Material Behavior in Powder Preform Forging

The basic deformation and fracture behavior of sintered powder materials was determined through simple compression tests for application to powder forging processes. Tests were carried out on an aluminum alloy powder at hot working temperatures. A well-defined relationship exists between the level of porosity and the lateral spread behavior of the material (as expressed by the plastic Poisson ratio). This information is utilized along with a plasticity theory previously developed by the authors to predict the densification and stresses in some simple forging operations. A comparison between theoretical and experimental values is given for compression of cylinders under frictional conditions. The limiting strains at fracture in the compression test reflect the influence of friction and geometry and fit a relation similiar to that found in cold forming processes. These results can be used to predict the limiting deformations to fracture in forging processes.