Generation and detection of defects in metallic parts fabricated by selective laser melting and electron beam melting and their effects on mechanical properties.

Gong, Haijun

doi:10.18297/etd/515

Cited by 28 publications

(23 citation statements)

References 72 publications

(107 reference statements)

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“…Additive manufacturing (AM) has been emerging as a technology with the ability to realize three‐dimensional shapes with complex geometries based on the layer‐by‐layer incremental manufacturing concept . Currently, there exist several representative AM techniques, including inkjet printing (IJP), fused deposition modeling (FDM), selective laser sintering (SLS), ultrafast laser processing, selective laser melting (SLM), and electron beam melting (EBM) . So far, many alloys, such as steels, titanium alloys, and aluminum alloys, have been used to fabricate products with excellent properties .…”

Section: Introductionmentioning

confidence: 99%

Additive Manufacturing of Titanium Alloys by Electron Beam Melting: A Review

et al. 2017

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Electron beam melting (EBM), as one of metal additive manufacturing technologies, is considered to be an innovative industrial production technology. Based on the layer-wise manufacturing technique, as-produced parts can be fabricated on a powder bed using the 3D computational design method. Because the melting process takes place in a vacuum environment, EBM technology can produce parts with higher densities compared to selective laser melting (SLM), particularly when titanium alloy is used. The ability to produce higher quality parts using EBM technology is making EBM more competitive. After briefly introducing the EBM process and the processing factors involved, this paper reviews recent progress in the processing, microstructure, and properties of titanium alloys and their composites manufactured by EBM. The paper describes significant positive progress in EBM of all types of titanium in terms of solid bulk and porous structures including Ti-6Al-4V and Ti-24Nb-4Zr-8Sn, with a focus on manufacturing using EBM and the resultant unique microstructure and service properties (mechanical properties, fatigue behaviors, and corrosion resistance properties) of EBM-produced titanium alloys.

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Section: Introductionmentioning

confidence: 99%

Additive Manufacturing of Titanium Alloys by Electron Beam Melting: A Review

et al. 2017

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“…These studies demonstrated a correlation between the energy density and the part density and allowed identifying a window of process parameters corresponding to good part density and quality. The study of Gong (2013) outlined different regions in the parameter space spanned by laser power and scan speed in SLM of Ti6Al4V ( Fig. 7): zone I corresponds to fully dense parts, zone II to over-melting conditions, zone III to incomplete melting and zone OH to over heating parameters.…”

Section: Processmentioning

confidence: 99%

“…When the beam passes over the deposited spatter, its larger size may prevent complete melting, which can result in formation of voids within the part. On the other hand, if the spatter is displaced by the recoating device (particle dragging), an irregularity of the powder bed can be produced, leading to a discontinuity in the material (Gong, 2013). The control of the shape of the laser power profile in SLM, or pulse shaping, was pointed out as a method to increase energy absorption and decrease spatter ejections (Mumtaz and Hopkinson, 2010).…”

Section: Processmentioning

confidence: 99%

Process defects andin situmonitoring methods in metal powder bed fusion: a review

Grasso

Colosimo

2017

Meas. Sci. Technol.

617

246

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Despite continuous technological enhancements of metal Additive Manufacturing (AM) systems, the lack of process repeatability and stability still represents a barrier for the industrial breakthrough. The most relevant metal AM applications currently involve industrial sectors (e.g., aerospace and bio-medical) where defects avoidance is fundamental. Because of this, there is the need to develop novel in-situ monitoring tools able to keep under control the stability of the process on a layer-by-layer basis, and to detect the onset of defects as soon as possible. On the one hand, AM systems must be equipped with in-situ sensing devices able to measure relevant quantities during the process, a.k.a. process signatures. On the other hand, in-process data analytics and statistical monitoring techniques are required to detect and localize the defects in an automated way. This paper reviews the literature and the commercial tools for insitu monitoring of Powder Bed Fusion (PBF) processes. It explores the different categories of defects and their main causes, the most relevant process signatures and the in-situ sensing approaches proposed so far. Particular attention is devoted to the development of automated defect detection rules and the study of process control strategies, which represent two critical fields for the development of future smart PBF systems.

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“…Since the mechanical properties of the LPBF as-built specimens can be affected by microstructural defects and material anisotropy, these characteristics must also be evaluated. The characteristics and influence of defects in LPBF were investigated systematically by Gong [53,95,96]. The tensile coupons with lower porosity reflected significant compromise on tensile properties.…”

Section: Optical Microscopy Is Among the Most Common Approaches Used mentioning

confidence: 99%

“…The final microstructure consists of columnar grains that include martensitic α' phase due to the fast cooling rate and grows towards the build direction. The schematic illustrates the phase transformations upon fast cooling in The measurement of columnar grain size for the bulk Ti-6Al-4V materials was carried out by using the linear intercept method following ASTM [95] (Fig. 2.20).…”

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confidence: 99%

Design, analysis, and application of a cellular material/structure model for metal based additive manufacturing process.

Zhang¹

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Powder bed fusion additive manufacturing (PBF-AM) has been broadly utilized to fabricate lightweight cellular structures, which have promising potentials in many engineering applications such as biomedical prosthesis, aerospace, and architectural structures due to their high performance-to-weight ratios and unique property tailorabilities. To date, there is still a lack of adequate understanding of how the cellular materials are influenced by both the geometry designs and process parameters, which significantly hinders the effective design of cellular structures fabricated by PBF-AM for critical applications. This study aims to demonstrate a cellular structure design methodology that integrates geometrical design and process-material property designs. Utilizing both analytical modeling and empirical modeling, this research aims to significantly improve the design flexibility and robustness of the metal PBF-AM cellular structures. vi Experimental designs were carried out to establish the process-material property knowledge for the Ti6Al4V using the EOS M270 laser powder bed fusion (LPBF) system. Using optical microscopy, scanning electron microscopy (SEM), micro-tensile testing and micro-hardness testing, the characteristics of thin struts with different strut dimensions and orientations under different process conditions were characterized and compared with those of the bulk materials from LPBF. The results clearly indicated significant effects of strut geometries (dimension and orientation angle) on their qualities. Struts with large orientation angle (i.e. more aligned to the build direction) exhibit lower process robustness and are sensitive to process parameters. Due to the resolution limitation of the LPBF process, the geometrical accuracies of the struts increases drastically when the designed dimension is smaller than 0.2 mm, with minimum achievable dimensions around 0.2 mm for the process parameters investigated in this study. On the other hand, the struts with smaller dimensions tend to exhibit higher mechanical properties, which might be associated with the smaller grain size and lower porosities. There also does not appear to be a single set of process parameters that would result in minimum porosities for struts with various dimensions. Adopting center-joint based unit cell design, an analytical model for unit cells with designable numbers of struts was established in the attempt to enhance the designabilility of the geometries. Timoshenko beam theory was verified to be the most accurate modeling method, although for large strut orientations Euler-Bernoulli beam theory might suffice. The analytical model for elastic modulus was verified by finite element analysis (FEA) and experiments. Additionally, predictable size effect was modeled for the cellular structures with the center join connectivity of 8 (octahedral). vii Employing the material property database for the cellular designs, the integrated material performance/structural geometry model was demonstrated for both single struts and small cellula...

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Generation and detection of defects in metallic parts fabricated by selective laser melting and electron beam melting and their effects on mechanical properties.

Cited by 28 publications

References 72 publications

Additive Manufacturing of Titanium Alloys by Electron Beam Melting: A Review

Additive Manufacturing of Titanium Alloys by Electron Beam Melting: A Review

Process defects andin situmonitoring methods in metal powder bed fusion: a review

Design, analysis, and application of a cellular material/structure model for metal based additive manufacturing process.

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