Browsing by Author "Dimitrov, D."

Now showing 1 - 6 of 6
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    Influence of process parameters on residual stress related distortions in selective laser melting
    (Elsevier, 2018) Mugwagwa, L.; Dimitrov, D.; Matope, S.; Yadroitsev, I.
    ENGLISH ABSTRACT: Residual stresses pose a major setback in Selective Laser Melting (SLM) and limit the applicability of the process, particularly from the standpoint of form accuracy and mechanical strength. The purpose of this paper is to investigate the influence of SLM parameters namely laser power and scanning speed on thermal stress related warping distortions and porosity. In this study, residual stress related distortions and achievable density for different process parameter combinations are presented simultaneously due to the profound influence of the porosity on residual stress relaxation. The paper also discusses the implications of the process parameters on the sustainability of the SLM process.
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    An introduction to rapid casting : development and investigation of process chains for sand casting of functional prototypes
    (SAIIE, 2007) Dimitrov, D.; Van Wijck, W.; De Beer, N.
    ENGLISH ABSTRACT: This paper discusses the results obtained from studies on different Rapid Tooling process chains in order to improve the design and manufacture of foundry equipment that is used for sand casting of prototypes in final material. These prototypes are intended for functional and pre-production tests of vehicles. The Three Dimensional Printing process is used as core technology. Subsequently, while considering aspects such as time, cost, quality (accuracy and surface roughness), and tool life, a framework is presented for the evaluation and selection of the most suitable process chain in accordance with specific requirements. This research builds on an in-depth characterisation of the accuracy and repeatability of a 3D printing process.
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    Investigating the impact of tool velocity on the process conditions in incremental forming of titanium sheets
    (Elsevier, 2017) Uheida, E. H.; Oosthuizen, G. A.; Dimitrov, D.
    ENGLISH ABSTRACT: This paper deals with a study focused on the single point incremental forming (SPIF) of titanium Grade 2 sheets. The direct impact of the sliding velocity of the forming tool on mechanical and thermal process loads was experimentally investigated. A wide range of spindle speeds and feed rates were examined at different forming conditions. The developed profiles of the mechanical and thermal demands during the SPIF of titanium sheets are presented and discussed. Forming temperature and force were directly related to the tool rotation speed, higher temperatures and lower reactional forces correspond to higher speeds. At very high rotation, failure conditions occurred and the ability to shape a CP Grade 2 sheet is decreased; these failures were mainly due to extreme heating, leading to termination of the tests concerned. The main objective of the study is to gain a better understanding of the combined effects that the varied relative motions at the tool/sheet contact zone have on the process conditions.
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    A methodology to evaluate the influence of part geometry on residual stresses in selective laser melting
    (Faculty of Engineering, Department of Industrial Engineering, Stellenbosch University, 2016) Mugwagwa, L.; Dimitrov, D.; Matope, S.; Becker, T. H.
    ENGLISH ABSTRACT: The subject of residual stresses induced by the Selective Laser Melting (SLM) process has been one of the main focus areas in literature over the past decade. It has been reported that residual stresses can be responsible for shape and dimensional distortions, cracking and compromised mechanical properties (reduced yield and fatigue strength). These shortfalls limit the applicability of SLM components in industry, particularly for the aerospace industry where part lifetime and hence fatigue life is of utmost concern. High temperature gradients have been reported to be responsible for the residual stress build up. A key aspect that has not been considered in literature is part geometry and orientation and its influence on residual stress levels. Thus, this study proposes a methodology for investigating this influence for different geometric features. In this work, samples were built from tool steel powders. The Hole Drilling Method (HDM) and X-Ray Diffraction (XRD) techniques are proposed for measuring residual stresses. Preliminary results show that the geometry of a part influences residual stress magnitudes and distributions, with sharper ends exhibiting higher stresses than less sharp specimen ends.
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    Three dimensional printing in the South African industrial environment
    (Southern African Institute for Industrial Engineering, 2008-05) Dimitrov, D.; Schreve, K.; De Beer, N.; Christiane, P.
    ENGLISH ABSTRACT: The current development of the rapid prototyping industry in South Africa is characterised by the strong dominance and fast growth in sales of three dimensional printers. Although it reflects the international trend, it seems that the industrial community lacks a clear appreciation of the real strength of this technology, especially with respect to the large variety of devices available today on the market. This paper surveys the current state and capabilities of three dimensional printing (3DP). Based on its technical background – the ink-jet printing known from the printer and plotter industry – a classification structure is developed and proposed. Different printing techniques and process concepts, together with their advantages and limitations, are described and analysed. Typical examples from three completely different application areas – manufacturing, medicine, and architecture – are presented and discussed. Some basic considerations for an informed selection of the right technology for a particular application are then presented.
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    Toward understanding the process limits of incremental sheet forming of titanium alloys
    (Faculty of Engineering, Department of Industrial Engineering, Stellenbosch University, 2016) Uheida, E. H.; Oosthuizen, G. A.; Dimitrov, D.
    Incremental sheet forming (ISF) process is characterised by high flexibility at low cost, and short replacement time. ISF as a process has received global attention. Particular areas include the aerospace industries, customized products for biomedical applications and prototyping in the automotive industry. Most applications can become competitive due to the flexibility offered by this manufacturing process. In this work, a background study and review of state-of-the-art ISF have been undertaken with the aim of providing a better understanding of the process limitations. The critical factors of incremental sheet forming were discussed and the mechanical and thermal process demands were identified. This information provides the foundation for developing a forming optimisation map.