Graduate Thesis Or Dissertation
 

Numerical Modeling of Powder Metallurgy Hot Isostatic Pressing

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/6h441278p

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  • Powder Metallurgy Hot Isostatic Pressing (PM-HIP) is a widely recognized powder metallurgy manufacturing process to produce near-net-shape and net-shape components. During general PM-HIP processes the metal powders are filled within a capsule (die), heated and loaded with high pressure simultaneously, and solidified to form the final product. Due to the large shrinkage during the solidification process, the deviations from the desired dimensions of the final part, impacting its functional and final strength of the material. Ensuring precise geometric accuracy in PM-HIP products, especially those with complex structures, remains a formidable challenge. This thesis, consisting of four distinct papers, is dedicated to the overarching objective of providing a computational solution to address the challenge of accurately predicting PM-HIP product dimensions with an acceptable accuracy level of up to 0.25 inches. The driving motivation behind this research is to empower manufacturers and engineers to achieve this remarkable level of precision in the prediction of PM-HIP product dimensions. Each of the four papers within this thesis focuses on a different aspect of the computational solution. Together, they present a comprehensive approach to tackle this complex problem and bridge the gap between theoretical design and the actual production of PM-HIP components. The research unfolds in two key stages: the first, simulating the powder filling stage, employing the Discrete Element Model (DEM); the second, encompassing the densification process, leverages the Finite Element Analysis (FEA). A novel approach is proposed to integrate critical thermal-mechanical functions of porous materials, encompassing elastic deformation, plastic deformation, thermal expansion, and creep, into the FEA model, thereby mirroring the behavior of powder materials during the densification process. The results affirm that this innovative approach can reliably predict the geometric dimensions and density distribution of the final product within the desired accuracy bounds. The academic contributions of this work are multi-faceted and encompass the following key aspects: • Development of a novel FEA approach that captures the dynamic behavior of porous materials with complex geometries throughout the ramping up, cooling, and solidification process. • Implementation of the new model using the ANSYS User Programming Feature (UPF) and Fortran platforms, thus facilitating the simulation of the PM-HIP process. • Evaluation of the simulation models through collaborative experiments with the Electric Power Research Institute (EPRI) for two distinct geometries, aiming to quantify performance in terms of geometric accuracy and density distribution. • Application of the developed method to optimize die geometry, enhancing geometric accuracy in the final product. • A comparison of different constitutive models based on different creep models for two different dies with experimental results. • Simulation of the pre-consolidation die filling process via the Discrete Element Method (DEM), providing insights into the influence of vibration parameters, including frequency, amplitude, and vibration direction, on the initial relative density. • A comprehensive investigation into segregation patterns concerning filling parameters, employing computational analysis to explore the influence of the PM-HIP die's geometry, the particle size distribution within the powder batch, as well as the vibration frequency, amplitude, and duration on segregation. This analysis is conducted through the application of discrete element method simulations.
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