What are the materials used in AM?
The variety of materials available for 3D printing as significantly expanded since the advent of this technology. Materials are provided in various states, including powder, filament, pellets, granules, resin, etc. Specific materials are now able to address specific applications (e.g., dental applications) with material properties that more appropriately suit the application. However, there are currently numerous materials from the wide range of 3D printer manufacturers to cover nearly any application. Below we present characteristics of the most general types of materials being used in AM today.
Polymers and Plastics
Nylon (Polyamide) is generally used in a powder state with the sintering procedure or in a filament state with the FDM procedure. It is a solid, flexible and strong plastic material that has shown to be reliable for 3D printing. It is naturally white but can be colored in pre- or post-printing processes. This material can likewise be combined (in powder format) with powdered aluminum to create another common 3D printing material for sintering — Alumide. Today many composite materials are possible by mixing polymers with other structural materials. The possibility to change the alloy composition on the fly is an incredible asset and unique material properties can result of these mixes. LayWood is an example of this. It is a specially created 3D printing material for entry level extrusion 3D printers. It comes in filament shape and is a wood/polymer composite (likewise alluded to as WPC). The aerospace industry can also make use of these unique properties; providing, for instance, differential heat dissipation along a structure or different densities and strengths according to specifics needs and not due to material restrictions.
ABS is another common plastic used for 3D printing. It is generally used with FDM 3D printers in a filament state. It is an especially solid plastic and it comes in a variety of colors. ABS can be purchased in filament state from various non-propreitary sources, which is another factor to it being so popular.
PLA is a bio-degradable plastic material that has picked up attraction with 3D printing for its sustainable and ecofriendly characteristics. It can be used in resin form for DLP/SL in addition to filament for the FDM procedure. It is offered in an assortment of colors, including transparent, which has turned out to be a valuable feature for specific uses of 3D printing. However, PLA is not as sturdy or as flexible as ABS.
ULTEM 9085 is a polymer filament (also in resin form) that is graded to be used in aerospace applications. Stratasys has high level 3D printing machines that can produce industrial ready parts with ULTEM, but also several entry and mid-level 3D printers are now offering different level of support for ULTEM 9085 (requires higher temperature and precision control).
Recently, new polymer resins have started to offer acceptable engineering material properties. This means that the parts can not only be used as prototypes, but also as functional parts. One example is the company FormLabs. In 2016, Formlabs presented a new engineering resin that can support most of the same ASTM standard strength and thermal tests of the ULTEM 895 plastics.
Figure 1: Typical PLA/ABS filament rolls for FDM systems.
Since polymers are among the most common materials used for FDM systems (from low to industrial level machines), we present a table that summarizes the most common FDM filaments with their principal characteristics (click for zoom image):
Figure 2: Common filament rolls for FDM systems.
A growing number of metals and metal composites are used for industrial level 3D printing. Two of the most well-known are aluminum and cobalt derivatives. Also, Stainless Steel is one of the strongest and more generally utilized metals for 3D printing and comes in powder shape for sintering, melting, and EBM processes. It is normally silver, however can be plated with different materials to give a gold or bronze effect. In the last couple of years Gold and Silver have been added to the range of metal materials that can be 3D printed directly, with evident applications over the jewelry segment. These are both exceptionally sturdy materials and are processed from their powder shape. Titanium is one of the strongest conceivable metal materials and has been used for 3D printing in industrial applications for quite a while. Provided in powder shape, it can be used for the sintering, melting and EBM process.
Figure 3: Metallic powder for EBM systems.
Ceramics are new in terms of materials that can be used for 3D printing with different levels of success. One particular thing to notice with these materials is that, post printing, the ceramic parts need to go through the same type of processes as any ceramic part will when using traditional methods -- in general firing and glazing. The alternative is used in PBF process or as composite filament in FDM.
Figure 4: Ceramic powder for PBF systems.
Metal and Paper sheets
Standard A4 copier paper and different metal sheets are additive manufacturing materials used by LOM and SDL processed provided by different companies (ceramics sheets are also used with LOM technologies). The paper material has many disadvantages, and perhaps the main one is that the part could act as no more than a prototype. However, the main key is particularly on an effortlessly reachable, practical material supply, that can be purchased locally. 3D printed models made with paper are safe, environmentally friendly, easily recyclable and require no post-processing. Paper 3D printers can be found on the low range of prices for these machines and they can be an excellent educational tool. The process is analogous with LOM fabrication where glue sticks together sheets of paper that are cut layer by layer through a cutter or laser.
Figure 5: Paper sheets for LOM systems.
Metallic sheets are use in LOM process and they usually get together by a Ultrasonic Consolidation (UC) process in which a mix of pressure and vibration produce a “cold soldering” between the sheets. It’s usually a hybrid system since it is mixed with a subtractive trimming process along the layers. Ceramic sheets in LOM process are less common but used in some specific applications.
Figure 6: Metal sheets in LOM systems with Ultrasonic Consolidation.
There is an enormous amount of research being directed into the potential of 3D printing bio materials for medical (and other) applications. Living tissue is being researched at various laboratories with the purpose of printing human organs for transplant, and also external tissues for substitution of body parts. Other research around this is centered on creating food.
Figure 7: Bio Material deposition systems.
Finally, a company that has a unique (proprietary) material offering, Stratasys, with its digital materials for the Objet Connex 3D printing platform. This means that standard Objet 3D printing materials can be combined during the printing process in various and specified concentrations to form new materials with the required properties. Up to 140 different Digital Materials can be realized from combining the existing primary materials in different ways.
Figure 8: Stratasys unique Multi-material jetting system.
Figure 9 presents a list of the most common materials used in AM with their main characteristics:
Figure 9: Most common materials used in AM with their main characteristics.
As we know, material in additive processes function by gradually creating or adding material layer by layer. The available materials in AM are constantly growing, a more complete list will include:
- Laminated fiber composite parts,
- Biological cells,
- Fiber reinforced plastic components,
- Metal powders and composites,
- Plastic powders,
- CERMETs or metal matrix ceramic composites.
Photopolymers are materials that can be transformed from liquids to solid products (Hausman and Horne, 2014) and stereolithography method is generally employed in this process. Polymer matrix ceramic or metal composites can be produced by 3D printing, SLS of polymer coated metal or ceramic powder, stereo-lithography, or fused deposition modeling. When it comes to metal 3D printing, aerospace appears to be the leading industry (Petrick & Simpson, 2013). Metallic parts produced with 3D printing frequently require additional finishing and post-processing steps to achieve specified tolerances (Petrick & Simpson, 2013). Even though it has been a challenge to use metal in AM for a long time, several distinctive methods, such as laser melting (LM), ultrasonic consolidation, and laser or electron beam melting (EB), have been implemented in AM in recent years (Horn and Harrysson 2012). Some types of filament use common painter's tape to stabilize the first layer of the product and the others implement materials like heat-resistant polyimide Kapton tape DuPont developed for NASA (Hausman and Horne, 2014).
Lyons reports that the polyaryletherketone (PAEK) based materials have the lowest risk for aerospace applications, considering very good flammability and chemical resistance, low moisture absorption, good mechanical performance, good resistance to creep and fatigue, compatibility with several methods of sterilization, and numerous material grades and supplier to choose from. Raw materials for SLS are determined from commercial off-the-shelf grades of PAEKs. The other alternative material for use in SLS is the polyamide family of materials. Lyons presents a comparative table about the thermal properties of polyamides and PAEK materials as given in Figure 10. Hausman and Horne express that the aerospace industry mostly uses metals such as titanium, materials that can withstand very high temperatures, or other materials providing good strength-to-weight ratio.
Figure 10: Comparison of Thermal properties of Polyamides and PAEK Family Materials
Let's review some of the materials and the technologies that use them: