Class 12 - Molding and Casting

Table Of Content

Assignment

3D Model

I decided to go for an “off-the-shelf” model in order to save time for hands-on part of the assignment.
I took a 3D model of a Lenin bust from thingiverse. With Rhino I added registration cilinders (10 mm high, 5 mm diameter) and casting cone.

Lenin_rhino.PNG

In order to manage the mesh with Rhino I had to decrease mesh size to 50% and convert other surfaces (cilinders, rectangles…) from nurbs to mesh.

Lenin_rhino2.PNG

With boolean operations I was able to make the 3D POSITIVE model for the milling machine, in order to make negative molds of my model.

Machining

I used V-Carve software to produce the files to control our Roland SRM 20 milling machine.
First load one of the two stl files made with Rhino:

vectric_load.PNG

Then set the margin. Here I made the error of adding too much space on the top of the model. The bottom of the model reslted to be too deep for 1/16’‘ tool

vectric_margin.PNG

Then set roughing parameters

vectric_rough.PNG

And set 1/8’‘ mill parameters

1-8 end mill.PNG

Set the finishing parameters. Since the job time was relatively short I decided to run twho passes at 90°

vectric_fin.PNG

And set 1/16’‘ mill parameters

1-16 end mill.PNG

Simulate the job

vectric_sim.PNG

Save two separate files for roughing and finishing:

vectric_save.PNG

Then I copied the files to another PC connected via USB to the machine.
First I made the XY zero to a corner of the wax block. Then I made the Z zero positioning the mill on the wax.
I used VPanel to control the job (spindle speed should not be lower than 8000).

VPanelSRM20.PNG

Finally I opened the first file with “cut” button. When you click “output” the machine starts milling.

VPanelSRM20cut.PNG

This video shows th mill hitting was borders. I had to stop the job and increase the height of the mill (and redo Z zero). This was a problem for the 1/16 mill since it is too short.

Molding

The mold had some problems due to a couple of accidents I had with the 1/16 mill.

finished_wax.jpg

I used TFC SiliconTyp 12 Shore 30 for molding (1:1 ratio, very soft).

silicon_setup.jpg

I made 30+30 g

silicon1.jpg

And I had to add 10+10 more

silicon2.jpg

After a sleepless night I got my first molds:

silicon3.jpg

My first cas wasn’t good at all since I didn’t mix correctly the components (I was worried to make bubbles):

first_try.jpg

Due to the accidents maching the wax, I had to fix the silicon molds before casting:

silicon4.jpg

I decided to make a second mold after aving the wax fixed:

fixed_wax.jpg

TFC SiliconTyp 4 Shore 85/90 (1:1 ratio, very hard mold)

new_cast2.jpg

This harder and faster type of silicon requires manual working of the two components

new_cast3.jpg

I mixed some material and the I had to make some more to finish the mold

new_cast4.jpg

In a few minutes I had a finished new mold (this type of mold is very useful to make vertical molds):

new_cast5.jpg

There were some imperfections to the registration cilinders (not important) and the adhesion of the two parts of material I added was not perfect:

new_cast1.jpg

In the end I had a new mold with a fixed model:

new_cast.jpg

Casting

After having the mold donne, it was time for casting.

cast.jpg

First I used Smooth-cast 325 with 1:1 ratio. First I tried 20+20, it was too much, the I went for 10+10 g.

smoothon.jpg

After a first fail (no reaction) this was an acceptable result:

white.jpg

I also tried Sintafoam HD with 0.6 ratio: 13.3 g A (base), 8 g B (agent)

sintafoam.jpg

After a first bad result I finally got a good result mixing better and faster the two components and casting them as soos as the reaction starts:

yellow.jpg

Here is my final result:

final_result.jpg

Recycling

There is a lot of wax that it milled and can be reused:

used_wax.jpg

I took a piece of 4 mm wood with a varnished side (it doesn’t stick to the molten wax)

wood.jpg

I put used wax in a pot on an electric stove (it melts at 120°C):

fusion.jpg

It took a few minutes to see my Lenin melting down:

lenin_fusion.jpg

Then I put the melt wax in the case I made (with a kerf setting of 0.2 notches were very strong to prevent the hot wax going out of the box)

new_wax.jpg

Class sources

Rhino 3D model lenin7.3dm
Antichità Belsito
Prochima
rtv530 “shore 90” (hard mold)
Smooth-on
Oomoo