Additive Manufacturing is a different way to create things. In this case, objects are formed by adding material while is converted from one state to another. This process is done “layer by layer” and this is what mainly define the Additive Manufacturing Concept.
The other 2 manufacturing techniques are Subtractive (CNC, turning or drilling) and Formative (Injection Molding, Casting or Stamping and Forging) which are more traditional ones than the additive technique.
3D Printers are more or less portable factories using Additive Manufacturing Technique for creating things. That´s why 3D printing and Additive Manufacturing are almost synonymous.
Different 3D Printer Technologies have been developed for many applications and each one has its own advantages and Disadvantages which worth to describe. Just remember the common factor in all Technologies: 3D Objects are created in a layer by layer fashion.
3D Printing Technologies
The Additive Manufacturing Process can be reached in different ways, implementing different methods for converting materials, using a variety of printing materials, etc. Many 3D Printers are available nowadays for all kind of applications.
Since the first 3D printer (SLA type, by the way) was created by 3D System on 1986, many types of 3D printers have born to meet Educational, Comercial and industrial requirements. DIY Cheaper 3D Printers have allowed every one be involved in the 3D printing world.
With a lot of types of 3D printers and new terms, a clear classification is necessary to understand how the mess is organized. ISO/ASTM 52900 is a good reference as all 3D printing technologies are well categorized there and will be our guidance for this classification.
Next, we list the main 3D Printing Technologies according to the ISO/ASTM 52900 standard:
- Material Extrusion (FFF or FDM)
- VAT Poymerization (SLA, DLP)
- Powder Bed Fusion (SLS, DMLS, SLM, EBM)
- Material Jetting (MJ, PJ, DOD)
- Binder Jetting (BJ)
- Direct Energy Deposition (LENS, LBMD)
- Sheet Lamination (LOM, UAM)
Let´s explore each one.
An Extrusion head is responsible for depositing, layer by layer, heated material over a printing bed following a pattern which corresponds to the 3D Object loaded in the Printer´s program.
FFF 3D Printers (also known as FDM 3D Printers) are Material Extrusion 3D Printers type. Spools of Polymer Filaments are the main printing material used with FFF 3D Printers.
Note: FFF stands for Fused Filament Fabrication and FDM stands for Fused Deposition Modeling.
The Filament Spool (or spools) is previously installed on the 3D printer. There are different types of filaments for multiple applications nowadays. Melting Temperature, color, strength, flexibility and diameter of the filament are the main features to take in account when selecting a 3D Filament.
A Nozzle is located in the print head and is previously heated in order to be able to melt the filament.
When the 3D printing work is started, a drive motor is in charge of pulling the filament and up to the print head where is then pushed through the heated nozzle.
Nozzle´s temperature depends on the type of filament to be melted. Different types of filament are available to meet requirements for the wide variety of types of filaments.
Nozzle´s diameter is another parameter to consider as filament diameter can be different depending of the type you want to use in your project.
Special Filaments (Nylon, PETG, etc) might require special nozzle, so you should consider it as part os your selection checklist.
As the filament is being melted by the nozzle, the extrusion head moves through a predetermined path to form the layers over the bed.
Movement of the print head can be different depending on the type of FFF 3D Printer you are using: Cartesian or Delta Printer. Cartesian 3D Printers moves the print head in the X, Y and Z axis over the build platform while Delta 3D printers follows a parallelogram movement.
The path followed by the print head is programmed in the 3D Printer´s firmware in that contains the 3D model converted in lines of gcode the 3D machine can understand.
Once the first layer is dispensed on the bed, the second layer´s construction is begun. Support Material may be needed for many non-simple 3D designs, so a good slicer program and 3D printer operator is recommended when printing medium-to-high complex 3D objects.
The printing bed Characteristics might be different depending on the meting temperature of filament used. ABS filament melts at a higher temperature than PLA filament, for example.
Bed´s working temperature is an important factor as removal of the printed object can be a challenge if bed is not the appropriate for the filament selected.
After the printing work is finished, the 3D piece can be removed from the build platform. A cooling time may be necessary before or after taking the printing object out of the printer.
Depending on the final appearance requirement for the printed part, a post processing work may be needed.
A light source converts liquid photosensitive resin into a solid object layer by layer following a point-wise fashion pattern which represents the 3D Model.
VAT Polymerization 3D Printers are called Resin 3D Printers and there are mainly three types available in the market:
- SLA 3D Printer
- DLP 3D Printer
- LCD 3D Printer
Note: SLA stands for StereoLithogrAphy, DLP stands for Direct Light Procesing and LCD stands for Liquid Crystal Display.
For all types of 3D printers, polymer resin is used as printed material in a liquid form. This resins are sold in UV Resistant bottles.
The resin is deposited in a VAT. A variety of resins are available for many applications. Selection of a resin type is an important step and is based upon its application, work temperature and the resin printer Technology.
Some 3D resins are only suitable to work with a specific type of printer: SLA, DLP or LCD. All brands sell resins for their printers which ensures an adequate creation of the object; specially when forming the first layer.
With the liquid resin already allocated in the tank (VAT), the 3D printing work can be started. The build platform moves in vertical to accomplish one of the two most common types of resin 3D printers designs: Bottom-Up or Top-Down.
In both cases, the build platform ingress the VAT of resin.
In Bottom-Up resin 3D Printers build platform is located at the bottom of VAT. A minimal separation between the platform surface and the tank´s floor is left with enough thickness to create the first layer.
The build platform moves up when every layer is created.
In Top-Down 3D Printers, the build platform is initially located almost out of the resin liquid. Only, a minimal between the upper part of the resin and the platform´s surface if kept with enough thickness for creation of the first layer.
The build platform moves down as layers are being solidified.
The light, located out of the tank, is in charge of curing the resin until each layer is solidified. Light source is the main difference between the 3 types of resin printers and determines its printing speed.
SLA 3D Printers use a laser beam guided with mirrors (galvos) to cure the resin layer by layer following a series of points and lines.
DLP 3D Printers use a Digital Light Projector Screen to flash images on the resin layer by layer using a Voxel approach. A DMD is required to control where the light is projected and generate the light pattern on the build surface.
Note: DMD stands for Digital Micromirror Device
LCD 3D Printers work similar to DLP 3D printers but using LEDs instead of projectors as the light source.
In any case, light source creates the 3D object based in the 3D model loaded in the 3D Printer´s firmware.
As with FFF 3D Printers, slicing is part of the process but is less complicated as resin 3D printers are closed in configuration and you can only set minimal parameters.
Supports may be needed and have to be considered during the slicing stage.
Powder Bed Fusion
Powder is heated up to almost its melting point using a CO2 laser beam which sinters each powder layer getting it fused together.
SLS, DMLS, SLM and EBM 3D printers lies on this technology. Differences between them relies on the type of material used and the heating source.
Note: SLS stands for Selective Laser Sintering, DMLS stands for Direct Metal Laser Sintering, SLM stands for Selective Laser Melting and EBM stands for Electron Beam Melting.
SLS 3D Printers use Polymer Powder while DLMS, SLM and EBM 3D Printers use metal powder as printing material.
When the printing work is started, the powder is extracted from the powder container and scattered over the build platform using a recoater blade. Every layer of powder is 0.1 mm of thickness.
The laser, located over the build platform, scans and sinters the powder layer following the predefined path according to the 3D model previously loaded in the printer´s firmware.
Selection of the right powder should be carefully done as it impacts the final strength and surface of the part.
Thermoplastic Polymer Polyamide (PA) is the most common type of powder used for SLS printers and Metal powders are used with DLMS, SLM and EBM printers.
The type of thermal source will be different for every type of Powder Bed Fusion Printer.
SLS and SLM use a laser scan with heaters while DLMS heats up the powder such as that can be fused together at a molecular level. EBM printers use an electron beam to induce fusion between the particles.
After each layer is finished, the build platform moves down to the construction of the next layer. Vertical movement corresponds to the layer thickness.
The recoater blade drags the new bin of powder over the last finished layer as the melting/fusion process for the next layer can continue.
When the printing work is finished, the 3D printed piece can be removed from the build platform. A cooling time have to be waited before the part can be removed from the build platform.
Printed objects are made with overflow material serving as supports. Removal of support powder is an important and delicate process that should be done by professionals to avoid damages on the piece.
Compress air blowing is the technique often used to remove the surplus powder from accurate zones of the object.
As always, post processing might be required (painting or polishing) depending on the project´s requirements.
With a Material Jetting 3D Printer, resin is dispensed over a building platform in form of droplets. After droplets are laid over the platform an UV light (installed in the same print head) is in charge of curing those droplets on the fly.
Material Jetting and DOD Printers are the two types of 3D Machines that lies on this technology.
Note: DOD stands for Drop on Demand.
Material Jetting printers use a two-parts print head which enables to do the jetting and curing of the resin at the same time. One part of the print head jets the droplets of resin while the second part cures the layer with UV light.
2 types of resins can be used together letting the printing of multi-material parts.
Resins for material Jetting Printers use to be proprietary. Viscosity of resin is an important factor to take in account as the very small size of the droplet holes have to be considered.
Print head moves through the programmed path over the build platform to create the piece layer by layer. The UV light is an integral part of the print head and is activated to solidify the layer after droplets are dispensed over the bed.
Deposition and curing of material is done in a line-wise fashion (like a scan), letting material being dispensed in a greater area per time improving build speed and performance.
When 2 types of resins are used, one material can be used for the build part and the other can be used for supports. Each material is deposited once at a time.
Once a layer is done, the build platform moves down the enough height to let the construction of the next layer.
After completion of the printing work, removal of the part, removal if supports and applying of color are easy tasks to do due to the high accuracy of the 3D Printer.
DOD 3D Printers have two print heads, instead of one used by material jetting printers. Moreover, DOD Printers follows a point-wise fashion for printing the objects.
Wax material are typically used with a DOD 3D Printer.