3D printing techologies

1. FDM/FFF

Fused Deposit Modeling or Fused Filament Fabrication is the most widespread and accessible 3D printing technology. It is suitable for printing various models and prototypes. The primary material used is a printing strand called filament, which has a diameter of 1.75 mm. Originally, a 3 mm diameter filament was used, but it was less precise in terms of dosage.

It gained its popularity not only due to its reliability but also because of its relatively understandable mechanics, reminiscent of a melting gun. FDM/FFF operates on a layering principle. The material used is a thermoplastic filament wound onto a spool attached to an extruder[1], which has its own motor and extrudes the filament through a heated nozzle. This nozzle maintains a constant temperature, rapidly melting the filament into a liquid that is then extruded through a small nozzle onto the build platform.

The nozzle moves slightly above the build platform, applying a layer along the X and Y axes. It then moves up along the Z-axis by one layer and continues to apply layers until the entire object is created. Some printers can also move the build platform horizontally.

In today's context, there are printers equipped with multiple extruders for combining filament colours or materials. The most well-known printers in this category are the Prusa printers from Czech manufacturers, which can use up to five extruders simultaneously.

1.1. Cartesian

The principle of the printer's movement is based on three linear axes, with the extruder pushing the material along the X and Z axes. The build platform moves along the Y axis. As a result, the build platform is rectangular in shape for most printers.

1.2. Delta

The extruder on the printer is suspended by three arms, which are joined together precisely at the extruder's location. The advantage lies in the movements performed along the Z-axis. On the contrary, the disadvantage is the requirement for high-precision calibration and construction of the printer, as well as demanding calculations for the motor movements of the individual arms.

1.3. Polar

The least used system of printers. The movement is based on a print head that moves on two axes and a rotating build platform. The printer is simple in construction, but the execution and preparation of a model for printing are relatively complicated.

Source: Zaklad do 3D Tisku s Jozefom Prušom – Jozef Pruša

2. SLA

Stereolithography is a technology based on the principle of resin solidification using UV radiation. These rays focus on one layer, and once it's completed, they move vertically to the next layer's dimensions. The cured surface is dipped back into the liquid and solidified. Thanks to the precision of UV lasers, these printers can create a relatively smooth and highly detailed surface compared to FDM/FFF technology. However, it takes longer, and the printing area is smaller. A disadvantage is also the higher cost, both for materials and the printer itself.

Digital Light Processing (DLP) is a technology very similar to SLA and is considered a subset of it. It utilizes almost the same principles and materials, but the difference lies in how the resin is exposed. DLP can emit UV rays precisely onto the desired layer arrangement, creating it all at once, unlike SLA, which uses a single-point laser. Due to this feature, DLP can work quickly regardless of the shape or complexity of the object. Another advantage is the possibility of simultaneously printing duplicate models without waiting.

A subcategory is Mask Stereolithography (MSLA), which employs UV LED for exposure. UV light passes only where pixels are displayed on the LCD screen (they shine white) and solidifies the model on those areas. As the display consists of square pixels at a precise resolution, the resolution always matches the LCD screen. For solidifying the entire layer at once, this technology is also time-independent regarding the number of objects.

However, these printers require additional equipment. The model isn't suitable for immediate use after printing, as it's sticky from uncured resin. It's recommended to dip it in isopropyl alcohol to wash away excess resin and then let the model solidify again.

3. SLS/DMLS

Another technology is SLS and DMLS, which differs from the previous ones by using powder as the material. The printer applies a thin layer of thermoplastic powder onto the build platform using an integrated roller, which is then fused in the areas of the final object. The roller then applies the next layer until the printing is completed. Another difference is that SLS can work with any material in powdered form that can be fused by a laser. This can include various types of metals, their alloys, ceramics, plastics, and more.

The resulting product is surrounded by the printing material, which needs to be removed. If a hollow product is being printed, it's necessary to create openings to allow the removal of uncured powder.

A similar method is Direct Metal Laser Sintering (DMLS), which operates on the same principle. The only difference is that the process works only with metals and their alloys.

Source: Úvod do 3D tlače - Alena Furdová, Denisa Fialová, Michal Marko, Peter Leško
             Zaklad do 3D Tisku s Jozefom Prušom – Jozef Pruša

3.1. SLM/EBM

Selective laser melting (SLM) works similarly to SLS, but it's a highly energetic process. The laser must generate enough heat for each layer to exceed the material's melting point. This involves melting particles, which solidify into the desired shape instead of being fused. However, it's limited to certain materials including steel, titanium, cobalt, aluminum, copper, gold, chromium, and tungsten. As a result, the produced product is extremely strong.

Electron Beam Melting (EBM), on the other hand, doesn't use a laser to melt the material, but an electron beam, which sets it apart from other methods.

4. Other technologies

Power bed printing/InkJet

The primary material is a powder deposited onto the build platform, along with a liquid binder to solidify the object. The result depends on the material selection, binder, and the way the binder is combined with the powder. It's one of the more popular printer types due to its similarity to home inkjet printers. However, instead of ink, the binder comes from the printhead. One of its advantages is the ability to combine individual colors and create new shades.

MultiJet/PolyJet

MultiJet, also known as PolyJet, is a method that similarly utilizes a printhead to print with multiple colors. However, it doesn't use powder; instead, it applies layers of UV-sensitive resin directly onto the build platform and then cures them using UV light to create a solid material. This method produces sturdier models compared to powder-based printers.

LOM

Laminated Object Manufacturing (LOM) uses continuous material, often in the form of plastic or paper, occasionally metal. A system of heated rollers extrudes the material onto the build platform. The heated rollers pass over the material, which is pressed onto the platform. The material is then trimmed using a computer-controlled knife or laser to achieve the desired shape.


Source:  Úvod do 3D tlače -  Alena Furdová, Denisa Fialová, Michal Marko, Peter Leško