MULTI-MATERIAL HEADBAND
Tools and Skills: User-Centered Design, Prototyping, Material Analysis, CAD in Fusion 360, UltiMaker Cura, FFF Multi-Material 3D Printing,
Project Brief
Design and print an assembly that implements a process that is unique to additive manufacturing methods. An example is a multi-material assembly, in which two different materials are printed at the same time to create interlocking parts. The materials’ properties must be leveraged so that their selection helps to achieve the assembly’s intended purpose.
Challenges
The main challenge of a multi-material print is ensuring that components made of different materials are properly interlocked. Since the two materials have different properties, they won’t naturally adhere to each other, so in order to ensure a proper connection, there must be enough overlap between the two materials so that their layers interlock with each other during the print.
Results
Initially, I was concerned that this project would be under-scoped, but after multiple printer difficulties and a failed print, I realized that my project was properly scoped after all. In the end, I became more efficient at CAD, learned a lot about printer set up, and produced a fully functional, personally customized, multi-material headband that I wear quite regularly now!
CONCEPT SELECTION & SKETCHES
Headbands are great because they keep hair out of your face without putting too much stress on your hairline. Fun fact about me: I have a pretty big head and really thick hair. As a result, most headbands are too small for my head and/or aren’t strong enough to hold my hair.
The goal of this project was to create a custom headband that pulls my hair back, fits comfortably, and stays on my head. I decided on a multi-material assembly that combines a tough, rigid material such as PLA to maintain strength and a softer, grippier material such as TPU to increase friction in specific areas and to alleviate pressure points.
PROTOTYPING & ITERATING
This 3D-printed, scary-looking “torture device” (real feedback, no lie), was my first prototype. I was testing for size, shape, and feel, and let’s just say that I definitely had some work to do. The band was too thick and was very stiff because the infill (20%) was too high. It wouldn’t flex at all, and it didn’t fit my head. While the teeth were too thick, tall, and pointy, they were effective in that they properly combed my hair back and held the band in position. Ultimately, I had to make some major changes to the band itself and some small tweaks to the teeth, but it wasn’t a far cry from the end product I was after.
Since I was pretty happy with the design of the teeth, I focused on the band for my next prototype. I decreased the width and thickness, and I lowered the infill to 10%, which made the band quite flexible but still sturdy. I also filleted the edges and the ends for a more standard headband look, and while this test was a little too big and circular for my head, I felt confident enough about the design to move forward.
MULTI-MATERIAL TEST PRINT
As mentioned, the biggest challenge of this project was ensuring that features made of different materials are properly interlocked. This test print was to make sure that the PLA (black) and the TPU (red) would stay adhered to each other upon being printed.
In order to alleviate pressure of the end of the band pressing behind my ears, I decided to use TPU, a rubbery, high friction material, for the ends. I designed a dove tail joint to interlock the TPU with the PLA, which did work in that it locked the TPU into the PLA. However, I didn’t account for the fact that the area where the faces met also had to be interlocked, which is why the TPU could be peeled away from the PLA.
I wanted the teeth to have some grip as well so that the headband wouldn’t slip off my head. In order to achieve this, I added a layer of TPU to the bottom of the teeth PLA teeth, connected by a similar dove tail joint used for the ends. This connection was much more successful, likely because there was more overlapping area between the two components.
FINAL CAD
Taking my findings from the test print, I adjusted my CAD accordingly. I kept the teeth basically the same but just made the TPU layer slightly thinner. As for the ends, I realized that I only needed the surface to be TPU, so I extended the PLA on the ends and enveloped them in TPU. This adjustment would make the ends less flimsy, and I was hoping that the increased overlapping area between the PLA and TPU would better adhere them to each other.
SLICED DESIGN
UltiMaker Cura is a slicing software, which slices a 3D model into layers so that it can be 3D printed. Since this is a multi-material print, it requires two printer nozzles, one for each material. When the printer is switching between materials, it extrudes some of the new material to clear the nozzle of any solidified filament and to ensure that it’s at the right temperature before printing the main product. The excess is what creates that cylinder in the top corner, and it is not part of the final print. Not including setup and heat up time, this print would take about 3.5 hours at 10% infill.
PRINT FAILS
My first attempt at a full print was rather unsuccessful. I overlooked a critical feature in my CAD, and there were issues with the printer set up and in print quality.
Unjoined features in CAD caused the band to snap down the middle when I was removing it from the print bed.
Uncalibrated XY offset between the printer nozzles caused misalignment between the TPU and the PLA.
Unleveled print bed caused some layers to melt together and others to delaminate from each other.
FINAL PRODUCT
Luckily, the issues that caused the print failure were easy to address. After some tweaking and another 3.5-hour print later, I had a final product! The headband is super effective in that it fits perfectly on my head, keeps my hair back, and stays on my head without slipping! I
