Make Silicone Molds and Cast Polyurethane Resin Parts

The infusion process is a common process for making simple silicone molds, and is generally suitable for making product models with simple rules. Next, I will share with you the whole process of making silicone molds and casting polyurethane resin through the infusion process through examples, so as to facilitate everyone to better understand the operation steps and precautions of this process.

The principle of the infusion process: build a mold frame, take the right amount of silicone raw materials and stir well, pour the mixed silicone on the master until it is completely covered, and remove the model after the silicone is completely cured, and the silicone mold making is finished. This process generally uses low hardness silica gel, because low hardness silica gel is relatively easier to demould and will not damage the master.

Tools and materials: Tin-cured silicone rubber, release agent, polyurethane casting resin, electronic scale, measuring cup, stirring bar.

1. As shown in the figure, build a suitable mold frame according to the size of the part model. To prevent the part model from shifting after pouring silicone, the master should be glued and fixed in the middle.

2. To avoid the silicone sticking to the master after molding and being difficult to separate, a release agent can be applied.

3. Weigh the appropriate amount of Part A liquid silicone and add Part B curing agent in the correct ratio. If there is no vacuum pump, you can reduce the proportion of curing agents to extend the operation time so that the air bubbles have more time to eliminate naturally, but pay attention to the minimum ratio should not be less than 100:1 otherwise it will lead to liquid silicone never curing.

4. If you have a vacuum pump, you can treat the air bubbles of silicone by vacuum defoaming to make the silicone mold more smooth and flat. Here we use 15 shore A low hardness and low viscosity silicone, although there is no vacuum de-foaming, it does not seem to have obvious bubbles.

5. Pour the mixed and stirred liquid silicone into the mold frame to cover the highest point of the master position by about 1-2 cm.

6. Liquid silicone is usually initially cured in 2-3 hours, and fully cured in about 12 hours. Remove the mold frame to separate the silicone mold from the master and perform simple trimming.

7. Weigh the polyurethane resin in a 1:1 ratio, one for part A and one for part B. Note that polyurethane materials are highly susceptible to moisture absorption, which can lead to air bubbles, and the mixing container should be clean and dry.

8. Pour the weighed part A and part B back and forth into each other and mix them. Since the operation time of polyurethane resin is very short only about 2 minutes, the operation should be quick and cast in the silicone mold immediately after mixing.

9. The resin material will begin to cure in 2-3 minutes and will be fully cured in 10-15 minutes. Note that the curing process of polyurethane resin will instantly release a lot of heat, so you should be careful not to reach out and touch it to avoid burns.


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