FE simulation of the development of flaws during injection forging

Abstract

Several types of flaws develop during the injection forging of components; among these a prominent form results from the instability of the free length of the billet. The material in the die cavity buckles or slides laterally along the anvil; consequently, die filling is effected by asymmetrical deformation of the billet. This FE simulation considers the influence of several parameters which influence the developments of flaws during injection forging. By considering friction conditions at the anvil, the aspect ratio of the primary deformation zone, the exit geometry and the inhomogeneity of the material, the types of flaws which are initiated and the subsequent die filling are simulated using ABAQUS code. Marginal changes in the friction conditions influence the stability of the billet; billets which were unstable when μ = 0.01 were, generally, sufficiently stable when μ = 0.03 to effect flawless die filling. Simulation confirms the experimentally proven, limiting aspect ratio of the primary deformation zone to be between T = 1.6 and 1.8. The deformation of the billet graduates from non-symmetrical deformation at aspect ratios greater than 1.7 to bending at ratios greater than 2.0. larger exit radii improve the flow characteristics and had been shown to reduce the energy requirements; however, the simulation shows that instability would occur at a lower aspect ratio when a large exit radius was incorporated in the injection chamber. Lack of inhomogeneity in the material will also result in instability and asymmetrical die filling at low aspect ratios.