3D printing, also known as additive manufacturing, is a prototyping process where a real object is created from a 3D model. The 3D CAD data is saved as an STL file and then sent to the 3D printer. The printer then prints the model layer by layer to form the complete model.
There are a number of technologies within 3D printing that use different ways of building up a part. SLA (stereolithography), SLS (selective laser sintering) and FDM (fused deposition modelling) are the 3 most common used technologies in 3D printing.
SLA (Stereolithography) is a process whereby a vat of UV curable photopolymer resin is cured by a laser to build parts one layer at a time. The STL file is sliced into single layers (typically 0.05mm to 0.15mm thick) and the laser draws the cross section of each layer. Once the layer has been drawn, the elevator platform descends by a distance equal to one layer. A resin-filled blade then sweeps across the vat, re-coating it with fresh resin. On the surface of this fresh resin, the next layer is then drawn. After being built, the excess resin is then washed off the parts, which are then cured in a UV oven.
SLA requires the use of support structures to attach the parts to the elevator platform and to hold them in place whilst building. Without these support structures, it would be almost impossible to build the complex shapes that SLA is renowned for. Once the build is complete, these supports are removed from the parts manually; usually they are broken away from the parts.
In SLS (Selective Laser sintering), a high power laser is used to sinter powdered material, binding the powder together to create a 3d shape. Similarly to SLA, in an SLS machine the laser scans cross-sections generated from a sliced STL model of the final part on the powder bed. After each layer has completed scanning, the powder bed is lowered by the thickness of one layer – the process is then repeated until the full part has been built.
Unlike in SLA and FDM, SLS does not require support structures in order to keep the parts stable within the build. This is due to the fact that the parts are always surrounded by powder – allowing for near-impossible geometries to be created.
Fused deposition modelling (FDM) is a process whereby thermoplastic material is extruded through a nozzle to build up a part layer by layer. The plastic filament is unwound from a coil and heated as is passes through the nozzle, which can be moved in both the X and Y axis. On some models, the nozzle can move up vertically, on others the bed can move downwards. Like SLA, FDM requires support structures, sometimes these are manufactured from the same material as the part & need to be broken away, and other machines have water soluble support structures that can be washed away once the part is built.