Doctoral Degrees (Industrial Engineering)
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Browsing Doctoral Degrees (Industrial Engineering) by browse.metadata.advisor "Damm, Oliver"
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- ItemLaser powder bed fusion of cemented tungsten carbide cutting tools(Stellenbosch : Stellenbosch University, 2022-04) Hagedorn-Hansen, Devon; Sacks, Natasha; Damm, Oliver; Matope, Stephen; Stellenbosch University. Faculty of Engineering. Dept. of Industrial Engineering.ENGLISH ABSTRACT: Cemented carbides are extremely hard, wear resistant materials, and one of the most widely used tool materials in numerous manufacturing industries. Metal cutting tools are commonly manufactured from cemented carbides using standard powder metallurgy processes such as the press and sinter process. The tooling market is highly competitive and the companies with the best research and development departments have the competitive advantage when it comes to cutting edge technology. However, historically, the development process for a new cutting tool or production technology is a lengthy and costly venture. The use of laser powder bed fusion (L-PBF) for research, development, and small-batch production of cemented tungsten carbide cutting tools has not been extensively reported, and commercialisation does not seem apparent as yet. While the usage of L-PBF to produce cutting tools may be beneficial to advancing cutting tool technology, the process has many inherent drawbacks that affect part quality. However, there are many changes to the current L-PBF process that can be investigated to improve the final quality of L-PBF-produced tools before post-processing. The successful application of L PBF technology could help develop and manufacture cutting tools at an improved rate. The aim of this study was to determine and manage the influences of certain factors encountered during L-PBF of tungsten carbide cobalt (WC-Co) and their effects on specific cutting tool properties and cutting performance to produce L-PBF cutting tools that could be comparable to a conventionally produced tool. To accomplish this, three powders were analysed and investigated for their use in the L-PBF process. Then, characterisation of an existing cutting tool was performed to be used as a quality benchmark for L-PBF cutting tools. After a reasonable understanding of powders and conventional cutting tools was obtained, single track scans were performed on a tool steel base plate to understand adhesion and the feasibility of using a conventional base plate. The next stage of the study involved understanding the effects of different laser parameters and scanning strategies on the track morphology, density, hardness, and cobalt content of L-PBF produced WC-12wt%Co samples. Various parameter optimisation methods and strategies were tested and L-PBF-produced cutting tools were utilised in preliminary cutting tests to determine their cutting ability and to deduce which factors had the greatest effects on cutting contact time. The L-PBF scanning strategy was observed to be the most significant factor for successful cutting operations. A diagonal raster strategy with an 80-degree alternating rotation produced the best cutting inserts for the specific insert geometry and grade. Verification WC-12wt%Co inserts were produced with L-PBF for final cutting tests. These inserts were comparable to conventionally produced tungsten carbide inserts with respect to cutting performance indicators such as contact time and workpiece surface roughness. On average, after roughly 16M30S contact time, the L-PBF cutting tools exhibited 0.7 mm maximum flank wear versus 0.4 mm for similar conventional inserts. These results suggest that L-PBF could, one day, be a viable solution for research, developments, and small-batch production of WC-Co cutting tools.
- ItemLaser powder bed fusion-centred approach to enable local drug delivery from a cementless hip stem(Stellenbosch : Stellenbosch University, 2021-03) Bezuidenhout, Martin Botha; Damm, Oliver; Sacks, Natasha; Dicks, Leon Milner Theodore; Stellenbosch University. Faculty of Engineering. Dept. of Industrial Engineering.ENGLISH ABSTRACT: Periprosthetic joint infection (PJI) resulting from colonisation of implant surfaces by pathogenic bacteria and subsequent biofilm formation is a devastating complication following total hip arthroplasty. It significantly reduces a patient’s quality of life and, in severe cases, can result in amputation or mortality. Treatment of PJI is associated with a substantial burden on healthcare and economic resources. The importance of research towards innovations in PJI prevention and treatment is emphasised. Local delivery of antimicrobial drugs is an effective approach to prevent and treat PJI as it enables high local drug concentrations while avoiding systemic side effects. Current practice is considered sub-optimal and appreciable research exists on the improvement of local drug delivery strategies. For cementless hip stems the focus tends to be on coatings and conditioning of the external implant surface. A significant research gap exists between external and internal drug delivery strategies where ‘internal’ refers to the incorporation of reservoir structures within the implant. Therefore, a prototype strategy utilising the internal volume of a cementless stem for a reservoir from which an antimicrobial drug can be delivered directly to the implant surface was investigated. The challenge of fabricating a cementless hip stem with intricate internal geometries can be effectively addressed through metal additive manufacturing (MAM). Industry is steadily incorporating MAM into process chains as the main production technology for the fabrication of high-value functional components. Laser powder bed fusion (LPBF) was applied in this study as MAM technology to fabricate a Ti6Al4V ELI demonstrator cementless hip stem with local drug delivery functionality. This required an interdisciplinary approach, for which a problem solving framework has been synthesised to aid in process chain development from an LPBF-centred perspective. The overall problem was decomposed into integrated partial and single problems which were systematically investigated through literature study and experimentation. An LPBF-centred solution was developed for the direct integration of permeable structures in a dense part using an in-process assembly method. Different levels of porosity were induced into permeable thin walls according to a systematically identified window for ranges of the process parameters, laser power and scanning speed. This resulted in tailorable release profiles for the model antibiotic vancomycin from an aqueous formulation. Released vancomycin retained its antibiotic efficacy against Staphylococcus aureus Xen 36 (methicillin sensitive) and Staphylococcus aureus Xen 31 (methicillin resistant), representing two of the most frequent pathogens in PJI. Solutions for single problems were recomposed for integrated solutions to partial problems, and subsequently for an overall prototype solution. The overall solution cementless hip stem prototype effectively prevented surface colonisation by Staphylococcus aureus Xen 31, confirming the efficacy of the developed local drug delivery strategy. These results were used to inductively refine the LPBF-centred interdisciplinary problem solving framework. The original contribution of the research corresponds to the experimentation and framework development phases respectively. This involves the systematic investigation of LPBF to enable local drug delivery and an LPBF-centred approach for interdisciplinary problem solving. Lastly, it contributes to the advancement of LPBF by demonstrating the application efficacy of the prototype solution.