Additive Manufacturing Processes
Although all additive manufacturing (AM) processes feature layer-by-layer fabrication of 3D objects, there are a number of production techniques. GE is currently engaged in offering solutions for four of the seven processes recognised by the American Society for Testing and Materials (ASTM), these include:
- Powder Bed Fusion
- Direct Metal Laser Melting (DMLM)
- Electron Beam Melting (EBM)
- Binder Jetting
AM and 3D printing continue to make inroads across broad areas of manufacturing in a 3D printing market that is experiencing exceptional growth.
Powder Bed Fusion Process
Powder Bed Fusion (PBF) is a additive manufacturing process common to a variety of additive printing and 3D printing techniques. It involves melting powder to a sufficient degree for the particles to fuse together. Particles are either 'sintered' (partially melted) or fully melted in various PBF processes. Thermal energy in the form of a laser, beams of electrons or a heated print head partially or fully melt plastic or metal powder. An ultrathin layer of material is spread by a roller or blade over the preceding layer. The powder is fed from a reservoir beneath or next to a build platform that lowers to accommodate each successive layer of powder. At the conclusion of the additive process, the unfused powder is blown or blasted away and gathered to be re-used for the next project.
A large powder bed Direct Metal Laser Melting (DMLM) machine being developed by GE Additive's concept laser allows build volumes of up to 1.1 x 1.1 x 0.3 meters. Generally Electron Beam Melting (EBM) is a faster additive manufacturing method than DMLM, although the layers are thicker and the surface is rougher. This is actually an advantage in the production of orthopedic titanium implants because the rough outer surface facilitates bone growth. The EBM process also produces parts with less residual stress and distortion, another advantage with implants, jet engine parts, and more. EBM works with a wide range of metals including titanium, stainless steel, copper and cobalt chrome.
Powder Bed Fusion Applications
PBF is ideal for almost every type of end manufacturing, allowing for the easy design and build of complex geometries. Parts typically possess high strength and stiffness with a large range of post-processing methods available.
Direct Metal Laser Melting (DMLM) Process
The direct metal laser melting (DMLM) additive manufacturing process, a form of powder bed fusion, involves the full melting of metal powder into liquid pools. As with other PBF processes, an .STL file is generated from computer-aided design data, which guides the “printing” of sequential, micro-thin layers of fully melted metal powders. Various metals can be used, including titanium, cobalt-chrome and aluminum alloys.
When printing is complete, excess powder is removed, leaving a high-resolution object with a smooth surface that usually requires little or no post-processing.
End-use parts and functional prototypes are both dense and homogeneous. In fact, full melting results in densities approaching 100 percent. DMLM machines produce functional prototypes in a fraction of the time required using traditional casting and machining. Fast design cycles meet deadlines in competitive environments. Designers, unencumbered by long-standing limitations, often come up with highly intricate concepts that dramatically reduce parts requirements.
The DMLM process yields components with mechanical properties equal to or greater than those produced using traditional means. For example, wing brackets for the Airbus A350 XWB have been printed using this powder bed fusion process.
In aerospace, DMLM has already been used to fabricate parts for jet engines and other airplane parts. For example, Fortune highlighted how GE is printing fuel nozzles for its LEAP engines using DMLM technology. Thanks to its AM’s ability to produce complex geometric structures, the design of the 3D-printed fuel nozzle reduces 20 traditionally fabricated parts down to just one. Newer multi-laser DMLM machines further enhance productivity.
At Frankfurt’s Formnext Show in November of 2017, GE Additive addressed size limitations with the BETA version of a new meter-class printer developed in its ATLAS program (Additive Technology Large Area System). The new machine combines enhanced build rates and fine resolution with a scalable architecture capable of increasing ‘Z’ axis dimensions to more than 1 meter.
DMLM is a particularly useful process for time-constrained projects and prototyping. Its ability to fabricate complex structures reduces assembly times and often increases structural integrity by reducing the number of components required.
Electron Beam Melting (EBM) Process
Electron beam melting (EBM) is another form of powder bed fusion technology and additive manufacturing process, through which metal powder is melted by of a beam of electrons gathered and focused by electromagnetic coils. Given the inherent nature of the 3000-watt electron gun, the process must be carried out in a vacuum chamber. EBM is used to print sophisticated parts and components of many kinds, including those that supply the aerospace and medical industries.
In the medical industry, EBM technology is used to fabricate one-of-a-kind orthopedic implants. The EBM process yields objects with slightly rough surfaces, so some machining is appropriate when smooth surfaces are stipulated. However, the rough surface is actually an advantage when fabricating implants because it promotes bone adhesion.
High-quality mechanical properties are achieved, in part due to temperature consistency that strengthens fused layers. EBM machines use titanium alloys to produce parts for high-temperature, high-stress aerospace applications. EBM parts are already being used in new jet engine designs and in rocket engine prototypes.
EBM can be a time and cost-effective way of producing high-density bespoke projects. Non-sintered powder can be recycled and fewer supports are required compared to DMLM
Transformative technology—Electron Beam Melting (EBM)
The EBM process utilizes a high-power electron beam that generates the energy needed for high melting capacity and high productivity. The hot process allows you to produce parts with no residual stress and the vacuum ensures a clean and controlled environment.
Binder Jetting Process
The binder jetting additive manufacturing process employs powdered material and a binding agent. Nozzles on these 3D printers deposit tiny droplets of a binder on an ultrafine layer of powdered metal, ceramic or glass. Multiple layers result from the powder bed moving downward after each layer is created. The resulting object is in a green state, so post-processing is required. For example, bronze may be used to infiltrate a metal object. This improves its mechanical properties enough to make it a functional component. A cyanoacrylate adhesive is a common infiltrant when the object is ceramic. However, ceramic objects produced by binder jetting are still fairly brittle, so they are primarily used as architectural models or models for sand casting.
Binder Jetting Applications
The binder jetting process is ideal for aesthetic applications like architectural and furniture design models. It is generally not used in functional applications due to its brittle nature.