Self-Supporting Structures Produced through Laser Powder Bed Fusion of AlSi10Mg Alloy: Surface Quality and Hole Circularity Tolerance Assessment
Abstract
:1. Introduction
2. Materials and Methods
2.1. Structure Design
2.2. L-PBF Process
2.3. Characterization Procedure
2.3.1. Confocal Microscopy
2.3.2. SEM-EDS
2.3.3. Circularity Tolerance Measurements
2.3.4. Density and Microstructure Analysis
3. Results and Discussion
3.1. Printability of the Designed Structures
3.2. Surface Quality of the Self-Supported Structures
3.3. Circularity Tolerance Assessment
3.4. Density and Microstructure Analysis
4. Conclusions
- Thin and self-supporting structures can be printed, within the same part, without defects and integrity issues with walls having an overhang angle up to 30°. The addition of further overhanging elements inclined at 15° and 0° causes job failure due to the excessive unsupported weight and warping.
- The surface quality assessment of thin overhanging walls, carried out through confocal microscopy, showed that the surface roughness decreased as a function of the increasing overhang angle. Moreover, the results showed also, as expected, that the downskin surfaces were rougher compared to the upskin ones. The worst case was represented by the elements with an overhang angle of 30°, with approximate values of Sa and Sz of 40 μm and 400 μm, respectively, whereas the best case was represented by the elements built vertically with respect to the build platform, with approximate values of Sa and Sz of 3 μm and 60 μm, respectively. The main cause of this result was the combination of the stair-step effect, balling effect and, most of all, the formation of dross due to the printing of the unsupported material.
- The circularity tolerance analysis, carried out on thicker structures having self-supported holes by means of CMM measurements, showed that the overall tolerance span was from 0.03 mm to 0.55 mm, with a maximum value for the 75° overhanging holes and a minimum for the holes oriented vertically with respect to the build platform. The tolerance trend showed that the holes with an overhang angle between 60° and 90° presented the worst quality due to the combined detrimental effects of gravity and the stair-case effect.
- The holes’ circularity tolerance was not significantly affected by their diameter, within the investigated range: for all three selected diameter values (4, 6, 8 mm), the same detrimental issues occurred, mainly represented by the presence of sintered powders in the upper regions of the holes.
- The proper densification of the material was not affected in any way by the challenging printing conditions, as proven by the density and the microstructure analysis. The latter showed also the typical microstructure features of the L-PBF-processed AlSi10Mg alloy, with only small gas inclusions present as defects.
- The obtained results could represent a series of helpful insights for designers, and, as a future remark, they could be extended as a function of different feedstock morphologies and recycling conditions.
Author Contributions
Funding
Acknowledgments
Conflicts of Interest
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Core | Upskin | Downskin | Contour | ||
---|---|---|---|---|---|
Laser power (W) | 300 | 370 | 220 | 350 | |
Scan speed (mm/s) | 730 | 1335 | 1000 | 1650 | |
Hatch distance (mm) | 0.10 | 0.13 | 0.13 | 0.17 | |
Laser spot (mm) | 0.08 | ||||
Layer thickness (mm) | 0.03 | ||||
Volumetric energy density (J/mm3) | 171 | 115 | 91.7 | 88.4 | |
Scan strategy | Raster (rotated by 67° between each layer) | ||||
Atmosphere | Ar (purity: 99.99%) |
Overhang Angle (°) | Average Relative Density | St. Dev (σ) |
---|---|---|
0 | 0.9964 | 0.0002 |
0 | 0.9959 | 0.0006 |
45 | 0.9956 | 0.001 |
60 | 0.9937 | 0.0026 |
75 | 0.9955 | 0.0005 |
90 | 0.9965 | 0.0005 |
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El Hassanin, A.; Squillace, A. Self-Supporting Structures Produced through Laser Powder Bed Fusion of AlSi10Mg Alloy: Surface Quality and Hole Circularity Tolerance Assessment. Metals 2022, 12, 2083. https://doi.org/10.3390/met12122083
El Hassanin A, Squillace A. Self-Supporting Structures Produced through Laser Powder Bed Fusion of AlSi10Mg Alloy: Surface Quality and Hole Circularity Tolerance Assessment. Metals. 2022; 12(12):2083. https://doi.org/10.3390/met12122083
Chicago/Turabian StyleEl Hassanin, Andrea, and Antonino Squillace. 2022. "Self-Supporting Structures Produced through Laser Powder Bed Fusion of AlSi10Mg Alloy: Surface Quality and Hole Circularity Tolerance Assessment" Metals 12, no. 12: 2083. https://doi.org/10.3390/met12122083