Investigation of the shrinkage defects of high ribs in extrusion processes with plane strain characteristics

Aluminum alloy forged wheel hubs are lightweight materials for electric vehicles. However, forming high-ribbed spokes is challenging due to potential shrinkage during high rib extrusion with plane strain characteristics. This study utilizes the finite element method to analyze the high-rib extrusion process with plane-strain characteristics. It is found that a region of tensile stress exists near the bottom fillet of the rib persisting until the high rib contour is fully filled. The position and size of this region remain largely unchanged during extrusion. Defining the occurrence of shrinkage defects as a critical state, the thickness is defined as the critical residual thickness. By constructing a stress state slip line field for plane-strain extrusion, a prediction formula for the critical residual thickness of high-rib extrusion is proposed. The proposed critical residual thickness is evaluated through finite element calculations and high-rib extrusion experiments. The results show that the critical residual thickness is linearly positively correlated with the half-width of the rib root and negatively correlated with the fillet radius of the rib root, taper angle, and shear friction coefficient. The initial blank thickness does not affect the critical residual thickness. The depth of the shrinkage increases linearly with the decrease in residual thickness. The experimental critical residual thickness can be determined by combining finite element calculations and extrusion experiments. The proposed theoretical formula for the critical residual thickness has an error of + 8.14% compared to the experimental critical residual thickness. This theoretical prediction is relatively conservative and can guide the design of high-rib extrusion forming billets to ensure defect-free high-rib forming.