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Week 12. Molding and Casting

Group Assignment:

  • Review the safety data sheets for each of your molding and casting materials.
  • Make and compare test casts with each of them.
  • Compare printing vs milling molds.

In our lab inventory for this week’s assignment, we’ve got some silicone rubber, hydrostone, and smooth-cast bright white liquid plastic.

Smooth-Cast™ 305

  • The Smooth-Cast™ 300 Series of liquid plastics provides ultra-low viscosity casting resins that produce bright white, virtually bubble-free castings without the need for vacuum degassing.
  • With a mix ratio of 1A:1B by volume or 100A:90B by weight and ideal for reproducing small to medium sculptures, prototype models, special effect props, and decorative jewelry.

Instruction:

  • Store and use materials in a warm, well-ventilated area. Wear safety gear like glasses, long sleeves, and gloves.
  • Apply a mold release agent before casting. Smooth-On products work well. Let it dry for 30 minutes.
  • Use clean tools and containers. Mix required ratio thoroughly.
  • Pour in one spot at the lowest point to reduce air bubbles.
  • Ensure good ventilation during curing. Demold time varies based on thickness. Post-cure for better results.

Go through this Safety Data Sheet for more information.

Test Cast

After carefully following the instructions, we conducted a test cast with the material. Adhering to the prescribed mixture ratio and casting it at room temperature, we achieved a successful outcome shown in the image below.

OOMOO™ Series Tin Cure Silicone Rubber

  • OOMOO™ 25 is user-friendly silicone rubber that don’t require complicated measuring or vacuum degassing.
  • They have a one-to-one mix ratio by volume, making them easy to use for beginners.
  • OOMOO™ 25 sets faster with a 15-minute pot life and cures in 75 minutes.

PROCESSING RECOMMENDATIONS

  • Ensure safety by working in a well-ventilated area and wearing safety gear like glasses, long sleeves.
  • Store materials at room temperature and stir Parts A and B thoroughly before use.
  • Applying a release agent like Ease Release™ 200 can ease demolding.
  • Thoroughly stir Part A and Part B before dispensing. Mix equal amounts of both parts in a clean container for about 3 minutes until the mixture has a uniform color.
  • For best results, pour the mixture in a single spot at the lowest point of the containment area, allowing it to flow uniformly over the model to minimize air bubbles.
  • Let it cure at room temperature (73°F/23°C) for the specified time (75 minutes for OOMOO™ 25) before demolding.
  • Post curing for an additional 4 hours at 150°F (65°C) can help eliminate residual moisture.

Here’s the Safety Data Sheet for OOMOO™ Series Tin Cure Silicone Rubber.

Test Cast

Due to the expiration of our OOMOO™ Series Tin Cure Silicone Rubber, we conducted the test cast using LSR-140 instead

Go through this Link to know more abut LSR.

USG HYDRO-STONE

USG Hydro-Stone® Gypsum Cement is perfect for crafting solid architectural and artistic pieces. It’s super tough, with high strength and excellent detail reproduction. Additional details include:

  • Normal Consistency: 32 lbs. water/100 lbs. product (15 kg water/45 kg product)
  • Hand Mix Vicat Set (Target): 19 - 25 minutes
  • Compressive Strength (One Hour After Set): 4000 psi (27.6 MPa)
  • Compressive Strength (Dry): 10,000 psi (68.9 MPa)
  • Density (Wet): 119 lbs./cu. ft. (1906 kg/m³)
  • Density (Dry): 108 lbs./cu. ft. (1730 kg/m³)
  • pH: 7.73
  • Maximum Expansion: 0.24%

MIXING INSTRUCTIONS:

  • Gather materials and ensure water and Hydrostone are at a stable temperature (70-100°F). Consistent temperature is crucial for consistent setting time.
  • Weigh out Hydrostone and water according to the required consistency for mixing. The ratio affects the final properties of the cast piece.
  • Slowly sift Hydrostone into water and let it soak for 1-2 minutes.
  • Proper mixing is essential for maximum strength.
  • Carefully pour the slurry into the mold to create a smooth surface and prevent air bubbles.
  • Pour into the deepest area to ensure even distribution.
  • Dry casts quickly in rooms or ovens with uniform, fast air circulation and equal temperatures.
  • Safe maximum drying temperature is 120°F to prevent calcination.

USG Hydro-Stone® Brand Gypsum Cement Data Sheet Link

Test Cast

LIQUID POLYURETHANE RUBBER (FLEXON)

Liquid Polyurethane Rubber is the two component resins. which cures at room temperature. Its cold casting product which will be useful for both molding and casting applications.

TECHNICAL GUIDELINES:

  • Stir/Shake the part A & B well before use.
  • Mixing Ratio will be depended on the hardness require. Our Lab has PUR 40 which has mixing ratio of 100:40 by weight.
  • Weigh the desire amount of Part A into a clean mixing container and also Part B.
  • Mix the Part A & B together by stirring with a stick until a uniform color is obtained.
  • Pour the deaired material slowly in a steady stream from one end of the mould so that the material flows evenly over the pattern.
  • A mold release agent may be applied on the pattern first to improve release.
  • Allow the rubber to cure for 24 hours at 25 Deg C before removing the cured rubber mold from the pattern.

For more technical and data sheet details, go through this Link

Test Cast

When we poured plastic liquid into a mold made from PUR 40, we discovered that the resulting product was defective, as depicted in the image above. It seems PUR 40 molds are typically designed for casting concrete and creating parts for industrial use.

Printing Vs Milling Mold

Note: For my own understanding, some of the following points are generated using chatGPT

Printing Milling
Printing molds is like making a mold out of layers of material, usually plastic or metal, built up from the bottom. It’s kind of like stacking Lego bricks to make a structure. Milling molds, on the other hand, is like carving a mold out of a block of material, often metal like aluminum or steel. It’s similar to sculpting, where you start with a solid block and then remove material until you get the shape you want.
Printing molds can be faster and cheaper for making complex shapes because you’re just adding material where you need it. Milling can be more precise and durable because you’re working directly with the final material, and there’s less chance of imperfections.
Since printing builds up layers, it’s easier to tweak the design and make changes along the way without much hassle. Milling is often more efficient for large-scale production because once the mold design is finalized, you can churn out multiple copies by milling them from raw material.
printing can handle intricate shapes and complex designs with ease. It can create geometries that might be difficult or impossible to achieve with milling. milling tends to produce smoother surface finishes compared to printing. Since milling cuts away material directly from a solid block, it can achieve finer details and smoother surfaces, which might be important for certain applications where surface finish is crucial.