Understanding the effect of laser scan strategy on residual stress in selective laser melting through thermo-mechanical simulation

Parry, Luke A.; Ashcroft, Ian; Wildman, Ricky D.

doi:10.1016/j.addma.2016.05.014

Cited by 408 publications

(331 citation statements)

References 26 publications

(31 reference statements)

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“…Preheating the powder bed can reduce the thermal gradient and cooling rate in SLM process and therefore efficiently reduce the residual stress accumulated in the components [96,[109][110][111]. Optimized scanning strategy (i.e., alternating scan direction [99,101], shorter scan length [112], lower scanning speed [112] and re-scanning [109]) can also significantly minimize the residual stress. Specifically, the "island" scanning strategy (i.e., each layer is divided into small islands, within each island the scan vector is alternately forwardand-backward, the vectors in the neighbouring islands are perpendicular to each other, and in the subsequent layer the island pattern is shifted slightly) has shown to effectively decrease the overall residual stress during process [108,113,114].…”

Section: Residual Stressmentioning

confidence: 99%

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Additively Manufactured Inconel 718 : Microstructures and Mechanical Properties

Deng

2018

Linköping Studies in Science and Technology. Licentiate Thesis

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Linköping 2018Cover image: A fracture surface of EBM IN718 after tensile test at room temperature.During the course of research underlying this thesis, Dunyong Deng was enrolled in Agora Materiae, a multidiciplinary doctoral program at Linköping University, Sweden. Printed by LiU-Tryck 2018 © Dunyong Deng AbstractAdditive manufacturing (AM), also known as 3D printing, has gained significant interest in aerospace, energy, automotive and medical industries due to its capabilities of manufacturing components that are either prohibitively costly or impossible to manufacture by conventional processes. Among the various additive manufacturing processes for metallic components, electron beam melting (EBM) and selective laser melting (SLM) are two of the most widely used powder bed based processes, and have shown great potential for manufacturing high-end critical components, such as turbine blades and customized medical implants. The futures of the EBM and SLM are doubtlessly promising, but to fully realize their potentials there are still many challenges to overcome.Inconel 718 (IN718) is a nickel-base superalloy and has impressive combination of good mechanical properties and low cost. Though IN718 is being mostly used as a turbine disk material now, the initial introduction of IN718 was to overcome the poor weldability of superalloys in 1960s, since sluggish precipitation of strengthening phases γ ′ /γ ′′ enables good resistance to strain-age cracking during welding or post weld heat treatment. Given the similarity between AM and welding processes, IN718 has been widely applied to the metallic AM field to facilitate the understandings of process-microstructure-property relationships.The work presented in this licentiate thesis aims to better understand microstructures and mechanical properties EBM and SLM IN718, which have not been systematically investigated. Microstructures of EBM and SLM IN718 have been characterized with scanning electron microscopy (SEM), transmission electron microscopy (TEM) and correlated with the process conditions. Monotonic mechanical properties (e.g., Vickers microhardness and tensile properties) have also been measured and rationalized with regards to the microstructure evolutions before and after heat treatments.For EBM IN718, the results show the microstructure is not homogeneous but dependant on the location in the components, and the anisotropic mechanical properties are probably attributed to alignment of porosities rather than texture.iii Post heat treatment can slightly increase the mechanical strength compared to the as-manufactured condition but does not alter the anisotropy. SLM IN718 shows significantly different microstructure and mechanical properties to EBM IN718. The as-manufactured SLM IN718 has very fine dendritic microstructure and Laves phases in the interdendrites, and is "work-hardened" by the residual strains and dislocations present in the material. Mechanical properties are different between horizontally and vertically built samples, and heat treatment can m...

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Section: Residual Stressmentioning

confidence: 99%

“…Differently, contour followed or following by hatch can vary from research to research [98,99]. And the contour is generally associated with lower power and lower scanning speed to improve the geometry accuracy and roughness, while the hatch is adjusted to higher power and higher scanning speed to increase the productivity [98,100].…”

Section: Processmentioning

confidence: 99%

Additively Manufactured Inconel 718 : Microstructures and Mechanical Properties

Deng

2018

Linköping Studies in Science and Technology. Licentiate Thesis

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“…Stress models built using ANSYS include those models developed by Zaeh and Branner [66] and Gu and He [67]. The studies by Li et al [68,69], Parry et al [70] and Vastola et al [71] were multiscale finite element models for fast and efficient prediction of part distortion, primarily intended to inform part designers and engineers.…”

Section: Stress and Distortion Modelsmentioning

confidence: 99%

Overhanging Features and the SLM/DMLS Residual Stresses Problem: Review and Future Research Need

2017

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Abstract:A useful and increasingly common additive manufacturing (AM) process is the selective laser melting (SLM) or direct metal laser sintering (DMLS) process. SLM/DMLS can produce full-density metal parts from difficult materials, but it tends to suffer from severe residual stresses introduced during processing. This limits the usefulness and applicability of the process, particularly in the fabrication of parts with delicate overhanging and protruding features. The purpose of this study was to examine the current insight and progress made toward understanding and eliminating the problem in overhanging and protruding structures. To accomplish this, a survey of the literature was undertaken, focusing on process modeling (general, heat transfer, stress and distortion and material models), direct process control (input and environmental control, hardware-in-the-loop monitoring, parameter optimization and post-processing), experiment development (methods for evaluation, optical and mechanical process monitoring, imaging and design-of-experiments), support structure optimization and overhang feature design; approximately 143 published works were examined. The major findings of this study were that a small minority of the literature on SLM/DMLS deals explicitly with the overhanging stress problem, but some fundamental work has been done on the problem. Implications, needs and potential future research directions are discussed in-depth in light of the present review.

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“…Stress models built using ANSYS include those models developed by Zaeh & Branner [66] and Gu & He [67]. The studies by Li et al [68][69], Parry et al [70], and Vastola et al [71] were multiscale finite element models for fast and efficient prediction of part distortion, primarily intended to inform part designers and engineers.…”

Section: Stress and Distortion Modelsmentioning

confidence: 99%

Overhanging Features and the SLM/DMLS Residual Stresses Problem: Review and Future Research Need

Patterson¹,

Messimer²,

Farrington³

2017

Preprint

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A useful and increasingly common additive manufacturing (AM) process is the selective laser melting (SLM) or direct metal laser sintering (DMLS) process. SLM/DMLS can produce fulldensity metal parts from difficult materials, but it tends to suffer from severe residual stresses introduced during processing. This limits the usefulness and applicability of the process, particularly in the fabrication of parts with delicate overhanging and protruding features. The purpose of this study was to examine the current insight and progress made toward understanding and eliminating the problem in overhanging and protruding structures. To accomplish this, a survey of literature was undertaken, focusing on process modeling (general, heat transfer, stress and distortion, and material models), direct process control (input and environmental control, hardware-in-the-loop monitoring, parameter optimization, and post-processing), experiment development (methods for evaluation, optical and mechanical process monitoring, imaging, and design-of-experiments), support structure optimization, and overhang feature design; approximately 140 published works were examined. The major findings of this study were that a small minority of the literature on SLM/DMLS deals explicitly with the overhanging stress problem, but some fundamental work has been done on the problem. Implications, needs, and potential future research directions are discussed in-depth in light of the present review.

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Understanding the effect of laser scan strategy on residual stress in selective laser melting through thermo-mechanical simulation

Cited by 408 publications

References 26 publications

Additively Manufactured Inconel 718 : Microstructures and Mechanical Properties

Additively Manufactured Inconel 718 : Microstructures and Mechanical Properties

Overhanging Features and the SLM/DMLS Residual Stresses Problem: Review and Future Research Need

Overhanging Features and the SLM/DMLS Residual Stresses Problem: Review and Future Research Need

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