Sheet Metal Formability: Simulation and Experiment (Finite Element, Wrinkling, Plasticity).

Abstract

Wall wrinkling behavior during sheet metal cupping has been studied both experimentally and numerically. To simulate the forming process, one and two-dimensional finite element (FEM) models were used to predict stresses, strains, and failure by necking or wall wrinkling. The FEM simulations explored the effects of normal and planar anisotropy, yield criteria, work hardening, and modulus compensated flow stress on the formability of conical cups. The effects of process variables such as blank diameter, punch and die radii, blankholder load, and friction were also examined using FEM. It was demonstrated that a flow criterion with planar anisotropy is necessary to accurately represent the distribution of hoop compression in the cup wall. For low R-value materials, the biaxial region under the punch may correlate better with experiment if the exponent in Hill's 1948 yield criterion is greater than 2. Experimental studies used a variety of sheet materials and tooling to allow for comparison to the FEM predictions. In addition to the conical cup experiments, some work was included using a rectangular taper-walled pan with corners geometrically the same as quarter-sections of the conical cups. The experimental and FEM trends observed in the conical cups were compared to the forming behavior of this non-axisymmetric geometry.