Browsing by Author "Yadroitsev, Igor"

Now showing 1 - 8 of 8
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    Effect of process parameters on residual stresses, distortions, and porosity in selective laser melting of maraging steel 300
    (MDPI, 2019) Mugwagwa, Lameck; Yadroitsev, Igor; Matope, Stephen
    ENGLISH ABSTRACT: Selective laser melting (SLM) is one of the most well-known additive manufacturing methods available for the fabrication of functional parts from metal powders. Although SLM is now an established metal additive manufacturing technique, its widespread application in industry is still hindered by inherent phenomena, one of which is high residual stresses. Some of the effects of residual stresses–such as warping and thermal stress-related cracking–cannot be corrected by post processing. Therefore, establishing input process parameter combinations that result in the least residual stress magnitudes and related distortions and/or cracking is critical. This paper presents the influence of laser power, scanning speed, and layer thickness on residual stresses, distortions and achievable density for maraging steel 300 steel parts in order to establish the most optimum input parameter combinations. An analysis of the interdependence between process outcomes shows that high residual stress magnitudes lead to high dimensional distortions in the finished parts, whilst porous parts suffer relatively lower residual stresses and associated distortions.
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    Effects of defects on mechanical properties in metal additive manufacturing : a review focusing on X-ray tomography insights
    (Elsevier, 2019) Du Plessis, Anton; Yadroitsava, Ina; Yadroitsev, Igor
    ENGLISH ABSTRACT: X-ray tomography has emerged as a uniquely powerful and non-destructive tool to analyze defects in additive manufacturing. Defects include unintended porosity, rough surfaces and deviations from design, which can have different root causes and can vary significantly among samples. Powder material properties, non-uniform delivery of the powder layer, deformation during manufacturing, deviations from optimal process-parameters caused by changes in the laser beam, the optical components and the scanning system operation, may result in lack of fusion pores, metallurgical pores, keyhole pores, etc. These different types of pores have different typical sizes, shapes and 3D distributions. All types of defects have effects on the mechanical properties of a final part. The use of X-ray tomography to visualize pores in parts (non-destructively) prior to mechanical testing has allowed us to improve our understanding of the effect of this porosity on the mechanical properties of the part (also referred to as “effect of defect”). This can provide the possibility to discriminate critical defects from harmless ones, and thereby build confidence in additivemanufacturing processes. This paper reviews the current state of knowledge with regard to the “effect of defect” in metal additivemanufacturing, and highlights some relevant examples from our recent work.
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    Influence of large artificial porosity on bending behaviour of TI6AL4V ELI additively manufactured specimens subjected to typical loads during mastication
    (Southern African Institute for Industrial Engineering, 2020) Wessels, Adriaan; Du Plessis, Anton; Yadroitsava, Ina; Els, Johan; Yadroitsev, Igor
    Effective quality control of implants made using additive manufacturing is an important task for suppliers to comply fully with existing regulations and certifications. To study the influence of porosity on the mechanical behaviour of mandibular implants produced by additive manufacturing, preliminary tests with longitudinal flat samples were performed with 3D point bending tests. Ti6Al4V Extra Low Interstitial (ELI) specimens with artificial porosity were designed and subjected to typical loads during mastication. In this work, a finite element simulation was constructed to investigate the bending behaviour of samples, which was consistent with the experimental results. The work shows that even large artificial cavities (designed up to 0.42 mm) do not significantly affect the strength of additively manufactured 2.5 mm-thick Ti6Al4V ELI specimens under typical static loads of mandibular implants, in the considered loading conditions, and for samples subjected to appropriate surface finishing and annealing heat treatment.
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    Investigation of the effect of scan vector length on residual stresses in selective laser melting of maraging steel 300
    (Southern African Institute for Industrial Engineering, 2019) Mugwagwa, Lameck; Dimitrov, Dimiter; Matope, Stephen; Yadroitsev, Igor
    ENGLISH ABSTRACT: Selective laser melting scanning strategies influence the quality characteristics of parts, such as form accuracy and residual stresses. Previous research on the effect of laser scanning strategy parameters (such as scan vector length) demonstrates that residual stresses decrease with scan vector length reduction. However, most of these studies overlook the associated porosity and how this can contribute to stress relief. In this work, three scan vector lengths were compared to evaluate their impact on residual stresses, achievable part density, and scanning time. Reducing the scan vector length generally lowers residual stresses magnitudes, but introduces porosity as a result of localised overheating.
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    Investigation of the effect of scan vector length on residual stresses in selective laser melting of maraging steel 300
    (Southern African Institute for Industrial Engineering, 2019-12-12) Mugwagwa, Lameck; Dimitrov, Dimiter; Matope, Stephen; Yadroitsev, Igor
    ENGLISH ABSTRACT: Selective laser melting scanning strategies influence the quality characteristics of parts, such as form accuracy and residual stresses. Previous research on the effect of laser scanning strategy parameters (such as scan vector length) demonstrates that residual stresses decrease with scan vector length reduction. However, most of these studies overlook the associated porosity and how this can contribute to stress relief. In this work, three scan vector lengths were compared to evaluate their impact on residual stresses, achievable part density, and scanning time. Reducing the scan vector length generally lowers residual stresses magnitudes, but introduces porosity as a result of localised overheating.
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    Mechanical properties and in situ deformation imaging of microlattices manufactured by laser based powder bed fusion
    (MDPI, 2019-09-09) Du Plessis, Anton; Kouprianoff, Dean-Paul; Yadroitsava, Ina; Yadroitsev, Igor
    ENGLISH ABSTRACT: This paper reports on the production and mechanical properties of Ti6Al4V microlattice structures with strut thickness nearing the single-track width of the laser-based powder bed fusion (LPBF) system used. Besides providing new information on the mechanical properties and manufacturability of such thin-strut lattices, this paper also reports on the in situ deformation imaging of microlattice structures with six unit cells in every direction. LPBF lattices are of interest for medical implants due to the possibility of creating structures with an elastic modulus close to that of the bones and small pore sizes that allow effective osseointegration. In this work, four different cubes were produced using laser powder bed fusion and subsequently analyzed using microCT, compression testing, and one selected lattice was subjected to in situ microCT imaging during compression. The in situ imaging was performed at four steps during yielding. The results indicate that mechanical performance (elastic modulus and strength) correlate well with actual density and that this performance is remarkably good despite the high roughness and irregularity of the struts at this scale. In situ yielding is visually illustrated.
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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.
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    X-Ray microcomputed tomography in additive manufacturing : a review of the current technology and applications
    (Mary Ann Liebert, Inc., 2018) Du Plessis, Anton; Yadroitsev, Igor; Yadroitsava, Ina; Le Roux, Stephan G.
    X-ray microcomputed tomography (microCT) has become an established method of testing and analyzing additively manufactured parts in recent years, being especially useful and accurate for dimensional measurement and porosity analysis. While this nondestructive analysis method is gaining traction among additive manufacturing (AM) researchers and engineers, the capabilities of the method are not yet fully appreciated and are still being developed. This review aims to summarize the many diverse ways this technique has been applied to AM, including new and specialized applications. Examples are shown of many of these newly developed methods, while also discussing the practicality and limitations of each. The review ends with perspectives on the most time- and cost-effective ways to make use of microCT for various AM applications from R&D up to industrial production, with suggestions for scan strategies for different types of analyses.