This design for a folding container needed a 3D printed prototype because of its overlapping parts and its silicone-like qualities. The actual product is designed to be injection molded silicone.
When the form is open flat the small petals overlap with the body, so the shape cannot be made from a sheet of material. This is why the prototype had to be 3D printed. Luckily I have access to a 3D printer that prints silicone-like materials.
I wanted to 3D print the shape in its partly open position to get the curvature of the form. I was worried that if I 3D printed the body flat, then it would not revert to the natural bowl-like shape that it should have.
This shape was designed using the help of a program called Ori-Revo. You can an instructable about using that program here.
Step 1: Hinge Testing
First I printed some test hinges to figure out what shape the hinges should be and also how much flexibility they should have. I wanted the hinges to not be an eyesore (create big bumps) but fold far enough so that they would close all the way, and be strong at the same time. I tried tests where the hinges and walls were all the same flexibility, and others where the hinges were printed with a more flexible material than the walls.
I decided that the best hinge was the one with two concentric circles. Almost all of the other hinges ended up falling apart over time. I chose the 40% flexible mix of resin because of its strength. It turned out that having different material flexibilities made it weaker.
Step 2: Creating the main body
First I modelled the form using a 3d modeling software that is on the cloud called Fusion 360, which you can get online for free on Autodesk’s website. I made the surfaces without hinges to make sure they were perfect before adding hinges.
Step 3: Adding Hinges and Petals
I then added hinges at the creases. This was difficult because I wasn’t sure what the form would be like at the intersection of the hinges. I decided to just extend the hinges until they intersected each other.
It was also hard to get the hinge to come to a point in the middle and flatten out. I made the hinge surface end earlier than the center point so that the loft would end as a flat line instead of a point.
After adding the hinges, I made the four petals that protrude from the main body.
Step 4: Exporting as Stl
At this point, I exported the file out of Fusion 360 because I was having a hard time thickening the surface to create a solid. I saved the surface as an .igs file and opened it in Solidworks. I then saved it as an .stl in Solidworks so that I could open it in Rhino. I did this because the .stl surfaces came out nicer in Solidworks than in Fusion and Rhino.
Step 5: Thickness and Repairing
In Rhino I used Offset Mesh to thicken the surface. I clicked the checkbox for Solidify so it would create a solid mesh, and created a thickness of 2mm.
I then used Netfabb to repair some broken surfaces and make sure the stl was perfect.
Step 6: Test Print
Now the file was finally ready to be sent to the 3D Printer as an stl.
Since this is a pretty large model, I decided to 3D print just a quarter of it first. The quarter print turned out well so I printed a full scale model.
Step 7: Final Print
This is the final 3D printed prototype.
It still needs some work with different flexibilities and hinging parts.