Materials for AM

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Note: Much of the following was excerpted from Wohlers Report 2022.

When additive manufacturing (AM) was introduced, the number of materials was limited. Some may argue that this is still the case. As the industry has advanced, the availability of materials has expanded to include many polymers, composites, metals, ceramics, and biomaterials. According to research for Wohlers Report 2022, polymers remain the most popular, followed by metals.

Polymers

Many polymers are available for AM, yet the offerings are still small compared to conventional processes (i.e., formative and subtractive manufacturing). Materials are typically selected by their properties, such as tensile strength, rigidity, biocompatibility, glass transition temperature, color, and transparency. Additional properties include moisture resistance, sterilization, fire retardancy, and smoke and toxicity emissions. Materials range from hard and stiff to soft, rubber-like elastomers.

Polymers are classified into two groups based on their behavior at high temperatures. Thermoplastics can be repeatedly melted, cooled, and solidified. They retain their properties, although some degradation can occur, particularly with repeated high-temperature exposure. Thermoset polymers are permanently cured once they are polymerized. After polymerization, thermosets do not melt like a thermoplastic would at high temperatures. Photopolymers, like those used in vat photopolymerization (VPP) and material jetting (MJT), are liquid thermoset resins that are polymerized when exposed to certain wavelengths of light.

Polymer part being printed using material extrusion, courtesy of BCN3D

Commonly used polymers include polycarbonate, polyamides (PA), and nylon, just to name a few. A few companies have developed 3D printers that extrude silicone rubber. The material is printed as a liquid and cures before the next layer is deposited. Other materials have been certified as biocompatible or food-grade. Some companies offer exotic filaments such as clay-filled and bone-like materials. Metal-filled PLA materials also exist, as do filaments composed of metal powder with PLA used as the binder.

Composites consist of two or more materials. One of the most common base materials for polymers is PA. Composite reinforcement materials include glass, aluminum, and carbon fibers, as well as advanced fibers such as Kevlar.

Metals

The range of metals and metal alloys available for AM continues to grow.

Choices include, but are not limited to, tool steels, stainless steels, titanium, aluminum, copper, and nickel-based alloys. Specialty metals for AM include gold, silver, platinum, palladium, tantalum, tungsten, and niobium. Many of these materials have been available for some time, yet their use for final part production has been limited. This is mainly due to the qualification and certification requirements in aerospace, healthcare, energy, and other sectors.

Most metal AM processes involve rapid melting and solidification of materials, which can lead to cracking in alloys not typically considered weldable. Metal AM processes include powder bed fusion (PBF), binder jetting (BJT), sheet lamination (SHL), directed energy deposition (DED), and more recently material extrusion (MEX).

Most metal AM parts require some form of post-processing, such as heat treatment or machining, to achieve desirable properties. Both BJT and MEX require a debinding and sintering step to achieve near-full density parts.

Copper parts made using a DED process, courtesy of xBeam

Ceramics and other materials

Several companies offer ceramics, blends, and other specialty materials. They can include photopolymers filled with ceramic particles. To produce fully or near fully dense parts, they are placed in a furnace, which burns out the binder and sinters the ceramic. BJT systems can also produce glass and ceramic parts.

Biocompatible materials are of growing interest in AM. Some metals, such as titanium alloy Ti-6Al-4V, can be implanted into human patients. The polymers PEEK and PEKK are also used to produce medical implants.

Additional materials that can be used in 3D printing include graphene, paper, concrete, foam, and food products such as chocolate.

 

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