Week 14: Molding & Casting

For this week's group assignment, we tried three different materials: Eco-Flex, plastic liquid, and --. We compared them with each other and with the mold-making methods (3D printing and milling).

Note: For this week, all the materials we used were from Smooth-On.

materials

Shore Scale

One of the most important things to consider when working with silicone materials is their hardness, which is measured on the Shore scale, so you can select the appropriate material for your application.

The Shore scale is a standardized system used to measure the hardness of materials. Here is the Shore scale for silicone materials:

shore scale

As you can see, there are three different types of Shore scales for silicone materials. The first one is the Shore A scale, which is used for softer materials; the second one is the Shore D scale, which is used for harder materials; and the third one is the Shore 00 scale, which is used for very soft materials.

Materials

For our tests, we used three different materials: Eco-Flex, a very soft and flexible material; Plastic Liquid, a hard and rigid material; and --.

We used a mold that was created previously for all the tests.

  1. Eco-Flex

    Eco-Flex is a very soft and flexible material. It has a Shore A hardness of 00-30, which means it is very soft and can be easily stretched and deformed.

    eco-flex eco-flex test

    It is important to read the technical specifications and safety data sheets before using any silicone material.

    Here is the data sheet for Eco-Flex material: Eco-Flex data sheet

    You can find more information about the material at the Eco-Flex website

    Note: It is important to check the pot and curing time before starting to work with any material. Eco-Flex has a 45 min pot time, which means that you have 45 minutes to work with the material before it starts to cure, and it has a curing time of 4 hours at room temperature.

    Process

    Here is the process for using Eco-Flex:

    1. Make sure to wear gloves and work in a well-ventilated area.
    2. Weigh the two parts of the Eco-Flex material in a 1:1 ratio by weight.
      3. eco-flex parts weighing eco-flex

      Note: Prepare a bit more Part A and Part B than you need, since some of the material will be lost during the process as it sticks to the cup walls.

    3. Mix Parts A and B of the Eco-Flex.
      4. mixing eco-flex
    4. Vacuum the mixture to remove any air bubbles that may have formed during mixing.
    5. Pour the mixture into the mold and make sure to fill all the cavities and remove any excess material.
    6. Allow the material to cure for at least four hours at room temperature, or speed up the curing process by placing it in an oven at 60°C for one hour.
      7. curing eco-flex
    7. Once the material is fully cured, you can demold it and use it for your application.
      8. demolding eco-flex
    Opinion

    Overall, we found that Eco-Flex is a great material for creating soft and flexible molds. It has enough pot time (45 minutes), which allows us to work with it comfortably without worrying about it curing too quickly, and it also has a good curing time (4 hours at room temperature).

  2. Plastic Liquid

    Plastic Liquid is a hard and rigid material. It has a Shore D hardness of 80, which means it is very hard and can withstand a lot of pressure and wear.

    plastic liquid plastic liquid test

    It is important to read the technical specifications and safety data sheets before using any material.

    Here is the data sheet for Plastic Liquid material: Plastic Liquid data sheet

    You can find more information about the material at the Plastic Liquid website

    Note: It is important to check the pot and curing time before starting to work with any material. Plastic Liquid has a 20 min pot time, which means that you have 20 minutes to work with the material before it starts to cure, and it has a curing time of 24 hours at room temperature.

    Process

    Here is the process for using Plastic Liquid:

    1. Make sure to wear gloves and work in a well-ventilated area.
    2. Weigh the two parts of the Plastic Liquid material in a 1:1 ratio by volume.
      3. plastic liquid parts
    3. Mix Parts A and B of the Plastic Liquid.

      4. We added color to the mixture.

      mixing plastic liquid coloring plastic liquid
    4. Pour the mixture into the mold and make sure to fill all the cavities and remove any excess material.
      5. pouring plastic liquid removing excess plastic liquid
    5. Allow the material to cure for at least 24 hours at room temperature, or speed up the curing process by placing it in an oven at 60°C for one hour.
      6. curing plastic liquid
    6. Once the material is fully cured, you can demold it and use it for your application.
      7. demolding plastic liquid
    Opinion

    Overall, we found that Plastic Liquid is a great material for creating hard and rigid molds. It has a short pot time (20 minutes), which means you need to work quickly and efficiently, and a long curing time (24 hours at room temperature), which requires advance planning.

    3. Compare Printing vs. Milling Molds

    We compared two common ways to make molds: 3D printing and milling. Both methods can produce accurate molds, but they differ in speed, surface finish, material choice, and cost.

    3D printing is faster to set up and works well for detailed shapes, especially when the design has undercuts or complex geometry. However, the printed surface often shows layer lines, so the mold may need post-processing before casting.

    Milling produces a smoother surface and is usually better for rigid molds and larger parts. It can be more precise for flat or shallow geometries, but it may take longer to machine and requires access to the right tooling and stock material.

    In our experience, 3D printing is more convenient for quick prototypes and complex forms, while milling is better when a cleaner finish and stronger mold body are needed. The best choice depends on the mold shape, the casting material, and the time available for fabrication.