scholarly journals Towards a Methodology for Component Design of Metallic AM Parts Subjected to Cyclic Loading

Metals ◽  
2021 ◽  
Vol 11 (5) ◽  
pp. 709
Author(s):  
Uwe Zerbst ◽  
Mauro Madia ◽  
Giovanni Bruno ◽  
Kai Hilgenberg
Keyword(s):  
Unsolved Problem ◽  
Fatigue Cracks ◽  
Special Focus ◽  
Laser Powder Bed Fusion ◽  
Powder Bed ◽  
Lack Of Fusion ◽  
Fatigue Design ◽  
Component Design ◽  
Similar Temperature ◽  
Potential Improvement

The safe fatigue design of metallic components fabricated by additive manufacturing (AM) is still a largely unsolved problem. This is primarily due to (a) a significant inhomogeneity of the material properties across the component; (b) defects such as porosity and lack of fusion as well as pronounced surface roughness of the as-built components; and (c) residual stresses, which are very often present in the as-built parts and need to be removed by post-fabrication treatments. Such morphological and microstructural features are very different than in conventionally manufactured parts and play a much bigger role in determining the fatigue life. The above problems require specific solutions with respect to the identification of the critical (failure) sites in AM fabricated components. Moreover, the generation of representative test specimens characterized by similar temperature cycles needs to be guaranteed if one wants to reproducibly identify the critical sites and establish fatigue assessment methods taking into account the effect of defects on crack initiation and early propagation. The latter requires fracture mechanics-based approaches which, unlike common methodologies, cover the specific characteristics of so-called short fatigue cracks. This paper provides a discussion of all these aspects with special focus on components manufactured by laser powder bed fusion (L-PBF). It shows how to adapt existing solutions, identifies fields where there are still gaps, and discusses proposals for potential improvement of the damage tolerance design of L-PBF components.

Process Mapping and In-Process Monitoring of Porosity in Laser Powder Bed Fusion Using Layerwise Optical Imaging

2018 ◽  
Vol 140 (10) ◽  
Author(s):  
Farhad Imani ◽  
Aniruddha Gaikwad ◽  
Mohammad Montazeri ◽  
Prahalada Rao ◽  
Hui Yang ◽  
...  
Keyword(s):  
Process Parameters ◽  
Process Conditions ◽  
Layer By Layer ◽  
Powder Bed Fusion ◽  
Laser Powder Bed Fusion ◽  
Powder Bed ◽  
Graph Theoretic ◽  
Lack Of Fusion ◽  
Spectral Graph ◽  
Optical Images

The goal of this work is to understand the effect of process conditions on lack of fusion porosity in parts made using laser powder bed fusion (LPBF) additive manufacturing (AM) process, and subsequently, to detect the onset of process conditions that lead to lack of fusion-related porosity from in-process sensor data. In pursuit of this goal, the objectives of this work are twofold: (1) quantify the count (number), size and location of pores as a function of three LPBF process parameters, namely, the hatch spacing (H), laser velocity (V), and laser power (P); and (2) monitor and identify process conditions that are liable to cause porosity through analysis of in-process layer-by-layer optical images of the build invoking multifractal and spectral graph theoretic features. These objectives are important because porosity has a significant impact on the functional integrity of LPBF parts, such as fatigue life. Furthermore, linking process conditions to defects via sensor signatures is the first step toward in-process quality assurance in LPBF. To achieve the first objective, titanium alloy (Ti–6Al–4V) test cylinders of 10 mm diameter × 25 mm height were built under differing H, V, and P settings on a commercial LPBF machine (EOS M280). The effect of these process parameters on count, size, and location of pores was quantified based on X-ray computed tomography (XCT) images. To achieve the second objective, layerwise optical images of the powder bed were acquired as the parts were being built. Spectral graph theoretic and multifractal features were extracted from the layer-by-layer images for each test part. Subsequently, these features were linked to the process parameters using machine learning approaches. Through these image-based features, process conditions under which the parts were built were identified with the statistical fidelity over 80% (F-score).

scholarly journals Physics-Based Predictive Model of Lack-of-Fusion Porosity in Laser Powder Bed Fusion Considering Cap Area

Crystals ◽  
2021 ◽  
Vol 11 (12) ◽  
pp. 1568
Author(s):  
Wenjia Wang ◽  
Steven Y. Liang
Keyword(s):  
Image Analysis ◽  
Cross Section ◽  
Void Fraction ◽  
Material Properties ◽  
Molten Pool ◽  
Analytical Modeling ◽  
Powder Bed Fusion ◽  
Laser Powder Bed Fusion ◽  
Powder Bed ◽  
Lack Of Fusion

This work proposed a computationally efficient analytical modeling strategy to calculate the product porosity in laser powder bed fusion (LPBF) induced by a lack-of-fusion defect, with the consideration of cap area in solidified molten pools, influence of powder bed characteristics on material properties, and un-melted powders in the lack-of-fusion portion. The powder packing pattern and powder bed void fraction were estimated by an advancing front method and the technique of image analysis. The effects of powder bed characteristics on the material properties were considered by analytical models with solid properties and powder bed void fraction as inputs. A physics-based thermal model was utilized to calculate the temperature distribution and molten pool size. The molten pool cross section in transvers direction was assumed to be dual half-elliptical. Based on this assumption and molten pool size, the geometry of the molten pool cross section with cap area was determined. The overlapping pattern of molten pools in adjacent scan tracks and layers was then obtained with given hatch space and layer thickness. The lack-of-fusion area fraction was obtained through image analysis of the overlapping pattern. The lack-of-fusion porosity was the multiplication of the lack-of-fusion area fraction and powder bed void fraction. The predictions of porosity under different process conditions were compared with experimental results of 316L stainless steel and showed a better predictive accuracy than the predictions that did not consider cap area. The proposed analytical modeling method has no numerical calculations, which ensures its low computational cost. Thus, the proposed model can be a convenient tool for the fast computation of lack-of-fusion-induced porosity and can help the quality control in LPBF.

scholarly journals Analytical Prediction of Balling, Lack-of-Fusion and Keyholing Thresholds in Powder Bed Fusion

2021 ◽  
Vol 11 (24) ◽  
pp. 12053
Author(s):  
Wenjia Wang ◽  
Jinqiang Ning ◽  
Steven Y. Liang
Keyword(s):  
Molten Pool ◽  
Laser Power ◽  
Computational Time ◽  
Process Conditions ◽  
Analytical Prediction ◽  
Powder Bed Fusion ◽  
Laser Powder Bed Fusion ◽  
Powder Bed ◽  
Lack Of Fusion ◽  
Analytical Thermal Model

This paper proposes analytical modeling methods for the prediction of balling, lack-of-fusion and keyholing thresholds in the laser powder bed fusion (LPBF) additive manufacturing. The molten pool dimensions were first predicted by a closed-form analytical thermal model. The effects of laser power input, boundary heat loss, powder size distribution and powder packing pattern were considered in the calculation process. The predicted molten pool dimensions were then employed in the calculation of analytical thresholds for these defects. Reported experimental data with different materials were compared to predictions to validate the presented analytical models. The predicted thresholds of these defects under various process conditions have good agreement with the experimental results. The computation time for the presented models is less than 5 min on a personal computer. The optimized process window for Ti6Al4V was obtained based on the analytical predictions of these defects. The sensitivity analyses of the value of threshold to the laser power and scanning speed were also conducted. The proposed analytical methods show higher computational efficiency than finite element methods, without including any iteration-based computations. The acceptable predictive accuracy and low computational time will make the proposed analytical strategy be a good tool for the optimization of process conditions for the fabrication of defects-free complex products in laser powder bed fusion.

scholarly journals Effect of Scan Strategies and Use of Support Structures on Surface Quality and Hardness of L-PBF AlSi10Mg Parts

Materials ◽  
2020 ◽  
Vol 13 (10) ◽  
pp. 2248 ◽  
Author(s):  
Ronny M. Gouveia ◽  
Francisco J. G. Silva ◽  
Eleonora Atzeni ◽  
Dušan Sormaz ◽  
Jorge Lino Alves ◽  
...  
Keyword(s):  
Residual Stress ◽  
Support Structures ◽  
Laser Powder Bed Fusion ◽  
Material Density ◽  
Powder Bed ◽  
Lack Of Fusion ◽  
Melt Pool ◽  
Heat Treated ◽  
Design Freedom ◽  
Specific Part

Additive manufacturing allows for a great degree of design freedom and is rapidly becoming a mainstream manufacturing process. However, as in all manufacturing processes, it has its limitations and specificities. Equipping engineers with this knowledge allows for a higher degree of optimization, extracting the most out of this technology. Therefore, a specific part design was devised and created via L-PBF (Laser Powder Bed Fusion) using AlSi10Mg powder. Certain parameters were varied to identify the influence on material density, hardness, roughness, residual stress and microstructures. It was found that on heat treated parts laser pattern strategy is one of the most influential aspects, showing that chessboard and stripes 67° improved outcome; average Ra roughness varied between 8–12 µm, residual stress was higher on vertical surfaces than horizontal surfaces, with the combination of support structures and stripes 67° strategies generating the lowest residual stress (205 MPa on a lateral/vertical face), hardness was non-orientation dependent and larger on samples with chessboard fabrication strategies, while microstructures were composed of α–Al dendrites surrounded by Si particles. The distribution and grain size of the microstructure is dependent on location regarding melt pool and HAZ area. Furthermore, Al–Mg oxides were encountered on the surface, along with pores generating from lack of fusion.

Quantification and prediction of lack-of-fusion porosity in the high porosity regime during laser powder bed fusion of Ti-6Al-4V

2021 ◽  
pp. 117426
Author(s):  
Patcharapit Promoppatum ◽  
Raghavan Srinivasan ◽  
Siu Sin Quek ◽  
Sabeur Msolli ◽  
Shashwat Shukla ◽  
...  
Keyword(s):  
High Porosity ◽  
Powder Bed Fusion ◽  
Laser Powder Bed Fusion ◽  
Powder Bed ◽  
Lack Of Fusion

scholarly journals Residual stresses and porosity in Ti-6Al-4V produced by laser powder bed fusion as a function of process atmosphere and component design

2021 ◽  
Vol 47 ◽  
pp. 102340
Author(s):  
C. Pauzon ◽  
T. Mishurova ◽  
S. Evsevleev ◽  
S. Dubiez-Le Goff ◽  
S. Murugesan ◽  
...  
Keyword(s):  
Residual Stresses ◽  
Powder Bed Fusion ◽  
Laser Powder Bed Fusion ◽  
Powder Bed ◽  
Component Design ◽  
Process Atmosphere

scholarly journals On the Relevance of Volumetric Energy Density in the Investigation of Inconel 718 Laser Powder Bed Fusion

Materials ◽  
2020 ◽  
Vol 13 (3) ◽  
pp. 538 ◽  
Author(s):  
Fabrizia Caiazzo ◽  
Vittorio Alfieri ◽  
Giuseppe Casalino
Keyword(s):  
Surface Roughness ◽  
Energy Density ◽  
Process Parameters ◽  
Vickers Hardness ◽  
Powder Bed Fusion ◽  
Processing Conditions ◽  
Laser Powder Bed Fusion ◽  
Powder Bed ◽  
Fractional Density ◽  
Experimental Variation

Laser powder bed fusion (LPBF) can fabricate products with tailored mechanical and surface properties. In fact, surface texture, roughness, pore size, the resulting fractional density, and microhardness highly depend on the processing conditions, which are very difficult to deal with. Therefore, this paper aims at investigating the relevance of the volumetric energy density (VED) that is a concise index of some governing factors with a potential operational use. This paper proves the fact that the observed experimental variation in the surface roughness, number and size of pores, the fractional density, and Vickers hardness can be explained in terms of VED that can help the investigator in dealing with several process parameters at once.

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