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Classification of Additive Manufacturing technologies (Eleonora Atzeni)

Classification of Additive Manufacturing technologies (Eleonora Atzeni)

The aim of this lecture is to give you an overview
of existing Additive Manufacturing process categories. After this lecture you will be able to describe
how different process categories make use of different types of materials
to shape a product’s geometry. You will also recognise which type of material
is used in different process categories. There are multiple processes developed
for additive manufacturing, which vary in material, process, final shape, surface finish. According to European Standard EN ISO 17296-2,
these are grouped into six basic categories based on material and machine technology used: – VAT Photopolymerisation
– Binder Jetting – Material Jetting
– Material Extrusion – Powder Bed Fusion
– Directed Energy Deposition VAT Photopolymerisation is defined as
“an AM process in which liquid photopolymer in a vat is selectively cured
by light-activated photopolymerization” The feedstock is a liquid photoreactive resin,
with or without filler, typically activated by a UV radiation from lasers or lamps. The ultraviolet (UV) light is used to cure
or harden the resin where required, whilst a platform moves the object being made downwards after each new layer is cured. Material jetting is defined as ”an AM process in which droplets of build material are selectively deposited” . The feedstock is a liquid photopolymer
or melted wax, with or without filler. The binding mechanism is a chemical reaction bonding, activated by a radiation light source, or adhesion by solidification of melted material. Material is jetted onto the build surface
or platform, where it solidifies and the model is built layer by layer. Material is deposited from a nozzle which
moves horizontally across the build platform. Binder jetting is defined as “an AM process
in which a liquid bonding agent is selectively deposited to join powder materials”. The binder jetting process uses two materials;
a powder based material, that is polymer, metal or ceramic, and a liquid binder. The binder acts as an adhesive between powder layers. A print head moves horizontally along
the x and y axes of the machine and deposits alternating layers of the build material
and the binding material. After each layer, the object being printed
is lowered on its build platform. Metals and ceramics are commonly consolidated
by sintering and infiltration with a melted material. Material extrusion is defined as
“an AM process in which material is selectively dispensed through a nozzle or orifice”. The feedstock is typically a thermoplastic
filament and binding occurs due thermal reaction. Material is drawn through a nozzle, where it is heated and is then deposited layer by layer. The nozzle can move horizontally and a platform
moves up and down vertically after each new layer is deposited. It is a commonly used technique used on many
inexpensive, domestic and hobby 3D printers. Powder bed fusion is defined as
“an AM process in which thermal energy selectively fuses regions of a powder bed”. The feedstock consists of various powders:
thermoplastic polymers, metal alloys, or ceramics. The thermal energy is transferred from laser
or electron beam. Powder bed fusion contains a range of technologies;
the main three are SLS, SLM and EBM. Powder bed fusion methods all start
with a powder bed: a thin layer of loose powder is smoothly spread flat over a build platform. This layer of powder is then passed over
by either a laser or electron beam which supplies significant heat to the powder. Then the build platform changes height,
a new layer of powder is deposited, and the process is repeated layer by layer
until the part is complete. Directed energy deposition is defined as
“an AM process in which focused thermal energy is used to fuse materials by melting
as they are deposited”. The feedstock is typically metal powder
or wire and the energy source is a laser, an electron beam or plasma transferred arc. A typical DED machine consists of a nozzle
mounted on a multi axis arm, which deposits melted material
onto the specified surface, where it solidifies. The principles and process categories described
in this lecture refer to commercially available technologies that have proven practically
useful and viable on the market for several years.

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