Week 17 : Wildcard week

• 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, and cooking.

Thermoforming a box for a lens and a mirror

To show that lens and mirror have been cleaned after work, we used to let them unmounted in the laser cutter.
Because this material is breakable, I wanted to make a box to store them.

I started by designing lens and mirror footprints in a cube. Then I added two circular holes to put finger to pull devices.
I worked on Freecad because my first idea was to print it in 3D and them to thermoform it to duplicate three times for each of our laser cutter.

Lens and mirror box Freecad file

Sketch on Inkscape

Thermoforming a 3D printing piece seems not to be possible because the sheet of plastic is hot and will heat the master piece. Master piece can distort or glue to the sheet.
So, I decided to mill the master piece. Not to make a long 3D milling, I redesign it under Inkscape to mill just five pockets and cut the outline.
At the end, I export the design in pdf.

Lens and mirror box Inkscape file

Milling master mould

I first search a mill to make the job. Pockets I wanted to mill are quite small and the only mill wich size can be not to big was a 1/8'' Tapered Ball Nose (77-102). As it's not a flat end mill, I set overlap to 10% not to have a bottom bad surface. I set spindle speed to 6000 rpm and linear speed to 40 mm/sec.

On Vcarve pro, I import my design in pdf.
I select the two polygonal shapes and made a pocket 6mm depth for lens and mirror.
I also made a pocket 9mm depth with the three circular shapes, big ones are to put fingers to pull lens and mirror and the last one is for a screw head on the mirror.
Then, I made the outline cut.

Thermoforming

Thermoforming is an interesting way to produce several pieces (small series) quite fast with only a master.
Whith my milled piece, I can now thermoform my store box.
I used a Formech compac mini
Fabrication process is :

• put your piece on a grid in the bottom part
• put a sheet of PET (width 250 mm , height 300mm, thickness 1.5 mm)
• fix it with the interlock system
• pull the heater part above the sheet
• wait the timer (60 seconds fo our sheet)
• remove the heater
• turn up the master piece
• vacuum the air (few seconds are enough)
• release and get the sheet

The most difficult is to remove the master piece after thermoforming. I had to put screws in the master piece to help me to pull. Next time, I should be aware of it when designing my piece, add chamfer, use conic shapes.
As MDF is a porous material, machine can vacuum through material and plastic can easily go in holes and pockets.