13. Molding and Casting

This week, I learned how to make a mold and use it to cast objects. I designed a 3D shape, milled it in wax, made a silicone mold, and then used it to create my final cast.

Group Assignment

As part of the group work, we had to review the safety data sheets for each of your molding and casting materials, then make and compare test casts with each of them compare printing vs machining molds.

This week's group assignment is documented on my friend Samrudhi's page

From this group assignment, I learned how important it is to carefully review safety data sheets (SDS) for casting materials. It helped me understand the specific properties of the SILASTIC™ RTV-3483 Mold-Making Base, such as its excellent flowability and tear resistance. Comparing the test casts also showed me how different molding techniques (like printing vs. machining) affect the final product. This experience taught me how to choose the right material based on its properties and application needs.

Individual Assignment

Positive Mold

A positive mold is the original model or shape from which a cast is made. It is the exact replica of the object that you want to create in another material.

Designing theCAD file

The first step in the process is to create a wax mould that will be milled with the milling machine. For doing this I have to create a 3d design to make a double sided mould. I am going to crete a toy bird.

To start with I reffrered to a youtube video to create this little bird. Link to the tutorial

I started by creating an offset plane above the base each at a 10 mm distance from the other. Go to Construct > Offset Plane.

To accurately sketch the bird, I imported an image of the toy bird as a reference. I placed the image using the Insert > Canvas option

After adjusting its size and position, I used the Spline tool to trace the outline of the bird directly on top of the image. This helped me maintain the proportions and details of the bird design.

Once the tracing was complete, I switched to each offset plane and created a circle at the same location on both planes. These circles would help give volume to the shape.

Then, I used the Loft tool to connect the two circles, which smoothly joined the shapes between the two planes. This gave the bird a soft, rounded 3D form—ideal for casting.

After lofting

Error: However, after lofting, I noticed that the body didn’t look symmetrical—the shape was uneven and slightly distorted. To fix this, I used the Split Body tool to cut the bird model in half along the central plane. I then deleted the flawed half and used the Mirror tool to regenerate the other side from the correct half. This gave me a perfectly symmetrical 3D shape, ready for molding.

Next, I needed to create a base to hold the silicone for casting. I created a rectangular box that would act as the mold frame. The box was slightly larger than the bird model, allowing enough space for the silicone to flow around the bird and form the mold.

I use the extrude function to convert the rectangle to a rectangular box around the bird.

Next, I needed to add some additional features to ensure the mold would work correctly for casting. I added a pouring hole at the top of the mold box. After this I mirrored the model. This was because I wanted to create two separate molds: one using the wax mold and the other using a 3D printed mold.

Milling the Wax mold

Before starting the milling process,me and my friend Samrudhi combined our files to ensure that both our designs would fit together and could be milled in one go.

MDX 40 Milling Machine

To create the wax mold, I used the MDX milling machine.Link to know more about the machinine

Before starting, it’s important to place the bits securely in the panel. The machine’s tool holder is where you insert the bits, ensuring they’re placed properly.

For the milling process, I used two types of milling bits: flat end and ball end bits. The flat-end bit is ideal for creating straight, flat surfaces. On the other hand, the ball-end bit is perfect for detailed, rounded surfaces and smaller, curved areas, allowing the machine to create finer features, such as the bird's curves and intricate details.

Before starting, I used a measuring tool to ensure the milling bit was positioned correctly. This tool helps set the bit's height relative to the wax block, ensuring that the cuts are accurate and that the bit doesn’t cut too deeply into the material.

After that place the wax block properly on the bed of the machine.

V Panel software for the Roland MDX-40

I visited the official Roland DG and searched for the software. Click on the highlighted box to download it Link to download the Vpanel

In VPanel, you can manually move the milling bit to a precise location above the material. Using the Move controls in VPanel, you can adjust the position of the tool in all three axes (X, Y, and Z).Once the bit is in the desired position, you set the origin by selecting Set Zero in VPanel.

Understanding SRP player

SRP Player is the software used to convert 3D models into milling instructions for the Roland MDX-40. It prepares your design by generating toolpaths based on the geometry of the model and the chosen milling bits. Link to download the SRP Player

Once you have downloaded the software load your 3d model. Next go Option > Add/Remove Tool

For this project, I added a 3.0mm square tool and a 6mm end mill

In SRP Player, you’ll need to configure the tool magazine. This allows the software to know what tool is currently in use. The tool magazine setting helps you manage which bit is inserted in the machine for each step of the milling process.

Choose the milling type from the options available.

After selecting the milling type, proceed to create the toolpath. This is where SRP Player generates the paths that the milling bit will follow during the cutting process.

You can adjust the flute diameter and length based on the tool that you are using

Once you’ve set all the parameters you can create the toolpath

With everything set up your milling is started.

Milling done

After the milling was completed, I carefully vacuumed the wax mold to remove any leftover material and debris.

3d printed mold

After completing the wax milling I 3d printed the other mold. For this I used a Bamboo Labs 3D printer which was at out lab.

To 3D print the mold, I first exported my design file from Fusion 360 in .STL format. Then, I opened the file in Bambu Studio, the slicing software for the Bamboo 3D printer. Link to download the software

In Bambu Studio i adjusted the layer height to 0.1mm for a balance between speed and detail, and selected PLA filament for printing.After slicing the model, I transferred the G-code to the printer

Final 3d printed mold

After I got the 3D printed mold, I noticed some layer lines and small imperfections on the surface. To make the mold smoother and ensure a better finish during casting, I gently sanded the surface using fine-grit sandpaper. This helped remove any rough textures caused by the printing process.

Negative mold

Once the positive molds (wax and 3D printed) were ready, the next step was to create the negative mold using silicone

What is a negative mold?

A negative mold is the hollow impression or cavity that is formed around a positive object (like your wax or 3D printed model). It captures all the surface details of the original shape, but in reverse—like a mirror image.

Safety Precautions

Before starting, I made sure to follow safety guidelines:

• I wore gloves to protect my skin from any chemical reaction or irritation.

• I worked in a well-ventilated area so that I wouldn’t inhale any fumes.

• I also wore a mask and safety glasses to protect myself from accidental splashes.

Mixing and Pouring the Silicone

Using a digital scale, I carefully weighed out Part A and Part B in the correct 1:10 ratio.

I poured both into a clean mixing cup and mixed it slowly and thoroughly.

Note: It's important to scrape the sides and bottom while mixing to ensure the two parts combine fully—this prevents soft or uncured spots in the final mold.

Once the silicone had a uniform consistency I slowly poured it into the mold box, starting from one corner and letting it naturally flow around the model. This helps avoid trapping air bubbles.

To further reduce bubbles, I gently tapped the mold box on the table. Then I left the mold undisturbed for for several hours—the time depends on the silicone brand, but mine took around 12 hours.

After curing, I carefully removed the wax or 3D printed model, leaving behind a clean, flexible negative mold ready for casting the final material.

Issue with registration keys

In my mold design, I included holes intended for 3D-printed dowels to act as registration keys. These were meant to ensure that the two parts of my mold align perfectly during the casting process.

However, I made a critical error in the design phase — I did not maintain sufficient wall thickness around these holes. As a result, the holes for the registration keys were positioned too close to the outer edge of the mold. I had only kept 2 mm of material between the edge of the hole and the outer surface of the mold.

When the wax block was milled, this lack of wall thickness led to two main problems:

• Incomplete Milling of the Holes: The toolpath could not fully mill out the holes for the dowels because they were too close to the boundary of the block.

• Weakened Mold Edges: Since the holes were near the boundary, the silicon surrounding them was missing altogether, which compromised the mold’s structure.

Reflection

This issue highlights the importance of allowing enough buffer space between critical features and the outer boundaries of the mold. In future designs, I will ensure:

• A minimum wall thickness of at least 5–8 mm around all holes and features.

If I had kept more space, the holes would have been milled cleanly and the mold would have aligned properly. This experience emphasized how important it is to design with manufacturing tolerances in mind

Comparison: Wax Milled Mold vs 3D Printed Mold

Feature	From Wax Milled Mold	From 3D Printed Mold
Surface Quality of Mold	Very smooth surface	Slight texture from layer lines
Detail Accuracy	High — smooth curves from milling	Moderate — show print linesand needs post processing
Effort Before Pouring	Minimal — ready after milling	Requires sanding before silicone pouring
Appearance	Clean and professional look	Shows facts from printing
Ideal Use Case	For fine finish and smooth casting	For quick prototyping or low-fidelity casting

Casting

Once the silicone negative mold was ready, I proceeded with casting to make the final positive object. In this step, the silicone mold acts like a container that captures all the details of the original design

Wax

The first casting I did was using wax. Instead of using wax pellets, I broke regular candles into smaller pieces

To melt the wax, I placed the broken candle pieces in a microwave. and heated them in short bursts. This helped control the temperature and prevented the wax from overheating or spilling. I stirred the wax between intervals to ensure even melting and to avoid hot spots

After the wax was fully melted, I carefully poured it into the silicone mold, making sure to fill all the cavities and avoid trapping air bubbles. To cool it down , I placed the mold in cool water to speed up the cooling process. This helped the wax solidify more quickly and evenly.

Once the wax had completely cooled and hardened, I carefully removed it from the mold.

My final cast

Water

After successfully casting the wax, I decided to try water casting to further test the mold's capabilities.

To do this, I filled the mold with water instead of wax. Once the mold was filled, I carefully placed it in the freezer, allowing the water to freeze into ice.

Once the ice had fully frozen, I removed the mold from the freezer and gently took out the ice cast.

The ice cast acted as a temporary positive replica, showing how the mold would perform when used with actual casting materials.

Exercise files

Below are the files for:

Mold file