**What is Rapid Prototyping?**
Additive (layered) manufacturing is a practical manufacturing method based on the principle of superimposing layers created according to the three-dimensional (3D) geometric data of objects using metal, plastic, composite, and organic materials. Additive manufacturing was previously known as rapid prototyping, which is a method mostly used for prototype production. This method was first introduced by 3D Systems Company in the 1980s with stereolithography (StereolithographySL) technology (1992). In those years, many additive manufacturing methods were developed, and patent applications were made. Later, these technologies were commercialized by companies. In the first half of the 1990s, following SL, Helysis Company laminated object manufacturing (LOM), Stratasys company melt deposition modeling (FDM), DTM Company selective laser sintering (Selective Laser Sintering SLS), EOS Company direct metal powder laser sintering (Direct Metal Laser Sintering-DMLS), Cubital Corporation solid ground curing (SGC), and Soligen Corporation 3D printing (Three Dimensional Printing-3DP) technologies have been commercialized and marketed (Danforth and Safari, 1996; Wohlers et al. Gornet, 2014).
The 3D printing (3DP) process is actually an additive manufacturing technology licensed by the Massachusetts Institute of Technology (MIT). A liquid binder is sprayed from the nozzle, which moves according to the 3D data produced by slicing software, onto the powder material in the powder bed, creating a layer. Then, the powder bed is lowered down to the thickness of the layer and plastered with powder material, and the solidification process is repeated according to the geometric data, and the new layer is formed on the existing layer. In this way, the whole object is obtained, and the unglued dust is cleaned (1996). This technology is called 3D printing because of its similarity to the inkjet printing technology used in 2D printers, and the machines working with this technology are called 3D printers. Later, technologies working with similar logic were developed, and these technologies were transferred to desktop machines and made available to large masses in homes and offices. The production methods on which these technologies are based are popularly known as 3D printing (3D printing), and the terms additive manufacturing and rapid prototyping have begun to be called 3D printing.
3D printing, which includes many different technologies, is a practical manufacturing method that allows objects designed in a digital environment to be converted into physical objects using additive manufacturing methods. Additive manufacturing, which is the basic logic of 3D printing, is the reverse of the machining method on which computer-aided production processes such as CNC milling and turning are based. In machining, a three-dimensional object is obtained by cutting and removing parts from a block of material. In the 3D printing method, the designed three-dimensional object is obtained by combining the material layers created successively. For this reason, with the additive manufacturing method, three-dimensional objects can be obtained using less material.
The most important reasons for choosing 3D printing technology are that it does not require additional production steps such as production line setup, mold design, and the design can be put into production immediately. At the same time, the development of home-type desktop 3D printers, which are capable of 3D manufacturing with high geometric accuracy and resolution by using the advantages of additive manufacturing, has been effective in making this technology stand out among other manufacturing methods. In addition, the production flexibility provided by the additive manufacturing concept provides a great advantage in the production of objects with freeform surfaces.
Another advantage of printers working with 3D printing method is that they allow cloud-based production. In this way, incoming orders are transmitted to the printer and production can be realized quickly with 3D printers with direct production capability without the need for any molds or lines. It is understood that 3D printers will have a very important place for industry 4.0, which includes technologies such as sensors, wireless communication, and robotic arms, as well as cloud technology.
Despite all the advantages of the 3D printing method, it is not economical for mass production, the part to be manufactured is limited to the dimensions of the 3D printer, and the low production speed limits the use of the method. In addition, the variety of materials used in 3D printing is also limited. However, new methods and technologies that allow the use of different materials are being developed day by day. Today, many types of plastic, metal, composite, and organic materials can be used in 3D printing manufacturing. The 3D printer technologies and materials most preferred by users in 2018 are presented in figure 1 and figure 2, respectively, according to Sculpteo's (2018) "The State of 3D Printing" report.