Recently researchers started to engineer the internal microstructure of materials. By not only focussing on the outer shape they are creating so called metamaterials. These objects are mostly based on 3D cell grids and can be used to create objects that allow for controlled directional movement. This allows users to create objects that perform mechanical functions (Ion et al., 2016).
When 3D printing these objects, they can be fabricated out of a single piece of material so that no further assembly is needed. For the TU Delft Course Technology for Concept Design (TfCD) we used the described technology to print a tin can cover which uses internally structured cells to clamp itself in place in the can.
Step 1: Supplies
- (Access to) a 3D printer
- A tin can (pineapples are the right size)
- Fusion 360 (or any other modelling tool)
- Cura (or any other slicing tool)
Step 2: Modelling
It is important to first determine which parts of the cover (or any other object) need to be rigid. In our case, it were the block shaped parts that clamped the cover into place. Then the parts that need to be able to move can be modelled. For our project we experimented with different shapes, but used the cell shapes developed by HSI as a starting point. Ofcourse you can experiment with your own shapes to get the right result. The wall thickness of these cells will depend on the type of material used and the specifications of your 3D printer. Since this will determine the stiffness of your object. For our project we used a wall thickness of 0.45mm.
Step 3: Simulation
To inspect how your model will bend it is recommended to run a displacement simulation within your CAD program. This will be the first test to see if your object will work as expected. Further adjustments can then be made to improve the functionality.
Step 4: Prepare Printing File
If you are satisfied with your design it can be printed. For slicing we used Cura with these settings:
- Layerheight: 0.25 mm
- Infill: 20%
- Temperature: 205 deg C
- Bed Temp: 60
- Print speed: 60 mm/s
Note: Check in the Layer view if the layers are sliced correctly and if no weird movements are made. If so, adjust the thickness of the bending strands in Fusion.
Step 5: Printing
The printer used is a Wanhao Duplicator i3 v2.1 and took around 50 minutes to print.
Our lid is printed in generic PLA, but other materials are probably better suited for this job, because we found that PLA is quite stiff and brittle. In the previous mentioned paper (Ion et al., 2016), TPE is used, though this would probably be too soft. In the Thingiverse link below, both a PLA and a TPE version are included.
Here a relevant piece about flexibility of filaments copied from filamentguide.net
Here are a few different kinds of Flexible Filament:
Thermoplastic elastomer (TPE) – sometimes referred to as thermoplastic rubber – is very flexible plastic. A lot of printers have difficulties printing with it, because of it’s softness which can result in extruder jams. A popular brand of TPE Filament is Ninjaflex.
Also known as Soft PLA, this is a modified, softer PLA plastic which is a generally stiffer than TPE. It’s available as Flex EcoPLA and other brands.
TPU stands for thermoplastic polyurethane, and has many useful properties, including elasticity, transparency, and resistance to oil, grease and abrasion.
I could find the relative softness of this Thermoplastic Co-Polyester, but it’s available as FlexFill from Formfutura.
I added this one after a comment. FPE (Flexibel PolyEster) is often compared with Soft-PLA, but FPE has much higher thermal resistance (glass transition temperature of 95 °C).
Step 6: Testing
The first version used wall thicknesses of 0.8 mm everywhere, so when printed in PLA, this became stiff as a rock. This version is better off printing in NinjaFlex. The second model did however work as intended. As can be seen in the picture, the center connections tend to buckle. The model is adjusted for that in the last iteration.
Download the files from Thingiverse.
Step 7: References
Ion, A., Frohnhofen, J., Wall, L., Kovacs, R., Alistar, M., Lindsay, J., . . . Baudisch, P. (2016). Metamaterial Mechanisms (Hasso Plattner Institute). Retrieved from https://hpi.de/fileadmin/user_upload/fachgebiete/....