The goal of this week is to learn how to use the resin casting fabrication system. To achieve this, we will practice by creating three-dimensional models from two-dimensional images using Grasshopper, and then proceed to fabricate the counter-mold and finally the mold.
The main learning area will be the use of silicone to create molds from a counter-mold and the handling of resins for testing and casting. Additionally, we will experiment with metal casting using sand molds. I will use silicone rubber as a mold material. To do this, I will learn how to properly mix it with additives, allowing it to be poured effectively over the mold.
The silicone mold will be filled with polyurethane resin, so documentation on its mixing, application, and curing times will also be reviewed.
Finally, information will be reviewed on sand for molds, its boxing process, and the subsequent pouring of zamac.
This week’s research includes the development of a brief script capable of receiving two-dimensional depth images (DEMs) and generating three-dimensional surfaces suitable for 3D printing the counter-mold, followed by the subsequent material casting steps.
1. It is necessary to determine the available materials and fully understand the safety requirements of each to avoid improper handling.
Silicone rubber is a flexible, durable material commonly used for mold making due to its excellent heat resistance, chemical stability, and ability to capture fine details.
Silicone Catalyst is a chemical agent used to accelerate the curing process of silicone rubber, enabling it to set and harden efficiently at room temperature.
Release Agent is a chemical product used to prevent materials from sticking to molds, ensuring easy and clean demolding.
Polyurethane Resin is a versatile, durable material used for casting and molding, known for its fast curing time and high resistance to impact and chemicals.
2. In a second phase, it is necessary to perform a comparison between the resins available in the laboratory for casting. Their basic attributes and mixing ratios will be compared.
3. A Grasshopper script is developed to convert DEM images into three-dimensional meshes.
4. Points are assigned on a rectangular mesh, which are linked to the nearest pixels of the scaled image. The image brightness is reinterpreted as a parameter, multiplied by a factor to enhance the topography, and a mesh is built from those points.
5. To ensure maximum quality of the counter-mold, the 3D mesh is printed in resin using SLA printing. Additionally, a support structure is modeled to be printed with FDM, saving time and material. A beveled detail is added to the meeting edges to allow for easy assembly and disassembly.
6. Once the pieces are fabricated, they are joined with rubber bands to press the box together and then allow for easy separation.
7. Approximately 113 ml of silicone rubber is used, mixed with 4 ml of catalyst. A uniform layer of spray release agent is applied. The silicone is mixed quickly and poured over the counter-mold. Afterward, it is left to cure and solidify to remove the mold the following day.
8. Approximately 95 grams of clear polyurethane resin is used, mixed with 4 grams of catalyst to accelerate its curing.
9. On the other hand, a casting with zamac was carried out. As a first step, the molding sand must be packed evenly inside a container box. This allows the piece to be pressed in and leave the necessary imprint for pouring the metal.
10. The compacted imprint is dusted with talcum powder to facilitate the demolding of the metal. Zamac is then placed in the crucible and heated to 385–485°C for melting.
11. Zamac is poured into the mold, allowed to cool, and then polished if necessary to enhance the details.
3D Model 1 3D Model 2 Molding Container