Manufacturing Process of Compression Molded Silicone Rubber Keypad: Step by Step Injection molding is the ideal choice for silicone rubber keypads. It provides silicone rubber keypads with high-precision dimensions, more complex designs, and excellent surface finish. For small to medium batches and larger sizes, silicone rubber keypads made using compression molding can provide consistent quality and performance for most industries. The process involves multiple steps.
Step 1: Prepare the tool
Compression molding molds generally include an upper mold (sometimes called a male mold) and a lower mold (sometimes called a female mold). Sometimes it is a three-layer mold including an upper, middle, and lower mold. The compression mold is usually made of high-quality metal materials and produced by internal EDM and CNC milling machines. The molding manufacturer will process the mold according to the complete keypad drawing provided by the customer or the approved internal drawing. The molding is generally surface-treated before sampling or mass production. For example, common mechanical treatment methods include sandpaper grinding, polishing, and sandblasting.
Step 2: Prepare materials
Solid silicone rubber is a high-viscosity, dough-like elastomer. Before molding, silicone of appropriate specifications is mixed with a strict proportion of curing agent and other additives, then stirred evenly to obtain a slightly cross-linked silicone rubber roll. This process can add multiple colors according to the requirements of the drawing or personal preference. Next, the silicone roll is cut into specific sizes by accurately weighing the silicone. Sometimes it is also called a silicone preform.
Step 3: Molding
The correct mold is placed on the appropriate plate vulcanizer and preheated. When the mold temperature reaches the preset temperature, the mold is opened and the silicone rubber preform is manually placed into the cavity surface. Sometimes this action is preceded by placing conductive carbon or metal pills on the mold. After the preparation is completed, the mold is closed. The mold must be kept at high pressure before it is ejected so that the solid silicone rubber can fill the required details and features.
Step 4: Curing
The silicone rubber is cured into the shape of the mold cavity through a chemical reaction at high temperature and high pressure. time of vulcanization, temperature, and pressure are the keys to making high-quality silicone rubber keypads. During this process, the mold must be heated to a specific temperature maintaining for a while until it becomes a solid elastomer. Depending on different design requirements, the curing time may take from a few seconds to a few minutes.
Step 5: Demolding
The mold is cooled to a suitable temperature after the curing process and then ejected from the vulcanizer machine. After the upper mold is opened, the operator uses an air gun to assist in removing the silicone rubber keypad from the mold cavity.
Step 6: Post-processing
Post-processing is a key step to achieving the perfect appearance and performance of silicone rubber keypads. These procedures may be trimming rough edges, printing, laser marking, assembly of different parts, surface spraying, glue dripping, etc.
Step 7: Reliability Testing
Depending on the design requirements, your silicone rubber keypad may need to undergo various tests during the manufacturing process to ensure the complete function, durability, tolerance, and reliability of these keypads. These tests include trigger force test, strike life test, electrical test, and alcohol wear test.