A brief introduction on additive manufacturing B

Introduction to AM processes

According to the common type of machine architecture and the involved material transformation, AM processes are subdivided into 7 categories:

Powder bed fusion

It comprehends Selective Laser Melting and Electron Beam Melting for metals, for example. It is the selective melting (or also sintering) of powders contained in a bed. A building chamber with a movable platform is needed, which goes down by a layer thickness every time a layer is finished; a recoating blade then spreads a new powder layer to be processed. The unmelted powder is recycled; post-processing to remove the excess powders and to improve mechanical properties and surface finishing is always required. Energy for melting is provided by a laser or an electron beam. The building chamber has at least an inert atmosphere. The process is typically used for polymers and metals. High resolution (SLM > EBM), dense parts, and assembly-within-build are achieved. 4D printing starts here (possibility to create chain-like objects capable to change their form, also to construct parts larger than the building bed).

Direct energy deposition

Simultaneous deposition of material and thermal energy to melt it occurs. This technique is typical for metals, in powder or wire form. Thermal energy is provided by a laser, an electron beam, or a plasma (not all combinations are possible). High building rates and large parts fabrication are possible, but the resolution is quite low. A great advantage is the possibility of repairing already existing objects. Post-processing is required to improve surface finishing and to remove supports, generally.

Sheet lamination

Each kind of material that can be reduced into sheets can be processed in this category: metals, thermoplastic polymers, advanced ceramics. Each sheet is clamped, US welded, glued, or thermally bonded to the previous one, creating the 3D object layer-by-layer.

Binder jetting

Selective deposition of a binder into a powder bed allows the layer-by-layer creation of a metallic, polymeric, ceramic, or composite 3D object. Similarly to powder bed fusion processes, the building platform goes down one layer each time the binder is completely deposited and a recoating blade spreads a new layer of powder. Multiple binder-depositing-heads are possible. Post-processing is required to improve mechanical properties and surface finishing.

Material jetting

Droplets of liquid polymers (photopolymers and thermoplastic) are selectively deposited – ink-jet printing. Solidification of these droplets must occur once deposited and not during flight or in the orifice. The process is scalable (possibility to increase printing heads) and fast – up to 1 MHz – but post-processing to remove supports and improve mechanical properties and surface finishing is always required.

Vat photopolymerization

A liquid photopolymer in a vat is selectively cured with UV light to create a 3D object layer-by-layer. High resolution is achieved. Post-processing generally consists of supports removal and additional curing in a UV oven. The materials are epoxy resins and acrylates.

Material extrusion

Commonly known as 3D printing, it consists of a deposition...