**2. General presentation on the main Rapid Prototyping and Rapid Tooling methods**

The manufacturing processes (most of them) are still quite expensive and the range of materials that can be used is still quite limited, even if in the last year's lot of progress has been made and quite new types of materials that are suitable to be used on the 3D printing technological methods occurred on the market [5].

Diversity of Rapid Prototyping methods is really impressive. The methods that are using molten plastic material that is heated up and extruded through a nozzle are the most spread and developed nowadays on the market [6]. Manufacturing of parts made of resin material by Vat polymerization (curing of the material using UV light) or manufacturing of different parts by Material Jetting or Binder Jetting, methods that are based on the use of different binders or fusing agents that are being sintered or cured by light are also 3D printing technological variants that are used on a larger scale in this field in the world [7]. Powder bed fusion or direct energy deposition methods are widely used to produce different types of metallic parts made by sintering or welding metallic powder grains in order to materialize one part made by 3D printing technologies [8, 9]. The parts can be made from a different range of metallic materials using these methods, starting with light materials like aluminum alloys or nickel alloys and ending with materials that have much higher strength like titanium alloys, tool steel alloys, etc. [10–13]. In the last year's lot of researches were reported

in this field regarding new types of metallic materials that were developed and tested, like copper-alloys, gold, tungsten, carbide, or diamond 3D printing [14].

Rapid Tooling methods, such as Vacuum Casting, Metal Spraying, Investment casting, and other similar technologies were also quite well developed in the last years for producing different types of molds that were used to conceive, develop, and test new types of materials that are not suitable to be used by 3D printing technologies [15–17].
