3D printing is a form of additive manufacturing, whereby material is extruded in a layer-by-layer process to form a 3D geometry. This runs contra to traditional manufacturing methods such as milling, grinding, drilling etc. which are methods of reductive/subtractive manufacturing, where unnecessary material is removed to reveal a final shape. By virtue of only using the material required to form, 3D printing is a much more economical production process.
Advances in material sciences and 3D printing technology have allowed additive manufacturing to play an increasing role across a multitude of industries: From defence to automotive and aerospace, to the fashion industry where you can find impossibly intricate trainer sole designs are now coming to the fore – even the dental industry where a 3D rendering of a person’s tooth profile can be printed with special medical- grade polymers that are now available.
There are several methods of 3D printing which all fall under 3 different technologies: sintering, melting, and stereolithography.
Sintering is a process where a material powder is heated to around 60 -80% of its melting point, which allows the powder to compact and strengthen its chemical bonds. This process is used with thermoplastic powders such as polyamide, although this technology been extended to metal powders as well
Melting is simply when materials (often powders) are melted together with a high energy appliance such as lasers or electric arcs.
Stereolithography utilises photopolymerisation to create parts. This is when short wave light like UV is absorbed by resins and allowed to cure in a layer-by-layer process. This is the premiere method of 3D printing, first developed in 1984.
Binder jetting deposits a thin layer of powered material, for example metal, polymer sand or ceramic, onto the build platform, after which drops of adhesive are deposited by a print head to bind the particles together. This builds the part layer by layer and once this is complete post processing may be necessary to finish the build. As examples of post processing, metal parts may be thermally sintered or infiltrated with a low melting point metal such as bronze, while full-colour polymer or ceramic parts may be saturated with cyanoacrylate adhesive.
Direct energy Depositioning
Direct energy depositioning uses focussed thermal energy such as an electric arc, laser or electron beam to fuse wire or powder feedstock as it is deposited. The process is traversed horizontally to build a layer, and layers are stacked vertically to create a part.
Fused Deposition Moulding (FDM)/ Fused Filament Fabrication (FFF)
Both forms above are a material extrusion process, the former being a patented process by Stratasys Ltd in 1989. A typical FDM machine would have a heated material deposited onto a build platform through a nozzle in a layer-by-layer process. The entire print chamber would be isolated and kept at around 90 degrees Celsius to maintain better control of the material properties and definition of the final product. Once the patent expired in 2009, FDM technology was reverse-engineered for improvements that allowed for more complex shapes to be formed and that didn’t require a heated environment in order to reduce costs – this became the model for FFF.
Selective Laser Sintering (SLS)/ Direct Laser Metal Sintering (DMLS)
These methods are a form of Powder Bed Fusion, where a laser scans the first layer and selectively sinters the powdered material based on the 3D CAD geometry. A new layer of powder is then deposited onto this layer and the process continues until the entire part is manufactured bottom-up. Both processes heat up powder particles to the point of molecular fusion (often 60 -80% of melting point), the only difference being that DMLS uses high powered lasers as a metals have high melting points, whereas SLS is reserved mostly for polymers.
VAT Photopolymerisation: Stereolithography (SLA)/ Digital Light Processing (DLP)
These processes both create parts layer-by-layer through the use of a light to selectively cure liquid resin in a vat. SLA uses a single point laser or UV source for the curing process, while DLP flashes a single image of each full layer onto the surface of the vat. Creating support structures are integral to the finish quality of any design features. Any support structures will also need to be removed and could leave blemishes or “pock-marks” which additional post-processing would be required to create a higher quality finish.
Ideal for parts with a high level of dimensional accuracy, these processes can create intricate details with a smooth finish, making them perfect for prototype production. These parts are not suitable for outdoor use as the colour and mechanical properties may degrade when exposed to UV light from the sun.
1. A 3D shape is either constructed or rendered using a suitable CAD modelling software package. This shape is then saved as a .stl file which has become the default for 3D print files. An .stl will convert a CAD geometry into a giant substructure of triangular shapes which a 3D printer can recognise.
2. The .stl file is imported on to specialised 3D printing software, which will fault-check and interprets the shape’s geometry as G-code, and separating it into layers
3. The file is then transmitted to the printer either via USB or WLAN where the printing process can begin.
4. Once the print is completed, there will likely be a cooldown period as the material returns to ambient temperature. Once cooldown has been reached, it may be necessary to remove and clean away excess material or to undertake additional measures to achieve a specific type of finish (e.g. – curing, sandblasting etc.) – this is known as post-processing. Once this has been completed, your finished part will be ready for purpose.