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.

Key Elements of Mold Casting:

1) Mould

The hollow form that defines the shape of the final object.
Can be reusable (metal molds) or single-use (sand molds, plaster molds).
Made from materials like metal, sand, silicone, or ceramic.

2) Casting Material

Typically metal (aluminum, iron, bronze), plastic resin, or plaster.
The material is melted or mixed and then poured into the mold.

3) Cooling or Curing

The material is left to cool (metal) or cure (resin/plastic) in the mold until it becomes solid.

4) Part Removal

The mold is either opened (if it's reusable) or broken away (if it's disposable), and the final cast part is removed.

Common Types of Mold Casting

Type	Description	Example Materials	Mold Type
Sand Casting	Molten metal poured into a sand mold	Iron, bronze, aluminum	Disposable (sand)
Die Casting	High-pressure metal casting using steel molds	Zinc, aluminum, magnesium	Reusable (metal)
Investment Casting	Wax pattern coated with ceramic, then melted out	Steel, titanium	Disposable (ceramic)
Plaster Mold Casting	Plaster used instead of sand for better finish	Aluminum, zinc	Disposable (plaster)
Resin Casting	Liquid plastic resin poured into silicone molds	Epoxy, polyurethane	Reusable (silicone)

Group Assignment

As part of our group casting assignment, I worked closely with my peers, including Devanshi and Mihir, to explore different materials, safety practices, and mold-making techniques. You can find a detailed breakdown of our collective work on Devanshi’s page here.

Safety First – What I Learned from SDS Review

Before we began working with silicone and water-based casting materials, I realized the importance of reading the Safety Data Sheets (SDS). This helped me understand:

How to handle silicone safely (e.g., use gloves and work in ventilated areas)
Why storage conditions affect leftover material usability
How even “safe” materials like flour-water paste or ice should be handled with care during freezing

This practice is something I’ll carry forward in all future material experiments.

Test Casting: Silicone vs Water

Due to resin being unavailable, we tested silicone and ice (water) for mold casting. Here’s what I personally observed:

Silicone gave a more professional and detailed finish, and the mold can be reused many times. However, it required accurate mixing and curing time.
Water casting was a creative, low-cost preview method. It gave us a quick way to visualize our mold design, even though it wasn’t durable or precise.

Mold Making: CNC Milling vs 3D Printing

We experimented with both CNC milling in wax and 3D printed molds. Here’s what I found valuable:

Milling gave us superior surface finish and precision. It taught me the value of toolpath strategy and speed control.
3D printing was much faster and customizable, especially useful when we had time or material constraints.

This comparison helped me better understand when to choose each method depending on the project’s time, resolution, and material requirements.

My Key Learnings

Safety is foundational: Reading SDS sheets made me more confident in handling unfamiliar materials.
Material choice shapes outcome: Even without resin, we could prototype effectively by choosing alternatives.
Process matters as much as product: Milling vs printing taught me how manufacturing methods impact quality and efficiency.
Collaboration multiplies learning: Working with Devanshi and Mihir gave me insights I might not have noticed on my own.

Individual Assignment

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)

Machine Used:

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

Software Used – VPanel & SRP Player

For milling the wax mold on the Roland SRM-20, two main software tools were used:

VPanel was used to control the milling machine and set the origin for all three axes (X, Y, Z). The tool was carefully moved to the desired starting point, and the zero points were defined to ensure accurate milling.
SRP Player was used for generating toolpaths. After importing the STL file of the mold design, the material size and origin were configured. The software automatically created both roughing and finishing passes, and a simulation preview helped verify the job before exporting the G-code.

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.

Mold Issue : Z-Axis Shift

While milling the spinning tops, we faced another issue. The Z-axis of the SRM-20 got slightly shifted, which affected the surface finish of Mihir and Devanshi’s molds. The top surface came out rough and uneven.

But they handled it smartly by doing some post-processing—they sanded the surfaces by hand using sandpaper, which made the finish surprisingly smooth and production-ready. A great reminder that even CNC flaws can be fixed with a bit of patience!

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.

After curing, I carefully removed the silicone mold. To test it out in a fun way, I poured water into both molds (the milled and the 3D printed versions) and froze them.

Milling Issue and Mold Defect

While milling the spinning top mold, we encountered a small but important issue. Since we used a 3mm milling bit, the tool couldn’t clear areas where the gap between the top surface and the mold wall was less than 3mm. As a result, a small uncut cavity was left in the mold.

Finally It Casted

When we poured water into this mold to create an ice spinning top, the water leaked through the uncut cavity, and the mold didn’t hold shape properly.

But we didn’t give up—we applied a simple jugaad! We sealed the cavity using flour paste, which temporarily blocked the leak. After sealing, we tried casting the ice again—and this time, it worked beautifully. The ice spinning top came out solid and well-formed!

Aside from the earlier leakage issue (which was solved using flour), the final results were amazing—the ice spinning top came out clean and ready to spin!

Learnings & Observations

Always design with tool clearance in mind, especially when using larger milling bits.
Proper alignment features are key for successful two-part molds.
Milled molds give smoother surfaces but require more precision.
3D printed molds are quicker to produce but can be less precise.
Bubble removal techniques like tapping and slow mixing are crucial for high-quality results.
When something goes wrong, a creative fix (like flour sealing) can save the day!

FILES

Spinning Top

Axe