Effect of Workpiece Anisotropy on Metal Flow and Forging Conditions in Hot Aluminium Forging
The workpiece in hot closed-die forging of aluminium is often taken from extruded forging stock that is known for strong crystallographic and morphological texture and thus anisotropic material properties. Anisotropy affects material flow and might lead to undesired shape of workpiece in the early stages of open-die forging process. Properties of the forging are also influenced by the orientation of the crystallographic and morphological texture in relation to direction of forging. In this investigation both experiments and finite element simulations are used to study how material flow depends on grain orientation inside the workpiece. In a laboratory hot forging process the effect of anisotropy on metal flow and forging conditions is investigated for three different aluminium alloys. Direction of forging is altered in comparison to orientation of the centre axis of the cylindrical workpiece applied. In addition, the effect of two different grain orientations inside initial workpiece is studied. Experiments are compared to simulations performed with the FEM-code DEFORM 3D, in which the Hill's anisotropic material description is implemented. Good accordance between experiment and simulation is obtained when the flow stress in the extrusion direction of the forging stock is assumed ~20% higher than in the two perpendicular directions. Comparison was made between shape of the partial forging and corresponding simulated shape in the early open-die forging stages of the process. The largest deviation of predicted dimension of forging was ~6% in one case, while average deviation only was ~1%. In two cases, however, distortions and orientation of grain structure inside final forging were predicted wrong in simulation. It is concluded that deformation of internal zones inside the forging characterized by heavy shear is not well predicted by DEFORM even when the implemented anisotropy model is used.
Dirk NOLTE, Henry VALBERG
Aluminium Forging, Hot Forging, Closed-die Forging, Open-die Forging, Anisotropy of Initial Workpiece, Grain Orientation.