Silicone mold is one of the simplest methods in rapid tooling. Generally, the 3D printing prototype is re molded with silicone rubber, but the service life is very short, only about 10-30 pieces. It has good elasticity and replication performance. The draft angle can not be considered when using silicone rubber compound mold, which will not affect the dimensional accuracy. It has good segmentation. It can directly carry out overall pouring without dividing the upper and lower molds, and then cut along the predetermined parting line and take out the mother mold.

RTV silicone rubber can be divided into addition molding and condensation type. The raw material and formula are silicone rubber with special mold. The product is sold in double packaging. Component A is rubber and component B is catalyst. When preparing, the room temperature, strength and hardness of the mold shall be considered to determine the weight preparation proportion of AB component. When the room temperature is 20-25 ℃, a: B = 100:1.5; When the chamber is low (but not lower than 10 degrees), properly increase 0.1-0.3 parts of component B; If the room temperature is high, it will be reduced by 0.1-0.3 parts in group B. The specific method is: determine the total dosage according to the mold volume, then weigh the components a and B accurately according to the proportion, place them in the vessel and stir evenly.

Mold silicone rubber operation method

1. Mix the mold silicone rubber and curing agent evenly. The appearance of the mold silicone rubber is a flowing liquid. Component A is silicone rubber and component B is curing agent. For example, take 100g silicone rubber and add 2G curing agent (Note: the silicone rubber and curing agent must be stirred evenly. If they are not stirred evenly, the curing and drying of the mold will be uneven, which will affect the service life and turnover times of the silicone rubber mold, and even cause the mold to be scrapped.

2. Vacuum exhaust bubble treatment. After the silicone rubber and curing agent are mixed evenly, the vacuum exhaust bubble link shall be carried out. The vacuum time shall not be too long, generally not more than 10 minutes, otherwise, the silicone rubber curing will produce cross-linking reaction, which can not be painted or poured, resulting in material waste.

3. Brushing operation process: pour the silicone rubber with bubbles on the master mold by brushing or pouring (apply isolation agent or release agent on the master mold before brushing or pouring) The mold must be brushed evenly. After 30 minutes, stick a layer of sand cloth or glass fiber cloth to increase the strength and tension of the mold; then apply the second brush, paste a layer of gauze or glass fiber cloth, and then apply silicone rubber. The treated mold has long service life, many times of mold turnover, long service life, cost saving and efficiency improvement.

4. Fabrication of external formwork. The general method is: surround the mold with rubber plate or wood board. One is to fill the mold frame with gypsum, and the other is to brush the external formwork with resin, brush a layer of resin, brush a layer of glass fiber cloth, then brush and stick, and repeat two or three layers to complete the external formwork.

5. The proportion of silicone rubber (silicone glue, silicon) and curing agent reflects the situation. It is recommended that the addition amount of curing agent should not exceed 5%. The larger the addition proportion of curing agent, the faster the curing time, the more brittle the mold and the shorter the service life. Silicone oil can also be added appropriately according to the product and process requirements to achieve better molding effect. Note that silicone oil should not be excessive (5% - 10%) Otherwise, the tensile force and hardness of the silicone mold will be affected.

2、 Precautions for making silicone rubber mold

1. Component B is a catalyst, which is easy to be hydrolyzed by moisture, so the cover should be tightly covered after use.

2. Once components a and B are mixed, the chemical reaction starts immediately, and the viscosity gradually increases, which can not be stopped. In order to avoid waste, they should be prepared with use according to the dosage, and should be used immediately after preparation without delay.

3. The mix proportion of groups A and B is related to the speed of chemical reaction and the performance of the mold. The more components of group B, the faster the reaction, the higher the strength and hardness of the product, but the toughness decreases. Therefore, accurate weighing is required.

4. Before preparation, mix component a up and down evenly, and then weigh.

5. The pouring method is suitable for the relief type, and the brushing method is suitable for the production of three-dimensional molds. For the casting of relief type molds, a frame with a length and width of 4-6cm larger than the original carving length and width should be made first. The frame should be flat and the inner surface should be smooth. During pouring, place the frame on a clean glass plate, and then place the prototype in the frame, leaving a gap of 2-3cm on each side (mold silicone rubber 25-35 yuan / kg).

Solution to bubbles in the manufacturing process of silicone rubber mold:

(1) Improve the design of flash groove and exhaust system;

(2) Increase the pressure of the press;

(3) Reduce the amount of release agent and spray it evenly;

(4) Material control moisture;

(5) Try adding some defoamer;

(6) Use cold runner;

(7) The exhaust slot can be added on the die by vacuum pumping with a vacuum machine.