Metal AM technology is in a constant state of innovation. Every few years a new technological breakthrough comes along to optimize or disrupt the industry. While the end goal remains the same — manipulating a metal substrate to form highly complex parts that can’t be conveniently manufactured using traditional methods — the methods themselves can vary, with their own unique drawbacks and benefits.
Let’s take a high-level view of metal additive manufacturing solutions, see how they work, and then explore what makes them popular within the metal additive manufacturing industry.
1. Laser Powder Bed Fusion (PBF-LB)
Laser powder bed fusion is a broad category that encompasses Selective Metal Sintering (SLM), Direct Metal Laser Sintering (DMLS), and Electron Beam Melting (EBM). While these methods differ in their execution, they mostly start out the same way. Within a highly controlled printer environment, a powdered metal is heated using lasers to form a liquid. As these layers cool, they bond with the layers below them until a part emerges. These layers are microns thick (or thin), which means the lasers need to be calibrated exactly to create the desired part. Because this process requires such close calibration and peak laser performance, it can yield highly complex parts.
It is worth noting that while “LPBF” is a common term, it is more of an industry shorthand. International Standards recognizes the process as Laser Beam Powder Bed Fusion, or PBF-LB, which is beginning to gain wider use in commercial applications.
Taken from a Sapphire XC 8 – Laser Metal AM Printer
4. Selective Laser Melting (SLM)
SLM is a subset of PBF-LB where the metal powder is completely melted using lasers, and then fuse together from the bottom up. The full melt of the powder enables parts to fuse together harder, which requires less post-processing.
3. Direct Metal Laser Sintering (DMLS)
DMLS is a frequently used term within the metal AM world, and is used interchangeably with SLM, although it is a bit of a misnomer. In the past, lasers would be used to sinter rather than fully melt the substrate. As a result, there is a level of porosity in the resulting part that typically requires a post-processing technique to achieve the desired hardness and surface finish. However, it is now much more common to fully melt the metal using SLM.
4. Electron Beam Melting (EBM)
While EBM begins in a similar way as other LPBF metal additive manufacturing, it differs in its heat source. Rather than using lasers, EBM uses an electron beam to melt the metal. EBM requires a highly controlled environment — a vacuum chamber — and, because electron beams create higher energy density than lasers, can create increased layer heights. As a result, EBM tends to be faster than SLM though may not express the same level of complexity.
5. Direct Energy Deposition (DED)
Whereas the various forms of PBF-LB take a bed of metal powder and melt it layer by layer to create a part, direct energy deposition (DED) deploys a feeder mechanism where the molten metal is blown through directly on the surface of the part. The process uses a thermal heat source such as a laser beam, electron beam, or plasma arc and takes direction from a CAD file to direct a CNC machining-like arm to apply the molten material. There are two forms of DED metal AM, powder and wire, which refers to the form of the metal feedstock.
DED isn’t often used for net-new parts since the process generally provides less resolution than PBF-LB printing. For example, DED printing is incapable of producing overhangs or complex internal channels. The process produces strong, dense parts that typically require surface finishing to remove roughness. One of the primary applications for DED is part repairs or adding additional structures onto existing parts.
6. Binder Jetting (BJT)
One of the more interesting metal 3D printing processes is binder jetting (BJT). Unlike the previously outlined processes that take powdered (or wire) metal and melt it to create the final part within the printer itself, BJT begins with a powder bed and selectively disperses a binding agent to create a rough draft, or green part. These green parts are fragile since they’re not melted and cooled, hardened metal, so they require a secondary process to provide that hardening. It’s a similar process to pottery, where clay is formed into a desired shape and then fired in a kiln to create the finished product.
In BJT, the green parts are placed into a furnace at temperatures near the melting point of the metal, which enables the powder particles to bond (sintering) and form a nearly fully dense part. BJT is a flexible 3D printing process, giving engineers the ability to utilize materials beyond metals, including composites and ceramics. Because the sintering process isn’t done in an inert environment, however, the materials that can be used in BJT are more limited than PBF-LB.
The Wide World of Metal Additive Manufacturing Solutions
Velo3D specializes in an advanced form of PBF-LB that connects pre-printing design software, advanced printing technology, and in-situ quality assurance to achieve a highly complex and controlled printing process that can be deployed at scale in a way other additive manufacturing services simply can’t.
And while there are benefits to all the metal additive manufacturing applications methods listed above — and many others we didn’t mention such as material extrusion, sheet lamination, bound powder deposition, and more — it’s important to understand your unique application and weigh the pros and cons before investing in the technology. Speaking to professionals in the industry is a key first step to choosing the right metal 3D printing process for you.
Reach out to speak to a Velo3D engineer today.
