Browsing by Author "Dimitrov, D. M."

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    Development of a model for predicting cycle time in hot stamping
    (Elsevier, 2018) Muvunzi, R.; Dimitrov, D. M.; Matope, S.; Harms, T. M.
    In manufacturing, reducing the cycle time results in lower production costs. The cycle time in a hot stamping process affects the quality characteristics (tensile strength) of formed parts. A faster cooling rate (˃27 K/s) of the blank guarantees the production of a part with the required microstructural properties (martensite). This compels researchers to continuously develop ways of increasing the manufacturing speed. On the other hand, it is important to predict the minimum cycle time for a given set of parameters which does not compromise the quality of formed parts. In this paper, a model for predicting the cycle time for a hot stamping process is presented. The lumped heat capacitance method is used in formulating the model since the temperature gradient across the blank and heat transfer within the plane of the blank are considered negligible. To validate the equation, a finite element simulation was conducted using Pam-Stamp software. The results show that the proposed model can be useful in further studies targeted towards cycle time reduction in hot sheet metal forming processes.
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    The effects of selective laser melting scan strategies on deviation of hybrid parts
    (Southern African Institute for Industrial Engineering, 2017-11-22) Hagedorn-Hansen, D.; Bezuidenhout, M. B.; Dimitrov, D. M.; Oosthuizen, G. A.
    ENGLISH ABSTRACT: The use of additive manufacturing to produce intricate part geometries in the aerospace, medical, and tool-and-die industries is increasingly incorporated in manufacturing process chains. However, the high costs, long production times, and material integrity issues associated with additive manufacturing technologies such as selective laser melting make the process suitable only for certain applications. In order to reduce selective laser melting production costs for selected parts, a combination of selective laser melting and milling can be used. Metal parts produced with this method are referred to as hybrid parts. A challenge in producing hybrid parts is to reduce the geometrical deviation due to process-induced warping. This paper discusses the effects of various laser scan strategies on the deviation of hybrid parts. A newly developed scan strategy is experimentally compared with its commercial counterpart with regard to as-built part warping and porosity. The novel strategy resulted in a significant reduction in warping and porosity.
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    High-speed 5-axis machining for tooling applications
    (Southern African Institute for Industrial Engineering, 2012-11) Saxer, M.; De Beer, N.; Dimitrov, D. M.
    ENGLISH ABSTRACT: In the modern metalworking industry, production moulds often have complex geometry, with undercut regions, small corner radii, sharp edges, deep cavities, or large cores. Conventional manufacturing process chains to machine these complex features are often lengthy and inefficient due to multiple steps. This article presents current results obtained through industry projects and experimental work using 5-axis high-speed machining with high-end CAD/CAM systems to improve process efficiency. Cost optimisation and lead time shortening can be clearly shown. This is of particular importance for South African manufacturing companies, where multi-axis HSC technology although not totally unknown is significantly under-used.