Rapid Manufacturing of Silicone Rubber Mold

With the rapid development of the machinery manufacturing industry, the demand for molds is increasing. A more complex mold often requires a combination of multiple pieces, which is not only expensive and long, but also difficult to ensure dimensional accuracy. The production of silicone rubber molds solves the problems of long molding cycle and high cost.

Silicone rubber mold manufacturing process is a relatively popular rapid mold manufacturing method. Because the silicone rubber mold has good flexibility and elasticity, it can make parts with complex structure, fine patterns, no draft angle, even with reverse draft angle, and deep grooves. The production cycle is short and the quality of the parts is high. A lot of attention. Due to the different shapes and sizes of the parts, the requirements for the strength of the silicone rubber mold are also different, so the molding methods are also different.

1). Type of mold silicone rubber material

At present, the silicone rubber used for molding is a two-component liquid silicone rubber, which is divided into two types: condensation type and addition type. These two mold silicone rubber materials have been widely used in many industries.

2). Features of silicone rubber material

Generally speaking, the shrinkage mold silicone rubber has low shear strength and is easy to be torn during the mold manufacturing process. Therefore, it is difficult to apply to those molds with deep patterns and complex shapes. In the process of manufacturing thick molds with condensation mold glue, the low-molecular substances such as ethanol produced during the condensation and cross-linking process are difficult to completely discharge, causing the mold to degrade and age when the mold is heated, which significantly affects its service life. At the same time, the discharge of low-molecular-weight substances such as ethanol causes the volume of the vulcanizate to shrink, resulting in the size of the mold being smaller than the corresponding prototype size. Therefore, condensed mold silicone rubber is mostly used in the manufacture of handicrafts with imprecise size requirements.

Addition mold silicone rubber adopts an addition vulcanization system and does not produce low-molecular compounds during vulcanization, so it has a very low linear shrinkage. The rubber compound can be deep-cured, and its physical properties, mechanical properties and heat resistance are excellent. It has become a variety that is being developed vigorously in the mold compound. Addition mold silicone rubber is suitable for manufacturing precision molds and casting molds, and the mold manufacturing process is simple, does not damage the prototype, and has good simulation.

Features of silicone rubber mold

Silicone rubber has good simulation, strength and extremely low shrinkage. It is simple and easy to use this material to make elastic molds, no special technology and equipment are needed, and it can be made in just a few hours at room temperature. Silicone rubber molds can withstand repeated use and poor operations, can maintain the precision tolerances of prototypes and mass-produced products, and can directly process parts with complex shapes, eliminating the need for milling and grinding processes, and demolding is very easy and greatly Shorten the trial production cycle of the product, and at the same time, the mold modification is also very convenient. In addition, because the silicone rubber mold has good elasticity, the convex and concave parts can also be taken out directly after casting, which is its unique feature.

These advantages of silicone rubber make it a leader in molding materials, and part of it has entered the field of mechanical manufacturing and competed with metal molds. At present, elastic molds made of silicone rubber have been used to replace metal molds to produce wax molds, plaster molds, ceramic molds, plastic parts, and even low melting point alloys such as lead, zinc and aluminum alloy parts. They are also used in light industry, plastics, food and antiques. The application of bronze ware and other industries continues to expand, which has played an inestimable role in the upgrading of products. Using silicone rubber to make molds can better utilize the advantages of RP&M technology.

Manufacturing of silicone rubber mold based on Rp Prototype

Because the prototype material produced by RP technology does not react with silicone rubber, it has not undergone deformation during the manufacturing process, and will not produce wrinkles, and can produce the same surface quality as precision plastic parts. The process of using RP prototype to make silicone mold is like below:

Manufacturing of silicone rubber mold based on Rp Prototype

Prototype surface treatment

The prototype made by RP method generally has step patterns or gaps between its laminated sections. Sanding and anti-seepage and strengthening treatment are required to improve the surface smoothness and moisture resistance and heat resistance of the prototype. Only the surface of the prototype is smooth enough to ensure the smoothness of the produced silicone mold cavity. This ensures that the remanufactured product has a high surface quality and is easy to remove from the silicone mold.

Making frame and fixed prototype

Design the shape and size of the casting frame according to the geometry of the prototype and the requirements of the use of the silicone mold. Before fixing the prototype, it is necessary to determine the position of the parting surface and the gate. The parting surface and gate position directly affect whether the cast product can be demolded smoothly and the product pouring quality is good or bad. When the parting surface and runner are selected and processed, the prototype is fixed in the mold box, as shown in the figure.

Silicone rubber metering, mixing and vacuum deaeration

The amount of silicone rubber should be accurately measured according to the size of the frame made and the specific gravity of the silicone rubber. Add the measured silicone rubber to the appropriate proportion of hardener, stir it evenly, and then vacuum defoam.  The defoaming time should be controlled according to the degree of vacuum reached.

Silicone rubber casting and curing

The silicone rubber mixture is vacuum degassed and poured into the mold frame where the prototype has been fixed, as shown in the upper right picture. After the silicone rubber is poured, in order to ensure that the cavity is completely filled, vacuum degassing is performed again, as shown in the lower right figure.

The purpose of degassing is to extract the gas mixed in the silica gel during the pouring process and the gas enclosed in the prototype cavity. The defoaming time should be appropriately longer than the defoaming time before pouring. The specific time should be determined according to the operating time of the selected silicone rubber material and the size of the prototype. After defoaming, the silicone mold can harden by itself or heat to harden. Heating hardening can shorten the hardening time.

Silicone rubber casting
Silicone rubber deaeration

Remove the frame, cut the mold and take out the prototype

When the silicone mold is hardened, the mold frame can be removed and the sprue rod can be removed. Refer to the mark on the parting surface of the prototype to cut the mold with a knife. Take out the prototype and clean the cavity of the silicone mold as necessary. The manufactured silicone rubber mold can be used to manufacture resin or plastic products in a vacuum.

Remove Frame
Remove Frame
cut mold
Cut the Mold
take out prototype
Take out Prototype
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