During the process of drop hammer forging, workpieces sometimes jump after strikes. The present research investigates the mechanism of the workpiece jump by means of experiments and numerical simulations. In the experiments, workpieces were struck by vertical symmetrical flat dies or vertical asymmetrical dies. A high-speed camera was used to measure the workpiece deformation, the position of workpieces during jumping and the position of the dies. Strain of lower dies and structures of the hammer were measured by strain gauges. Vibration of the antirattler under the hammer, elastic vibration of lower dies and structures of the hammer, and contact area between workpieces and dies were analyzed by numerical simulations. The results indicate that workpieces jump by adhesive force between workpieces and dies, and by elastic vibration of lower dies and structures of the hammer.
