Directed Energy Deposition (DED) is a 3D printing method which uses a focused energy source, such as a plasma arc, laser or electron beam to melt a material which is simultaneously deposited by a nozzle. As with other additive manufacturing processes, DED systems can be used to add material to existing components, for repairs, or occasionally to build new parts.
The DED process is known by other names, including Laser Engineered Net Shaping (LENS), Direct Metal Deposition (DMD), Electron Beam Additive Manufacturing (EBAM), Directed Light Fabrication, and 3D Laser Cladding, depending on the exact application or method used.
The DED process begins with the creation of a 3D model using CAD software. This model is then sliced into layers with software to represent the layers that are required to create the finished workpiece.
Directed Energy Deposition works by depositing material that has been melted onto a specified surface where it solidifies, fusing materials together to form a structure. DED machines typically use a nozzle that is mounted on a multi axis arm which can move in multiple directions, allowing for variable deposition. The process is typically performed within a controlled chamber with reduced oxygen levels. With electron beam-based systems the process is performed in a vacuum , while laser-based systems use a fully inert chamber when working with reactive metals. It is also possible to use a shielding gas to shroud the part and prevent contamination during metal 3D printing.
DED uses a heat source to melt a powder or wire as it is deposited onto the surface of an object. While powder provides greater accuracy in deposition, wire is more efficient with regards to material use.
The material is added layer-by-layer and solidifies from the melt pool to create new features. Layers are typically 0.25mm to 0.5mm thick. The cooling times for materials are very fast at around 1000-5000 °C per second. The cooling time affects the final grain structure although overlapping in the material can cause re-melting, which creates a uniform but alternating microstructure.
In most cases, the object remains in a fixed position while the arm moves to lay down the material. However, this can be reversed with the use of a platform, which moves while the arm remains stationary.
Typically used to work on metal parts, this process can also be used with polymers and ceramics. Almost any weldable metal can be additively manufactured using DED, including aluminium, inconel, niobium, stainless steel, tantalum, titanium and titanium alloys, and tungsten.
The advantages of Directed Energy Deposition include the ability to control the grain structure, which allows the process to be used for the repair of high quality functional parts. This does require a balance between accuracy and speed, since higher speeds equal a lower level of accuracy and a less consistent microstructure.
DED allows for the production of relatively large parts with minimal tooling.
This process also allows for the creation of components with composition gradients or hybrid structures using multiple materials with differing compositions
The finish created will vary depending on the material used and may require some post processing to achieve the desired effect. The material use for DED is still relatively limited and fusion-based processes still require further research to move them into mainstream use.
Research has shown that Directed Energy Deposition is ten times faster and five times less expensive than Powder Bed Fusion (PBF) when creating mid-size metal parts. The study tested the two methods in building a 150mm diameter, 200mm tall metal part from Inconel. The geometry of the part was designed to be built without support structures in order to ensure comparable parameters.
The advantages of DED are evident in that material use as well as cooling and build times are greatly reduced compared to PBF.
Directed Energy Deposition can be used to fabricate parts, but is generally used for repair or to add material to existing components. Generally-speaking, the applications for DED fall into three categories; near-net-shape parts, feature additions, and repair.
DED can produce similar parts to those created with conventional machining. This means that, for DED to be chosen, these parts need to be for applications where conventional manufacture is expensive or slow. This makes the process ideal for producing machined parts from expensive or hard to cut metals. As a result, DED lends itself to the production of items such as aerospace brackets, tanks, and ribs. Near-Net-Shape part manufacture tends to be used primarily within the aerospace, defence, power and marine sectors. While this process can offer improved product design, time saving and cost reductions, it is not deemed suitable for small, high volume applications due to the fixed price structure and post processing requirements.
Since DED can be used to print onto existing parts it is ideal for adding additional features to existing parts. Advances in multi-axis robotics and software has allowed for increasingly complex shapes to be built, which is particularly useful if the added feature is expensive to produce with conventional techniques.
DED also allows for multiple metals to be used by changing the feedstock while printing. To achieve this successfully there are important technical considerations around design and bonding properties for dissimilar metals.
Direct Energy Deposition is increasingly replacing conventional methods for the repair of parts. Since it is an automated process, DED provides high levels of control and repeatability, which is particularly important for complex and precise parts. The process is already used for applications such as the repair of damaged turbine blades or propellers.
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