Additive Manufacturing Materials Information
Many materials can be used for additive manufacturing and 3D printing and new ones are still being developed. Depending on the manufacturing machine, different materials in different form factors are used.
There are many metals that are used in producing an additive manufactured part. They include:
- iron based sintered powder metal
- stainless steel
- bronze and nickel
Metal additive manufacturing, or MAM, often uses a process that starts with a digital model and produces a part layer by layer activating and solidifying a metal powder until a “green” component is ready for sintering, which renders the part usable as a working piece. Metal additive manufacturing processes that use a layering technique include laser sintering (LM/SLS/SLFS), electron beam melting (EBM), fused deposition modeling (FDM)/extrusion, laser powder forming (LPF), and selective inkjet binding (SIB).
Metal powders are produced using one of several processes. Metal powders can vary widely in size, but also in shape (spherical to irregular), depending on these processes. Water atomization is the most prevalent metal powder production methodology. It is also the most economical. High pressure water impacts a molten metal stream and small particles that are created have a rapid cooling rate. As a result, powder particles are tough and irregular in shape. These irregular shapes are less desirable for additive manufacturing. Water atomization can be tweaked to produce more spherical powders and at a higher cost. However, under certain conditions, it is possible to produce spherical powders with a particle size distribution optimized for additive manufacturing.
Gas atomization is preferred as a production method for MAM bound metal powders. Here, the feedstock is melted and the molten mixture is forced through a nozzle. High-velocity gas impinges into the flowing molten metal and reduces it to fine droplets. Spheres form as the metal droplets fall to the bottom of an atomization tower. Other lesser used metal powder techniques include plasma atomization, electrode induction atomization, and centrifugal atomization
Thermoplastics, carbon fiber, and other composites are also used in additive manufacturing. FDM filament is made of various thermoplastics. These are melted in the nozzle and used to manufacture parts. Plastics have different properties that need to be chosen based on the machine capability and the desired properties of the finished part.
ABS is one of the most common plastics for AM. It has good strength and heat resistance and many printers are capable of printing with it. It is a plastic that is suitable as a finished product as well as for prototyping. It requires a heated bed for printing and has a tendency to curl as it cools making it a little more difficult to print with.
PLA is a very common plastic to print with due to its ease of use and low temperature requirements. It has good strength but is not very flexible, making it somewhat brittle. It also has poor heat resistance and can melt in a hot environment like a hot car. It is a great material for prototyping, but not that good as a finished product.
PETG offers many of the benefits of ABS such as high temperatures but with the ease of printing of PLA. It also offers reasonable strength and has a lot of flexibility making it stronger for some uses.
Polyamide (nylon) is one of the stronger materials used in the AM process. It can be difficult to print with due to its temperature requirements, but can be printed in many FDM printers with minor modifications to the hot end nozzle.
ULTEM™ is an amorphous thermoplastic polyetherimide (PEI) resin. This is currently one of the strongest materials available for FDM printing, but is difficult to print with due to its temperature requirements. Most printers are not capable of utilizing this material unless they have been designed for it. In addition to producing strong finished parts, they also have high thermal and chemical resistance.
Flexible filaments are filaments used in FDM printers that allow for flexibility in a finished part. Flexible filaments are most often made from thermoplastic polyurethane (TPU). They allow you to make things like wrist bands and phone cases or other flexible shapes like custom ink stamps. Many printers may require slight modification to successfully print with flexible materials.
Mold making filament is typically designed to work like wax in a lost wax casting process. The finished part is designed to melt out of a cavity that has been cast around the part so that a negative of the part can be obtained.
Support materials are materials like polyvinyl alcohol (PVA), which is water soluble and is commonly used to support a part during printing. Once the part is done, the part can be submerged in water and the PVA support will dissolve.
Other filaments exist such as those filled with metal or carbon fibers as well as specialty filaments that glow in the dark or change colors upon UV exposure.
Stereolithography and polymer jetting are processes that use a liquid resin that hardens when it is exposed to UV and visible light. In stereolithography type printing, the part is grown by exposing each layer of resin to light while lifting the part out of the resin or otherwise shifting the layer being worked on. This method relies on optical components such as a DLP projector or lasers to cure resins in specific shapes.
In polymer jetting (Polyjet), a printing head sprays out small amounts of liquid resin to form a new layer, which is then cured with UV lights. This method is similar to a 2-D ink jet printer that allows it to combine multiple resins in a single print.
Light and radiation cured resin (UV, visible, and other) is a liquid resin that is cured with energy typically in the form of UV light to become a plastic object. Resins are designed to simulate most material properties available with other printing methods. Curable resin allows for parts of all colors, shapes, and densities as well as flexible parts and composites. Resin can also be used to create molds for casting parts directly or wax-like resin for use in casting. Most recently, a resin that allows parts to be made out of glass was developed.
Selective laser sintering (SLS) is a method of manufacturing that uses a laser to heat a power material to bond the power particles together. Layers of powder are added and bonded until the part is finished. Direct metal laser sintering (DMLS) is essentially the same process as SLS except that it is done with metal instead of plastic. SLS does not require support materials as the powder acts as a support during printing but does require an exit hole for the power to be removed after.
Powdered plastics are similar to many of the FDM filament in a powder form, any thermoplastic can potentially be used with an SLS machine.
Polyamide (nylon) is one of the most common plastics used for SLS since it provides good strength and works well with the machines. Nylon powder is often filled with other particles such as glass or aluminum, which can increase the temperature resistance or strength of a part.
Ceramic and glass can also be used with the SLS process. The same method is used to bond the particles together. In the case of glass, parts are not transparent but instead have an opaque look and do not have the same strength as transparent glass. Ceramics can sometimes be used to directly create molds for metal casting.
Wire fed metal printing is another method for 3D printing that has, for the most part, only been done experimentally but could become more prominent in the future. This method could be similar to the FDM type approach but with metal. Little information is available on this method and the materials that would be used. Some experiments have used a process and material similar to MIG welding.
One of the older and currently less used methods of additive manufacturing works by laminating layers of materials. In this process, the materials used can be adhesive coated paper, plastic, or metal that are glued together and cut to shape.
With the right equipment, many other materials are also usable with the additive manufacturing process such as carbon fiber, concrete, and clay.