Molding and Casting

What is Molding and Casting?

Molding and casting is a powerful fabrication process used to replicate 3D objects by creating a negative mold (usually with silicone or rubber) and then casting materials like resin, chocolate, or even ice into it. It's widely used in industrial manufacturing, art, product prototyping, and more. First, you make a positive model, then you create a mold around it, and finally, you cast your chosen material inside to form a copy. In this week’s assignment, we explored both subtractive machining (milling) and additive manufacturing (3D printing) to create our molds, which we then cast with silicone.

Planning & Group Collaboration

Our lab had limited wax blocks, so teamwork became essential. I teamed up with Devanshi and Mihir, and we decided to combine our designs into a single milling job on one wax block. The block size was 15 x 8 cm, with a thickness of 5 cm, so we each scaled and arranged our parts accordingly to make the most of the space.

Designing in Fusion 360

My initial idea was to design an axe.

I sketched the basic outline of the axe.

Extruded the sketch to give it volume.
Applied fillets and chamfers to smoothen edges and improve aesthetics.
Added side walls around the model to form the mold cavity.

After finalizing our designs, we compiled them into one Fusion 360 file and prepared it for milling.

Milling the Mold (Using SRM-20)

We used the SRM-20 milling machine with SRM Player software to prepare and mill the wax.

Milling Workflow: - Set the X, Y, Z axis origins.

Chose the correct orientation of the toolpath.

Set the cutting depth and ensured it cut from the top surface.

Selected Wax as the material.

Chose a 3mm round-end milling tool.

Created roughing and finishing passes for smoother results.

After milling, I noticed a design flaw: my axe was asymmetrical, and I had only made a one-sided mold. Initially, I thought I could cast it twice and stick the parts together, but I realized this wouldn’t work since the design needed a mirrored second half.

Iteration: Designing a Spinning Top

After identifying the issue with the axe, I moved on to a second design: a spinning top.

Key Features:

Designed using the Revolve tool around a central axis to achieve symmetry.

Added fillets for smooth edges.

Created a two-part mold system.
Added four cylindrical alignment pegs to ensure the molds fit together perfectly.

These pegs were 3D printed and added to the corners of the mold design.

To compare different fabrication techniques, I made two molds of the spinning top:

CNC milled mold using the wax block.
3D printed mold using the same model.

Silicone Casting Process

We used RTV silicone rubber for casting, mixed with a curing agent in a 10:1 ratio.

Since I was working with my teammates, we prepared a shared batch:

700 ml of silicone
70 ml of hardener

Safety & Mixing:

Wore gloves, safety glasses, and apron throughout the process.
Mixed the silicone slowly in circular motions to minimize air bubbles.
Used tapping and shaking techniques after pouring to help trapped air escape.

We poured the silicone into both the 3D printed and milled molds and let it cure for 12 hours in a safe space.