16. Molding and casting¶

Download files:¶

Assignment Objectives:¶

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:

Review the safety data sheets for each of your molding and casting materials, then make and compare test casts with each of them.

Group Assignment¶

In this part we read and reviewed the technical and safety datasheet of casting and molding material we have in the lab.

Molding and Casting Material¶

The image and table blow show the material we have in the labs.

Silicone Rubber and Urethane Resins

Material	Category	Series	Supplier
OOMOO™ 30	Silicone Rubber-Tin Cure	OOMOO™	Smooth-on
OOMOO™ 25	Silicone Rubber-Tin Cure	OOMOO™	Smooth-on
Mold Max™ 60	Silicone Rubber-Tin Cure	Mold Max™	Smooth-on
SORTA-Clear™ 18	Silicone Rubber-Tin Cure	SORTA-Clear™	Smooth-on
Smooth-Cast® 305	Urethane Resins	Smooth-Cast®	Smooth-on

The first 4 material are liquid silicone rubber and the last one is liquid plastic. We compared the liquid silicone rubber material (the first 4)

Compare Tool

The image lists the key differences between the 4 liquid rubber materials. For example, there are operational differences like pot life and cure time, and there are finish differences like end product color.

Safety and Technical Datasheet¶

Technical and safety datasheets are linked for each material. The technical datasheet provides operational data like technical specs and processing recommendations. The safety datasheet describes different hazards associated to the material and risk levels. Note that SORTA-Clear™ 18 is the only safe food material.

For example, the following risks are listed in the safety datasheet of Smooth-Cast® 305.

Risks and Hazards

And also, the following first aid measures are listed in the safety datasheet for the same material.

First Aid Measures

In the technical datasheet information about working on the material could be found. For example, for OOMOO™ 25 the following guidelines are listed (in addition to safety ticket!).

Safety

Machinable Wax¶

In the lab we have 3 sizes of machinable wax (dimensions in cm). This will be used to mill the positive mold of the final product.

Wax sizes

Material Test Casts¶

We will complete this section when we have access to lab.

Individual Assignment¶

What will I will model and cast¶

I made a second a 3D parametric generator that generate a Fibonacci model for my final project, in a wax with 153x153x72 mm.

Blender model

Fibonacci Mold by kilani on Sketchfab

Molding¶

Prepare the CNC machine¶

Make a clear cut in a mdf board to fit the wax inside it, in artcam I create a box with size a little biger than the wax dimensions by 2mm, with center locations of x=885mm and y=130mm.

Artcam 01

Give the box dogbone filets around the corners to fit the wax, then cut using endmill 6mm with 6mm collet.

Endmill 6mill

Artcam 02

I used a hot glue gun to fix the wax into the mdf board.

preparing wax 01

preparing wax 02

Zero the Z-axis on the wax, there is no need to zero the X and Y axis.

preparing wax 03

Prepare the CNC gcode¶

I imported the STL file into the artcam from Relief, and put the center of the model in coordination x=885mm and y=130mm, same as the box because there is no need to zero the X and Y axis.

Artcam 03

Then Adjust the material height into 77mm.

Artcam 04

I started it of to use the Tool clearance strategy Spiral in Box for Finishing Option, but I check it on NC studio simulation to get the time and it was around 3 hours, then I changed it back to raster.
And for the Roughing Options I used Offset, because my 3D model shape is round, and is the better Tool clearance strategy for it, and machining time reduced to 1.5 hour.

Artcam 05

Roughing toolpath¶

Using the same endmill 6mm to rough the wax.

Endmill 6mill

Finishing toolpath¶

I used Tapered End Mill 1/4 inch Shank with 1.5mm Ball Nose for the finishing toolpath.

End Mill 1/4 inch Shank with 1.5mm Ball Nose

Unexpected problem¶

I had bad finishing, because the ArtCam file settings was using low resolution

Unexpected problem

I made a new Artcam file and increased the resolution

Fix the problem 01

And with the same exact size and location of the mold.

Fix the problem 02

And I continue with bad part to remind myself in the future to not the same mistake again.

Continue finishing the engrave¶

Then I decided to smooth the first part by going down with the Z-axis by 0.2mm to give smooth finish, but still showing.

Hero shoot mold!¶

Hero shoot mold

Casting Silicone¶

Casting silicone will give the negative of the mold.

Casting Silicone OOMOO™ 25¶

I could not use OOMOO™ 25 because its self live has expired.

expired OOMOO™ 25

Casting Silicone OOMOO™ 30¶

I mixed the part by weight, from the OOMOO™ 30 page the mix ratio is:

Mix Ratio By Weight 100A:130B

I calculate the volume of the 3d model and the mold box using an addon in Blender called Mesh: 3D Print toolbox.

blender volume

And we got the values in mm³, and we convert to cm³:

Volume of the model is 189.45 cm³.
Volume of the mold box is 409.48 cm³

Pour on mold Estimator

And we get the weight in grams 296g.

Steps¶

Using a brush, I covered the model with release agent “grease”

Casting OOMOO 30 01

Measuring the weight of A and B to the ratio mention before, the mixing them until the color changed to Light Blue.

Casting OOMOO 30 02

Casting OOMOO 30 03

Pour OOMOO 30 mix into the mold, I used a paper cup to mix, and it was hard to see the parts A and B are mixed properly, in the end of the cast I had un mixed parts, but it did not matter.

Casting OOMOO 30 04