Effects of inter layer time and build height on resulting properties of 316L stainless steel processed by laser powder bed fusion

Mohr, Gunther; Altenburg, Simon J.; Hilgenberg, Kai

doi:10.1016/j.addma.2020.101080

Cited by 60 publications

(87 citation statements)

References 26 publications

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“…Both graphs show that a slower cooling is observed as

increases. The graphs are shown for the first 10 s of cooling which is close to typical ILT values used in LPBF [ 11 , 23 , 26 ]. The crucial observation here is that in both graphs the topmost point cools down to approximately 10–

of its highest temperature value in this time frame.…”

Section: Thermal Modeling Simplifications and Comparison Metricsmentioning

confidence: 72%

“…Another interesting observation made on the same data is that the recorded temperatures increase with the height at which thermocouples are placed. The effect of build height is also investigated by Hilgenberg [ 11 ] and slower cooling is reported for increasing part height. As a qualitative comparison, this is in accordance with cooling curves shown in Figure 8 b, since

.…”

Section: Thermal Modeling Simplifications and Comparison Metricsmentioning

confidence: 99%

“…The observations from the one-dimensional analytical model and experimental data from literature indicates that the ILT in the LPBF process allows for ample cooling between the layers. Moreover, it is also recommended as good manufacturing practice to design process such that appropriate cooling happens between two successive layers [ 11 ]. This suggests that the previously deposited layers do not significantly affect the peak temperatures recorded for the next layer.…”

Section: Thermal Modeling Simplifications and Comparison Metricsmentioning

confidence: 99%

“…More recently, it has been studied for the LPBF process as well. For example Hilgenberg [ 11 ] used in situ thermography for observing cooling conditions during the process. It is reported that heat accumulation increases with increasing build height.…”

Section: Introductionmentioning

confidence: 99%

“…Therefore, both these phenomena jointly determine the overall thermal history of the part, which subsequently has a direct effect on the final part quality. For example, Hilgenberg [ 11 ] performed metallographic analysis to study the influence of heat accumulation on observed microstructures. It is suggested in this paper that specific temperature ranges which are important from the context of phase transformations should be considered while analyzing the influence of heat accumulation.…”

Section: Introductionmentioning

confidence: 99%

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Fast Detection of Heat Accumulation in Powder Bed Fusion Using Computationally Efficient Thermal Models

et al. 2020

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The powder bed fusion (PBF) process is a type of Additive Manufacturing (AM) technique which enables fabrication of highly complex geometries with unprecedented design freedom. However, PBF still suffers from manufacturing constraints which, if overlooked, can cause various types of defects in the final part. One such constraint is the local accumulation of heat which leads to surface defects such as melt ball and dross formation. Moreover, slow cooling rates due to local heat accumulation can adversely affect resulting microstructures. In this paper, first a layer-by-layer PBF thermal process model, well established in the literature, is used to predict zones of local heat accumulation in a given part geometry. However, due to the transient nature of the analysis and the continuously growing domain size, the associated computational cost is high which prohibits part-scale applications. Therefore, to reduce the overall computational burden, various simplifications and their associated effects on the accuracy of detecting overheating are analyzed. In this context, three novel physics-based simplifications are introduced motivated by the analytical solution of the one-dimensional heat equation. It is shown that these novel simplifications provide unprecedented computational benefits while still allowing correct prediction of the zones of heat accumulation. The most far-reaching simplification uses the steady-state thermal response of the part for predicting its heat accumulation behavior with a speedup of 600 times as compared to a conventional analysis. The proposed simplified thermal models are capable of fast detection of problematic part features. This allows for quick design evaluations and opens up the possibility of integrating simplified models with design optimization algorithms.

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“…Both graphs show that a slower cooling is observed as

of its highest temperature value in this time frame.…”

Section: Thermal Modeling Simplifications and Comparison Metricsmentioning

confidence: 72%

.…”

Section: Thermal Modeling Simplifications and Comparison Metricsmentioning

confidence: 99%

Section: Thermal Modeling Simplifications and Comparison Metricsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Fast Detection of Heat Accumulation in Powder Bed Fusion Using Computationally Efficient Thermal Models

et al. 2020

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Internal Stress Evolution and Subsurface Phase Transformation in Titanium Parts Manufactured by Laser Powder Bed Fusion—An In Situ X‐Ray Diffraction Study

et al. 2021

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Laser powder bed fusion (LPBF) is a metal additive manufacturing technology, which enables the manufacturing of complex geometries for various metals and alloys. Herein, parts made from commercially pure titanium are studied using in situ synchrotron radiation diffraction experiments. Both the phase transformation and the internal stress buildup are evaluated depending on the processing parameters. For this purpose, evaluation approaches for both temperature and internal stresses from in situ diffraction patterns are presented. Four different parameter sets with varying energy inputs and laser scanning strategies are investigated. A combination of a low laser power and scanning speed leads to a more homogeneous stress distribution in the observed gauge volumes. The results show that the phase transformation is triggered during the primary melting and solidification of the powder and subsurface layers. Furthermore, the stress buildup as a function of the part height during the manufacturing process is clarified. A stress maximum is formed below the part surface, extending into deeper layers with increasing laser power. A temperature evaluation approach for absolute internal stresses shows that directional stresses decrease sharply during laser impact and reach their previous magnitude again during cooling.

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Triaxial Residual Stress in Laser Powder Bed Fused 316L: Effects of Interlayer Time and Scanning Velocity

et al. 2022

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The control of residual stress (RS) remains a challenge in the manufacturing of metallic parts using the laser powder bed fusion process (LPBF). This layer‐by‐layer manufacturing approach gives rise to complex triaxial RS distributions, which require extensive characterization effort for a broader acceptance of LPBF in industry. This study focuses on the distribution of bulk triaxial RS and surface RS in LPBF austenitic steel 316L. The RS are determined by X‐ray and neutron diffraction to characterize the RS distribution. Variations in the LPBF parameters interlayer time (ILT) and scanning velocity and their influence on the temperature distribution and resulting RS is investigated using thermographic data from in situ process monitoring. The RS in the LPBF 316L is tensile at the surface and compressive in the bulk. The RS is directly related to the thermal history of the part as shown by the in situ thermography data. Shorter ILT leads to higher temperatures of the part during the manufacturing, which decrease the RS and RS formation mechanisms. Interestingly, the surface RS does not agree with this observation. This study highlights the benefit of using multiple RS determination methods and in situ thermography monitoring to characterize the RS in LPBF processed parts.

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Effects of inter layer time and build height on resulting properties of 316L stainless steel processed by laser powder bed fusion

Cited by 60 publications

References 26 publications

Fast Detection of Heat Accumulation in Powder Bed Fusion Using Computationally Efficient Thermal Models

Fast Detection of Heat Accumulation in Powder Bed Fusion Using Computationally Efficient Thermal Models

Internal Stress Evolution and Subsurface Phase Transformation in Titanium Parts Manufactured by Laser Powder Bed Fusion—An In Situ X‐Ray Diffraction Study

Triaxial Residual Stress in Laser Powder Bed Fused 316L: Effects of Interlayer Time and Scanning Velocity

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