Browsing by Author "Dimitrov, Dimitri"

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    The effect of cutting parameters on surface integrity in milling TI6AL4V
    (Southern African Institute for Industrial Engineering, 2016) Oosthuizen, Tiaan; Nunco, Keshav; Conradie, Pieter; Dimitrov, Dimitri
    The objective of machining performance is to reduce operational costs and to increase the production rate while maintaining or improving the required surface integrity of the machined component. Together with industrial partners, several benchmark titanium components were selected and machined to achieve this. Titanium alloys are used extensively in several industries due to its unique strength-to-weight ratio and corrosion resistance. Its properties, however, also make it susceptible to surface integrity damage during machining operations. The research objectives of this study were to understand the effect of cutting parameters on surface integrity to ensure that machined components are within the required surface quality tolerances. The effect of cutting speed and feed rate on surface roughness, micro-hardness, and the microstructure of the work piece were studied for milling Ti6Al4V. The surface roughness increased with a greater feed rate and a decrease in cutting speed. The maximum micro-hardness was 23 per cent harder than the bulk material. Plastic deformation and grain rotation below the machined surface were found with the rotation of the grain lines in the direction of feed. There was no evidence of subsurface defects for any of the cutting conditions tested.
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    Effect of milling strategy and tool geometry on machining cost when cutting titanium alloys
    (SAIIE, 2015) Conradie, Pieter; Oosthuizen, Tiaan; Dimitrov, Dimitri; Saxe, Mike
    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.
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    Heat treatment of TI-6AL-4V produced by laserCUSING
    (SAIIE, 2015) Becker, Thorsten; Van Rooyen, Melody; Dimitrov, Dimitri
    LaserCUSING® is a selective laser melting (SLM) process that is capable of manufacturing parts by melting powder with heat input from a laser beam. LaserCUSING demonstrates potential for producing the intricate geometries specifically required for biomedical implants and aerospace applications. One main limitation to this form of rapid prototyping is the lack of published studies on the material performance of the resulting material. Studies of the material’s performance are often complicated by dependence on several factors, including starting powder properties, laser parameters, and post-processing heat treatments. This study aims to investigate the mechanical properties of LaserCUSING-produced Ti-6Al-4V and its performance relative to the conventional wrought counterpart. A combination of conventional and LaserCUSING-tailored heat treatments is performed. The resulting microstructures are studied and linked to the properties obtained from hardness tests. The findings highlight that LaserCused Ti-6Al-4V is competitive with traditional materials, provided that optimal parameters are chosen and parts are subject to tailored post-processing. In the as-built condition, LaserCused Ti-6Al-4V displays superior strength and hardness as a result of a martensitic microstructure, and a poorer performance in ductility. However, the material performance can be improved using tailored heat treatments. Careful consideration must be given to suitable post-processing before application in critical components in the aerospace or biomedical industry can occur.
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    On the impact of different system strategies on the material performance of selective laser melting- manufactured TI6AL4V components
    (Southern African Institute for Industrial Engineering, 2016-11) Dimitrov, Dimitri; Becker, Thorsten Hermann; Yadroitsev, Igor; Booysen, Gerry
    ENGLISH ABSTRACT: Selective Laser Melting (SLM) is a powder-based additive manufacturing process that has gained substantial interest in recent years due to its feasibility of producing geometrically- complex metallic components for end-use in various industries, with or without post-treatment procedures. This paper presents recent research undertaken on different scanning strategies and process parameters with the purpose of providing an overview of the achievable material performance of Ti6Al4V components, and comparing its properties with the conventionally-produced parts. In order to understand their output, differences in the building strategies of the systems studied are analysed, and their influence on the resulting mechanical and metallurgical properties is highlighted.