There are mainly 11 types of 3D printing technology available as explained:
Stereolithography (SLA):
SLA is among world’s first 3D printing technology. It was invented by Chuck Hull in 1986, who later founded the company 3D Systems to commercialize the technology.
An SLA printer uses mirrors, known as galvanometers, with one positioned at the x-axis and another at the y-axis. These galvanometers rapidly aim a laser beam across a vat of resin, selectively curing and solidifying a cross-section of the object inside this building area, building it up layer by layer.
SLA printers are mainly used in producing parts with high levels of details, smooth surface finish, and tight tolerances. It’s widely used in the medical industry. The common applications include anatomical models and microfluidics.
Most SLA printers use a solid-state laser to cure parts. The disadvantage of these types of 3D printing technology using a point laser is that it can take longer to trace the cross-section of an object when compared to DLP.
Selective Laser Sintering (SLS):
Creating an object with Powder Bed Fusion (PBF) technology and polymer powder is generally known as Selective Laser Sintering (SLS). The SLS process was developed in the 1980s by Carl Deckard. After expiration of industrial patents, these types of 3D printing technology are becoming increasingly common with lower cost.
During Selective Laser Sintering, tiny particles of plastic, ceramic or glass are fused together by heat from a high-power laser to form a solid, three-dimensional object.
Objects printed with SLS technology are made with powder materials, most commonly plastics, such as nylon, which are dispersed in a thin layer on top of the build platform inside an SLS machine. A laser, which is controlled by a computer program tells it what object to “print,” pulses down on the platform, tracing a cross-section of the object onto the powder.
The laser heats up the powder either to just below its boiling point (sintering) or above its boiling point (melting), which then fuses the particles in the powder together to a solid form. Once the initial layer is constructed, the platform of the SLS machine drops down, usually by less than 0.1mm, thus exposing a new layer of powder for the laser to trace and fuse them together. This process continues till the entire object is printed.
Unlike other methods of 3D printing, SLS requires very little additional tooling once an object is printed, meaning that objects don’t usually have to be sanded or otherwise altered once they come out of the SLS machine. SLS doesn’t require the use of additional supports to hold an object together while it is being printed. Such supports are often necessary with other 3D printing methods, such as stereolithography or fused deposition modeling, making these methods more time-consuming compared to SLS.
SLS is particularly useful for industries that need only a small quantity of objects printed with high quality materials. One such example of this is the aerospace industry, in which SLS is used to build prototypes for airplane parts.
Material Jetting (MJ):
Also referred as PolyJet, Material Jetting stands out among other 3D printing technologies for its ability to produce highly accurate parts with a smooth surface finish. Since its emergence in the late 1990s, Material Jetting is an ideal 3D printing technology for producing full-colour, visual prototypes, injection moulds and casting patterns.
Material Jetting is an inkjet printing process in which printheads are used to deposit a liquid photoreactive material onto a build platform layer upon layer. Similar to Stereolithography (SLA), Material Jetting uses a UV light to solidify the material. The methods of material deposition may vary from printer to printer and can involve either a Continuous or Drop-on-Demand (DOD) jetting approach.
Objects made with Material Jetting require support, which is printed simultaneously during the build from a dissolvable material that’s removed during the post-processing stage. Material Jetting is one of the only types of 3D printing technology to offer objects made from multi-material printing and full-color.
Digital Light Processing (DLP):
Digital light processing is similar to SLA in the respect that it cures liquid resin using light. Though, the main difference between the two technologies is that DLP uses a digital light projector screen whereas SLA uses a UV laser. This means DLP 3D printers can image an entire layer of the build all at once, which result in faster build speeds. While commonly used for rapid prototyping, the higher throughput of DLP printing makes it suitable for low-volume production runs of plastic parts.
Fused Deposition Modeling (FDM):
Fused deposition modeling (FDM) is one of the most common 3D printing technologies for plastic parts. An FDM printer works by extruding a plastic filament layer-by-layer onto the build platform. It’s a cost-effective and quick method for building physical models. There are few instances where FDM can be used for functional testing but the technology is limited as the parts having relatively rough surface finishes and lacking strength.
Depending on the geometry of the object, it is sometimes necessary to add support structures, for example, if a model has steep overhanging parts. Sometimes, they are also referred to as Fused Filament Fabrication or FFF.
Masked Stereolithography (MSLA):
Masked Stereolithography utilizes an LED array as its light source, shining UV light through an LCD screen displaying a single layer slice as a mask — hence the name.
MSLA takes this DLP technology one step further, by removing the projector and mirror and replaces them with an LCD and a bright LED light. A vat of resin sits above the LCD, separated by a very thin layer of Fluorinated Ethylene Propylene (FEP) plastic. The LCD displays the desired shape by turning off individual pixels where the resin needs to be cured, while all of the other pixels are illuminated.
One of the most obvious points of differences between FDM and Masked SLA is the significantly higher resolutions that a masked SLA machine can replicate. This means, not only a masked SLA printer is capable of printing models with significantly higher resolution, but it is also far more capable of printing extremely high detail that FDM printing simply isn’t able to recreate.
Drop on Demand (DOD):
Drop on Demand is a 3D printing process where droplets of material are selectively deposited and cured on a build plate. Using photopolymers or wax droplets that cure when exposed to light, the objects are built up one layer at a time. The nature of the Material Jetting process allows different materials to be printed in the same object.
One application for this technology is to fabricate support structures from a different material to the model being produced.
Common Applications: full color product prototypes; injection mold-like prototypes; low run injection molds; medical models etc.
Weaknesses: brittle, not suitable for mechanical parts printing; higher cost than SLA/DLP for visual purposes.
Sand Binder Jetting (SBJ):
Binder Jetting is an additive manufacturing process in which a binding agent is deposited to join powder particles. Layers of material are then bonded to form the object. In Sand Binder Jetting (SBJ) the powder is bound using a polymer binding agent. Sand Binder Jetting is often used in modeling and in the creation of sand cast molds for manufacturing.
Advantages:
1. Binder Jetting produces full-color prototypes and metal parts at a fraction of the cost compared to DMLS/SLM and Material Jetting respectively.
2. Binder Jetting can manufacture very large parts and complex metal geometries, as it is not limited by any thermal effects (e.g. warping).
3. The manufacturing capabilities of SBJ are excellent for low to medium batch production.
Disadvantages:
1. Only rough details can be printed with SBJ, as the parts are very brittle in their green state and may fracture during post processing.
2. Compared to other 3D printing processes, Binder Jetting offers a limited material selection.
Metal Binder Jetting:
Binder Jetting can be used for the fabrication of metal objects as well. Here metal powder is bound using a polymer binding agent. Producing metal objects using Binder Jetting allows the production of complex structures that is well beyond the capabilities of conventional manufacturing techniques.
Direct Metal Laser Sintering (DMLS)/ Selective Laser Melting (SLM):
Both Direct Metal Laser Sintering (DMLS) and Selective Laser Melting (SLM) produce objects in a similar manner to SLS. The main difference is that these types of 3D printing technology are applied to the production of metal parts.
It’s often used to reduce metal quantity, multi-part assemblies into a single component or lightweight parts with internal channels or hollowed out features. DMLS is viable for both prototyping and production requirement since parts are as dense as those produced with traditional metal manufacturing methods like machining or casting. Creating metal components with complex structures also makes it suitable for medical applications where a part design must mimic an organic structure.
Unlike SLS, the DMLS and SLM processes require structural support, to limit the possibility of any distortion that may occur (despite the fact that the surrounding powder provides physical support). Furthermore, DMLS/SLM parts are at risk of warping due to the residual stresses produced during printing, because of the high temperatures. Parts are also typically treated with after printing, while still attached to the build plate, to relieve any stresses in the parts after printing.
Electron Beam Melting (EBM):
Electron beam melting is another metal 3D printing technology that uses an electron beam which is controlled by electromagnetic coils to melt the metal powder. Distinct from other Powder Bed Fusion techniques, Electron Beam Melting (EBM) uses a high energy beam or electrons, to induce fusion in the particles of metal powder.
A focused electron beam scans across a thin layer of powder, causing localized melting and solidification over a specific cross-sectional area. These areas are built up to create a solid object.
Compared to SLM and DMLS types of 3D printing technology, EBM generally has a superior build speed due to its higher energy density. Though, things like minimum feature size, powder particle size, layer thickness, and surface finish are typically larger. Also important to note is that EBM parts are fabricated in a vacuum, and the process can only be used with conductive materials.