Nondestructive Testing for Additive Manufacturing 241

absorbent

The ability to soak up, or absorb, a liquid easily. Developers used during liquid penetrant testing are highly absorbent.

additive manufacturing

AM. The process of joining or solidifying materials to make an object based on a three-dimensional (3D) computer model. Additive manufacturing methods typically build up layers of material to create an object.

alternating current

AC. A current formed when electrons flow in one direction and then the opposite direction. Alternating current usually reverses direction 60 times per second.

AM

Additive manufacturing. The process of joining or solidifying materials to make an object based on a three-dimensional (3D) computer model. Additive manufacturing methods typically build up layers of material to create an object.

ammeter

An instrument that measures current flow in an electrical circuit. Ammeters can be used to detect changes in impedance during eddy current testing.

amplitude

A measurement of voltage level. In ultrasonic testing, the flaw detector displays amplitude signals, which are then interpreted by a certified technician.

binder

An adhesive material that holds together other materials. Binders hold together powdered materials to make a solid part in binder jetting.

binder jetting

An additive manufacturing method in which liquid binder is used to join powdered materials to create a part. Binder jetting can use a variety of powdered build materials, including polymer, metal, and sand.

build platform

The flat surface on which a part is additively manufactured. The build platform can either be a permanent machine surface from which parts are removed or a surface that can be removed from a machine once the build is complete.

casting

A general category of metalworking processes that involves pouring a liquid material into a hollow mold and allowing the material to cool into a solid shape. Casting includes methods such as investment and sand casting.

catastrophic failure

The sudden and complete breakdown of a part or machine. Catastrophic failure can be hazardous to workers as it may result in flying debris, unexpected and fast machine movement, and employee injury.

ceramic

A hard, brittle material that can withstand high temperatures and resist corrosion. Ceramics can be used as build materials in some additive manufacturing methods, such as material extrusion and binder jetting.

certification

Validation that an individual has achieved a certain level of expertise in a specific area. Certifications may be awarded by a school, a professional organization, or another governing body.

color-contrast

Brightly colored and clearly distinguishable. Indications made by color-contrast penetrants or detection media are easily visible in ambient light.

composite

A group of materials that are made by mixing together two or more of the following groups: metals, plastics, and ceramics. Composites are sometimes used as build material in some additive manufacturing methods, such as material extrusion and directed energy deposition.

conductive

Able to act as a path for the movement of electricity. Conductive materials, which include many types of metals, form magnetic fields when energized.

consumables

Any material or substance that is used up in a process or wears out over time. A variety of consumables are used during nondestructive testing methods, including liquid penetrant, developer, detection media, x-ray film, and couplant.

couplant

A substance, usually an oil, that coats a test piece in ultrasonic testing. Couplants help transmit sound waves from an ultrasonic probe into a part.

defects

A severe discontinuity, or flaw, that can cause a part to be rejected. Defects can be detected through visual inspection or other forms of nondestructive testing.

density

A measure of the amount of mass within the given volume of an object or substance. The density of a part affects how much radiation it absorbs during radiographic testing.

destructive testing

A category of inspection processes that evaluate a part's properties and performance using methods that lead to part failure. Destructive testing renders a part unusable.

developer

A highly absorbent substance that helps to draw penetrant to the surface of a part during liquid penetrant testing. Developers help to create clear visible indications of surface discontinuities and defects.

directed energy deposition

DED. An additive manufacturing method in which focused thermal energy is used to melt materials as they are deposited on a build platform. Directed energy deposition often uses metal powder or wire as build materials.

discontinuities

A flaw or imperfection in the specified and expected structure of a part or material. Discontinuities are not always defects.

dwell time

An intentional delay or pause of a specified length in a process. During liquid penetrant testing, both the penetrant and developer are left undisturbed on the surface of a part for a specified dwell time length.

eddy current testing

ECT. A nondestructive testing method that uses electromagnetic induction to locate surface and near-surface discontinuities and defects. Eddy current testing is limited to use on electrically conductive materials.

eddy currents

An electric current generated when a conductive material is placed near an alternating magnetic field. Eddy currents produce a secondary magnetic field during eddy current testing.

electromagnetic induction

The process of generating an electrical current in conductive material by exposing it to an alternating magnetic field. Electromagnetic induction forms the basis of eddy current testing.

electromagnetic radiation

Energy emitted in the form of particles or waves. Exposure to electromagnetic radiation, which is used during radiographic testing, can pose significant health hazards if technicians do not take appropriate safety measures.

electron beam

A narrow stream of focused electrons that create thermal energy. Electron beams are sometimes used in additive manufacturing methods, including directed energy deposition (DED) and powder bed fusion (PBF).

end-use

Designed to be used directly by a consumer or directly in another manufactured product. End-use products created by additive manufacturing include medical implants, custom dental devices, and camera equipment.

flaw detector

A device that displays voltage level as amplitude signals. Flaw detectors are connected to transducers during ultrasonic testing.

fluorescent

Glowing a bright yellow-green color. Indications made by fluorescent penetrants or detection particles are only visible under ultraviolet (UV) light.

fluoroscopic screen

A screen, lit from behind by fluorescent lights, that displays a radiograph image. Fluoroscopic screens allow for immediate viewing of radiographic testing results.

forging

A general category of metalworking processes that involves compressing bulk metal at elevated temperatures. Forging creates very strong parts but can also leave raised sections that must be smoothed out.

frequency

The rate at which an alternating current changes direction or a sound wave vibrates within a given amount of time. Frequency is measured in hertz (Hz).

gamma rays

A type of electromagnetic wave with a high frequency and short wavelength. Gamma rays, which have greater penetration depths than x-rays, are sometimes used to view the interior of solid objects during radiographic testing.

illuminance

The amount and intensity of light falling onto and spreading over a surface. Specifications for visual testing often requires a minimum level of illuminance.

imaging system

An assembly of components that records and collects images of a created during x-ray computed tomography. The imaging system is connected to a computer, which uses specialized software to reconstruct a series of two-dimensional (2D) images into a three-dimensional (3D) image.

impedance

A measure of reactance and resistance in an alternating current (AC) circuit. Impedance is calculated to measure the total opposition to current flow in an AC circuit.

indications

A sign or marking that clearly points out the presence of a discontinuity. Indications in liquid penetrant testing are created with color-contrast penetrant or fluorescent penetrant, while indications in magnetic particle testing are created by particles of detection media.

internal channels

A pathway for air, coolants, or other substances to travel through the inside of a part. Internal channels are most easily created through additive manufacturing processes.

laser

A device that generates an intense beam of light that can be precisely aimed and controlled. Lasers are used to selectively solidify or combine materials in a number of additive manufacturing (AM) methods, including powder bed fusion (PBF), vat photopolymerization, and directed energy deposition (DED).

lattice structures

A repeating, symmetrical pattern of crossing strips of material that leave diamond- or square-shaped gaps between them. Lattice structures provide excellent strength to a part.

liquid penetrant testing

LPT. A nondestructive testing method that uses a dye or a fluorescent liquid to locate discontinuities and defects on a material's surface. Liquid penetrant testing relies on capillary action to draw the liquid into minuscule surface openings on a part.

machining

A general category of subtractive manufacturing processes that involves removing material to form an object. Machining includes methods such as milling, turning, and drilling that remove material using cutting tools.

magnifying lenses

A simple optical instrument consisting of a small, handheld lens that is designed to enlarge an object for the viewer. Magnifying lenses can be used to aid with visual testing of manufactured parts.

material extrusion

An additive manufacturing method that uses a nozzle to dispense material, usually a thermoplastic filament, onto a build platform. Material extrusion is sometimes referred to as either fused deposition modeling (FDM) or fused filament fabrication (FFF).

material jetting

An additive manufacturing method in which droplets of build material are selectively deposited onto a build platform. Material jetting, or multi-jet modeling (MJM), often uses ultraviolet (UV) light to cure photopolymer build material.

micro computed tomography

MicroCT. An advanced radiographic NDT method that creates a three-dimensional (3D) image of a part's interior and exterior out of multiple two-dimensional (2D) radiographs. Micro computed tomography, or x-ray computer tomography, produces high-resolution images that show very fine part details.

microscopes

An optical instrument consisting of one or more lenses that is designed to greatly magnify, or enlarge, objects that may be too small to seen by the human eye. Microscopes can be used to aid with visual testing of manufactured parts.

microscopic

Too small to be visible to the human eye without the use of a microscope. Microscopic surface discontinuities can be difficult to detect during visual testing, but they can be easily detected using other nondestructive testing methods, such as ultrasonic testing.

NDT

Nondestructive testing. A category of inspection processes that evaluate a part's properties and performance using methods that do not damage or permanently alter the part. NDT methods can be used to locate discontinuities and defects in parts made by additive manufacturing processes.

nondestructive testing

NDT. A category of inspection processes that evaluate a part's properties and performance using methods that do not damage or permanently alter the part. Nondestructive testing methods can be used to locate discontinuities and defects in parts made by additive manufacturing processes.

optical instruments

A category of devices that processes light waves to enhance an image so it can be viewed more clearly. Optical instruments are sometimes used to enhance visual testing.

penetrant

A low viscosity liquid that is readily drawn into minute cracks or voids when applied to a surface. Penetrants create clear, highly visible indications of surface discontinuities and defects during liquid penetrant testing.

personal protective equipment

PPE. An article of clothing or a device worn to minimize exposure to hazards and prevent injury. Personal protective equipment may include safety glasses, safety gloves, ear plugs, respirators, or steel-toed boots.

photopolymer

A thermoset polymer that cures and hardens when exposed to ultraviolet (UV) light. Photopolymers can be used as build materials in additive manufacturing methods, such as material jetting and vat photopolymerization.

physical reference standards

A part that has been intentionally manufactured to contain a specific type of discontinuity or defect, which can be used as a comparison during nondestructive testing. Physical reference standards specific to additive manufacturing processes have not yet been established.

polishing

An abrasive finishing process used to improve the surface of a part to a very fine finish. Polishing results in a smooth and shiny part surface.

porous

Full of holes or having many voids. Porous materials are able to easily absorb liquids, making them difficult to inspect using liquid penetrant testing.

post-processing

A finishing process used to clean, grind, or otherwise prepare an additive manufacturing part for shipping to a manufacturer or other consumer. Common additive manufacturing post-processing steps include removing support structures, heat treating, improving surface finish, and bringing the part into tolerance.

powder bed fusion

PBF. An additive manufacturing process that uses adhesives, heat, or light to bond areas in a container of powder plastic, metal, ceramic, or other material. Select laser sintering (SLS) and direct metal laser sintering (DMLS) are powder bed fusion methods.

PPE

Personal protective equipment. An article of clothing or a device worn to minimize exposure to hazards and prevent injury. PPE may include safety glasses, safety gloves, ear plugs, respirators, or steel-toed boots.

processing time

The amount of time it takes for a computer to complete all necessary operations for a task. The amount of processing time needed during x-ray computed tomography (x-ray CT) makes it a much slower process than conventional radiographic testing (RT).

production batch

A specific number of the same part that moves through the production cycle. Destructive testing is performed on a number of sample parts taken at random from a production batch.

radiation source

A device that emits x-rays or gamma rays during radiographic testing. Radiation sources include x-ray machines or certain radioactive elements.

radiograph

A type of two-dimensional (2D) image produced on a sensitive screen or film by x-rays or gamma rays. Radiographs show the interior of a solid object to be viewed.

radiographic testing

RT. A nondestructive testing method that uses electromagnetic radiation, in the form of x-rays or gamma rays, to produce a picture of the internal structure of a material. In a radiographic testing image, discontinuities and defects in a material appear as dark spots.

recording media

A radiation-sensitive device that creates a radiograph image of the interior of a part during radiographic testing. Recording media includes special types of photographic film or fluoroscopic screens.

reflect

To be sent backward in the opposite direction. Discontinuities and defects reflect sound waves travelling through a part during ultrasonic testing.

repeatability

The ability of a process to produce consistent and uniform results. Repeatability of visual testing often depends on several variables, including inspector training and testing environment.

resolution

The amount of pixels and detail in an image. High-resolution three-dimensional images are created during x-ray computed tomography.

rework

The process of running a part through an additional and unplanned manufacturing step. Rework is necessary when a part is not produced within the correct tolerance or has poor surface finish or other discontinuities.

sheet lamination

An additive manufacturing method that forms an object by bonding sheets of material together using an adhesive, heat, or pressure. Sheet lamination processes include selective deposition lamination (SDL), laminated object manufacturing (LOM), and ultrasonic consolidation (UC).

small-batch runs

The production of a limited number of parts, usually less than 500. Small-batch runs can be cost effective using additive manufacturing technology.

software

A set of coded instructions or programs that control computer hardware functions and operations. Specialized software is used to reconstruct a three-dimensional image out of multiple two-dimensional images in x-ray computed tomography (x-ray CT).

sound waves

A vibration, or disturbance, of matter caused by the movement of energy. The high-frequency sound waves used in ultrasonic testing are beyond the range of normal human hearing.

specifications

A description of the essential physical and technical properties of a finished part. Specifications outline important information, including finished part dimensions and how the part must respond to forces acting upon it.

standards

An established policy regarding specific product requirements or a particular practice or method. Standards cover a range of topics, from the required properties of a material to the documentation necessary across the supply chain.

subsurface

Below or beneath the exterior of an object. Subsurface discontinuities can only be detected using certain nondestructive testing methods, such as magnetic particle, eddy current, ultrasonic, or radiographic testing.

surface finish

The degree of roughness and variation on the surface of a part after it has been manufactured. A part's surface finish can affect the use of certain nondestructive testing methods.

thermoplastic

A group of plastics that can be repeatedly heated, cooled, and shaped. Thermoplastics are often used in material extrusion additive manufacturing processes.

thermoset

A group of plastics that are permanently hardened by heating. Thermosets can be used as build materials in some additive manufacturing methods, such as vat photopolymerization and material jetting.

transducer

A probe-like device that converts one form of energy, such as electrical, into another form of energy, such as mechanical. In ultrasonic testing, transducers convert electrical energy into vibrational sound waves.

ultrasonic consolidation

UC. A sheet lamination process that uses high-frequency vibrations to bond successive layers of material together to build a final part. Ultrasonic consolidation most frequently uses sheets of metal foil or tape as build material.

ultrasonic testing

UT. A nondestructive testing method that uses high-frequency ultrasonic waves to detect internal part discontinuities and defects. During ultrasonic testing, reflected sound waves are converted into electrical signals, which technicians then evaluate for any indications.

ultraviolet light

UV light. A wavelength of light that is invisible to the naked eye because it consists of very short wavelengths. Ultraviolet light is used to selectively solidify liquid photopolymer in material jetting and vat photopolymerization, as well as to view the results of a liquid penetrant test that uses fluorescent-coated particles.

UV light

Ultraviolet light. A wavelength of light that is invisible to the naked eye because it consists of very short wavelengths. UV light is used to selectively solidify liquid photopolymer in material jetting and vat photopolymerization, as well as to view the results of a liquid penetrant test that uses fluorescent-coated particles.

vat photopolymerization

An additive manufacturing method in which a part is built by curing layers of a photopolymer with ultraviolet (UV) light. Vat photopolymerization processes include stereolithography (SLA) and digital light processing (DLP).

video borescopes

An optical instrument that consists of a slender fiber-optic tube with a magnifying lens at one end and a video camera on the other end. Video borescopes can be used to aid in the visual testing of manufactured parts, especially inspecting areas that are inaccessible by other means.

vision systems

An advanced optical instrument that collects data and forms an image, which is interpreted by a computer to determine an appropriate position or to see an object. Vision systems can aid in the visual testing of manufactured parts.

visual testing

VT. A nondestructive testing (NDT) method that requires an inspector to closely examine a part for surface discontinuities or defects. Visual testing is often used as a primary inspection method and then followed with other NDT methods.

voltage

A measure of electrical pressure or potential that causes current to flow in a circuit. Voltage is measured in volts (V).

voltmeter

An instrument that measures the voltage flowing between two points in an electrical circuit. Voltmeters can be used to detect changes in impedance during eddy current testing.

x-ray computed tomography

X-ray CT. An advanced radiographic NDT method that creates a three-dimensional (3D) image of a part's interior and exterior out of multiple two-dimensional (2D) radiographs. X-ray computed tomography, which is sometimes referred to as micro computed tomography (microCT), produces high-resolution images that show very fine part details.

x-rays

A type of electromagnetic wave with a high frequency and short wavelength. X-rays are used to view the interior of solid objects during radiographic testing.