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Week 7: Molding and Casting

Objective:

This week, the focus was on mastering the art of molding and casting, involving both group and individual assignments:

  1. Group Assignment:

    • Identify the requirements of different casting materials.
    • Perform a test on the researched materials by casting with them.

  2. Individual Assignment:

    • Design a 3D piece that meets specific design requirements.
    • Use the Roland SRM-20 Compact Milling Machine to cut the design from a piece of rectangular wax, creating the positive mold.
    • Fill the wax mold with a material to create the negative mold.
    • Cast the negative mold with another material to produce the final product.

As I mentioned last week, due to the large number of students in my batch, we were divided into three groups: CNC Machining, 3D Printing, and Molding & Casting. This division allowed each group to focus on gathering information that would benefit us in our final project. This week, I was part of the Molding and Casting group, and the experience was both educational and fun 😄.

Group Assignment: Exploring Casting Materials 🧪

In this week, our group worked with the Roland SRM-20 Compact Milling Machine. This machine is designed for precision cutting and is particularly useful for creating molds with intricate details. The machine uses various drill sizes to carve out designs from wax blocks, which are then used to create molds for casting.

Machine Details and Recommendations

  • Minimum Detail Size: The smallest drill bit available is 1.6mm in diameter, meaning the design must have no details smaller than 1.6mm to avoid damaging the bit or the design.
  • Maximum Design Height: The maximum height for designs is around 8mm, based on the length of the drill bit. Going beyond this height could result in incomplete or inaccurate cuts.
  • Design Recommendations: Ensure there are no undercuts in the design. The design should be 2.5D, meaning it should have varying heights but no overhangs that the milling machine cannot cut.

Group Task

To start, we were divided again into smaller groups of two members each. Our task was to research different casting materials, understanding their properties, safety measures, and best practices for using them. The purpose of this assignment was to review and compare test casts of these materials. My group focused on Material 4: Graffiti Resin Multi Use.

Here’s a summary of our findings:

Material 1: RTV2 Silicone Rubber

  • Safety: Non-toxic and skin-safe.
  • Process Steps:
    1. Ensure the surface to be molded is clean.
    2. Apply a release agent to the surface if needed.
    3. Mix the silicone thoroughly for at least 30 seconds before adding the curing agent.
    4. Complete the casting quickly after preparation.
    5. Mix well after adding the curing agent.
    6. Remove air bubbles from the mixture before pouring.
    7. Do not touch the silicone until it has fully cured (24 hours).
  • Mix Ratio: 1:1 by weight (silicone to curing agent).
  • Cured Material State: White, flexible material.
  • Work Time: 30-40 mins
  • Cure Time: 24 hrs
  • Result: A flexible and durable mold that captured fine details well.

Material 2: “Oatmeal” Melt & Pour Soap Base

  • Safety: Keep away from eyes.
  • Process Steps:
    1. Choose soap materials (Clear and White Melt and Pour Soap Base).
    2. Melt the soap at 60-71°C.
    3. Add colors and fragrances.
    4. Pour into silicone or plastic molds.
  • Work Time: 20 sec - 1 min in the microwave
  • Cure Time: 4 hours
  • Cured Material State: Solid
  • Result: A solid, soap-like material that can be easily customized with colors and scents.

Material 3: Mada PLASTER (STANDARD PLASTER)

  • Safety:
    1. Wear gloves.
    2. Keep away from eyes and mouth.
    3. Keep out of children’s reach.
  • Process Steps:
    1. Mix 32 liters of water with 40 kg of plaster.
    2. Allow to soak, then mix thoroughly.
    3. Pour into the mold and allow to set.
  • Mix Ratio: 32 liters of water to 40 kg of plaster.
  • Work Time: 5 mins
  • Cure Time: 15 mins
  • Cured Material State: Solid, white
  • Result: A strong, solid material ideal for creating rigid molds.

Material 4: Graffiti Resin Multi Use (Our Research)

  • Safety:
    1. Keep out of children’s reach.
    2. Store in a dry place at 20-25°C.
    3. Wear protective gloves and a mask (especially for pregnant women).
    4. In case of contact with eyes, rinse with water.
  • Process Steps:
    1. Prepare tools and safety equipment.
    2. Weigh and mix equal amounts of resin and hardener (1:1 for Fast Cure Resin or 1:0.6 for Multi Use Resin).
    3. Mix thoroughly for 3 minutes.
    4. Add desired colors.
    5. Pour into silicone molds.
    6. Allow to cure for 8-12 hours.
    7. Carefully remove the cured resin from the mold.
  • Mix Ratio: 1:1 (Resin: Hardener for Fast Cure) or 1:0.6 (Resin: Hardener for Multi Use).
  • Work Time: 45 minutes at room temperature.
  • Cure Time: 8-12 hours.
  • Cured Material State: Solid.
  • Result: A durable, glossy finish ideal for artistic creations and functional items.

If you are interested in seeing our research, along with the Group Assignment images and the source links used to find that research, please download this PDF document file to access it.

Group Assignment: Cast Testing 🧪

After conducting our research, we moved on to the practical part of our group assignment: cast testing. For this, we used the Graffiti Resin Multi Use material from our research. We placed the resin into molds that we had designed as a group—a crystal-shaped design and a gear-shaped design. This test was crucial to understanding the material’s properties and how well it would perform under real-world conditions.

I found it interesting that despite the thorough mixing, some air bubbles were still visible, so we used a blower to remove them before pouring the mixture into the mold. After waiting 24 hours for it to cure, we were thrilled with the result, though I did accidentally cover the eyes and mouth of the design. Despite this, the final piece looked extremely cool, and I was quite pleased with the outcome 😄.

Individual Assignment: Designing, Molding, and Casting a 3D Piece 🎨

Designing the 3D Piece 🖋️

At first, I was at a loss for ideas, feeling the pressure to complete this assignment quickly so I could focus on the unfinished CNC design from last week (which, as you may recall, was filled with software crashes and frustrations). I initially considered using a pre-made design—something I found on Google, like a cute cat—but then I thought, Am I really just going to keep copy-pasting designs I find online? Where’s my creativity? So, I pushed myself to come up with something unique, something that would be entirely my own creation.

After some contemplation (and perhaps a bit of frustration 😂), I decided to just start drawing in SolidWorks without overthinking it. The result was a quirky character that looked like a kid from The Incredibles, with an angry expression, two teeth, spiky hair, and six fingers! It was a bit unconventional, but I decided to keep it 😂.

Angry-Child by Ahmed-Alaali on Sketchfab

In case you are interested in downloading the design’s STL & SolidWorks file: Click here to download the STL file and here for the SolidWorks file

Considerations:

  • Fillets: I added fillets to every part of the sketch to ensure smooth transitions between surfaces and to accommodate the milling bit’s movement.

  • Gaps: I made sure that the gaps between features like the nose holes, teeth, and fingers were more than 1.6mm to comply with the machine’s limitations.

  • No Undercuts: I avoided any undercuts in the design to ensure it could be milled without issues.

Once I was satisfied with the design, I saved it as a DXF file, ready for the next step.

Molding & Casting Process 🏗️

The molding and casting process involved several key steps, each essential to producing a detailed final product:

Step 1: Creating the Positive Mold

  • Design Preparation and Milling Setup:

    • I started by combining my design with my partner’s into a single .stl file using TinkerCAD. This allowed us to mill both designs from a single block of wax.

    • We loaded the combined file into the SRP Player software to operate the Roland SRM-20 Compact Milling Machine, taking care to meet the machine’s constraints, such as the minimum detail size of 1.6mm and a maximum design height of 8mm.

    • In the SRP Player software, we previewed our designs. I noticed a flaw in my design that didn’t appear in TinkerCAD but did in SolidWorks. After identifying the issue, we quickly resolved it using an online tool to fix the SolidWorks file before re-importing it.

  • Milling Process:

    • Surfacing: We began by surfacing the wax block to create a flat, smooth surface. This step was crucial for ensuring an even milling process.
    • Roughing: Next, we performed roughing, where most of the material was removed to shape the design roughly. This step made the final milling more efficient by reducing the material left for finishing.
    • Finishing: Finally, we used a 3/32 inch BN cutting tool to carry out the finishing stage, which involved precise cuts to create the detailed features of the design.

  • Parameters and Execution:

    • Cutting Bit: 3.18mm (used for specific cuts).
    • Design Height: 8mm.
    • Machine Speed: 80 mm/s.
    • Estimated Milling Time: 2.2 hours.
    • Watching the design slowly emerge from the wax block was fascinating, and the positive mold captured all the details beautifully.
Step 2: Creating the Negative Mold

  • Silicone Preparation:

    • After completing the positive mold, we prepared the silicone mixture. To determine the exact amount of silicone needed, we filled the positive mold with water and measured it. This step ensured we had the correct volume.
    • Mixing the silicone evenly was challenging, as we needed to avoid air bubbles that could affect the final mold quality.

  • Pouring and Curing:

    • We carefully poured the silicone mixture into the wax mold, ensuring it filled all gaps and covered the entire surface.
    • Once poured, the silicone was left to cure, after which we removed the negative mold from the wax block. The silicone mold was flexible, making it easy to remove the final cast without damaging it.
Step 3: Final Casting

  • Casting Material Selection:

    • For the final casting, I chose to use Graffiti Resin Multi-Use, the same material we had experimented with in our group assignment. This resin was durable and provided a glossy finish, making it ideal for my project.

  • Casting Process:

    • After mixing the resin and hardener, I added a bit of color to give my piece a unique touch. I then poured the mixture into the silicone mold, carefully using a blower to remove any air bubbles.
    • The resin was left to cure for 8-12 hours, after which I removed the final product from the mold.

  • Final Outcome:

    • The final piece turned out as I had envisioned—a solid, glossy product that captured all the details perfectly. The quirky and amusing design added a playful touch to the project 😄.

Reflection:

This week’s assignment was incredibly rewarding, allowing me to delve into the molding and casting process while pushing my creative boundaries. From the design phase to the final casting, I learned the importance of planning, precision, and patience.

The group assignment provided valuable insights into the properties of different casting materials, which I applied in my individual work. The experience of resolving design flaws and executing each step meticulously made the final product even more gratifying 😊.

Last update: October 21, 2024