3D Printing, Desktop Metal, 3D Printing Materials

How to Print an Enclosed Cavity in Metal

By Rich Annino on April 30, 2019

TriMech has had the complete Desktop Metal Studio System for over five months now, and we’ve had the opportunity to create some incredible parts with it during that time. One of our favorite parts so far is a heatsink, which utilizes the Studio System’s Bound Metal Deposition (BMD) printing technology to its advantage, in order to print a captured hollow cavity that requires absolutely no support or post-processing, which can’t be machined and is impossible for other metal printing technologies on the market to create.

Metal Heatsinks Final Result

Advantages of Bound Metal Deposition (BMD) Printing

Most 3D metal printers on the market use a laser to sinter particles of fine metal powder together, one layer at a time. While this is great for high-resolution metal parts, the support removal process is significantly more complex than both traditional plastic 3D printing methods, as well as the Desktop Metal Studio Printer. This is mainly because there is no secondary support material, which means that your supports are made of the same material as your build. This can make the removal more complicated and potentially damaging to the part. Also, any metal powder captured in a hollow cavity is essentially going to be stuck inside of the part permanently unless machined out in post-processing, in which case you would be left with a hole in the part. Finally, these laser-based machines can be up to five times the cost of the system we used to make these heatsinks, so depending on your application, this type of 3D metal printer is most likely not a practical solution.

The Desktop Metal Studio System uses Bound Metal Deposition (BMD) technology, which is similar to the Fused Deposition Modeling (FDM) that our Stratasys thermoplastic printers use, though it uses rods of metal material bound together with resin and wax agents instead of a fragile continuous filament wireDesktop Metal Studio. The primary similarity to Stratasys FDM is that this technology extrudes lines of material to create each slice by creating an outer contour and filling that contour with interior rasters to give the part strength and dimensional accuracy stability. Any area of our Studio System parts that are fairly thick is going to have a semi-hollow infill by default. However, no matter what, we’re going to have a consistent thickness to our outer wall, and the layer lines that it prints are also going to have a consistent thickness.

What this allows us to do is to create overhanging features called “Self-Supporting Angles”, which are angles less than 40 degrees that can print without supports underneath them, as we can build each new layer hanging partially over thin air as long as approximately half of that bead of material is printed over the layer below it.

Self-Supporting Angle Desktop Metal

>> Click here to read our blog Optimizing Your Design for 3D Printing

Using a Hollow Cavity in a Design

In our heatsink design, we’ve created a pipe that goes in a circular pattern through all of the fins of the part. From there, we hollowed it out, but instead of making it rounded like a typical pipe that would require supports due to the shallow angles involved, we can create either a teardrop shape, or a pointed oval that resembles a football.

>> Click here to learn more about round vs. diamond hole

As long as the top point of the hollow cavity isn’t rounded and the angle up to it is under 40 degrees, this cavity will print with no supports in it. Using this concept, we’ll end up with a part that is impossible to print on any other metal technology and that is also impossible to machine due to how the hollow tube is embedded inside of the fins as a single piece of metal.Heatsink 3D CAD Design

Proof of Concept

The concept of self-supporting angles absolutely does work, both in FDM and BMD and it’s a great one. Remember to take this into consideration as you’re designing your models in CAD because it can:

  • Substantially reduce the cost and print time of the part (supports take longer to print and waste material)
  • Make post-processing of the part easier
  • Allow some parts, like the heatsinks from our scenario, to have features that are impossible to create otherwise

These images show how the interior channel is being printed with nothing inside and completes successfully without anything supporting the interior heat pipe other than the layers of material below it.

Heatsink Printing

Heatsink Preview

Following the print process, we removed any leftover strings of metal or interface material and cleaned the parts up a bit using either sandpaper or X-acto knives, as the parts in the green state are essentially like a very hard clay at this point and are easy to work with. We then put them into the Studio System Debinder to dissolve out the primary binding agent.

Heatsink in Desktop Metal Debinder

Once the parts were completed in the Debinder cycle, we put them into the Furnace to remove the secondary binder and sinter the parts together fully. When the Furnace completed, we needed to break them off of their base by hitting the part on a flat surface. The ceramic interface material that prints between the part and its supporting base turns to dust during sintering, allowing us to easily remove the part from its base.

Heatsink Debinder Cycle

Metal Printing Process Summary

Printing full metal parts that have self-supported hollow interior features is easy! It all starts in the CAD design, where you create your model thinking about where the Studio System’s Fabricate software is going to want to put supports and modify those features in a way where it removes this need. Once you have that design, you can send it to the printer, debind the parts, and sinter them. That said, if you don’t have a Desktop Metal Studio System yet, contact us and we’ll help you get from design to sintered metal part!

Are you interested in learning more about how to print other objects with the Desktop Metal Studio System? Click on the button below to download our guide, "Walkthrough: Creating Metal Bottle Openers Using the Desktop Metal Studio System."

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