Heat transfer in lattice structures during metal additive manufacturing: numerical exploration of temperature field evolution David Downing, Martin Leary, Matthew McMillan, Ahmad Alghamdi and Milan Brandt RMIT Centre for Additive Manufacturing, School of Engineering, RMIT University, Melbourne, Australia Abstract Purpose – Metal additive manufacturing is an inherently thermal process, with intense localised heating and for sparse lattice structures, often rapid uneven cooling. Thermal effects influence manufactured geometry through residual stresses and may also result in non-isotropic material properties. This paper aims to increase understanding of the evolution of the temperature field during fabrication of lattice structures through numerical simulation. Design/methodology/approach – This paper uses a reduced order numerical analysis based on “best-practice” compromise found in literature to explore design permutations for lattice structures and provide first-order insight into the effect of these design variables on the temperature field. Findings – Instantaneous and peak temperatures are examined to discover trends at select lattice locations. Insights include the presence of vertical struts reduces overall lattice temperatures by providing additional heat transfer paths; at a given layer, the lower surface of an inclined strut experiences higher temperatures than the upper surface throughout the fabrication of the lattice; during fabrication of the lower layers of the lattice, isolated regions of material can experience significantly higher temperatures than adjacent regions. Research limitations/implications – Due to the simplifying assumptions and multi-layer material additions, the findings are qualitative in nature. Future research should incorporate additional heat transfer mechanisms. Practical implications – These findings point towards thermal differences within the lattice which may manifest as dimensional differences and microstructural changes in the built part. Originality/value – The paper provides qualitative insights into the effect of local geometry and topology upon the evolution of temperature within lattice structures fabricated in metal additive manufacturing. Keywords Thermal conductivity, Layered manufacturing, Rapid prototyping, Computational model, Numerical simulation, Finite element analysis Paper type Research paper 1. Project summary Metal additive manufacturing (MAM) is inherently a thermal process with both short term and long term transient behaviours. MAM is well suited to the fabrication of complex lattice structures. Numerical simulation is used to gain insight into the effects that lattice topology and associated local dimensions have upon the temperature distribution within the lattice during fabrication. These findings point towards thermal differences within the lattice which may manifest as dimensional differences and microstructural changes in the built part. 2. Additive manufacturing Additive manufacturing (AM) is a technique whereby physical items are built by processes in which material is joined incrementally to form the required geometry and detailed features (Tan et al., 2017; Zhai et al., 2014). The material units are brought together and joined (including melted, sintered and bonded). This can be contrasted to traditional manufacturing, which generally involves bulk casting and forming processes (formative manufacturing), followed by a series of material removal processes such as cutting, drilling and trimming from the larger part (subtractive manufacturing) (ISO/ASTM, 2015). There are many technical and commercial benefits to the AM process, some of those offered in Wohlers’ reports include (Wohlers and Caffrey, 2015; Wohlers et al., 2017) reduced time and costs invested in tools compared to formative manufacturing; agility to change part dimensions with every build for prototyping and small batch runs; reduced part count by creating forms with internal cavities; and lightweighting by removing unnecessary material needed The current issue and full text archive of this journal is available on Emerald Insight at: https://www.emerald.com/insight/1355-2546.htm Rapid Prototyping Journal 26/5 (2020) 911–928 © Emerald Publishing Limited [ISSN 1355-2546] [DOI 10.1108/RPJ-11-2018-0288] The authors acknowledge use of facilities within the RMIT Advanced Manufacturing Precinct. D.D. would like to acknowledge support from Lockheed Martin and from the Australian Research Council under ARC Centre for Additive Biomanufacturing. Received 9 November 2018 Revised 27 September 2019 Accepted 2 December 2019 911