13. Moulding and Casting¶
Group Assignment¶
As part of the group assignment, I created a parametric model of a small panel using Grasshopper. The model allows for customization of panel size, the number of holes in the pattern, element distribution and other parameters.
After setting the parameters in Grasshopper, I needed to bake the shape for further work. To do this, I selected the node with the final result, right-clicked on it, and chose Bake. In the window that appeared, I selected the desired layer and clicked OK. The shape then appeared in Rhino’s workspace as a regular 3D object.
After that, I handed the model over to Mkhitar so he could prepare the file for milling a wax model. This wax model was later used to create a plaster mold.
We poured plaster into the wax mold after first spraying it with a silicone release spray to make demolding easier and to prevent the plaster from sticking.
After removing the mold from the plaster, we melted aluminum in the furnace and tried to pour it into the mold. However, during the casting process, the mold cracked, and we were not able to obtain a proper metal model. We used regular construction plaster, which is not suitable for working with high temperatures. The failure most likely happened due to the plaster’s low heat resistance and possibly because of moisture trapped inside. When the molten metal came into contact with the moisture, it could have instantly turned into steam, causing internal pressure and cracking the mold.
We decided to try printing a mold on a 3D printer and using it for casting. We poured polyurethane plastic, silicone, and plaster into this mold, experimenting with different materials and evaluating how they interacted with the 3D-printed surface.
The polyurethane plastic model cast well, but due to air bubbles in the mixture, some unwanted surface defects appeared. This may have been caused by insufficient mixing or the lack of degassing before pouring.
We weren’t able to remove the plaster version from the mold because it broke during the demolding process. Most likely, the plaster was too fragile for this type of removal or hadn’t fully cured.
Due to shrinkage of the plastic mold after 3D printing, gaps appeared between its parts, causing the silicone to leak out continuously. This made the casting process more difficult and affected the final quality.
Individual Assignment¶
As part of my individual assignment, I decided to bring to life one of my original snake sketches, which I often draw in my free time. This image is personally meaningful to me, so I chose it as the basis for the casting.
To begin, I created a digital silhouette of the snake in Rhino, using one of my hand-drawn sketches as a reference. I focused on preserving the characteristic curves and smooth lines to capture the dynamic and expressive nature of the figure.
3D Modeling with Rhino¶
After completing the outlines and individual elements for the relief, I used the Surface from Network of Curve tool in Rhino. First, I selected the side contours, then added the curves forming the relief to create a 3D surface. This tool allowed me to smoothly connect the curves and generate a complex shape that matched my original sketch.
After some work on the shape and final surface adjustments, I achieved the following result.
Mold Creation in Fusion 360¶
After completing the model of the snake in Rhino, I transferred it to Fusion 360 using the STEP format. In Fusion 360, I applied the physical material ‘brass’ to the model, which allowed me to see how many grams of material would be needed to fill it.
To create the mold, I used basic tools such as Intersect, Merge, and Mirror in Fusion. I measured the available wax and modeled a body with matching dimensions, which I will select later as the base model for the manufacturing process. During the mold design, I also added sprues and gas vents in advance to ensure better metal flow and casting quality
This is what the model looks like after the modeling process is completed.
After completing design i switch to manufacturing tab.
CNC File Preparation and G-code Generation¶
In the Manufacturing tab, within the Milling section, I created a new setup. In this Setup, it is necessary to select the machine model that will be used for the machining process. Also i selected the model which i’m going to mill.
I could not find the exact Roland model used in our lab, so I selected one of the available machine models with the same dimensions. This allows me to proceed with the setup while ensuring compatibility with our equipment.
After that, I selected the model I had previously created with the dimensions of my wax block as stock model.
The first toolpath I selected was 3D Pocket Clear, designed for roughing out large areas with a big end mill.
Hear is the settings i used for pocketing.
Next for finishing i used Contour tool.
Setting four Contour clearing.
I used a 1/8” flat end mill for the Pocket operation and a 1/8” ball end mill for the Contour operation.
After generating the toolpaths, I had the option to export them either as a single G-code file or as individual files. Due to the need to change the end mill between operations, I decided to generate a separate G-code file for each toolpath by right-clicking on it and selecting Create NC Program.
In the next opened window for Post i chose Roland ISO and only change the file name.
After completing the roughing pass with the 3D Pocket toolpath, this is how the wax block appears.
Creating a Plaster Mold¶
Once the final contouring was done using the ball end mill, the model took its final shape. Compared to the roughing stage, the surface is now much cleaner and the details are more defined.
After both sides of the model were finished — the roughing and finishing operations were complete, and the shape had the desired form — I moved on to the next step. It was time to make a plaster mold intended for metal casting. This is an important part of the process, since the quality of the plaster mold directly affects how well the final metal piece will turn out.
Before pouring the plaster, the wax model needs to be properly prepared. To do this, it should be evenly coated with a thin layer of silicone release spray. This step ensures that, once the plaster has hardened, the wax model can be easily removed without damaging either the model or the mold itself. The release layer makes it much easier to separate the parts and helps preserve all the fine details of the final casting.
For metal casting, I needed a special type of plaster designed for jewelry casting. This plaster can withstand high temperatures and ensures precise reproduction of fine details in the mold.
Molding gypsum mixtures are used for precision casting with lost-wax patterns in jewelry, dental, artistic, and small-scale industrial applications. They consist of gypsum, quartz flour, and special additives, providing high detail reproduction, heat resistance up to 700 °C, and compressive strength up to 20 MPa, allowing for castings with minimal shrinkage and high accuracy.
Typical properties of such mixtures: working time 8–20 minutes, setting time 10–30 minutes, compressive strength after 24 hours 8–20 MPa, porosity after drying is 20–40% of the total volume of the dry mold, ensuring good gas permeability. Heat resistance reaches up to 700 °C without structural failure, and casting accuracy is within 0.05–0.1 mm. These values are average and may vary slightly, as the mixture was purchased from a local jewelry supply store.
I mixed plaster with water using a ratio of approximately 2 parts plaster to 1.2 parts water by weight. First, I poured water into a clean container, then gradually added the plaster, allowing it to absorb the water for 1–2 minutes. After that, I mixed the blend until it reached a uniform, medium-thick consistency without lumps. The mixture started to thicken within 7–10 minutes, so I prepared the mold in advance and poured the plaster immediately after mixing.
To avoid unwanted air pockets in the plaster mold, it’s important to remove air bubbles before pouring. This can be done using a vacuum chamber or by applying light vibration, for example, using a vibrating table to release trapped air from the mixture before it sets. After 30–40 minutes, the plaster had fully set and could be carefully removed from the mold. To remove the mold, I lightly tapped the back side of the form, and thanks to the silicone spray, I was able to extract the mold without much effort and without damaging it.
Despite using vibration, I wasn’t able to achieve a perfectly smooth and even mold surface. This could be due to insufficient vibration time, a mixture that was too thick, or air bubbles that were not fully removed.
Metal Casting Process¶
At first, I planned to cast a snake figure using a brass alloy and even purchased some brass granules. The melting point of brass ranges from approximately 800 °C to 950 °C, depending on the composition. I managed to melt the brass granules, but our furnace couldn’t reach the required temperature of around 1100 °C necessary for proper metal casting.
As a result, I decided to use lead instead, since it has a much lower melting point — around 327 °C — which made it possible to carry out the casting with the available equipment.
The final lead casting of the snake looks as follows. During the heating process, the plaster mold began to crack, most likely due to residual moisture or a rapid increase in temperature. Despite this, the mold maintained its overall structure, and I was able to complete the casting successfully. The lead flowed well into the main parts of the mold, and after cooling, I was able to remove the casting without significant damage. Considering the conditions and equipment limitations, the result was satisfactory.
After the casting was completed, sprues remained on the piece—these are the channels through which the molten lead flowed into the mold. I carefully removed the excess metal by cutting off the sprues, then cleaned and smoothed the connection points using a set of needle files. This helped to even out the surface and remove any burrs. Next, I performed preliminary sanding to smooth out any irregularities that had formed during casting. As a final step, I polished the piece using a rotary tool with an appropriate polishing bit. As a result, the surface became smoother and the object gained a cleaner, more finished appearance.
Conclusion¶
In this assignment, I went through the entire process from idea to a finished metal object. I started with sketching and 3D modeling in Rhino and Fusion 360. Then, I created several versions of the mold — using plaster, silicone, and a 3D-printed plastic mold.
During the process, I experimented with different casting materials, including brass, aluminum, and lead. Some attempts were unsuccessful: the plaster mold cracked, the plastic mold shrank, and the polyurethane plastic parts contained unwanted air bubbles.
Despite these challenges, I successfully completed a lead casting, removed the sprues, and refined the piece through manual filing and polishing.
This project gave me valuable hands-on experience in 3D modeling, mold preparation, metal casting, and post-processing. I learned how to adapt to difficulties and find alternative solutions. In the end, I produced a finished metal object and was satisfied with both the result and the process.
Going forward, I’ll be able to apply these skills to create more complex forms and experiment with different metals. I now have a better understanding of the possible issues at each stage of the casting process and how to prevent them. This experience was an important step in developing my technical and design abilities.