3D Printing Technologies
3D printing refers to additive manufacturing that allow printing of 3D objects via deposition of successive layers of material in layer-by-layer arrangement (Jiang and Zhao, 2015). Different types of multi-material 3D printers are introduced below (Javeed Shaikh Mohammed, 2016):
Fused Deposition Modeling (FDM) 3D Printers:
This is currently the most popular 3D printing technology in this manufacturing process. 3D parts are produced by melting a thermoplastic filament or metal wire. A thermoplastic filament or metal wire is fed through a hot extruder that melts and extrudes the filament through the print head. The FDM printers deposit melted thermoplastic in a layer-by-layer format to create 3D objects (Chia and Wu, 2015; Gross et al., 2014).
The FDM 3D printed objects have higher anisotropy and lower costs compared to SLA or SLS 3D printed objects (Stansbury and Idacavage, 2016). One of the problems with the FDM printed 3D parts is their porosity, which prevents their direct use in applications that require air-tight or water-proof sealing
Stereolithography (SLA) Printers:
Stereolithography builds 3D objects using UV curable photopolymer liquid resins. Similar to FDM printers, SLA printers build 3D objects in a layer-by-layer format. A focused source of UV light cures the liquid resin in a layer-by-layer format, while the build platform of the printer slowly pulls the printed 3D object into the liquid resin bath by a distance equal to one-layer thickness.
A major advantage of SLA printers over the FDM printers is the ability to print high resolution intricate details of small-scale features with surface finish similar to injection molded parts (Chae et al., 2015). Also, the bonding strength between the layers is stronger in the case of SLA printed objects leading to good strength and minimal anisotropy in their structure and properties (Stansbury and Idacavage, 2016). One of the limitations with most of the SLA printers is that they use proprietary resins, and also the choices of colors are limited compared to FDM filaments.
Selective Laser Sintering (SLS) Printers:
SLS is an additive manufacturing process in which uses a high power laser (such as carbon dioxide laser) to fuse small particles of plastic, metal, ceramic or glass powders. These powders are typically in the size range of 20–150 µm (Hunt et al., 2014). A 3D printing technology that uses similar principle to SLS except that high power solid-state lasers are used to melt metal powders in inert gas atmospheres is known as Selective Laser Melting (SLM) (Abdelaal and Darwish, 2013). SLM yields denser metal objects compared to SLS 3D printing. In general, SLS (or SLM) 3D printing yields 3D objects with high mechanical strength and low porosity (Do et al., 2015).
Binder Jetting:
In this process a binder is selectively deposited onto the powder bed, bonding these areas together to form a solid part one layer at a time. The materials commonly used in Binder Jetting are metals, sand, and ceramics.