Metal Laser Powder Bed Fusion Research Articles

A Review of Model Inaccuracy and Parameter Uncertainty in Laser Powder Bed Fusion Models and Simulations.

This paper presents a comprehensive review on the sources of model inaccuracy and parameter uncertainty in metal laser powder bed fusion (L-PBF) process. Metal additive manufacturing (AM) involves multiple physical phenomena and parameters that potentially affect the quality of the final part. To capture the dynamics and complexity of heat and phase transformations that exist in the metal L-PBF process, computational models and simulations ranging from low to high fidelity have been developed. Since it is difficult to incorporate all the physical phenomena encountered in the L-PBF process, computational models rely on assumptions that may neglect or simplify some physics of the process. Modeling assumptions and uncertainty play significant role in the predictive accuracy of such L-PBF models. In this study, sources of modeling inaccuracy at different stages of the process from powder bed formation to melting and solidification are reviewed. The sources of parameter uncertainty related to material properties and process parameters are also reviewed. The aim of this review is to support the development of an approach to quantify these sources of uncertainty in L-PBF models in the future. The quantification of uncertainty sources is necessary for understanding the tradeoffs in model fidelity and guiding the selection of a model suitable for its intended purpose.

Heat Treatment of Alloy 718 Made by Additive Manufacturing for Oil and Gas Applications

The ability to consolidate parts in complex assemblies using metal additive manufacturing offers transformational product development opportunities. Specifically, the high value capability for printing complex shapes and channels using metal laser powder bed fusion is a key enabler to realizing this vision. A thorough understanding of microstructure and defects specific to industry standard heat treatments and thermal processing is essential for fielding additively manufactured parts. The goal of this work was to evaluate oil and gas application specific heat treatments on Alloy 718 built using laser powder bed fusion. In the present study, the influence of heat treatment steps relevant to the use of Alloy 718 for components under American Petroleum Institute Specification 6A have been investigated. Multiple heat treatment conditions as well as hot isostatic pressing were studied and compared to the as-built material using a combination of thermodynamic simulations and metallurgical characterization. The overall conclusion of this study is that none of the studied heat treatment approaches is appropriate for American Petroleum Institute Specification 6A and that specific thermal post-processing routes compliant to the specification need to be considered.

Correlation of meltpool characteristics and residual stresses at high laser intensity for metal lpbf process

ABSTRACTSelective Laser Melting (SLM) commonly referred as Metal Laser Powder Bed Fusion (LPBF) processes, proved in the last decade to be suitable for the manufacturing of complex metallic components. In order to fulfil industrial needs from various industries (e.g. aerospace, tooling, energy production, medical), Machine manufacturers have increased the productivity of the LPBF-process mainly by increasing the number and maximum power of lasers. However, this strategy also affects the magnitude of residual stresses generated in the consolidated material. This study analyses the residual stresses in SS316L components by XRD measurement, where a correlation to the meltpool dimensions could be found and verified for different laser power and scan speeds. The results provide fundamentals to assess the gain in productivity, and to establish generic guidelines for the optimization of residual stresses at high laser power.

Low cost irregular feed stock for laser powder bed fusion

Spherical powders are almost exclusively deployed for metal laser powder bed fusion (LPBF) additive manufacturing (AM). In this work, low-cost irregular powder feedstock is studied for its potential in three key areas to meet minimum AM process requirements, namely: (1) hopper flow, (2) layer spreading, and (3) de-powdering. Irregular water-atomized Iron powder was used as the study population, while spherical plasma-atomized Inconel 625 powder was used as the control. Powder flow characteristics were obtained using a FT4 Powder Rheometer (Freeman Technology). Layer spreading was evaluated indirectly via powder bed density measurements. Measurements were quantified by using printed artifacts for captive powder and evaluated using isopropanol infiltration and three-dimensional computed tomography (CT) imaging (Zeiss Xradia 520 Versa). Powder clearing from fine channels was quantified through vision-based measurements of printed artifacts (Dino-Lite DinoCapture 2.0). The results from this work demonstrated that: (1) A larger opening and steeper hopper angle are necessary to maintain a mass flow regime with the irregular powder. (2) Powder bed density is similarly consistent across the bed indicating adequate spreadability. (3) Water-atomized Iron powder has better de-powdering characteristics in the smallest cleared 0.6 mm diameter features, likely due to its 15% lower bed density.

Real-time monitoring of laser powder bed fusion process using high-speed X-ray imaging and diffraction

We employ the high-speed synchrotron hard X-ray imaging and diffraction techniques to monitor the laser powder bed fusion (LPBF) process of Ti-6Al-4V in situ and in real time. We demonstrate that many scientifically and technologically significant phenomena in LPBF, including melt pool dynamics, powder ejection, rapid solidification, and phase transformation, can be probed with unprecedented spatial and temporal resolutions. In particular, the keyhole pore formation is experimentally revealed with high spatial and temporal resolutions. The solidification rate is quantitatively measured, and the slowly decrease in solidification rate during the relatively steady state could be a manifestation of the recalescence phenomenon. The high-speed diffraction enables a reasonable estimation of the cooling rate and phase transformation rate, and the diffusionless transformation from β to α’ phase is evident. The data present here will facilitate the understanding of dynamics and kinetics in metal LPBF process, and the experiment platform established will undoubtedly become a new paradigm for future research and development of metal additive manufacturing.

Overview of modelling and simulation of metal powder bed fusion process at Lawrence Livermore National Laboratory

The metal laser powder bed fusion additive manufacturing process uses high power lasers to build parts layer upon layer by melting fine metal powders. Qualification of parts produced using this technology is broadly recognised as a significant challenge. Physics based process models have been identified as being foundational to qualification of additively manufactured metal parts. In the present article, a multiscale modelling strategy is described that will serve as the foundation upon which process control and part qualification can be built. This includes a model at the scale of the powder that simulates single track/single multilayer builds and provides powder bed and melt pool thermal data. A second model computationally builds a complete part and predicts manufactured properties (residual stress, dimensional accuracy) in three dimensions. Modelling is tied to experiment through data mining.