☞ This is the 13648 article published by Metal Processing (mw1950pub)

Editor’s Note

Metal 3D printing is considered the pinnacle of all 3D printing. When it comes to strength and durability, nothing compares to metal. The earliest patent for metal 3D printing was DMLS (Direct Metal Laser Sintering), obtained by Germany’s EOS in the 1990s. Since then, metal 3D printing has gradually developed many types of printing processes. Today, each metal 3D printer typically uses one of the following four types of processes: powder bed fusion, binder jetting, direct energy deposition, and material extrusion.

△ Metal 3D PrintingMetal Powder Bed FusionCommon Processes: DMLS (Direct Metal Laser Sintering), SLM (Selective Laser Melting), and EBM (Electron Beam Melting).Description: Metal parts produced using PBF melting technology can reduce residual stress and internal defects, making them ideal for demanding applications in the Aerospace and Automotive industries.

• Direct Metal Laser Sintering (DMLS): Can be used to build objects from almost any metal alloy. DMLS spreads a very thin layer of metal powder on the surface to be printed. A laser slowly and steadily passes through the surface to sinter this powder, fusing the metal particles together even without being heated to a fully molten state. Additional layers of powder are then applied and sintered, thus “printing” one cross-section of the object at a time. Once printing is complete, the object cools slowly, and excess powder can be reclaimed and reused from the build chamber. The main advantage of DMLS is that the objects produced have no residual stress and internal defects, which is extremely important for metal parts under high stress (such as aerospace or automotive parts), while the main disadvantage is that it is very expensive.
• Selective Laser Melting (SLM): Uses a high-power laser to fully melt each layer of metal powder rather than just sintering it, resulting in printed objects that are very dense and strong. Currently, this process can only be used with certain metals, such as stainless steel, tool steel, titanium, cobalt-chromium alloys, and aluminum. The high temperature gradients that occur during the SLM manufacturing process can also lead to internal stresses and misalignments in the final product, compromising its physical properties.
• Electron Beam Melting (EBM): Very similar to selective laser melting, capable of generating dense metal structures. The difference between these two technologies is that EBM uses an electron beam instead of a laser to melt the metal powder. Currently, electron beam melting can only be used with a limited number of metals. Although cobalt-chromium alloys can also be used, titanium alloys remain the primary raw material for this process. This technology is mainly used for manufacturing parts in the aerospace industry.

Technical Advantages: Can manufacture almost any geometric shape with high precision. A wide range of metals can be used, including the lightest titanium alloys and the strongest nickel superalloys, which are difficult to process with traditional manufacturing techniques. Mechanical properties can rival forged metals, and they can be machined, coated, and treated like traditionally manufactured metal parts.Technical Disadvantages: High material, machinery, and operational costs. Parts must be connected to the build plate via support structures (to prevent warping), which generates waste and requires manual post-processing removal. Build sizes are limited, and handling metal powders is hazardous, requiring strict process controls.△ PBF Powder Bed FusionMetal Binder JettingCommon Processes: MJF (Multi Jet Fusion), NPJ (Nano Particle Jetting)Description: This technology uses inkjet to selectively drop a binder onto a flat powder bed. The areas receiving the droplets will be cured, while the remaining powder stays loose. This step is repeated layer by layer until the entire object is generated. This process can handle materials like metal, sand, and ceramics. Since metal binder jetting machines operate at room temperature, warping does not occur and supports are not needed. Therefore, binder jetting machines can be much larger than powder bed fusion machines and can stack objects to fully utilize the entire build chamber, making it a popular choice for small batch production and on-demand manufacturing.Technical Advantages: Can print large volumes, parts do not need to be connected to the build plate, allowing for nesting to utilize all available build volume. Fewer geometric restrictions, and supports are usually unnecessary. No warping occurs, allowing for larger parts to be made. Printing speed is very fast, and costs are lower than powder bed fusion metal printing.Technical Disadvantages: Parts must undergo a time-consuming debinding and furnace sintering process after printing, and machine and material costs are high. Porosity is higher than powder bed fusion, so mechanical properties are not as good, and fewer materials are available.△ Binder Jetting 3D PrinterDirect Energy DepositionCommon Processes: DED (Direct Energy Deposition), WAAM (Wire Arc Additive Manufacturing), LMD (Laser Metal Deposition)Description: This method deposits metal, either metal powder or wire, which is then immediately impacted by high energy (achieved through plasma arc, laser, or electron beam for melting). The energy melts the metal, and the molten pool is immediately lowered into 3D space, manipulated by a robotic arm. It is very similar to welding, so one of its main applications is to repair existing metal parts and enhance their functionality.Technical Advantages: Metal wire is the most affordable form of metal 3D printing material, and some machines can even use two different metal powders to create alloys and material gradients. 5-axis and 6-axis motion can produce models without the use of support materials. Can repair damaged metal parts and add new components. Large build volume, efficient material usage, high part density, good mechanical properties, and fast printing speeds.Technical Disadvantages: Part surface quality is poor, often requiring machining and finishing, and small details are difficult or impossible to achieve. High machinery and operational costs.△ Laser Metal Deposition (LMD)Metal Material ExtrusionCommon Processes: FDM (Fused Deposition Modeling) /FFF (Fused Filament Fabrication)Description: This technology was created to enable affordable metal 3D printing for small and medium-sized enterprises. Design studios, machine shops, and small manufacturers use metal material extruders to iterate designs, create fixtures, and complete small batch production. The latest development in the field is metal wire, which can be used in most desktop FDM 3D printers, making metal 3D printing accessible to almost everyone. The working principle of metal material extrusion:

• Polymer filaments or wires infused with metal particles are 3D printed layer by layer according to the designed shape.
• Clean the 3D printed parts to remove some of the binder.
• Place the parts in a sintering furnace, where the metal particles melt into solid metal.

Technical Advantages: Affordable, easy and safe to operate.Technical Disadvantages: Parts must undergo the same debinding and sintering processes as those printed using binder jetting. Greater restrictions on geometry and supports are needed to prevent warping, and parts have high porosity, unable to achieve the same mechanical properties as forged metals. Parts are not as dense as those made with PBF or DED, and shrinkage in the furnace is less predictable.△ Samples from Markforged Metal X 3D Printer [Image Source: Markforged]Other Metal 3D Printing ProcessesJoule Printing: Digital Alloys’ Joule Printing looks very similar to DED, but the metal wire is melted using electric current instead of being heated with an arc or beam. This allows for faster printing speeds, and it has been demonstrated to print up to 2 kilograms of titanium per hour.Liquid Metal Additive Manufacturing: Vader Systems has created a liquid metal additive manufacturing technology that deposits liquid metal droplets at 1200°C in a manner similar to inkjet printing.Electrochemical Deposition: Exaddon’s CERES nanoscale metal 3D printer can manufacture metal objects smaller than a human hair using electrochemical deposition.DLP Metal Printing: ADMATEC and Prodways offer metal DLP printing. Similar to metal material extrusion, metal powder is mixed with light-curable polymer resin, and 3D printed parts must undergo the same debinding and sintering processes as those in the metal material extrusion method.Cold Spray Metal Printing: Cold spray metal printing was initially used by NASA to construct metal objects in space. Its main feature is speed (6 kilograms of aluminum or copper per hour), but the downside is that it is not very accurate. Australian companies Titomic and SPEE3D are leaders in this technology.Ultrasonic Consolidation (UAM): Uses sound to bond thin layers of metal foil together, processing away excess material from each layer before bonding the next layer, thus combining additive and subtractive manufacturing. Fabrisonic’s SonicLayer 3D printer series uses this technology.Laser Engineering Net Shaping (LENS): A laser-based method that requires a highly controlled environment. This process requires a sealed chamber, often using argon to remove oxygen, keeping oxidation levels as low as possible. LENS lasers have power ranges from 500W to 4kW. It can be used to process titanium, stainless steel, and chromium-nickel iron alloys. Despite the challenges of maintaining an oxygen-free chamber, LENS offers users better precision and control.Electron Beam Freeform Fabrication (EBF3): Originally developed by NASA, this method is primarily used in the aerospace industry. It can create complex geometries without wasting any material and is capable of producing lightweight shapes to promote fuel savings.△ Digital Alloys’ Joule 3D Printing Process [Image Source: Digital Alloys]

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☞ Source: Digital Alloys ☞ Article Edited by: Sophia ☞ Media Cooperation: 010-88379790-519

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