Additive manufacturing is being more broadly adopted in industrial applications – not only for producing new metal parts but also for repair and replacement of existing parts. Billions of dollars are spent in the U.S. annually to repair or replace metal parts due to corrosion or wear. Approximately one-third of these costs could be reduced by broader application of metal additive manufacturing as well as considerable reduction in lead times.
Metal additive manufacturing, and more specifically – directed energy deposition (DED) – saves time and cost for industrial repair applications and this is what we explore further in this blog post. We’ll explain the basics of directed energy deposition, how it differs from traditional and other additive manufacturing processes, and show real-world directed energy deposition repair applications that make it easier to justify the adoption of metal additive manufacturing for repair applications.
The two most common methods used for metal additive manufacturing today are Powder Bed Fusion (PBF) and Directed Energy Deposition (DED). While PBF is primarily used for printing new parts, DED can both print new 3D metal parts, and also add materials to existing components enabling a broader range of applications such as repair, surface modification, and hybrid manufacturing which combines DED with traditional subtractive processes. If you are a machinist working with metal, you need to know about DED.
What’s the difference between directed energy deposition and powder bed fusion?
DED systems continuously blow powder with a gas (typically Argon) through nozzles directed at the focal point of a high-powered laser. The resultant molten pool of metal (sometimes referred to as a weld pool) is then moved using a motion control system and the part is built up in free space. The entire process is visible as the part is grown layer by layer.
PBF systems use a laser to selectively melt a bed of metallic powder layer by layer to build up the physical part. After the first layer is spread and selectively melted, the bed is filled again with a second layer of powder and the process is repeated until the part is fully formed. The end result is buried in a cake of powder and is not visible until the excess powder is removed in post processing, along with any support structures built with the part.
Both metal additive manufacturing processes have advantages. The DED method is faster, more productive for mid to large size parts, and better at adding material to existing parts, such as part modification or repair applications. It is popular for its high deposition rates and building/repairing of larger parts quickly. The PBF method is better at building smaller, more complex-shaped parts, and produces a better surface finish.
What are the benefits of DED?
There are many benefits to using the DED process. It can process quickly almost any type of metal. DED systems can accommodate build volumes from mid-size to very large parts. Systems can operate from 3 axes up to simultaneous 5 axes or more, allowing for building of parts with complex geometries. Typically, the part is moved under the laser, which stays in a vertical position within a laser-safe sealed environment. Laser-safe glass allows users to be able to watch as parts are built, modified, or repaired.
Because it forms a metallurgical bond (like welding but with an extremely small heat-affected zone), parts are built fully dense and with final material properties similar to that of wrought material. Because the part can be moved about multiple axes during building, support structures are not needed. Since metal powders can be blended on the fly during building, material properties of existing parts can be enhanced layer by layer through stronger alloying or use of materials with corrosion or wear resistant properties. Repaired parts can actually have enhanced material properties so they are better than when first built. All these benefits coupled with the DED process’s rapid material deposition rate makes it very attractive for production applications.
What applications are best served with DED?
A number of key applications for component repair can be most efficiently handled with DED. For example, the US Army Anniston depot used DED to repair engine components for the M1 Abrams tank. Operating in a desert environment, tank engines such as the Honeywell AGT 1500 were experiencing extreme amounts of wear, requiring shorter interval maintenance cycles. The AGT 1500 engine components are difficult to repair with traditional methods due to distortion effects caused by the high-heat welding process. With DED, a highly-focused laser beam delivered energy exactly to the repair area, and since the process has an extremely small heat-affected zone, little residual stresses remained and distortion was negligible, enabling repair of these engine components. This allowed the Army to repair rather than replace worn engine components saving over $5 million per year.
Another example is an electronic satellite housing where a hybrid process was used to reduce manufacturing costs and time to market. In this example, the disk base of the housing was machined from a billet and the thin wall structures were built up using DED. The hybrid process reduced lead time by six months while also eliminating the need for specialized tooling.
Even small organizations like a local New Mexico salsa factory have reaped benefits from DED processing for repair applications. When the salsa production line was shut down due to a broken helical gear, no spare gears were in stock and there was an eight-week lead time to deliver a replacement, which would have meant a significant loss in production capacity during the busy holiday season. Using DED, the Inconel helical gear was repaired and the production line was back in operation in one day.
These few examples show how DED is easy to deploy, provides a fast ROI, and a practical pathway for organizations to develop more advanced additive manufacturing applications.