In this post I would like to give a brief introduction into 3D printing techniques and materials. As a relative newcomer to 3D printing myself, this is a good exercise for me to become more familiar with the current 3D printing landscape.
Each application is unique, so it makes sense to throughly understand what options are available to you when printing your 3D objects.
This survey is by no means exhaustive, it’s a just a start to help any novice to quickly get up to speed on the ever-evolving advancements of 3D printing tech. Since this topic is fairly large in scope, I will break this post into two parts as to not overwhelm you with too much information - part one follows:
As of this writing there are over 90 material options available in 3D printing. Most 3D print applications center around either plastic or metal materials. Ceramics and advanced composites are used in more specialized, commercial contexts. A good way to approach this complex topic is to categorize these materials by specific 3D printing technologies. In general there are roughly ten different types 3D printing processes. In this post we will focus on four of the most common and by extension will cover the more popular materials employed by these processes.
SLA - Stereolithography
Stereolithography or SLA is the oldest 3D printing technology available today. It was invented in 1984 by Chuck Hull (this point can be debated - there are claims of SLA emerging from Japan as well as France).
Stereolithography is an additive manufacturing process meaning that a material is progressively added as opposed to being removed like in a subtractive process such as CNC machining etc.
SLA in essence involves a tank of liquid photo-polymerizing resin, an ultra-violet laser and a build plate. The laser draws a cross section of the object via data from a CAD file on the bottom surface of the tank. Once the UV laser makes contact with the resin a chemical reaction takes place curing or solidifying the resin layer. After a layer is cured, it binds itself to the previous printed layer. The build plate moves up slightly and the laser draws the next cross section until the entire 3D form emerges on the build plate.
The liquid resins used for SLA printing are thermoset polymers. A wide variety of resins are commercially available and are usually selected based on their application area which includes general prototyping, engineering, dental/medical and castable resins. The following resins map to the preceding application areas:
• Standard Resin - features smooth finish, high detail, tends to be brittle, used for general prototyping. Example: Formlabs Draft Resin
• Clear Resin - same as standard resin but can be post-processed to near optical transparency. Example: Formlabs Clear Resin
• Engineering Resin - high stiffness and resistance to loads. Simulates injection molded parts. Example: Accura Xtreme White 200 (ABS-like)
• Dental/Medical Resins - high biocompatibility, high precision, smooth finish. Example: BioMed Amber Resin
• Castable Resin - used for creating mold patterns (jewelry), high detail, low ash percentage after burnout. Example: Formlabs Castable Wax 40 Resin
3D printing brands that focus on the SLA process are: Carbon, Formlabs, 3D Systems, Prusa (SL1), XYZ Printing, and FlashForge. They are many more and it seems like the list keeps growing by the day as this process is continually made more available at lower price points.
FDM - Fused Deposition Modeling
I started with SLA because it is the oldest available 3D printing technology to date. That being said, Fused Deposition Modeling (FDM) or Fused Filament Fabrication (FFF) is the most widely used.
This additive manufacturing process is the least complex as it basically represents a material extrusion. A 3D print is built by selectively depositing melted material in a pre-determined path layer by layer. The materials used are thermoplastic polymers and come in a filament form (i.e. coiled wire).
In the FDM process, the filament is loaded into the printer. The extrusion head or nozzle is the point where the heated filament is passed thru and deposited to create a 3D print. The nozzle is attached to a 3-axis mechanism that allows it to be positioned in the X,Y and Z directions. The material is deposited in thin layers via data from a CAD file. It quickly cools, solidifies and via continuous passes a 3D form object is realized.
In general, FDM print quality is not as good when compared to SLA. SLA machines print at a higher resolution or Z-Axis layer height. SLA printers range from 25 to 300 microns (thousandth of a millimeter, i.e .025mm to .300mm). FDM printers typically print in the Z-axis at 100 to 300 microns (.100 to .300mm).
Another key difference between FDM and SLA is that FDM printers produce a mechanical bond between layers. SLA 3D printers create chemical bonds by cross-linking photopolymers across layers. These bonds provide high lateral strength, resulting in isotropic parts, meaning that the strength of the parts does not change with orientation.
As with SLA materials, thermoplastic polymers come in a wide range of options to suit a specific need or application. What follows is an overview of materials used in FDM printing.
For general prototyping or everyday work - ABS and PLA are the most common materials. ABS (Acrylonitrile Butadiene Styrene) has good strength and temperature resistance and is more durable than PLA. PLA (Polyactic Acid) is very easy to print with, captures high detail but is brittle and has low impact strength.
For engineering applications Nylon PA12 and PETG are typically used. PA12 (Nylon Polymide) offers excellent visual quality, high detail, has excellent wear and chemical resistance but has poor humidity resistance. PETG (Polyethylene Terephthalate Glycol) is food safe, strong and is very easy to print with.
In very technical situations where materials need to perform at a high degree PEEK and PEI are the standouts here. PEEK (Polyether Ether Ketone) is a high performance material with outstanding chemical resistance, excellent mechanical strength across a broad temperature range and good dimensional stability.
PEI (Polyetherimide) is an engineered thermoplastic with an excellent strength to weight ratio and strong fire/chemical resistance. Both of these materials are very expensive to print with and are only used in the most demanding commercial applications.
Popular FDM printing based brands include: Makerbot, Prusa, Elegoo, MarkForged (metals, composites), Creality, Monoprice, Ultimaker and Raise3D. As mentioned FDM printing is the most popular 3D printing tech used today primarily for it's ease of use and accessible price points. You can pick up a decent FDM printer online anywhere from $250 to $400 USD.
In part two of this post we will explore a few additional 3D printing methods and materials employed today - see you there.
Thank you, until next time! - Andreu O.