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18. Wildcard week

Assignment

Design and produce something with a digital fabrication process (incorporating computer-aided design and manufacturing) not covered in another assignment, documenting the requirements that your assignment meets, and including everything necessary to reproduce it.

Possibilities include (but are not limited to) composites, textiles, biotechnology, robotics, folding, and cooking.

Summary

This week, I’ve used a thermoformer, and learned from the molds I used, what are its limits, and what need to be done to have a good thermoformed mold.

Files are available here

Materials and processes

Having my final project in mind, my first idea was to work on felt or velvet and related materials needed to make it hold on a structure in order to obtain a deployable origami structure… But delivery schedule for the materials is short, so I decided to use the brand new Mayku FormBox thermoformer that has arrived in the lab:

I decided to reuse the molds made for the mold and casting assignment, and to adapt them to this thermoforming process. Redesign is done in Fusion360:

  • Mold 1: A flat surface is added below the four cubes to hold them together.
  • Mold 2: Small holes of 1mm diameter are added in the bottom of the cavities to allow the air to be vacuum cleaned and the form sheet to fit to the cavities.

Files are available here

Both molds are then 3D printed with PLA on the PRUSA MK3 printer of the Fablab. The thermoformer requires indeed a mold that is strong enough to resist the temperature and pressure applied during the process:

The idea is to compare the efficiency of the process for the two molds, as they are supposed to provide the same shape, knowing that the shape are at the limits of the thermoformer capabilities…

I enlarge a bit the holes with a 1.5mm mill, as some holes seem to be in bad shape…
I add an additional hole in the middle of the mold 1:

mold1 mold2

With the chosen structures, the second of the three rules for thermoforming is not applied:

  • Remove all undercuts: OK
  • Add draft angles: NOK
  • Add air holes: OK

Moreover, the height/width ratio may be to big, and having four structures close together will probably causes difficulties…

The structure is small, and we want to test the capabilities of the process, so let’s try…

Two types of sheets are available:

  • form sheets: white / satin surfaces / easy to cut / ready to paint / durable / replicates fine details
  • cast sheets: transparent / reusable molds / food safe / non-stick surface / flexible / easy to cut.

As I plant to make chocolates for the french fabmanagers ;-), I’ll use cast sheets

The manufacturer provides settings data, but it quickly appears that the times provided are not long enough, the material is not soft enough. I’ll look at the sheet deformation, and when the curvature is really visible, I press it down to the mold.

Here are the results, after some difficult but successful extraction of the molds!!

mold1 mold2

As expected, not ideal process:

  • mold 1 doesn’t provide closed cubic volumes as the cast sheet didn’t stick on the bottom plate, but the sheet thickness is quite fair, except in the center.
    Adding additional holes on the plate between the plates doesn’t really improve the process…
  • mold 2 provides nice cubic volumes, but the sheet thickness in the bottom of the volumes is too thin, so thin that one of the cube is drilled..

But this doesn’t stop us to make chocolates. Let’s use mold 2:

melting chocolate with some water in the microwave, and pouring the chocolate in the mold,

oups, it leaks a bit…

a few hours in the fridge, and here we have:

Good appetite!

Still to do if I had time....

The process is far from ideal, but I’ve learned a lot on it, and I could make a perfect reusable mold with details!!