Each technology has its suitable materials. Not all materials will work for every project, so it is important to carefully select the material and process before start the manufature (sometimes even before the design process). Starting from this point, what materials should you use, and which technology fits better your project?
All the processes and materials have a common result: Starting from different shapes (filament, powder, liquid..) they finally become solid pieces.
For a very short and simplist summary, we could say that thermoplastics filaments are used for FDM (Fused Deposition Modeling), thermosets resins for SLA (Stereolitography), and nylon, polypropilene and other powders for SLS (Selective Laser Sintering). Stainless steel powder is used in DMLS (Direct Metal Laser Sintering) and BJ (Binder Jetting) allow us to use sandstone in full-color or ceramic for printing.
FDM (Fused Deposition Modeling)
I am not going to extensively explain again what is FDM about and how does it works, you can read more about It on “Interested on FDM 3D printing?” post. However, let’s see the main materials of use as FDM also offers a wide range of possibilities.
- PLA: Most used printing filament. Cheap, biodegradable and easy to use. Recommended for prototypes or ornamental products. Not suitable for mechanical nor high temperature applications. It is also not easy to be glued.
- ABS: Second most used printing filament. It is also economic, but not biodegradable. Less used than PLA due to its printing needs, as it requires heated bed and an enclosure is recommended for avoiding warping or layer problems due to shrinkage (usually happens by too fast cooling). It is mechanically suitable for final part prints and most home printers already incluse heated bed, so its use is being popularized. It can be post-processed with acetone for a glossy finish,
- PETG: Its low shrinkage, no warping, high impact and heat resistance compared to PLA and ABS is making that PETG becomes more and more popular. It can be used for parts that are in contact with foor or liquids. Need to carefully check printing parameters.
- TPU: Thermoplastic Elastomers are used for creating rubber-like parts. It has excellent elongation, so it is suitable for tubes, grips, sealing gaskets and orthopedic soles. Can be easily flexed and compressed.
- PC: Polycarbonate is a very strong biocompatible thermoplastic. It is a good option for surgical planning models, tools and other medical devices and food-packaging applications because It can be sterilized.
- Nylon: High impact resistance. It is used for industrial printing final parts with really good mechanical performing. High durability but It is very sensible to moisture and it is offen affected by warping. To print Nylon succesfully is very hard, layer addhesion can be a problem. It is commonly mixed with fibers like Kevlar, Carbon or Fiberglass to improve its strength, flexibility or heat resistence.
- PEI: Polyetherimide offers outstanding strength and thermal stablity. In addition It is biocompatible, so its main uses include medical and food production industries and automotive applications. It is a pioneering thermoplastic able even to be used under steam applications. By this reasion, PEI is used for exemple for autoclave-sterilizable medical devices.
- PEEK: Polyether ether ketone is used for engineering applications.
It offers excellent mechanical and chemical resistance properties that are retained to high temperatures. Extensively used in aerospace, automotive industry and cranial implants
SLA is a technology that uses UV light to photopolymerize resins layer by layer. Resins previously have short carbon chains into their composition, but being exposed to UV light, they merge (photopolymerization) forming strong and long cross-linked chains that will make the process irreversible.
Parts need to be post processed under UV light to finish its polymerization . This exposure closes the structural chains and improve the mechanical properties of the printed part.
What materials are used in SLA?
As can be guessed, irreversible cross-linked chains give us a clue that we are talking about thermosetting plastics. As opposite as it happen with termoplastics like ABS or PLA in FDM, when the resin get solidified, the process can not be reversed. Following are some example of resins that are used for SLA printing:
- Tough resin: Similar to ABS FDM filament, but with better mechanical properties. It balances high impact strength with compliance. Ideal for parts that need to return to their starting shape after releasing force applied. Good for prototyping strong functional parts.
- High temperature resin: Works well for higher temperature processes such as casting or thermoforming. Can be exposed to temperatures up to 230ºC at 0.45 MPa. High detailed parts with specific uses can be printed with it.
- Castable resin: Used for direct investment casting, giving direct way from 3D design to final parts with low tool investment in jewellery.
- Dental SG resin (Class 1 biocompatible): Used for dental products based on patient’s personalized design for treatments like orthodontic. It can be also used for pilot drill guides.
- Flexible resin: It can simulate approx 80A durometer rubber mainly used for parts that need to bend and compress like ergonomic parts.
- Ceramic resin: Feels like traditional ceramics. After fire, silica-filled Ceramic Resin becomes a pure ceramic part suitable for food use, microwave, freezer…
SLS (Selective Laser Sintering)
It belongs to the Powder Bed Fusion family and, as other printers from this family, a laser selectively sinters the polymer powder placed layer by layer on the bed, fusing it together usng a CO₂ laser that melts the raw material.
This process offer a really high degree of freedom for design because the unpolymerized powder works as support structure. It is commonly used for printing tough and geometrically complex components. Thermoplastic powders are mainly used and main features of SLS printed paarts are high mechanical properties and dimensional accuracy.
As it does not use support structures, complex features (even internals) can be done without adding post-processing time.
Some of used materials are:
- Flex TPE: A combination of TPE and elastomeric polyurethane, for elastic prototypes with about Shore 40A
- Nylon 11 FR: Excellent material with fire retardancy. It passes FAR 25.853 12 Second and 30 Second Burn tests. Fine resolution and high detail.
- Nylon 12 GF: Glass-Filled Nylon 12 with higher tensile modulus. Excellent material stiffness, high dimensional stability and resistence to temperature. Also available carbon-filled (Nylon 12 CF). Fine resolution and high detail.
- PP: Excellent elongation resistence. Polypropilene has no warpage and good chemical resistance. Its main advantage is that parts can be welded.
- PS: Polystyrene is used in most standard foundry processes.
There are many more materials for each process (and even more processes). For now the list ends here, but I will be completing it as time passes, looking for interesting and new materials.