G.A. Oosthuizen

Titanium-Based Hip Stems with Drug Delivery Functionality through Additive Manufacturing

Postoperative infections are a major concern in patients that receive implants. These infections generally occur in areas with poor blood flow and pathogens do not always respond to antibiotic treatment. With the latest developments in nanotechnology, the incorporation of antibiotics into prosthetic implants may soon become a standard procedure. The success will, however, depend on the ability to control the release of antibiotics at concentrations high enough to prevent the development of antibiotic-resistant strains. Through additive manufacturing, antibiotics can be incorporated into cementless femoral stems to produce prosthetic devices with antimicrobial properties. With the emerging increase in resistance to antibiotics, the incorporation of antimicrobial compounds other than antibiotics, preferably drugs with a broader spectrum of antimicrobial activity, will have to be explored. This review highlights the microorganisms associated with total hip arthroplasty (THA), discusses the advantages and disadvantages of the latest materials used in hip implants, compares different antimicrobial agents that could be incorporated, and addresses novel ideas for future research.

Effect of milling strategy and tool geometry on machining cost when cutting titanium alloys

The growing demands on aerospace manufacturers to cut more difficult-to-machine materials at increasing material removal rates require that manufacturers enhance their machining capability. This requires a better understanding of the effects of milling strategies and tool geometries on cutting performance. Ti6Al4V is the most widely-used titanium alloy in the aerospace industry, due to its unique combination of properties. These properties also make the alloy very challenging to machine. Complex aerospace geometries necessitate large material removal, and are therefore generally associated with high manufacturing costs. To investigate the effect of milling strategy and tool geometry on cutting performance, the new constant engagement milling strategy was firstly compared with a conventional approach. Thereafter, a component was milled with different cutting tool geometries. Cost savings of more than 40% were realised by using a constant engagement angle milling strategy. A reduction of 38% in machining time was achieved by using tools with a land on the rake side of the cutting edge. These incremental improvements made it possible to enhance the overall performance of the cutting process.

Delivery of Antibiotics from Cementless Titanium-Alloy Cubes May Be a Novel Way to Control Postoperative Infections

Bacterial colonisation and biofilm formation onto orthopaedic devices are difficult to eradicate. In most cases infection is treated by surgical removal of the implant and cleaning of the infected area, followed by extensive treatment with broad-spectrum antibiotics. Such treatment causes great discomfort, is expensive, and is not always successful. In this study we report on the release of vancomycin through polyethersulfone membranes from channels in cementless titanium-alloy cubes. The cubes were constructed with LaserCUSING from Ti6Al4V ELI powder. Vancomycin was released by non-Fickian anomalous (constraint) diffusion. Approximately 50% of the vancomycin was released within the first 17 h. However, sustained delivery of vancomycin for 100 h was possible by reinjecting the channels. Refillable implants may be a novel way to control postoperative infections.

INVESTIGATING OF ECO- AND ENERGY-EFFICIENT LUBRICATION STRATEGIES FOR THE DRILLING OF LIGHT METAL ALLOYS

Energy use will be one of the main drivers for the achievement of more eco-efficient drilling processes in the automotive industry. Industry awareness of the environmental impact of used cutting emulsions, and the negative effect on worker health, has increased sharply. This has led to innovative lubrication methods such as through-spindle minimal quantity lubrication (MQL) for drilling aluminium-silicon alloys. In this work the performance of MQL at different cutting speeds and feed rates has been investigated using infrared temperature measurements. The results indicate that MQL is a feasible ecoefficient alternative to conventional flood cooling when drilling aluminium-silicon alloys. OPSOMMING Energiebenutting maak een van die hoofdryfvere uit om eko-doeltreffendheid te behaal in boorprosesse in die motornywerheid. Nywerheidsbewustheid van die omgewingsimpak van gebruikte sny-vloeistowwe, en die negatiewe effek daarvan op werkergesondheid, het skerp toegeneem. Hierdie bewustheid het aanleiding gegee tot die ontwikkeling van smeringsmetodes soos deur-spil minimale hoeveelheid smering (Engels: Minimal Quantity Lubrication, MQL) vir die boor van aluminium-silikon legerings. In hierdie werk word die prestasie van MQL ondersoek teen verskillende snyspoed- en voertempo-kondisies deur middel van infra-rooi temperatuurmeting. Die resultate dui daarop dat MQL ’n lewensvatbare eko-vriendelike alternatief tot konvensionele vloedverkoeling is, wanneer aluminium-silikon legerings geboor word.

Energy content and combustion behaviour of loose biomass available in Limpopo

Solid biomass continues to be the primary energy source for a significant proportion of Sub-Saharan African society. It is estimated that 80% of energy for heating and cooking in this subcontinent is derived from round wood biomass resulting in estimated annual rate of deforestation of 0.7%. This is unsustainable. This is despite the existence of a substantial resource of loose biomass (forest and agricultural residues) that is produced and disposed of annually. However, one major challenge in harnessing loose biomass as a source of energy is low energy density and poor combustion behaviour. Biomass briquetting technologies can be deployed to improve energy density and combustion behaviour of loose biomass. This requires understanding of the energy content in locally available loose biomass sources. This paper investigates the calorific values (energy content) and combustion behaviour of loose biomass collected from a region in the Limpopo Province of South Africa. The aim of the investigation is to understand the energy value and hence viability of using such loose biomass with the overall goal of developing recipes for biomass briquetting in the region. Calorific values were measured for 12 samples of loose biomass and their combustion behaviour analysed. Certain loose biomass sources are then identified as potential briquetting candidates.

Comparative assessment of process combination for Ti6Al4V components

Purpose The purpose of this paper is to investigate the combination of selective laser melting (SLM) and 5-axis CNC milling to produce parts from titanium powder. The aim is to achieve a more resource-efficient manufacturing process by reducing material wastage and machining time, while adhering to quality requirements. Design/methodology/approach A benchmark titanium aerospace component is manufactured with two different approaches using subtractive and additive manufacturing technologies. The first component is produced from a solid billet using only 5-axis CNC milling. The second component is grown from powder using SLM to produce a net-shaped part of which the final shape and part accuracy are achieved through 5-axis CNC milling. The potential saving of material and machining time of the process combination is evaluated by comparing it to the conventional purely CNC approach. The form accuracy, surface finish, mechanical properties and tool wear for the two processes are also compared. Findings The results show that the process combination can be used to produce Ti components that adhere to aerospace standards. With the process combination, a material saving of 87 per cent was achieved along with a reduction of 21 per cent in machining time. Further improvements are possible using optimized SLM build and machining strategies. Originality/value This paper presents the results of a resource efficiency assessment on the combination of SLM and 5-axis CNC milling for the titanium alloy, Ti6Al4V. It is expected that this process combination can make a significant contribution towards reducing material wastage and machining time for aerospace applications.

Combustion behaviour of loose biomass briquettes resulting from agricultural and forestry residues

Reliance on round wood for heating and cooking has increased the percentage of deforestation to 0.7% per annum especially within sub-Saharan region where communities live off the electricity supply grid. The majority of these communities rely on agriculture and forestry activities for sustenance. Therefore, large amounts of agricultural and forestry residues are produced annually although they are considered to be of low energy content. This paper investigates the combustion behaviour of the loose biomass briquettes produced from residues collected from a rural community in the Limpopo Province of South Africa. These included mopane leaves, ground nut shells, sugar cane leaves, yellow thatching grass, cactus plant and cow dung among others. Biomass briquettes were produced from these residues for various proportions and compaction pressures (6, 12 and 19 MPa) with cow dung or cactus plant as a binder. The produced briquettes were tested for energy content and burnt in a biomass briquette stove while monitoring mass decay or burn rate and temperatures. The optimum briquettes were found to be of the cow dung binding compacted at a pressure of 19 MPa.

RESOURCE-EFFICIENT PROCESS CHAINS TO MANUFACTURE PATIENT-SPECIFIC PROSTHETIC FINGERS

The high cost of quality prostheses, together with the lack of trained prosthetists, makes it challenging to obtain prosthetic devices in developing communities. Modern 3D digitising techniques and additive manufacturing (AM) technologies are gaining popularity in the bio-medical industry and, in the case of prosthesis production, reduce the need for a trained prosthetist. The objective of this research was to develop a new resource-efficient process chain for the manufacturing of prosthetic fingers using additive manufacturing technologies, and to compare it with the traditional (Sculptor) process chain. Fused deposition modelling (FDM), open-source FDM, 3-dimensional printing (3DP), and stereolithography (SLA) were evaluated in terms of their costs, time, material usage, and aesthetic quality. The surface qualities produced with the different additive manufacturing technologies were also compared. The results showed that 3DP was the preferred technology and was the best candidate for the production of prosthesis in terms of cost, quality, and time for developing communities. SLA produced the highest aesthetic quality prosthesis, but was the most expensive. It was concluded that using the additive manufacturing technology process chain to produce prosthetic fingers is faster and more cost effective than the traditional method.

CFD evaluation of premixed and non-premixed models as suitable representatives of fixed-bed biomass combustor freeboard

This paper presents a comparison of the performance of two numerical (CFD) models with experimental data obtained for a fixed-bed biomass domestic cooking stove. The two numerical models are two different representations of the possible behavior of the gas region of the combustor under consideration. The one model considers the pyrolysis products emanating from the fuel bed to be premixed with the oxidant (air), while the other model supposes that the pyrolysis products combusting in the freeboard enter this region through a stream that is separate from that of the oxidant. The geometry of the combustion chamber of the stove from which the experimental data was obtained is cylindrical with 11cm diameter and 25 cm depth. The study particularly monitors the exit flame temperature of the cylindrical combustor through the use of k-type thermocouples in the experimental case. The fuel used in the experiment is peanut shells. The premixed model achieved an exit temperature of 435K while the non-premixed model achieved an exit temperature of 747.9K. On the other hand, the highest experimentally obtained temperature is 778.15K whereas the average experimentally obtained temperature is 641.15K. Consequently the non-premixed model is chosen as the better representative of the freeboard.

Using palletised work-holding to emulate 5-axis machining of aerospace components in the developing world

This paper proposes the application of precision pallet technology, together with common 3-axis milling, to machine certain complex aerospace components that are normally 5-axis machined. In this approach a set of different customised precision pallets are used to present each complex plane to the 3-axis machine as a series of horizontal planes for machining. After machining one surface, the pallet is exchanged for another that has been pre-setup in machining time. Trials confirm the viability of the approach, with capital recovery in less than a year. OPSOMMING Hierdie artikel stel die aanwending van presisiepallettegnologie, saam met gewone 3-as frees, voor om komplekse lug- en ruimtevaartkomponente te vervaardig. Die gebruiklike metode om hierdie komponente te vervaardig vereis 5-as masjinering. In die voorgestelde benadering word ’n stel verskillende pasgemaakte presisiepalette gebruik om elke komplekse vlak as ’n reeks horisontale vlakke te posisioneer vir masjinering. Die gevolg is dat eenvoudige en vinnige vlakfrees voldoende is. Nadat een vlak gemasjineer is, word die pallet vervang met ’n ander wat vooraf opgestel is gedurende masjineringstyd. Toetse bevestig die lewensvatbaarheid, met kapitaaldelging in minder as ’n jaar.