10. Molding and casting¶

Group assignment :

Review the safety data sheets for each of your molding and casting materials
Make and compare test casts with each of them

Individual assignment :

Design a mold around the stock and tooling that you’ll be using
Mill it (rough cut + (at least) three-axis finish cut)
Use it to cast parts

Group assignment¶

Link to ULB Group : link

For the group work, I analysed the products available to me. We received Crystal Clear resin, RTV Silicone, but also classic and phosporescent colorants and a release agent.

Crystal Clear resin datasheet¶

Transparent casting and coating. Two component colourless epoxy system.

W241: Recommended maximum casting thickness 100mm

W242: Max. recommended casting thickness 10mm

Colour: colourless

Viscosity at mixing: 650-950

Density: 1.10-1.14

Mixing ratio: 100:45

Potlife with W241: 75-95min

Potlife with W242: 35-45min

Demoulding time with W241 : 36-48h

Demoulding time with W242 : 18-24h

Danger

H315: causes skin irritation

H317: May cause skin allergy

H318: Causes serious eye damage

H411: Toxic to aquatic organisms, causing long-term adverse effects

P261: Avoid breathing dust/fume/gas/mist/vapour/air

P273: Avoid release to the environment

P800: Wear protective gloves/protective clothing/eye protection/face protection

P305+P351+P338: In case of contact with eyes: rinse cautiously with water for several minutes. Remove contact lenses if present and easily removable. Continue rinsing

P310: Call a poison control centre or doctor immediately.

Silicone RTV¶

RTV silicone is suitable for the reproduction of figures, artefacts and similar objects. It is a 2-component material consisting of RTV and RTV hardener. Curing at room temperature.

Technical data with RTV hardener

Colour: White

Hardness Shore A:25

Demoulding after 24 hours at 23° CPréparation du matériel

Potlife: 36-60min

Mixing ratio by weight: 100:5

Tensile strength: 2.8

Elongation at break: 380%.

Tear strength: 2.0kN/m

Linear Shrinkage: <0.8

Relative density: <0.3%.

Relative density: 1.08

Viscosity: 20.000-25.000 mPa

Individual assignment:¶

Design on Fusion 360¶

I have made a name tag for the fablab. It is small but complete enough for the demonstration. After looking at the time estimates for the machine, I decided to make the part on the “big” digital milling machine.

First step, roughing with a 3mm milling cutter

Optimal load : 1.2mm
Minimal cutting Radius : 0.3mm
Maximum Roughing Stepdown : 1mm
Fine Stepdown : 0.1mm

Then roughen with a 1mm milling

Optimal load : 0.4mm
Minimal cutting Radius : 0.1mm
Maximum Roughing Stepdown : 0.5mm
Fine Stepdown : 0.05mm

With a 0.6mm milling

Contour

Maximum Stepdown : 0.2mm

Pocket for b and a : 0.6mm

Maximum Stepover : 0.57mm
Finishing stepdown : 0.1mm

3d surface finish with 0.6mm milling

Stepover : 0.1mm
Maximum Stepdown : 0.2mm
Nb Stepdown : 1

Download :

Work in CNC Mekanika¶

A first pass with a 3mm milling

A second pass with a 1mm milling

We finish with a 0.6mm milling

I am quite happy with the result

Mould creation¶

Let’s go for the casting of the part.

Preparation of the material

Weighing is extremely important. The ratio of 100:5 must be respected.

Mix for a few minutes without making bubbles

Spray is applied to facilitate demoulding in the final phase

The silicone must be cast to make the mould

We wait about 24 hours to see the result

Creating resin parts¶

Danger

obligatory protection

Weighing is extremely important. The ratio of 100:45 must be respected.

we start pouring

A few drops of dye are added

We add the second component

Mix well to avoid bubbles

We prepare the parts to be moulded and we cast our mixture

We heat to make the bubbles disappear.

To remedy the bubbles, several solutions are available to us:

1 - Pour really slowly without any sudden movement (not the easiest)
2 - Use a vacuum box (we don't have one at the fablab)
3 - Heat the resin until the bubbles disappear. (this last option was used here with a "thermal stripper")

Final Result¶

Bonus¶

In an art shop, I found some silicone moulding compound. It is ready in 5 to 10 minutes and the mould can be used 50 times.

Mixture, 1/1

So I made several moulds to carry out several tests. The first one, with a phosporescent powder, the second and the third with different dyes and the last one with wax