Additive Manufacturing: Material Deposition

I want to start off the 3D Printing Press by giving a little background additive manufacturing. In my own journey of teaching myself about AM, I found that there was never a great source describing all the different flavors of 3D printing. So, here it is; my beginner's map to additive manufacturing. I did draw a little inspiration from AMCRC's paper on AM [1] but I compiled the diagrams into one flow chart that makes more sense to me.

As you can see, there are three main branches of AM: material deposition, powder bed, and liquid processes. All branches use the same basic concept of layer-by-layer manufacturing, printing one cross section of the design on top of another, but each branch has their unique properties. I named some of the main processes within these branches, but of course there are other lesser used AM processes that aren't listed. I'll try to cover these in future blog posts.

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Today, I'm going to dive into the left most branch: material deposition. Material deposition includes the type of "3D printing" most people might think of; the part is built up layer by layer by feeding material through a nozzle. The build stage and/or the nozzle moves to create the 2D design of each layer. There are three main types of material deposition: extrusion, blown powder deposition, cold spray.

Extrusion
Extrusion, sometimes called fused deposition modeling (FDM), can be used for almost any type of material that can be made into a filament or even pellets (See this Kick Starter that is trying to make cheaper printers using this method). The figure below shows a "desktop" printer, but industrial printers work similarly. In addition to a filament, you have a printer bed and a heated nozzle where the filament is fed through. The nozzle diameter can be changed, a smaller diameter giving greater resolution but taking more time, or additional nozzles for different material/colors can be added. When printing thermoplastics (i.e.: ABS, PLA), the printer beds are heated which may seem counter intuitive, but you actually want to keep the part slightly warm to prevent warping. As thermoplastic cool, they tend to shrink. If different layers of the part cools at different rates, you'll often get distortions in your final product [2].

This desktop printer is made by Lulzbot.

Extrusion can be used for more than plastics though. Like I said, extrusion can use any material int he form of a filament or pellet. Wire extrusion is used to print metals, although this requires the addition of a laser to melt the wire filament as it exits the nozzle. The extrusion method can even food. Yes, food. A quick Google search will give you tons of hits of small business printing cakes, chocolates and even ice cream. I personally would not mind printing a Nutella design like this one. But I'll stick to engineering plastics for now.

Source: Mashable.

Blown Powder

Blown Powder, also known as Laser Metal Deposition (LMD), blows a fine layer of metallic powder along the previous layer of the part while a laser oriented normal to the surface melts the particles which fuse with the base metal when cooled [3].

Source: EPMA

The cool thing about blown powder printing is that it can be used to repair a damaged part, potentially saving tons of money (and making happy customers) in the world of after-market products. LMD is also used for coatings. A wide range of materials are used in LMD, including hard metals like Ti 6-4 and high strength steels [4].

Cold Spray

Though the process is exactly what it sounds like, cold spray seems to defy all logic. Metallic powder is sprayed at extremely high velocities (Mach 4, to be exact) onto a part or substrate and essentially stick to the lower layer. Like LMD, cold spray can be used to coat a part or add material to a newly built part or to a repaired part. Not using heat in this printing process means that the part for repair is not jeopardized by high temps and can be repaired to near original condition [5]. GE Aerospace seems to be the main user of cold spray technologies but smaller companies have also been exploring this AM method.

Those are the heavy hitters in material deposition. Keep an eye out for my Acronym Dictionary I'm currently putting together (it's easy to get lost in the alphabet soup of AM). If you have any questions or comments, please don't hesitate to either comment below or use the message box on the side of this blog!

Sources:
[1] Advance Manufacturing CRC, Additive Manufacturing Categories Process and Materials: http://amcrc.com.au/wp-content/uploads/2013/03/ADDITIVE-MANUFACTURING-CATEGORIES-PROCESSES.pdf
[2] ReRap, Heated Bed Wiki: http://reprap.org/wiki/Heated_Bed
[3] European Powder Metallurgy Association, Additive Manufacturing Technology: http://www.epma.com/additive-manufacturing-technology
[4] TWI, Laser Metal Depostion: http://www.twi-global.com/technologies/welding-surface-engineering-and-material-processing/additive-manufacturing/laser-metal-deposition/
[5] 3Ders, GE's new Cold Spray 3D printing technology to build up and repair parts: http://www.3ders.org/articles/20131114-ge-new-cold-spray-3d-printing-technology-to-build-up-and-repair-parts.html