The Desktop Metal Printing process allows you to produce solid metal parts, in-house, in an office environment. The entire process is based off the metal injection molding process, or MIM. The MIM process involves making tooling to inject a metal powder/polymer/binder mixture into the desired shape. The parts are in a ‘green’ state and not full strength yet. Then the part is put through a debinder tank of liquid, to remove the binding agent from the metal, leaving the part in an even weaker ‘brown’ state. Finally, the parts are put into a furnace to sinter them into a solid metal part. This allows for the creation of near-net-shape parts that can be made faster and with less machining needed than forging or casting of the parts.
Below is a comparison between the MIM process(on-top) and the DM process(on bottom)
One of the downsides of the MIM process is that the parts need to be debound to remove the binding agent from them prior to sintering in the furnace. This is an issue because as the parts get thicker the debinding liquid will take longer and longer to penetrate all of the way into the part to be able to remove the binding agents. This effectively puts a hard limit on how thick a MIM part can be because the debinding time will scale up exponentially with part thickness.
Desktop Metal allows us to get around this constraint by being able to print parts that are not 100% solid. The Desktop Metal printer can print parts without the need of a tooling mold like MIM, in a way that is very similar to a fused deposition modeling (FDM) printer. The material starts as a rigid rod of metal powder mixed with polymers and debinding powder. The printer heats up the material only hot enough to melt the plastic polymers in it and not hot enough to melt the metal powders, making it a safe and easy operation and does not induce any high temperature stresses into the part. Using the technology’s ability to print at a self-supporting angle that doesn’t need support material, the inside of larger solid parts can be printed with a hollow infill pattern. This will be useful to allow the part to debind faster yet keep the part a very strong metal piece. If your part needs the strength of over 0.5 inches thick of solid steel, it would be better suited to make it with another production method.
For overhanging sections of the part or steeper angles the printer will print a support structure under it so the part will not deform during the sinter process. The bulk of the support material is the same metal for the structure but there will be a single layer of a ceramic material separating the support from the part itself. This ceramic will turn into a powder in the furnace and prevent the part and the support from fusing together during the sintering cycle. As an added bonus, at the end of the process when you get the solid metal parts and support structure, you can separate them by hand without needing to use any other powered equipment or tools.
Parts can be post processed at any stage during the process. For example you can hand sand down the exposed surfaces of the printed part before it gets sintered for a better surface finish without the need to involve any larger power tools.
In the next post we will go more in depth on the Debinder process.
Sr. Applications Engineer – 3D Printing/3D Scanning/Solidworks
Computer Aided Technology, Inc.