Molding & Casting

Task Requirments:

Explain how you designed your 3D mould and created your rough and finish toolpaths for machining
Show how you made your mould and cast the parts
Describe problems and how you fixed them
Include your design files and ‘hero shot’ photos of the mould and the final object

Idea:

The idea is to make a simple and small coin 15mm in diameter through a small mould that simulates a cold runner injection mould and allow me to cast more than one part in the same mould.

This is a useful link to understand the different types of injection moulding, the cold runner mould mainly comsists of a sprue that is filled with materials and then distributed through the runners to fill the cavitites of the part through the gates as shown in the photo below:

The gates are like tabs that are made when routing or cutting to hold parts together and are designed to be easily break.

The Design will be based on a two sided mould one that contains the sprue and half of the runners, gates and part - the other side will containd the other halfs.

Design:

First i set the parameters in fusion and i tried to make the smallest possible mould to save machine timings.

Then I proceeded with the part design including the sprue, runners and gates.

i made a construction plan in the middle of the final part and i splitted the design to two bodies

Finally i exported the two bodies as stl

Milling the Mould

Machine: Roland MDX40A
Tool: Ball Nose 4mm
Tool path Software: Roland SRP player

I imported the stl of the bottom mould to Roland SRP player

Then i adjusted the process following the next steps:

Position the mould in the right direction

Select: Faster cutting time, Model with many curved surfaces, cut top only

Choose the right tool

Choose material: Acrylic, and stock size just bigger than the model to save time and materials "SRP mills the model in the middle of the stock"

Create toolpath and preview the results for any errors.

Perform Cutting: Save the Roughing and finishing toolpathes as ".prn"

Vpanel Software:

From the Vpanel software:

move the XY axis to the center of the model
set the Z axis using sensors
Press Cut, Import the roughing file
Start Cut
After roughing is finished import the Finishing file and start cut again

After 1 hour i had my mould finished

I repeated the whole step for the upper mould

Casting The Mould

Material: Silicone Rubber + Hardner

I used a sensitive scale to add the hardner to silicone rubber by 3% concentration as stated on the pack.

I used a tongue depressor to stir the mixture, make sure to stir slowly and in 8 shape movements to reduce the air bubbles

I casted the silicone to the acrylic mould, pouring from a high distance to try to eliminate the bubbles.

I hit the mould to the ground several times to get the bublles to the top

I left it to dry overnight and this is what i got !

Casting the part:

Material: Transparent Epoxy + Hardner

I alligned the two sides of the mould and taped them together, making sure the tape is not tight not to bend the mould and also allow air to escape.

Again i used sensitive scale to add the hardner to epoxy with 1 to 2 ratio as instructed on the pack

I stirred very slowly to minimize the air bubbles and poured the mixture to the sprue "mould hole"

I moved the mould to all directions for the epoxy to fill the whole mould

I left it overnight

Failure:

Because the mould size was small and the gates was tiny also the epoxy is very viscous, the mould didn't fill and here is what i got.

Second try:

I figured out that i need to apply pressure to the epoxy to force it through the runners and then the gates to fill the cavities in the mould

I used my baby nasal aspirator refills to put it in the sprue after adding the epoxy and blow air through it.

Again i left overnight, and the results was ok, except for one part

Areas for improvment:

The gates need to be larger

The runners needs to be deeper with inclination to facilitate mould filling