3D printing materials include plastics, ceramics, and composites. However, metal 3D printing or metal additive manufacturing (metal AM) perhaps offers the greatest promise for engineers in high-value industries like aerospace, automotive, energy, and industrial manufacturing.
Unlike thermoplastic or resin 3D printers, metal additive manufacturing systems are typically large, expensive, and used exclusively in industrial environments due to their rigorous material handling, operational, and post-processing requirements. However, they are capable of producing high-strength, geometrically complex parts from a range of materials, including titanium, steel, aluminum, and superalloys.
This article looks at how metal 3D printing works, exploring four principal metal 3D printing technologies in addition to key industrial applications, benefits and limitations, and future trends.
Metals can be 3D printed in different ways. All metal printing processes be considered industrial manufacturing technologies, though material extrusion is the technology most similar to plastic 3D printing and therefore the most accessible for SMEs and non-industrial users.
Powder bed fusion (PBF) is both the most common metal 3D printing technology and the most established: the first commercial PBF printer (the EOS EOSINT M160) was launched in 1994. The technology can be separated into two distinct subcategories.
Laser PBF includes well-known metal 3D printing technologies like direct metal laser sintering (DMLS) and Selective Laser Melting (SLM). Suppliers of DMLS systems include EOS and 3D Systems, while SLM is a proprietary technology owned by Nikon SLM Solutions.
During the laser PBF process, a high-precision laser melts particles of metal powder on a powder bed, moving from one 2D layer to the next to form a complete 3D part. It can be used to create small to medium-size parts with high material density and very high geometrical complexity.
Benefits of the technology include part strength, density, and complexity, as well as broad material compatibility. Limitations include high costs and post-processing requirements such as cutting the part from the bed with a bandsaw and removing support structures, which can create discrete surface imperfections.
Electron Beam Melting (EBM) uses an electron beam to fuse metal particles instead of a laser, making the process faster but less precise. It otherwise shares characteristics and advantages with laser PBF. Colibri Additive (formerly GE Additive) is the only supplier of EBM systems, which previously fell under the now-retired Arcam brand.
Like laser PBF, Directed Energy Deposition (DED) uses a laser to form metal parts. However, this process blows metal powder (or deposits metal wire) from a printhead, to which the laser is also mounted, instead of fusing particles on a bed of powder. The laser is focused onto a spot by a system of lenses, creating a melt pool where the powder is deposited. Overall, material properties of printed parts are similar to PBF.
One advantage of DED over PBF is that 3D printing can take place on top of an existing substrate. It can therefore be deployed for the repair of cast or machined metal parts. Some DED systems have a multi-axis setup to allow the printhead to access different areas of the substrate. Another advantage is part size, with some machines (those from Sciaky and DMG Mori, for example) offering very large build envelopes. Other manufacturers of DED systems include Trumpf, and Prodways.
Binder jetting is a form of metal 3D printing that uses a binding adhesive agent instead of a heat source to form metal parts. It has been popularized by companies like ExOne, Desktop Metal, and HP (Metal Jet). The binder jetting system spreads a layer of powder on the print bed, then selectively deposits the binder onto the powder from a printhead, joining the metal particles together. The printing process is fast, and many parts can be printed simultaneously.
Binder jetting produces “green” parts that must go through a debinding and sintering stage in a furnace to remove the adhesive material and reduce the porosity of the metal. This increases total process time and typically results in parts less dense than those made using the above techniques.
Like binder jetting, metal material extrusion uses a binder material to form metal powders. However, in this case the binder and metal powder is combined into an FFF-style filament prior to processing. A computer-controlled printhead extrudes the filament onto the print bed layer by layer, forming the green 3D part. Post-processing steps include washing and sintering to remove the polymer binder and create a fully metallic part.
One key benefit of metal extrusion is material handling. Bound filaments are safer to store and carry than loose powders, which can lead to reduced facility and labor costs. Machines from disruptive companies like Desktop Metal and Markforged are also priced lower than powder-style machines.
Material jetting, a major 3D printing technology in plastic 3D printing, is rarely used for metal printing. However, Nano Particle Jetting technology from XJet uses an inkjet-like material jetting process to make metal parts, supporting two grades of stainless steel.
Other niche metal 3D printing technologies include high-speed processes like kinetic consolidation, ultrasonic consolidation, and friction consolidation.
Metal 3D printing is used to produce final parts for industrial applications, often at small-batch production scale. Some key applications can be found in the table below.
Compared to traditional metal manufacturing processes like casting, machining, and forging, metal 3D printing offers numerous advantages. These include:
The challenges and limitations of metal 3D printing include:
Metal 3D printing technologies continue to evolve. One of the biggest areas of focus in metal 3D printing is the development of post-processing solutions that facilitate seamless part production at scale. These developments are in line with Industry 4.0 trends and the overall digitization of manufacturing.
Automated and integrated solutions for material handling, support removal, debinding and sintering, part identification and sorting, and quality control are as important to the advancement of metal 3D printing as the manufacturing technology itself, as they enable faster and more cost-effective production cycles.
Elsewhere, material science drives some of the current and future trends in metal 3D printing. In recent years, copper 3D printing capabilities have increased across virtually all technological categories, enabling the production of high-value parts like heat exchangers. Development of new superalloys and printable refractory metals also represents an exciting opportunity for the industry.
Another emerging trend in metal 3D printing is increased accessibility for non-industrial users. Pioneers like Desktop Metal and Markforged have developed high-quality metal 3D printers that do not require extensive material handling or environmental control considerations. Their machine costs are also relatively low.
Most forms of metal 3D printing work by sintering or binding particles of metal powder to form a 2D layer, then proceeding to form subsequent layers that are themselves sintered or bound to each previous layer. Post-processing steps like heat treatment are then applied to finalize the part and impart its desired properties.
Metal 3D printing represents a major value-generating opportunity for industrial users, as it can significantly shorten cycle times, reduce supply chain complexity, and improve part performance.
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