Metal 3D printing is often considered the pinnacle of all 3D printing techniques. In terms of strength and durability, nothing surpasses metal. The earliest patent for metal 3D printing was Direct Metal Laser Sintering (DMLS), obtained by EOS from Germany in the 1990s. Since then, metal 3D printing has progressively developed various printing techniques. Nowadays, metal 3D printing services typically employ one of the following four processes: Powder Bed Fusion, Binder Jetting, Direct Energy Deposition, and Material Extrusion.
1. Powder Bed Fusion (PBF)
Key techniques: Direct Metal Laser Sintering (DMLS), Selective Laser Melting (SLM), and Electron Beam Melting (EBM).
Using PBF melting technology to produce metal parts can reduce residual stress and internal defects, making it an ideal choice for stringent applications in the aerospace and automotive industries.
Direct Metal Laser Sintering (DMLS)
It can be used to construct objects from virtually any metal alloy. DMLS disperses a very thin layer of metal powder on the surface to be printed. A laser then slowly and steadily passes over the surface to sinter the powder, causing the internal particles of the metal to fuse, even if they are not heated to a fully molten state. Then, additional layers of powder are applied and sintered, thus printing one cross-section of the object at a time. Once the printing is complete, the object is allowed to cool slowly, and the excess powder can be collected from the build chamber for reuse. The main advantage of DMLS is that it produces objects with minimal residual stress and internal defects, which is critically vital for metal parts subjected to high stress (such as aerospace or automotive components). However, a main drawback is its considerable cost.
Selective Laser Melting (SLM)
SLM employs a high-powered laser to completely melt each layer of metal powder, rather than merely sintering it. This process results in printed objects that are notably dense and sturdy. Currently, this technique is only applicable to certain metals, such as stainless steel, tool steel, titanium, cobalt-chromium alloys, and aluminum. The high-temperature gradients that emerge during the SLM manufacturing process can lead to internal stresses and dislocations in the final product, potentially compromising its physical properties.
Electron Beam Melting (EBM)
EBM closely parallels Selective Laser Melting in its ability to create dense metal structures. The key difference between these two techniques is that EBM utilizes an electron beam, not a laser, to melt the metal powder. Currently, Electron Beam Melting can be applied to a limited selection of metals. While cobalt-chromium alloys can also be used, titanium alloys remain the predominant material for this process. It is primarily applied in the manufacture of aerospace industry components.
Advantages of Powder Bed Fusion
PBF metal 3D printing service allows for the high-precision fabrication of nearly any geometric shape. It offers a broad spectrum of applicable metals, including the lightest titanium alloys and the most durable nickel superalloys - materials that are typically challenging to work with using conventional manufacturing methods. The mechanical properties can compete with those of forged metals, and similar to traditionally manufactured metal parts, they can be machined, coated, and treated.
Disadvantages of Powder Bed Fusion
The costs associated with materials, machinery, and operation are high. Parts must be attached to the build plate using support structures to prevent distortion, which results in waste and necessitates manual post-processing for removal. Due to the limited size of the build and the hazards associated with the handling of metal powder, stringent process control is required.
2. Metal Binder Jetting
Key techniques: Multi Jet Fusion (MJF), Nanoparticle Jetting (NPJ)
With this technology, a binder is selectively deposited onto a powder bed using inkjet printing. The areas receiving the binder droplets solidify, while the untouched powder remains loose. This technique is iterated layer by layer until the entire object is formed. The printer can work with different materials, including metals, sand, and ceramics. Since metal binder jetting operates at room temperature, it eliminates warping and the need for support. As a result, binder jetting machines can exceed the size of powder bed fusion machines, allowing for object stacking to maximize the usage of the build chamber. It makes it an appealing choice for small-batch production and on-demand manufacturing.
Multi Jet Fusion (MJF)
This method initiates with a layer of powder, followed by the application of a fusing agent. Concurrently, a detailing agent is sprayed to maintain the precision of the object's edges. Subsequently, a heat source is applied to complete the layer. This process is repeated until the 3D object is fully realized.
Nanoparticle Jetting (NPJ)
This approach begins by loading metal in liquid form into the 3D printer. During printing, a liquid imbued with metal nanoparticles is jetted to shape the object. The excess liquid then evaporates upon heating, leaving behind the metal part, which undergoes low-temperature sintering to finalize the shaping process. This method can utilize conventional inkjet printheads and removes support structures via melting without external force. It theoretically allows for limitless additions, offering designers increased freedom. Besides metal materials, its breakthrough in ceramic technology has expanded its applications to dentistry, medical, and specific industrial fields.
Advantages of Metal Binder Jetting
It facilitates large-scale printing and eliminates the need for parts to be connected to the build plate, enabling nesting to optimize all available build volume. It has fewer geometric constraints and typically doesn't require support. Warping is prevented, facilitating the creation of larger parts. The printing speed is impressively fast, and it's more cost-effective than powder bed fusion metal printing.
Disadvantages of Metal Binder Jetting
Parts must go through a time-consuming degreasing and furnace sintering process after printing; machine and material costs are high. The porosity is higher than powder bed fusion, so the mechanical performance is not as good, and there are fewer material options.
3. Direct Energy Deposition (DED)
Key techniques: Direct Metal Deposition (DED), Wire Arc Additive Manufacturing (WAAM), Laser Material Deposition (LMD)
This process involves the extrusion of metal, either as a powder or wire, which is then instantly subjected to a high-energy impact to induce melting. This can be achieved through a plasma arc, laser, or electron beam. The energy fuses the metal, and the resulting molten pool is rapidly guided into a 3D space via a robotic arm for precise positioning. Bearing a strong resemblance to welding, one of its primary applications is the repair and enhancement of existing metal components.
Direct Metal Deposition (DED)
This technique employs a laser to create a molten pool in the deposition region, which moves rapidly. Material, in the form of powder or wire, is directly introduced into the high-temperature molten zone. Upon melting, it is deposited layer by layer, making it ideal for manufacturing large-scale metal components.
Wire Arc Additive Manufacturing (WAAM )
WAAM is a variant of DED technology that utilizes arc welding processes to 3D print metal parts. The process is managed by a robotic arm, with the structure being built on a base material or substrate. Once complete, the component can be separated from the base material. The metal wire is extruded in bead-like formations onto the substrate while in a molten state. As these beads coalesce, they form a layer of metal material. This procedure is repeated layer by layer until the desired metal part is achieved.
Laser Material Deposition (LMD)
Laser Material Deposition (LMD) is a welding procedure that introduces material into a molten pool created by a high-power laser for welding and shaping. LMD falls under the category of Directed Energy Deposition (DED) processes. The filler material, typically in powder form, is injected through a conical ring nozzle surrounding the laser beam. The added material forms a weld seam that then coats the underlying metal. This process is used for cladding applications to enhance the wear resistance of parts, in repair applications where the material is added to worn parts, or in free-form manufacturing of complex geometries (3D printing). Compared to other types of welding, LMD results in smaller heat-affected zones, low dilution, and low residual stress in components.
Advantages of Direct Energy Deposition
Metal wire is the most affordable form of metal 3D printing material. Some machines can even use two different types of metal powder to manufacture alloys and material gradients. 5-axis and 6-axis motion can produce models without the use of support materials. It can repair damaged metal parts and add new components. It features a large build volume, efficient material usage, high part density, good mechanical performance, and fast printing speed.
Disadvantages of Direct Energy Deposition
The surface quality of parts is generally poor and usually requires machining and finishing. Small details are difficult or impossible to achieve. Mechanical and operational costs are high.
4. Metal Material Extrusion
Key techniques: Fused Deposition Modeling (FDM) / Fused Filament Fabrication (FFF )
This technology is purposefully designed to make metal 3D printing affordable, hence making it accessible to small and medium-sized enterprises. Design studios, mechanical workshops, and small manufacturers utilize metal material extrusion machines when iterating designs, building fixtures and jigs, and executing small-scale production. A recent advancement in this field is the use of metal wire, compatible with most desktop FDM 3D printers, thus democratizing access to metal 3D printing.
FDM (Fused Deposition Modeling), also known as FFF (Fused Filament Fabrication), leverages the thermoplasticity and adhesive properties of thermoplastic materials to build up layers under computer control. The material is first transformed into a filament and then fed into the extruder by a feeding mechanism. Inside the extruder, it's heated and melted. As the extruder moves along the part's contour and fill trajectory, it extrudes the melted material. This material rapidly solidifies, adhering to the surrounding material and forming layers.
Advantages of Metal Material Extrusion
Cost-effective, user-friendly, and safe operation.
Disadvantages of Metal Material Extrusion
Parts must undergo a debinding and sintering process similar to binder jetted parts. More constraints are required on geometry and support to prevent warping. The parts exhibit a high porosity rate and do not reach the same mechanical properties as traditionally forged metal. The density of parts is not as high as those produced using Powder Bed Fusion (PBF) or Direct Energy Deposition (DED), and shrinkage during furnace processing can be unpredictable.
SLS (Selective Laser Sintering) is also one of the most commonly used 3D metal printing services. Typically, it is used to print PA (Nylon) materials in rapid prototyping.
The 3D printing industry is developing very fast. Stay tuned with us to keep posted!
Source: translated majorly from 南极熊3D打印