Metal AM Research Articles

Using confocal fusion for measurement of metal AM surface texture

The highly complex nature of as printed metal AM surfaces pose other challenges for making measurements compared to surfaces made with many conventional processing methods. The high complexity is caused by high aspect ratios, a mix of high and low reflexivity, steep angles etc. It is not clear which method is the most suitable for measuring these surfaces. The objective of this study was to compare four different measurement modes available in one instrument to evaluate the advantages and drawbacks of the respective techniques regarding measurements of metal AM surfaces. The evaluated measurement modes are Confocal Microscopy, Coherence Scanning Interferometry, Focus Variation and Confocal Fusion. The effect of advantages and drawbacks of studied techniques was tested on typical surfaces produced by L-PBF process. Surfaces printed at 0° and 90° inclinations were compared regarding the measurement results achieved from the different methods. The Power Spectral Density analysis and visual comparison were used for the examination of studied measurements methods. Besides the comparison of areal measurements acquired by different modes available in the instrument also extracted profile measurements were compared with profile images acquired using an Optical Microscope. This study reveals that confocal fusion is a promising technique for AM surface characterisation, due to the highest amount of valid data points in the typical measurement. The new approach developed in the study showed that PSD analysis can be used for evaluation of fill in algorithms incorporated in different software. Results of the profile comparisons help to illustrate features that can be depicted by surface measurements, applying different measurement principles, as well as enables comparison of raw profile data between different types of measurements. Further investigation of measurements on AM surfaces in the frequency domain will bring more understanding about the limitations of measurement techniques.

Derivation of optimum abrasive for improving magnetic polishing rate for hybrid metal AM titanium alloy and creating a polishing prediction model

Derivation of optimum abrasive for improving magnetic polishing rate for hybrid metal AM titanium alloy and creating a polishing prediction model

Avi Cohen, Vice President of XJet highlights some of the challenges and advances in ceramics and metal AM

Avi Cohen, Vice President of XJet highlights some of the challenges and advances in ceramics and metal AM

A review of computational modeling in powder-based additive manufacturing for metallic part qualification

PurposeAdditive manufacturing (AM) is revolutionizing the manufacturing industry due to several advantages and capabilities, including use of rapid prototyping, fabrication of complex geometries, reduction of product development cycles and minimization of material waste. As metal AM becomes increasingly popular for aerospace and defense original equipment manufacturers (OEMs), a major barrier that remains is rapid qualification of components. Several potential defects (such as porosity, residual stress and microstructural inhomogeneity) occur during layer-by-layer processing. Current methods to qualify AM parts heavily rely on experimental testing, which is economically inefficient and technically insufficient to comprehensively evaluate components. Approaches for high fidelity qualification of AM parts are necessary.Design/methodology/approachThis review summarizes the existing powder-based fusion computational models and their feasibility in AM processes through discrete aspects, including process and microstructure modeling.FindingsCurrent progresses and challenges in high fidelity modeling of AM processes are presented.Originality/valuePotential opportunities are discussed toward high-level assurance of AM component quality through a comprehensive computational tool.

Understanding grain evolution in additive manufacturing through modeling

Variability in the mechanical properties of additively manufactured metal parts is a key concern for their application in service. One of the parameters affecting the above-mentioned property is solidification texture which is driven by scan patterns and other process variables. Understanding of how these textures arise in the AM process can provide a pathway to control these features which ultimately decide the final structural material properties. In this work, a Cellular Automata (CA) based two-dimensional microstructure model is formulated and implemented to understand grain evolution in AM. Grain evolution in multilayer depositions using various scan patterns in Directed Energy Deposition (DED), Metal Laser Sintering/Selective Laser Melting (MLS/SLM), and Electron Beam Melting (EBM) is presented and qualitatively compared with reported literature. Results show strong correlation of scan patterns with evolving grain orientations. Variability in grain size and orientation evolution during SLM and EBM processing of metallic materials showed direct influence by exposure to different cooling rates and thermal gradients. The similarities between the simulated and reported results lead us to conclude CA based modeling for predicting grain orientation and size in metal AM processes is useful for prediction of continuum level structural properties at global and local length scales.

Metal AM Partnerships

News of alliances in the metal AM arena have hit the news over recent months, as various firms target production systems for AM manufacture of metal components. Andrew Allcock has this overview of some of the more significant announcements

Industrial needs and available techniques for geometry assurance for metal AM parts with small scale features and rough surfaces

From an industrial perspective this paper aims to explore the state of the art regarding GD&T for metal additive manufacturing, specifically regarding product definition and inspection. The available techniques for geometry assurance for parts with small scale features and rough surfaces are evaluated in terms of suitability for the task and readiness for industrial implementation. It is found that many of the remaining challenges seem to be related to processing of data rather than obtaining data. Current difficulties are related to issues such as calibration, surface determination and defining the most relevant parameters to tolerance and inspect.

Directional and notch effects on the fatigue behavior of as-built DMLS Ti6Al4V

The metal additive manufacturing technology produces components of any geometrical complexity directly from a computer model. Full exploitation of metal AM technology may result in parts that can be lighter in weight, cheaper to produce, and have complex geometries that are difficult or impossible to produce with conventional methods. Two aspects significantly affecting the fatigue behavior of DMLS Ti6Al4V are investigated: (i) the as-built surface condition, which is known to introduce a significant knock-down factor in fatigue with respect to the machined condition, and (ii) the presence of a geometrical notch, which affect conventional materials but has not yet been studied in metal AM parts. After the preliminary determination of the reference unnotched fatigue response, the notch fatigue behavior of as-built DMLS Ti6Al4V specimens is determined. Four different notch fatigue factors are estimated including the influence of notch direction with respect to build direction and the notch fabrication conditions.

Longitudinal Milling and Fine Abrasive Finishing Operations to Improve Surface Integrity of Metal AM Components

Growing market of additive manufacturing and in particular, metal AM has allowed the manufacturers to produce a wide variety of complex designs with near-net shape in minimum time without the need for custom tooling. However, the application of additive manufactured components in various applications, e.g., biomechanical contacts, naval and aerospace components are limited due to its poor surface integrity and part feature tolerance limits. Traditional methods, e.g., milling, do provide solution to some of the post-processing needs, however, results in poor material utilization, requires custom tooling or may be completely infeasible for complex geometries. In the current work, we focus on developing a post-processing strategy by coupling traditional machining processes with non-traditional fine abrasive finishing (FAF) methods. Preliminary results on 316 L stainless steel components fabricated via laser powder-bed fusion suggests that the proposed post-processing strategy can be used to (a) selectively impart surface finish Sa < 25 nm, and (b) reduce the surface porosity by ∼89% when compared to the as-fabricated sample.

Neutron Characterization for Additive Manufacturing

Abstract Neutron-based imaging and measurement techniques are an ideal complement to x-ray methods for characterizing additively manufactured materials and components. This article presents examples showing how neutron radiography and residual strain measurements reveal the internal structure and stress distributions in highly engineered turbine blades produced by additive processes. It also discusses the development of neutron characterization tools at ORNL and a recent effort in which they were used to evaluate stress-relief treatments for large-scale metal AM structures.