time (t2) components) must be optimized. During t1, the stamping tool (punch and die) is closed, for cooling of the part. The t2 components (i.e., inlet transfer time, press forming time (closing and opening), and outlet transfer time) define the production output that ensures process performance. However, cost is the main driver in automotive applications. Here, a cycle-time calculation based on the design of experiments (DOE) is proposed for formulating cost-effective formulas. An iterative one-dimensional heat transfer model for each DOE step is set up to simulate 10 hot stamping cycles; the part temperature after quenching in cycle number 10 (where steady conditions are achieved) was selected as the process output variable to be controlled in the DOE. Several DOE variables were considered. The DOE results were employed for the proposal of a simplified formula, which helps in assessing the cycle time with its excellent trade-off between calculation cost and reliability. The formula was validated by laboratory tests.