3D Printing Using Density Control

 In 30 days of education

One of the novel aspects of 3D printing is the ability to finely control the amount and location of density within the object. This blog post explores ways to do that to create one-of-a-kind models and explains some of our kits which use this unique feature of 3D printing.

3D Printing Using Density Control

3D printing is an amazing technology, capable of creating models that are unable to be created using any other method while still being cost-effective. One of the novel aspects of 3D printing is the ability to finely control the amount and location of density within the object. Unlike traditional materials, these objects are not completely solid. Nor are they completely hollow – that is, unless you specify it. They are exactly as solid or as hollow as you prescribe when you build and slice the model.

If you’re unfamiliar with the term “slicing” the model, that refers to the computational calculations which “slice” the object into individual layers to be printed. Since FFF printers build the object one layer at a time, the object must be translated from a three-dimensional object into a series of stacked two dimensional objects. This additional step allows for the creator to be able to control what’s going on inside the model as well as outside.

When setting up slicing settings for your 3D printed objects, it’s important to consider more than just speed and layer resolution. (For info on how to set up optimal slicing settings, visit yesterday’s blog post here). You also need to consider the amount of infill you need for your object. Infill is the percentage of the interior of your object you want to be filled with filament. So, the higher the infill, the greater the density of the object. But be warned, every spool of filament is slightly different. The density of the filament will vary between brands, colors, and even spools, so try to print density-sensitive kits all from the same spool of filament for optimal results and test your prints before integrating them into the classroom

Check out a few of our STEM kits which utilize 3D printing’s ability to create variable density within an object below and get ideas for how to do the same in your classroom or makerspace.

Density Cubes Kit

This kit is as simple as it gets. Adjust infill on three different sized cubes to create cubes that sink, cubes that float, and cubes which are somewhere in between. They look identical on the outside, forcing students to consider what must be different on the inside to cause the change in behavior. Plus, due to the ability to fine-tune the amount of infill, we’ve created cubes that are nearly neutrally buoyant. Adjust the temperature and salinity of the water to make the cube’s density equal to that of the water’s for a memorable lesson on density and object properties! To see a video of this kit in action, click here.

New York Balance Kit

Not your typical New York Balance, this one can also address proportional reasoning. This is because we can control the infill on the weights and the holders to ensure they weigh the same amount.

Balancing Currency Kit

In this kit we use our fine control of density to create blocks which are equivalent by weight to their value, so students can literally balance equations to determine the value of each type of coin. See a video of this kit in action here.

Loaded Dice Kit and Loaded Coins Kit

How do you 3D print loaded dice and coins? Simply, you control where the infill is on the inside of the object. For these kits, we’ve actually set up the print settings to be 100% solid. However, we’ve designed the interior of the object to have a hole cut out of it. That way, we can fill the object completely solid while maintaining air space on the inside exactly where we want it. This allows us to weight one or two sides of the dice to suit our needs.

Thin Meter Stick Ramp Kit: Moments of Inertia Expansion

This kit was designed in a very similar fashion to the Loaded Coins and Dice Kits. Designed to showcase the effect the weight distribution has on torque, we created two cylinders which are completely identical from the outside and weigh the same amount, but in which the weight was distributed differently. For one cylinder, the weight has been forced into the center of the circle. For the second, the weight is around the exterior ring. Students can place the two cylinders back to back on a ramp and see that one will significantly outpace the other when given the chance. To see a video of this kit in action, click here.

Cell Membrane Kit

This kit uses density-control to create something unlike anywhere else. The hydrophillic phospholipid headgroups are printed either solid or nearly hollow to force them to float or sink. All of the hydrophobic fatty acid chains on the phospholipids are printed with 100% infill. However, there is an invisible air-bubble built into one set of fatty acid chains, forcing them to sink in an upright manner. When assembled according to the provided instructions, these sneaky phospholipids will self-orient into a phospholipid bilayer when dropped in water. This model realistically demonstrates the behavior and motion found within the cell membrane, but it does it through density instead of biochemical polarity. (Which is important for teachers to point out, since the water is actually behaving in a reverse manner than it does in actual cell membranes.) To see a video of this kit in action, click here.

Dice

If 3D printing dice of any sort (that aren’t designed to be loaded), it’s important to ensure the dice produce fair results. To do this, we print all our dice at 25% infill to make sure there’s an equitable distribution of weight inside the model as well as out.

Pantograph Kit

By now I’m sure you’ve caught on to the idea. But where does this kit use density control? The C-clamp included in this kit is printed separately from the remainder of the kit because we’ve set it up to print with a higher amount of infill so that it’s sturdier and can withstand pressure being placed upon it.

How do you use density when 3D printing? Share in the comments section below!

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