Molding and Casting
Molding and Casting
This assignment focuses on documenting our learning during the Molding and Casting week. It includes understanding various materials used in the molding and casting processes, analyzing their weight ratios, reviewing their Safety Data Sheets (SDS), and creating test casts.
Objectives
• Review the Safety Data Sheets (SDS) for each molding and casting material to understand their properties, hazards, and handling requirements.
• Make test casts using each material to observe their performance and characteristics.
• Compare and analyze different mold-making processes based on material behavior, ease of use, and final casting quality..
In this assignment, Dr. Sujit and I conducted the molding and casting of a cylinder using various materials.
Materials
1. Ecoflex rubber- platinum catalysed silicones
2. RTV2 Silicone rubber - 15C white
3. Forticast ERS LV
Basic conecpt of Molding and Casting
Molding and casting are among the most widely used manufacturing processes for producing complex shapes and components with high precision and repeatability.
A mold or mould is a hollowed-out form used to shape materials such as plastic, glass, metal, or ceramic in their liquid or pliable state. Once the material is introduced into the mold, it solidifies and takes on the mold’s shape. Molds serve as the counterpart to casts in manufacturing processes. A widely used method, known as bi-valve molding, involves two separate molds—each forming one half of the final object.
We individually tested all the materials mentioned above and reviewed their respective Safety Data Sheets, which included key information such as density, mixing ratio, and curing time. Utilizing the various molding and casting materials available at the Sanjivani Fab Lab, we created test casts to observe their proportions, mixing techniques, and curing behaviors. Through this hands-on process, we gained a clear understanding of which materials are suitable for use as mold-making materials and which are best suited for casting.
Ecoflex rubber- platinum catalysed silicones
Ecoflex rubber is a soft and stretchy silicone that's simple to use. It has two parts, A and B, which you mix in equal amounts by weight or volume. It hardens on its own at room temperature and doesn’t shrink. The liquid is not thick, so it’s easy to mix and remove air bubbles. After it sets, the rubber stays very 4 soft, strong, and can stretch a lot without breaking. It also returns to its original shape after stretching.
Once it hardens, Ecoflex™ 00-50 is safe to use on skin and has been tested and certified by an lab
Ecoflex™ rubbers are water-white translucent silicones that can be color pigmented using Silc Pig™ pigments to create a wide range of color effects. For applications requiring lower viscosity, Smooth-On’s Silicone Thinner™ can be added to the mixture. Additionally, THI-VEX™ silicone thickener may be incorporated by weight into Ecoflex™ silicones to achieve a brushable consistency. These versatile rubbers are suitable for various applications, including the creation of prosthetic appliances, cushioning in orthotic devices, and use in special effects.
For safety, always use Ecoflex™ rubbers in a place with good airflow. Wear safety glasses, long sleeves, and rubber gloves to avoid getting the material on your skin. Use only vinyl gloves—do not use latex gloves, as they can stop the rubber from curing properly. Keep and use the material at room temperature (73°F or 23°C). If the temperature is too warm, the rubber will cure too fast and won’t last as long. Also, storing it in hot places can shorten how long you can keep and use it. These products don’t last forever, so try to use them as soon as you can.
Ecoflex™ silicone might not cure properly if it touches certain materials. This can make the rubber feel sticky or not harden at all. Things like latex gloves, sulfur-based clay, tin-cure silicone, some types of wood, or freshly made epoxy, polyester, or urethane can cause this problem. To be safe, always test a small amount of Ecoflex™ on the surface you plan to use. If it doesn’t cure or stays gummy, that means there’s cure inhibition.
Since every project is different, it’s best to do a small test first. To help prevent problems, you can spray the surface with a clear acrylic sealer and let it dry completely before using Ecoflex™. But even with a sealer, silicone might still not cure on clay that has a lot of sulfur—so always test first to make sure it works.
Ecoflex™ 00-50 material is used to make a small cylinder for testing purposes. This allows we to check how the silicone cures and performs before starting a full project. It's a simple way to ensure there are no issues with cure inhibition or material compatibility.
To prepare Ecoflex™ 00-50, combine equal amounts of Part A and Part B liquids by weight or volume.For the test, I combined 15 grams of Ecoflex™ 00-50 Part A and 15 grams of Part B, making a total of 30 grams.
I mixed the liquid rubber thoroughly to ensure both parts were fully blended. Then, I poured the mixture over the prepared model and allowed it to cure. After curing, it formed a solid, flexible rubber mold. Finally, the cylinder mold is ready.
RTV2 Silicone rubber - 15C white
RTV2 silicone rubber, specifically the 15C white formulation, is a two-part silicone that cures at room temperature. It is easy to mix and has good flowability, making it simple to apply. This material is resistant to chemicals and high temperatures, and it’s commonly used to create molds or sealants. It also offers a long working time, along with excellent tear and tensile strength, making it a durable and reliable choice for various applications.
Key Features of RTV2 Silicone Rubber (15C White Formulation):
Two-Part System: Requires mixing of Part A and Part B before use, allowing for a controlled and reliable curing process.
Room Temperature Curing: Cures at room temperature without the need for heat or special equipment, making it convenient for most workspaces.
Good Flowability: Flows easily and fills intricate molds, making it ideal for capturing fine details.
High Strength: Offers excellent tear and tensile strength, making it durable for repeated use.
Chemical Resistance: Resists acids, alkalis, and other chemicals, allowing for use in harsh environments.
Temperature Resistance: Can withstand a wide range of temperatures, making it suitable for both hot and cold conditions.
Ease of Demolding: Once cured, the silicone is easy to remove from even complex molds without damaging the mold or the original.
Moldmaking Applications: Ideal for creating molds for plaster, ceramics, resins, wax, and some metals.
Sealing Uses: Suitable for sealing and bonding in industrial and automotive applications due to its flexibility and durability.
Shore Hardness (15C): Indicates a soft and flexible rubber, offering a balance between durability and ease of use in delicate moldmaking.
To make a silicone mold using RTV2 Silicone Rubber 15C White, I start with a total of 30 grams of material.Since the mixing ratio is 20:1, I divide it as 28.5 grams of base silicone and 1.5 grams of catalyst. Then, I measure out 28.5 g of the base and 1.5 g of the catalyst accurately.
I pour them into a mixing cup and stir slowly and thoroughly for a few minutes to get a smooth, even mix without air bubbles.
After mixing, I pour the silicone gently into one corner of the mold box so it flows over the master evenly. I leave the mold undisturbed to cure at room temperatur for about 24 hours. Once it’s fully set, I carefully take the mold out and remove the master. Now the mold is ready for use, and I store any leftover materials properly for the next time.
Forticast ERS LV
Forticast ERS LV is a clear, castable epoxy system designed for applications where both optical clarity and high strength are essential. This versatile material is ideal for producing small functional parts, thanks to its mechanical durability, and is widely used in the creation of decorative items through casting, owing to its brilliant transparency. Additionally, Forticast ERS LV serves as an excellent mould-making material for printing pads.
One of its key features is its low viscosity, which enables the resin to penetrate fine details effectively, making it suitable for encapsulation and detailed castings. It is formulated to perform well even without a vacuum chamber, minimizing bubble entrapment to a certain extent during the curing process. The recommended mixing ratio is 2:1 (by weight or volume), ensuring optimal curing and performance characteristics.
Features of Forticast ERS LV:
Optically Clear Finish: Provides excellent transparency, ideal for decorative castings and encapsulations.
High Mechanical Strength: Suitable for creating small, functional parts that require durability.
Low Viscosity: Flows easily into fine details, making it ideal for intricate moulds and encapsulations.
Bubble Resistance: Can be used without a vacuum chamber with minimal bubble entrapment.
Good Dimensional Stability: Maintains shape and size accuracy after curing.
Versatile Applications: Commonly used in decorative resin art, mould-making for printing pads, and small part fabrication.
User-Friendly Mixing Ratio: Simple 2:1 mix ratio (base: hardener) by weight or volume.
Clear Cure: Cures to a clear, glossy finish suitable for artistic and commercial use.
To create a mold using Forticast ERS LV, measure the resin and hardener in a 2:1 ratio by weight or volume—for example, 20 grams of resin to 10 grams of hardener.
Pour both parts into a clean container and stir slowly and thoroughly for 3 to 5 minutes, scraping the sides and bottom to ensure a complete mix while avoiding air entrapment. Although Forticast ERS LV has a low viscosity that helps minimize bubbles
After mixing, slowly pour the resin into the mold, starting from one corner and letting it flow naturally to fill the details. Leave the mold undisturbed at room temperature for 24 hours to fully cure.
Finally, all three molds made from different materials—RTV2 Silicone Rubber (15C White), RTV2 Silicone (20:1 ratio), and Forticast ERS LV Epoxy Resin—are successfully completed and ready for use. Each mold has been carefully prepared, cured, and demolded according to its specific procedure, ensuring high-quality results
