With the last few years’ rapid innovation, 3D printing is poised to change a variety of additive manufacturing processes. People are starting to see fused deposition modeling (FDM) 3D-printer kiosks at stores, such as Home Depot and FedEx. Some people have even purchased printers for home use. However, these 3D printers are mainly used for plastic products.
The emergence of metal 3D printing is now piquing the interest of the advanced manufacturing industry, which has recognized the technology as a viable process for producing a low-number series of complex metal parts.
There are four types of metal 3D printing. We will go through each one, discuss the advantages and disadvantages along with the applications.
The first two types are not geared towards producing the final products, so we will briefly cover them.
Sheet Lamination—this technology is mainly used for prototyping but not for production. The printing process involves bounding sheets of material with force. After the sheets are bounded, it is cut into the final shape. This is a pretty inexpensive and fast process, but not capable of producing complex geometry.
Directed Energy Deposition—this technology is mainly used to repair or add materials to the existing objects. Nozzle moves around and deposits materials (wire or powder) onto the existing object’s surface. Sources such as laser, electron beam or plasma arc are used to melt the materials and the process continues until the final repair or addition is done
The following two types are capable producing complex geometry final products.
Binder Jetting—this technology requires a build chamber, one piston for metal powder feed, another piston for the build platform, inkjet print head for applying “glue” and a roller. To build each layer, the inkjet head applies liquid agent to bond the powder and form into a cross-section artifacts on the powder bed. Once the layer is done, the powder feed piston goes up and the build platform piston goes down while the roller spread a new layer of powder onto the existing layer. This process continues until the 3D object is printed. The remaining powder is cleaned off and used for later usage.
This technology applies to any kind of materials that is in powder format and does not need support structure. For metal print, it requires the thermal post-processing to increase the parts’ density and strength.
Binder jetting does not use heat, there are no residual stresses created, thus no need to relieve the stresses in the post-processing operation. It is also a relatively cheap and fast technology and can print large objects. It also has a very wide range of supporting materials, because any materials that can be in powder format can be used. Full color parts are also possible. The limitation is that it requires the thermal post-processing to increase the parts’ density and strength through sintering and this may cause dimensional shrinkage.
Maximal build envelope: 4’000 x 2’000 x 1’000 mm3
Minimum feature size: 0.1 mm
Typical tolerance: +/-0.13 mm
Minimum layer thickness: 0.09 mm
Powder Bed Fusion—this technology basically uses two types of sources to fuse or melt the powder together. One is electron beam and another is laser. Selective Laser Sintering (SLS), Selective Laser Melting (SLM), Direct Metal Laser Sintering (DMLS), Electron Beam Melting (EBM), and Selective Heating Melting (SHM) are all part of Powder Bed Fusion. The common part of all Powder Bed Fusion processes is that it all involves spreading powder onto the previous layer. Electron Beam Melting requires a vacuum. SHM is slightly different that it requires a heated print head to fuse the powder together. Source fuse/melt the powder into cross section layer and new powder got spread on the previous layer by roller or blade and this process continues until the final object is built. Metals such as stainless steel, titanium, aluminum, cobalt chrome, steel are supported by DMLS, SLS and SLM. Titanium, cobalt chrome and copper are supported by EBM. PBF type of technology is relatively inexpensive, supports a range of materials and no supporting structure is needed. However, it is also a relatively slow process, has size limit and requires quite high energy.
Spec for Laser Sintering
Maximal build envelope: 550x550x750 mm3
Minimum feature size: 0.15 mm
Typical tolerance: +/-0.25 mm (can be improved through post-processing)
Minimum layer thickness: 0.1 mm
Spec for Electron Beam Melting
Maximal build envelope: 350 x 350 x 380mm3
Minimum feature size: 0.1 mm
Typical tolerance: +/- 0.2 mm (can be improved through machining)
Minimum layer thickness: 0.05 mm
Typical surface finish: 20.3 – 25.4microns RA (can be improved through post-processing)
Density: Up to 99.9%
With the maturation of additive manufacturing, especially metal 3D printing, we will see more and more applications in medical equipment, automotive parts, oil & gas equipment, semiconductor, and more. The revolution and disruption of the manufacturing world by 3D printing is inevitable.