The overall structure of thermosetting liquid silicone rubber injection molds has many similarities with the mold structure used for thermoplastic rubber materials, but the two also have many core differences that cannot be ignored. The viscosity of liquid silicone rubber compound is generally low, and even under extremely low injection pressure, it can be filled in a very short time. This makes the design of the exhaust system inside the mold crucial, and even a slight negligence can cause product defects. In addition, the state change law of liquid silicone rubber in the mold is completely different from that of thermoplastic rubber. It does not shrink in the mold during the cooling process like thermoplastic rubber. Instead, it expands in volume during the heating stage and only undergoes slight shrinkage when cooled after demolding. This results in the finished product not always staying on the side of the convex mold as expected, but rather being more likely to remain in the larger surface area of the mold cavity, bringing many additional variables to the subsequent demolding process.

Shrinkage rate is the core parameter that needs to be calibrated first in the design process of liquid silicone rubber molds. Although the rubber material does not shrink during the entire vulcanization process in the mold, the product usually experiences a shrinkage of 2.5% to 3% after demolding and complete cooling. The specific shrinkage value is determined to some extent by the formula of the rubber material itself, but from the perspective of mold design, the shrinkage rate is also affected by multiple external factors, including the actual working temperature of the mold, the self temperature of the rubber material during demolding, as well as the holding pressure inside the mold cavity and the subsequent compression state of the rubber material. The placement of injection points also changes the shrinkage performance, and the shrinkage rate in the direction of the adhesive flow is usually greater than that perpendicular to the flow direction. The external dimensions of the product also have a significant effect on the shrinkage rate. Products with larger thickness may have a smaller overall shrinkage rate than thin-walled products. If the production process includes a secondary vulcanization process, the product may also experience additional shrinkage.

The determination of the position of the parting line is a key step that needs to be finalized in the early stage of the design of liquid silicone rubber injection molds. The exhaust function of the mold mainly relies on the exhaust grooves set on the parting line. These exhaust grooves must be arranged in the area where the rubber material finally fills and reaches, so as to minimize the residual bubbles inside the product and reduce the strength loss at the junction of the rubber material. Due to the extremely low viscosity of liquid silicone rubber, the fitting accuracy of the parting line must be strictly controlled, otherwise it is easy to encounter glue overflow problems. Even if the accuracy control is fully in place, fine traces of the parting line can often be seen on the surface of the final molded product. The smoothness of demolding is largely determined by the geometric structure of the product and the position of the parting surface. If a slight chamfer structure is designed on the product, it can ensure that the adhesion of the product to the target half mold is uniform and consistent, avoiding unexpected sticking during demolding.