Applications of non-destructive testing techniques for post-process control of additively manufactured parts

Lü, Qing; Wong, Chee How

doi:10.1080/17452759.2017.1357319

Cited by 81 publications

(37 citation statements)

References 55 publications

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“…A porous silica cubic sample with 20 layers ( Figure 10 ) was successfully fabricated via SLS followed by furnace sintering, and the relative density was only 46.8%. Firstly, the silica sample was evaluated by visual inspection since it is quick, simple, and cheap to perform to most specimens [ 26 ], and the sample showed a porous-like and crack-free surface. Defects such as cracks were not observed in the cross-section of the sample ( Figure 10 c).…”

Section: Resultsmentioning

confidence: 99%

Selective Laser Sintering of Porous Silica Enabled by Carbon Additive

Chang

et al. 2017

Materials

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The aim of this study is to investigate the possibility of a freeform fabrication of porous ceramic parts through selective laser sintering (SLS). SLS was proposed to manufacture ceramic green parts because this additive manufacturing technique can be used to fabricate three-dimensional objects directly without a mold, and the technique has the capability of generating porous ceramics with controlled porosity. However, ceramic printing has not yet fully achieved its 3D fabrication capabilities without using polymer binder. Except for the limitations of high melting point, brittleness, and low thermal shock resistance from ceramic material properties, the key obstacle lies in the very poor absorptivity of oxide ceramics to fiber laser, which is widely installed in commercial SLS equipment. An alternative solution to overcome the poor laser absorptivity via improving material compositions is presented in this study. The positive effect of carbon additive on the absorptivity of silica powder to fiber laser is discussed. To investigate the capabilities of the SLS process, 3D porous silica structures were successfully prepared and characterized.

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Section: Resultsmentioning

confidence: 99%

Selective Laser Sintering of Porous Silica Enabled by Carbon Additive

Chang

et al. 2017

Materials

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“…As a remedy for porosity in the as-built alloys, hot isostatic pressing (HIP) is always performed at high temperatures and high pressures for a couple of hours after AM processing in order to close and eliminate internal voids [ 19 ]. HIP can be regarded as a homogenization process performed in the single-phase field at a very high temperature.…”

Section: Grain Morphology Controlmentioning

confidence: 99%

Grain Structure Control of Additively Manufactured Metallic Materials

2017

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Grain structure control is challenging for metal additive manufacturing (AM). Grain structure optimization requires the control of grain morphology with grain size refinement, which can improve the mechanical properties of additive manufactured components. This work summarizes methods to promote fine equiaxed grains in both the additive manufacturing process and subsequent heat treatment. Influences of temperature gradient, solidification velocity and alloy composition on grain morphology are discussed. Equiaxed solidification is greatly promoted by introducing a high density of heterogeneous nucleation sites via powder rate control in the direct energy deposition (DED) technique or powder surface treatment for powder-bed techniques. Grain growth/coarsening during post-processing heat treatment can be restricted by presence of nano-scale oxide particles formed in-situ during AM. Grain refinement of martensitic steels can also be achieved by cyclic austenitizing in post-processing heat treatment. Evidently, new alloy powder design is another sustainable method enhancing the capability of AM for high-performance components with desirable microstructures.

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“…Furthermore, the annular array PAUT possesses similar detection accuracy, regardless the ultrasonic incident detection on deposition surface or printing surface of the AM titanium specimen. It is known that the minimal detectable defect size is closely determined by the wavelength the wavelength of the ultrasound, which varies inversely with the frequency of the probe as the speed of ultrasound is constant in a specific material [23]. In particular when the defect size is close to half-wavelength, there will be significant diffraction phenomenon accompanied with negligible reflected echo.…”

Section: Forming Orientation Dependence Of Annular Array Pautmentioning

confidence: 99%

Phased array ultrasonic testing of micro-flaws in additive manufactured titanium block

Wang

et al. 2020

Mater. Res. Express

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While titanium components manufactured by additive manufacturing have been widely used in direct molding of complex components, their performance is strongly affected by existing internal flaws generated in the unique manufacturing process. Thus, how to efficiently and accurately characterize geometrical characteristics of internal flaws is critical for enhancing applications of additive manufactured titanium components. In the present work, an effective non-destructive method by using phased array ultrasonic testing is proposed to characterize sub-millimeter artificial deep bottom holes in additive manufactured TC18 titanium block. Specifically, a phased array ultrasonic testing platform integrated with total focusing method-based post-processing algorithm is established. Flat bottom holes with a diameter of 0.8 mm and a depth of 5.0 mm in 55 mm-sized cube titanium block are detected using both linear and annular array transducers. Experimental results show that preexisting holes can be characterized by both linear and annular transducers, in despite of accompanied high acoustic attenuation. Furthermore, the annular phased array ultrasonic testing has higher detection accuracy and resolution than the linear phased array one, for its stronger capability of sound field focusing. More importantly, the annular phased array ultrasonic testing shows similar high testing accuracy in different relative orientations between forming orientation of the titanium component and sound wave propagation direction. These findings provide an effective strategy for the non-destructive ultrasonic testing of titanium components by additive manufacturing.

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Applications of non-destructive testing techniques for post-process control of additively manufactured parts

Cited by 81 publications

References 55 publications

Selective Laser Sintering of Porous Silica Enabled by Carbon Additive

Selective Laser Sintering of Porous Silica Enabled by Carbon Additive

Grain Structure Control of Additively Manufactured Metallic Materials

Phased array ultrasonic testing of micro-flaws in additive manufactured titanium block

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