There are 3 main types of 3D Printing – FDM, SLS and SLA. Within this series we will be discussing FDM, also known as Fused Deposition Modeling.
Fused Deposition Modeling (FDM) works by laying down consecutive layers of material at high temperatures, allowing the adjacent layers to cool and bond together before the next layer is deposited. The resolution of FDM rapid prototyping is limited by the accuracy of the motors and user calibration, as well as the print time available. Print time increases linearly as part tolerances become tighter.
FDM print tolerances range from 0.05 mm to 0.5 mm with the industry average coming in at around 0.2 mm. Some interesting benefits of Fused Deposition Modeling include the ability to easily customize infills of the objects being printed. This means that it is very simple to print prototype models for fit and finish checks with low infill, or even hollow, in order to save on material costs.
Stereolithography (SLA) is another example of building a model layer by layer, but instead of extruding molten plastic through a nozzle, the process requires a liquid plastic resin called a photopolymer which is then cured by an ultraviolet (UV) laser. This process is even more comparable to a CNC operation as the SLA machine requires an excess amount of photopolymer to complete the print. An SLA machine typically stores the excess photopolymer in a tank below the print bed. As the print process continues, the bed is lowered further into the tank curing each layer consecutively along the way.
Once the final layer is complete the bed is raised out of the tank, exposing the solid 3D model. SLA has a higher resolution but longer print time than FDM
Selective Laser Sintering (SLS) is a very exciting technology which directly fuses particles together layer by layer, through a high energy pulse laser.
Similar to SLA, this process starts with a tank full of bulk material, but this time in powder form. As the print continues, the bed lowers itself for each new layer as done in the SLS process. Overhangs are naturally supported by the excess bulk powder material making those features much more simple to print than using FDM. The bulk material is typically heated to just under its transition temperature to allow for faster particle fusion and print moves. SLS is the preferred rapid-prototyping method of metals and exotic materials, however, there are additional costs in energy used for fabricating with this method which may reverse any savings realized in the material cost.