Terminology for NDT in additive manufacturing

NDT Terms for use in the inspection of Additively Manufactured Parts

 

Additive Manufacturing Terms Used in NDT
Term Definition
Cracks Separation of material which may be intergranular or transgranular due to internal or surface stresses caused by temperature differences during sintering and/or residual stresses upon cooling. This may occur as an embedded or surface separation.
Geometrical Accuracy Geometry does not meet engineering dimensions
Inclusion Foreign material either non-metallic or metallic that has been incorporated into the deposited material.  Inclusions are typically oxides, nitrides, hydrides, carbides, or a combination thereof and may or may not have some coherency with the surrounding material. Inclusions may be formed due to contamination of the chamber gas, input material or dirty build chamber.
Key Holing An object generally resembling a key hole shape formed due to instability of the keyhole or vapor cavity during processing.  These types of voids are created when the energy density is sufficiently high to cause a large depth to width ratio of the keyhole that results in hydrodynamic instability of the surrounding liquid metal and results in a collapse that creates a void at the root of the keyhole.
Lack of Fusion (LOF) n – 1. flaws caused by incomplete fusion between the build plate or previously deposited layer 2. inadequate penetration of a deposited layer into the previous layer or improper hatch spacing between two successive passes.  3. Fusion between the entire metal surfaces and between adjoining welds are not complete. Voids that are created by lack of fusion may also contain unconsolidated powder. Can be associated with a “stop/start” location.
Lack of Powder Insufficient powder present caused by insufficient powder feed.
Porosity An unintentional empty or gas filled spherical feature of a given diameter.  n – property, presence f circular spheres*  in a part making it less than fully dense. DISCUSSION- Porosity may be quantified as a ration, expressed as a percentage of the volume of voids to the total volume of the part. * The difference between a  pore and a void is the pore is empty spherical object displaying a diameter. A void is an empty object without  reference to a shape.
Porosity, Gas 1. Typically spherical in shape, but can also be somewhat faceted, gas porosity is caused by absorption of a gaseous species that forms pores during solidification. 2 With a sufficient source of the gaseous species, pores may be intermittent within the deposit or elongated due to the moving solidification front. 3. Sources of the porosity may be traced to the presence of contamination of the powder or wire, which may be on the surface or within the cavity of hollow powder particles, impurities within the process gas, such as moisture, or contamination of the substrate material, such as hydrocarbons or thick oxides, or vaporization of high vapor pressure species within the deposition material, such as aluminum in titanium alloys containing aluminum.
Unconsolidated Powder Un-melted/unconsolidated/unintentional powder trapped within the part cavities. Powder particle partially fused to the surface that may be removed easily.
Void An unintentional empty gas filled feature with two dimensions. 1 n, – 1. flaws created during the build process that are empty or filled with partially or wholly un‑sintered or un-fused powder or wire creating pockets. Voids are distinct from gas porosity, and are the result of lack of fusion. Voids occurring at a sufficient quantity, size and distribution inside a part can reduce its strength in their vicinity. Voids are also distinct from intentionally added open cells that reduce weight. Like gas porosity, voids cause a part to be less than fully dense. Typically occurs internally in the build part. Not possible to detect by physical examination of the part.  2. Voids or porosity that grow across a single layer (subset Layer). 3 Voids or porosity that grow along the axis infringing of more than one layer (subset cross layer)

 

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