Читать книгу Metal Additive Manufacturing - Ehsan Toyserkani - Страница 17

The American Society for Testing and Materials (ASTM) and International Standards Organization (ISO) have jointly established two committees to develop standards for the AM industry. The joint committees have proposed the definition of AM based on an active standard of ASTM ISO/ASTM52900, developed by Subcommittee F42.91, as

“Additive manufacturing (AM) is process of joining materials to make parts from 3D model data, usually layer upon layer, as opposed to subtractive manufacturing and formative manufacturing methodologies.”

This standard also elaborates on the functionality of manufactured parts as

The functionality of a manufactured object is derived from the combination of the object's geometry and properties. In order to achieve this combination, a manufacturing process is made up of a series of operations and sub‐processes that bring the shape of the intended geometry to a material capable of possessing the desired properties. The shaping of materials into objects within a manufacturing process can be achieved by one, or combinations of three basic principles: Formative shaping, subtractive shaping and additive shaping.

The same standard categorizes AM into seven processes as:

 Binder Jetting

 Directed Energy Deposition

 Material Extrusion

 Material Jetting

 Powder Bed Fusion

 Sheet Lamination

 VAT Photopolymerization

The same standard briefly defines each of these AM processes:

Binder jetting, an additive manufacturing process in which a liquid bonding agent is selectively deposited to join powder materials.

Directed energy deposition, an additive manufacturing process in which focused thermal energy is used to fuse materials by melting as they are being deposited. Note, “Focused thermal energy” means that an energy source (e.g. laser, electron beam, or plasma arc) is focused to melt the materials being deposited.

Material extrusion, an additive manufacturing process in which material is selectively dispensed through a nozzle or orifice.

Material jetting, an additive manufacturing process in which droplets of build material are selectively deposited. Note: Example materials include photopolymer and wax.

Powder bed fusion, an additive manufacturing process in which thermal energy selectively fuses regions of a powder bed.

Sheet lamination, an additive manufacturing process in which sheets of material are bonded to form a part.

Vat photopolymerization, an additive manufacturing process in which liquid photopolymer in a vat is selectively cured by light‐activated polymerization.

From these processes, almost all have been used for metal AM. However, industry has embraced the following processes for metal manufacturing more widely (note that the sequence shows the domination of each process in the market): (i) Powder Bed Fusion, (ii) Directed Energy Deposition, (iii) Binder Jetting, (iv) Material Extrusion, (v) Material Jetting, and (vi) Sheet Lamination. The first three are the most popular technologies for metal AM. In Chapter 2, these processes are explained in detail.

In all these processes, when it comes to metal AM, several main concepts are shared: (i) motion systems, (ii) energy or binding sources, and (iii) material delivery mechanisms. Chapter 3 will explain the main components used in the three major metal AM processes.