3D Printing Processes — A General Overview

10 min readJul 26, 2020

Starting from the first photopolymerisation technique developed by Dr. Hideo Kodama in 1981, many different 3D printing processes have been developed over the years. It began with development of a technique similar to today’s Stereolithography (SLA) by Dr. Kodama, first commercial 3D Printing Product SLA-1 by 3D Systems Corporation of Charles Hull was introduced in 1988. The patents for Selective Laser Sintering (SLS) and Fused Deposition Modelling (FDM) were filed during the same time.

Today, the list has hit two digits and is still growing with solving the challenges occurring in the existing technologies. In this article, we will be over-viewing some of the important technologies from this list.

Material Extrusion

Similar to the plastic and metal extrusion processes used for making pipes and rods, material extrusion in 3D printing is used to selectively lay down the molten material (generally thermoplastic) layer by layer on a platform to form an object.

Fused Deposition Modelling (FDM)

Fused Deposition Modelling or Fused Filament Fabrication (FFF) is currently the most widely used 3D Printing Technology in the world. Every 3D printing enthusiast first gets introduced to this technology. Due to its easy to use interface, relatively cheap, and wide range of materials, people prefer to use this technology over others.

How does it work?

FDM printers use a 3 axis Cartesian coordinate system to lay down the molten material. It can be a linear or delta type configuration as per the printer specifications. Both the specifications generally serve the same purpose and yield similar results, but have some advantages and drawbacks of using them. More on that later.
As shown in the image, a filament spool of thermoplastic material is loaded on the printer through the extruder nozzle. The heating element present in the extruder kit melts the material. When it reaches the tip of the nozzle and is laid down on the bed, the material is cooled down using fans attached to the extruder kit. Due to its instant solidification, it does not change its shape.
The predetermined path (G-code) decides where to lay down the material and where not to. The motion is controlled by a motor attached to a gear driving the filament in both forward and reverse direction.
The overhangs are supported by support material to ensure the object’s shape doesn’t change. Using multi extruder setup, we can also use dissolvable supports for ease of removal and ensuring better surface finish.

Advantages

Wide range of materials
The most cost effective technology of all
Shorter lead times

Disadvantages

Anisotropic nature lowers the strength of the parts
Poor Surface Finish as compared to other technologies
Low resolution and dimensional accuracy

Vat Polymerization

Vat Polymerization technique uses UV curable resins to form 3D objects. The resin is exposed to a light source which cures the resin, the build plate moves up or down as per the construction to complete the 3D object. Stereolithography (SLA), Digital Light Processing (DLP) and Liquid Crystal Display(LCD) are derivatives of Vat Polymerization having minimal differences.

Stereolithography (SLA)

SLA is the oldest of the 3D printing techniques which uses thermoset polymers which are cured using an irreversible process called photopolymerization. The technique is used for parts having high resolution and intricate details.

How does it work?

SLA technique uses a laser projector which projects laser beam onto galvanometers which directs it to the transparent bottom of the resin tank.
The laser point follows a predetermined path and cures the resin. The support structure is printed along with the object.
When one layer is completed, the platform retracts and the surface is recoated with the resin using a sweeper blade and the process repeats until the part is completely built.

Advantages

High dimensional accuracy and resolution
Can imitate very intricate design in the part
Different materials like clear, castable, and flexible are available as per application
Very high surface finish

Disadvantages

Not ideal for functional prototypes
Prolonged exposure to sunlight degrades the visual appearance
Support structures and post processing is compulsory
Small build size with desktop machines
Costly setup for industrial purposes

Digital Light Processing (DLP)

Digital light processing uses similar technology like SLA and the only difference is the light source. Instead of laser projection it projects an image of the layer which is directed through an intermediate device called as Digital Micromirror Device (DMD).

Liquid Crystal Display (LCD)

LCD is also a similar process like SLA and DLP, the only difference being the light source. The LCD uses an array of LED lights and a LCD screen between the array of lights and the resin. The light is selectively passed through the LCD screen. This method does not need any device to direct the light source to the resin tank.

Material Jetting (MJ)

Material Jetting uses a similar principle used in inkjet 2D printers. A thermoset acrylic photopolymer in liquid form is used in this process. The droplets of the material are laid down on the platform which are then exposed to an ultraviolet light source to be solidified.

Material Jetting uses multiple printheads with an ability to print different material with each head in a line format causing it to be easily used for multi-color, multi-material printing with dissolvable supports.

How does it work?

The resin is heated to 30–60oC temperature to make it viscous to be used for printing.
The printhead travels over the platform releasing droplets of the material on the desired locations.
The UV light source attached to the printhead itself starts curing and solidifying the droplets at the same time.
Once a layer is completed, then the platform moves down to make space for another layer to be printed. The process repeats until the object is built completely.

Advantages

Very smooth surface finish
High dimensional accuracy
Multi-material, Multi-color capability makes it ideal for visual prototypes
Homogeneous mechanical and thermal properties

Disadvantages

Not suitable for functional prototypes
Prolonged exposure to sunlight degrades the part geometry and appearance
Very costly

Drop On Demand (DOD)

The DOD process is based on Material Jetting technology creating wax-like parts for investment casting purposes.

Binder Jetting (BJ)

Think of a bowl of flour we use to make the dough. The key ingredients are flour and water and the water acts as a binder between two particles of flour. Same principle is used in Binder Jetting technique. A tank is filled with powder, which transfers it on the bed layer by layer to be bound by the binding material. The process is used to make large sand casting cores and moulds and figurines.

How does it work?

A sweeper blade recoats the powder bed with the powder material, usually sand, silica, or metal powders.
The binder or glue is then released through the nozzles attached to the carriage on desired locations. Colored ink is released for colored objects.
The bed moves down after completion of one layer and the process is repeated until the part is printed completely.
The part is left in the powder for it to cure and gain strength. After removing from the bed, excess powder is cleaned with pressurized air.

Advantages

Cheaper than the Material Jetting, DMLS, or SLM.
Large build size
No thermal effects
Good for low to medium batch production

Disadvantages

High porosity
Less mechanical strength
Rough detailing possible
Material limitations

Powder Bed Fusion for Polymers

The powder bed fusion technology layer by layer fuses the polymer powders thermally. Generally Nylon powder is used in the process. Selective Laser Sintering (SLS) and Multi Jet Fusion (MJF) are two derivatives of powder bed fusion technology for polymers.

Selective Laser Sintering (SLS)

SLS uses thermoplastic polymers in granular form. The laser selectively sinters the material layer by layer. This technology is good for small batch productions, gives high design freedom and is suitable for functional prototypes using polymers.

How does it work?

The build surface and the powder tank is heated just below the melting temperature of the polymer.
The sweeper blade coats a layer over the platform.
A CO2 laser scans and traces the complete cross section of the layer desired for the object.
The platform moves down one layer once the process is finished and continues until the part is completed.
The part is kept as it is in the unsintered powder to be cooled down. After that, the excess powder is cleaned using compressed air and can be reused.

Advantages

Isotropic mechanical properties
Ideal for functional prototypes
No support requirement
Good for small and medium batch production

Disadvantages

Long lead times
Not ideal for watertight application
Grainy and porous surface finish
Small holes and large flats cannot be printed

Multi Jet Fusion (MJF)

Developed by Hewlett and Packard, MJF is similar to SLS technology and has a difference in the way the powder is sintered. An ink having infrared light absorption properties is released where the material is to be fused. An infrared light source then passes over the surface to fuse the material together.

The MJF technology offers faster cooling times and greater recyclability of the material, which offers a great deal when it comes to larger quantities.

Powder Bed Fusion for Metals

The principle remains the same for Metal 3D printing using Powder Bed Fusion. Selective Laser Melting (SLM) and Direct Metal Laser Sintering (DMLS) are two derivatives of Powder Bed Fusion for Metals. Both technologies use granular metal powders and are also fused using a high power laser.

Selective Laser Melting (SLM)

The SLM process uses powder of materials having a single melting temperature to be fused together to completely melt the particles and form a solid metal part. Basically a single metal component.

Direct Metal Laser Sintering (DMLS)

The DMLS process uses a mixture of powders having multiple melting temperatures and are fused on a molecular level at higher temperatures.

The working process of both the techniques is similar.

How does it work?

The build chamber is filled up with inert gas and heated up to reduce the oxidation effect on the parts.
The bed is then coated with a layer of metal powder.
A high powered laser scans and fuses the entire desired area to make the part completely solid.
The platform is then lowered and another layer of metal powder is spread over the surface to be sintered. The process repeats itself until the whole part is built.

Advantages

Complex parts can be manufactured for critical applications
Topological, and dimensional optimization of parts is possible
Excellent mechanical properties

Disadvantages

High cost
Limited build size
DFM of designs for metal 3D printing needs to be done again

Other Notable 3D Printing Processes

Electron Beam Melting (EBM)

Electron Beam Melting process uses an electron beam to fuse metal powder placed in vacuum. The process is carried at around 1000oC. The powder is basically pre-alloyed as compared to a mixture in DMLS. It has superior build quality because of high energy density and the scanning method.

Ultrasonic Additive Manufacturing (UAM)

UAM can be defined as sheet lamination derivative. The metal foils are bonded using scrubbing with ultrasonic vibrations. The metal foils are not melted and thus this process is classified as a low temperature process.

Concrete and Clay 3D Printing

With the use of fundamentals of the FDM 3D printing, concrete or clay is laid down layer by layer. Recently a two storied house was built in europe. The clay 3D printing enables to produce very unique, unusual, and beautiful patterned products.