Browsing by Author "Makhetha, William Motsoko Ishmael"

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    The effect of LPBF post-processing solutions on material properties to meet functional Ti-6Al-4V requirements
    (Stellenbosch : Stellenbosch University, 2023-03) Makhetha, William Motsoko Ishmael; Becker, Thorsten Hermann; Sacks, Natasha; Stellenbosch University. Faculty of Engineering. Dept. of Industrial Engineering.
    ENGLISH ABSTRACT: Broadly, additive manufacturing (AM) is defined as a canopy term of manufacturing technologies used to join material layer by layer to make three-dimensional (3D) products from computer aided design (CAD) models. Additive manufacturing is well known for polymer processing, but there is a growing interest to optimize capabilities for metal additive manufacturing (MAM) technologies. While various materials are being explored for MAM, more research has been conducted on titanium alloys such as Ti-6Al-4V. The combined properties of this alloy make it an excellent choice for structural parts in applications such as airframes, aero-engines and bio-medical devices. Although the potential of MAM technologies such as laser powder bed fusion (LPBF) are well recognized in industry and research communities, with parts already finding applications in aircraft components and medical implants, the drawbacks associated with as-built parts continue to impede its wider application and update. Despite the ongoing efforts to improve the integrity by process parameter optimization, the as-built parts are inherently characterized by high surface roughness, high residual stresses, martensitic microstructure, high porosity and anisotropic properties. Therefore, post-processing solutions are essential to link the as-built parts with industry specific functional requirements. There is a significant range of post-processing solutions available, however there is no open literature on clear post-processing frameworks. Consequently, there is lack of clear guidelines to help in the selection of the most feasible post-processing solutions. This research project was conducted to address this gap by providing a methodological guideline on the available post-processing solutions for making LPBF Ti-6Al-4V parts which qualify for application. All research activities were organized into five phases. The approach used was to extract existing knowledge from the literature to find key areas of consensus with the aim of gaining a better understanding of the links between the process and integrity of the parts produced. This understanding was then used to develop a conceptual LPBF post-processing framework for industry application, which was then validated through experiments. The validation was planned in collaboration with Aerosud, which provided directives from the industry perspective. The directive was to define what it means for a part to be qualified, which in turn informed what aspects of the proposed framework needed to be carried out through the experiments. The directives were in accordance with the safety classification and quality level assigned to aircraft parts. The research findings add to the body of knowledge on how industries should apply the AM technology with two important novelties. Firstly, the presentation of four key attributes (microstructure, porosity, residual stresses, and surface roughness) into one framework. Secondly, a holistic approach, which in turn offers the end-users of the AM technology an opportunity to clearly and quickly identify possible options when seeking to qualify Ti-6Al-4V parts produced by LPBF. The author concludes that the study is unique in that, as opposed to previous studies, it emphasizes the need for such attributes to be considered collectively towards qualifying the LPBF Ti-6Al-4V parts because of their shared influence on mechanical properties.