Processes
3D Printing Processes
After reading this section, you will have a complete overview of today's 3D printing landscape.
Quickly learn about the most popular processes and materials, as well as actionable decision making tools to help you select the optimal 3D printing process for your application.
The different types of 3D printing
The ISO/ASTM 52900 standard categorized all different types of 3D printing under one of these seven groups:
Material Extrusion (FDM): Material is selectively dispensed through a nozzle or orifice
Vat Polymerization (SLA & DLP): Liquid photopolymer in a vat is selectively cured by UV light
Powder Bed Fusion (SLS, DMLS & SLM): A high-energy source selectively fuses powder particles
Material Jetting (MJ): Droplets of material are selectively deposited and cured
Binder Jetting (BJ): Liquid bonding agent selectively binds regions of a powder bed
Direct Energy Deposition (LENS, LBMD): A high-energy source fuses material as it is deposited
Sheet Lamination (LOM, UAM): Sheets of material are bonded and formed layer-by-layer
An infographic with all currently available 3D printing technologies is available for download. It illustrates the seven 3D printing categories, the main materials each group can print with and the most popular printer manufacturers.
Get instant access to the high-resolution PDF version of the Additive Manufacturing Technologies poster for free.
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The next sections will introduce you to the basic operating principles and pro's and con's of the six main 3D printing processes today.
After reading this chapter, you will be able to make educated decisions about which 3D printing technology is best suited for your particular application.
Fused Deposition Modelling (FDM)
In FDM, a spool of filament is loaded into the printer and then fed to the extrusion head, which is equipped with a heated nozzle. Once the nozzle reaches the desired temperature, a motor drives the filament through it, melting it.
The printer moves the extrusion head, laying down melted material at precise locations, where it cools and solidifies (like a very precise hot-glue gun). When a layer is finished, the build platform moves down and the process repeats until the part is complete.
After printing, the part is usually ready to use but it might require some post-processing, such as removal of the support strucures or surface smoothing.
FDM is the most cost-effective way of producing custom thermoplastic parts and prototypes. It also has the shortest lead times - as fast as next-day-delivery - due to the high availability of the technology. A wide range of thermoplastic materials is available for FDM, suitable for both prototyping and some functional applications.
As of limitations, FDM has the lowest dimensional accuracy and resolution compared to the other 3D printing technologies. FDM parts are likely to have visible layer lines, so post-processing is often required for a smooth surface finish. Additionally, the layer adhesion mechanism makes FDM parts inherently anisotropic. This means that they will be weaker in one direction and are generally unsuitable for critical applications.
Learn more about FDM 3D printing →
Low-cost prototyping
Fast turn-around (less than 24 hours)
Functional applications (non-critical load)
Limited dimensional accuracy
Visible layer lines (can be post-processed)
Anisotropic mechanical properties
Popular FDM materials
FDM is the most widely available 3D printing process, mainly used for low-cost prototyping and design verification with very fast turn around times.
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Stereolithography & Digital Light Processing (SLA & DLP)
SLA and DLP are similar processes that both use a UV light source to cure (solidify) liquid resin in a vat layer-by-layer. SLA uses a single-point laser to cure the resin, while DLP uses a digital light projector to flash a single image of each layer all at once.
After printing, the part needs to be cleaned from the resin and exposed to a UV source to improve its strength. Next, the support structures are removed and, if a high quality surface finish is required, additional post-processing steps are carried out.
SLA/DLP can produce parts with very high dimensional accuracy, intricate details and a very smooth surface finish ideal that are ideal for visual prototypes. A large range of speciality materials, such as clear, flexible, castable and biocompatible resins, or materials taylored for specific industrial applications, are also available.
Generally, SLA/DLP parts are more brittle than FDM parts, so they are not best suited for functional prototypes. Also, SLA parts must not be used outdoors, as their mechanical properties and color degrades when they are exposed to UV radiation from the sun. Support structures are always required in SLA/DLP which may leave small blemishes in the surfaces they come in contact with that need extra post-processing to remove.
Learn more about SLA/DLP 3D printing →
High accuracy & intricate details
Smooth surface ideal for visual prototypes
Large range of specialty materials
Produces relatively brittle parts
Degrade with exposure to sunlight
Removal of support marks required
Popular SLA/DLP materials
SLA is most suitable for visual applications where an injection mold-like, smooth surface finish, and a high level of feature detail are required.
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Selective Laser Sintering (SLS)
The SLS process begins with heating up a bin of polymer powder to a temperature just below the melting point of the material. A recoating blade or roller then deposits a very thin layer of powder - typically 0.1 mm thick - onto the build platform.
A CO2 laser scans the surface of the powder bed and selectively sinters the particles, binding them together. When the entire cross-section is scanned, the building platform moves down one layer and the process repeats. The result is a bin filled with parts surrounded by unsintered powder.
After printing, the bin needs to cool before the parts are removed from the unsintered powder and cleaned. Some post-processing steps can then be employed to improve their visual appearance, such as polishing or dying.
SLS parts have very good, almost-isotropic mechanical properties, so they are ideal for functional parts and prototypes. Since no support structures are required (the unsintered powder acts as support), designs with very complex geometries can be easily manufactured. SLS is also excellent for small-to-medium batch production (up to 100 parts), since the bin can be filled throughout its volume and multiple parts can be printed at a single production run.
SLS printers are usually high-end industrial systems. This limits the availability of the technology and increases its cost and turn-around times (compared to FDM or SLA, for example). SLS parts have a naturally grainy surface and some internal porosity. If a smooth surface or watertightness is required, additional post-processing steps are needed. Beware that large flat surfaces and small holes need special attention, as they are susceptible to thermal warping and oversintering.
Learn more about the SLS process →
Ideal for functional prototypes
Complex geometries - no support needed
Small batch production capabilities
Higher cost than FDM or SLA
Slower turn-around due to batch production
Grainy surface & internal porosity
Popular SLS materials
SLS is used for both prototyping and small-batch production of functional plastic parts with good mechanical properties.
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SLS vs. MJF
A competing technology with similar benefits to SLS is MJF, which was introduced in 2016 by HP. Both technologies create parts that are visually and mechanically almost indistinguishable.
Learn about the differences of SLS and MJF →
Material Jetting (PolyJet)
Material Jetting works in a similar way to standard inkjet printing. However, instead of printing a single layer of ink on a piece of paper, multiple layers of material are deposited upon each other to create a solid part.
Multiple print heads jet hundreds of tiny droplets of photopolymer onto the build platform, which are then solidified (cured) by the UV light source. After a layer is complete, the build platform moves down one layer and the process repeats.
Support structures are always required in Material Jetting. A water-soluble material is used as support that can be easily dissolved during post-processing and that is printed at the same time as the structural material.
Material Jetting is the most precise 3D printing technology (with SLA/DLP being a close second). It is one of the few 3D printing processes that offers multi-material and full-color printing capabilities. Material Jetted parts have a very smooth surface - comparable to injection molding - and very high dimensional accuracy, making them ideal for realistic prototypes and parts that need an excellent visual appearance.
Material Jetting is one of the most expensive 3D printing processes and this high cost may make it financially unviable for some applications. Moreover, parts produced with Material Jetting are not best suited for functional applications. Like SLA/DLP, the materials used with this process are thermosets, so the produced parts tend to be brittle. They are also photosensitive and their properties will degrade over time with exposure to sunlight.
Learn more about the Material Jetting process →
High accuracy & very fine details
Injection molding-like finish
Multi-material & full-color capabilities
The most expensive plastic 3D printing process
Mechanical properties degrade over time
Produces relatively brittle parts
Popular Materials Jetting materials
Material Jetting produces parts of the highest dimensional accuracy with a very smooth surface finish, used for both visual prototypes and tooling manufacturing.
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Direct Metal Laser Sintering & Selective Laser Melting (DMLS & SLM)
Direct Metal Laser Sintering (DMLS) and Selective Laser Melting (SLM) produce parts in a similar way to SLS: a laser source selectively bonds together powder particles layer-by-layer. The main difference, of course, is that DMLS and SLM produce parts out of metal.
The difference between the DMLS and SLM processes is subtle: SLM achieves a full melt of the powder particles, while DMLS heats the metal particles to a point that they fuse together on a molecular level instead.
Support structures are always required in DMLS and SLM to minimize the distortion caused by the high temperatures required to fuse the metal particles. After printing, the metal supports need to be removed either manually or through CNC machining. Machining can also be employed to improve the accuracy of critical features (e.g. holes). Finally, the parts are thermally treated to eliminate any residual stresses.
DMLS/SLM is ideal for manufacturing metal parts with complex geometries that traditional manufacturing methods cannot produce. DMLS/SLM parts can be (and should be) topology optimized to maximize their performance while minimizing their weight and amount of material used. DMLS/SLM parts have excellent physical properties, often surpassing the strength of the rough metal. Many metal alloys that are difficult to process with other technologies, such as metal superalloys, are available in DMLS/SLM.
The costs associated with DMLS/SLM 3D printing are high: parts produced with this processes typically cost between $5,000 and $25,000. For this reason, DMLS/SLM should only be used to manufacture parts that cannot be produced with any other method. Moreover, the build size of modern metal 3D printing systems is limited, as the required precise manufacturing conditions are difficult to maintain for bigger build volumes.
Learn more about the DMLS/SLM process →
Highly complex, topology optimized metal parts
Parts with excellent material properties
Ideal for high-end engineering applications
Very high manufacturing costs
Specialized CAD software knowledge required
Limited build volume
Popular DMLS/SLM materials
DMLS/SLM produce high performance, end-use metal 3D printed parts for industrial applications in aerospace, automotive and medical.
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Metal 3D printing technologies compared
Metal 3D printing is on the rise. So we wrote a comprehensive guide to help you get a complete overview of today's metal 3D printing landscape.
Read the complete guide to Metal 3D printing →
Binder Jetting
Binder Jetting is a flexible technology with diverse applications, ranging from low-cost metal 3D printing, to full-color prototyping and large sand casting mold production.
In Binder Jetting, a thin layer of powder particles (metal, acrylic or sandstone) is first deposited onto the build platform. Then droplets of adhesive are ejected by a inkjet printhead to selectively bind the powder particles together and build a part layer-by-layer.
After the print is complete, the part is removed from the powder and cleaned. At this stage it is very brittle and additional post-processing is required. For metal parts this involves thermal sintering (similar to Metal Injection Molding) or infiltration with a low melting-point metal (for example, bronze), while full-color parts are infiltrated with cyanoacrylate adhesive.
Binder Jetting can produce metal parts and full-color prototypes at a fraction of the cost of DMLS/SLM or Material Jetting respectively. Very large sandstone parts can also be manufactured with Binder Jetting, as the process is not limited by thermal effects (for example, warping). Since no support structures are needed during printing, metal Binder Jetting parts can have very complex geometries and, like SLS, low-to-medium batch production is possible by filling up the whole build volume.
Metal Binder Jetting parts have lower mechanical properties than the bulk material though, due to their porosity. Due to the special post-processing requirements of Binder Jetting, special design restrictions apply. Very small details, for example, cannot be printed, as the parts are very brittle out of the printer and may break. Metal parts might also deform during the sintering or infiltration step if not supported properly.
Learn more about the Binder Jetting process →
Low-cost batch production of metal parts
Full-color prototyping in acrylic or sand
Very large printing capabilities in sand
Inferior material properties to DMLS/SLM
Design restriction due to post-processing
Fine details may not be printable
Popular Binder Jetting materials
Binder Jetting is most commonly used for full-color parts, low-cost metal printing, and large sand casting molds.
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How to select the right 3D printing process
Selecting the optimal 3D printing process for a particular application can be difficult. There are often more than one process that are suitable and each of them offers different benefits, like greater dimensional accuracy, superior material properties or better surface finish.
For this reason, we have prepared decision making tools and generalized guidelines to help you select the right 3D printing process.
Generally, there are three main things you always need to consider:
The required material properties: strength, hardness, impact strength etc.
The functional & visual design requirements: smooth surface, strength, heat resistance etc.
The capabilities of the 3D printing process: accuracy, available print volume, layer height etc.
With these considerations in mind, identifying the best solution for your application should become straightforward. We have prepared a detailed guide to help you with the technical details or you can se this decision trees bellow for a quick reference.