A Novel Ironing Process with Extra High Thickness Reduction: Constrained Ironing

A new ironing method entitled constrained ironing is proposed for producing thin-walled cans and components with uniform thickness. This method based on compressive stresses could reach a higher ironing limit ratio or thickness reduction ratio (TRR) without interruption for additional processing such as multi-stage ironing and annealing between different stages. When the constrained ironing starts, the punch pushes the constrained material to reduce the thickness from the outer surface of the cup. The state of the stresses is fully compressive in this new process while it is tensile in the conventional ironing method. The results showed that after constrained ironing process, the tensile strength and hardness increased to 204 MPa and 85 HV, respectively, from the initial values of 71 MPa and 25 HV. Thus, very high TRR is achievable in the constrained ironing process. Obtaining a higher TRR about 80% after only single stage ironing, removing the annealing stages, and obtaining higher strength and hardness of the ironed cup are several advantages of the proposed method. This novel and simple process could be very promising for the industrial applications to replace the conventional process and to reduce the final product cost.