What Is the Role of Directed Energy Deposition (DED)? We Are Still Discovering It

What is the application for directed energy deposition? What is DED’s role? The answer is changing. In fact, it has changed so much, it may now be time to revise our understanding of the place and possibilities of this AM process.

For a long time, the short answer to the question “What is DED for?” would generally have been “repair.” When it comes to making a complete metal part from scratch, moving a laser through a bed of powder (à la laser powder bed fusion) is often more efficient than moving the flow of powder and the laser together in DED. But when it comes to repairing an existing component like a tool or a turbine blade, the ability to target metal placement is invaluable. No one at any time would have claimed repair was DED’s only use, but repair has long been a distinctive strength. Now, two important developments have served to advance DED’s role.

First, the range of practical options in DED have expanded. Alongside blown-powder systems, wire-fed systems are now at least as accessible if not more so. The latter systems provide faster deposition rate, allowing complete metal parts and big metal parts to be made more quickly and cheaply than previously. They also improve ease of use, as spools of wire make material handling easy. Add to this the arrival of cold-spray AM systems performing metal deposition without the difficulty of a liquid-to-solid transition. This type of metal 3D printing is DED as well, just with the “directed energy” applied to propulsion rather than melting.

Then, the second development, which has proceeded at about the same pace as the first, is an increased questioning of casting. Additive cannot compete with the speed and economy of casting at its best, but foundry capacity is limited, and like every limited resource, that capacity gets allocated. Production parts at the production volumes most natural to casting continue to be made this way, but as this work fills foundry schedules, the work that is at all marginal or suboptimal for casting gets scheduled out farther. Replacement parts and lower-quantity production fit this description. The same phenomenon applies to forging capacity as well. For the chance to get free of this kind of supply constraint, and also get free of the need to maintain tooling for a part that might see a long service life, OEMs and part buyers increasingly are taking a second look at AM and valuing it differently. Thus, as DED becomes more capable for making parts, the constraints on established part-making are giving it more to do.

Some sense of how much this is all coming to mean can be found in various pieces we have posted recently — various stories offering different pictures of DED in action, whether blown-powder, wire-fed or cold-spray systems. The applications include adding features, including a simple feature for a production part, or much more elaborate features added to a part that, as it happens, starts out being made through powder bed fusion. The applications also include DED being used to make complete parts, and there are a variety of these. They range from a replacement part within a unique system to low-volume substitutes for castings to production hardware for which DED is the qualified process able to stand fully in forging or casting’s place. And then DED still excels for repair. As a complement to repairing turbine blades, consider repair of a massive turbine shaft.

What does DED do? Not everything. And some sense of this can be found in our coverage as well. Powder bed fusion is needed for precise forms with inner complexity; it is needed for precision parts in the most demanding metals. Every AM process is still advancing — it is the nature of a new and still-young category of manufacturing that this is so.

But the processes are prone to advance at different rates, and this is what produces category lines being redrawn. What does DED do? It adds features, makes repairs and produces runs of production parts. Those uses were always there as possibilities, but now we know DED to be suited to them all, which is maybe more than we had come to expect. For any additive process we think we “know,” for any in which the application seems to have been decided, we should stay tuned. All these technologies are still moving and changing, and none of the final words have been written.