Desktop Metal
For those who are unfamiliar, Desktop Metal is a company that specializes in 3D printers. During my time at the company, they were mainly focused on metal 3D printing. The two main systems at the time were the Studio System and the Production System which I will describe in a little more detail here.
The Studio System
The Studio System is Desktop Metal's first 3D printing solution. This system utilizes a process called Bound Metal Deposition (BMD), a process in which metal powder is formed into a rod using a polymer binding agent. This allows the material rods to be safe to handle without the use of PPE. These rods are then loaded into the printer and are pushed through the printing nozzle. They are heated up and extruded through the nozzle to dispense material layer by layer onto the print bed to form a part.
The Studio System contains two nozzles. The first releases the bound metal powder while the second nozzle prints an interface layer which separates the metal to keep it from forming together in later steps in the process. This interface material is placed between the part and it's supports to allow for easy support removal unlike in some other metal 3D printing processes such as SLM which require post-processing machining to remove supports.
The Studio System prints parts with infill. This is a way to lightweight the parts and minimize cost. Rather than printing fully dense parts, the system will print a lattic structure within the part. This helps in the debind stage to allow the fluid to fully access all points of the part. This infill density can be altered within the printing parameters (slicing) in the setup of the build.
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Once a part is printed it is considered a "green part" and is ready for the debinding process. For debind, the part is loaded into the debinder. Once closed, the operator can start the process in which the tank will fill up with debind fluid. This fluid will remove excess binder from the rods while still leaving enough to hold the part together.
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After debind, the part is ready for the sintering stage in which it is placed in a furnace and heated to its melting point to burn off the remaining binder and bond together the metal particles into a full metal part. After this phase, the part is a real metal part and can be handled as so. In this step, the interface material will also heat up and turn to a powder. This allows to the easy removal of the supports with minimal effort as shown in the video below.
Part in "Green" Stage after Printing
Part in Debind Stage
Part in Sintering Stage
The Production System
The Production System is more focused toward mass production rather than rapid prototyping. This system is built to produce lots of parts in a single build. The Production System utilizes a process called Binder Jetting in which metal powder is spread across the build box in an even layer and a print head with thousands of nozzles passes over and dispenses a binding agent over the powder. This binding agent is only printed in the areas in which the parts should be connected. This process continues layer by layer until the build box is full. Additionally, the system uses single pass jetting meaning that it prints in both directions of the print head motion. That is, it will print when the nozzle heads move to the left and when the nozzle heads move to the right.
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Once the print is complete it goes to a crosslinking step in which the binding agent is heated to activate it and to better hold the part together. Once it is crosslinked, the part goes to a depowdering stage in which all of the excess powder that was not bound together gets brushed away and transfered to be sifted and reused in another build.
After the part is depowdered, the Production System utilized a similar sintering stage in which the build box is placed in a furnace and heated to its melting point to bond together the metal particles into a full metal part.