PREDICTION OF DEFECTS IN METAL-FORMING - APPLICATION TO WIRE DRAWING

Defects appear in metal forming processes when some instability conditions are obtained or when the material is too much damaged. Searching in that second direction, for the wire drawing process, it has been shown that the reduction rate rho and the semi-cone die angle-alpha has a large influence on the quality of the final wire. One remarkable result is that friction coefficient f has no direct effect on the damage evolution. Friction conditions are important for the surperfacial aspect of the product but have no effect on the inner quality of the wire. Systematical finite element simulations, for different range of (alpha, rho), have been carried out, and using an isotropic scalar damage law, the influence of these two parameters has been studied. The maximum value of the damage function in the wire has been drawn with respect to alpha and rho. That graphic provides a useful way to optimize the process geometry and if it is associated with a damage criterion, it allows us to predict which geometrical conditions can be chosen so that defects may not occur.