The effects of geometry and laser power on the porosity and melt pool formation in additively manufactured 316L stainles
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ORIGINAL ARTICLE
The effects of geometry and laser power on the porosity and melt pool formation in additively manufactured 316L stainless steel Sebastiano Piazza 1,2 & Brian Merrigan 1 & Denis P. Dowling 1 & Mert Celikin 1 Received: 19 June 2020 / Accepted: 28 September 2020 # Springer-Verlag London Ltd., part of Springer Nature 2020
Abstract The present work investigates the effects of geometry and laser power on the porosity and melt pool formation for 316L stainless steel samples fabricated using the laser powder bed fusion (LPBF) technique. Both cylindrical and conical parts with the same heights were processed at a range of laser powers (60–70 W). An analytical model was used to select a suitable laser power, based on the established processing parameters, but also to predict the resultant melt pool dimensions. Based on the combination of experimental work and mathematical modelling, a novel geometrical factor is proposed, which was demonstrated to successfully improve the implemented model. A decrease in melt pool depths towards the building direction was determined in all the printed samples; this was however not predicted by the mathematical model. Furthermore, the variation in heat extraction exhibited by the conical and cylindrical parts allows the correlation between the melt pool dimensions and the geometrical factor. Finally, the influence of conical and cylindrical shapes on part hardness with increasing distance from the build plate was demonstrated; based on this comparison, it was determined that the cone geometries exhibit both a higher Vickers hardness and density. Keywords Additive manufacturing . 316L stainless steel . Laser power . Geometry . Melt pool . Modelling
1 Introduction Laser powder bed fusion (LPBF) is a promising technology, during which a laser beam selectively melts regions of metallic powder layer-upon-layer [1]. This technique combines the flexibility of ease of part printing while avoiding cost penalties related to both the optimization of product design and manufacturing [2]. LBPF is finding a range of commercial applications, especially in the aerospace and biomedical fields, where complex geometries and relatively low production rates are needed; the most widely used alloys are Ti-6Al-4V and stainless steel [3]. For the widespread use of this processing technology in structural applications, it is clearly important that there is a consistency within the mechanical properties of the parts obtained during replicated part printing operations. However, the effect of porosity level and microstructure on
* Mert Celikin [email protected] 1
School of Mechanical and Materials Engineering, University College Dublin, Belfield, Dublin, Ireland
2
Department of Industrial Engineering, University of Padova, 35131 Padova, Italy
mechanical performance is different for Ti-6Al-4V and 316L stainless steel [4]. For Ti-6Al-4V parts, microstructural tuning through postprocessing such as hot isostatic pressing (HIP) is necessary, if the fabricated part is to achieve the desired mechanica
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