The effect of scan path on thermal gradient during selective laser melting
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ORIGINAL ARTICLE
The effect of scan path on thermal gradient during selective laser melting Benjamin Blackford 1 & Gene Zak 1 & Il Yong Kim 1 Received: 29 May 2020 / Accepted: 9 August 2020 # Springer-Verlag London Ltd., part of Springer Nature 2020
Abstract High thermal gradients during selective laser melting (SLM) can generate residual stresses due to uneven volumetric expansion, which can lead to weak or cracked parts. In SLM, scan path refers to the route the laser takes during a single layer of solidification, and has a direct impact on thermal gradient, and by association residual stress. This work uses a finite element model to compare the thermal gradients generated by nine different scan paths, six of which have been tested and discussed in literature, and three of which are proposed in this document. This study found that scan paths which subdivide powder layers into smaller areas were found to produce fewer areas of high thermal gradient, as well as a lower total average gradient when compared to paths that scan the full layer without subdivision. One of the new scan path concepts, named the “subsectioned spiral method”, produced the most favorable results. Of the six non-transient data categories retrieved, the subsectioned spiral scan path outperformed all eight other paths, with improvements ranging between 6 and 44% compared with the baseline path. Keywords Additive manufacturing . Finite element modeling . Scan path . Residual stress . Thermal gradient
1 Introduction Selective laser melting (SLM) is an additive manufacturing (AM) method that uses a powder bed and high-powered laser to heat and melt cross sections of successive powder layers [1]. This technology provides advantages over traditional manufacturing methods such as reducing design-tomanufacture time, as well as providing greater design freedom [2, 3]. Additive manufacturing is particularly well suited to advanced design methods such as topology optimization, a design tool that creates optimal designs that can be difficult to manufacture using traditional manufacturing methods [4]. Despite these advantages, there are limitations holding back
* Benjamin Blackford [email protected] Gene Zak [email protected] Il Yong Kim [email protected] 1
Queen’s University, 99 University Ave, Kingston, ON K7L 3 N6, Canada
SLM and additive manufacturing in general. One of these limitations is the potential negative effect on dimension tolerances and structural integrity due to thermal gradients and residual stress introduced during the manufacturing process. Residual stress refers to stresses that form during the manufacturing process and are not resolved after completion of the part. These stresses can cause cracking, distortion, and reduced fatigue performance, so ensuring these stresses are kept to a minimum is critical [3, 5]. During selective laser melting, thermal stresses are formed due to nonuniform heating of the powder [6, 7]. Residual stress generation in SLM can be represented by two mechanisms: the temperature gradient model (TGM)
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