Metal 3D printing is considered the pinnacle of all 3D printing technologies. When it comes to strength and durability, nothing compares to metal. The earliest patent for metal 3D printing was for 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. Nowadays, each metal 3D printer typically uses one of four types of processes: Powder Bed Fusion, Binder Jetting, Direct Energy Deposition, and Material Extrusion.
△Metal 3D Printing
Metal Powder Bed Fusion
Common 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 choices for demanding applications in aerospace and automotive industries.
Direct Metal Laser Sintering (DMLS): Can be used to build objects from nearly any metal alloy. In DMLS, a very thin layer of metal powder is spread over the surface to be printed. A laser slowly and steadily traverses the surface to sinter this powder, fusing the internal particles of the metal together, even without being heated to a fully molten state. Additional layers of powder are then applied and sintered, effectively “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 components), while the main disadvantage is that it is very expensive.
Selective Laser Melting (SLM): Uses a high-power laser to completely 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 for 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. The mechanical properties can rival those of forged metals, and they can be machined, coated, and treated just like traditionally manufactured metal parts.
Technical Disadvantages: High material, mechanical, 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 to remove. Limited build sizes, and the handling of metal powders poses hazards, necessitating strict process controls.
△PBF Powder Bed Fusion
Metal Binder Jetting
Common 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 are cured, while the remaining powder remains loose. This step is repeated layer by layer until the entire object is generated. This process can handle materials such as metal, sand, ceramics, etc. Since metal binder jetting machines operate at room temperature, there is no warping and no need for supports. Thus, binder jetting machines can be much larger than powder bed fusion machines and can nest 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 nesting to utilize all available build volume. There are fewer restrictions on geometries, and supports are usually not needed. 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 sintering process after printing, and the machine and material costs are high. The porosity is higher than that of powder bed fusion, resulting in poorer mechanical properties, and there are fewer material options available.
△Binder Jetting 3D Printer
Direct Energy Deposition
Common Processes: DED (Direct Metal Deposition), WAAM (Wire Arc Additive Manufacturing), LMD (Laser Metal Deposition)
Description: This method deposits metal, either in powder or wire form, which is then immediately impacted by high energy (which can be achieved through plasma arc, laser, or electron beam to achieve melting). The energy melts the metal, and the molten pool is immediately deposited in 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 the functionality of parts.
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. Damaged metal parts can be repaired, and new components can be added. Large build volumes, efficient material usage, high part density, good mechanical properties, and fast printing speeds.
Technical Disadvantages: Parts have poorer surface quality, typically requiring machining and finishing, and small details are difficult or impossible to achieve. High mechanical and operational costs.
△Laser Metal Deposition (LMD)
Metal Material Extrusion
Common Processes: FDM (Fused Deposition Modeling), FFF (Fused Filament Fabrication)
Description: This technology was created specifically to make affordable metal 3D printing accessible for small and medium enterprises. Design studios, machine shops, and small manufacturers use metal material extruders to iterate designs, create fixtures and jigs, and complete small batch production. The latest development in the field is metal filament, which can be used in most desktop FDM 3D printers, making metal 3D printing accessible to almost everyone.
How Metal Material Extrusion Works:
Polymer filaments or wires infused with small metal particles are 3D printed layer by layer according to the designed shape.
Cleaning 3D printed parts to remove some of the binder.
Parts are placed in a sintering furnace, where the metal particles melt into solid metal.
Technical Advantages: Affordable, easy to operate safely.
Technical Disadvantages: Parts must undergo the same debinding and sintering process as binder jetted parts. More restrictions on geometries and supports are needed to prevent warping, and parts have high porosity, failing to achieve the same mechanical properties as forged metals. Parts are not as dense as those produced using PBF or DED, and shrinkage during sintering is less predictable.
△Samples from the Markforged Metal X 3D Printer [Image Source: Markforged]
Other Metal 3D Printing Processes
Joule Printing
Joule Printing from Digital Alloys looks very similar to DED, but the metal wire is melted using electrical current instead of heating with an arc or beam. This allows for faster printing speeds, with up to 2 kilograms of titanium printed per hour currently demonstrated.
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 create metal objects smaller than the width of 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 photopolymer resin, and 3D printed parts must undergo the same debinding and sintering process as those produced using metal material extrusion.
Cold Spray Metal Printing
Cold spray metal printing was originally used by NASA to construct metal objects in space. Its main feature is speed (6 kilograms of aluminum or copper per hour), while the disadvantage 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, machining away excess material from each layer before bonding the next layer, thus combining additive and subtractive manufacturing. Fabrisonic’s SonicLayer 3D printer series employs this technology.
Laser Engineering Net Shaping (LENS)
Is a laser-based method that requires a highly controlled environment. This process needs a sealed chamber, often using argon to displace oxygen, keeping oxidation levels as low as possible. LENS lasers have a power range from 500W to 4kW. It can be used for processing titanium, stainless steel, and chromium-nickel alloys. Although maintaining an oxygen-free chamber presents challenges, LENS provides users with better precision and control.
Electron Beam Freeform Fabrication (EBF3)
Originally developed by NASA, it is a method primarily used in the aerospace industry. This method 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]
Source: Mufeng Machinery
