Hybrid extrusion and multidirectional forging additive manufacturing technique
File(s)
Author(s)
Jintana, Patawee
Type
Thesis
Abstract
Additive manufacturing (AM) is a well-established technique for prototyping and producing components in small to medium batch sizes. However, AM parts commonly exhibit defects, coarse grain structures, and anisotropic properties, which lead to inferior tensile performance. To address these limitations, a hybrid extrusion and multidirectional forging (MDF) approach was proposed, integrating extrusion-based AM with hot MDF within a single manufacturing platform.
A prototype system was designed, built, and evaluated using solid pure tin filament to assess the effectiveness of the proposed technique. The microstructure and tensile properties of the fabricated samples were systematically analysed to elucidate the mechanisms governing microstructural refinement and mechanical enhancement during hot forging, as well as the influence of key processing parameters.
Compared with as-built AM samples, MDF produced substantial improvements in both microstructure and tensile performance, exceeding the capabilities of uniaxial forging. Specifically, porosity was reduced by 55% and average grain size by 35%, while yield stress, ultimate tensile strength, and maximum elongation increased by factors of 12.5, 5.0, and 2.6, respectively.
Optimisation of MDF parameters identified the number of repeated forging blows and the reduction ratio as the most influential factors. Increasing the number of forging blows tenfold reduced porosity and grain size by 68% and 38%, respectively, while increasing tensile yield strength, ultimate tensile strength, and maximum elongation by factors of 3.6, 2.8, and 2.8. In addition, doubling the number of forging blows reduced the maximum texture intensity from 24 to 8.7, indicating the development of a more isotropic microstructure. Increasing the reduction ratio by 10% also reduced porosity by 37%, decreased grain size by 43%, and enhanced yield stress, ultimate tensile strength, and maximum elongation by 47%, 35%, and 88%, respectively.
A prototype system was designed, built, and evaluated using solid pure tin filament to assess the effectiveness of the proposed technique. The microstructure and tensile properties of the fabricated samples were systematically analysed to elucidate the mechanisms governing microstructural refinement and mechanical enhancement during hot forging, as well as the influence of key processing parameters.
Compared with as-built AM samples, MDF produced substantial improvements in both microstructure and tensile performance, exceeding the capabilities of uniaxial forging. Specifically, porosity was reduced by 55% and average grain size by 35%, while yield stress, ultimate tensile strength, and maximum elongation increased by factors of 12.5, 5.0, and 2.6, respectively.
Optimisation of MDF parameters identified the number of repeated forging blows and the reduction ratio as the most influential factors. Increasing the number of forging blows tenfold reduced porosity and grain size by 68% and 38%, respectively, while increasing tensile yield strength, ultimate tensile strength, and maximum elongation by factors of 3.6, 2.8, and 2.8. In addition, doubling the number of forging blows reduced the maximum texture intensity from 24 to 8.7, indicating the development of a more isotropic microstructure. Increasing the reduction ratio by 10% also reduced porosity by 37%, decreased grain size by 43%, and enhanced yield stress, ultimate tensile strength, and maximum elongation by 47%, 35%, and 88%, respectively.
Version
Open Access
Date Issued
2025-10-02
Date Awarded
2026-03-01
Copyright Statement
Attribution-NonCommercial 4.0 International Licence (CC BY-NC)
License URL
Advisor
Jiang, Jun
Sponsor
Development and Promotion of Science and Technology Talents Project (DPST), The Royal Thai Government
Publisher Department
Department of Mechanical Engineering
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)