Akila's week 10 at Fab academy

1. Group assignment: Safety datasheets of materials used and test casting

We read the datasheets for liquid silicone, liquid plastic and Moldmax-60 high heat-resistant liquid silicone rubber.

As per the datasheet, 10% of the curing agent (Part B) had to be mixed with the silicone rubber base. The curing time is 24 hours.

This is liquid plastic. 60% of the hardener (Part B) has to be mixed thoroughly with 100% of the resin (Part A). The setting and drying time is approximately 2 hours.

These are various colour dyes. A pinch of the desired dye has to be added during the mixing process.

Weighing out the components.

Mixing thoroughly, scraping the sides and the bottom of the container. Take care not to create many bubbles.

You must pour the mix from a greater height than depicted in this photo. Pour in a thin line, at the lowest point in the mould and let the liquid flow by itself to occupy the crevices.

After 24 hours, the test cast of Moldmax-60 is all set.

After 24 hours, the test casts of plastic and silicone rubber are all set.

2. Designing and milling the mold

Download the design file (.f3d) here

Measured the dimensions of the 3D-printed rings to make this sketch in Fusion 360.

After extruding the rings to different heights as in the 3D-printed object, realized that the top of the mould has to be of equal height throughout. The liquid poured will just fill all the portions.

Tried adding a step to denote the place where the excess portions on the rings can be manually cut off.

Again realized that it is not possible to add the steps when using the 3mm diameter tool bit.

Decided to go with this design and cut off the excess portions manually.

At the Modela milling machine with the wax block to mill my mould.

The new 3mm toolbit.

The double-sided tape at the bottom of the wax block to hold it on the machine bed.

I had saved my design, slightly tilted in space. Hence the toolpath generated was incorrect.

Set the tilt right but the view is now topsy-turvy. Had to set that right again in Fusion 360.

At the right orientation, the toolpath is generated perfectly and is sent to the machine to mill. I used a 3mm diameter tool bit, with rough cut.

The mold.

Cleaning up.

Collecting the wax dust for recycling.

3. Casting

From the volume of the design obtained from Fusion 360, calculated that I needed around 8.5g of liquid mix inside the mould. 7727.158mm^3=7.727158cm^3; Silicone density=1.1 gm/cm^3;Mass=volumexdensity=8.4998738g

As per the datasheet for liquid silicone rubber (LSR-1), 10% of the curing agent (Part B) had to be mixed with the silicone rubber base.

Mixing thoroughly, scraping the sides and the bottom of the container. Take care not to create many bubbles.

Added a couple of copper wire loops to facilitate pulling out the mould after curing.

Wrong way to pour. Sheer panic start.

You must pour the mix from a greater height, to avoid air bubbles. Pour in a thin line, at the lowest point in the mould and let the liquid flow by itself to occupy the crevices.

Left it for 48 hours (over the weekend) to cure, although only 24 hours is specified in the datasheet.

All set and ready to be taken out of the mold.

Excess portions to be cut off to match the original dimensions. However, the bridges between the rings had to be wider to accommodate the tool bit and the wall had to be thicker or silicone would stretch and tear.

Cutting away the excess with a pen-knife.

4. Metal casting

Download the design file (.f3d) here
I had to repeat this assignment in the week of 17-23 June because I had earlier not fulfilled the requirements of following a 3-step process, starting from the positive mold in wax. I tried making a hollow box with lids to close the top and bottom. I assumed that the metal I was going to use would be magnetic and I could use magnet pieces to integrate the box. This was a fail. Bismuth is diamagnetic (repels magnets!). Anyways, I learnt the process and looking forward to trying more designs in the future.