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= Additive Friction Stir Deposition = Additive friction stir deposition is a type of additive manufacturing for metal parts. It is modeled off of friction stir welding, and is able to 3D print metals while keeping them in a solid state.

History
Additive friction stir deposition was developed by Aeroprobe. It has since been put under the control of MELD, which is a part of Aeroprobe, and rebranded to the same name.

Description
Additive friction stir deposition is similar to other 3D printing methods, in that the piece is built by depositing layers of material, one on top of the other until the desired shape is created. This is achieved through the use of frictional heat on created by a rotating shoulder. Material is forced through this shoulder as it rotates, which then plasticizes and creates a layer of the material on the substrate, the base that is being printed on.

The current resolution of the process is limited to roughly 10 mm, making it a near net shaping process.

Materials
Additive friction stir deposition has been used to 3D print a variety of different materials. There are two types of input material the machine can use, either a metal powder or a solid metal rod. If a powder is used, multiple materials can be put in so that a metal matrix composite (MMC) is obtained. So far, two categories of MMC have been created: an aluminum one and a copper one. The aluminum MMCs were Al-SiC, Al-Fe, Al-W, and Al-Mo. The copper MMCs were Cu-W and Cu-Ta.

Many different materials have been used for either powder or solid metal single material printing. For steel, both HY 80 and stainless 316 L have been printed. Aluminum series 1xxx, 2xxx, 5xxx, 6xxx, and 7xxx have all been printed. Magnesium alloys have also been printed, specifically AZ31. WE43, E675, AMX602, and E21. Also titanium Ti64 and nickel aluminum bronze have both been printed using this technique.

This process can print with the substrate being the same material as what is being deposited, or it can print with the substrate and the deposited material being different.

Characteristics
The most important properties of additive friction stir deposition are the solid state process, and the resulting microstructure, as well as how much material can be deposited. In other types of additive manufacturing, such as beam based 3D printing, the process melts material and then lets it solidify in order to create the desired shape. This has a negative impact on the microstructure of the material. For additive friction stir deposition, the entire process is conducted at 60% to 90% of the material’s melting temperature. This means that the process is entirely performed in the solid state, which has positive impacts on the microstructure and stress state of the printed material. The microstructure created by this process is characterized by very fine, equiaxed grains. These fine grains are created because of the dynamic recrystallization that occurs during the process. Another effect of the recrystallization is that the deposited material has lower residual stresses. This is also aided by the low temperature that additive friction stir deposition is performed at.

The other impressive quality of additive friction stir deposition is how much material it can print. Additive friction stir deposition can print out 1000cm3/hr of aluminum. Comparatively, electron beam additive manufacturing can create 80 cm3/hr of material, and laser powder bed sintering and laser metal deposition are even slower than that. The only other process that’s comparable to additive friction stir deposition in terms of build rate is wire-based electron beam free-form fabrication.

The process of additive friction stir deposition is a very new one, and more information about it is being discovered every day.