HIP Modeling Methodology Based on the Inherent Process Anisotropy

摘要

The 'net shape' HIP approach is based on computer programs with embedded engineering models of powder consolidation, shrinkage and surface formation that use the computer aided design (CAD) of the part needed and of the HIP tooling. Densification pattern during HIP, which is the 'key' to 'net shape' technology is determined by the capsule and powder materials rheology and is, at the initial stages, controlled by the capsule's plastic stiffness. However, dilatometric experiments on HIP of capsules with powder revealed that even at the final stages of densification when the capsule is pliable, deformations are not uniform and follow the dominating radial or axial component though the pressure is isostatic and of uniform density. Deformation pattern is determined by a form of deformation history, such that some 'anisotropy' generated during this history becomes inherent and this, in turn, controls the process of shrinkage even under uniform pressure of HIP. Following this approach, the equations describing the material model during HIP have been modified and appropriate experiments carried out for their parametrical identification. Anisotropic behavior of powder material during 'net shape' HIP consolidation, discovered during special experiments with porous samples, was demonstrated experimentally and by introducing an anisotropy module within the entire HIP process numerical model.